Solution Combustion Synthesis of Nanosized Copper Chromite and Its Use as a Burn Rate Modifier in Solid Propellants

Nano sized copper chromite, which is used as a burn rate accelerator for solid propellants, was synthesized by the solution combustion process using citric acid and glycine as fuel. Pure spinel phase copper chromite (CuCr2O4) was synthesized, and the effect of different ratios of Cu-Cr ions in the initial reactant and various calcination temperatures on the final properties of the material were examined. The reaction time for the synthesis with glycine was lower compared to that with citric acid. The synthesized samples from both fuel cycles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area analysis, and scanning electron microscope (SEM). Commercial copper chromite that is currently used in solid propellant formulation was also characterized by the same techniques. XRD analysis shows that the pure spinel phase compound is formed by calcination at 700 degrees C for glycine fuel cycle and between 750 and 800 degrees C for citric acid cycle. XPS results indicate the variation of the oxidation state of copper in the final compound with a change in the Cu-Cr mole ratio. SEM images confirm the formation of nano size spherical shape particles. The variation of BET surface area with calcination temperature was studied for the solution combusted catalyst. Burn rate evaluation of synthesized catalyst was carried out and compared with the commercial catalyst. The comparison between BET surface area and the burn rate depicts that surface area difference caused the variation in burn rate between samples. The reason behind the reduction in surface area and the required modifications in the process are also described.

ZnO and ZnO/polyglycine modified carbon paste electrode for electrochemical investigation of dopamine

Present work describes the characterization of commercially available ZnO and its electrochemical investigation of dopamine in the presence of ascorbic acid. ZnO was characterized by powder XRD, UV-visible absorption, fluorescence, infrared spectroscopy and scanning electron microscopy. The carbon paste electrode was modified with ZnO and ZnO/polyglycine for further electrochemical investigation of dopamine. The modified electrode shows good electrocatalytic activity towards the detection of dopamine with a reduction in overpotential. The ZnO/polyglycine modified carbon paste electrode (CPE/ZnO/Pgl) shows excellent electrochemical enhancement of peak currents for both dopamine (DA) and ascorbic acid (AA) and for simultaneous detection of DA in the presence of high concentrations of AA with 0.214 V oxidation peak potential differences between them at pH 7.4. From the scan rate variation and concentration, the oxidation of DA and AA was found to be adsorption-controlled. The use of CPE/ZnO/Pgl is demonstrated for the detection of DA in blood serum and injection samples. This journal is © The Royal Society of Chemistry 2012.

Nonlinear Refraction and Two-Photon Absorption in Dense 2Bi(2)O(3)-B2O3 Glasses

High density transparent glasses (7.86 g/cc) were fabricated in the 2Bi(2)O(3)-B2O3 (BBO) system. Optical band gap of the obtained glasses was found to be 2.6eV. The refractive index measured for these glasses was 2.25 +/- 0.05 at lambda=543 nm. Nonlinear refraction and absorption studies were carried out on the BBO glasses using z-scan technique a lambda=532 nm of 10 ns pulse width. The nonlinear refractive index obtained was n(2)=12.1x10(-14) cm(2)/W and nonlinear absorption coefficient was beta=15.2 cm/GW. The n(2) and beta values of the BBO glasses were large compared to the other reported high index bismuth based oxide glass systems in the literature. These were attributed to the high density, high linear refractive index, low band gap and two photon absorption associated with these glasses. The electronic origin of large nonlinearities was discussed based on bond-orbital theory.

