534 research outputs found
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Effects of c-axis Josephson coupling on dissipation, flux dynamics and the mechanism of high-T{sub c} superconductivity
Measurements of the c-axis transport in highly anisotropic HTS materials strongly indicate that Josephson coupling is involved. This conclusion affects various properties of the HTS cuprates, including the irreversibility behavior for transport in the ab planes, the direct c-axis transport and potentially the mechanism of Cooper pairing
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Effects of vortex-vortex interactions on ion-track pinning in high T{sub c} superconductors
Many superconductor applications rely on the ability to pin vortex lattices. This ability depends on structural defects to pin individual vortices, but vortex-vortex interactions often play an important role in pinning the other vortices. Experimental progress on this complex problem can be made by introducing random arrays of well-defined pinning centers and studying the flux dynamics for a range of vortex densities (i.e., fields). Results of such studies in epitaxial Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub y} films containing ion tracks show the importance of vortex-vortex interactions. As an example, the effective pinning field of the defects rises to many times the ion-dose field for temperatures well below {Tc}
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Determination of the temperature dependence of the penetration depth of Nb in Nb/AlO{sub x}/Nb Josephson junctions from a resistive measurement in a magnetic field
The temperature dependence of the penetration depth of Nb films was determined from resistive transitions of Nb/AlO{sub x}/Nb Josephson junctions in a constant magnetic field applied parallel to the junction planes. Distinct resistance peaks were observed as temperature decreases and those peaks were found to appear when the total flux threading the junction equals an integral multiple of the flux quantum. From this condition, the authors have determined the penetration depth at those peak positions. The temperature dependence was well described by the either dirty local limit or the two-fluid model. This method can be useful for highly fluctuating system like high-temperature superconductors
Theory of the c-Axis Penetration Depth in the Cuprates
Recent measurements of the London penetration depth tensor in the cuprates
find a weak temperature dependence along the c-direction which is seemingly
inconsistent with evidence for d-wave pairing deduced from in-plane
measurements. We demonstrate in this paper that these disparate results are not
in contradiction, but can be explained within a theory based on incoherent
quasiparticle hopping between the CuO2 layers. By relating the calculated
temperature dependence of the penetration depth \lambda_c(T) to the c-axis
resistivity, we show how the measured ratio \lambda_c^2(0) / \lambda_c^2(T) can
provide insight into the behavior of c-axis transport below Tc and the related
issue of ``confinement.''Comment: 4 pages, REVTEX with psfig, 3 PostScript figures included in
compressed for
Electrical transport, thermal transport, and elastic properties of M2AlC (M=Ti, Cr, Nb, and V)
Physical Review B: Condensed Matter and Materials Physics, 72(11): pp. 115120-1—115120-6. Retrieved September 19, 2006 from http://www.mse.drexel.edu/max/pdf%20references/drexel_pdfs/papers/2005/HettingerPRB%202005_NSF.pdf. DOI: http://dx.doi.org/10.1103/PhysRevB.72.115120In this paper we report on a systematic investigation, in the 5 to 300 K temperature regime, of the electronic,
magnetotransport, thermoelectric, thermal, and elastic properties of four M2AlC phases: Ti2AlC, V2AlC,
Cr2AlC, and Nb2AlC. The electrical conductivity, Hall coefficient, and magnetoresistances are analyzed within
a two-band framework assuming a temperature-independent charge carrier concentration. As with other
MAX-phase materials, these ternaries are nearly compensated, viz. the densities and mobilities of electrons and
holes are almost equal. There is little correlation between the Seebeck and Hall coefficients. With Young’s and
shear moduli in the 270 GPa and 120 GPa range, respectively, the phases studied herein are reasonably stiff.
With room temperature thermal conductivities in the 25 W/m K range (45 W/m K for V2AlC) they are also
good thermal conductors
Frequency Characteristics of Visually Induced Motion Sickness
This article was published in the journal, Human Factors [Sage Publications / © Human Factors and Ergonomics Society.]. The definitive version is available at: http://dx.doi.org/10.1177/0018720812469046Objective: The aim of this study was to explore
the frequency response of visually induced motion
sickness (VIMS) for oscillating linear motion in the foreand-
aft axis.
Background: Simulators, virtual environments,
and commercially available video games that create an
illusion of self-motion are often reported to induce
the symptoms seen in response to true motion. Often
this human response can be the limiting factor in the
acceptability and usability of such systems. Whereas
motion sickness in physically moving environments
is known to peak at an oscillation frequency around
0.2 Hz, it has recently been suggested that VIMS peaks
at around 0.06 Hz following the proposal that the
summed response of the visual and vestibular selfmotion
systems is maximized at this frequency. Methods: We exposed 24 participants to random
dot optical flow patterns simulating oscillating foreand-
aft motion within the frequency range of 0.025 to
1.6 Hz. Before and after each 20-min exposure, VIMS was
assessed with the Simulator Sickness Questionnaire.
Also, a standard motion sickness scale was used to rate
symptoms at 1-min intervals during each trial.
Results: VIMS peaked between 0.2 and 0.4 Hz with
a reducing effect at lower and higher frequencies.
Conclusion: The numerical prediction of the
“crossover frequency” hypothesis, and the design
guidance curve previously proposed, cannot be accepted
when the symptoms are purely visually induced.
Application: In conditions in which stationary
observers are exposed to optical flow that simulates
oscillating fore-and-aft motion, frequencies around 0.2
to 0.4 Hz should be avoided
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Direct evidence for, and the nature of, Josephson coupling between Cu-O bilayers in a highly-anisotropic superconductor
The angular-dependent, c-axis resistivity for oxygen-deficient YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} single crystals is shown to be a maximum for fields parallel to the c-axis, i.e., for zero macroscopic Lorentz force, and agrees with a series stack of Josephson tunnel junctions. The c-axis component of field dominates the c-axis dissipation in most cases. The results indicate the possibility of an unusual normal-state c-axis conductance and that the c-axis junctions may be extremely underdamped
Wild Animals in Our Backyard. A Contextual Approach to the Intrinsic Value of Animals
As a reflection on recent debates on the value of wild animals we examine the question of the intrinsic value of wild animals in both natural and man-made surroundings. We examine the concepts being wild and domesticated. In our approach we consider animals as dependent on their environment, whether it is a human or a natural environment. Stressing this dependence we argue that a distinction can be made between three different interpretations of a wild animal’s intrinsic value: a species-specific, a naturalistic, and an individualistic interpretation. According to the species-specific approach, the animal is primarily considered as a member of its species; according to the naturalistic interpretation, the animal is seen as dependent on the natural environment; and according to the individualistic approach, the animal is seen in terms of its relationship to humans. In our opinion, the species-specific interpretation, which is the current dominant view, should be supplemented—but not replaced by—naturalistic and individualistic interpretations, which focus attention on the relationship of the animal to the natural and human environments, respectively. Which of these three interpretations is the most suitable in a given case depends on the circumstances and the opportunity for the animal to grow and develop according to its nature and capabilities
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