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Soft Matter and Biological Physics

News / Highlights / Colloquium

EPJ E Colloquium - The role of acoustic streaming in vertically vibrated granular beds

Photo by Robert Hartley and co-workers at Duke University (Robert Behringer’s Group)

A recent EPJ E Colloquium by Jose Manuel Valverde looks at the fundamental physics that causes convection and fluidization in vibrated beds of particles with large inertia. The author examines the question of whether acoustic streaming arising from oscillatory viscous flows might play a role on the onset of convection and fluidization in vertically vibrated granular beds.

Acoustic streaming, first observed by Faraday in 1831, is an enigmatic phenomenon that has puzzled physicists for a long time. It occurs when a viscous fluid oscillates in the presence of a solid boundary. The dissipation of energy by viscous friction leads to a secondary steady circulation of fluid in a boundary layer near the surface of the solid, which enhances the gas-solid viscous interaction. Granular beds display, at sufficiently high vibrational intensities, surface patterns that bear a stunning resemblance to the surface ripples (Faraday waves) observed for low viscosity liquids. This suggests that the granular bed transits to a liquid-like regime, despite the large inertia of the particles.


EPJ E Highlight - How supercooled water is prevented from turning into ice

Representative configurations of ice in its Ic format, which is a simulation in a cube with 216 molecules, Ih format, which is in a rectangular cell with 432 molecules, and in liquid water

Calculating the energy barrier that keeps liquid water below zero from immediately turning into ice provides the key to understanding its ability to be compressed as temperature drops

Water behaves in mysterious ways. Especially below zero, where it is dubbed supercooled water, before it turns into ice. Physicists have recently observed the spontaneous first steps of the ice formation process, as tiny crystal clusters as small as 15 molecules start to exhibit the recognisable structural pattern of crystalline ice. This is part of a new study, which shows that liquid water does not become completely unstable as it becomes supercooled, prior to turning into ice crystals. The team reached this conclusion by proving that an energy barrier for crystal formation exists throughout the region in which supercooled water’s compressibility continues to rise. Previous work argued that this barrier vanished as the liquid gets colder. These findings have been published in EPJ E by Connor Buhariwalla from St. Francis Xavier University in Antigonish, Canada and colleagues.


EPJ E Colloquium – The importance of rheology in tissue development

Our understanding of biomechanics increasingly improves through the use of physics models. There are some intriguing biological questions regarding the interplay between the behaviour of cells and the mechanics at the level of tissues. For example, how does a collective behavior, not apparent at the cell scale, emerge at the tissue level? Or how can the mechanical state of a tissue affect the cell division rate or the orientation of cells undergoing division?

The authors of this new EPJ E Colloquium entitled “Mechanical Formalism for Tissue Dynamics” think that the interplay between genes and mechanics is key to understanding how the adult shape emerges from a developing tissue.


EPJ E Highlight - Space lab to elucidate how liquid cocktails mix

International Space Station salutes the Sun. © NASA/ESA

Zero-gravity experiments can tell us a great deal about the effects of temperature change on the concentrations of three different liquids that are mixed together

What does space experimentation have in common with liquid cocktails? Both help in understanding what happens when multiple fluids are mixed together and subjected to temperature change - a phenomenon ubiquitous in nature and industrial applications such as oil fluids contained in natural reservoirs. The latest experimental data performed in zero gravity on the International Space Station is now available in the newly published Topical Issue of EPJ E. The results constitute the first set of highly accurate and broadly validated data on the thermodiffusion effects that occur when three different liquids are mixed. Such experiments were made possible by a collaboration of space agencies including the ESA, NASA, CSA and ROSCOSMOS.


EPJ E Highlight - Rodeo in liquid crystal

Binding of a dipolar microsphere with a point monopole on a fiber.

Scientists have achieved an unprecedented level of control over defects in liquid crystals that can be engineered for applications in liquid matter photonics

Sitting with a joystick in the comfort of their chairs, scientists can play “rodeo” on a screen magnifying what is happening under their microscope. They rely on optical tweezers to manipulate an intangible ring created out of liquid crystal defects capable of attaching a microsphere to a long thin fibre. Maryam Nikkhou and colleagues from the Jožef Stefan Institute, in Ljubljana, Slovenia, recently published in EPJ E the results of work performed under the supervision of Igor Muševič. They believe that their findings could ultimately open the door to controlling the flow of light using light of a specific frequency in the Gigahertz range in liquid crystal photonic microdevices.


