Spatial and frequency averaging techniques for a polarimetricscatterometer system

Radar scattering signals from distributed targets exhibit fading due to interference associated with coherent scattering from individual scatterers within the resolution volume. Uncertainty in radar measurements which arises as a result of fading is reduced by averaging independent samples. Independent samples are obtained by collecting the radar returns from nonoverlapping footprints (spatial averaging) and/or nonoverlapping frequencies (frequency agility techniques). An improved formulation of fading characteristics for the spatial averaging and frequency agility technique is derived by taking into account the rough surface scattering process. Kirchhoff's approximation is used to describe rough surface scattering. Expressions for fading decorrelation distance and decorrelation bandwidth are derived. Rough surface scattering measurements are performed between L and S bands. Measured frequency and spatial correlation coefficients show good agreement with theoretical results     

Self-Assembly and Neurotoxicity of β-Amyloid (21–40) Peptide Fragment: The Regulatory Role of GxxxG Motifs

The three GxxxG repeating motifs from the C-terminal region of β-amyloid (Aβ) peptide play a significant role in regulating the aggregation kinetics of the peptide. Mutation of these glycine residues to leucine greatly accelerates the fibrillation process but generates a varied toxicity profile. Using an array of biophysical techniques, we demonstrated the uniqueness of the composite glycine residues in these structural repeats. We used solvent relaxation NMR spectroscopy to investigate the role played by the surrounding water molecules in determining the corresponding aggregation pathway. Notably, the conformational changes induced by Gly³³ and Gly³⁷ mutations result in significantly decreased toxicity in a neuronal cell line. Our results indicate that G³³xxxG³⁷ is the primary motif responsible for Aβ neurotoxicity, hence providing a direct structure–function correlation. Targeting this motif, therefore, can be a promising strategy to prevent neuronal cell death associated with Alzheimer's and other related diseases, such as type II diabetes and Parkinson's.     

Experimental and simulation studies on the effect of suction opening orientation on solar vertical chimney

The zero energy building considered is a single storey building in Tiruchirappalli city retrofitted with various green features. This study investigated the effect of a suction opening orientation on a vertical solar chimney (VSC), integrated into a one-storey building. It was designed, manufactured and tested through selection of different suction openings for the entry of air, including right, left, front, back, both right and left and both front and back sides. Genetic algorithm (GA) calculates maximum air flow rate for a building with VSC for better suction opening, in Tiruchirappalli's dry, environmental conditions. GA is a useful technique for finding an improved suction opening specifically in the presence of a host of independent parameters which are large. The obtained results are related to fluid flow temperature distribution along the chimney, mass flow rate and air change per hour. The findings between the GA and the experimental results show sound agreement.     

Synthesis and characterization of novel poly(aniline-co-m-aminoacetophenone) copolymer nanocomposites using dodecylbenzene sulfonic acid as a soft template

A series of dodecylbenzene sulphonic acid (DBSA) doped poly(aniline-co-m-aminoacetophenone) copolymer composites of different compositions were synthesized in micellar solution of DBSA to obtain nanosphere morphology with enhanced processability. The plausible mechanism for the formation of poly(aniline-co-m-aminoacetophenone)-DBSA copolymer composite has been presented. These DBSA doped copolymer composites were characterized by UV–Visible, FTIR spectroscopy and XRD analysis techniques. UV–Vis absorption spectrum of the composites showed 325 and 637 nm which corresponds to the π–π* and n–π* transition. In FTIR spectroscopy a broad band around 2,924 cm^?1 corresponds to C–H vibration of DBSA indicating good agreement with the characteristic bands of DBSA. The sharp band at 1,292 cm^?1 is assigned to C–N stretching mode of vibration of N–Ph–N units. The X-ray diffraction of composites reveals that these composites are amorphous in nature. The number of diffraction peaks decreased with increase in the m-aminoacetophenone content. It indicates that these composites are amorphous in nature. Morphological studies (SEM) reveal that these composites have a spherical morphology with the average size of 100–200 nm. These composites exhibit electrical conductivity value of 0.744 × 10^?3 S/cm and enhanced solubility than polyaniline. Moreover, at the presented work, the DBSA doped copolymer composites were obtained in high yields by keeping an oxidant to co-monomer ratio of 1:1.     

