1,959 research outputs found
Giant proximity effect in a phase-fluctuating superconductor
When a tunneling barrier between two superconductors is formed by a normal
material that would be a superconductor in the absence of phase fluctuations,
the resulting Josephson effect can undergo an enormous enhancement. We
establish this novel proximity effect by a general argument as well as a
numerical simulation and argue that it may underlie recent experimental
observations of the giant proximity effect between two cuprate superconductors
separated by a barrier made of the same material rendered normal by severe
underdoping.Comment: 4 pages, 3 figures; version to appear in PRL (results of simulations
in 3d added). For related work and info visit
http://www.physics.ubc.ca/~fran
The Effect of Disclosure on Consumer Knowledge of Credit Terms: A Longitudinal Study
Early evaluations of Truth‐in‐Lending have observed impressive gains in consumer knowledge about interest rates. Contrary to original goals, consumers with more education, income, and debt experience have benefited far more than low‐income and minority consumers. How will these results change over time as consumers gain credit experience with the aid of disclosure? Has disclosure improved consumer understanding about finance charges, and what factors beyond socio‐economic status might have enhanced consumer knowledge of credit terms? These questions are addressed in this report of a large sample of California households surveyed at two points in time. The longitudinal analysis shows individual changes in knowledge, the effects of credit experience on learning, and a projection of future levels of credit knowledge
Superfluid density of superconductor-ferromagnet bilayers
We report the first measurements of the effective superfluid density n_S(T)
\propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where
\lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers
were sputtered in ultrahigh vacuum in quick succession onto oxidized Si
substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses
vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as
Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at
d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several
times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni
thickness long after T_C has stopped changing. We argue that this indicates a
substantial superfluid density inside the ferromagnetic Ni films.Comment: 13 pages, 2 figures, MMM 2007 proceeding
Effects of Breeding Season Length and Calving Season on Range Beef Cow Productivity
A 5-yr study was conducted beginning in 1983 with 460 cows to evaluate the effects of three breeding seasons (30,45, and 70 d in length) and two times of spring calving, March (early) and April (late), on cattle production under Nebraska Sandhills range conditions. Criteria evaluated included pregnancy and weaning percentages, calving date and distribution, cow weights and body condition at four intervals, calf birth and weaning weights, and cow productivity. The 30-d breeding season included a 10-d estrus synchronization and AI period; in the other breeding seasons only natural breeding was used. The same sires were used over the entire study period. Percentage of cows pregnant and percentage of calves weaned were lower (P \u3c .01) for cows bred for 30 d than for cows bred for 45 or 70 d. Average calving dates were similar among the breeding groups within the early and late calving herds. Pregnancy rates from AI were higher (P \u3c .01) for the cows calving in April (64%) than for the cows calving in March (41%). Cows calving in April lost less weight between precalving and prebreeding and were heavier (P \u3c .05) at prebreeding time than the cows calving in March. Calf weaning weights were not different (P \u3e .10) among any of the breeding season groups or between the two calving herds when calves were weaned at a similar age. Cow productivity (calf weaning weight per breeding female) was highest (P \u3c .05) for the cows bred for 70 d (186 kg), intermediate for the cows bred for 45 d (172 kg), and lowest for cows bred for 30 d (162 kg). No difference in cow productivity was found between the two calving herds (early, 172 kg and late, 175 kg). We concluded that cows bred for 70 d had the highest productivity and that an April calving season was as productive as a March calving season in the Nebraska Sandhills
Towards understanding the variability in biospheric CO2 fluxes:Using FTIR spectrometry and a chemical transport model to investigate the sources and sinks of carbonyl sulfide and its link to CO2
Understanding carbon dioxide (CO2) biospheric processes is of great importance because the terrestrial exchange drives the seasonal and interannual variability of CO2 in the atmosphere. Atmospheric inversions based on CO2 concentration measurements alone can only determine net biosphere fluxes, but not differentiate between photosynthesis (uptake) and respiration (production). Carbonyl sulfide (OCS) could provide an important additional constraint: it is also taken up by plants during photosynthesis but not emitted during respiration, and therefore is a potential means to differentiate between these processes. Solar absorption Fourier Transform InfraRed (FTIR) spectrometry allows for the retrievals of the atmospheric concentrations of both CO2 and OCS from measured solar absorption spectra. Here, we investigate co-located and quasi-simultaneous FTIR measurements of OCS and CO2 performed at five selected sites located in the Northern Hemisphere. These measurements are compared to simulations of OCS and CO2 using a chemical transport model (GEOS-Chem). The coupled biospheric fluxes of OCS and CO2 from the simple biosphere model (SiB) are used in the study. The CO2 simulation with SiB fluxes agrees with the measurements well, while the OCS simulation reproduced a weaker drawdown than FTIR measurements at selected sites, and a smaller latitudinal gradient in the Northern Hemisphere during growing season when comparing with HIPPO (HIAPER Pole-to-Pole Observations) data spanning both hemispheres. An offset in the timing of the seasonal cycle minimum between SiB simulation and measurements is also seen. Using OCS as a photosynthesis proxy can help to understand how the biospheric processes are reproduced in models and to further understand the carbon cycle in the real world
