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Shiv Nadar University

(SoNS) School of Natural Sciences

We report the modification of molecular beam epitaxy grown strain-relaxed single crystalline Si1-xGex layers for x=0.5 and 0.7 as a result of irradiation with 100 MeV Au ions at 80 K. The samples were structurally characterized by Rutherford backscattering spectrometry/channeling, transmission electron microscopy (TEM) and high-resolution X-ray diffraction before and after irradiation with fluences of 5×1010, 1×1011 and 1×1012 ions/cm2, respectively. No track formation was detected in both the samples from TEM studies and finally, the crystalline to amorphous phase transformation at 1×1012 ions/cm2 was examined to be higher for Si0.3Ge0.7 layers compared to Si0.5Ge 0.5 layers. © 2005 Elsevier Ltd. All rights reserved.

Physics

World University root node

Solid State Communications

Composition dependent structural modification in relaxed Si 1-xGex films by 100 MeV Au beam

Single-phase Pb1-xMnxS (0.03 ≤ x ≤ 0.37) nanoparticle films were prepared using an electroless solution growth technique. Face centered cubic structure with a decrease of lattice parameter for an increase of x in the alloy films was observed. Composition dependence of optical and electrical properties is discussed. The optical bandgap (Eg) could be varied from 1.50 to 2.50 eV by changing the x in the range 0.03 ≤ x ≤ 0.37 for the films. Effect of the grain size and the effect of alloying on optical properties are distinguished for the ternary nanoparticle films. Variable range hopping has been identified as mechanism for conduction in the p-type semiconductor Pb1-xMnxS nanoparticle films. Mobility μ of the majority carriers shows a decrease with increase in Mn concentration x and follows a T0.4 temperature dependence, indicating the surface scattering of carriers in the nanoparticle films. © 2006 The Electrochemical Society. All rights reserved.

Journal of the Electrochemical Society

Study of solution grown variable bandGap Pb1-xMnxS semiconductor nanoparticle films

The structure of L-valinol [(S)-(+)-2-amino-3-methylbutan-1-ol or hydroxylated L-valine], C5H13NO, has been determined at 100 K by single-crystal X-ray diffraction. The independent atom model geometry, Flack parameter and figures of merit are compared with results from an invariom structure refinement. The latter provides H-atom positions free of independent atom model bias and therefore yields a more accurate hydrogen-bond pattern, and the geometry from invariom refinement shows an improved agreement with results from a quantum chemical geometry optimization. © 2006 International Union of Crystallography.

Chemistry

Acta Crystallographica Section C: Crystal Structure Communications

Invariom-model refinement of L-valinol

Verhandlungen der Deutschen Physikalischen Gesellschaft

The highly distorted hcp lattices of zinc and cadmium: Comparison of different ab-initio approaches

We provide some explicit examples wherein the Schrödinger equation for the Morse potential remains exactly solvable in a position-dependent mass background. Furthermore, we show how in such a context, the map from the full line (-∞, ∞) to the half-line (0, ∞) may convert an exactly solvable Morse potential into an exactly solvable Coulomb one. This generalizes a well-known property of constant-mass problems. © World Scientific Publishing Company.

Fulltext

Modern Physics Letters A

Morse potential and its relationship with the Coulomb in a position-dependent mass background

To lowest order of perturbation theory we show that an equivalence can be established between a PT -symmetric generalized quartic anharmonic oscillator model and a Hermitian position-dependent mass Hamiltonian h. An important feature of h is that it reveals a domain of couplings where the quartic potential could be attractive, vanishing or repulsive. We also determine the associated physical quantities. © Institute of Physics, Academy of Sciences of Czech Republic 2006.

