732 research outputs found
Twistfield Perturbations of Vertex Operators in the Z_2-Orbifold Model
We apply Kadanoff's theory of marginal deformations of conformal field
theories to twistfield deformations of Z_2 orbifold models in K3 moduli space.
These deformations lead away from the Z_2 orbifold sub-moduli-space and hence
help to explore conformal field theories which have not yet been understood. In
particular, we calculate the deformation of the conformal dimensions of vertex
operators for p^2<1 in second order perturbation theory.Comment: Latex2e, 19 pages, 1 figur
180 KNEE KINEMATICS AND KINETICS OF GAIT ARE ALTERED BY STOCHASTIC RESONANCE STIMULATION AND KNEE SLEEVE IN KNEE OSTEOARTHRITIS
The changing trend in nitrate concentrations in major aquifers due to historical nitrate loading from agricultural land across England and Wales from 1925 to 2150
Nitrate is necessary for agricultural productivity, but can cause considerable problems if released into aquatic systems. Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. However, this nitrate time-lag has rarely been considered in environmental water management. Against this background, this paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. An additional process-based component was constructed for the saturated zone of significant aquifers in England and Wales. This uses a simple flow model which requires modelled recharge values, together with published aquifer properties and thickness data. A spatially distributed and temporally variable nitrate input function was also introduced. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. The results are also indicative of the trend in the flux of groundwater nitrate entering rivers through baseflow. The model thus enables the magnitude and timescale of groundwater nitrate response to be factored into source apportionment tools and to be taken into account alongside current planning of land-management options for reducing nitrate losses
Interactions between fine-grained sediment delivery, river bed deposition and salmonid spawning success
Salmonids clean river bed gravels to lay their eggs. However, during the incubation period fine sediment
infiltrates the bed. This has been found to limit the success of salmonid spawning, as fine sediment reduces gravel
permeability resulting in intra-gravel flow velocities and O2 concentrations decreasing. The success of salmonid
spawning is therefore a function of the coincidence of fine sediment delivery and the development of the salmonid
eggs. The presence of fine sediment also exerts sub-lethal effects on the rate of egg development with a negative
feedback slowing and extending the incubation process meaning the eggs are in the gravels for longer and
susceptible to more potential sediment delivery events. The SIDO (Sediment Intrusion and Dissolved Oxygen)- UK model is a physically-based numerical model which simulates the effect of fine sediment deposition on the
abiotic characteristics of the salmonid redd, along with the consequences for egg development and survival. This
model is used to investigate the interactions and feedbacks between the timing and concentrations of suspended
sediment delivery events, and the deposition of fine sediment within the gravel bed, and the consequences of this
on the rate of egg development and survival. The model simulations suggest that egg survival is highly sensitive
to suspended sediment concentrations, particularly to changes in the supply rate of sand particles. The magnitude,
frequency and specific timing of sediment delivery events effects egg survival rates. The modelling framework is
also used to investigate the impact of the rate of gravel infilling by sediment. The hypotheses of continual, discrete
event and non-linear decline in the rate of infilling are investigated
Assessing the potential impacts of a revised set of on-farm nutrient and sediment âbasicâ control measures for reducing agricultural diffuse pollution across England
The need for improved abatement of agricultural diffuse water pollution represents cause for concern throughout the world. A critical aspect in the design of on-farm intervention programmes concerns the potential technical cost-effectiveness of packages of control measures. The European Union (EU) Water Framework Directive (WFD) calls for Programmes of Measures (PoMs) to protect freshwater environments and these comprise âbasicâ (mandatory) and âsupplementaryâ (incentivised) options. Recent work has used measure review, elicitation of stakeholder attitudes and a process-based modelling framework to identify a new alternative set of âbasicâ agricultural sector control measures for nutrient and sediment abatement across England. Following an initial scientific review of 708 measures, 90 were identified for further consideration at an industry workshop and 63 had industry support. Optimisation modelling was undertaken to identify a shortlist of measures using the Demonstration Test Catchments as sentinel agricultural landscapes. Optimisation selected 12 measures relevant to livestock or arable systems. Model simulations of 95% implementation of these 12 candidate âbasicâ measures, in addition to business-as-usual, suggested reductions in the national agricultural nitrate load of 2.5%, whilst corresponding reductions in phosphorus and sediment were 11.9% and 5.6%, respectively. The total cost of applying the candidate âbasicâ measures across the whole of England was estimated to be ÂŁ450 million per annum, which is equivalent to ÂŁ52 per hectare of agricultural land. This work contributed to a public consultation in 2016
Thermal diffusion of supersonic solitons in an anharmonic chain of atoms
We study the non-equilibrium diffusion dynamics of supersonic lattice
solitons in a classical chain of atoms with nearest-neighbor interactions
coupled to a heat bath. As a specific example we choose an interaction with
cubic anharmonicity. The coupling between the system and a thermal bath with a
given temperature is made by adding noise, delta-correlated in time and space,
and damping to the set of discrete equations of motion. Working in the
continuum limit and changing to the sound velocity frame we derive a
Korteweg-de Vries equation with noise and damping. We apply a collective
coordinate approach which yields two stochastic ODEs which are solved
approximately by a perturbation analysis. This finally yields analytical
expressions for the variances of the soliton position and velocity. We perform
Langevin dynamics simulations for the original discrete system which fully
confirm the predictions of our analytical calculations, namely noise-induced
superdiffusive behavior which scales with the temperature and depends strongly
on the initial soliton velocity. A normal diffusion behavior is observed for
very low-energy solitons where the noise-induced phonons also make a
significant contribution to the soliton diffusion.Comment: Submitted to PRE. Changes made: New simulations with a different
method of soliton detection. The results and conclusions are not different
from previous version. New appendixes containing information about the system
energy and soliton profile
Dark soliton states of Bose-Einstein condensates in anisotropic traps
Dark soliton states of Bose-Einstein condensates in harmonic traps are
studied both analytically and computationally by the direct solution of the
Gross-Pitaevskii equation in three dimensions. The ground and self-consistent
excited states are found numerically by relaxation in imaginary time. The
energy of a stationary soliton in a harmonic trap is shown to be independent of
density and geometry for large numbers of atoms. Large amplitude field
modulation at a frequency resonant with the energy of a dark soliton is found
to give rise to a state with multiple vortices. The Bogoliubov excitation
spectrum of the soliton state contains complex frequencies, which disappear for
sufficiently small numbers of atoms or large transverse confinement. The
relationship between these complex modes and the snake instability is
investigated numerically by propagation in real time.Comment: 11 pages, 8 embedded figures (two in color
Professionalism, Golf Coaching and a Master of Science Degree: A commentary
As a point of reference I congratulate Simon Jenkins on tackling the issue of professionalism in coaching. As he points out coaching is not a profession, but this does not mean that coaching would not benefit from going through a professionalization process. As things stand I find that the stimulus article unpacks some critically important issues of professionalism, broadly within the context of golf coaching. However, I am not sure enough is made of understanding what professional (golf) coaching actually is nor how the development of a professional golf coach can be facilitated by a Master of Science Degree (M.Sc.). I will focus my commentary on these two issues
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