17,556 research outputs found
Bioactive composites for bone tissue engineering
One of the major challenges of bone tissue engineering is the production of a suitable scaffold material. In this review the current composite materials options available are considered covering both the methods of both production and assessing the scaffolds. A range of production routes have been investigated ranging from the use of porogens to produce the porosity through to controlled deposition methods. The testing regimes have included mechanical testing of the materials produced through to in vivo testing of the scaffolds. While the ideal scaffold material has not yet been produced, progress is being made
Mixed Phase in Compact Starts : M-R relations and radial oscillations
It is believed that quark stars or neutron stars with mixed phase in the core
have smaller radii compared to ordinary compact stars. With the recent
observation of several low radius objects, typically a radius of for
star of mass in low mass X-ray binaries (LMXB), it has become very
important to understand the nature of these objects. An accurate determination
of mass-radius relationship of these objects provide us with a physical
laboratory to study the composition of high density matter and the nature of
phase transition. We study the effect of quark and nuclear matter mixed phase
on mass radius relationship and radial oscillations of neutron stars. We find
that the effect of the mixed phase is to decrease the maximum mass of a stable
neutron star and to decrease the radial frequencies .Comment: guest contribution at Int. Workshop on Astronomy & Relativistic
Astrophysics (IWARA 03)held at Olinda-PE (Brazil) from Oct. 12-17,200
Acceleration and Deceleration in Curvature Induced Phantom Model of the Late and Future Universe, Cosmic Collapse as Well as its Quantum Escape
Here, cosmology of the late and future universe is obtained from
-gravity with non-linear curvature terms and ( being the
Ricci scalar curvature). It is different from -dark enrgy models, where
non-linear curvature terms are taken as gravitational alternative of dark
energy. In the present model, neither linear nor no-linear curvature terms are
taken as dark energy. Rather, dark energy terms are induced by curvature terms
in the Friedmann equation derived from -gravitational equations. It has
advantage over - dark energy models in the sense that the present model
satisfies WMAP results and expands as during matter-dominance.
So, it does not have problems due to which -dark energy models are
criticized. Curvature-induced dark energy, obtained here, mimics phantom.
Different phases of this model, including acceleration and deceleration during
phantom phase, are investigated here.It is found that expansion of the universe
will stop at the age ( being the present
age of the universe) and after this epoch, it will contract and collapse by the
time . Further,it is shown that universe will
escape predicted collapse (obtained using classical mechanics) on making
quantum gravity corrections relevant near collapse time due to extremely high
energy density and large curvature analogous to the state of very early
universe. Interestingly, cosmological constant is also induced here, which is
very small in classical domain, but very high in quantum domain.Comment: 33 page
The young cluster NGC 2282 : a multi-wavelength perspective
We present the analysis of the stellar content of NGC~2282, a young cluster
in the Monoceros constellation, using deep optical and IPHAS photometry
along with infrared (IR) data from UKIDSS and -IRAC. Based on the
stellar surface density analysis using nearest neighborhood method, the radius
of the cluster is estimated as 3.15\arcmin. From optical spectroscopic
analysis of 8 bright sources, we have classified three early B-type members in
the cluster, which includes, HD 289120, a previously known B2V type star, a
Herbig Ae/Be star (B0.5 Ve) and a B5 V star. From spectrophotometric analyses,
the distance to the cluster has been estimated as 1.65 kpc. The -band
extinction map is estimated using nearest neighborhood technique, and the mean
extinction within the cluster area is found to be A 3.9 mag. Using
IR colour-colour criteria and H-emission properties, we have
identified a total of 152 candidate young stellar objects (YSOs) in the region,
of which, 75 are classified as Class II, 9 are Class I YSOs. Our YSO catalog
also includes 50 H-emission line sources, identified using slitless
spectroscopy and IPHAS photometry data. Based on the optical and near-IR
colour-magnitude diagram analyses, the cluster age has been estimated to be in
the range of 2 5 Myr, which is in agreement with the estimated age from
disc fraction ( 58\%). Masses of these YSOs are found to be
0.12.0 M. Spatial distribution of the candidate YSOs shows spherical
morphology, more or less similar to the surface density map.Comment: 16 pages, 19 Figure
Incidence of HI 21-cm absorption in strong FeII systems at
We present the results from our search for HI 21-cm absorption in a sample of
16 strong FeII systems ((MgII ) \AA\ and
(FeII ) or \AA) at
using the Giant Metrewave Radio Telescope and the Green Bank Telescope. We
report six new HI 21-cm absorption detections from our sample, which have
increased the known number of detections in strong MgII systems at this
redshift range by %. Combining our measurements with those in the
literature, we find that the detection rate of HI 21-cm absorption increases
with , being four times higher in systems with
\AA\ compared to systems with \AA. The (HI)
associated with the HI 21-cm absorbers would be
cm, assuming a spin temperature of K (based on HI 21-cm
absorption measurements of damped Lyman- systems at this redshift
range) and unit covering factor. We find that HI 21-cm absorption arises on an
average in systems with stronger metal absorption. We also find that quasars
with HI 21-cm absorption detected towards them have systematically higher
values than those which do not. Further, by comparing the velocity
widths of HI 21-cm absorption lines detected in absorption- and galaxy-selected
samples, we find that they show an increasing trend (significant at
) with redshift at , which could imply that the absorption
originates from more massive galaxy haloes at high-. Increasing the number
of HI 21-cm absorption detections at these redshifts is important to confirm
various trends noted here with higher statistical significance.Comment: 17 pages, 10 figures, 8 tables, accepted for publication in MNRA
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