physicsworld--2020-11-24--Perovskites could be platforms for exciton condensates - Physics World

Organic-inorganic perovskite materials are usually studied in the context of making solar cells and other photovoltaic devices .
Now researchers from the Institute of Semiconductors at the Chinese Academy of Sciences in Beijing have shown that these hybrid halide materials could also be ideal platforms for realizing Bose-Einstein condensates of excitons ( electron-hole pairs ) .
Such condensates , which appear as vortex patterns , could be produced at liquid nitrogen temperatures – positively balmy , by the standard of the field – thanks to the long lifetimes of the excitons in the materials and their huge binding energies .
@ @ @ @ @ @ @ all the bosonic atoms or particles in a gas collapse into the same quantum ground state and can therefore be described by the same wavefunction .
Such collapses are triggered by cooling the gas until the de Broglie wavelength of its constituent atoms or particles is comparable to the distance between them .
Once in this state , the atoms or particles behave as a superfluid , flowing without friction .
Researchers made the first BEC in 1995 from rubidium atoms .
Since then , condensates have been observed in various other types @ @ @ @ @ @ @ and magnons as well as other species of atoms and molecules .
In all cases , however , the phenomenon has only appeared at ultralow temperatures of no more than a few Kelvin above absolute zero .
To make BECs easier to study – and perhaps also to put their amazing properties to practical use – researchers have long sought to increase the temperature at which they form .
One way of doing this might be to make a BEC using excitons , which are bosons composed of the bound states of two @ @ @ @ @ @ @ a positively charged hole , or electron vacancy .
These fermions are bound together via weak Coulomb interactions that cause them to form dipoles .
Since these bound states are much lighter than atoms , they can be packed together with higher density – meaning that they ought to Bose condense at much higher temperatures .
That , at least , is the theory .
Unfortunately , previous attempts to make such excitonic BECs – for example in semiconductor wells and graphene – have succeeded only at disappointingly low temperatures of around 1 @ @ @ @ @ @ @ binding energy in these material systems .
In their new work , researchers led by Kai Chang studied a 2D hybrid perovskite with the chemical formula ( PEA ) PbI .
Perovskites in general are promising thin-film solar-cell materials thanks to the fact that they can absorb light over a broad range of solar spectrum wavelengths .
Electrons and holes have a long lifetime in these materials too ( that is , they can diffuse through the material over long lengths ) and this is the property that Chang and colleagues focused on @ @ @ @ @ @ @ has a stable layered structure comprising layers of [ PbI ] 4− octahedra and long-chain organic molecules with the formula C H C H NH + ( abbreviated PEA+ ) .
The inorganic PbI layers are sandwiched between two organic layers and have effective potential barriers with energies of 8.1 eV .
These barriers make ( PEA ) PbI behave like stacked quantum wells confined by “ hard-wall ” energy potentials , the researchers explain .
Using first-principles calculations and a theoretical framework known as the Keldysh model , the researchers calculated a @ @ @ @ @ @ @ for the excitons in monolayer ( PEA ) PbI , a value that agrees with that obtained in laboratory experiments .
“ The Keldysh model is a standard treatment for describing 2D excitons with ‘ unscreened ’ Coulomb interactions and the large exciton binding energy we calculated means that the critical temperature of the exciton BEC could approach the liquid nitrogen regime ( 77 K ) , ” team member Dong Zhang tells Physics World .
The researchers studied their flakes of ( PEA ) PbI further by applying an electric field perpendicular @ @ @ @ @ @ @ found that the applied field slightly changed the material ’ s binding energy , while also causing all the electron-hole dipoles to line up in the same direction .
In this situation , the interaction between the dipoles becomes repulsive .
When the researchers then “ pumped ” the flakes of the ( PEA ) PbI using pulses from a laser , they found that the repulsive dipole-dipole interaction created by the perpendicular electric field can drive the laterally confined excitons into various vortex patterns .
The time it takes for these vortices @ @ @ @ @ @ @ the lifetime of the exciton itself and the result is a stable pattern with a certain number of vortices rotating at the centre .
Members of the team , who report their work in Chinese Physics Letters , say they now plan to study exciton BEC in few-layered hybrid perovskites as opposed to just monolayer ones .
“ We will also be looking at how to manipulate exciton vortices and make vortex-based information-storage porotype devices , ” Zhang says .

Laser pumping applied on a perovskite monolayer and the emerging exciton vortices. Courtesy: D Zhang
Organic–inorganic perovskite materials are usually studied in the context of making solar cells and other photovoltaic devices. Now researchers from the Institute of Semiconductors at the Chinese Academy of Sciences in Beijing have shown that these hybrid halide materials could also be ideal platforms for realizing Bose–Einstein condensates of excitons (electron–hole pairs). Such condensates, which appear as vortex patterns, could be produced at liquid nitrogen temperatures – positively balmy, by the standard of the field – thanks to the long lifetimes of the excitons in the materials and their huge binding energies.
Bose–Einstein condensation (BEC) occurs when all the bosonic atoms or particles in a gas collapse into the same quantum ground state and can therefore be described by the same wavefunction. Such collapses are triggered by cooling the gas until the de Broglie wavelength of its constituent atoms or particles is comparable to the distance between them. Once in this state, the atoms or particles behave as a superfluid, flowing without friction.
Exciton BECs
Researchers made the first BEC in 1995 from rubidium atoms. Since then, condensates have been observed in various other types of particles, including polaritons, photons and magnons as well as other species of atoms and molecules. In all cases, however, the phenomenon has only appeared at ultralow temperatures of no more than a few Kelvin above absolute zero.
To make BECs easier to study – and perhaps also to put their amazing properties to practical use – researchers have long sought to increase the temperature at which they form. One way of doing this might be to make a BEC using excitons, which are bosons composed of the bound states of two fermions: a negatively charged electron and a positively charged hole, or electron vacancy. These fermions are bound together via weak Coulomb interactions that cause them to form dipoles. Since these bound states are much lighter than atoms, they can be packed together with higher density – meaning that they ought to Bose condense at much higher temperatures.
That, at least, is the theory. Unfortunately, previous attempts to make such excitonic BECs – for example in semiconductor wells and graphene – have succeeded only at disappointingly low temperatures of around 1 K, due to the small exciton binding energy in these material systems.
Calculating the exciton binding energy
In their new work, researchers led by Kai Chang studied a 2D hybrid perovskite with the chemical formula (PEA) 2 PbI 4 . Perovskites in general are promising thin-film solar-cell materials thanks to the fact that they can absorb light over a broad range of solar spectrum wavelengths. Electrons and holes have a long lifetime in these materials too (that is, they can diffuse through the material over long lengths) and this is the property that Chang and colleagues focused on.
The team’s chosen perovskite has a stable layered structure comprising layers of [PbI 6 ]4− octahedra and long-chain organic molecules with the formula C 6 H 5 C 2 H 4 NH 3 + (abbreviated PEA+). The inorganic PbI 4 layers are sandwiched between two organic layers and have effective potential barriers with energies of 8.1 eV. These barriers make (PEA) 2 PbI 4 behave like stacked quantum wells confined by “hard-wall” energy potentials, the researchers explain.
Using first-principles calculations and a theoretical framework known as the Keldysh model, the researchers calculated a binding energy as high as 238.5 meV for the excitons in monolayer (PEA) 2 PbI 4 , a value that agrees with that obtained in laboratory experiments. “The Keldysh model is a standard treatment for describing 2D excitons with ‘unscreened’ Coulomb interactions and the large exciton binding energy we calculated means that the critical temperature of the exciton BEC could approach the liquid nitrogen regime (77 K),” team member Dong Zhang tells Physics World.
Vortex patterns
The researchers studied their flakes of (PEA) 2 PbI 4 further by applying an electric field perpendicular to them. From this, they found that the applied field slightly changed the material’s binding energy, while also causing all the electron–hole dipoles to line up in the same direction. In this situation, the interaction between the dipoles becomes repulsive.
When the researchers then “pumped” the flakes of the (PEA) 2 PbI 4 using pulses from a laser, they found that the repulsive dipole–dipole interaction created by the perpendicular electric field can drive the laterally confined excitons into various vortex patterns. The time it takes for these vortices to evolve is on a par with the lifetime of the exciton itself and the result is a stable pattern with a certain number of vortices rotating at the centre.
Members of the team, who report their work in Chinese Physics Letters, say they now plan to study exciton BEC in few-layered hybrid perovskites as opposed to just monolayer ones. “We will also be looking at how to manipulate exciton vortices and make vortex-based information-storage porotype devices,” Zhang says.


physicsworld--2020-11-24--Carbon ions team up with immunotherapy to tackle advanced tumours - Physics World

