5,987 research outputs found
Recommended from our members
Observations related to chronologic and gynecologic age in pregnant adolescents.
A low chronologic age (less than or equal to 15 years) and low gynecologic age (less than or equal to 2 years) have been considered factors that increase medical complications among adolescent pregnant women. Gynecologic age (GA) is defined in this study as age in years at conception minus age at menarche. Two hundred twelve consecutive pregnant teenagers were followed prospectively in the Teen OB Clinic at the University of California, San Diego Medical Center, between August 1978 and July 1981. The clinic population consisted of 37.3 percent Whites, 35.8 percent Hispanics, 20.8 percent Blacks, and 6.1 percent other (mostly Indochinese). Sixty-eight percent of the patients were funded by MediCal. The patient population was divided by chronological age (CA) at conception into those 15 years or less or 16 years or older. A low chronological age was found to be a significant risk factor for premature rupture of membranes. Teenagers with a low gynecologic age (less than or equal to 2) had a lower mean pre-pregnancy weight and body mass index (Kg/M2) than teenagers with a higher gynecologic age. In this study, we did not find that a low CA or GA was correlated with a higher frequency of pregnancy-induced hypertension, prenatal medical problems, obstetrical problems at labor or delivery, or an excessive number of low-birthweight infants
Tracing a relativistic Milky Way within the RAMOD measurement protocol
Advancement in astronomical observations and technical instrumentation
implies taking into account the general relativistic effects due the
gravitational fields encountered by the light while propagating from the star
to the observer. Therefore, data exploitation for Gaia-like space astrometric
mission (ESA, launch 2013) requires a fully relativistic interpretation of the
inverse ray-tracing problem, namely the development of a highly accurate
astrometric models in accordance with the geometrical environment affecting
light propagation itself and the precepts of the theory of measurement. This
could open a new rendition of the stellar distances and proper motions, or even
an alternative detection perspective of many subtle relativistic effects
suffered by light while it is propagating and subsequently recorded in the
physical measurements.Comment: Proceeding for "Relativity and Gravitation, 100 Years after Einstein
in Prague" to be published by Edition Open Access, revised versio
Quasiblack holes with pressure: General exact results
A quasiblack hole is an object in which its boundary is situated at a surface
called the quasihorizon, defined by its own gravitational radius. We elucidate
under which conditions a quasiblack hole can form under the presence of matter
with nonzero pressure. It is supposed that in the outer region an extremal
quasihorizon forms, whereas inside, the quasihorizon can be either nonextremal
or extremal. It is shown that in both cases, nonextremal or extremal inside, a
well-defined quasiblack hole always admits a continuous pressure at its own
quasihorizon. Both the nonextremal and extremal cases inside can be divided
into two situations, one in which there is no electromagnetic field, and the
other in which there is an electromagnetic field. The situation with no
electromagnetic field requires a negative matter pressure (tension) on the
boundary. On the other hand, the situation with an electromagnetic field
demands zero matter pressure on the boundary. So in this situation an
electrified quasiblack hole can be obtained by the gradual compactification of
a relativistic star with the usual zero pressure boundary condition. For the
nonextremal case inside the density necessarily acquires a jump on the
boundary, a fact with no harmful consequences whatsoever, whereas for the
extremal case the density is continuous at the boundary. For the extremal case
inside we also state and prove the proposition that such a quasiblack hole
cannot be made from phantom matter at the quasihorizon. The regularity
condition for the extremal case, but not for the nonextremal one, can be
obtained from the known regularity condition for usual black holes.Comment: 18 pages, no figures; improved introduction, added references,
calculations better explaine
The Formation of non-Keplerian Rings of Matter about Compact Stars
The formation of energetic rings of matter in a Kerr spacetime with an
outward pointing acceleration field does not appear to have previously been
noted as a relativistic effect. In this paper we show that such rings are a
gravimagneto effect with no Newtonian analog, and that they do not occur in the
static limit. The energy efficiency of these rings can, depending of the
strength of the acceleration field, be much greater than that of Keplerian
disks. The rings rotate in a direction opposite to that of compact star about
which they form. The size and energy efficiency of the rings depend on the
fundamental parameters of the spacetime as well as the strength the
acceleration field.Comment: 19 pages, 7 figures, 1 diagram. Figures are included in the text
using the "graphicx" package. If you do not have this package you can use
epsfig, or another package as long as you alter the tex file appropriately.
