3,499 research outputs found
Intersoliton forces in the Wess-Zumino model
The spectrum of supersymmetric domain wall solitons of the Wess-Zumino model
is known to be discontinuous across a curve (of marginal stability) in the
moduli space of quartic superpotentials. Here we show how this phenomenon can
be understood from the behavior of the long-range inter-soliton force, which we
compute by a method due to Manton.Comment: 10 pages, 4 figures, latex. Version 3, to appear in PLB, corrects
minor error
Probing a Secluded U(1) at B-factories
A secluded U(1) gauge field, kinetically mixed with Standard Model
hypercharge, provides a `portal' mediating interactions with a hidden sector at
the renormalizable level, as recently exploited in the context of WIMP dark
matter. The secluded U(1) symmetry-breaking scale may naturally be suppressed
relative to the weak scale, and so this sector is efficiently probed by medium
energy electron-positron colliders. We study the collider signatures of the
minimal secluded U(1) model, focusing on the reach of B-factory experiments
such as BaBar and BELLE. In particular, we show that Higgs-strahlung in the
secluded sector can lead to multi-lepton signatures which probe the natural
range for the kinetic mixing angle of 10^(-2)-10^(-3) over a large portion of
the kinematically accessible parameter space.Comment: 14 pages, 3 figure
Weyl corrections to holographic conductivity
For conformal field theories which admit a dual gravitational description in
anti-de Sitter space, electrical transport properties, such as conductivity and
charge diffusion, are determined by the dynamics of a U(1) gauge field in the
bulk and thus obey universality relations at the classical level due to the
uniqueness of the Maxwell action. We analyze corrections to these transport
parameters due to higher-dimension operators in the bulk action, beyond the
leading Maxwell term, of which the most significant involves a coupling to the
bulk Weyl tensor. We show that the ensuing corrections to conductivity and the
diffusion constant break the universal relation with the U(1) central charge
observed at leading order, but are nonetheless subject to interesting bounds
associated with causality in the boundary CFT.Comment: 15 pages, v2: references adde
A simple reactive-transport model of calcite precipitation in soils and other porous media
Calcite formation in soils and other porous media generally occurs around a localised source of reactants, such as a plant root or soil macro-pore, and the rate depends on the transport of reactants to and from the precipitation zone as well as the kinetics of the precipitation reaction itself. However most studies are made in well mixed systems, in which such transport limitations are largely removed. We developed a mathematical model of calcite precipitation near a source of base in soil, allowing for transport limitations and precipitation kinetics. We tested the model against experimentally-determined rates of calcite precipitation and reactant concentrationâdistance profiles in columns of soil in contact with a layer of HCO3â-saturated exchange resin. The model parameter values were determined independently. The agreement between observed and predicted results was satisfactory given experimental limitations, indicating that the model correctly describes the important processes. A sensitivity analysis showed that all model parameters are important, indicating a simpler treatment would be inadequate. The sensitivity analysis showed that the amount of calcite precipitated and the spread of the precipitation zone were sensitive to parameters controlling rates of reactant transport (soil moisture content, salt content, pH, pH buffer power and CO2 pressure), as well as to the precipitation rate constant. We illustrate practical applications of the model with two examples: pH changes and CaCO3 precipitation in the soil around a plant root, and around a soil macro-pore containing a source of base such as urea
Emissions Trading with Profit-Neutral Permit Allocations
This paper examines the operation of an emissions trading scheme (ETS) in a Cournot oligopoly. We study the impact of the ETS on industry output, price, costs, emissions, and profits. In particular, we develop formulae for the number of emissions permits that have to be freely allocated to firms in order to neutralize any adverse impact the ETS may have on profits. These formulae tell us that the profit impact of the ETS is usually limited. Indeed, under quite general conditions, industry profits are preserved so long as firms are freely allocated a fraction of their total demand for permits, with this fraction being lower than the industry's Herfindahl index.Emissions trading, permit allocation, profit-neutrality, cost pass-through, abatement, grandfathering