Immunotherapy using checkpoint inhibitors is an emerging cancer treatment that has recently had great success in treating metastatic cancer .
The technique works by blocking checkpoint proteins ( such as CTLA-4 or PD-1 ) that stop the patient ’ s immune system from attacking cancer cells , and reactivating the immune system to fight cancer .
Unfortunately , however , only a fraction of patients respond to such immunotherapy and only certain tumour types can be treated .
To increase its potential pool of patients and cancers , immunotherapy can be combined with radiation therapy , which under certain conditions @ @ @ @ @ @ @ has also been proposed that charged particles – such as the carbon-ion beams already used clinically to treat certain cancers – could prove more effective than X-rays in this combination .
To investigate this idea further , an international research team headed up at the GSI Helmholtz Centre for Heavy Ion Research has compared the efficacy of carbon-ion radiotherapy and conventional X-ray radiotherapy in combination with checkpoint inhibitors in a mouse bone tumour model .
The researchers report their findings in the International Journal of Radiation Oncology , Biology , Physics .
“ @ @ @ @ @ @ @ carbon ions and immunotherapy are a good match , ” explains lead author Alexander Helm .
“ The most prominent is actually the peculiar pattern of cell death that is induced by carbon ions compared with conventional radiotherapy .
It is hypothesized that this very cell death is more immunogenic , which will eventually lead to a more efficient activation of the immune response and a better elimination of metastases .
These effects , nonetheless , depend on the combination with immunotherapy to boost such immune responses.
” The researchers , also from @ @ @ @ @ @ @ in Japan , conducted their experiments at the accelerator in Chiba , Japan .
They inoculated mice in both hind legs with osteosarcoma cells , a bone tumour that is generally considered radioresistant .
They then treated each mouse with a 10 Gy dose of either carbon ions or X-rays , in combination with two immune checkpoint inhibitors : anti-PD-1 and anti-CTLA-4 .
Tumours on the animals ’ left legs ( representing primary tumours ) were irradiated , while those on the right legs ( abscopal tumours ) were kept out of the @ @ @ @ @ @ @ irradiated , with either carbon ions or X-rays , demonstrated reduced growth compared with untreated mice .
Tumour growth was better controlled in mice that received irradiation plus immunotherapy than in animals treated with radiotherapy alone , suggesting a synergistic effect likely based on the additional immune response boost by the checkpoint inhibitors .
In mice receiving the combination treatments , growth of the unirradiated abscopal tumours also decreased .
This reduced growth was most pronounced when the animals received a combination of carbon ions plus checkpoint inhibitors .
The team also examined @ @ @ @ @ @ @ lung metastases , which form spontaneously from the bone tumours in the mice .
When combined with immunotherapy , both radiation types essentially suppressed the metastases .
As found previously , the combination of carbon ions plus checkpoint inhibitors had the greatest effect , resulting in the least number of metastases .
Carbon-ion irradiation alone also significantly reduced the number of lung metastases compared with the control group , comparable with results in animals that received only checkpoint inhibitors .
This was not the case for mice treated with X-rays .
The team @ @ @ @ @ @ @ radiotherapy and checkpoint inhibitors has the highest potential to control distal metastases in this mouse model and could provide a potential clinical option for treatment of advanced tumours .
Corresponding author Marco Durante , director of the department of biophysics at GSI , has previously demonstrated that carbon ions and protons have physical advantages over X-rays that enable drastically improved sparing of healthy tissue during radiotherapy .
In fact , charged particles spare circulating immune cells in the blood much more than X-rays , which is necessary for an efficient immune response .
@ @ @ @ @ @ @ the mechanisms underlying these immune responses .
Understanding these mechanisms should allow them to tailor radiation treatments to increase immune response activation .
“ For example , the radiotherapy fractionation scheme has been shown to have a crucial role on the immunogenicity of the induced cell death , ” explains Helm .
“ Hypofractionation , in which higher doses are applied in a shorter time span ( than with conventional radiotherapy ) , has been reported as beneficial – and carbon ions are a perfect match for hypofractionation .
”

Lead author Alexander Helm from GSI’s department of biophysics working with cell cultures on the GSI/FAIR campus. (Courtesy: Adrian Rodríguez Rodríguez/GSI)
Immunotherapy using checkpoint inhibitors is an emerging cancer treatment that has recently had great success in treating metastatic cancer. The technique works by blocking checkpoint proteins (such as CTLA-4 or PD-1) that stop the patient’s immune system from attacking cancer cells, and reactivating the immune system to fight cancer. Unfortunately, however, only a fraction of patients respond to such immunotherapy and only certain tumour types can be treated.
To increase its potential pool of patients and cancers, immunotherapy can be combined with radiation therapy, which under certain conditions also triggers an immune response. It has also been proposed that charged particles – such as the carbon-ion beams already used clinically to treat certain cancers – could prove more effective than X-rays in this combination.
To investigate this idea further, an international research team headed up at the GSI Helmholtz Centre for Heavy Ion Research has compared the efficacy of carbon-ion radiotherapy and conventional X-ray radiotherapy in combination with checkpoint inhibitors in a mouse bone tumour model. The researchers report their findings in the International Journal of Radiation Oncology, Biology, Physics.
“There are several explanations as to why carbon ions and immunotherapy are a good match,” explains lead author Alexander Helm. “The most prominent is actually the peculiar pattern of cell death that is induced by carbon ions compared with conventional radiotherapy. It is hypothesized that this very cell death is more immunogenic, which will eventually lead to a more efficient activation of the immune response and a better elimination of metastases. These effects, nonetheless, depend on the combination with immunotherapy to boost such immune responses.”
Radiation comparisons
The researchers, also from the Parthenope University of Naples and NIRS-QST in Japan, conducted their experiments at the accelerator in Chiba, Japan. They inoculated mice in both hind legs with osteosarcoma cells, a bone tumour that is generally considered radioresistant. They then treated each mouse with a 10 Gy dose of either carbon ions or X-rays, in combination with two immune checkpoint inhibitors: anti-PD-1 and anti-CTLA-4. Tumours on the animals’ left legs (representing primary tumours) were irradiated, while those on the right legs (abscopal tumours) were kept out of the radiation field.
Tumours that were directly irradiated, with either carbon ions or X-rays, demonstrated reduced growth compared with untreated mice. Tumour growth was better controlled in mice that received irradiation plus immunotherapy than in animals treated with radiotherapy alone, suggesting a synergistic effect likely based on the additional immune response boost by the checkpoint inhibitors.
In mice receiving the combination treatments, growth of the unirradiated abscopal tumours also decreased. This reduced growth was most pronounced when the animals received a combination of carbon ions plus checkpoint inhibitors.
The team also examined the effects of the various treatments on lung metastases, which form spontaneously from the bone tumours in the mice. When combined with immunotherapy, both radiation types essentially suppressed the metastases. As found previously, the combination of carbon ions plus checkpoint inhibitors had the greatest effect, resulting in the least number of metastases.
Carbon-ion irradiation alone also significantly reduced the number of lung metastases compared with the control group, comparable with results in animals that received only checkpoint inhibitors. This was not the case for mice treated with X-rays.
The team concludes that a combination of high-energy carbon-ion radiotherapy and checkpoint inhibitors has the highest potential to control distal metastases in this mouse model and could provide a potential clinical option for treatment of advanced tumours. Corresponding author Marco Durante, director of the department of biophysics at GSI, has previously demonstrated that carbon ions and protons have physical advantages over X-rays that enable drastically improved sparing of healthy tissue during radiotherapy. In fact, charged particles spare circulating immune cells in the blood much more than X-rays, which is necessary for an efficient immune response.
The researchers are now working to discover the mechanisms underlying these immune responses. Understanding these mechanisms should allow them to tailor radiation treatments to increase immune response activation.
“For example, the radiotherapy fractionation scheme has been shown to have a crucial role on the immunogenicity of the induced cell death,” explains Helm. “Hypofractionation, in which higher doses are applied in a shorter time span (than with conventional radiotherapy), has been reported as beneficial – and carbon ions are a perfect match for hypofractionation.”


physicsworld--2020-11-25--Helen Berman: the crystallographer who pioneered the Protein Data Bank - Physics World

