159 research outputs found
Nonperturbative renormalization in a scalar model within Light-Front Dynamics
Within the covariant formulation of Light-Front Dynamics, in a scalar model
with the interaction Hamiltonian , we calculate
nonperturbatively the renormalized state vector of a scalar "nucleon" in a
truncated Fock space containing the , and sectors. The
model gives a simple example of non-perturbative renormalization which is
carried out numerically. Though the mass renormalization diverges
logarithmically with the cutoff , the Fock components of the "physical"
nucleon are stable when .Comment: 22 pages, 5 figure
Final State Interaction in Exclusive Reactions
Contributions of nucleon-nucleon (NN) correlations, meson exchange currents
and the residual final state interactions (FSI) on exclusive two-nucleon
knock-out reactions induced by electron scattering are investigated. All
contributions are derived from the same realistic meson exchange model for the
NN interaction. Effects of correlations and FSI are determined in a consistent
way by solving the NN scattering equation, the Bethe-Goldstone equation, for
two nucleons in nuclear matter. One finds that the FSI re-scattering terms are
non-negligible even if the two nucleons are emitted back to back.Comment: 8 pages, 5 figure
On isovector meson exchange currents in the Bethe-Salpeter approach
We investigate the nonrelativistic reduction of the Bethe-Salpeter amplitude
for the deuteron electrodisintegration near threshold energies. To this end,
two assumptions have been used in the calculations: 1) the static approximation
and 2) the one iteration approximation. Within these assumptions it is possible
to recover the nonrelativistic result including a systematic extension to
relativistic corrections. We find that the so-called pair current term can be
constructed from the -wave contribution of the deuteron Bethe-Salpeter
amplitude. The form factor that enters into the calculation of the pair current
is constrained by the manifestly gauge independent matrix elements.Comment: 15 pages, incl. 3 figures, to be published Phys. Rev.
Nucleon-Nucleon Correlations and Two-Nucleon Currents in Exclusive () Reactions
The contributions of short-range nucleon-nucleon (NN) correlations, various
meson exchange current (MEC) terms and the influence of isobar
excitations (isobaric currents, IC) on exclusive two-nucleon knockout reactions
induced by electron scattering are investigated. The nuclear structure
functions are evaluated for nuclear matter. Realistic NN interactions derived
in the framework of One-Boson-Exchange model are employed to evaluate the
effects of correlations and MEC in a consistent way. The correlations
correlations are determined by solving the Bethe-Goldstone equation. This
yields significant contributions to the structure functions W_L and W_T of the
(e,e'pn) and (e,e'pp) reactions. These contributions compete with MEC
corrections originating from the and exchange terms of the same
interaction. Special attention is paid to the so-called 'super parallel'
kinematics at momentum transfers which can be measured e.g. at MAMI in Mainz.Comment: 14 pages, 8 figures include
Short-range and tensor correlations in the O(e,epn) reaction
The cross sections for electron induced two-nucleon knockout reactions are
evaluated for the example of the O(e,epn)N reaction leading to
discrete states in the residual nucleus N. These calculations account
for the effects of nucleon-nucleon correlations and include the contributions
of two-body meson exchange currents as the pion seagull, pion in flight and the
isobar current contribution. The effects of short-range as well as tensor
correlations are calculated within the framework of the coupled cluster method
employing the Argonne V14 potential as a model for a realistic nucleon-nucleon
interaction. The relative importance of correlation effects as compared to the
contribution of the meson exchange currents depends on the final state of the
residual nucleus. The cross section leading to specific states, like e.g. the
ground state of N, is rather sensitive to the details of the correlated
wave function.Comment: 16 pages, 9 figures include
Cost-effectiveness of a community-delivered multicomponent intervention compared with enhanced standard care of obese adolescents: cost-utility analysis alongside a randomised controlled trial (the HELP trial)
OBJECTIVE: To undertake a cost-utility analysis of a motivational multicomponent lifestyle-modification intervention in a community setting (the Healthy Eating Lifestyle Programme (HELP)) compared with enhanced standard care. DESIGN: Cost-utility analysis alongside a randomised controlled trial. SETTING: Community settings in Greater London, England. PARTICIPANTS: 174 young people with obesity aged 12-19 years. INTERVENTIONS: Intervention participants received 12 one-to-one sessions across 6 months, addressing lifestyle behaviours and focusing on motivation to change and self-esteem rather than weight change, delivered by trained graduate health workers in community settings. Control participants received a single 1-hour one-to-one nurse-delivered session providing didactic weight-management advice. MAIN OUTCOME MEASURES: Mean costs and quality-adjusted life years (QALYs) per participant over a 1-year period using resource use data and utility values collected during the trial. Incremental cost-effectiveness ratio (ICER) was calculated and non-parametric bootstrapping was conducted to generate a cost-effectiveness acceptability curve (CEAC). RESULTS: Mean intervention costs per participant were £918 for HELP and £68 for enhanced standard care. There were no significant differences between the two groups in mean resource use per participant for any type of healthcare contact. Adjusted costs were significantly higher in the intervention group (mean incremental costs for HELP vs enhanced standard care £1003 (95% CI £837 to £1168)). There were no differences in adjusted QALYs between groups (mean QALYs gained 0.008 (95% CI -0.031 to 0.046)). The ICER of the HELP versus enhanced standard care was £120 630 per QALY gained. The CEAC shows that the probability that HELP was cost-effective relative to the enhanced standard care was 0.002 or 0.046, at a threshold of £20 000 or £30 000 per QALY gained. CONCLUSIONS: We did not find evidence that HELP was more effective than a single educational session in improving quality of life in a sample of adolescents with obesity. HELP was associated with higher costs, mainly due to the extra costs of delivering the intervention and therefore is not cost-effective. TRIAL REGISTRATION NUMBER: ISRCTN9984011
