Hilbert W*-modules and coherent states

Hilbert C*-module valued coherent states was introduced earlier by Ali, Bhattacharyya and Shyam Roy. We consider the case when the underlying C*-algebra is a W*-algebra. The construction is similar with a substantial gain. The associated reproducing kernel is now algebra valued, rather than taking values in the space of bounded linear operators between two C*-algebras.

In situ structural studies on orthorhombic SnS micro-crystals

In situ powder X-ray diffraction (XRD) studies on 3D micro-crystalline tin (II) sulfide (SnS) were carried out at different temperatures. While increasing temperature, the crystal structure of SnS remains stable as orthorhombic, whereas its lattice parameters and unit-cell volume are considerably varied. Further, these 3D micro-crystalline structures have showed a negative thermal expansion along the a-axis and positive expansion along the b- and c-axes. However, the overall drop along the a-axis of SnS crystals is nearly equal to their expansion along the c-axis. The observed changes in the structural properties of SnS micro-crystallites with temperature are discussed and reported.

Performance of telecommunication modules to 0.5µS-100kHz ring wave surges

This paper presents an experimental investigations performed on various electronic components used in telecommunication networks and those used in avionics for the ring wave surge voltages. IEEE Std C 62.41.1-2002 specifies a stringent requirement of waveforms to be applied for the evaluation of telecom components. To meet the necessary requirements in the absence of commercial equipment for generating the required waveforms, special efforts were made to fabricate a ring wave surge generator as per prescribed standards. The developed surge generator is capable of delivering an output of 0.5 mu s-100kHz which meets the requirements of telecom standards prescribed for evaluation of various modules used in low voltage ac power circuits used in communication networks. The results of the experimental investigations obtained on various modules used in communication networks are presented.

Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. Although computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the widely separated length and time scales. Here, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening, resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the mobility anisotropy emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. We expect our results to influence materials fabrication strategies for atomic and block copolymeric polycrystals as well.

Nanoindentation in Crystal Engineering: Quantifying Mechanical Properties of Molecular Crystals

Nanoindentation is a technique for measuring the elastic modulus and hardness of small amounts of materials. This method, which has been used extensively for characterizing metallic and inorganic solids, is now being applied to organic and metalorganic crystals, and has also become relevant to the subject of crystal engineering, which is concerned with the design of molecular solids with desired properties and functions. Through nanoindentation it is possible to correlate molecular-level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid-state reactivity. Recent developments and exciting opportunities in this area are highlighted in this Minireview.

Interaction between a notch and cylindrical voids in aluminum single crystals: Experimental observations and numerical simulations

A combined 3D finite element simulation and experimental study of interaction between a notch and cylindrical voids ahead of it in single edge notch (tension) aluminum single crystal specimens is undertaken in this work. Two lattice orientations are considered in which the notch front is parallel to the crystallographic 10 (1) over bar] direction. The flat surface of the notch coincides with the (010) plane in one orientation and with the (1 (1) over bar1) plane in the other. Three equally spaced cylindrical voids are placed directly ahead of the notch tip. The predicted load-displacement curves, slip traces, lattice rotation and void growth from the finite element analysis are found to be in good agreement with the experimental observations for both the orientations. Finite element results show considerable through-thickness variation in both hydrostatic stress and equivalent plastic slip which, however, depends additionally on the lattice orientation. The through-thickness variation in the above quantities affects the void growth rate and causes it to differ from the center-plane to the free surface of the specimen. (c) 2012 Elsevier Ltd. All rights reserved.

