Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Multipole interference in the second-harmonic optical radiation from gold nanoparticles

We provide experimental evidence of higher multipole (magnetic dipole and electric quadrupole) radiation in second-harmonic (SH) generation from arrays of metal nanoparticles. Fundamental differences in the radiative properties of electric dipoles and higher multipoles yield opposite interference effects observed in the SH intensities measured in the reflected and transmitted directions. These interference effects clearly depend on the polarization of the fundamental field, directly indicating the importance of multipole effects in the nonlinear response. We estimate that higher multipoles contribute up to 20% of the total emitted SH field amplitude for certain polarization configurations.     

A nodal Godunov method for Lagrangian shock hydrodynamics on unstructured tetrahedral grids

We present a nodal Godunov method for Lagrangian shock hydrodynamics. The method is designed to operate on three‐dimensional unstructured grids composed of tetrahedral cells. A node‐centered finite element formulation avoids mesh stiffness, and an approximate Riemann solver in the fluid reference frame ensures a stable, upwind formulation. This choice leads to a non‐zero mass flux between control volumes, even though the mesh moves at the fluid velocity, but eliminates volume errors that arise due to the difference between the fluid velocity and the contact wave speed. A monotone piecewise linear reconstruction of primitive variables is used to compute interface unknowns and recover second‐order accuracy. The scheme has been tested on a variety of standard test problems and exhibits first‐order accuracy on shock problems and second‐order accuracy on smooth flows using meshes of up to O(10⁶) tetrahedra. Copyright © 2014 John Wiley & Sons, Ltd.     

The asymptotic number of labeled connected graphs with a given number of vertices and edges

Let c(n, q) be the number of connected labeled graphs with n vertices and q ≤ N = (2n ) edges. Let x = q/n and k = q ? n. We determine functions w_k ? 1. a(x) and φ(x) such that c(n, q) ? w_k(q^N)eⁿφ(x)+a(x) uniformly for all n and q ≥ n. If ? > 0 is fixed, n→ ∞ and 4q > (1 + ?)n log n, this formula simplifies to c(n, q) ? (N^q) exp(–ne^?2q/n). on the other hand, if k = o(n^1/2), this formula simplifies to c(n, n + k) ? 1/2 w_k (3/π)^1/2 (e/12k)^k/2nⁿ?^(3k?1)/2.     

Central and local limit theorems for the coefficients of polynomials of binomial type

We introduce the problem of establishing a central limit theorem for the coefficients of a sequence of polynomials P_n(x) of binomial type; that is, a sequence P_n(x) satisfying $\text{exp}\text{(xg(u)) = ∑}{}_{\mathrm{n=0}}{}^{\mathrm{\infty }}\text{P}{}_{\mathrm{n}}\text{(x)(}\text{u}{}^{\mathrm{n}}\text{n!}\text{)}$ for some (formal) power series g(u) lacking constant term. We give a complete answer in the case when g(u) is a polynomial, and point out the widest known class of nonpolynomial power series g(u) for which the corresponding central limit theorem is known true. We also give the least restrictive conditions known for the coefficients of P_n(x) which permit passage from a central to a local limit theorem, as well as a simple criterion for the generating function g(u) which assures these conditions on the coefficients of P_n(x). The latter criterion is a new and general result concerning log concavity of doubly indexed sequences of numbers with combinatorial significance. Asymptotic formulas for the coefficients of P_n(x) are developed.     

On the Location of the Maximum Stirling Number(s) of the Second Kind

Let S(n, k) denote Stirling numbers of the second kind, and K_n be the integer(s) such that S(n, K_n) ? S(n, k) for all k. We determine the value(s) of K_n to within a maximum error of 1.     

Growth and physical properties of the decagonal Al–Cu–Co quasicrystal grown from the ternary melt

Large faceted single-grain quasicrystals of the approximate composition Al_63.2Cu_19.5Co_17.3 and with a high degree of structural perfection are obtained through the slow cooling of a ternary melt with initial composition Al₆₅Cu₂₉Co₆. X-ray diffraction patterns of crushed single-grain samples are exceptionally sharp, indicating a high degree of structural order, with no evidence of secondary phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even-n layers but diffuse scattering in the odd-n layers. Temperature-dependent magnetization, electrical resistivity and specific heat are measured using bars cut perpendicular and parallel to the c axis and show diamagnetic behaviour: γ?≈?0.5?mJ?mol^?1?K^?2, ρ _c(2?K)?≈?52?μΩ?cm and ρ _q(2?K)?≈?283?μΩ?cm.     

Thermodynamic and transport properties of superconducting Mg10B2

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter kappa approximately 26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 10(5) A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn.     

Direct observation of spontaneous weak ferromagnetism in the superconductor ErNi2B2C

Neutron measurements show that superconducting ErNi2B2C (T(C) = 11 K) develops antiferromagnetic spin density wave magnetic order (T(N) = 6 K), which squares up with decreasing temperature yielding a series of higher-order magnetic Bragg peaks with odd harmonics. Below T(WFM) = 2.3 K where magnetization indicates a net moment develops, even-order Bragg peaks develop which low field (approximately 3 Oe) polarized beam measurements show are magnetic in origin. The data directly demonstrate the existence of a net magnetization with a periodicity of 20a, confirming the microscopic coexistence of spontaneous weak ferromagnetism with superconductivity.     

EFFECT OF DIETARY LIPID ON UV LIGHT CARCINOGENESIS IN THE HAIRLESS MOUSE

Abstract— Isocaloric feeding of diets varying in lipid content to albino hairless mice has shown that their susceptibility to skin tumorigenesis induced by simulated solar UV light was not affected by the level of polyunsaturated fat, 5% or 20%. However a qualitative effect of dietary lipid was demonstrated. Mice fed 20% saturated fat were almost completely protected from UV tumorigenesis when compared with mice fed 20% polyunsaturated fat. Multiple latent tumours were detected in the saturated fat-fed mice by subsequent dietary replenishment, suggesting that a requirement for dietary unsaturated fat exists for the promotion stage of UV-induced skin carcinogenesis.