Thermal decomposition of haloethanols: single pulse shock tube and ab initio studies

This paper reports single pulse shock tube and ab initio studies on thermal decomposition of 2-fluoro and 2-chloroethanol at T=1000–1200 K. Both molecules have HX (X = F/Cl) and H2O molecular elimination channels. The CH3CHO formed by HX elimination is chemically active and undergoes secondary decomposition resulting in the formation of CH4, C2H6, and C2H4. A detailed kinetic simulation indicates that the formation of C2H4 could not be quantitatively explained as arising exclusively from secondary CH3CHO decomposition. Contributions from primary radical processes need to be considered to explain C2H4 quantitatively. Ab initio calculations on HX and H2O elimination reactions from the haloethanols at HF, MP2, and DFT levels with various basis sets up to 6/311++G**are reported. It is pointed out that due to strong correlations between A and Eα, comparison of these two parameters between experimental and theoretical results could be misleading.

High resolution facies record on late Holocene flood plain sediments from lower reaches of Narmada Valley, Western India

A high resolution quantitative granulometric record for site Uchediya 21A degrees 43'2.22aEuro(3) N, 73A degrees 6'26.22aEuro(3) E; 10 m a. s. l.] gives understanding towards accretion history of the late Holocene flood plain in the lower reaches of Narmada River. Two sediment facies (sandy and muddy) and seven subfacies (sandy subfacies: St(MS+FS+CS), SmFS+MS, Sl(FS+VFS), and St(MS + CS); muddy subfacies: FmSILT+VFS+FS, FmSILT+VFS (O) and FmSILT+VFS (T)) are identified based on cluster analysis supplemented with sedimentary structures observed in field and other laboratory data. Changes in hydrodynamics are further deduced based on various sedimentological parameters and their ratios leading to arrive at a depositional model.

Towards a broadband chirped pulse Fourier transform microwave spectrometer

This article gives a brief review of microwave spectroscopy and the experimental techniques used for obtaining microwave spectrum of molecules and complexes since 1950s. It presents a brief summary of the pulsed nozzle Fourier transform microwave (PNFTMW) spectrometer, fabricated in our laboratory, and discusses some of the important results obtained using the spectrometer. The most significant among the results from this spectrometer is the direct structural determination of weakly bound complexes involving H2O/H2S. These have challenged the conventional wisdom on hydrogen bonding leading us to propose a modern definition for the same through IUPAC. The limitations of the PNFTMW spectrometer and the need for the new chirped pulse Fourier transform microwave spectrometer are discussed as well. Moreover, preliminary results from our laboratory on generating a 1 A mu s chirped pulse of 1 GHz bandwidth are given.

Numerical analysis on thermoacoustic prime movers for development of pulse tube cryocoolers

Thermo Acoustic Prime Movers (TAPMs) are being considered as the ideal choice for driving the Pulse Tube Cryocoolers replacing the conventional compressors. The advantages are the absence of moving components and they can be driven by low grade energy as such as fuel, gas, solar energy, waste heat etc. While the development of such TAPMs is in progress in our laboratory, their design and fabrication should be guided by numerical modeling and this may be done by several methods such as solving the energy equation 1], enthalpy flow model 2], CFD 3], etc. We have used CFD technique, since it provides a better insight into the velocity and temperature profiles. The analysis is carried out by varying parameters such as (a) temperature difference across the stack, (b) stack and resonator lengths and (c) different working fluids such as air, nitrogen, argon etc. The theoretical results are compared with the experimental data wherever possible and they are in reasonably good agreement with each other. The analysis indicate that (i) larger temperature difference across the stack leads to increased acoustic amplitude, (ii) longer resonator leads to decrease in frequency with lesser amplitude and (iii) there exists an optimal stack length for the best performance of TAPM. These results are presented here.

Development of moving magnet type linear motor for dual piston compressor for pulse tube cryocooler

This paper describes the design, fabrication and testing of a moving magnet type linear motor of dual piston configuration for a pulse tube cryocooler for ground applications. Eight radially magnetized segmented magnets were used to form one set of a magnet ring. Four magnet rings of such type were constructed, in which one pair of rings has north-pole on its outer diameter and south-pole on inner diameter, while the other pair is it's complementary. The magnets were mounted with opposite poles together on the magnet holder with an axial moving shaft having a piston mounted on both ends of the shaft. The shaft movement was restricted to the axial direction by using C-clamp type flexures, mounted on both sides of the shaft. The force requirement for driving the compressor was calculated based on which the electrical circuit of motor is designed by proper selection of wire gauge and Ampere-turns. The flexure spring force estimation was done through simulation using ANSYS 11.0 and was verified experimentally; while the magnet spring force was determined experimentally. The motor with mounted piston was tested using a variable voltage and variable frequency power supply capable of driving 140 watts of load.

