physicsworld--2020-11-05--The importance of keeping up with career opportunities despite the pandemic - Physics World

We ’ ve all spent a lot more time at home recently following the COVID-19 pandemic .
During lockdown you may have obtained new skills or attended online meetings wearing pyjamas beneath a blouse or shirt .
The unprecedented nature of COVID-19 has seen most labs close , leading to more time with the family , the ability to easily flex hours , no commuting as well as instant access to the kitchen and the kettle .
Enthusiasm for this new way of working was initially high , but once the difficulty of balancing 24-hour childcare , fighting constant distractions @ @ @ @ @ @ @ apparent the novelty soon wore off .
For many PhD students , postdocs and academics , the lack of face-to-face communication and the limited access to facilities are an inconvenience .
Online meetings are less productive and there ’ s the constant challenge of engaging a class of students on Zoom when they are just names on a screen .
Those of us who are settled are more fortunate , but for graduates , PhD students and postdocs , the prospect of a career “ next step ” seems more precarious and unsettling @ @ @ @ @ @ @ searching for a new position usually involved an in-person meeting with prospective colleagues and seeing workplaces and labs .
Travel restrictions have taken this to the virtual world but despite tremendous effort it is not the same .
Given the logistical challenges of moving abroad , staying put during a global pandemic might seem the wisest and most attractive option .
Yet now could be the perfect moment to look beyond current travel restrictions and quarantines and take advantage of the many positives of working abroad .
After all , fortune favours the @ @ @ @ @ @ @ of moving to a new job is making new collaborations and networking .
Working alongside active and renowned researchers increases your influence in the field , builds your reputation and exposes you to the heated arguments and bold ideas at the forefront of academic debates .
Whether right or wrong , progression in your academic career can very much depend on who you know and with whom you have published .
Sometimes funding is only available elsewhere or perhaps the pay and workers ’ rights are preferable in another country .
In certain @ @ @ @ @ @ @ PhD is considered a job with a contract laying out employee benefits and rights , paid holiday hours , the expected teaching requirements and a fixed salary with bonuses .
Financial security and written employee protection are no longer an unpredictability , but a given .
Heading to pastures new will also expose you to a new environment .
No two labs are the same and , by switching , scientists develop their own experience-based methods and means of thinking .
Perhaps after working in a single-group lab for a few years you @ @ @ @ @ @ @ a diverse range of experiments and experimentalists is more desirable .
Perhaps the new lab accepts external users , allowing interests to develop in the science and materials being studied outside your main expertise .
By changing labs , you can leave your mark and take away knowledge with you for future endeavours .
Moving to a new country is daunting and potentially accompanied by language barriers and culture shocks .
Deviating from your own comfort zone , you ’ ll experience new geographical landscapes , cities , people , food and an @ @ @ @ @ @ @ modern world , the ability to up sticks to another country generates a greater respect and understanding of the world we live in .
Many collaborators have made similar choices leading to Christian holidays celebrated together with Thanksgiving , Eid , Russian New Year or Cinco de Mayo – all being a reason to share laughter and time with each other ( I ’ ve thought of teaching ceilidh dances and toasting a haggis on Burns ’ Night , but drew the line at reciting Scottish poems to students ) .
For those @ @ @ @ @ @ @ of a stable living situation can feel somewhat far-fetched .
Maybe there seems little reason to buy a house because dealing with short-term rentals in foreign countries requires less commitment .
Feeling “ at home ” , however , does not need to correlate with owning a piece of land .
For some it can simply mean being comfortable in a work environment or getting by easily while out shopping or using public transport .
For others , it could be joining a choir , signing up to a sports team , making @ @ @ @ @ @ @ or wine shop ) , or simply feeling at peace .
Although the transition requires effort in the initial stages , the rewards outweigh the fears .
Science is a global and collaborative endeavour and while conferences and meetings may have gone online for the foreseeable future , information and expertise can still physically travel .
Tempting though it may be to stay put during these testing times , keeping an open mind and looking outwards could be worth the risk .
If there is an exciting opportunity abroad , overlook the barriers @ @ @ @ @ @ @ .
Don ’ t reject today what you would regret tomorrow .

Physics World, where it appeared under the headline "Keeping up with opportunities" . Members of the Institute of Physics can enjoy the full issue Taken from the November 2020 issue of, where it appeared under the headline "Keeping up with opportunities" . Members of the Institute of Physics can enjoy the full issue via the Physics World app
Caitlin Duffy says it is more critical than ever to consider your next career move despite the challenges posed by the COVID-19 pandemic
Pack mentality A move abroad for work might offer great reward despite COVID-19. (Courtesy: iStock/Dean Mitchell)
We’ve all spent a lot more time at home recently following the COVID-19 pandemic. During lockdown you may have obtained new skills or attended online meetings wearing pyjamas beneath a blouse or shirt. The unprecedented nature of COVID-19 has seen most labs close, leading to more time with the family, the ability to easily flex hours, no commuting as well as instant access to the kitchen and the kettle. Enthusiasm for this new way of working was initially high, but once the difficulty of balancing 24-hour childcare, fighting constant distractions and maintaining a healthy work–life balance became apparent the novelty soon wore off.
For many PhD students, postdocs and academics, the lack of face-to-face communication and the limited access to facilities are an inconvenience. Online meetings are less productive and there’s the constant challenge of engaging a class of students on Zoom when they are just names on a screen. Those of us who are settled are more fortunate, but for graduates, PhD students and postdocs, the prospect of a career “next step” seems more precarious and unsettling than ever.
Before the pandemic, searching for a new position usually involved an in-person meeting with prospective colleagues and seeing workplaces and labs. Travel restrictions have taken this to the virtual world but despite tremendous effort it is not the same. Given the logistical challenges of moving abroad, staying put during a global pandemic might seem the wisest and most attractive option. Yet now could be the perfect moment to look beyond current travel restrictions and quarantines and take advantage of the many positives of working abroad. After all, fortune favours the bold.
The global village
Perhaps the most beneficial part of moving to a new job is making new collaborations and networking. Working alongside active and renowned researchers increases your influence in the field, builds your reputation and exposes you to the heated arguments and bold ideas at the forefront of academic debates. Whether right or wrong, progression in your academic career can very much depend on who you know and with whom you have published. Sometimes funding is only available elsewhere or perhaps the pay and workers’ rights are preferable in another country. In certain European nations, for example, a PhD is considered a job with a contract laying out employee benefits and rights, paid holiday hours, the expected teaching requirements and a fixed salary with bonuses. Financial security and written employee protection are no longer an unpredictability, but a given.
Heading to pastures new will also expose you to a new environment. No two labs are the same and, by switching, scientists develop their own experience-based methods and means of thinking. Perhaps after working in a single-group lab for a few years you might discover that a multi-group lab with a diverse range of experiments and experimentalists is more desirable. Perhaps the new lab accepts external users, allowing interests to develop in the science and materials being studied outside your main expertise. By changing labs, you can leave your mark and take away knowledge with you for future endeavours.
Moving to a new country is daunting and potentially accompanied by language barriers and culture shocks. Deviating from your own comfort zone, you’ll experience new geographical landscapes, cities, people, food and an alternative way of living. In the modern world, the ability to up sticks to another country generates a greater respect and understanding of the world we live in. Many collaborators have made similar choices leading to Christian holidays celebrated together with Thanksgiving, Eid, Russian New Year or Cinco de Mayo – all being a reason to share laughter and time with each other (I’ve thought of teaching ceilidh dances and toasting a haggis on Burns’ Night, but drew the line at reciting Scottish poems to students).
For those chasing the academic dream, the concept of a stable living situation can feel somewhat far-fetched. Maybe there seems little reason to buy a house because dealing with short-term rentals in foreign countries requires less commitment. Feeling “at home”, however, does not need to correlate with owning a piece of land. For some it can simply mean being comfortable in a work environment or getting by easily while out shopping or using public transport. For others, it could be joining a choir, signing up to a sports team, making friends, finding a local café (or wine shop), or simply feeling at peace. Although the transition requires effort in the initial stages, the rewards outweigh the fears.
Science is a global and collaborative endeavour and while conferences and meetings may have gone online for the foreseeable future, information and expertise can still physically travel. Tempting though it may be to stay put during these testing times, keeping an open mind and looking outwards could be worth the risk. If there is an exciting opportunity abroad, overlook the barriers and complications of COVID-19 and pursue it. Don’t reject today what you would regret tomorrow.


physicsworld--2020-11-05--Antibody-doped gold nanoparticles provide a rapid COVID-19 test - Physics World

