1,351 research outputs found

### Fluids confined in wedges and by edges: From cluster integrals to thermodynamic properties referred to different regions

Recently, new insights in the relation between the geometry of the vessel
that confines a fluid and its thermodynamic properties were traced through the
study of cluster integrals for inhomogeneous fluids. In this work I analyze the
thermodynamic properties of fluids confined in wedges or by edges, emphasizing
on the question of the region to which these properties refer. In this context,
the relations between the line-thermodynamic properties referred to different
regions are derived as analytic functions of the dihedral angle $\alpha$ , for
$0<\alpha<2\pi$ , which enables a unified approach to both edges and wedges. As
a simple application of these results, I analyze the properties of the confined
gas in the low-density regime. Finally, using recent analytic results for the
second cluster integral of the confined hard sphere fluid, the low density
behavior of the line thermodynamic properties is analytically studied up to
order two in the density for $0<\alpha<2\pi$ and by adopting different
reference regions.Comment: 8 pages, 7 figure

### Host Galaxies of Young Dust-Reddened Quasars

We present results on a multiwavelength campaign to identify the nature of dust-reddened Type 1 quasars. These quasars were selected by matching FIRST, 2MASS and very red optical counterparts with r' − K > 5. We find a very high fraction of Low Ionization Broad Absorption Line Quasars (LoBALs) among AGN selected with this method, perhaps a sign of quasar feedback. From X-ray observations and Balmer decrement measurements, the obscuring dust is most likely located in a cold absorber such as the host galaxy, rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample of these sources showed a very high fraction of interacting and merging systems. The quasars appear to be very young in which dust from the merging galaxies is still settling in. Spitzer IRS and MIPS data show star formation signatures and deep Silicate absorption features in these objects, but overall the quasar is the dominant source in the Mid-infrared

### An exact formalism to study the thermodynamic properties of hard-sphere systems under spherical confinement

This paper presents a modified grand canonical ensemble which provides a new
simple and efficient scheme to study few-body fluid-like inhomogeneous systems
under confinement. The new formalism is implemented to investigate the exact
thermodynamic properties of a hard sphere (HS) fluid-like system with up to
three particles confined in a spherical cavity. In addition, the partition
function of this system was used to analyze the surface thermodynamic
properties of the many-HS system and to derive the exact curvature dependence
of both the surface tension and adsorption in powers of the density. The
expressions for the surface tension and the adsorption were also obtained for
the many- HS system outside of a fixed hard spherical object. We used these
results to derive the dependence of the fluid-substrate Tolman length up to
first order in density.Comment: 6 figures. The paper includes new exact results about hard spheres
fluid-like system

### Fluids confined in wedges and by edges: Virial series for the line-thermodynamic properties of hard spheres

This work is devoted to analyze the relation between the thermodynamic properties of a confined fluid and the shape of its confining vessel. Recently, new insights in this topic were found through the study of cluster integrals for inhomogeneous fluids that revealed the dependence on the vessel shape of the low density behavior of the system. Here, the statistical mechanics and thermodynamics of fluids confined in wedges or by edges is revisited, focusing on their cluster integrals. In particular, the well known hard sphere fluid, which was not studied in this framework so far, is analyzed under confinement and its thermodynamic properties are analytically studied up to order two in the density. Furthermore, the analysis is extended to the confinement produced by a corrugated wall. These results rely on the obtained analytic expression for the second cluster integral of the confined hard sphere system as a function of the opening dihedral angle 0 < β < 2π. It enables a unified approach to both wedges and edges.Fil: Urrutia, Ignacio. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

### Mean properties and Free Energy of a few hard spheres confined in a spherical cavity

We use analytical calculations and event-driven molecular dynamics
simulations to study a small number of hard sphere particles in a spherical
cavity. The cavity is taken also as the thermal bath so that the system
thermalizes by collisions with the wall. In that way, these systems of two,
three and four particles, are considered in the canonical ensemble. We
characterize various mean and thermal properties for a wide range of number
densities. We study the density profiles, the components of the local pressure
tensor, the interface tension, and the adsorption at the wall. This spans from
the ideal gas limit at low densities to the high-packing limit in which there
are significant regions of the cavity for which the particles have no access,
due the conjunction of excluded volume and confinement. The contact density and
the pressure on the wall are obtained by simulations and compared to exact
analytical results. We also obtain the excess free energy for N=4, by using a
simulated-assisted approach in which we combine simulation results with the
knowledge of the exact partition function for two and three particles in a
spherical cavity.Comment: 11 pages, 9 figures and two table

