Superconducting study of the intermettalic YNi₂B₂C single crystal and several high-Tc materials

Magnetization studies on a single crystal of YNi2B2C superconductor have revealed significant effects of nonlocality in the superconductive state and have displayed a significant angular variation in normal state. The 17 mg crystal was studied at temperatures Τ from above Τc(15 K) to 2 ~ 3 K, in magnetic fields Η applied parallel and perpendicular to the (001)-crystal axis, within magnetic fields from zero to Η Ηc2, the upper critical field. The material exhibited little magnetic irreversibility, with a critical current density ~ 10-4 x J0, the depairing current density. This nearly reversible behavior has allowed an analysis of its equilibrium properties: the thermodynamic critical field Hc(T), Hc2(T), and the magnetization M(H,T) in both the normal and superconductive states. Near Tc, the equilibrium magnetization M of the clean single crystal of YNi2B2C was standard London-like with M α ln(H) Well below Tc however, M is shown to deviate significantly from this simple local London predictions, but the behavior is well described by non-local London theory, which is a more general theory derived by Kogan et al. [Phys. Rev. B 54, 12386 (1996)]. The non-local analysis yields reasonable values for the nonlocality radius ρ and London penetration depth λ. The T dependence of λ was obtained from both non-local London analysis at low temperatures and a standard local-London analysis near Τc. Contrary to the exponential dependence expected for simple s-wave pairing, the nearly Τ3behavior for λ(7) below 10 K seems to give evidence for a more complex, perhaps non-jwave pairing scheme. In addition, the normal state magnetic susceptibility was measured -IVin the temperature regime between 16 K and 295 K in an applied field of 10 kG, for the magnetic field applied parallel or perpendicular to the crystalline (OOl)-direction. The material exhibited a large anisotropy between the two field orientations, particularly in the low temperature regime. Furthermore, according to heat capacity studies of YNi2B2C, the material appears to deviate from both weak- and strong-coupling superconductive mechanisms, but agrees relatively well with predictions [Ce,super∝t3] of a medium-coupling formalism. From magnetization and heat capacity studies, the deduced values of the Ginzburg-Landau parameters κ1 and κ2 increase considerably as T decreases. This is consistent with the material\u27s long electronic mean fi-ee path and the observation of non local electrodynamics. Several features of high temperature superconductors were investigated in complementary work. In studies of the effects of adding elemental Ag to high Τc superconducting HgBa2Cu04+ materials, a series of polycrystalline AgJIgBa2Cu04+j materials (with molar fraction x = 0, 0.05, 0.1, 0.3, and 0.5) were investigated. The processing with Ag at elevated temperatures led to changes in superconducting properties. These are consistently interpreted in terms of the superconducting hole density, calculated from the London penetration depth λ by analysis of the equilibrium magnetization M using standard London theory. The irreversible magnetic properties of these materials are dominated by surface barrier effects and are well described in terms of thermally activated tunneling of pancake vortices through a surface barrier. For practical applications, vortex pinning in high-Tc superconducting (HTS) materials is very important. To pin vortices strongly, splayed columnar tracks produced -Vusing a fission process, induced by high energy (GeV) proton irradiation, have been formed in several HTS materials. Overall, the magnetic hysteresis ΔM (α J) of the materials is greatly increased by the splayed columnar defects. The hysteresis or persistent current density first increases with increasing the proton fluence Φp, then passes through an optimal proton fluence, and finally decreases at much higher Φp. In contrast with ΔM (α J)that is enhanced significantly by the columnar defects, the superconducting transition temperature Tc is suppressed somewhat, with a material-dependent rate. By analyzing the decay rate of J with a time in a Maley analysis, the effective pinning energy U(J) was obtained with both irradiated and unirradiated materials. The net pinning potential barrier of vortices is clearly enhanced by the splayed columnar tracks, from 0.8 GeV proton irradiation. In general, these splayed columnar defects lead to significant enhancements in the vortex pinning effect within the HTS materials investigated

Confronting the fourth generation two Higgs doublet model with the phenomenology of heavy Higgs bosons

A sequential fourth generation is known to be excluded because the non-decoupling contribution to $\kappa_g$, the Higgs coupling modifier with a gluon pair, is unacceptably large. Recently a new way to save the model was suggested in the Type-II two Higgs doublet model: if the Yukawa couplings of down-type fermions have wrong-sign, the contributions from $t'$ and $b'$ to $\kappa_g$ are cancelled. We study the theoretical and experimental constraints on this model, focusing on the heavy Higgs bosons. Two constraining features are pointed out. First the exact wrong-sign limit does not allow the alignment, which makes the perturbative unitarity for the scalar-scalar scattering put the upper bounds on the heavy Higgs boson masses like $M_H, M_A \lesssim 920$ GeV and $M_{H^\pm} \lesssim 620$ GeV. Secondly, the Yukawa couplings of the fourth generation fermions to the heavy Higgs bosons are generically large as being proportional to the heavy fermion mass and, for the down-type fermions, to $\tan\beta$ as well. The gluon fusion productions of $H$ and $A$ through the fourth generation quark loops become significant. We found that the current LHC data on $pp \to Z Z$ for $H$ along with the theoretical and indirect constraints exclude the model at leading order.Comment: 30 pages with 17 figure

A Logical Model and Data Placement Strategies for MEMS Storage Devices

MEMS storage devices are new non-volatile secondary storages that have outstanding advantages over magnetic disks. MEMS storage devices, however, are much different from magnetic disks in the structure and access characteristics. They have thousands of heads called probe tips and provide the following two major access facilities: (1) flexibility: freely selecting a set of probe tips for accessing data, (2) parallelism: simultaneously reading and writing data with the set of probe tips selected. Due to these characteristics, it is nontrivial to find data placements that fully utilize the capability of MEMS storage devices. In this paper, we propose a simple logical model called the Region-Sector (RS) model that abstracts major characteristics affecting data retrieval performance, such as flexibility and parallelism, from the physical MEMS storage model. We also suggest heuristic data placement strategies based on the RS model and derive new data placements for relational data and two-dimensional spatial data by using those strategies. Experimental results show that the proposed data placements improve the data retrieval performance by up to 4.0 times for relational data and by up to 4.8 times for two-dimensional spatial data of approximately 320 Mbytes compared with those of existing data placements. Further, these improvements are expected to be more marked as the database size grows.Comment: 37 page

Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment

Motivated by the recently measured muon's anomalous magnetic moment $a_{\mu}$, we examine the supersymmetry contribution to $a_{\mu}$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_{\mu}$ allowed by other experimental constraints, e.g. b --> s\gamma and the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_{\mu}$ within the $2\sigma$ bound. In many other models, b --> s\gamma favors $a^{SUSY}_{\mu}$ smaller than either the $-1\sigma$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).Comment: RevTeX, 29 pages, 14 eps figures, figure for deflected anomaly mediation is corrected, reference adde

Genome-wide analysis to predict protein sequence variations that change phosphorylation sites or their corresponding kinases

We define phosphovariants as genetic variations that change phosphorylation sites or their interacting kinases. Considering the essential role of phosphorylation in protein functions, it is highly likely that phosphovariants change protein functions and may constitute a proportion of the mechanisms by which genetic variations cause individual differences or diseases. We categorized phosphovariants into three subtypes and developed a system that predicts them. Our method can be used to screen important polymorphisms and help to identify the mechanisms of genetic diseases