71 research outputs found

### Módulo de control de pacientes y pago de tratamientos dentales del sistema de gestión de la clínica de odontopediatría, en la Facultad de Odontología de la Universidad de San Carlos de Guatemala

Se describe el proyecto de creación del módulo de control de pacientes y pago de tratamientos dentales de la Clínica Dental de Odontopediatría, en la Facultad de Odontología de la Universidad de San Carlos de Guatemala.
El documento trata de mostrar al interesado el trabajo realizado para la construcción del sistema, incluyendo la concepción inicial, el análisis y el diseño de la solución. El informe se encuentra divido en cuatro capítulos principales: Fase de Investigación, Fase Técnico Profesional, Sistema de Gestión de la Práctica Clínica y Fase de Enseñanza Aprendizaje

### Constraints for hypothetical interactions from a recent demonstration of the Casimir force and some possible improvements

The Casimir force is calculated in the configuration of a spherical lens and
a disc of finite radius covered by $Cu$ and $Au$ thin layers which was used in
a recent experiment. The correction to the Casimir force due to finiteness of
the disc radius is shown to be negligible. Also the corrections are discussed
due to the finite conductivity, large-scale and short-scale deviations from the
perfect shape of the bounding surfaces and the temperature correction. They
were found to be essential when confronting the theoretical results with
experimental data. Both Yukawa-type and power-law hypothetical forces are
computed which may act in the configuration under consideration due to the
exchange of light and/or massless elementary particles between the atoms of the
lens and the disc. New constraints on the constants of these forces are
determined which follow from the fact that they were not observed within the
limits of experimental errors. For Yukawa-type forces the new constraints are
up to 30 times stronger than the best ones known up today. A possible
improvement of experimental parameters is proposed which gives the possibility
to strengthen constraints on Yukawa-type interactions up to $10^4$ times and on
power-law interactions up to several hundred times.Comment: 15 pages, 3 figures, subm. to Phys. Rev.

### Constraints on Non-Newtonian Gravity from Recent Casimir Force Measurements

Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.Comment: 20 pages, crckbked.cls is used, to be published in: Proceedings of
the 18th Course of the School on Cosmology and Gravitation: The Gravitational
Constant. Generalized Gravitational Theories and Experiments (30 April- 10
May 2003, Erice). Ed. by G. T. Gillies, V. N. Melnikov and V. de Sabbata,
20pp. (Kluwer, in print, 2003

### Particle creation in a Robertson-Walker Universe revisited

We reanalyze the problem of particle creation in a 3+1 spatially closed
Robertson-Walker space-time. We compute the total number of particles produced
by this non-stationary gravitational background as well as the corresponding
total energy and find a slight discrepancy between our results and those
recently obtained in the literatur

### Higher order conductivity corrections to the Casimir force

The finite conductivity corrections to the Casimir force in two
configurations are calculated in the third and fourth orders in relative
penetration depth of electromagnetic zero oscillations into the metal. The
obtained analytical perturbation results are compared with recent computations.
Applications to the modern experiments are discussed.Comment: 15 pages, 4 figure

### On "Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field"

Recently the paper "Schwinger Mechanism for Gluon Pair Production in the
Presence of Arbitrary Time Dependent Chromo-Electric Field" by G. C. Nayak was
published [Eur. Phys. J. C 59, 715 (2009); arXiv:0708.2430]. Its aim is to
obtain an exact expression for the probability of non-perturbative gluon pair
production per unit time per unit volume and per unit transverse momentum in an
arbitrary time-dependent chromo-electric background field. We believe that the
obtained expression is open to question. We demonstrate its inconsistency on
some well-known examples. We think that this is a consequence of using the
so-called "shift theorem" [arXiv:hep-th/0609192] in deriving the expression for
the probability. We make some critical comments on the theorem and its
applicability to the problem in question.Comment: 4 page

