(Press-News.org) Many solids are produced from melting. Depending on how quickly they cool off, invariably, internal tensile stresses begin to build up. One example are Prince Rupert's Drops, or Dutch tears: you can hit their thick end with a hammer without breaking them while a slight pressure applied to their thin end is enough to shatter the entire tear. The properties of safety or even gorilla glass are determined to a large extent by their internal tensile stresses. However, until now, our understanding of the unique characteristics exhibited by the condition of the glass as compared with a tough molten mass was spotty at best. Now, a collaboration of several German and Cretian research teams has offered a surprisingly simple model to explain the difference between glass and molten materials.
The HZB's contribution was by chemist Dr. Miriam Siebenbürger of the Institute for Soft Matter and Functional Materials. Siebenbürger came up with a rather elegant model system consisting of spherical plastic particles in aqueous solution (a mixture known as a suspension). Due to the tiny size of the particles – each having a diameter of around 150 nanometer – they float in the aqueous solution but never sediment. The nanoparticles are covered by a thermosensitive "shell", whose thickness can be adjusted by varying the temperature, causing them to shrink and grow reversibly in a continuous manner. This allows the chemist to convert her samples from a densely packaged "glass" into a less dense, more fluid state, in other words melt them down. Through a series of rheological measurements, Miriam Siebenbürger was able to determine how quickly the internal tensions in her samples could relax at different particle packing densities.
For this purpose, she placed the samples in-between two parallel plates, which she counter-rotated relative to each other to produce shearing forces within the sample. After reaching a stationary state of shearing stress at a constant shearing rate, the rotating plates were actively stopped. Next, the force it takes to stop the plates to zero shear rate, and which is a gauge for internal tensions, was measured. In the process, the critical difference between the fluid and glassy state became apparent:
Whereas the fluid tensions dissipated without a trace, a proportion of the tensions was maintained in the glassy state. The results are fitting nicely into the theoretical model developed by a group of Constance physicists who calculated the behavior of hard spheres at different packing densities. What's more, measurements of the internal tensile stresses and dynamics of larger-sized particles (in the m range) by Cretian and Düsseldorf researchers and the molecular dynamics simulation of hard spheres by a team of researchers from Cologne and Mainz exhibit similar patterns of behavior. The scientists are convinced that their findings apply to all types of glass that are created as a result of their high packing densities including metallic glass, which is mainly used for high-tech applications. The researchers' findings have now been published in the renowned scientific journal, Physical Review Letters.
INFORMATION:
To the report in Phys. Rev. Letters:
http://link.aps.org/doi/10.1103/PhysRevLett.110.215701
DOI: 10.1103/PhysRevLett.110.215701
M. Ballauff, J. M. Brader, S. U. Egelhaaf, M. Fuchs, J. Horbach, N. Koumakis, M. Krüger, M. Laurati, K. J. Mutch, G. Petekidis, M. Siebenbürger, Th. Voigtmann, and J. Zausch, "Residual Stresses in Glasses", Phys. Rev. Lett. 110, 215701 (2013).
Crystal-clear method for distinguishing between glass and fluids
2013-05-28
ELSE PRESS RELEASES FROM THIS DATE:
Rats have a double view of the world
2013-05-28
This news release is available in German. Scientists from the Max Planck Institute for Biological Cybernetics in Tübingen, using miniaturised high-speed cameras and high-speed behavioural tracking, discovered that rats move their eyes in opposite directions in both the horizontal and the vertical plane when running around. Each eye moves in a different direction, depending on the change in the animal's head position. An analysis of both eyes' field of view found that the eye movements exclude the possibility that rats fuse the visual information into a single image ...
How do plants grow toward the light?
2013-05-28
The growth of plants toward light is particularly important at the beginning of their lifecycle. Many seeds germinate in the soil and get their nutrition in the dark from their limited reserves of starch and lipids. Reaching for the surface, the seedlings rapidly grow upwards against the gravitational pull, which provides an initial clue for orientation. With the help of highly sensitive light-sensing proteins, they find the shortest route to the sunlight – and are even able to bend in the direction of the light source.
"Even mature plants bend toward the strongest light. ...
When perks don't work
2013-05-28
New research from UBC's Sauder School of Business reveals that giving a free bump in service can backfire for retailers if the perk is given randomly in front of others.
