Designs of all-optical NOR gates using SOA based MZI

The paper investigates the non-linear behavior of semiconductor optical amplifier with Mach–Zehnder interferometer (SOA-MZI) configuration which makes it to work as a logic gate. The two designs of NOR gate based on SOA-MZI have been verified. The basic principal of both designs are same. The summation of data pulses have been taken and inverted to perform a NOR operation. In the design, the first 3 dB coupler creates a phase difference of π/2 in clock pulse and data pulse while passing through two interferometer arms. The clock and data pulses pass through SOA which attenuates the clock pulse wherever the data pulse is present. After passing through second 3 dB coupler a phase difference of π/2 is again created. Therefore, if the clock pulse is in the same phase will be added and if it is out of phase, will be canceled. The designs have been investigated at different bit-rates to achieve higher extinction ratio (ER), Q-factor and bit-error rate (BER) for different pump currents of SOA.     

Design and performance analysis in multiuser optical CDMA systems

The article presents comparative performance analysis of the proposed Optical CDMA system for 32 and 16 users with two dimensional codes. Numerical simulations have been done under interference significant environment, considering noise and dark current at data rates 2.5, 5, 7.5 and 10 Gbps over single mode fiber for transmission distance of more than 270 km. Results illustrate overall good performance, degraded with augment in bit rate and transmission distance, impervious with raise in number of simultaneous active users. Depicts significant performance improvement with inclusion of forward error correction RS (255,239), for low attenuation and chirp factor. It perceived, this is one of the efficient functional techniques for next generation broadband optical networks together with higher security owing to encoding and decoding, as it allow multiple users in the network to access the same fiber channel asynchronously.     

Tuning electrochemical potential of LiCoO2 with cation substitution: first-principles predictions and electronic origin

With a goal to improve the performance of LiCoO₂ as a cathode material in Li-ion batteries, we simulate substitution of various elements (X = Be, Mg, Al, Ga, Si and Ti) for Co using first-principles density functional theory and predict changes in its electrochemical potential. While the electrochemical potential of LiCoO₂ is enhanced with substitution of Be, Mg, Al and Ga for Co, an opposite effect is predicted of Si and Ti substitution. We determine the electronic origin of these changes in electrochemical potential using (a) Bader method of topological analysis of charge density, (b) partial density of electronic states to estimate oxidation states of metal and oxygen, and charge re-distribution upon lithiation. We find that the distribution of electronic charge donated by Li is influenced by the nature of the X–O bond. A larger electron transfer to O (in XO₆ octahedron) upon lithiation leads to stronger Li intercalation and thereby higher electrochemical voltage. Our findings provide a platform for a rational design of cathode materials in Li batteries with enhanced voltage.     

Droplet shape analysis and permeability studies in droplet lipid bilayers

We apply optical manipulation to prepare lipid bilayers between pairs of water droplets immersed in an oil matrix. These droplet pairs have a well-defined geometry allowing the use of droplet shape analysis to perform quantitative studies of the dynamics during bilayer formation and to determine time-dependent values for the droplet volumes, bilayer radius, bilayer contact angle, and droplet center-line approach velocity. During bilayer formation, the contact angle rises steadily to an equilibrium value determined by the bilayer adhesion energy. When there is a salt concentration imbalance between droplets, there is a measurable change in the droplet volume. We present an analytical expression for this volume change and use this expression to calculate the bilayer permeability to water.     

Dopant induced morphologies of ZnS nanoparticles

We have reported the synthesis of cubic (zinc blende) phase ZnS: Ni²⁺ nanoparticles using a simple wet‐chemical method. Synthesized ZnS: Ni²⁺ nanoparticles had been characterized by X‐ray diffraction (XRD) and Energy Dispersive X‐ray (EDX) analysis. Surface morphologies were studied using Scanning Electron Microscopy (SEM). Fourier Transform Infrared (FTIR) spectra of selected samples were also carried out to confirm the presence of capping agent on the surface of the material. We have demonstrated that various morphologies like spherical, tetrapods, sheet and long‐armed multipods are emerged by simple chemical route without any vigorous reaction parameters and changing the concentration of dopant ions only. The probable mechanism for such morphologies has also been suggested.     

