1,801 research outputs found
Potential use of Niti implant for intra-articular fracture of phalax
Session - New Developments in Orthopaedic Implant Materialspublished_or_final_versio
Particle acceleration and the origin of gamma-ray emission from Fermi Bubbles
Fermi LAT has discovered two extended gamma-ray bubbles above and below the
galactic plane. We propose that their origin is due to the energy release in
the Galactic center (GC) as a result of quasi-periodic star accretion onto the
central black hole. Shocks generated by these processes propagate into the
Galactic halo and accelerate particles there. We show that electrons
accelerated up to ~10 TeV may be responsible for the observed gamma-ray
emission of the bubbles as a result of inverse Compton (IC) scattering on the
relic photons. We also suggest that the Bubble could generate the flux of CR
protons at energies > 10^15 eV because the shocks in the Bubble have much
larger length scales and longer lifetimes in comparison with those in SNRs.
This may explain the the CR spectrum above the knee.Comment: 5 pages, 4 figures. Expanded version of the contribution to the 32nd
ICRC, Beijing, #0589. To appear in the proceeding
Wnt-C59 arrests stemness and suppresses growth of nasopharyngeal carcinoma in mice by inhibiting the Wnt pathway in the tumor microenvironment
Wnt/β-catenin signaling is responsible for the generation of cancer stem cells (CSCs) in many human tumors, including nasopharyngeal carcinoma (NPC). Recent studies demonstrate that Wnt or PORCN inhibitor, Wnt-C59, inhibits tumor growth in MMTV-WNT1 transgenic mice. The effect of Wnt-C59 in human tumors is not clear. In this study, the NPC cell lines investigated manifest heterogeneous responses to Wnt-C59 treatment. Wnt-C59 decreased tumor growth of SUNE1 cells in mice immediately following the administration of Wnt-C59. Mice injected with HNE1 cells did not develop visible tumors after the treatment of Wnt-C59, while control mice developed 100% tumors. Wnt-C59 inhibited stemness properties of NPC cells in a dosage-dependent manner by arresting sphere formation in both HNE1 and SUNE1 cells. Thus, Wnt-C59 has the potential to eradicate CSCs in human tumors. Active β-catenin and Axin2 proteins were strongly expressed in stromal cells surrounding growing tumors, confirming the importance of Wnt signaling activities in the microenvironment being driving forces for cell growth. These novel findings confirm the ability of Wnt-C59 to suppress Wnt-driven undifferentiated cell growth in NPC. Both anti-Wnt signaling and anti-CSC approaches are feasible strategies in cancer therapy.published_or_final_versio
Asteroid lightcurves from the Palomar Transient Factory survey: Rotation periods and phase functions from sparse photometry
We fit 54,296 sparsely-sampled asteroid lightcurves in the Palomar Transient
Factory to a combined rotation plus phase-function model. Each lightcurve
consists of 20+ observations acquired in a single opposition. Using 805
asteroids in our sample that have reference periods in the literature, we find
the reliability of our fitted periods is a complicated function of the period,
amplitude, apparent magnitude and other attributes. Using the 805-asteroid
ground-truth sample, we train an automated classifier to estimate (along with
manual inspection) the validity of the remaining 53,000 fitted periods. By this
method we find 9,033 of our lightcurves (of 8,300 unique asteroids) have
reliable periods. Subsequent consideration of asteroids with multiple
lightcurve fits indicate 4% contamination in these reliable periods. For 3,902
lightcurves with sufficient phase-angle coverage and either a reliably-fit
period or low amplitude, we examine the distribution of several phase-function
parameters, none of which are bimodal though all correlate with the bond albedo
and with visible-band colors. Comparing the theoretical maximal spin rate of a
fluid body with our amplitude versus spin-rate distribution suggests that, if
held together only by self-gravity, most asteroids are in general less dense
than 2 g/cm, while C types have a lower limit of between 1 and 2 g/cm,
in agreement with previous density estimates. For 5-20km diameters, S types
rotate faster and have lower amplitudes than C types. If both populations share
the same angular momentum, this may indicate the two types' differing ability
to deform under rotational stress. Lastly, we compare our absolute magnitudes
and apparent-magnitude residuals to those of the Minor Planet Center's nominal
, rotation-neglecting model; our phase-function plus Fourier-series
fitting reduces asteroid photometric RMS scatter by a factor of 3.Comment: 35 pages, 29 figures. Accepted 15-Apr-2015 to The Astronomical
Journal (AJ). Supplementary material including ASCII data tables will be
available through the publishing journal's websit
VI-Band Follow-Up Observations of Ultra-Long-Period Cepheid Candidates in M31
The ultra-long period Cepheids (ULPCs) are classical Cepheids with pulsation
periods exceeding days. The intrinsic brightness of ULPCs are ~1
to ~3 mag brighter than their shorter period counterparts. This makes them
attractive in future distance scale work to derive distances beyond the limit
set by the shorter period Cepheids. We have initiated a program to search for
ULPCs in M31, using the single-band data taken from the Palomar Transient
