Tuesday, November 08, 2022

WWII

Allies’ successful first invasion but a ‘botched’ job: Operation Torch, 80 years on

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French soldier Louis Laplace described the shock for the Vichy forces as the Allies landed. “All of a sudden the sirens were going off; it was the first time I heard them in North Africa,” recounted the soldier in Vichy forces’ anti-aircraft division. “A few minutes later, we saw a plane flying low over the water, releasing a curtain of smoke. And then I realised that he was American.”

The British and Americans had decided on the operation a few months before. Winston Churchill’s advocacy of landings in North Africa triumphed over widespread scepticism in Washington. Franklin D. Roosevelt was receptive to Churchill’s strategic vision, overriding his military staff

Roosevelt wanted US troops involved in a big operation in the fight against Nazi Germany “to stifle popular clamour at home for action”, noted Richard Overy, a professor of history at Exeter University and the author of several books on the Second World War including ‘Why the Allies Won. The US president was “also aware of America’s growing dependence on Middle Eastern oil, and Torch would be a way of getting a foothold on an area close to the oil”, Overy continued.

Torch was part of the climax of the long-running North Africa campaign – the predominant theatre for the Western Allies at this point in the war. Britain won a series of resounding victories over fascist Italy in the desert, but were forced onto the back foot when Adolf Hitler deployed German troops under General Erwin Rommel to rescue the Italians.

Then Torch was executed just before the British completed their remarkable victory in the Battle of El Alamein in Egypt on November 11, when Field Marshal Bernard Montgomery’s forces defeated Rommel’s Afrika Corps – the turning point for the Western Allies against Nazi Germany.

The Allies relied on local resistance to carry out the landings, however small it was. In Algeria, they were able to rely on a group of around 400 Résistants which had formed upon the Fall of France in May 1940; French pied noirs in Algeria mainly backed Vichy at the time. The vast majority of the Resistance band were young Jews appalled at the Vichy regime’s anti-Semitic measures. Medical student José Aboulker, who became the leader of the network in Algiers, was among them.

‘Very tough fighting’

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With strong contributions from monarchist Resistance fighter Henri d’Astier de la Vigerie, they gave “tactical information to make the Anglo-American landings easier”, said French historian Tramor Quemeneur, author of the book 8 novembre 1942, Résistance et débarquement allié en Afrique du Nord  (“November 8, 1942: the Resistance and the Allied Landings in North Africa”).

Torch was a colossal logical undertaking, with some 107,000 Allied troops deployed (84,000 American and 23,000 British) as well as 110 transport ships. The high command selected nine landing sites on the North African coast; six in Morocco and three in Algeria.

In Algiers, that Resistance of some 400 people made it easy to put the Vichy forces out of action. They seized the strategic administrative and military centres in the Algerian city and arrested the main military leaders, including Admiral François Darlan – a hugely important figure, formerly the number two to Vichy’s leader Marshall Philippe Pétain, and at that point the commander-in-chief of the Vichy French army – and General Alphonse Juin, commander-in-chief of Vichy forces in North Africa.

But elsewhere things were much more difficult for the Allies. Despite the Resistance taking out the Vichy high command, nearly 500 American and British troops were killed.

“The fighting was very tough,” Quemeneur observed. Vichy officers benefitted from some intelligence regarding the landing plan in Oran. In Morocco and the city of Oran on the Algerian coast, Vichy forces were “ordered to fight – and they did”, the French historian put it. By fighting the Allies directly, Vichy removed any hint of ambiguity about its pro-Nazi position.

“Torch was a pretty botched operation, prepared in haste with [inexperienced] US troops and too little equipment,” Overy said. “Success depended on Montgomery’s progress in the […] desert, and assistance from British air force commanders in getting combined and effective use of air power. In the end, German and Italian forces were bled white by British naval and air power in the Mediterranean, which blockaded the Axis forces in Tunsia. Nevertheless, for the Americans it was a long learning curve, with no real experience to go on.”

Five days after Montgomery’s forces clinched their victory over Rommel over in Egypt, the Allies defeated their opponents in Morocco and Algeria on November 16.

