1,866 research outputs found
REGIONAL DIFFERENCES IN THE CONTRIBUTION OF OFF-FARM WORK TO INCOME INEQUALITY
This paper uses the concept of the Gini Coefficient and data from the 1991 Farm Costs and Returns Survey (FCRS) to measure the role of off-farm income and that of other income sources in the size distribution of farm operator households' total personal income. Disaggregated FCRS data by region and by level of participation in off-farm employment show that nonparticipating farm operator households have, as a group, higher income inequality than participating households. The results also indicate that, irrespective of the off-farm work status of the farm operator household, the distribution of income among households in the North Central region is least unequal and that in the West is most unequal.Labor and Human Capital,
Noise-induced chaos: a conditioned random dynamics perspective
We consider transitions to chaos in random dynamical systems induced by an
increase of noise amplitude. We show how the emergence of chaos (indicated by a
positive Lyapunov exponent) in a logistic map with bounded additive noise can
be analysed in the framework of conditioned random dynamics through expected
escape times and conditioned Lyapunov exponents for a compartmental model
representing the competition between contracting and expanding behaviour. We
find that the noise-induced transition to chaos is caused by a rapid decay of
the expected escape time from the contracting compartment, while all other
order parameters remain approximately constant.Comment: 6 pages, 6 figure
Emergence of Zipf's Law in the Evolution of Communication
Zipf's law seems to be ubiquitous in human languages and appears to be a
universal property of complex communicating systems. Following the early
proposal made by Zipf concerning the presence of a tension between the efforts
of speaker and hearer in a communication system, we introduce evolution by
means of a variational approach to the problem based on Kullback's Minimum
Discrimination of Information Principle. Therefore, using a formalism fully
embedded in the framework of information theory, we demonstrate that Zipf's law
is the only expected outcome of an evolving, communicative system under a
rigorous definition of the communicative tension described by Zipf.Comment: 7 pages, 2 figure
Exploring the randomness of Directed Acyclic Networks
The feed-forward relationship naturally observed in time-dependent processes
and in a diverse number of real systems -such as some food-webs and electronic
and neural wiring- can be described in terms of so-called directed acyclic
graphs (DAGs). An important ingredient of the analysis of such networks is a
proper comparison of their observed architecture against an ensemble of
randomized graphs, thereby quantifying the {\em randomness} of the real systems
with respect to suitable null models. This approximation is particularly
relevant when the finite size and/or large connectivity of real systems make
inadequate a comparison with the predictions obtained from the so-called {\em
configuration model}. In this paper we analyze four methods of DAG
randomization as defined by the desired combination of topological invariants
(directed and undirected degree sequence and component distributions) aimed to
be preserved. A highly ordered DAG, called \textit{snake}-graph and a
Erd\:os-R\'enyi DAG were used to validate the performance of the algorithms.
Finally, three real case studies, namely, the \textit{C. elegans} cell lineage
network, a PhD student-advisor network and the Milgram's citation network were
analyzed using each randomization method. Results show how the interpretation
of degree-degree relations in DAGs respect to their randomized ensembles depend
on the topological invariants imposed. In general, real DAGs provide disordered
values, lower than the expected by chance when the directedness of the links is
not preserved in the randomization process. Conversely, if the direction of the
links is conserved throughout the randomization process, disorder indicators
are close to the obtained from the null-model ensemble, although some
deviations are observed.Comment: 13 pages, 5 figures and 5 table
Robustness of the European power grids under intentional attack
The power grid defines one of the most important technological networks of
our times and sustains our complex society. It has evolved for more than a
century into an extremely huge and seemingly robust and well understood system.
But it becomes extremely fragile as well, when unexpected, usually minimal,
failures turn into unknown dynamical behaviours leading, for example, to sudden
and massive blackouts. Here we explore the fragility of the European power grid
under the effect of selective node removal. A mean field analysis of fragility
against attacks is presented together with the observed patterns. Deviations
from the theoretical conditions for network percolation (and fragmentation)
under attacks are analysed and correlated with non topological reliability
measures.Comment: 7 pages, 4 figure
The irreducible unitary representations of the extended Poincare group in (1+1) dimensions
We prove that the extended Poincare group in (1+1) dimensions is
non-nilpotent solvable exponential, and therefore that it belongs to type I. We
determine its first and second cohomology groups in order to work out a
classification of the two-dimensional relativistic elementary systems.
