6,530 research outputs found
Time-Delayed transfer functions simulations for LMXBs
Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)
have demonstrated that Bowen flourescence is a very efficient tracer of the
companion star in LMXBs. We present a numerical code to simulate time-delayed
transfer functions in LMXBs, specific to the case of reprocessing in emission
lines. The code is also able to obtain geometrical and binary parameters by
fitting observed (X-ray + optical) light curves using simulated annealing
methods. In this work we present the geometrical model for the companion star
and the analytical model for the disc and show synthetic time-delay transfer
functions for different orbital phases and system parameters.Comment: Contribution presented at the conference "Interacting Binaries:
Accretion, Evolution and Outcomes", held in Cefalu, Sicily (Italy) in July
2004. To be published by AIP (American Institute of Physics), eds. L. A.
Antonelli, L. Burderi, F. D'Antona, T. Di Salvo, G.L. Israel, L. Piersanti,
O. Straniero, A. Tornambe. 4 pages, 4 figure
Experimental evidence of localized oscillations in the photosensitive chlorine dioxide-iodine-malonic acid reaction
The interaction between Hopf and Turing modes has been the subject of active research in recent years. We present here experimental evidence of the existence of mixed Turing-Hopf modes in a two-dimensional system. Using the photosensitive chlorine dioxide-iodine-malonic acid reaction (CDIMA) and external constant background illumination as a control parameter, standing spots oscillating in amplitude and with hexagonal ordering were observed. Numerical simulations in the Lengyel-Epstein model for the CDIMA reaction confirmed the results
Convolutional Goppa Codes
We define Convolutional Goppa Codes over algebraic curves and construct their
corresponding dual codes. Examples over the projective line and over elliptic
curves are described, obtaining in particular some Maximum-Distance Separable
(MDS) convolutional codes.Comment: 8 pages, submitted to IEEE Trans. Inform. Theor
Nonuniversality in the pair contact process with diffusion
We study the static and dynamic behavior of the one dimensional pair contact
process with diffusion. Several critical exponents are found to vary with the
diffusion rate, while the order-parameter moment ratio m=\bar{rho^2}
/\bar{rho}^2 grows logarithmically with the system size. The anomalous behavior
of m is traced to a violation of scaling in the order parameter probability
density, which in turn reflects the presence of two distinct sectors, one
purely diffusive, the other reactive, within the active phase. Studies
restricted to the reactive sector yield precise estimates for exponents beta
and nu_perp, and confirm finite size scaling of the order parameter. In the
course of our study we determine, for the first time, the universal value m_c =
1.334 associated with the parity-conserving universality class in one
dimension.Comment: 9 pages, 5 figure
Exact Solution of the Munoz-Eaton Model for Protein Folding
A transfer-matrix formalism is introduced to evaluate exactly the partition
function of the Munoz-Eaton model, relating the folding kinetics of proteins of
known structure to their thermodynamics and topology. This technique can be
used for a generic protein, for any choice of the energy and entropy
parameters, and in principle allows the model to be used as a first tool to
characterize the dynamics of a protein of known native state and equilibrium
population. Applications to a -hairpin and to protein CI-2, with
comparisons to previous results, are also shown.Comment: 4 pages, 5 figures, RevTeX 4. To be published in Phys. Rev. Let
Multi-copy programmable discrimination of general qubit states
Quantum state discrimination is a fundamental primitive in quantum statistics
where one has to correctly identify the state of a system that is in one of two
possible known states. A programmable discrimination machine performs this task
when the pair of possible states is not a priori known, but instead the two
possible states are provided through two respective program ports. We study
optimal programmable discrimination machines for general qubit states when
several copies of states are available in the data or program ports. Two
scenarios are considered: one in which the purity of the possible states is a
priori known, and the fully universal one where the machine operates over
generic mixed states of unknown purity. We find analytical results for both,
the unambiguous and minimum error, discrimination strategies. This allows us to
calculate the asymptotic performance of programmable discrimination machines
when a large number of copies is provided, and to recover the standard state
discrimination and state comparison values as different limiting cases.Comment: Based on version published in Physical Review A, some errors in
appendix A corrected. 13 pages, 4 figure
Critical wetting of a class of nonequilibrium interfaces: A mean-field picture
A self-consistent mean-field method is used to study critical wetting
transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang
(KPZ) interfaces in the presence of a bounding substrate. In the case of
positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary,
interfaces corresponding to negative nonlinearities lead to three different
regimes of critical behavior for the surface order-parameter: (i) a trivial
Gaussian regime, (ii) a weak-fluctuation regime with a trivially located
critical point and nontrivial exponents, and (iii) a highly non-trivial
strong-fluctuation regime, for which we provide a full solution by finding the
zeros of parabolic-cylinder functions. These analytical results are also
verified by solving numerically the self-consistent equation in each case.
Analogies with and differences from equilibrium critical wetting as well as
nonequilibrium complete wetting are also discussed.Comment: 11 pages, 2 figure
On the masses and evolutionary status of the black hole binary GX 339-4. A twin system of XTE J1550-564?
We apply the K-correction to the black hole LMXB GX 339-4 which implies Mx >
6 Msun by only assuming that the companion is more massive than ~0.17 Msun, the
lower limit allowed by applying a 'stripped-giant' model. This evolutionary
model successfully reproduces the observed properties of the system. We obtain
a maximum mass for the companion of M2 < 1.1 Msun and an upper limit to the
mass ratio of q(=M2/Mx)< 0.125. The high X-ray activity displayed by the source
suggests a relatively large mass transfer rate which, according to the model,
results in M2 > 0.3 Msun and Mx > 7 Msun. We have also applied this scenario to
the black hole binary XTE J1550-564, which has a similar orbital period but the
donor is detected spectroscopically. The model successfully reproduces the
observed stellar parameters.Comment: 5 pages, 2 tables, 1 figues. Accepted for publication in MNRA
- âŠ