Alternatively you could print the figures out seperatel
Reissner-Nordstrom and charged gas spheres
The main point of this paper is a suggestion about the proper treatment of
the photon gas in a theory of stellar structure and other plasmas. This problem
arises in the study of polytropic gas spheres, where we have already introduced
some innovations. The main idea, already advanced in the contextof neutral,
homogeneous, polytropic stellar models, is to base the theory firmly on a
variational principle. Another essential novelty is to let mass distribution
extend to infinity, the boundary between bulk and atmosphere being defined by
an abrupt change in the polytropic index, triggered by the density. The logical
next step in this program is to include the effect of radiation, which is a
very significant complication since a full treatment would have to include an
account of ionization, thus fieldsrepresenting electrons, ions, photons,
gravitons and neutral atoms as well. In way of preparation, we consider models
that are charged but homogeneous, involving only gravity, electromagnetism and
a single scalar field that represents both the mass and the electric charge; in
short, anon-neutral plasma. While this work only represents a stage in the
development of a theory of stars, without direct application to physical
systems, it does shed some light on the meaning of the Reissner-Nordstrom
solution of the modified Einstein-Maxwell equations., with an application to a
simple system.Comment: 19 pages, plain te
Control of DNA minor groove width and Fis protein binding by the purine 2-amino group.
The width of the DNA minor groove varies with sequence and can be a major determinant of DNA shape recognition by proteins. For example, the minor groove within the center of the Fis-DNA complex narrows to about half the mean minor groove width of canonical B-form DNA to fit onto the protein surface. G/C base pairs within this segment, which is not contacted by the Fis protein, reduce binding affinities up to 2000-fold over A/T-rich sequences. We show here through multiple X-ray structures and binding properties of Fis-DNA complexes containing base analogs that the 2-amino group on guanine is the primary molecular determinant controlling minor groove widths. Molecular dynamics simulations of free-DNA targets with canonical and modified bases further demonstrate that sequence-dependent narrowing of minor groove widths is modulated almost entirely by the presence of purine 2-amino groups. We also provide evidence that protein-mediated phosphate neutralization facilitates minor groove compression and is particularly important for binding to non-optimally shaped DNA duplexes
Cosmological perturbations in -essence model
Subhorizon approximation is often used in cosmological perturbation theory.
In this paper, however, it is shown that the subhorizon approximation is not
always a good approximation at least in case of -essence model. We also show
that the sound speed given by -essence model exerts a huge influence on the
time evolution of the matter density perturbation, and the future observations
could clarify the differences between the CDM model and -essence
model.Comment: 21 pages, sentences and equations are corrected, conclusions are
changed a littl
Inhibition of inducible Nitric Oxide Synthase expression by an acetonic extract from Feijoa sellowiana Berg. fruits.
Feijoa sellowiana Berg. fruits and especially the acetonic extract have been shown to possess biological activities, although the responsible compounds have never been identified. The present study was designed to evaluate the anti-inflammatory activity of an acetonic extract from F. sellowiana Berg. fruits on the nitric oxide (NO) pathway, which plays an important role in inflammation. To this aim the J774 cell line, which expresses inducible nitric oxide synthase (iNOS) following stimulation with lipopolysaccharide (LPS), has been utilized, and the effects of this extract and its fractions on NO production, iNOS protein expression, and signal pathways involved in its regulation have been evaluated. This study demonstrates that at least some part of the anti-inflammatory activity of the acetonic extract is due to the suppression of NO production by flavone and stearic acid. The mechanism of this inhibition seems to be related to an action on the expression of the enzyme iNOS through the attenuation of nuclear factor ÎşB (NF-ÎşB) and/or mitogen-activated protein kinase (MAPK) activation
Black holes in scalar-tensor gravity
Hawking has proven that black holes which are stationary as the endpoint of
gravitational collapse in Brans--Dicke theory (without a potential) are no
different than in general relativity. We extend this proof to the much more
general class of scalar-tensor and f(R) gravity theories, without assuming any
symmetries apart from stationarity.Comment: v1: 4 pages; v2: typos corrected, published versio
A note on the factorization conjecture
We give partial results on the factorization conjecture on codes proposed by
Schutzenberger. We consider finite maximal codes C over the alphabet A = {a, b}
with C \cap a^* = a^p, for a prime number p. Let P, S in Z , with S = S_0 +
S_1, supp(S_0) \subset a^* and supp(S_1) \subset a^*b supp(S_0). We prove that
if (P,S) is a factorization for C then (P,S) is positive, that is P,S have
coefficients 0,1, and we characterize the structure of these codes. As a
consequence, we prove that if C is a finite maximal code such that each word in
C has at most 4 occurrences of b's and a^p is in C, then each factorization for
C is a positive factorization. We also discuss the structure of these codes.
The obtained results show once again relations between (positive)
factorizations and factorizations of cyclic groups
- …