4,157 research outputs found
Galaxy Peculiar Velocities and Infall onto Groups
We perform statistical analyses to study the infall of galaxies onto groups
and clusters in the nearby Universe. The study is based on the UZC and SSRS2
group catalogs and peculiar velocity samples. We find a clear signature of
infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30
h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers
per second. We obtain a significant increase in the infall amplitude with group
virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups
with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km
s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed,
V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding
groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},
whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall
can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results
are compared with the results obtained from mock group and galaxy samples
constructed from numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results from
the mock catalogs and the observations. The infall of galaxies onto groups is
suitably reproduced in the simulations and, as in the observations, larger
virial mass and luminosity groups exhibit the largest galaxy infall amplitudes.
We derive estimates of the integrated mass overdensities associated with groups
by applying linear theory to the infall velocities after correcting for the
effects of distance uncertainties obtained using the mock catalogs. The
resulting overdensities are consistent with a power law with \delta \sim 1 at r
\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure
Gas phase water in the surface layer of protoplanetary disks
Recent observations of the ground state transition of HDO at 464 GHz towards
the protoplanetary disk of DM Tau have detected the presence of water vapor in
the regions just above the outer disk midplane (Ceccarelli et al 2005). In the
absence of non-thermal desorption processes, water should be almost entirely
frozen onto the grain mantles and HDO undetectable. In this Letter we present a
chemical model that explores the possibility that the icy mantles are
photo-desorbed by FUV (6eV < h nu < 13.6eV) photons. We show that the average
Interstellar FUV field is enough to create a layer of water vapor above the
disk midplane over the entire disk. Assuming a photo-desorption yield of
10^{-3}, the water abundance in this layer is predicted to be ~ 3 x 10^{-7} and
the average H2O column density is ~ 1.6x 10^{15} cm^{-2}. The predictions are
very weakly dependent on the details of the model, like the incident FUV
radiation field, and the gas density in the disk. Based on this model, we
predict a gaseous HDO/H2O ratio in DM Tau of ~1%. In addition, we predict the
ground state transition of water at 557 GHz to be undetectable with ODIN and/or
HSO-HIFI.Comment: 13 pages, 4 figures. Astrophysical Journal Letters, in pres
Methodology for sensor calibration in agro-industrial facilities
The rising need of precision in several sectors, agriculture included, brings to the development of new monitoring systems customised for the specific application. These systems often take advantages of probes offered by the market, however, the integration between market probes and home-built systems, requires tests to validate the recorded measurements.This paper provides a methodology to perform a calibration procedure when the probes fail the validation test.The results show the comparison of the measurements collected by investigated sensors and reference sensor coupled with the application of simple correlation methods can bring to an improvement of the sensor precision as far as to pass the validation test
Imaging stray magnetic field of individual ferromagnetic nanotubes
We use a scanning nanometer-scale superconducting quantum interference device
to map the stray magnetic field produced by individual ferromagnetic nanotubes
(FNTs) as a function of applied magnetic field. The images are taken as each
FNT is led through magnetic reversal and are compared with micromagnetic
simulations, which correspond to specific magnetization configurations. In
magnetic fields applied perpendicular to the FNT long axis, their magnetization
appears to reverse through vortex states, i.e.\ configurations with vortex end
domains or -- in the case of a sufficiently short FNT -- with a single global
vortex. Geometrical imperfections in the samples and the resulting distortion
of idealized mangetization configurations influence the measured stray-field
patterns.Comment: 14 pages, 4 figure
Infrared Observations of Hot Gas and Cold Ice toward the Low Mass Protostar Elias 29
We have obtained the full 1-200 um spectrum of the low luminosity (36 Lsun)
Class I protostar Elias 29 in the Rho Ophiuchi molecular cloud. It provides a
unique opportunity to study the origin and evolution of interstellar ice and
the interrelationship of interstellar ice and hot core gases around low mass
protostars. We see abundant hot CO and H2O gas, as well as the absorption bands
of CO, CO2, H2O and ``6.85 um'' ices. We compare the abundances and physical
conditions of the gas and ices toward Elias 29 with the conditions around
several well studied luminous, high mass protostars. The high gas temperature
and gas/solid ratios resemble those of relatively evolved high mass objects
(e.g. GL 2591). However, none of the ice band profiles shows evidence for
significant thermal processing, and in this respect Elias 29 resembles the
least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude
that the heating of the envelope of the low mass object Elias 29 is
qualitatively different from that of high mass protostars. This is possibly
related to a different density gradient of the envelope or shielding of the
ices in a circumstellar disk. This result is important for our understanding of
the evolution of interstellar ices, and their relation to cometary ices.Comment: 18 pages and 14 figures, accepted for publication in A&
Structural analysis of the architecture and in situ localization of the main S-layer complex in Deinococcus radiodurans
Bacterial surface layers are paracrystalline assemblies of proteins that provide the first line of defense against environmental shocks. Here, we report the 3D structure, in situ localization, and orientation of the S-layer deinoxanthin-binding complex (SDBC), a hetero-oligomeric assembly of proteins that in Deinococcus radiodurans represents the main S-layer unit. The SDBC is resolved at 11-Ă… resolution by single-particle analysis, while its in situ localization is determined by cryo-electron crystallography on intact cell-wall fragments leading to a projection map at 4.5-Ă… resolution. The SDBC exhibits a triangular base with three comma-shaped pores, and a stalk departing orthogonally from the center of the base and oriented toward the intracellular space. Combining state-of-the-art techniques, results show the organization of this S-layer and its connection within the underlying membranes, demonstrating the potential for applications from nanotechnologies to medicine
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