Refraction-based photonic crystal diode

A system composed of air holes in a dielectric host to form two square photonic crystals, with the same orientation and lattice constant but different scatterer radii, making an interface along their body diagonals, is numerically demonstrated to facilitate unidirectional light transmission. Band structure computations are carried out via the plane wave expansion method, whereas finite-difference time-domain simulations are carried out to investigate the transient behavior. Unidirectional light transmission is achieved over two adjacent stop bands along the ΓX direction, which are circumvented in the forward direction by scaling down the wave vector and rotating the surface normal. Contrast ratios as high as 0.9 are attained within the lower stop band.     

Exact Solutions for Fractional Differential-Difference Equations by (G′/G)-Expansion Method with Modified Riemann-Liouville Derivative

In this paper, the ($G′/G$)-expansion method is suggested to establish new exact solutions for fractional differential-difference equations in the sense of modified Riemann–Liouville derivative. The fractional complex transform is proposed to convert a fractional partial differential difference equation into its differential difference equation of integer order. With the aid of symbolic computation, we choose nonlinear lattice equations to illustrate the validity and advantages of the algorithm. It is shown that the proposed algorithm is effective and can be used for many other nonlinear lattice equations in mathematical physics and applied mathematics.     

Symbolic computation of conservation laws and exact solutions of a coupled variable-coefficient modified Korteweg–de Vries system

In this paper we study a generalized coupled variable-coefficient modified Korteweg–de Vries (CVCmKdV) system that models a two-layer fluid, which is applied to investigate the atmospheric and oceanic phenomena such as the atmospheric blockings, interactions between the atmosphere and ocean, oceanic circulations and hurricanes. The conservation laws of the CVCmKdV system are derived using the multiplier approach and a new conservation theorem. In addition to this, a similarity reduction and exact solutions with the aid of symbolic computation are computed.     

Torsion in equivariant cohomology

Partially supported by an NSF grant.     

The effect of carbonaceous contamination on the investigation of the surface oxide on silicon by angle-resolved XPS

The carbon-contaminated native oxide layer on a standard silicon wafer was investigated by angle-resolved signal ratio X-ray photoelectron spectroscopy (AR/SR/XPS). The results, based on intensity measurements of C_1s , O_1s , Si _2p ⁴⁺ and Si^elemental _2p showed the carbon to be ingested into the oxide to a mean depth of 0.4 nm, and the oxide to consist of a fully oxidized layer ( 1 nm) on top, followed by a suboxidic layer (0.8 nm). The conclusions are that the depth location of the carbonaceous contamination is of cardinal importance for the correct interpretation of the oxidic data, and that for well studied systems routine measurements at two take-off angles suffice for quantitative results.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

A simple and selective flow-injection spectrophotometric determination of copper(II) by using acetylsalicylhydroxamic acid

A new simple, and rapid flow-injection spectrophotometric method is developed for the determination of trace amounts of Cu(II) by using a new chromogenic reagent acetylsalicylhydroxamic acid (AcSHA). The method is based on the formation of colored Cu(II)-(AcSHA)₂ complex. The optimum conditions for the chromogenic reaction of Cu(II) with AcSHA is studied and the colored (green) complex is selectively monitored at λ_max 700 nm. With the reagent carrier solvent (dimethylsulfoxide (DMSO) and acetate buffer, pH 4.2) flow-rate of 1 ml min⁻¹, a detection limit (2S) of 1 μg l⁻¹ Cu(II) was obtained at a sampling rate of 80 sample h⁻¹. The calibration graph was linear in the Cu(II) concentration range 5-120 μg l⁻¹. The relative standard deviation (n=10) was 0.64% for a sample containing 60 μg l⁻¹ Cu(II). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied to determine trace amounts of copper(II) in river and seawater samples. The accuracy of the method was demonstrated by the analysis of standard reference materials C12X3500 and C14XHS 50.     

Hexa-BODIPY Linked-Triazole Based on a Cyclotriphosphazene Core as a Highly Selective and Sensitive Fluorescent Sensor for Fe<Superscript>2+</Superscript> Ions

A new type of fluorescent chemosensor based on tethered hexa-borondipyrromethene cyclotriphosphazene platform (HBTC) linked via triazole groups was designed and synthesized. Its sensing behavior toward metal ions was investigated by ultraviolet-visible and fluorescence spectroscopies. Addition of a Fe²⁺ ion to a tetrahydrofuran solution of HBTC gave a visual color change as well as a significantly quenched fluorescence emission, while other tested 19 metal ions induced no color or spectral changes. This compound was found to be highly selective and sensitive for Fe²⁺ with a low limit of detection (2.03 μM) which is, to the best of our knowledge, the superior than the previously studied chemosensors for Fe²⁺.

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Flow injection spectrophotometric determination of iron(III) using diphenylamine-4-sulfonic acid sodium salt

A highly sensitive and very simple spectrophotometric flow-injection analysis (FIA) method for the determination of iron(III) at low concentration levels is presented. The method is based on the measurement of absorbance intensity of the red complex at 410 nm formed by iron(III) and diphenylamine-4-sulfonic acid sodium salt (DPA-4-SA). It is a simple, highly sensitive, fast, and low cost alternative method using the color developing reagent DPA-4-SA in acetate buffer at pH 5.50 and the flow-rate of 1 mL min⁻¹ with the sample throughput of 60 h⁻¹. The method provided a linear determination range between 5 μg L⁻¹ and 200 μg L⁻¹ with the detection limit (3S) of 1 μg L⁻¹ of iron(III) using the injection volume of 20 μL. FIA variables influencing the system performance were optimized. The amount of iron(III) and total iron in river and seawater samples was successfully determined. Repeatability of the measurements was satisfactory at the relative standard deviation of 3.5 % for 5 determinations of 10 μg L⁻¹ iron(III). The accuracy of the method was evaluated using the standard addition method and checked by the analysis of the certified material Std Zn/Al/Cu 43 XZ3F.     

Enhanced visible-light photocatalytic performance of Fe3O4 nanopyramids for water splitting and dye degradation

Journal of Solid State Electrochemistry - Iron oxide (Fe3O4) pyramid nanostructures were synthesized via a co-precipitation method, without using surfactants or template, for photocatalytic and...