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Shiv Nadar University

(SoNS) School of Natural Sciences

We demonstrate doping of nanocrystalline CdS thin films with Co ions by ion implantation at an elevated temperature of 573 K. The modifications caused in structural and optical properties of these films are investigated. Co-doping does not lead to amorphization or formation of any secondary phase precipitate for dopant concentrations in the range of 0.34-10.8 at.% used in the present study. However, we observe a systematic reduction in the d-spacing with increasing cobalt concentration. Optical band gap of CdS does not show any obvious change upon Co-doping. In addition, implantation gives rise to grain growth and increase in the surface roughness. The results are discussed in the light of ion-matter interaction in the keV regime. © The Royal Society of Chemistry 2010.

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Physics

Fulltext

Nanoscale

Effect of substrate temperature on implantation doping of Co in CdS nanocrystalline thin films

We prove two theorems. The first theorem reduces to a scalar situation the well known vector-valued generalization of the Helson-Lowdenslager theorem that characterizes the invariant subspaces of the operator of multiplication by the coordinate function z on the vector-valued Lebesgue space L2(T ℂn). Our approach allows us to prove an equivalent version of the vector-valued Helson-Lowdenslager theorem in a completely scalar setting, thereby eliminating the use of range functions and partial isometries. The other three major advantages provided by our characterization are: (i) we provide precise necessary and sufficient conditions for the presence of reducing subspaces inside simply invariant subspaces; (ii) we give a complete description of the wandering vectors; (iii) we prove the theorem in the setting of all the Lebesgue spaces Lp (0 &lt; p ≤ ∞). Our second theorem generalizes the first theorem along the lines of de Branges' generalization of Beurling's theorem by characterizing those Hilbert spaces that are simply invariant under multiplication by zn and which are contractively contained in Lp (1 ≤ p ≤ ∞). This also generalizes a theorem of Paulsen and Singh [Proc. Amer. Math. Soc. 129 (2000)] as well as the main theorem of Redett [Bull. London Math. Soc. 37 (2005)]. © Instytut Matematyczny PAN, 2010.

Mathematics

Studia Mathematica

A finite multiplicity Helson-Lowdenslager-de Branges theorem

In this work, an extended elliptic function method is proposed and applied to the generalized shallow water wave equation. We systematically investigate on how to classify new exact travelling wave solutions expressible in terms of quasi-periodic elliptic integral functions and doubly periodic Jacobian elliptic functions. The derived new solutions include rational, periodic, singular and solitary wave solutions. An interesting comparison with the canonical procedure is provided. In some cases the obtained elliptic solution has singularity at a certain region in the whole space. For such solutions we have computed the effective region where the obtained solution is free from such a singularity. © 2010 The Royal Swedish Academy of Sciences.

Physica Scripta

New exact solutions of a generalized shallow water wave equation

We continue the previous study on the existence of different intermediate Hamiltonians in type A N-fold supersymmetric systems and carry out an exhaustive investigation on the N=3 case. In contrast with the N=2 case, we find various patterns in the existence of intermediate Hamiltonians due to the presence of two different intermediate positions in a factorized type A 3-fold supercharge. In addition, all the N=3 models are strictly restricted to at most elliptic type, which enables us to make the complete classification of the systems which admit intermediate Hamiltonians. Finally, we show realizations of third-order parasupersymmetry and variant generalized 3-fold superalgebras by such systems. © 2010 Elsevier Inc.

Annals of Physics

Existence of different intermediate Hamiltonians in type A N-fold supersymmetry II. The N=3 case

As NMR Investigation In An Itinerant Ferromagnet PrCoAsO

We study the dynamics of a disease under administration of a vaccine and antiviral drug, where the disease transmits directly from the parents to the offspring (vertical transmission) and also through contact with infective individuals (horizontal transmission). While vaccination to those susceptible reduces the horizontal transmission, administration of the antiviral drug to infected individuals lessens the chance of vertical transmission. Thus the vaccine and antiviral drug play different roles in controlling the disease, which has both vertical and horizontal transmission. We develop a 3D model with Susceptible-Infected-Recovered under vaccination to the susceptible and antiviral treatment to the infected and consider a control theoretic approach using the Pontryagin maximum principle to analyse the cost-effectiveness of the control process. Our results demonstrate that a mixed intervention strategy of vaccination and antiviral drug in a proper ratio is the most effective way to control the disease. We show that cost-effectiveness of both intervention strategies intimately depends on disease-related parameters, such as force of infection, probability of being infected to offspring from infected mothers, loss of immunity or reinfection and also on cost of treatment. © 2010 Taylor & Francis.

