Characterization of individual ferromagnetic nanowires by in-plane magnetic measurements of arrays

We present a phenomenological model for the interaction field in ferromagnetic nanowire arrays and use it to obtain the effective anisotropy field of individual nanowires, from the in-plane saturation field of the array. In contrast to other methods which may be used to estimate this parameter, the proposed strategy requires no knowledge of the saturation magnetization nor of the nanowire radius. Applied to three arrays of different compositions, this approach yields an equivalent anisotropy field of the individual nanowires approximately equal to _Ms/2$M_{\mathrm{s}}/2$, indicating that its origin is the demagnetizing field of the wire.     

Vocal development in captive harbor seal pups, Phoca vitulina richardii: age, sex, and individual differences

The goal of this research was to determine when harbor seal pup vocalizations become sufficiently distinctive to allow individual recognition. A total of 4593 calls were analyzed from 15 captive pups. Nineteen were harsh, broadband, staccato calls used in an aggressive context. The rest were tonal "mother attraction calls," having an inverted "v"- or "u"-shaped spectrogram with harmonics and a fundamental frequency around 200-600 Hz. Calls were individually distinctive even in pups less than 2 weeks old, suggesting that mothers may be able to recognize pup vocalizations at this early age. Classification rates from discriminant function analysis were generally comparable to those of other phocids and less than in otariids, supporting the theory that recognition is more highly developed in otariids. Significant differences were found between male and female pup calls, and there were significant interactions between pup sex and age. The results of this study should be interpreted with caution until the findings are verified in wild harbor seal pups.     

Constructing permutation arrays from groups

Let M(n, d) be the maximum size of a permutation array on n symbols with pairwise Hamming distance at least d. We use various combinatorial, algebraic, and computational methods to improve lower bounds for M(n, d). We compute the Hamming distances of affine semilinear groups and projective semilinear groups, and unions of cosets of AGL(1, q) and PGL(2, q) with Frobenius maps to obtain new, improved lower bounds for M(n, d). We give new randomized algorithms. We give better lower bounds for M(n, d) also using new theorems concerning the contraction operation. For example, we prove a quadratic lower bound for \(M(n,n-2)\) for all \(n\equiv 2 \pmod 3\) such that \(n+1\) is a prime power.     

Bounds on Exponential Sums and the Polynomial Waring Problem Mod p

Estimates are given for the exponential a prime and f a nonzero integer polynomial, of interestin cases where the Weil bound is worse than trivial. The resultsextend those of Konyagin for monomials to a general polynomial.Such bounds readily yield estimates for the corresponding polynomialWaring problem mod p, namely the smallest such that f(x₁)+...+f(x)N(mod p) is solvable in integers for any N.     

Ferromagnetism in the Hubbard Model: A Constructive Approach

It is believed that strong ferromagnetic orders in some solids are generated by subtle interplay between quantum many-body effects and spin-independent Coulomb interactions between electrons. Here we describe our rigorous and constructive approach to ferromagnetism in the Hubbard model, which is a standard idealized model for strongly interacting electrons in a solid. We introduce a class of Hubbard models in any dimensions which are nonsingular in the sense that both the Coulomb interaction and the density of states (at the Fermi level) are finite. We then prove that the ground states of the models exhibit saturated ferromagnetism, i.e., have maximum total spins. Combined with our earlier results, the present work provides nonsingular models of itinerant electrons with only spin-independent interactions where low energy behaviors are proved to be that of a healthy ferromagnetic insulator.     

High order moments of character sums

We establish the upper bound

with a prime and any positive integer, the sum being over all nonprincipal multiplicative characters .

     

A new anomaly of temperature dependence of Mössbauer parameters in the EuBa2(Cu0.98 119Sn0.01 57Fe0.01)3O7-δ superconductor

The total area of the⁵⁷Fe Mössbauer spectra of the EuBa₂ (Cu_0.98 ¹¹⁹Sn_0.01 ⁵⁷Fe_0.01)₃O₇- superconductor exhibited a highly usual anomalous temperature dependence, i.e. it increased monotonously with increasing temperature between 120 and 300 K. We found also anomalous changes in the⁵⁷Fe Mössbauer parameters around T_c. These latter changes could be associated with phonon softening and low temperature phase transformation.     

First observation of structural changes around the Tc in TlBaCaCuO4.5+y superconductor studied by57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectroscopy was used to study⁵⁷Fe doped high T_c TlBaCaCuO_4.5+y superconductor between 70 and 295 K. Significant anomalous changes in the shape of the Mössbauer spectrum were observed around the T_c /105–120 K/. This experimental fact could be reproduced. Our finding can be associated with structural changes taking place around the T_c in TlBaCaCuO_4.5+y superconductor.     

Generalization of the fourth‐order Hylleraas functional for the case of a non‐Hermitian unperturbed Hamiltonian

Generalization of the fourthorder Hylleraas functional form have been performed for the case of nonHermitian operators. Our new formulas are relevant when the Hermitian Born–Oppenheimer Hamiltonian is decomposed into a nonHermitian unperturbed part and also a nonHermitian perturbation. The results can be used to develop BSSEfree intermolecular perturbation theory up to fourthorder.