Multilevel Dodecagonal Space Vector Generation for Open-end Winding Induction Motor Drive Using Conventional Three Level Inverters

A novel dodecagonal space vector structure for induction motor drive is presented in this paper. It consists of two dodecagons, with the radius of the outer one twice the inner one. Compared to existing dodecagonal space vector structures, to achieve the same PWM output voltage quality, the proposed topology lowers the switching frequency of the inverters and reduces the device ratings to half. At the same time, other benefits obtained from existing dodecagonal space vector structure are retained here. This includes the extension of the linear modulation range and elimination of all 6+/-1 harmonics (n=odd) from the phase voltage. The proposed structure is realized by feeding an open-end winding induction motor with two conventional three level inverters. A detailed calculation of the PWM timings for switching the space vector points is also presented. Simulation and experimental results indicate the possible application of the proposed idea for high power drives.

Seismic response of reinforced soil retaining wall models: Influence of backfill relative density

This paper presents the results of shaking table tests on model reinforced soil retaining walls in the laboratory. The influence of backfill relative density on the seismic response was studied through a series of laboratory model tests on retaining walls. Construction of model retaining walls in the laminar box mounted on shaking table, instrumentation and results from the shaking table tests are described in detail. Three types of walls: wrap- and rigid-faced reinforced soil walls and unreinforced rigid-faced walls constructed to different densities were tested for a relatively small excitation. Wrap-faced walls are further tested for higher base excitation at different frequencies and relative densities. It is observed from these tests that the effect of backfill density on the seismic performance of reinforced retaining walls is pronounced only at very low relative density and at the higher base excitation. The walls constructed with higher backfill relative density showed lesser face deformations and more acceleration amplifications compared to the walls constructed with lower densities when tested at higher base excitation. The response of wrap- and rigid-faced retaining walls is not much affected by the backfill relative density when tested at smaller base excitation. The effects of facing rigidity were evaluated to a limited extent. Displacements in wrap-faced walls are many times higher compared to rigid-faced walls. The results obtained from this study are helpful in understanding the relative performance of reinforced soil retaining walls constructed to when subjected to smaller and higher base excitation for the range of relative density employed in the testing program. (C) 2007 Elsevier Ltd. All rights reserved.

The key enzyme in galactose metabolism, UDP-galactose-4-epimerase, affects cell-wall integrity and morphology in Candida albicans even in the absence of galactose

The enzyme UDP-galactose-4-epimerase (GAL10) catalyzes a key step in galactose metabolism converting UDP-galactose to UDPglucose which then can get metabolized through glycolysis and TCA cycle thus allowing the cell to use galactose as a carbon and energy source. As in many fungi, a functional homolog of GAL10 exists in Candida albicans. The domainal organization of the homologs from Saccharomyces cerevisiae and C albicans show high degree of homology having both mutarotase and an epimerase domain. The former is responsible for the conversion of beta-D-galactose to alpha-D-galactose and the hitter for epimerization of UDP-galactose to UDP-glucose. Absence of C albicans GAL10 (CaGAL10) affects cell-wall organization, oxidative stress response, biofilm formation and filamentation. Cagal10 mutant cells tend to flocculate extensively as compared to the wild-type cells. The excessive filamentation in this mutant is reflected in its irregular and wrinkled colony morphology. Cagal10 strain is more susceptible to oxidative stress when tested in presence of H2O2. While the S. cerevsiae GAL10 (ScGAL10), essential for survival in the presence of galactose, has not been reported to have defects in the absence of galactose, the C albicans homolog shows these phenotypes during growth in the absence of galactose. Thus a functional CaGal10 is required not only for galactose metabolism but also for normal hyphal morphogenesis, colony morphology, maintenance of cell-wall integrity and for resistance to oxidative stress even in the absence of galactose. (c) 2006 Elsevier Inc. All rights reserved.

R3Mn1.5CuV0.5O9 (R = Y, Ho, Er, Tm, Yb and Lu) and Lu3Mn3-3xCu2xVxO9: New noncentro symmetric oxides related to YMnO3

We report formation of new noncentrosymmetric oxides of the formula, R3Mn1.5CuV0.5O9 for R = Y, Ho, Er, Tm, Yb and Lu, possessing the hexagonal RMnO3 (space group P6(3)cm) structure. These oxides could be regarded as the x = 0.5 members of a general series R3Mn3-3xCu2xVxO9. Investigation of the Lu-Mn-Cu-V-O system reveals the existence of isostructural solid solution series, Lu3Mn3-3xCu2xVxO9 for 0 < x <= 0.75. Magnetic and dielectric properties of the oxides are consistent with a random distribution of Mn3+, Cu2+ and V5+ atoms that preserve the noncentrosymmetric RMnO3 structure. (c) 2006 Elsevier Ltd. All rights reserved.

