scholarly journals How many ways a cell can move: the modes of self-propulsion of an active drop

Soft Matter ◽  
2020 ◽  
Vol 16 (12) ◽  
pp. 3106-3124 ◽  
Author(s):  
Aurore Loisy ◽  
Jens Eggers ◽  
Tanniemola B. Liverpool
Keyword(s):  
Solid Surfaces ◽  
Active Matter ◽  
Cell Locomotion ◽  
Special Cases ◽  
A Cell ◽  
General Physical ◽  
Physical Principles

Modelling a cell as a deformable drop of active matter, we classify the types of cell locomotion on solid surfaces based on general physical principles. Previous models are special cases of our framework and we identify a new self-propulsion mode.

scholarly journals Geometric Effect for Biological Reactors and Biological Fluids

2018 ◽  
Vol 5 (4) ◽  
pp. 110 ◽  
Author(s):  
Kazusa Beppu ◽  
Ziane Izri ◽  
Yusuke Maeda ◽  
Ryota Sakamoto
Keyword(s):  
Biological Fluids ◽  
Biological Systems ◽  
Self Organization ◽  
Active Matter ◽  
Confined Space ◽  
Self Organized ◽  
Motile Cells ◽  
Recent Developments ◽  
A Cell

As expressed “God made the bulk; the surface was invented by the devil” by W. Pauli, the surface has remarkable properties because broken symmetry in surface alters the material properties. In biological systems, the smallest functional and structural unit, which has a functional bulk space enclosed by a thin interface, is a cell. Cells contain inner cytosolic soup in which genetic information stored in DNA can be expressed through transcription (TX) and translation (TL). The exploration of cell-sized confinement has been recently investigated by using micron-scale droplets and microfluidic devices. In the first part of this review article, we describe recent developments of cell-free bioreactors where bacterial TX-TL machinery and DNA are encapsulated in these cell-sized compartments. Since synthetic biology and microfluidics meet toward the bottom-up assembly of cell-free bioreactors, the interplay between cellular geometry and TX-TL advances better control of biological structure and dynamics in vitro system. Furthermore, biological systems that show self-organization in confined space are not limited to a single cell, but are also involved in the collective behavior of motile cells, named active matter. In the second part, we describe recent studies where collectively ordered patterns of active matter, from bacterial suspensions to active cytoskeleton, are self-organized. Since geometry and topology are vital concepts to understand the ordered phase of active matter, a microfluidic device with designed compartments allows one to explore geometric principles behind self-organization across the molecular scale to cellular scale. Finally, we discuss the future perspectives of a microfluidic approach to explore the further understanding of biological systems from geometric and topological aspects.

scholarly journals A Critical Review of Works Pertinent to the Einstein-Bohr Debate and Bell’s Theorem

Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 163
Author(s):  
Karl Hess
Keyword(s):  
Quantum Theory ◽  
Physical Reality ◽  
Point Of View ◽  
Statistical Sampling ◽  
Necessary And Sufficient Condition ◽  
Special Cases ◽  
General Physical ◽  
Necessary And Sufficient ◽  
Physical Features ◽  
Chsh Inequalities

This review is related to the Einstein-Bohr debate and to Einstein–Podolsky–Rosen’s (EPR) and Bohm’s (EPRB) Gedanken-experiments as well as their realization in actual experiments. I examine a significant number of papers, from my minority point of view and conclude that the well-known theorems of Bell and Clauser, Horne, Shimony and Holt (CHSH) deal with mathematical abstractions that have only a tenuous relation to quantum theory and the actual EPRB experiments. It is also shown that, therefore, Bell-CHSH cannot be used to assess the nature of quantum entanglement, nor can physical features of entanglement be used to prove Bell-CHSH. Their proofs are, among other factors, based on a statistical sampling argument that is invalid for general physical entities and processes and only applicable for finite “populations”; not for elements of physical reality that are linked, for example, to a time-like continuum. Bell-CHSH have, furthermore, neglected the subtleties of the theorem of Vorob’ev that includes their theorems as special cases. Vorob’ev found that certain combinatorial-topological cyclicities of classical random variables form a necessary and sufficient condition for the constraints that are now known as Bell-CHSH inequalities. These constraints, however, must not be linked to the observables of quantum theory nor to the actual EPRB experiments for a variety of reasons, including the existence of continuum-related variables and appropriate considerations of symmetry.

