204 research outputs found
Ballistic electron transport through magnetic domain walls
Electron transport limited by the rotating exchange-potential of domain walls
is calculated in the ballistic limit for the itinerant ferromagnets Fe, Co, and
Ni. When realistic band structures are used, the domain wall magnetoresistance
is enhanced by orders of magnitude compared to the results for previously
studied two-band models. Increasing the pitch of a domain wall by confinement
in a nano-structured point contact is predicted to give rise to a strongly
enhanced magnetoresistance.Comment: 4 pages, 2 figures; to appear in PRB as a brief repor
Hard Loop Approach to Anisotropic Systems
Anisotropic systems of quarks and gluons, which at least for sufficiently
short space-time intervals can be treated as homogeneous and static, are
considered. The gluon polarization tensor of such a system is explicitly
computed within the semiclassical kinetic and Hard Loop diagrammatic theories.
The equivalence of the two approaches is demonstrated. The quark self energy is
computed as well, and finally, the dispersion relations of quarks and gluons in
the anisotropic medium are discussed.Comment: 10 pages, revised to appear in Phys. Rev.
Nucleon Charge and Magnetization Densities from Sachs Form Factors
Relativistic prescriptions relating Sachs form factors to nucleon charge and
magnetization densities are used to fit recent data for both the proton and the
neutron. The analysis uses expansions in complete radial bases to minimize
model dependence and to estimate the uncertainties in radial densities due to
limitation of the range of momentum transfer. We find that the charge
distribution for the proton is significantly broad than its magnetization
density and that the magnetization density is slightly broader for the neutron
than the proton. The neutron charge form factor is consistent with the Galster
parametrization over the available range of Q^2, but relativistic inversion
produces a softer radial density. Discrete ambiguities in the inversion method
are analyzed in detail. The method of Mitra and Kumari ensures compatibility
with pQCD and is most useful for extrapolating form factors to large Q^2.Comment: To appear in Phys. Rev. C. Two new figures and accompanying text have
been added and several discussions have been clarified with no significant
changes to the conclusions. Now contains 47 pages including 21 figures and 2
table
Configuration-interaction calculations of positron binding to group-II elements
The configuration-interaction (CI) method is applied to the study of positronic magnesium (e+Mg), positronic calcium (e+Ca), and positronic strontium (e+Sr). The CI expansion was seen to converge slowly with respect to Lmax, the maximum angular momentum of any orbital used to construct the CI basis. Despite doing explicit calculations with Lmax=10, extrapolation corrections to the binding energies for the Lmax→∞ limit were substantial in the case of e+Ca (25%) and e+Sr (50%). The extrapolated binding energies were 0.0162 hartree for e+Mg, 0.0165 hartree for e+Ca, and 0.0101 hartree for e+Sr. The static-dipole polarizabilities for the neutral parent atoms were computed as a by-product, giving 71.7a03, 162a03, and 204a03 for Mg, Ca, and Sr, respectively
Meson exchange currents in electromagnetic one-nucleon emission
The role of meson exchange currents (MEC) in electron- and photon-induced
one-nucleon emission processes is studied in a nonrelativistic model including
correlations and final state interactions. The nuclear current is the sum of a
one-body and of a two-body part. The two-body current includes pion seagull,
pion-in-flight and the isobar current contributions. Numerical results are
presented for the exclusive 16O(e,e'p)15N and 16O(\gamma,p)15N reactions. MEC
effects are in general rather small in (e,e'p), while in (\gamma,p) they are
always large and important to obtain a consistent description of (e,e'p) and
(\gamma,p) data, with the same spectroscopic factors. The calculated (\gamma,p)
cross sections are sensitive to short-range correlations at high values of the
recoil momentum, where MEC effects are larger and overwhelm the contribution of
correlations.Comment: 9 pages, 6 figure
The ‘talk o’ the toon’?:An examination of the Heart of Midlothian and Hibernian football rivalry in Edinburgh, Scotland
Heart of Midlothian (Hearts) and Hibernian (Hibs) Football Clubs are historic football rivals based in Edinburgh, Scotland. Both clubs have past and present connections to sectarian identities resulting in their rivalry often being reductively labelled “a mini Old Firm” (a mini Rangers v Celtic rivalry). This reductionism misunderstands the genuine ethno-religious (sectarian) connections of both Edinburgh clubs and overlooks other significant factors that underpin and sustain the rivalry in 21st century Scotland. Hearts have British and military-related ‘remembrance’ signifiers and Hibs have Irish-Catholic signifiers and these do continue – under quite specific and sporadic conditions - to linger today. Yet both clubs also have additional aspects to their identities which underpin the rivalry and these relate to a failed take-over of Hibs by Hearts, to playing style, social class and geographical place. Utilising semi-structured and unstructured interviews and observation, we conclude that the Hearts-Hibs rivalry has entered a post-sectarian period where lingering sectarian signifiers sometimes reveal themselves - often when the two clubs play the Glasgow clubs Celtic and Rangers – but where more often, largely overlooked elements constitute the rivalry to a greater extent for large sections of both respective groups of supporters
Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles
We have made the first measurements of the virtual Compton scattering (VCS)
process via the H exclusive reaction in the nucleon resonance
region, at backward angles. Results are presented for the -dependence at
fixed GeV, and for the -dependence at fixed near 1.5 GeV.
