3,706 research outputs found
Development of an inducible mouse model of iRFP713 to track recombinase activity and tumour development in vivo
While the use of bioluminescent proteins for molecular imaging is a powerful technology to further our understanding of complex processes, fluorescent labeling with visible light fluorescent proteins such as GFP and RFP suffers from poor tissue penetration and high background autofluorescence. To overcome these limitations, we generated an inducible knock-in mouse model of iRFP713. This model was used to assess Cre activity in a Rosa Cre-ER background and quantify Cre activity upon different tamoxifen treatments in several organs. We also show that iRFP can be readily detected in 3D organoid cultures, FACS analysis and in vivo tumour models. Taken together we demonstrate that iRFP713 is a progressive step in in vivo imaging and analysis that widens the optical imaging window to the near-infrared spectrum, thereby allowing deeper tissue penetration, quicker image acquisition without the need to inject substrates and a better signal to background ratio in genetically engineered mouse models (GEMMs)
Thermal production of axino Dark Matter
We reconsider thermal production of axinos in the early universe, adding: a)
missed terms in the axino interaction; b) production via gluon decays
kinematically allowed by thermal masses; c) a precise modeling of reheating. We
find an axino abunance a few times larger than previous computations.Comment: 6 pages, 2 figures. Final version, to appear on JHE
Field theory of absorbing phase transitions with a non-diffusive conserved field
We investigate the critical behavior of a reaction-diffusion system
exhibiting a continuous absorbing-state phase transition. The
reaction-diffusion system strictly conserves the total density of particles,
represented as a non-diffusive conserved field, and allows an infinite number
of absorbing configurations. Numerical results show that it belongs to a wide
universality class that also includes stochastic sandpile models. We derive
microscopically the field theory representing this universality class.Comment: 13 pages, 1 eps figure, RevTex styl
Canonical Solution of Classical Magnetic Models with Long-Range Couplings
We study the canonical solution of a family of classical spin
models on a generic -dimensional lattice; the couplings between two spins
decay as the inverse of their distance raised to the power , with
. The control of the thermodynamic limit requires the introduction of
a rescaling factor in the potential energy, which makes the model extensive but
not additive. A detailed analysis of the asymptotic spectral properties of the
matrix of couplings was necessary to justify the saddle point method applied to
the integration of functions depending on a diverging number of variables. The
properties of a class of functions related to the modified Bessel functions had
to be investigated. For given , and for any , and lattice
geometry, the solution is equivalent to that of the model, where the
dimensionality and the geometry of the lattice are irrelevant.Comment: Submitted for publication in Journal of Statistical Physic
GALEX UV Color Relations for Nearby Early-Type Galaxies
We use GALEX/optical photometry to construct color-color relationships for
early-type galaxies sorted by morphological type. We have matched objects in
the GALEX GR1 public release and the first IR1.1 internal release, with the RC3
early-type galaxies having a morphological type -5.5<T<-1.5 with mean error in
T<1.5, and mean error on (B-V)T<0.05. After visual inspection of each match, we
are left with 130 galaxies with a reliable GALEX pipeline photometry in the
far-UV and near-UV bands. This sample is divided into Ellipticals (-5.5<T<-3.5)
and Lenticulars (-3.5<T<-1.5). After correction for the Galactic extinction,
the color-color diagrams FUV-NUV vs. (B-V)_{Tc} are plotted for the two
subsamples. We find a tight anti-correlation between the FUV-NUV and (B-V)_{Tc}
colors for Ellipticals, the UV color getting bluer when the (B-V)_{Tc} get
redder. This relationship very likely is an extension of the color-metallicity
relationship into the GALEX NUV band. We suspect that the main source of the
correlation is metal line blanketing in the NUV band. The FUV-NUV vs B-V
correlation has larger scatter for lenticular galaxies; we speculate this
reflects the presence of low level star formation. If the latter objects (i.e.
those that are blue both in FUV-NUV and B-V) are interpreted as harboring
recent star formation activity, this would be the case for a few percent (~4%)
of Ellipticals and ~15% of Lenticulars; this would make about 10% of early-type
galaxies with residual star formation in our full sample of 130 early-type
galaxies. We also plot FUV-NUV vs. the Mg_2 index and central velocity
dispersion. We find a tight anti-correlation between FUV-NUV and the Mg_2
index(...).Comment: 25 pages, 5 figures, accepted for publication in ApJS (abstract
abridged), typos corrected in section 2.