Tandem Conveyor Queues

1989 ◽  
Vol 3 (4) ◽  
pp. 517-536
Author(s):  
F. Baccelli ◽  
E.G. Coffman ◽  
E.N. Gilbert
Keyword(s):  
Boundary Value Problem ◽  
Joint Distribution ◽  
Queueing System ◽  
The Other ◽  
Riemann Boundary Value Problem ◽  
Riemann Boundary ◽  
Special Cases ◽  
A Cell ◽  
Service Times ◽  
Input Position

This paper analyzes a queueing system in which a constant-speed conveyor brings new items for service and carries away served items. The conveyor is a sequence of cells each able to hold at most one item. At each integer time, a new cell appears at the queue's input position. This cell holds an item requiring service with probability a, holds a passerby requiring no service with probability b, and is empty with probability (1– a – b). Service times are integers synchronized with the arrival of cells at the input, and they are geometrically distributed with parameter μ. Items requiring service are placed in an unbounded queue to await service. Served items are put in a second unbounded queue to await replacement on the conveyor in cells at the input position. Two models are considered. In one, a served item can only be placed into a cell that was empty on arrival; in the other, the served item can be placed into a cell that was either empty or contained an item requiring service (in the latter case unloading and loading at the input position can take place in the same time unit). The stationary joint distribution of the numbers of items in the two queues is studied for both models. It is verified that, in general, this distribution does not have a product form. Explicit results are worked out for special cases, e.g., when b = 0, and when all service times are one time unit (μ = 1). It is shown how the analysis of the general problem can be reduced to the solution of a Riemann boundary-value problem.

scholarly journals The interaction of atoms and molecules with solid surfaces VIII—The exchange of energy between a gas and a solid

1937 ◽  
Vol 158 (894) ◽  
pp. 269-279 ◽  
Keyword(s):  
Morse Potential ◽  
Accommodation Coefficient ◽  
Solid Surfaces ◽  
Adsorbed State ◽  
Thermal Accommodation ◽  
Special Cases ◽  
Thermal Accommodation Coefficient ◽  
The Right ◽  
Energy Interchange

In previous papers of this series the problem of energy interchange between a gas atom and a solid has been discussed for the case when the gas atom makes a transition between two adsorbed states or between an adsorbed state and a free state. In this paper we shall discuss the case of a transition between two free states and apply the results to the determination of the thermal accommodation coefficient. In recent years a number of theoretical papers on this subject have appeared, following the new and accurate experimental work of Roberts, who worked with helium and neon on tungsten. The authors, however, neglect, or only roughly take into account, the attractive field which is known to exist between the solid and the gas; the fact that atoms become adsorbed on the surface is clear evidence of the existence of such a field. In this paper we shall suppose that the interaction potentials between solid and gas atom can be represented by a Morse potential function, for it has the right characteristics; in that it is attractive at large distances and repulsive at small ones, and has a minimum in between. The formulae of this paper are accordingly more general than previous ones and contain them as special cases. They are applicable to experimental results such as those of neon on tungsten for which earlier theories would not be adequate.

scholarly journals Bounds on the power of proofs and advice in general physical theories

2016 ◽  
Vol 472 (2190) ◽  
pp. 20160076 ◽  
Author(s):  
Ciarán M. Lee ◽  
Matty J. Hoban
Keyword(s):  
Quantum Theory ◽  
Quantum Structure ◽  
Interactive Proof ◽  
Interactive Proof Systems ◽  
Proof Systems ◽  
Local Measurements ◽  
General Physical ◽  
Adjoint Operators ◽  
Physical Features ◽  
Physical Principles

