44 research outputs found
Mechanisms for the generation of HREE mineralization in carbonatites: Evidence from Huanglongpu, China.
The Hunaglongpu carbonatites, Qinling Mountains, China, are exceptional as they form both an economic Mo resource, and are enriched in the HREE compared to typical carbonatites, giving a metal profile that may closely match projected future demand. The carbonatites at the level currently exposed appear to be transitional between magmatic and hydrothermal processes. The multistage dykes and veins are cored by quartz which hosts a fluid inclusion assemblage with a high proportion of sulphate daughter or trapped minerals, and later stage, cross-cutting veins are rich in barite-celestine. The REE mineral paragenesis evolves from monazite, through apatite and bastnäsite to Ca-REE fluorcabonates, with an increase in HREE enrichment at every stage. Radio-isotope ratios are typical of enriched mantle sources and sulphur stable isotopes are consistent with magmatic S sources. However, Mg stable isotopes are consistent with a component of recycled subducted marine carbonate in the source region, The HREE enrichment is a function of both unusual mantle source for the primary magmas and REE mobility and concentration during post-magmatic modification in a sulphate-rich hydrothermal system. Aqueous sulphate is a none specific ligand for the REE, and this coupled with crystal fraction lead to HREE enrichment during subsolidus alteration.The attached document is the authors’ submitted version of these conference proceedings. You are advised to consult the publisher’s version if you wish to cite from it
Standard random walks and trapping on the Koch network with scale-free behavior and small-world effect
A vast variety of real-life networks display the ubiquitous presence of
scale-free phenomenon and small-world effect, both of which play a significant
role in the dynamical processes running on networks. Although various dynamical
processes have been investigated in scale-free small-world networks, analytical
research about random walks on such networks is much less. In this paper, we
will study analytically the scaling of the mean first-passage time (MFPT) for
random walks on scale-free small-world networks. To this end, we first map the
classical Koch fractal to a network, called Koch network. According to this
proposed mapping, we present an iterative algorithm for generating the Koch
network, based on which we derive closed-form expressions for the relevant
topological features, such as degree distribution, clustering coefficient,
average path length, and degree correlations. The obtained solutions show that
the Koch network exhibits scale-free behavior and small-world effect. Then, we
investigate the standard random walks and trapping issue on the Koch network.
Through the recurrence relations derived from the structure of the Koch
network, we obtain the exact scaling for the MFPT. We show that in the infinite
network order limit, the MFPT grows linearly with the number of all nodes in
the network. The obtained analytical results are corroborated by direct
extensive numerical calculations. In addition, we also determine the scaling
efficiency exponents characterizing random walks on the Koch network.Comment: 12 pages, 8 figures. Definitive version published in Physical Review
Reaching for the stars – JWST/NIRSpec spectroscopy of a lensed star candidate at z = 4.76
We present JWST/NIRSpec observations of a highly magnified star candidate at a photometric redshift of zphot ≃ 4.8, previously detected in JWST/NIRCam imaging of the strong lensing (SL) cluster MACS J0647+7015 (z = 0.591). The spectroscopic observation allows us to precisely measure the redshift of the host arc at zspec = 4.758 ± 0.004, and the star’s spectrum displays clear Lyman- and Balmer-breaks commensurate with this redshift. A fit to the spectrum suggests a B-type super-giant star of surface temperature K with either a redder F-type companion ( K) or significant dust attenuation (AV ≃ 0.82) along the line of sight. We also investigate the possibility that this object is a magnified young globular cluster rather than a single star. We show that the spectrum is in principle consistent with a star cluster, which could also accommodate the lack of flux variability between the two epochs. However, the lack of a counter image and the strong upper limit on the size of the object from lensing symmetry, r ≲ 0.5 pc, could indicate that this scenario is somewhat less likely – albeit not completely ruled out by the current data. The presented spectrum seen at a time when the Universe was only ∼1.2 Gyr old showcases the ability of JWST to study early stars through extreme lensing
Reaching for the stars -- JWST/NIRSpec spectroscopy of a lensed star candidate at
We present JWST/NIRSpec observations of a highly magnified star candidate at
a photometric redshift of , previously detected in
JWST/NIRCam imaging of the strong lensing (SL) cluster MACS J0647+7015
(). The spectroscopic observation allows us to precisely measure the
redshift of the host arc at , and the star's