Secular trends in under-reporting in young people
Original article can be found at: http://journals.cambridge.org/action/displayJournal?jid=BJN Copyright The Authors. DOI: 10.1079/BJN20041307National survey data show that reported energy intake has decreased in recent decades despite a rise in the prevalence of obesity. This disparity may be due to a secular increase in under-reporting or a quantitatively greater decrease in energy expenditure. This study examines the extent of under-reporting of energy intake in the National Diet and Nutrition Survey (NDNS) in young people aged 4â18 years in 1997 using published equations to calculate estimated energy requirements. It explores secular changes by comparison with the Diets of British School Children (DBSC) survey in 10â11- and 14â15-year-olds in 1983. In the NDNS, under-reporting (estimated energy requirements â energy intake) represented 21 % of energy needs in girls and 20 % in boys. The magnitude of under-reporting increased significantly with age (P<0·001) and was higher in overweight than lean individuals over 7 years of age. To compare reported energy intake in DBSC and NDNS, the estimated physical activity level from dietary records (dPAL=reported energy intake/predicted BMR) was calculated. If there were no under-reporting, dPAL would represent the subject's true activity level. However, dPAL from the NDNS was significantly lower than that from the DBSC by 8 % and 9 % in boys and girls for those aged 10â11 years, and by 14 % and 11 % for 14â15-year-olds respectively, reaching physiologically implausible levels in the 14â15-year-old girls (dPAL=1·17). If activity levels have remained constant between the two surveys, under-reporting has increased by 8â14 %. The evidence supports a secular trend towards increased under-reporting between the two surveys, but the precise magnitude cannot be quantified in the absence of historical measures of energy expenditure.Peer reviewe
Electron Beam Induced Current Analysis of Voltage Breakdown Sites in Thin MOS Oxides
Voltage breakdown sites on thin (\u3c 100 A) MOS capacitors have been identified by the electron beam induced current (EBIC) technique, using a scanning electron microscope (SEM). EBIC spots coincide with voltage breakdown locations and their image intensity can be changed by varying the applied bias or the electron beam accelerating voltage. Total current and the number of EBIC spots were the same in both accumulation and depletion conditions for a fixed beam potential and bias voltage. This suggests that the observed EBIC spots were due to defects in the oxide only. This EBIC method for identifying defects has been found very useful in characterizing thin MOS oxides
A simple reactive-transport model of calcite precipitation in soils and other porous media
Calcite formation in soils and other porous media generally occurs around a localised source of reactants, such as a plant root or soil macro-pore, and the rate depends on the transport of reactants to and from the precipitation zone as well as the kinetics of the precipitation reaction itself. However most studies are made in well mixed systems, in which such transport limitations are largely removed. We developed a mathematical model of calcite precipitation near a source of base in soil, allowing for transport limitations and precipitation kinetics. We tested the model against experimentally-determined rates of calcite precipitation and reactant concentrationâdistance profiles in columns of soil in contact with a layer of HCO3â-saturated exchange resin. The model parameter values were determined independently. The agreement between observed and predicted results was satisfactory given experimental limitations, indicating that the model correctly describes the important processes. A sensitivity analysis showed that all model parameters are important, indicating a simpler treatment would be inadequate. The sensitivity analysis showed that the amount of calcite precipitated and the spread of the precipitation zone were sensitive to parameters controlling rates of reactant transport (soil moisture content, salt content, pH, pH buffer power and CO2 pressure), as well as to the precipitation rate constant. We illustrate practical applications of the model with two examples: pH changes and CaCO3 precipitation in the soil around a plant root, and around a soil macro-pore containing a source of base such as urea
Scoping biological indicators of soil quality Phase II. Defra Final Contract Report SP0534
This report presents results from a field assessment of a limited suite of potential biological indicators of soil quality to investigate their suitability for national-scale soil monitoring
- âŠ