The Germans responded to the landings by occupying the whole of France on November 11, not just the north and Atlantic coastline. The so-called Free Zone in the south, administered by Vichy, no longer existed. Then on November 22, the Allies cemented their success in Operation Torch by signing a political and military co-operation agreement with Darlan as he switched sides.

As well as humiliating Vichy, Operation Torch led to the Western Allies’ successful Italian campaign, starting with the landings on Sicily in 1943. “Torch paved the way for the defeat of Benito Mussolini’s regime as well as the withering of Axis strength in the Mediterranean,” Quemeneur observed.

But unlike the Soviet victory at Stalingrad and the British victory at El Alamein, Torch was not significant enough to be a “pivotal moment” in the fight against Nazi Germany, said French historian Jean-Marie Guillon.

Eventually, the Western Allies’ decisive blow to Nazi Germany came from the D-Day landings in 1944. “The only way victory could be achieved in the West was invasion from Britain and victory in the Battle of the Atlantic,” Overy put it. “Torch contributed very little to this except to show how deficient amphibious warfare doctrine was, and the need to introduce very great improvements.”

The post Allies’ successful first invasion but a ‘botched’ job: Operation Torch, 80 years on appeared first on France 24.

Veteran French designer Philippe Starck now looks to space


Philippe Starck, the prolific French architect and designer who has made everything from lemon juicers to wind turbines, shows no sign of slowing down and is increasingly turning his eye to space.



French designer Philippe Starck says space is part of 'necessary change'© JOEL SAGET

Visiting an exhibition at the Museum of Decorative Arts in Paris featuring some his early work, the 73-year-old seemed bemused by the volume of items on display.

"I don't have the software for periods and dates," he told AFP when asked about the period.

"To me, the 1980s were like being abandoned in an Amazon jungle with nothing to eat, wild animals everywhere, a rusty machete... I just did what I could. And when you do what you can, you don't remember what's going on elsewhere."

Starck made his name as an interior decorator for Paris nightclubs in the 1970s, before landing a dream commission to refurbish the Elysee Palace apartments for president Francois Mitterrand in 1983.

He went on to design luxurious hotels and restaurants around the world.

But he also gave the world an uber-electic range of everyday items, from his futuristic lemon juicer to electric bikes, toothbrushes, water bottles -- and on to boats, wind turbines and control towers.

- 'Pure creativity' -

There was always a hint of humour and surrealism, he said, but also a desire to "democratise design" by keeping things affordable.

"We managed to remove two zeros from prices," he said. "At the time, in today's prices, sitting on something designer cost 20,000 euros, which wasn't right. Today, it's 700 euros, which isn't bad."

These days, Starck cares less about household objects and has his eyes on bigger things.

There is a long-awaited "laboratory for pure creativity" being built in Qatar, and immediately after the exhibition, he was due at the launch of a new hydrogen energy project.

But his real focus appears to be skyward: working with US company Axiom Space on the living quarters it plans to connect to the International Space Station, and teaming up with NASA for a new astronaut training camp.

The focus on space is part of our "necessary change" as a species, he said.

"Except when we're dead, we've been fixed by gravity, but that's clearly over, so I'm tackling it head-on."

Some early memories remain -- being left with some old toys and his grandfather's workbench during the holidays as a young child: "I made my first items on that workbench and I haven't stopped since."

A surreal early inspiration comes to him: seeing Mick Jagger dancing around with a neon tube in some film.

"I found it extraordinary and chic -- I thought to myself that someone should make it for real so that everyone could be Jagger for a minute."

Poll documents the critical role of people over 50 as caregivers and helpers for older loved ones

Supporting everything from health care needs and personal care to home repairs and finances brings both challenges and rewards

Reports and Proceedings

MICHIGAN MEDICINE - UNIVERSITY OF MICHIGAN

More than half of people over 50 say they’ve helped at least one person over 65 take care of their health, personal hygiene, home or finances in the past two years, a new University of Michigan poll finds.

And more than 70% of this group provided such help to someone they don’t live with -- whether it’s a parent, another relative or a neighbor.