Researchers in Italy have developed a rapid test for COVID-19 based around a colour-shifting solution of gold nanoparticles .
They claim that their low-cost test performs better than other rapid diagnostic tools , with a similar accuracy to the gold-standard polymerase chain reaction ( PCR ) tests .
Since the relaxing of lockdowns around the world that were designed to control the spread of COVID-19 , cases of the viral disease have risen again .
There are now fears of a winter “ second wave ” with more cases , hospitalizations and deaths than earlier in the year .
Effective @ @ @ @ @ @ @ the outbreak .
Tests that detect genetic material from the virus that causes the disease – SARS-CoV-2 – in a blood sample using PCR are considered the gold-standard due to their high sensitivity .
But these tests require specialist equipment and trained personnel , leading to longer than ideal turnaround times .
While some countries have successfully scaled up such tests , this has proved difficult elsewhere .
Antigen-based tests on samples from the back of the nose and throat are quicker and cheaper .
These use paper strips that change colour in @ @ @ @ @ @ @ antigens – and can provide results in less than half-an-hour .
But they have a lower sensitivity than PCR-based tests , leading to more false-negative results .
This is a particular issue in later stages of infection when there can be a drop in viral load .
Now , researchers in Italy claim to have developed a test that approaches the sensitivity of PCR-based tests yet provides results in minutes .
The trick to this colourimetric test is to create a solution of gold nanoparticles that collect on the virus and cause a @ @ @ @ @ @ @ liquid .
Physicist Raffaele Velotta , of University of Naples Federico II , and his colleagues achieved this by attaching antibodies targeting three surface proteins of SARS-CoV-2 to the nanoparticles .
This allows the nanoparticles to recognise and coat the virus , Velotta tells Physics World .
In a study reported in ACS Sensors , the researchers analysed 94 frozen samples from nasopharyngeal swabs that had previously been tested by PCR : 45 positive and 49 negative .
The colourimetric test achieved an accuracy of more than 95 % , including when analysing @ @ @ @ @ @ @ .
In the test , the colour of the solution changed from red to purple when SARS-CoV-2 was present .
This change was detected using a commercial colourimeter that could read 50 samples in less than a minute .
Velotta explains that a solution of free gold nanoparticles will have a certain colour due to the wavelengths of light that the solution absorbs .
But if you add a sample containing SARS-CoV-2 to the solution , the resulting aggregation of the virus and the nanoparticles causes a shift in the absorption peak , @ @ @ @ @ @ @ .
“ This shift is sometime visible even to the naked eye , but this is only possible when the viral load is very high , ” he says .
As the exact colour change depends on the amount of virus in the sample , this test could also allow decisions to be made about how infectious someone is and whether they need to be quarantined .
“ Although the nanoparticle aggregation for biosensing in itself is not new , it seems that no other rapid test worldwide exploits such a technique , @ @ @ @ @ @ @ of detection of the molecular gold-standard analysis ( real-time PCR ) , ” says Velotta .
He adds that the researchers have also been testing fresh samples .
“ We are noticing the sensitivity is higher and the test is much more reliable , ” he explains .
Velotta hopes that the test will start being used in labs in the next couple of weeks .
And the researchers have been testing the technique on saliva samples , which are much easier to take and more pleasant for the patient than nasopharyngeal swabs @ @ @ @ @ @ @ he hopes that such saliva tests will be possible in a month or two .

Left: SARS-CoV-2 proteins (spike, membrane and envelope) and gold nanoparticles functionalized with their corresponding antibodies are shown in dark red, violet and grey, respectively. The pink solution contains anti-SARS-CoV-2 functionalized gold nanoparticles. Right: the nanoparticles form a layer on the virus surface, leading to a colour change in the solution. (Courtesy: ACS Sens. 10.1021/acssensors.0c01742)
Researchers in Italy have developed a rapid test for COVID-19 based around a colour-shifting solution of gold nanoparticles. They claim that their low-cost test performs better than other rapid diagnostic tools, with a similar accuracy to the gold-standard polymerase chain reaction (PCR) tests.
Since the relaxing of lockdowns around the world that were designed to control the spread of COVID-19, cases of the viral disease have risen again. There are now fears of a winter “second wave” with more cases, hospitalizations and deaths than earlier in the year.
Effective testing is seen as crucial to controlling the outbreak. Tests that detect genetic material from the virus that causes the disease – SARS-CoV-2 – in a blood sample using PCR are considered the gold-standard due to their high sensitivity. But these tests require specialist equipment and trained personnel, leading to longer than ideal turnaround times. While some countries have successfully scaled up such tests, this has proved difficult elsewhere.
Antigen-based tests on samples from the back of the nose and throat are quicker and cheaper. These use paper strips that change colour in the presence of specific viral proteins – antigens – and can provide results in less than half-an-hour. But they have a lower sensitivity than PCR-based tests, leading to more false-negative results. This is a particular issue in later stages of infection when there can be a drop in viral load.
Now, researchers in Italy claim to have developed a test that approaches the sensitivity of PCR-based tests yet provides results in minutes. The trick to this colourimetric test is to create a solution of gold nanoparticles that collect on the virus and cause a detectable change in the colour of the liquid.
Physicist Raffaele Velotta, of University of Naples Federico II, and his colleagues achieved this by attaching antibodies targeting three surface proteins of SARS-CoV-2 to the nanoparticles. This allows the nanoparticles to recognise and coat the virus, Velotta tells Physics World.
Raffaele Velotta (right) and first author Bartolomeo Della Ventura. (Courtesy: Raffaele Velotta)
In a study reported in ACS Sensors, the researchers analysed 94 frozen samples from nasopharyngeal swabs that had previously been tested by PCR: 45 positive and 49 negative. The colourimetric test achieved an accuracy of more than 95%, including when analysing samples with a very low viral load. In the test, the colour of the solution changed from red to purple when SARS-CoV-2 was present. This change was detected using a commercial colourimeter that could read 50 samples in less than a minute.
Velotta explains that a solution of free gold nanoparticles will have a certain colour due to the wavelengths of light that the solution absorbs. But if you add a sample containing SARS-CoV-2 to the solution, the resulting aggregation of the virus and the nanoparticles causes a shift in the absorption peak, and the colour of the solution changes. “This shift is sometime visible even to the naked eye, but this is only possible when the viral load is very high,” he says.
As the exact colour change depends on the amount of virus in the sample, this test could also allow decisions to be made about how infectious someone is and whether they need to be quarantined.
“Although the nanoparticle aggregation for biosensing in itself is not new, it seems that no other rapid test worldwide exploits such a technique, which we showed to approach the limit of detection of the molecular gold-standard analysis (real-time PCR),” says Velotta. He adds that the researchers have also been testing fresh samples. “We are noticing the sensitivity is higher and the test is much more reliable,” he explains.
Velotta hopes that the test will start being used in labs in the next couple of weeks. And the researchers have been testing the technique on saliva samples, which are much easier to take and more pleasant for the patient than nasopharyngeal swabs. The results are promising, and he hopes that such saliva tests will be possible in a month or two.


physicsworld--2020-11-04--Milky Way magnetar could be the source of a fast radio burst - Physics World

The first fast radio burst ( FRB ) detected in the Milky Way appears to be coming from a magnetar , which is a highly magnetic neutron star .
If magnetars are confirmed to be a source of FRBs , it would be a huge leap forward in our understanding of these mysterious bursts .
The double-peaked FRB comprised two rapid-fire radio bursts that arrived within 28.9 ms of one another on 28 April 2020 .
The signal came from the direction of the magnetar SGR 1935+2154 , which is located an estimated 30,000 light-years away near the centre of @ @ @ @ @ @ @ first detected by the Canadian Hydrogen Intensity Mapping Experiment ( CHIME ) , which is a radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia .
Earlier in April , there had been a flurry of X-ray flares detected by NASA ’ s Swift satellite , and two stronger-than-average flares were seen to occur at exactly the same time as the radio bursts .
The FRB is about 3000 times more powerful than any radio emissions previously detected from a known magnetar .
However , it is still ten times weaker @ @ @ @ @ @ @ means that the FRB would probably not have been detected if it originated from outside the Milky Way , says Kiyoshi Masui of the Massachusetts Institute of Technology , who is an author of a paper in Nature describing the discovery .
The FRB was also seen by astronomers working on the STARE2 radio telescope in the US , who also report in Nature .
A third team used the FAST telescope in China to do follow-up observations and has also published in Nature .
The nearest extragalactic magnetar is about 500 million @ @ @ @ @ @ @ SGR 1935+2154 occurred at that distance , it would have appeared 200 million times fainter .
“ However , there are presumably many extragalactic FRBs that are too faint for us to see , so this burst would have been in that category , ” adds Masui .
There are currently less than 30 known magnetars in the Milky Way .
This small number “ makes life hard ” when trying to understand their behaviour , says Adam Deller , who is an astrophysicist at Swinburne University of Technology in Australia , and @ @ @ @ @ @ @ .
However , “ If we can make a secure link between the type of burst that this galactic magnetar gives off and extragalactic FRBs , then having a source on our doorstep is game-changing , ” he says .
It would allow astronomers to observe features that are too faint to be seen in FRBs in other galaxies , such as weaker bursts and X-ray flares .
Indeed , follow-up observations have already detected more radio bursts coming from SGR 1935+2154 , but these have so far been much weaker than April @ @ @ @ @ @ @ year , Deller was part of a team of scientists who used parallax to measure the precise distance to a magnetar called XTE J1810-197 .
This is the first magnetar known to emit radio pulses , albeit far less energetic than an FRB .
Knowing the distance to the magnetar allows scientists to calculate the strength of its radio emissions .
This allowed the team to estimate that the SGR 1935+2154 FRB is thousands of times brighter than the radio pulses emanating from XTE J1810-197 .
Despite the discovery , scientists still do @ @ @ @ @ @ @ magnetar can produce an FRB , or even if all FRBs are produced by magnetars .
Observations show that FRBs can be divided into at least two population types – those that repeat , which include SGR 1935+2154 , and much more powerful blasts that appear to be one-off events .
Proposals for the FRB mechanism include synchrotron masers and even asteroids colliding with magnetars .
One other popular theory is that quantum effects produce a torrent of electrons that interact with a magnetar ’ s incredibly strong magnetic field , which in @ @ @ @ @ @ @ strength of 2.2×1014 gauss .
“ Near magnetars , the magnetic field is so strong that it can cause pairs of electrons and positrons to be spontaneously created out of the vacuum using energy contained in the magnetic field , ” says Masui .
These electrons then move like electric currents through the magnetic field , producing the brief blasts of radio waves .
To confirm that at least some extragalactic FRBs are produced by magnetars , astronomers would like to see X-ray bursts coincide with an FRB , as was the case @ @ @ @ @ @ @ the undetermined formation mechanism of FRBs , it is not clear what their relationship with the X-ray flares are .
“ They must be related in some way , but it ’ s funny that X-rays are not always accompanied by radio bursts , ” says Masui .
Understanding that connection , through study of SGR 1935+2154 and other magnetars , could be the key to unlocking at least some of the mysteries surrounding FRBs .

