physicsworld--2020-08-10--Affordable medical physics technologies tackle global health disparities - Physics World

The theme of the recent 2020 Joint AAPM|COMP Virtual Meeting was “ Improving Health Quality .
Increasing Global Impact ” .
The need to focus on global health is clear .
While the burden of cardiac disease and cancer is rising disproportionately among low- and middle-income countries , such countries often have little or no access to quality imaging and radiotherapy technologies for timely diagnosis and effective treatment .
There ’ s also a growing need for involvement of qualified medical physicists to ensure the safe delivery of high-quality care to patients .
“ COVID-19 has taught us one lesson @ @ @ @ @ @ @ local health is global health , ” stated AAPM President M Saiful Huq .
“ Innovation in one part of the world , be it in the fight against COVID-19 or against cancer or any other disease , can benefit everyone across the globe .
Collaborations between professionals from high-income and low- and middle-income countries can lead to innovations and development that can benefit all.
” In a dedicated symposium examining affordable medical physics technology for the developing world , speakers described a range of new and emerging low-cost healthcare systems .
Douglas @ @ @ @ @ @ @ Boulder Community Health , described a project to develop automated quality control ( QC ) for diagnostic and mammographic facilities .
“ Implementation of regular QC programmes is poor for radiography throughout the world and for mammography , in many parts of the world , ” he explained .
“ Regulations for quality assurance tend to be weak or non-existent.
” And with diagnostic medical physics support minimal in many parts of the world , facilities often have little or no guidance on how to implement a quality assurance programme .
“ Imaging @ @ @ @ @ @ @ ever being tested , ” Pfeiffer noted .
To remedy this situation , the IAEA set up a project to implement remote , automated and quantitative QC for radiography and mammography .
The aim , explained Pfeiffer , is that one clinically qualified medical physicist will be able to support multiple facilities to ensure adequate and consistent imaging performance , which is important for areas of the world that are underserved by medical physicists .
In the proposed workflow , images of simple test objects are acquired locally and then either evaluated at @ @ @ @ @ @ @ physicist for remote analysis .
The project team designed two inexpensive and easy to fabricate test objects – a radiographic phantom and a mammography phantom – both made from PMMA , copper and aluminium .
The team also developed an automated tool for image analysis ( ATIA ) .
The ATIA software extracts relevant data from the DICOM header of the image , and then reports a series of measured and calculated values : signal-to-noise ratio ; signal difference-to-noise ratio ; modulator transfer function ; normalized noise power spectrum ; and detectability index @ @ @ @ @ @ @ CSV file for further analysis .
Pfeiffer explained that the detectability index is a new metric that helps directly relate phantom measurements to clinical performance .
It can also be directly linked to a specific clinical task , such as detection of microcalcifications or small nodules , for example .
“ The IAEA programme allows a clinically qualified medical physicist and the local technologist to remotely monitor clinical performance with minimal investment and time per unit .
Due to its simplicity , training is straightforward.
” Pfeiffer concluded .
“ Regular radiographic QC @ @ @ @ @ @ @ countries .
This system makes it possible to perform QC on a regular basis , since it takes just a single exposure per unit and analysis can be automated.
” Relatively inexpensive imaging systems , such as X-ray and hand-held ultrasound scanners , combined with automated image analysis have enormous potential for countries with a lack of doctors .
Bram van Ginneken from Radboud University Medical Center described two such systems – firstly a scheme to automate tuberculosis ( TB ) diagnosis .
“ Every day , about 4500 people die from tuberculosis @ @ @ @ @ @ @ And the burden of disease is concentrated in Asia and Africa.
” In some aspects , van Ginneken said , TB has similarities to COVID-19 .
Both are diagnosed using RT-PCR ( reverse transcription polymerase chain reaction ) tests , which are expensive , time consuming and not always available .
As such , for both infections , imaging also plays an important diagnostic role .
One big difference , however , is that there ’ s an effective , $ 10 cure available for TB .
There is , therefore , a @ @ @ @ @ @ @ van Ginneken and colleagues are creating an automated screening process based on X-ray imaging .
First , high-risk people receive a chest X-ray , which takes just one minute to record and process .
If the X-ray looks suspicious , then the subject undergoes an Xpert diagnostic sputum test , waits two hours , and then receives a diagnosis .
If TB is confirmed , they can be treated immediately .
Van Ginneken explained that the X-ray and Xpert machines can be easily set up , for example , on a bus that @ @ @ @ @ @ @ the example of a clinic in Zambia where the team placed their digital X-ray machine in a shipping container .
He noted that even smaller systems are coming onto the market , such as a completely portable X-ray machine in a backpack .
“ It is quite heavy , but you can carry it anywhere , ” he said .
“ There is an X-ray tube , a detector , a battery pack and a solar panel to charge the battery.
” To detect signs of TB on the X-ray images , the @ @ @ @ @ @ @ .
The latest version of CAD4TB is based on deep learning , which can train classifiers to easily obtain very good performance .
“ It is already operational in over 45 countries throughout the world and we are screening about 5000 people per day , ” said van Ginneken .
The team has also created a version of the software to detect COVID-19 on chest X-rays .
“ We have already received funding to test this CAD4COVID together with CAD4TB in a joint screening in Lesotho , ” said van Ginneken .
“ @ @ @ @ @ @ @ the right part of healthcare system : find the severe COVID cases , less severe cases , TB cases and people who might have both diseases.
” Van Ginneken and colleagues are also applying deep learning techniques to help reduce maternal deaths by performing ultrasound imaging and analysis during pregnancy .
“ Every day , about 800 women dies as direct result of pregnancy , ” he said .
“ 99 % of these deaths happen in low-resource countries.
” The scheme is based on a low-cost portable ultrasound device that can be @ @ @ @ @ @ @ image analysis .
To analyse the ultrasound images and automatically detect any pregnancy risks , the team developed the BabyChecker software .
This software uses deep learning to determine gestational age , predict delivery date , identify twins and detect a foetus in the breech position , which indicates a high-risk pregnancy .
While it is relatively simple to perform automatic measurements to determine gestation , it is essential to acquire the correct image frames .
To achieve this without requiring extensive training , the team implemented a sweep protocol , in which @ @ @ @ @ @ @ over the abdomen ( three vertical , three horizontal ) .
The resulting video contains all the required information .
“ We have trained midwives in Ethiopia to perform these six sweeps , and saw that in two hours we can train somebody who has never used ultrasound before to perform sweeps in the right way , ” said van Ginneken .
The deep learning software classifies every frame in the video , in real time , as one of six types : head , part-head , body , side view , detached @ @ @ @ @ @ @ , for example , detect “ head ” frames located at the top of the sweeps , indicating a breech position , or find “ head ” frames at either end , suggesting the mother is having twins .
BabyChecker runs all of the deep learning networks in real time on the smartphone .
The system also provides feedback during sweep acquisition to ensure the scans are performed correctly .
“ We found that countries with limited resources are very open to the use of AI to improve healthcare , ” van Ginneken @ @ @ @ @ @ @ we can rapidly develop these applications.
” Alongside medical imaging technologies , there ’ s also a real need to bring radiotherapy to lower-income countries .
One approach , according to Magdalena Bazalova-Carter from the University of Victoria , could lie in the use of kilovoltage X-rays .
While kilovoltage X-rays are common in diagnostic imaging , they are not the obvious choice for radiotherapy .
It is difficult to deliver a high dose to deep-seated targets at kilovoltage energies , while low machine output compared with megavoltage linacs necessitates long treatment times @ @ @ @ @ @ @ kilovoltage X-rays , ” Bazalova-Carter explained .
“ The shielding for a kilovoltage beam doesn ’ t have to be seven feet of concrete and the technology used is not as expensive .
You could save a lot of money by using kilovoltage X-rays , which might be interesting for low- and middle-income countries.
” With this in mind , Bazalova-Carter and her former PhD student Dylan Breitkreutz , in collaboration with Michael Weil , have developed a kilovoltage arc therapy ( KVAT ) system .
The KVAT source uses one-dimensional scanning of @ @ @ @ @ @ @ , combined with collimation , to generate a linear array of focused kilovoltage beams that can be used to deliver arc therapy to generate conformal spherical dose distributions at depth .
For treatment planning , the team combined Monte Carlo simulations using the EGSnrc code with the Radify treatment planning system developed at McGill University .
As the KVAT collimators are designed to deliver spherical dose distributions , while human targets are typically not spherical , the team used sphere packing to deliver dose to irregular targets .
Bazalova-Carter showed an example of @ @ @ @ @ @ @ dose distributions of the KVAT lung plan with a stereotactic ablative radiotherapy ( SABR ) plan showed that a higher volume received lower doses with KVAT , as expected , but met all Radiation Therapy Oncology Group ( RTOG ) dose constraints .
Dose–volume histograms revealed that dose to the ribs was higher with KVAT ; however , the oesophagus dose , for example was higher for SABR .
She noted that KVAT treatment time is indeed still an issue , taking about 49 min to deliver a 12 Gy fraction .
The @ @ @ @ @ @ @ is currently under development by industrial partner Precision RT .

