Laguerre-Gaussian beam scintillation on slant paths

Scintillation evaluations for Laguerre-Gaussian (LG) beams for slant paths are made using Rytov approximation. On- and off-axis scintillation is formulated and calculated up to several tens of kilometers of slant distances for different zenith angles. Scintillation index variations against radial receiver point and different source sizes are also investigated. In all cases evaluated, it is found that LG beams with higher radial mode numbers result in less scintillation than Gaussian beam. Kolmogorov spectrum function is utilized in the scintillation calculations.     

A collocation approach for solving linear complex differential equations in rectangular domains

In this paper, a collocation method is presented to find the approximate solution of high‐order linear complex differential equations in rectangular domain. By using collocation points defined in a rectangular domain and the Bessel polynomials, this method transforms the linear complex differential equations into a matrix equation. The matrix equation corresponds to a system of linear equations with the unknown Bessel coefficients. The proposed method gives the analytic solution when the exact solutions are polynomials. Numerical examples are included to demonstrate the validity and applicability of the technique and the comparisons are made with existing results. The results show the efficiency and accuracy of the present work. All of the numerical computations have been performed on a computer using a program written in MATLAB v7.6.0 (R2008a). Copyright © 2012 John Wiley & Sons, Ltd.     

Controlling the surface chemistry of graphite by engineered self-assembled peptides

The systematic control over surface chemistry is a long-standing challenge in biomedical and nanotechnological applications for graphitic materials. As a novel approach, we utilize graphite-binding dodecapeptides that self-assemble into dense domains to form monolayer-thick long-range-ordered films on graphite. Specifically, the peptides are rationally designed through their amino acid sequences to predictably display hydrophilic and hydrophobic characteristics while maintaining their self-assembly capabilities on the solid substrate. The peptides are observed to maintain a high tolerance for sequence modification, allowing control over surface chemistry via their amino acid sequence. Furthermore, through a single-step coassembly of two differently designed peptides, we predictably and precisely tune the wettability of the resulting functionalized graphite surfaces from 44° to 83°. The modular molecular structures and predictable behavior of short peptides demonstrated here give rise to a novel platform for functionalizing graphitic materials that offers numerous advantages, including noninvasive modification of the substrate, biocompatible processing in an aqueous environment, and simple fusion with other functional biological molecules.     

On-chip optical filters with designable characteristics based on an interferometer with embedded silicon photonic structures

We demonstrate chip-scale flat-top filters at near-IR wavelengths using negative index photonic crystal based Mach-Zehnder interferometers. Supported by full three-dimensional numerical simulations, we experimentally demonstrate a new approach for engineering high-pass, low-pass, bandpass, and band-reject filters, based on designing the photonic band diagram both within the bandgap frequency region and away from it. We further show that our approach can be used to design filters that have tunable multilevel response for different sections of the spectrum and for different polarizations. This configuration enables deterministic control of the bandwidth and the rejection ratio of filters for integrated photonic circuits.     

Broadband circular polarizer based on high-contrast gratings

A circular polarizer, which is composed of periodic and two-dimensional dielectric high-contrast gratings, is designed theoretically such that a unity conversion efficiency is achieved at λ(0)=1.55 μm. The operation is obtained by the achievement of the simultaneous unity transmission of transverse magnetic and transverse electric waves with a phase difference of π/2, meaning that an optimized geometrical anisotropy is accomplished. By the utilization of the rigorous coupled-wave analysis and finite-difference time-domain methods, it is shown that a percent bandwidth of ～50% can be achieved when the operation bandwidth is defined as the wavelengths for which the conversion efficiency exceeds 0.9.     

