A Selective Catalytic Oxidation of Ascorbic Acid at the Aminopyrimidyl Functionalized‐Conductive Polymer Electrode

A simple detection method of ascorbic acid (AA) through selective catalytic oxidation has been developed using a novel conducting polymer poly‐3′‐(2‐aminopyrimidyl)‐2,2′:5′,2“‐terthiophene (pAPTT). The pAPTT electrode showed an excellent selectivity in facilitating the electron transfer of AA and blocked the interferences of cationic species due to the positively charged pAPTT film. This method proved to be effective in the determination of AA in the presence of various biological interfering species. The dynamic range of AA detection was from 10 to 200 µM and the detection limit was 1.4±0.06 µM.     

Synthesis and antimicrobial activity of a new class of methyleneamine‐linked bis‐heterocycles

A new class of methyleneamine‐linked bis‐heterocycles that exhibit antimicrobial activity was synthesized. Bromination of 1 followed by condensation with thiourea gave 3 . The reaction of 3 with propargyl bromide in dry toluene under inert atmosphere led to the formation of 4 . Its subsequent reaction with different aromatic azides 5 using CuSO₄.5H₂O‐sodiumascorbate system in a 2:1 mixture of water and tert‐butylalcohol yielded the title compounds 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j in good yields. The identities of these compounds were confirmed following elemental analysis, IR, ¹H, ¹³C NMR, and mass spectral studies. All the title compounds exhibited pronounced in vitro antibacterial and antifungal activities. J. Heterocyclic Chem., (2011).     

Entrapment and kinetic resolution of stabilized axial and equatorial conformers of spiro-β-lactams

The facile synthesis of the stabilized axial and equatorial conformers of spiro-β-lactams was achieved via entrapment of cyclohexanone imines (Schiff bases) with acetoxyacetyl chloride in a [2 + 2]-cycloaddition reaction followed by their kinetic resolution. The immobilization of the racemic substrates on an inert solid support significantly reduced the reaction time and improved the enantioselectivity of conformers during kinetic resolution. The mechanism of the formation of the spiro-β-lactams was explored using B3LYP/6-31+G* level quantum chemical calculations.     

A 3-approximation algorithm for the facility location problem with uniform capacities

We consider the facility location problem where each facility can serve at most U clients. We analyze a local search algorithm for this problem which uses only the operations of add, delete and swap and prove that any locally optimum solution is no more than 3 times the global optimum. This improves on a result of Chudak and Williamson who proved an approximation ratio of ${3+2\sqrt{2}}$ for the same algorithm. We also provide an example which shows that any local search algorithm which uses only these three operations cannot achieve an approximation guarantee better than 3.     

Thermal annealing effects on the magnetic behavior of Ce2NiSi3

We have investigated the crystallographic, magnetic and thermodynamic properties of the as-cast and annealed Ce₂NiSi₃ alloys, crystallizing in the AlB₂-type hexagonal structure. The DC-magnetic susceptibility data show that the as-cast sample exhibits an antiferromagnetic (AFM) ordering below T_N= 3.8 K, whereas the annealed sample shows, at 4.2 K, a magnetic transition of AFM nature and, around 2.5 K, an additional anomaly. The specific heat shows a peak with at 3.8 K for the as cast sample, which shifts to lower temperatures when the magnetic field increases, consistent with the antiferromagnetic nature of the transition. On the other hand, in the annealed alloy, the maximum of the specific heat peak reaches at 4.2 K, and no additional anomalies were observed. The different magnetic behavior between the as-cast and annealed samples is attributed to thermal effects on the structural disorder of nickel and silicon atoms, as already observed in other isotypic R₂TSi₃ alloys, where R=U or Ce, and T= transition metal.     

Flattop all-fiber wavelength interleaver for DWDM transmission: Design analysis, parameter optimization, fabrication and characterization recipe

Flattop response within the passband is an important desirable feature of any wavelength selective component that goes into a DWDM optical network. In this paper, we report design and fabrication recipe for realizing wavelength interleavers/slicers with flattop wavelength response, configured around unbalanced all-fiber 2-stage Mach-Zehnder interferometers (MZI). Based on a comprehensive analysis, we have developed a design process/algorithm to determine the optimum splitting ratios as well as the relationship between the splitting ratios of the couplers that constitute the 2-stage MZI, to achieve a flattop wavelength response. The implication of the second delay line with respect to its presence in the upper/lower arm of the second stage of the MZI is highlighted through an algebraic analysis. This revealed that there would be corresponding changes in the optimum splitting ratios of the couplers. These features of our design analysis were then exploited to fabricate a wavelength interleaver with a near box-like response, which validated our algorithm. The polarization dependent losses of the device were measured to be ≈ 0.4 dB. Our analysis and fabrication recipe should be useful in the realization of flattop all-fiber wavelength interleavers for deployment in DWDM networks of high spectral efficiency.     

Performance parameters for highly-focused electromagnetic waves

New performance parameters are presented for electromagnetic focusing systems of high numerical aperture. The field in the focal region is expanded into either electric/magnetic dipole components, or transverse electric/magnetic components. The treatments can be applied to the important case of electric dipole waves, where the focused polarization distribution is the same as that of an electric dipole. For the limiting case of a system of unity numerical aperture, the transverse focus for a focused electric dipole field is sharpened up by 19% compared with an aplanatic system with plane-polarized input, while at the same time the focal intensity for a given input power is increased by 17%. This should be contrasted with using a pupil filter, in which case, as the focal spot is made smaller the focal intensity also decreases. Pure TE polarization results in an even smaller central lobe. Other inhomogeneous polarizations can also be investigated as linear combinations of electric/magnetic or TE/TM components.