26,019 research outputs found
Overlap Distribution of the Three-Dimensional Ising Model
We study the Parisi overlap probability density P_L(q) for the
three-dimensional Ising ferromagnet by means of Monte Carlo (MC) simulations.
At the critical point P_L(q) is peaked around q=0 in contrast with the double
peaked magnetic probability density. We give particular attention to the tails
of the overlap distribution at the critical point, which we control over up to
500 orders of magnitude by using the multi-overlap MC algorithm. Below the
critical temperature interface tension estimates from the overlap probability
density are given and their approach to the infinite volume limit appears to be
smoother than for estimates from the magnetization.Comment: 7 pages, RevTex, 9 Postscript figure
Large-scale Monte Carlo simulations of the isotropic three-dimensional Heisenberg spin glass
We study the Heisenberg spin glass by large-scale Monte Carlo simulations for
sizes up to 32^3, down to temperatures below the transition temperature claimed
in earlier work. The data for the larger sizes show more marginal behavior than
that for the smaller sizes, indicating the lower critical dimension is close
to, and possibly equal to three. We find that the spins and chiralities behave
in a quite similar manner.Comment: 8 pages, 8 figures. Replaced with published versio
Selection Effects, Biases, and Constraints in the Calan/Tololo Supernova Survey
We use Monte Carlo simulations of the Calan/Tololo photographic supernova
survey to show that a simple model of the survey's selection effects accounts
for the observed distributions of recession velocity, apparent magnitude,
angular offset, and projected radial distance between the supernova and the
host galaxy nucleus for this sample of Type Ia supernovae (SNe Ia). The model
includes biases due to the flux-limited nature of the survey, the different
light curve morphologies displayed by different SNe Ia, and the difficulty of
finding events projected near the central regions of the host galaxies. From
these simulations we estimate the bias in the zero-point and slope of the
absolute magnitude-decline rate relation used in SNe Ia distance measurements.
For an assumed intrinsic scatter of 0.15 mag about this relation, these
selection effects decrease the zero-point by 0.04 mag. The slope of the
relation is not significantly biased. We conclude that despite selection
effects in the survey, the shape and zero-point of the relation determined from
the Calan/Tololo sample are quite reliable. We estimate the degree of
incompleteness of the survey as a function of decline rate and estimate a
corrected luminosity function for SNe Ia in which the frequency of SNe appears
to increase with decline rate (the fainter SNe are more common). Finally, we
compute the integrated detection efficiency of the survey in order to infer the
rate of SNe Ia from the 31 events found. For a value of Ho=65 km/sec/Mpc we
obtain a SN Ia rate of 0.21(+0.30)(-0.13) SNu. This is in good agreement with
the value 0.16+/-0.05 SNu recently determined by Capellaro et al. (1997).Comment: 36 pages, 19 figures as extra files, to appear in the A
Mass Predictions for Pseudoscalar Charmonium and Bottomonium Hybrids in QCD Sum-Rules
Masses of the pseudoscalar charmonium and bottomonium
hybrids are determined using QCD Laplace sum-rules. The effects of the
dimension-six gluon condensate are included in our analysis and result in a
stable sum-rule analysis, whereas previous studies of these states were unable
to optimize mass predictions. The pseudoscalar charmonium hybrid is predicted
to have a mass of approximately 3.8 GeV and the corresponding bottomonium
prediction is 10.6 GeV. Calculating the full correlation function, rather than
only the imaginary part, is shown to be necessary for accurate formulation of
the sum-rules. The charmonium hybrid mass prediction is discussed within the
context of the X Y Z resonances.Comment: 10 pages, 7 embedded figures. Analysis extended and refined in v
Non-equilibrium dynamics of gene expression and the Jarzynski equality
In order to express specific genes at the right time, the transcription of
genes is regulated by the presence and absence of transcription factor
molecules. With transcription factor concentrations undergoing constant
changes, gene transcription takes place out of equilibrium. In this paper we
discuss a simple mapping between dynamic models of gene expression and
stochastic systems driven out of equilibrium. Using this mapping, results of
nonequilibrium statistical mechanics such as the Jarzynski equality and the
fluctuation theorem are demonstrated for gene expression dynamics. Applications
of this approach include the determination of regulatory interactions between
genes from experimental gene expression data
Social work in movement: marketisation, differentiation and managerial performativity in Sweden and England
This article considers the changing nature of social work in England and Sweden in the context of neoliberal reforms, and the consequences of the ongoing shifts to marketisation and differentiation, managerialism and performativity. Drawing on secondary sources and some interview data from English and Swedish social workers, the article argues that social workers in England and Sweden face similar shifts as marketisation, differentiation, managerialism and its related performativity reshape the occupation, all related to the influence of the macro-context of neoliberalism. ‘Evidence based practice’ has become elevated as an important approach in line with increasing managerialism and performativity, affecting micro processes of everyday working life. Differences between the two countries lie largely in the timing of reforms and how social workers respond to them in organised ways – through mobilisation within the profession in England and through trades unions and local authorities in Sweden. The changes create uncertainty for social workers; while they are not merely passive victims of change they face difficult conditions in which to forge alternative models of professional practice. Contrary to what might have been expected, given the different social, political and historical legacies in Sweden and England of social democracy and liberalism respectively, comparing the social work occupation in these two countries finds many more similarities than differences in how marketisation, differentiation, managerialism and performativity impact on the occupation
Charge superconductivity from pair density wave order in certain high temperature superconductors
A number of spectacular experimental anomalies\cite{li-2007,fujita-2005} have
recently been discovered in certain cuprates, notably {\LBCO} and {\LNSCO},
which exhibit unidirectional spin and charge order (known as ``stripe order'').
