A power system simulator for transient stability studies

Imperial Users onl

Quasideterminant Darboux solutions of Noncommutative Equations of Langmuir Oscillations

This article encloses some results on nonncommutative analogue of nonabelian equations of Langmuir oscillations. One of the main contributions of this work is to construct the Darbboux transformation for the solution of that equation in noncommutative framework incorporating associated discrete Lax system. Further the standard Darboux transformation on arbitrary eigenfunctions of the Lax system are presented in quasideterminants for few index values. Moreover, these computations include the derivation of noncommutative version of nonabelian discrete nonlinear Schr$\ddot{o}$dinger which coincides with its classical model under commutative limit. The end portion of this article reveals the identity of noncommutative formalism incorporating a derivation of an equation of motion which coincides with its existing commutative form in background zero value of spectral parameter

Transform domain distributed video coding using larger transform blocks

Distributed Video Coding (DVC) displays promising performance at low spatial resolutions but begins to struggle as the resolution increases. One of the limiting aspects is its 4x4 block size of Discrete Cosine Transform (DCT) which is often impractical at higher resolutions. This paper investigates the impact of exploiting larger DCT block sizes on the performance of transform domain DVC at higher spatial resolutions. In order to utilize a larger block size in DVC, appropriate quantisers have to be selected and this has been solved by means of incorporating a content-aware quantisation mechanism to generate image specific quantisation matrix for any DCT block size. Experimental results confirm that the larger 8x8 block size consistently exhibit superior RD performance for CIF resolution sequences compared to the smaller 4x4 block sizes. Significant PSNR improvement has been observed for 16x16 block size at 4CIF resolution with up to 1.78dB average PSNR gain compared to its smaller block alternatives

A content-aware quantisation mechanism for transform domain distributed video coding

The discrete cosine transform (DCT) is widely applied in modern codecs to remove spatial redundancies, with the resulting DCT coefficients being quantised to achieve compression as well as bit-rate control. In distributed video coding (DVC) architectures like DISCOVER, DCT coefficient quantisation is traditionally performed using predetermined quantisation matrices (QM), which means the compression is heavily dependent on the sequence being coded. This makes bit-rate control challenging, with the situation exacerbated in the coding of high resolution sequences due to QM scarcity and the non-uniform bit-rate gaps between them. This paper introduces a novel content-aware quantisation (CAQ) mechanism to overcome the limitations of existing quantisation methods in transform domain DVC. CAQ creates a frame-specific QM to reduce quantisation errors by analysing the distribution of DCT coefficients. In contrast to the predetermined QM that is applicable to only 4x4 block sizes, CAQ produces QM for larger block sizes to enhance compression at higher resolutions. This provides superior bit-rate control and better output quality by seeking to fully exploit the available bandwidth, which is especially beneficial in bandwidth constrained scenarios. In addition, CAQ generates superior perceptual results by innovatively applying different weightings to the DCT coefficients to reflect the human visual system. Experimental results corroborate that CAQ both quantitatively and qualitatively provides enhanced output quality in bandwidth limited scenarios, by consistently utilising over 90% of available bandwidth

