Effect of heat treatment on Ag/Y-Ba-Cu-O contact resistance

The contact resistance (R _c) of the metal/YBCO interface has been studied in pressed indium, painted colloidal silver and thermally-evaporated silver contact pads. Indium contacts always show the highest resistance amongst these three systems. In thermally-evaporated Ag contacts, post-deposition thermal treatments show favourable effects on the reduction ofR _c. Heat treatment in oxygen atmosphere in two steps is essential to reduce theR _c values. Significant improvement in obtaining low resistivity contacts has been attributed to the diffusion of silver atoms to grain boundaries at the surface of YBCO and to the enrichment of oxygen-deficient layer at the interface during thermal treatment.     

Functoriality of the BGG Category 𝒪††

This article aims to contribute to the study of algebras with triangular decomposition over a Hopf algebra, as well as the BGG Category 𝒪. We study functorial properties of 𝒪 across various setups. The first setup is over a skew group ring, involving a finite group Γ acting on a regular triangular algebra A. We develop Clifford theory for A?Γ, and obtain results on block decomposition, complete reducibility, and enough projectives. 𝒪 is shown to be a highest weight category when A satisfies one of the “Conditions (S);” the BGG Reciprocity formula is slightly different because the duality functor need not preserve each simple module.

Next, we turn to tensor products of such skew group rings; such a product is also a skew group ring. We are thus able to relate four different types of Categories 𝒪; more precisely, we list several conditions, each of which is equivalent in any one setup, to any other setup, and which yield information about 𝒪.     

Molecular mechanisms of polypeptide aggregation in human diseases

Protein aggregation is implicated in a plethora of neurodegenerative diseases. The proteins found to aggregate in these diseases are unrelated in their native structures and amino acid sequences, but form similar insoluble fibrils with characteristic cross-beta sheet morphologies called amyloid in the aggregated state. While both the mechanism of aggregation and the structure of the aggregates are not fully understood at the molecular level, recent studies provide strong support for the idea that protein aggregation into highly stable, insoluble amyloid structures is a general property of the polypeptide chain. For proteins with a unique native state, it is known that aggregation occurs under conditions that promote native-state destabilization in vitro and in vivo. Taken together, the results of several important recent investigations suggest three broad molecular frameworks that may underlie the conversion of normally soluble peptides and proteins into insoluble amyloid fibrils: (1) edge-strand hydrogen bonding, (2) domain-swapping, and (3) self-association of amyloidogenic fragments. We argue that these underlying scenarios are not mutually exclusive and may be protein-dependent - i.e., a protein with a high content of hinge-regions may aggregate via a runaway domain-swap, whereas a protein with a high content of amyloidogenic fragments may aggregate primarily by the self-association of these fragments. These different scenarios provide frameworks to understand the molecular mechanism of polypeptide aggregation.     

Quantized symplectic oscillator algebras of rank one

A quantized symplectic oscillator algebra of rank 1 is a PBW deformation of the smash product of the quantum plane with . We study its representation theory, and in particular, its category .     

Optical properties of rare earth doped strontium aluminate (SAO) phosphors: A review

After the first news on rare earth (RE) doped strontium aluminate (SAO) phosphors in late 1990s, researchers all over the world geared up to develop stable and efficient persistent phosphors. Scientists studied various features of long lasting phosphors (LLP) and tried to earmark appropriate mechanism. However, about two decades after the discovery of SrAl₂O₄: Eu²⁺, Dy³⁺, the number of persistent luminescent materials is not significant. In this review, we present an overview of the optical characteristics of RE doped SAO phosphors in terms of photoluminescence (PL), thermoluminescence (TL) and afterglow spectra. Also, we refresh the work undertaken to study diverse factors like dopant concentration, temperature, surface energy, role of activator, etc. Simultaneously, some of our important findings on SAO are reported and discussed in the end.     