Quantum theory presents us with the tools for computational and communication advantages over classical theory. One approach to uncovering the source of these advantages is to determine how computation and communication power vary as quantum theory is replaced by other operationally defined theories from a broad framework of such theories. Such investigations may reveal some of the key physical features required for powerful computation and communication. In this paper, we investigate how simple physical principles bound the power of two different computational paradigms which combine computation and communication in a non-trivial fashion: computation with advice and interactive proof systems. We show that the existence of non-trivial dynamics in a theory implies a bound on the power of computation with advice. Moreover, we provide an explicit example of a theory with no non-trivial dynamics in which the power of computation with advice is unbounded. Finally, we show that the power of simple interactive proof systems in theories where local measurements suffice for tomography is non-trivially bounded. This result provides a proof that Q M A is contained in P P , which does not make use of any uniquely quantum structure—such as the fact that observables correspond to self-adjoint operators—and thus may be of independent interest.

scholarly journals From amplitudes to contact cosmological correlators

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
James Bonifacio ◽  
Enrico Pajer ◽  
Dong-Gang Wang
Keyword(s):  
Commutative Algebra ◽  
Point Contact ◽  
De Sitter ◽  
Reconstruction Formula ◽  
The Past ◽  
Sitter Spacetime ◽  
General Scalar ◽  
General Physical ◽  
Lorentz Boosts ◽  
Physical Principles

Abstract Our understanding of quantum correlators in cosmological spacetimes, including those that we can observe in cosmological surveys, has improved qualitatively in the past few years. Now we know many constraints that these objects must satisfy as consequences of general physical principles, such as symmetries, unitarity and locality. Using this new understanding, we derive the most general scalar four-point correlator, i.e., the trispectrum, to all orders in derivatives for manifestly local contact interactions. To obtain this result we use techniques from commutative algebra to write down all possible scalar four-particle amplitudes without assuming invariance under Lorentz boosts. We then input these amplitudes into a contact reconstruction formula that generates a contact cosmological correlator in de Sitter spacetime from a contact scalar or graviton amplitude. We also show how the same procedure can be used to derive higher-point contact cosmological correlators. Our results further extend the reach of the boostless cosmological bootstrap and build a new connection between flat and curved spacetime physics.

scholarly journals Hyaluronan and a cell-associated hyaluronan binding protein regulate the locomotion of ras-transformed cells.

1991 ◽  
Vol 112 (5) ◽  
pp. 1041-1047 ◽  
Author(s):  
E A Turley ◽  
L Austen ◽  
K Vandeligt ◽  
C Clary
Keyword(s):  
Binding Sites ◽  
Binding Protein ◽  
Experimental Period ◽  
Cell Binding ◽  
Ras Gene ◽  
Hybrid Gene ◽  
Cell Locomotion ◽  
A Cell ◽  
Dose Dependent ◽  
Hyaluronan Binding

Hyaluronan (HA) and one of its cell binding sites, fibroblast hyaluronan binding protein (HABP), is shown to contribute to the regulation of 10T1/2 cell locomotion that contain an EJ-ras-metallothionein (MT-1) hybrid gene. Promotion of the ras-hybrid gene with zinc sulfate acutely stimulates, by 6-10-fold, cell locomotion. After 10 h, locomotion drops to two- to threefold above that of uninduced cells. Several observations indicate increased locomotion is partly regulated by HA. These include the ability of a peptide that specifically binds HA (HABR) to reduce locomotion, the ability of HA (0.001-0.1 micrograms/ml), added at 10-30 h after induction to stimulate locomotion back to the original, acute rate, and the ability of an mAb specific to a 56-kD fibroblast HABP to block locomotion. Further, both HA and HABP products are regulated by induction of the ras gene. The effect of exogenous HA is blocked by HABR, is dose-dependent and specific in that chondroitin sulfate or heparan have no significant effect. Stimulatory activity is retained by purified HA and lost upon digestion with Streptomyces hyaluronidase indicating that the activity of HA resides in its glycosaminoglycan chain. Uninduced cells are not affected by HA, HABR, or mAb and production of HA or HABP is not altered during the experimental period. These results suggest that ras-transformation activates an HA/HABP locomotory mechanism that forms part of an autocrine motility mechanism. Reliance of induced cells on HA/HABP for locomotion is transient and specific to the induced state.

