1,108 research outputs found
A WIMP Detector with Two-Phase Liquid Xenon
We describe the liquid-xenon dark-matter detector program of the UCLA-Torino
team. A two-phase detector, ZEPLIN II, for the Boulby Mine is a good match for
the current search for WIMP dark matter.Comment: 3 pages with 4 figures; for Proceedings, Sixth Int'l Wksp. On Topics
in Astroparticle and Underground Physics, TAUP99 (College de France, Paris,
Sept. 6-10, 1999), to be published in Nucl. Phys. B(PS
Regulating the effects of GPR21, a novel target for type 2 diabetes
Type 2 diabetes is a chronic metabolic disorder primarily caused by insulin resistance to which obesity is a major contributor. Expression levels of an orphan G protein-coupled receptor (GPCR), GPR21, demonstrated a trend towards a significant increase in the epididymal fat pads of wild type high fat high sugar (HFHS)-fed mice. To gain further insight into the potential role this novel target may play in the development of obesity-associated type 2 diabetes, the signalling capabilities of the receptor were investigated. Overexpression studies in HEK293T cells revealed GPR21 to be a constitutively active receptor, which couples to Gα(q) type G proteins leading to the activation of mitogen activated protein kinases (MAPKs). Overexpression of GPR21 in vitro also markedly attenuated insulin signalling. Interestingly, the effect of GPR21 on the MAPKs and insulin signalling was reduced in the presence of serum, inferring the possibility of a native inhibitory ligand. Homology modelling and ligand docking studies led to the identification of a novel compound that inhibited GPR21 activity. Its effects offer potential as an anti-diabetic pharmacological strategy as it was found to counteract the influence of GPR21 on the insulin signalling pathway
Photometric Identification of Type Ia Supernovae at Moderate Redshift
Large photometric surveys with the aim of identifying many Type Ia supernovae
(SNe) at moderate redshift are challenged in separating these SNe from other SN
types. We are motivated to identify Type Ia SNe based only on broadband
photometric information, since spectroscopic determination of the SN type, the
traditional method, requires significant amounts of time on large telescopes.
We consider the possible observables provided by a large synoptic photometry
survey. We examine the optical colors and magnitudes of many SN types from
z=0.1 to z=1.0, using space-based ultraviolet spectra and ground-based optical
spectra to simulate the photometry. We also discuss the evolution of colors
over the SN outburst and the use of host galaxy characteristics to aid in the
identification of Type Ia SNe. We consider magnitudes in both the SDSS
photometric system and in a proposed filter system with logarithmically spaced
bandpasses. We find that photometric information in four bands covering the
entire optical spectrum appears capable of providing identification of Type Ia
SNe based on their colors at a single observed epoch soon after maximum light,
even without independent estimates of the SN redshift. Very blue filters are
extremely helpful, as at moderate redshift they sample the restframe
ultraviolet spectrum where the SN types are very different. We emphasize the
need for further observations of SNe in the restframe ultraviolet to fully
characterize, refine, and improve this method of SN type identification.Comment: AASTeX, 37 pages with 12 figures, being resubmitted to A.J. Figures
3, 4 and 9 updated, minor typos correcte
First operation of a liquid Argon TPC embedded in a magnetic field
We have operated for the first time a liquid Argon TPC immersed in a magnetic
field up to 0.55 T. We show that the imaging properties of the detector are not
affected by the presence of the magnetic field. The magnetic bending of the
ionizing particle allows to discriminate their charge and estimate their
momentum. These figures were up to now not accessible in the non-magnetized
liquid Argon TPC.Comment: 9 pages, 3 figure
Conhecimentos tácitos e explícitos e a formação de professores : uma reflexão sobre possibilidades na prática de ensino de Física
Resum no disponibl
Signatures of an eruptive phase before the explosion of the peculiar core-collapse SN 2013gc
We present photometric and spectroscopic analysis of the peculiar
core-collapse SN 2013gc, spanning seven years of observations. The light curve
shows an early maximum followed by a fast decline and a phase of almost
constant luminosity. At +200 days from maximum, a brightening of 1 mag is
observed in all bands, followed by a steep linear luminosity decline after +300
d. In archival images taken between 1.5 and 2.5 years before the explosion, a
weak source is visible at the supernova location, with mag20. The
early supernova spectra show Balmer lines, with a narrow (560 km
s) P-Cygni absorption superimposed on a broad (3400 km s)
component, typical of type IIn events. Through a comparison of colour curves,
absolute light curves and spectra of SN 2013gc with a sample of supernovae IIn,
we conclude that SN 2013gc is a member of the so-called type IId subgroup. The
complex profile of the H line suggests a composite circumstellar medium
geometry, with a combination of lower velocity, spherically symmetric gas and a
more rapidly expanding bilobed feature. This circumstellar medium distribution
has been likely formed through major mass-loss events, that we directly
observed from 3 years before the explosion. The modest luminosity
( near maximum) of SN 2013gc at all phases, the very small amount
of ejected Ni (of the order of M), the major
pre-supernova stellar activity and the lack of prominent [O I] lines in
late-time spectra support a fall-back core-collapse scenario for the massive
progenitor of SN~2013gc.Comment: 20 pages, 11 figures, 8 tables, accepted by MNRA
A Study of the Residual 39Ar Content in Argon from Underground Sources
The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.Comment: 21 pages, 10 figure
The early spectral evolution of SN 2004dt
Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN
Ia) 2004dt, focusing our attention on the early epochs.
Methods. Observation triggered soon after the SN 2004dt discovery allowed us
to obtain a spectrophotometric coverage from day -10 to almost one year (~353
days) after the B band maximum. Observations carried out on an almost daily
basis allowed us a good sampling of the fast spectroscopic evolution of SN
2004dt in the early stages. To obtain this result, low-resolution, long-slit
spectroscopy was obtained using a number of facilities.
Results. This supernova, which in some absorption lines of its early spectra
showed the highest degree of polarization ever measured in any SN Ia, has a
complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is
present, moving at velocities as high as ~16,700 km/s, with some
intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the
spectra based on standard density profiles of the ejecta fails to reproduce the
observed features, whereas enhancing the density of outer layers significantly
improves the fit. Our analysis indicates the presence of clumps of
high-velocity, intermediate-mass elements in the outermost layers, which is
also suggested by the spectropolarimetric data.Comment: 13 pages, 15 figures, accepted for pubblication in Astronomy and
Astrophysic
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