We have recently proposed to interpret these observations as evidence for a
novel ``striped superconducting'' state, in which the superconducting order
parameter is modulated in space, such that its average is precisely zero. Here,
we show that thermal melting of the striped superconducting state can lead to a
number of unusual phases, of which the most novel is a charge
superconducting state, with a corresponding fractional flux quantum .
These are never-before observed states of matter, and ones, moreover, that
cannot arise from the conventional Bardeen-Cooper-Schrieffer (BCS) mechanism.
Thus, direct confirmation of their existence, even in a small subset of the
cuprates, could have much broader implications for our understanding of high
temperature superconductivity. We propose experiments to observe fractional
flux quantization, which thereby could confirm the existence of these states.Comment: 5 pages, 2 figures; new version in Nature Physics format with a
discussion of the effective Josephson coupling J2 and minor changes. Mildly
edited abstract. v3: corrected versio
Grundstate Properties of the 3D Ising Spin Glass
We study zero--temperature properties of the 3d Edwards--Anderson Ising spin
glass on finite lattices up to size . Using multicanonical sampling we
generate large numbers of groundstate configurations in thermal equilibrium.
Finite size scaling with a zero--temperature scaling exponent describes the data well. Alternatively, a descriptions in terms of Parisi
mean field behaviour is still possible. The two scenarios give significantly
different predictions on lattices of size .Comment: LATEX 9pages,figures upon request ,SCRI-9
Beleefd praten over water : hoe overheden met bewoners en belanghebbenden communiceren over veranderingen in het waterbeheer
Steeds vaker worden burgers actief betrokken bij het waterbeheer. Toch is participatie niet per definitie een garantie voor succes. Het slagen van burgerparticipatie hangt onder andere samen met het gestelde doel, het vinden van de juiste vorm en de mogelijkheid om het doel aan te laten sluiten bij bredere vormen van gebiedsontwikkeling. Alterra maakte drie praktijkhandelingen voor participatie, belevingsonderzoek en communicatie in het waterbeheer. Dit deel gaat over ‘beleefd praten over water’, oftewel het met respect communiceren over de belangen van alle betrokkenen. Het beschrijft inzichten in de communicatie van waterbeheerders met bewoners en belanghebbenden. Een goede communicatie kan bijdragen aan draagvlak voor veranderingen in het waterbeheer. Deze inzichten zijn gegroeid in een leergemeenschap waarin waterbeheerders en sociale wetenschappers ervaringen uitwisselden aan de hand van praktijkcases binnen het Leven met Water-project WaterTeken
Entropy-based analysis of the number partitioning problem
In this paper we apply the multicanonical method of statistical physics on
the number-partitioning problem (NPP). This problem is a basic NP-hard problem
from computer science, and can be formulated as a spin-glass problem. We
compute the spectral degeneracy, which gives us information about the number of
solutions for a given cost and cardinality . We also study an extension
of this problem for partitions. We show that a fundamental difference on
the spectral degeneracy of the generalized () NPP exists, which could
explain why it is so difficult to find good solutions for this case. The
information obtained with the multicanonical method can be very useful on the
construction of new algorithms.Comment: 6 pages, 4 figure
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