This kind of caregiving and other help -- almost all of it unpaid -- doesn’t just affect the older adult receiving it, according to new data from the National Poll on Healthy Aging. It also impacts the people over 50 who are doing the helping.

Nearly all say they get something positive out of the experience. But many say it’s more difficult than they expected -- especially for those helping an older adult who has many needs, or someone with mild cognitive impairment, Alzheimer’s disease or another type of dementia, the poll finds.

The poll is based at the U-M Institute for Healthcare Policy and Innovation and supported by AARP and Michigan Medicine, U-M’s academic medical center.

The new results are being presented this week by poll deputy director Erica Solway, Ph.D., at the Gerontological Society of America meeting. November is also National Family Caregivers Month.

“The challenges of helping someone you know as they grow older should not be underestimated, but neither should the potential rewards,” says Courtney Polenick, Ph.D., an assistant professor of psychiatry and caregiving researcher at Michigan Medicine who worked with the poll team. “These data show the importance of supporting those who help our nation’s oldest adults. Not only have 54% of people over 50 done this in the past two years during the pandemic, but about two-thirds of that group are actively doing it right now.”

The poll asked people between the age of 50 and 80 whether they had helped at least one person over age 65 with a variety of tasks in the past two years, ranging from food shopping and house cleaning to bathing, dressing, going to medical appointments, managing medications, helping with health insurance and financial duties, and home repairs and modifications.

“I see this routinely in my primary care practice, and I know the value that spouses, grown children and close friends can bring to the health and well-being of older adults,” says poll director Jeffrey Kullgren, M.D., M.P.H., M.S., an associate professor of internal medicine at Michigan Medicine and researcher at the VA Ann Arbor Healthcare System. “But there is almost no formal mechanism for our society to recognize or compensate them for what they do.”

Assistance with health needs

Often, the kind of support given by family and friends goes on for years, and a person may find themselves helping multiple older adults, the poll shows. About a third of people over 50 who have provided this kind of help say they’ve been doing it for five years or more. And 41% have helped more than one older person.

The type of help covers a wide range of duties. One-third of people over 50 had helped a person over 65 with health care tasks, including going to doctor’s appointments with them or communicating with the person’s providers on their behalf. About 15% of people over 50 have helped someone over 65 manage their medications, and the same percentage had helped someone over 65 navigate their health insurance coverage.

Such help, other research has shown, can raise the chance that an older adult will manage chronic conditions effectively or get preventive care.

That’s why many clinics, hospitals and health systems allow adult patients to designate another adult to access the online patient portal system on their behalf, so they can schedule appointments and see information such as medications and test results. But the poll shows that among those who are currently helping a person over 65 with health care tasks, only 12% communicated with the person’s health care provider through a patient portal.

Increasing this kind of “proxy” patient portal access by spouses, adult children and other trusted helpers could enhance care, Kullgren and Polenick note.

Help beyond health

Help goes beyond health care, the poll shows. Nearly a third of people over 50 had helped a person over 65 with home maintenance, a similar percentage (31%) helped with food shopping or cooking, and a slightly lower percentage (22%) had helped a person over 65 manage their finances.

On the more personal side of life, 16% of people over 50 had helped a person over 65 dress, bathe or take care of other personal tasks – even if they don’t have the same kind of training that home health aides receive for these sometimes complex tasks.

“Caregiving for an older adult is a complex experience that affects 48 million caregivers in the U.S. from an emotional, health and financial perspective,” says Indira Venkat, senior vice president, AARP Research. “If you are not currently a caregiver, at some point in your life you either will be a caregiver or need a caregiver. It’s important that we consider the unique needs of caregivers and ensure they have the support to care for themselves as well as their loved ones.”

Positives and negatives

Nearly all (96%) helpers and caregivers over age 50 say there’s a positive aspect to offering this kind of help, including feeling appreciated (52%), having a sense of purpose (45%) and growing closer to family or friends (35%). A majority said it made them more aware of their own future health and personal care needs, and about a third said it made them focus more on their own health or motivated them to prepare a will, trust or advanced care directive.

