22,903 research outputs found
One-parameter scaling theory for DNA extension in a nanochannel
Experiments measuring DNA extension in nanochannels are at odds with even the
most basic predictions of current scaling arguments for the conformations of
confined semiflexible polymers such as DNA. We show that a theory based on a
weakly self-avoiding, one-dimensional "telegraph" process collapses
experimental data and simulation results onto a single master curve throughout
the experimentally relevant region of parameter space and explains the
mechanisms at play.Comment: Revised version. 5 pages, 4 figures, revised version, supplementary
informatio
On the origin of white dwarfs with carbon-dominated atmospheres: the case of H1504+65
We explore different evolutionary scenarios to explain the helium deficiency
observed in H1504+65, the most massive known PG1159 star. We concentrate mainly
on the possibility that this star could be the result of mass loss shortly
after the born-again and during the subsequent evolution through the [WCL]
stage. This possibility is sustained by recent observational evidence of
extensive mass-loss events in Sakurai's object and is in line with the recent
finding that such mass losses give rise to PG1159 models with thin helium-rich
envelopes and large rates of period change, as demanded by the pulsating star
PG1159-035. We compute the post born again evolution of massive sequences by
taking into account different mass-loss rate histories. Our results show that
stationary winds during the post-born-again evolution fail to remove completely
the helium-rich envelope so as to explain the helium deficiency observed in
H1504+65. Stationary winds during the Sakurai and [WCL] stages only remove at
most half of the envelope surviving the violent hydrogen burning during the
born-again phase. In view of our results, the recently suggested evolutionary
connection born-again stars --> H1504+65 --> white dwarfs with carbon-rich
atmospheres is difficult to sustain unless the whole helium-rich envelope could
be ejected by non-stationary mass-loss episodes during the Sakurai stage.Comment: 5 pages, 2 figures. To be published in Astronomy & Astrophysic
The structure of classical extensions of quantum probability theory
On the basis of a suggestive definition of a classical extension of quantum mechanics in terms of statistical models, we prove that every such classical extension is essentially given by the so-called Misra–Bugajski reduction map. We consider how this map enables one to understand quantum mechanics as a reduced classical statistical theory on the projective Hilbert space as phase space and discuss features of the induced hidden-variable model. Moreover, some relevant technical results on the topology and Borel structure of the projective Hilbert space are reviewed
Exact Energy-Time Uncertainty Relation for Arrival Time by Absorption
We prove an uncertainty relation for energy and arrival time, where the
arrival of a particle at a detector is modeled by an absorbing term added to
the Hamiltonian. In this well-known scheme the probability for the particle's
arrival at the counter is identified with the loss of normalization for an
initial wave packet. Under the sole assumption that the absorbing term vanishes
on the initial wave function, we show that and , where denotes the mean
arrival time, and is the probability for the particle to be eventually
absorbed. Nearly minimal uncertainty can be achieved in a two-level system, and
we propose a trapped ion experiment to realize this situation.Comment: 8 pages, 2 figure
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Monitoring Insect Parasites in a Cotton Pest Management Program
This item is part of the Agricultural Experiment Station archive. It was digitized from a physical copy provided by the University Libraries at the University of Arizona. For more information, please email CALS Publications at [email protected]
Area Decay Law Implementation for Quark String Fragmentation
We apply the Area Decay Law (ADL) straightforwardly to simulate a quark
string hadronization and compare the results with the explicit analytic
calculations. We show that the usual "inclusive" Monte--Carlo simulations do
not correspond to the ADL because of two mistakes: not proper simulation of
two--dimensional probability density and lack of an important combinatorial
factor in a binary tree simulation. We also show how to simulate area decay law
"inclusively" avoiding the above--mentioned mistakes.Comment: 5 pages (REVTEX) + 3 figures (available in ps format from
G.G.Leptoukh , IPGAS-HE/93-3, to be
published in Phys. Rev.
Evidence for Hydrodynamic Evolution in Proton-Proton Scattering at LHC Energies
In scattering at LHC energies, large numbers of elementary scatterings
will contribute significantly, and the corresponding high multiplicity events
will be of particular interest. Elementary scatterings are parton ladders,
identified with color flux-tubes. In high multiplicity events, many of these
flux tubes are produced in the same space region, creating high energy
densities. We argue that there are good reasons to employ the successful
procedure used for heavy ion collisions: matter is assumed to thermalizes
quickly, such that the energy from the flux-tubes can be taken as initial
condition for a hydrodynamic expansion. This scenario gets spectacular support
from very recent results on Bose-Einstein correlations in scattering at
900 GeV at LHC.Comment: 11 pages, 20 figure
Neutron-irradiation effects in LaO0.9F0.1FeAs superconductor
The effect of atomic disorder induced by neutrons irradiation on
superconducting and normal state properties of polycrystalline LaFeAsO_0.9F_0.1
was investigated. The irradiation of the sample by a moderate neutron fluence F
= 1.6*1019 cm^-2 at Tirr = 50 +- 10 C leads to the suppression of
superconductivity which recovers almost completely after annealing at
temperatures Tann < 750 C. It is shown that the reduction of superconducting
transition temperature Tc under atomic disordering is not determined solely by
the value of Hall concentration nH, i.e. doping level, but is governed by the
reduction of electronic relaxation time. This behavior can be described
qualitatively by universal Abrikosov-Gorkov equation which presents evidence on
the anomalous type of electrons pairing in Fe-based superconductors.Comment: 8 pages, 11 figure
Distillability and positivity of partial transposes in general quantum field systems
Criteria for distillability, and the property of having a positive partial
transpose, are introduced for states of general bipartite quantum systems. The
framework is sufficiently general to include systems with an infinite number of
degrees of freedom, including quantum fields. We show that a large number of
states in relativistic quantum field theory, including the vacuum state and
thermal equilibrium states, are distillable over subsystems separated by
arbitrary spacelike distances. These results apply to any quantum field model.
It will also be shown that these results can be generalized to quantum fields
in curved spacetime, leading to the conclusion that there is a large number of
quantum field states which are distillable over subsystems separated by an
event horizon.Comment: 25 pages, 2 figures. v2: Typos removed, references and comments
added. v3: Expanded introduction and reference list. To appear in Rev. Math.
Phy
Quantum spin chains with site dissipation
We use Monte Carlo simulations to study chains of Ising- and XY-spins with
dissipation coupling to the site variables. The phase diagram and critical
exponents of the dissipative Ising chain in a transverse magnetic field have
been computed previously, and here we consider a universal ratio of
susceptibilities. We furthermore present the phase diagram and exponents of the
dissipative XY-chain, which exhibits a second order phase transition. All our
results compare well with the predictions from a dissipative field
theory
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