- Published on 28 June 2019
Active fluids are living matter or biologically inspired systems, consisting of self-propelled units that burn stored or ambient energy and turn it into work, eventually giving rise to systematic movement. In a new Topical Review paper published in EPJE, authors from groups in Bari (University of Bari, INFN, and the Istituto Applicazioni Calcolo, CNR) and the Center for Life Nano Science, La Sapienza, Rome describe the use of Lattice Boltzmann Methods (LBM) in the study of large scale properties of active fluids.
- Published on 04 June 2019
Hydrocarbons trapped within porous media are easier to model with computer simulations than researchers previously assumed – a discovery that opens up new possibilities for thermodynamics research.
Hidden deep below our feet, petroleum reservoirs are made up of hydrocarbons like oil and natural gas, stored within porous rock. These systems are particularly interesting to physicists, as they clearly show how temperature gradients between different regions affect the gradients of fluid pressures and compositions. However, because these reservoirs are so hard to access, researchers can only model them using data from a few sparse points, meaning many of their properties can only be guessed at. In a new study published in EPJ E, physicists from France and Vietnam, led by Guillaume Galliero at the University of Pau, have found that this guesswork actually isn’t necessary. They show that if the right choices are made when constructing models, no assumptions are needed in order to calculate the impact of temperature gradients on pressure and composition gradients.
- Published on 03 June 2019
The orientation of the ordered molecules that make up nematic liquid crystals can change under electric fields, and can be used to detect subtle electrical effects.
You may not know it, but you probably spend several hours a day looking at nematic liquid crystals; they are used in virtually every smartphone, computer and TV screen. They are liquids composed of elongated molecules, which in some situations can be oriented in a curious way termed the 'dowser texture', which is sensitive to external conditions. Physicists Pawel Pieranski of the Universite Paris-Sud, Paris, France and Maria Helena Godinho of Universidade Nova de Lisboa, Lisbon, Portugal have now published a paper in EPJ E that shows that the dowser texture responds to electric fields in different ways in different nematic materials.
- Published on 08 May 2019
A new study suggests the pattern of fibres in tissues is similar to the petals of a flower
Collagen fibrils are a major component of the connective tissues found throughout the animal kingdom. The cable-like assemblies of long biological molecules combine to form tissues as varied as skin, corneas, tendons or bones. The development of these complex tissues is the subject of a variety of research efforts, focusing on the steps involved and the respective contributions of genetics and physical chemistry to their development. Now, two researchers at the Universite Paris-sud in Orsay, France, have shed new light on how complex collagen fibrils form. In a new study published in EPJ E, the authors focus on one of the hierarchical steps, in which molecules spontaneously associate in long and dense axisymmetric fibres, known as type I collagen fibrils.
- Published on 26 April 2019
A new model of red blood flowing through narrow capillaries shows that the cells change shape and alignment, allowing plasma to flow down the sides
Blood consists of a suspension of cells and other components in plasma, including red blood cells, which give it its red colour. When blood flows through the narrowest vessels in the body, known as the capillaries, the interactions between the cells become much more important. In a new study published in EPJ E, a team of researchers led by Ignacio Pagonabarraga from the University of Barcelona, Spain, has now developed a mathematical model of how red blood cells flow in narrow, crowded vessels. This could help design more precise methods for intravenous drug delivery, as well as 'microfluidic chips' incorporating artificial capillaries, which could offer faster, simpler and more precise blood-based diagnoses.
- Published on 03 April 2019
Using computational models to investigate how liquid drops behave on surfaces
Whether we're aware of it or not, in day-to-day life we often witness an intriguing phenomenon: the breakup of jets of liquid into chains of droplets. It happens when it rains, for example, and it is important for inkjet printers. However, little is known about what happens when a liquid jet, also known as a liquid filament, breaks up on top of a substrate. According to a new study, the presence of a nearby surface changes the way the filament breaks up into smaller droplets. In a new paper published by Andrew Dziedzic at the New Jersey Institute of Technology in Newark, New Jersey, USA, and colleagues in EPJ E, computer simulations are used to show that a filament is more likely to break up near a surface.
EPJ E Topical Review: Gyrotactic phytoplankton in laminar and turbulent ﬂows: A dynamical systems approach
- Published on 20 March 2019
Biological and geophysical fluids host a sea of microorganisms many of which are motile. An often overlooked aspect of the life of such microorganisms is that the fluids where they are suspended are not still but flowing. In this brief review published in EPJ E, the authors aim to describe some of the interesting phenomena that can emerge due to the modification of the microorganisms' swimming direction by velocity gradients, which affect both the individual motion of microorganisms and their spatial distribution in dilute suspensions.
- Published on 06 February 2019
Moving around small objects using capillary forces is a phenomenon that has stimulated scientists trying to understand the fundamental mechanisms at play. It is also important for many industrial, technological and analytical processes, for example micro-fluidics, oil and gas displacement, mineral flotation, miniature robot and biomechanics. In this EPJ E topical review article Jianlin Liu and Shanpeng Li present a critical review of capillarity-driven migration in which many examples are presented and explained. The small objects in question are non-deformable objects, such as particles, rods, disks and metal sheets as well as soft objects, such as droplets and bubbles. The authors clarify some misunderstandings on the conventional views on these systems.
- Published on 15 January 2019
A new study presents new models describing how the adsorption of calcium, barium and strontium ions onto biological membranes may affect the functions of cells
Ions with two positive electrical charges, such as calcium ions, play a key role in biological cell membranes. The adsorption of ions in solution onto the membrane surface is so significant that it affects the structural and functional properties of the biological cells. Specifically, ions interact with surface molecules such as a double layer of lipids, or liposomes, formed from phosphatidylcholines (PC). In a new study published in EPJ E, Izabela Dobrzyńska from the University of Białystok, Poland, develops a mathematical model describing the electrical properties of biological membranes when ions such as calcium, barium and strontium adsorb onto them at different pH levels. Her works helps shed light on how ion adsorption reduces the effective surface concentration of add-on molecules with a specific function that can take part in biochemical reactions. These factors need to be taken into account when studying the diverse phenomena that occur at the lipid membrane in living cells, such as ion transport mechanisms.
EPJ E Highlight - Sac with spiral surface patterns facilitate substance delivery through biological membranes
- Published on 17 December 2018
Faceted microfilms made up of liquid crystals arranged in spiral patterns can help squeeze through membranes and deliver helpful molecules
Imagine a micron-sized ball of fluid enclosed in a thin film, similar to the film in soap bubbles, but made up of molecules resembling liquid crystal. These molecules can lower their overall energy by aligning their directions with their ever-changing neighbours—a state referred to as smectic phase. This means stacks of parallel stripe-like liquid-crystal layers form in the film. In a new study published in EPJ E, Francesco Serafin, affiliated with both Syracuse University, New York, and the Kavli Institute for Theoretical Physics (KITP) at UCSB, USA, together with his advisor Mark Bowick, also at the KITP, and Sid Nagel, from the University of Chicago, IL,USA, map out all the possible smectic patterns of such spherical films, or sac, at zero temperature. They determine the conditions under which it becomes easier for such sacs to pass through biological membranes and, potentially, deliver molecules attached to them at specific locations.