1,229 research outputs found
The Temporal and Spatial Scale of Microevolution: Fine-scale Color Pattern Variation in the Lake Erie Watersnake
Question: What is the temporal and spatial scale of microevolution?
Hypotheses: The combined effects of natural selection and gene flow result in variation in
heritable traits on fine spatial and geographic scales.
Organism: The Lake Erie watersnake, Nerodia sipedon insularum.
Field site: US and Canadian islands in western Lake Erie.
Methods: We tested for variation in colour pattern frequency within islands, among islands,
and over time using data from nearly annual censuses conducted since 1980, museum
specimens, and published sources. We compared FST for a presumptive major colour pattern
locus to FST for allozyme loci to determine whether spatial variation exceeded that expected by
chance. We computed effective population size (Ne) based on temporal frequency changes in
presumptive colour pattern alleles to determine whether temporal variation exceeded that
expected by chance (Ne significantly less than ∞).
Conclusions: Morph frequencies did not differ significantly within islands or between
islands separated by short distances. Morph frequencies did sometimes differ significantly
among distant islands and among sampling periods from 1980 to the present, but no more than
expected by chance. In contrast, a marked change in morph frequency occurred between
historic (prior to 1961) and recent (1980–2003) samples. Possible mechanisms include changes
in the strength of selection (due to changes in predator assemblages and visual environments)
and rates of gene flow (due to changes in island watersnake population size)
Scenario of inflationary cosmology from the phenomenological models
Choosing the three phenomenological models of the dynamical cosmological term
, viz., , and
where is the cosmic scale factor, it has been shown by
the method of numerical analysis that the three models are equivalent for the
flat Universe . The evolution plots for dynamical cosmological term
vs. time and also the cosmic scale factor vs. are drawn
here for . A qualitative analysis has been made from the plots which
supports the idea of inflation and hence expanding Universe.Comment: 12 latex pages with 12 figures; Replaced with the revised version;
Accepeted for `J. Non-lin. Frac. Phen. Sci. Engg.
A new technological procedure using sucrose as porogen compound to manufacture porous biphasic calcium phosphate ceramics of appropriate micro- and macrostructure
In the domain of implantable materials, the porosity and pore size distribution of a material in contact with bone is decisive for bone ingrowth and thus the control of the porosity is of great interest. The use of a new porogen agent, i.e. sucrose is proposed to create a porosity in biphasic calcium phosphate blocks. The technological procedure is as follows: sucrose and mineral powder are mixed, then compressed by isostatic compression and sintering finally eliminates sucrose. Blocks obtained were compared to a manufactured product: Triosite® (Zimmer, Etupes, France) which porosity is created through a naphthalene sublimation process.Results have shown that the incorporation of sucrose allows the preparation of porous blocks with controlled porosity varying from 40 to 80% and with macro-, meso- and microporosity characteristics depending on the percentage of sucrose added as well as on the granulometry of both sucrose and mineral powder
Amplitude and phase representation of quantum invariants for the time dependent harmonic oscillator
The correspondence between classical and quantum invariants is established.
The Ermakov Lewis quantum invariant of the time dependent harmonic oscillator
is translated from the coordinate and momentum operators into amplitude and
phase operators. In doing so, Turski's phase operator as well as
Susskind-Glogower operators are generalized to the time dependent harmonic
oscillator case. A quantum derivation of the Manley-Rowe relations is shown as
an example
Analytical and numerical investigation of escape rate for a noise driven bath
We consider a system-reservoir model where the reservoir is modulated by an
external noise. Both the internal noise of the reservoir and the external noise
are stationary, Gaussian and are characterized by arbitrary decaying
correlation functions. Based on a relation between the dissipation of the
system and the response function of the reservoir driven by external noise we
numerically examine the model using a full bistable potential to show that one
can recover the turn-over features of the usual Kramers' dynamics when the
external noise modulates the reservoir rather than the system directly. We
derive the generalized Kramers' rate for this nonequilibrium open system. The
theoretical results are verified by numerical simulation.Comment: Revtex, 25 pages, 5 figures. To appear in Phys. Rev.
Five Dimensional Cosmological Models in General Relativity
A Five dimensional Kaluza-Klein space-time is considered in the presence of a
perfect fluid source with variable G and . An expanding universe is
found by using a relation between the metric potential and an equation of
state. The gravitational constant is found to decrease with time as whereas the variation for the cosmological constant follows as
, and
where is the equation of state parameter and is the scale factor.Comment: 13 pages, 4 figures, accepted in Int. J. Theor. Phy
Gauge-fixing, semiclassical approximation and potentials for graded Chern-Simons theories
We perform the Batalin-Vilkovisky analysis of gauge-fixing for graded
Chern-Simons theories. Upon constructing an appropriate gauge-fixing fermion,
we implement a Landau-type constraint, finding a simple form of the gauge-fixed
action. This allows us to extract the associated Feynman rules taking into
account the role of ghosts and antighosts. Our gauge-fixing procedure allows
for zero-modes, hence is not limited to the acyclic case. We also discuss the
semiclassical approximation and the effective potential for massless modes,
thereby justifying some of our previous constructions in the Batalin-Vilkovisky
approach.Comment: 46 pages, 4 figure
Anisotropic Bose-Einstein condensates and completely integrable dynamical systems
A Gaussian ansatz for the wave function of two-dimensional harmonically
trapped anisotropic Bose-Einstein condensates is shown to lead, via a
variational procedure, to a coupled system of two second-order, nonlinear
ordinary differential equations. This dynamical system is shown to be in the
general class of Ermakov systems. Complete integrability of the resulting
Ermakov system is proven. Using the exact solution, collapse of the condensate
is analyzed in detail. Time-dependence of the trapping potential is allowed
Scenario of Accelerating Universe from the Phenomenological \Lambda- Models
Dark matter, the major component of the matter content of the Universe,
played a significant role at early stages during structure formation. But at
present the Universe is dark energy dominated as well as accelerating. Here,
the presence of dark energy has been established by including a time-dependent
term in the Einstein's field equations. This model is compatible with
the idea of an accelerating Universe so far as the value of the deceleration
parameter is concerned. Possibility of a change in sign of the deceleration
parameter is also discussed. The impact of considering the speed of light as
variable in the field equations has also been investigated by using a well
known time-dependent model.Comment: Latex, 9 pages, Major change
Stochastic motion of test particle implies that G varies with time
The aim of this letter is to propose a new description to the time varying
gravitational constant problem, which naturally implements the Dirac's large
numbers hypothesis in a new proposed holographic scenario for the origin of
gravity as an entropic force. We survey the effect of the Stochastic motion of
the test particle in Verlinde's scenario for gravity\cite{Verlinde}. Firstly we
show that we must get the equipartition values for which
leads to the usual Newtonian gravitational constant. Secondly,the stochastic
(Brownian) essence of the motion of the test particle, modifies the Newton's
2'nd law. The direct result is that the Newtonian constant has been time
dependence in resemblance as \cite{Running}.Comment: Accepted in International Journal of Theoretical Physic
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