2,064 research outputs found
Hermitian symmetric polynomials and CR complexity
Properties of Hermitian forms are used to investigate several natural
questions from CR Geometry. To each Hermitian symmetric polynomial we assign a
Hermitian form. We study how the signature pairs of two Hermitian forms behave
under the polynomial product. We show, except for three trivial cases, that
every signature pair can be obtained from the product of two indefinite forms.
We provide several new applications to the complexity theory of rational
mappings between hyperquadrics, including a stability result about the
existence of non-trivial rational mappings from a sphere to a hyperquadric with
a given signature pair.Comment: 19 pages, latex, fixed typos, to appear in Journal of Geometric
Analysi
Hydromagnetic and gravitomagnetic crust-core coupling in a precessing neutron star
We consider two types of mechanical coupling between the crust and the core
of a precessing neutron star. First, we find that a hydromagnetic (MHD)
coupling between the crust and the core strongly modifies the star's
precessional modes when ; here is the
Alfven crossing timescale, and and are the star's spin and
precession periods, respectively. We argue that in a precessing pulsar PSR
B1828-11 the restoring MHD stress prevents a free wobble of the crust relative
to the non-precessing core. Instead, the crust and the proton-electron plasma
in the core must precess in unison, and their combined ellipticity determines
the period of precession. Link has recently shown that the neutron superfluid
vortices in the core of PSR B1828-11 cannot be pinned to the plasma; he has
also argued that this lack of pinning is expected if the proton Fermi liquid in
the core is type-I superconductor. In this case, the neutron superfluid is
dynamically decoupled from the precessing motion. The pulsar's precession
decays due to the mutual friction between the neutron superfluid and the plasma
in the core. The decay is expected to occur over tens to hundreds of precession
periods and may be measurable over a human lifetime. Such a measurement would
provide information about the strong n-p interaction in the neutron-star core.
Second, we consider the effect of gravitomagnetic coupling between the neutron
superfluid in the core and the rest of the star and show that this coupling
changes the rate of precession by about 10%. The general formalism developed in
this paper may be useful for other applications.Comment: 6 page
Identifying entanglement using quantum "ghost" interference and imaging
We report a quantum interference and imaging experiment which quantitatively
demonstrates that Einstein-Podolsky-Rosen (EPR) type entangled two-photon
states exhibit both momentum-momentum and position-position correlations,
stronger than any classical correlation. The measurements show indeed that the
uncertainties in the sum of momenta and in the difference of positions of the
entangled two-photon satisfy both EPR inequalities D(k1+k2)<min(D(k1),D(k2))
and D(x1-x2)<min(D(x1),D(x2)). These two inequalities, together, represent a
non-classicality condition. Our measurements provide a direct way to
distinguish between quantum entanglement and classical correlation in
continuous variables for two-photons/two photons systems.Comment: We have changed Eq.(2) from one inequality to two inequalities. The
two expressions are actually consistent with each other, but the new one
represents a more stringent condition for entanglement and, in our opinion,
better explains the original idea of EPR. We have clarified this point in the
paper. 4 pages; submitted to PR
Evolution of Migrating Planets Undergoing Gas Accretion
We analyze the orbital and mass evolution of planets that undergo run-away
gas accretion by means of 2D and 3D hydrodynamic simulations. The disk torque
distribution per unit disk mass as a function of radius provides an important
diagnostic for the nature of the disk-planet interactions. We first consider
torque distributions for nonmigrating planets of fixed mass and show that there
is general agreement with the expectations of resonance theory. We then present
results of simulations for mass-gaining, migrating planets. For planets with an
initial mass of 5 Earth masses, which are embedded in disks with standard
parameters and which undergo run-away gas accretion to one Jupiter mass (Mjup),
the torque distributions per unit disk mass are largely unaffected by migration
and accretion for a given planet mass. The migration rates for these planets
are in agreement with the predictions of the standard theory for planet
migration (Type I and Type II migration). The planet mass growth occurs through
gas capture within the planet's Bondi radius at lower planet masses, the Hill
radius at intermediate planet masses, and through reduced accretion at higher
planet masses due to gap formation. During run-away mass growth, a planet
migrates inwards by only about 20% in radius before achieving a mass of ~1
Mjup. For the above models, we find no evidence of fast migration driven by
coorbital torques, known as Type III migration. We do find evidence of Type III
migration for a fixed mass planet of Saturn's mass that is immersed in a cold
and massive disk. In this case the planet migration is assumed to begin before
gap formation completes. The migration is understood through a model in which
the torque is due to an asymmetry in density between trapped gas on the leading
side of the planet and ambient gas on the trailing side of the planet.Comment: 26 pages, 29 figures. To appear in The Astrophysical Journal vol.684
(September 20, 2008 issue
Tomographic test of Bell's inequality for a time-delocalized single photon
Time-domain balanced homodyne detection is performed on two well-separated
temporal modes sharing a single photon. The reconstructed density matrix of the
two-mode system is used to prove and quantify its entangled nature, while the
Wigner function is employed for an innovative tomographic test of Bell's
inequality based on the theoretical proposal by Banaszek and Wodkiewicz [Phys.
