A current error space vector based hysteresis controller with constant switching frequency and simple online boundary computation for VSI fed IM drive

This paper proposes a simple current error space vector based hysteresis controller for two-level inverter fed Induction Motor (IM) drives. This proposed hysteresis controller retains all advantages of conventional current error space vector based hysteresis controllers like fast dynamic response, simple to implement, adjacent voltage vector switching etc. The additional advantage of this proposed hysteresis controller is that it gives a phase voltage frequency spectrum exactly similar to that of a constant switching frequency space vector pulse width modulated (SVPWM) inverter. In this proposed hysteresis controller the boundary is computed online using estimated stator voltages along alpha and beta axes thus completely eliminating look up tables used for obtaining parabolic hysteresis boundary proposed in. The estimation of stator voltage is carried out using current errors along alpha and beta axes and steady state model of induction motor. The proposed scheme is simple and capable of taking inverter upto six step mode operation, if demanded by drive system. The proposed hysteresis controller based inverter fed drive scheme is simulated extensively using SIMULINK toolbox of MATLAB for steady state and transient performance. The experimental verification for steady state performance of the proposed scheme is carried out on a 3.7kW IM.

The Archaeometallurgical Implications of New Findings of Traditional Crafts of Making High Tin ‘Delta’ Bronze Mirrors and ‘Beta’ Bronze Vessels in Kerala State of South India

New metallurgical and ethnographic observations of the traditional manufacture of specular high-tin bronze mirrors in Kerala state of southern India are discussed, which is an exceptional example of a surviving craft practice of metal mirror-making in the world. The manufacturing process has been reconstructed from analytical investigations made by Srinivasan following a visit late in 1991 to a mirror making workshop and from her technical studies of equipment acquired by Glover in March 1992 from another group of mirror makers from Pathanamthita at an exhibition held at Crafts Museum, Delhi. Finished and unfinished mirror from two workshops were of a binary, copper-tin alloy of 33% tin which is close to the composition of pure delta phase, so that these mirrors are referred to here as ‘delta’ bronzes. For the first time, metallurgical and field observations were made by Srinivasan in 1991 of the manufacture of high-tin ‘beta’ bonze vessels from Palghat district, Kerala, i‥e of wrought and quenched 23% tin bronze. This has provided the first metallurgical record for a surviving craft of high-tin bronze bowl making which can be directly related to archaeological finds of high-tin bronze vessels from the Indian subcontinent and Southeast Asia. New analytical investigations are presented of high-tin beta bronzes from the Indian subcontinent which are some of the earliest reported worldwide. These coupled with the archaeometallurgical evidence suggests that these high-tin bronze techniques are part of a long, continuing, and probably indigenous tradition of the use of high-tin bronzes in the Indian subcontinent with finds reported even from Indus Valley sites. While the source of tin has been problematic, new evidence on bronze smelting slags and literary evidence suggests there may have been some sources of tin in South India.

Denaturant mediated unfolding of both native and molten globule states of maltose binding protein are accompanied by large [Delta]Cp's

Maltose binding protein (MBP) is a large, monomeric two domain protein containing 370 amino acids. In the absence of denaturant at neutral pH, the protein is in the native state, while at pH 3.0 it forms a molten globule. The molten globule lacks a tertiary circular dichroism signal but has secondary structure similar to that of the native state. The molten globule binds 8-anilino-1-naphthalene sulfonate (ANS). The unfolding thermodynamics of MBP at both pHs were measured by carrying out a series of isothermal urea melts at temperatures ranging from 274–329 K. At 298 K, values of [Delta]G°, [Delta]Cp, and Cm were 3.1 ± 0.2 kcal mol−1, 5.9 ± 0.8 kcal mol−1 K−1 (15.9 cal (mol-residue)−1 K−1), and 0.8 M, respectively, at pH 3.0 and 14.5 ± 0.4 kcal mol−1, 8.3 ± 0.7 kcal mol−1 K−1 (22.4 kcal (mol-residue)−1 K−1), and 3.3 M, respectively, at pH 7.1. Guanidine hydrochloride denaturation at pH 7.1 gave values of [Delta]G° and [Delta]Cp similar to those obtained with urea. The m values for denaturation are strongly temperature dependent, in contrast to what has been previously observed for small globular proteins. The value of [Delta]Cp per mol-residue for the molten globule is comparable to corresponding values of [Delta]Cp for the unfolding of typical globular proteins and suggests that it is a highly ordered structure, unlike molten globules of many small proteins. The value of [Delta]Cp per mol-residue for the unfolding of the native state is among the highest currently known for any protein.

