The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. ...This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La(0.67)Sr(0.33)MnO(3)/SrRuO(3), through magnetization and polarized neutron reflectometry measurements. We ...reveal that the magnetization reversal process of the La(0.67)Sr(0.33)MnO(3) biased layer critically depends on the frozen-in spin structure of the SrRuO(3) biasing layer during the cooling process. Furthermore, we observe unexpected double-shifted hysteresis loops of the biased layer that originates from the formation of lateral 180° magnetic domains within the biasing layer, a new mechanism not found in conventional exchange-bias systems.
Abstract
Introduction:
The timing of shift start affects motorcoach drivers’ ratings of sleepiness. Here we compare the start of work sleepiness ratings to those made at the end of work among ...commercial motorcoach drivers.
Methods:
Seventy-eight commercial motorcoach drivers were monitored for approximately one month as they completed their usual work and rest schedules. Drivers kept a sleep/work diary, continuously wore an actigraph to record sleep/wake, and self-rated their sleepiness with the Karolinska Sleepiness Scale at the start and end of work periods. Sleep duration within each 24-hour period preceding duty start was summed, and shift end times were binned into morning (06:00 to 13:59), afternoon (14:00 to 21:59), and night (22:00 to 05:59). Changes in sleepiness ratings were analysed using linear mixed-effects models.
Results:
During the study period 1,518 work periods were observed, though pre- and post- work ratings for both measures were available for only 1306 shifts. Work periods tended to end in the afternoon (mean = 17:24 ± 5:46) and averaged 9.2 (± 3.0) hours in duration. Drivers obtained a mean of 6.4 (± 1.6) hours of sleep during the 24 hours prior to duty start. Subjective sleepiness ratings were highest following shifts that ended in the night. Post-shift sleepiness ratings were predicted by rating at shift start, duration of shift, and timing of shift end. Total sleep time in the 24 hours of shift start did not predict end-of-shift sleepiness ratings.
Conclusion:
Duration of pre-work sleep did not predict sleepiness scores at the end of the shift, while operational factors such as shift length, shift timing, and the pre-work sleepiness ratings were important in determining end-of-shift sleepiness levels. Though shift timing is usually dictated by commercial demands in motorcoach operations, these data suggest that shift timing is an important consideration in managing sleepiness.
Support (If Any):
Funded by the Federal Motor Carrier Safety Administration.
We report a significant enhancement of the upper critical field Hc2 of different MgB2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities ...rho, we show a clear trend of an increase in Hc2 as rho increases. One particular high resistivity film had a zero-temperature Hc2(0) well above the Hc2 values of competing non-cuprate superconductors such as Nb3Sn and Nb-Ti. Our high-field transport measurements give record values T and T for high resistivity films and T for untextured bulk polycrystals. The highest Hc2 film also exhibits a significant upward curvature of Hc2(T) and a temperature dependence of the anisotropy parameter opposite to that of single crystals: gamma(T) decreases as the temperature decreases, from to . This remarkable Hc2 enhancement and its anomalous temperature dependence are a consequence of the two-gap superconductivity in MgB2, which offers special opportunities for further Hc2 increases by tuning of the impurity scattering by selective alloying on Mg and B sites. Our experimental results can be explained by a theory of two-gap superconductivity in the dirty limit. The very high values of Hc2(T) observed suggest that MgB2 can be made into a versatile, competitive high-field superconductor.
Regular arrays of magnetic perovskite dots less than 100 nm in diameter (see Figure) are made by a process incorporating pulsed laser deposition, patterning with electron‐beam lithography, and ...exposure to neutralized 200 eV Ar ions. The nanodots preserve the magnetic properties of large‐area magnetic perovskite films, and are the smallest structures made of these materials to date.
