135 research outputs found
On q-Gaussians and Exchangeability
The q-Gaussians are discussed from the point of view of variance mixtures of
normals and exchangeability. For each q< 3, there is a q-Gaussian distribution
that maximizes the Tsallis entropy under suitable constraints. This paper shows
that q-Gaussian random variables can be represented as variance mixtures of
normals. These variance mixtures of normals are the attractors in central limit
theorems for sequences of exchangeable random variables; thereby, providing a
possible model that has been extensively studied in probability theory. The
formulation provided has the additional advantage of yielding process versions
which are naturally q-Brownian motions. Explicit mixing distributions for
q-Gaussians should facilitate applications to areas such as option pricing. The
model might provide insight into the study of superstatistics.Comment: 14 page
Probability densities for the sums of iterates of the sine-circle map in the vicinity of the quasi-periodic edge of chaos
We investigate the probability density of rescaled sum of iterates of
sine-circle map within quasi-periodic route to chaos. When the dynamical system
is strongly mixing (i.e., ergodic), standard Central Limit Theorem (CLT) is
expected to be valid, but at the edge of chaos where iterates have strong
correlations, the standard CLT is not necessarily to be valid anymore. We
discuss here the main characteristics of the central limit behavior of
deterministic dynamical systems which exhibit quasi-periodic route to chaos. At
the golden-mean onset of chaos for the sine-circle map, we numerically verify
that the probability density appears to converge to a q-Gaussian with q<1 as
the golden mean value is approached.Comment: 7 pages, 7 figures, 1 tabl
Strictly and asymptotically scale-invariant probabilistic models of correlated binary random variables having {\em q}--Gaussians as limiting distributions
In order to physically enlighten the relationship between {\it
--independence} and {\it scale-invariance}, we introduce three types of
asymptotically scale-invariant probabilistic models with binary random
variables, namely (i) a family, characterized by an index ,
unifying the Leibnitz triangle () and the case of independent variables
(); (ii) two slightly different discretizations of
--Gaussians; (iii) a special family, characterized by the parameter ,
which generalizes the usual case of independent variables (recovered for
). Models (i) and (iii) are in fact strictly scale-invariant. For
models (i), we analytically show that the probability
distribution is a --Gaussian with . Models (ii) approach
--Gaussians by construction, and we numerically show that they do so with
asymptotic scale-invariance. Models (iii), like two other strictly
scale-invariant models recently discussed by Hilhorst and Schehr (2007),
approach instead limiting distributions which are {\it not} --Gaussians. The
scenario which emerges is that asymptotic (or even strict) scale-invariance is
not sufficient but it might be necessary for having strict (or asymptotic)
--independence, which, in turn, mandates --Gaussian attractors.Comment: The present version is accepted for publication in JSTA
Circle grid fractal plate as a turbulent generator for premixed flame: an overview
This review paper focuses to ascertain a new approach in turbulence generation on the structure of premixed flames and external combustion using a fractal grid pattern. This review paper discusses the relationship between fractal pattern and turbulence flow. Many researchers have explored the fractal pattern as a new concept of turbulence generators, but researchers rarely study fractal turbulence generators on the structure premixed flame. The turbulent flow field characteristics have been studied tand investigated in a premixed combustion application. In terms of turbulence intensity, most researchers used fractal grid that can be tailored so that they can design the characteristic needed in premixed flame. This approach makes it extremely difficult to determine the exact turbulent burning velocity on the velocity fluctuation of the flow. The decision to carry out additional research on the effect circle grid fractal plate as a turbulent generator for premixed flame should depends on the blockage ratio and fractal pattern of the grid.
