6,167 research outputs found
Synchronized and Desynchronized Phases of Exciton-Polariton Condensates in the Presence of Disorder
Condensation of exciton-polaritons in semiconductor microcavities takes place
despite in plane disorder. Below the critical density the inhomogeneity of the
potential seen by the polaritons strongly limits the spatial extension of the
ground state. Above the critical density, in presence of weak disorder, this
limitation is spontaneously overcome by the non linear interaction, resulting
in an extended synchronized phase. This mechanism is clearly evidenced by
spatial and spectral studies, coupled to interferometric measurements. In case
of strong disorder, several non phase-locked (independent) condensates can be
evidenced. The transition from synchronized phase to desynchronized phase is
addressed considering multiple realizations of the disorder.Comment: 11 pages, 4 figures,corrected typos, added figure
Imaging and spectroscopy of galaxies associated with two z~0.7 damped Lyman-alpha absorption systems
We have identified galaxies near two quasars which are at the redshift of
damped Lyman-alpha (DLA) systems in the UV spectra of the quasars. Both
galaxies are actively forming stars. One galaxy has a luminosity close to the
break in the local galaxy luminosity function, L*, the other is significantly
fainter than L* and appears to be interacting with a nearby companion. Despite
the strong selection effects favoring spectroscopic identification of the most
luminous DLA galaxies, many of the spectroscopically-identified DLA galaxies in
the literature are sub-L*, suggesting that the majority of the DLA population
is probably sub-L*, in contrast to MgII absorbers at similar redshifts whose
mean luminosity is close to L*.Comment: 9 pages, to appear in AJ, November 2003 issu
A MMT/Hectospec Redshift Survey of 24 Micron Sources in the Spitzer First Look Survey
We present a spectroscopic survey using the MMT/Hectospec fiber spectrograph
of 24 micron sources selected with the Spitzer Space Telescope in the Spitzer
First Look Survey. We report 1296 new redshifts for 24 micron sources,
including 599 with f(24micron) > 1 mJy. Combined with 291 additional redshifts
for sources from the Sloan Digital Sky Survey (SDSS), our observing program was
highly efficient and is ~90% complete for i' 1 mJy,
and is 35% complete for i' < 20.5 mag and 0.3 mJy < f(24micron) < 1 mJy. Our
Hectospec survey includes 1078 and 168 objects spectroscopically classified as
galaxies and QSOs, respectively. Combining the Hectospec and SDSS samples, we
find 24 micron-selected galaxies to z < 0.98 and QSOs to z < 3.6, with mean
redshifts of = 0.27 and =1.1. As part of this publication, we
include the redshift catalogs and the reduced spectra; these are also available
online (http://mips.as.arizona.edu/~papovich/fls) and through the NASA/IPAC
Infrared Science Archive (http://irsa.ipac.caltech.edu).Comment: Accepted for publication in the Astronomical Journal, AASTEX format,
23 pages, 7 figures (some in color). This replacement is the accepted
version, and includes minor changes from previous version. Data tables and
spectra available at http://mips.as.arizona.edu/~papovich/fls or at
http://irsa.ipac.caltech.ed
Combination of selenium and green tea improves the efficacy of chemoprevention in a rat colorectal cancer model by modulating genetic and epigenetic biomarkers
Dietary supplementation of selenium and green tea holds promise in cancer prevention. In this study, we evaluated the
efficacies of selenium and green tea administered individually and in combination against colorectal cancer in an
azoxymethane (AOM)-induced rat colonic carcinogenesis model and determined the underlying mechanisms of the
protection. Four-week old Sprague-Dawley male rats were fed with diets containing 0.5% green tea extract, 1ppm selenium
as selenium-enriched milk protein, or combination of 1ppm selenium and 0.5% green tea extract. Animals received 2 AOM
(15 mg/kg) treatments to induce colonic oncogenesis. Rats were killed 8 or 30 wk later after the last AOM to examine the
effect of dietary intervention on aberrant crypt foci (ACF) formation or tumor development. On sacrifice, colons were
examined for ACF and tumors, the mRNA levels of SFRP5 and Cyclin D1, and the proteins levels of Ăź-catenin, COX-2, Ki-67,
DNMT1 and acetyl histone H3. The combination of selenium and green tea resulted in a significant additive inhibition of
large ACF formation, this effect was greater than either selenium or green tea alone, P,0.01; the combination also had a
significant additive inhibition effect on all tumor endpoints, the effect of the combination diet on tumor incidence,