Rev. Lett. 82, 2009 (1999)]. Provided some auxiliary assumptions are made, a
clear violation of Banaszek-Bell's inequality is found.Comment: 7 pages, 3 figures: revised version with additional material;
accepetd for publication in Phys. Rev.
Immunolocalization of Nesfatin-1 in the Gastrointestinal Tract of the Common Bottlenose Dolphin Tursiops truncatus
SIMPLE SUMMARY: Nesfatin-1 (Nesf-1) is a neuropeptide that plays important roles in regulating food intake, mainly related to its anorexigenic effect, and it is mainly distributed in the digestive systems of all vertebrates. With this study, we expand knowledge on the localization of Nesf-1 in the digestive tract of an aquatic mammalian species, the common bottlenose dolphin (Tursiops truncatus), allowing comparative study on terrestrial mammals. Dolphin tissue samples (three gastric chambers and intestine) were provided by the Mediterranean Marine Mammal Tissue Bank of the Department of Comparative Biomedicine and Food Science of the University of Padova (Italy). ABSTRACT: First identified as an anorexigenic peptide, in the last decades, several studies have suggested that Nesfatin-1 (Nesf-1) is a pleiotropic hormone implicated in numerous regulatory processes in peripheral organs and tissues. In vertebrates, Nesf-1 is indeed expressed in the central nervous system and peripheral organs. In this study, we characterized the pattern of Nesf-1 distribution within the digestive tract of the common bottlenose dolphin (Tursiops truncatus), composed of three gastric chambers and an intestine without a clear subdivision in the small and large intestine, also lacking a caecum. Our results indicated that Nesf-1 is widely distributed in cells of the mucosal epithelium of the gastric chambers. Most of the immunoreactivity was observed in the second chamber, compared to the first and third chambers. Immunopositivity was also found in nerve fibers and neurons, scattered or/and clustered in ganglion structures along all the examined gastrointestinal tracts. These observations add new data on the highly conserved role of Nesf-1 in the mammalian digestive system
Seismic assessment and rehabilitation of a historical theatre based on a macro-element strategy
The structural and seismic assessment of the 19th-century Petruzzelli theater in Bari (Italy) is presented. The macro-elements strategy was adopted to dismantle the whole structure in parts. The steel dome was verified through dynamic multi-modal analysis based on finite element model. Each masonry macro-element was firstly verified through a kinematic analysis aiming at excluding local collapse mechanisms. Afterwards, a nonlinear static analysis was carried out in order to evaluate its overall seismic capacity. The effectiveness of linear or nonlinear analyses and of the macro-element strategy compared with other modeling techniques is also discussed. After highlighting the structural deficiencies of the theater, upgrading solutions are proposed with consideration of the safety needs and the architectural preservation requirements based on the historical importance of the buildin
Evolution of Giant Planets in Eccentric Disks
We investigate the interaction between a giant planet and a viscous
circumstellar disk by means of high-resolution, two-dimensional hydrodynamical
simulations. We consider planet masses that range from 1 to 3 Jupiter masses
(Mjup) and initial orbital eccentricities that range from 0 to 0.4. We find
that a planet can cause eccentricity growth in a disk region adjacent to the
planet's orbit, even if the planet's orbit is circular. Disk-planet
interactions lead to growth in a planet's orbital eccentricity. The orbital
eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within
about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1
Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial
eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits.
Radial migration is directed inwards, but slows considerably as a planet's
orbit becomes eccentric. If a planet's orbital eccentricity becomes
sufficiently large, e > ~0.2, migration can reverse and so be directed
outwards. The accretion rate towards a planet depends on both the disk and the
planet orbital eccentricity and is pulsed over the orbital period. Planet mass
growth rates increase with planet orbital eccentricity. For e~0.2 the mass
growth rate of a planet increases by approximately 30% above the value for e=0.
For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when
the planet is near the apocenter. Similar accretion modulation occurs for flow
at the inner disk boundary which represents accretion toward the star.Comment: 20 pages 16 figures, 3 tables. To appear in The Astrophysical Journal
vol.652 (December 1, 2006 issue
A decidable policy language for history-based transaction monitoring
Online trading invariably involves dealings between strangers, so it is
important for one party to be able to judge objectively the trustworthiness of
the other. In such a setting, the decision to trust a user may sensibly be
based on that user's past behaviour. We introduce a specification language
based on linear temporal logic for expressing a policy for categorising the
behaviour patterns of a user depending on its transaction history. We also
present an algorithm for checking whether the transaction history obeys the
stated policy. To be useful in a real setting, such a language should allow one
to express realistic policies which may involve parameter quantification and
quantitative or statistical patterns. We introduce several extensions of linear
temporal logic to cater for such needs: a restricted form of universal and
existential quantification; arbitrary computable functions and relations in the
term language; and a "counting" quantifier for counting how many times a
formula holds in the past. We then show that model checking a transaction
history against a policy, which we call the history-based transaction
monitoring problem, is PSPACE-complete in the size of the policy formula and
the length of the history. The problem becomes decidable in polynomial time
when the policies are fixed. We also consider the problem of transaction
monitoring in the case where not all the parameters of actions are observable.
We formulate two such "partial observability" monitoring problems, and show
their decidability under certain restrictions
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