The VCS data show resonant structures in the first and second resonance
regions. The observed -dependence is smooth. The measured ratio of
H to H cross sections emphasizes the different
sensitivity of these two reactions to the various nucleon resonances. Finally,
when compared to Real Compton Scattering (RCS) at high energy and large angles,
our VCS data at the highest (1.8-1.9 GeV) show a striking -
independence, which may suggest a transition to a perturbative scattering
mechanism at the quark level.Comment: 20 pages, 8 figures. To appear in Phys.Rev.
Socioeconomic status, non-communicable disease risk factors, and walking speed in older adults: Multi-cohort population based study
Objective To assess the association of low socioeconomic status and risk factors for non-communicable diseases (diabetes, high alcohol intake, high blood pressure, obesity, physical inactivity, smoking) with loss of physical functioning at older ages. Design Multi-cohort population based study. Setting 37 cohort studies from 24 cou
Maternal anthropometry for prediction of pregnancy outcomes: Memorandum from a USAID/WHO/PAHO/MotherCare meeting
The meeting discussed two main areas concerning maternal anthropometry in developing countries: (1) how various anthropometric indicators can be best utilized for assessing and monitoring the nutritional status of women at different times in their reproductive lives, and (2) the predictive value of various anthropometric indicators for identifying benefit or risk for maternal and perinatal/neonatal health and nutritional outcomes of pregnancy. The indicators discussed were prepregnancy weight, height, weight gain in pregnancy, arm circumference, weight-for-height and body mass index (weight (kg)/height (m)2). Some 50 experts reached consensus on the tools for assessing maternal nutritional status for widespread field application in developing countries, and on priority research needs. This Memorandum summarizes the general recommendations which have important and immediate field applications, as well as priority research issues related to specific indicators
Chronic obstructive pulmonary disease and related phenotypes: polygenic risk scores in population-based and case-control cohorts
Background Genetic factors influence chronic obstructive pulmonary disease (COPD) risk, but the individual variants
that have been identified have small effects. We hypothesised that a polygenic risk score using additional variants
would predict COPD and associated phenotypes.
Methods We constructed a polygenic risk score using a genome-wide association study of lung function (FEV1 and
FEV1/forced vital capacity [FVC]) from the UK Biobank and SpiroMeta. We tested this polygenic risk score in nine
cohorts of multiple ethnicities for an association with moderate-to-severe COPD (defined as FEV1/FVC <0·7 and FEV1
<80% of predicted). Associations were tested using logistic regression models, adjusting for age, sex, height, smoking
pack-years, and principal components of genetic ancestry. We assessed predictive performance of models by area
under the curve. In a subset of studies, we also studied quantitative and qualitative CT imaging phenotypes that
reflect parenchymal and airway pathology, and patterns of reduced lung growth.
Findings The polygenic risk score was associated with COPD in European (odds ratio [OR] per SD 1·81
[95% CI 1·74–1·88] and non-European (1·42 [1·34–1·51]) populations. Compared with the first decile, the tenth decile
of the polygenic risk score was associated with COPD, with an OR of 7·99 (6·56–9·72) in European ancestry and
4·83 (3·45–6·77) in non-European ancestry cohorts. The polygenic risk score was superior to previously described
genetic risk scores and, when combined with clinical risk factors (ie, age, sex, and smoking pack-years), showed
improved prediction for COPD compared with a model comprising clinical risk factors alone (AUC 0·80 [0·79–0·81]
vs 0·76 [0·75–0·76]). The polygenic risk score was associated with CT imaging phenotypes, including wall area
percent, quantitative and qualitative measures of emphysema, local histogram emphysema patterns, and destructive
emphysema subtypes. The polygenic risk score was associated with a reduced lung growth pattern.
Interpretation A risk score comprised of genetic variants can identify a small subset of individuals at markedly
increased risk for moderate-to-severe COPD, emphysema subtyp
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