Alternative potentials for the electromagnetic field

The electromagnetic field can be expressed in terms of two complex potentials $\alpha, \beta ,$ which are related to the Debye potentials. The evolution equations for these potentials are derived, which are separable either in parabolic coordinates (leading to the radiation fields) or in radial coordinates (multipole fields). Potentials corresponding to focused wave fields as well as plane waves are discussed. A conserved radiation density can be constructed in terms of these potentials, which is positive (negative) for positive (negative) helicity radiation.Comment: 13 pages, plainTex, slightly amended version of origina

A model of interplanetary and coronal magnetic fields

Model of interplanetary and solar magnetic field structure above photosphere using Green function solution to Maxwell equation

Habitat selection and population regulation in temporally fluctuating environments

Understanding and predicting the distribution of organisms in heterogeneous environments lies at the heart of ecology, and the theory of density-dependent habitat selection (DDHS) provides ecologists with an inferential framework linking evolution and population dynamics. Current theory does not allow for temporal variation in habitat quality, a serious limitation when confronted with real ecological systems. We develop both a stochastic equivalent of the ideal free distribution to study how spatial patterns of habitat use depend on the magnitude and spatial correlation of environmental stochasticity and also a stochastic habitat selection rule. The emerging patterns are confronted with deterministic predictions based on isodar analysis, an established empirical approach to the analysis of habitat selection patterns. Our simulations highlight some consistent patterns of habitat use, indicating that it is possible to make inferences about the habitat selection process based on observed patterns of habitat use. However, isodar analysis gives results that are contingent on the magnitude and spatial correlation of environmental stochasticity. Hence, DDHS is better revealed by a measure of habitat selectivity than by empirical isodars. The detection of DDHS is but a small component of isodar theory, which remains an important conceptual framework for linking evolutionary strategies in behavior and population dynamics

Functional Forms for the Squeeze and the Time-Displacement Operators

Using Baker-Campbell-Hausdorff relations, the squeeze and harmonic-oscillator time-displacement operators are given in the form $\exp[\delta I] \exp[\alpha (x^2)]\exp[\beta(x\partial)] \exp[\gamma (\partial)^2]$, where $\alpha$, $\beta$, $\gamma$, and $\delta$ are explicitly determined. Applications are discussed.Comment: 10 pages, LaTe

Isgur - Wise Functions for Confined Light Quarks in a Colour Electric Potential

We explore the influence on the Isgur-Wise function of the colour electric potential between heavy and light quarks in mesons. It is shown that in bag models, its inclusion tends to restore light quark flavour symmetry relative to the MIT bag predictions, and that relative to this model it flattens the Isgur-Wise function. Results compare very well with observations.Comment: 9 pages, 1 figure (available upon request), Latex, TPJU - 4/9

In vitro assessment of Clostridium difficile PCR ribotype 002: the most prevalent C. difficile ribotype in the United Kingdom.

