Current distribution in superconducting multistrands for ac use before and after quenching

A superconducting multistranded cable is used to realize high current capacity for ac use. The critical current value of the cable is reported to be less than the simple summation of the individual critical current value of each strand. The causes for such a degradation of the critical current value have not been revealed. This paper investigates the current distribution in multistrands before and after their quenching by using seven-strand superconducting cable and 7x7 cable. The following experimental results are derived: (1) the quenching is initiated at one strand in the cable; (2) the current in the quenched strand is transferred into the other strands; (3) an avalanche of quenching is induced among the strands; and (4) the central strand is quenched finally among the strands. The critical current values of the 7- and 7 × 7-stranded cables also are measured. These values are in good agreement with the predicted values based on the mutual inductance among the strands. It is concluded that the unbalance of the current distribution in the superconducting multistrands can be one of the promising causes for the degradation of the critical current value.     

An improved space-vector-based hysteresis current controller

In this paper, an improved space-vector-based hysteresis current controller (SVBHCC) is proposed. The controller determines a set of space vectors from a region detector and applies a space voltage vector selected according to the main HCC. A set of space vectors including the zero voltage vector to reduce the number of switchings is determined from the information of the current errors, which are wider than those of the main HCC. A simple hardware implementation is proposed and the good experimental results of the SVBHCC for a squirrel cage motor are also shown     

A line-voltage-sensorless synchronous rectifier

A line-voltage-sensorless control for three-phase pulsewidth-modulated (PWM) synchronous rectifiers is presented. A line synchronization and unity power factor control are described. Indirect synchronization without sensing the line voltage allows a standard vector-controlled inverter to be used as a synchronous rectifier without requiring any additional hardware. Furthermore, the line synchronization can be properly operated under line voltage distortion or notching and line frequency variation. All control functions are implemented with a single-chip microcontroller. It is shown via experimental results that the proposed controller gives good performance for the synchronous rectifier     

A power-factor controller for single-phase PWM rectifiers

A novel power-factor controller for single-phase pulsewidth modulated rectifiers is proposed. The unity power-factor controller for a sinusoidal input current is derived using the feedback linearization concept. Two active switches and two diodes are utilized for AC-to-DC power conversion. Experimental results obtained on a 4 kW prototype are discussed     

Mutations in calpastatin and μ-calpain are associated with meat tenderness,flavor and juiciness in Hanwoo (Korean cattle): Molecular modeling of the effects of substitutions in the calpastatin/μ-calpain complex

The objective of this study was to evaluate the effects of seven single nucleotide polymorphisms (SNPs) in Calpain 1 and Calpastatin genes previously associated with meat tenderness attributes in other cattle breeds in Korean Hanwoo cattle. The Hanwoo resource population was used to study association of 7 SNPs with beef tenderness, flavor, juiciness, intramuscular fat and shear force. In this association study, CAST:c.182A > G (+ 0.14, P = 0.04) and CAST:c.1985G > C (− 0.12, P = 0.02) had significant effects on juiciness, but no effects on other traits. In contrast, CAPN1:c.1589G > A was associated with meat tenderness (P = 0.01) and juiciness (P = 0.04). The CAPN1:c.1589G > A (Val530Ile) SNP marker displayed significant effect on the meat tenderness score which is strongly supported by molecular modeling of the CAPN1:c.1589G > A (Val530Ile) variant that inhibits CAST protein from binding more strongly than the wild-type protein, which may explain its effect on meat tenderness.     

Three-phase unbalanced-voltage compensators

In this paper, three-phase unbalanced-voltage compensators using ac choppers are proposed. The proposed three-phase unbalanced-voltage compensators are made up of three single-phase ac choppers and transformers for unbalanced-voltage compensation and output voltage regulation. The proposed compensators use ac choppers which solve the commutation problem, limit the switch voltage stress to the maximum line voltage, and also raise efficiency using regenerative dc snubbers. Compared with previous unbalanced-voltage compensators that use complex voltage source inverters, the proposed unbalanced-voltage compensators use ac choppers and utilize source or output line voltages in 30° phase shift with the phase voltages as the input of the ac chopper. Then, the proposed compensators give high efficiency, fast dynamics, simple power circuit, and reduced control circuit. It is also shown via some simulation and experimental results that the presented unbalanced-voltage compensators give good dynamic and steady state performances.     

An improved zero-voltage and zero-current-switching full-bridge PWMconverter using a simple resonant circuit

An improved zero-voltage and zero-current-witching full-bridge pulsewidth modulation (ZVZCS-FB-PWM) DC-to-DC converter is presented and analyzed. An auxiliary resonant circuit, which consists of a switch and a capacitor, are added to provide zero-current switching (ZCS) conditions to the primary lagging-leg switches. Due to the auxiliary circuit, when the primary current is being extinguished, the voltage applied on the leakage inductance of the transformer is larger than DC-link voltage. This large voltage increases the maximal output current that can be handled in ZCS. Furthermore, the auxiliary switch softly turns on and turns off     

Reaction pathway of NiAl/WC nanocomposite synthesized from mechanical activated NiAlWC powder system

In this work, the mechanism of WC formation during mechanical alloying and subsequent annealing of nickel, aluminum, tungsten, and graphite powder mixtures was investigated. X-ray diffraction was used to evaluate phase changes. Microstructural and morphological evaluations of the powders were examined by FESEM and TEM. The XRD results confirmed that phase changes occurred by increasing milling time. After 10?h of ball milling, NiAl and W₂C phases formed and new tungsten carbides were synthesized by increasing of milling time. After 40?h, W was consumed completely and WC, WC_1-x, W₂C carbides along with NiAl were produced. After heat treatment of 40?h milled powder, W₂C and WC_1-x phases disappeared and NiAl/WC nanocomposite was formed. The results confirmed that the WC formation was a gradual reaction controlled by atomic diffusion.     

Comments on "On some bounds in the algebraic Riccati and Lyapunov equations"

Results presented by Moil in the paper, which give some bounds for the trace and the determinant of the positive definite solution to the algebraic Riccati matrix equation, are shown to be erroneous, and suggestions to remedy these errors are made.     

Optimal regulators using time-weighted quadratic performance index with prespecified closed-loop eigenvalues

Optimization of linear time-invariant systems, using a given time-weighted quadratic performance index, is investigated for the prespecified closed-loop eigenvalues. The necessary conditions have simple forms and this algorithm gives a considerable amount of computational time savings compared to the previous algorithms [1]-[2].