When Helen Berman was working as an X-ray crystallographer at the Institute for Cancer Research ( ICR ) in Philadelphia in 1969 , she and a handful of other colleagues realized that the field was about to be inundated .
Until then , determining the structure of proteins – describing the positions of its individual atoms – was a time-consuming process , requiring complex diffraction data to be produced and interpreted by hand .
Most proteins have tens of thousands of atoms , and back then barely a dozen or so protein structures had been determined .
But Berman , @ @ @ @ @ @ @ realized that improved instrumentation and new computational methods would soon send the number of protein structures skyrocketing .
A proper database able to archive voluminous numbers of structures in a standard form was urgently needed , she felt .
Accomplishing that goal would require extensive computing capabilities and state-of-the-art computer graphics .
And so it was that at a 1971 conference at the Cold Spring Harbor Laboratory on Long Island , New York , Berman and her colleagues broached the subject with Walter Hamilton , a renowned crystallographer from Brookhaven National Laboratory , @ @ @ @ @ @ @ Bank ( PDB ) that year .
Berman ’ s intuition was correct : entries in the PDB grew exponentially from seven in 1971 to 100 by 1982 , 1000 in 1993 and 10,000 in 1999 .
Today the PDB has almost 170,000 , making it the most important open-access , digital-data resource in biology .
But in 1998 , when Berman moved the PDB to Rutgers University , she sensed another imminent crisis .
While initially X-ray crystallography was the main tool for determining protein structures , it was soon joined by @ @ @ @ @ @ @ and cryogenic electron microscopy ( cryo-EM ) .
Researchers were therefore increasingly having to turn to “ integrative ” structure determination based on data from multiple experimental methods , not just cryo-EM and NMR but also chemical crosslinking , small angle scattering , Förster resonance energy transfer and others .
Berman thought this pointlessly hampered research since users had to navigate different data management practices .
Seeking a way to allow these differently determined protein models to be entered into a single repository , she immediately realised that each community had not only @ @ @ @ @ @ @ data , but had also developed a different language , standards , criteria for acceptability , and different limits on the possible positions of individual atoms in a protein .
For a while , Berman overcame this obstacle by fitting integrative structures into the PDB case-by-case , but it was gruelling work .
As she told me , she realized , “ No way this is gon na scale !
” Berman tried for a while to expand the PDB standards and give them to the different communities involved in integrative modelling , @ @ @ @ @ @ @ .
Each community worked differently , making sense of data using procedures and standards appropriate to their research ; their members feared that new standards imposed from outside would interfere with creativity and success .
Reactions ranged from polite lack of interest to outright hostility : the day after one presentation , for example , a researcher sent Berman an offensive message insisting he had no intention of doing what “ Madame President ” wanted .
Her first thought was : “ How can I get this guy on my side ?
” @ @ @ @ @ @ @ .
Or as Berman politely puts it : “ Scientists are not usually skilled at social engineering.
” She therefore decided to leave the standards to the communities themselves , befriending members , tracking down the experts , and explaining how success would benefit their communities .
Most importantly , she listened to why they felt certain things might be impossible in practice .
“ That way , the leaders of each community remained the leaders , ” says Andrej Sali , a structural biologist at the University of California , San Francisco @ @ @ @ @ @ @ They kept taking care of their corner of the universe.
” However , the communities needed to figure out ways to exchange data and communicate with each other .
The result was PDB-Dev – a flexible test platform that can accommodate different types of integrative structures before they are eventually archived in the PDB .
It succeeded in bringing structural biologists and the different experimental communities together , with two committees – one to archive models and exchange data , and the other to validate different models .
PDB-Dev released its first structure @ @ @ @ @ @ @ the head of the PDB in 2014 , but continues her involvement in it , including leading a workshop last year .
“ It ’ s a work in progress , ” she admits .
“ As each structure comes in , we find a new set of problems that we hadn ’ t thought of before.
” PDB-Dev now has 61 structures and aims to fold into the PDB over the next five years .
Berman attributes some of her success to her own family background : her father was a surgeon @ @ @ @ @ @ @ while her mother was a community health organizer in poor neighbourhoods of Brooklyn .
“ Her talent was to get people to talk together , ” Berman said .
“ The next step is to show people that there ’ s a problem.
” In much the same way , she feels , her skill lies in encouraging scientists to speak outside their technical vocabularies in language those in other communities can understand – including why some things could not work .
After one of Berman ’ s presentations , an audience member @ @ @ @ @ @ @ sounded like the work of the American political economist Elinor Ostrom ( 1933–2012 ) .
As someone who specialized in describing the principles of managing resources in diverse communities , Ostrom found that the wrong approach was to seek a “ theory ” for managing combined practices of different groups ; the key is to get them to work together first .
Or , as Berman puts it : “ Science is alive , a fluid thing .
Making it go is community work .
”

Physics World, where it appeared under the headline "The bank of success". Members of the Institute of Physics can enjoy the full issue Taken from the November 2020 issue of, where it appeared under the headline "The bank of success". Members of the Institute of Physics can enjoy the full issue via the Physics World app
After helping to set up the first major repository of protein structures 50 years ago, Helen Berman is now significantly expanding its scope, as Robert P Crease finds out
Community minded Helen Berman, who helped pioneer the Protein Data Bank. (Courtesy: Photograph by Nick Romanenko, © Rutgers University)
When Helen Berman was working as an X-ray crystallographer at the Institute for Cancer Research (ICR) in Philadelphia in 1969, she and a handful of other colleagues realized that the field was about to be inundated. Until then, determining the structure of proteins – describing the positions of its individual atoms – was a time-consuming process, requiring complex diffraction data to be produced and interpreted by hand. Most proteins have tens of thousands of atoms, and back then barely a dozen or so protein structures had been determined.
But Berman, who was an ICR research associate, realized that improved instrumentation and new computational methods would soon send the number of protein structures skyrocketing. A proper database able to archive voluminous numbers of structures in a standard form was urgently needed, she felt. Accomplishing that goal would require extensive computing capabilities and state-of-the-art computer graphics.
And so it was that at a 1971 conference at the Cold Spring Harbor Laboratory on Long Island, New York, Berman and her colleagues broached the subject with Walter Hamilton, a renowned crystallographer from Brookhaven National Laboratory, inspiring him to create the Protein Data Bank (PDB) that year. Berman’s intuition was correct: entries in the PDB grew exponentially from seven in 1971 to 100 by 1982, 1000 in 1993 and 10,000 in 1999. Today the PDB has almost 170,000, making it the most important open-access, digital-data resource in biology.
Off-the-scale problems
But in 1998, when Berman moved the PDB to Rutgers University, she sensed another imminent crisis. While initially X-ray crystallography was the main tool for determining protein structures, it was soon joined by nuclear magnetic resonance spectroscopy (NMR) and cryogenic electron microscopy (cryo-EM). Researchers were therefore increasingly having to turn to “integrative” structure determination based on data from multiple experimental methods, not just cryo-EM and NMR but also chemical crosslinking, small angle scattering, Förster resonance energy transfer and others.
Berman thought this pointlessly hampered research since users had to navigate different data management practices. Seeking a way to allow these differently determined protein models to be entered into a single repository, she immediately realised that each community had not only created different ways to store and manage data, but had also developed a different language, standards, criteria for acceptability, and different limits on the possible positions of individual atoms in a protein.
For a while, Berman overcame this obstacle by fitting integrative structures into the PDB case-by-case, but it was gruelling work. As she told me, she realized, “No way this is gonna scale!” Berman tried for a while to expand the PDB standards and give them to the different communities involved in integrative modelling, but it didn’t go well. Each community worked differently, making sense of data using procedures and standards appropriate to their research; their members feared that new standards imposed from outside would interfere with creativity and success.
Reactions ranged from polite lack of interest to outright hostility: one researcher sent Berman an offensive message insisting he had no intention of doing what “Madame President” wanted. Robert P Crease
Reactions ranged from polite lack of interest to outright hostility: the day after one presentation, for example, a researcher sent Berman an offensive message insisting he had no intention of doing what “Madame President” wanted. Her first thought was: “How can I get this guy on my side?” Figuring that out wasn’t easy. Or as Berman politely puts it: “Scientists are not usually skilled at social engineering.”
She therefore decided to leave the standards to the communities themselves, befriending members, tracking down the experts, and explaining how success would benefit their communities. Most importantly, she listened to why they felt certain things might be impossible in practice. “That way, the leaders of each community remained the leaders,” says Andrej Sali, a structural biologist at the University of California, San Francisco, who works with Berman. “They kept taking care of their corner of the universe.”
However, the communities needed to figure out ways to exchange data and communicate with each other. The result was PDB-Dev – a flexible test platform that can accommodate different types of integrative structures before they are eventually archived in the PDB. It succeeded in bringing structural biologists and the different experimental communities together, with two committees – one to archive models and exchange data, and the other to validate different models. PDB-Dev released its first structure in 2016.
Read more My favourite Nobel prize: X-ray diffraction to deduce crystal structure
Berman stepped down as the head of the PDB in 2014, but continues her involvement in it, including leading a workshop last year. “It’s a work in progress,” she admits. “As each structure comes in, we find a new set of problems that we hadn’t thought of before.” PDB-Dev now has 61 structures and aims to fold into the PDB over the next five years.
The critical point
Berman attributes some of her success to her own family background: her father was a surgeon and professor at a medical school, while her mother was a community health organizer in poor neighbourhoods of Brooklyn. “Her talent was to get people to talk together,” Berman said. “The next step is to show people that there’s a problem.” In much the same way, she feels, her skill lies in encouraging scientists to speak outside their technical vocabularies in language those in other communities can understand – including why some things could not work.
After one of Berman’s presentations, an audience member told her that what she was doing sounded like the work of the American political economist Elinor Ostrom (1933–2012). As someone who specialized in describing the principles of managing resources in diverse communities, Ostrom found that the wrong approach was to seek a “theory” for managing combined practices of different groups; the key is to get them to work together first. Or, as Berman puts it: “Science is alive, a fluid thing. Making it go is community work.”