Failure Behavior of Pultruded GFRP Members Under Combined Bending and Torsion

Glass fiber reinforced polymer (GFRP) composite sections, manufactured through pultrusion process, are known for their high strength-to-weight ratio, corrosion resistance, low thermal conductivity, electric and magnetic transparency, low life cycle cost and ease of fabrication. They are being widely applied in infrastructure systems.;The load response of thin-walled GFRP composite sections is different from that of isotropic slender members. For instance, stress variation exists across the wall thickness and the FRP members are more prone to warping and local buckling including shear-lag. The literature survey revealed that the response of pultruded GFRP sections under combined bending and torsion has not yet been studied both in terms of the strength and stiffness.;Thru this research, the behavior of full scale sections was investigated under bending, torsion and combined bending and torsion. The shapes under investigation include circular, square and wide-flange with dimensions from 2 to 6 and lengths from 24 to 144 . The analytical part is based on modified flexural and torsional theories for anisotropic materials.;Due to the absence of any formulation on combined bending and torsion of orthotropic sections, the formulae for isotropic sections were extended for orthotropic ones. Some finite element analysis models were also included to make a comparison.;The experimental work consists of (i) determining the laminate properties at coupon level through tension-tests, shear-tests, burnout-tests and microscopy, and (ii) investigating the behavior of full-length samples under 3-point bending, pure torsion and combined bending and torsion. Under torsion and combined loading, a dedicated apparatus was designed, fabricated, instrumented and calibrated at WVU-CFC Major Units laboratory. This apparatus is capable of incorporating samples of cross-sections up to 6 x6 and lengths up to 144 ; with the angle of twist measurement ranging from +60° to -60°.;It was found from coupon tests that strength and modulus values are measurable with a reasonable range of accuracy, but fiber alignment and fiber volume fraction may vary along the cross-section. The bending behavior of full-length closed-sections was controlled by strength and that of wide-flange sections was due to flange-buckling. The torsional behavior of closed sections was also strength controlled, while the wide-flange section practically showed no torsional strength. The behavior under combined bending and torsion was influenced by principal stresses and maximum shear stresses under the effect of compressive bending and torsional shear stresses. On the T/Tmax - M/Mmax interaction curve, some of the data-points agreed-well with the ideal curve, while the others lay beyond that. The reasons of deviation were investigated to be load rate, variations in fiber content and different types of losses in the apparatus

Optimization and validation of high performance liquid chromatography-ultra violet method for quantitation of metoprolol in rabbit plasma: application to pharmacokinetic studies

Purpose: To develop a sensitive, simple and validated high performance liquid chromatography (HPLC) analytical method for the determination of metoprolol tartrate in rabbit plasma.Methods: Mobile phase of methanol and 50 mM ammonium dihydrogen phosphate solution (50:50) at pH 3.05 was used for separation of metoprolol on BDS hypersil C18 column at a wavelength of 223 nm. Flow rate and retention time were 0.6 mL/min and 7.4 min, respectively. For pharmacokinetic study, rabbits were given an oral dose of 8 mg/kg of metoprolol in solution form. Blood samples were taken from jugular vein of the rabbits after drug administration and analysed by HPLC.Results: Separation of metoprolol was not interfered with other components in plasma. The calibration curve was linear in the range of 25 - 1000 ng/mL (r2 = 0.997). Lower limits of detection (LLOD) and quantitation (LLOQ) were 8.87 and 25 ng/mL, respectively. Relative standard deviation (RSD) of intraday and inter-day precision was < 14.27 and 7.61 %, respectively. Relative error of accuracy was between 4.85 and 14.37 %. Maximum plasma concentration (Cmax), time to maximum plasma concentration (Tmax) and half-life (t½) after metoprolol oral administration in rabbits were 186.29 ng/mL, 0.50 h and 2.27 h, respectively.Conclusion: A simple, accurate and precise HPLC-UV method for metoprolol determination in rabbit plasma has been successfully developed and applied to a pharmacokinetic study.Keywords: HPLC-UV, Metoprolol, Pharmacokinetics, Rabbit plasma, Liquid-liquid extraction, Validatio

Terms-of-Trade Shocks, External Adjustments and Growth in Pakistan: How Much to Sacrifice

Pakistan is largely considered as having balance of payments constrained economy. These constraints become more intense when external shocks hit, such as unfavorable changes in the country’s external terms-of-trade. In this paper, we attempt to document the cost to the economy when sailing through such shocks. Empirical estimates show substantial external adjustment takes place after the terms-of-trade bust in case of Pakistan. These adjustments largely work through income effect as the role of expenditure switching effect is estimated to be lower, though overtime increasing. Our main finding is about the cost to the domestic output when such shocks hit, which we call a sacrifice ratio. We find this impact is quite large, albeit decreasing overtime. We also find that the role of exchange rate policy is an important determinant of how large that sacrifice ratio will be. From the policy perspective, including monetary policy, these are important findings as they provide insights to policymakers about choices they can make during the stress times

