Mixed-State Hall Effect in HgBa2CaCu2O6+δ Thin Films with Columnar Defects

The mixed state Hall effect has been studied in high quality HgBa₂CaCu₂O_6+δ thin films while the pinning strength is modified by the irraddition of columnar defects. It has been shown that the pinning strength can be significantly improved by columnar defects. The sign reversal in Hall resistivity is found to be nearly independent of pinning while the scaling behavior between Hall resistivity (ρ_xy) and longitudinal resistivity (ρ_xx) is influenced by pinning. The exponent β in the scaling law β _xy ～ β _xy ^β decrease from 1.8 ± 0.1 to 1.5 ± 0.1 as pinning is enhanced. This results suggest that the sign reversal and the scaling are unrelated, and pinning is not the mechanism of the sign reversal.     

The elastic Green's function for the pinned flux-line lattice in a type II superconductor

The elastic Green's function for the pinned flux-line lattice in the critical state is defined and evaluated in the coherent potential approximation. The presence of pinning sites contributes an additional restoring force, which must be calculated within a complete theory of the critical state, but which can be measured. Results are given for the dependence of the Green's function on the density of strong flux-line pins, and a criterion is derived for the applicability of the dilute-limit approximation. This criterion is never satisfied near the upper and lower critical fields. Assuming that the pins all interact sufficiently strongly with the flux-line lattice to exceed the threshold criterion, we find that the Green's function decreases (the flux-line lattice becomes more rigid) with increasing pin density.Research sponsored by the Division of Materials Science, U.S. Department of Energy under contract W-7405-eng-26 with the Union Carbide Corporation.     

The statistical summation of weak flux-line pins in type II superconductors

A random array of flux-line-pinning defects is shown to produce instabilities in the flux-line lattice and a significant bulk pinning-force density even if the pins individually fail to satisfy the threshold criterion. A simplified model defect-flux-line interaction is used to obtain approximate expressions for the critical pinning-force densityF _c.The theory predicts that in materials with a dilute array of weak pinsF _cdepends only weakly on magnetic field except within narrow peaks near the upper and lower critical fields. The width of the peaks increases as the pins are made denser or stronger. A broad, dome-shaped peak inF _cand scaling-law behavior, both of which are usually associated with large-F _cmaterials, is the strong-pinning limit of this theory. This limit may be reached either by making the pins very strong or very dense. The results forF _cagree at least qualitatively with a number of experimental observations.     

Ultrasonic vocalizations by male house mice (Mus musculus) to novel odors: Roles of infant and adult experience.

Conducted 2 experiments to examine 70-kHz ultrasonic courtship vocalizations by adult male mice to novel odors following exposure to these odors in infancy and/or adulthood. Exp I, with 72 males, demonstrated that adult males normally do not vocalize to the urine of female rats but would if adult female mice odorized with female rat urine were repeatedly encountered postpubertally. On the other hand, encountering their own mother odorized with female rat urine from birth until weaning did not promote vocalizations to the urine of female rats. Exp II, with 100 males, examined vocalizations to the urine of female mice whose urinary odor was altered by the ingestion of fenugreek, a spice. Greater amounts of vocalization again were seen by males that as adults encountered females that had ingested fenugreek. Again, experience with the novel odor during infancy was not associated with elevated vocalizations during adulthood either to fenugreek-altered urine or to the fenugreek odor itself. Vocalizations to 2 different novel odors occurred only after an adult male had encountered an adult female odorized with the novel odor. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Male mouse (Mus musculus) attraction to airborne urinary odors of conspecifics and to food odors: Effects of food deprivation.

Five experiments demonstrated that 112 male mice were strongly attracted to the urinary odors of females, and that male urinary odors were considerably less attractive. The strong attraction to female urinary odors did not require that the males have postweaning experience with females. Males with continuous access to food and water were much more strongly attracted to female urinary odors than to the airborne food odors. Female urinary odors remained more attractive than food odors after 24-hr food deprivation, and only after 48-hr deprivation did the attractiveness of food odors approximate that of female urine. Although 48-hr food deprivation appeared to equalize the attractiveness of urinary and food odors, this regimen did so not by diminishing the attractiveness of female urine but rather by increasing the attractiveness of food odors. It is argued that the attraction that male mice exhibited to female urinary odors in this odor-testing apparatus reflected, at least in part, a biologically important precopulatory communication system. (29 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The influence of thermally activated flux creep on the ac response of a hard superconductor

A theoretical and experimental study is presented of the influence of thermally activated flux creep on the ac response of a type II superconductor in the mixed state. The theory describes the ac response of a cylindrical superconductor in the mixed state in an axial dc magnetic field and a superposed parallel ac field of low amplitude and low frequency. Thermally activated flux creep gives rise to flux motion at the peak and the valley of the sinusoidal ac applied field and a frequency-independent phase shift of the voltage induced in a pickup coil wound about the sample. The instantaneous voltage at the peak or valley of the ac applied field is related to the critical-current density J _c and the pinning-energy barrier normalized by the temperature U/kT. The ac loss voltage and the voltage waveform were measured for a cold-worked NbZr sample. For temperatures T below 4.2 K, the measured values of kT/U are nearly proportional to the temperature. Both J _c and U were observed to depend on magnetic field history.Research sponsored by the Division of Materials Science, U.S. Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corporation.     

Measurement of intracellular free zinc in living cortical neurons: routes of entry

We used the ratioable fluorescent dye mag-fura-5 to measure intracellular free Zn2+ ([Zn2+]i) in cultured neocortical neurons exposed to neurotoxic concentrations of Zn2+ in concert with depolarization or glutamate receptor activation and identified four routes of Zn2+ entry. Neurons exposed to extracellular Zn2+ plus high K+ responded with a peak cell body signal corresponding to a [Zn2+]i of 35-45 nM. This increase in [Zn2+]i was attenuated by concurrent addition of Gd3+, verapamil, omega-conotoxin GVIA, or nimodipine, consistent with Zn2+ entry through voltage-gated Ca2+channels. Furthermore, under conditions favoring reverse operation of the Na+-Ca2+ exchanger, Zn2+ application induced a slow increase in [Zn2+]i and outward whole-cell current sensitive to benzamil-amiloride. Thus, a second route of Zn2+ entry into neurons may be via transporter-mediated exchange with intracellular Na+. Both NMDA and kainate also induced rapid increases in neuronal [Zn2+]i. The NMDA-induced increase was only partly sensitive to Gd3+ or to removal of extracellular Na+, consistent with a third route of entry directly through NMDA receptor-gated channels. The kainate-induced increase was highly sensitive to Gd3+ or Na+ removal in most neurons but insensitive in a minority subpopulation ("cobalt-positive cells"), suggesting that a fourth route of neuronal Zn2+ entry is through the Ca2+-permeable channels gated by certain subtypes of AMPA or kainate receptors.