Guessing and compression subject to distortion

The problem of guessing a random string is revisited. The relation-ship between guessing without distortion and compression is extended to the case when source alphabet size is countably in¯nite. Further, similar relationship is established for the case when distortion allowed by establishing a tight relationship between rate distortion codes and guessing strategies.

Texture and grain boundary character distribution during Equal Channel Angular Extrusion of some two-phase copper alloys

In the present work, a thorough investigation of evolution of microstructure and texture has been carried out to elucidate the evolution of texture and grain boundary character distribution (GBCD) during Equal Channel Angular Extrusion (ECAE) of some model two-phase materials, namely Cu-0.3Cr and Cu-40Zn. Texture of Cu-0.3Cr alloy is similar to that reported for pure copper. On the other hand, in Cu-40Zn alloy, texture evolution in α and β (B2) phases are interdependent. In Cu-0.3Cr alloy, there is a considerable decreases in volume fraction of low angle boundaries (LAGBs), only a slight increase in CSL boundaries, but increase in high angle grain boundaries (HAGBs) from 1 pass to 4 passes for both the routes. In the case of Cu-40Zn alloy, there is an appreciable increase in CSL volume fraction.

Rhodium Carbenoid Mediated C-H Activation of a Tertiary Methyl Group: An Enantiospecific Approach to the Angular Triquinanes Norsilphiperfolane and Norcameroonanes

An enantiospecific synthesis of the angular triquinane system present in the sesquiterpenes cameroonanes and silphiperfolanes has been accomplished, starting from 5-isopropenyl-2-methylcyclopent-1-ene-1-methanol [readily available in three steps from (R)-limonene] employing an intramolecular rhodium carbenoid insertion into the C-H bond of a tertiary methyl group for the construction of the triquinane system.

Enantiospecific synthesis of angular triquinanes

The enantiospecific synthesis of angular triquinanes has been developed starting from the readily available (S)-campholenaldehyde. Two alternate strategies have been used, one employing a Johnson's orthoester Claisen rearrangement followed by an intramolecular cyclopropanation and regioselective cyclopropane ring cleavage, and a second one based on a RCM reaction. (C) 2011 Elsevier Ltd. All rights reserved.

Effect of equal channel angular extrusion on wear and corrosion behavior of the orthopedic Ti-13Nb-13Zr alloy in simulated body fluid

We report investigations on the texture, corrosion and wear behavior of ultra-fine grained (UFG) Ti-13Nb-Zr alloy, processed by equal channel angular extrusion (ECAE) technique, for biomedical applications. The microstructure obtained was characterized by X-ray line profile analysis, scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). We focus on the corrosion resistance and the fretting behavior, the main considerations for such biomaterials, in simulated body fluid. To this end. potentiodynamic polarization tests were carried out to evaluate the corrosion behavior of the UFG alloy in Hanks solution at 37 degrees C. The fretting wear behavior was carried out against bearing steel in the same conditions. The roughness of the samples was also measured to examine the effect of topography on the wear behavior of the samples. Our results showed that the ECAE process increases noticeably the performance of the alloy as orthopedic implant. Although no significant difference was observed in the fretting wear behavior, the corrosion resistance of the UFG alloy was found to be higher than the non-treated material. (c) 2012 Elsevier B.V. All rights reserved.

Equal channel angular pressing processing routes and associated structure modification: a differential scanning calorimetry and X-ray line profile analysis

The effectiveness of different routes of equal channel angular pressing (A, B-c, and C) is studied for commercially pure copper. The stored energy and the activation energy of recrystallization for the deformed samples were quantified using differential scanning calorimetry and X-ray diffraction line profile analysis. Results of the study revealed that the dislocation density and the stored energy are higher in the case of route B-c deformed sample. The activation energy for recrystallization is lower for route B-c. (C) 2012 International Centre for Diffraction Data doi:10.1017/S0885715612000310]

Angular amplification by a diffraction grating for chiro-optical measurements

The angles at which a light beam gets diffracted by a grating depend strongly on the direction of incidence for diffraction angles close to a right angle. Accordingly, it is possible to amplify small beam deflections by placing a grating at an optimal orientation to the light path. We use this principle to amplify small beam deviations arising out of a light beam refracting at the interface of an optically active medium, and demonstrate a new technique of enhancing the limit of detection of chiro-optical measurements. (C) 2012 Optical Society of America

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.

