Magneto-transport Properties and Thermally Activated Flux Flow in Ba(Fe 0 . 9 1 Co 0 . 0 9 ) 2 As 2 Superconductor

Thermally assisted flux flow (TAFF) based on magneto-resistivity and ac susceptibility measurements is studied in a Ba(Fe_0.91Co_0.09)₂As₂(T _c=25.3 K) sample in magnetic fields up to 18 T. In addition to the upper critical field μ ₀ H _c2 and the coherence length ξ(0), the flux flow activation energy U(T,H) has also been determined. The resistive transition width is proportional to μ ₀ H, in contrast to Tinkham’s theoretical prediction. By applying Fisher’s model, the glass melting transition temperature T _g, which occurs in the upper TAFF state and not in the zero resistivity vortex solid regime, is calculated. The onset of TAFF temperature and the crossover temperature T _x from TAFF to flux flow are determined. By contrasting the ac susceptibility data with the resistivity data, considerable flux penetration appears even in the zero resistivity state, in addition to ac losses. The H-T phase diagram is drawn and shows weak pinning regime as the field approaches μ ₀ H _c2, and the strength of the weak pinning decreases to 0 with increasing magnetic field from 0 to 18 T.     

Post-thaw sperm motility, cAMP concentration and membrane lipid peroxidation after stimulation with pentoxifylline and platelet-activating factor

Earlier studies have demonstrated that pentoxifylline (PTX) and platelet-activating factor (PAF) can significantly improve the motion parameters of post-thaw human spermatozoa. This study has investigated the effects of PAF, PTX and their combination on cyclic adenosine monophosphate (cAMP) concentrations and membrane lipid peroxidation (LPO) in post-thaw human spermatozoa. Washed spermatozoa from normal volunteers (n = 10) were cryopreserved in Test-yolk buffer using a standard protocol. After 2 weeks the sperm samples were thawed, washed and incubated with either 1 microM PAF, 3 mM PTX or 0.5 microM PAF plus 1.5 mM PTX. Video sequences were recorded at 0, 30, 60, and 120 min for analysis of sperm motion parameters using the Cell Track Sperm Analysis System. Concentrations of cAMP were assessed by radioimmunoassay, and LPO levels were measured by malondialdehyde-thiobarbituric acid reactivity. Our studies indicate a time-course stimulatory effect with overall maximal stimulation observed in samples treated with the combination of PAF and PTX. The maximal stimulation of percentage motility compared to control was observed at 60 min in samples treated with PAF, PTX, or PAF plus PTX. PAF plus PTX stimulated straight-line velocity (VSL), curvilinear velocity (VCL) and lateral head displacement (ALH) after 30 min incubation. The primary effect of PAF was observed on VSL, while the main effect of PTX was on VCL. cAMP concentrations were 3-fold higher than controls in samples treated with PTX or PAF plus PTX. cAMP concentrations in PAF-treated samples did not differ significantly from controls. No significant differences were observed between any groups for LPO.(ABSTRACT TRUNCATED AT 250 WORDS)     

Compact all-diode-pumped femtosecond laser source based on chirpedpulse optical parametric amplification in periodically poledKTiOPO4

1 kHz chirped pulse optical parametric amplification in periodically poled KTiOPO₄ achieving 20 μJ amplified signal pulse energy at 1.573 μm and 320 fs pulse duration after recompression is reported     

Middle cerebral artery microneurosurgical embolectomy

Cerebral embolism carries significant mortality and morbidity rates. Middle cerebral artery embolectomies which have been carried out in man with variable results, have been reported by different authors, In order to define a time limit for embolectomies before irreversible damage has been incurred, an experimental embolus model was used in dogs. It was observed that embolectomy carried out at 2, 3, and up to 5 hours after embolism was relatively safe and effective. Beyond 5 hours, embolectomy carried an increased risk of death and morbidity.     

