5,480 research outputs found
Massive, Absorption-selected Galaxies at Intermediate Redshifts
The nature of absorption-selected galaxies and their connection to the
general galaxy population have been open issues for more than three decades,
with little information available on their gas properties. Here we show, using
detections of carbon monoxide (CO) emission with the Atacama Large
Millimeter/submillimeter Array (ALMA), that five of seven high-metallicity,
absorption-selected galaxies at intermediate redshifts, ,
have large molecular gas masses, and high molecular gas fractions (. Their modest star
formation rates (SFRs), yr, then
imply long gas depletion timescales, Gyr. The
high-metallicity absorption-selected galaxies at appear
distinct from populations of star-forming galaxies at both ,
during the peak of star formation activity in the Universe, and lower
redshifts, . Their relatively low SFRs, despite the large
molecular gas reservoirs, may indicate a transition in the nature of star
formation at intermediate redshifts, .Comment: 8 pages, 3 figures; accepted for publication in Astrophysical Journal
Letters. Minor changes to match the version in press in ApJ
Modelling elliptical galaxies: phase-space constraints on two-component (gamma1,gamma2) models
In the context of the study of the properties of the mutual mass distribution
of the bright and dark matter in elliptical galaxies, present a family of
two-component, spherical, self-consistent galaxy models, where one density
distribution follows a gamma_1 profile, and the other a gamma_2 profile
[(gamma_1,gamma_2) models], with different total masses and ``core'' radii. A
variable amount of Osipkov-Merritt (radial) orbital anisotropy is allowed in
both components. For these models, I derive analytically the necessary and
sufficient conditions that the model parameters must satisfy in order to
correspond to a physical system. Moreover, the possibility of adding a black
hole at the center of radially anisotropic gamma models is discussed,
determining analytically a lower limit of the anisotropy radius as a function
of gamma. The analytical phase-space distribution function for (1,0) models is
presented, together with the solution of the Jeans equations and the quantities
entering the scalar virial theorem. It is proved that a globally isotropic
gamma=1 component is consistent for any mass and core radius of the
superimposed gamma=0 model; on the contrary, only a maximum value of the core
radius is allowed for the gamma=0 model when a gamma=1 density distribution is
added. The combined effects of mass concentration and orbital anisotropy are
investigated, and an interesting behavior of the distribution function of the
anisotropic gamma=0 component is found: there exists a region in the parameter
space where a sufficient amount of anisotropy results in a consistent model,
while the structurally identical but isotropic model would be inconsistent.Comment: 29 pages, LaTex, plus 5 .eps figures and macro aaspp4.sty - accepted
by ApJ, main journa
Comparison of 7T 16-channel Dual-row Transmit Arrays
We evaluated and compared the performance of an inductively decoupled and overlapped dual-row transmit arrays for MRI at 7T. For the evaluated designs, the coupling between adjacent elements in the same row was higher for the overlapped compared to the non-overlapped configuration. However the transmit efficiencies for the circular polarization mode of both coils were similar. For comparisons of array transmit performance, consideration of array-internal losses as well as reflected and radiated power is very important, because their sum can be as high as 55% of the total transmit power
NICMOS Snapshot Survey of Damped Lyman Alpha Quasars
We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap
Begging and parental care in relation to offspring need and condition in the barn swallow (Hirundo rustica)
Parents are selected to maximize their fitness by allocating
care among their progeny in relation to the differential reproductive
value of offspring. Nestlings have been hypothesized to
signal need for parental care reliably through their begging behavior,
but offspring condition as reflected by their reproductive value may
likewise affect begging and hence provisioning. We assessed the relative
importance of need and condition in determining begging behavior
and feeding rate of nestling barn swallows (Hirundo rustica)
through short-term starvation, a challenge to their immune system
with a foreign antigen negatively affecting condition, and brood size
manipulation. Food deprivation but not condition or brood size
manipulation increased nestling begging rate. Parents fed offspring
depending on both need and condition but only when feeding broods
that were reduced or of normal size. In enlarged broods, offspring
received less food per capita than in reduced broods, and parents
did not discriminate among nestlings relative to their need or condition.
Thus, nestlings signal their need by increased solicitation.
Parents allocate food to offspring dependent on both need and condition,
with these effects depending on parental workload as determined
by experimental brood size
Natural products improve healthspan in aged mice and rats: a systematic review and meta-analysis
Over the last decades a decrease in mortality has paved the way for late onset pathologies such as cardiovascular, metabolic or neurodegenerative diseases. This evidence has led many researchers to shift their focus from researching ways to extend lifespan to finding ways to increase the number of years spent in good health; “healthspan” is indeed the emerging concept of such quest for ageing without chronic or disabling diseases and dysfunctions. Regular consumption of natural products might improve healthspan, although the mechanisms of action are still poorly understood. Since preclinical studies aimed to assess the efficacy and safety of these compounds are growing, we performed a systematic review and meta-analysis on the effects of natural products on healthspan in mouse and rat models of physiological ageing. Results indicate that natural compounds show robust effects improving stress resistance and cognitive abilities. These promising data call for further studies investigating the underlying mechanisms in more depth
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