State Dependent Attempt Rate modeling of single cell IEEE 802.11 WLANs with homogeneous nodes and Poisson packet arrivals

We study a State Dependent Attempt Rate (SDAR) approximation to model M queues (one queue per node) served by the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol as standardized in the IEEE 802.11 Distributed Coordination Function (DCF). The approximation is that, when n of the M queues are non-empty, the (transmission) attempt probability of each of the n non-empty nodes is given by the long-term (transmission) attempt probability of n saturated nodes. With the arrival of packets into the M queues according to independent Poisson processes, the SDAR approximation reduces a single cell with non-saturated nodes to a Markovian coupled queueing system. We provide a sufficient condition under which the joint queue length Markov chain is positive recurrent. For the symmetric case of equal arrival rates and finite and equal buffers, we develop an iterative method which leads to accurate predictions for important performance measures such as collision probability, throughput and mean packet delay. We replace the MAC layer with the SDAR model of contention by modifying the NS-2 source code pertaining to the MAC layer, keeping all other layers unchanged. By this model-based simulation technique at the MAC layer, we achieve speed-ups (w.r.t. MAC layer operations) up to 5.4. Through extensive model-based simulations and numerical results, we show that the SDAR model is an accurate model for the DCF MAC protocol in single cells. (C) 2012 Elsevier B.V. All rights reserved.

Probing ultrafast carrier dynamics, nonlinear absorption and refraction in core-shell silicon nanowires

We investigate the relaxation dynamics of photogenerated carriers in silicon nanowires consisting of a crystalline core and a surrounding amorphous shell, using femtosecond time-resolved differential reflectivity and transmission spectroscopy at 3.15 eV and 1.57 eV photon energies. The complex behaviour of the differential transmission and reflectivity transients is the mixed contributions from the crystalline core and the amorphous silicon on the nanowire surface and the substrate where competing effects of state-filling and photoinduced absorption govern the carrier dynamics. Faster relaxation rates are observed on increasing the photogenerated carrier density. Independent experimental results on crystalline silicon-on-sapphire (SOS) help us in separating the contributions from the carrier dynamics in crystalline core and the amorphous regions in the nanowire samples. Further, single-beam z-scan nonlinear transmission experiments at 1.57 eV in both open- and close-aperture configurations yield two-photon absorption coefficient beta (similar to 3 cm/GW) and nonlinear refraction coefficient gamma (-2.5 x 10 (-aEuro parts per thousand 4) cm(2)/GW).

Large nonlinear refraction and two photon absorption in ferroelectric Bi2VO5.5 thin films

Ferroelectric c-oriented Bi2VO5.5 (BVO) thin films (thickness approximate to 300 nm) were fabricated by pulsed laser deposition on corning glass substrates. Nonlinear refractive index (n(2)) and two photon absorption coefficient (beta) were measured by Z-scan technique at 532 nm wavelength delivering pulses with 10 ns duration. Relatively large values of n(2) = 2.05 +/- 0.2 x 10(-10) cm(2)/W and beta = 9.36 +/- 0.3 cm/MW were obtained for BVO thin films. Origin of the large optical nonlinearities in BVO thin films was discussed based on bond-orbital theory of transition metal oxides. (c) 2012 Elsevier B.V. All rights reserved.

DNA targeting polyaza macrobicyclic dizinc(II) complexes promoting high in vitro caspase dependent anti-proliferative activity against human carcinoma cancer cells

A series of macrobicyclic dizinc(II) complexes Zn2L1-2B](ClO4)(4) (1-6) have been synthesized and characterized (L1-2 are polyaza macrobicyclic binucleating ligands, and B is the N,N-donor heterocyclic base (viz. 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen)). The DNA and protein binding, DNA hydrolysis and anticancer activity of these complexes were investigated. The interactions of complexes 1-6 with calf thymus DNA were studied by spectroscopic techniques, including absorption, fluorescence and CD spectroscopy. The DNA binding constant values of the complexes were found to range from 2.80 x 10(5) to 5.25 x 10(5) M-1, and the binding affinities are in the following order: 3 > 6 > 2 > 5 > 1 > 4. All the dizinc(II) complexes 1-6 are found to effectively promote the hydrolytic cleavage of plasmid pBR322 DNA under anaerobic and aerobic conditions. Kinetic data for DNA hydrolysis promoted by 3 and 6 under physiological conditions give observed rate constants (k(obs)) of 5.56 +/- 0.1 and 5.12 +/- 0.2 h(-1), respectively, showing a 10(7)-fold rate acceleration over the uncatalyzed reaction of dsDNA. Remarkably, the macrobicyclic dizinc(II) complexes 1-6 bind and cleave bovine serum albumin (BSA), and effectively promote the caspase-3 and caspase-9 dependent deaths of HeLa and BeWo cancer cells. The cytotoxicity of the complexes was further confirmed by lactate dehydrogenase enzyme levels in cancer cell lysate and content media.

