Studies of solar and stellar flares using multi-instrument data

Solar flares were first observed by plain eye in white light by William Carrington in England in 1859. Since then these eruptions in the solar corona have intrigued scientists. It is known that flares influence the space weather experienced by the planets in a multitude of ways, for example by causing aurora borealis. Understanding flares is at the epicentre of human survival in space, as astronauts cannot survive the highly energetic particles associated with large flares in high doses without contracting serious radiation disease symptoms, unless they shield themselves effectively during space missions. Flares may be at the epicentre of man s survival in the past as well: it has been suggested that giant flares might have played a role in exterminating many of the large species on Earth, including dinosaurs. Having said that prebiotic synthesis studies have shown lightning to be a decisive requirement for amino acid synthesis on the primordial Earth. Increased lightning activity could be attributed to space weather, and flares. This thesis studies flares in two ways: in the spectral and the spatial domain. We have extracted solar spectra using three different instruments, namely GOES (Geostationary Operational Environmental Satellite), RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) and XSM (X-ray Solar Monitor) for the same flares. The GOES spectra are low resolution obtained with a gas proportional counter, the RHESSI spectra are higher resolution obtained with Germanium detectors and the XSM spectra are very high resolution observed with a silicon detector. It turns out that the detector technology and response influence the spectra we see substantially, and are important to understanding what conclusions to draw from the data. With imaging data, there was not such a luxury of choice available. We used RHESSI imaging data to observe the spatial size of solar flares. In the present work the focus was primarily on current solar flares. However, we did make use of our improved understanding of solar flares to observe young suns in NGC 2547. The same techniques used with solar monitors were applied with XMM-Newton, a stellar X-ray monitor, and coupled with ground based Halpha observations these techniques yielded estimates for flare parameters in young suns. The material in this thesis is therefore structured from technology to application, covering the full processing path from raw data and detector responses to concrete physical parameter results, such as the first measurement of the length of plasma flare loops in young suns.

Direct Top-Quark Width Measurement at CDF

We present a measurement of the top-quark width using $t\bar{t}$ events produced in $p\bar{p}$ collisions at Fermilab's Tevatron collider and collected by the CDF II detector. In the mode where the top quark decays to a $W$ boson and a bottom quark, we select events in which one $W$ decays leptonically and the other hadronically~(lepton + jets channel) . From a data sample corresponding to 4.3~fb$^{-1}$ of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of $W$ boson that decays hadronically are reconstructed for each event and compared with templates of different top-quark widths~($\Gamma_t$) and deviations from nominal jet energy scale~($\Delta_{JES}$) to perform a simultaneous fit for both parameters, where $\Delta_{JES}$ is used for the {\it in situ} calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95$\%$ confidence level~(CL) of $\Gamma_t $

Measurement of the b-hadron production cross section using decays to μ-D0X final states in pp̅ collisions at √s=1.96 TeV

We report a measurement of the production cross section for b hadrons in pp̅ collisions at √s=1.96  TeV. Using a data sample derived from an integrated luminosity of 83  pb-1 collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, Hb, partially reconstructed in the semileptonic decay mode Hb→μ-D0X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum pT>9  GeV/c and rapidity |y|<0.6 is σ=1.30  μb±0.05  μb(stat)±0.14  μb(syst)±0.07  μb(B), where the uncertainties are statistical, systematic, and from branching fractions, respectively. The differential cross sections dσ/dpT are found to be in good agreement with recent measurements of the Hb cross section and well described by fixed-order next-to-leading logarithm predictions.

Measurement of the b-hadron production cross section using decays to μ-D0X final states in pp̅ collisions at √s=1.96 TeV

We report a measurement of the production cross section for b hadrons in pp̅ collisions at √s=1.96  TeV. Using a data sample derived from an integrated luminosity of 83  pb-1 collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, Hb, partially reconstructed in the semileptonic decay mode Hb→μ-D0X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum pT>9  GeV/c and rapidity |y|<0.6 is σ=1.30  μb±0.05  μb(stat)±0.14  μb(syst)±0.07  μb(B), where the uncertainties are statistical, systematic, and from branching fractions, respectively. The differential cross sections dσ/dpT are found to be in good agreement with recent measurements of the Hb cross section and well described by fixed-order next-to-leading logarithm predictions.