The CAD4TB software detects signs of tuberculosis on X-ray images, helping to provide rapid, automated disease screening. (Courtesy: Delft Imaging)
The theme of the recent 2020 Joint AAPM|COMP Virtual Meeting was “Improving Health Quality. Increasing Global Impact”. The need to focus on global health is clear. While the burden of cardiac disease and cancer is rising disproportionately among low- and middle-income countries, such countries often have little or no access to quality imaging and radiotherapy technologies for timely diagnosis and effective treatment. There’s also a growing need for involvement of qualified medical physicists to ensure the safe delivery of high-quality care to patients.
“COVID-19 has taught us one lesson: global health is local health and local health is global health,” stated AAPM President M Saiful Huq. “Innovation in one part of the world, be it in the fight against COVID-19 or against cancer or any other disease, can benefit everyone across the globe. Collaborations between professionals from high-income and low- and middle-income countries can lead to innovations and development that can benefit all.”
In a dedicated symposium examining affordable medical physics technology for the developing world, speakers described a range of new and emerging low-cost healthcare systems.
Increasing imaging standards
Douglas Pfeiffer, a clinical medical physicist at Boulder Community Health, described a project to develop automated quality control (QC) for diagnostic and mammographic facilities.
“Implementation of regular QC programmes is poor for radiography throughout the world and for mammography, in many parts of the world,” he explained. “Regulations for quality assurance tend to be weak or non-existent.” And with diagnostic medical physics support minimal in many parts of the world, facilities often have little or no guidance on how to implement a quality assurance programme. “Imaging devices may go their entire lives without ever being tested,” Pfeiffer noted.
To remedy this situation, the IAEA set up a project to implement remote, automated and quantitative QC for radiography and mammography. The aim, explained Pfeiffer, is that one clinically qualified medical physicist will be able to support multiple facilities to ensure adequate and consistent imaging performance, which is important for areas of the world that are underserved by medical physicists.
In the proposed workflow, images of simple test objects are acquired locally and then either evaluated at the facility or transmitted to the medical physicist for remote analysis. The project team designed two inexpensive and easy to fabricate test objects – a radiographic phantom and a mammography phantom – both made from PMMA, copper and aluminium.
Images of simple test phantoms help provide automated quality control for radiography and mammography. (Courtesy: Douglas Pfeiffer)
The team also developed an automated tool for image analysis (ATIA). The ATIA software extracts relevant data from the DICOM header of the image, and then reports a series of measured and calculated values: signal-to-noise ratio; signal difference-to-noise ratio; modulator transfer function; normalized noise power spectrum; and detectability index. The results are exported in a CSV file for further analysis.
Pfeiffer explained that the detectability index is a new metric that helps directly relate phantom measurements to clinical performance. It can also be directly linked to a specific clinical task, such as detection of microcalcifications or small nodules, for example.
“The IAEA programme allows a clinically qualified medical physicist and the local technologist to remotely monitor clinical performance with minimal investment and time per unit. Due to its simplicity, training is straightforward.” Pfeiffer concluded. “Regular radiographic QC has been neglected, even in developed countries. This system makes it possible to perform QC on a regular basis, since it takes just a single exposure per unit and analysis can be automated.”
Low-cost TB screening
Relatively inexpensive imaging systems, such as X-ray and hand-held ultrasound scanners, combined with automated image analysis have enormous potential for countries with a lack of doctors. Bram van Ginneken from Radboud University Medical Center described two such systems – firstly a scheme to automate tuberculosis (TB) diagnosis. “Every day, about 4500 people die from tuberculosis,” he pointed out. “And the burden of disease is concentrated in Asia and Africa.”
In some aspects, van Ginneken said, TB has similarities to COVID-19. Both are diagnosed using RT-PCR (reverse transcription polymerase chain reaction) tests, which are expensive, time consuming and not always available. As such, for both infections, imaging also plays an important diagnostic role. One big difference, however, is that there’s an effective, $10 cure available for TB.
There is, therefore, a strong case for TB screening. And van Ginneken and colleagues are creating an automated screening process based on X-ray imaging. First, high-risk people receive a chest X-ray, which takes just one minute to record and process. If the X-ray looks suspicious, then the subject undergoes an Xpert diagnostic sputum test, waits two hours, and then receives a diagnosis. If TB is confirmed, they can be treated immediately.
Van Ginneken explained that the X-ray and Xpert machines can be easily set up, for example, on a bus that can travel between sites. He shared the example of a clinic in Zambia where the team placed their digital X-ray machine in a shipping container. He noted that even smaller systems are coming onto the market, such as a completely portable X-ray machine in a backpack. “It is quite heavy, but you can carry it anywhere,” he said. “There is an X-ray tube, a detector, a battery pack and a solar panel to charge the battery.”
To detect signs of TB on the X-ray images, the team developed computer-aided detection software called CAD4TB. The latest version of CAD4TB is based on deep learning, which can train classifiers to easily obtain very good performance. “It is already operational in over 45 countries throughout the world and we are screening about 5000 people per day,” said van Ginneken.
The team has also created a version of the software to detect COVID-19 on chest X-rays. “We have already received funding to test this CAD4COVID together with CAD4TB in a joint screening in Lesotho,” said van Ginneken. “The goal is to get people into the right part of healthcare system: find the severe COVID cases, less severe cases, TB cases and people who might have both diseases.”
Pregnancy risk prediction
Van Ginneken and colleagues are also applying deep learning techniques to help reduce maternal deaths by performing ultrasound imaging and analysis during pregnancy. “Every day, about 800 women dies as direct result of pregnancy,” he said. “99% of these deaths happen in low-resource countries.”
The scheme is based on a low-cost portable ultrasound device that can be directly attached to a smartphone for real-time image analysis. To analyse the ultrasound images and automatically detect any pregnancy risks, the team developed the BabyChecker software. This software uses deep learning to determine gestational age, predict delivery date, identify twins and detect a foetus in the breech position, which indicates a high-risk pregnancy.
While it is relatively simple to perform automatic measurements to determine gestation, it is essential to acquire the correct image frames. To achieve this without requiring extensive training, the team implemented a sweep protocol, in which the ultrasound probe is swept six times over the abdomen (three vertical, three horizontal). The resulting video contains all the required information.
“We have trained midwives in Ethiopia to perform these six sweeps, and saw that in two hours we can train somebody who has never used ultrasound before to perform sweeps in the right way,” said van Ginneken.
The deep learning software classifies every frame in the video, in real time, as one of six types: head, part-head, body, side view, detached transducer or other. These classifications can, for example, detect “head” frames located at the top of the sweeps, indicating a breech position, or find “head” frames at either end, suggesting the mother is having twins.
BabyChecker runs all of the deep learning networks in real time on the smartphone. The system also provides feedback during sweep acquisition to ensure the scans are performed correctly. “We found that countries with limited resources are very open to the use of AI to improve healthcare,” van Ginneken concluded. “With deep learning, we can rapidly develop these applications.”
Low‐cost arc therapy
Alongside medical imaging technologies, there’s also a real need to bring radiotherapy to lower-income countries. One approach, according to Magdalena Bazalova-Carter from the University of Victoria, could lie in the use of kilovoltage X-rays.
Magdalena Bazalova-Carter, Dylan Breitkreutz and colleagues are developing a low-cost kilovoltage arc therapy system. (Courtesy: Magdalena Bazalova-Carter)
While kilovoltage X-rays are common in diagnostic imaging, they are not the obvious choice for radiotherapy. It is difficult to deliver a high dose to deep-seated targets at kilovoltage energies, while low machine output compared with megavoltage linacs necessitates long treatment times.
“But there are advantage of kilovoltage X-rays,” Bazalova-Carter explained. “The shielding for a kilovoltage beam doesn’t have to be seven feet of concrete and the technology used is not as expensive. You could save a lot of money by using kilovoltage X-rays, which might be interesting for low- and middle-income countries.”
With this in mind, Bazalova-Carter and her former PhD student Dylan Breitkreutz, in collaboration with Michael Weil, have developed a kilovoltage arc therapy (KVAT) system. The KVAT source uses one-dimensional scanning of the electron beams onto the treatment anode, combined with collimation, to generate a linear array of focused kilovoltage beams that can be used to deliver arc therapy to generate conformal spherical dose distributions at depth.
For treatment planning, the team combined Monte Carlo simulations using the EGSnrc code with the Radify treatment planning system developed at McGill University. As the KVAT collimators are designed to deliver spherical dose distributions, while human targets are typically not spherical, the team used sphere packing to deliver dose to irregular targets.
Bazalova-Carter showed an example of a lung cancer treatment plan. Comparing dose distributions of the KVAT lung plan with a stereotactic ablative radiotherapy (SABR) plan showed that a higher volume received lower doses with KVAT, as expected, but met all Radiation Therapy Oncology Group (RTOG) dose constraints. Dose–volume histograms revealed that dose to the ribs was higher with KVAT; however, the oesophagus dose, for example was higher for SABR. She noted that KVAT treatment time is indeed still an issue, taking about 49 min to deliver a 12 Gy fraction.
The KVAT system with a 200 kV beam is currently under development by industrial partner Precision RT.


physicsworld--2020-08-10--Simple, routine QA enhances contrast-enhanced mammography - Physics World