But two-thirds (65%) also reported challenges. For instance, many said that helping brought on physical or emotional fatigue (34%), challenged their work-life balance (31%) or wasn’t supported by family or friends (19%). Nearly a quarter (22%) said they lacked time for their own self-care.

Nearly half (47%) of those who helped someone with five or more types of tasks said they felt it was somewhat or much more difficult than they had expected. That’s compared with only 12% of those who helped with just one or two types of tasks.

Memory and cognitive issues in the people being helped also increase the challenge. In all, 45% of those helping a person with mild cognitive impairment, and 58% of those helping someone with Alzheimer’s or other type of dementia, say it’s more difficult than they expected. That’s compared with 15% of those who help someone without either of these conditions.

AARP has tools, information, and support available for caregivers. The AARP Family Caregiving website, at www.aarp.org/caregiving, provides an easy way to join an online community of other caregivers, learn about local services, get helpful information and connect with others who understand caregiving challenges.

The poll report is based on findings from a nationally representative survey conducted by NORC at the University of Chicago for IHPI, and administered online and via phone in July 2022 among 2,163 adults aged 50 to 80. The sample was subsequently weighted to reflect the U.S. population. Read past National Poll on Healthy Aging reports and about the poll methodology

NYU Tandon researchers explore a more frictionless future

Elisa Riedo’s and her lab team’s discovery of a fundamental law of friction leads to new materials that can minimize energy loss

Reports and Proceedings

NYU TANDON SCHOOL OF ENGINEERING

NYU Tandon researchers explore a more frictionless future 

IMAGE: MEASURING ATOMIC SHEAR: IN THIS RENDERING, A NANO-SCALE TIP PULLS ATOMS SO THEY SLIDE ON TOP OF OTHERS. view more 

CREDIT: MARTIN REJHON

BROOKLYN, New York, Thursday, November 3, 2022 -- Professor of Chemical and Biomolecular Engineering Elisa Riedo and her team have discovered a fundamental friction law that is leading to a deeper understanding of energy dissipation in friction and the design of two-dimensional materials capable of minimizing energy loss.

Friction is an everyday phenomenon; it allows drivers to stop their cars by breaking and dancers to execute complicated moves on various floor surfaces. It can, however, also be an unwanted effect that drives the waste of large amounts of energy in industrial processes, the transportation sector, and elsewhere. Tribologists–those who study the science of interacting surfaces in relative motion–have estimated that one-quarter of global energy losses are due to friction and wear. 

While friction is extremely widespread and relevant in technology, the fundamental laws of friction are still obscure, and only recently have scientists been able to use advances in nanotechnology to understand, for example, the microscopic origin of da Vinci’s law, which holds that frictional forces are proportional to the applied load.

Now, Riedo and her NYU Tandon postdoctoral researcher Martin Rejhon have found a new method to measure the interfacial shear between two atomic layers and discovered that this quantity is inversely related to friction, following a new law.

This work–conducted in collaboration with NYU Tandon graduate student Francesco Lavini, and colleagues from the International School for Advanced Studies, the International Center for Theoretical Physics in Trieste Italy, as well as Prague’s Charles University–could lead to more efficient manufacturing processes, greener vehicles, and a generally more sustainable world. 

“The interaction between a single atomic layer of a material and its substrate governs its electronic, mechanical, and chemical properties,” Riedo explains, “so gaining insight into that topic is important, on both fundamental and technological levels, in finding ways to reduce the energy loss caused by friction.” 

The researchers studied bulk graphite and epitaxial graphene films grown with different stacking orders and twisting, measuring the hard-to-access interfacial transverse shear modulus of an atomic layer on a substrate. They discovered that the modulus (a measure of the material’s ability to resist shear deformations and remain rigid) is largely controlled by the stacking order and the atomic layer-substrate interaction and demonstrated its importance in controlling and predicting sliding friction in supported two-dimensional materials. Their experiments showed a general reciprocal relationship between friction force per unit contact area and interfacial shear modulus for all the graphite structures they investigated. 

Their 2022 paper, "Relation between interfacial shear and friction force in 2D materials" was published online in Nature Nanotechnology and was funded by the U.S. Department of Energy Office of Science and the U.S. Army Research Office.