Moreover, all irreducible unitary representations of the extended Poincare
group are constructed by the orbit method. The most physically interesting
class of irreducible representations corresponds to the anomaly-free
relativistic particle in (1+1) dimensions, which cannot be fully quantized.
However, we show that the corresponding coadjoint orbit of the extended
Poincare group determines a covariant maximal polynomial quantization by
unbounded operators, which is enough to ensure that the associated quantum
dynamical problem can be consistently solved, thus providing a physical
interpretation for this particular class of representations.Comment: 12 pages, Revtex 4, letter paper; Revised version of paper published
in J. Math. Phys. 45, 1156 (2004
Discovery of a massive variable star with Z=Zo/36 in the galaxy DDO 68
The Local Volume dwarf galaxy DDO 68, from the spectroscopy of its two
brightest HII regions (Knots 1 and 2) was designated as the second most
metal-poor star-forming galaxy [12+log(O/H)=7.14]. In the repeated spectral
observations in 2008 January with the 6-m telescope (BTA) of the HII region
Knot 3 [having 12+log(O/H)=7.10+-0.06], we find a strong evidence of a
transient event related to a massive star evolution. From the follow-up
observation with the higher spectral resolution in 2008 February, we confirm
this phenomenon, and give parameters of its emission-line spectrum comprising
of Balmer HI and HeI lines. The luminosities of the strongest transient lines
(Ha, Hb) are of a few 10^36 erg s^-1. We also detected an additional continuum
component in the new spectrum of Knot 3, which displays the spectral energy
distribution raising to ultraviolet. The estimate of the flux of this continuum
leads us to its absolute V-band magnitude of ~-7.1. Based on the spectral
properties of this transient component, we suggest that it is related to an
evolved massive star of luminous blue variable type with Z=Zo/36. We briefly
discuss observational constraints on parameters of this unique (in the aspect
of the record low metallicity of the progenitor massive star) event and propose
several lines of its study.Comment: 6 pages, 5 Postscript figures, to appear in MNRAS Letters in June
2008 issu
Dyadic Predictors of Child Body Shame in a Polish and Italian Sample
The present study aimed at assessing the predictors (related to the functioning of a parent-child dyad) of child body shame. Therefore, in the main analysis we examined relationships among child body shame, child perfectionism, child body dissatisfaction, parent body shame, parent perfectionism, and parent body dissatisfaction. In our main hypothesis we assumed that higher levels of the abovementioned parent functioning-related variables would be associated with higher child body shame after accounting for the effects of the foregoing child functioning-related variables. The analysis finally included complete data from 420 participants, i.e., a 115 Polish and 95 Italian parent-child dyad. Participants completed: (a) child: the Objectified Body Consciousness Scale for Youth, the Child-Adolescent Perfectionism Scale, the Children’s Body Image Scale/the Figure Rating Scale; (b) parent: the Objectified Body Consciousness Scale, the Frost Multidimensional Perfectionism Scale, and the Contour Drawing Rating Scale. The results of a correlational analysis show that in both the Polish and Italian samples, the higher the level of child body shame, the higher the level of the following variables: child perfectionism, child body dissatisfaction, parent perfectionism, and parent body dissatisfaction. Interestingly, the only insignificant relationship in both samples is the association between body shame in both members of the child-parent dyad. Moreover, all steps of the regressions were significant in both Polish and Italian samples. It turned out that only in the Italian sample were all predictors significantly associated with a child’s body shame (in the Polish sample there was no significant association between child’s body shame and parent’s perfectionism). To sum up, the above studies show the importance of considering the functioning of the parent-child dyad in understanding child body shame. These findings suggest that parents’ attitudes toward their bodies and their beliefs about an ideal self should be taken into account when planning interventions to improve children’s and adolescents’ attitudes toward their bodies. This is so because it is possible for children to internalize their parents’ beliefs about how to look and how critical one should be of themselves, which can result in strong body shame when they are not perfect enough against the internalized ideal. Therefore, it is also necessary to make parents aware that children’s attitude toward their body is often a reflection of parents’ attitude toward the body