Performances of single and two-stage pulse tube cryocoolers under different vacuum levels with and without thermal radiation shields

Single and two-stage Pulse Tube Cryocoolers (PTC) have been designed, fabricated and experimentally studied. The single stage PTC reaches a no-load temperature of similar to 29 K at its cold end, the two-stage PTC reaches similar to 2.9 K in its second stage cold end and similar to 60 K in its first stage cold end. The two-stage Pulse Tube Cryocooler provides a cooling power of similar to 250 mW at 4.2 K. The single stage system uses stainless steel meshes along with Pb granules as its regenerator materials, while the two-stage PTC uses combinations of Pb along with Er3Ni/HoCu2 as the second stage regenerator materials. Normally, the above systems are insulated by thermal radiation shields and mounted inside a vacuum chamber which is maintained at high vacuum. To evaluate the performance of these systems in the possible conditions of loss of vacuum with and without radiation shields, experimental studies have been performed. The heat-in-leak under such severe conditions has been estimated from the heat load characteristics of the respective stages. The experimental results are analyzed to obtain surface emissivities and effective thermal conductivities as a function of interspace pressure.

Space-vector-based hybrid pulse width modulation technique to reduce line current distortion in induction motor drives

Pulse width modulation (PWM) techniques involving different switching sequences are used in space vector-based PWM generation for reducing line current ripple in induction motor drives. This study proposes a hybrid PWM technique employing five switching sequences. The proposed technique is a combination of continuous PWM, discontinuous PWM (DPWM) and advanced bus clamping PWM methods. Performance of the proposed PWM technique is evaluated and compared with those of the existing techniques on a constant volts per hertz induction motor drive. In terms of total harmonic distortion in the line current, the proposed method is shown to be superior to both conventional space vector PWM (CSVPWM) and DPWM over a fundamental frequency range of 32-50 Hz at a given average switching frequency. The reduction in harmonic distortion is about 42% over CSVPWM at the rated speed of the drive.

PULSE-PHASE-RESOLVED SPECTROSCOPY OF VELA X-1 WITH SUZAKU

We present a detailed pulse-phase-resolved spectral analysis of the persistent high-mass X-ray binary pulsar Vela X-1 observed with Suzaku during 2008 June. The pulse profiles exhibit both intensity and energy dependence with multiple peaks at low energies and double peaks at higher energies. The source shows some spectral evolution over the duration of the observation and care has been taken to average over data with minimum spectral variability for the analysis. We model the continuum with a phenomenological partial covering high-energy cutoff model and a more physical partial covering thermal Comptonization model (CompTT) excluding the time ranges having variable hardness ratio and intensity dependence. For both the models, we detect a cyclotron resonant scattering feature (CRSF) and its harmonic at similar to 25 keV and similar to 50 keV. Both the CRSF fundamental and harmonics parameters are strongly variable over the pulse phase, with the ratio of the two line energies deviating from the classical value of 2. The continuum parameters also show significant variation over the pulse phase and give us some idea about the changing physical conditions that are seen with the changing viewing angle at different pulse phases and obscuration by the accretion stream at some pulse phases.

Spectral-spatial MODIS image analysis using swarm intelligence algorithms and region based segmentation for flood assessment

This paper discusses an approach for river mapping and flood evaluation based on multi-temporal time-series analysis of satellite images utilizing pixel spectral information for image clustering and region based segmentation for extracting water covered regions. MODIS satellite images are analyzed at two stages: before flood and during flood. Multi-temporal MODIS images are processed in two steps. In the first step, clustering algorithms such as Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) are used to distinguish the water regions from the non-water based on spectral information. These algorithms are chosen since they are quite efficient in solving multi-modal optimization problems. These classified images are then segmented using spatial features of the water region to extract the river. From the results obtained, we evaluate the performance of the methods and conclude that incorporating region based image segmentation along with clustering algorithms provides accurate and reliable approach for the extraction of water covered region.

Generation of a short-duration ultrawideband chirped-pulse using CRLH transmission lines

In this paper we present the various design issues related to CRLH-Transmission lines for the generation of short duration Ultra-Wideband chirped-pulse. The major parameters of the CRLH Transmission lines affecting the BandWidth are discussed and methods to increase BandWidth are also suggested. Also presented is the role of components of CRLH Transmission lines in determining the chirp duration. The techniques of controlling the chirp duration by regulating these components are also discussed. Simulations results are also included.

Integration of speckle de-noising and image segmentation using synthetic aperture radar image for flood extent extraction

Flood is one of the detrimental hydro-meteorological threats to mankind. This compels very efficient flood assessment models. In this paper, we propose remote sensing based flood assessment using Synthetic Aperture Radar (SAR) image because of its imperviousness to unfavourable weather conditions. However, they suffer from the speckle noise. Hence, the processing of SAR image is applied in two stages: speckle removal filters and image segmentation methods for flood mapping. The speckle noise has been reduced with the help of Lee, Frost and Gamma MAP filters. A performance comparison of these speckle removal filters is presented. From the results obtained, we deduce that the Gamma MAP is reliable. The selected Gamma MAP filtered image is segmented using Gray Level Co-occurrence Matrix (GLCM) and Mean Shift Segmentation (MSS). The GLCM is a texture analysis method that separates the image pixels into water and non-water groups based on their spectral feature whereas MSS is a gradient ascent method, here segmentation is carried out using spectral and spatial information. As test case, Kosi river flood is considered in our study. From the segmentation result of both these methods are comprehensively analysed and concluded that the MSS is efficient for flood mapping.