Simon Baines, Iye Ameh, Jane Freeman, W.N. Fawley, M.H. Wilcox, ‘In vitro assessment of Clostridium difficile PCR ribotype 002: the most prevalent C. difficile ribotype in the United Kingdom’, poster presented at the 25th European Congress on Clinical Microbiology and Infectious Diseases, Copenhagen, Denmark, 25-28 August, 2015.Background: Clostridium difficile infection (CDI) causes substantial morbidity and healthcare expenditure across Europe. UK prevalence of C. difficile PCR ribotype 027 (NAP1) has declined dramatically recently and other ribotypes have emerged, including ribotype 002 (CD002); now the most prevalent UK ribotype. CD002 is also responsible for CDI in many countries across Europe, including: France, Germany, Ireland, and The Netherlands. We assessed the in vitro phenotypic characteristics of CD002 from across Europe to determine traits that may contribute to its increasing clinical prevalence. Material/methods: Sixty CD002 were studied: UK isolates from 2007-2008 (geographically distinct, N=15), UK isolates from 2011-2013 (19 locations, N=22), and non-UK European isolates from 2012-2014 (N=23, 20 locations). Antimicrobial susceptibilities (13 antimicrobials) were evaluated using an agar incorporation method. Maximum specific growth rates (μmax) were calculated and cytotoxin titres (log10-relative units, RU) determined using Vero cell cytotoxicity assays. Biofilm formation was quantified using 96-well microtitre plate assays and sporulation capacities assessed in liquid culture by quantifying spore-formation over 120 h (CFU/mL). Results: All isolates were susceptible metronidazole, vancomycin, tetracycline and linezolid (MICs ≤2 mg/L). Clindamycin resistance (MIC ≥8 mg/L) was more common in non-UK CD002 (30%) than UK strains (5-13%). Resistance to erythromycin, clarithromycin, nitrofurantoin, chloramphenicol, and moxifloxacin was uncommon (5-7%). MICs for penicillin’s remained below resistance breakpoints, regardless of origin, in all but one isolate (ampicillin MIC 2 mg/L). All CD002 were resistant to trimethoprim (MICs >128 mg/L) and ciprofloxacin (MICs ≥8 mg/L). One MDR strain (UK, 2007) was observed that was macrolide, fluoroquinolone, ampicillin, and nitrofurantoin resistant. Significantly faster μmax was seen in non-UK CD002 (0.92 ±0.058 h-1) than recent/older UK strains (0.76 ±0.063/0.69 ±0.028 h-1 respectively) (P<0.001). Cytotoxin production did not differ significantly (median titres 2-3 RU) between CD002 groups. Recent UK/non-UK CD002 formed significantly greater biofilms by 3 days than asynchronous UK CD002 (P<0.001). Sporulation studies demonstrated that recent UK/non-UK CD002 sporulated more at 24 h than older UK CD002; 18.6-fold/31.2-fold respectively (P<0.05), but by 120 h sporulation did not differ. Conclusions: Recent CD002 from diverse European locations were assessed for traits that may help to explain emergence of CD002 in the UK and compared to asynchronous CD002. Previous studies demonstrated elevated CD002 μmax compared to hypervirulent ribotypes 027/078; and the present study demonstrated that recent non-UK CD002 μmax were significantly further elevated vs. UK isolates. Non-UK CD002 were more clindamycin resistant, but other antimicrobial susceptibilities were similar between CD002 groups. Recent CD002 demonstrated significantly increased sporulation capacities at 24 h and more extensive 3 day biofilm formation compared to asynchronous UK CD002, which could enhance their survival and transmission early in an episode CDI. Further phenotypic and genetic studies are required to evaluate further characteristics of CD002 that may be associated with its emergence in the UK.Peer reviewedFinal Published versio

Development of a chromium-thoria alloy

Low temperature ductility and high temperature strength of pure chromium and chromium-thoria alloy prepared from vapor deposited powder

Short-term genome stability of serial Clostridium difficile ribotype 027 isolates in an experimental gut model and recurrent human disease

Copyright: © 2013 Eyre et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedClostridium difficile whole genome sequencing has the potential to identify related isolates, even among otherwise indistinguishable strains, but interpretation depends on understanding genomic variation within isolates and individuals.Serial isolates from two scenarios were whole genome sequenced. Firstly, 62 isolates from 29 timepoints from three in vitro gut models, inoculated with a NAP1/027 strain. Secondly, 122 isolates from 44 patients (2–8 samples/patient) with mostly recurrent/on-going symptomatic NAP-1/027 C. difficile infection. Reference-based mapping was used to identify single nucleotide variants (SNVs).Across three gut model inductions, two with antibiotic treatment, total 137 days, only two new SNVs became established. Pre-existing minority SNVs became dominant in two models. Several SNVs were detected, only present in the minority of colonies at one/two timepoints. The median (inter-quartile range) [range] time between patients’ first and last samples was 60 (29.5–118.5) [0–561] days. Within-patient C. difficile evolution was 0.45 SNVs/called genome/year (95%CI 0.00–1.28) and within-host diversity was 0.28 SNVs/called genome (0.05–0.53). 26/28 gut model and patient SNVs were non-synonymous, affecting a range of gene targets.The consistency of whole genome sequencing data from gut model C. difficile isolates, and the high stability of genomic sequences in isolates from patients, supports the use of whole genome sequencing in detailed transmission investigations.Peer reviewe

K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC

We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039) with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of the nucleus and the obscured star cluster at R = 1900. The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}= 9600 L_sun.Comment: 4 pages, 4 embedded figures, uses emulateapj.sty. To appear in ApJL. Also available at http://astro.berkeley.edu/~agilber

General Approach to Functional Forms for the Exponential Quadratic Operators in Coordinate-Momentum Space

In a recent paper [Nieto M M 1996 Quantum and Semiclassical Optics, 8 1061; quant-ph/9605032], the one dimensional squeezed and harmonic oscillator time-displacement operators were reordered in coordinate-momentum space. In this paper, we give a general approach for reordering multi-dimensional exponential quadratic operator(EQO) in coordinate-momentum space. An explicit computational formula is provided and applied to the single mode and double-mode EQO through the squeezed operator and the time displacement operator of the harmonic oscillator.Comment: To appear in J. Phys. A: Mathematics and Genera