271 research outputs found
Mitochondrial Dna Replacement Versus Nuclear Dna Persistence
In this paper we consider two populations whose generations are not
overlapping and whose size is large. The number of males and females in both
populations is constant. Any generation is replaced by a new one and any
individual has two parents for what concerns nuclear DNA and a single one (the
mother) for what concerns mtDNA. Moreover, at any generation some individuals
migrate from the first population to the second.
In a finite random time , the mtDNA of the second population is completely
replaced by the mtDNA of the first. In the same time, the nuclear DNA is not
completely replaced and a fraction of the ancient nuclear DNA persists. We
compute both and . Since this study shows that complete replacement of
mtDNA in a population is compatible with the persistence of a large fraction of
nuclear DNA, it may have some relevance for the Out of Africa/Multiregional
debate in Paleoanthropology
Effect of migration in a diffusion model for template coexistence in protocells
The compartmentalization of distinct templates in protocells and the exchange
of templates between them (migration) are key elements of a modern scenario for
prebiotic evolution. Here we use the diffusion approximation of population
genetics to study analytically the steady-state properties of such prebiotic
scenario. The coexistence of distinct template types inside a protocell is
achieved by a selective pressure at the protocell level (group selection)
favoring protocells with a mixed template composition. In the degenerate case,
where the templates have the same replication rate, we find that a vanishingly
small migration rate suffices to eliminate the segregation effect of random
drift and so to promote coexistence. In the non-degenerate case, a small
migration rate greatly boosts coexistence as compared with the situation where
there is no migration. However, increase of the migration rate beyond a
critical value leads to the complete dominance of the more efficient template
type (homogeneous regime). In this case, we find a continuous phase transition
separating the homogeneous and the coexistence regimes, with the order
parameter vanishing linearly with the distance to the transition point
MARKOV DIFFUSIONS IN COMOVING COORDINATES AND STOCHASTIC QUANTIZATION OF THE FREE RELATIVISTIC SPINLESS PARTICLE
We revisit the classical approach of comoving coordinates in relativistic
hydrodynamics and we give a constructive proof for their global existence under
suitable conditions which is proper for stochastic quantization. We show that
it is possible to assign stochastic kinematics for the free relativistic
spinless particle as a Markov diffusion globally defined on . Then
introducing dynamics by means of a stochastic variational principle with
Einstein's action, we are lead to positive-energy solutions of Klein-Gordon
equation. The procedure exhibits relativistic covariance properties.Comment: 31 pages + 1 figure available upon request; Plain REVTe
The Settlement of Madagascar: What Dialects and Languages Can Tell Us
The dialects of Madagascar belong to the Greater Barito East group of the Austronesian family and it is widely accepted that the Island was colonized by Indonesian sailors after a maritime trek that probably took place around 650 CE. The language most closely related to Malagasy dialects is Maanyan, but Malay is also strongly related especially for navigation terms. Since the Maanyan Dayaks live along the Barito river in Kalimantan (Borneo) and they do not possess the necessary skill for long maritime navigation, they were probably brought as subordinates by Malay sailors. In a recent paper we compared 23 different Malagasy dialects in order to determine the time and the landing area of the first colonization. In this research we use new data and new methods to confirm that the landing took place on the south-east coast of the Island. Furthermore, we are able to state here that colonization probably consisted of a single founding event rather than multiple settlements.To reach our goal we find out the internal kinship relations among all the 23 Malagasy dialects and we also find out the relations of the 23 dialects to Malay and Maanyan. The method used is an automated version of the lexicostatistic approach. The data from Madagascar were collected by the author at the beginning of 2010 and consist of Swadesh lists of 200 items for 23 dialects covering all areas of the Island. The lists for Maanyan and Malay were obtained from a published dataset integrated with the author's interviews
On the stochastic mechanics of the free relativistic particle
Given a positive energy solution of the Klein-Gordon equation, the motion of
the free, spinless, relativistic particle is described in a fixed Lorentz frame
by a Markov diffusion process with non-constant diffusion coefficient. Proper
