1,390 research outputs found
CLIC Background Studies and optimization of the innermost tracker elements
The harsh machine background at the Compact Linear Collider (CLIC) forms a
strong constraint on the design of the innermost part of the tracker. For the
CLIC Conceptual Design Report, the detector concepts developed for the
International Linear Collider (ILC) were adapted to the CLIC environment. We
present the new layout for the Vertex Detector and the Forward Tracking Disks
of the CLIC detector concepts, as well as the background levels in these
detectors. We also study the dependence of the background rates on technology
parameters like thickness of the active layer and detection threshold.Comment: 7 pages, 5 figures, LCWS 201
Moment Equations for a Spatially Extended System of Two Competing Species
The dynamics of a spatially extended system of two competing species in the
presence of two noise sources is studied. A correlated dichotomous noise acts
on the interaction parameter and a multiplicative white noise affects directly
the dynamics of the two species. To describe the spatial distribution of the
species we use a model based on Lotka-Volterra (LV) equations. By writing them
in a mean field form, the corresponding moment equations for the species
concentrations are obtained in Gaussian approximation. In this formalism the
system dynamics is analyzed for different values of the multiplicative noise
intensity. Finally by comparing these results with those obtained by direct
simulations of the time discrete version of LV equations, that is coupled map
lattice (CML) model, we conclude that the anticorrelated oscillations of the
species densities are strictly related to non-overlapping spatial patterns.Comment: 10 pages, 3 figure
Renormalization of the Periodic Scalar Field Theory by Polchinski's Renormalization Group Method
The renormalization group (RG) flow for the two-dimensional sine-Gordon model
is determined by means of Polchinski's RG equation at next-to-leading order in
the derivative expansion. In this work we have two different goals, (i) to
consider the renormalization scheme-dependence of Polchinski's method by
matching Polchinski's equation with the Wegner-Houghton equation and with the
real space RG equations for the two-dimensional dilute Coulomb-gas, (ii) to go
beyond the local potential approximation in the gradient expansion in order to
clarify the supposed role of the field-dependent wave-function renormalization.
The well-known Coleman fixed point of the sine-Gordon model is recovered after
linearization, whereas the flow exhibits strong dependence on the choice of the
renormalization scheme when non-linear terms are kept. The RG flow is compared
to those obtained in the Wegner-Houghton approach and in the dilute gas
approximation for the two-dimensional Coulomb-gas.Comment: 14 pages, LaTeX, 1 figure; J. Phys. G (in press
Renormalization-Group Analysis of the Generalized sine-Gordon Model and of the Coulomb Gas for d >= 3 Dimensions
Renormalization-group (RG) flow equations have been derived for the
generalized sine-Gordon model (GSGM) and the Coulomb gas (CG) in d >= 3 of
dimensions by means of Wegner's and Houghton's, and by way of the real-space RG
approaches. The UV scaling laws determined by the leading-order terms of the
flow equations are in qualitative agreement for all dimensions d >= 3,
independent of the dimensionality, and in sharp contrast to the special case d
= 2. For the 4-dimensional GSGM it is demonstrated explicitly (by numerical
calculations), that the blocked potential tends to a constant effective
potential in the infrared (IR) limit, satisfying the requirements of
periodicity and convexity. The comparison of the RG flows for the
three-dimensional GSGM, the CG, and the vortex-loop gas reveals a significant
dependence on the renormalization schemes and the approximations used.Comment: 19 pages, 8 figure
Moment equations in a Lotka-Volterra extended system with time correlated noise
A spatially extended Lotka-Volterra system of two competing species in the
presence of two correlated noise sources is analyzed: (i) an external
multiplicative time correlated noise, which mimics the interaction between the
system and the environment; (ii) a dichotomous stochastic process, whose jump
rate is a periodic function, which represents the interaction parameter between
the species. The moment equations for the species densities are derived in
Gaussian approximation, using a mean field approach. Within this formalism we
study the effect of the external time correlated noise on the ecosystem
dynamics. We find that the time behavior of the order moments are
independent on the multiplicative noise source. However the behavior of the
order moments is strongly affected both by the intensity and the
correlation time of the multiplicative noise. Finally we compare our results
with those obtained studying the system dynamics by a coupled map lattice
model.Comment: 12 pages, 7 figures, to appear in Acta Phys. Pol.
