5,582 research outputs found
Alternative model of the Antonov problem
Astrophysical systems will never be in a real Thermodynamic equilibrium: they
undergo an evaporation process due to the fact that the gravity is not able to
confine the particles. Ordinarily, this difficulty is overcome by enclosing the
system in a rigid container which avoids the evaporation. We proposed an
energetic prescription which is able to confine the particles, leading in this
way to an alternative version of the Antonov isothermal model which unifies the
well-known isothermal and polytropic profiles. Besides of the main features of
the isothermal sphere model: the existence of the gravitational collapse and
the energetic region with a negative specific heat, this alternative model has
the advantage that the system size naturally appears as a consequence of the
particles evaporation.Comment: RevTex4, 9 pages, 10 figures, Version Submitted to PR
Quantum correlations in Newtonian space and time: arbitrarily fast communication or nonlocality
We investigate possible explanations of quantum correlations that satisfy the
principle of continuity, which states that everything propagates gradually and
continuously through space and time. In particular, following [J.D. Bancal et
al, Nature Physics 2012], we show that any combination of local common causes
and direct causes satisfying this principle, i.e. propagating at any finite
speed, leads to signalling. This is true even if the common and direct causes
are allowed to propagate at a supraluminal-but-finite speed defined in a
Newtonian-like privileged universal reference frame. Consequently, either there
is supraluminal communication or the conclusion that Nature is nonlocal (i.e.
discontinuous) is unavoidable.Comment: It is an honor to dedicate this article to Yakir Aharonov, the master
of quantum paradoxes. Version 2 contains some more references and a clarified
conclusio
Star-forming Clumps in Local Luminous Infrared Galaxies
We present HST narrowband near-infrared imaging of Paα and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ~90 to 900 pc and star formation rates (SFRs) of ~1 × 10⁻³ to 10 M⊙ yr⁻¹, with median values for extranuclear clumps of 170 pc and 0.03 M⊙ yr⁻¹. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 10⁵ M ⊙. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1–3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs
C-GOALS II. Chandra Observations of the Lower Luminosity Sample of Nearby Luminous Infrared Galaxies in GOALS
We analyze Chandra X-ray observatory data for a sample of 63 luminous
infrared galaxies (LIRGs), sampling the lower-infrared luminosity range of the
Great Observatories All-Sky LIRG survey (GOALS), which includes the most
luminous infrared selected galaxies in the local universe. X-rays are detected
for 84 individual galaxies within the 63 systems, for which arcsecond
resolution X-ray images, fluxes, infrared and X-ray luminosities, spectra and
radial profiles are presented. Using X-ray and MIR selection criteria, we find
AGN in (315)% of the galaxy sample, compared to the (386)% previously
found for GOALS galaxies with higher infrared luminosities (C-GOALS I). Using
mid-infrared data, we find that (599)% of the X-ray selected AGN in the
full C-GOALS sample do not contribute significantly to the bolometric
luminosity of the host galaxy. Dual AGN are detected in two systems, implying a
dual AGN fraction in systems that contain at least one AGN of (2914)%,
compared to the (1110)% found for the C-GOALS I sample. Through analysis
of radial profiles, we derive that most sources, and almost all AGN, in the
sample are compact, with half of the soft X-ray emission generated within the
inner kpc. For most galaxies, the soft X-ray sizes of the sources are
comparable to those of the MIR emission. We also find that the hard X-ray
faintness previously reported for the bright C-GOALS I sources is also observed
in the brightest LIRGs within the sample, with
L.Comment: 24 pages, 13 figures, 11 tables, accepted for publication in A&
Guiding of cold atoms by a red-detuned laser beam of moderate power
We report measurements on the guiding of cold Rb atoms from a
magneto-optical trap by a continuous light beam over a vertical distance of 6.5
mm. For moderate laser power (85 mW) we are able to capture around 40% of
the cold atoms. Although the guide is red-detuned, the optical scattering rate
at this detuning (70 GHz) is acceptably low. For lower detuning (30
GHz) a larger fraction was guided but radiation pressure starts to push the
atoms upward, effectively lowering the acceleration due to gravity. The
measured guided fraction agrees well with an analytical model.Comment: final version, 6 pages, incl. 6 figure
Properties of lightly doped t-J two-leg ladders
We have numerically investigated the doped t-J ladder using exact
diagonalization. We have studied both the limit of strong inter-chain coupling
and isotropic coupling. The ladder scales to the Luther-Emery liquid regime in
the strong inter-chain coupling limit. In this strong coupling limit there is a