Computational and Mathematical Methods in Medicine

Optimal control of vertically transmitted disease: An integrated approach

Computer Physics Communications

A general purpose Fortran 90 electronic structure program for conjugated systems using Pariser--Parr--Pople model

Experimental charge density distributions in two known conformational polymorphs (orange and yellow) of coumarin 314 dye are analyzed based on multipole modeling of X-ray diffraction data collected at 100 K. The experimental results are compared with the charge densities derived from multipole modeling of theoretical structure factors obtained from periodic quantum calculation with density functional theory (DFT) method and B3LYP/6-31G(d,p) level of theory. The presence of disorder at the carbonyl oxygen atom of ethoxycarbonyl group in the yellow form, which was not identified earlier, is addressed here. The investigation of intermolecular interactions, based on Hirshfeld surface analysis and topological properties via quantum theory of atoms in molecule and total electrostatic interaction energies, revealed significant differences between the polymorphs. The differences of electrostatic nature in these two polymorphic forms were unveiled via construction of three-dimensional deformation electrostatic potential maps plotted over the molecular surfaces. The lattice energies evaluated from ab initio calculations on the two polymorphic forms indicate that the yellow form is likely to be the most favorable thermodynamically. The dipole moments derived from experimental and theoretical charge densities and also from Lorentz tensor approach are compared with the single-molecule dipole moments. In each case, the differences of dipole moments between the polymorphs are identified. © 2010 American Chemical Society.

Chemistry

Crystal Growth and Design

Experimental and theoretical charge density analysis of polymorphic structures: The case of coumarin 314 dye

The performance attained by electronic devices incorporating more than a single molecule is in part limited by weak electronic coupling between molecules. By implementing designed supramolecular interactions, chemists have begun taking control of the nanoscale ordering of the active layer in an effort to move beyond the trial and error tuning of the device morphology. This review describes current progress in solid-state devices in which the molecular components possess designed supramolecular interactions - as opposed to non-specific cohesive forces - used to instill or modify functionality. Supramolecular organic devices for applications in solar energy conversion, light-emitting diodes, field-effect transistors, storage and logic functions are covered. © 2010 Elsevier B.V.

Coordination Chemistry Reviews

Harnessing supramolecular interactions in organic solid-state devices: Current status and future potential

Steady state and time-resolved fluorescence spectroscopic techniques have been used to explore the Stokes shift dynamics and rotational relaxation of a dipolar solute probe in molten mixtures of acetamide (CH3CONH 2) with sodium and potassium thiocyanates (Na /KSCN) at T ∼ 318 K and several other higher temperatures. The dipolar solute probe employed for this study is coumarin 153 (C153). Six different fractions (f) of KSCN of the following ternary mixture composition, 0.75CH3CONH2 + 0.25[(1 - f)NaSCN + fKSCN], have been considered. The estimated experimental dynamic Stokes shift for these systems ranges between 1800 and 2200 cm -1 (±250 cm-1), which is similar to what has been observed with the same solute probe in several imidazolium cation based room temperature ionic liquids (RTIL) and in pure amide solvents. Interestingly, this range of estimated Stokes shift, even though not corresponding to the megavalue of static dielectric constant reported in the literature for a binary mixture of molten CH3CONH2 and NaSCN, exhibits a nonmonotonic KSCN concentration dependence. The magnitudes of the dynamic Stokes shift detected in the present experiments are significantly less than the estimated ones, as nearly 40-60% of the total shift is missed due to the limited time resolution employed (full-width at half-maximum of the instrument response function ∼70 ps). The solvation response function, constructed from the detected shifts in these systems, exhibits triexponential decay with the fastest time constant (τ1) in the 10-20 ps range, which might be much shorter if measured with a better time resolution. The second time constant (τ2) lies in the 70-100 ps range, and the third one (τ3) ranges between 300 and 800 ps. Both these time constants (τ2 and τ3) show alkali metal ion concentration dependence and exhibit viscosity decoupling at higher viscosity in the NaSCN-enriched region. Time dependent rotational anisotropy has been found to be biexponential at all mixture compositions studied. Both the average solvation (〈τs〉) and rotation (〈τr〉) times of C153 in these mixtures exhibit fractional power law dependence on medium viscosity (〈τx〉 ∞ νp, x being solvation or rotation). For solvation, p is found to be 0.46, which is very different from that obtained for common polar and nonpolar solvents, and RTILs (p ≈ 1). For rotation, p ≈ 0.65, which is again different from the value (p ≈ 1) obtained for common polar solvents and RTILs but very similar to that (p ≈ 0.6) found for nonpolar solvents. In addition, experimentally measured average rotation times in these mixtures are found to exhibit slip behavior in the low ν/T region, which gradually transforms to subslip as ν/T increases. Calculations using a recently developed semimolecular theory predict a total dynamic Stokes shift for C153 (dipolar solute) in these molten mixtures near ∼1600 cm-1 where the solute-solvent (dipole-dipole) and the ion-solute (ion-dipole) interactions contribute respectively ∼80% and ∼20% to the calculated total shift. Like in experiments, the theoretically predicted solvation response function in the overdamped limit at each mixture composition has been found to be triexponential. The calculations in the underdamped limit, however, suggest a biphasic decay where a composition independent subpicosecond component and a much slower component with the time constant spreading over 150-850 ps contribute equally to constitute the total decay. The calculated average solvation times in this limit are found to be in better agreement with experimental results than the predictions from the overdamped limit. © 2010 American Chemical Society.