Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Granular materials not so puzzling after all, physicists find

25.08.2003


Understanding the physics of granular materials is important in industries that handle and process large amounts of the materials, such as pills and powders in the pharmaceutical and food industries and sand in the construction business.



But the problem of how to model granular materials has perplexed physicists. In particular, they’d like to better understand how the temperature within an assemblage of granular material affects the system’s dynamics. That understanding will help scientists determine whether the same thermodynamic principles that apply to systems at equilibrium also apply to systems that are far from equilibrium, such as living organisms.

In a paper to be published in the Aug. 21 issue of the journal Nature, a multinational team that includes University of Michigan physicist Franco Nori describes experiments in which the team devised an unusual "thermometer" and used it to test the soundness of the temperature concept in a continuously shaken container of tiny beads.


Temperature measurements actually are a reflection of how excited individual particles in a material are, be they molecules of air or grains of sand. In a gas, for instance, molecules vibrate and constantly collide with one another like extremely bouncy rubber balls. If the gas was trapped in a box, the microscopic motion would never stop and the temperature would remain constant. This so-called equilibrium state is possible because no loss of energy occurs in the molecules’ chaotic dancing.

In the work described in the Nature paper, the researchers explored the question of whether temperature can be similarly defined for systems that are not at equilibrium, especially those in which energy is dissipated during collisions. If it can, that means that equilibrium thermodynamic concepts can be generalized to far-from-equilibrium situations.

The question has practical implications for understanding natural phenomena such as the formation of order from disorder (a process known as pattern formation) and the extraction of motion out of randomness (biological Brownian motors). For these non-equilibrium situations, the lack of a definition of temperature and related parameters has prevented scientists from completely understanding the systems involved.

The researchers used an experimental set-up that they compare to a pinball machine, with balls moving around in a closed space. In a standard pinball machine, however, the balls are launched one at a time and bounce from one obstacle to the next. In the experimental system, thousands of tiny beads move almost imperceptibly due to the gentle shaking of the container in which they are held, colliding with each other and with the container walls. Because the beads are not perfectly elastic, energy is dissipated during these collisions. Only the external vibration of the container maintains the beads’ chaotic motion; if the container isn’t constantly shaken, the beads quickly stop moving.

In this experimental model of a non-equilibrium system, the researchers used a device called a torsion oscillator to act as a thermometer. The torsion oscillator---a wire with a cone-shaped probe at the end---was immersed in the container of beads. When the container was shaken, the beads bombarded the probe, causing the wire to oscillate back and forth like a clock spring.

By looking at the resulting motion of the wire, the scientists were able to determine whether the measured "temperature" followed the rules one would expect in an equilibrium energy conserving system ---a system in which energy is not dissipated in collisions. To their surprise, they found that temperature did follow the expected rules, leading them to conclude that even for a dissipative system, a few parameters---such as temperature---can be used to extract essential information concealed in the disordered motion of billions of particles.

In addition to Nori of the Institute of Physical and Chemical Research (RIKEN) in Japan and the Center for Theoretical Physics at the University of Michigan, the research team included: Gianfranco D’Anna and Patrick Mayor of the Ecole Polytechnique Federale de Lausanne in Lausanne, Switzerland; Alain Barrat of the Universite de Paris-Sud in Paris, France; Vittorio Loreto of the Center for Statistical Mechanics and Complexity in Rome, Italy; and Franco Nori of the Institute of Physical and Chemical Research (RIKEN) in Japan and the.

The researchers hope their results will stimulate new ideas in the description of non-equilibrium physics.


###

Nancy Ross Flanigan | EurekAlert!
Further information:
http://www-personal.engin.umich.edu/~nori/
http://www.riken.go.jp/engn/r-world/research/lab/frontier/quantum/digital/index.html
http://igahpse.epfl.ch/htc/

More articles from Physics and Astronomy:

nachricht Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology

nachricht A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Study shines light on brain cells that coordinate movement

26.06.2017 | Life Sciences

Smooth propagation of spin waves using gold

26.06.2017 | Physics and Astronomy

Switchable DNA mini-machines store information

26.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>