For women who undergo breast-cancer screening , the dread news of a suspicious finding on their mammogram or ultrasound scan is all too often compounded by an anxious wait for a follow-up exam that can take weeks to schedule .
To streamline that disjointed patient journey and fast-track diagnosis , GE Healthcare is working with clinical partners and technology vendors to enhance the accuracy of 3D mammography – also known as digital breast tomosynthesis ( DBT ) – by exploiting a complementary imaging modality called contrast-enhanced spectral mammography ( CESM ) .
A case study in this regard is the @ @ @ @ @ @ @ Centre in France .
In collaboration with GE , the Paris-based institute is rewriting the rulebook on breast-cancer screening .
The goal : to give patients a definitive cancer diagnosis and treatment plan on the same day via multimodality investigations that dovetail the capabilities of GE Healthcare ’ s Senographe Pristina™ system for DBT imaging and CESM ( the latter is known commercially as SenoBright™ HD ) .
To date , more than 20,000 women have participated in the One-Stop Clinic , with 75 % of those patients receiving a diagnosis on the @ @ @ @ @ @ @ model – and indeed the wider clinical context – CESM has emerged as a key imaging technology for diagnosis and staging of primary breast cancer , offering superior sensitivity and specificity versus DBT alone .
Deployed in tandem with DBT – in particular for women with denser breast tissue – CESM improves diagnostic accuracy through the injection of an iodinated contrast agent into the bloodstream ( using the same protocol as for contrast-enhanced CT ) .
In this way , the contrast agent enters general circulation but only enhances the region of clinical @ @ @ @ @ @ @ the original mammogram ) for subsequent imaging .
“ The underlying principle of CESM is energy subtraction , ” explains Remy Klausz , principal engineer for breastcare engineering at GE Healthcare Imaging .
In brief , the CESM system acquires images at two different X-ray energies , with algorithms generating a recombined image – essentially subtracting the low-energy image from the high-energy image – to cancel out the images of background structures from regular breast tissue , enhancing areas of contrast uptake .
“ In this way , ” Klausz adds , “ @ @ @ @ @ @ @ while significantly reducing false-positives – and without the considerable time and expense associated with follow-on functional imaging with breast MRI.
” From a commercial perspective , CESM continues to gain traction in the medical imaging community – though it ’ s also evident that not all mammography specialists are convinced .
Some clinicians are uncomfortable with the injection of contrast agents in a mammography setting , while others are sceptical of CESM ’ s consistency – i.e .
whether the modality will reliably demonstrate the presence or absence of iodine in suspect breast @ @ @ @ @ @ @ of course , are equally important : a suspicious area seen in the regular mammogram is likely to be non-cancerous if there is no contrast uptake , while enhanced contrast reveals a possibly cancerous lesion .
To address this cultural resistance , GE Healthcare has teamed up with CIRS , a US manufacturer of tissue-equivalent phantoms and simulators for medical imaging , radiation therapy and procedural training , to develop a simple yet comprehensive phantom for routine quality assurance ( QA ) of CESM systems .
“ Our motivation is to encourage more @ @ @ @ @ @ @ explains Klausz .
“ Working with CIRS , we ’ ve come up with a versatile and easy-to-use phantom that , in just a few minutes , will give the radiologist full confidence that their CESM equipment is operating to specification.
” The original concept for the CESM phantom came from Klausz and his colleagues at GE Healthcare ( see “ Anatomy of a phantom ” , below ) .
After drafting the detailed technical specifications and concept drawings , Klausz approached the CIRS engineering management team with the idea for a joint @ @ @ @ @ @ @ leading provider of breast-equivalent phantom materials , ” he adds , “ so I had full confidence in their team ’ s ability to deliver what I was looking for.
” It took around six months from those initial discussions to first prototype , with CIRS granted full commercial rights to the phantom under the terms of the collaboration agreement .
“ Making a phantom is not our core competency at GE Healthcare , ” explains Klausz .
“ Our motivation here is to provide a QA enabling technology to support wider clinical @ @ @ @ @ @ @ & D customers can now purchase the resulting Model 022 CESM phantom on a commercial basis from CIRS .
What ’ s more , the Model 022 uses the same frame geometry as the vendor ’ s DBT phantom , also some common parts , to further streamline QA protocols across DBT and CESM modalities .
Klausz concludes : “ My recommendation would be to deploy the Model 022 phantom ahead of every CESM session .
It ’ s just a simple visual check – no measurement is needed – to confirm that @ @ @ @ @ @ @ machine point of view .
”

Quality-assurance specialist CIRS has teamed up with GE Healthcare to commercialize an easy-to-use breast-equivalent phantom for contrast-enhanced spectral mammography
Complementary capabilities: when deployed in tandem with DBT, commercial CESM systems, such as GE Healthcare’s SenoBright™ HD (shown above), provide a key imaging modality for diagnosis and staging of primary breast cancer. (Courtesy: GE Healthcare)
For women who undergo breast-cancer screening, the dread news of a suspicious finding on their mammogram or ultrasound scan is all too often compounded by an anxious wait for a follow-up exam that can take weeks to schedule. To streamline that disjointed patient journey and fast-track diagnosis, GE Healthcare is working with clinical partners and technology vendors to enhance the accuracy of 3D mammography – also known as digital breast tomosynthesis (DBT) – by exploiting a complementary imaging modality called contrast-enhanced spectral mammography (CESM).
A case study in this regard is the One-Stop Clinic at the Gustave Roussy Cancer Centre in France. In collaboration with GE, the Paris-based institute is rewriting the rulebook on breast-cancer screening. The goal: to give patients a definitive cancer diagnosis and treatment plan on the same day via multimodality investigations that dovetail the capabilities of GE Healthcare’s Senographe Pristina™ system for DBT imaging and CESM (the latter is known commercially as SenoBright™ HD). To date, more than 20,000 women have participated in the One-Stop Clinic, with 75% of those patients receiving a diagnosis on the same day.
Within this one-stop patient model – and indeed the wider clinical context – CESM has emerged as a key imaging technology for diagnosis and staging of primary breast cancer, offering superior sensitivity and specificity versus DBT alone. Deployed in tandem with DBT – in particular for women with denser breast tissue – CESM improves diagnostic accuracy through the injection of an iodinated contrast agent into the bloodstream (using the same protocol as for contrast-enhanced CT). In this way, the contrast agent enters general circulation but only enhances the region of clinical interest (a suspect lesion identified in the original mammogram) for subsequent imaging.
“The underlying principle of CESM is energy subtraction,” explains Remy Klausz, principal engineer for breastcare engineering at GE Healthcare Imaging. In brief, the CESM system acquires images at two different X-ray energies, with algorithms generating a recombined image – essentially subtracting the low-energy image from the high-energy image – to cancel out the images of background structures from regular breast tissue, enhancing areas of contrast uptake. “In this way,” Klausz adds, “CESM can demonstrate suspicious lesions otherwise ignored while significantly reducing false-positives – and without the considerable time and expense associated with follow-on functional imaging with breast MRI.”
Prioritizing the QA
From a commercial perspective, CESM continues to gain traction in the medical imaging community – though it’s also evident that not all mammography specialists are convinced. Some clinicians are uncomfortable with the injection of contrast agents in a mammography setting, while others are sceptical of CESM’s consistency – i.e. whether the modality will reliably demonstrate the presence or absence of iodine in suspect breast tissue time after time. Both, of course, are equally important: a suspicious area seen in the regular mammogram is likely to be non-cancerous if there is no contrast uptake, while enhanced contrast reveals a possibly cancerous lesion.
To address this cultural resistance, GE Healthcare has teamed up with CIRS, a US manufacturer of tissue-equivalent phantoms and simulators for medical imaging, radiation therapy and procedural training, to develop a simple yet comprehensive phantom for routine quality assurance (QA) of CESM systems. “Our motivation is to encourage more clinical users to adopt CESM,” explains Klausz. “Working with CIRS, we’ve come up with a versatile and easy-to-use phantom that, in just a few minutes, will give the radiologist full confidence that their CESM equipment is operating to specification.”
The original concept for the CESM phantom came from Klausz and his colleagues at GE Healthcare (see “Anatomy of a phantom”, below). After drafting the detailed technical specifications and concept drawings, Klausz approached the CIRS engineering management team with the idea for a joint development project. “CIRS is a leading provider of breast-equivalent phantom materials,” he adds, “so I had full confidence in their team’s ability to deliver what I was looking for.”
It took around six months from those initial discussions to first prototype, with CIRS granted full commercial rights to the phantom under the terms of the collaboration agreement. “Making a phantom is not our core competency at GE Healthcare,” explains Klausz. “Our motivation here is to provide a QA enabling technology to support wider clinical acceptance of CESM.”
Clinical and R&D customers can now purchase the resulting Model 022 CESM phantom on a commercial basis from CIRS. What’s more, the Model 022 uses the same frame geometry as the vendor’s DBT phantom, also some common parts, to further streamline QA protocols across DBT and CESM modalities.
Klausz concludes: “My recommendation would be to deploy the Model 022 phantom ahead of every CESM session. It’s just a simple visual check – no measurement is needed – to confirm that everything is working as expected from a machine point of view.”
Anatomy of a phantom The Model 022 CESM phantom represents an average human breast in size and shape, demonstrating the presence or absence of iodine in tissues via different iodine concentrations and non-iodinated breast-tissue substitutes (see figure 1). The phantom consists of four slabs: A 10 mm thick target slab is made up of breast-equivalent materials representative of a 50:50 ratio of gland and adipose tissue. The slab contains two sets of four plugs, each set comprising plugs with clinically relevant iodine concentrations of 0.25, 0.5, 1.0 and 2.0 mg/cm 2 A fifth plug, made of 100% glandular tissue-equivalent material, is positioned in the centre of each plug group to mimic a glandular lesion.
is made up of breast-equivalent materials representative of a 50:50 ratio of gland and adipose tissue. The slab contains two sets of four plugs, each set comprising plugs with clinically relevant iodine concentrations of 0.25, 0.5, 1.0 and 2.0 mg/cm A fifth plug, made of 100% glandular tissue-equivalent material, is positioned in the centre of each plug group to mimic a glandular lesion. The background slab, 25 mm thick, is made of two halves (100% adipose-equivalent material and 100% glandular-equivalent material) to test iodine separation from the background over a wide range of densities.
is made of two halves (100% adipose-equivalent material and 100% glandular-equivalent material) to test iodine separation from the background over a wide range of densities. The top and bottom slabs are 10 mm thick, made from 100% adipose-equivalent material, and have rounded edges to mimic the realistic shape of a compressed breast. Fig 1: The layout of the Model 022 CESM phantom has been arranged to match the shape and mounting of the CIRS DBT QA phantom. A magnetic fixture allows for repeatable alignment and positioning. (Courtesy: GE Healthcare and CIRS)


physicsworld--2020-08-07--Physics in the pandemic: ‘There are some great experiments that can be done safely and simply at hom

Physics in the pandemic: ‘There are some great experiments that can be done safely and simply at home’ - Physics World

