2,893 research outputs found
Proposal for an experiment to search for Randall-Sundrum type corrections to Newton's law of gravitation
String theory, as well as the string inspired brane-world models such as the
Randall-Sundrum (RS) one, suggest a modification of Newton's law of gravitation
at small distance scales. Search for modifications of standard gravity is an
active field of research in this context. It is well known that short range
corrections to gravity would violate the Newton-Birkhoff theorem. Based on
calculations of RS type non-Newtonian forces for finite size spherical bodies,
we propose a torsion balance based experiment to search for the effects of
violation of this celebrated theorem valid in Newtonian gravity as well as the
general theory of relativity. We explain the main principle behind the
experiment and provide detailed calculations suggesting optimum values of the
parameters of the experiment. The projected sensitivity is sufficient to probe
the Randall-Sundrum parameter up to 10 microns.Comment: 4 pages and 5 figures, figures improved, minor clarifications and few
references added, final version to appear in PRD (rapid communications
Reproductive tract infections among married women in peri-urban areas of Karachi, Pakistan: A population-based study
Background: Reproductive Tract Infections (RTIs) is a major public health problem. In Pakistan, there is dearth of information about the prevalence of RTIs among women and their health seeking behavior. A study was conducted to determine the prevalence, number and types of RTIs among women residing in squatter settlements in Karachi and their health seeking behavior.Methods: The respondents were married non-pregnant women aged 15–49 years residing in peri-urban areas of Karachi, Pakistan. The interviews with women were followed by their physical and pelvic examinations. Samples swabs collected from vagina and endocervix were tested in laboratory.Results: Overall, 23.8% of the women had laboratory-diagnosed RTIs. Nearly 2.6% had trichomoniasis and 1.7% were positive for syphilis. Bacterial vaginosis was diagnosed in 8.8% and vaginal candidiasis in 13.2 %.Conclusion: The study indicates a high prevalence of RTIs among women with Bacterial vaginosis and trichomoniasis to be the most prevalent endogenous infection and STI respectively. The women considered many symptoms as normal and did not seek treatment. These are the cases that have a potential to remain infected for a long time
A symmetry for vanishing cosmological constant
Two different realizations of a symmetry principle that impose a zero
cosmological constant in an extra-dimensional set-up are studied. The symmetry
is identified by multiplication of the metric by minus one. In the first
realization of the symmetry this is provided by a symmetry transformation that
multiplies the coordinates by the imaginary number i. In the second realization
this is accomplished by a symmetry transformation that multiplies the metric
tensor by minus one. In both realizations of the symmetry the requirement of
the invariance of the gravitational action under the symmetry selects out the
dimensions given by D = 2(2n+1), n=0,1,2,... and forbids a bulk cosmological
constant. Another attractive aspect of the symmetry is that it seems to be more
promising for quantization when compared to the usual scale symmetry. The
second realization of the symmetry is more attractive in that it is posible to
make a possible brane cosmological constant zero in a simple way by using the
same symmetry, and the symmetry may be identified by reflection symmetry in
extra dimensions.Comment: Talk in the conference IRGAC 2006, 2nd International Conference on
Quantum Theories and Renormalization Group in Gravity and Cosmology,
Barcelon
Robustness of One-Dimensional Photonic Bandgaps Under Random Variations of Geometrical Parameters
The supercell method is used to study the variation of the photonic bandgaps
in one-dimensional photonic crystals under random perturbations to thicknesses
of the layers. The results of both plane wave and analytical band structure and
density of states calculations are presented along with the transmission
cofficient as the level of randomness and the supercell size is increased. It
is found that higher bandgaps disappear first as the randomness is gradually
increased. The lowest bandgap is found to persist up to a randomness level of
55 percent.Comment: Submitted to Physical Review B on April 8 200
Aspects of Scalar Field Dynamics in Gauss-Bonnet Brane Worlds
The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to
a complicated Friedmann equation which simplifies to in the
asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to
whereas & give rise to high energy Gauss-Bonnet (GB) regime and
the standard GR respectively. Amazingly, while evolving from RS regime to high
energy GB limit, one passes through a GR like region which has important
implications for brane world inflation. For tachyon GB inflation with
potentials investigated in this paper, the scalar to
tensor ratio of perturbations is maximum around the RS region and is
generally suppressed in the high energy regime for the positive values of .
The ratio is very low for at all energy scales relative to GB inflation
with ordinary scalar field. The models based upon tachyon inflation with
polynomial type of potentials with generic positive values of turn out to
be in the observational contour bound at all energy scales varying
from GR to high energy GB limit. The spectral index improves for the
lower values of and approaches its scale invariant limit for in the
high energy GB regime. The ratio also remains small for large negative
values of , however, difference arises for models close to scale invariance
limit. In this case, the tensor to scale ratio is large in the GB regime
whereas it is suppressed in the intermediate region between RS and GB. Within
the frame work of patch cosmologies governed by , the behavior
of ordinary scalar field near cosmological singularity and the nature of
scaling solutions are distinguished for the values of .Comment: 15 pages, 10 eps figures; appendix on various scales in GB brane
world included and references updated; final version to appear in PR
Oscillation threshold of a clarinet model: a numerical continuation approach
This paper focuses on the oscillation threshold of single reed instruments.
Several characteristics such as blowing pressure at threshold, regime
selection, and playing frequency are known to change radically when taking into
account the reed dynamics and the flow induced by the reed motion. Previous
works have shown interesting tendencies, using analytical expressions with
simplified models. In the present study, a more elaborated physical model is
considered. The influence of several parameters, depending on the reed
properties, the design of the instrument or the control operated by the player,
are studied. Previous results on the influence of the reed resonance frequency
are confirmed. New results concerning the simultaneous influence of two model
parameters on oscillation threshold, regime selection and playing frequency are
presented and discussed. The authors use a numerical continuation approach.
Numerical continuation consists in following a given solution of a set of
equations when a parameter varies. Considering the instrument as a dynamical
system, the oscillation threshold problem is formulated as a path following of
Hopf bifurcations, generalizing the usual approach of the characteristic
equation, as used in previous works. The proposed numerical approach proves to
be useful for the study of musical instruments. It is complementary to
analytical analysis and direct time-domain or frequency-domain simulations
since it allows to derive information that is hardly reachable through
simulation, without the approximations needed for analytical approach
Quintessential Inflation on the Brane and the Relic Gravity Wave Background
Quintessential inflation describes a scenario in which both inflation and
dark energy (quintessence) are described by the same scalar field. In
conventional braneworld models of quintessential inflation gravitational
particle production is used to reheat the universe. This reheating mechanism is
very inefficient and results in an excessive production of gravity waves which
violate nucleosynthesis constraints and invalidate the model. We describe a new
method of realizing quintessential inflation on the brane in which inflation is
followed by `instant preheating' (Felder, Kofman & Linde 1999). The larger
reheating temperature in this model results in a smaller amplitude of relic
gravity waves which is consistent with nucleosynthesis bounds. The relic
gravity wave background has a `blue' spectrum at high frequencies and is a
generic byproduct of successful quintessential inflation on the brane.Comment: 9 pages, 5 eps figures. Discussion and one eps figure summarizing the
GB correction to steep brane world inflation added, typos corrected and
references added; final version to appear in PR
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