Anomalous temperature dependence of phonons and photoluminescence bands in pyrochlore Er(2)Ti(2)O(7): signatures of structural deformation at 130 K

We report a Raman study of single crystal pyrochlore Er(2)Ti(2)O(7) as a function of temperature from 12 to 300 K. In addition to the phonons, various photoluminescence (PL) lines of Er(3+) in the visible range are also observed. Our Raman data show an anomalous red-shift of two phonons (one at similar to 200 cm(-1) and another at similar to 520 cm(-1)) upon cooling from room temperature which is attributed to phonon-phonon anharmonic interactions. However, the phonons at similar to 310, 330, and 690 cm(-1) initially show a blue-shift upon cooling from room temperature down to about 130 K, followed by a red-shift, indicating a structural deformation at similar to 130 K. The intensities of the PL bands associated with the transitions between the various levels of the ground state manifold ((4)I(15/2)) and the (2)H(11/2) as well as (4)S(3/2) excited state manifolds of Er(3+) show a change at similar to 130 K. Moreover, the temperature dependence of the peak position of the two PL bands shows a change in their slope (d(omega)/d(T)) at similar to 130 K, thus further strengthening the proposal of a structural deformation. The temperature dependence of the peak positions of the PL bands has been analyzed using the theory of optical dephasing in crystals.

Magnetic and Mechanical Anisotropy in a Manganese 2-Methylsuccinate Framework Structure

Hybrid inorganic-organic framework materials exhibit unique properties that can be advantageously tuned through choice of the inorganic and organic components and by control of the crystal structure. We present a new hydrothermally prepared 3D hybrid framework, [Mn(2-methylsuccinate)](n) (1), comprising alternating 2D manganese oxide sheets and isolated MnO(6) octahedra, pillared via syn, anti-syn carboxylates. Powder magnetic characterization shows that the compound is a homospin Mn(II) ferrimagnet below 2.4 K. The easy-axis is revealed by single-crystal magnetic susceptibility studies and a magnetic structure is proposed. Anisotropic elastic moduli and hardness, observed through nanoindentation on differing crystal facets, were correlated with specific structural features. Such measurements of anisotropy are not commonly undertaken, yet allow for a more comprehensive understanding of structure-property relationships.

Raman signatures of pressure induced electronic topological and structural transitions in Bi2Te3

We report Raman signatures of electronic topological transition (ETT) at 3.6 GPa and rhombohedral (alpha-Bi2Te3) to monoclinic (beta-Bi2Te3) structural transition at similar to 8 GPa. At the onset of ETT, a new Raman mode appears near 107 cm(-1) which is dispersionless with pressure. The structural transition at similar to 8 GPa is marked by a change in pressure derivative of A(1g) and E-g mode frequencies as well as by appearance of new modes near 115 cm(-1) and 135 cm(-1). The mode Grilneisen parameters are determined in both the alpha and beta-phases. (C) 2011 Elsevier Ltd. All rights reserved.

An efficient one-pot synthesis and photoinduced DNA cleavage studies of 2-chloro-3-(5-aryl-4,5-dihydroisoxazol-3-yl)quinolines

4,5-Dihydroisoxazoles continue to attract considerable interest due to their wide spread biological activities. Here, we identify an efficient protocol for the preparation of 4,5-dihydroisoxazoles (2-isaxazolines) (4a-g) from quinolinyl chalcones. The nucleolytic activities of synthesized compounds were investigated by agarose gel electrophoresis. All these compounds were showed the remarkable DNA cleavage activity (concentration dependent) with pUC19 DNA at 365 nm UV light. The DNA cleavage activity was significantly enhanced by the presence of iminyl and carboxy radicals of DIQ. (C) 2012 Elsevier Ltd. All rights reserved.