Engineering Electromagnetic Properties of Periodic Nanostructures Using Electrostatic Resonances

Electromagnetic properties of periodic two-dimensional sub-wavelength structures consisting of closely-packed inclusions of materials with negative dielectric permittivity $\epsilon$ in a dielectric host with positive $\epsilon_h$ can be engineered using the concept of multiple electrostatic resonances. Fully electromagnetic solutions of Maxwell's equations reveal multiple wave propagation bands, with the wavelengths much longer than the nanostructure period. It is shown that some of these bands are described using the quasi-static theory of the effective dielectric permittivity $\epsilon_{qs}$, and are independent of the nanostructure period. Those bands exhibit multiple cutoffs and resonances which are found to be related to each other through a duality condition. An additional propagation band characterized by a negative magnetic permeability develops when a magnetic moment is induced in a given nano-particle by its neighbors. Imaging with sub-wavelength resolution in that band is demonstrated

Soft Spin Wave Near nu=1: Evidence for a Magnetic Instability in Skyrmion Systems

The ground state of the two dimensional electron gas near $\nu$=1 is investigated by inelastic light scattering measurements carried down to very low temperatures. Away from $\nu$=1, the ferromagnetic spin wave collapses and a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave shows soft behavior as its energy increases with temperature and reaches the Zeeman energy for temperatures above 2 K. The observed softening indicates an instability of the two dimensional electron gas towards a magnetic order that breaks spin rotational symmetry. We discuss our findings in light of the possible existence of a Skyrme crystal.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Phase Transition in the Number Partitioning Problem

Number partitioning is an NP-complete problem of combinatorial optimization. A statistical mechanics analysis reveals the existence of a phase transition that separates the easy from the hard to solve instances and that reflects the pseudo-polynomiality of number partitioning. The phase diagram and the value of the typical ground state energy are calculated.Comment: minor changes (references, typos and discussion of results

Life expectancy at birth and all-cause mortality among people with personality disorder

Objective: It is well established that serious mental illness is associated with raised mortality, yet few studies have looked at the life expectancy of people with personality disorder (PD). This study aims to examine the life expectancy and relative mortality in people with PD within secondary mental health care. Methods: We set out to examine this using a large psychiatric case register in southeast London, UK. Mortality was obtained through national mortality tracing procedures. In a cohort of patients with a primary diagnosis of PD (n = 1836), standardised mortality ratios (SMRs) and life expectancies at birth were calculated, using general population mortality statistics as the comparator. Results: Life expectancy at birth was 63.3 years for women and 59.1 years for men with PD—18.7 years and 17.7 years shorter than females and males respectively in the general population in England and Wales. The SMR was 4.2 (95% CI: 3.03–5.64) overall; 5.0 (95% CI: 3.15–7.45) for females and 3.5 (95% CI: 2.17–5.47) for males. The highest SMRs were found in the younger age groups for both genders. Conclusion: People with PD using mental health services have a substantially reduced life expectancy, highlighting the significant public health burden of the disorder

A parametric study of cognitive defusion and the believability and discomfort of negative self-relevant thoughts

A previous time series study showed that rapidly repeating a single word version of a negative self-referential thought reduced the discomfort and the believability associated with that thought. The present parametric study examined whether durations of word repetition were differentially effective in altering the discomfort and believability of negative self-referential thought. In two studies, both discomfort and believability varied systematically with the duration of word repetition. The effects of rapid repetition on emotional discomfort bottomed out after 3 to 10 seconds of rapid repetition, while the effects on believability did so after 20 to 30 seconds of repetition. This study lends support to the cognitive defusion interpretation of the effect of word repetition, suggesting that emotional discomfort and believability may be distinctive functional aspects of cognitive events

Muon-spin relaxation measurements on the dimerized spin-1/2 chains NaTiSi2O6 and TiOCl

We report muon spin relaxation (muSR) and magnetic susceptibility investigations of two Ti3+ chain compounds which each exhibit a spin gap at low temperature, NaTiSi2O6 and TiOCl. From these we conclude that the spin gap in NaTiSi2O6 is temperature independent, with a value of 2*Delta=660(50)K, arising from orbital ordering at Too = 210K; the associated structural fluctuations activate the muon spin relaxation rate up to temperatures above 270K. In TiOCl we find thermally activated spin fluctuations corresponding to a spin gap 2*Delta=420(40)K below Tc1=67K. We also compare the methods used to extract the spin gap and the concentration of free spins within the samples from muSR and magnetic susceptibility data.Comment: 4 pages, 3 figure

Investigating the effects of cyclic topology on the performance of a plastic degrading enzyme for polyethylene terephthalate degradation

Agitation is a commonly encountered stress for enzymes during all stages of production and application, but investigations that aim to improve their tolerance using topological engineering have yet to be reported. Here, the plastic-degrading enzyme IsPETase was cyclized in a range of topologies including a cyclic monomer, cyclic dimer and catenane using SpyTag/SpyCatcher technologies, and their tolerance towards different stresses including mechanical agitation was investigated. The cyclic dimer and catenane topologies were less susceptible to agitation-induced inactivation resulting in enhancement of polyethylene terephthalate (PET) degradation. While contrary to conventional belief, cyclic topologies did not improve tolerance of IsPETase towards heat or proteolytic treatment, the close proximity of active sites in the dimeric and catenane variants was found to enhance PET conversion into small soluble products. Together, these findings illustrate that it is worthwhile to explore the topology engineering of enzymes used in heterogeneous catalysis as it improves factors that are often overlooked in homogeneous catalysis studies

Optimisation problems and replica symmetry breaking in finite connectivity spin-glasses

A formalism capable of handling the first step of hierarchical replica symmetry breaking in finite-connectivity models is introduced. The emerging order parameter is claimed to be a probability distribution over the space of field distributions (or, equivalently magnetisation distributions) inside the cluster of states. The approach is shown to coincide with the previous works in the replica symmetric case and in the two limit cases m=0,1 where m is Parisi's break-point. As an application to the study of optimization problems, the ground-state properties of the random 3-Satisfiability problem are investigated and we present a first RSB solution improving replica symmetric results.Comment: 16 pages Revtex file, 1 figure; amended version with two new appendices; to be published in J.Phys.

Central Powering of the Largest Lyman-alpha Nebula is Revealed by Polarized Radiation

High-redshift Lyman-alpha blobs are extended, luminous, but rare structures that appear to be associated with the highest peaks in the matter density of the Universe. Their energy output and morphology are similar to powerful radio galaxies, but the source of the luminosity is unclear. Some blobs are associated with ultraviolet or infrared bright galaxies, suggesting an extreme starburst event or accretion onto a central black hole. Another possibility is gas that is shock excited by supernovae. However some blobs are not associated with galaxies, and may instead be heated by gas falling into a dark matter halo. The polarization of the Ly-alpha emission can in principle distinguish between these options, but a previous attempt to detect this signature returned a null detection. Here we report on the detection of polarized Ly-alpha from the blob LAB1. Although the central region shows no measurable polarization, the polarized fraction (P) increases to ~20 per cent at a radius of 45 kpc, forming an almost complete polarized ring. The detection of polarized radiation is inconsistent with the in situ production of Ly-alpha photons, and we conclude that they must have been produced in the galaxies hosted within the nebula, and re-scattered by neutral hydrogen.Comment: Published in the August 18 issue of Nature. 1750 words, 3 figures, and full Supplementary Information. Version has not undergone proofing. Reduced and processed data products are available here: http://obswww.unige.ch/people/matthew.hayes/LymanAlpha/LabPol