Factores asociados con casos esporádicos de salmonelosis en niños de 1 a 7 años. Estudio de casos y controles
ObjetivoEl conocimiento de los factores de riesgo de la salmonelosis proviene en gran parte de los estudios de brotes de toxiinfección alimentaria, pero es menos conocida la epidemiologÃa de los casos esporádicos. Sin embargo, muchos de los casos atendidos en el sistema sanitario son esporádicos, especialmente niños. Este estudio pretende aportar conocimientos sobre algunos de los determinantes de esos casos.MétodosEstudio de casos y controles (113 niños) de hospital y atención primaria. Casos incidentes de diarrea en niños de 1 a 7 años ocurridos entre diciembre de 1994 y diciembre de 1995 y con coprocultivo positivo a Salmonella. Controles de igual procedencia pero con coprocultivo positivo a Campylobacter o virus. Se estudian factores alimentarios, del entorno de los casos y antecedentes próximos. Se calculan las Odds Ratio (OR) ajustadas por los factores relacionados, edad, sexo y época del año mediante regresión logÃstica.ResultadosEl consumo de carne picada del comercio durante los tres dÃas previos a la diarrea, OR=4,07 (1,20–13,8) y OR=5,63 (1,34–23,6) para cada grupo control, la posesión de animales domésticos, OR=8,27 (1,96–34,9) y la toma de antibióticos en la semana previa a la diarrea, OR=4,75 (0,84–27,0) estuvieron epidemiológicamente asociados con la enfermedad.ConclusionesLa epidemiologÃa de los casos esporádicos de salmonelosis en niños de esta edad parece diferir de la de los tÃpicamente asociados a brotes de infección alimentaria, y es más compleja. El consumo de carne picada en el comercio, la toma previa de antibióticos y la posesión de animales domésticos pueden suponer un riesgo para la salmonelosis infantil y habrÃan de ser considerados en futuros estudios sobre esta materia.BackgroundKnowledge about salmonellosis risk factors mainly comes from foodborne outbreaks, and we know little about sporadic cases epidemiology. However most of the cases are sporadic, specially children. This study aims to find out some of determinants of these cases.MethodsA case-control study with incident cases and controls from the same base population (laboratory diagnosed cases). Cases were children 1–7 years old, afected by diarrohea with culture stools positive to Salmonella between decembre 1994 and decembre 1995. Controls from the same source, but positive culture to Campylobacter or viruses. We study food and other environmental risk factors. Odds ratio (OR) are calculated adjusted for age, sex, and year period (cool and cold) by logistic regression.ResultsEating minced meat during three days before symptoms, OR 4,07 (1.20–13.8) and OR 5.63 (1.34–23.6); pets, OR 8.27 (1.96–34.9), and antibiotics the week before symptoms, OR 4.75 (0.84–27.0) were epidemiologicaly associated with salmonelosis diarrohea.ConclusionsEpidemiology of salmonelosis sporadic cases in children seems diferent to the foodborne associated cases and is more complex. Minced meat tree days before symptoms, antibiotics the week before symptoms, and pets could be a risk for this kind of cases. Future studies must also take account of this factors
p75 neurotrophin receptor regulates energy balance in obesity
Obesity and metabolic syndrome reflect the dysregulation of molecular pathways that control energy homeostasis. Here, we show that the p75 neurotrophin receptor (p75NTR) controls energy expenditure in obese mice on a high-fat diet (HFD). Despite no changes in food intake, p75NTR-null mice were protected from HFD-induced obesity and remained lean as a result of increased energy expenditure without developing insulin resistance or liver steatosis. p75NTR directly interacts with the catalytic subunit of protein kinase A (PKA) and regulates cAMP signaling in adipocytes, leading to decreased lipolysis and thermogenesis. Adipocyte-specific depletion of p75NTR or transplantation of p75NTR-null white adipose tissue (WAT) into wild-type mice fed a HFD protected against weight gain and insulin resistance. Our results reveal that signaling from p75NTR to cAMP/PKA regulates energy balance and suggest that non-CNS neurotrophin receptor signaling could be a target for treating obesity and the metabolic syndrome
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