spectrum displays clear Lyman- and Balmer-breaks commensurate with this
redshift. A fit to the spectrum suggests a B-type super-giant star of surface
temperature K with either a redder F-type
companion (K) or significant dust attenuation
() along the line of sight. We also investigate the possibility
that this object is a magnified young globular cluster rather than a single
star. We show that the spectrum is in principle consistent with a star cluster,
which could also accommodate the lack of flux variability between the two
epochs. However, the lack of a counter image and the strong upper limit on the
size of the object from lensing symmetry, pc, could indicate
that this scenario is somewhat less likely -- albeit not completely ruled out
by the current data. The presented spectrum seen at a time when the Universe
was only Gyr old showcases the ability of JWST to study early stars
through extreme lensing.Comment: Accepted for publication in MNRAS letters. v2 updated to match the
published versio
Early Results from GLASS-JWST. XIX: A High Density of Bright Galaxies at in the Abell 2744 Region
We report the detection of a high density of redshift galaxies
behind the foreground cluster Abell 2744, selected from imaging data obtained
recently with NIRCam onboard {\it JWST} by three programs -- GLASS-JWST,
UNCOVER, and DDT\#2756. To ensure robust estimates of the lensing magnification
, we use an improved version of our model that exploits the first epoch of
NIRCam images and newly obtained MUSE spectra, and avoids regions with
where the uncertainty may be higher. We detect seven bright
galaxies with demagnified rest-frame mag,
over an area of sq. arcmin. Taking into account photometric
incompleteness and the effects of lensing on luminosity and cosmological
volume, we find that the density of galaxies in the field is
about () larger than the average at mag reported so far. The density is even higher when considering only
the GLASS-JWST data, which are the deepest and the least affected by
magnification and incompleteness. The GLASS-JWST field contains 5 out of 7
galaxies, distributed along an apparent filamentary structure of 2 Mpc in
projected length, and includes a close pair of candidates with mag having a projected separation of only 16 kpc. These findings suggest
the presence of a overdensity in the field. In addition to
providing excellent targets for efficient spectroscopic follow-up observations,
our study confirms the high density of bright galaxies observed in early {\it
JWST} observations, but calls for multiple surveys along independent lines of
sight to achieve an unbiased estimate of their average density and a first
estimate of their clustering.Comment: Accepted for publication in ApJL, 13 pages, 4 figure
Polymorphisms of TP53 codon 72 with breast carcinoma risk: evidence from 12226 cases and 10782 controls
<p>Abstract</p> <p>Background</p> <p>Previously, TP53 codon 72 polymorphisms have been implicated as risk factors for various cancers. A number of studies have conducted on the association of TP53 codon 72 polymorphisms with susceptibility to breast carcinoma and have yielded inconclusive results. The aim of the present study was to derive a more precise estimation of the relationship.</p> <p>Methods</p> <p>We conducted a search in the Medline, EMBASE, OVID, Sciencedirect, and Chinese National Knowledge Infrastructure (CNKI) without a language limitation, covering all papers published up to Jan 2009. The associated literature was acquired through deliberate searching and selected based on the established inclusion criteria for publications.</p> <p>Results</p> <p>A total of seventeen case-control studies, including 12226 cases and 10782 controls, met the included criteria and thus were selected. Ultimately, the relevant data were extracted and further analyzed using systematic meta-analyses. Overall, no associations of TP53 codon 72 polymorphisms with breast carcinoma were observed (for Arg/Arg vs Pro/Pro: OR = 1.20; 95%CI = 0.96–1.50; for dominant model: OR = 1.12; 95%CI = 0.96–1.32; for recessive model: OR = 1.13; 95%CI = 0.98–1.31). In the subgroup analysis by ethnicity, statistically similar results were obtained when the data were stratified as Asians, Caucasians and Africans.</p> <p>Conclusion</p> <p>Collectively, the results of the present study suggest that <it>TP53 codon 72 </it>polymorphisms might not be a low-penetrant risk factor for developing breast carcinoma.</p
All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class
mission concept that will provide essential contributions to multimessenger
astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in
the 200 keV to 10 GeV energy range with a wide field of view, good spectral
resolution, and polarization sensitivity. Therefore, AMEGO is key in the study
of multimessenger astrophysical objects that have unique signatures in the
gamma-ray regime, such as neutron star mergers, supernovae, and flaring active
galactic nuclei. The order-of-magnitude improvement compared to previous MeV
missions also enables discoveries of a wide range of phenomena whose energy
output peaks in the relatively unexplored medium-energy gamma-ray band