The GALEX Ultraviolet Atlas of Nearby Galaxies
We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its far-ultraviolet (FUV; λ_(eff) = 1516 Å) and near-ultraviolet (NUV; λ_(eff) = 2267 Å) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate [SFR]) of galaxies in the local universe. From the surface brightness profiles obtained we have computed asymptotic magnitudes, colors, and luminosities, along with the concentration indices C31 and C42. We have also morphologically classified the UV surface brightness profiles according to their shape. This data set has been complemented with archival optical, near-infrared, and far-infrared fluxes and colors. We find that the integrated (FUV − K) color provides robust discrimination between elliptical and spiral/irregular galaxies and also among spiral galaxies of different subtypes. Elliptical galaxies with brighter K-band luminosities (i.e., more massive) are redder in (NUV − K) color but bluer in (FUV − NUV) (a color sensitive to the presence of a strong UV upturn) than less massive ellipticals. In the case of the spiral/irregular galaxies our analysis shows the presence of a relatively tight correlation between the (FUV − NUV) color (or, equivalently, the slope of the UV spectrum, β) and the total infrared-to-UV ratio. The correlation found between (FUV − NUV) color and K-band luminosity (with lower luminosity objects being bluer than more luminous ones) can be explained as due to an increase in the dust content with galaxy luminosity. The images in this Atlas along with the profiles and integrated properties are publicly available through a dedicated Web page
The two-dimensional quantum Heisenberg antiferromagnet: effective Hamiltonian approach to the thermodynamics
In this paper we present an extensive study of the thermodynamic properties
of the two-dimensional quantum Heisenberg antiferromagnet on the square
lattice; the problem is tackled by the pure-quantum self-consistent harmonic
approximation, previously applied to quantum spin systems with easy-plane
anisotropies, modeled to fit the peculiar features of an isotropic system.
Internal energy, specific heat, correlation functions, staggered
susceptibility, and correlation length are shown for different values of the
spin, and compared with the available high-temperature expansion and quantum
Monte Carlo results, as well as with the available experimental data.Comment: 14 pages, 13 Postscript figures embedded by psfig.sty; revisions:
paper shortened, some parts moved in the appendices, 4 figures replaced by 2
only, minor errors correcte
Superconducting nanowire photon number resolving detector at telecom wavelength
The optical-to-electrical conversion, which is the basis of optical
detectors, can be linear or nonlinear. When high sensitivities are needed
single-photon detectors (SPDs) are used, which operate in a strongly nonlinear
mode, their response being independent of the photon number. Nevertheless,
photon-number resolving (PNR) detectors are needed, particularly in quantum
optics, where n-photon states are routinely produced. In quantum communication,
the PNR functionality is key to many protocols for establishing, swapping and
measuring entanglement, and can be used to detect photon-number-splitting
attacks. A linear detector with single-photon sensitivity can also be used for
measuring a temporal waveform at extremely low light levels, e.g. in
long-distance optical communications, fluorescence spectroscopy, optical
time-domain reflectometry. We demonstrate here a PNR detector based on parallel
superconducting nanowires and capable of counting up to 4 photons at
telecommunication wavelengths, with ultralow dark count rate and high counting
frequency
The Look-back Time Evolution of Far-Ultraviolet Flux from the Brightest Cluster Elliptical Galaxies at z < 0.2
We present the GALEX UV photometry of the elliptical galaxies in Abell
clusters at moderate redshifts (z < 0.2) for the study of the look-back time
evolution of the UV upturn phenomenon. The brightest elliptical galaxies (M_r <
-22) in 12 remote clusters are compared with the nearby giant elliptical
galaxies of comparable optical luminosity in the Fornax and Virgo clusters. The
sample galaxies presented here appear to be quiescent without signs of massive
star formation or strong nuclear activity, and show smooth, extended profiles
in their UV images indicating that the far-UV (FUV) light is mostly produced by
hot stars in the underlying old stellar population. Compared to their
counterparts in nearby clusters, the FUV flux of cluster giant elliptical
galaxies at moderate redshifts fades rapidly with ~ 2 Gyrs of look-back time,
and the observed pace in FUV - V color evolution agrees reasonably well with
the prediction from the population synthesis models where the dominant FUV
source is hot horizontal-branch stars and their progeny. A similar amount of
color spread (~ 1 mag) in FUV - V exists among the brightest cluster elliptical
galaxies at z ~ 0.1, as observed among the nearby giant elliptical galaxies of
comparable optical luminosity.Comment: Accepted for publication in the Special GALEX ApJ Supplement,
December 200
Magnetization Signature of Topological Surface States in a Non-Symmorphic Superconductor
Superconductors with nontrivial band structure topology represent a class of materials with unconventional and potentially useful properties. Recent years have seen much success in creating artificial hybrid structures exhibiting the main characteristics of 2D topological superconductors. Yet, bulk materials known to combine inherent superconductivity with nontrivial topology remain scarce, largely because distinguishing their central characteristic—the topological surface states—has proved challenging due to a dominant contribution from the superconducting bulk. In this work, a highly anomalous behavior of surface superconductivity in topologically nontrivial 3D superconductor In2Bi, where the surface states result from its nontrivial band structure, itself a consequence of the non-symmorphic crystal symmetry and strong spin–orbit coupling, is reported. In contrast to smoothly decreasing diamagnetic susceptibility above the bulk critical field, Hc2, as seen in conventional superconductors, a near-perfect, Meissner-like screening of low-frequency magnetic fields well above Hc2 is observed. The enhanced diamagnetism disappears at a new phase transition close to the critical field of surface superconductivity, Hc3. Using theoretical modeling, the anomalous screening is shown to be consistent with modification of surface superconductivity by the topological surface states. The possibility of detecting signatures of the surface states using macroscopic magnetization provides a new tool for the discovery and identification of topological superconductor
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