Volatility Transmission of Overnight Rate along the Yield Curve in Pakistan

This paper presented the empirical results of the volatility transmission of overnight rate along the yield curve in case of Pakistan. The results indicate that the volatility transmission of overnight repo rate is higher at the shorter end of the yield curve while lower at the longer end. These results are in line with both theoretical and empirical underpinning of the interest rates volatility transmission process found in other countries. Moreover, the results also suggest that the pass-through level of overnight volatility transmission to other market interest rates decreased after State Bank of Pakistan (SBP) adopted the interest rate corridor framework in August 2009. This indicates the enhancement of effective and smooth transmission of SBP policy rate changes to other market interest rates under the current framework. However, absence of any explicit desired level of operational target in the monetary policy framework of SBP still imparts higher volatility in interest rates when compared to other countries following the similar interest rate corridor framework

Volatility Transmission of Overnight Rate along the Yield Curve in Pakistan

This paper presented the empirical results of the volatility transmission of overnight rate along the yield curve in case of Pakistan. The results indicate that the volatility transmission of overnight repo rate is higher at the shorter end of the yield curve while lower at the longer end. These results are in line with both theoretical and empirical underpinning of the interest rates volatility transmission process found in other countries. Moreover, the results also suggest that the pass-through level of overnight volatility transmission to other market interest rates decreased after State Bank of Pakistan (SBP) adopted the interest rate corridor framework in August 2009. This indicates the enhancement of effective and smooth transmission of SBP policy rate changes to other market interest rates under the current framework. However, absence of any explicit desired level of operational target in the monetary policy framework of SBP still imparts higher volatility in interest rates when compared to other countries following the similar interest rate corridor framework

Modeling and Characterization of X-ray Image Detectors

The flat-panel image detectors capture an X-ray image electronically, and enable a smooth clinical transition to digital radiography by replacing traditional film/cassette based system. They provide excellent X-ray images and have been commercialized for different X-ray imaging modalities. However, there still remain significant scientific challenges in these detectors associated with dark current and ghosting which constitute critical performance requirements for modalities such as digital fluoroscopy. This doctoral dissertation involves both experimental characterization and physics-based theoretical modelling of time and bias dependent dark current behaviour and X-ray induced change in sensitivity (ghosting) in X-ray imaging detectors. The theoretical investigations are based on the physics of the individual phenomenon and a systematic solution of physical equations in the photoconductor layer; (i) semiconductor continuity equations (ii) Poisson’s equation, and (iii) trapping rate equations. The theoretical model has been validated with the measured and published experimental results. The developed dark current model has been applied to a-Se and poly-HgI2 based detectors (direct conversion detectors), and a-Si:H p-i-n photodiode (indirect conversion detectors). The validation of the model with the experimental results determines the physical mechanisms responsible for the dark current in X-ray imaging detectors. The dark current analysis also unveils the important material parameters such as trap center concentrations in the blocking layers, trap depths, and effective barrier heights for injecting carriers. The analysis is important for optimization of the dark current consistent with having good transport properties which can ultimately improve the dynamic range of the detector. The physical mechanisms of sensitivity reduction (ghosting) and its recovery has been investigated by exposing a-Se detector at high dose and then monitoring the recovery process under (i) resting the samples (natural recovery), (ii) reversing the bias polarity and magnitude, and (iii) shining light. The continuous monitoring of the sensitivity as a function of exposure and time reveals the ghosting mechanisms in a-Se mammography detectors. This research finds a faster sensitivity recovery by reversing the bias during the natural recovery process. The sensitivity recovery mechanisms (e.g., recombination between trapped and oppositely charged free carrier, trapping of oppositely charged free carriers, or relaxation of trap centers) have been qualitatively investigated by validating the simulation results with the experimental data. The ghost removal mechanisms and techniques are important to improve the image quality which can ultimately lead to the reduction of the patient exposure consistent with better diagnosis for different X-ray imaging modalities