Estimation of raindrop size distribution from spaceborne Radar observations

The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar uses surface reference method to estimate the attenuation encountered in the observation of radar reflectivity. The cumulative attenuation estimated from the surface reference method can be distributed along the radar range using a power law relation between the specific attenuation (k) and reflectivity factor (Z). A physical interpretation of the variability in the k-Z relation can be provided with the normalized drop size distributions. This paper describes an algorithm to estimate the drop size distribution (DSD) parameters from the measured attenuation and reflectivity values obtained from TRMM precipitation radar observations. Coincident data collected with ground polarimetric radar during the TRMM field campaigns is used to cross-validate the estimates of drop size distribution parameters obtained from the TRMM precipitation radar. The results of cross validation show fairly good agreement with the drop size distribution parameters retrieved from TRMM precipitation radar and the ground-radar-based estimates. The algorithm is subsequently used to generate monthly global maps of DSD. The global distribution of DSDs is critically important for development of retrieval algorithms used by the Global Precipitation Mission Radiometers.     

Polarization isolation requirements for linear dual-polarization weather Radar in simultaneous transmission mode of operation

A dual-polarization radar system operating in simultaneous transmission mode of both horizontal and vertical polarization states is a viable implementation if only copolar measurements are needed. The simultaneous transmission of horizontal and vertical polarizations results in an arbitrary elliptical polarization state transmitted, whereas the reception states in horizontal and vertical polarizations are neither copolar nor cross-polar to the transmitted state. Because of this, it is often referred as the hybrid mode. Previous studies have shown that the hybrid mode in the linear horizontal and vertical polarization basis is capable of providing measurements similar to the alternate transmission mode for most measurement conditions. These findings are based on the assumption of perfect sensing systems. This paper presents the results of radar system limitations on hybrid mode measurements that in turn are converted to system requirements. It is shown that the polarization purity requirement is more stringent for the hybrid mode compared to the alternate mode of operation.     

Pulse compression for weather radars

Wideband waveform techniques, such as pulse compression, allow for accurate weather radar measurements in a short data acquisition time. However, for extended targets such as precipitation systems, range sidelobes mask and corrupt observations of weak phenomena occurring near areas of strong echoes. Therefore, sidelobe suppression is extremely important in precisely determining the echo scattering region. A simulation procedure has been developed to accurately describe the signal returns from distributed weather targets, with pulse compression; waveform coding. This procedure is unique and improves on earlier work by taking into account the effect of target reshuffling during the pulse propagation time which is especially important for long duration pulses. The simulation procedure is capable of generating time series from various input range profiles of reflectivity, mean velocity, spectrum width, and SNR. Results from the simulation are used to evaluate the performance of phase coded pulse compression in conjunction with matched and inverse compression filters. The evaluation is based on comparative analysis of the integrated sidelobe level and Doppler sensitivity after the compression process. Pulse compression data from the CSU-CHILL radar is analyzed. The results from simulation and the data analysis show that pulse-compression techniques indeed provide a viable option for faster scanning rates while still retaining good accuracy in the estimates of various parameters that can be measured using a pulsed-Doppler radar. Also, it is established that with suitable sidelobe suppression filters, the range-time sidelobes can be suppressed to levels that are acceptable for operational and research applications     

Enhancing Tool Life in High-Speed Machining of Compacted Graphite Iron (CGI) Using Controlled Modulation

The application of controlled, low-frequency modulation superimposed onto the cutting process??modulation-assisted machining (MAM)??is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500?m/min). The tool life is at least one order of magnitude greater than that in conventional machining. The improvement in wear performance is a consequence of a reduction in the severity of the tool?Cwork contact conditions in MAM: reduction in intimacy of the contact, formation of discrete chips, enhanced fluid action, and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The MAM configuration employing feed-direction modulation appears feasible for implementation at high speeds and offers a potential solution to this challenging class of industrial machining applications.     

FEM Comparison of Ball and Roller Bullgears

A structural finite element model has been developed for calculating the forces transmitted through the rolling elements (load distribution) in a bullgear assembly. The elastic structural model consists of 3-D beam elements used to approximate the global race deflection and non-linear springs that approximate the combined rolling element/raceway contact deflections. For rollers, an upperbound on the contact stress (assuming linear variation of force along the length of the roller) is estimated by modeling the rollers as pairs of nonlinear springs. The finite element approach iteratively solves the contact forces at each, rolling element. Contact stresses are then calculated from the contact, forces using Hertz contact theory. This approach is applied to analyze two proposed designs of ball and crossed roller bearing, bullgear assemblies used for rotating the radar antenna on top of a ship's mast. The loads analyzed include those arising from wind loading and from out-of-flatness of the inner race of the bearings due to deflection of the mast. The distribution of the load and the maximum contact stresses for the proposed bullgear assemblies are estimated and compared. It is found that the maximum contact stress in the crossed roller bearing is less than that in the ball bearing for both types of loads. Furthermore, the analysis shows that the out-of-flatness loading produces significantly higher stresses than wind loading.     

Prominent catalytic activity of mesoporous molecular sieves in the vapor phase dehydration of cyclohexanol to cyclohexene

Cerium incorporated KIT-6 mesoporous materials were synthesized through direct hydrothermal method and characterized by using X-ray diffraction (XRD), nitrogen sorption isotherm (BET), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma -atomic emission spectroscopy (ICP-AES), diffuse reflectance ultraviolet visible spectroscopy (DRS-UV-Vis), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. It appeared that stable cerium ions were inserted into the silica framework of KIT-6, thus generating acid properties in their host materials. The catalytic activity of Ce-KIT-6 materials was evaluated in the vapor phase dehydration of cyclohexanol to cyclohexene and dicyclohexyl ether at different temperatures with various Si/Ce molar ratios. Ce-KIT-6 (25) showed higher activity with 54% cyclohexanol conversion and 64% selectivity to cyclohexene. The catalytic results indicated that Ce-KIT-6 mesoporous materials could be used as versatile and stable acid catalysts.     

Performance Analysis of Wireless Network with Opportunistic Spectrum Sharing via Cognitive Radio Nodes

Cognitive radio (CR) is found to be an emerging key for efficient spectrum utilization. In this paper, spectrum sharing among service providers with the help of cognitive radio has been investigated. The technique of spectrum sharing among service providers to share the licensed spectrum of licensed service providers in a dynamic manner is considered. The performance of the wireless network with opportunistic spectrum sharing techniques is analyzed. Thus, the spectral utilization and efficiency of sensing is increased, the interference is minimized, and the call blockage is reduced.     

Dexterity of gold catalysis in controlling the regioselectivity of cycloaddition reactions

Gold catalysis in the last two decade has witnessed remarkable improvements in terms of efficiency and scope of application in numerous organic reactions. In particular, the unique ability of gold catalysts to activate π-bonds to effect various cycloaddition reactions has received significant attention. However, the catalytic application of gold in creating new opportunities for the regioselective cycloaddition reactions went largely unnoticed. Steric/electronic environment of substrates, ancillary ligand and reaction time seems to be some of the associated regio-directing factors in the gold-catalyzed cycloaddition reactions. Hence, in this review on gold catalyzed regioselective cycloaddition reactions, a complete update about the different types of gold-catalyzed cycloaddition of substrates like alkynes, alkenes, allenes, and ynamides along with the factors governing the selectivity is discussed. Applications towards natural product synthesis and tandem reactions to showcase the synthetic utility of such processes are also highlighted.