EPJ E Highlight - Building sound foundations: a matter of granular dynamics

The behaviour of the granular medium sand can be modelled using a hydrodynamics theory, a new study shows. © sergign / Fotolia

Applying the hydrodynamics approach to granular matter helps explain its wide range of behaviour, regardless of whether the material is solid- or fluid-like

Sand, rocks, grains, salt or sugar are what physicists call granular media. A better understanding of granular media is important - particularly when mixed with water and air, as it forms the foundations of houses and off-shore windmills. Until recently, there was no single theory that could account for granular media’s flows at different speeds. Now, a new theory dubbed GSH, which stands for granular solid hydrodynamics, is supplementing previous models of granular material that work only for narrow speed ranges. And Yimin Jiang from Central South University, Changsha, China and Mario Liu from the University of Tübingen, Germany have now applied GSH to different experimental circumstances, for a wide range of flow speeds, in a study published in EPJ E.


EPJE: New section about tips and tricks in soft matter and biological physics


EPJE Associate Editors Kari Dalnoki-Veress and James A. Forrest open the journal for submissions of a new type of paper: Tips and Tricks.

Underpinning the scientific enterprise there is often some crucial numerical recipe, a sample cell configuration, a sample preparation method, or experimental design. In some cases more emails were shared describing a trick than citations gathered by the paper where a brief description was provided. Typically such details are only briefly described in the journal literature, passed only from student to student, or simply shared as a ‘personal communication’. Sometimes such enabling techniques are not passed on at all. In all such cases, the scientific community as a whole is missing out, lacking a way to document this knowledge and to build on it. Moreover, while the specific research of some team may not be directly relevant to another, a transformative computational or experimental methodology can form the commonality between researchers working in different fields.

2015 will see the launch of a new section of EPJ E: Tips and Tricks.


EPJ E Highlight - How do vertebrates take on their form?

Modeling of the fold formation mechanism. A sheet of rubber on which a (stiffer) paper label is stuck buckles along the boundary between the stiff zone and the soft zone when it is stretched. This reproduces the formation of folds along the boundaries between cellular domains. © VF-CNRS-MSC/EDP Sciences-SIF-Springer SBM

A simple physical mechanism that can be assimilated to folding, or buckling, means that an unformed mass of cells can change in a single step into an embryo organized as a typical vertebrate. This is the main conclusion of work by a team involving physicists from the Laboratoire Matière et Systèmes Complexes (CNRS/Université Paris Diderot) and a biologist from the Laboratoire de Biologie du Développement (CNRS/UPMC).

Thanks to microscopic observations and micromechanical experiments, the scientists have discovered that the pattern that guides this folding is present from the early stages of development. The folds that will give a final shape to the animal form along the boundaries between cell territories with different properties. This work has shed light on the mechanism for the formation of vertebrates and thus how they appeared during evolution. These findings have just been published in EPJ E.


EPJ E Highlight - Optical manipulation of particles of all shapes and sizes

Ellipsoidal particle levitating at the optical beam waist, with its long axis aligned to the beam axis. © B. M. Mihiretie et al.

A new study of how particles may respond to the mechanical effects of light helps improve optical manipulation and remote sensing of non-spherical particles.

Manipulation of small objects by light has gained in popularity in the past few years. Now, scientists have performed the first systematic analysis of the behaviour of ellipsoidal particles manipulated by laser beams. The work shows that such particles are constantly moving in and out of the reach of an optical beam, creating oscillations. These findings by a team of researchers from the University of Bordeaux, France, have just been published in EPJ E. This work could help understand the unusual behaviour of rod-like particles manipulated by optical tweezers. Ultimately, the theoretical part of this work could contribute numerical models of how complicated shapes and large sizes scatter laser light. Numerous applications exist in fluid engineering and remote sensing methods.


EPJE: Francesco Sciortino joins the EPJE board as Editor in Chief

After five years of impeccable service as Editor-in-Chief of the soft matter part, EPJ E must say thank you and goodbye to Professor Daan Frenkel, as part of the journal’s process of continuous renewal. We are delighted to announce the arrival of his successor as of January 1st 2015: Professor Francesco Sciortino of the University of Rome La Sapienza. Sciortino started his scientific career with an experimental PhD on the phase behavior of biopolymers solutions at the University of Palermo, and shortly after moved on to numerical simulation methods in which he has become a renowned expert. He has held various appointments through the years in Boston, Cagliari, Bordeaux, Western Ontario, and Paris. His research interests are varied and include: self-assembly in colloidal systems and protein solutions, bio-functionalized colloids, aggregation phenomena in colloidal systems, cluster phases and gels, thermodynamics of anomalous liquids, thermodynamics of supercooled liquids and their glass transition, percolation and phase transitions in complex liquids. We wish Francesco Sciortino great success as EPJE EiC, in connecting the journal with the soft matter community to EPJE. Daan Frenkel will continue to sit on the journal Advisory Board.
F. Graner and F. Sciortino
I am perfectly satisfied by this layout. Let me thank you for the wonderful editorial work.

Pasquale Ciarletta, UPMC, France

ISSN (Print Edition): 1292-8941
ISSN (Electronic Edition): 1292-895X

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