“Our results can be generalized to other 2D materials as well,” Riedo, who heads NYU Tandon’s PicoForce Lab, asserts. “This presents a way to control atomic sliding friction and other interfacial phenomena, and has potential applications in miniaturized moving devices, the transportation  industry, and other realms.”

“Elisa’s work is a great example of NYU Tandon’s commitment to a more sustainable future,” Dean Jelena Kovačević says, “and a testament to the research being done at our newly launched Sustainable Engineering Initiative, which focuses on tackling climate change and environmental contamination through a four-pronged approach we’re calling AMRAd, for Avoidance, Mitigation, Remediation and Adaptation.”

 

About the New York University Tandon School of Engineering

The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute. A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences as part of a global university, with close connections to engineering programs at NYU Abu Dhabi and NYU Shanghai. NYU Tandon is rooted in a vibrant tradition of entrepreneurship, intellectual curiosity, and innovative solutions to humanity’s most pressing global challenges. Research at Tandon focuses on vital intersections between communications/IT, cybersecurity, and data science/AI/robotics systems and tools and critical areas of society that they influence, including emerging media, health, sustainability, and urban living. We believe diversity is integral to excellence, and are creating a vibrant, inclusive, and equitable environment for all of our students, faculty and staff. For more information, visit engineering.nyu.edu.

Substance use disorders linked to poor health outcomes in wide range of physical health conditions

Peer-Reviewed Publication

UNIVERSITY OF CAMBRIDGE

People who have a past history of hospitalisation because of substance use disorders have much worse outcomes following the onset of a wide range of physical health conditions, according to researchers in the UK and Czechia.

In a study published today in The Lancet Psychiatry, researchers looked at the risk of mortality and loss of life-years among people who developed 28 different physical health conditions, comparing those who had previously been hospitalised with substance use disorder against those who had not.

They found that patients with most of the health conditions were more likely than their counterparts to die during the study period if they had been hospitalised with substance use disorder prior to the development of these conditions. For most subsequent health conditions, people with substance use disorders also had shorter life-expectancies than did individuals without substance use disorders.

One in twenty people worldwide aged 15 years or older lives with alcohol use disorder, while around one in 100 people have psychoactive drug use disorders. Although substance use disorders have considerable direct effects on health, they are also linked to a number of physical and mental health conditions. Consequently, the presence of these contributes to higher risk of mortality and shorter lifespan in people with substance use disorders.

To explore this link further, researchers analysed patient records from Czech nationwide registers of all-cause hospitalisations and deaths during the period from 1994-2017. They used a novel design, estimating the risk of death and life-years lost after the onset of multiple specific physical health conditions in individuals with a history of hospitalisation for substance use disorders, when compared with matched counterparts without substance use disorder but with the same physical health condition.

Although the study only looked at people living in Czechia, the researchers believe the results are likely to be similar in other countries, too.

They found that people with pre-existing substance use disorders were more likely than their counterparts to have died during the study following the development of 26 out of 28 physical health conditions. For seven of these conditions – including atrial fibrillation, hypertension, and ischaemic heart disease – the risk was more than doubled. In most cases, people with substance use disorders have shorter life-expectancies than their counterparts.

Lead author Tomáš Formánek, a PhD student at the National Institute of Mental Health, Czechia, and the University of Cambridge, said: “Substance use disorders seem to have a profound negative impact on prognosis following the development of various subsequent physical health conditions, in some cases dramatically affecting the life expectancy of the affected people.”

It is not clear why this should be the case, though the researchers say there are a number of possible reasons. It is already known that substance use has a direct negative impact on physical health and is associated with lifestyle factors that affect our health, such as smoking, lack of exercise, and poor diet. Similarly, people with substance use disorders are less likely to take part in screening and prevention programmes for diseases such as cancer and diabetes and are less likely to use preventive medication, such as drugs to prevent hypertension. There are also some factors not directly related to substance use, such as diagnostic overshadowing, meaning the misattribution of physical symptoms to mental disorders. Such misattribution can subsequently contribute to under-diagnosis, late diagnosis, and delayed treatment in affected individuals.

