Vortex Dynamics in Bi2Sr2CaCu2O8 Single Crystal with Low Density Columnar Defects Studied by Magnetic Force Microscope

We have studied vortex dynamics in Bi₂Sr₂CaCu₂O₈ single crystal with low density columnar defects by using a magnetic force microscope. Single crystal Bi₂Sr₂CaCu₂O₈ sample was irradiated by 1.3 GeV uranium ion to form artificial pinning centers along the crystalline c-axis. The irradiation dose corresponded to a matching field of 20 gauss. The radius of an individual vortex is approximately 140 nm, which is close to the penetration depth of this material. Magnetic force microscope (MFM) images show that intrinsic crystalline defects such as stacking fault dislocations are very effective pinning centers for vortices in addition to the pinning centers due to ion bombardment. By counting the number of vortex, we found that the flux trapped at each pinning center is a single flux quantum. At higher magnetic field, the vortex structure showed an Abrikosov lattice disturbed only by immobile vortices located at pinning centers. When increasing or decreasing the external magnetic field, the spatial distribution of vortices showed a Bean model like behavior.     

Evidence of flexoelectricity in polymer-dispersed liquid crystals

The linear electro-optic response of polymer-dispersed liquid crystal films has been studied. Micrometer-sized droplets of a cyanobiphenyl mixture (E7) were formed in a Norland Optical Adhesive 65 photopolymer by photopolymerization-induced phase separation. Samples with various average nematic droplet sizes were systematically investigated. The temperature dependence of the first-harmonic electro-optic spectra was obtained. Peculiar peaks and double peaks in the phase spectra were found at temperatures close to the clearing point. Samples with narrow distributions of droplet sizes were characterized by a double peak of the amplitude spectra in the low-frequency range. A flexoelectric origin of the first-harmonic spectra in confined nematic systems is discussed.     

Entropy Based Approach to Data Loss Reparation Through the Indeterminate Fine-Grained Parallel Computation

The new method of a gap recovery in symbol sequences is presented. A covering is combined from the suitable reasonably short strings of the parts of a sequence available for observation. Two criteria are introduced to choose the best covering. It must yield the maximum of entropy of a frequency dictionary developed over the sequence obtained due to the recovery, if an overlapping combined from the copies of strings from the available parts of the sequence exists. The second criterion identifies the best covering in case when one has to use any string to cover the gap; here the best covering must yield the minimum of specific entropy of the frequency dictionary developed over the available parts of the sequence against the one developed over the entire sequence obtained due to the recovery. Kirdin kinetic machine which is the ideal fine-grained structureless computer has been used to resolve the problem of the reconstruction of a gap in symbol sequence.     

Ionizing-Radiation Response of the GaAs/(Al, Ga)As PHEMT: A Comparison of Gamma- and X-ray Results

An experiment is reported on the effect of ⁶⁰Co gamma rays or 45-keV x-ray photons on the GaAs/(Al, Ga)As PHEMT. It is shown that x-ray treatment can improve the dc performance of the device in some cases. This finding is attributed in part to the annealing or modification of DX centers.     

Effect of proton radiation on the kinetics of phosphorescence decay in the ceramic material ZnS-Cu

The results of studying the dose dependences of the decay kinetics of phosphorescence excited by X-ray radiation in luminescent ZnS-Cu ceramic material before and after irradiation with 50-MeV protons are considered. An anomalous variation in the exponent of the hyperbolic phosphorescence curves was observed experimentally as the accumulated light sum increased. It is found from an analysis of the data obtained that two processes are involved in the decay: one of these is monomolecular and corresponds to the first-order kinetics; the other is bimolecular and corresponds to the second-order kinetics. Transitions of charge carriers delocalized from traps occur at the nonradiative-recombination centers induced by proton radiation. Recombination of these charge carriers at the emission centers in the course of decay is described by the second-order kinetics.     

Electromagnetic coupling effects on the cavity measurement of antenna efficiency

Electromagnetic coupling effects on the antenna in a conducting cavity are studied theoretically and experimentally. It is observed in experiments that at the resonant frequencies of the cavity, the input resistance of the antenna attains values two or three orders of magnitude higher than that at frequencies away from resonance. It is shown via theoretical analysis that the input resistance of the antenna measured at the resonant frequencies of the cavity is not merely the loss resistance desired in computing the antenna efficiency, but is actually the sum of the loss resistance of the antenna and the coupling resistance between the antenna and cavity. This coupling effect is demonstrated quantitatively by numerical computations for dipole and monopole antennas. The computational results for the input resistance are in agreement with the measured data. A method is proposed to avoid the cavity-antenna antiresonance in the measurement.     

Exploiting the high-frequency performance of low-voltage low-power SC filters

This paper investigates the design of low-voltage low-power switched-capacitor (SC) filters for high-frequency applications by using the clock-booster approach. In particular, our proposed SC filter architecture uses single-ended double-sampling integrator cells based on low-voltage operational transconductance amplifiers which take advantage of dynamic biasing and the clock-booster technique to drive the switch transistors. To validate its high-frequency capability, two low-pass elliptic SC filters respectively with a corner frequency of 6 and 8-MHz, were designed in a 0.35-/spl mu/m CMOS process. Both are suitable for telecom applications and can operate with a power supply as low as 1.5 V, while dissipating 11 mW. Measurements showed that for an output amplitude of 1 V/sub pp/, their total harmonic distortions were maintained well below -40 dB in their bandwidths. Comparisons with other SC filter implementations in the literature, which highlight the quality of our implementation are also provided.     

The impact of publicly funded basic research: an integrative extension of Martin and Salter

This paper provides an integrative literature review of the research on the impact of the public funding of basic research, extending previous work done at the Science Policy Research Unit (SPRU), University of Sussex, East Sussex, UK. "Impact" is measured in terms of publications, patents, new drugs, employment, and new start-up companies. The primary focus of this paper is on empirical studies of the impact of biomedical research. However, a few key theoretical papers and empirical papers with a broader industrial focus are also reviewed to provide a more complete perspective. Conclusions, including an alternative view that basic research need not be public supported, and future research opportunities in this area are also discussed.     

Vibration thresholds for fretting corrosion in electrical connectors

Single frequency vibration tests were used to induce fretting corrosion in tin alloy plated contacts. The samples used in this study were connectors consisting of 25 pairs of mated pin and socket contacts. Experimental results for a variety of vibration levels, frequencies, and wiring tie-off lengths are presented. The experiments consisted of running a series of vibration tests at each frequency where the excitation level was stepped through a range of g-levels. During each test run contact resistance was monitored as a performance characteristic. The results exhibit threshold behavior at each frequency for the onset of fretting degradation. Typically a plateau region was observed where similar g-levels produced similar fretting rates. It was also found that outside the plateau region the g-levels varied according to the dynamic behavior of the mechanical system. In addition, a transfer matrix model was used to analyze these results. An empirical fit of the data correlated well with the model when damping was used. This analysis revealed the importance of the bending moment induced at the contact interface as a result of excitation levels and tie-off configurations. Consequently, it is concluded that dynamic response of the mechanical system under various g-levels and tie off configurations can greatly impact the performance of a connector system subjected to vibration stresses.