Factory, and identified eight possible candidates. In this work, we presented
the VI-band follow-up observations of these eight candidates. Based on our
VI-band light curves of these candidates and their locations in the
color-magnitude diagram and the Period-Wesenheit diagram, we verify two
candidates as being truly ULPCs. The six other candidates are most likely other
kinds of long-period variables. With the two confirmed M31 ULPCs, we tested the
applicability of ULPCs in distance scale work by deriving the distance modulus
of M31. It was found to be mag. The large error
in the derived distance modulus, together with the large intrinsic dispersion
of the Period-Wesenheit (PW) relation and the small number of ULPCs in a given
host galaxy, means that the question of the suitability of ULPCs as standard
candles is still open. Further work is needed to enlarge the sample of
calibrating ULPCs and reduce the intrinsic dispersion of the PW relation before
re-considering ULPCs as suitable distance indicators.Comment: 13 pages, with 14 Figures and 4 Tables (one online table). AJ
accepte
De-Excitation Gamma-ray Line Emission from the Galactic Center
International audienceA future detection of de-excitation gamma-ray lines from the Galactic center region would provide unique information on the high-energy processes induced by the the central black hole and the physical conditions of the emitting region. We analyse the intensity of nuclear de-excitation lines in the direction of the Galactic center produced by subrelativistic protons, which are generated by star capture by the central black hole. With the metallicity two times higher than the solar one the total flux in gamma-ray lines of energies below 8 MeV is about 10−4 cm−2 s−1. The most promising lines for detection are those at 4.44 and 6.2 MeV, with a predicted flux in each line of 10−5 photons cm−2 s−1. We also analyze the possibility of detection of these lines by INTEGRAL and future missions
Asteroid Spin-Rate Study using the Intermediate Palomar Transient Factory
Two dedicated asteroid rotation-period surveys have been carried out using
data taken on January 6-9 and February 20-23 of 2014 by the Intermediate
Palomar Transient Factory (iPTF) in the ~band with -min cadence.
The total survey area covered 174~deg in the ecliptic plane. Reliable
rotation periods for 1,438 asteroids are obtained from a larger data set of
6,551 mostly main-belt asteroids, each with ~detections. Analysis of
1751, PTF based, reliable rotation periods clearly shows the "spin barrier" at
~hours for "rubble-pile" asteroids. We also found a new large-sized
super-fast rotator, 2005 UW163 (Chang et al., 2014), and other five candidates
as well. Our spin-rate distributions of asteroids with ~km shows
number decrease when frequency greater than 5 rev/day, which is consistent to
that of the Asteroid Light Curve Database (LCDB, Warner et al., 2009) and the
result of (Masiero et al., 2009). We found the discrepancy in the spin-rate
distribution between our result and (Pravec et al., 2008, update 2014-04-20) is
mainly from asteroids with mag that might be primarily due to
different survey strategies. For asteroids with ~km, we found a
significant number drop at rev/day. The YORP effect timescale for
small-sized asteroid is shorter that makes more elongate objets spun up to
reach their spin-rate limit and results in break-up. The K-S test suggests a
possible difference in the spin-rate distributions of C- and S-type asteroids.
We also find that C-type asteroids have a smaller spin-rate limit than the
S-type, which agrees with the general sense that the C-type has lower bulk
density than the S-type.Comment: Submitted to ApJ (Jan, 2015). Accepted by ApJ (June, 2015). The whole
set of the folded lightcurves will be available on the published articl
The Fermi Bubble as a Source of Cosmic Rays in the Energy Range > 10E15 eV
The {\it Fermi} Large Area Telescope has recently discovered two giant
gamma-ray bubbles which extend north and south of the Galactic center with
diameters and heights of the order of kpc. We suggest that the
periodic star capture processes by the Galactic supermassive black hole Sgr
A, with a capture rate of
yr and an energy release of erg per capture, can
result in hot plasma injecting into the Galactic halo at a wind velocity of
cm s. The periodic injection of hot plasma can produce a
series of shocks. Energetic protons in the bubble are re-accelerated when they
interact with these shocks. We show that for energy larger than
eV, the acceleration process can be better described by the stochastic
second-order Fermi acceleration.
We propose that hadronic cosmic rays (CRs) within the ``knee'' of the
observed CR spectrum are produced by Galactic supernova remnants distributed in
the Galactic disk. Re-acceleration of these particles in the Fermi Bubble
produces CRs beyond the knee. With a mean CR diffusion coefficient in this
energy range in the bubble cm s, we can
reproduce the spectral index of the spectrum beyond the knee and within. The
conversion efficiency from shock energy of the bubble into CR energy is about
10\%. This model provides a natural explanation of the observed CR flux,
spectral indices, and matching of spectra at the knee.Comment: 43 pages, 8 figues, to be published in the Astrophysical Journal;
version 2, 45 pages, 8 figures, added references and corrected typo
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