physicsworld--2020-11-26--US president-elect Joe Biden set to put science centre stage - Physics World

One of Joe Biden ’ s first moves as he became US president-elect earlier this month was to appoint a new coronavirus advisory panel .
Featuring senior figures such as Vivek Murthy , a former US surgeon general , and David Kessler , a former commissioner of the Food and Drug Administration , the approach brought relief to many and contrasted sharply with the anti-science rhetoric of departing US president Donald Trump .
While Biden emphasized that his administration will be “ built on a bedrock of science ” , the election failed to deliver a convincing majority for the @ @ @ @ @ @ @ agenda could face an uphill battle in Congress .
For many in the US scientific community , however , Biden ’ s election represents a return to normality that had disappeared during the four years of Donald Trump .
“ [ Physicists ] have expressed delight at the election result and look forward to working with the new administration , ” says physicist Philip Bucksbaum from Stanford University , who is president of the American Physical Society ( APS ) .
That view is backed by Michael Moloney , chief executive of the @ @ @ @ @ @ @ , who says that many scientists will now be “ eager ” to serve in the next government .
Yet the prospective benefits of a science-friendly administration face obstacles .
In the short term , Trump ’ s refusal to concede defeat has slowed down exchanges of information necessary for a smooth transition on 20 January , particularly when it comes to containing COVID-19 .
The Trump administration has also announced fresh appointments and actions intended to continue its policy of emphasizing economics over science .
In mid-November , for example , the @ @ @ @ @ @ @ overseeing the National Climate Assessment , which provides the basis for regulations on global warming .
His intended replacement is the University of Delaware geographer David Legates , who denies anthropogenic climate change .
A longer-term difficulty is the failure of a “ blue wave ” to emerge during the elections , which Democrats had hoped would give them control of the Senate and increase their majority in the House of Representatives .
The party in fact lost seats , although not its majority , in the House , while control of the @ @ @ @ @ @ @ two Senate seats in Georgia on 5 January .
An unlikely Democratic win in both seats would produce a Senate divided 50–50 giving the deciding vote to vice-president-elect Kamala Harris .
But even with that achievement , the administration could face problems pursuing its science-based agenda given that much legislation requires 60 votes in the Senate to move forward .
Biden will have some immediate opportunities to fulfil his vow of relying on science .
He has nominated Avril Haines , who has an undergraduate degree in physics from the University of Chicago @ @ @ @ @ @ @ His administration is also expected to soon overturn three Trump administration actions by re-joining the Paris climate agreement , the World Health Organization and the Joint Comprehensive Plan of Action on Iran .
Biden can achieve those aims with executive orders that do not need Senate approval and he can also renew the START treaty on nuclear-weapons reduction , which expires on 5 February .
“ Certainly , the physics community is interested in seeing an extension , ” adds Bucksbaum .
Hope has also emerged regarding climate change , with insiders seeing @ @ @ @ @ @ @ to take a nuanced view of the issue .
“ The scientific evidence has got stronger and the potential outcomes of climate change scarier , ” says former US presidential science adviser Neal Lane , who is a senior fellow in science and technology policy at Rice University .
“ A lot of Republican senators realize there ’ s a problem here and that they must find a way to change.
” Indeed , Illinois Representative Bill Foster , the only PhD physicist in Congress , adds that Republicans on the House Science @ @ @ @ @ @ @ Republican leader Kevin McCarthy – have already proposed doubling the US research budget to help develop technologies to mitigate climate change .
During Trump ’ s presidency , the Environmental Protections Agency ( EPA ) overturned several government regulations intended to protect other aspects of the environment such as limits on toxic chemicals in the air and soil , the commercial use of government-owned land and the efficiency of car fleets .
Since it used executive orders for several of those actions , the Biden administration can counter with its own orders .
@ @ @ @ @ @ @ quickly overturn Trump ’ s severe restrictions on immigration .
“ AIP has been on the record about how limits to immigration negatively impact the scientific enterprise as well as how increasing diversity , accessibility and belonging within the STEM workforce will lead to better scientific outcomes , ” says Moloney .
Those views are backed by Bucksbaum , who says that the APS is working to persuade the new administration to overturn a Trump proposal that would limit certain overseas students ’ visas to two years , rather than the traditional duration @ @ @ @ @ @ @ of graduate studies .
As Biden announces nominees for his cabinet , the science community will focus attention on the new presidential science adviser to replace the current incumbent , atmospheric scientist Kelvin Droegemeier .
Lane would like to see a woman in the role for the first time and believes it should be a cabinet-level position .
“ The first science adviser needs to have a good understanding of health issues , ” he says .
“ They should be the key point person in dealing with the pandemic on the ground.
@ @ @ @ @ @ @ .
In an interview with Aviation Week after the election , current NASA administrator Jim Bridenstine announced he would resign – even if Biden asked him to stay on .
A former Oklahoma Congressman who has led the agency since April 2018 , Bridenstine overcame initial suspicions about his attitude to climate change and many think he has run NASA smoothly and efficiently such as advancing the schedule for human Moon landings .
“ He ’ s managed to work well with both [ political ] parties , ” says Lane , a @ @ @ @ @ @ @ done a good job working with SpaceX and moving toward stronger partnerships with the private sector.
” Whether the rest of the government ’ s science-based agencies can work as effectively as NASA remains to be seen .
Several political pundits assert that Biden is a natural conciliator , whose long service in Congress has gained him the respect of Republican legislators .
That could help him to achieve agreement on science-friendly policies .
“ It will be important for both Republicans and Democrats to focus on bipartisan issues , ” says Bucksbaum @ @ @ @ @ @ @ the historical position of being something that everybody likes.
” The American Physical Society ( APS ) has sharpened its criteria when choosing the locations in which to hold future meetings , saying it will ask the leadership of possible cities to report on local policing policies and related demographic issues .
The society will , in particular , examine statistics on the use of force by the local police ; policies on police use of strangleholds and other methods of restraint ; as well as the status of investigations into the deaths @ @ @ @ @ @ @ cities will be expected to train all their police in de-escalation methods ; have evaluations of policing performance that include shootings and deaths of unarmed individuals by police officers ; as well as have “ a well-defined plan and timetable for improving local policing practices ” .
The policy has been introduced following the use of excessive force by the police , particularly against members of under-represented or minority groups .
“ We became aware that members of our community are vulnerable in ways we had never imagined , and we resolved to @ @ @ @ @ @ @ the University of Kentucky , who chairs the APS ’ s committee on scientific meetings .
APS president Philip Bucksbaum of Stanford University told Physics World that the membership has been the motivation for the move .
“ We hear loud and clear that our members see that they shouldn ’ t have to go to meetings in cities where they feel unsafe and threatened , ” he says .