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Scale relativity and fractal space-time: theory and applications
In the first part of this contribution, we review the development of the
theory of scale relativity and its geometric framework constructed in terms of
a fractal and nondifferentiable continuous space-time. This theory leads (i) to
a generalization of possible physically relevant fractal laws, written as
partial differential equation acting in the space of scales, and (ii) to a new
geometric foundation of quantum mechanics and gauge field theories and their
possible generalisations. In the second part, we discuss some examples of
application of the theory to various sciences, in particular in cases when the
theoretical predictions have been validated by new or updated observational and
experimental data. This includes predictions in physics and cosmology (value of
the QCD coupling and of the cosmological constant), to astrophysics and
gravitational structure formation (distances of extrasolar planets to their
stars, of Kuiper belt objects, value of solar and solar-like star cycles), to
sciences of life (log-periodic law for species punctuated evolution, human
development and society evolution), to Earth sciences (log-periodic
deceleration of the rate of California earthquakes and of Sichuan earthquake
replicas, critical law for the arctic sea ice extent) and tentative
applications to system biology.Comment: 63 pages, 14 figures. In : First International Conference on the
Evolution and Development of the Universe,8th - 9th October 2008, Paris,
Franc
Scans for signatures of selection in Russian cattle breed genomes reveal new candidate genes for environmental adaptation and acclimation
Domestication and selective breeding has resulted in over 1000 extant cattle breeds. Many of these breeds do not excel in important traits but are adapted to local environments. These adaptations are a valuable source of genetic material for efforts to improve commercial breeds. As a step toward this goal we identified candidate regions to be under selection in genomes of nine Russian native cattle breeds adapted to survive in harsh climates. After comparing our data to other breeds of European and Asian origins we found known and novel candidate genes that could potentially be related to domestication, economically important traits and environmental adaptations in cattle. The Russian cattle breed genomes contained regions under putative selection with genes that may be related to adaptations to harsh environments (e.g., AQP5, RAD50, and RETREG1). We found genomic signatures of selective sweeps near key genes related to economically important traits, such as the milk production (e.g., DGAT1, ABCG2), growth (e.g., XKR4), and reproduction (e.g., CSF2). Our data point to candidate genes which should be included in future studies attempting to identify genes to improve the extant breeds and facilitate generation of commercial breeds that fit better into the environments of Russia and other countries with similar climates
Inequalities in higher education in low‐ and middle‐income countries:A scoping review of the literature
Motivation: Higher education is regarded as a key instrument to enhance socioeconomic mobility andreduce inequalities. Recent literature reviews have examined inequalities in the higher education systemsof high-income countries, but less is known about the situation in low- and middle-income countries,where higher education is expanding fast.Purpose: The article reviews the academic literature on higher education in low- and middle-incomecountries using a research framework inspired by social justice and capability approaches. It considers the financial, socio-cultural, human, and political resource domains on which people draw, and how they relate to access, participation, and outcomes in higher education.Methods: A literature search for studies explicitly discussing in-country inequalities in higher education revealed 22 publications. Substantial knowledge gaps remain, especially regarding the political (and decision-making) side of inequalities; the ideologies and philosophies underpinning higher education systems; and the linkages between resource domains, both micro and macro.Findings: The review highlights key elements for policy-makers and researchers: (1) the financial lens alone is insufficient to understand and tackle inequalities, since these are also shaped by human and other non-financial factors; (2) socio-cultural constructs are central in explaining unequal outcomes; and (3) inequalities develop throughout one’s life and need to be considered during, but also before and afterhigher education. The scope of inequalities is wide, and the literature offers a few ideas for short-term fixes such as part-time and online education.Policy implications: Inclusive policy frameworks for higher education should include explicit goals related to (in)equality, which are best measured in terms of the extent to which certain actions or choices are feasible for all. Policies in these frameworks, we argue, should go beyond providing financial support, and also address socio-cultural and human resource constraints and challenges in retention, performance, and labour market outcomes. Finally, they should consider relevant contextual determinants of inequalities.</p
Detached Eddy Simulation for Turbulent Flows in a Pipe with a Snowflake Fractal Orifice
Regional adaptation defines sensitivity to future ocean acidification
Physiological responses to temperature are known to be a major determinant of species distributions and can dictate the sensitivity of populations to global warming. In contrast, little is known about how other major global change drivers, such as ocean acidification (OA), will
shape species distributions in the future. Here, by integrating population genetics with experimental data for growth and mineralization, physiology and metabolomics, we
demonstrate that the sensitivity of populations of the gastropod Littorina littorea to future OA is shaped by regional adaptation. Individuals from populations towards the edges of the natural latitudinal range in the Northeast Atlantic exhibit greater shell dissolution and the inability to upregulate their metabolism when exposed to low pH, thus appearing most sensitive to low seawater pH. Our results suggest that future levels of OA could mediate
temperature-driven shifts in species distributions, thereby influencing future biogeography and the functioning of marine ecosystems
Reduction of apoptosis and preservation of mitochondrial integrity under ischemia/reperfusion injury is mediated by estrogen receptor β
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