Menstruation doesn't change how your brain works -- period

Normonal changes during the menstrual cycle have no impact on aspects of cognition, study shows

Source: Frontiers

Summary:

It has long been assumed that your period affects your brain's performance. A new study set out to determine whether changes in hormones during the menstrual cycle really do change how well brains work. By increasing the sample size and following participants over more than one menstrual cycle, they found evidence that your brain's performance isn't affected by your cycle.

FULL STORY

---

Levels of estrogen, progesterone and testosterone in one's system have no impact on the working memory, cognitive bias or ability to pay attention to two things at once.

Credit: © Creative-Touch / Fotolia

                A new study published in Frontiers in Behavioral Neuroscience is setting out to change the way we think about the menstrual cycle. While it's often been assumed that anyone who's menstruating isn't working at top mental pitch, Professor Brigitte Leeners and her team of researchers have found evidence to suggest that that's not the case. They examined three aspects of cognition across two menstrual cycles, and found that the levels of estrogen, progesterone and testosterone in your system have no impact on your working memory, cognitive bias or ability to pay attention to two things at once. While some hormones were associated with changes across one cycle in some of the women taking part, these effects didn't repeat in the following cycle. Overall, none of the hormones the team studied had any replicable, consistent effect on study participants' cognition.

            Professor Leeners, team lead, said: "As a specialist in reproductive medicine and a psychotherapist, I deal with many women who have the impression that the menstrual cycle influences their well-being and cognitive performance." Wondering if this anecdotal evidence could be scientifically proven -- and questioning the methodology of many existing studies on the subject -- the team set out to shed some light on this controversial topic.
The study published today uses a much larger sample than usual, and (unlike most similar studies) follows women across two consecutive menstrual cycles. The team, working from the Medical School Hannover and University Hospital Zürich, recruited 68 women to undergo detailed monitoring to investigate changes in three selected cognitive processes at different stages in the menstrual cycle. While analysis of the results from the first cycle suggested that cognitive bias and attention were affected, these results weren't replicated in the second cycle. The team looked for differences in performance between individuals and changes in individuals' performance over time, and found none.
                Professor Leeners said, "The hormonal changes related to the menstrual cycle do not show any association with cognitive performance. Although there might be individual exceptions, women's cognitive performance is in general not disturbed by hormonal changes occurring with the menstrual cycle."
Professor Leeners cautions, however, that there's more work to do. While this study represents a meaningful step forward, larger samples, bigger subsamples of women with hormone disorders, and further cognitive tests would provide a fuller picture of the way that the menstrual cycle affects the brain. In the meantime, Professor Leeners hopes her team's work will start the long process of changing minds about menstruation.

---

Strange silk: Find out Why rappelling spiders don't spin out of control

Dragline silk from golden orb weaver spiders dissipates energy to prevent spinning

Source: American Institute of Physics

Summary:

Researchers show that unlike human hair, metal wires or synthetic fibers, spider silk partially yields when twisted. This property quickly dissipates the energy that would otherwise send an excited spider spinning on the end of its silk. A greater understanding of how spider silk resists spinning could lead to biomimetic fibers that mimic these properties for potential uses in violin strings, helicopter rescue ladders and parachute cords.

FULL STORY

---

The golden silk orb weaver (Nephila pilipes) creates dragline silk that prevents it from spinning while hanging from its web.

Credit: Kai Peng of Huazhong University of Science and Technology

               The last time you watched a spider drop from the ceiling on a line of silk, it likely descended gracefully on its dragline instead of spiraling uncontrollably, because spider silk has an unusual ability to resist twisting forces.