Texture evolution in high strain rate deformed Cu-10Zn alloy

High strain rate deformation behavior of Cu-10Zn alloy was studied. A weak texture with fine grain size was observed at high strain rate. The weak texture has been attributed to activity of higher number of slip systems under dynamic loading conditions. Twinning has minimal role on texture. (C) 2012 Elsevier B.V. All rights reserved.

Ex Situ X-ray Diffraction, X-ray Absorption Near Edge Structure, Electron Spin Resonance, and Transmission Electron Microscopy Study of the Hydrothermal Crystallization of Vanadium Oxide Nanotubes: An Insight into the Mechanism of Formation

The nucleation and growth of vanadium oxide nanotubes (VOx-NT) have been followed by a combination of numerous ex situ techniques. long the hydrothermal process. Intermediate solid phases extracted at different reaction times have been characterized by powder X-ray diffraction, scanning and transmission electron microscopy, electron spin resonance, and V-K edge :X-ray absorption near-edge structure spectroscopy. The supernatant vanadate solutions extracted during the hydrothermal treatment have been studied by liquid V-51 NMR and flame. spectroscopy. For short durations of the hydrothermal synthesis, the initial V2O5-surfactant intercalate. is progressively transformed into VOx-NT whose crystallization starts to be detected after a hydrothermal treatment of 24 h. Upon heating from 24 h to 7 days, VOx-NT are obtained in larger amount and with an improved crystallinity. The detection of soluble amines and cyclic metavanadate V4O12](4-) in the supernatant solution along the hydrothermal process suggests that VOx-NT result from a dissolution precipitation mechanism. Metavanadate species V4O12](4-) could behave as molecular precursors in the polymerization reactions leading to VOx-NT.

The influence of temperature and strain rate on the deformation response and microstructural evolution during hot compression of a titanium alloy Ti-6Al-4V-0.1B

Hot deformation behavior of a hypoeutectic Ti-6Al-4V-0.1B alloy in (alpha + beta) phase field is investigated in the present study with special reference to flow response, kinetics and microstructural evolution. For a comparison, the base alloy Ti-6Al-4V was also studied under identical conditions. Dynamic recovery of alpha phase occurs at low temperatures while softening due to globularization and/or dynamic recrystallization dominates at high temperatures irrespective of boron addition. Microstructural features for both the alloys display bending and kinking of alpha lamellae for near alpha test temperatures. Unlike Ti-6Al-4V, no sign of instability formation was observed in Ti-6Al-4V-0.1B for any deformation condition except for cavitation around TiB particles, due to deformation incompatibility and strain accumulation at the particle-matrix interface. The absence of macroscopic instabilities and early initiation of softening mechanisms as a result of boron addition has been attributed to microstructural features (e.g. refined prior beta grain and alpha colony size, absence of grain boundary alpha layer, presence of TiB particles at prior beta boundaries, etc.) of the respective alloys prior to deformation. (C) 2012 Elsevier B.V. All rights reserved.

