1,430 research outputs found
Leptogenesis from Pseudo-Scalar Driven Inflation
We examine recent claims for a considerable amount of leptogenesis, in some
inflationary scenarios, through the gravitational anomaly in the lepton number
current. We find that when the short distances contributions are properly
included the amount of lepton number generated is actually much smaller.Comment: JHEP style, 11 pages. Corrected typ
Assessment of the Availability and Accessibility of Emergency Obstetric Care Services in Murtala Mohammed Specialist Hospital, Kano, Nigeria
Background: The availability of emergency obstetric care services is measured by the number of facilities that perform all the signal functions in relation to the size of the population. When personnel have carried out the seven signal functions of basic emergency obstetric care services in the 3-month period before the assessment, the facility is considered to be a fully functioning basic facility. This study assessed the availability and accessibility of Emergency Obstetrics Care (EmOC) Service provision.Methodology: A cross-sectional descriptive study was carried out in Murtala Muhammad Specialist Hospital among 246 women presenting with obstetric emergency using client exit interview, check list and record review from an adapted UNDP/WHO/UNICEF EMOC performance standard for hospital. Data analysis was done with SSPS version 20 and Permission was obtained from the hospital and consent from the clients.Result: The study revealed that the laboratory was in good shape with a score of 11 out of the 15 points. In the labour ward, the percentage availability was 63.3%. In the theatre, percentage availability was 85.4%. The hospital offers comprehensive EmOC service. The Obstetrics and Gynaecology department had only 11 medical doctors, 126 nurse-midwives training, 1 anaesthesiologist, 1 pharmacist and few other auxiliary workers. Out of the total of 204 health personnel in this department, only 13 (6.4%) were trained in EmOC service.Conclusion: The human resources availability and equipments needed for the provision of EmOC services were inadequate when compared with the performance standard adopted. Geographical access was poor as majority of the respondents had to travel over long distances to utilize the facility. Therefore, there is need for the staff to be trained on EmOC among others
Accelerated expansion of the universe driven by tachyonic matter
It is an accepted practice in cosmology to invoke a scalar field with
potential when observed evolution of the universe cannot be
reconciled with theoretical prejudices. Since one function-degree-of-freedom in
the expansion factor can be traded off for the function , it is
{\it always} possible to find a scalar field potential which will reproduce a
given evolution. I provide a recipe for determining from in
two cases:(i) Normal scalar field with Lagrangian used in quintessence/dark energy
models. (ii) A tachyonic field with Lagrangian , motivated by recent string theoretic
results. In the latter case, it is possible to have accelerated expansion of
the universe during the late phase in certain cases. This suggests a string
theory based interpretation of the current phase of the universe with tachyonic
condensate acting as effective cosmological constant.Comment: 4 pages; uses revtex
On the Initial Conditions for Brane Inflation
String theory gives rise to various mechanisms to generate primordial
inflation, of which ``brane inflation'' is one of the most widely considered.
In this scenario, inflation takes place while two branes are approaching each
other, and the modulus field representing the separation between the branes
plays the role of the inflaton field. We study the phase space of initial
conditions which can lead to a sufficiently long period of cosmological
inflation, and find that taking into account the possibility of nonvanishing
initial momentum can significantly change the degree of fine tuning of the
required initial conditions.Comment: 11 pages, 2 figure
Absence of self-averaging in the complex admittance for transport through random media
A random walk model in a one dimensional disordered medium with an
oscillatory input current is presented as a generic model of boundary
perturbation methods to investigate properties of a transport process in a
disordered medium. It is rigorously shown that an admittance which is equal to
the Fourier-Laplace transform of the first-passage time distribution is
non-self-averaging when the disorder is strong. The low frequency behavior of
the disorder-averaged admittance, where , does not coincide with the low frequency behavior of the admittance for any
sample, . It implies that the Cole-Cole plot of
appears at a different position from the Cole-Cole plots of of any
sample. These results are confirmed by Monte-Carlo simulations.Comment: 7 pages, 2 figures, published in Phys. Rev.
Inflation and Brane Gases
We investigate a new way of realizing a period of cosmological inflation in
the context of brane gas cosmology. It is argued that a gas of co-dimension one
branes, out of thermal equilibrium with the rest of the matter, has an equation
of state which can - after stabilization of the dilaton - lead to power-law
inflation of the bulk. The most promising implementation of this mechanism
might be in Type IIB superstring theory, with inflation of the three large
spatial dimensions triggered by ``stabilized embedded 2-branes''. Possible
applications and problems with this proposal are discussed.Comment: 7 pages, uses REVTeX, version to appear in Phys. Rev.
Survival and residence times in disordered chains with bias
We present a unified framework for first-passage time and residence time of
random walks in finite one-dimensional disordered biased systems. The
derivation is based on exact expansion of the backward master equation in
cumulants. The dependence on initial condition, system size, and bias strength
is explicitly studied for models with weak and strong disorder. Application to
thermally activated processes is also developed.Comment: 13 pages with 2 figures, RevTeX4; v2:minor grammatical changes, typos
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Can the clustered dark matter and the smooth dark energy arise from the same scalar field ?
Cosmological observations suggest the existence of two different kinds of
energy densities dominating at small ( Mpc) and large ( Mpc) scales. The dark matter component, which dominates at small scales,
contributes and has an equation of state while
the dark energy component, which dominates at large scales, contributes
and has an equation of state . It is
usual to postulate wimps for the first component and some form of scalar field
or cosmological constant for the second component. We explore the possibility
of a scalar field with a Lagrangian L =- V(\phi) \sqrt{1 - \del^i \phi \del_i
\phi} acting as {\it both} clustered dark matter and smoother dark energy and
having a scale dependent equation of state. This model predicts a relation
between the ratio of the energy densities of the
two dark components and expansion rate of the universe (with ) in the form . For , we get
which is consistent with observations.Comment: Revised to match the published version. Minor changes and a reference
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Supersymmetry Breaking and Dilaton Stabilization in String Gas Cosmology
In this Note we study supersymmetry breaking via gaugino condensation in
string gas cosmology. We show that the same gaugino condensate which is
introduced to stabilize the dilaton breaks supersymmetry. We study the
constraints on the scale of supersymmetry breaking which this mechanism leads
to.Comment: 11 page
The second and third Sonine coefficients of a freely cooling granular gas revisited
In its simplest statistical-mechanical description, a granular fluid can be
modeled as composed of smooth inelastic hard spheres (with a constant
coefficient of normal restitution ) whose velocity distribution
function obeys the Enskog-Boltzmann equation. The basic state of a granular
fluid is the homogeneous cooling state, characterized by a homogeneous,
isotropic, and stationary distribution of scaled velocities, .
The behavior of in the domain of thermal velocities ()
can be characterized by the two first non-trivial coefficients ( and
) of an expansion in Sonine polynomials. The main goals of this paper are
to review some of the previous efforts made to estimate (and measure in
computer simulations) the -dependence of and , to report new
computer simulations results of and for two-dimensional systems,
and to investigate the possibility of proposing theoretical estimates of
and with an optimal compromise between simplicity and accuracy.Comment: 12 pages, 5 figures; v2: minor change
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