Nucleation dynamics and pool boiling characteristics of high pressure refrigerant using thermochromic liquid crystals

This paper reports an experimental investigation of oscillating temperature field beneath a single isolated nucleation site using a non-invasive TLC (thermochromic liquid crystal) based thermography technique. Empirical correlations are presented to demonstrate the influence of system pressure and wall heat flux on different ebullition characteristics in the nucleate pool boiling regime of refrigerant R-134a. TLC transient response and two-phase flow structure are captured using synchronized, high resolution imaging. It is observed that the area of influence of nucleation site exhibits a two-part distinct transient behavior during the bubble growth period and broadens to a maximum of 1.57 times the bubble diameter at the instant of bubble departure. This is accompanied by a sharp fall of 2.5 degrees C in the local excess temperature at the nucleation site, which results in momentary augmentation (similar to 40%) in the local heat transfer coefficient at the nucleation origin. The enhanced heat transfer rate observed during the bubble peel-off event is primarily due to transient micro-convection in the wake of the retreating bubble. Further, the results indicate that a slight increase in system pressure from 813.6 to 882.5 kPa has no considerable effect on either the wall superheat or the overall heat transfer coefficient and ebullition frequency. In addition, correlations have been obtained for bubble Reynolds number, Jackob number and the dimensionless bubble generation frequency in terms of modified boiling number.

Magnetic and transport relaxation property of La0.85Sr0.15CoO3 single crystals

Here, we present a comprehensive investigation of the dc magnetization and magnetotransport studies on La0.85Sr0.15CoO3 single crystals grown by the optical float zone method. The spin freezing temperature in the ac susceptibility study shifts to lower value at higher dc field and this is well described by the de Almeida-Thouless line which is the characteristic of SG behavior. The Magnetotransport study shows that the sample exhibits a huge negative MR of similar to 70% at 10 K which monotonically decreases with the increase in temperature. Besides, the magnetization and the resistivity relaxation give strong indication that the MR scales with sample's magnetization. In essence, all the present experimental findings evidence the SG behavior of La0.85Sr0.15CoO3 single crystals.

Synthon identification in co-crystals and polymorphs with IR spectroscopy. Primary amides as a case study

IR spectroscopy has been widely employed to distinguish between different crystal forms such as polymorphs, clathrates, hydrates and co-crystals. IR has been used to monitor co-crystal formation and single synthon detection. In this work, we have developed a strategy to identify multiple supramolecular synthons in polymorphs and co-crystals with this technique. The identification of multiple synthons in co-crystals with IR is difficult for several reasons. In this paper, a four step method involving well assigned IR spectral markers that correspond to bonds in a synthon is used. IR spectra of three forms of the co-crystal system, 4-hydroxybenzoic acid: 4,4'-bipyridine (2 : 1), show clear differences that may be attributed to differences in the synthon combinations existing in the forms (synthon polymorphism). These differences were picked out from the three IR spectra and the bands analysed and assigned to synthons. Our method first identifies IR marker bands corresponding to (covalent) bonds in known/model crystals and then the markers are mapped in known co-crystals having single synthons. Thereafter, the IR markers are queried in known co-crystals with multiple synthons. Finally they are queried in unknown co-crystals with multiple synthons. In the last part of the study, the N-H stretching absorptions of primary amides that crystallize with the amide dimers linked in a ladder like chain show two specific absorptions which are used as marker absorptions and all variations of this band structure have been used to provide details on the environment around the dimer. The extended dimer can accordingly be easily distinguished from the isolated dimer.

Analysis of designed beta-hairpin peptides: molecular conformation and packing in crystals

