4,173 research outputs found
Strategies for the evolution of sex
We find that the hypothesis made by Jan, Stauffer and Moseley [Theory in
Biosc., 119, 166 (2000)] for the evolution of sex, namely a strategy devised to
escape extinction due to too many deleterious mutations, is sufficient but not
necessary for the successful evolution of a steady state population of sexual
individuals within a finite population. Simply allowing for a finite
probability for conversion to sex in each generation also gives rise to a
stable sexual population, in the presence of an upper limit on the number of
deleterious mutations per individual. For large values of this probability, we
find a phase transition to an intermittent, multi-stable regime. On the other
hand, in the limit of extremely slow drive, another transition takes place to a
different steady state distribution, with fewer deleterious mutations within
the asexual population.Comment: RevTeX, 11 pages, multicolumn, including 12 figure
Low-temperature heat transfer in nanowires
The new regime of low-temperature heat transfer in suspended nanowires is
predicted. It takes place when (i) only ``acoustic'' phonon modes of the wire
are thermally populated and (ii) phonons are subject to the effective elastic
scattering. Qualitatively, the main peculiarities of heat transfer originate
due to appearance of the flexural modes with high density of states in the wire
phonon spectrum. They give rise to the temperature dependence of the
wire thermal conductance. The experimental situations where the new regime is
likely to be detected are discussed.Comment: RevTex file, 1 PS figur
Low-frequency noise as a source of dephasing of a qubit
With the growing efforts in isolating solid-state qubits from external
decoherence sources, the material-inherent sources of noise start to play
crucial role. One representative example is electron traps in the device
material or substrate. Electrons can tunnel or hop between a charged and an
empty trap, or between a trap and a gate electrode. A single trap typically
produces telegraph noise and can hence be modeled as a bistable fluctuator.
Since the distribution of hopping rates is exponentially broad, many traps
produce flicker-noise with spectrum close to 1/f. Here we develop a theory of
decoherence of a qubit in the environment consisting of two-state fluctuators,
which experience transitions between their states induced by interaction with
thermal bath. Due to interaction with the qubit the fluctuators produce
1/f-noise in the qubit's eigenfrequency. We calculate the results of qubit
manipulations - free induction and echo signals - in such environment. The main
problem is that in many important cases the relevant random process is both
non-Markovian and non-Gaussian. Consequently the results in general cannot be
represented by pair correlation function of the qubit eigenfrequency
fluctuations. Our calculations are based on analysis of the density matrix of
the qubit using methods developed for stochastic differential equations. The
proper generating functional is then averaged over different fluctuators using
the so-called Holtsmark procedure. The analytical results are compared with
simulations allowing checking accuracy of the averaging procedure and
evaluating mesoscopic fluctuations. The results allow understanding some
observed features of the echo decay in Josephson qubits.Comment: 18 pages, 8 figures, Proc. of NATO/Euresco Conf. "Fundamental
Problems of Mesoscopic Physics: Interactions and Decoherence", Granada,
Spain, Sept.200
Non-Gaussian dephasing in flux qubits due to 1/f-noise
Recent experiments by F. Yoshihara et al. [Phys. Rev. Lett. 97, 167001
(2006)] and by K. Kakuyanagi et al. (cond-mat/0609564) provided information on
decoherence of the echo signal in Josephson-junction flux qubits at various
bias conditions. These results were interpreted assuming a Gaussian model for
the decoherence due to 1/f noise. Here we revisit this problem on the basis of
the exactly solvable spin-fluctuator model reproducing detailed properties of
the 1/f noise interacting with a qubit. We consider the time dependence of the
echo signal and conclude that the results based on the Gaussian assumption need
essential reconsideration.Comment: Improved fitting parameters, new figur
Lattice QCD with mixed actions
We discuss some of the implications of simulating QCD when the action used
for the sea quarks is different from that used for the valence quarks. We
present exploratory results for the hadron mass spectrum and pseudoscalar meson
decay constants using improved staggered sea quarks and HYP-smeared overlap
valence quarks. We propose a method for matching the valence quark mass to the
sea quark mass and demonstrate it on UKQCD clover data in the simpler case
where the sea and valence actions are the same.Comment: 15 pages, 10 figures some minor modification to text and figures.
Accepted for publicatio
Non-visual functions of crustacean eyestalk ganglia
Ablation experiments demonstrated that in several crustacean groups, the proximal eyestalk ganglia are important in a variety of behavior patterns: 1. Chemical elicitation of feeding via the antennules is altered in lobsters, hermit crabs, and some brachyuran crabs by bilateral eyestalk ablation; the ablation of one antennule and the contralateral eyestalk is effective in lobsters and hermit crabs;Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47106/1/359_2005_Article_BF01245153.pd
On the statistics of superlocalized states in self-affine disordered potentials
We investigate the statistics of eigenstates in a weak self-affine disordered
potential in one dimension, whose Gaussian fluctuations grow with distance with
a positive Hurst exponent . Typical eigenstates are superlocalized on
samples much larger than a well-defined crossover length, which diverges in the
weak-disorder regime. We present a parallel analytical investigation of the
statistics of these superlocalized states in the discrete and the continuum
formalisms. For the discrete tight-binding model, the effective localization
length decays logarithmically with the sample size, and the logarithm of the
transmission is marginally self-averaging. For the continuum Schr\"odinger
equation, the superlocalization phenomenon has more drastic effects. The
effective localization length decays as a power of the sample length, and the
logarithm of the transmission is fully non-self-averaging.Comment: 21 pages, 6 figure
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