Stefan Hutzler and Denis Weaire are in the School of Physics , Trinity College Dublin , Ireland .
Their postgraduate student Ali Irannezhad currently performs his experiments in his home in Tehran , Iran .
This post is part of a series on how the COVID-19 pandemic is affecting the personal and professional lives of physicists around the world .
If you ’ d like to share your own perspective , please contact us at pwld @ ioppublishing.org .
With COVID-19 sending universities and schools into a long summer hibernation , how are we to adapt to our confinement ?
@ @ @ @ @ @ @ be a solitary , online affair , as it has for most of the pandemic so far , with many of us cooped up in tiny bedrooms .
Indeed , it will be interesting to see what lasting effect online lecturing has on traditional teaching methods .
It ’ s fair to say we academics have not always been honest with ourselves about the quality of our university lecturing : in the late 1990s , one of us ( DW ) , wrote a humorous “ lateral-thoughts ” article in Physics World about @ @ @ @ @ @ @ on the torture of the ill-prepared lecturer confronted by a smart student .
But what about experimental physics ?
Doing simulated experiments on a screen holed up in our bedrooms can surely never be an adequate substitute for the real thing ?
However , we think there are some great experiments that can be done safely and simply at home , using materials that are readily at hand .
Mostly they relate to classical mechanics or elementary properties of materials .
After all , as physicists like Eric Mazur from Harvard University have @ @ @ @ @ @ @ best training for rigorous thought , with even apparently trivial experiments throwing up teasing challenges .
Consider one experiment we recently wrote about in the American Journal of Physics .
Take a convenient number of ball bearings or similar hard spheres .
Place them in a tube with stoppers at both ends , lay it horizontally , and then agitate it slightly to encourage the system to equilibriate .
( Immersing the balls in oil will help . )
Turns out that if you compress the chain of hard spheres enough by adjusting @ @ @ @ @ @ @ above ) .
What ’ s more , the buckling is localized , rather like the “ kinks ” and “ solitons ” in many non-linear systems .
There ’ s also an interesting difference depending on whether you use an odd or even number of balls .
You could even try using soft bubbles inside of hard spheres .
And having got your data , why not try to replicate your results by computer simulation , perhaps using Python programming ?
As the great John Von Neumann once said , the computer @ @ @ @ @ @ @ is supposed to release mathematics from the narrow confines of linear problems .
Another hard-sphere experiment is Newton ’ s cradle , commonly associated with Isaac Newton , who by the way made some of his greatest achievements while isolating in the countryside during the plagues that ravaged Britain in 1665 and 1666 .
It ’ s not hard to understand the basic properties of what ’ s now a classic executive desk toy , but all good scientists will want to look at it more closely .
That ’ s exactly what @ @ @ @ @ @ @ 1999 , as we did too five years later in a paper called “ Rocking Newton ’ s cradle ” .
In the standard textbook description of Newton ’ s cradle , only one sphere is ever in motion .
However , if you look really carefully , you ’ ll notice that all spheres can be moving at the same time .
Theory and computer simulations confirm this , and attribute it to the finite elastic modulus of the spheres .
What about soap bubbles , brought from the kitchen ?
Stare @ @ @ @ @ @ @ , or with the help of a magnifying glass , and you ’ ll see local order amongst the chaos .
Three soap films , for example , always meet in a line under an angle of 120o , while four such lines meet under the tetrahedral angle of 109.4o .
The lines are called Plateau borders in honour of the Belgian scientist Joseph Plateau who was the first to describe them in a series of experiments .
Indeed , he may well have done some of them himself at home after blinding @ @ @ @ @ @ @ ( in the interests of science ) .
Or rather than grabbing bubbles from the kitchen sink , how about blowing air through a straw into some soapy water ?
Blowing carefully ( or using an aquarium pump borrowed from your fish ) results in the generation of bubbles of equal size .
These crystallize spontaneously to form a hexagonal pattern ( triangular lattice ) on top of the soap solution , with some defects , such as dislocations , amongst them .
In 1947 the Nobel-prize-winning physicist Lawrence Bragg and his colleague @ @ @ @ @ @ @ raft at the Cavendish Laboratory , Cambridge , as a source of inspiration for the study of crystalline defects .
There wasn ’ t a plague on , but these two great physicists may have been examining such simple classical physics because the Second World War was only just over and had left even Cambridge University impoverished .
There ’ s even more entertainment and food for thought from 3D structures formed by monodisperse bubbles , which the photographer Kym Cox recently brought to prominence last year in New Scientist and the New @ @ @ @ @ @ @ was one of us ( SH ) who taught her the tricks of how to make these amazing structures in her own kitchen .
Finally , let ’ s look at the Euler disc , named in honour of the great mathematician Leonhard Euler ( though there ’ s not evidence he originated it ) .
All you need is a simple , flat disc , preferably a heavy one although a large coin will do .
Spin it on a firm , flat surface and you ’ ll notice it gradually subsides @ @ @ @ @ @ @ But instead of a dignified , gradual exponential approach to equilibrium , the coin heads dramatically towards a crisis , emitting a sound of ever increasing frequency .
It suddenly settles – not with a whimper but a bang .
( If you ’ re using a really heavy disc , try not to wake the neighbours… ) Our challenge to you is to find a way of measuring this intriguing sound .
But if you want the explanation , Keith Moffatt ( who like Newton was at Trinity College Cambridge ) has @ @ @ @ @ @ @ , As a side note , a previous paper of his led one of the present authors ( DW ) , while still an undergraduate , to throw eggs out of his second-story student room on to an adjacent lawn ; Moffatt claimed they wouldn ’ t break , and he was ( mostly ) right .
Some day soon we ’ ll all return to our schools and labs , where remarkable and expensive equipment awaits us .
When that happy day arrives , perhaps our time at home will have let @ @ @ @ @ @ @ of the many visual phenomena that are already around us .
Those phenomena may look trivial , but they can be challenging , teaching us to speculate and analyse until we get to the heart of the matter .
And as so often in physics , simple matters may tempt us to go deeper and deeper still .
Precautionary note : None of our suggestions should pose any significant hazards in the home environment , but we advise you to take all necessary precautions and care while carrying out any experiments

Stefan Hutzler and Denis Weaire are in the School of Physics, Trinity College Dublin, Ireland. Their postgraduate student Ali Irannezhad currently performs his experiments in his home in Tehran, Iran. This post is part of a series on how the COVID-19 pandemic is affecting the personal and professional lives of physicists around the world. If you’d like to share your own perspective, please contact us at pwld@ioppublishing.org.
Inside thinking: Ali Irannezhad – a PhD student at Trinity College Dublin – performing sphere-buckling experiments in his home in Tehran, where he temporarily returned during the COVID-19 shutdown. The apparatus, designed by himself, was built in a local workshop. (Courtesy: Ali Irannezhad)
With COVID-19 sending universities and schools into a long summer hibernation, how are we to adapt to our confinement? Teaching and research will probably continue to be a solitary, online affair, as it has for most of the pandemic so far, with many of us cooped up in tiny bedrooms.
Indeed, it will be interesting to see what lasting effect online lecturing has on traditional teaching methods. It’s fair to say we academics have not always been honest with ourselves about the quality of our university lecturing: in the late 1990s, one of us (DW), wrote a humorous “lateral-thoughts” article in Physics World about the horrors of university life, focusing on the torture of the ill-prepared lecturer confronted by a smart student.
But what about experimental physics? Doing simulated experiments on a screen holed up in our bedrooms can surely never be an adequate substitute for the real thing?
However, we think there are some great experiments that can be done safely and simply at home, using materials that are readily at hand. Mostly they relate to classical mechanics or elementary properties of materials. After all, as physicists like Eric Mazur from Harvard University have long argued, classical physics is the best training for rigorous thought, with even apparently trivial experiments throwing up teasing challenges.
Line of action
Consider one experiment we recently wrote about in the American Journal of Physics. Take a convenient number of ball bearings or similar hard spheres. Place them in a tube with stoppers at both ends, lay it horizontally, and then agitate it slightly to encourage the system to equilibriate. (Immersing the balls in oil will help.)
Pushing in on one side of a cylinder containing a line of spheres causes the initially linear chain to buckle, with the buckling becoming more and more localised as the compression goes up (Courtesy: Stefan Hutzler)
Turns out that if you compress the chain of hard spheres enough by adjusting the stoppers, it buckles (see above). What’s more, the buckling is localized, rather like the “kinks” and “solitons” in many non-linear systems. There’s also an interesting difference depending on whether you use an odd or even number of balls. You could even try using soft bubbles inside of hard spheres.
And having got your data, why not try to replicate your results by computer simulation, perhaps using Python programming? As the great John Von Neumann once said, the computer (which he helped to invent) is supposed to release mathematics from the narrow confines of linear problems.
Cradle of genius
Another hard-sphere experiment is Newton’s cradle, commonly associated with Isaac Newton, who by the way made some of his greatest achievements while isolating in the countryside during the plagues that ravaged Britain in 1665 and 1666. It’s not hard to understand the basic properties of what’s now a classic executive desk toy, but all good scientists will want to look at it more closely. That’s exactly what John Hinch and Sébastien Saint-Jean did in 1999, as we did too five years later in a paper called “Rocking Newton’s cradle”.
In the standard textbook description of Newton’s cradle, only one sphere is ever in motion. However, if you look really carefully, you’ll notice that all spheres can be moving at the same time. Theory and computer simulations confirm this, and attribute it to the finite elastic modulus of the spheres.
All at once: the standard textbook description of Newton’s cradle says there’s only ever one sphere in motion. But after the first impact of the sphere on the right, the entire chain begins to break up so that all spheres are in motion. (Courtesy: Stefan Hutzler)
Bubbles and borders
What about soap bubbles, brought from the kitchen? Stare into a foam with the naked eye, or with the help of a magnifying glass, and you’ll see local order amongst the chaos. Three soap films, for example, always meet in a line under an angle of 120o, while four such lines meet under the tetrahedral angle of 109.4o. The lines are called Plateau borders in honour of the Belgian scientist Joseph Plateau who was the first to describe them in a series of experiments. Indeed, he may well have done some of them himself at home after blinding himself by rashly staring at the Sun (in the interests of science).
Or rather than grabbing bubbles from the kitchen sink, how about blowing air through a straw into some soapy water? Blowing carefully (or using an aquarium pump borrowed from your fish) results in the generation of bubbles of equal size. These crystallize spontaneously to form a hexagonal pattern (triangular lattice) on top of the soap solution, with some defects, such as dislocations, amongst them.
In 1947 the Nobel-prize-winning physicist Lawrence Bragg and his colleague John Nye studied such a 2D bubble raft at the Cavendish Laboratory, Cambridge, as a source of inspiration for the study of crystalline defects. There wasn’t a plague on, but these two great physicists may have been examining such simple classical physics because the Second World War was only just over and had left even Cambridge University impoverished.
There’s even more entertainment and food for thought from 3D structures formed by monodisperse bubbles, which the photographer Kym Cox recently brought to prominence last year in New Scientist and the New York Times. In fact, it was one of us (SH) who taught her the tricks of how to make these amazing structures in her own kitchen.
Don’t wake the neighbours
Finally, let’s look at the Euler disc, named in honour of the great mathematician Leonhard Euler (though there’s not evidence he originated it). All you need is a simple, flat disc, preferably a heavy one although a large coin will do. Spin it on a firm, flat surface and you’ll notice it gradually subsides, as its energy is dissipated. But instead of a dignified, gradual exponential approach to equilibrium, the coin heads dramatically towards a crisis, emitting a sound of ever increasing frequency. It suddenly settles – not with a whimper but a bang. (If you’re using a really heavy disc, try not to wake the neighbours…)
Our challenge to you is to find a way of measuring this intriguing sound. But if you want the explanation, Keith Moffatt (who like Newton was at Trinity College Cambridge) has written eruditely on the subject in Nature, As a side note, a previous paper of his led one of the present authors (DW), while still an undergraduate, to throw eggs out of his second-story student room on to an adjacent lawn; Moffatt claimed they wouldn’t break, and he was (mostly) right.
Some day soon we’ll all return to our schools and labs, where remarkable and expensive equipment awaits us. When that happy day arrives, perhaps our time at home will have let us bring a deeper appreciation and admiration of the many visual phenomena that are already around us. Those phenomena may look trivial, but they can be challenging, teaching us to speculate and analyse until we get to the heart of the matter. And as so often in physics, simple matters may tempt us to go deeper and deeper still.
Precautionary note: None of our suggestions should pose any significant hazards in the home environment, but we advise you to take all necessary precautions and care while carrying out any experiments


physicsworld--2020-08-07--A map of quantum physics, sound of a wave-function collapse, famous physicists as dogs - Physics Wor