A rate-one full-diversity low-complexity space-time-frequency block code (STFBC) for 4-Tx MIMO-OFDM

It is known that by employing space-time-frequency codes (STFCs) to frequency selective MIMO-OFDM systems, all the three diversity viz spatial, temporal and multipath can be exploited. There exists space-time-frequency block codes (STFBCs) designed using orthogonal designs with constellation precoder to get full diversity (Z.Liu, Y.Xin and G.Giannakis IEEE Trans. Signal Processing, Oct. 2002). Since orthogonal designs of rate one exists only for two transmit antennas, for more than two transmit antennas STFBCs of rate-one and full-diversity cannot be constructed using orthogonal designs. This paper presents a STFBC scheme of rate one for four transmit antennas designed using quasi-orthogonal designs along with co-ordinate interleaved orthogonal designs (Zafar Ali Khan and B. Sundar Rajan Proc: ISIT 2002). Conditions on the signal sets that give full-diversity are identified. Simulation results are presented to show the superiority of our codes over the existing ones.

A systematic design of high-rate full-diversity space-frequency codes for MIMO-OFDM systems

This paper presents a systematic construction of high-rate and full-diversity space-frequency block codes for MIMO-OFDM systems. While all prior constructions offer only a maximum rate of one complex symbol per channel use, our construction yields rate equal to the number of transmit antennas and simultaneously achieves full-diversity. The proposed construction works for arbitrary number of transmit antennas and arbitrary channel power delay profile. A key step in this construction is the generalization of the stacked matrix code design criteria given by Bolcskei et.al., (IEEE WCNC 2000). Explicit equivalence of our generalized code design criteria with the Hadamard-product based criteria of W. Su et.al., (lEEE Trans. Sig. Proc. Nov 2003) is established and new high-rate codes are constructed using our criteria.

A unified construction of space-time codes with optimal rate-diversity tradeoff

The problem of constructing space-time (ST) block codes over a fixed, desired signal constellation is considered. In this situation, there is a tradeoff between the transmission rate as measured in constellation symbols per channel use and the transmit diversity gain achieved by the code. The transmit diversity is a measure of the rate of polynomial decay of pairwise error probability of the code with increase in the signal-to-noise ratio (SNR). In the setting of a quasi-static channel model, let n(t) denote the number of transmit antennas and T the block interval. For any n(t) <= T, a unified construction of (n(t) x T) ST codes is provided here, for a class of signal constellations that includes the familiar pulse-amplitude (PAM), quadrature-amplitude (QAM), and 2(K)-ary phase-shift-keying (PSK) modulations as special cases. The construction is optimal as measured by the rate-diversity tradeoff and can achieve any given integer point on the rate-diversity tradeoff curve. An estimate of the coding gain realized is given. Other results presented here include i) an extension of the optimal unified construction to the multiple fading block case, ii) a version of the optimal unified construction in which the underlying binary block codes are replaced by trellis codes, iii) the providing of a linear dispersion form for the underlying binary block codes, iv) a Gray-mapped version of the unified construction, and v) a generalization of construction of the S-ary case corresponding to constellations of size S-K. Items ii) and iii) are aimed at simplifying the decoding of this class of ST codes.

BER analysis of space-time block codes from generalized complex orthogonal designs for M-PSK

In this paper, we present an analysis for the bit error rate (BER) performance of space-time block codes (STBC) from generalized complex orthogonal designs for M-PSK modulation. In STBCs from complex orthogonal designs (COD), the norms of the column vectors are the same (e.g., Alamouti code). However, in generalized COD (GCOD), the norms of the column vectors may not necessarily be the same (e.g., the rate-3/5 and rate-7/11 codes by Su and Xia in [1]). STBCs from GCOD are of interest because of the high rates that they can achieve (in [2], it has been shown that the maximum achievable rate for STBCs from GCOD is bounded by 4/5). While the BER performance of STBCs: from COD (e.g., Alamouti code) can be simply obtained from existing analytical expressions for receive diversity with the same diversity order by appropriately scaling the SNR, this can not be done for STBCs from GCOD (because of the unequal norms of the column vectors). Our contribution in this paper is that we derive analytical expressions for the BER performance of any STBC from GCOD. Our BER analysis for the GCOD captures the performance of STBCs from COD as special cases. We validate our results with two STBCs from GCOD reported by Su and Xia in [1], for 5 and 6 transmit antennas (G(5) and G(6) in [1]) with rates 7/11 and 3/5, respectively.

Space-Vector-Based Hybrid Pulsewidth Modulation Techniques for Reduced Harmonic Distortion and Switching Loss

Novel switching sequences can be employed in spacevector-based pulsewidth modulation (PWM) of voltage source inverters. Differentswitching sequences are evaluated and compared in terms of inverter switching loss. A hybrid PWM technique named minimum switching loss PWM is proposed, which reduces the inverter switching loss compared to conventional space vector PWM (CSVPWM) and discontinuous PWM techniques at a given average switching frequency. Further, four space-vector-based hybrid PWM techniques are proposed that reduce line current distortion as well as switching loss in motor drives, compared to CSVPWM. Theoretical and experimental results are presented.

