121,917 research outputs found
Bound States in n Dimensions (Especially n = 1 and n = 2)
We stress that in contradiction with what happens in space dimensions , there is no strict bound on the number of bound states with the same
structure as the semi-classical estimate for large coupling constant and give,
in two dimensions, examples of weak potentials with one or infinitely many
bound states. We derive bounds for one and two dimensions which have the
"right" coupling constant behaviour for large coupling.Comment: Talk given by A. Martin at Les Houches, October 2001, to appear in
"Few-Body Problems
Noise correlations, entanglement, and Bell inequalities
The aim of this chapter is to describe two situations where positive noise
correlations can be directly monitored using a transport experiment, either
with a superconductor or with a correlated electron system. To be more precise,
the present text reflects the presentations made by the three authors during
the Delft NATO workshop. Bell inequalities and quantum mechanical non-locality
with electrons injected from a superconductor will be addressed first. Next,
noise correlations will be computed in a carbon nanotube where electrons are
injected in the bulk from a STM tip. The first topic is the result of an
ongoing collaboration with G. Lesovik and G. Blatter over the years. The
unifying theme is that in both branched quantum circuits, entanglement is
explicit and can be illustrated via noise correlations. Entanglement can be
achieved either for pairs of electrons in the case of superconductor sources
connected to Fermi liquid leads, or alternatively for pairs of quasiparticle
excitations of the correlated electron fluid.Comment: 24 pages, 7 figures, Proceedings of the NATO ARW workshop on Quantum
Noise, Y. Nazarov and Y. Blanter editors (Kluwer 2002
Visible-IR Colors and Lightcurve Analysis of Two Bright TNOs: 1999 TC36 and 1998 SN165
We report on observations of two bright Trans-Neptunian Objects (TNOs) - 1999
TC36 and 1998 SN165}- during two observational campaigns, as part of the Meudon
Multicolor Survey of Outer Solar System Objects. V-J color was measured for
1999 TC36 (V-J=2.34+/-0.18), which combined with previous measured colors in
the visible, indicate a red reflectivity spectrum at all wavelengths.
Photometric V-band lightcurves were taken for both objects over a time span of
around 8 hours. We have determined a possible rotational period of P=10.1+/-0.8
h for 1998 SN165, making it the seventh TNO with an estimated period. From its
lightcurve variation of Dm=0.151(+0.022/-0.030), we have inferred an asymmetry
ratio of a/b >=1.148(+0.024/-0.031). For 1999 TC36, we did not detect any
rotational period or periodic signal variation within the uncertainties, but
the analysis of its lightcurve hints to a slight systematic magnitude decrease.Comment: Accepted for publication in New Astronomy (13 pages, inc. 4 figures
Two-Page Book Embeddings of 4-Planar Graphs
Back in the Eighties, Heath showed that every 3-planar graph is
subhamiltonian and asked whether this result can be extended to a class of
graphs of degree greater than three. In this paper we affirmatively answer this
question for the class of 4-planar graphs. Our contribution consists of two
algorithms: The first one is limited to triconnected graphs, but runs in linear
time and uses existing methods for computing hamiltonian cycles in planar
graphs. The second one, which solves the general case of the problem, is a
quadratic-time algorithm based on the book-embedding viewpoint of the problem.Comment: 21 pages, 16 Figures. A shorter version is to appear at STACS 201
Structural and mutagenic analysis of the RM controller protein C.Esp1396I
Bacterial restriction-modification (RM) systems are comprised of two complementary enzymatic activities that prevent the establishment of foreign DNA in a bacterial cell: DNA methylation and DNA restriction. These two activities are tightly regulated to prevent over-methylation or auto-restriction. Many Type II RM systems employ a controller (C) protein as a transcriptional regulator for the endonuclease gene (and in some cases, the methyltransferase gene also). All high-resolution structures of C-protein/DNA-protein complexes solved to date relate to C.Esp1396I, from which the interactions of specific amino acid residues with DNA bases and/or the phosphate backbone could be observed. Here we present both structural and DNA binding data for a series of mutations to the key DNA binding residues of C.Esp1396I. Our results indicate that mutations to the backbone binding residues (Y37, S52) had a lesser affect on DNA binding affinity than mutations to those residues that bind directly to the bases (T36, R46), and the contributions of each side chain to the binding energies are compared. High-resolution X-ray crystal structures of the mutant and native proteins showed that the fold of the proteins was unaffected by the mutations, but also revealed variation in the flexible loop conformations associated with DNA sequence recognition. Since the tyrosine residue Y37 contributes to DNA bending in the native complex, we have solved the structure of the Y37F mutant protein/DNA complex by X-ray crystallography to allow us to directly compare the structure of the DNA in the mutant and native complexes
Bright solitary waves of atomic Bose-Einstein condensates under rotation
We analyse the rotation of bright solitary waves formed of atomic
Bose-Einstein condensates with attractive atomic interactions. By employing a
variational technique and assuming an irrotational quadrupolar flow field, we
map out the variational solutions in the rotating frame. In particular, we show
that rotation has a considerable stabilising effect on the system,
significantly raising the critical threshold for collapse of the bright
solitary waves.Comment: 4 pages, 3 figure
Universal amplitude ratios in the 3D Ising Universality Class
We compute a number of universal amplitude ratios in the three-dimensional
Ising universality class. To this end, we perform Monte Carlo simulations of
the improved Blume-Capel model on the simple cubic lattice. For example, we
obtain A_+/A_-=0.536(2) and C_+/C_-=4.713(7), where A_+- and C_+- are the
amplitudes of the specific heat and the magnetic susceptibility, respectively.
The subscripts + and - indicate the high and the low temperature phase,
respectively. We compare our results with those obtained from previous Monte
Carlo simulations, high and low temperature series expansions, field theoretic
methods and experiments.Comment: 18 pages, two figures, typos corrected, discussion on finite size
corrections extende
Comparing supernova remnants around strongly magnetized and canonical pulsars
The origin of the strong magnetic fields measured in magnetars is one of the
main uncertainties in the neutron star field. On the other hand, the recent
discovery of a large number of such strongly magnetized neutron stars, is
calling for more investigation on their formation. The first proposed model for
the formation of such strong magnetic fields in magnetars was through
alpha-dynamo effects on the rapidly rotating core of a massive star. Other
scenarios involve highly magnetic massive progenitors that conserve their
strong magnetic moment into the core after the explosion, or a common envelope
phase of a massive binary system. In this work, we do a complete re-analysis of
the archival X-ray emission of the Supernova Remnants (SNR) surrounding
magnetars, and compare our results with all other bright X-ray emitting SNRs,
which are associated with Compact Central Objects (CCOs; which are proposed to
have magnetar-like B-fields buried in the crust by strong accretion soon after
their formation), high-B pulsars and normal pulsars. We find that emission
lines in SNRs hosting highly magnetic neutron stars do not differ significantly
in elements or ionization state from those observed in other SNRs, neither
averaging on the whole remnants, nor studying different parts of their total
spatial extent. Furthermore, we find no significant evidence that the total
X-ray luminosities of SNRs hosting magnetars, are on average larger than that
of typical young X-ray SNRs. Although biased by a small number of objects, we
found that for a similar age, there is the same percentage of magnetars showing
a detectable SNR than for the normal pulsar population.Comment: 16 pages, 5 figures, Accepted for publication in MNRA
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