In a new paper appearing this week in Applied Physics Letters, from AIP Publishing, researchers from China and the U.K. showed that unlike human hair, metal wires or synthetic fibers, spider silk partially yields when twisted. This property quickly dissipates the energy that would otherwise send an excited spider spinning on the end of its silk.
"Spider silk is very different from other, more conventional materials," said Dabiao Liu of Huazhong University of Science and Technology. "We find that the dragline from the web hardly twists, so we want to know why."
              A greater understanding of how spider silk resists spinning could lead to biomimetic fibers that mimic these properties for multiple potential uses such as in violin strings, helicopter rescue ladders and parachute cords. "If we understood how spider silk achieves this, then maybe we could incorporate the properties into our own synthetic ropes," said David Dunstan of Queen Mary University of London.
Spiders use dragline silk for the outer rim and spokes of their webs, and as a lifeline when dropping to the ground. The material has intrigued scientists because of its incredible strength, stretchiness and ability to conduct heat, but little research has focused on its torsional properties -- how it responds to twisting.
Researchers used a torsion pendulum, the same tool used by Henry Cavendish to weigh the Earth in the 1790s, to investigate dragline silk from two species of golden silk orb weavers. They collected strands of silk from captive spiders and suspended the strands inside a cylinder using two washers at the end to mimic a spider. The cylinder isolated the silk from environmental disturbances and kept the strand at a constant humidity, because water can cause the fibers to contract. A rotating turntable twisted the silk while a high-speed camera recorded the silk's back and forth oscillations over hundreds of cycles.
Unlike synthetic fibers and metals, spider silk deforms slightly when twisted, which releases more than 75 percent of its potential energy, and the oscillations rapidly slow. After twisting, the silk partially snaps back.
              The team suspects that this unusual behavior is linked to the silk's complex physical structure, consisting of a core of multiple fibrils inside a skin. Each fibril has segments of amino acids in organized sheets and others in unstructured looping chains. They propose that torsion causes the sheets to stretch like elastic, and warp the hydrogen bonds linking the chains, which deform like plastic. The sheets can recover their original shape, but the chains remain partially deformed. The pendulum exhibits this change with reduced magnitude of the silk's oscillations, as well as a shifting of the equilibrium point of the oscillation.
The group will continue to investigate how spider silk reacts to twisting in this way and is also looking into how it maintains its stiffness during torsion, what effect humidity has and to what degree air helps dissipate the energy. "There is a lot of further work needed," Dunstan said. "This spider silk is displaying a property that we simply don't know how to recreate ourselves, and that is fascinating."

---

Your hands may reveal the struggle to maintain self-control

Study shows decision-making in real time

Source: Ohio State University

Summary:

It takes just a few seconds to choose a cookie over an apple and wreck your diet for the day. But what is happening during those few seconds while you make the decision? In a new study, researchers watched in real time as people's hands revealed the struggle they were under to choose the long-term goal over short-term temptation. The work represents a new approach to studying self-control.

FULL STORY

---

         It takes just a few seconds to choose a cookie over an apple and wreck your diet for the day.

Credit: Jeff Grabmeier

        It takes just a few seconds to choose a cookie over an apple and wreck your diet for the day.