Bursting discovery: the CHIME telescope. (Courtesy: Andre Renard/CHIME Collaboration)
The first fast radio burst (FRB) detected in the Milky Way appears to be coming from a magnetar, which is a highly magnetic neutron star. If magnetars are confirmed to be a source of FRBs, it would be a huge leap forward in our understanding of these mysterious bursts.
The double-peaked FRB comprised two rapid-fire radio bursts that arrived within 28.9 ms of one another on 28 April 2020. The signal came from the direction of the magnetar SGR 1935+2154, which is located an estimated 30,000 light-years away near the centre of the Milky Way. The FRB was first detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which is a radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia.
Earlier in April, there had been a flurry of X-ray flares detected by NASA’s Swift satellite, and two stronger-than-average flares were seen to occur at exactly the same time as the radio bursts.
Powerful signal
The FRB is about 3000 times more powerful than any radio emissions previously detected from a known magnetar. However, it is still ten times weaker than the weakest extragalactic FRB.
This means that the FRB would probably not have been detected if it originated from outside the Milky Way, says Kiyoshi Masui of the Massachusetts Institute of Technology, who is an author of a paper in Nature describing the discovery. The FRB was also seen by astronomers working on the STARE2 radio telescope in the US, who also report in Nature. A third team used the FAST telescope in China to do follow-up observations and has also published in Nature.
The nearest extragalactic magnetar is about 500 million light-years away. Had the burst from SGR 1935+2154 occurred at that distance, it would have appeared 200 million times fainter. “However, there are presumably many extragalactic FRBs that are too faint for us to see, so this burst would have been in that category,” adds Masui.
There are currently less than 30 known magnetars in the Milky Way. This small number “makes life hard” when trying to understand their behaviour, says Adam Deller, who is an astrophysicist at Swinburne University of Technology in Australia, and who was not involved in the research.
Secure link needed
However, “If we can make a secure link between the type of burst that this galactic magnetar gives off and extragalactic FRBs, then having a source on our doorstep is game-changing,” he says. It would allow astronomers to observe features that are too faint to be seen in FRBs in other galaxies, such as weaker bursts and X-ray flares. Indeed, follow-up observations have already detected more radio bursts coming from SGR 1935+2154, but these have so far been much weaker than April’s double-peaked FRB.
Earlier this year, Deller was part of a team of scientists who used parallax to measure the precise distance to a magnetar called XTE J1810-197. This is the first magnetar known to emit radio pulses, albeit far less energetic than an FRB. Knowing the distance to the magnetar allows scientists to calculate the strength of its radio emissions. This allowed the team to estimate that the SGR 1935+2154 FRB is thousands of times brighter than the radio pulses emanating from XTE J1810-197.
Despite the discovery, scientists still do not understand the mechanism by which a magnetar can produce an FRB, or even if all FRBs are produced by magnetars. Observations show that FRBs can be divided into at least two population types – those that repeat, which include SGR 1935+2154, and much more powerful blasts that appear to be one-off events.
Quantum effects
Proposals for the FRB mechanism include synchrotron masers and even asteroids colliding with magnetars. One other popular theory is that quantum effects produce a torrent of electrons that interact with a magnetar’s incredibly strong magnetic field, which in the case of SGR 1935+2154 has a strength of 2.2×1014 gauss.
“Near magnetars, the magnetic field is so strong that it can cause pairs of electrons and positrons to be spontaneously created out of the vacuum using energy contained in the magnetic field,” says Masui. These electrons then move like electric currents through the magnetic field, producing the brief blasts of radio waves.
To confirm that at least some extragalactic FRBs are produced by magnetars, astronomers would like to see X-ray bursts coincide with an FRB, as was the case with SGR 1935+2154. However, given the undetermined formation mechanism of FRBs, it is not clear what their relationship with the X-ray flares are.
“They must be related in some way, but it’s funny that X-rays are not always accompanied by radio bursts,” says Masui. Understanding that connection, through study of SGR 1935+2154 and other magnetars, could be the key to unlocking at least some of the mysteries surrounding FRBs.


physicsworld--2020-11-04--‘Hyperbolic hedgehog’ steers active droplets in a liquid crystal - Physics World

Liquid crystals can be used to direct the motion of self-propelled particles , reveals new research done in the US .
In a paper published in Nature , researchers in Oleg Lavrentovich ’ s group at Kent State University describes how it moved a stabilized droplet of active bacteria along a pre-determined path by harnessing the broken symmetry of a liquid crystal .
The researchers found that by aligning the crystal molecules they could force the droplet to move in a straight line , in contrast to its random motion in a Newtonian fluid .
It is hoped that this @ @ @ @ @ @ @ organisms .
Experimental models are vital to the study of human cell migration and division .
Because of their small size , the hydrodynamics of a cell in a fluid is driven by viscosity and sensitive to its diameter , so a successful model must be of a comparable size to the cell of interest .
Most experimental active particles such as bacteria are too small to be used as model cells , but they can form a larger active particle when confined inside a droplet .
In this research , the interior @ @ @ @ @ @ @ subtilis bacteria , and its surface was stabilized with surfactant .
These “ active droplets ” are motile , but unlike a cell , which can direct its motion , the droplet follows a random walk and so its displacement averaged over a long period of time is zero .
The aim of this research was to extend the active droplet system to create a particle that moves along a fixed path .
It is the spherical symmetry of an active droplet that ensures it moves randomly , so symmetry breaking is needed @ @ @ @ @ @ @ achieved this by putting the droplet in a liquid crystal .
A liquid crystal that favours molecular alignment ( such structures are called nematics ) will nevertheless evolve topological defects that persist over large distances .
Characteristic defect patterns in the liquid crystal molecule alignment can be created by obstacles and boundaries , such as walls , and in this case the droplets themselves .
The surfactant forces the liquid crystal molecules into perpendicular alignment with the droplet surface , and this boundary condition competes with the parallel alignment of the molecules at @ @ @ @ @ @ @ defect on one side of the droplet called a hyperbolic hedgehog .
To move the droplet on a fixed trajectory , the researchers exploited the non-Newtonian properties of liquid crystals .
Like all liquids , a liquid crystal flows when subject to shear stress , but the velocity of the flow depends on the alignment of its molecules .
A shear is provided by bacteria moving together along the inside of the droplet , which occurs at high concentrations , when turbulent vortices form .
The liquid crystal outside the droplet begins to @ @ @ @ @ @ @ the molecules means that the flow is asymmetric .
The liquid crystal moves around the droplet away from the hedgehog , resulting in a force that pushes the droplet forwards .
This propulsion dominates over viscous drag , with the velocity increasing with particle diameter up to 140 micron , approximately the size of a human egg cell .
For larger droplets , the topological defects become spherically symmetric ( resembling Saturn ’ s rings ) causing the droplet to move equally to the left and right .
Smaller droplets were also found @ @ @ @ @ @ @ they did not contain enough bacteria to form vortices .
In this system , subject to appropriate boundary conditions , the droplet path can be controlled by the alignment of the liquid crystal .
The researchers showed this for a liquid crystal where the molecules are aligned in concentric circles and the active droplets follow the alignment in a circular path .
The researchers will , in a separate study , investigate the interaction between active droplets in a liquid crystal , where they form chains .
Cell migration underpins biological processes such @ @ @ @ @ @ @ the spread of cancer .
The research demonstrates directed migration of an active droplet , which could make the system a viable model for studying cell movement .