Measurement of the b-hadron production cross section using decays to μ-D0X final states in pp̅ collisions at √s=1.96 TeV

We report a measurement of the production cross section for b hadrons in p-pbar collisions at sqrt{s}=1.96 TeV. Using a data sample derived from an integrated luminosity of 83 pb^-1 collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, H_b, partially reconstructed in the semileptonic decay mode H_b -> mu^- D^0 X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum p_T > 9 GeV/c and rapidity |y|

A note on the measurement of travel times using bender and extender elements

By using the bender and extender elements tests, the travel times of the shear (S) and the primary (P) waves were measured for dry sand samples at different relative densities and effective confining pressures. Three methods of interpretations, namely, (i) the first time of arrival, (ii) the first peak to peak, and (iii) the cross-correlation method, were employed. All the methods provide almost a unique answer associated with the P-wave measurements. On contrary, a difference was noted in the arrival times obtained from the different methods for the S-wave due to the near field effect. The resonant column tests in the torsional mode were also performed to check indirectly the travel time of the shear wave. The study reveals that as compared to the S-wave, it is more reliable to depend on the arrival times' measurement for the P-wave. (C) 2010 Elsevier Ltd. All rights reserved.

A note on the measurement of travel times using bender and extender elements

By using the bender and extender elements tests, the travel times of the shear (S) and the primary (P) waves were measured for dry sand samples at different relative densities and effective confining pressures. Three methods of interpretations, namely, (i) the first time of arrival, (ii) the first peak to peak, and (iii) the cross-correlation method, were employed. All the methods provide almost a unique answer associated with the P-wave measurements. On contrary, a difference was noted in the arrival times obtained from the different methods for the S-wave due to the near field effect. The resonant column tests in the torsional mode were also performed to check indirectly the travel time of the shear wave. The study reveals that as compared to the S-wave, it is more reliable to depend on the arrival times’ measurement for the P-wave.

Effect of mode of rolling on development of texture and microstructure in two-phase (alpha plus beta) brass

The evolution of microstructure and texture during deformation of two-phase (alpha + beta) brass was studied for different initial microstructure and texture. The deformation processing involved unidirectional and multi-step cross-rolling. The bulk textures were determined by measuring the pole figures and calculating the orientation distribution function ODF for both alpha (fcc) and beta (bcc) phases, while the microstructure and other microstructural parameters were measured through optical microscopy and scanning electron microscopy with electron back scatter diffraction (SEM-EBSD). Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are significantly different. The variation in initial texture had a pronounced effect on the development of texture in the alpha phase during subsequent deformation. (C) 2010 Elsevier B.V. All rights reserved.

Elimination of common mode voltage and fifth and seventh harmonics in a multilevel inverter fed IM drive using 12-sided polygonal voltage spacephasor

A multilevel inverter with 12-sided polygonal voltage space vector structure is proposed in this paper. The present scheme provides elimination of common mode voltage variation and 5(th) and 7(th) order harmonics in the entire operating range of the drive. The proposed multi level structure is achieved by cascading only the conventional two-level inverters with asymmetrical DC link voltages. The bandwidths problems associated with conventional hexagonal voltage space vector structure current controllers, due to the presence of 5(th) and 7(th) harmonics, in the over modulation region, is absent in the present 12-sided structure. So a linear voltage control up to 12-step operation is possible, from the present twelve sided scheme, with less current control complexity. An open-end winding structure is used for the induction motor drive.

Amplitude Frequency Response Measurement: A Simple Technique

A simple method is described to combine a modern function generator and a digital oscilloscope to configure a setup that can directly measure the amplitude frequency response of a system. This is achieved by synchronously triggering both instruments, with the function generator operated in the ``Linear-Sweep'' frequency mode, while the oscilloscope is operated in the ``Envelope'' acquisition mode. Under these conditions, the acquired envelopes directly correspond to the (input and output signal) spectra, whose ratio yields the amplitude frequency response. The method is easy to configure, automatic, time-efficient, and does not require any external control or interface or programming. This method is ideally suited to impart hands-on experience in sweep frequency response measurements, demonstrate resonance phenomenon in transformer windings, explain the working principle of an impedance analyzer, practically exhibit properties of network functions, and so on. The proposed method is an inexpensive alternative to existing commercial equipment meant for this job and is also an effective teaching aid. Details of its implementation, along with some practical measurements on an actual transformer, are presented.