But what is happening during those few seconds while you make the decision?
In a new study, researchers watched in real time as people's hands revealed the struggle they were under to choose the long-term goal over short-term temptation. The work represents a new approach to studying self-control.
            In one key experiment, participants viewed pictures of a healthy and an unhealthy food choice on opposite sides of the top of a computer screen and moved a cursor from the center bottom to select one of the foods.
People who moved the cursor closer to the unhealthy treat (even when they ultimately made the healthy choice) later showed less self-control than did those who made a more direct path to the healthy snack.
"Our hand movements reveal the process of exercising self-control," said Paul Stillman, co-author of the study and postdoctoral researcher in psychology at The Ohio State University.
"You can see the struggle as it happens. For those with low self-control, the temptation is actually drawing their hand closer to the less-healthy choice."
The results may shed light on a scholarly debate about what's happening in the brain when humans harness willpower.
            Stillman conducted the study with Melissa Ferguson, professor of psychology, and Danila Medvedev, a former undergraduate student, both from Cornell University. Their research will appear in the journal Psychological Science.
The study involved several experiments. In one, 81 college students made 100 decisions involving healthy versus unhealthy food choices.
In each trial, they clicked a "Start" button at the bottom of the screen. As soon as they did, two images appeared in the upper-left and upper-right corners of the screen, one a healthy food (such as Brussels sprouts) and the other an unhealthy one (such as a brownie).
They were told to choose as quickly as possible which of the two foods would most help them meet their health and fitness goals. So there was a "correct" answer, even if they were tempted by a less healthy treat.
Before the experiment began, the participants were told that after they finished they would be given one of the foods they chose in the experiment. At the end, however, they could freely choose whether they wanted an apple or a candy bar.
         The results showed that those who chose the candy bar at the end of the experiment those with lower self-control  had tended to veer closer to the unhealthy foods on the screen.
"The more they were pulled toward the temptation on the computer screen, the more they actually chose the temptations and failed at self-control," Stillman said.
But for those with higher levels of self-control, the path to the healthy food was more direct, indicating that they experienced less conflict.
In two other studies, similar results occurred in a completely different scenario, in which college students could decide whether they would rather accept $25 today or $45 in 180 days. Those with lower levels of self-control had mouse trajectories that were clearly different from those with higher self-control, suggesting differences in how they were dealing with the decisions.
            "This mouse-tracking metric could be a powerful new tool to investigate real-time conflict when people have to make decisions related to self-control," he said.
The findings also offer new evidence in a debate about how decision-making in self-control situations unfolds, Stillman said.
When the researchers mapped the trajectories people took with the cursor in the first experiment, they observed that most participants did not automatically start directly toward the unhealthy treat before abruptly switching course back to the healthy food. Rather, the trajectories appear curved, as if both the temptation and goal were competing from the beginning.
                                                                                                                                                                         Why is that important?
         Some researchers have argued that there are two systems in our brain that are involved in a self-control decision: one that's impulsive and a second that overcomes the impulses to exert willpower. But if that were the case, the trajectories seen in this study should look different than they do, Stillman said.
If dual systems underlie these choices, there should be a relatively straight line toward the unhealthy food while people are under the influence of the impulsive first system and then an abrupt change in direction toward the healthy food as the system in charge of self-control kicks in.
"That's not what we found," Stillman said. "Our results suggest a more dynamical process in which the healthy and unhealthy choices are competing from the very beginning in our brains and there isn't an abrupt change in thinking. That's why we get these curved trajectories."
Stillman said these results should help lead to a more accurate view of how our cognitive processes unfold to allow us to resist temptation.

---

First battery-free cellphone makes calls by harvesting ambient power

Source: University of Washington

Summary:

Engineers have designed the first battery-free cellphone that can send and receive calls using only a few microwatts of power, which it harvests from ambient radio signals or light. It's a major step forward in moving beyond chargers, cords and dying phones.

FULL STORY

---

          UW engineers have designed the first battery-free cellphone that can send and receive calls using only a few microwatts of power.

Credit: Mark Stone/University of Washington

University of Washington researchers have invented a cellphone that requires no batteries -- a major leap forward in moving beyond chargers, cords and dying phones. Instead, the phone harvests the few microwatts of power it requires from either ambient radio signals or light.

