Cryogenic-coolant He4-superconductor dynamic and static interactions

A composite superconducting material (NbTi-Cu) was evaluated with emphasis on post quench solid cooling interaction regimes. The quasi-steady runs confirm the existence of a thermodynamic limiting thickness for insulating coatings. Two distinctly different post quench regimes of coated composites are shown to relate to the limiting thickness. Only one regime,, from quench onset to the peak value, revealed favorable coolant states, in particular in He2. Transient recovery shows favorable recovery times from this post quench regime (not drastically different from bare conductors) for both single coated specimens and a coated conductor bundle

Quantum Bit Regeneration

Decoherence and loss will limit the practicality of quantum cryptography and computing unless successful error correction techniques are developed. To this end, we have discovered a new scheme for perfectly detecting and rejecting the error caused by loss (amplitude damping to a reservoir at T=0), based on using a dual-rail representation of a quantum bit. This is possible because (1) balanced loss does not perform a ``which-path'' measurement in an interferometer, and (2) balanced quantum nondemolition measurement of the ``total'' photon number can be used to detect loss-induced quantum jumps without disturbing the quantum coherence essential to the quantum bit. Our results are immediately applicable to optical quantum computers using single photonics devices.Comment: 4 pages, postscript only, figures available at http://feynman.stanford.edu/qcom

Ground-state configuration space heterogeneity of random finite-connectivity spin glasses and random constraint satisfaction problems

We demonstrate through two case studies, one on the p-spin interaction model and the other on the random K-satisfiability problem, that a heterogeneity transition occurs to the ground-state configuration space of a random finite-connectivity spin glass system at certain critical value of the constraint density. At the transition point, exponentially many configuration communities emerge from the ground-state configuration space, making the entropy density s(q) of configuration-pairs a non-concave function of configuration-pair overlap q. Each configuration community is a collection of relatively similar configurations and it forms a stable thermodynamic phase in the presence of a suitable external field. We calculate s(q) by the replica-symmetric and the first-step replica-symmetry-broken cavity methods, and show by simulations that the configuration space heterogeneity leads to dynamical heterogeneity of particle diffusion processes because of the entropic trapping effect of configuration communities. This work clarifies the fine structure of the ground-state configuration space of random spin glass models, it also sheds light on the glassy behavior of hard-sphere colloidal systems at relatively high particle volume fraction.Comment: 26 pages, 9 figures, submitted to Journal of Statistical Mechanic

THE RESPONSE OF WHOLE BODY VIBRATION ON TAI CHI AND WEIGHT-LIFTING ATHLETES

Whole body vibration (WBV) is a new technique which may improve leg muscle strength. Many researchers have studied the effect of whole body vibration recently. But study of effects of vibration stimulus to different activity type athletes, such as Tai Chi (N=12) and Weight-lifting (N=15) athletes is lacking. In this study we examine that question. The subjects were asked to stand in a half-squat posture without additional load on a vibration platform with 7 vibration frequencies (5, 9, 12, 16, 20, 24, 30 Hz) at 4 mm amplitude and maintained for 30 seconds. The effect of WBV would be different on different sport subjects’ perceived exertion. We discovered that the subject’s perception may be related with the acceleration of the subject’s head. Using whole body vibration training to improve muscle power and strength depends on the particular sport’s training emphasis to setup the appropriate training protocol such as amplitude and frequency

Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs

If strong electron-electron interactions between neighboring Fe atoms mediate the Cooper pairing in iron-pnictide superconductors, then specific and distinct anisotropic superconducting energy gaps \Delta_i(k) should appear on the different electronic bands i. Here we introduce intra-band Bogoliubov quasiparticle scattering interference (QPI) techniques for determination of \Delta_i(k) in such materials, focusing on LiFeAs. We identify the three hole-like bands assigned previously as \gamma, \alpha_2 and \alpha_1, and we determine the anisotropy, magnitude and relative orientations of their \Delta_i(k). These measurements will advance quantitative theoretical analysis of the mechanism of Cooper pairing in iron-based superconductivity

Flammability and tensile properties of polylactide nanocomposites with short carbon fibers

[[abstract]]Nanocomposites of polylactide (PLA) with aluminum hydroxide (ATH), short carbon fibers (CF), and montmorillonite (MMT) were prepared via direct melt blending. The exfoliated and intercalated clay structures with some aggregations in the PLA matrix were observed. The tensile strength and elongation at break of the PLA composite caused by the high content of the retardant ATH were improved by adding modified MMT and CF to replace a portion of ATH in the PLA matrix. The thermal degradation temperatures and char residue of the PLA/ATH/MMT/CF nanocomposites as determined by thermogravimetric analysis were higher than without MMT. Furthermore, a novel method was proposed to analyze the flammability of composite using an infrared camera, which could capture the apparent thermal image of the sample during UL 94 V test. It was found that, with addition of the MMT and short CF, a more effective insulation layer could be formed on the ablating surface of the PLA/ATH composite, and the high thermal conductivity of the CF might increase the release rate of heat from the surface composite during burn, thus the PLA/ATH/MMT nanocomposite containing short carbon fibers having a V-0 rating without flaming dripping could be obtained.[[incitationindex]]SCI[[booktype]]電子

Carrier dynamics and coherent acoustic phonons in nitride heterostructures

We model generation and propagation of coherent acoustic phonons in piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode structure and compute the time resolved reflectivity signal in simulated pump-probe experiments. Carriers are created in the InGaN wells by ultrafast pumping below the GaN band gap and the dynamics of the photoexcited carriers is treated in a Boltzmann equation framework. Coherent acoustic phonons are generated in the quantum well via both deformation potential electron-phonon and piezoelectric electron-phonon interaction with photogenerated carriers, with the latter mechanism being the dominant one. Coherent longitudinal acoustic phonons propagate into the structure at the sound speed modifying the optical properties and giving rise to a giant oscillatory differential reflectivity signal. We demonstrate that coherent optical control of the differential reflectivity can be achieved using a delayed control pulse.Comment: 14 pages, 11 figure

Doubling of the bands in overdoped Bi2Sr2CaCu2O8-probable evidence for c-axis bilayer coupling

We present high resolution ARPES data of the bilayer superconductor Bi2Sr2CaCu2O8 (Bi2212) showing a clear doubling of the near EF bands. This splitting approaches zero along the (0,0)-(pi,pi) nodal line and is not observed in single layer Bi2Sr2CuO6 (Bi2201), suggesting that the splitting is due to the long sought after bilayer splitting effect. The splitting has a magnitude of approximately 75 meV near the middle of the zone, extrapolating to about 100 meV near the (pi,0) poin