Multi frequency interrogation of polypyrrole based gas sensors for organic vapors

Polypyrrole exhibits reversible changes in their direct current resistance on exposure to organic volatiles. However, one needs to employ an array of such sensors to discriminate organic volatiles present in a mixture. Hence, polypyrrole based gas sensor is designed for the detection and discrimination of different organic volatiles. Multi frequency impedance measurement technique is used to detect the organic vapors, such as acetone, ethanol and Isopropyl alcohol, in the gas phase, over a frequency range 10 Hz to 2 MHz. The sensor response is monitored by measuring the changes in its capacitance, resistance and the dissipation factor upon exposure to organic volatiles. It is observed that the capacitive property of the sensor is more sensitive to these volatiles than its resistive property. Each volatile responds to the sensor in terms of dissipation factor at specific frequency and found that the peak magnitude has a linear relationship with their concentrations.

Process-kinetics in facing targets sputtering of multi-component oxide thin films

The kinetics of the processes in facing targets sputtering of multicomponent oxide films is presented. The novel configuration of the process exhibits an enhanced ionization efficiency. Discharge diagnostics performed using optical emission spectroscopy revealed strong dependence of plasma parameters on process conditions. Numerical simulation based on thermalization and diffusion of sputtered atoms has been performed to estimate the transport efficiency in off-axis mode. Composition, structure and epitaxial quality of YBa2Cu3O7-x films prepared was found to be strongly dependent on atomic flux ratios (of Cu/Y and Ba/Y) arriving at the substrate, resputtering effect and phase stability of YBa2Cu3O7-x These studies have been shown to be useful in understanding the complex processes that occur in sputtering of multicomponent films. (C) 1999 Elsevier Science S.A. All rights reserved.

Spray characterization of gasoline-ethanol blends from a multi-hole port fuel injector

This work reports the measured spray structure and droplet size distributions of ethanol-gasoline blends for a low-pressure, multi-hole, port fuel injector (PFI). This study presents previously unavailable data for this class of injectors which are widely used in automotive applications. Specifically, gasoline, ethanol, and gasoline-ethanol blends containing 10%, 20% and 50% ethanol were studied using laser backlight imaging, and particle/droplet image analysis (PDIA) techniques. The fuel mass injected, spray structure and tip penetrations, droplet size distributions, and Sauter mean diameter were determined for the blends, at two different injection pressures. Results indicate that the gasoline and ethanol sprays have similar characteristics in terms of spray progression and droplet sizes in spite of the large difference in viscosity. It appears that the complex mode of atomization utilized in these injectors involving interaction of multiple fuel jets is fairly insensitive to the fuel viscosity over a range of values. This result has interesting ramifications for existing gasoline fuel systems which need to handle blends and even pure ethanol, which is one of the renewable fuels of the future. (C) 2012 Elsevier Ltd. All rights reserved.

Decentralized linear quadratic power system stabilizers for multi-machine power systems

Linear quadratic stabilizers are well-known for their superior control capabilities when compared to the conventional lead-lag power system stabilizers. However, they have not seen much of practical importance as the state variables are generally not measurable; especially the generator rotor angle measurement is not available in most of the power plants. Full state feedback controllers require feedback of other machine states in a multi-machine power system and necessitate block diagonal structure constraints for decentralized implementation. This paper investigates the design of Linear Quadratic Power System Stabilizers using a recently proposed modified Heffron-Phillip's model. This model is derived by taking the secondary bus voltage of the step-up transformer as reference instead of the infinite bus. The state variables of this model can be obtained by local measurements. This model allows a coordinated linear quadratic control design in multi machine systems. The performance of the proposed controller has been evaluated on two widely used multi-machine power systems, 4 generator 10 bus and 10 generator 39 bus systems. It has been observed that the performance of the proposed controller is superior to that of the conventional Power System Stabilizers (PSS) over a wide range of operating and system conditions.

Identification of coherent synchronous generators in a multi- machine power system using support vector clustering

This paper illustrates the application of a new technique, based on Support Vector Clustering (SVC) for the direct identification of coherent synchronous generators in a large interconnected Multi-Machine Power Systems. The clustering is based on coherency measures, obtained from the time domain responses of the generators following system disturbances. The proposed clustering algorithm could be integrated into a wide-area measurement system that enables fast identification of coherent clusters of generators for the construction of dynamic equivalent models. An application of the proposed method is demonstrated on a practical 15 generators 72-bus system, an equivalent of Indian Southern grid in an attempt to show the effectiveness of this clustering approach. The effects of short circuit fault locations on coherency are also investigated.