scholarly journals Physical limit to concentration sensing in a changing environment

2019 ◽  
Author(s):  
Thierry Mora ◽  
Ilya Nemenman
Keyword(s):  
Cross Section ◽  
Biochemical Network ◽  
Square Root ◽  
Changing Environments ◽  
Physical Limit ◽  
Theoretic Problem ◽  
Specific Receptors ◽  
Kinetics Of ◽  
Characteristic Fluctuation ◽  
Linear Field

AbstractCells adapt to changing environments by sensing ligand concentrations using specific receptors. The accuracy of sensing is ultimately limited by the finite number of ligand molecules bound by receptors. Previously derived physical limits to sensing accuracy have assumed that the concentration was constant and ignored its temporal fluctuations. We formulate the problem of concentration sensing in a strongly fluctuating environment as a non-linear field-theoretic problem, for which we find an excellent approximate Gaussian solution. We derive a new physical bound on the relative error in concentration c which scales as δc/c ~ (Dacτ)−1/4 with ligand diffusivity D, receptor cross-section a, and characteristic fluctuation time scale τ, in stark contrast with the usual Berg and Purcell bound δc/c ~ (DacT)−1/2 for a perfect receptor sensing concentration during time T. We show how the bound can be achieved by a simple biochemical network downstream the receptor that adapts the kinetics of signaling as a function of the square root of the sensed concentration.

The use of bioluminescence as a reporter to study the adherence of the plant growth promoting rhizopseudomonads 7NSK2 and ANP15 to canola roots

1993 ◽  
Vol 39 (3) ◽  
pp. 329-334 ◽  
Author(s):  
J. Boelens ◽  
D. Zoutman ◽  
J. Campbell ◽  
W. Verstraete ◽  
W. Paranchych
Keyword(s):  
Plant Growth ◽  
Freundlich Isotherm ◽  
Root Surface ◽  
Broad Host Range ◽  
Bacterial Bioluminescence ◽  
Range Vector ◽  
Plant Growth Promoting ◽  
Specific Receptors ◽  
Growth Promoting ◽  
Kinetics Of

The adherence of the plant growth promoting rhizopseudomonads Pseudomonas aeruginosa 7NSK2 and Pseudomonas fluorescens ANP15 to canola roots (Brassica campestris L. c.v. Tobin) was examined by means of a bacterial bioluminescence system. The bioluminescence broad host range vector pDLUX-I was constructed from pLAFR-I and the lux A–E genes of Vibrio fischerii. This vector was conjugally transferred into the plant growth promoting rhizopseudomonads 7NSK2 and ANP15. The transformed strains were constitutively bioluminescent at an optimal temperature of 21 °C. The measured bioluminescence was directly proportional to the density of the bacteria in suspension and was the same for both planktonic and sessile bacteria adhering to the root surface. The adherence of the plant growth promoting rhizopseudomonads was proportional to the density of the bacterial inoculum, approached saturation at 60 min, and was reversible. The kinetics of the microbial adhesion was described by a Freundlich isotherm suggesting that the adherence of the bacteria to the canola root surface does not involve specific receptors. We conclude that the pDLUX-I vector is an easy and accurate way to study the kinetics of microbial adherence to the rhizoplane.Key words: rhizopseudomonads, bioluminescence, adhesion, plant growth promotion.not available

Interaction Of Fibrinogen With Platelets In Plasma

1981 ◽  
Author(s):  
G Marguerie ◽  
M J Larrieu ◽  
E F Plow
Keyword(s):  
Initial Rate ◽  
Platelet Rich Plasma ◽  
Human Platelets ◽  
Affinity Constant ◽  
Single Class ◽  
Fibrinogen Binding ◽  
Rate Of Reaction ◽  
Specific Receptors ◽  
Higher Temperature ◽  
Kinetics Of

Fibrinogen binds to specific receptors on washed human platelets and these sites are induced by ADP. This interaction is assumed to be the basis for the participation of the molecule in ADP-stimulated platelet aggregation, but fibrinogen binding to platelets in plasma has not been directly demonstrated. In this study, we have characterized the binding of 125 I-fibrinogen to platelets in the platelet rich plasma (PRP) of afibrinogene- mic patients. In either citrated or heparinized PRP, association of fibrinogen with platelets was demonstrable and was dependent on ADP dose. This binding was time dependent and reached equilibrium in 10 to 15 min. At 22°C, the rate constants of association were kon = 0.9×10-6 M-1 min-1 in plasma compared to kon = 0.6×l0-6M-1 min-1 in Tyrode’s buffer indicating that initial rate of reaction was similar in both milieu. The kinetics of binding in plasma were the same at 37°C and 22°C but fewer molecules were bound at the higher temperature. In the PRP, saturable binding of fibrinogen to the platelet was achieved at concentrations greater than 0.5 μM. A linear Scatchard plot was derived which indicated a single class of binding site with an affinity constant of Ka = 1.8×106 M-1 and 32,000 fibrinogen molecules were maximally bound per platelet. These values are essentially identical to those obtained with washed platelets. In buffer, platelet-bound fibrinogen becomes progressively nondissociab1e , and this stabilization occurred to a partial extent in plasma. In sum, these results establish that the previously defined steps in ADP-induced binding of fibrinogen to platelet occur in plasma.