simple picture of the excitation spectrum that can be continued to explain the
behavior at isotropic coupling. At J=0 we have indications of a ferromagnetic
ground state. At a large the ladder is phase separated into holes and a
Heisenberg ladder. At intermediate coupling the ground state shows hole pairing
with a modified d-wave symmetry. The excitation spectrum separates into a
limited number of quasiparticles which carry charge and spin and a triplet magnon mode. At half-filling the former vanish but the latter
evolves continuously into the magnon band of the spin liquid. At low doping the
quasiparticles form a dilute Fermi gas with a strong attraction but
simultaneously the Fermi wave vector, as would be measured in photoemission, is
large. The dynamical structure factors are calculated and are found to be very
similar to calculations on 2D clusters
Superconducting gap anisotropy of LuNi2B2C thin films from microwave surface impedance measurements
Surface impedance measurements of LuNi2B2C superconducting thin films as a
function of temperature have been performed down to 1.5 K and at 20 GHz using a
dielectric resonator technique. The magnetic penetration depth closely
reproduces the standard B.C.S. result, but with a reduced value of the energy
gap at low temperature. These data provide evidence for an anisotropic s-wave
character of the order parameter symmetry in LuNi2B2C. From the evaluation of
the real part of complex conductivity, we have observed constructive (type II)
coherence effects in the electromagnetic absorption below Tc.Comment: 15 pages, 4 figure
The elusive source of quantum effectiveness
We discuss two qualities of quantum systems: various correlations existing
between their subsystems and the distingushability of different quantum states.
This is then applied to analysing quantum information processing. While quantum
correlations, or entanglement, are clearly of paramount importance for
efficient pure state manipulations, mixed states present a much richer arena
and reveal a more subtle interplay between correlations and distinguishability.
The current work explores a number of issues related with identifying the
important ingredients needed for quantum information processing. We discuss the
Deutsch-Jozsa algorithm, the Shor algorithm, the Grover algorithm and the power
of a single qubit class of algorithms. One section is dedicated to cluster
states where entanglement is crucial, but its precise role is highly
counter-intuitive. Here we see that distinguishability becomes a more useful
concept.Comment: 8 pages, no figure
Integrable discretizations of derivative nonlinear Schroedinger equations
We propose integrable discretizations of derivative nonlinear Schroedinger
(DNLS) equations such as the Kaup-Newell equation, the Chen-Lee-Liu equation
and the Gerdjikov-Ivanov equation by constructing Lax pairs. The discrete DNLS
systems admit the reduction of complex conjugation between two dependent
variables and possess bi-Hamiltonian structure. Through transformations of
variables and reductions, we obtain novel integrable discretizations of the
nonlinear Schroedinger (NLS), modified KdV (mKdV), mixed NLS, matrix NLS,
matrix KdV, matrix mKdV, coupled NLS, coupled Hirota, coupled Sasa-Satsuma and
Burgers equations. We also discuss integrable discretizations of the
sine-Gordon equation, the massive Thirring model and their generalizations.Comment: 24 pages, LaTeX2e (IOP style), final versio
Minard revisited: exploring augmented reality in information design
This study intends to test and confirm the interest and viability of incorporating augmented reality (AR) technologies in cultural mediation driven by information design, focusing on narrative representation. It is specifically intended to explore semantic relations between reality and virtuality in augmented narratives, ie. expanded narratives through the multimodality enhanced by the use of interactive processes based in augmented reality systems. Departing from Charles Minard’s Figurative Map (1869), three experiments were conducted, in order to reinterpret the program embodied in that artefact, testing several hypotheses in which, through augmented reality, the combination of different modes and media configures different semantic relations between real and virtual. The action-reflection approach undertaken with Figurative Map experiments enabled us to observe and openly systematize different augmented reality functions regarding the physical instance, which can potentially expand traditional forms of information design. Although they are not entirely extrapolatable, the proposal of virtual functions regarding reality were repurposed and adapted from the illustration field, specifically from the semantic relation between text and image. It is acknowledged that this is an open model to be reconsidered and reformulated through several action-reflection iterations and fostered through the narrative study.publishe
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