A map of quantum physics, sound of a wave-function collapse, famous physicists as dogs - Physics World

Above is a video by the physicist , YouTuber and quantum cartographer Dominic Walliman , who describes a map of @ @ @ @ @ created .
The map introduces quantum mechanics by providing bite-sized chunks of information that are @ @ @ @ @ gives an overview of the quantum world and the academic disciplines that study it .
@ @ @ @ @ look at the map – and quantum mechanics – in much more detail .
“ @ @ @ @ @ of a wave-function collapse , and if so , what would it sound like ?
@ @ @ @ @ the Max Planck Institute for Quantum Optics in Germany .
To find out why the @ @ @ @ @ , indistinguishable from any other click , ” read his preprint on arXiv : “ @ @ @ @ @ jumps ” .
The Internet and the World Wide Web were invented for very serious @ @ @ @ @ scientific communication – but now they are the realm of “ Famous physicists imagined as @ @ @ @ @ m not saying that ’ s necessarily a bad thing , so enjoy .

Above is a video by the physicist, YouTuber and quantum cartographer Dominic Walliman, who describes a map of quantum physics that he has created. The map introduces quantum mechanics by providing bite-sized chunks of information that are organized in a way that gives an overview of the quantum world and the academic disciplines that study it. Walliman then goes on to look at the map – and quantum mechanics – in much more detail.
“Could we hear the pop of a wave-function collapse, and if so, what would it sound like?” asks Antoine Tilloy of the Max Planck Institute for Quantum Optics in Germany. To find out why the “sound is disappointingly banal, indistinguishable from any other click,” read his preprint on arXiv: “The subtle sound of quantum jumps”.
The Internet and the World Wide Web were invented for very serious reasons of national defence and scientific communication – but now they are the realm of “Famous physicists imagined as dogs”. I’m not saying that’s necessarily a bad thing, so enjoy.


physicsworld--2020-08-07--Magnetic topological insulators change phase under pressure - Physics World

In 2019 , researchers discovered that two intrinsically magnetic materials , MnBi Te and MnBi Te , can behave as topological insulators – materials that are electrically insulating in bulk , but conduct electricity well on the surface .
A team led by Yangpeng Qi from ShanghaiTech University has now demonstrated that it is possible to induce phase transitions in these layered heterostructures by applying high pressures to them , thereby tuning their crystal structure and electronic properties .
The results could further our understanding of the interplay between magnetism and topology in these and related materials , they say @ @ @ @ @ @ @ behaviour , topological insulators can also exhibit various exotic quantum effects , including the quantum anomalous Hall effect ( QAHE ) and quantum phases such as axion insulating states .
However , many of these effects only appear when the materials are doped with magnetic impurities .
The drawback to such doping is that it also introduces disorder in the material ’ s crystal lattice , making it difficult for researchers to study any quantum phenomena present .
Intrinsically magnetic topological insulators such as MnBi Te and MnBi Te avoid this problem , @ @ @ @ @ @ @ structure similar to that of Bi Te , which is a typical topological insulator at ambient conditions .
In their work , Qi and colleagues applied pressures of up 50 GPa to MnBi Te and MnBi Te using a diamond anvil cell apparatus that squeezes a sample between the flattened tips of gem-grade diamond crystals .
The small size of the tips ( 400 microns ) make it possible to reach such high pressures with only small applied forces .
The researchers performed high-pressure resistivity measurements within this cell , as well as @ @ @ @ @ @ @ X-ray diffraction .
The latter experiments were performed at the Advanced Photon Source and the Shanghai Synchrotron Radiation Facility .
Qi and colleagues found that the antiferromagnetism normally displayed in MnBi Te and MnBi Te gradually disappears as pressure increases , while the conductance and crystal structure of the material also dramatically changes .
However , through ab initio band structure calculations , the team discovered that applied pressure does not change the topological nature of the two systems until a structural phase transition occurs at a pressure of more than 16 GPa @ @ @ @ @ @ @ materials ’ bulk and surface states respond differently to applied pressure , producing two types of macroscopic resistivity that are in competition with each other .
Since MnBi Te and MnBi Te are layered materials , the researchers expected that their electrical transport and magnetic properties would be sensitive to the competition between interlayer and intralayer interactions – which can indeed be tuned by adjusting external pressure .
Their resistivity measurements at pressures up to 34 GPa revealed metal-like conduction in the low-pressure range ( around 3 GPa ) , with a metal-semiconductor @ @ @ @ @ @ @ than about 12 GPa .
They also noted that the materials ’ resistivity undergoes a metallization at pressure above around 16 GPa and does not change significantly with further increases in pressure .
“ Our combined theoretical and experimental research establishes MnBi Te and MnBi Te as highly tunable magnetic topological insulators , in which phase transitions and new electronic states emerge upon compression , ” Qi tells Physics World .
“ We now plan to search for other layered topological materials that behave in the same way.
” The work is reported @ @ @ @ @

Crystal structure of Bi 2 Te 3 . Courtesy: Chinese Physics Letters
In 2019, researchers discovered that two intrinsically magnetic materials, MnBi 2 Te 4 and MnBi 2 Te 7 , can behave as topological insulators – materials that are electrically insulating in bulk, but conduct electricity well on the surface. A team led by Yangpeng Qi from ShanghaiTech University has now demonstrated that it is possible to induce phase transitions in these layered heterostructures by applying high pressures to them, thereby tuning their crystal structure and electronic properties. The results could further our understanding of the interplay between magnetism and topology in these and related materials, they say.
In addition to their unusual conducting behaviour, topological insulators can also exhibit various exotic quantum effects, including the quantum anomalous Hall effect (QAHE) and quantum phases such as axion insulating states. However, many of these effects only appear when the materials are doped with magnetic impurities. The drawback to such doping is that it also introduces disorder in the material’s crystal lattice, making it difficult for researchers to study any quantum phenomena present.
Similar crystal structure to Bi 2 Te 3
Intrinsically magnetic topological insulators such as MnBi 2 Te 4 and MnBi 2 Te 7 avoid this problem, crystallizing instead into an orderly, layered structure similar to that of Bi 2 Te 3 , which is a typical topological insulator at ambient conditions. In their work, Qi and colleagues applied pressures of up 50 GPa to MnBi 2 Te 4 and MnBi 2 Te 7 using a diamond anvil cell apparatus that squeezes a sample between the flattened tips of gem-grade diamond crystals. The small size of the tips (400 microns) make it possible to reach such high pressures with only small applied forces.
The researchers performed high-pressure resistivity measurements within this cell, as well as in situ high-pressure Raman spectroscopy and synchrotron X-ray diffraction. The latter experiments were performed at the Advanced Photon Source and the Shanghai Synchrotron Radiation Facility.
Antiferromagnetism gradually disappears as pressure increases
Qi and colleagues found that the antiferromagnetism normally displayed in MnBi 2 Te 4 and MnBi 2 Te 7 gradually disappears as pressure increases, while the conductance and crystal structure of the material also dramatically changes. However, through ab initio band structure calculations, the team discovered that applied pressure does not change the topological nature of the two systems until a structural phase transition occurs at a pressure of more than 16 GPa. They also observed that the two materials’ bulk and surface states respond differently to applied pressure, producing two types of macroscopic resistivity that are in competition with each other.
Since MnBi 2 Te 4 and MnBi 2 Te 7 are layered materials, the researchers expected that their electrical transport and magnetic properties would be sensitive to the competition between interlayer and intralayer interactions – which can indeed be tuned by adjusting external pressure. Their resistivity measurements at pressures up to 34 GPa revealed metal-like conduction in the low-pressure range (around 3 GPa), with a metal-semiconductor transition occurring at increased pressures of greater than about 12 GPa. They also noted that the materials’ resistivity undergoes a metallization at pressure above around 16 GPa and does not change significantly with further increases in pressure.
“Our combined theoretical and experimental research establishes MnBi 2 Te 4 and MnBi 4 Te 7 as highly tunable magnetic topological insulators, in which phase transitions and new electronic states emerge upon compression,” Qi tells Physics World. “We now plan to search for other layered topological materials that behave in the same way.”
The work is reported in Chinese Physics Letters.


physicsworld--2020-08-07--‘Cartwheeling’ light reveals new type of polarized light-matter interaction - Physics World