Observation of bulk like magnetic ordering below the blocking temperature in nanosized zinc ferrite

We investigated the magnetic behavior of nanosized zinc ferrite with the help of vibrating sample magnetometry and in-field Mössbauer spectroscopy. The nanoparticles of zinc ferrite with crystallite size ranging from 10 to 62 nm were synthesized by a nitrate method. The structure and phase were determined with the help of X-ray diffraction. Attributes of cation inversion were found with the calculated values of lattice parameter. The saturation magnetization decreases with the increase in crystallite size at room temperature, while these values are almost the same at 10 K for all the samples except the one with crystallite size of 10 nm. The thermal magnetization measurement shows a decrease in blocking temperature with increase in particle size for these samples. The synthesized samples exhibit the presence of antiferromagnetic ordering below the blocking temperature as investigated by in-field Mössbauer spectroscopy.     

Selective reductive transformations using samarium diiodide-water

Samarium diiodide (SmI(2)) is one of the most important reductive electron transfer reagents available in the laboratory. Key to the popularity of SmI(2) is the ability of additives and co-solvents to tune the properties of the reagent. Over the last decade water has emerged as a particularly valuable additive, opening up new chemical space and leading to the discovery of unprecedented selectivity and new reactions promoted by SmI(2). In this Feature Article we review recent progress in the application of SmI(2)-H(2)O systems, with an emphasis on mechanistic considerations and the development of new transformations.     

New parasite inhibitors encompassing novel conformationally-locked 5'-acyl sulfamoyl adenosines

We describe the design, synthesis and biological evaluation of conformationally-locked 5'-acyl sulfamoyl adenosine derivatives as new parasitic inhibitors against Trypanosoma and Leishmania. The conformationally-locked (3'-endo, North-type) nucleosides have been synthesized by covalently attaching a 4'-CH(2)-O-2' bridge () across C2'-C4' of adenosine in order to reduce the conformational flexibility of the pentose ring. This is designed to decrease the entropic penalty for complex formation with the target protein, which may improve free-energy of stabilization of the complex leading to improved potency. Conformationally-locked 5'-acyl sulfamoyl adenosine derivatives (16-22) were tested against parasitic protozoans for the first time in this work, and showed potent inhibition of Trypanosoma cruzi, Trypanosoma brucei, Trypanosoma rhodesiense and Leishmania infantum with IC(50) = 0.25-0.51 μM. In particular, the potent 5'-pentanyl acyl sulfamoyl adenosine derivative 17 (IC(50) = 0.25 μM) against intracellular L. infantum amastigotes and Trypanosoma subspecies is interesting in view of its almost insignificant cytotoxicity in murine macrophage host cells (CC(50) >4 μM) and in diploid human fibroblasts MRC-5 cell lines (CC(50) 4 μM). This work also suggests that variable alkyl chain length of the acyl group on the acylsulfamoyl side chain at 5' can modulate the toxicity of 5'-O-sulfamoylnucleoside analogues. This conformationally-locked sulfamoyl adenosine scaffold presents some interesting possibilities for further drug design and lead optimization.     

Microcomputer-based simulation of heat conduction between solid of tapered shape and the fluid

Simulating the heat conduction in between a solid conducting body immersed in fluid at a given temperature is a difficult task, particularly when the body is tapered in shape and the costs have to be kept low. The body in question is cylindrical, symmetrical about z-axis, tapered in shape and has been heated to a high temperature before being immersed into the fluid. The heat conduction equation in cylindrical polar coordinates with all derivative boundary conditions is attempted to be solved in two ways – first analytically making use of Bessel's function and then by numerical modelling with the help of Finite Difference method, and equations thus formed have been solved through ADI explicit and Implicit (Peaceman Rachford) scheme on microcomputer. The paper is an account of work already done on this and includes further possibilities for general solution with analytical methods and a suitable low-cost numerical solution. Also possible analogy with flow of fluids have been explored. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)