scholarly journals Gliding Direction of Mycoplasma mobile

2015 ◽  
Vol 198 (2) ◽  
pp. 283-290 ◽  
Author(s):  
Hanako Morio ◽  
Taishi Kasai ◽  
Makoto Miyata
Keyword(s):  
Solid Surface ◽  
Thermal Fluctuation ◽  
Solid Surfaces ◽  
Cell Axis ◽  
Content Type ◽  
Propulsion Force ◽  
A Cell ◽  
The Right ◽  
Triton X ◽  
Unique Mechanism

ABSTRACTMycoplasma mobileglides in the direction of its cell pole by a unique mechanism in which hundreds of legs, each protruding from its own gliding unit, catch, pull, and release sialylated oligosaccharides fixed on a solid surface. In this study, we found that 77% of cells glided to the left with a change in direction of 8.4° ± 17.6° μm−1displacement. The cell body did not roll around the cell axis, and elongated, thinner cells also glided while tracing a curved trajectory to the left. Under viscous conditions, the range of deviation of the gliding direction decreased. In the presence of 250 μM free sialyllactose, in which the binding of the legs (i.e., the catching of sialylated oligosaccharides) was reduced, 70% and 30% of cells glided to the left and the right, respectively, with changes in direction of ∼30° μm−1. The gliding ghosts, in which a cell was permeabilized by Triton X-100 and reactivated by ATP, glided more straightly. These results can be explained by the following assumptions based on the suggested gliding machinery and mechanism: (i) the units of gliding machinery may be aligned helically around the cell, (ii) the legs extend via the process of thermal fluctuation and catch the sialylated oligosaccharides, and (iii) the legs generate a propulsion force that is tilted from the cell axis to the left in 70% and to the right in 30% of cells.IMPORTANCEMycoplasmas are bacteria that are generally parasitic to animals and plants. SomeMycoplasmaspecies form a protrusion at a pole, bind to solid surfaces, and glide. Although these species appear to consistently glide in the direction of the protrusion, their exact gliding direction has not been examined. This study analyzed the gliding direction in detail under various conditions and, based on the results, suggested features of the machinery and the mechanism of gliding.

Cell Crawling Assisted by Contractile Stress Induced Retraction

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Sitikantha Roy ◽  
Feng Miao ◽  
H. Jerry Qi
Keyword(s):  
Cell Movement ◽  
Focal Adhesions ◽  
Receptor Ligand ◽  
Produce Cell ◽  
Cell Locomotion ◽  
Cell Crawling ◽  
Parametric Studies ◽  
Contractile Stress ◽  
A Cell ◽  
Locomotion Speed

Cell locomotion is a result of a series of synchronized chemo-mechanical processes. Crawling-type cell locomotion consists of three steps: protrusion, translocation, and retraction. Previous works have shown that both protrusion and retraction can produce cell movement. For the latter, a cell derives its propulsive force from retraction induced protrusion mechanism, which was experimentally verified by Chen (1979, “Induction of Spreading During Fibroblast Movement,” J. Cell Biol., 81, pp. 684–691). In this paper, using finite element method, we take a computational biomimetic approach to study cell crawling assisted by contractile stress induced de-adhesion at the rear of the focal adhesion zone (FAZ). We assume the formation of the FAZ is driven by receptor-ligand bonds and nonspecific interactions. The contractile stress is generated due to the molecular activation of the intracellular actin-myosin machinery. The exerted contractile stress and its time dependency are modeled in a phenomenological manner as a two-spring mechanosensor proposed by Schwarz (2006, “Focal Adhesions as Mechanosensors: The Two-Spring Model,” BioSystems, 83(2–3), pp. 225–232). Through coupling the kinetics of receptor-ligand bonds with contractile stress, de-adhesion can be achieved when the stall value of the contractile stress is larger than a critical one. De-adhesion at the rear end of the FAZ causes a redistribution of elastic energy and induces cell locomotion. Parametric studies were conducted to investigate the connection between the cell locomotion speed and stall stress, and receptor-ligand kinetics. Finally, we provide a scaling relationship that can be used to estimate the cell locomotion speed.

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