scholarly journals Physical Basis of Large Microtubule Aster Growth

2016 ◽  
Author(s):  
Keisuke Ishihara ◽  
Kirill S. Korolev ◽  
Timothy J. Mitchison
Keyword(s):  
Traveling Waves ◽  
Polymer Networks ◽  
Fixed Number ◽  
Biophysical Model ◽  
Animal Cells ◽  
Spatial Coordination ◽  
Egg Extract ◽  
The Standard Model ◽  
Theoretical Predictions ◽  
Microtubule Aster

AbstractMicrotubule asters - radial arrays of microtubules organized by centrosomes - play a fundamental role in the spatial coordination of animal cells. The standard model of aster growth assumes a fixed number of microtubules originating from the centrosomes. However, aster morphology in this model does not scale with cell size, and we recently found evidence for non-centrosomal microtubule nucleation. Here, we combine autocatalytic nucleation and polymerization dynamics to develop a biophysical model of aster growth. Our model predicts that asters expand as traveling waves and recapitulates all major aspects of aster growth. As the nucleation rate increases, the model predicts an explosive transition from stationary to growing asters with a discontinuous jump of the growth velocity to a nonzero value. Experiments in frog egg extract confirm the main theoretical predictions. Our results suggest that asters observed in large frog and amphibian eggs are a meshwork of short, unstable microtubules maintained by autocatalytic nucleation and provide a paradigm for the assembly of robust and evolvable polymer networks.

scholarly journals Physical basis of large microtubule aster growth

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Keisuke Ishihara ◽  
Kirill S Korolev ◽  
Timothy J Mitchison
Keyword(s):  
Polymer Networks ◽  
Fixed Number ◽  
Biophysical Model ◽  
Large Fish ◽  
Animal Cells ◽  
Spatial Coordination ◽  
Egg Extract ◽  
The Standard Model ◽  
Theoretical Predictions ◽  
Microtubule Aster

Microtubule asters - radial arrays of microtubules organized by centrosomes - play a fundamental role in the spatial coordination of animal cells. The standard model of aster growth assumes a fixed number of microtubules originating from the centrosomes. However, aster morphology in this model does not scale with cell size, and we recently found evidence for non-centrosomal microtubule nucleation. Here, we combine autocatalytic nucleation and polymerization dynamics to develop a biophysical model of aster growth. Our model predicts that asters expand as traveling waves and recapitulates all major aspects of aster growth. With increasing nucleation rate, the model predicts an explosive transition from stationary to growing asters with a discontinuous jump of the aster velocity to a nonzero value. Experiments in frog egg extract confirm the main theoretical predictions. Our results suggest that asters observed in large fish and amphibian eggs are a meshwork of short, unstable microtubules maintained by autocatalytic nucleation and provide a paradigm for the assembly of robust and evolvable polymer networks.

scholarly journals Charming loops in exclusive rare FCNC B-decays

2019 ◽  
Vol 222 ◽  
pp. 01007 ◽  
Author(s):  
Dmitri Melikhov
Keyword(s):  
Standard Model ◽  
Gain Control ◽  
New Physics ◽  
Beyond The Standard Model ◽  
Reliable Control ◽  
B Decays ◽  
Flavour Changing Neutral Currents ◽  
Neutral Currents ◽  
The Standard Model ◽  
Theoretical Predictions

Rare B-decays induced by flavour-changing neutral currents (FCNC) is one of the promising candidates for probing physics beyond the Standard model. However, for identifying potential new physics from the data, reliable control over QCD contributions is necessary. We focus on one of such QCD contributions – the charming loops – that potentially can lead to difficulties in disentangling new physics effects from the observable and discuss the possibility to gain control over theoretical predictions for charming loops.

scholarly journals Minimal biophysical model of combined antibiotic action

2020 ◽  
Author(s):  
Bor Kavčič ◽  
Gašper Tkačik ◽  
Tobias Bollenbach
Keyword(s):  
Drug Interactions ◽  
Resistance Genes ◽  
Drug Effects ◽  
Higher Order ◽  
Biophysical Model ◽  
Entropy Maximization ◽  
Theoretical Predictions ◽  
Physiological Feedback ◽  
Growth Laws ◽  
Predictive Theory

Phenomenological relations such as Ohm’s or Fourier’s law have a venerable history in physics, but are still scarce in biology. This situation restrains predictive theory. Here, we build on bacterial “growth laws,” which capture physiological feedback between translation and cell growth, to construct a minimal biophysical model for the combined action of ribosome-targeting antibiotics. Our model predicts drug interactions like antagonism or synergy solely from responses to individual drugs. We systematically refine the model by including direct physical interactions of different drugs on the ribosome. In a limiting case, our model provides a mechanistic underpinning for recent predictions of higher-order interactions derived using entropy maximization. It further makes parameter-free predictions for combined drug effects on cells carrying resistance genes and for drugs that mimic poor nutrient environments. We show experimentally that resistance genes can drastically alter drug interactions in notable agreement with our theoretical predictions. While minimal, the model is readily adaptable and opens the door to predicting interactions of second and higher-order in a broad range of biological systems.