The Role of Strain Rate Response on Tribological Behavior of Metals

In an effort to study the role of strain rate response on the tribological behavior of metals, room temperature experiments were conducted by sliding commercially pure titanium and a-iron pins against an H-11 die steel flats of various surface textures. The steel flat surface textures were specifically prepared to allow for imposing varying amounts of strain rates at the contacting interface during sliding motion. In the experiments, it was observed that titanium (a harder material than iron) formed a transfer layer on H-11 steel surface textures that produced higher strain rates. In contrast, the titanium pins abraded the steel surfaces that produced lower strain rates. The iron pins were found to abrade the H-11 steel surface regardless of the surface texture characteristics. This unique tribological behavior of titanium is likely due to the fact that titanium undergoes adiabatic shear banding at high strain rates, which creates pathways for lower resistance shear planes. These shear planes lead to fracture and transfer layer formation on the surface of the steel flat, which ultimately promotes a higher strain rate of deformation at the asperity level. Iron does not undergo adiabatic shear banding and thus more naturally abrades the surfaces. Overall, the results clear indicated that a materials strain rate response can be an important factor in controlling the tribological behavior of a plastically deforming material at the asperity level. DOI: 10.1115/1.4007675]

Diversity-Rate Trade-off for Fading Channels with Power Control

We consider a complex, additive, white Gaussian noise channel with flat fading. We study its diversity order vs transmission rate for some known power allocation schemes. The capacity region is divided into three regions. For one power allocation scheme, the diversity order is exponential throughout the capacity region. For selective channel inversion (SCI) scheme, the diversity order is exponential in low and high rate region but polynomial in mid rate region. For fast fading case we also provide a new upper bound on block error probability and a power allocation scheme that minimizes it. The diversity order behaviour of this scheme is same as for SCI but provides lower BER than the other policies.

Channel estimation using minimum bit error rate framework for BPSK signals

We consider the design of a linear equalizer with a finite number of coefficients in the context of a classical linear intersymbol-interference channel with additive Gaussian noise for channel estimation. Previous literature has shown that Minimum Bit Error Rate(MBER) based detection has outperformed Minimum Mean Squared Error (MMSE) based detection. We pose the channel estimation problem as a detection problem and propose a novel algorithm to estimate the channel based on the MBER framework for BPSK signals. It is shown that the proposed algorithm reduces BER compared to an MMSE based channel estimation when used in MMSE or MBER detection.

Full-rate full-diversity achieving MIMO precoding with partial CSIT

In this paper, we consider a slow-fading nt ×nr multiple-input multiple-output (MIMO) channel subjected to block fading. Reliability (in terms of achieved diversity order) and rate (in number of symbols transmitted per channel use) are of interest in such channels. We propose a new precoding scheme which achieves both full diversity (nt ×nrth order diversity) as well as full rate (nt symbols per channel use) using partial channel state information at the transmitter (CSIT). The proposed scheme achieves full diversity and improved coding gain through an optimization over the choice of constellation sets. The optimization maximizes dmin2 for our precoding scheme subject to an energy constraint. The scheme requires feedback of nt - 1 angle parameter values, compared to 2ntnr real coefficients in case of full CSIT. Further, for the case of nt × 1 system, we prove that the capacity achieved by the proposed scheme is same as that achieved with full CSIT. Error rate performance results for nt = 3,4,8 show that the proposed scheme performs better than other precoding schemes in the literature; the better performance is due to the choice of the signal sets and the feedback angles in the proposed scheme.

A finite-rate-of-innovation signal sampling perspective of the source-filter model of speech production

We consider the speech production mechanism and the asso- ciated linear source-filter model. For voiced speech sounds in particular, the source/glottal excitation is modeled as a stream of impulses and the filter as a cascade of second-order resonators. We show that the process of sampling speech signals can be modeled as filtering a stream of Dirac impulses (a model for the excitation) with a kernel function (the vocal tract response),and then sampling uniformly. We show that the problem of esti- mating the excitation is equivalent to the problem of recovering a stream of Dirac impulses from samples of a filtered version. We present associated algorithms based on the annihilating filter and also make a comparison with the classical linear prediction technique, which is well known in speech analysis. Results on synthesized as well as natural speech data are presented.