Senior author Professor Peter Jones from the Department of Psychiatry, University of Cambridge, added: “These results show how important it is not to compartmentalise health conditions into mind, brain or body. All interact leading here to the dramatic increases in mortality from subsequent physical illnesses in people with substance use disorders. There are clear implications for preventive action by clinicians, health services and policy developers that all need to recognise these intersections.”

Co-author Dr Petr Winkler from the National Institute of Mental Health, Czechia, said: “It is also important to consider that the majority of people with substance use disorders go undetected. They often do not seek a professional help and hospitalisations for these conditions usually come only at very advanced stages of illness. Alongside actions focused on physical health of people with substance use disorders, we need to equally focus on early detection and early intervention in substance use disorders.”

The research was funded by the National Institute for Health and Care Research (NIHR) Applied Research Collaboration East of England at Cambridge and Peterborough NHS Foundation Trust.

Reference

Formánek, T et al.  Mortality and life-years lost following subsequent physical comorbidity in people with pre-existing substance use disorders: a national registry-based retrospective cohort study of hospitalised individuals in Czechia. The Lancet Psychiatry; 3 Nov 2022; DOI: 10.1016/S2215-0366(22)00335-2

 

First glimpse of what gravity looks like on cosmological scales

A team of international scientists have reconstructed gravity to find a more robust way of understanding the cosmos

Peer-Reviewed Publication

UNIVERSITY OF PORTSMOUTH

Scientists from around the world have reconstructed the laws of gravity, to help get a more precise picture of the Universe and its constitution.

The standard model of cosmology is based on General Relativity, which describes gravity as the curving or warping of space and time. While the Einstein equations have been proven to work very well in our solar system, they had not been observationally confirmed to work over the entire Universe. 

An international team of cosmologists, including scientists from the University of Portsmouth in England, has now been able to test Einstein's theory of gravity in the outer-reaches of space. 

They did this by examining new observational data from space and ground-based telescopes that measure the expansion of the Universe, as well as the shapes and the distribution of distant galaxies. 

The study, published in Nature Astronomy, explored whether modifying General Relativity could help resolve some of the open problems faced by the standard model of cosmology.  

Professor Kazuya Koyama, from the Institute of Cosmology and Gravitation at the University of Portsmouth, said: “We know the expansion of the universe is accelerating, but for Einstein’s theory to work we need this mysterious cosmological constant.

“Different measurements of the rate of cosmic expansion give us different answers, also known as the Hubble tension. To try and combat this, we altered the relationship between matter and spacetime, and studied how well we can constrain deviations from the prediction of General Relativity. The results were promising, but we’re still a long way off a solution.”

Possible modifications to the General Relativity equation are encased in three phenomenological functions describing the expansion of the Universe, the effects of gravity on light, and the effects on matter. Using a statistical method known as the Bayesian inference, the team reconstructed the three functions simultaneously for the first time.

“Partial reconstructions of these functions have been done in the last 5 to 10 years, but we didn't have enough data to accurately reconstruct all three at the same time”, added Professor Koyama.

“What we found was that current observations are getting good enough to get a limit on deviations from General Relativity. But at the same time, we find it's very difficult to solve this problem we have in the standard model even by extending our theory of gravity.

“One exciting prospect is that in a few years’ time we’ll have a lot more data from new probes. This means that we will be able to continue improving the limits on modifications to General Relativity using these statistical methods.”

Up and coming missions will deliver a highly accurate 3D map of the clustered matter in the Universe, which cosmologists call large scale structure. These will offer an unprecedented insight into gravity at large distances. 

Professor Levon Pogosian, from Simon Fraser University in Canada, said: “As the era of precision cosmology is unfolding, we are on the brink of learning about gravity on cosmological scales with high precision. Current data already draws an interesting picture, which, if confirmed with higher constraining power, could pave the way to resolving some of the open challenges in cosmology.”

Surface melting of glass

Konstanz physicists make a surprising discovery when they detect surface melting in glasses

Peer-Reviewed Publication

UNIVERSITY OF KONSTANZ

In 1842, the famous British researcher Michael Faraday made an amazing observation by chance: A thin layer of water forms on the surface of ice, even though it is well below zero degrees. So the temperature is below the melting point of ice, yet the surface of the ice has melted. This liquid layer on ice crystals is also why snowballs stick together.