On the move: a time sequence of images showing the motion of a droplet in the liquid crystal. (Courtesy: Hend Baza)
Liquid crystals can be used to direct the motion of self-propelled particles, reveals new research done in the US. In a paper published in Nature, researchers in Oleg Lavrentovich’s group at Kent State University describes how it moved a stabilized droplet of active bacteria along a pre-determined path by harnessing the broken symmetry of a liquid crystal. The researchers found that by aligning the crystal molecules they could force the droplet to move in a straight line, in contrast to its random motion in a Newtonian fluid. It is hoped that this system could be used to model microscopic organisms.
Experimental models are vital to the study of human cell migration and division. Because of their small size, the hydrodynamics of a cell in a fluid is driven by viscosity and sensitive to its diameter, so a successful model must be of a comparable size to the cell of interest. Most experimental active particles such as bacteria are too small to be used as model cells, but they can form a larger active particle when confined inside a droplet.
In this research, the interior of a droplet was filled with Bacillus subtilis bacteria, and its surface was stabilized with surfactant. These “active droplets” are motile, but unlike a cell, which can direct its motion, the droplet follows a random walk and so its displacement averaged over a long period of time is zero. The aim of this research was to extend the active droplet system to create a particle that moves along a fixed path.
Symmetry breaking and liquid crystals
It is the spherical symmetry of an active droplet that ensures it moves randomly, so symmetry breaking is needed to direct its motion. The researchers achieved this by putting the droplet in a liquid crystal.
Broken symmetry: topological defects in a nematic liquid crystal. (Courtesy: Minutemen/CC BY-SA 3.0)
A liquid crystal that favours molecular alignment (such structures are called nematics) will nevertheless evolve topological defects that persist over large distances. Characteristic defect patterns in the liquid crystal molecule alignment can be created by obstacles and boundaries, such as walls, and in this case the droplets themselves.
Hyperbolic hedgehog
The surfactant forces the liquid crystal molecules into perpendicular alignment with the droplet surface, and this boundary condition competes with the parallel alignment of the molecules at the confining walls. This produces a defect on one side of the droplet called a hyperbolic hedgehog.
To move the droplet on a fixed trajectory, the researchers exploited the non-Newtonian properties of liquid crystals. Like all liquids, a liquid crystal flows when subject to shear stress, but the velocity of the flow depends on the alignment of its molecules.
Hyperbolic hedgehog: the lines show the orientation of the liquid crystal molecules. The figure also shows the bacteria-containing droplet. (Courtesy: Mojtaba Rajabi)
A shear is provided by bacteria moving together along the inside of the droplet, which occurs at high concentrations, when turbulent vortices form. The liquid crystal outside the droplet begins to flow, and the apolar alignment of the molecules means that the flow is asymmetric. The liquid crystal moves around the droplet away from the hedgehog, resulting in a force that pushes the droplet forwards. This propulsion dominates over viscous drag, with the velocity increasing with particle diameter up to 140 micron, approximately the size of a human egg cell.
Spherical symmetry
For larger droplets, the topological defects become spherically symmetric (resembling Saturn’s rings) causing the droplet to move equally to the left and right. Smaller droplets were also found to be unsuitable for directed motion because they did not contain enough bacteria to form vortices.
In this system, subject to appropriate boundary conditions, the droplet path can be controlled by the alignment of the liquid crystal. The researchers showed this for a liquid crystal where the molecules are aligned in concentric circles and the active droplets follow the alignment in a circular path. The researchers will, in a separate study, investigate the interaction between active droplets in a liquid crystal, where they form chains.
Cell migration underpins biological processes such as tissue repair, embryo development and the spread of cancer. The research demonstrates directed migration of an active droplet, which could make the system a viable model for studying cell movement.


physicsworld--2020-11-04--3D printed fibres make efficient respiratory sensors - Physics World

The coronavirus responsible for the current COVID-19 pandemic is transmitted through respiratory droplets and aerosols emitted when people cough , sneeze , talk and breathe .
Face masks reduce transmission by trapping many of these infectious particles at their source , but questions remain over which mask types and materials are most effective .
A team of researchers at Cambridge University in the UK has now developed non-contact , wearable , portable sensors that measure the amount of moisture that leaks through a face mask during normal breathing , rapid breathing and coughing .
The new devices are based on @ @ @ @ @ @ @ the researchers report that they significantly outperform comparable commercial sensors .
Sensors made from small conducting fibres are especially useful for measuring volumes of fluids and gases .
However , such fibres are hard to print and incorporate into electronic devices , while manufacturing them at scale poses additional difficulties .
One challenge is that the high aspect ratio of these mechanically flexible and transparent small-diameter conducting fibres makes them hard to manipulate individually .
To handle these fragile fibres , therefore , transparent nano- and micro-fibre-based devices are generally mounted on a @ @ @ @ @ @ @ substrates mask the very optomechanical properties that the sensor is designed to exploit , and they also drastically reduce the surface area-to-volume ratio of the fibre array .
In addition , circuits with good fibre-to-fibre conductivity often require multiple procedures or post-fibre synthesis treatments to make .
To overcome these problems , team leader Yan Yan Shery Huang and colleagues developed a quick , one-step fibre manufacturing process that they call inflight fibre printing ( iFP ) .
The process begins with a mixture of silver or a biocompatible conducting polymer known as @ @ @ @ @ @ @ the silver/PEDOT : PSS solution is heated to ensure that it rapidly solidifies , and a core-shell nozzle is used to coat it with a thin ( 10-20 nm ) layer of polyethylene oxide .
The result is a highly pure conducting-core fibre structure that is encased in a protective polymer sheath and can be connected to copper contact pads with minimized contact resistance .
Notably , the iFP technique creates and bonds thin , conducting fibre arrays directly , without any need for post-processing .
In addition to their good optoelectrical characteristics @ @ @ @ @ @ @ ’ s iFP PEDOT : PSS fibre arrays makes them permeable to moisture .
By measuring how the resistance of end-to-end fibres evolves in response to changes in humidity , Huang and colleagues were able to organize the fibre arrays in a way that optimizes their sensitivity to these changes .
The result is a system in which the resistance of the iFP fibres increases linearly as relative humidity rises from 55 to 90 % at room temperature .
The researchers also report that their iFP fibres responded faster than a commercial humidity @ @ @ @ @ @ @ water .
To test their iFP fibre arrays , the researchers fabricated two types of respiratory moisture sensor .
In the first , they printed a single layer of PEDOT : PSS onto a 3D-printed plastic frame to create a sensor that attaches to the exterior of a disposable mask .
The team found that the resistance of the fibre arrays in this wearable , non-contact and non-invasive respiration-rate monitoring device returned to its baseline level less than three seconds after normal breathing .
A commercial sensor , in contrast , takes roughly @ @ @ @ @ @ @ unlike commercial sensors , the fibre-array sensor proved adept at detecting rapid breathing patterns ( roughly 1.2 seconds per breath cycle ) that can indicate shortness of breath .
The second type of sensor consisted of PEDOT : PSS fibre arrays as front and back layers , with a sound-detecting suspended piezoelectric polymer nanofibre layer sandwiched in between .
Since the entire sensor is transparent and permeable to air , the researchers say that it could be attached to a phone camera and used to collect multiple types of information – such as @ @ @ @ @ @ @ in breath humidity – at the same time .
In a final series of experiments , Huang and colleagues configured their system to detect respiratory moisture that flows through a mask when the wearer breathes and coughs .
In surgical masks , they found that most moisture leakage occurs at the front – implying that such masks redirect some exhaled breath out around the nose area and through the front of the mask .
N95 masks tended to leak from the top and sides while FFP2-grade masks – which are designed to filter @ @ @ @ @ @ @ particles – were found to be more effective at reducing the flow of breath through the front of the mask .
Both types of mask , however , weakened the flow of exhaled breath when worn correctly .
The team also found that when a mask-wearing person coughs , the resistance of the fibres increases much more steeply than when the person lets out a long breath – confirming that the strength of the airflow during coughing is higher than when exhaling normally .
According to the researchers , who report their work @ @ @ @ @ @ @ these could find use in mobile-health diagnostics and assessments , where their low cost ( at 50p for the single-layer sensor and around £2 for the tri-layer device ) makes them particularly attractive .
The fibres themselves may also have biological applications beyond respiratory sensing .
Because the fibres can be made with diameters below the typical size of a cell ( a few microns ) , the researchers say they could be used to guide the movement of cells and detect this dynamic process as electrical signals .