Czechoslovak Journal of Physics

PT-symmetric quartic anharmonic oscillator and position-dependent mass in a perturbative approach

Hematopoietic stem cells (HSCs) possess a distinct ability to perpetuate through self-renewal and to generate progeny that differentiate into mature cells of myeloid and lymphoid lineages. A better understanding of the molecular mechanisms by which HSCs replicate and differentiate from the perspective of developing new approaches for HSC transplantation is necessary for further advances. The interaction of the receptor tyrosine kinase-c-KIT-with its ligand stem cell factor plays a key role in HSC survival, mitogenesis, proliferation, differentiation, adhesion, homing, migration, and functional activation. Evidence that activating site-directed point mutations in the c-KIT gene contributes to its ligand-independent constitutive activation, which induces enhanced proliferation of HSCs, is accumulating. Similarly, and equally important, self-renewal is a process by which HSCs generate daughter cells via division. Self-renewal is necessary for retaining the HSC pool. Therefore, elucidating the molecular machinery that governs self-renewal is of key importance. The transcription factor, HOXB4 is a key molecule that has been reported to induce the in vitro expansion of HSCs via self-renewal. However, critical downstream effector molecules of HOXB4 remain to be determined. This concisely reviewed information on c-KIT and HOXB4 helps us to update our understanding of their function and mechanism of action in self-renewal, proliferation, and differentiation of HSCs, particularly modulation by c-KIT mutant interactions, and HOXB4 overexpression showing certain therapeutic implications. © Mary Ann Liebert, Inc.

Life Sciences

Stem Cells and Development

Stem cell c-KIT and HOXB4 genes: Critical roles and mechanisms in self-renewal, proliferation, and differentiation

The temperature dependent Schottky diode characteristics of epitaxial junctions between Nb:SrTi O3 (Nb concentrations: 0.5%) and Fe3 O4 are studied. Epitaxial thin films of Fe3 O4 were grown on Nb:SrTi O3 substrates by pulsed laser deposition technique. The films and heterointerfaces were characterized by x-ray diffraction, Z -contrast transmission electron microscopy, magnetic susceptibility, four-probe in-plane resistivity, and the temperature dependent junction current-voltage (I-V) characteristics. The nonlinear nature of the characteristics is analyzed within the framework of thermionic emission theory. Junction parameters such as the Schottky barrier height (φB) and ideality factor (η) are extracted. The temperature evolution of these parameters shows interesting and systematic trends, with remarkable changes near the Verwey transition (TV =120 K). The magnetic field dependence of I-V characteristic data is also recorded and a spin polarization of ∼80% is estimated for the magnetite electrode. © 2006 American Institute of Physics.

Journal of Applied Physics

Interfacial characteristics of a Fe 3O 4Nb/(0.5%): SrTiO 3 oxide junction

Detailed investigation of the charge density distribution in concomitant polymorphs of 3-acetylcoumarin in terms of experimental and theoretical densities shows significant differences in the intermolecular features when analyzed based on the topological properties via the quantum theory of atoms in molecules. The two forms, triclinic and monoclinic (Form A and Form B), pack in the crystal lattice via weak C-H⋯O and C-H⋯π interactions. Form A results in a head-to-head molecular stack, while Form B generates a head-to-tail stack. Form A crystallizes in P1̄ (Z′ = 2) and Form B crystallizes in P21/n (Z′ = 1). The electron density maps of the polymorphs demonstrate the differences in the nature of the charge density distribution in general. The charges derived from experimental and theoretical analysis show significant differences with respect to the polymorphic forms. The molecular dipole moments differ significantly for the two forms. The lattice energies evaluated at the HF and DFT (B3LYP) methods with 6-31G** basis set for the two forms clearly suggest that Form A is the thermodynamically stable form as compared to Form B. Mapping of electrostatic potential over the molecular surface shows dominant variations in the electronegative region, which bring out the differences between the two forms. © 2006 American Chemical Society.

Crystal Growth and Design

Topological analysis of charge density distribution in concomitant polymorphs of 3-acetylcoumarin, a case of packing polymorphism

We have illustrated the utility of WTs throughout this chapter, for cleaning, smoothing, and denoising data, as well as the benefits of their direct use as molecular property descriptors. It is clear from the examples cited that this versatile technology can identify and quantify important features within spectra or property distributions of chemical interest for use in both classification and regression models, to achieve near-linear scaling in electronic structure calculations and serve to control the quality of a basis set in ab initio molecular dynamics simulations. The evolution of wavelets in chemistry parallels the development of ever more sophisticated computational methods and hardware performance. In a relatively short period of time, wavelet methods have grown in importance from a noise filter and baseline correction tool to a fundamental component of modern data analysis, computational chemistry, and knowledge discovery. Copyright © 2006 Wiley-VCH, John Wiley & Sons, Inc.