Technologies that rely on interactions between matter and polarized light usually stick to the well-understood effects of linear or circular polarization .
Researchers at Rice University in the US have now opened the door to fresh approaches by studying how matter reacts to an additional form of polarization .
This form , known as “ trochoidal ” polarization , is characterized by a “ cartwheeling ” motion in light ’ s electric field that can occur in either a clockwise or anticlockwise direction .
Since matter can distinguish between these two directions , trochoidal dichroism could be used to develop @ @ @ @ @ @ @ in which the direction of the electromagnetic field rotates in a helical or “ corkscrew-like ” fashion as it propagates through space , is commonly used to study the conformation of small biomolecules such as proteins , DNA and amino acids .
These studies are possible because such molecules are chiral – that is , their structures have a “ handedness ” that makes them absorb left- and right-circularly-polarized light differently , a phenomenon known as dichroism .
Linear polarization is also widely used , for example to control reflections and glare in @ @ @ @ @ @ @ researchers studied is very different from these more familiar types .
Rather than following a helical progression , the direction of the electromagnetic field in trochoidal light turns end-over-end as it propagates , rotating either clockwise or anticlockwise as it goes .
“ Rather like a rolling hula hoop , ” explains study lead author Lauren McCarthy .
The Rice researchers generated their trochoidal light waves by total internal reflection of linearly polarized light at an air-glass interface .
This type of reflection produces a polarized evanescent wave – a light wave that @ @ @ @ @ @ @ an ordinary , free light wave – and McCarthy and colleagues were able to tune its trochoidal properties by changing the polarization of the incident light .
The team then studied how pairs of particles known as gold plasmonic nanorods scattered this light .
These particles are made from a metallic nanostructure that can be fine-tuned to absorb and scatter light of different frequencies thanks to the physics of plasmons – quasiparticles that arise when light interacts with the electrons in the metal and causes them to oscillate .
While trochoidal light polarization @ @ @ @ @ @ @ McCarthy and colleagues are the first to use plasmonic nanoparticles to study how it interacts with matter .
“ Using a dark-field microscope and spectrometer , we found that clockwise and anticlockwise trochoidal polarizations interacted differently with pairs of plasmonic nanorods oriented at 90° from each other , ” she tells Physics World .
“ Indeed , the wavelengths of light the nanorod pairs scattered changed when we switched the trochoidal polarizations from clockwise to anticlockwise , which is a well-understood indicator of dichroism.
” Previous studies on trochoidal polarization have focused on @ @ @ @ @ @ @ angular momentum of the light ’ s electric field , which can enable light propagation in one direction , McCarthy adds .
“ Our study has instead looked at the spectroscopic signatures of matter irradiated with clockwise and anticlockwise light polarizations.
” Members of the team , who report their work in PNAS , say that trochoidal dichroism could aid the development of spectroscopic techniques that are complementary to established linear and circular dichroism spectroscopies .
“ Ultimately , dichroism is an optical indicator of molecular geometry , ” McCarthy says .
“ @ @ @ @ @ @ @ nature , would be ideally suited to probe cartwheeling charge motion in molecules , while circular dichroisms could probe helical charge motion.
” The researchers would now like to observe signatures of trochoidal dichroism in molecular systems , such as certain light-harvesting molecular antennas that feature charge motion that is both cartwheeling and helical .
Such structures are expected to be particularly sensitive to trochoidal dichroism .

Rice University graduate student Lauren McCarthy. (Courtesy: Jeff Fitlow/Rice University)
Technologies that rely on interactions between matter and polarized light usually stick to the well-understood effects of linear or circular polarization. Researchers at Rice University in the US have now opened the door to fresh approaches by studying how matter reacts to an additional form of polarization. This form, known as “trochoidal” polarization, is characterized by a “cartwheeling” motion in light’s electric field that can occur in either a clockwise or anticlockwise direction. Since matter can distinguish between these two directions, trochoidal dichroism could be used to develop novel spectroscopic tools.
Circularly-polarized light, in which the direction of the electromagnetic field rotates in a helical or “corkscrew-like” fashion as it propagates through space, is commonly used to study the conformation of small biomolecules such as proteins, DNA and amino acids. These studies are possible because such molecules are chiral – that is, their structures have a “handedness” that makes them absorb left- and right-circularly-polarized light differently, a phenomenon known as dichroism. Linear polarization is also widely used, for example to control reflections and glare in sunglasses.
The light polarization the Rice researchers studied is very different from these more familiar types. Rather than following a helical progression, the direction of the electromagnetic field in trochoidal light turns end-over-end as it propagates, rotating either clockwise or anticlockwise as it goes. “Rather like a rolling hula hoop,” explains study lead author Lauren McCarthy.
Measuring light scattered from plasmonic nanorods
The Rice researchers generated their trochoidal light waves by total internal reflection of linearly polarized light at an air-glass interface. This type of reflection produces a polarized evanescent wave – a light wave that exists only near a surface, unlike an ordinary, free light wave – and McCarthy and colleagues were able to tune its trochoidal properties by changing the polarization of the incident light.
The team then studied how pairs of particles known as gold plasmonic nanorods scattered this light. These particles are made from a metallic nanostructure that can be fine-tuned to absorb and scatter light of different frequencies thanks to the physics of plasmons – quasiparticles that arise when light interacts with the electrons in the metal and causes them to oscillate.
While trochoidal light polarization has been observed in previous experiments, McCarthy and colleagues are the first to use plasmonic nanoparticles to study how it interacts with matter. “Using a dark-field microscope and spectrometer, we found that clockwise and anticlockwise trochoidal polarizations interacted differently with pairs of plasmonic nanorods oriented at 90° from each other,” she tells Physics World. “Indeed, the wavelengths of light the nanorod pairs scattered changed when we switched the trochoidal polarizations from clockwise to anticlockwise, which is a well-understood indicator of dichroism.”
Spectroscopic signatures
Previous studies on trochoidal polarization have focused on properties such as the unique transverse spin angular momentum of the light’s electric field, which can enable light propagation in one direction, McCarthy adds. “Our study has instead looked at the spectroscopic signatures of matter irradiated with clockwise and anticlockwise light polarizations.”
Members of the team, who report their work in PNAS, say that trochoidal dichroism could aid the development of spectroscopic techniques that are complementary to established linear and circular dichroism spectroscopies. “Ultimately, dichroism is an optical indicator of molecular geometry,” McCarthy says. “Trochoidal polarizations, owing to their cartwheeling nature, would be ideally suited to probe cartwheeling charge motion in molecules, while circular dichroisms could probe helical charge motion.”
The researchers would now like to observe signatures of trochoidal dichroism in molecular systems, such as certain light-harvesting molecular antennas that feature charge motion that is both cartwheeling and helical. Such structures are expected to be particularly sensitive to trochoidal dichroism.


physicsworld--2020-08-07--Artificial stupidity - Physics World

Artificial stupidity - Physics World

Not so long ago , machine learning was a novelty in physics .
Although physicists have always been quick to adopt new computing techniques , the early problems that this variant of artificial intelligence ( AI ) could solve – such as recognizing handwriting , identifying cats in photos and beating humans at backgammon – were not the sort of problems that got physicists out of bed in the morning .
Consequently , the term “ machine learning ” did not appear on the Physics World website until 2009 , and for several years afterwards it cropped up only sporadically @ @ @ @ @ @ @ the situation began to change .
Medical physicists discovered that training a machine to identify cats was not so different from training it to identify cancers .
Materials scientists learned that AIs could optimize the properties of new alloys , not just backgammon scores .
Before long , the rest of the physics community was finding reasons to join the machine-learning party .
A quick scan of the Physics World archive shows that since 2017 , physicists have used machine learning to , among other things , enhance optical storage , stabilize synchrotron @ @ @ @ @ @ @ femtosecond laser patterning , spot gravitational waves and find the best LED phosphor in a list of 100,000 compounds .
Indeed , machine-learning applications have spread so rapidly that they are no longer remarkable .
Soon , they may even be routine – a sure sign of a technology ’ s success .
All of which makes this an excellent time for physicists to pick up a copy of You Look Like a Thing and I Love You – a deft , informative and often screamingly funny primer on the ways that machine @ @ @ @ @ @ @ go wrong .
And by “ go wrong ” , author Janelle Shane isn ’ t talking about machines becoming hyper-intelligent and overthrowing the puny humans who invented them .
In fact , the opposite is true : most of AI ’ s problems arise not because algorithms are too intelligent , but because they are approximately as bright as an earthworm .
Shane is well placed to comment on algorithms ’ daft behaviour .
Since 2016 she has regularly entertained readers of her blog AI Weirdness by giving neural networks ( a @ @ @ @ @ @ @ of text and asking them to produce new text in a similar style .
Many useful AIs are “ trained ” in exactly this fashion , but Shane ’ s peculiar genius is to feed her algorithms cultural oddments such as paint colours , recipes and ice-cream flavours , rather than ( say ) crystallographic data .
The results – a warm shade of pink the neural network dubs “ Stanky Bean ” ; a recipe for “ clam frosting ” ; and ( my personal favourite ) an ice-cream flavour called “ @ @ @ @ @ @ @ eccentric and often endearing .
The book ’ s title is another example : apparently , “ you look like a thing and I love you ” is an algorithm ’ s idea of a great pick-up line .
Frankly , I ’ ve heard worse .
A book full of such slip-ups would be worth reading purely for comedic value , but these bloopers have points as well as punchlines .
“ Necrostar with Chocolate Person ” , for example , is the logical result of taking an AI that knows how @ @ @ @ @ @ @ asking it to generate ice cream flavours instead .
This process is known as transfer learning , and it ’ s a common shortcut for AI developers , saving hours of computing time that would otherwise be wasted in teaching the algorithm to generate words from scratch .
Similarly , recipes for clam frosting exist in part because AIs don ’ t “ understand ” food like a human does , but also because they have short memories .
Hence , by the time the algorithm reaches the last ingredient in a recipe @ @ @ @ @ @ @ the first .
AI amnesia also explains why algorithms can ( and do ) generate sentence-by-sentence summaries of sporting matches , but book reviews are beyond them – at least for now .
The most fascinating – and serious – problem with AIs is not their stupidity or forgetfulness , though .
It ’ s their propensity to behave in ways their creators never intended .
Shane illustrates this with a chapter on training simulated robots to walk .
The idea is to start with a robot that can barely wriggle , give @ @ @ @ @ @ @ mechanism that rewards progress , and allow the AI to evolve ever-more-efficient propulsion methods .
But whereas real evolution has produced several viable means of locomotion , an AI given this challenge is extremely likely to cheat .
A robot asked to move from A to B , for example , may grow to an equivalent height and fall over .
If the human programmer rules out this class of “ solutions ” , the robot may evolve an awkward spinning gait or exploit flaws in the simulation ’ s physics to teleport @ @ @ @ @ @ @ Shane notes , “ It ’ s as if the [ walking ] games were being played by very literal-minded toddlers.
” Robots that fall over are amusing .
Algorithms that preferentially reject job applications from women are not .
Both are real examples ; both stem from AI ’ s love of shortcuts .
Picking the best person for a job is hard , even ( especially ? )
for a computer .
However , if the AI has been trained on successful CVs from a company with a pre-existing diversity problem @ @ @ @ @ @ @ its chances of picking the “ right ” applicants if it rejects CVs that mention women ’ s colleges or girls ’ soccer .
In some ways , AIs that learn undesirable lessons from biased data are merely the latest example of the old programming maxim “ garbage in , garbage out ” .
But there is a twist .
Unlike human-authored code , machine-learning algorithms are a black box .
You can ’ t ask an AI why it thinks “ Stanky Bean ” is a desirable name for a paint colour @ @ @ @ @ @ @ applicant from a majority-Black neighbourhood as a higher credit risk .
It won ’ t be able to tell you .
What you can do , though , is educate yourself about the ways machine learning can fail , and for this , You Look Like a Thing and I Love You is an excellent place to start .
As Shane puts it , “ When you ask an AI to draw a cat or write a joke , its mistakes are the same sorts of mistakes it makes when processing fingerprints or @ @ @ @ @ @ @ s glaringly obvious that something ’ s gone wrong when the cat has six legs and the joke has no punchline .
Plus , it ’ s really hilarious .
”