Effect of Ligand Density Gradient on the Adhesion Kinetics of Biological Membranes

2007 ◽  
Vol 1063 ◽  
Author(s):  
Alireza Sarvestani ◽  
Esmaiel Jabbari
Keyword(s):  
Elastic Membrane ◽  
Square Root ◽  
Front Edge ◽  
Ligand Density ◽  
Surface Gradient ◽  
Diffusion Controlled ◽  
Adhesion Zone ◽  
Edge Displacement ◽  
Kinetics Of ◽  
Effect Of Surface

ABSTRACTAn analytical model is developed for the effect of surface gradient in ligand density on the adhesion kinetics of a curved elastic membrane with mobile receptors. The displacement and speed of spreading at the edge of the adhesion zone as well as the density profile of receptors along the membrane are predicted as a function of time. According to results, in the diffusion-controlled regime, the front edge displacement of adhesion zone and the rate of membrane spreading decreased with increasing ligand density in a certain direction. Furthermore, the displacement of the edge of the adhesion zone did not scale with the square root of time, as observed on substrates with uniform ligand density.

scholarly journals Inductor coil of the highest possible $$\mathbf {Q}$$

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
A. Rikhter ◽  
M. M. Fogler
Keyword(s):  
Cross Section ◽  
Numerical Optimization ◽  
Square Root ◽  
Q Factor ◽  
Thin Wire ◽  
Inductor Coil ◽  
The Cross

Abstract The geometry of an inductor made of a long thin wire and having the highest possible Q-factor is found by numerical optimization. As frequency increases, the Q-factor first grows linearly and then according to a square-root law, while the cross-section of the optimal coil evolves from near-circular to sickle-shaped.

Kinetics of limestone decomposition in hot metal

2018 ◽  
Vol 115 (6) ◽  
pp. 611 ◽  
Author(s):  
Biao Tang ◽  
Qifu Xiang ◽  
Jing Wang ◽  
Yunlong Zhang ◽  
Xingyi Li ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat Conduction ◽  
Cross Section ◽  
Gas Flow ◽  
Kinetic Equations ◽  
Product Layer ◽  
Hot Metal ◽  
Shrinking Core ◽  
Kinetics Of ◽  
Limestone Calcination

Compared with the traditional limestone calcination, this paper focuses on the conditions and temperature in hot metal where limestone calcines in converter steelmaking process. Considering heat transfer, mass transfer driven by concentration gradient and mass transfer (CO2 gas flow) driven by pressure gradient, macro kinetic models are established to describe limestone decomposition rate respectively. The method of rotating cylinder sample is used in the experiment of limestone decomposition in hot metal. The image processing software Image-Pro Plus is used to analyze the cross section of limestone calcined to get the unreacted core radius of cross section of cylindrical limestone. The results show that the decomposition mechanism of limestone follows the unreacted shrinking core model, the heat conduction of lime layer is the controlling step, the heat conduction and CO2 migration through the product layer determine the rate of limestone decomposition, and the corresponding kinetic equations are established.

Using Collision Cross Section Distributions to Assess the Distribution of Collision Cross Section Values

2020 ◽  
Author(s):  
Aidan France ◽  
Lukasz Migas ◽  
Eleanor Sinclair ◽  
Bruno Bellina ◽  
Perdita Barran
Keyword(s):  
Gas Phase ◽  
Cross Section ◽  
Collision Cross Section ◽  
Drift Cell ◽  
Cell Mobility ◽  
Linear Field ◽  
Field Drift

In this study we explore the use of collision cross section distributions to allow comparability of IM-MS data for proteins on different instruments. We present measurements on seven standard proteins across three IM-MS configurations, namely an Agilent 6560 IM QToF, a Waters Synapt G2 possessing a TWIMS cell and a modified Synapt G2 possessing an RF confining linear field drift cell. Mobility measurements were taken using both He and N<sub>2</sub> as the drift gases. To aid comparability across instruments and best assess the corresponding gas-phase conformational landscapes of the protein ‘standards’ we present the data in the form of averaged collision cross section distributions.

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