The control of switching DC-DC converters-a general LWR problem

The control of switching DC-DC converters is reviewed. It is regarded as a general linear quadratic regulator (LQR) problem, and an innovative optimal and robust digital controller is proposed. The control strategy adopted can achieve good regulation, rejection of modest disturbances, and the ability to cater to switching converters with RHP zeros. This controller design is a general approach that is applicable to all PWM-type DC-DC converters with their circuit topologies known or unknown. Modern CAD techniques are used to reach the final control law. Application to a published Cuk converter is used as an example, and the performance is evaluated     

On the method of Eilenberger for inhomogeneous superconductors

The theory of Eilenberger, modified to take into account the effect of the surface, is applied to the problem of the penetration of a weak magnetic field into a semiinfinite superconductor, and the standard result for the vector potential is derived by linearizing the Eilenberger equations. The dominant term in the asymptotic behaviour is argued to be monotonic for both large and small values of the Ginzburg-Landau parameterk _gl . ForT≠ 0, there is a small intermediate range of values ofk _gl for which the dominant term is oscillatory, but these oscillations are not related to those found by Eilenberger and Büttner in the isolated vortex problem for smallK _gl . From an analysis of these results, we conclude that the absence of the Eilenberger-Büttner oscillations in the field penetration problem cannot be used as an argument against their existence in other problems; in particular, a separate investigation is required for the isolated vortex problem.     

Forward Error Correction for an ARQ Scheme

This paper examines the use of BCH error-correcting codes in improving the performance of a stop-and-wait automatic repeat-request (ARQ) scheme over random error and Rayleigh fading channels. Two models are analyzed. The first model considers the effect of forward error correction on the mean wasted time per message. The second model assumes a Poisson arrival process for the messages and examines the effect of forward error correction on the mean time between the arrival of a message and its successful transmission. In both models, our results indicate that the performance of the ARQ scheme can be substantially improved by the use of forward error correction.     

Diffraction effects in the Josephson tunneling between type II superconductors near Hc2

When the lattice of vortices on one side of a SIS tunneling junction moves with respect to that of the other side, we point out that the Josephson current should oscillate in magnitudes and directions as a function of time. The oscillatory behaviour is caused mainly by the diffraction effects of the variation of the order parameter in the mixed state with vortex motion.     

Sorption and diffusion of toluene in isotropic and oriented linear polyethylene

Sorption and diffusion of toluene vapor in linear polyethylene with mass-fraction crystallinity between 0.48 and 0.82 and draw ratios λ up to 10 have been studied at 30°C. The sorbed concentration in the amorphous phase C_a is little affected by crystallinity, indicating that the free-volume fraction is roughly the same for all isotropic samples. However, the diffusion path becomes more tortuous with increasing crystalline content, thereby leading to a sixfold drop in the zero-concentration diffusion coefficient D₀. Drawing has more drastic effects, reducing C_a and D₀ by factors of 4 and 60, respectively, as λ increases to 10. These large changes result from the transformation of the initially spherulitic material into a fibrous structure, which is composed of aligned microfibrils with taut tie molecules lying on the outer boundaries. The effects of crystallinity and orientation on the concentration dependence of the diffusion coefficient are also discussed.     

A stereoselective cyclization to carbafuranose derivatives starting from 1,4-bis-epoxides

[reactions: see text] A concise synthesis of highly functionalized cyclopentane derivatives via a Brook rearrangement mediated stereoselective linchpin cyclization reaction involving tert-butyldimethylsilyl-1,3-dithianyllithium and homochiral 1,4-bis-epoxides is described.     

Probing the interior of neutron stars with gravitational waves

We show here how the internal structure of a neutron star can be inferred from its gravitational wave spectrum. Under the premise that the frequencies and damping rates of a few w-mode oscillations are found, we apply an inversion scheme to determine its mass, radius, and density distribution. In addition, an accurate equation of state of nuclear matter can also be determined.     

High-resolution angular measurement using surface-plasmon-resonance via phase interrogation at optimal incident wavelengths

It is demonstrated that ultrahigh-resolution angular measurement can be achieved via surface-plasmon-resonance excitation in which the phase difference between p- and s-polarized reflected waves is monitored as a function of the incidence angle. Resolutions down to 1.9 x 10(-6) deg are obtained by performing the measurements at optimal incident wavelengths. This represents an order of magnitude improvement compared with previously reported values.