scholarly journals Higgs-mass predictions in the MSSM and beyond

2021 ◽  
Vol 81 (5) ◽  
Author(s):  
P. Slavich ◽  
S. Heinemeyer ◽  
E. Bagnaschi ◽  
H. Bahl ◽  
M. Goodsell ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Distinctive Feature ◽  
Higgs Mass ◽  
Precise Measurement ◽  
Current Status ◽  
Comprehensive Overview ◽  
The Standard Model ◽  
Supersymmetric Models ◽  
Theoretical Predictions ◽  
The Many

AbstractPredictions for the Higgs masses are a distinctive feature of supersymmetric extensions of the Standard Model, where they play a crucial role in constraining the parameter space. The discovery of a Higgs boson and the remarkably precise measurement of its mass at the LHC have spurred new efforts aimed at improving the accuracy of the theoretical predictions for the Higgs masses in supersymmetric models. The “Precision SUSY Higgs Mass Calculation Initiative” (KUTS) was launched in 2014 to provide a forum for discussions between the different groups involved in these efforts. This report aims to present a comprehensive overview of the current status of Higgs-mass calculations in supersymmetric models, to document the many advances that were achieved in recent years and were discussed during the KUTS meetings, and to outline the prospects for future improvements in these calculations.

scholarly journals Primordial nucleosynthesis with varying fundamental constants

2020 ◽  
Vol 633 ◽  
pp. L11 ◽  
Author(s):  
M. T. Clara ◽  
C. J. A. P. Martins
Keyword(s):  
Standard Model ◽  
Broad Class ◽  
Statistical Significance ◽  
Structure Constant ◽  
Big Bang ◽  
Fine Structure Constant ◽  
Fundamental Constants ◽  
Primordial Nucleosynthesis ◽  
The Standard Model ◽  
Theoretical Predictions

Primordial nucleosynthesis is an observational cornerstone of the Hot Big Bang model and a sensitive probe of physics beyond the standard model. Its success has been limited by the so-called lithium problem, for which many solutions have been proposed. We report on a self-consistent perturbative analysis of the effects of variations in nature’s fundamental constants, which are unavoidable in most extensions of the standard model, on primordial nucleosynthesis, focusing on a broad class of Grand Unified Theory models. A statistical comparison between theoretical predictions and observational measurements of 4He, D, 3He and, 7Li consistently yields a preferred value of the fine-structure constant α at the nucleosynthesis epoch that is larger than the current laboratory one. The level of statistical significance and the preferred extent of variation depend on model assumptions but the former can be more than four standard deviations, while the latter is always compatible with constraints at lower redshifts. If lithium is not included in the analysis, the preference for a variation of α is not statistically significant. The abundance of 3He is relatively insensitive to such variations. Our analysis highlights a viable and physically motivated solution to the lithium problem, which warrants further study.

Tuning the Elasticity of Biopolymer Gels for Optimal Wound Healing

2005 ◽  
Vol 897 ◽  
Author(s):  
Penelope Georges ◽  
Margaret McCormick ◽  
Lisa Flanagan ◽  
Yo-El Ju ◽  
Evelyn Sawyer ◽  
...  
Keyword(s):  
Cell Structure ◽  
Polymer Networks ◽  
Neuronal Cell ◽  
Mesh Size ◽  
Cell Types ◽  
Animal Cells ◽  
Normal Environment ◽  
Biopolymer Gels ◽  
Soft Polymer ◽  
And Function

AbstractSoft polymer networks with large mesh size, not flat rigid surfaces, are the normal environment for most animal cells. Cell structure and function depend on the stiffness of the surfaces on which cells adhere as well as on the type of adhesion complex by which the cell binds its extracellular ligand. Many cell types, including fibroblasts and endothelial cells, switch from a round to spread morphology as stiffness is increased between 1000 and 10,000 Pa. Coincident with the change in morphology are a host of differences in protein phosphorylation levels, expression of integrins, and changes in cytoskeletal protein expression and assembly. In contrast, other cells types such as neutrophils and platelets do not require rigid substrates in order to spread, and neurons extend processes better on soft (50 Pa) materials than on stiffer gels. We compare the stiffness sensing of four cell types: platelets, neurons and astrocytes, a glial cell type derived from embryonic rat brain, and melanoma cells. Astrocytes switch from a round to spread morphology as substrate stiffness increases, but do so over a stiffness range 10 times softer than that over which fibroblasts alter morphology. Stiffness-dependent morphologic changes observed from studies of cells grown on surfaces of protein-laminated polyacrylamide gels that have linear elasticity are also seen when cells are on matrices of natural biopolymers such as fibrin. Biopolymer gels like fibrin can be formed with appropriate stiffness to optimize for neuronal cell survival and patterning, and may have utility for repair of damaged neural tissues. The complex non-linear rheology of fibrin and other gels formed by semi-flexible biopolymers that exhibit strain-stiffening provide additional mechanisms by which cells can respond to and actively remodel the mechanical features of their environment.