multiplicity and size was greater than selenium or green tea alone, P,0.01. Rats fed the combination diet showed marked
reduction of DNMT1 expression and induction of histone H3 acetylation, which were accompanied by restoration of SFRP5
mRNA in normal-appearing colonic crypts. The combination diet also significantly reduced Ăź-catenin nuclear translocation,
Cyclin D1 expression and cell proliferation. These data show, for the first time, that combination of selenium and green tea is
more effective in suppressing colorectal oncogenesis than either agent alone. The preventive effect is associated with
regulation of genetic and epigenetic biomarkers implicated in colonic carcinogenesis
Z_3-graded exterior differential calculus and gauge theories of higher order
We present a possible generalization of the exterior differential calculus,
based on the operator d such that d^3=0, but d^2\not=0. The first and second
order differentials generate an associative algebra; we shall suppose that
there are no binary relations between first order differentials, while the
ternary products will satisfy the cyclic relations based on the representation
of cyclic group Z_3 by cubic roots of unity. We shall attribute grade 1 to the
first order differentials and grade 2 to the second order differentials; under
the associative multiplication law the grades add up modulo 3. We show how the
notion of covariant derivation can be generalized with a 1-form A, and we give
the expression in local coordinates of the curvature 3-form. Finally, the
introduction of notions of a scalar product and integration of the Z_3-graded
exterior forms enables us to define variational principle and to derive the
differential equations satisfied by the curvature 3-form. The Lagrangian
obtained in this way contains the invariants of the ordinary gauge field tensor
F_{ik} and its covariant derivatives D_i F_{km}.Comment: 13 pages, no figure
Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218
We report the detection of a z~7 galaxy strongly lensed by the massive galaxy
cluster Abell 2218 (z=0.175) at 3.6 and 4.5 um using the Spitzer Observatory
and at 1.1 um using the Hubble Space Telescope. The new data indicate a refined
photometric redshift in the range of 6.6-6.8 depending on the presence of
Ly-alpha emission. The spectral energy distribution is consistent with having a
significant Balmer break, suggesting that the galaxy is in the poststarburst
stage with an age of at least ~50 Myr and quite possibly a few hundred Myr.
This suggests the possibility that a mature stellar population is already in
place at such a high redshift. Compared with typical Lyman break galaxies at
z~3-4, the stellar mass is an order of magnitude smaller (~10^{9} Msun), but
the specific star formation rate (star formation rate/M_{star}) is similarly
large (> 10^{-9} yr^{-1}), indicating equally vigorous star-forming activity.Comment: 11 pages, 2 figures, 2 tables; Accepted for publication in ApJ
Screening and management of viral hepatitis and hepatocellular carcinoma in Mongolia: results from a survey of Mongolian physicians from all major provinces of Mongolia
published_or_final_versio
Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings
Granular packings slowly driven towards their instability threshold are
studied using a digital imaging technique as well as a nonlinear acoustic
method. The former method allows us to study grain rearrangements on the
surface during the tilting and the latter enables to selectively probe the
modifications of the weak-contact fraction in the material bulk. Gradual ageing
of both the surface activity and the weak-contact reconfigurations is observed
as a result of repeated tilt cycles up to a given angle smaller than the angle
of avalanche. For an aged configuration reached after several consecutive tilt
cycles, abrupt resumption of the on-surface activity and of the weak-contact
rearrangements occurs when the packing is subsequently inclined beyond the
previous maximal tilting angle. This behavior is compared with literature
results from numerical simulations of inclined 2D packings. It is also found
that the aged weak-contact configurations exhibit spontaneous restoration
towards the initial state if the packing remains at rest for tens of minutes.
When the packing is titled forth and back between zero and near-critical
angles, instead of ageing, the weak-contact configuration exhibits "internal
weak-contact avalanches" in the vicinity of both the near-critical and zero
angles. By contrast, the stronger-contact skeleton remains stable
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