Ferroelectric gated electrical transport in CdS nanotetrapods

Complex nanostructures such as branched semiconductor nanotetrapods are promising building blocks for next-generation nanoelectronics. Here we report on the electrical transport properties of individual CdS tetrapods in a field effect transistor (FET) configuration with a ferroelectric Ba(0.7)Sr(0.3)TiO(3) film as high-k, switchable gate dielectric. A cryogenic four-probe scanning tunneling microscopy (STM) is used to probe the electrical transport through individual nanotetrapods at different temperatures. A p-type field effect is observed at room temperature, owing to the enhanced gate capacitance coupling. And the reversible remnant polarization of the ferroelectric gate dielectric leads to a well-defined nonvolatile memory effect. The field effect is shown to originate from the channel tuning in the arm/core/arm junctions of nanotetrapods. At low temperature (8.5 K), the nanotetrapod devices exhibit a ferroelectric-modulated single-electron transistor (SET) behavior. The results illustrate how the characteristics of a ferroelectric such as switchable polarization and high dielectric constant can be exploited to control the functionality of individual three-dimensional nanoarchitectures.     

High intergrain critical current density in fine-grain (Ba0.6K0.4)Fe2As2 wires and bulks

The K- and Co-doped BaFe(2)As(2) (Ba-122) superconducting compounds are potentially useful for applications because they have upper critical fields (H(c2)) of well over 50?T, H(c2) anisotropy γ < 2and thin-film critical current densities J(c) exceeding 1?MA?cm(-2) (refs 1-4) at 4.2?K. However, thin-film bicrystals of Co-doped Ba-122 clearly exhibit weak link behaviour for [001] tilt misorientations of more than about 5°, suggesting that textured substrates would be needed for applications, as in the cuprates. Here we present a contrary and very much more positive result in which untextured polycrystalline (Ba(0.6)K(0.4))Fe(2)As(2) bulks and round wires with high grain boundary density have transport critical current densities well over 0.1?MA?cm(-2) (self-field, 4.2?K), more than 10 times higher than that of any other round untextured ferropnictide wire and 4-5 times higher than the best textured flat wire. The enhanced grain connectivity is ascribed to their much improved phase purity and to the enhanced vortex stiffness of this low-anisotropy compound (γ~1-2) when compared with YBa(2)Cu(3)O(7-x) (γ~5).     

Knapsack packing networks

A knapsack packing neural network of 4n units with both low-order and conjunctive asymmetric synapses is derived from a non-Hamiltonian energy function. Parallel simulations of randomly generated problems of size n in {5, 10, 20} are used to compare network solutions with those of simple greedy fast parallel enumerative algorithms.     

Effects of alprostadil and prazosin on motility, viability and membrane integrity of human sperm

PURPOSE: We evaluated the effects of alprostadil, prazosin hydrochloride, and alprostadil/prazosin hydrochloride, agents used in the clinical treatment of male erectile dysfunction, on the motility, viability and membrane integrity of human sperm. MATERIALS AND METHODS: Ten healthy volunteers provided semen samples that were incubated with 0.4 mg./ml. alprostadil, 0.1 and 0.2 mg./ml. prazosin hydrochloride and 0.4 mg./ml. alprostadil plus 0.1 mg./ml. prazosin hydrochloride for 2 hours. Control incubations included polyethylene glycol 1450, the formulation vehicle for the clinical use of alprostadil and prazosin, and Ham's F-10 buffer. Serial evaluations of percent sperm motility, percent viability, membrane function (by hypo-osmotic swelling test) and several computer generated measurements of sperm motion, including straight line velocity, curvilinear velocity, linearity and amplitude of lateral head displacement, were made. RESULTS: None of the agents had a significant impact on the percentage of motile or viable sperm or on sperm membrane function. Incubation with 0.2 mg./ml. prazosin reduced straight line velocity and curvilinear velocity significantly compared with the other agents. These changes were most likely a direct result of the viscosity of the 0.2 mg./ml. prazosin solution and not a cellular or metabolic effect on the sperm. CONCLUSIONS: Alprostadil and prazosin hydrochloride at doses used in transurethral therapy for erectile dysfunction have no effect on the motility, viability and membrane integrity of human sperm.