           The team also made Skype calls using its battery-free phone, demonstrating that the prototype made of commercial, off-the-shelf components can receive and transmit speech and communicate with a base station.
The new technology is detailed in a paper published July 1 in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.
"We've built what we believe is the first functioning cellphone that consumes almost zero power," said co-author Shyam Gollakota, an associate professor in the Paul G. Allen School of Computer Science & Engineering at the UW. "To achieve the really, really low power consumption that you need to run a phone by harvesting energy from the environment, we had to fundamentally rethink how these devices are designed."
          The team of UW computer scientists and electrical engineers eliminated a power-hungry step in most modern cellular transmissions converting analog signals that convey sound into digital data that a phone can understand. This process consumes so much energy that it's been impossible to design a phone that can rely on ambient power sources.
Instead, the battery-free cellphone takes advantage of tiny vibrations in a phone's microphone or speaker that occur when a person is talking into a phone or listening to a call.
           An antenna connected to those components converts that motion into changes in standard analog radio signal emitted by a cellular base station. This process essentially encodes speech patterns in reflected radio signals in a way that uses almost no power.
To transmit speech, the phone uses vibrations from the device's microphone to encode speech patterns in the reflected signals. To receive speech, it converts encoded radio signals into sound vibrations that that are picked up by the phone's speaker. In the prototype device, the user presses a button to switch between these two "transmitting" and "listening" modes.
Using off-the-shelf components on a printed circuit board, the team demonstrated that the prototype can perform basic phone functions transmitting speech and data and receiving user input via buttons. Using Skype, researchers were able to receive incoming calls, dial out and place callers on hold with the battery-free phone.
            "The cellphone is the device we depend on most today. So if there were one device you'd want to be able to use without batteries, it is the cellphone," said faculty lead Joshua Smith, professor in both the Allen School and UW's Department of Electrical Engineering. "The proof of concept we've developed is exciting today, and we think it could impact everyday devices in the future."
The team designed a custom base station to transmit and receive the radio signals. But that technology conceivably could be integrated into standard cellular network infrastructure or Wi-Fi routers now commonly used to make calls.
"You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it," said co-author Vamsi Talla, a former UW electrical engineering doctoral student and Allen School research associate. "And if every house has a Wi-Fi router in it, you could get battery-free cellphone coverage everywhere."
            The battery-free phone does still require a small amount of energy to perform some operations. The prototype has a power budget of 3.5 microwatts.
The UW researchers demonstrated how to harvest this small amount of energy from two different sources. The battery-free phone prototype can operate on power gathered from ambient radio signals transmitted by a base station up to 31 feet away.
Using power harvested from ambient light with a tiny solar cell -- roughly the size of a grain of rice the device was able to communicate with a base station that was 50 feet away.
Many other battery-free technologies that rely on ambient energy sources, such as temperature sensors or an accelerometer, conserve power with intermittent operations. They take a reading and then "sleep" for a minute or two while they harvest enough energy to perform the next task. By contrast, a phone call requires the device to operate continuously for as long as the conversation lasts.
            "You can't say hello and wait for a minute for the phone to go to sleep and harvest enough power to keep transmitting," said co-author Bryce Kellogg, a UW electrical engineering doctoral student. "That's been the biggest challenge -- the amount of power you can actually gather from ambient radio or light is on the order of 1 or 10 microwatts. So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech."
Next, the research team plans to focus on improving the battery-free phone's operating range and encrypting conversations to make them secure. The team is also working to stream video over a battery-free cellphone and add a visual display feature to the phone using low-power E-ink screens.

Giant molecular cages made for energy conversion and drug delivery

Source: Trinity College Dublin

Summary:

The porous, 'sponge'-type molecules have an enormous internal surface area. This allows their use as 'molecular flasks' or 'molecular containers' that change the reactivity and properties of encapsulated molecules.

FULL STORY

---

This is a diagram showing the molecular cage structure.

Credit: Professor Wolfgang Schmitt, Trinity College Dublin

             Scientists from Trinity College Dublin and AMBER, the Science Foundation Ireland-funded materials science research centre hosted in Trinity College Dublin, have created 'molecular cages' that can maximise the efficiency of converting molecules in chemical reactions, and that may in future also be used as sensors and drug-delivery agents. The cages can be packed with different molecules, many of which have a specific task or functionality. Incredibly, a teaspoon of powder containing these cages provides a greater internal surface area to boost reactivity and storage capacity than would be provided by an entire football field (4000 m2/g).