On the applicability of the layered sine-Gordon model for Josephson-coupled high-T_c layered superconductors
We find a mapping of the layered sine-Gordon model to an equivalent gas of
topological excitations and determine the long-range interaction potentials of
the topological defects. This enables us to make a detailed comparison to the
so-called layered vortex gas, which can be obtained from the layered
Ginzburg-Landau model. The layered sine-Gordon model has been proposed in the
literature as a candidate field-theoretical model for Josephson-coupled
high-T_c superconductors, and the implications of our analysis for the
applicability of the layered sine-Gordon model to high-T_c superconductors are
discussed. We are led to the conjecture that the layered sine--Gordon and the
layered vortex gas models belong to different universality classes. The
determination of the critical temperature of the layered sine-Gordon model is
based on a renormalization-group analysis.Comment: 7 pages, accepted for publication in J. Phys.: Condens. Matte
A practical method for calculating thermally-induced stresses in pile foundations used as heat exchangers
Thermo-active piles are capable of providing both structural stability as foundations and low carbon heating and cooling as ground source heat exchangers. When subjected to heating or cooling, the soil surrounding the pile restricts its expansion or contraction, giving rise to thermally-induced axial stresses, which need to be considered during design. Previous numerical studies often assume axisymmetry of the problem and/or a simplification of the heating or cooling mechanism of the pile. To simulate accurately the development of thermallyinduced axial stresses, this paper presents a computational study comprising three dimensional fully coupled thermo-hydro-mechanical finite element analyses conducted using the Imperial College Finite Element Program (ICFEP), where the heating of a thermo-active pile is simulated by prescribing a flow of hot water through the heat exchanger pipes within the pile. The effects of pipe arrangement on thermally-induced axial stresses are investigated by considering three different cases – single U loop, double U-loop and triple U-loop. Since threedimensional analyses are computationally expensive, a simplified method using a combination of two-dimensional analyses is proposed to estimate the thermally-induced axial stresses, which is subsequently validated and shown to yield accurate results
Wave-function renormalization for the Coulomb-gas in Wegner-Houghton's RG method
The RG flow for the sine-Gordon model is determined by means of the method of
Wegner and Houghton in next-to-leading order of the derivative expansion. For
small values of the fugacity this agrees with the well-known RG flow of the
two-dimensional Coulomb-gas found in the dilute gas approximation and a
systematic way of obtaining higher-order corrections to this approximation is
given.Comment: 4 pages, 2 figure
Renormalization-Group Analysis of the Generalized Sine-Gordon Model and of the Coulomb Gas for D \u3e 3 Dimensions
Renormalization-group (RG) flow equations have been derived for the generalized sine-Gordon model (GSGM) and the Coulomb gas (CG) in d ≥ 3 of dimensions by means of the Wegner-Houghton method, and by way of the real-space RG approach. The UV scaling laws determined by the leading-order terms of the flow equations are in qualitative agreement for all dimensions d ≥ 3, independent of the dimensionality, and in sharp contrast to the special case d=2. For the 4-dimensional GSGM it is demonstrated explicitly (by numerical calculations) that the blocked potential tends to a constant effective potential in the infrared limit, satisfying the requirements of periodicity and convexity. The comparison of the RG flows for the three-dimensional GSGM, the CG, and the vortex-loop gas reveals a significant dependence on the renormalization schemes and the approximations used
Interplay of fixed points in scalar models
We performed the renormalization group analysis of scalar models exhibiting
spontaneous symmetry breaking. It is shown that an infrared fixed point appears
in the broken symmetric phase of the models, which induces a dynamical scale,
that can be identified with the correlation length. This enables one to
identify the type of the phase transition which shows similarity to the one
appearing in the crossover scale. The critical exponent of the
correlation length also proved to be equal in the crossover and the infrared
scaling regimes.Comment: 11 pages, 4 figure
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