Physics World, where it appeared under the headline "'Delight' as Biden elected US president". Members of the Institute of Physics can enjoy the full issue Taken from the December 2020 issue of, where it appeared under the headline "'Delight' as Biden elected US president". Members of the Institute of Physics can enjoy the full issue via the Physics World app from 1 December.
Physicists welcome the election of Joe Biden as US president but he faces challenges to unite a divided Congress, as Peter Gwynne reports
A new era beckons Joe Biden – shown here with vice-president elect Kamala Harris – will have many science-related issues to contend with when he becomes the 46th US president on 20 January. (Courtesy: Andrew Harnik/AP/Shutterstock)
One of Joe Biden’s first moves as he became US president-elect earlier this month was to appoint a new coronavirus advisory panel. Featuring senior figures such as Vivek Murthy, a former US surgeon general, and David Kessler, a former commissioner of the Food and Drug Administration, the approach brought relief to many and contrasted sharply with the anti-science rhetoric of departing US president Donald Trump. While Biden emphasized that his administration will be “built on a bedrock of science”, the election failed to deliver a convincing majority for the former vice-president, meaning that his science-based agenda could face an uphill battle in Congress.
For many in the US scientific community, however, Biden’s election represents a return to normality that had disappeared during the four years of Donald Trump. “[Physicists] have expressed delight at the election result and look forward to working with the new administration,” says physicist Philip Bucksbaum from Stanford University, who is president of the American Physical Society (APS). That view is backed by Michael Moloney, chief executive of the American Institute of Physics (AIP), who says that many scientists will now be “eager” to serve in the next government.
Yet the prospective benefits of a science-friendly administration face obstacles. In the short term, Trump’s refusal to concede defeat has slowed down exchanges of information necessary for a smooth transition on 20 January, particularly when it comes to containing COVID-19. The Trump administration has also announced fresh appointments and actions intended to continue its policy of emphasizing economics over science. In mid-November, for example, the administration removed Michael Kuperberg from his post overseeing the National Climate Assessment, which provides the basis for regulations on global warming. His intended replacement is the University of Delaware geographer David Legates, who denies anthropogenic climate change.
A longer-term difficulty is the failure of a “blue wave” to emerge during the elections, which Democrats had hoped would give them control of the Senate and increase their majority in the House of Representatives. The party in fact lost seats, although not its majority, in the House, while control of the Senate now depends on run-off elections for two Senate seats in Georgia on 5 January. An unlikely Democratic win in both seats would produce a Senate divided 50–50 giving the deciding vote to vice-president-elect Kamala Harris. But even with that achievement, the administration could face problems pursuing its science-based agenda given that much legislation requires 60 votes in the Senate to move forward.
Reversing policies
Biden will have some immediate opportunities to fulfil his vow of relying on science. He has nominated Avril Haines, who has an undergraduate degree in physics from the University of Chicago, as director of national intelligence. His administration is also expected to soon overturn three Trump administration actions by re-joining the Paris climate agreement, the World Health Organization and the Joint Comprehensive Plan of Action on Iran. Biden can achieve those aims with executive orders that do not need Senate approval and he can also renew the START treaty on nuclear-weapons reduction, which expires on 5 February. “Certainly, the physics community is interested in seeing an extension,” adds Bucksbaum.
Biden will have some immediate opportunities to fulfil his vow of relying on science
Hope has also emerged regarding climate change, with insiders seeing signs that some Republican legislators have begun to take a nuanced view of the issue. “The scientific evidence has got stronger and the potential outcomes of climate change scarier,” says former US presidential science adviser Neal Lane, who is a senior fellow in science and technology policy at Rice University. “A lot of Republican senators realize there’s a problem here and that they must find a way to change.” Indeed, Illinois Representative Bill Foster, the only PhD physicist in Congress, adds that Republicans on the House Science Committee – with the approval of House Republican leader Kevin McCarthy – have already proposed doubling the US research budget to help develop technologies to mitigate climate change.
During Trump’s presidency, the Environmental Protections Agency (EPA) overturned several government regulations intended to protect other aspects of the environment such as limits on toxic chemicals in the air and soil, the commercial use of government-owned land and the efficiency of car fleets. Since it used executive orders for several of those actions, the Biden administration can counter with its own orders.
The Biden administration is also expected to quickly overturn Trump’s severe restrictions on immigration. “AIP has been on the record about how limits to immigration negatively impact the scientific enterprise as well as how increasing diversity, accessibility and belonging within the STEM workforce will lead to better scientific outcomes,” says Moloney. Those views are backed by Bucksbaum, who says that the APS is working to persuade the new administration to overturn a Trump proposal that would limit certain overseas students’ visas to two years, rather than the traditional duration sufficient to take individuals through the completion of graduate studies.
New appointments
As Biden announces nominees for his cabinet, the science community will focus attention on the new presidential science adviser to replace the current incumbent, atmospheric scientist Kelvin Droegemeier. Lane would like to see a woman in the role for the first time and believes it should be a cabinet-level position. “The first science adviser needs to have a good understanding of health issues,” he says. “They should be the key point person in dealing with the pandemic on the ground.” Read more Nobel laureates endorse Joe Biden for US president
Another open post is NASA boss. In an interview with Aviation Week after the election, current NASA administrator Jim Bridenstine announced he would resign – even if Biden asked him to stay on. A former Oklahoma Congressman who has led the agency since April 2018, Bridenstine overcame initial suspicions about his attitude to climate change and many think he has run NASA smoothly and efficiently such as advancing the schedule for human Moon landings. “He’s managed to work well with both [political] parties,” says Lane, a fellow Oklahoman. “He’s done a good job working with SpaceX and moving toward stronger partnerships with the private sector.”
Whether the rest of the government’s science-based agencies can work as effectively as NASA remains to be seen. Several political pundits assert that Biden is a natural conciliator, whose long service in Congress has gained him the respect of Republican legislators. That could help him to achieve agreement on science-friendly policies. “It will be important for both Republicans and Democrats to focus on bipartisan issues,” says Bucksbaum. “Science can then return to the historical position of being something that everybody likes.”
American Physical Society tightens rules on meeting locations The American Physical Society (APS) has sharpened its criteria when choosing the locations in which to hold future meetings, saying it will ask the leadership of possible cities to report on local policing policies and related demographic issues. The society will, in particular, examine statistics on the use of force by the local police; policies on police use of strangleholds and other methods of restraint; as well as the status of investigations into the deaths of individuals in police custody. Candidate cities will be expected to train all their police in de-escalation methods; have evaluations of policing performance that include shootings and deaths of unarmed individuals by police officers; as well as have “a well-defined plan and timetable for improving local policing practices”. The policy has been introduced following the use of excessive force by the police, particularly against members of under-represented or minority groups. “We became aware that members of our community are vulnerable in ways we had never imagined, and we resolved to act,” says Susan Gardner of the University of Kentucky, who chairs the APS’s committee on scientific meetings. APS president Philip Bucksbaum of Stanford University told Physics World that the membership has been the motivation for the move. “We hear loud and clear that our members see that they shouldn’t have to go to meetings in cities where they feel unsafe and threatened,” he says.


physicsworld--2020-11-26--Deep-learning model enables rapid lymphoma detection in PET/CT images - Physics World

Whole-body positron emission tomography combined with computed tomography ( PET/CT ) is a cornerstone in the management of lymphoma ( cancer in the lymphatic system ) .
PET/CT scans are used to diagnose disease and then to monitor how well patients respond to therapy .
However , accurately classifying every single lymph node in a scan as healthy or cancerous is a complex and time-consuming process .
Because of this , detailed quantitative treatment monitoring is often not feasible in clinical day-to-day practice .
Researchers at the University of Wisconsin-Madison have recently developed a deep-learning model that can perform this @ @ @ @ @ @ @ valuable physician time and make quantitative PET/CT treatment monitoring possible for a larger number of patients .
To acquire PET/CT scans , patients are injected with a sugar molecule marked with radioactive fluorine-18 ( 18F-fluorodeoxyglucose ) .
When the fluorine atom decays , it emits a positron that instantly annihilates with an electron in its immediate vicinity .
This annihilation process emits two back-to-back photons , which the scanner detects and uses to infer the location of the radioactive decay .
Because tumours grow faster than most healthy tissue , they must consume @ @ @ @ @ @ @ tracer will therefore be drawn towards the lymphoma lesions , making them visible in the PET/CT scan .
However , other types of tissue , such as certain fatty tissues , can “ light up ” the scans in a similar manner , which can lead to false positives .
In their study , published in Radiology : Artificial Intelligence , Amy Weisman and colleagues investigated lesion-identifying deep-learning models built from different configurations of convolutional neural networks ( CNNs ) .
They trained , tested and validated these models using PET/CT scans of @ @ @ @ @ @ @ large B-cell lymphoma .
For this purpose , a single radiologist delineated lesions within each scan and classified each one on a scale from 1–5 , depending on how sure they were that a lesion was malignant .
The researchers found that a model consisting of three CNNs performed best , identifying 85 % of manually contoured lesions ( 923 of 1087 , the so-called true positive rate ) .
At the same time , it falsely identified four lesions per patient ( the false positive rate ) .
The time to evaluate @ @ @ @ @ @ @ minutes using manual delineation to under two minutes for the model .
It is extremely difficult to classify every lymph node in a scan as cancerous or not with 100 % certainty .
Because of this , if two radiologists delineate lesions for the same patient , they are not likely to agree with each other completely .
When a second radiologist evaluated 20 of the scans , their true positive rate was 96 % , while they marked on average 3.7 malignant nodes per patient that their colleague had not .
In @ @ @ @ @ @ @ had a true positive rate of 90 % , at 3.7 false positives per scan – making its predictions almost as good as the variation between two observers .
Often , one of the biggest hurdles in creating this type of model is that training it requires a large number of carefully delineated scans .
The study authors tested how well their model performed depending upon the number of patients used for training .
Interestingly , they found that a model trained on 40 patients performed just as well as one trained on @ @ @ @ @ @ @ the detailed lesion delineations for training the models proved a more challenging task : “ Physicians and radiologists don ’ t need to carefully segment the tumours , and they don ’ t need to label a lesion on a scale from 1 to 5 in their daily routine .
So asking our physicians to sit down and make decisions like that was really awkward for them , ” she explains .
The initial awkwardness was quickly overcome , though , says Weisman .
“ Because of this , Minnie ( one of @ @ @ @ @ @ @ close during the time she was segmenting for us – and I could just text her and say ‘ What was going on with this image/lesion ?
’ .
Having a relationship like that was super helpful.
” Future research will focus on incorporating additional , and more diverse , data .
“ Acquiring more data is always the next step for improving a model and making sure it won ’ t fail once it ’ s being used , ” says Weisman .
At the same time , the group is working @ @ @ @ @ @ @ to use and interact with the model in their daily work .