### Two hard spheres in a pore: Exact Statistical Mechanics for different shaped cavities

The Partition function of two Hard Spheres in a Hard Wall Pore is studied
appealing to a graph representation. The exact evaluation of the canonical
partition function, and the one-body distribution function, in three different
shaped pores are achieved. The analyzed simple geometries are the cuboidal,
cylindrical and ellipsoidal cavities. Results have been compared with two
previously studied geometries, the spherical pore and the spherical pore with a
hard core. The search of common features in the analytic structure of the
partition functions in terms of their length parameters and their volumes,
surface area, edges length and curvatures is addressed too. A general framework
for the exact thermodynamic analysis of systems with few and many particles in
terms of a set of thermodynamic measures is discussed. We found that an exact
thermodynamic description is feasible based in the adoption of an adequate set
of measures and the search of the free energy dependence on the adopted measure
set. A relation similar to the Laplace equation for the fluid-vapor interface
is obtained which express the equilibrium between magnitudes that in extended
systems are intensive variables. This exact description is applied to study the
thermodynamic behavior of the two Hard Spheres in a Hard Wall Pore for the
analyzed different geometries. We obtain analytically the external work, the
pressure on the wall, the pressure in the homogeneous zone, the wall-fluid
surface tension, the line tension and other similar properties

### Quantum gravity corrections to particle interactions

An heuristic semiclassical procedure that incorporates quantum gravity
induced corrections in the description of photons and spin 1/2 fermions is
reviewed. Such modifications are calculated in the framework of loop quantum
gravity and they arise from the granular structure of space at short distances.
The resulting effective theories are described by power counting
nonrenormalizable actions which exhibit Lorentz violations at Planck length
scale. The modified Maxwell and Dirac equations lead to corrections of the
energy momentum relations for the corresponding particle at such scale. An
action for the relativistic point particle exhibiting such modified dispersion
relations is constructed and the first steps towards the study of a consistent
coupling between these effective theories are presented.Comment: 12 pages, no figures, MPL LaTeX style; Invited talk at the " First
IUCAA Meeting on the Interface of Gravitational and Quantum Realms", Pune,
17-21 December 200

### Spectral energy distributions of quasars selected in the mid-infrared

We present preliminary results on fitting of SEDs to 142 z>1 quasars selected
in the mid-infrared. Our quasar selection finds objects ranging in extinction
from highly obscured, type-2 quasars, through more lightly reddened type-1
quasars and normal type-1s. We find a weak tendency for the objects with the
highest far-infrared emission to be obscured quasars, but no bulk systematic
offset between the far-infrared properties of dusty and normal quasars as might
be expected in the most naive evolutionary schemes. The hosts of the type-2
quasars have stellar masses comparable to those of radio galaxies at similar
redshifts. Many of the type-1s, and possibly one of the type-2s require a very
hot dust component in addition to the normal torus emission.Comment: 4 pages, 2 figures, to appear in the proceedings of The Spectral
Energy Distribution of Galaxies, Preston, September 2011, eds R.J. Tuffs &
C.C. Popesc

### Closed-cycle, low-vibration 4 K cryostat for ion traps and other applications

In-vacuo cryogenic environments are ideal for applications requiring both low
temperatures and extremely low particle densities. This enables reaching long
storage and coherence times for example in ion traps, essential requirements
for experiments with highly charged ions, quantum computation, and optical
clocks. We have developed a novel cryostat continuously refrigerated with a
pulse-tube cryocooler and providing the lowest vibration level reported for
such a closed-cycle system with 1 W cooling power for a <5 K experiment. A
decoupling system suppresses vibrations from the cryocooler by three orders of
magnitude down to a level of 10 nm peak amplitudes in the horizontal plane.
Heat loads of about 40 W (at 45 K) and 1 W (at 4 K) are transferred from an
experimental chamber, mounted on an optical table, to the cryocooler through a
vacuum-insulated massive 120 kg inertial copper pendulum. The 1.4 m long
pendulum allows installation of the cryocooler in a separate, acoustically
isolated machine room. In the laser laboratory, we measured the residual
vibrations using an interferometric setup. The positioning of the 4 K elements
is reproduced to better than a few micrometer after a full thermal cycle to
room temperature. Extreme high vacuum on the $10^{-15}$ mbar level is achieved.
In collaboration with the Max-Planck-Intitut f\"ur Kernphysik (MPIK), such a
setup is now in operation at the Physikalisch-Technische Bundesanstalt (PTB)
for a next-generation optical clock experiment using highly charged ions

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