7,159 research outputs found
Casimir Effect in the Presence of Minimal Lengths
It is expected that the implementation of minimal length in quantum models
leads to a consequent lowering of Planck's scale. In this paper, using the
quantum model with minimal length of Kempf et al \cite{kempf0}, we examine the
effect of the minimal length on the Casimir force between parallel plates.Comment: 10 pages, 2 figure
Nitrogen, helium, and argon reveal the magmatic signature of fumarole gases and episodes of outgassing from upper-crustal magma reservoirs. The case of the Nisyros caldera (Aegean Arc, Greece)
The chemical composition of gases emitted by active volcanoes reflects both magma degassing and
shallower processes, such as fluid-rock hydrothermal interaction and mixing with atmospheric-derived
fluids. Untangling the magmatic fluid endmember within surface gas emission is therefore challenging,
even with the use of well-known magma degassing tracers such as noble gases. Here, we investigate
the deep magmatic fluid composition at the Nisyros caldera (Aegean Arc, Greece) by measuring nitrogen
and noble gas abundances and isotopes in naturally degassing fumaroles. Gas samples were collected
from 32 fumarolic vents at water-boiling temperature between 2018 and 2021. These fumaroles are
admixtures of magmatic fluids typical of subduction zones, groundwater (or air saturated water, ASW),
and air. The N2, He, and Ar composition of the magmatic endmember is calculated by reverse mixing
modeling and shows N2/He = 31.8 ± 4.5, N2/Ar = 281.6, d15N = +7 ± 3 ‰, 3He/4He = 6.2 Ra (where Ra is
air 3He/4He), and 40Ar/36Ar = 551.6 ± 19.8. Although N2/He is significantly low with respect to typical values
for arc volcanoes (1,000–10,000), the contribution of subducted sediments to the Aegean Arc magma
generation is reflected by the positive d15N values of Nisyros fumaroles. The low N2/He ratio indicates
N2-depletion due to solubility-controlled differential degassing of an upper-crustal silicic (dacitic/
rhyodacitic) melt in a high-crystallinity reservoir. We compare our 2018–2021 data with N2, He, and
Ar values collected from the same fumaroles during a hydrothermal unrest following the seismic crisis
in 1996–1997. Results show additions of both magmatic fluid and ASW during this unrest. In the same
period, fumarolic vents display an increase in magmatic species relative to hydrothermal gas, such as
CO2/CH4 and He/CH4 ratios, an increase of 50 C in the equilibrium temperature of the hydrothermal
system (up to 325 C), and greater amounts of vapor separation. These variations reflect an episode of
magmatic fluid expulsion during the seismic crisis. The excess of heat and mass supplied by the
magmatic fluid injection is then dissipated through boiling of deeper and peripheral parts of the
hydrothermal system. Reverse mixing modeling of fumarolic N2-He-Ar has therefore important ramifications
not only to disentangle the magmatic signature from gases emitted during periods of dormancy, but
also to trace episodes of magmatic outgassing and better understand the state of the upper crustal
reservoir
Pedicle screw augmentation with bone cement enforced Vicryl mesh
Copia digital. Madrid : Ministerio de EducaciĂłn, Cultura y Deporte, 201
Co-axial dual-core resonant leaky fibre for optical amplifiers
We present a co-axial dual-core resonant leaky optical fibre design, in which
the outer core is made highly leaky. A suitable choice of parameters can enable
us to resonantly couple power from the inner core to the outer core. In a
large-core fibre, such a resonant coupling can considerably increase the
differential leakage loss between the fundamental and the higher order modes
and can result in effective single-mode operation. In a small-core single-mode
fibre, such a coupling can lead to sharp increase in the wavelength dependent
leakage loss near the resonant wavelength and can be utilized for the
suppression of amplified spontaneous emission and thereby gain equalization of
an optical amplifier. We study the propagation characteristics of the fibre
using the transfer matrix method and present an example of each, the
large-mode-area design for high power amplifiers and the wavelength tunable
leakage loss design for inherent gain equalization of optical amplifiers.Comment: 6 page
Casimir Energy of a BEC: From Moderate Interactions to the Ideal Gas
Considering the Casimir effect due to phononic excitations of a weakly
interacting dilute {BEC}, we derive a re-normalized expression for the zero
temperature Casimir energy of a {BEC} confined to a parallel
plate geometry with periodic boundary conditions. Our expression is formally
equivalent to the free energy of a bosonic field at finite temperature, with a
nontrivial density of modes that we compute analytically. As a function of the
interaction strength, smoothly describes the transition from
the weakly interacting Bogoliubov regime to the non-interacting ideal {BEC}.
For the weakly interacting case, reduces to leading order to
the Casimir energy due to zero-point fluctuations of massless phonon modes. In
the limit of an ideal Bose gas, our result correctly describes the Casimir
energy going to zero.Comment: 12 pages, 3 figures, accepted for publication in JPA. New version
with corrected typos and an additional appendi
Bianchi I Quantum cosmology in the Bergmann-Wagoner theory
The Wheeler-DeWitt equation is considered in the context of generalized
scalar-tensor theories of gravitation for Bianchi type I cosmology. Exact
solutions are found for two selfinteracting potentials and arbitary coupling
function. The WKB wavefunctions are obtained and a family of solutions
satisfying the Hawking-Page regularity conditions of wormholes are found.Comment: 12 pages, Latex fil
Time ordering and counting statistics
The basic quantum mechanical relation between fluctuations of transported
charge and current correlators is discussed. It is found that, as a rule, the
correlators are to be time-ordered in an unusual way. Instances where the
difference with the conventional ordering matters are illustrated by means of a
simple scattering model. We apply the results to resolve a discrepancy
concerning the third cumulant of charge transport across a quantum point
contact.Comment: 19 pages, 1 figure; inconsequential mistake and typos correcte
- …