10,619 research outputs found
Formation of the frozen core in critical Boolean Networks
We investigate numerically and analytically the formation of the frozen core
in critical random Boolean networks with biased functions. We demonstrate that
a previously used efficient algorithm for obtaining the frozen core, which
starts from the nodes with constant functions, fails when the number of inputs
per node exceeds 4. We present computer simulation data for the process of
formation of the frozen core and its robustness, and we show that several
important features of the data can be derived by using a mean-field
calculation
Scaling laws in critical random Boolean networks with general in- and out-degree distributions
We evaluate analytically and numerically the size of the frozen core and
various scaling laws for critical Boolean networks that have a power-law in-
and/or out-degree distribution. To this purpose, we generalize an efficient
method that has previously been used for conventional random Boolean networks
and for networks with power-law in-degree distributions. With this
generalization, we can also deal with power-law out-degree distributions. When
the power-law exponent is between 2 and 3, the second moment of the
distribution diverges with network size, and the scaling exponent of the
nonfrozen nodes depends on the degree distribution exponent. Furthermore, the
exponent depends also on the dependence of the cutoff of the degree
distribution on the system size. Altogether, we obtain an impressive number of
different scaling laws depending on the type of cutoff as well as on the
exponents of the in- and out-degree distributions. We confirm our scaling
arguments and analytical considerations by numerical investigations
Regional Imbalances and Aggregate Performance in a Leading Sector Model of the Labour Market: An analysis of Italian data 1977-1991
This paper presents a model in which wages throughout the economy depend only on the labour market conditions in some low-unemployment sector. In equilibrium, a labour demand shift towards the primary sector tends to raise the unemployment rate everywhere else in the economy and leaves wages unchanged. Overall this implies an increase in aggregate unemployment. Based on SHIW micro data for the period 1977-1991 we find that wages in Italy depend only on the tightness of the labour market in the North. We estimate that around 15% of the increase in aggregate unemployment in Italy can be explained by a shift in labour demand in favour of the North not matched by an equal shift in labour supply.
Regional Mismatch and Unemployment: Theory and Evidence from Italy, 1977-1998
This paper describes the functioning of a two-region economy characterized by asymmetric wage-setting. Labor market tightness in one region (the leading-region) affects wages in the whole economy. In equilibrium, net labor demand shifts towards the leading region raise unemployment in the rest of the economy and leave regional wages unchanged, causing an increase in aggregate unemployment. This model has some success in explaining the evolution of regional unemployment rates in Italy during the period 1977-1998. Based on SHIW micro data on earnings and ISTAT data on unemployment rates we find strong evidence that wages in Italy only respond to labor market tightness in the North. We estimate that around one third of the increase in aggregate unemployment in Italy can be explained by regional mismatch, mainly due to an excess labor supply growth in the South.regional imbalances; wage curve; unemployment.
Self-similar gelling solutions for the coagulation equation with diagonal kernel
We consider Smoluchowski's coagulation equation in the case of the diagonal
kernel with homogeneity . In this case the phenomenon of gelation
occurs and solutions lose mass at some finite time. The problem of the
existence of self-similar solutions involves a free parameter , and one
expects that a physically relevant solution (i.e. nonnegative and with
sufficiently fast decay at infinity) exists for a single value of ,
depending on the homogeneity . We prove this picture rigorously for
large values of . In the general case, we discuss in detail the
behaviour of solutions to the self-similar equation as the parameter
changes
Multiclass latent locally linear support vector machines
Kernelized Support Vector Machines (SVM) have gained the status of off-the-shelf classifiers, able to deliver state of the art performance on almost any problem. Still, their practical use is constrained by their computational and memory complexity, which grows super-linearly with the number of training samples. In order to retain the low training and testing complexity of linear classifiers and the exibility of non linear ones, a growing, promising alternative is represented by methods that learn non-linear classifiers through local combinations of linear ones. In this paper we propose a new multi class local classifier, based on a latent SVM formulation. The proposed classifier makes use of a set of linear models that are linearly combined using sample and class specific weights. Thanks to the latent formulation, the combination coefficients are modeled as latent variables. We allow soft combinations and we provide a closed-form solution for their estimation, resulting in an efficient prediction rule. This novel formulation allows to learn in a principled way the sample specific weights and the linear classifiers, in a unique optimization problem, using a CCCP optimization procedure. Extensive experiments on ten standard UCI machine learning datasets, one large binary dataset, three character and digit recognition databases, and a visual place categorization dataset show the power of the proposed approach
Monte Carlo determination of the critical coupling in theory
We use lattice formulation of theory in order to investigate
non--perturbative features of its continuum limit in two dimensions. In
particular, by means of Monte Carlo calculations, we obtain the critical
coupling constant in the continuum, where is the {\em
unrenormalised} coupling. Our final result is .Comment: Version published on Phys. Rev. D. We added a reference and modified
a couple of sentence
QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi
Recent preliminary PHENIX data are consistent with a negative and sizable
longitudinal double-spin asymmetry A_LL^pi for pi^0 production at moderate
transverse momentum p_perp \simeq 1 - 4 GeV and central rapidity. By means of a
systematic investigation of the relevant degrees of freedom we show that the
perturbative QCD framework at leading power in p_perp produces at best a very
small negative asymmetry in this kinematic range.Comment: 4 pages, 3 figures, final version published in PRL (only minor
changes; note: title changed in published version
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