Determination of the critical current density in the d-wave superconductor YBCO under applied magnetic fields by nodal tunneling
We have studied nodal tunneling into YBa2Cu3O7-x (YBCO) films under magnetic
fields. The films' orientation was such that the CuO2 planes were perpendicular
to the surface with the a and b axis at 450 form the normal. The magnetic field
was applied parallel to the surface and perpendicular to the CuO2 planes. The
Zero Bias Conductance Peak (ZBCP) characteristic of nodal tunneling splits
under the effect of surface currents produced by the applied fields. Measuring
this splitting under different field conditions, zero field cooled and field
cooled, reveals that these currents have different origins. By comparing the
field cooled ZBCP splitting to that taken in decreasing fields we deduce a
value of the Bean critical current superfluid velocity, and calculate a Bean
critical current density of up to 3*10^7 A/cm2 at low temperatures. This
tunneling method for the determination of critical currents under magnetic
fields has serious advantages over the conventional one, as it avoids having to
make high current contacts to the sample.Comment: 8 pages, 2 figure
Proximity Effect Enhancement Induced by Roughness of SN Interface
Critical temperature reduction is considered for a thin film of
a layered superconductor (S) with a rough surface covered by a thick layer of a
normal metal (N). The roughness of the SN interface increases the penetration
of electrons from the normal metal into the superconductor and leads to an
enhancement of the proximity effect. The value of induced by the
roughness of the SN interface can be much higher than for a film
with a plain surface for an extremely anisotropic layered superconductor with
the coherence lengths .Comment: 2 page
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0
The importance of transport model uncertainties for the estimation of CO2 sources and sinks using satellite measurements
This study presents a synthetic model intercomparison to investigate the importance of transport model errors for estimating the sources and sinks of CO2 using satellite measurements. The experiments were designed for testing the potential performance of the proposed CO2 lidar A-SCOPE, but also apply to other space borne missions that monitor total column CO2. The participating transport models IFS, LMDZ, TM3, and TM5 were run in forward and inverse mode using common a priori CO2 fluxes and initial concentrations. Forward simulations of column averaged CO2 (xCO2) mixing ratios vary between the models by s=0.5 ppm over the continents and s=0.27 ppm over the oceans. Despite the fact that the models agree on average on the sub-ppm level, these modest differences nevertheless lead to significant discrepancies in the inverted fluxes of 0.1 PgC/yr per 106 km2 over land and 0.03 PgC/yr per 106 km2 over the ocean. These transport model induced flux uncertainties exceed the target requirement that was formulated for the A-SCOPE mission of 0.02 PgC/yr per 106 km2, and could also limit the overall performance of other CO2 missions such as GOSAT. A variable, but overall encouraging agreement is found in comparison with FTS measurements at Park Falls, Darwin, Spitsbergen, and Bremen, although systematic differences are found exceeding the 0.5 ppm level. Because of this, our estimate of the impact of transport model uncerainty is likely to be conservative. It is concluded that to make use of the remote sensing technique for quantifying the sources and sinks of CO2 not only requires highly accurate satellite instruments, but also puts stringent requirements on the performance of atmospheric transport models. Improving the accuracy of these models should receive high priority, which calls for a closer collaboration between experts in atmospheric dynamics and tracer transpor
Andreev bound states in normal and ferromagnet/high-Tc superconducting tunnel junctions
Ag/BSCCO and Fe/Ag/BSCCO planar tunnel junctions were constructed in order to
study experimentally the effect of an exchange potential on the spin polarized
current transported through Andreev bound states appearing at the interface
with a superconductor with broken time reversal pairing symmetry. The zero bias
conductance peak (ZBCP) resulting from the Andreev bound states (ABS) is split
into two symmetric peaks shifted at finite energies when the counterlectrode is
normal. Four asymmetric peaks are observed when the ferromagnetic spin
polarized charge reservoir is added, due to the combined effect of a
spin-filtering exchange energy in the barrier, which is a spin dependent
phenomenon, and the spin independent effect of a broken time reversal symmetry
(BTRS). The polarization in the iron layer leads to asymmetry. Due to the shift
of ABS peaks to finite energies, the conductance at zero energy behaves as
predicted by recent theoretical developments for pure d-wave junctions without
Andreev reflections.Comment: 4 pages, 2 figures. Submitted to Physica
- …