The research group at the University of Wisconsin-Madison. From left to right: Timothy Perk, Alison Roth, Peter Ferjančič, Robert Jeraj, Daniel Huff, Brayden Schott, Ali Deatsch, Victor Santoro Fernandes, Amy Weisman, Vince Streif. (Courtesy: Amy Weisman)
Whole-body positron emission tomography combined with computed tomography (PET/CT) is a cornerstone in the management of lymphoma (cancer in the lymphatic system). PET/CT scans are used to diagnose disease and then to monitor how well patients respond to therapy. However, accurately classifying every single lymph node in a scan as healthy or cancerous is a complex and time-consuming process. Because of this, detailed quantitative treatment monitoring is often not feasible in clinical day-to-day practice.
Researchers at the University of Wisconsin-Madison have recently developed a deep-learning model that can perform this task automatically. This could free up valuable physician time and make quantitative PET/CT treatment monitoring possible for a larger number of patients.
To acquire PET/CT scans, patients are injected with a sugar molecule marked with radioactive fluorine-18 (18F-fluorodeoxyglucose). When the fluorine atom decays, it emits a positron that instantly annihilates with an electron in its immediate vicinity. This annihilation process emits two back-to-back photons, which the scanner detects and uses to infer the location of the radioactive decay.
Because tumours grow faster than most healthy tissue, they must consume more energy. Much of the radioactive tracer will therefore be drawn towards the lymphoma lesions, making them visible in the PET/CT scan. However, other types of tissue, such as certain fatty tissues, can “light up” the scans in a similar manner, which can lead to false positives.
Neural networks: accurate and fast
In their study, published in Radiology: Artificial Intelligence, Amy Weisman and colleagues investigated lesion-identifying deep-learning models built from different configurations of convolutional neural networks (CNNs). They trained, tested and validated these models using PET/CT scans of 90 patients with Hodgkin lymphoma or diffuse large B-cell lymphoma. For this purpose, a single radiologist delineated lesions within each scan and classified each one on a scale from 1–5, depending on how sure they were that a lesion was malignant.
The researchers found that a model consisting of three CNNs performed best, identifying 85% of manually contoured lesions (923 of 1087, the so-called true positive rate). At the same time, it falsely identified four lesions per patient (the false positive rate). The time to evaluate a single scan was cut from 35 minutes using manual delineation to under two minutes for the model.
It is extremely difficult to classify every lymph node in a scan as cancerous or not with 100% certainty. Because of this, if two radiologists delineate lesions for the same patient, they are not likely to agree with each other completely. When a second radiologist evaluated 20 of the scans, their true positive rate was 96%, while they marked on average 3.7 malignant nodes per patient that their colleague had not. In these 20 patients, the deep-learning model had a true positive rate of 90%, at 3.7 false positives per scan – making its predictions almost as good as the variation between two observers.
Expected, and unexpected, challenges
Often, one of the biggest hurdles in creating this type of model is that training it requires a large number of carefully delineated scans. The study authors tested how well their model performed depending upon the number of patients used for training. Interestingly, they found that a model trained on 40 patients performed just as well as one trained on 72.
Amy Weisman celebrates her online PhD defence. This study formed part of her thesis work.
According to Weisman, obtaining the detailed lesion delineations for training the models proved a more challenging task: “Physicians and radiologists don’t need to carefully segment the tumours, and they don’t need to label a lesion on a scale from 1 to 5 in their daily routine. So asking our physicians to sit down and make decisions like that was really awkward for them,” she explains.
The initial awkwardness was quickly overcome, though, says Weisman. “Because of this, Minnie (one of our physicians) and I got really close during the time she was segmenting for us – and I could just text her and say ‘What was going on with this image/lesion?’. Having a relationship like that was super helpful.”
Future research will focus on incorporating additional, and more diverse, data. “Acquiring more data is always the next step for improving a model and making sure it won’t fail once it’s being used,” says Weisman. At the same time, the group is working on finding the best way for clinicians to use and interact with the model in their daily work.


physicsworld--2020-11-26--Magnetic perovskite gets the lead out - Physics World

A new “ double perovskite ” material could become a more environmentally friendly platform for spintronics devices thanks to its lead-free nature .
While the material in its current form is only magnetic below 30 K – too low for practical applications – developers at Linköping University in Sweden , together with colleagues in the US , the Czech Republic , Japan , Australia and China , say that their preliminary experiments are nevertheless a promising step towards making rapid and energy-efficient information storage devices from this novel optoelectronic material .
Halide perovskites in general have an ABX structure , @ @ @ @ @ @ @ MA ) or formamidinium ( FA ) ; B is lead or tin ; and X is chlorine , bromine or iodine .
Materials of this type absorb light over a broad range of solar spectrum wavelengths thank to their tunable bandgaps , and the electrons and holes within them diffuse quickly over long distances ( high charge carrier mobility and lifetime ) .
These properties make them attractive building blocks for high-performance optoelectronic devices such as solar cells , light-emitting diodes , lasers and photodetectors .
Recently , researchers discovered that lead @ @ @ @ @ @ @ thanks to lead ’ s strong spin-orbit coupling .
This coupling links the motion of an electron to its quantum spin , and its strength determines how much the intrinsic spin of an electron will interact with the magnetic field induced as the electron moves through the material .
Such a coupling is therefore important not only for the magnetic properties of a material , but also for the performance of any spintronics devices – that is , devices that exploit the spin of an electron as well as its charge – that @ @ @ @ @ @ @ , lead-based halide perovskites were thought to be the only materials in their class to possess this desirable magnetic property .
Because lead is toxic for humans , animals and the wider environment , its presence has limited the materials ’ development .
Now , however , a team led by Feng Gao has created a new perovskite material that retains the magnetic properties of its lead-based cousin but contains paramagnetic iron ions ( Fe3+ ) instead of lead .
The team created this material by incorporating the iron ions into a perovskite @ @ @ @ @ @ @ and bromine , with the chemical formula Cs AgBiBr .
In a series of measurements made using near edge X-ray absorption fine structure ( NEXAFS ) and solid-state nuclear magnetic resonance ( ssNMR ) techniques , Gao and colleagues showed that Fe3+ replaces Bi3+ in this iron-alloyed double perovskite and forms FeBr clusters that are evenly distributed throughout the material ’ s crystal structure .
According to combined SQUID ( superconducting quantum interference device ) and ESR ( electron spin resonance ) measurements , the new perovskite material is magnetic at temperatures below @ @ @ @ @ @ @ temperature is too low for practical applications , he also points out that the material is still at a very early stage in its development .
The researchers add that they are not even completely sure what is causing its magnetic response , although their results suggest that it is probably due to a weak ferromagnetic or anti-ferromagnetic response from localized regions in the material .
“ If so , we have a whole new class of halide double perovskite alloys that can potentially be used for spintronics applications , ” Gao says @ @ @ @ @ @ @ , not least to obtain the magnetic properties at higher temperatures.
” The researchers , who report their work in Science Advances , say they now plan to repeat their experiments at higher pressures and use chemical co-doping and alloying to try to retain the material ’ s magnetic properties at higher temperatures .
“ We will also be focusing on the structure-property relationships of magnetic double perovskites to better understand how to design these materials , ” Gao tells Physics World .
“ We hope that our work will encourage future efforts @ @ @ @ @ @ @ and energy-efficient information storage .
”

Lead-free magnetic perovskites. Credit: Thor Balkhed
A new “double perovskite” material could become a more environmentally friendly platform for spintronics devices thanks to its lead-free nature. While the material in its current form is only magnetic below 30 K – too low for practical applications – developers at Linköping University in Sweden, together with colleagues in the US, the Czech Republic, Japan, Australia and China, say that their preliminary experiments are nevertheless a promising step towards making rapid and energy-efficient information storage devices from this novel optoelectronic material.
Halide perovskites in general have an ABX 3 structure, where A is caesium, methylammonium (MA) or formamidinium (FA); B is lead or tin; and X is chlorine, bromine or iodine. Materials of this type absorb light over a broad range of solar spectrum wavelengths thank to their tunable bandgaps, and the electrons and holes within them diffuse quickly over long distances (high charge carrier mobility and lifetime). These properties make them attractive building blocks for high-performance optoelectronic devices such as solar cells, light-emitting diodes, lasers and photodetectors.
Spin-related properties
Recently, researchers discovered that lead halide perovskites also boast interesting spin properties thanks to lead’s strong spin-orbit coupling. This coupling links the motion of an electron to its quantum spin, and its strength determines how much the intrinsic spin of an electron will interact with the magnetic field induced as the electron moves through the material. Such a coupling is therefore important not only for the magnetic properties of a material, but also for the performance of any spintronics devices – that is, devices that exploit the spin of an electron as well as its charge – that are made from it.
Until now, lead-based halide perovskites were thought to be the only materials in their class to possess this desirable magnetic property. Because lead is toxic for humans, animals and the wider environment, its presence has limited the materials’ development.
Preliminary experiments
Now, however, a team led by Feng Gao has created a new perovskite material that retains the magnetic properties of its lead-based cousin but contains paramagnetic iron ions (Fe3+) instead of lead. The team created this material by incorporating the iron ions into a perovskite made of caesium, silver, bismuth and bromine, with the chemical formula Cs 2 AgBiBr 6 . In a series of measurements made using near edge X-ray absorption fine structure (NEXAFS) and solid-state nuclear magnetic resonance (ssNMR) techniques, Gao and colleagues showed that Fe3+ replaces Bi3+ in this iron-alloyed double perovskite and forms FeBr 6 clusters that are evenly distributed throughout the material’s crystal structure.
According to combined SQUID (superconducting quantum interference device) and ESR (electron spin resonance) measurements, the new perovskite material is magnetic at temperatures below 30 K. While Gao acknowledges that this temperature is too low for practical applications, he also points out that the material is still at a very early stage in its development. The researchers add that they are not even completely sure what is causing its magnetic response, although their results suggest that it is probably due to a weak ferromagnetic or anti-ferromagnetic response from localized regions in the material.
“If so, we have a whole new class of halide double perovskite alloys that can potentially be used for spintronics applications,” Gao says. “But more research is needed, not least to obtain the magnetic properties at higher temperatures.”
The researchers, who report their work in Science Advances, say they now plan to repeat their experiments at higher pressures and use chemical co-doping and alloying to try to retain the material’s magnetic properties at higher temperatures. “We will also be focusing on the structure-property relationships of magnetic double perovskites to better understand how to design these materials,” Gao tells Physics World. “We hope that our work will encourage future efforts in exploring spintronic double perovskites for rapid and energy-efficient information storage.”


