343 research outputs found
Direct perturbation theory on the shift of Electron Spin Resonance
We formulate a direct and systematic perturbation theory on the shift of the
main paramagnetic peak in Electron Spin Resonance, and derive a general
expression up to second order. It is applied to one-dimensional XXZ and
transverse Ising models in the high field limit, to obtain explicit results
including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE
Aspects of electrostatics in a weak gravitational field
Several features of electrostatics of point charged particles in a weak,
homogeneous, gravitational field are discussed using the Rindler metric to
model the gravitational field. Some previously known results are obtained by
simpler and more transparent procedures and are interpreted in an intuitive
manner. Specifically: (i) We show that the electrostatic potential of a charge
at rest in the Rindler frame is expressible as A_0=(q/l) where l is the affine
parameter distance along the null geodesic from the charge to the field point.
(ii) We obtain the sum of the electrostatic forces exerted by one charge on
another in the Rindler frame and discuss its interpretation. (iii) We show how
a purely electrostatic term in the Rindler frame appears as a radiation term in
the inertial frame. (In part, this arises because charges at rest in a weak
gravitational field possess additional weight due to their electrostatic
energy. This weight is proportional to the acceleration and falls inversely
with distance -- which are the usual characteristics of a radiation field.)
(iv) We also interpret the origin of the radiation reaction term by extending
our approach to include a slowly varying acceleration. Many of these results
might have possible extensions for the case of electrostatics in an arbitrary
static geometry. [Abridged Abstract]Comment: 26 pages; accepted for publication in Gen.Rel.Gra
In search of community history
This editorial response to the preceding article by Dennis Mills addresses the meaning of community history. Rejecting an over-tight definition, we argue for a methodologically distinct community history, combining a micro-historical approach with a sensitivity to the discursive construction of the term 'community'. Furthermore the role of family and community historians should be to adapt a critical stance towards contemporary meanings of both past 'communities' and past 'families'. The article concludes that Withington and Shephard's schema for approaching the history of 'community' offers a practical way forward for the family and community historian
Between overt and covert research: concealment and disclosure in an ethnographic study of commercial hospitality
This article examines the ways in which problems of concealment emerged in an ethnographic study of a suburban bar and considers how disclosure of the research aims, the recruitment of informants, and elicitation of information was negotiated throughout the fieldwork. The case study demonstrates how the social context and the relationships with specific informants determined overtness or covertness in the research. It is argued that the existing literature on covert research and covert methods provides an inappropriate frame of reference with which to understand concealment in fieldwork. The article illustrates why concealment is sometimes necessary, and often unavoidable, and concludes that the criticisms leveled against covert methods should not stop the fieldworker from engaging in research that involves covertness
Two Mathematically Equivalent Versions of Maxwell's Equations
This paper is a review of the canonical proper-time approach to relativistic
mechanics and classical electrodynamics. The purpose is to provide a physically
complete classical background for a new approach to relativistic quantum
theory. Here, we first show that there are two versions of Maxwell's equations.
The new version fixes the clock of the field source for all inertial observers.
However now, the (natural definition of the effective) speed of light is no
longer an invariant for all observers, but depends on the motion of the source.
This approach allows us to account for radiation reaction without the
Lorentz-Dirac equation, self-energy (divergence), advanced potentials or any
assumptions about the structure of the source. The theory provides a new
invariance group which, in general, is a nonlinear and nonlocal representation
of the Lorentz group. This approach also provides a natural (and unique)
definition of simultaneity for all observers. The corresponding particle theory
is independent of particle number, noninvariant under time reversal (arrow of
time), compatible with quantum mechanics and has a corresponding positive
definite canonical Hamiltonian associated with the clock of the source.
We also provide a brief review of our work on the foundational aspects of the
corresponding relativistic quantum theory. Here, we show that the standard
square-root and the Dirac equations are actually two distinct
spin- particle equations.Comment: Appeared: Foundations of Physic
The CLAS12 Backward Angle Neutron Detector (BAND)
The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted
at backward angles of to , with momenta between
and MeV/c. It is positioned 3 meters upstream of the target, consists of
rows and layers of cm by cm scintillator bars, and read
out on both ends by PMTs to measure time and energy deposition in the
scintillator layers. Between the target and BAND there is a 2 cm thick lead
wall followed by a 2 cm veto layer to suppress gammas and reject charged
particles. This paper discusses the component-selection tests and the detector
assembly. Timing calibrations (including offsets and time-walk) were performed
using a novel pulsed-laser calibration system, resulting in time resolutions
better than ps (150 ps) for energy depositions above 2 MeVee (5 MeVee).
Cosmic rays and a variety of radioactive sources were used to calibration the
energy response of the detector. Scintillator bar attenuation lengths were
measured. The time resolution results in a neutron momentum reconstruction
resolution, \% for neutron momentum MeV/c.