It was not until about 140 years later, in 1985, that this "surface melting" could be scientifically confirmed under controlled laboratory conditions. By now, surface melting has been demonstrated in a variety of crystalline materials and is scientifically well understood: Several degrees below the actual melting point, a liquid layer only a few nanometres thick forms on the surface of the otherwise solid material. Because the surface properties of materials play a crucial role in their use as, e.g. catalysts, sensors, battery electrodes and more, surface melting is not only of fundamental importance but also in view of technical applications.

It must be emphasized that this process has absolutely nothing to do with the effect of, say, taking an ice cube out of the freezer and exposing it to ambient temperature. The reason why an ice cube melts on its surface first under such conditions is that the surface is significantly warmer than the ice cube's interior.

Surface melting detected in glass
In crystals with periodically arranged atoms, the thin liquid layer on the surface is typically detected by scattering experiments, which are very sensitive to the presence of atomic order. Since liquids are not arranged in a regular pattern, such techniques can therefore clearly resolve the appearance of a thin liquid film on top of the solid. This approach, however, does not work for glasses (i.e. disordered, amorphous materials) because there is no difference in the atomic order between the solid and the liquid. Therefore, surface melting of glasses has remained rather unexplored with experiments.

To overcome the above-mentioned difficulties, Clemens Bechinger, physics professor at the University of Konstanz, and his colleague Li Tian used a trick: instead of studying an atomic glass, they produced a disordered material made of microscopic glass spheres known as colloids. In contrast to atoms, these particles are about 10,000 times larger and can be observed directly under a microscope.

The researchers were able to demonstrate the process of surface melting in such a colloidal glass because the particles near the surface move much faster compared to the solid below. At first glance, such behaviour is not entirely unexpected, since the particle density at the surface is lower than in the underlying bulk material. Therefore, particles close to the surface have more space to move past each other, which makes them faster. 

A surprising discovery
What surprised Clemens Bechinger and Li Tian, however, was the fact that even far below the surface, where the particle density has reached the bulk value, the particle mobility is still significantly higher compared to the bulk material. The microscope images show that this previously unknown layer is up to 30 particle diameters thick and continues from the surface into the deeper regions of the solid in a streak-like pattern. "This layer which reaches far into the material has interesting material properties since it combines liquid and solid features", Bechinger explains.

As a consequence, the propertie of thin, disordered films depend very much on their thickness. In fact, this property is already being exploited in their use as thin ionic conductors in batteries, which are found to have a significantly higher ionic conductivity compared to thick films. With the new insights gained from the experiments, however, this behaviour can now be understood quantitatively and thus be optimized for technical applications.

 

Key facts:

  • Original publication: Tian, L., Bechinger, C. Surface melting of a colloidal glass. Nat Commun 13, 6605 (2022).
    DOI: 10.1038/s41467-022-34317-2
    Link: https://www.nature.com/articles/s41467-022-34317-2
  • Professor Clemens Bechinger is a professor of colloidal systems at the University of Konstanz. His research interests include phase transitions in colloidal systems and non-equilibrium states at the particle level. Clemens Bechinger is a principal investigator at the Cluster of Excellence "Centre for the Advanced Study of Collective Behaviour".
  • Li Tian is a doctoral researcher in the research team of Clemens Bechinger. She conducts research on the assembly of anisotropic micron-sized colloidal particles with critical Casimir forces.

Note to editors:
You can download an image here: https://www.uni-konstanz.de/fileadmin/pi/fileserver/2022/Oberflaechenschmelzen_von_Glaesern.jpg

Caption: Microscope image of surface melting of glass in a colloidal system. Highly mobile particles (red) mark the melting process at the surface. Remarkable is the fact that these highly dynamic regions extend far into the material and thus influence its properties.
Image: research team Bechinger, University of Konstanz

 

Contact:

University of Konstanz

Communications and Marketing

Email: kum@uni-konstanz.de

 

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