             This enormous intrinsic surface area relative to the weight of the structure in combination with the solubility offers great promise for energy conversion, while the structure blueprint (hollow, with sub-cages) allows different molecules to be discretely contained within. This latter feature is key in increasing the potential uses for these 'metal-organic-organic polyhedra' (MOP), because it means materials can be packed so as to react only when specific conditions present themselves.
One such example is in bio-sensing and drug-delivery, with a biological cue required to kick-start a chemical reaction. For example, a drug could be encapsulated in one of these MOP in the knowledge that it would only be released at the specific target site, where a specific biological molecule would trigger its release.
              The researchers behind the breakthrough, which has just been published in leading international journal Nature Communications, also hope to develop light-active porous, metal-organic materials for use in green energy. The dream would be to create a molecule that could simply use light to convert energy essentially replicating the way plants produce energy via photosynthesis.
Professor in Chemistry at Trinity College Dublin, and Investigator in AMBER, Wolfgang Schmitt, led the research. He said: "We have essentially created a molecular 'flask' or better 'sponge' that can hold different molecules until a specific set of conditions spark them into life."
"Hollow cage-type molecular structures have attracted a lot of scientific attention because of these features, but as the number of potential applications has grown and the target systems and environments become more complex, progress has been hampered by the lack of structures with sufficiently large inner cavities and surface areas."
               "The MOP we have just created is among the largest ever made, comprising a number of internal sub-cages, providing numerous different binding sites. The nano-sized compartments can potentially change the reactivity and properties of molecules that are encapsulated within the confined inner spaces and, as such, these cages can be used to promote distinct chemical reactions. Thus, these molecules have the potential to mimic biological enzymes."
The journal article describes the structure of the new cage molecule, which is composed of 36 copper atoms and is made up of 96 individual components.

---

Check out The sharpest laser in the world

New laser with a linewidth of only 10 mHz developed

Source: Physikalisch-Technische Bundesanstalt (PTB)

Summary:

With a linewidth of only 10 mHz, the laser that the researchers have now developed has established a new world record.

FULL STORY

---

This is one of the two silicon resonators.

Credit: PTB

               No one had ever come so close to the ideal laser before: theoretically, laser light has only one single color (also frequency or wavelength). In reality, however, there is always a certain linewidth. With a linewidth of only 10 mHz, the laser that the researchers from the Physikalisch-Technische Bundesanstalt (PTB) have now developed together with US researchers from JILA, a joint institute of the National Institute of Standards and Technology and the University of Colorado Boulder, has established a new world record. This precision is useful for various applications such as optical atomic clocks, precision spectroscopy, radioastronomy and for testing the theory of relativity. The results have been published in the current issue of Physical Review Letters.

