Weyl nodes in periodic structures of superconductors and spin active materials

Motivated by recent progress in epitaxial growth of proximity structures of s-wave superconductors (S) and spin-active materials (M), we show that the periodic structure of S and M can behave effectively as a superconductor with pairs of point nodes, near which the low energy excitations are Weyl fermions. A simple toy model, where M is described by a Kronig-Penney potential with both spin-orbit coupling and exchange field, is proposed and solved to obtain the phase diagram of the nodal structure, the spin texture of the Weyl fermions, as well as the zero energy surface states in the form of open Fermi lines ("Fermi arcs"). Going beyond the simple model, a lattice model with alternating layers of S and magnetic $Z_2$ topological insulators (M) is solved. The calculated spectrum confirms previous prediction of Weyl nodes based on tunneling Hamiltonian of Dirac electrons. Our results provide further evidence that periodic structures of S and M are well suited for engineering gapless topological superconductors.Comment: Research article, contribution to theme issue "Andreev bound states" ed. Laura H. Greene and James A. Saul

Acculturation to Global Consumer Culture (AGCC): testing the validity of the AGCC scale and some preliminary results from the United Kingdom

This paper presents preliminary results from a study focused on acculturation to Global Consumer Culture (GCC) conducted in the UK. In particular, this paper’s aims are to test the validity of the original ‘Acculturation to Global Consumer Culture’ (AGCC) scale in a new cultural context, and to present preliminary results about the relation between acculturation to GCC and demographic factors, technological anxiety, and compulsive buying. This paper is based on online questionnaire completed by 340 respondents in the UK. The psychometric properties of this scale were verified via confirmatory factor analysis, and a new, shorter scale was proposed. Some results about the links between acculturation to GCC and demographics, technological anxiety, and compulsive buying were presented and discussed within the context of extant GCC research. Limitations and further research were discussed. Key words: consumer culture, global consumer culture, acculturation to global consumer cultur

Absence of long-range order in a triangular spin system with dipolar interactions

Antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that next nearest neighbor interaction $J_2$ enhances the frustration and leads to a spin liquid for $J_2/J_1\in (0.08,0.15)$. In addition, DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at small dipole titling angle $\theta\in[0,10^\circ)$. In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, $\theta\in [0,54^\circ)$, for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG) which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.Comment: 5 pages, 2 figures and the supplementary material

Return mobilities of highly skilled young people to a post-conflict region: the case of Kurdish-British to Kurdistan – Iraq

Building upon insights from recent studies on the ‘return mobilities’ of children of migrants to their parents’ country of origin, this paper focuses on the motives of highly skilled young people from the UK who migrate to their parental post-conflict region (Kurdistan-Iraq), an area that has experienced long-term conflict and profound economic and political instability. The existing studies on children of migrants’ return mobilities place more emphasis on cultural and economic considerations while paying little attention to the associated ideological and political elements. Based on interviews concerning 32 highly skilled young British-Kurdish people’s migration to Kurdistan-Iraq, this paper argues that the transnational mobilities of the 1.5 generation and second generation of refugee-diasporas are more driven by the collective trauma of their parents’ displacement, their feeling of expulsion and intergenerational articulation with an imagined homeland, than they are by economic considerations and/or nostalgia. The Kurdish political aspiration to develop Kurdish institutions and a national economy for a potential statehood in Northern Iraq has also created hope among young Kurdish people and influenced their motivations to ‘return’. In this context, this paper focuses on the political, ideological and emotional dimensions of return mobilities and draws attention to return mobilities among a new generation of refugees to their parental post-conflict homeland

A note on the conservation characteristics of baled grass silages ensiled with different additives.

peer-reviewedThe effects of contrasting conventional silage additives on chemical composition, aerobic stability and deterioration, and mould development in baled silage were investigated. Herbage from a grassland sward was wilted for 24 h and treated with acid (formic or sulphuric), sugar (molasses), bacterial (Lactobacillus plantarum, L. plantarum + Serratia rubidaea + Bacillus subtilis, or L. buchneri) or sugar + bacterial (molasses + L. plantarum) additives prior to baling and wrapping. Silage made without an additive preserved well and had a low incidence of mould growth, and the effects of additives were minor or absent. It is concluded that little practical benefit was realised when conventional additives were applied to wilted, leafy, easy-to-ensile grass prior to baling and ensilage

Scrambling dynamics and many-body chaos in a random dipolar spin model

Is there a quantum many-body system that scrambles information as fast as a black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for chaos, but it requires random all-to-all couplings of Majorana fermions that are hard to realize in experiments. Here we examine a quantum spin model of randomly oriented dipoles where the spin exchange is governed by dipole-dipole interactions. The model is inspired by recent experiments on dipolar spin systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We map out the phase diagram of this model by computing the energy level statistics, spectral form factor, and out-of-time-order correlation (OTOC) functions. We find a broad regime of many-body chaos where the energy levels obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at different times: Its early-time dynamics is characterized by an exponential growth, while the approach to its saturated value at late times obeys a power law. The temperature scaling of the Lyapunov exponent $\lambda_L$ shows that while it is well below the conjectured bound $2\pi T$ at high temperatures, $\lambda_L$ approaches the bound at low temperatures and for large number of spins.Comment: 7 pages, 8 figures with updated reference