iFP fibre sensor attached to a face covering. (Courtesy: University of Cambridge)
The coronavirus responsible for the current COVID-19 pandemic is transmitted through respiratory droplets and aerosols emitted when people cough, sneeze, talk and breathe. Face masks reduce transmission by trapping many of these infectious particles at their source, but questions remain over which mask types and materials are most effective. A team of researchers at Cambridge University in the UK has now developed non-contact, wearable, portable sensors that measure the amount of moisture that leaks through a face mask during normal breathing, rapid breathing and coughing. The new devices are based on transparent, micron-sized electronic fibres, and the researchers report that they significantly outperform comparable commercial sensors.
One-step printing process
Sensors made from small conducting fibres are especially useful for measuring volumes of fluids and gases. However, such fibres are hard to print and incorporate into electronic devices, while manufacturing them at scale poses additional difficulties. One challenge is that the high aspect ratio of these mechanically flexible and transparent small-diameter conducting fibres makes them hard to manipulate individually. To handle these fragile fibres, therefore, transparent nano- and micro-fibre-based devices are generally mounted on a substrate. The downside is that such substrates mask the very optomechanical properties that the sensor is designed to exploit, and they also drastically reduce the surface area-to-volume ratio of the fibre array. In addition, circuits with good fibre-to-fibre conductivity often require multiple procedures or post-fibre synthesis treatments to make.
To overcome these problems, team leader Yan Yan Shery Huang and colleagues developed a quick, one-step fibre manufacturing process that they call inflight fibre printing (iFP). The process begins with a mixture of silver or a biocompatible conducting polymer known as PEDOT:PSS. During printing, the silver/PEDOT:PSS solution is heated to ensure that it rapidly solidifies, and a core-shell nozzle is used to coat it with a thin (10-20 nm) layer of polyethylene oxide. The result is a highly pure conducting-core fibre structure that is encased in a protective polymer sheath and can be connected to copper contact pads with minimized contact resistance. Notably, the iFP technique creates and bonds thin, conducting fibre arrays directly, without any need for post-processing.
Free-standing and permeable to moisture flow
In addition to their good optoelectrical characteristics, the free-standing nature of the team’s iFP PEDOT:PSS fibre arrays makes them permeable to moisture. By measuring how the resistance of end-to-end fibres evolves in response to changes in humidity, Huang and colleagues were able to organize the fibre arrays in a way that optimizes their sensitivity to these changes. The result is a system in which the resistance of the iFP fibres increases linearly as relative humidity rises from 55 to 90% at room temperature. The researchers also report that their iFP fibres responded faster than a commercial humidity sensor when sprayed with a mist of water.
To test their iFP fibre arrays, the researchers fabricated two types of respiratory moisture sensor. In the first, they printed a single layer of PEDOT:PSS onto a 3D-printed plastic frame to create a sensor that attaches to the exterior of a disposable mask. The team found that the resistance of the fibre arrays in this wearable, non-contact and non-invasive respiration-rate monitoring device returned to its baseline level less than three seconds after normal breathing. A commercial sensor, in contrast, takes roughly 10 seconds. What is more, unlike commercial sensors, the fibre-array sensor proved adept at detecting rapid breathing patterns (roughly 1.2 seconds per breath cycle) that can indicate shortness of breath.
The second type of sensor consisted of PEDOT:PSS fibre arrays as front and back layers, with a sound-detecting suspended piezoelectric polymer nanofibre layer sandwiched in between. Since the entire sensor is transparent and permeable to air, the researchers say that it could be attached to a phone camera and used to collect multiple types of information – such as image, sound and local spatial variations in breath humidity – at the same time.
Detecting the flow of respiratory moisture
In a final series of experiments, Huang and colleagues configured their system to detect respiratory moisture that flows through a mask when the wearer breathes and coughs. In surgical masks, they found that most moisture leakage occurs at the front – implying that such masks redirect some exhaled breath out around the nose area and through the front of the mask. N95 masks tended to leak from the top and sides while FFP2-grade masks – which are designed to filter out at least 94% of airborne particles – were found to be more effective at reducing the flow of breath through the front of the mask. Both types of mask, however, weakened the flow of exhaled breath when worn correctly. The team also found that when a mask-wearing person coughs, the resistance of the fibres increases much more steeply than when the person lets out a long breath – confirming that the strength of the airflow during coughing is higher than when exhaling normally.
According to the researchers, who report their work in Science Advances, portable sensors like these could find use in mobile-health diagnostics and assessments, where their low cost (at 50p for the single-layer sensor and around £2 for the tri-layer device) makes them particularly attractive. The fibres themselves may also have biological applications beyond respiratory sensing. Because the fibres can be made with diameters below the typical size of a cell (a few microns), the researchers say they could be used to guide the movement of cells and detect this dynamic process as electrical signals.


physicsworld--2020-11-04--Microtube implosions could produce megatesla magnetic fields - Physics World

A newly discovered mechanism known as microtube implosion could make it possible to generate magnetic fields 1000 times stronger than any yet seen in the laboratory .
According to the researchers who developed it at Japan ’ s Osaka University , the new method could be used to generate super-strong magnetic fields for fundamental research in fields such as materials science , quantum electrodynamics and astrophysics .
To date , the strongest magnetic fields produced in the laboratory have been in the kilotesla ( kT ) range .
This is far stronger than the magnetic field of the Earth , @ @ @ @ @ @ @ and substantially exceeds the fields produced in magnetic tomography ( MRI ) machines ( about 1 T ) .
While fields in this lower range are important experimental tools , stronger fields could make it possible to study fundamental physics phenomena in areas such as plasma and beam physics , astrophysics and solar physics .
Researchers are therefore exploring various ways of producing such super-strength fields – including collisional shocks , gamma rays and fusion in strongly magnetized plasmas , as well as explosives , high-power lasers and devices known as z-pinches , @ @ @ @ @ @ @ astronomers to recreate the hot plasmas that exist inside stars .
Most of these approaches begin by taking the magnetic flux from “ pre-seeded ” strong magnetic fields and attempting to confine it within hollow cylindrical structures .
A team led by Masakatsu Murakami has now used a similar physical configuration , but with a twist : the ultrahigh magnetic fields in its microtube implosion technique are generated by the spin currents created as charged particles are spun around by the Lorentz force , which acts on moving charged particles in a magnetic @ @ @ @ @ @ @ researchers simulated using high-intensity laser pulses of around 1020–1022 W/cm2 to irradiate a micron-sized plastic tube lined with a structured “ target ” material .
This intense radiation produces “ hot ” electrons ( that is , electrons with a lot of kinetic energy ) that have temperatures equivalent to a few tens of mega-electron volts ( MeV ) .
These high-energy electrons cause the target material in the tube to ionize , producing a plasma that subsequently expands into the tube at near-relativistic speeds ( the implosion ) .
In an idealized @ @ @ @ @ @ @ , this procedure will not generate strong magnetic fields .
However , the researchers found that if they introduced a kilotesla-order magnetic field into their simulated system , they could generate an “ extraordinary ” magnetic field at the centre of the microtube that is 100–1000 times stronger than the pre-seeded field .
Such strong magnetic fields are expected only in celestial bodies like neutron stars and black holes , Murakami says .
So what is happening ?
Murakami explains that during the implosion , the Lorentz force deflects the ions and electrons @ @ @ @ @ @ @ that they become twisted – an effect known as Larmor gyration .
The resultant collective motion of the relativistic charge particles around the central axis of the microtube produces strong spin currents with densities of around 1015 ampere/cm2 .
These spin currents , he says , are what subsequently generate megatesla-order magnetic fields in the centre of the tube .
“ Our new study , detailed in Scientific Reports , is a proof-of-principle that current laser technology can be used to create megatesla-sized magnetic fields , ” Murakami tells Physics World .
“ @ @ @ @ @ @ @ such as particle acceleration , developing compact fusion devices and electron-positron pair creation using the new concept of microtube implosion .
”

A microtube implosion. (Credit: M Murakami)
A newly discovered mechanism known as microtube implosion could make it possible to generate magnetic fields 1000 times stronger than any yet seen in the laboratory. According to the researchers who developed it at Japan’s Osaka University, the new method could be used to generate super-strong magnetic fields for fundamental research in fields such as materials science, quantum electrodynamics and astrophysics.
To date, the strongest magnetic fields produced in the laboratory have been in the kilotesla (kT) range. This is far stronger than the magnetic field of the Earth, which is 0.3–0.5 × 10–4 T, and substantially exceeds the fields produced in magnetic tomography (MRI) machines (about 1 T). While fields in this lower range are important experimental tools, stronger fields could make it possible to study fundamental physics phenomena in areas such as plasma and beam physics, astrophysics and solar physics. Researchers are therefore exploring various ways of producing such super-strength fields – including collisional shocks, gamma rays and fusion in strongly magnetized plasmas, as well as explosives, high-power lasers and devices known as z-pinches, which have been used for decades by astronomers to recreate the hot plasmas that exist inside stars.
Magnetic fields generated by spin currents
Most of these approaches begin by taking the magnetic flux from “pre-seeded” strong magnetic fields and attempting to confine it within hollow cylindrical structures. A team led by Masakatsu Murakami has now used a similar physical configuration, but with a twist: the ultrahigh magnetic fields in its microtube implosion technique are generated by the spin currents created as charged particles are spun around by the Lorentz force, which acts on moving charged particles in a magnetic field.
In their work, the researchers simulated using high-intensity laser pulses of around 1020–1022 W/cm2 to irradiate a micron-sized plastic tube lined with a structured “target” material. This intense radiation produces “hot” electrons (that is, electrons with a lot of kinetic energy) that have temperatures equivalent to a few tens of mega-electron volts (MeV). These high-energy electrons cause the target material in the tube to ionize, producing a plasma that subsequently expands into the tube at near-relativistic speeds (the implosion).
In an idealized configuration with no pre-seeded magnetic fields present, this procedure will not generate strong magnetic fields. However, the researchers found that if they introduced a kilotesla-order magnetic field into their simulated system, they could generate an “extraordinary” magnetic field at the centre of the microtube that is 100–1000 times stronger than the pre-seeded field. Such strong magnetic fields are expected only in celestial bodies like neutron stars and black holes, Murakami says.
Proof-of-principle experiment
So what is happening? Murakami explains that during the implosion, the Lorentz force deflects the ions and electrons in the plasma in opposite directions so that they become twisted – an effect known as Larmor gyration. The resultant collective motion of the relativistic charge particles around the central axis of the microtube produces strong spin currents with densities of around 1015 ampere/cm2. These spin currents, he says, are what subsequently generate megatesla-order magnetic fields in the centre of the tube.
“Our new study, detailed in Scientific Reports, is a proof-of-principle that current laser technology can be used to create megatesla-sized magnetic fields,” Murakami tells Physics World. “We now plan to investigate high-energy-density physics such as particle acceleration, developing compact fusion devices and electron-positron pair creation using the new concept of microtube implosion.”


physicsworld--2020-11-04--FLASH radiotherapy mechanism may arise from immune cell sparing - Physics World