### Analytic approach to the thermal Casimir force between metal and dielectric

The analytic asymptotic expressions for the Casimir free energy, pressure and
entropy at low temperature in the configuration of one metal and one dielectric
plate are obtained. For this purpose we develop the perturbation theory in a
small parameter proportional to the product of the separation between the
plates and the temperature. This is done using both the simplified model of an
ideal metal and of a dielectric with constant dielectric permittivity and for
the realistic case of the metal and dielectric with frequency-dependent
dielectric permittivities. The analytic expressions for all related physical
quantities at high temperature are also provided. The obtained analytic results
are compared with numerical computations and good agreement is found. We
demonstrate for the first time that the Lifshitz theory, when applied to the
configuration of metal-dielectric, satisfies the requirements of thermodynamics
if the static dielectric permittivity of a dielectric plate is finite. If it is
infinitely large, the Lifshitz formula is shown to violate the Nernst heat
theorem. The implications of these results for the thermal quantum field theory
in Matsubara formulation and for the recent measurements of the Casimir force
between metal and semiconductor surfaces are discussed.Comment: 34 pages, 3 figures, elsart.cls is used, to appear in Ann. Phys.
(N.Y.), 200

### Microscopic origin of universality in Casimir forces

The microscopic mechanisms for universality of Casimir forces between
macroscopic conductors are displayed in a model of classical charged fluids.
The model consists of two slabs in empty space at distance $d$ containing
classical charged particles in thermal equilibrium (plasma, electrolyte). A
direct computation of the average force per unit surface yields, at large
distance, the usual form of the Casimir force in the classical limit (up to a
factor 2 due to the fact that the model does not incorporate the magnetic part
of the force). Universality originates from perfect screening sum rules obeyed
by the microscopic charge correlations in conductors. If one of the slabs is
replaced by a macroscopic dielectric medium, the result of Lifshitz theory for
the force is retrieved. The techniques used are Mayer expansions and integral
equations for charged fluids.Comment: 31 pages, 0 figures, submitted to Journal of Statistical Physic

### The Casimir effect for parallel plates at finite temperature in the presence of one fractal extra compactified dimension

We discuss the Casimir effect for massless scalar fields subject to the
Dirichlet boundary conditions on the parallel plates at finite temperature in
the presence of one fractal extra compactified dimension. We obtain the Casimir
energy density with the help of the regularization of multiple zeta function
with one arbitrary exponent and further the renormalized Casimir energy density
involving the thermal corrections. It is found that when the temperature is
sufficiently high, the sign of the Casimir energy remains negative no matter
how great the scale dimension $\delta$ is within its allowed region. We derive
and calculate the Casimir force between the parallel plates affected by the
fractal additional compactified dimension and surrounding temperature. The
stronger thermal influence leads the force to be stronger. The nature of the
Casimir force keeps attractive.Comment: 14 pages, 2 figure

### Surface-impedance approach solves problems with the thermal Casimir force between real metals

The surface impedance approach to the description of the thermal Casimir
effect in the case of real metals is elaborated starting from the free energy
of oscillators. The Lifshitz formula expressed in terms of the dielectric
permittivity depending only on frequency is shown to be inapplicable in the
frequency region where a real current may arise leading to Joule heating of the
metal. The standard concept of a fluctuating electromagnetic field on such
frequencies meets difficulties when used as a model for the zero-point
oscillations or thermal photons in the thermal equilibrium inside metals.
Instead, the surface impedance permits not to consider the electromagnetic
oscillations inside the metal but taking the realistic material properties into
account by means of the effective boundary condition. An independent derivation
of the Lifshitz-type formulas for the Casimir free energy and force between two
metal plates is presented within the impedance approach. It is shown that they
are free of the contradictions with thermodynamics which are specific to the
usual Lifshitz formula for dielectrics in combination with the Drude model. We
demonstrate that in the impedance approach the zero-frequency contribution is
uniquely fixed by the form of impedance function and does not need any of the
ad hoc prescriptions intensively discussed in the recent literature. As an
example, the computations of the Casimir free energy between two gold plates
are performed at different separations and temperatures. It is argued that the
surface impedance approach lays a reliable framework for the future
measurements of the thermal Casimir force.Comment: 21 pages, 3 figures, to appear in Phys. Rev.

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