               Lasers were once deemed a solution without problems -- but that is now history. More than 50 years have passed since the first technical realization of the laser, and we cannot imagine how we could live without them today. Laser light is used in numerous applications in industry, medicine and information technologies. Lasers have brought about a real revolution in many fields of research and in metrology -- or have even made some new fields possible in the first place.
One of a laser's outstanding properties is the excellent coherence of the emitted light. For researchers, this is a measure for the light wave's regular frequency and linewidth. Ideally, laser light has only one fixed wavelength (or frequency). In practice, the spectrum of most types of lasers can, however, reach from a few kHz to a few MHz in width, which is not good enough for numerous experiments requiring high precision.
Research has therefore focused on developing ever better lasers with greater frequency stability and a narrower linewidth. Within the scope of a nearly 10-year-long joint project with the US colleagues from JILA in Boulder, Colorado, a laser has now been developed at PTB whose linewidth is only 10 mHz (0.01 Hz), hereby establishing a new world record. "The smaller the linewidth of the laser, the more accurate the measurement of the atom's frequency in an optical clock. This new laser will enable us to decisively improve the quality of our clocks," PTB physicist Thomas Legero explains.
                In addition to the new laser's extremely small linewidth, Legero and his colleagues found out by means of measurements that the emitted laser light's frequency was more precise than what had ever been achieved before. Although the light wave oscillates approx. 200 trillion times per second, it only gets out of sync after 11 seconds. By then, the perfect wave train emitted has already attained a length of approx. 3.3 million kilometers. This length corresponds to nearly ten times the distance between Earth and the moon.
Since there was no other comparably precise laser in the world, the scientists working on this collaboration had to set up two such laser systems straight off. Only by comparing these two lasers was it possible to prove the outstanding properties of the emitted light.
               The core piece of each of the lasers is a 21-cm long Fabry-Pérot silicon resonator. The resonator consists of two highly reflecting mirrors which are located opposite each other and are kept at a fixed distance by means of a double cone. Similar to an organ pipe, the resonator length determines the frequency of the wave which begins to oscillate, i.e., the light wave inside the resonator. Special stabilization electronics ensure that the light frequency of the laser constantly follows the natural frequency of the resonator. The laser's frequency stability -- and thus its linewidth -- then depends only on the length stability of the Fabry-Pérot resonator.
                The scientists at PTB had to isolate the resonator nearly perfectly from all environmental influences which might change its length. Among these influences are temperature and pressure variations, but also external mechanical perturbations due to seismic waves or sound. They have attained such perfection in doing so that the only influence left was the thermal motion of the atoms in the resonator. This "thermal noise" corresponds to the Brownian motion in all materials at a finite temperature, and it represents a fundamental limit to the length stability of a solid. Its extent depends on the materials used to build the resonator as well as on the resonator's temperature.
                For this reason, the scientists of this collaboration manufactured the resonator from single-crystal silicon which was cooled down to a temperature of -150 °C. The thermal noise of the silicon body is so low that the length fluctuations observed only originate from the thermal noise of the dielectric SiO2/Ta2O5 mirror layers. Although the mirror layers are only a few micrometers thick, they dominate the resonator's length stability. In total, the resonator length, however, only fluctuates in the range of 10 attometers. This length corresponds to no more than a ten-millionth of the diameter of a hydrogen atom. The resulting frequency variations of the laser therefore amount to less than 4 × 10-17 of the laser frequency.
The new lasers are now being used both at PTB and at JILA in Boulder to further improve the quality of optical atomic clocks and to carry out new precision measurements on ultracold atoms. At PTB, the ultrastable light from these lasers is already being distributed via optical waveguides and is then used by the optical clocks in Braunschweig.
             "In the future, it is planned to disseminate this light also within a European network. This plan would allow even more precise comparisons between the optical clocks in Braunschweig and the clocks of our European colleagues in Paris and London," Legero says. In Boulder, a similar plan is in place to distribute the laser across a fiber network that connects between JILA and various NIST labs.
The scientists from this collaboration see further optimization possibilities. With novel crystalline mirror layers and lower temperatures, the disturbing thermal noise can be further reduced. The linewidth could then even become smaller than 1 mHz.

---

Study reveals mysterious equality with which grains pack it in

For the first time, researchers have been able to test a theory explaining the physics of how substances like sand and gravel pack together

Source: St John's College, University of Cambridge

Summary:

For the first time, researchers have been able to test a theory explaining the physics of how substances like sand and gravel pack together, helping them to understand more about some of the most industrially processed materials on the planet.

FULL STORY

---

          A huge range of materials are classified as granular – including sand, gravel, snow, nuts, coal, rice, barley, coffee and cereals. Globally, they are the second-most processed type of material in industry, after water.

Credit: © forton / Fotolia

          At the moment they come together, the individual grains in materials like sand and snow appear to have exactly the same probability of combining into any one of their many billions of possible arrangements, researchers have shown.

