185 research outputs found
Anemia Prevalence among Pregnant Women and Birth Weight in Five Areas in China
Objectives: To investigate the current prevalence of anemia among pregnant women in different areas of China and the association with birth weight and educational level. Methods: A total of 6,413 women aged 24-37 in the third trimester of pregnancy from five areas were randomly selected from all gravidas who gave birth in the hospitals from 1999 to 2003. Blood hemoglobin concentration (Hb) was measured by the cyanomethemoglobin method; Hb <110 g/l was considered as anemia. Results: The overall prevalence of anemia was 58.6%, ranging from 48.1 to 70.5% in the five areas. There was a significant difference in the prevalence of anemia between women who have mental jobs and those who have physical jobs (52.3 vs. 61.1%, p <0.01). The prevalence of anemia depended on the level of education: with 52.9, 62.4 and 66.5%, for college, secondary school and primary education, respectively, and the difference was statistically significant (p = 0.005). Results showed that higher birth weight was associated with Hb concentrations ranging from 90 to 140 g/l, whereas lower birth weight occurred below 80 g/l and above 140 g/l Hb. Conclusions: The prevalence of anemia in Chinese pregnant women was high both in rural areas and towns. Area of residence, education level and type of job influenced the prevalence of anemia. Low maternal Hb concentrations influenced birth weight
Formation of the seed black holes: a role of quark nuggets?
Strange quark nuggets (SQNs) could be the relics of the cosmological QCD
phase transition, and they could very likely be the candidate of cold quark
matter if survived the cooling of the later Universe, although the formation
and evolution of these SQNs depend on the physical state of the hot QGP
(quark-gluon plasma) phase and the state of cold quark matter. We reconsider
the possibility of SQNs as cold dark matter, and find that the formation of
black holes in primordial halos could be significantly different from the
standard scenario. In a primordial halo, the collision between gas and SQNs
could be frequent enough, and thus the viscosity acting on each SQN would
decrease its angular momentum and make it to sink into the center of the halo,
as well as heat the gas. The SQNs with baryon numbers less than could
assemble in the center of the halo before the formation of primordial stars. A
black hole could form by merger of these SQNs, and then its mass could quickly
become about or higher, by accreting the surrounding SQNs or
gas. The black holes formed in this way could be the seeds for the supermassive
black holes at redshift as high as .Comment: 15 page
On Hoyle-Narlikar-Wheeler mechanism of vibration energy powered magneto-dipole emission of neutron stars
We revisit the well-known Hoyle-Narlikar-Wheeler proposition that neutron
star emerging in the magnetic-flux-conserving process of core-collapse
supernova can convert the stored energy of Alfven vibrations into power of
magneto-dipole radiation. We show that the necessary requirement for the energy
conversion is the decay of internal magnetic field. In this case the loss of
vibration energy of the star causes its vibration period, equal to period of
pulsating emission, to lengthen at a rate proportional to the rate of magnetic
field decay. These prediction of the model of vibration powered neutron star
are discussed in juxtaposition with data on pulsating emission of magnetars
whose radiative activity is generally associated with the decay of ultra strong
magnetic field.Comment: Accepted for publication in Astrophysics & Space Scienc
On the role of pressure anisotropy for relativistic stars admitting conformal motion
We investigate the spacetime of anisotropic stars admitting conformal motion.
The Einstein field equations are solved using different ansatz of the surface
tension. In this investigation, we study two cases in details with the
anisotropy as: [1] [2] where, n, and are arbitrary constants.
The solutions yield expressions of the physical quantities like pressure
gradients and the mass.Comment: 21 pages, accepted for publication in 'Astrophysics and Space
Science
What can the braking indices tell us about pulsars' nature?
As a result of observational difficulties, braking indices of only six
rotation-powered pulsars are obtained with certainty, all of which are
remarkably smaller than the value () expected for pure magnetodipole
radiation model. This is still a real fundamental question not being well
answered after nearly forty years of the discovery of pulsar. The main problem
is that we are shamefully not sure about the dominant mechanisms that result in
pulsars' spin-down. Based on the previous works, the braking index is
re-examined, with a conclusion of suggesting a constant gap potential drop for
pulsars with magnetospheric activities. New constrains on model parameters from
observed braking indices are presented.Comment: 10 pages, 4 figures, submitted to "Advances in Space Research"
(Proceedings of COSPAR 2006
The Extremely Long-period X-Ray Source in a Young Supernova Remnant: A Thorne-Żytkow Object Descendant?
Recent glitches detected in the Crab pulsar
From 2000 to 2010, monitoring of radio emission from the Crab pulsar at
Xinjiang Observatory detected a total of nine glitches. The occurrence of
glitches appears to be a random process as described by previous researches. A
persistent change in pulse frequency and pulse frequency derivative after each
glitch was found. There is no obvious correlation between glitch sizes and the
time since last glitch. For these glitches and
span two orders of magnitude. The pulsar suffered the
largest frequency jump ever seen on MJD 53067.1. The size of the glitch is
6.8 Hz, 3.5 times that of the glitch occured in
1989 glitch, with a very large permanent changes in frequency and pulse
frequency derivative and followed by a decay with time constant 21 days.
The braking index presents significant changes. We attribute this variation to
a varying particle wind strength which may be caused by glitch activities. We
discuss the properties of detected glitches in Crab pulsar and compare them
with glitches in the Vela pulsar.Comment: Accepted for publication in Astrophysics & Space Scienc
Pulsars as Fantastic Objects and Probes
Pulsars are fantastic objects, which show the extreme states of matters and
plasma physics not understood yet. Pulsars can be used as probes for the
detection of interstellar medium and even the gravitational waves. Here I
review the basic facts of pulsars which should attract students to choose
pulsar studies as their future projects.Comment: Invited Lecture on the "First Kodai-Trieste Workshop on Plasma
Astrophysics", Kodaikanal Obs, India. Aug.27-Sept.7th, 2007. In: "Turbulence,
Dynamos, Accretion Disks, Pulsars and Collective Plasma Processes". Get a
copy from: http://www.springerlink.com/content/978-1-4020-8867-
Generalized Second Law of Thermodynamics in Gravity with Entropy Corrections
We study the generalized second law (GSL) of thermodynamics in
cosmology. We consider the universe as a closed bounded system filled with
component fluids in the thermal equilibrium with the cosmological boundary. We
use two different cosmic horizons: the future event horizon and the apparent
horizon. We show the conditions under which the GSL will be valid in specific
scenarios of the quintessence and the phantom energy dominated eras. Further we
associate two different entropies with the cosmological horizons: with a
logarithmic correction term and a power-law correction term. We also find the
conditions for the GSL to be satisfied or violated by imposing constraints on
model parameters.Comment: 17 pages, no figure, title changed, version accepted for publication
in Astrophysics and Space Scienc
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