Final performance of the BAND with CLAS12 is shown, including electron-neutral
particle timing spectra and a discussion of the off-time neutral contamination
as a function of energy deposition threshold.Comment: 17 pages, 25 figures, 3 tables. Accepted for publication in NIM-
Welshness in British Wales: Negotiating national identity at the margins
Popular interpretations of national identity often focus on the unifying qualities of nationhood. However, societies frequently draw hierarchical distinctions between the people and places who are ‘most national’, and those who are ‘least national’. Little attention is paid to these marginal places within the nation and the experiences of their inhabitants. This article helps to address this by analysing the ‘less Welsh’ British Wales region of Wales, a country that has traditionally possessed a hierarchical, regionally constituted nationhood. The article studies the British Wales region both ‘from above’ – considering how some areas develop as ‘less national’ – and ‘from below’, introducing empirical ethnographic work into ‘everyday Welshness’ in this area. Whilst previous work on hierarchical nationhood focuses on how hierarchies are institutionalized by the state, this article demonstrates how people at the margins of the nation actively negotiate their place in the nation. Whilst people in this area expressed a strong Welshness, they also struggled to place themselves in the nation because they had internalized their lowly place within the national hierarchy. The article demonstrates the importance of place and social class for national identity construction and draws attention to the role of power in the discursive construction of hierarchical nationhood
The developmental impact of prenatal stress, prenatal dexamethasone and postnatal social stress on physiology, behaviour and neuroanatomy of primate offspring: studies in rhesus macaque and common marmoset
RATIONALE: Exposure of the immature mammalian brain to stress factors, including stress levels of glucocorticoids, either prenatally or postnatally, is regarded as a major regulatory factor in short- and long-term brain function and, in human, as a major aetiological factor in neuropsychiatric disorders. Experimental human studies are not feasible and animal studies are required to demonstrate causality and elucidate mechanisms. A number of studies have been conducted and reviewed in rodents but there are relatively few studies in primates. OBJECTIVES: Here we present an overview of our published studies and some original data on the effects of: (1) prenatal stress on hypothalamic-pituitary-adrenal (HPA) re/activity and hippocampus neuroanatomy in juvenile-adolescent rhesus macaques; (2) prenatal dexamethasone (DEX) on HPA activity, behaviour and prefrontal cortex neuroanatomy in infant-adolescent common marmosets; (3) postnatal daily parental separation stress on HPA re/activity, behaviour, sleep and hippocampus and prefrontal cortex neuroanatomy in infant-adolescent common marmoset. RESULTS: Prenatal stress increased basal cortisol levels and reduced neurogenesis in macaque. Prenatal DEX was without effect on HPA activity and reduced social play and skilled motor behaviour in marmoset. Postnatal social stress increased basal cortisol levels, reduced social play, increased awakening and reduced hippocampal glucocorticoid and mineralocorticoid receptor expression in marmoset. CONCLUSIONS: Perinatal stress-related environmental events exert short- and long-term effects on HPA function, behaviour and brain status in rhesus macaque and common marmoset. The mechanisms mediating the enduring effects remain to be elucidated, with candidates including increased basal HPA function and epigenetic programming
Metadevice for intensity modulation with sub-wavelength spatial resolution
Effectively continuous control over propagation of a beam of light requires light modulation with pixelation that is smaller than the optical wavelength. Here we propose a spatial intensity modulator with sub-wavelength resolution in one dimension. The metadevice combines recent advances in reconfigurable nanomembrane metamaterials and coherent all-optical control of metasurfaces. It uses nanomechanical actuation of metasurface absorber strips placed near a mirror in order to control their interaction with light from perfect absorption to negligible loss, promising a path towards dynamic beam diffraction, light focusing and holography without unwanted diffraction artefacts
Resistance through realism : Youth subculture films in 1970s (and 1980s) Britain
This document is the Accepted Manuscript version of the following article: Nathaniel Weiner, ‘Resistance through realism: Youth subculture films in 1970s (and 1980s) Britain’. The final, definitive version of this paper has been published in European Journal of Cultural Studies, November 2015, DOI: https://doi.org/10.1177/1367549415603376. Published by SAGE Publishing.Film scholars have argued that the British social realist films of the late 1950s and early 1960s reflect the concerns articulated by British cultural studies during the same period. This article looks at how the social realist films of the 1970s and early 1980s similarly reflect the concerns of British cultural studies scholarship produced by the University of Birmingham’s Centre for Contemporary Cultural Studies during the 1970s. It argues that the Centre for Contemporary Cultural Studies’ approach to stylised working-class youth subcultures is echoed in the portrayal of youth subcultures in the social realist films Pressure (1976), Bloody Kids (1979), Babylon (1980) and Made in Britain (1982). This article explores the ways in which these films show us both the strengths and weaknesses of the Centre for Contemporary Cultural Studies’ work on subcultures.Peer reviewe
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