The new paper shows that consumers experience social discomfort when singled out for spontaneous special treatment, which may cause them to close their wallets.
"Managerial wisdom guiding service and retail industries assumes that consumers get an uptick in esteem when they're allowed to skip a queue or get an upgrade," says Assistant Professor JoAndrea Hoegg, a co-author of the forthcoming study to ...
Long-term benefits of selective dorsal rhizotomy in children with spastic cerebral palsy
2013-05-28
Charlottesville, VA (May 28, 2013). Selective dorsal rhizotomy (SDR) is a surgical procedure used to treat spasticity in some children with spastic cerebral palsy. This procedure appears to be effective, but for how long? Researchers from Montreal, Quebec, Canada,* set out to find the answer to this question by studying data from the McGill University Rhizotomy Database on 102 pediatric patients with long-term follow-up. The researchers found that, in the majority of children with spastic cerebral palsy, the benefits of SDR last throughout adolescence and into early adulthood. ...
Family studies suggest rare genetic mutations team up to cause schizophrenia
2013-05-28
Using a novel method of analyzing genetic variations in families, researchers at Johns Hopkins have found that individually harmless genetic variations affecting related biochemical processes may team up to increase the risk of schizophrenia. They say their findings, reported May 28 in Translational Psychiatry, bring some clarity to the murky relationship between genetics and schizophrenia, and may lead to a genetic test that can predict which medications will be effective for individual patients.
"It's long been clear that schizophrenia runs in families, but schizophrenia ...
African-Americans experience longer delays between diagnosis and treatment of prostate cancer
2013-05-28
Among men with prostate cancer, African Americans experience longer treatment delays after being diagnosed than Caucasians. That is the finding of an analysis published early online in CANCER, a peer-reviewed journal of the American Cancer Society. The study suggests that efforts are needed to reduce racial disparities in prostate cancer care in order to provide earlier treatment for African Americans.
To see if there is a difference in the time from cancer diagnosis to initiation of treatment for African American men compared with Caucasian men with prostate cancer, ...
Findings may help overcome hurdle to successful bone marrow transplantation
2013-05-28
Blood diseases such as leukemia, multiple myeloma, and myelodysplasia can develop from abnormal bone marrow cells and a dysfunctional bone marrow microenvironment that surrounds these cells. Until now, researchers have been unable to replace the cells that make up the bone marrow microenvironment. Researchers reporting in the May 28 issue of the Cell Press journal Developmental Cell have found that eliminating a gene in the cells found in this microenvironment causes them to die, therefore enabling donor cells to replace them. In addition to providing a better understanding ...
Engineered stem cell advance points toward treatment for ALS
2013-05-28
MADISON, Wis. — Transplantation of human stem cells in an experiment conducted at the University of Wisconsin-Madison improved survival and muscle function in rats used to model ALS, a nerve disease that destroys nerve control of muscles, causing death by respiratory failure.
ALS (amyotrophic lateral sclerosis) is sometimes called "Lou Gehrig's disease." According to the ALS Association, the condition strikes about 5,600 Americans each year. Only about half of patients are alive three years after diagnosis.
In work recently completed at the UW School of Veterinary ...
Dealing with 'crap' to improve water quality
2013-05-28
RIVERSIDE, Calif. (http://www.ucr.edu) — To better understand how bacteria impact the environment a former University of California, Riverside graduate student spent nearly a year building a system that replicates a human colon, septic tank and groundwater and "fed" the colon three times a day during weeklong experiments to simulate human eating.
Ian Marcus, who recently earned his Ph.D. from the UC Riverside Bourns College of Engineering, said discussion of the research often left people a bit perplexed.
"People would give a kind-of-interested-but-definitely-don't-talk-about-it-during-dinner ...
White Mountains hikers often underprepared
2013-05-28
PROVIDENCE, R.I. [Brown University] — Hikers in New Hampshire's White Mountain National Forest often hit the trail less prepared than they should be, according to a study that gauged readiness by how many of 10 essential items the hikers brought along.
Young and inexperienced hikers were most likely to lack multiple items recommended by the State of New Hampshire's HikeSafe program, according to a paper in press at the journal Wilderness & Environmental Medicine. Hikers were also less likely to prepare fully if they were planning a short hike, even though those can quickly ...