Objectively measured physical activity and sedentary behaviour in obese adolescents, and their relationship with fatness and metabolic outcomes
PURPOSE: To describe the physical activity (PA) and sedentary behaviour (SB) levels of obese adolescents (12-19 year-olds), and investigate the association of SB and moderate-to-vigorous PA (MVPA) with fatness and metabolic outcomes. METHODS: Baseline measurements were obtained from 102 obese (body mass index (BMI)>95th centile UK1990 reference) adolescents participating in a multicomponent obesity treatment trial- the Healthy Eating and Lifestyle Programme. PA/SB were measured with ActiGraph accelerometers (15-second epochs), time spent in SB, PA and MVPA was derived using Evenson et al’s (2007) cut-points, and participants were included for analyses if providing ≥3 valid days (≥10hours wear-time). Total, low- and high density lipoprotein cholesterol, triglycerides, insulin and glucose were obtained from fasting blood samples. Height, weight and waist circumference were measured by trained staff, fat mass (FM) and fat-free mass (FFM) were determined from bio-impedance analyses, and BMI and FM Index (FM/height2) were derived. Sex differences were assessed with chi-square or Mann-Whitney U tests, and associations of MVPA and SB with fatness and metabolic outcomes were assessed with univariable and multivariable linear regression. RESULTS: Adolescents spent a median of 4.5 hours/day in PA (including 38.5 min/day MVPA) and 12.7 hours/day in SB, with 86% spending over two thirds of their day in SB. Boys spent more time in MVPA than girls (median: 48.6min versus 35.9min; p=0.004), and were more likely to meet guidelines of ≥60 min/day in MVPA (24.3% versus 9.2%; p=0.04). Univariable regressions showed significant associations of MVPA with FM Index (B= -0.05), FM (B= -0.11) and FFM (B=0.14), and SB with Insulin (B=-0.02; all p<0.05). After including MVPA and SB in the same model and adjusting for age, sex, and wear-time, only MVPA remained significantly associated with FM Index (B= -0.05; p=0.04) and FFM (B= 0.13; p=0.008). CONCLUSIONS: Most adolescents did not meet current UK PA guidelines, and spent a worryingly high proportion of their day in SB. Although causality cannot be inferred, results highlight theimportance of promoting MVPA to improve the body composition profiles of obese adolescents
Recommended from our members
Description of the resolution hierarchy of the global coupled HadGEM3-GC3.1 model as used in CMIP6 HighResMIP experiments
CMIP6 HighResMIP is a new experimental design for global climate model simulations that aims to assess the impact of model horizontal resolution on climate simulation fidelity. We describe a hierarchy of global coupled model resolutions based on the HadGEM3-GC3.1 model that range from an atmosphere-ocean resolution of 130 km-1° to 25 km-1/12°, all using the same forcings and initial conditions. In order to make such high resolution simulations possible, the experiments have a short 30 year spinup, followed by at least century-long simulations with both constant forcing (to assess drift and the focus of this work), and historic forcing.
We assess the change in model biases as a function of both atmosphere and ocean resolution, together with the effectiveness and robustness of this new experimental design. We find reductions in the biases in top of atmosphere radiation components and cloud forcing. There are significant reductions in some common surface climate model biases as resolution is increased, particularly in the Atlantic for sea surface temperature and precipitation, primarily driven by increased ocean resolution. There is also a reduction in drift from the initial conditions both at the surface and in the deeper ocean at higher resolution. Using an eddy-present and eddy-rich ocean resolution enhances the strength of the North Atlantic ocean circulation (boundary currents, overturning circulation and heat transports), while an eddy-present ocean resolution has a considerably reduced Antarctic Circumpolar Current strength. All models have a reasonable representation of El Nino – Southern Oscillation. In general the biases present after 30 years of simulations do not change character markedly over longer timescales, justifying the experimental design
Quasi-Elastic Scattering in the Inclusive (He, t) Reaction
The triton energy spectra of the charge-exchange C(He,t) reaction
at 2 GeV beam energy are analyzed in the quasi-elastic nucleon knock-out
region. Considering that this region is mainly populated by the charge-exchange
of a proton in He with a neutron in the target nucleus and the final proton
going in the continuum, the cross-sections are written in the distorted-wave
impulse approximation. The t-matrix for the elementary exchange process is
constructed in the DWBA, using one pion- plus rho-exchange potential for the
spin-isospin nucleon- nucleon potential. This t-matrix reproduces the
experimental data on the elementary pn np process. The calculated
cross-sections for the C(He,t) reaction at to triton
emission angle are compared with the corresponding experimental data, and are
found in reasonable overall accord.Comment: 19 pages, latex, 11 postscript figures available at
[email protected], submitted to Phy.Rev.
- …