physicsworld--2020-11-26--Medicare Radiation Oncology Alternative Payment Model: what you need to know - Physics World

Join our webinar with Shawn Prince and Awais Mirza from Accuray who will provide an overview of the finalized Medicare @ @ @ @ @ ( RO-APM ) .
This payment model is designed to test whether bundled , prospective @ @ @ @ @ , episode-based payments to physician group practices , hospital outpatient departments and freestanding radiation therapy @ @ @ @ @ care , reduces Medicare expenditures , while preserving or enhancing the quality of care for @ @ @ @ @ covered in this webinar will include : Shawn Prince has an undergraduate degree in Business @ @ @ @ @ University and a Master ’ s of Business Administration degree from Arizona State University .
@ @ @ @ @ of Patient Access at Accuray .
His previous professional experience includes reimbursement and sales for @ @ @ @ @ .

Available to watch now, explore Accuray’s Medicare Radiation Oncology Alternative Payment Model
Want to learn more on this subject? Watch now
Join our webinar with Shawn Prince and Awais Mirza from Accuray who will provide an overview of the finalized Medicare Radiation Oncology Alternative Payment Model (RO-APM). This payment model is designed to test whether bundled, prospective, site-neutral, modality agnostic, episode-based payments to physician group practices, hospital outpatient departments and freestanding radiation therapy centers for radiotherapy episodes of care, reduces Medicare expenditures, while preserving or enhancing the quality of care for Medicare beneficiaries.
Key topics covered in this webinar will include:
A detailed review of the RO-APM.
RO-APM model implementation timelines and processes.
RO-APM billing requirements and timelines.
Want to learn more on this subject? Watch now
Shawn Prince has an undergraduate degree in Business Administration from The Ohio State University and a Master’s of Business Administration degree from Arizona State University. Shawn is a Senior Director of Patient Access at Accuray. His previous professional experience includes reimbursement and sales for various pharmaceutical and biotechnology companies.
Awais Mirza is the senior manager of patient access with Accuray. Within the patient access department, Awais works to secure appropriate coding, reimbursement coverage and payment from both Medicare and commercial insurers. He has an expansive background in clinical and administrative radiation oncology and has worked for a number of hospitals as a licensed radiation therapist and administrative manager/leader prior to joining Accuray.


physicsworld--2020-11-25--Borexino spots solar neutrinos from elusive fusion cycle - Physics World

Neutrinos produced by the elusive carbon–nitrogen–oxygen ( CNO ) cycle in the Sun have been observed for the first time – confirming a theory first proposed over 80 years ago .
The observation was made by physicists working on Italy ’ s Borexino detector and provides an important insight into how stars power themselves by converting hydrogen into helium .
Now that the CNO neutrinos have been detected , future studies could help resolve the mystery surrounding the “ metallicity ” of the Sun – the abundance of carbon , nitrogen and oxygen in the star .
Astrophysicists believe that @ @ @ @ @ @ @ processes of nuclear fusion .
One is called the pp chain and accounts for 99 % of fusion energy in the Sun .
It involves a pair of protons fusing to create deuterium , which then fuses with a third proton to create helium-3 .
Finally , two helium-3 nuclei fuse to create a helium-4 .
There are two other branches of the pp chain that also produce helium-4 via the intermediary production of lithium , beryllium and boron .
The second process is the CNO cycle , which was proposed independently in @ @ @ @ @ @ @ von Weizsacker .
It is believed to account for about 1 % of fusion energy in Sun-sized stars — but is thought to dominate the energy output of larger stars .
The cycle is driven by the fusion of protons with carbon , nitrogen and oxygen nuclei in a six-step process that creates one helium-4 nucleus before repeating itself .
Both the pp and CNO processes involve the emission of distinct spectra of solar neutrinos .
In 2018 the Borexino collaboration made a comprehensive measurement of the solar neutrinos produced by the pp @ @ @ @ @ @ @ detector have measured the much weaker neutrino signal from the CNO cycle .
To do so , the physicists had to overcome detection challenges posed by the relatively low energy and flux of the CNO neutrinos .
Borexino comprises 278 tonne of ultrapure liquid scintillator and detects solar neutrinos when they collide with electrons in the scintillator .
As the electron recoils it produces light , which is captured by an array of photomultiplier tubes .
Despite the huge flux of solar neutrinos that passes through Borexino , collisions rarely happen and only @ @ @ @ @ @ @ As a result , the detector is located deep under Gran Sasso mountain to shield it from cosmic rays , which would completely overwhelm the neutrino signal .
Furthermore , the scintillator contains very low levels of radioactive impurities , which also contribute to the background signal .
The data in this study were acquired during phase-III of the Borexino experiment , which ran for over 1000 h in July 2016–February 2020 .
Because the CNO signal is very weak , the researchers had to account for background from two low-level impurities – @ @ @ @ @ @ @ the signal expected from CNO neutrinos .
The team also had to account for neutrinos created by the proton–electron–proton process in the Sun , which can also be mistaken for CNO neutrinos .
By painstakingly characterizing these background signals , the team was able detect neutrinos from the CNO process with a statistical significance of 5.1σ – above the 5σ level is considered a discovery in particle physics .
As well as confirming the longstanding ideas of Bethe and von Weizsacker , the measurement also backs the current belief that about 1 % @ @ @ @ @ @ @ the CNO cycle .
While the result does provide a measure of the abundance of carbon , nitrogen and oxygen in the Sun , it is not precise enough to resolve the “ metallicity puzzle ” of the Sun .
This mystery has emerged recently as spectrographic measurements of the opacity of the Sun and helioseismological measurements of the speed of sound in the Sun suggest conflicting values for metallicity .
Following Borexino ’ s success , future improvements to neutrino detectors could address this mystery .
The result also provides an important @ @ @ @ @ @ @ dominate fusion within stars larger than the Sun .
The research is described in Nature .