Physics World. Members of the Institute of Physics can enjoy the full issue Taken from the August 2020 issue of. Members of the Institute of Physics can enjoy the full issue via the Physics World app
Margaret Harris reviews You Look Like a Thing and I Love You: How Artificial Intelligence Works and Why It’s Making the World a Weirder Place by Janelle Shane
Not so long ago, machine learning was a novelty in physics. Although physicists have always been quick to adopt new computing techniques, the early problems that this variant of artificial intelligence (AI) could solve – such as recognizing handwriting, identifying cats in photos and beating humans at backgammon – were not the sort of problems that got physicists out of bed in the morning. Consequently, the term “machine learning” did not appear on the Physics World website until 2009, and for several years afterwards it cropped up only sporadically.
In the mid-2010s, though, the situation began to change. Medical physicists discovered that training a machine to identify cats was not so different from training it to identify cancers. Materials scientists learned that AIs could optimize the properties of new alloys, not just backgammon scores. Before long, the rest of the physics community was finding reasons to join the machine-learning party. A quick scan of the Physics World archive shows that since 2017, physicists have used machine learning to, among other things, enhance optical storage, stabilize synchrotron beams, predict cancer evolution, improve femtosecond laser patterning, spot gravitational waves and find the best LED phosphor in a list of 100,000 compounds. Indeed, machine-learning applications have spread so rapidly that they are no longer remarkable. Soon, they may even be routine – a sure sign of a technology’s success.
All of which makes this an excellent time for physicists to pick up a copy of You Look Like a Thing and I Love You – a deft, informative and often screamingly funny primer on the ways that machine learning can (and often does) go wrong. And by “go wrong”, author Janelle Shane isn’t talking about machines becoming hyper-intelligent and overthrowing the puny humans who invented them. In fact, the opposite is true: most of AI’s problems arise not because algorithms are too intelligent, but because they are approximately as bright as an earthworm.
Shane is well placed to comment on algorithms’ daft behaviour. Since 2016 she has regularly entertained readers of her blog AI Weirdness by giving neural networks (a type of machine-learning algorithm) a body of text and asking them to produce new text in a similar style. Many useful AIs are “trained” in exactly this fashion, but Shane’s peculiar genius is to feed her algorithms cultural oddments such as paint colours, recipes and ice-cream flavours, rather than (say) crystallographic data. The results – a warm shade of pink the neural network dubs “Stanky Bean”; a recipe for “clam frosting”; and (my personal favourite) an ice-cream flavour called “Necrostar with Chocolate Person” – are eccentric and often endearing. The book’s title is another example: apparently, “you look like a thing and I love you” is an algorithm’s idea of a great pick-up line. Frankly, I’ve heard worse.
A book full of such slip-ups would be worth reading purely for comedic value, but these bloopers have points as well as punchlines. “Necrostar with Chocolate Person”, for example, is the logical result of taking an AI that knows how to generate names of heavy-metal bands and asking it to generate ice cream flavours instead. This process is known as transfer learning, and it’s a common shortcut for AI developers, saving hours of computing time that would otherwise be wasted in teaching the algorithm to generate words from scratch. Similarly, recipes for clam frosting exist in part because AIs don’t “understand” food like a human does, but also because they have short memories. Hence, by the time the algorithm reaches the last ingredient in a recipe, it’s long since forgotten the first. AI amnesia also explains why algorithms can (and do) generate sentence-by-sentence summaries of sporting matches, but book reviews are beyond them – at least for now.
The most fascinating – and serious – problem with AIs is not their stupidity or forgetfulness, though. It’s their propensity to behave in ways their creators never intended. Shane illustrates this with a chapter on training simulated robots to walk. The idea is to start with a robot that can barely wriggle, give it a “goal” and a mechanism that rewards progress, and allow the AI to evolve ever-more-efficient propulsion methods. But whereas real evolution has produced several viable means of locomotion, an AI given this challenge is extremely likely to cheat. A robot asked to move from A to B, for example, may grow to an equivalent height and fall over. If the human programmer rules out this class of “solutions”, the robot may evolve an awkward spinning gait or exploit flaws in the simulation’s physics to teleport itself to the new location. As Shane notes, “It’s as if the [walking] games were being played by very literal-minded toddlers.”
Robots that fall over are amusing. Algorithms that preferentially reject job applications from women are not
Robots that fall over are amusing. Algorithms that preferentially reject job applications from women are not. Both are real examples; both stem from AI’s love of shortcuts. Picking the best person for a job is hard, even (especially?) for a computer. However, if the AI has been trained on successful CVs from a company with a pre-existing diversity problem, it may find it can boost its chances of picking the “right” applicants if it rejects CVs that mention women’s colleges or girls’ soccer.
In some ways, AIs that learn undesirable lessons from biased data are merely the latest example of the old programming maxim “garbage in, garbage out”. But there is a twist. Unlike human-authored code, machine-learning algorithms are a black box. You can’t ask an AI why it thinks “Stanky Bean” is a desirable name for a paint colour, or why it treats a loan applicant from a majority-Black neighbourhood as a higher credit risk. It won’t be able to tell you. What you can do, though, is educate yourself about the ways machine learning can fail, and for this, You Look Like a Thing and I Love You is an excellent place to start. As Shane puts it, “When you ask an AI to draw a cat or write a joke, its mistakes are the same sorts of mistakes it makes when processing fingerprints or sorting medical images, except it’s glaringly obvious that something’s gone wrong when the cat has six legs and the joke has no punchline. Plus, it’s really hilarious.”


physicsworld--2020-08-06--Bending hairs and compliant microstructures make razor blades dull - Physics World

New insights into why a hard steel razor blade is dulled by cutting soft hairs have been gained by a trio of researchers at the Massachusetts Institute of Technology .
Gianluca Roscioli , Seyedeh Mohadeseh Taheri-Mousavi and Cemal Cem Tasan did a series of experiments that recreate the shaving process and found that dulling is a result of microscopic variations in the structure of a blade and the angle at which a cut is made .
The team suggests that nanoscale improvements to blades could boost the performance of cutting tools .
Most modern cutting edges are made of hardened @ @ @ @ @ @ @ commonly cut materials such as hair and food .
Indeed , the steel used to make razors is more than 50-times harder than human hair .
As a result , scientists have long been puzzled exactly why such blades dull so rapidly after cutting seemingly soft materials .
It had long been assumed that sharp edges are dulled by basic wear mechanisms such as the cracking of brittle steel surfaces and the rounding of edges .
However , little had been known about how these processes relate to the complex ways that blades @ @ @ @ @ @ @ on a microscopic scale .
Roscioli and colleagues investigated this process by using an electron microscope to observe how commercial razor blades cut individual hairs and bunches of hair in real time .
They found that two things affected how the blades were dulled by cutting the hair .
When a razorblade slices through a hair that is fixed to the skin , the hair bends away from the blade – thus changing the cutting angle .
At some angles , the blade is subject to a large shear force that is perpendicular @ @ @ @ @ @ @ believe this causes the deformation and chipping of the blade — because this damage was not observed in experiments where the cutting angle was controlled to eliminate perpendicular shear .
The second thing that appeared to affect the dulling process is microstructural variation along the edge of the blade .
A steel blade is made of tiny microstructures , some of which are stiff and some of which are compliant .
Normally , this composition is advantageous because it prevents the propagation of cracks .
But the material can be damaged if a @ @ @ @ @ @ @ brunt of the cutting .
In the razor blades studied by the team , the chances of this occurring depended both on the size of the microstructures and the position of the boundary between stiff and compliant regions within the cross section of a hair .
The team concludes that razor blades and other sharp tools could be improved by using more homogenous microstructures at the cutting edge .
This could be achieved using nanostructured alloys , for example .
The research is described in Science .

