2,262 research outputs found
The Birth-Death-Mutation process: a new paradigm for fat tailed distributions
Fat tailed statistics and power-laws are ubiquitous in many complex systems.
Usually the appearance of of a few anomalously successful individuals
(bio-species, investors, websites) is interpreted as reflecting some inherent
"quality" (fitness, talent, giftedness) as in Darwin's theory of natural
selection. Here we adopt the opposite, "neutral", outlook, suggesting that the
main factor explaining success is merely luck. The statistics emerging from the
neutral birth-death-mutation (BDM) process is shown to fit marvelously many
empirical distributions. While previous neutral theories have focused on the
power-law tail, our theory economically and accurately explains the entire
distribution. We thus suggest the BDM distribution as a standard neutral model:
effects of fitness and selection are to be identified by substantial deviations
from it
Nonlocal competition and logistic growth: patterns, defects and fronts
Logistic growth of diffusing reactants on spatial domains with long range
competition is studied. The bifurcations cascade involved in the transition
from the homogenous state to a spatially modulated stable solution is
presented, and a distinction is made between a modulated phase, dominated by
single or few wavenumbers, and the spiky phase, where localized colonies are
separated by depleted region. The characteristic defects in the periodic
structure are presented for each phase, together with the invasion dynamics in
case of local initiation. It is shown that the basic length scale that controls
the bifurcation is the width of the Fisher front, and that the total population
grows as this width decreases. A mix of analytic results and extensive
numerical simulations yields a comprehensive examination of the possible phases
for logistic growth in the presence of nonlocal competition
On Higgs and sphaleron effects during the leptogenesis era
We discuss the effects of various processes that can be active during the
leptogenesis era, and present the Boltzmann equations that take them into
account appropriately. A non-vanishing Higgs number asymmetry is always
present, enhancing the washout of the lepton asymmetry. This is the main new
effect when leptogenesis takes place at GeV, reducing the final
baryon asymmetry and tightening the leptogenesis bound on the neutrino masses.
If leptogenesis occurs at lower temperatures, electroweak sphalerons partially
transfer the lepton asymmetry to a baryonic one, while Yukawa interactions and
QCD sphalerons partially transfer the asymmetries of the left-handed fields to
the right-handed ones, suppressing the washout processes. Depending on the
specific temperature range in which leptogenesis occurs, the final baryon
asymmetry can be enhanced or suppressed by factors of order 20%--40% with
respect to the case when these effects are altogether ignored.Comment: one reference adde
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The Legumes: The Earliest Domesticated Plants in the Near East?
Anthropolog
Ancient technology and punctuated change: Detecting the emergence of the Edomite Kingdom in the Southern Levant.
While the punctuated equilibrium model has been employed in paleontological and archaeological research, it has rarely been applied for technological and social evolution in the Holocene. Using metallurgical technologies from the Wadi Arabah (Jordan/Israel) as a case study, we demonstrate a gradual technological development (13th-10th c. BCE) followed by a human agency-triggered punctuated "leap" (late-10th c. BCE) simultaneously across the entire region (an area of ~2000 km2). Here, we present an unparalleled, diachronic archaeometallurgical dataset focusing on elemental analysis of dozens of well-dated slag samples. Based on the results, we suggest punctuated equilibrium provides an innovative theoretical model for exploring ancient technological changes in relation to larger sociopolitical conditions-in the case at hand the emergence of biblical Edom-, exemplifying its potential for more general cross-cultural applications
X-rays Diffraction Study On The Iron Nano Particles Prepared By Two Steps Milling Method
X-RAYS DIFFRACTION STUDY ON THE IRON NANO PARTICLES PREPARED BY TWO STEPS MILLING METHOD. X-rays diffraction study on the iron nanoparticles prepared by two-step milling method has been carried out. First, the raw material of micro-sized Fe was crushed by High Energy Milling (HEM) in the presence of isopropyl alcohol, here in after referred to as FI precursor. FI precursor then was crushed again with planetary balls mill in Cetyl-Trimethyl- Ammonium Bromide (CTAB)media, here in after referred to as FC sample. The phases analysis in the two samples were carried out by X-rays diffraction technique using the Rietveld method. Crystallites size were calculated with the Debye-Scherrer formula and the size of particles were measured by means of Particles Size Analyzer (PSA). The magnetic properties of the two samples were characterized with Vibration Sample Magnetometer (VSM). The analysis result showed that each of FI and FC samples consist of Fe, γ-Fe2O3 and Fe3O4 phases in the formof the nano-sized powder ranging fromaround 7 to 10 nm. PSA data indicate that the particle size of FI and FC are the same, i.e., 7.5 nm with narrow size distribution. The VSM data revealed that both FI and FC samples display super paramagnetic behavior at room temperature. The magnetization value in FC sample has been reduced due to more of the mass fraction of Fe transforms into iron oxide phases. The particle size is generally not the same as the size of the crystallites and in particular for the nano-sized particles, the size of crystallites could be equal to or greater than the particle size due to the presence of polycrystalline aggregates
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