1,035 research outputs found
The Poincare-Birkhoff theorem in Quantum Mechanics
Quantum manifestations of the dynamics around resonant tori in perturbed
Hamiltonian systems, dictated by the Poincar\'e--Birkhoff theorem, are shown to
exist. They are embedded in the interactions involving states which differ in a
number of quanta equal to the order of the classical resonance. Moreover, the
associated classical phase space structures are mimicked in the
quasiprobability density functions and their zeros.Comment: 5 pages, 3 figures, Full resolution figures available at
http://www.df.uba.ar/users/wisniaki/publications.htm
A 0535+26: an X-ray/Optical Tour
We compiled X-ray and Optical observations of the accreting X-ray binary
system A 0535+262 since its discovery in 1975, that will allow us to shed light
on the unpredictable behavior of this binary system. We present the data in
terms of the Be-disk interaction with the neutron star companion. In addition,
we show recent results from the continuous monitoring of this source by the
Gamma-ray Burst Monitor(GBM), on board the Fermi observatory, since its launch
in 2008 June 11.Comment: 4 pages, 5 figures, Conference proceeding of "Astrophysics of Neutron
Stars 2010 - a conference in honor of M. Ali Alpar", 2-6 August 2010, Cesme,
Izmir, Turke
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
We study the spectral and temporal behavior of the High Mass X-ray Binary A
0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of
a normal (type I) outburst in August/September 2005. We compare the studied
behavior with that observed during the outburst. We analyse RXTE observations
that monitored A 0535+26 during the outburst. We complete spectral and timing
analyses of the data. We study the evolution of the pulse period, present
energy-dependent pulse profiles both at the initial pre-outburst flare and
close to outburst maximum, and measure how the cyclotron resonance-scattering
feature (hereafter CRSF) evolves. We present three main results: a constant
period P=103.3960(5)s is measured until periastron passage, followed by a
spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s
at MJD 53618, and P remains constant again at the end of the main outburst. The
spin-up provides evidence for the existence of an accretion disk during the
normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst
flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies
significantly during both pre-outburst flare and main outburst, evolves
strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be
published in parallel to Postnov et al. 200
Peculiar outburst of A 0535+26 observed with INTEGRAL, RXTE and Suzaku
A normal outburst of the Be/X-ray binary system A0535+26 has taken place in
August 2009. It is the fourth in a series of normal outbursts that have occured
around the periastron passage of the source, but is unusual by starting at an
earlier orbital phase and by presenting a peculiar double-peaked light curve. A
first "flare" (lasting about 9 days from MJD 55043 on) reached a flux of 440
mCrab. The flux then decreased to less than 220 mCrab, and increased again
reaching 440 mCrab around the periastron at MJD 55057. Target of Opportunity
observations have been performed with INTEGRAL, RXTE and Suzaku. First results
of these observations are presented, with special emphasis on the cyclotron
lines present in the X-ray spectrum of the source, as well as in the pulse
period and energy dependent pulse profiles of the source.Comment: 6 pages, Accepted for publication on PoS, Proceedings of "The Extreme
sky: Sampling the Universe above 10 keV", held in Otranto (Italy) in October
200
The first crystal structure of human RNase6 reveals a novel substrate binding and cleavage site arrangement
Human RNase 6 is a cationic secreted protein that belongs to the RNase A superfamily. Its expression is induced in neutrophils and monocytes upon bacterial infection, suggesting a role in host defence. We present here the crystal structure of RNase 6 obtained at a 1.72 Ă… resolution, being the first report for the protein threedimensional structure and thereby setting the basis for functional studies. The structure shows an overall kidney shaped globular fold shared with the other known family members. Three sulphate anions bound to RNase 6 were found, interacting to residues at the main active site (His15, His122 and Gln14) and cationic surface exposed residues (His36, His39, Arg66 and His67). Kinetic characterization, together with prediction of protein -nucleotide complexes by molecular dynamics, was applied to analyse the RNase 6 substrate nitrogenous base and phosphate selectivity. Our results reveal that, although RNase 6 is a moderate catalyst in comparison to the pancreatic RNase type, its structure includes lineage specific features that facilitate its activity towards polymeric nucleotide substrates. In particular, enzyme interactions at the substrate 5' end can provide an endonuclease type cleavage pattern. Interestingly, the RNase 6 crystal structure revealed a novel secondary active site conformed by the His36-His39 dyad that facilitates the polynucleotide substrate catalysis
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