“ FLASH radiotherapy is potentially a game-changing technology , ” said Jian-Yue Jin , speaking at the recent ASTRO 2020 Annual Meeting .
“ It can significantly spare normal tissues , as demonstrated in various animal models by various research groups .
However , the mechanism of FLASH is not well understood.
” Jin , from Seidman Cancer Center , University Hospitals , and Case Western Reserve University , described how he and his colleagues are using computational modelling to study potential mechanisms of FLASH radiotherapy , where radiation delivered at high dose rates ( 40 Gy/s and above ) @ @ @ @ @ @ @ normal tissue .
In particular , the team is investigating the hypothesis that FLASH dose rates significantly reduce the killing of circulating immune cells during radiotherapy , which contributes to the reported FLASH effect .
The team devised a computational model to determine the effect of radiation dose rate on immune cell killing .
The model , which assumes that all immune cells are within the circulating blood , considers an irradiated blood volume that takes up A % of cardiac output and contains B % of the total circulating blood .
The @ @ @ @ @ @ @ irradiated location and is , for example , 100 % for the heart , 50 % for the lung and 15 % for the whole brain .
B % is dependent on the total irradiated volume , with a value of 5–10 % for a tumour and 100 % for the whole body .
The researchers used their model to calculate the irradiated blood volume and dose to this volume for various values of A % and B % , doses of 2–50 Gy and blood circulation times of 60 s ( for @ @ @ @ @ @ @ ( for a mouse ) .
They then used the linear-quadratic model to calculate the percentage of circulating immune cells killed at conventional and FLASH dose rates , simulating dose rates from 1.7 mGy/s to 333 Gy/s .
The model revealed that the killing of circulating immune cells reduces dramatically as dose rate increases .
Jin shared an example with parameters chosen to reflect 30 Gy irradiation of a human lung .
“ The percentage of circulating immune cells killed was reduced from 95 % at very low dose rates to only 10 @ @ @ @ @ @ @ , ” he explained .
Looking at the effects of blood circulation time and the irradiated location revealed that the threshold dose rate for the FLASH effect to occur increases as circulation time decreases and as A % increases .
“ This threshold dose rate depends on many factors , ” said Jin .
“ For mice , it is about 10 Gy/s for whole brain , 40 Gy/s for lung and abdomen and 90 Gy/s for the heart .
This result is similar to reported FLASH effects in experiments.
” Jin pointed @ @ @ @ @ @ @ may be a factor of 10 lower in humans than in mice .
“ This is very important , because it suggests that X-ray-based FLASH systems can be developed and are not as challenging as we previously thought , ” he explained .
The model also showed that the FLASH effect on immune cells increases at higher values of dose per fraction .
The FLASH effect becomes prominent at larger than 20 Gy/fraction and vanishes at low doses of less than 2 Gy/fraction .
Jin noted that the FLASH effect also vanishes when @ @ @ @ @ @ @ total-body irradiation .
“ FLASH dose rates dramatically reduce killing of circulating immune cells , ” Jin concluded .
“ The immune system plays an important role in repairing normal tissue damage by radiation , and radiation-induced lymphopenia [ a reduction in immune cells in the blood ] is associated with poor tumour control and patient survival .
Therefore FLASH-related sparing of immune cells may have a positive effect on both normal tissue sparing and tumour control.
” Jin added that oxygen depletion – another potential FLASH mechanism – may have a positive @ @ @ @ @ @ @ a negative effect on tumour control .
“ Therefore , the FLASH effect may be the combined effect of the sparing of immune cells and oxygen depletion , ” he told the ASTRO audience .

Jian-Yue Jin is using computational modelling to study the potential mechanisms underlying FLASH radiotherapy. (Courtesy: Jian-Yue Jin)
“FLASH radiotherapy is potentially a game-changing technology,” said Jian-Yue Jin, speaking at the recent ASTRO 2020 Annual Meeting. “It can significantly spare normal tissues, as demonstrated in various animal models by various research groups. However, the mechanism of FLASH is not well understood.”
Jin, from Seidman Cancer Center, University Hospitals, and Case Western Reserve University, described how he and his colleagues are using computational modelling to study potential mechanisms of FLASH radiotherapy, where radiation delivered at high dose rates (40 Gy/s and above) destroys tumours while vastly reducing damage to normal tissue. In particular, the team is investigating the hypothesis that FLASH dose rates significantly reduce the killing of circulating immune cells during radiotherapy, which contributes to the reported FLASH effect.
The team devised a computational model to determine the effect of radiation dose rate on immune cell killing. The model, which assumes that all immune cells are within the circulating blood, considers an irradiated blood volume that takes up A% of cardiac output and contains B% of the total circulating blood. The value of A% depends upon the irradiated location and is, for example, 100% for the heart, 50% for the lung and 15% for the whole brain. B% is dependent on the total irradiated volume, with a value of 5–10% for a tumour and 100% for the whole body.
The researchers used their model to calculate the irradiated blood volume and dose to this volume for various values of A% and B%, doses of 2–50 Gy and blood circulation times of 60 s (for an adult human) and 5–10 s (for a mouse). They then used the linear-quadratic model to calculate the percentage of circulating immune cells killed at conventional and FLASH dose rates, simulating dose rates from 1.7 mGy/s to 333 Gy/s.
The model revealed that the killing of circulating immune cells reduces dramatically as dose rate increases. Jin shared an example with parameters chosen to reflect 30 Gy irradiation of a human lung. “The percentage of circulating immune cells killed was reduced from 95% at very low dose rates to only 10% at the very high dose rates,” he explained.
Looking at the effects of blood circulation time and the irradiated location revealed that the threshold dose rate for the FLASH effect to occur increases as circulation time decreases and as A% increases. “This threshold dose rate depends on many factors,” said Jin. “For mice, it is about 10 Gy/s for whole brain, 40 Gy/s for lung and abdomen and 90 Gy/s for the heart. This result is similar to reported FLASH effects in experiments.”
Jin pointed out that the level of this threshold may be a factor of 10 lower in humans than in mice. “This is very important, because it suggests that X-ray-based FLASH systems can be developed and are not as challenging as we previously thought,” he explained.
The model also showed that the FLASH effect on immune cells increases at higher values of dose per fraction. The FLASH effect becomes prominent at larger than 20 Gy/fraction and vanishes at low doses of less than 2 Gy/fraction. Jin noted that the FLASH effect also vanishes when B% is 100%, representing total-body irradiation.
“FLASH dose rates dramatically reduce killing of circulating immune cells,” Jin concluded. “The immune system plays an important role in repairing normal tissue damage by radiation, and radiation-induced lymphopenia [a reduction in immune cells in the blood] is associated with poor tumour control and patient survival. Therefore FLASH-related sparing of immune cells may have a positive effect on both normal tissue sparing and tumour control.”
Jin added that oxygen depletion – another potential FLASH mechanism – may have a positive effect on normal tissue sparing, but a negative effect on tumour control. “Therefore, the FLASH effect may be the combined effect of the sparing of immune cells and oxygen depletion,” he told the ASTRO audience.


physicsworld--2020-11-04--Why we need to support research into university physics education - Physics World

Over the past century the Institute of Physics ( IOP ) , which publishes Physics World , has strengthened the case for physics by highlighting the many benefits that the discipline brings to society .
Those advantages include not just technological developments but education too , both of which allow physicists to apply their knowledge and skills to understand and improve the world .
However , training a person to “ think like a physicist ” requires time , effort and a supportive environment , which is why strengthening physics teaching in schools and boosting diversity are so important .
@ @ @ @ @ @ @ usually established at school , it is at university that physicists really gain the skills that they need for a successful career in academia or industry .
Such skills are a mix of the highly technical – for example , advanced computer simulations – and the generic such as communication and team-working skills .
So , to train the next generation of physicists as best as we can , it is essential we understand not just how students learn but how students learn physics too .
Those issues will be tackled this month @ @ @ @ @ @ @ IOP ’ s higher education and history of physics groups .
Examining developments in physics teaching and learning in higher education during the last century , the meeting will touch on changes in the way students learn and have been taught over the past 100 years .
Many factors have played a role in those changes , including revolutions in physics , technology and society .
Breakthrough discoveries can be gamechangers when it comes to teaching , explaining and illustrating difficult concepts .
Meanwhile , the advent and democratization of tools enabling communication @ @ @ @ @ @ @ and access to an overwhelming volume of information have also completely changed how we teach .
Even events like the two world wars or the current COVID-19 pandemic have massively disrupted learning and teaching in higher education .
Following lockdown earlier this year , the learning and teaching community came together to address some of the most pressing issues that affect physics higher-education institutions .
The Learning and Teaching in Higher Education-Physics held several virtual meetings that became a place where colleagues could share ideas .
Issues that were touched upon included how @ @ @ @ @ @ @ run and assess labs , lectures , group work and tutorials , as well as how to be more inclusive and better supervise postgraduate research students .
Common sense , self-reflection and experience all play a big part in defining individual approaches to teaching undergraduate or postgraduate students .
Yet what is clear is that there is a real need for more research in this area .
We all recognize the importance of evidence-based research , but it takes time and money – both of which are scarce .
Academics researching physics learning @ @ @ @ @ @ @ teaching and administration duties and it is often a challenge to find the time to design and successfully run research experiments in physics education .
Sadly , external research funding to support postgraduate researchers and pay the salaries of researchers to do this work is extremely rare .
There are no opportunities to compete for grants that would allow for the development of consistent and sustainable research programmes on how students from diverse backgrounds learn physics – a subject with many practical , mathematical , conceptual and technical challenges .
Thanks to one-off @ @ @ @ @ @ @ people who care deeply and passionately about educating physics students , there has been some good work in physics higher-education research in the UK .
But the most important developments in the field have emerged from other countries – especially those that have made significant streams of funding available to researchers .
Of particular note is the US National Science Foundation , which for years has consistently supported physics education research .
Looking ahead towards the next hundred years of physics in the UK , it is high time that UK research councils @ @ @ @ @ @ @ benefits that physics higher-education research brings to the training of the next generations of physicists .
UK Research and Innovation ( UKRI ) – the umbrella organization for the UK ’ s seven research councils – must therefore recognize its responsibility to adequately support higher education research in physics as well as in other technical subjects .
The IOP , together with its sister learned societies , can play a big role in guiding UKRI towards achieving this important goal for university education .
The physics higher-education community is ready to help .