time is an increasing stochastic process and we derive a probabilistic
generalization of the equation . A
random time-change transformation provides the bridge between the and the
domain. In the domain, we obtain an \M^4-valued Markov process
with singular and constant diffusion coefficient. The square modulus of the
Klein-Gordon solution is an invariant, non integrable density for this Markov
process. It satisfies a relativistically covariant continuity equation
Lexical evolution rates by automated stability measure
Phylogenetic trees can be reconstructed from the matrix which contains the
distances between all pairs of languages in a family. Recently, we proposed a
new method which uses normalized Levenshtein distances among words with same
meaning and averages on all the items of a given list. Decisions about the
number of items in the input lists for language comparison have been debated
since the beginning of glottochronology. The point is that words associated to
some of the meanings have a rapid lexical evolution. Therefore, a large
vocabulary comparison is only apparently more accurate then a smaller one since
many of the words do not carry any useful information. In principle, one should
find the optimal length of the input lists studying the stability of the
different items. In this paper we tackle the problem with an automated
methodology only based on our normalized Levenshtein distance. With this
approach, the program of an automated reconstruction of languages relationships
is completed
2d frustrated Ising model with four phases
In this paper we consider a 2d random Ising system on a square lattice with
nearest neighbour interactions. The disorder is short range correlated and
asymmetry between the vertical and the horizontal direction is admitted. More
precisely, the vertical bonds are supposed to be non random while the
horizontal bonds alternate: one row of all non random horizontal bonds is
followed by one row where they are independent dichotomic random variables. We
solve the model using an approximate approach that replace the quenched average
with an annealed average under the constraint that the number of frustrated
plaquettes is keep fixed and equals that of the true system. The surprising
fact is that for some choices of the parameters of the model there are three
second order phase transitions separating four different phases:
antiferromagnetic, glassy-like, ferromagnetic and paramagnetic.Comment: 17 pages, Plain TeX, uses Harvmac.tex, 4 ps figures, submitted to
Physical Review
The Slippery Slope of MIS Academia: A Discussion of the Quest for Relevance in Our Discipline
The MIS discipline faces the need to periodically re-establish its relevance to both academics and practitioners. Evolving technology forces our discipline to change at a rate far exceeding that of other business disciplines. In the workplace, rapidly evolving IT management issues and technologies have led corporations to manage technical employees differently than other employees. In academia, however, MIS faculty are faced with the same expectations as other business faculty. The current model of MIS as an academic discipline has many issues that make staying current and relevant very difficult. The result is that MIS research and teaching lag practice. One might argue that as the field matures, we are falling further behind. This paper is the outcome of a panel discussion held during the 2006 Americas Conference on Information Systems in Acapulco, Mexico. The panel discussed the assertions that MIS is on a Slippery Slope that threatens our existence as a business discipline and that our current model encourages irrelevance, both in research and in teaching. Panel members were asked to share their views on five questions relative to the Slippery Slope from their unique perspectives
Evolution of the most recent common ancestor of a population with no selection
We consider the evolution of a population of fixed size with no selection.
The number of generations to reach the first common ancestor evolves in
time. This evolution can be described by a simple Markov process which allows
one to calculate several characteristics of the time dependence of . We also
study how is correlated to the genetic diversity.Comment: 21 pages, 10 figures, uses RevTex4 and feynmf.sty Corrections :
introduction and conclusion rewritten, references adde
Genetic Polymorphism in Evolving Population
We present a model for evolving population which maintains genetic
polymorphism. By introducing random mutation in the model population at a
constant rate, we observe that the population does not become extinct but
survives, keeping diversity in the gene pool under abrupt environmental
changes. The model provides reasonable estimates for the proportions of
polymorphic and heterozygous loci and for the mutation rate, as observed in
nature
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