Close shave: electron microscope image of a razorblade cutting human hair. (Courtesy: Gianluca Roscioli/Tasan Group/MIT)
New insights into why a hard steel razor blade is dulled by cutting soft hairs have been gained by a trio of researchers at the Massachusetts Institute of Technology. Gianluca Roscioli, Seyedeh Mohadeseh Taheri-Mousavi and Cemal Cem Tasan did a series of experiments that recreate the shaving process and found that dulling is a result of microscopic variations in the structure of a blade and the angle at which a cut is made. The team suggests that nanoscale improvements to blades could boost the performance of cutting tools.
Most modern cutting edges are made of hardened steel, which is much harder than commonly cut materials such as hair and food. Indeed, the steel used to make razors is more than 50-times harder than human hair. As a result, scientists have long been puzzled exactly why such blades dull so rapidly after cutting seemingly soft materials.
It had long been assumed that sharp edges are dulled by basic wear mechanisms such as the cracking of brittle steel surfaces and the rounding of edges. However, little had been known about how these processes relate to the complex ways that blades and materials interact during the cutting process on a microscopic scale.
Roscioli and colleagues investigated this process by using an electron microscope to observe how commercial razor blades cut individual hairs and bunches of hair in real time. They found that two things affected how the blades were dulled by cutting the hair.
Perpendicular shear
When a razorblade slices through a hair that is fixed to the skin, the hair bends away from the blade – thus changing the cutting angle. At some angles, the blade is subject to a large shear force that is perpendicular to the sharp edge. The team believe this causes the deformation and chipping of the blade — because this damage was not observed in experiments where the cutting angle was controlled to eliminate perpendicular shear.
The second thing that appeared to affect the dulling process is microstructural variation along the edge of the blade. A steel blade is made of tiny microstructures, some of which are stiff and some of which are compliant. Normally, this composition is advantageous because it prevents the propagation of cracks. But the material can be damaged if a compliant region of the blade does the brunt of the cutting. In the razor blades studied by the team, the chances of this occurring depended both on the size of the microstructures and the position of the boundary between stiff and compliant regions within the cross section of a hair.
The team concludes that razor blades and other sharp tools could be improved by using more homogenous microstructures at the cutting edge. This could be achieved using nanostructured alloys, for example.
The research is described in Science.


physicsworld--2020-08-06--Quantum dots track two-dimensional diffusion in cells - Physics World

Quantum dots diffuse within living cells in a nearly two-dimensional fashion .
This result , which was obtained using a new 3D microscopy technique that can track single particles , sheds fresh light on intracellular diffusion – a process that is critical for moving molecules around the cell and for mediating other important activities .
According to study leader Hui Li , a biophysicist at the Chinese Academy of Sciences in Beijing and Beijing Normal University , the 2D motion he and his colleagues observed is robust and stems from the complex architectures of the flat “ adherent ” biological @ @ @ @ @ @ @ ideal probes for studying intracellular diffusion in living cells .
They are similar in size to intracellular macromolecules and can be made to mimic biological materials relatively easily , by coating their surfaces with organic molecules .
Previous studies , however , relied mainly on two-dimensional measurements of their movement , with the assumption that three-dimensional diffusion is an extension of 2D diffusion and is isotropic .
The new work reveals that diffusion is in fact highly anisotropic , thanks to the heterogenous architectures of various cell structures .
From the quasi-2D diffusion @ @ @ @ @ @ @ infer the presence of planar structures within the cytoplasm – the thick solution composed mainly of water , salt and proteins that fills each cell and is enclosed by the cell membrane .
They also suggest that these planar structures provide a means of rapidly and efficiently transporting molecules by diffusion within the cells .
Li and colleagues obtained their result using an extension of a 2D single-particle tracking ( SPT ) instrument that they developed in 2015 .
Like its predecessor , the new 3D SPT relies on tracking single quantum dots @ @ @ @ @ @ @ of the most common types of biological cell , and the model of choice for cellular studies .
While the earlier method was only able to measure the positions of particles in the lateral ( x and y directions ) , it nevertheless revealed a heterogenous and compartmentalized diffusion behaviour in the endoplasmic reticulum – a cellular structure that plays a major role in protein synthesis , folding and transport .
It could not , however , show how the dots actually diffused through the cytoplasm in all three directions in space .
@ @ @ @ @ @ @ it can measure the axial ( z-direction ) positions of the particles as well as their lateral ones – with a resolution as small as 35 nm .
To improve on their 2D SPT microscope , the Beijing researchers had to construct two additional components for it : a focus-locking apparatus to eliminate vertical drift ; and a two-focal imaging apparatus to measure axial positions of particles from off-focused diffraction rings .
In their experiments , the researchers loaded their quantum dots into the cytoplasm of cultured human ( A549 ) cancer cells @ @ @ @ @ @ @ their new 3D SPT approach , they then “ joined up ” the dots to construct their trajectory through the cytoplasm .
This technique allowed them to analyse trajectories in terms of motion type ( that is , Browning motion , sub-diffusion or confined motion ) , and also yielded information on parameters such as diffusion rates .
“ Intracellular diffusion is critical for molecule translocation in cells and mediates many important cellular processes , ” Li tells Physics World .
“ Our finding suggests that cells may utilize the architecture of the @ @ @ @ @ @ @ and regulate macromolecule transport.
” Indeed , the quasi-2D diffusion of the dots with constrained movement in the axial direction appears to effectively promote molecular translocation and shorten particle diffusion times .
Members of the Beijing team , who report their work in Chinese Physical Letters , now plan to combine their 3D SPT technique with dynamical subcellular imaging to better explore the relationship between the quasi-2D diffusion they have observed and cell architecture .
“ We are also investigating intracellular diffusion in fast-migrating cells to further elucidate the physical mechanisms behind cell @ @ @ @ @ @ @ This is our most exciting project right now .
”

3D tracking of QDs in A549 cells and dynamical analysis of their trajectories. Courtesy: Chinese Physics Letters
Quantum dots diffuse within living cells in a nearly two-dimensional fashion. This result, which was obtained using a new 3D microscopy technique that can track single particles, sheds fresh light on intracellular diffusion – a process that is critical for moving molecules around the cell and for mediating other important activities. According to study leader Hui Li, a biophysicist at the Chinese Academy of Sciences in Beijing and Beijing Normal University, the 2D motion he and his colleagues observed is robust and stems from the complex architectures of the flat “adherent” biological cells they studied.
Quantum dots make ideal probes for studying intracellular diffusion in living cells. They are similar in size to intracellular macromolecules and can be made to mimic biological materials relatively easily, by coating their surfaces with organic molecules. Previous studies, however, relied mainly on two-dimensional measurements of their movement, with the assumption that three-dimensional diffusion is an extension of 2D diffusion and is isotropic.
The new work reveals that diffusion is in fact highly anisotropic, thanks to the heterogenous architectures of various cell structures. From the quasi-2D diffusion behaviour they observed, Li and colleagues infer the presence of planar structures within the cytoplasm – the thick solution composed mainly of water, salt and proteins that fills each cell and is enclosed by the cell membrane. They also suggest that these planar structures provide a means of rapidly and efficiently transporting molecules by diffusion within the cells.
3D single-particle tracking microscopy
Li and colleagues obtained their result using an extension of a 2D single-particle tracking (SPT) instrument that they developed in 2015. Like its predecessor, the new 3D SPT relies on tracking single quantum dots in “adherent” cells – one of the most common types of biological cell, and the model of choice for cellular studies.
While the earlier method was only able to measure the positions of particles in the lateral (x and y directions), it nevertheless revealed a heterogenous and compartmentalized diffusion behaviour in the endoplasmic reticulum – a cellular structure that plays a major role in protein synthesis, folding and transport. It could not, however, show how the dots actually diffused through the cytoplasm in all three directions in space. The new method overcomes this shortcoming because it can measure the axial (z-direction) positions of the particles as well as their lateral ones – with a resolution as small as 35 nm.
Joining up the dots
To improve on their 2D SPT microscope, the Beijing researchers had to construct two additional components for it: a focus-locking apparatus to eliminate vertical drift; and a two-focal imaging apparatus to measure axial positions of particles from off-focused diffraction rings.
In their experiments, the researchers loaded their quantum dots into the cytoplasm of cultured human (A549) cancer cells. Once they localized the particles using their new 3D SPT approach, they then “joined up” the dots to construct their trajectory through the cytoplasm. This technique allowed them to analyse trajectories in terms of motion type (that is, Browning motion, sub-diffusion or confined motion), and also yielded information on parameters such as diffusion rates.
“Intracellular diffusion is critical for molecule translocation in cells and mediates many important cellular processes,” Li tells Physics World. “Our finding suggests that cells may utilize the architecture of the cytoplasm to control the intracellular diffusion dynamics and regulate macromolecule transport.” Indeed, the quasi-2D diffusion of the dots with constrained movement in the axial direction appears to effectively promote molecular translocation and shorten particle diffusion times.
Members of the Beijing team, who report their work in Chinese Physical Letters, now plan to combine their 3D SPT technique with dynamical subcellular imaging to better explore the relationship between the quasi-2D diffusion they have observed and cell architecture. “We are also investigating intracellular diffusion in fast-migrating cells to further elucidate the physical mechanisms behind cell diffusion,” Li says. “This is our most exciting project right now.”


physicsworld--2020-08-06--Creating new technologies using 2D materials, supernova wreaked havoc on Earth, quantum go versus AI

Creating new technologies using 2D materials, supernova wreaked havoc on Earth, quantum go versus AI - Physics World

Atomically thin 2D materials such as graphene have unique electronic and mechanical properties that could revolutionize how electronics are manufactured @ @ @ @ @ and graphene tattoos that monitor blood pressure are just two of the examples given by @ @ @ @ @ with Physics World ’ s Margaret Harris .
Akinwande is professor of electrical and computer @ @ @ @ @ Texas at Austin and he also talks about how 2D materials could be used to @ @ @ @ @ for mobile phones .
Did the explosion of a nearby star cause a huge extinction @ @ @ @ @ years ago ?
The science writer Logan Chipkin joins us to talk about new claims @ @ @ @ @ how a connection between a supernova and the “ Hangenberg Crisis ” could be verified @ @ @ @ @ about how physicists in China have built a quantum version of the ancient board game @ @ @ @ @ .
While their invention is designed to challenge artificial intelligence systems , it would also @ @ @ @ @ game .

Atomically thin 2D materials such as graphene have unique electronic and mechanical properties that could revolutionize how electronics are manufactured and used. Foldable radios and graphene tattoos that monitor blood pressure are just two of the examples given by Deji Akinwande in a conversation with Physics World’s Margaret Harris. Akinwande is professor of electrical and computer engineering at the University of Texas at Austin and he also talks about how 2D materials could be used to make better memories and switches for mobile phones.
Did the explosion of a nearby star cause a huge extinction event on Earth 259 million years ago? The science writer Logan Chipkin joins us to talk about new claims from astronomers – and explains how a connection between a supernova and the “Hangenberg Crisis” could be verified.
Finally, we chat about how physicists in China have built a quantum version of the ancient board game go – using entangled photons. While their invention is designed to challenge artificial intelligence systems, it would also change how humans play the game.