Prevention of photooxidation in blue-green emitting Cu doped ZnSe nanocrystals

This communication highlights unstable blue-green emitting Cu doped ZnSe nanocrystals stabilized by diluting the surface Se with a calculated amount of S.

Seismic response of wrap-faced reinforced soil-retaining wall models using shaking table tests

This paper presents the results of shaking table tests on geotextile-reinforced wrap-faced soil-retaining walls. Construction of model retaining walls in a laminar box mounted on a shaking table, instrumentation, and results from the shaking table tests are discussed in detail. The base motion parameters, surcharge pressure and number of reinforcing layers are varied in different model tests. It is observed from these tests that the response of the wrap-faced soil-retaining walls is significantly affected by the base acceleration levels, frequency of shaking, quantity of reinforcement and magnitude of surcharge pressure on the crest. The effects of these different parameters on acceleration response at different elevations of the retaining wall, horizontal soil pressures and face deformations are also presented. The results obtained from this study are helpful in understanding the relative performance of reinforced soil-retaining walls under different test conditions used in the experiments.

Improved switching frequency variation control of hysteresis controlled voltage source inverter-fed IM drives using current error space vector

A constant switching frequency current error space vector-based hysteresis controller for two-level voltage source inverter-fed induction motor (IM) drives is proposed in this study. The proposed controller is capable of driving the IM in the entire speed range extending to the six-step mode. The proposed controller uses the parabolic boundary, reported earlier, for vector selection in a sector, but uses simple, fast and self-adaptive sector identification logic for sector change detection in the entire modulation range. This new scheme detects the sector change using the change in direction of current error along the axes jA, jB and jC. Most of the previous schemes use an outer boundary for sector change detection. So the current error goes outside the boundary six times during sector change, in one cycle,, introducing additional fifth and seventh harmonic components in phase current. This may cause sixth harmonic torque pulsations in the motor and spread in the harmonic spectrum of phase voltage. The proposed new scheme detects the sector change fast and accurately eliminating the chance of introducing additional fifth and seventh harmonic components in phase current and provides harmonic spectrum of phase voltage, which exactly matches with that of constant switching frequency voltage-controlled space vector pulse width modulation (VC-SVPWM)-based two-level inverter-fed drives.

Structural and photoelectrical characterization of hot wall deposited CuInSe2 thin films and the fabrication of CuInSe2 based solar cells

Films of CuInSe2 were deposited onto glass substrates by a hot wall deposition method using bulk CuInSe2 as a source material. All the deposited CuInSe2 films were found to be polycrystalline in nature exhibiting the chalcopyrite structure with the crystallite orientation along (101),(112),(103),(211),(220),(312) and (400) directions. The photocurrent was found to increase with increase in film thickness and also with increase of light intensity. Photocurrent spectra show a peak related to the band-to-band transition. The spectral response of CuInSe2 thin films was studied by allowing the radiation to pass through a series of interference filters in the wavelength range 700-1200 rim. Films of higher thickness exhibited higher photosensitivity while low thickness films exhibited moderate photosensitivity. CuInSe2-based Solar cells with different types of buffer layers such as US, Cdse, CuInSe2 and CdSe0.7Te0.3 were fabricated. The current and voltage were measured using an optical power meter and an electrometer respectively. The fabricated solar cells were illuminated using 100 mW/cm(2) white light under AM1 conditions. (C) 2006 Elsevier Inc. All rights reserved.

Velocity-Space Contours of Collision Integrals

Based on the recently found closed-form expressions of the Boltzmann collision integrals in a rigid-sphere gas for multi-Maxwellian distributions, a few typical sets of contour surfaces of the integrals in the space of molecular velocities are presented. These show graphically the tendency toward equilibrium under the influence of collisions. A brief preliminary comparison with Monte Carlo results is also given.

Low PAPR full-diversity space-frequency codes for MIMO-OFDM systems

Use of precoding transforms such as Hadamard Transforms and Phase Alteration for Peak to Average Power Ratio (PAPR) reduction in OFDM systems are well known. In this paper we propose use of Inverse Discrete Fourier Transform (IDFT) and Hadamard transform as precoding transforms in MIMO-OFDM systems to achieve low peak to average power ratio (PAPR). We show that while our approach using IDFT does not disturb the diversity gains of the MIMO-OFDM systems (spatial, temporal and frequency diversity gains), it offers a better trade-off between PAPR reduction and ML decoding complexity compared to that of the Hadamard transform precoding. We study in detail the amount of PAPR reduction achieved for the following two recently proposed full-diversity Space-Frequency coded MIMO-OFDM systems using both the IDFT and the Hadamard transform: (i) W. Su. Z. Safar, M. Olfat, K. J. R. Liu (IEEE Trans. on Signal Processing, Nov. 2003), and (ii) W. Su, Z. Safar, K. J. R. Liu (IEEE Trans. on Information Theory, Jan. 2005).