Fusion reactor: the Sun as seen by NASA’s Solar Dynamics Observatory. (Courtesy: NASA)
Neutrinos produced by the elusive carbon–nitrogen–oxygen (CNO) cycle in the Sun have been observed for the first time – confirming a theory first proposed over 80 years ago. The observation was made by physicists working on Italy’s Borexino detector and provides an important insight into how stars power themselves by converting hydrogen into helium. Now that the CNO neutrinos have been detected, future studies could help resolve the mystery surrounding the “metallicity” of the Sun – the abundance of carbon, nitrogen and oxygen in the star.
Astrophysicists believe that stars convert hydrogen to helium via two processes of nuclear fusion. One is called the pp chain and accounts for 99% of fusion energy in the Sun. It involves a pair of protons fusing to create deuterium, which then fuses with a third proton to create helium-3. Finally, two helium-3 nuclei fuse to create a helium-4. There are two other branches of the pp chain that also produce helium-4 via the intermediary production of lithium, beryllium and boron.
The second process is the CNO cycle, which was proposed independently in 1938 by Hans Bethe and Carl Friedrich von Weizsacker. It is believed to account for about 1% of fusion energy in Sun-sized stars — but is thought to dominate the energy output of larger stars. The cycle is driven by the fusion of protons with carbon, nitrogen and oxygen nuclei in a six-step process that creates one helium-4 nucleus before repeating itself.
Both the pp and CNO processes involve the emission of distinct spectra of solar neutrinos. In 2018 the Borexino collaboration made a comprehensive measurement of the solar neutrinos produced by the pp chain.
Detection challenges
Now physicists working on the detector have measured the much weaker neutrino signal from the CNO cycle. To do so, the physicists had to overcome detection challenges posed by the relatively low energy and flux of the CNO neutrinos.
Borexino comprises 278 tonne of ultrapure liquid scintillator and detects solar neutrinos when they collide with electrons in the scintillator. As the electron recoils it produces light, which is captured by an array of photomultiplier tubes. Despite the huge flux of solar neutrinos that passes through Borexino, collisions rarely happen and only tens of neutrinos are detected daily. As a result, the detector is located deep under Gran Sasso mountain to shield it from cosmic rays, which would completely overwhelm the neutrino signal. Furthermore, the scintillator contains very low levels of radioactive impurities, which also contribute to the background signal.
The data in this study were acquired during phase-III of the Borexino experiment, which ran for over 1000 h in July 2016–February 2020. Because the CNO signal is very weak, the researchers had to account for background from two low-level impurities – bismuth-210 and carbon-11 – that can mimic the signal expected from CNO neutrinos. The team also had to account for neutrinos created by the proton–electron–proton process in the Sun, which can also be mistaken for CNO neutrinos.
Painstaking characterization
By painstakingly characterizing these background signals, the team was able detect neutrinos from the CNO process with a statistical significance of 5.1σ – above the 5σ level is considered a discovery in particle physics. As well as confirming the longstanding ideas of Bethe and von Weizsacker, the measurement also backs the current belief that about 1% of solar fusion energy is created by the CNO cycle.
While the result does provide a measure of the abundance of carbon, nitrogen and oxygen in the Sun, it is not precise enough to resolve the “metallicity puzzle” of the Sun. This mystery has emerged recently as spectrographic measurements of the opacity of the Sun and helioseismological measurements of the speed of sound in the Sun suggest conflicting values for metallicity. Following Borexino’s success, future improvements to neutrino detectors could address this mystery.
The result also provides an important confirmation of how the CNO cycle should dominate fusion within stars larger than the Sun.
The research is described in Nature.


physicsworld--2020-11-25--Optimizing MLC leaf speed could improve radiotherapy plan quality - Physics World

Increasing the multileaf collimator ( MLC ) leaf speed may help improve the quality of volumetric modulated arc therapy ( VMAT ) plans , according to a study published in the Journal of Applied Clinical Medical Physics .
Researchers in Beijing investigated seven MLCs with different maximum leaf speeds to investigate their influence on plan quality .
They determined that VMAT plans for locally advanced nasopharyngeal carcinoma ( NPC ) and rectal cancer improved significantly when maximum MLC leaf speeds were increased from 1 to 3.5 cm/s .
VMAT delivers highly conformal radiation dose to a targeted tumour , sparing @ @ @ @ @ @ @ consist of several sets of metallic leaves , are used to shape the radiation beam as it exits the linear accelerator ( linac ) .
In addition to improving the dose distribution , MLCs are highly efficient and reduce treatment time .
However , dose leakage and transmission through MLC leaves can occur , negatively impacting treatment plan quality .
To achieve highly modulated dose distribution , MLCs need to move at a high speed when the gantry rotates .
But what is the optimum speed required to achieve the highest quality VMAT @ @ @ @ @ @ @ To answer this question , the research team – from the National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital , Chinese Academy of Medical Sciences and Peking Union Medical College – investigated six NPC cases , representing complex clinical treatments , and nine rectal cancer cases , representing simple treatments .
All patients had previously received VMAT at the National Cancer Center .
Principal investigator Jianrong Dai and first author Jiayun Chen configured seven treatment plans for each patient , representing seven linacs configured with maximum MLC leaf speeds ( MMLS ) @ @ @ @ @ @ @ 3.5 , 5.0 , 7.5 and 10.0 cm/s .
Automated VMAT plans with identical initial optimization parameters were designed based on the centre ’ s clinical protocols , thereby eliminating interoperator variability .
The VMAT plans were calculated using 6 MV photons , with a maximum variable dose rate of 600 MU/min .
Gantry angle spacing , arc and collimator rotation direction and degrees , and maximum rotation time of each arc were identical for all plans .
The researchers evaluated the plans and scored them using the Plan Quality Algorithm ( PQA @ @ @ @ @ @ @ ( PQM ) of the ESTRO QUASIMODO project .
The PQA provided an objective method by which to quantify plan quality , while the PQM provided a fair comparison of plan results .
Plan scores for rectal cancer increased dramatically when the MMLS increased from 1 to 3.5 cm/s , but only grew slowly beyond that speed .
The researchers believe that high leaf speeds helped smooth out variations in dose distributions , either through small fields or by the leaves blocking high-dose regions for organs-at-risk .
Findings were similar , but not @ @ @ @ @ @ @ “ Plan quality is greatly improved as MMLS increases from 1 to 3.5 cm/s ; above that , the quality change is marginal , ” write the authors .
“ It demonstrated that the MMLS influences plan quality regardless of the tumour size.
” It should be noted that actual MLC performance depends on a number of other considerations , such as leakage and reliability , for example , and further research is needed to evaluate how speed affects clinically deployed models .
The authors tell Physics World that the team has now @ @ @ @ @ @ @ of two major MLC characteristics : MLC leaf speed , as examined in this study ; and MLC transmission , for patients with advanced lung cancer , published in Medical Dosimetry .
The team ’ s future research will incorporate the interactions of dose rate , gantry speed and MLC speed , to obtain a more comprehensive representation of their dosimetric effects .

Treatment plan dose distributions for a locally advanced nasopharyngeal carcinoma case with three targets, using MLCs with maximum leaf speeds of 1.0 cm/s (a, b) and 3.5 cm/s (c, d). The 3.5 cm/s MLC achieved better plan quality. (Courtesy: CC BY 4.0/J. Appl. Clin. Med. Phys. 10.1002/acm2.13020)
Increasing the multileaf collimator (MLC) leaf speed may help improve the quality of volumetric modulated arc therapy (VMAT) plans, according to a study published in the Journal of Applied Clinical Medical Physics. Researchers in Beijing investigated seven MLCs with different maximum leaf speeds to investigate their influence on plan quality. They determined that VMAT plans for locally advanced nasopharyngeal carcinoma (NPC) and rectal cancer improved significantly when maximum MLC leaf speeds were increased from 1 to 3.5 cm/s.
VMAT delivers highly conformal radiation dose to a targeted tumour, sparing surrounding healthy tissue. MLCs, which consist of several sets of metallic leaves, are used to shape the radiation beam as it exits the linear accelerator (linac). In addition to improving the dose distribution, MLCs are highly efficient and reduce treatment time. However, dose leakage and transmission through MLC leaves can occur, negatively impacting treatment plan quality.
To achieve highly modulated dose distribution, MLCs need to move at a high speed when the gantry rotates. But what is the optimum speed required to achieve the highest quality VMAT plan for specific types of cancer?
To answer this question, the research team – from the National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College – investigated six NPC cases, representing complex clinical treatments, and nine rectal cancer cases, representing simple treatments. All patients had previously received VMAT at the National Cancer Center.
Principal investigator Jianrong Dai and first author Jiayun Chen configured seven treatment plans for each patient, representing seven linacs configured with maximum MLC leaf speeds (MMLS) of 1.0, 1.5, 2.25, 3.5, 5.0, 7.5 and 10.0 cm/s. Automated VMAT plans with identical initial optimization parameters were designed based on the centre’s clinical protocols, thereby eliminating interoperator variability. The VMAT plans were calculated using 6 MV photons, with a maximum variable dose rate of 600 MU/min. Gantry angle spacing, arc and collimator rotation direction and degrees, and maximum rotation time of each arc were identical for all plans.
The researchers evaluated the plans and scored them using the Plan Quality Algorithm (PQA) tool and the Plan Quality Metric (PQM) of the ESTRO QUASIMODO project. The PQA provided an objective method by which to quantify plan quality, while the PQM provided a fair comparison of plan results.
Plan scores for rectal cancer increased dramatically when the MMLS increased from 1 to 3.5 cm/s, but only grew slowly beyond that speed. The researchers believe that high leaf speeds helped smooth out variations in dose distributions, either through small fields or by the leaves blocking high-dose regions for organs-at-risk. Findings were similar, but not as dramatic, for NPC cases.
“Plan quality is greatly improved as MMLS increases from 1 to 3.5 cm/s; above that, the quality change is marginal,” write the authors. “It demonstrated that the MMLS influences plan quality regardless of the tumour size.”
It should be noted that actual MLC performance depends on a number of other considerations, such as leakage and reliability, for example, and further research is needed to evaluate how speed affects clinically deployed models.
The authors tell Physics World that the team has now studied the effect on treatment plan quality of two major MLC characteristics: MLC leaf speed, as examined in this study; and MLC transmission, for patients with advanced lung cancer, published in Medical Dosimetry. The team’s future research will incorporate the interactions of dose rate, gantry speed and MLC speed, to obtain a more comprehensive representation of their dosimetric effects.