The finding, by an international team of academics at the University of Cambridge, UK, and Brandeis University in the US, appears to confirm a decades-old mathematical theory which has never been proven, but provides the basis for better understanding granular materials -- one of the most industrially significant classes of material on the planet.
          A granular material is anything that comprises solid particles that can be seen individually with the naked eye. Examples include sand, gravel, snow, coal, coffee, and rice.
If correct, the theory demonstrated in the new study points to a fact of remarkable -- and rather mysterious mathematical symmetry. It means, for example, that every single possible arrangement of the grains of sand within a sand dune is exactly as probable as any another.
The study was led by Stefano Martiniani, who is based at New York University but undertook the research while completing his PhD at St John's College, University of Cambridge.
           "Granular materials are so widely-used that understanding their physics is very important," Martiniani said.  "This theory gives us a very simple and elegant way to describe their behaviour. Clearly, something very special is happening in their physics at the moment when grains pack together in this way."
The conjecture that Martiniani tested was first proposed in 1989 by the Cambridge physicist Sir Sam F. Edwards, in an effort to better understand the physical properties of granular materials.                                  Globally, these are the second-most processed type of material in industry (after water) and staples of sectors such as energy, food and pharmaceuticals. In the natural world, vast granular assemblies, such as sand dunes, interact directly with wind, water and vegetation. Yet the physical laws that determine how they behave in different conditions are still poorly understood. Sand, for example, behaves like a solid when jammed together, but flows like a liquid when loose.
              Understanding more about the mechanics of granular materials is of huge practical importance. When they jam during industrial processing, for example, it can cause significant disruption and damage. Equally, the potential for granular materials to "unjam" can be disastrous, such as when soil or snow suddenly loosens, causing a landslide or avalanche.
At the heart of Edwards' proposal was a simple hypothesis: If one does not explicitly add a bias when preparing a jammed packing of granular materials -- for example by pouring sand into a container -- then any possible arrangement of the grains within a certain volume will occur with the same probability.
This is the analogue of the assumption that is at the heart of equilibrium statistical mechanics -- that all states with the same energy occur with equal probability. As a result the Edwards hypothesis offered a way for researchers to develop a statistical mechanics framework for granular materials, which has been an area of intense activity in the last couple of decades.
But the hypothesis was impossible to test -- not least because above a handful of grains, the number of possible arrangements becomes unfathomably huge. Edwards himself died in 2015, with his theory still the subject of heated scientific debate.
                Now, Martiniani and colleagues have been able to put his conjecture to a direct test, and to their surprise they found that it broadly holds true. Provided that the grains are at the point where they have just jammed together (or are just about to separate), all possible configurations are indeed equally likely.
Helpfully, this critical point -- known as the jamming transition -- is also the point of practical significance for many of the granular materials used in industry. Although Martiniani modelled a system comprising soft spheres, a bit like sponge tennis balls, many granular materials are hard grains that cannot be compressed further once in a packed state.
"Apart from being a very beautiful theory, this study gives us the confidence that Edwards' framework was correct," Martiniani said. "That means that we can use it as a lens through which to look at a whole range of related problems."
              Aside from informing existing processes that involve granular materials, there is a wider significance to better understanding their mechanics. In physics, a "system" is anything that involves discrete particles operating as part of a wider network. Although bigger in scale, the way in which icebergs function as part of an ice floe, or the way that individual vehicles move within a flow of traffic (and indeed sometimes jam), can be studied using a similar theoretical basis.
Martiniani's study was undertaken during his PhD under the supervision of Professor Daan Frenkel. It built on earlier research in which he developed new methods for calculating the probability of granular systems packing into different configurations, despite the vast numbers involved. In work published last year, for example, he and colleagues used computer modelling to work out how many ways a system containing 128 tennis balls could potentially be arranged. The answer turned out to be ten unquadragintilliard -- a number so huge that it vastly exceeds the total number of particles in the universe.
             In the new study, the researchers employed a sampling technique which attempts to compute the probability of different arrangements of grains without actually looking at the frequency with which these arrangements occur. Rather than taking an average from random samples, the method involves calculating the limits of the possibility of specific arrangements, and then calculates the overall probability from this.
The team applied this to a computer model of 64 soft spheres -- an imaginary system which could therefore be "over-compressed" after reaching the jamming transition point. In an over-compressed state, the different arrangements were found to have different probabilities of occurrence. But as the system decompressed to the point of the jamming transition, at which the grains were effectively just touching, the researchers found that all probabilities became equal -- exactly as Edwards predicted.
"In 1989, we didn't really have the means of studying whether Edwards was right or not," Martiniani added. "Now that we do, we can understand more about how granular materials work; how they flow, why they get stuck, and how we can use and manage them better in a whole range of different situations."
The study, "Numerical test of the Edwards conjecture shows that all packings become equally probable at jamming" is published in the journal Nature Physics.

---