Nonlinear Biomedical Physics

EPJ E Highlight - No assumptions needed to simulate petroleum reservoirs

Modelling reservoirs: easier than we thought? https://commons.wikimedia.org/wiki/ File:Contour_map_software_screen_ snapshot_of_isopach_map_for_ 8500ft_deep_OIL_reservoir_with_ a_Fault_line.jpg

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.

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EPJ E Highlight - Dowsing for electric fields in liquid crystals

Following the change in orientation of the molecules in the dowser texture yields a shape that resembles the wooden dowsing rods used in previous centuries to locate groundwater. Left: © Pawel Pieranski, Right: https://en.wikipedia.org/wiki/ Dowsing#/media/File: 18th_century_dowser.jpg

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.

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EPJ E Highlight - Collagen fibres grow like a sunflower

Phyllotactic pattern with concentric circles.

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.

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EPJ E Highlight - How red blood cells behave in crowded vessels

Red blood cells flowing through a blood vessel. https://pixabay.com/illustrations/blood-cells-red-medical-medicine-1813410/

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.

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EPJ E Highlight - Liquid jets break up more readily on a substrate

Filaments.

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.

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EPJ E Topical Review: Gyrotactic phytoplankton in laminar and turbulent flows: A dynamical systems approach

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.

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EPJE Topical Review: how capillarity drives the movement of small objects

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.

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EPJ E Highlight - How ion adsorption affects biological membranes’ functions

Coverage of the lipid bilayer membrane surface with ions, as a function of pH.

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.

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EPJ E Highlight - Sac with spiral surface patterns facilitate substance delivery through biological membranes

Introducing bend in the liquid crystal layers.

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.

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EPJ E Highlight - The physics of extracting gas from shale formations

Microscopic model of the shale structure.

A new study outlines the key parameters affecting the production of gas from shale reservoirs, by simulating what is happening at the microscopic scale.

Extracting gas from new sources is vital in order to supplement dwindling conventional supplies. Shale reservoirs host gas trapped in the pores of mudstone, which consists of a mixture of silt mineral particles ranging from 4 to 60 microns in size, and clay elements smaller than 4 microns. Surprisingly, the oil and gas industry still lacks a firm understanding of how the pore space and geological factors affect gas storage and its ability to flow in the shale. In a study published in EPJ E, Natalia Kovalchuk and Constantinos Hadjistassou from the University of Nicosia, Cyprus, review the current state of knowledge regarding flow processes occurring at scales ranging from the nano- to the microscopic during shale gas extraction. This knowledge can help to improve gas recovery and lower shale gas production costs.

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Section Editors-in-Chief
W. Klonowski, A. Stefanovska, J. Tuszynski, M.-T. Huett and V. Jirsa
ISSN (Electronic Edition): 2195-0008

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