Antiferromagnetic resonance in ferroborate NdFe3_3(BO3_3)$_4

The AFMR spectra of the NdFe$_3$(BO$_3$)$_4$ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of magnetic anisotropy the compound is an "easy-plane" antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields $H_{a1}$=1.14 kOe and $H_{a2}$=60 kOe and magnetic excitation gaps $\Delta\nu_1$=101.9 GHz and $\Delta \nu_2$=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width. At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed

Quantum Gravity effects near the null black hole singularity

The structure of the Cauchy Horizon singularity of a black hole formed in a generic collapse is studied by means of a renormalization group equation for quantum gravity. It is shown that during the early evolution of the Cauchy Horizon the increase of the mass function is damped when quantum fluctuations of the metric are taken into account.Comment: 15 Pages, one figure. Minor changes in the presentation, to appear on Phys.Rev.

The influence of Prenatal DHA supplementation on individual domains of behavioral functioning in school‐aged children: Follow‐up of a randomized controlled trial

Docosahexaenoic acid (DHA) accumulates in the fetal brain during pregnancy and is thought to have a role in supporting neurodevelopment. We conducted a multicenter, double-blind, randomized controlled trial in women with a singleton pregnancy who were <21 weeks’ gestation at trial entry. Women were provided with 800 mg DHA/day or a placebo supplement from trial entry until birth. When children reached seven years of age, we invited parents to complete the Strengths and Difficulties Questionnaire (SDQ), the Behavior Rating Inventory of Executive Function (BRIEF), and the Conners 3rd Edition Attention-Deficit Hyperactivity Disorder (ADHD) Index to assess child behavior and behavioral manifestations of executive dysfunction. There were 543 parent–child pairs (85% of those eligible) that participated in the follow-up. Scores were worse in the DHA group than the placebo group for the BRIEF Global Executive, Behavioral Regulation and Metacognition Indexes, and the Shift, Inhibit, Monitor, Working Memory, and Organization of Materials scales, as well as for the Conners 3 ADHD index, and the SDQ Total Difficulties score, Hyperactivity/Inattention score, and Peer Relationship Problems score. In this healthy, largely term-born sample of children, prenatal DHA supplementation conferred no advantage to childhood behavior, and instead appeared to have an adverse effect on behavioral functioning, as assessed by standardized parental report scales.Jacqueline F. Gould, Peter J. Anderson, Lisa N. Yelland, Robert A. Gibson, and Maria Makride

Low energy and dynamical properties of a single hole in the t-Jz model

We review in details a recently proposed technique to extract information about dynamical correlation functions of many-body hamiltonians with a few Lanczos iterations and without the limitation of finite size. We apply this technique to understand the low energy properties and the dynamical spectral weight of a simple model describing the motion of a single hole in a quantum antiferromagnet: the $t-J_z$ model in two spatial dimension and for a double chain lattice. The simplicity of the model allows us a well controlled numerical solution, especially for the two chain case. Contrary to previous approximations we have found that the single hole ground state in the infinite system is continuously connected with the Nagaoka fully polarized state for $J_z \to 0$. Analogously we have obtained an accurate determination of the dynamical spectral weight relevant for photoemission experiments. For $J_z=0$ an argument is given that the spectral weight vanishes at the Nagaoka energy faster than any power law, as supported also by a clear numerical evidence. It is also shown that spin charge decoupling is an exact property for a single hole in the Bethe lattice but does not apply to the more realistic lattices where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to appear in Phys. Rev

Disordered Hubbard Model with Attraction: Coupling Energy of Cooper Pairs in Small Clusters

We generalize the Cooper problem to the case of many interacting particles in the vicinity of the Fermi level in the presence of disorder. On the basis of this approach we study numerically the variation of the pair coupling energy in small clusters as a function of disorder. We show that the Cooper pair energy is strongly enhanced by disorder, which at the same time leads to the localization of pairs.Comment: revtex, 5 pages, 6 figure

Interpolatory methods for H∞\mathcal{H}_\infty model reduction of multi-input/multi-output systems

We develop here a computationally effective approach for producing high-quality $\mathcal{H}_\infty$-approximations to large scale linear dynamical systems having multiple inputs and multiple outputs (MIMO). We extend an approach for $\mathcal{H}_\infty$ model reduction introduced by Flagg, Beattie, and Gugercin for the single-input/single-output (SISO) setting, which combined ideas originating in interpolatory $\mathcal{H}_2$-optimal model reduction with complex Chebyshev approximation. Retaining this framework, our approach to the MIMO problem has its principal computational cost dominated by (sparse) linear solves, and so it can remain an effective strategy in many large-scale settings. We are able to avoid computationally demanding $\mathcal{H}_\infty$ norm calculations that are normally required to monitor progress within each optimization cycle through the use of "data-driven" rational approximations that are built upon previously computed function samples. Numerical examples are included that illustrate our approach. We produce high fidelity reduced models having consistently better $\mathcal{H}_\infty$ performance than models produced via balanced truncation; these models often are as good as (and occasionally better than) models produced using optimal Hankel norm approximation as well. In all cases considered, the method described here produces reduced models at far lower cost than is possible with either balanced truncation or optimal Hankel norm approximation

Consumer mobility and well-being among changing places and shifting ethnicities

International audience(Market)places are spatial entities which individuals and groups might experience as meaningful. By highlighting the role of place in ethnic consumer research, this article argues that increased mobility and changing places render relatively stable notions of ethnicity outdated. We identify three main trajectories to revitalize future research on ethnicity. First, we demonstrate the need for research on ethnic identity to be underpinned by a better understanding of the role of place in identity processes. Second, we contend that the established migration/acculturation paradigm should be replaced by the mobility/adaptiveness paradigm. Third, we consider the profound effects of interethnic contact among mobile and immobile populations within shared places on individual and societal well-being

Cryptoferromagnetic state in superconductor-ferromagnet multilayers

We study a possibility of a non-homogeneous magnetic order (cryptoferromagnetic state) in heterostructures consisting of a bulk superconductor and a ferromagnetic thin layer that can be due to the influence of the superconductor. The exchange field in the ferromagnet may be strong and exceed the inverse mean free time. A new approach based on solving the Eilenberger equations in the ferromagnet and the Usadel equations in the superconductor is developed. We derive a phase diagram between the cryptoferromagnetic and ferromagnetic states and discuss the possibility of an experimental observation of the CF state in different materials.Comment: 4 pages, 1 figur