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Shiv Nadar University

(SoNS) School of Natural Sciences

The interrelationship of latency period in viral infection and overall infection process in host community are of critical importance in context of pest control programme. Both of them regulate the overall system stability as they are dynamically linked to predation by natural enemies in the system. The present paper deals with the role of latency period in viral infection through mathematical modeling and analysis. We propose a four dimensional mathematical model with delayed infection in pest community. It is shown that there exists a certain value of delay, say T* such that for T &gt; T* the system exhibits global stability towards disease-free equilibrium. But for T &lt; T* system exhibits stability switches of the endemic equilibrium. Finally, some conclusive remarks have been drawn through numerical simulations of the model. © 2007 Elsevier Inc. All rights reserved.

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Mathematics

Mathematical Biosciences

Role of latency period in viral infection: A pest control model

The object of the present paper is to study an integrated pest management (IPM) problem in an agroecosystem (paddy-fish culture) through mathematical modeling and analysis, where release of sterile males and spraying of pesticide have been used as control measures for pest population. Using optimal analysis of the model, we have shown that restricted and proper use of control measures might enhance the crop production of the system in an economically viable way. The paper also considers the vulnerability of the underlined ecosystem due to the effect of temperature on the pest growth. Using Liapunov-like function, we have found out a suitable range of temperature, where this IPM strategy remains effective. Some important remarks have finally been made on the basis of numerical simulation. © 2006 Elsevier Inc. All rights reserved.

An improved integrated pest management model under 2-control parameters (sterile male and pesticide)

Ion implantation used for doping quartz with photoactive impurity atoms amorphizes the matrix already at moderate fluences. Following our recent studies on dynamic, laser-induced or chemical epitaxy of ion-irradiated α-quartz, this paper focuses on the cathodoluminescence (CL) spectra obtained after Ge, Ba, Rb and double Rb/Ge ion implantation, under the conditions of dynamic or chemical epitaxy. In addition to "intrinsic" subbands in the CL-spectra, several blue and violet bands correlated with the particular implanted ion species were observed. In the case of Ba, nearly complete dynamic epitaxial growth was achieved, but not for Ge. In the case of Rb, full chemical epitaxy was obtained upon annealing in oxygen or air, but the CL output decreased above 1000 K due to Rb outdiffusion. Double Rb/Ge implantation and annealing in air appears as a very promising novel route to achieve high CL light output and full recrystallization. © 2005 Elsevier B.V. All rights reserved.

Physics

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Epitaxy and cathodoluminescence in α-quartz after Ge, Ba and Rb ion implantation

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

Theoretical Investigations of Core-level Spectroscopies in Strongly Correlated Systems My Parents My Teachers

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.

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.