scholarly journals CHARM MIXING IN THE STANDARD MODEL AND BEYOND

2006 ◽  
Vol 21 (27) ◽  
pp. 5686-5693 ◽  
Author(s):  
ALEXEY A. PETROV
Keyword(s):  
Cp Violation ◽  
Standard Model ◽  
New Physics ◽  
Mixing Parameters ◽  
The Standard Model ◽  
Theoretical Predictions ◽  
Charm Mixing

The motivation most often cited in searches for [Formula: see text] mixing and CP-violation in charm system lies with the possibility of observing a signal from New Physics which dominates that from the Standard Model. We review recent theoretical predictions and experimental constraints on [Formula: see text] mixing parameters, concentrating on possible effects of New Physics.

scholarly journals Constraints on Theoretical Predictions Beyond the Standard Model from the Casimir Effect and Some Other Tabletop Physics

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 47
Author(s):  
Galina L. Klimchitskaya
Keyword(s):  
Standard Model ◽  
Laboratory Experiments ◽  
Yukawa Potential ◽  
Casimir Effect ◽  
Beyond The Standard Model ◽  
Quantum Vacuum ◽  
Power Type ◽  
Exotic Particles ◽  
The Standard Model ◽  
Theoretical Predictions

We review the hypothetical interactions predicted beyond the Standard Model which could be constrained by using the results of tabletop laboratory experiments. These interactions are described by the power-type potentials with different powers, Yukawa potential, other spin-independent potentials, and by the spin-dependent potentials of different kinds. In all these cases the current constraints on respective hypothetical interactions are considered which follow from the Casimir effect and some other tabletop physics. The exotic particles and constraints on them are discussed in the context of problems of the quantum vacuum, dark energy, and the cosmological constant.

scholarly journals Mixing and CP Violation in the Charm System

2021 ◽  
Vol 71 (1) ◽  
Author(s):  
Alexander Lenz ◽  
Guy Wilkinson
Keyword(s):  
Cp Violation ◽  
Online Publication ◽  
Charm Physics ◽  
Science Volume ◽  
Current Status ◽  
Annual Review ◽  
Publication Date ◽  
Theoretical Understanding ◽  
The Standard Model ◽  
Theoretical Predictions

In recent years charm physics has undergone a renaissance, which has been catalyzed by an unexpected and impressive set of experimental results from the B factories, the Tevatron, and LHCb. The existence of [Formula: see text] oscillations is now well established, and the recent discovery of CP violation in D0 decays has further renewed interest in the charm sector. In this article, we review the current status of charm-mixing and CP-violation measurements and assess their agreement with theoretical predictions within the Standard Model and beyond. We look forward to the great improvements in experimental precision that can be expected over the coming two decades and to the prospects for corresponding advances in theoretical understanding. Expected final online publication date for the Annual Review of Nuclear and Particle Science, Volume 71 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Residual Elastic Strains in Autofrettaged Tubes: Elastic–Ideally Plastic Model Analysis

2006 ◽  
Vol 129 (1) ◽  
pp. 77-81 ◽  
Author(s):  
Alexander M. Korsunsky
Keyword(s):  
Global Minimum ◽  
Elastic Limit ◽  
Treatment Process ◽  
Tube Wall ◽  
Fixed Number ◽  
The Other ◽  
Quadratic Functional ◽  
Theoretical Predictions ◽  
Analytical Formulas ◽  
Elastic Strains

Autofrettage is a treatment process that uses plastic deformation to create a state of permanent residual stress within thick-walled tubes by pressurizing them beyond the elastic limit. The present paper presents explicit analytical formulas for residual elastic strains within the tube wall derived on the basis of the classical elastic–ideally plastic solution. Then the problem is addressed of rational interpretation of the radial and hoop residual elastic strains measured at a fixed number of points. To this end, the mismatch between the experimental measurements and theoretical predictions of the residual elastic strains is represented in the form of quadratic functional, J, the minimum of which is sought in terms of the problem parameters, namely, the material yield stress, σY, and the radial position of the elastic-plastic boundary, c. It is shown that J shows an approximately parabolic variation in terms of either parameter when the other is fixed, and that therefore the global minimum of J can be readily found. This procedure is implemented and applied to a set of experimental data on neutron diffraction measurements (Venter, A.M., de Swardt, R.R., and Kyriacou, S., 2000, J. Strain Anal., 35, pp. 459–469). In conclusion, further applications of this family of interpretation approaches are discussed.

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