37,917 research outputs found
Photoabsorption spectra in the continuum of molecules and atomic clusters
We present linear response theories in the continuum capable of describing
photoionization spectra and dynamic polarizabilities of finite systems with no
spatial symmetry. Our formulations are based on the time-dependent local
density approximation with uniform grid representation in the three-dimensional
Cartesian coordinate. Effects of the continuum are taken into account either
with a Green's function method or with a complex absorbing potential in a
real-time method. The two methods are applied to a negatively charged cluster
in the spherical jellium model and to some small molecules (silane, acetylene
and ethylene).Comment: 13 pages, 9 figure
Dual Response Models for the Fractional Quantum Hall Effect
It is shown that the Jain mapping between states of integer and fractional
quantum Hall systems can be described dynamically as a perturbative
renormalization of an effective Chern-Simons field theory. The effects of
mirror duality symmetries of toroidally compactified string theory on this
system are studied and it is shown that, when the gauge group is compact, the
mirror map has the same effect as the Jain map. The extrinsic ingredients of
the Jain construction appear naturally as topologically non-trivial field
configurations of the compact gauge theory giving a dynamical origin for the
Jain hierarchy of fractional quantum Hall states.Comment: 8 pages LaTe
Threshold shift and above-threshold multiphoton ionization of atomic hydrogen in intense laser fields
This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.32.2769.Accurate ab initio nonperturbative L2 non-Hermitian Floquet calculations for intensity-dependent threshold shifts and ground-state total ionization widths (rates) for one-, two-, and three-photon-dominant intense-field ionization of atomic hydrogen are presented. The results show the importance of both the ac Stark shift and the pondermotive potential in the determination of the net threshold shift. In addition, branching ratios to individual continua have been estimated, yielding physical insights regarding the general features and mechanisms of the frequency- and intensity-dependent continuum-continuum transitions and ‘‘peak switching’’ phenomena in the above-threshold ionization processes
Dynamical Description of Spectral Flow in N=2 Superconformal Field Theories
We show how the spectral flow between the Neveu-Schwarz and Ramond sectors of N=2 superconformal field theories can be described in three dimensions in terms of the propagation of charged particles coupled to a a Chern-Simons gauge theory. Quantum mechanical mixing between the degenerate Chern-Simons vacua interpolates between the different boundary conditions of the two sectors and so provides a dynamical picture for the GSO-projection
Zero mode in the time-dependent symmetry breaking of theory
We apply the quartic exponential variational approximation to the symmetry
breaking phenomena of scalar field in three and four dimensions. We calculate
effective potential and effective action for the time-dependent system by
separating the zero mode from other non-zero modes of the scalar field and
treating the zero mode quantum mechanically. It is shown that the quantum
mechanical properties of the zero mode play a non-trivial role in the symmetry
breaking of the scalar theory.Comment: 10 pages, 3 figure
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An on-going investigation into the ecological determinants of Lyme disease in the South Downs National Park, South East England: the potential for 'One Health' based interventions
Lyme borreliosis (LB) is a tick-borne infectious disease, with UK annual diagnoses trebling over the last two decades. The widening UK distribution of the main LB tick vector (Ixodes ricinus) has been linked to deer population expansion. However, the wider ecological determinants that affect the density of infected ticks are poorly understood. Deer have key roles in most, but not all, UK LB disease systems, but they are non-competent hosts for the pathogen itself, and small mammals or birds are usually obligatory disease reservoirs. In addition, the relapsing fever spirochete Borrelia miyomotoi was detected in the UK in 2014, but the spread and extent of this emerging human pathogen is still unknown. To date, five sites have been drag-sampled across the South Downs National Park (SDNP); with ticks being successfully obtained from all sites. In addition, ticks have been collected from a further sixteen sites where individual or multiple deer were sampled. Currently, ticks are undergoing genetic analysis to determine the host animals involved in the disease cycle, and the presence of Borrelia sp. The study aims to provide a mapped assessment of LB risk across the South Downs National Park, and identify the disease reservoir community composition. The results will help elucidate the causal factors in the SDNP, and support development of policies that avoid or minimise conflicts between public and ecosystem health
Cortisol levels in response to starting school in children at increased risk for social phobia
Background: Research on depression has identified hyperactivity of the HPA axis as a
potential contributory factor to the intergenerational transmission of affective symptoms. However,
this has not yet been examined in the context of social phobia. The current study compared HPA axis
activity in response to a universal social stressor (starting school) in children of 2 groups of women:
one with social phobia and one with no history of anxiety (comparison group). To determine specificity
of effects of maternal social phobia, a third group of children were also examined whose mothers had
generalised anxiety disorder (GAD).
Method: Children provided salivary cortisol samples in the morning, afternoon and at bedtime across 3
time-blocks surrounding the school start: a month before starting school (baseline), the first week at
school (stress response), and the end of the first school term (stress recovery). Child behavioural
inhibition at 14 months was also assessed to explore the influence of early temperament on later stress
responses.
Results: All children displayed an elevation in morning and afternoon cortisol from baseline during the
first week at school, which remained elevated until the end of the first term. Children in the social
phobia group, however, also displayed an equivalent elevation in bedtime cortisol, which was not
observed for comparison children or for children of mothers with GAD. Children in the social phobia
group who were classified as 'inhibited' at 14 months displayed significantly higher afternoon cortisol
levels overall.
Summary: A persistent stress response to school in the morning and afternoon is typical for all
children, but children of mothers with social phobia also display atypical elevations in evening cortisol
levels when at school - signalling long-term disruption of the circadian rhythm in HPA axis activity.
This is the first study to report HPA axis disruption in children at risk of developing social phobia, and
future research should aim to determine whether this represents a pathway for symptom
development, taking early temperament into account
Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory
Two different adsorption configurations of benzene on the Si(001)-(2 x 1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vdW-DF), which accounts for the effect of van der Waals forces. In contrast to the Perdew-Burke-Ernzerhof (PBE), revPBE, and other generalized-gradient approximation functionals, the vdW-DF finds that, for most coverages, the adsorption energy of the butterfly structure is greater than that of the tight-bridge structure
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Ecological determinants of Lyme borreliosis hazard in the South Downs National Park and the potential for One Health based interventions (work in progress)
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