Abstract The suprachiasmatic nucleus (SCN) is a circadian oscillator and biological clock. Cell-to-cell communication is important for synchronization among SCN neuronal oscillators and the great ...majority of SCN neurons use GABA as a neurotransmitter, the principal inhibitory neurotransmitter in the adult CNS. Acting via the ionotropic GABAA receptor, a chloride ion channel, GABA typically evokes inhibitory responses in neurons via Cl− influx. Within the SCN GABA evokes both inhibitory and excitatory responses although the mechanism underlying GABA-evoked excitation in the SCN is unknown. GABA-evoked depolarization in immature neurons in several regions of the brain is a function of intracellular chloride concentration, regulated largely by the cation-chloride cotransporters NKCC1 (sodium/potassium/chloride cotransporter for chloride entry) and KCC1-4 (potassium/chloride cotransporters for chloride egress). It is well established that changes in the expression of the cation-chloride cotransporters through development determines the polarity of the response to GABA. To understand the mechanisms underlying GABA-evoked excitation in the SCN, we examined the SCN expression of cation-chloride cotransporters. Previously we reported that the K+ /Cl− cotransporter KCC2, a neuron-specific chloride extruder conferring GABA's more typical inhibitory effects, is expressed exclusively in vasoactive intestinal peptide (VIP) and gastrin-releasing peptide (GRP) neurons in the SCN. Here we report that the K+ /Cl− cotransporter isoforms KCC4 and KCC3 are expressed solely in vasopressin (VP) neurons in the rat SCN whereas KCC1 is expressed in VIP neurons, similar to KCC2. NKCC1 is expressed in VIP, GRP and VP neurons in the SCN as is WNK3, a chloride-sensitive neuron-specific with no serine–threonine kinase which modulates intracellular chloride concentration via opposing actions on NKCC and KCC cotransporters. The heterogeneous distribution of cation-chloride cotransporters in the SCN suggests that Cl− levels are differentially regulated within VIP/GRP and VP neurons. We suggest that GABA's excitatory action is more likely to be evoked in VP neurons that express KCC4.
MOVPE growth of Ga(As)SbN on GaSb substrates Huang, J.Y.T.; Mawst, L.J.; Jha, S. ...
Journal of crystal growth,
11/2008, Letnik:
310, Številka:
23
Journal Article, Conference Proceeding
Recenzirano
GaSb
1−
y
N
y
and GaAs
1−
y
−
z
Sb
y
N
z
alloys on GaSb substrates were grown by metalorganic vapor phase epitaxy (MOVPE) as potential materials for mid-infrared wavelength emission. Nitrogen ...incorporation was found to increase with the presence of As in GaAsSbN when compared with that of GaSbN. Low-temperature (LT) photoluminescence (PL) measurements indicated the co-addition of nitrogen and arsenic reduced the energy bandgap relative to that of GaSb. LT (16
K) PL emission near 2.25
μm was observed from GaAsSbN with an arsenic content of ∼10% and a nitrogen content of ∼0.08%.
The effect of the quantum-well nitride content on the differential gain and linewidth enhancement factor of dilute-nitride GaAs-based near 1.3- mu m lasers was studied. Gain-guided and ridge ...waveguide lasers with 0%, 0.5%, and 0.8% nitrogen content InGaAsN quantum wells were characterized. Experiment shows that the linewidth enhancement factor is independent on the nitride content, and is in the range 1.7-2.5 for lambda =1.22--1.34 mu m dilute-nitride GaAs-based lasers. Differential gain and index with respect to either current or carrier concentration are reduced in dilute-nitride devices.
SUMMARY
Daytime performance changes were examined during chronic sleep restriction or augmentation and following subsequent recovery sleep. Sixty‐six normal volunteers spent either 3 (n = 18), 5 (n= ...16), 7 (n = 16), or 9 h (n = 16) daily time in bed (TIB) for 7 days (restriction/augmentation) followed by 3 days with 8 h daily TIB (recovery). In the 3‐h group, speed (mean and fastest 10% of responses) on the psychomotor vigilance task (PVT) declined, and PVT lapses (reaction times greater than 500 ms) increased steadily across the 7 days of sleep restriction. In the 7‐ and 5‐h groups speed initially declined, then appeared to stabilize at a reduced level; lapses were increased only in the 5‐h group. In the 9‐h group, speed and lapses remained at baseline levels. During recovery, PVT speed in the 7‐ and 5‐h groups (and lapses in the 5‐h group) remained at the stable, but reduced levels seen during the last days of the experimental phase, with no evidence of recovery. Speed and lapses in the 3‐h group recovered rapidly following the first night of recovery sleep; however, recovery was incomplete with speed and lapses stabilizing at a level comparable with the 7‐ and 5‐h groups. Performance in the 9‐h group remained at baseline levels during the recovery phase. These results suggest that the brain adapts to chronic sleep restriction. In mild to moderate sleep restriction this adaptation is sufficient to stabilize performance, although at a reduced level. These adaptive changes are hypothesized to restrict brain operational capacity and to persist for several days after normal sleep duration is restored, delaying recovery.
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