1,456 research outputs found
Can black holes be torn up by phantom dark energy in cyclic cosmology?
Infinitely cyclic cosmology is often frustrated by the black hole problem. It
has been speculated that this obstacle in cyclic cosmology can be removed by
taking into account a peculiar cyclic model derived from loop quantum cosmology
or the braneworld scenario, in which phantom dark energy plays a crucial role.
In this peculiar cyclic model, the mechanism of solving the black hole problem
is through tearing up black holes by phantom. However, using the theory of
fluid accretion onto black holes, we show in this paper that there exists
another possibility: that black holes cannot be torn up by phantom in this
cyclic model. We discussed this possibility and showed that the masses of black
holes might first decrease and then increase, through phantom accretion onto
black holes in the expanding stage of the cyclic universe.Comment: 6 pages, 2 figures; discussions adde
Modelling of InSAR (LOS) changes by means of 3D extended pressured bodies with free geometry. Application to Campi Flegrei.
InSAR measures can provide information about changes in distance between the ground and the satellite in radar
line-of-sight (LOS) direction. Sometimes, as in the case of volcanic activity, the corresponding ground deformations
can be modeled by means of pressure and/or mass sources. Usually, point sources and regular prolate or
oblate bodies are used as source geometry for deformation. In this communication, we show a new method for
non-linear inversion of position and gravity changes as produced by extended bodies with a free geometry. Their
structures are described as aggregation of elemental sources with anomalous density and pressure, and they are
modeled to fit the whole data and to keep some regularity conditions. A growth process permits to build general
geometrical configurations. The method is tested by application to data of gravity and InSAR (LOS data for ascending
and descending orbits) for the volcanic area of Campi Flegrei (Italy). Results are drawn with respect a
structural gravimetric model and compared with previous models
Jamming coverage in competitive random sequential adsorption of binary mixture
We propose a generalized car parking problem where cars of two different
sizes are sequentially parked on a line with a given probability . The free
parameter interpolates between the classical car parking problem of only
one car size and the competitive random sequential adsorption (CRSA) of a
binary mixture. We give an exact solution to the CRSA rate equations and find
that the final coverage, the jamming limit, of the line is always larger for a
binary mixture than for the uni-sized case. The analytical results are in good
agreement with our direct numerical simulations of the problem.Comment: 4 pages 2-column RevTeX, Four figures, (there was an error in the
previous version. We replaced it (including figures) with corrected and
improved version that lead to new results and conclusions
Kinetics and Jamming Coverage in a Random Sequential Adsorption of Polymer Chains
Using a highly efficient Monte Carlo algorithm, we are able to study the
growth of coverage in a random sequential adsorption (RSA) of self-avoiding
walk (SAW) chains for up to 10^{12} time steps on a square lattice. For the
first time, the true jamming coverage (theta_J) is found to decay with the
chain length (N) with a power-law theta_J propto N^{-0.1}. The growth of the
coverage to its jamming limit can be described by a power-law, theta(t) approx
theta_J -c/t^y with an effective exponent y which depends on the chain length,
i.e., y = 0.50 for N=4 to y = 0.07 for N=30 with y -> 0 in the asymptotic limit
N -> infinity.Comment: RevTeX, 5 pages inclduing figure
Superprocesses as models for information dissemination in the Future Internet
Future Internet will be composed by a tremendous number of potentially
interconnected people and devices, offering a variety of services, applications
and communication opportunities. In particular, short-range wireless
communications, which are available on almost all portable devices, will enable
the formation of the largest cloud of interconnected, smart computing devices
mankind has ever dreamed about: the Proximate Internet. In this paper, we
consider superprocesses, more specifically super Brownian motion, as a suitable
mathematical model to analyse a basic problem of information dissemination
arising in the context of Proximate Internet. The proposed model provides a
promising analytical framework to both study theoretical properties related to
the information dissemination process and to devise efficient and reliable
simulation schemes for very large systems
advanced electric propulsion diagnostic tools at iom
Abstract Recently, we have set up an Advanced Electric Propulsion Diagnostic (AEPD) platform [1] , which allows for the in-situ measurement of a comprehensive set of thruster performance parameters. The platform utilizes a five-axis-movement system for precise positioning of the thruster with respect to the diagnostic heads. In the first setup (AEPD1) an energy-selective mass spectrometer (ESMS) and a miniaturized Faraday probe for ion beam characterization, a telemicroscope and a triangular laser head for measuring the erosion of mechanical parts, and a pyrometer for surface temperature measurements were integrated. The capabilities of the AEPD1 platform were demonstrated with two electric propulsion thrusters, a gridded ion thruster RIT 22 (Airbus Defence & Space, Germany, [13]) and a Hall effect thruster SPT 100D EM1 (EDB Fakel, Russia, [1] , [4] ), in two different vacuum facilities
Gravitational Coupling and Dynamical Reduction of The Cosmological Constant
We introduce a dynamical model to reduce a large cosmological constant to a
sufficiently small value. The basic ingredient in this model is a distinction
which has been made between the two unit systems used in cosmology and particle
physics. We have used a conformal invariant gravitational model to define a
particular conformal frame in terms of large scale properties of the universe.
It is then argued that the contributions of mass scales in particle physics to
the vacuum energy density should be considered in a different conformal frame.
In this manner, a decaying mechanism is presented in which the conformal factor
appears as a dynamical field and plays a key role to relax a large effective
cosmological constant. Moreover, we argue that this model also provides a
possible explanation for the coincidence problem.Comment: To appear in GR
Bosonic Quartic Couplings at LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W-
gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q
q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After
a careful study of the backgrounds and how to extract them from the data, we
show that the process p p -> j j gamma l+ l- is potentially the most sensitive
to deviations from the Standard Model, improving the sensitivity to anomalous
couplings by up to a factor 10^4 (10^2) with respect to the present direct
(indirect) limits.Comment: 18 pages, 2 figures, revised versio
A model of the Universe including Dark Energy accounted for by both a Quintessence Field and a (negative) Cosmological Constant
In this work we present a model of the universe in which dark energy is
modelled explicitely with both a dynamical quintessence field and a
cosmological constant. Our results confirm the possibility of a future
collapsing universe (for a given region of the parameter space), which is
necessary for a consistent formulation of string theory and quantum field
theory. We have also reproduced the measurements of modulus distance from
supernovae with good accuracy.Comment: 11 pages, 4 figures, only the results for the single exponential
potential are preserved. One author added. Some changes in the reference
section. Submitted to Physical Review
The relative age effect on physical fitness in preschool children
The aim of the present study was to investigate the existence of a relative age effect (RAE) on physical fitness of preschoolers. Anthropometry and physical fitness were assessed in 3147 children (3–5 years old) using the PREFIT battery. Based on the birth year, participants were divided into 3year groups (3-, 4- and 5-years). Within each year group, 4quarter groups were created: quarter 1, preschoolers born from January to March; quarter 2, from April to June; quarter 3, from July to September; quarter 4, from October to December. The MANCOVA analysis revealed a main effect of year group (Wilks’ ¿ = 0.383; F10, 5996 = 369.64; p < 0.001, ¿p 2 = 0.381) and of quarter (Wilks’ ¿ = 0.874; F15, 8276.6 = 27.67; p < 0.001; ¿p 2 = 0.044) over the whole battery of tests. To the best of our knowledge, this is the first study to report the existence of RAE at the preschool stage. In general, performance improved as the relative age increased (i.e., those born in quarter 1 performed better than those in the other quarters). Individualization strategies should be addressed within the same academic year not only in elementary or secondary years but also in preschoolers
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