Optimal Tc_c of cuprates: role of screening and reservoir layers

We explore the role of charge reservoir layers (CRLs) on the superconducting transition temperature of cuprate superconductors. Specifically, we study the effect of CRLs with efficient short distance dielectric screening coupled capacitively to copper oxide metallic layers. We argue that dielectric screening at short distances and at frequencies of the order of the superconducting gap, but small compared to the Fermi energy can significantly enhance T$_c$, the transition temperature of an unconventional superconductor. We discuss the relevance of our qualitative arguments to a broader class of unconventional superconductors.Comment: 8 Pages, 4 figure

Topological organisation of the phosphatidylinositol 4,5-bisphosphate-phospholipase C resynthesis cycle: PITPs bridge the ER-PM gap

Phospholipase C (PLC) is a receptor-regulated enzyme that hydrolyses phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at the plasma membrane (PM) triggering three biochemical consequences, the generation of soluble inositol 1,4,5-trisphosphate (IP3), membrane-associated diacylglycerol (DG) and the consumption of PM PI(4,5)P2 Each of these three signals triggers multiple molecular processes impacting key cellular properties. The activation of PLC also triggers a sequence of biochemical reactions, collectively referred to as the PI(4,5)P2 cycle that culminates in the resynthesis of this lipid. The biochemical intermediates of this cycle and the enzymes that mediate these reactions are topologically distributed across two membrane compartments, the PM and the endoplasmic reticulum (ER). At the PM, the DG formed during PLC activation is rapidly converted into phosphatidic acid (PA) that needs to be transported to the ER where the machinery for its conversion into PI is localised. Conversely, PI from the ER needs to be rapidly transferred to the PM where it can be phosphorylated by lipid kinases to regenerate PI(4,5)P2 Thus, two lipid transport steps between membrane compartments through the cytosol are required for the replenishment of PI(4,5)P2 at the PM. Here, we review the topological constraints in the PI(4,5)P2 cycle and current understanding how these constraints are overcome during PLC signalling. In particular, we discuss the role of lipid transfer proteins in this process. Recent findings on the biochemical properties of a membrane-associated lipid transfer protein of the PITP family, PITPNM proteins (alternative name RdgBα/Nir proteins) that localise to membrane contact sites are discussed. Studies in both Drosophila and mammalian cells converge to provide a resolution to the conundrum of reciprocal transfer of PA and PI during PLC signalling

Performance Evaluation of Computation Intensive Tasks in Grid

Grid computing is a special type of parallel computing, which allows us to unite pools of servers, storage systems, and networks into a single large virtual super computer. Grid computing has the advantages of solving complex problems in a shorter time and also makes better use of the existing hardware. It can take advantage of underutilized resources to meet business requirements while minimizing additional costs. There are many Grid setup tools available. In this paper, Globus Toolkit, an open source tool for grid enabled applications, is considered. Initially grid is established between two systems running Linux, using Globus Toolkit. A simple matrix multiplication program, which is capable of running both in grid and stand alone systems, is developed. The application is executed in single system varying the order of the matrices. The same application is split into two sub jobs and run on two grid machines with different orders. Finally the results of the execution are compares and the results are presented in graphs. The work can be extended further to find the type of parallelizing suitable for the application developed. Similarly, FP tree algorithm is taken and the data sets are fed into different machine and in stand alone system. A suitable load balancing mechanism for grid application is discussed. The sections in the paper are arranged as following; Introduction to Grid, Grid setup using Globus toolkit, splitting of the matrix application, FP tree algorithm, performance results, future works, conclusion and references

Location of Solution Channels and Sinkholes at Dam Sites and Backwater Areas by Seismic Methods: Part II

Four seismic field methods and a laboratory method are used to determine shear wave propagation velocities and shear moduli for two sites. The four seismic methods are: standard seismic refraction survey, down hole shooting refraction survey, transient Rayleigh wave survey, and crosshole shooting survey. A torsional resonant column apparatus was used for the laboratory tests. The cross hole shooting method gave the best results because direct measurements were made. Criteria for using this method are given. Methods which measure compression wave velocity give inconsistent results because the conversion to shear wave velocity is very sensitive to Poisson\u27s ratio. Laboratory tests data gave consistently low values. Strength reduction due to sampling was one cause advanced. Laboratory tests also showed increase in values with time. Strength and time effect corrections were applied to the laboratory data and then comparisons were made with the field data

Superconductivity from repulsive interactions in the two dimensional electron gas

We present a well-controlled perturbative renormalization group (RG) treatment of superconductivity from short-ranged repulsive interactions in a variety of model two dimensional electronic systems. Our analysis applies in the limit where the repulsive interactions between the electrons are small compared to their kinetic energy.Comment: 10 pages 3 figure

The Drosophila photoreceptor as a model system for studying signalling at membrane contact sites

Several recent studies have demonstrated the existence of membrane contact sites (MCS) between intracellular organelles in eukaryotic cells. Recent exciting studies have also demonstrated the existence of biomolecular interactions at these contact sites in mediating changes in the membrane composition of the cellular compartments. However, the role of such contact sites in regulating organelle function and physiological processes remains less clear. In this review we discuss the existence of a contact site between the plasma membrane (PM) and the endoplasmic reticulum (ER) inDrosophilaphotoreceptors. Further, we discuss the role of specific proteins present at this location in regulating phospholipid turnover and its impact in regulating a physiological process, namely phototransduction

Superconductivity in the repulsive Hubbard model: an asymptotically exact weak-coupling solution

We study the phase diagram of the Hubbard model in the limit where U, the onsite repulsive interaction, is much smaller than the bandwidth. We present an asymptotically exact expression for T$_c$, the superconducting transition temperature, in terms of the correlation functions of the non-interacting system which is valid for arbitrary densities so long as the interactions are sufficiently small. Our strategy for computing T$_c$ involves first integrating out all degrees of freedom having energy higher than an unphysical initial cutoff $\Omega_0$. Then, the renormalization group (RG) flows of the resulting effective action are computed and T$_c$ is obtained by determining the scale below which the RG flows in the Cooper channel diverge. We prove that T$_c$ is independent of $\Omega_0$. Using this method, we find a variety of unconventional superconducting ground states in two and three dimensional lattice systems and present explicit results for T$_c$ and pairing symmetries as a function of the electron concentration.Comment: 18 pages, 17 figure