NMR, UV, FT-IR, FT-Raman spectra and molecular structure (monomeric and dimeric structures) investigation of nicotinic acid N-oxide: A combined experimental and theoretical study

In this work, the experimental and theoretical UV, NMR, and vibrational features of nicotinic acid N-oxide (abbreviated as NANO, C(6)H(5)NO(3)) were studied. The ultraviolet (UV) absorption spectrum of studied compound that dissolved in water was examined in the range of 200-800nm. FT-IR and FT-Raman spectra in solid state were observed in the region 4000-400cm(-1) and 3500-50cm(-1), respectively. The (1)H and (13)C NMR spectra in DMSO were recorded. The geometrical parameters, energies and the spectroscopic properties of NANO were obtained for all four conformers from density functional theory (DFT) B3LYP/6-311++G(d,p) basis set calculations. There are four conformers, C(n), n=1-4 for this molecule. The computational results identified the most stable conformer of title molecule as the C1 form. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies, were performed by CIS approach. Finally the calculation results were applied to simulate infrared, Raman, and UV spectra of the title compound which show good agreement with observed spectra.     

A detailed investigation of the electronic properties of a multi-layer spherical quantum dot with a parabolic confinement

In this work, we aim a detailed investigation of the electronic properties of a spherical multi-layer quantum dot with and without a hydrogenic impurity. The structure is introduced in the form of core/shell/well/shell layers. The core and well layers are defined by the parabolic electronic potentials. We carry out the effect of the core radius and layer thickness on the energy levels, their wave functions, binding energies of the impurity and the probability distributions. In order to determine the sublevel eigenvalues and eigenfunctions, the Schrödinger equation is solved full numerically by shooting method in the frame of the effective mass approximation. The results are analyzed in detail as a function of the layer thicknesses and their probable physical reasons are tried to be explained. It is found that the electronic properties and impurity binding energies are strongly depending on the layer thicknesses.     

Single-step fabrication of patterned gold film array by an engineered multi-functional peptide

This study constitutes a demonstration of the biological route to controlled nano-fabrication via modular multi-functional inorganic-binding peptides. Specifically, we use gold- and silica-binding peptide sequences, fused into a single molecule via a structural peptide spacer, to assemble pre-synthesized gold nanoparticles on silica surface, as well as to synthesize nanometallic particles in situ on the peptide-patterned regions. The resulting film-like gold nanoparticle arrays with controlled spatial organization are characterized by various microscopy and spectroscopy techniques. The described bio-enabled, single-step synthetic process offers many advantages over conventional approaches for surface modifications, self-assembly and device fabrication due to the peptides' modularity, inherent biocompatibility, material specificity and catalytic activity in aqueous environments. Our results showcase the potential of artificially-derived peptides to play a key role in simplifying the assembly and synthesis of multi-material nano-systems in environmentally benign processes.     

Design, synthesis, and biological activities of some branched carbasugars: construction of a substituted 6-oxabicyclo[3.2.1]nonane skeleton

Transformation of cyclohexa-2,4-diene-1,2-diylbis(methylene) diacetate to various carbasugars is described. Photooxygenation of a cyclohexadiene derivative gave a bicyclicendoperoxide, which was reduced with thiourea to [2-[(acetyloxy)methyl]cyclohexa-2,4-dien-1-yl]methyl acetate. Epoxidation of the remaining double bond followed by epoxide ring-opening and hydrolysis of the acetate groups gave one of the target hexols. The bicyclic endoperoxide was rearranged to a diepoxide with CoTPP. The diepoxide was reacted with sulfamic acid in acetic anhydride, resulting in the formation of a new branched carbasugar as well as in the formation of cyclitols with a 6-oxabicyclo[3.2.1]nonane skeleton. The mechanism of the formation of the products is discussed. The inhibition activity of six cyclitol derivatives was tested against α-glycosidase.     

Symmetries of boundary layer equations of power-law fluids of second grade

A modified power-law fluid of second grade is considered. The model is a combination of power-law and second grade fluid in which the fluid may exhibit normal stresses, shear thinning or shear thickening behaviors. The equations of motion are derived for two dimensional incompressible flows, and from which the boundary layer equations are derived. Symmetries of the boundary layer equations are found by using Lie group theory, and then group classification with respect to power-law index is performed. By using one of the symmetries, namely the scaling symmetry, the partial differential system is transformed into an ordinary differential system, which is numerically integrated under the classical boundary layer conditions. Effects of power-law index and second grade coefficient on the boundary layers are shown and solutions are contrasted with the usual second grade fluid solutions.