Physics World, where it appeared under the headline "Supporting the next generation". Members of the Institute of Physics can enjoy the full issue Taken from the November 2020 issue of, where it appeared under the headline "Supporting the next generation". Members of the Institute of Physics can enjoy the full issue via the Physics World app
Nicolas Labrosse says that UK research funders must accept their responsibility to fund higher education research in physics
Investing in the future More funding for education research is needed to carry out research into how students learn physics. (Courtesy: iStock/Steve Debenport)
Over the past century the Institute of Physics (IOP), which publishes Physics World, has strengthened the case for physics by highlighting the many benefits that the discipline brings to society. Those advantages include not just technological developments but education too, both of which allow physicists to apply their knowledge and skills to understand and improve the world. However, training a person to “think like a physicist” requires time, effort and a supportive environment, which is why strengthening physics teaching in schools and boosting diversity are so important.
While the foundations of physics knowledge are usually established at school, it is at university that physicists really gain the skills that they need for a successful career in academia or industry. Such skills are a mix of the highly technical – for example, advanced computer simulations – and the generic such as communication and team-working skills. So, to train the next generation of physicists as best as we can, it is essential we understand not just how students learn but how students learn physics too.
Talking points
Those issues will be tackled this month at a meeting jointly organized by the IOP’s higher education and history of physics groups. Examining developments in physics teaching and learning in higher education during the last century, the meeting will touch on changes in the way students learn and have been taught over the past 100 years. Many factors have played a role in those changes, including revolutions in physics, technology and society. Breakthrough discoveries can be gamechangers when it comes to teaching, explaining and illustrating difficult concepts. Meanwhile, the advent and democratization of tools enabling communication with almost unlimited numbers of other individuals and access to an overwhelming volume of information have also completely changed how we teach. Even events like the two world wars or the current COVID-19 pandemic have massively disrupted learning and teaching in higher education.
Following lockdown earlier this year, the learning and teaching community came together to address some of the most pressing issues that affect physics higher-education institutions. The Learning and Teaching in Higher Education-Physics held several virtual meetings that became a place where colleagues could share ideas. Issues that were touched upon included how to move teaching online, how to run and assess labs, lectures, group work and tutorials, as well as how to be more inclusive and better supervise postgraduate research students. Common sense, self-reflection and experience all play a big part in defining individual approaches to teaching undergraduate or postgraduate students. Yet what is clear is that there is a real need for more research in this area.
The most important developments in physics higher-education research have emerged from other countries such as the US
Setting goals
We all recognize the importance of evidence-based research, but it takes time and money – both of which are scarce. Academics researching physics learning and teaching at university level have significant teaching and administration duties and it is often a challenge to find the time to design and successfully run research experiments in physics education. Sadly, external research funding to support postgraduate researchers and pay the salaries of researchers to do this work is extremely rare. There are no opportunities to compete for grants that would allow for the development of consistent and sustainable research programmes on how students from diverse backgrounds learn physics – a subject with many practical, mathematical, conceptual and technical challenges.
Thanks to one-off funding initiatives and to the dedication of people who care deeply and passionately about educating physics students, there has been some good work in physics higher-education research in the UK. But the most important developments in the field have emerged from other countries – especially those that have made significant streams of funding available to researchers. Of particular note is the US National Science Foundation, which for years has consistently supported physics education research.
Looking ahead towards the next hundred years of physics in the UK, it is high time that UK research councils fund researchers appropriately and stop neglecting the benefits that physics higher-education research brings to the training of the next generations of physicists. UK Research and Innovation (UKRI) – the umbrella organization for the UK’s seven research councils – must therefore recognize its responsibility to adequately support higher education research in physics as well as in other technical subjects. The IOP, together with its sister learned societies, can play a big role in guiding UKRI towards achieving this important goal for university education. The physics higher-education community is ready to help.


physicsworld--2020-11-03--Defining QA best practice in MR-guided radiotherapy - Physics World

The Elekta Unity MR-guided radiotherapy ( MR/RT ) system is rewriting the rulebook in radiation oncology , opening up new possibilities for the visualization of the tumour target , as well as its surrounding anatomy , with exceptional soft-tissue contrast both prior to and during treatment .
While it ’ s still early days for MR/RT deployment , the anticipated patient outcomes – when realized at scale – already look compelling .
Consider the fundamental biology : tumour shape and position relative to healthy tissue evolve over the course of a radiotherapy treatment programme – and can even change during @ @ @ @ @ @ @ of MR/RT to detect those changes and adapt therapy accordingly – in effect , helping clinicians to “ see what they treat ” in real-time – means that radiation oncology teams are now able to improve the precision of radiation delivery , more effectively treating the tumour while sparing healthy tissue and minimizing damage to adjacent organs at risk and other critical structures .
If the upward trajectory for MR/RT is clear , the operational reality of adding a 1.5 T MRI scanner into the treatment mix is , unsurprisingly , one of @ @ @ @ @ @ @ radiotherapy modalities – not least in terms of defining a rigorous , standardized and streamlined approach to MR/RT quality assurance ( QA ) .
For starters , QA products not only need to be compatible with use in a magnetic field – i.e .
classified as MR-conditional – they need to be MR-visible as well .
Equally important is workflow efficiency : MR/RT QA needs to ensure simple and quick verification of the treatment procedure to confirm that radiation is being delivered to the patient as intended , while at the same time @ @ @ @ @ @ @ of specialist radiotherapy QA vendors addressing this challenge is PTW of Freiburg , Germany , which has developed a portfolio of high-precision dosimetry solutions for MR/RT early-adopters , with products to enable acceptance testing , beam data commissioning , as well as machine- and patient-specific QA .
The latest addition to PTW ’ s MR/RT product line is the RUBY QA phantom , which comes with a variety of exchangeable , application-specific inserts to enable medical physicists to verify the entire radiotherapy equipment chain – from imaging and treatment planning through targeting , @ @ @ @ @ @ @ the main advantages of RUBY is its modularity – comprising a base phantom with a series of inserts for different QA tasks , ” explains Daniela Poppinga , a research scientist and product manager at PTW .
The daily couch-check , for example , uses the linac QA insert plus base phantom , while there ’ s a system QA insert for the end-to-end QA .
The latter includes MR-visible elements , CT-visible inhomogeneities , as well as the option to insert a detector for dose measurements .
“ For the end-to-end test @ @ @ @ @ @ @ user can see the system QA insert in their MR images .
With this insert it ’ s possible to test the whole MR-Linac workflow chain – basically every step the patient goes through.
” It ’ s worth noting that RUBY was originally developed to support other advanced treatment modalities – including intensity-modulated radiation therapy ( IMRT ) , volumetric modulated-arc therapy ( VMAT ) and hypofractionated procedures such as stereotactic body radiotherapy ( SBRT ) .
Subsequently , the phantom and inserts have been optimized for MR/RT QA testing – a @ @ @ @ @ @ @ shaped with first-hand inputs from clinical scientists in the department of radiation oncology at University Hospital Tübingen , Germany .
“ We ’ re impressed with the functionality of the RUBY phantom , ” says Marcel Nachbar , a medical physicist with QA responsibility for the Tübingen clinic ’ s Elekta Unity system .
“ One of the neat aspects of RUBY is its multipurpose functionality , such that inserts for the Elekta Unity MR-Linac can be deployed on our conventional linacs as well.
” In September 2018 , University Hospital Tübingen was @ @ @ @ @ @ @ treating patients with the Elekta Unity MR/RT machine – since when Nachbar and his colleagues have delivered well over 3000 treatment fractions with Unity .
“ Daily QA is pretty straightforward and comprises mostly checks of the MR system [ signal-to-noise and scaling factors ] and workflow checks , ” explains Nachbar .
There are other weekly , biweekly and monthly checks , though , that go above and beyond what ’ s needed for conventional RT linacs .
“ We have MR QA , linac QA and hybrid/end-to-end QA to evaluate the @ @ @ @ @ @ @ systems , ” he adds .
Operationally , the PTW–Tübingen collaboration looks like a win-win : the Tübingen team gets to evaluate the RUBY phantom for future deployment in its Unity workflow ; meanwhile PTW gains insights from the clinical “ sharp-end ” to inform ongoing requirements-gathering for RUBY innovations tailored to MR/RT daily and end-to-end QA .
With this in mind , Poppinga and Nachbar formed part of a joint project team that recently evaluated the use of RUBY ( plus patient QA insert ) for treatment plan verification in combination with @ @ @ @ @ @ @ We were able to verify the treatment for one complex small-volume case , ” explains Nachbar .
“ We used the PTW detector insert combined with a micro ionization chamber [ PinPoint 3D ] to get an excellent representation of this small target volume , with the differences between measurements and treatment planning system all within 2 % .
” Meanwhile , a second study evaluated the use of RUBY ( plus system QA insert ) as an end-to-end phantom for Elekta Unity – specifically to address the complexities associated with adaptive MR/RT @ @ @ @ @ @ @ scientists showed that both of the possible Unity workflows could be fully tested with RUBY – i.e .
“ adapt-to-position ” ( in which the dose distribution is repositioned on a daily basis to track changes in tumour position ) and “ adapt-to-shape ” ( with daily recontouring and reoptimization to take account of rotation or deformation of the tumour target or nearby organs at risk ) .
“ On end-to-end testing , the RUBY phantom really did simplify our QA workflow , ” Nachbar concludes .
“ As such , it ’ @ @ @ @ @ @ @ implemented as is for point-dose MR/RT treatment plan verification and end-to-end QA.
” Looking ahead , though , Nachbar also sees plenty of scope for the RUBY phantom to streamline and consolidate other MR/RT QA checks into a single platform – for example , monitoring the difference between the MR and MVIC isocentre , the stability of which needs to be tested on a weekly or biweekly basis .
• Register for the upcoming PTW webinar Quality Assurance of the Elekta Unity MR-Linac : A Clinical Experience ( 19 November 2020 ) .