Minimization of grid current distortion in parallel-connected converters through carrier interleaving

Identical parallel-connected converters with unequal load sharing have unequal terminal voltages. The difference in terminal voltages is more pronounced in case of back-to-back connected converters, operated in power-circulation mode for the purpose of endurance tests. In this paper, a synchronous reference frame based analysis is presented to estimate the grid current distortion in interleaved, grid-connected converters with unequal terminal voltages. Influence of carrier interleaving angle on rms grid current ripple is studied theoretically as well as experimentally. Optimum interleaving angle to minimize the rms grid current ripple is investigated for different applications of parallel converters. The applications include unity power factor rectifiers, inverters for renewable energy sources, reactive power compensators, and circulating-power test set-up used for thermal testing of high-power converters. Optimum interleaving angle is shown to be a strong function of the average of the modulation indices of the two converters, irrespective of the application. The findings are verified experimentally on two parallel-connected converters, circulating reactive power of up to 150 kVA between them.

Analysis of Bandwidth-Unit-Vector-Distortion Tradeoff in PLL During Abnormal Grid Conditions

Phase-locked loops (PLLs) are necessary in applications which require grid synchronization. Presence of unbalance or harmonics in the grid voltage creates errors in the estimated frequency and angle of a PLL. The error in estimated angle has the effect of distorting the unit vectors generated by the PLL. In this paper, analytical expressions are derived which determine the error in the phase angle estimated by a PLL when there is unbalance and harmonics in the grid voltage. By using the derived expressions, the total harmonic distortion (THD) and the fundamental phase error of the unit vectors can be determined for a given PLL topology and a given level of unbalance and distortion in the grid voltage. The accuracy of the results obtained from the analytical expressions is validated with the simulation and experimental results for synchronous reference frame PLL (SRF-PLL). Based on these expressions, a new tuning method for the SRF-PLL is proposed which quantifies the tradeoff between the unit vector THD and the bandwidth of the SRF-PLL. Using this method, the exact value of the bandwidth of the SRF-PLL can be obtained for a given worst case grid voltage unbalance and distortion to have an acceptable level of unit vector THD. The tuning method for SRF-PLL is also validated experimentally.

Effect of equal channel angular pressing on grain refinement and texture evolution in a biomedical alloy Ti-13Nb-13Zr

Evolution of texture and concomitant grain refinement during Equal Channel Angular Pressing (ECAP) of Ti - 13Nb - 13Zr alloy has been presented. Sub-micron sized equiaxed grains with narrow grain size distribution could be achieved after eight pass at 873 K. A characteristic ECAP texture evolved in alpha phase till four passes while the evolution of characteristic ECAP texture in the beta phase could be observed only beyond the fourth pass. On increasing the deformation up to eight passes, the texture in alpha phase weakens while the beta phase shows an ideal ECAP texture. A weaker texture, low dislocation density and high crystallite size values in alpha phase suggest the occurrence of dynamic recrystallization. The absence of texture evolution in beta phase till four passes can be attributed to local lattice rotations. The characteristic ECAP texture in the eight pass deformed sample is attributed to delayed dynamic recrystallization in the beta phase. (C) 2013 Elsevier Inc. All rights reserved.

A Novel Design Method for SOGI-PLL for Minimum Settling Time and Low Unit Vector Distortion

Phase-locked loops (PLLs) are necessary in grid connected systems to obtain information about the frequency, amplitude and phase of the grid voltage. In stationary reference frame control, the unit vectors of PLLs are used for reference generation. It is important that the PLL performance is not affected significantly when grid voltage undergoes amplitude and frequency variations. In this paper, a novel design for the popular single-phase PLL topology, namely the second-order generalized integrator (SOGI) based PLL is proposed which achieves minimum settling time during grid voltage amplitude and frequency variations. The proposed design achieves a settling time of less than 27.7 ms. This design also ensures that the unit vectors generated by this PLL have a steady state THD of less than 1% during frequency variations of the grid voltage. The design of the SOGI-PLL based on the theoretical analysis is validated by experimental results.