2,283 research outputs found
Derivation of Distances with the Tully-Fisher Relation: The Antlia Cluster
The Tully-Fisher relation is a correlation between the luminosity and the HI
21cm line width in spiral galaxies (LLW relation). It is used to derive galaxy
distances in the interval 7 to 100 Mpc. Closer, the Cepheids, TRGB and Surface
Brightness Fluctuation methods give a better accuracy. Further, the SNIa are
luminous objects still available for distance measurement purposes, though with
a dramatically lower density grid of measurements on the sky. Galaxies in
clusters are all at the same distance from the observer. Thus the distance of
the cluster derived from a large number of galaxies (N) has an error reduced
according to the square root of N. However, not all galaxies in a cluster are
suitable for the LLW measurement. The selection criteria we use are explained
hereafter; the important point being to avoid Malmquist bias and to not
introduce any systematics in the distance measurement.Comment: Moriond0
Anatomy of Ursa Majoris
A nearby friable cloud in Ursa Majoris contains 270 galaxies with radial
velocities 500 < VLG < 1500 km s^-1 inside the area of RA= [11h; 13h] and DEC=
[+40deg; +60deg]. At present, 97 galaxies of them have individual distance
estimates. We use these data to clarify the structure and kinematics of the UMa
complex. According to Makarov & Karachentsev (2011), most of the UMa galaxies
belong to seven bound groups, which have the following median parameters:
velocity dispersion of 58 km s^-1, harmonic projected radius of 300 kpc, virial
mass of 2.10^12 Msol, and virial- mass-to-K-band-luminosity of 27Msol/Lsol.
Almost a half of the UMa cloud population are gas-rich dwarfs (Ir, Im, BCD)
with active star formation seen in the GALEX UV-survey. The UMa groups reside
within 15-19 Mpc from us, being just at the same distance as Virgo cluster. The
total virial mass of the UMa groups is 4.10^13 Msol, yielding the average
density of dark matter in the UMa cloud to be Omega_m = 0.08, i.e. a factor
three lower than the cosmic average. This is despite the fact that the UMa
cloud resides in a region of the Universe that is an apparent overdensity. A
possible explanation for this is that most mass in the Universe lies in the
empty space between clusters. Herewith, the mean distances and velocities of
the UMa groups follow nearly undisturbed Hubble flow without a sign of the
'Z-wave" effect caused by infall toward a massive attractor. This constrains
the total amount of dark matter between the UMa groups within the cloud volume.Comment: correction of a typo in the abstract, 18 pages, 2 figures. accepted
for MNRAS, nov 26, 201
The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles
Engineered inorganic nanoparticles are essential components in the
development of nanotechnologies. For applications in nanomedicine, particles
need to be functionalized to ensure a good dispersibility in biological fluids.
In many cases however, functionalization is not sufficient : the particles
become either coated by a corona of serum proteins or precipitate out of the
solvent. In the present paper, we show that by changing the coating of iron
oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small
carboxylated polymers (poly(acrylic acid)), the colloidal stability of the
dispersion is improved and the adsorption/internalization of iron towards
living mammalian cells is profoundly affected. Citrate-coated particles are
shown to destabilize in all fetal-calf-serum based physiological conditions
tested, whereas the polymer coated particles exhibit an outstanding
dispersibility as well as a structure devoid of protein corona. The
interactions between nanoparticles and human lymphoblastoid cells are
investigated by transmission electron microscopy and flow cytometry. Two types
of nanoparticle/cell interactions are underlined. Iron oxides are found either
adsorbed on the cellular membranes, or internalized into membrane-bound
endocytosis compartments. For the precipitating citrate-coated particles, the
kinetics of interactions reveal a massive and rapid adsorption of iron oxide on
the cell surfaces. The quantification of the partition between adsorbed and
internalized iron was performed from the cytometry data. The results highlight
the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.Comment: 21 pages, 11 figures, accepted at Biomaterials (2011
Giant disk galaxies : Where environment trumps mass in galaxy evolution
We identify some of the most HI massive and fastest rotating disk galaxies in
the local universe with the aim of probing the processes that drive the
formation of these extreme disk galaxies. By combining data from the Cosmic
Flows project, which has consistently reanalyzed archival galaxy HI profiles,
and 3.6m photometry obtained with the Spitzer Space Telescope, with which
we can measure stellar mass, we use the baryonic Tully-Fisher (BTF)
relationship to explore whether these massive galaxies are distinct. We discuss
several results, but the most striking is the systematic offset of the
HI-massive sample above the BTF. These galaxies have both more gas and more
stars in their disks than the typical disk galaxy of similar rotational
velocity. The "condensed" baryon fraction, , the fraction of the baryons
in a dark matter halo that settle either as cold gas or stars into the disk, is
twice as high in the HI-massive sample than typical, and almost reaches the
universal baryon fraction in some cases, suggesting that the most extreme of
these galaxies have little in the way of a hot baryonic component or cold
baryons distributed well outside the disk. In contrast, the star formation
efficiency, measured as the ratio of the mass in stars to that in both stars
and gas, shows no difference between the HI-massive sample and the typical disk
galaxies. We conclude that the star formation efficiency is driven by an
internal, self-regulating process, while is affected by external factors.