The crystal structures of several designed peptide hairpins have been determined in order to establish features of molecular conformations and modes of aggregation in the crystals. Hairpin formation has been induced using a centrally positioned (D)Pro-Xxx segment (Xxx = (L)Pro, Aib, Ac(6)c, Ala; Aib = alpha-aminoisobutyric acid; Ac(6)c = 1-aminocyclohexane-1-carboxylic acid). Structures of the peptides Boc-Leu-Phe-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe (1), Boc-Leu-Tyr-Val-(D)Pro-(L)Pro-Leu-Phe-Val-OMe (2, polymorphic forms labeled as 2a and 2b), Boc-Leu-Val-Val-(D)Pro-(L)Pro-Leu-Val-Val-OMe (3), Boc-Leu-Phe-Val-(D)Pro-Aib-Leu-Phe-Val-OMe (4, polymorphic forms labeled as 4a and 4b), Boc-Leu-Phe-Val-(D)Pro-Ac(6)c-Leu-Phe-Val-OMe (5) and Boc-Leu-Phe-Val-(D)Pro-Ala-Leu-Phe-Val-OMe (6) are described. All the octapeptides adopt type II' beta-turn nucleated hairpins, stabilized by three or four cross-strand intramolecular hydrogen bonds. The angle of twist between the two antiparallel strands lies in the range of -9.8 degrees to -26.7 degrees. A detailed analysis of packing motifs in peptide hairpin crystals is presented, revealing three broad modes of association: parallel packing, antiparallel packing and orthogonal packing. An attempt to correlate aggregation modes in solution with observed packing motifs in crystals has been made by indexing of crystal faces in the case of three of the peptide hairpins. The observed modes of hairpin aggregation may be of relevance in modeling multiple modes of association, which may provide insights into the structure of insoluble polypeptide aggregates.

H/F isosteric substitution to attest different equi-energetic molecular conformations in crystals

The sequential replacement of aromatic H-atoms by F-atoms in 1,6-bis(phenylcarbonate) hexa-2,4-diyne allows access to its possible iso-energetic ``syn'', ``gauche'' and ``anti'' conformations.

Resolution of Singularities for a Class of Hilbert Modules

Let M be the completion of the polynomial ring C(z) under bar] with respect to some inner product, and for any ideal I subset of C (z) under bar], let I] be the closure of I in M. For a homogeneous ideal I, the joint kernel of the submodule I] subset of M is shown, after imposing some mild conditions on M, to be the linear span of the set of vectors {p(i)(partial derivative/partial derivative(w) over bar (1),...,partial derivative/partial derivative(w) over bar (m)) K-I] (., w)vertical bar(w=0), 1 <= i <= t}, where K-I] is the reproducing kernel for the submodule 2] and p(1),..., p(t) is some minimal ``canonical set of generators'' for the ideal I. The proof includes an algorithm for constructing this canonical set of generators, which is determined uniquely modulo linear relations, for homogeneous ideals. A short proof of the ``Rigidity Theorem'' using the sheaf model for Hilbert modules over polynomial rings is given. We describe, via the monoidal transformation, the construction of a Hermitian holomorphic line bundle for a large class of Hilbert modules of the form I]. We show that the curvature, or even its restriction to the exceptional set, of this line bundle is an invariant for the unitary equivalence class of I]. Several examples are given to illustrate the explicit computation of these invariants.

Gap renormalization of molecular crystals from density-functional theory

Fundamental gap renormalization due to electronic polarization is a basic phenomenon in molecular crystals. Despite its ubiquity and importance, all conventional approaches within density-functional theory completely fail to capture it, even qualitatively. Here, we present a new screened range-separated hybrid functional, which, through judicious introduction of the scalar dielectric constant, quantitatively captures polarization-induced gap renormalization, as demonstrated on the prototypical organic molecular crystals of benzene, pentacene, and C-60. This functional is predictive, as it contains system-specific adjustable parameters that are determined from first principles, rather than from empirical considerations.

Growth and characterization of L-histidinium 2-nitrobenzoate single crystals: A new NLO material

Crystals of a new nonlinear optical (NLO) material, viz., L-histidinium 2-nitrobenzoate (LHNB) (1) were grown by slow evaporation of an aqueous solution containing equimolar concentrations of L-histidine and 2-nitrobenzoic acid. The structure of the title compound which crystallizes in the non-centrosymmetric monoclinic space group P2(1) was elucidated using single crystal X-ray intensity data. The UV-Vis-NIR spectrum of 1 reveals its transparent nature while the vibrational spectra confirm the presence of the functional groups in 1. The thermal stability and second harmonic generation (SHG) conversion efficiency of 1 were also investigated. (C) 2012 Elsevier GmbH. All rights reserved.