Multiple tests of association with biological annotation metadata

We propose a general and formal statistical framework for multiple tests of association between known fixed features of a genome and unknown parameters of the distribution of variable features of this genome in a population of interest. The known gene-annotation profiles, corresponding to the fixed features of the genome, may concern Gene Ontology (GO) annotation, pathway membership, regulation by particular transcription factors, nucleotide sequences, or protein sequences. The unknown gene-parameter profiles, corresponding to the variable features of the genome, may be, for example, regression coefficients relating possibly censored biological and clinical outcomes to genome-wide transcript levels, DNA copy numbers, and other covariates. A generic question of great interest in current genomic research regards the detection of associations between biological annotation metadata and genome-wide expression measures. This biological question may be translated as the test of multiple hypotheses concerning association measures between gene-annotation profiles and gene-parameter profiles. A general and rigorous formulation of the statistical inference question allows us to apply the multiple hypothesis testing methodology developed in [Multiple Testing Procedures with Applications to Genomics (2008) Springer, New York] and related articles, to control a broad class of Type I error rates, defined as generalized tail probabilities and expected values for arbitrary functions of the numbers of Type I errors and rejected hypotheses. The resampling-based single-step and stepwise multiple testing procedures of [Multiple Testing Procedures with Applications to Genomics (2008) Springer, New York] take into account the joint distribution of the test statistics and provide Type I error control in testing problems involving general data generating distributions (with arbitrary dependence structures among variables), null hypotheses, and test statistics.Comment: Published in at http://dx.doi.org/10.1214/193940307000000446 the IMS Collections (http://www.imstat.org/publications/imscollections.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Theory of interacting fermions in shaken square optical lattice

We develop a theory of weakly interacting fermionic atoms in shaken optical lattices based on the orbital mixing in the presence of time-periodic modulations. Specifically, we focus on fermionic atoms in circularly shaken square lattice with near resonance frequencies, i.e., tuned close to the energy separation between $s$-band and the $p$-bands. First, we derive a time-independent four-band effective Hamiltonian in the non-interacting limit. Diagonalization of the effective Hamiltonian yields a quasi-energy spectrum consistent with the full numerical Floquet solution that includes all higher bands. In particular, we find that the hybridized $s$-band develops multiple minima and therefore non-trivial Fermi surfaces at different fillings. We then obtain the effective interactions for atoms in the hybridized $s$-band analytically and show that they acquire momentum dependence on the Fermi surface even though the bare interaction is contact-like. We apply the theory to find the phase diagram of fermions with weak attractive interactions and demonstrate that the pairing symmetry is $s+d$-wave. Our theory is valid for a range of shaking frequencies near resonance, and it can be generalized to other phases of interacting fermions in shaken lattices.Comment: 12 pages with 5 figures. Comments and reference suggestions are welcom

Conservation characteristics of baled grass silages differing in duration of wilting, bale density and number of layers of plastic stretch-film

peer-reviewedThe effects of duration of wilting, bale density and number of layers of plastic stretchfilm used to wrap bales on the conservation characteristics of baled grass silage was investigated. Grass from the primary growth of a Lolium perenne dominant sward was wilted for 24, 48 or 72 h. For each duration of wilting, 54 cylindrical bales (1.2 m nominal diameter) were made with the baler at a high or low density setting for alternate bales. Bales were wrapped with 2, 4 or 6 layers of plastic stretch-film and stored outdoors for 295 days. Two layers of plastic stretch-film resulted in inferior preservation, lower digestibility and extensive mould growth and deteriorated silage. Substantial improvement occurred to each of these characteristics from applying four layers of stretch-film (P<0.05), while six layers of stretch-film brought little further improvement. When four or six layers of stretch-film were used, extensive wilting restricted fermentation and improved the standard of preservation with the apparently difficult-to-preserve herbage used in this experiment. However, under the anaerobic conditions provided by four or six layers of stretch-film neither progressive wilting nor bale density had a major effect on digestibility, or the extent of surface mould growth or deteriorated silage. It can be concluded that a minimum of four layers of conventional black plastic stretch-film were required to achieve suitably anaerobic conditions, and that the additional benefits from six layers were small. Once anaerobic conditions were achieved, extensive wilting improved the conservation characteristics of baled grass silage made from a difficult-to-preserve crop, whereas bale density had little impact

Global consumer culture positioning: the use of global consumer culture positioning appeals across four European countries

This study proposes a framework of advertising appeals which could be used to express global consumer culture positioning (GCCP) strategy in advertising. The paper examines the use of such appeals in print advertising from four European countries comparing 847 advertisements for durable and non-durable goods from Poland, Hungary, Ireland and the UK. Contrary to expectations, GCCP appeals were more often used in advertisements for non-durable goods than durable goods. The study confirmed the expectation that GCCP appeals would be more frequently used in advertising in less developed markets than in more developed markets. The proposed framework of GCCP appeals may be useful to practitioners wishing to use this positioning strategy