Effects of random inhomogeneity on radar measurements and rain rateestimation

The authors study the sampling effect on radar measurements of inhomogeneous media and the resultant rain estimation. A two-level drop size distribution (DSD) model is proposed, in which DSD parameters are assumed to be variable for representing the sampling effects. The dependence of statistical moments on the variation of DSD parameters are calculated and applied to radar-based rain estimation     

Hydrothermal synthesis of Ba(Ti, Sn)O3 fine powders and dielectric properties of the corresponding ceramics

Fine powders of submicron-sized crystallites of BaTiO₃ were prepared at 85–130°C by the hydrothermal method, starting from TiO₂.ξH₂O gel and Ba(OH)₂ solution. The products obtained below 110°C incorporated considerable amounts of H₂O and OH⁻ in the lattice. As-prepared BaTiO₃ is cubic and converts to the tetragonal phase after heat treatment at 1200°C, accompanied by the loss of residual OH⁻ ions. Hydrothermal reaction of SnO₂.ξH₂O gel with Ba(OH)₂ at 150–260°C gives rise to the hydrated phase, BaSn(OH)₆.3H₂O, due to the amphoteric nature of SnO₂.ξH₂O which stabilises Sn(OH)₆²⁻ anions in basic media. On heating in air or releasing the pressure in situ at 260°C, BaSn(OH)₆.3H₂O converts to BaSnO₃ through an intermediate, BaSnO(OH)₄. Solid solutions of Ba(Ti,Sn)O₃ are directly formed from (TiO₂ + SnO₂)..ξH₂O gel up to 35 mol% SnO₂. At higher Sn contents, the hydrothermal products are mixtures of BaSn(OH)₆.3H₂O and BaTiO₃, which on annealing at 1000°C result in monophasic Ba(Ti,Sn)O₃. The sintering characteristics and the dielectric properties of the ceramics prepared out of these fine powders are presented. The dielectric properties of fine-grained Ba(Ti,Sn)O₃ ceramics are explained on the basis of the prevailing diffuse phase transition behaviour.     

A Low-cost Reconfigurable Field-programmable Gate Array Based Three-phase Shunt Active Power Filter for Current Harmonic Elimination and Power Factor Constraints

Non-linear loads, such as switched mode power supply, adjustable-speed drives, arc furnaces, etc., result in deterioration of power quality in terms of current harmonics and reactive power demand. Shunt active power filters are widely used to compensate the current harmonics, thereby improving power quality. Digital signal processors and microcontroller units used in digital control of shunt active power filters are constrained by a complex algorithm structure, adaptability, accuracy, the absence of feedback loop delays, and larger execution time. Shunt active power filters require a faster computation update rate to maintain the closed-loop bandwidth, accurate sensing of voltage and current, proper estimation of parameters, and a high frequency pulse-width modulation. In this article, a low-cost single all-on-chip field-programmable gate array implements the digital control of a three-phase shunt active power filter. This proposed implementation scheme has much less execution time and boosts the overall performance of the system. All required tasks of a typical shunt active power filter are implemented with a low-cost single all-on chip field-programmable gate array module that provides freedom to reconfigure for any other applications. Additional features, such as anti-windup, over-sampling, and time multiplexing, are also added to improve the overall performance. The proposed system is designed to meet IEEE 519 and IEC EN 61000-3 recommendations in terms of harmonic elimination and unity power factor requirements. The entire algorithm is coded, processed, and simulated using Xilinx 12.1 ISE Suite to estimate the advantages of the proposed system. This code is also defused on the low-cost single all-on-chip Xilinx Spartan 3A DSP-XC3SD1800 laboratory prototype, and experimental results obtained match with simulated counterparts. The proposed control scheme for the shunt active power filter results in reduces current harmonics under dynamic and steady-state operating conditions.     

MAPMCECCM: a mutual authentication protocol for mobile cloud environment using Chebyshev Chaotic Map

Telecommunication Systems - Cloud services are expanding tremendously in mobile environment with the advent of wireless technology. However, privacy in accessing the cloud services securely is the...