PTW’s modular RUBY phantom is being optimized to support daily and end-to-end quality assurance (QA) for the Elekta Unity MR-Linac treatment system
Multipurpose functionality The latest addition to PTW’s MR/RT product line is the RUBY QA phantom, shown here in the MR bore with body coil. (Courtesy: PTW)
The Elekta Unity MR-guided radiotherapy (MR/RT) system is rewriting the rulebook in radiation oncology, opening up new possibilities for the visualization of the tumour target, as well as its surrounding anatomy, with exceptional soft-tissue contrast both prior to and during treatment. While it’s still early days for MR/RT deployment, the anticipated patient outcomes – when realized at scale – already look compelling. Consider the fundamental biology: tumour shape and position relative to healthy tissue evolve over the course of a radiotherapy treatment programme – and can even change during an individual treatment session. The ability of MR/RT to detect those changes and adapt therapy accordingly – in effect, helping clinicians to “see what they treat” in real-time – means that radiation oncology teams are now able to improve the precision of radiation delivery, more effectively treating the tumour while sparing healthy tissue and minimizing damage to adjacent organs at risk and other critical structures.
If the upward trajectory for MR/RT is clear, the operational reality of adding a 1.5 T MRI scanner into the treatment mix is, unsurprisingly, one of significantly increased system complexity versus more established radiotherapy modalities – not least in terms of defining a rigorous, standardized and streamlined approach to MR/RT quality assurance (QA). For starters, QA products not only need to be compatible with use in a magnetic field – i.e. classified as MR-conditional – they need to be MR-visible as well. Equally important is workflow efficiency: MR/RT QA needs to ensure simple and quick verification of the treatment procedure to confirm that radiation is being delivered to the patient as intended, while at the same time maximizing patient throughput.
The QA challenge
Among a posse of specialist radiotherapy QA vendors addressing this challenge is PTW of Freiburg, Germany, which has developed a portfolio of high-precision dosimetry solutions for MR/RT early-adopters, with products to enable acceptance testing, beam data commissioning, as well as machine- and patient-specific QA. The latest addition to PTW’s MR/RT product line is the RUBY QA phantom, which comes with a variety of exchangeable, application-specific inserts to enable medical physicists to verify the entire radiotherapy equipment chain – from imaging and treatment planning through targeting, dosimetry and delivery.
Daniela Poppinga “One of the main advantages of RUBY is its modularity.” (Courtesy: PTW)
“One of the main advantages of RUBY is its modularity – comprising a base phantom with a series of inserts for different QA tasks,” explains Daniela Poppinga, a research scientist and product manager at PTW. The daily couch-check, for example, uses the linac QA insert plus base phantom, while there’s a system QA insert for the end-to-end QA. The latter includes MR-visible elements, CT-visible inhomogeneities, as well as the option to insert a detector for dose measurements. “For the end-to-end test,” adds Poppinga, “the user can see the system QA insert in their MR images. With this insert it’s possible to test the whole MR-Linac workflow chain – basically every step the patient goes through.”
It’s worth noting that RUBY was originally developed to support other advanced treatment modalities – including intensity-modulated radiation therapy (IMRT), volumetric modulated-arc therapy (VMAT) and hypofractionated procedures such as stereotactic body radiotherapy (SBRT). Subsequently, the phantom and inserts have been optimized for MR/RT QA testing – a product development initiative that’s been shaped with first-hand inputs from clinical scientists in the department of radiation oncology at University Hospital Tübingen, Germany. “We’re impressed with the functionality of the RUBY phantom,” says Marcel Nachbar, a medical physicist with QA responsibility for the Tübingen clinic’s Elekta Unity system. “One of the neat aspects of RUBY is its multipurpose functionality, such that inserts for the Elekta Unity MR-Linac can be deployed on our conventional linacs as well.”
The QA opportunity
In September 2018, University Hospital Tübingen was among the first clinical sites to start treating patients with the Elekta Unity MR/RT machine – since when Nachbar and his colleagues have delivered well over 3000 treatment fractions with Unity. “Daily QA is pretty straightforward and comprises mostly checks of the MR system [signal-to-noise and scaling factors] and workflow checks,” explains Nachbar. There are other weekly, biweekly and monthly checks, though, that go above and beyond what’s needed for conventional RT linacs. “We have MR QA, linac QA and hybrid/end-to-end QA to evaluate the effective interworking between the MR and linac systems,” he adds.
Marcel Nachbar “On end-to-end testing, the RUBY phantom really did simplify our QA workflow.” (Courtesy: University Hospital Tübingen)
Operationally, the PTW–Tübingen collaboration looks like a win-win: the Tübingen team gets to evaluate the RUBY phantom for future deployment in its Unity workflow; meanwhile PTW gains insights from the clinical “sharp-end” to inform ongoing requirements-gathering for RUBY innovations tailored to MR/RT daily and end-to-end QA. With this in mind, Poppinga and Nachbar formed part of a joint project team that recently evaluated the use of RUBY (plus patient QA insert) for treatment plan verification in combination with the Unity imaging system MVIC. “We were able to verify the treatment for one complex small-volume case,” explains Nachbar. “We used the PTW detector insert combined with a micro ionization chamber [PinPoint 3D] to get an excellent representation of this small target volume, with the differences between measurements and treatment planning system all within 2%.”
Meanwhile, a second study evaluated the use of RUBY (plus system QA insert) as an end-to-end phantom for Elekta Unity – specifically to address the complexities associated with adaptive MR/RT. In this case, the PTW–Tübingen scientists showed that both of the possible Unity workflows could be fully tested with RUBY – i.e. “adapt-to-position” (in which the dose distribution is repositioned on a daily basis to track changes in tumour position) and “adapt-to-shape” (with daily recontouring and reoptimization to take account of rotation or deformation of the tumour target or nearby organs at risk).
“On end-to-end testing, the RUBY phantom really did simplify our QA workflow,” Nachbar concludes. “As such, it’s clear that RUBY can already be implemented as is for point-dose MR/RT treatment plan verification and end-to-end QA.” Looking ahead, though, Nachbar also sees plenty of scope for the RUBY phantom to streamline and consolidate other MR/RT QA checks into a single platform – for example, monitoring the difference between the MR and MVIC isocentre, the stability of which needs to be tested on a weekly or biweekly basis.
Register for the upcoming PTW webinar Quality Assurance of the Elekta Unity MR-Linac: A Clinical Experience (19 November 2020).


physicsworld--2020-11-03--Quality assurance of the Elekta Unity MR-Linac: a clinical experience - Physics World

Join our webinar with Marcel Nachbar of the University Hospital of Tübingen , one of the first clinical sites to successfully implement the Elekta Unity high-field MR-Linac .
During the webinar , Marcel will talk about the technical and dosimetric challenges of the Elekta Unity system , provide an overview of dedicated PTW equipment and its effective use in clinical routine , and share his experience of establishing a comprehensive quality assurance programme .
• Clinical applications and technical overview of the Elekta Unity high-field MR-Linac .
• Clinical workflow and current limitations of the Elekta Unity system .
• @ @ @ @ @ @ @ assurance of the MR imaging system for anatomical and functional imaging .
Quality assurance of the medical linear accelerator using PTW equipment , including beam data collection ; output check ; profile check ; isocenter check ; and patient plan verification .
Independent end-to-end testing .
Don ’ t miss this opportunity to learn more about safe and effective quality assurance in MR-guided radiotherapy .
Marcel Nachbar , MSc , is a medical physics expert ( MPE ) .
He currently works at the Department of Radiation Oncology , University of Tübingen , @ @ @ @ @ @ @ the Elekta Unity system .
His professional focus is on MR-guided adaptive radiotherapy .

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