We also found that the most massive HI detected galaxies are located
preferentially in filaments. We present the first evidence of an environmental
effect on galaxy evolution using a dynamical definition of a filament.Comment: 14 pages, in press MNRA
Circuit approach to photonic heat transport
We discuss the heat transfer by photons between two metals coupled by a
linear element with a reactive impedance. Using a simple circuit approach, we
calculate the spectral power transmitted from one resistor to the other and
find that it is determined by the photon transmission coefficient, which
depends on the impedances of the metals and the coupling element. We study the
total photonic power flow for different coupling impedances, both in the linear
regime, where the temperature difference between the metals is small, and in
the non-linear regime of large temperature differences.Comment: 6 pages, 6 figure
Star Formation in Nearby Isolated Galaxies
We use the FUV fluxes measured with the GALEX to study the star formation
properties of galaxies collected in the "Local Orphan Galaxies" catalog (LOG).
Among 517 LOG galaxies having radial velocities V(LG) < 3500 km/s and Galactic
latitudes |b|> 15 degr, 428 objects have been detected in FUV. We briefly
discuss some scaling relations between the specific star formation rate (SSFR)
and stellar mass, HI-mass, morphology, and surface brightness of galaxies
situated in extremely low density regions of the Local Supercluster. Our sample
is populated with predominantly late-type, gas-rich objects with the median
morphological type of Sdm. Only 5% of LOG galaxies are classified as early
types: E, S0, S0/a, however, they systematically differ from normal E and S0
galaxies by lower luminosity and presence of gas and dust. We find that almost
all galaxies in our sample have their SSFR below 0.4 [Gyr^{-1}]. This limit is
also true even for a sample of 260 active star-burst Markarian galaxies
situated in the same volume. The existence of such a quasi-Eddington limit for
galaxies seems to be a key factor which characterizes the transformation of gas
into stars at the current epoch.Comment: 10 pages, 8 figures, 3 table
Local spectroscopy of a proximity superconductor at very low temperature
We performed the local spectroscopy of a Normal-metal--Superconductor (N-S)
junction with the help of a very low temperature (60 mK) Scanning Tunneling
Microscope (STM). The spatial dependence of the local density of states was
probed locally in the vicinity of the N-S interface. We observed spectra with a
fully-developed gap in the regions where a thin normal metal layer caps the
superconductor dot. Close to the S metal edge, a clear pseudo-gap shows up,
which is characteristic of the superconducting proximity effect in the case of
a long normal metal. The experimental results are compared to the predictions
of the quasiclassical theory.Comment: 7 pages, 3 figure
From Spitzer Galaxy Photometry to Tully-Fisher Distances
This paper involves a data release of the observational campaign: Cosmicflows
with Spitzer (CFS). Surface photometry of the 1270 galaxies constituting the
survey is presented. An additional ~ 400 galaxies from various other Spitzer
surveys are also analyzed. CFS complements the Spitzer Survey of Stellar
Structure in Galaxies, that provides photometry for an additional 2352
galaxies, by extending observations to low galactic latitudes (|b|<30 degrees).
Among these galaxies are calibrators, selected in K band, of the Tully-Fisher
relation. The addition of new calibrators demonstrate the robustness of the
previously released calibration. Our estimate of the Hubble constant using
supernova host galaxies is unchanged, H0 = 75.2 +/- 3.3 km/s/Mpc.
Distance-derived radial peculiar velocities, for the 1935 galaxies with all the
available parameters, will be incorporated into a new data release of the
Cosmicflows project. The size of the previous catalog will be increased by 20%,
including spatial regions close to the Zone of Avoidance.Comment: Accepted for publication in MNRAS, 16 pages, 14 figures, 6 table
Two philosophies for solving non-linear equations in algebraic cryptanalysis
Algebraic Cryptanalysis [45] is concerned with solving of particular systems of multivariate non-linear equations which occur in cryptanalysis. Many different methods for solving such problems have been proposed in cryptanalytic literature: XL and XSL method, Gröbner bases, SAT solvers, as well as many other. In this paper we survey these methods and point out that the main working principle in all of them is essentially the same. One quantity grows faster than another quantity which leads to a “phase transition” and the problem becomes efficiently solvable. We illustrate this with examples from both symmetric and asymmetric cryptanalysis. In this paper we point out that there exists a second (more) general way of formulating algebraic attacks through dedicated coding techniques which involve redundancy with addition of new variables. This opens numerous new possibilities for the attackers and leads to interesting optimization problems where the existence of interesting equations may be somewhat deliberately engineered by the attacker
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