Insights from the sea: Structural biology of marine polyketide synthases

Covering: up to the end of 2011The world's oceans are a rich source of natural products with extremely interesting chemistry. Biosynthetic pathways have been worked out for a few, and the story is being enriched with crystal structures of interesting pathway enzymes. By far, the greatest number of structural insights from marine biosynthetic pathways has originated with studies of curacin A, a poster child for interesting marine chemistry with its cyclopropane and thiazoline rings, internal cis double bond, and terminal alkene. Using the curacin A pathway as a model, structural details are now available for a novel loading enzyme with remarkable dual decarboxylase and acetyltransferase activities, an Fe(2+)/α-ketoglutarate-dependent halogenase that dictates substrate binding order through conformational changes, a decarboxylase that establishes regiochemistry for cyclopropane formation, and a thioesterase with specificity for β-sulfated substrates that lead to terminal alkene offloading. The four curacin A pathway dehydratases reveal an intrinsic flexibility that may accommodate bulky or stiff polyketide intermediates. In the salinosporamide A pathway, active site volume determines the halide specificity of a halogenase that catalyzes for the synthesis of a halogenated building block. Structures of a number of putative polyketide cyclases may help in understanding reaction mechanisms and substrate specificities although their substrates are presently unknown.     

Exact elliptic compactons in generalized Korteweg–De Vries equations

Using the action principle, and assuming a solitary wave of the generic form u(x,t) = AZ(β(x + q(t)), we derive a general theorem relating the energy, momentum, and velocity of any solitary wave solution of the generalized Korteweg‐De Vries equation K*(l,p). Specifically we find that , where l,p are nonlinearity parameters. We also relate the amplitude, width, and momentum to the velocity of these solutions. We obtain the general condition for linear and Lyapunov stability. We then obtain a two‐parameter family of exact solutions to these equations, which include elliptic and hyper‐elliptic compacton solutions. For this general family we explicitly verify both the theorem and the stability criteria. © 2006 Wiley Periodicals, Inc. Complexity 11: 30–34, 2006     

Surface effects and diffusive phase transition in ferroelectric thin films: A self-consistent approach

A self-consistent Landau phenomenological approach has been used to study the ferroelectric transition in films in the presence of various surface effects such as depolarization and strain. The polarization distribution of the film is computed and its variation with respect to temperature, thickness and strain is determined. The gradual decrease in polarization across the transition shows the diffusive behavior which is confirmed from the soft mode and the dielectric susceptibility analysis. The critical thickness below which ferroelectricity disappears is also computed. The degree of diffuseness in the transition is obtained from the susceptibility exponent which shows more and more diffusive behavior for smaller and smaller film thickness.     

Diffusion of a Ga adatom on the GaAs(001)‐c(4 × 4)‐heterodimer surface: A first principles study

The adsorption and diffusion behavior of a Ga adatom on the GaAs (001)‐c(4 × 4)-heterodimer surface were studied by employing ab initio density functional theory (DFT) computations in the local density approximation. Structural and bonding features of the c(4 × 4)-heterodimer reconstruction surface were examined. A comparison with the c(4 × 4)-ss reconstruction was performed. Minimum energy sites (MES) on the c(4 × 4)-heterodimer surface were located by mapping the potential energy surface for a Ga adatom. Barriers for diffusion of a Ga adatom between the neighboring MES were calculated by using top hopping- and exchange-diffusion mechanisms. We proposed two unique diffusion pathways for a Ga adatom diffusing between the global minimums of two neighboring unit cells. Signature differences between electronic structures of top hopping- and exchange‐diffusion mechanisms were studied for relevant atoms. We observed a higher diffusion barrier for exchange mechanism compared to top hopping.     

Effect of NaF on optical and structural properties of CdxZn1−xS nano crystalline films

This work investigates the effect of NaF on optical and structural properties of nano crystalline Cd_xZn_1?xS films. The Cd_xZn_1?xS films are prepared through chemical bath deposition (CBD) technique in aqueous alkaline bath and their subsequent condensation on substrates. The as-obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–VIS absorption spectroscopy. Micro structural features, obtained from XRD analysis confirm the formation of cubic phase of undoped as well as NaF doped Cd_xZn_1?xS nano particles while SEM observations depict non-uniform distribution of grains. These results show the average grain size of pure as well as NaF doped samples to range from 50 to 90 nm. Tauc's plots, extracted from absorption spectra exhibit absorption to be dominating mainly in blue-green region of visible spectrum. The room-temperature photoluminescence (PL) spectra of Cd_xZn_1?xS samples show a peak around 425 nm, which gets blue shifted for doped sample indicating improvement in PL properties on its addition.