Close to Optimal Cell Sensing Ensures the Robustness of Tissue Differentiation Process: The Avian Photoreceptor Mosaic Case

The way that progenitor cell fate decisions and the associated environmental sensing are regulated to ensure the robustness of the spatial and temporal order in which cells are generated towards a fully differentiating tissue still remains elusive. Here, we investigate how cells regulate their sensing intensity and radius to guarantee the required thermodynamic robustness of a differentiated tissue. In particular, we are interested in finding the conditions where dedifferentiation at cell level is possible (microscopic reversibility), but tissue maintains its spatial order and differentiation integrity (macroscopic irreversibility). In order to tackle this, we exploit the recently postulated Least microEnvironmental Uncertainty Principle (LEUP) to develop a theory of stochastic thermodynamics for cell differentiation. To assess the predictive and explanatory power of our theory, we challenge it against the avian photoreceptor mosaic data. By calibrating a single parameter, the LEUP can predict the cone color spatial distribution in the avian retina and, at the same time, suggest that such a spatial pattern is associated with quasi-optimal cell sensing. By means of the stochastic thermodynamics formalism, we find out that thermodynamic robustness of differentiated tissues depends on cell metabolism and cell sensing properties. In turn, we calculate the limits of the cell sensing radius that ensure the robustness of differentiated tissue spatial order. Finally, we further constrain our model predictions to the avian photoreceptor mosaic.     

Study of protein-probe complexation equilibria and protein-surfactant interaction using charge transfer fluorescence probe methyl ester of N,N-dimethylamino naphthyl acrylic acid

In this paper, we demonstrate the interaction between intramolecular charge transfer (ICT) probe—Methyl ester of N,N-dimethylamino naphthyl acrylic acid (MDMANA) with bovine serum albumin (BSA) using absorption and fluorescence emission spectroscopy. The nature of probe protein binding interaction, fluorescence resonance energy transfer from protein to probe and time resolved fluorescence decay measurement predict that the probe molecule binds strongly to the hydrophobic cavity of the protein. Furthermore, the interaction of the anionic surfactant sodium dodecyl sulphate (SDS) with water soluble protein BSA has been investigated using MDMANA as fluorescenece probe. The changes in the spectral characteristics of charge transfer fluorescence probe MDMANA in BSA-SDS environment reflects well the nature of the protein-surfactant binding interaction such as specific binding, non-cooperative binding, cooperative binding and saturation binding.     

Synthesis and study of optical and electrical characteristics of a hybrid structure of single wall carbon nanotubes and silver nanoparticles

Ag nanoparticles of average size 20 nm have been deposited on SWCNT surfaces following a very lucid wet chemical process. The SWCNT/Ag nanohybrid material has been characterized using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) analysis and Raman spectroscopy. Both optical and electrical properties of the hybrid have been studied. The hybrid material has been synthesized at 60 °C and treated to higher temperatures. About three-fold increase in photoluminescence (PL) emission intensity has been achieved when the hybrid sample has been treated to 500 °C. DC conductivity at varying temperatures from 77–473 K has been studied. The conductivity of Ag-decorated SWCNTs increased up to 1.76 times of that of pristine SWCNT at a low temperature of 180 K. This hybrid material can find wide application as conducting filler in polymer composite which other filler materials seldom possess.     

Study of a periodically forced magnetohydrodynamic system using Floquet analysis and nonlinear Galerkin modelling

Nonlinear Dynamics - We present a detailed study of Rayleigh–Bénard magnetoconvection with periodic gravity modulation and uniform vertical magnetic field. Linear stability analysis is...     

Dynamics of prestressed semiflexible polymer chains as a model of cell rheology

We report on a model of a prestressed nonlinear semiflexible polymer chain that links thermally driven dynamics to the creep behavior of living cells. Numerical simulations show that the chain's creep follows a power law with an exponent that decreases with increasing prestress. This is related to the propagation of free energy through the chain in response to stretching, where the propagation speed is regulated by the prestress via the chain's nonlinear elasticity. These results indicate that the main aspects of cell rheology are consistent with the dynamics of single polymer chains under tension.     

Variational wave-function study of the triangular lattice supersolid

We present a variational wave function which explains the behavior of the supersolid state formed by hard-core bosons on the triangular lattice. The wave function is a linear superposition of only and all configurations minimizing the repulsion between the bosons (which it thus implements as a hard constraint). Its properties can be evaluated exactly--in particular, the variational minimization of the energy yields (i) the surprising and initially controversial spontaneous density deviation from half-filling (ii) a quantitatively accurate estimate of the corresponding density wave (solid) order parameter.     

Two-fractal overlap time series: Earthquakes and market crashes

We find prominent similarities in the features of the time series for the (model earthquakes or) overlap of two Cantor sets when one set moves with uniform relative velocity over the other and time series of stock prices. An anticipation method for some of the crashes have been proposed here, based on these observations.      

Sulfur ligand mediated electrochemistry of gold surfaces and nanoparticles: What,how, and why

Gold surfaces and gold nanoparticles are widely used. The surfaces and nanoparticles often have to be coated by sulfur-bound organic ligands, which both provide stability and participate in many desired processes. We overview here what, how, and why it is that the core Au-S surface bond offers such versatile structure and function.

1. Download : Download high-res image (104KB)
2. Download : Download full-size image