2,184 research outputs found
Microwave Conductivity due to Impurity Scattering in a d-wave Superconductor
The self-consistent t-matrix approximation for impurity scattering in
unconventional superconductors is used to interpret recent measurements of the
temperature and frequency dependence of the microwave conductivity of YBCO
crystals below 20K. In this theory, the conductivity is expressed in terms of a
fequency dependent single particle self-energy, determined by the impurity
scattering phase shift which is small for weak (Born) scattering and approaches
for unitary scattering. Inverting this process, microwave
conductivity data are used to extract an effective single-particle self-energy
and obtain insight into the nature of the operative scattering processes. It is
found that the effective self-energy is well approximated by a constant plus a
linear term in frequency with a small positive slope for thermal quasiparticle
energies below 20K. Possible physical origins of this form of self-energy are
discussed.Comment: 5 pages, 4 figure
Phase Separation by Entanglement of Active Polymerlike Worms
We investigate the aggregation and phase separation of thin, living T.
tubifex worms that behave as active polymers. Randomly dispersed active worms
spontaneously aggregate to form compact, highly entangled blobs, a process
similar to polymer phase separation, and for which we observe power-law growth
kinetics. We find that the phase separation of active polymerlike worms does
not occur through Ostwald ripening, but through active motion and coalescence
of the phase domains. Interestingly, the growth mechanism differs from
conventional growth by droplet coalescence: the diffusion constant
characterizing the random motion of a worm blob is independent of its size, a
phenomenon that can be explained from the fact that the active random motion
arises from the worms at the surface of the blob. This leads to a fundamentally
different phase-separation mechanism that may be unique to active polymers.Comment: 4 pages, 4 figure
Toolboxes and handing students a hammer: The effects of cueing and instruction on getting students to think critically
Developing critical thinking skills is a common goal of an undergraduate
physics curriculum. How do students make sense of evidence and what do they do
with it? In this study, we evaluated students' critical thinking behaviors
through their written notebooks in an introductory physics laboratory course.
We compared student behaviors in the Structured Quantitative Inquiry Labs
(SQILabs) curriculum to a control group and evaluated the fragility of these
behaviors through procedural cueing. We found that the SQILabs were generally
effective at improving the quality of students' reasoning about data and making
decisions from data. These improvements in reasoning and sensemaking were
thwarted, however, by a procedural cue. We describe these changes in behavior
through the lens of epistemological frames and task orientation, invoked by the
instructional moves
Survival of the d-wave superconducting state near the edge of antiferromagnetism in the cuprate phase diagram
In the cuprate superconductor , hole doping in the
layers is controlled by both oxygen content and the degree of oxygen-ordering.
At the composition , the ordering can occur at room
temperature, thereby tuning the hole doping so that the superconducting
critical temperature gradually rises from zero to 20 K. Here we exploit this to
study the c-axis penetration depth as a function of temperature and doping. The
temperature dependence shows the d-wave superconductor surviving to very low
doping, with no sign of another ordered phase interfering with the nodal
quasiparticles. The only apparent doping dependence is a smooth decline of
superfluid density as Tc decreases.Comment: 4 pages, 3 figure
Effect of swelling clays in the instability of clayey soils Case study: Quicksand and Quickclay
The aim of this work is to study the effect of swelling clays on the instability of two soils, quicksand and quickclay, famous for their high damaging effect. The complex flow behavior of these materials is based on the X-Rays diffraction characterization results and the preparation of laboratory quicksand and laboratory quickclay, which mimic exactly the flow behavior of these two natural soils. We show that a spectacular liquefaction of the Quicksand and Quickclay occurs when a stress is applied to the material. By constructing both 'laboratory quicksand' and ‘laboratory Quickclay’, we demonstrate that the liquefaction is due to the structure of these two soils. The presence of both swelling clays and salt play a key effect on the instability of the two soils
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