1,163 research outputs found
Study of multiple hologram recording in lithium niobate
The results of detailed experimental and theoretical considerations relating to multiple hologram recording in lithium niobate are reported. The following problem areas are identified and discussed: (1) the angular selectivity of the stored holograms, (2) interference effects due to the crystal surfaces, (3) beam divergence effects, (4) material recording sensitivity, and (5) scattered light from material inhomogeneities
Study of multiple hologram recording in lithium niobate
The results of a number of theoretical and experimental studies relating to multiple hologram recording in lithium niobate are reported. The analysis of holographic gratings stored in lithium niobate has been extended to cover a more realistic range of physical situations. A new successful dynamic (feedback) theory for describing recording, nondestructive reading, erasure, enhancement, and angular sensitivity has been developed. In addition, the possible architectures of mass data storage systems have been studied
A laser scanner for 35mm film
The design, construction, and testing of a laser scanning system is described. The scanner was designed to deliver a scanned beam over a 2.54 cm by 2.54 cm or a 5.08 cm by 5.08 cm format. In order to achieve a scan resolution and rate comparable to that of standard television, an acousto-optic deflector was used for one axis of the scan, and a light deflecting galvanometer for deflection along the other axis. The acoustic optic deflector has the capability of random access scan controlled by a digital computer
Thickness dependent Curie temperatures of ferromagnetic Heisenberg films
We develop a procedure for calculating the magnetic properties of a
ferromagnetic Heisenberg film with single-ion anisotropy which is valid for
arbitrary spin and film thickness. Applied to sc(100) and fcc(100) films with
spin S=7/2 the theory yields the layer dependent magnetizations and Curie
temperatures of films of various thicknesses making it possible to investigate
magnetic properties of films at the interesting 2D-3D transition.Comment: 9 pages, 2 figures, accepted (Solid State Commun.
Extending the generalized Chaplygin gas model by using geometrothermodynamics
We use the formalism of geometrothermodynamics (GTD) to derive fundamental
thermodynamic equations that are used to construct general relativistic
cosmological models. In particular, we show that the simplest possible
fundamental equation, which corresponds in GTD to a system with no internal
thermodynamic interaction, describes the different fluids of the standard model
of cosmology. In addition, a particular fundamental equation with internal
thermodynamic interaction is shown to generate a new cosmological model that
correctly describes the dark sector of the Universe and contains as a special
case the generalized Chaplygin gas model.Comment: 18 pages, 7 figures. Section added: Basics aspects of
geometrothermodynamic
Specific heat anomalies of open quantum systems
The evaluation of the specific heat of an open, damped quantum system is a
subtle issue. One possible route is based on the thermodynamic partition
function which is the ratio of the partition functions of system plus bath and
of the bath alone. For the free damped particle it has been shown, however,
that the ensuing specific heat may become negative for appropriately chosen
environments. Being an open system this quantity then naturally must be
interpreted as the change of the specific heat obtained as the difference
between the specific heat of the heat bath coupled to the system degrees of
freedom and the specific heat of the bath alone. While this difference may
become negative, the involved specific heats themselves are always positive;
thus, the known thermodynamic stability criteria are perfectly guaranteed. For
a damped quantum harmonic oscillator, instead of negative values, under
appropriate conditions one can observe a dip in the difference of specific
heats as a function of temperature. Stylized minimal models containing a single
oscillator heat bath are employed to elucidate the occurrence of the anomalous
temperature dependence of the corresponding specific heat values. Moreover, we
comment on the consequences for the interpretation of the density of states
based on the thermal partitionfunction.Comment: 7 pages, 6 figures, new title and some modifications of the main tex
Macroscopic equations for the adiabatic piston
A simplified version of a classical problem in thermodynamics -- the
adiabatic piston -- is discussed in the framework of kinetic theory. We
consider the limit of gases whose relaxation time is extremely fast so that the
gases contained on the left and right chambers of the piston are always in
equilibrium (that is the molecules are uniformly distributed and their
velocities obey the Maxwell-Boltzmann distribution) after any collision with
the piston. Then by using kinetic theory we derive the collision statistics
from which we obtain a set of ordinary differential equations for the evolution
of the macroscopic observables (namely the piston average velocity and
position, the velocity variance and the temperatures of the two compartments).
The dynamics of these equations is compared with simulations of an ideal gas
and a microscopic model of gas settled to verify the assumptions used in the
derivation. We show that the equations predict an evolution for the macroscopic
variables which catches the basic features of the problem. The results here
presented recover those derived, using a different approach, by Gruber, Pache
and Lesne in J. Stat. Phys. 108, 669 (2002) and 112, 1177 (2003).Comment: 13 pages, 7 figures (revTeX4) The paper has been completely rewritten
with new derivation and results, supplementary information can be found at
http://denali.phys.uniroma1.it/~cencini/Papers/cppv07_supplements.pd
Maximal work extraction from quantum systems
Thermodynamics teaches that if a system initially off-equilibrium is coupled
to work sources, the maximum work that it may yield is governed by its energy
and entropy. For finite systems this bound is usually not reachable. The
maximum extractable work compatible with quantum mechanics (``ergotropy'') is
derived and expressed in terms of the density matrix and the Hamiltonian. It is
related to the property of majorization: more major states can provide more
work. Scenarios of work extraction that contrast the thermodynamic intuition
are discussed, e.g. a state with larger entropy than another may produce more
work, while correlations may increase or reduce the ergotropy.Comment: 5 pages, 0 figures, revtex
Geometrothermodynamics
We present the fundamentals of geometrothermodynamics, an approach to study
the properties of thermodynamic systems in terms of differential geometric
concepts. It is based, on the one hand, upon the well-known contact structure
of the thermodynamic phase space and, on the other hand, on the metric
structure of the space of thermodynamic equilibrium states. In order to make
these two structures compatible we introduce a Legendre invariant set of
metrics in the phase space, and demand that their pullback generates metrics on
the space of equilibrium states. We show that Weinhold's metric, which was
introduced {\it ad hoc}, is not contained within this invariant set. We propose
alternative metrics which allow us to redefine the concept of thermodynamic
length in an invariant manner and to study phase transitions in terms of
curvature singularities.Comment: Revised version, to be published in Jour. Math. Phy
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