543 research outputs found
A Determination of the Hubble Constant from Cepheid Distances and a Model of the Local Peculiar Velocity Field
We present a measurement of the Hubble Constant based on Cepheid distances to
27 galaxies within 20 Mpc. We take the Cepheid data from published measurements
by the Hubble Telescope Key Project on the Distance Scale (H0KP). We calibrate
the Cepheid Period-Luminosity (PL) relation with data from over 700 Cepheids in
the LMC obtained by the OGLE collaboration; we assume an LMC distance modulus
of 18.50 mag (d=50.1 kpc). Using this PL calibration we obtain new distances to
the H0KP galaxies. We correct the redshifts of these galaxies for peculiar
velocities using two distinct velocity field models: the phenomenological model
of Tonry et al. and a model based on the IRAS density field and linear
gravitational instability theory. We combine the Cepheid distances with the
corrected redshifts for the 27 galaxies to derive H_0, the Hubble constant. The
results are H_0 = 85 +/- 5 km/s/Mpc (random error) at 95% confidence when the
IRAS model is used, and 92 +/- 5 km/s/Mpc when the phenomenological model is
used. The IRAS model is a better fit to the data and the Hubble constant it
returns is more reliable. Systematic error stems mainly from LMC distance
uncertainty which is not directly addressed by this paper. Our value of H_0 is
significantly larger than that quoted by the H0KP, H_0 = 71 +/- 6 km/s/Mpc.
Cepheid recalibration explains ~30% of this difference, velocity field analysis
accounts for ~70%. We discuss in detail possible reasons for this discrepancy
and future study needed to resolve it.Comment: 33 pages, 8 embedded figures. New table, 5 new references, text
revision
Photo-induced magnetization enhancement in two-dimensional weakly anisotropic Heisenberg magnets
By comparing the photo-induced magnetization dynamics in simple layered
systems we show how light-induced modifications of the magnetic anisotropy
directly enhance the magnetization. It is observed that the spin precession in
(CH3NH3)2CuCl4, initiated by a light pulse, increases in amplitude at the
critical temperature TC. The phenomenon is related to the dependence of the
critical temperature on the axial magnetic anisotropy. The present results
underline the possibility and the importance of the optical modifications of
the anisotropy, opening new paths toward the control of the magnetization state
for ultrafast memories.Comment: 5 pages, 3 figures, supplementary info as SIr.pd
SEASONAL BEHAVIOUR OF KERATINOPHILIC FUNGI ISOLATED FROM PARKS SOIL IN MILAN
Soil samples collected from 10 parks in Milan were examined for the presence of keratinophilic fungi by the Orr’s hair baiting technique. The organisms isolated and their frequency were as follows: Arthroderma uncinatum and its anamorph Keratinomyces ajelloi were dominantand recovered from 22.5% - 43.7% and 40% - 50% of the soil samples collected in summer and winter respectively. Myceliophthora vellerea was isolated in 31.2% of the samples, particularly in winter, Microsporum gypseum in winter (20%) and Trichophyton terrestre (10%) in summer.Chrysosporium keratinophilum (16.2% in summer and 18.7% in winter) C. indicum (15% s- 23.7% w), C. pannicola (5% s - 37% w). Aphanoascus fulvescens was isolated in summer (23.7%). Among the cycloheximide-resistant keratinophilic fungi Alternaria alternata (27.5% s – 33.7% w), Paecilomyces lilacinus (26.2% s - 18.7% w) and Acremonium strictum (8.7% s - 20% w) also were observed. The distribution of the different species is discussed.
A road to hydrogenating graphene by a reactive ion etching plasma
We report the hydrogenation of single and bilayer graphene by an
argon-hydrogen plasma produced in a reactive ion etching (RIE) system.
Electronic transport measurements in combination with Raman spectroscopy are
used to link the electric mean free path to the optically extracted defect
concentration. We emphasize the role of the self-bias of the graphene in
suppressing the erosion of the akes during plasma processing. We show that
under the chosen plasma conditions the process does not introduce considerable
damage to the graphene sheet and that hydrogenation occurs primarily due to the
hydrogen ions from the plasma and not due to fragmentation of water adsorbates
on the graphene surface by highly accelerated plasma electrons. For this reason
the hydrogenation level can be precisely controlled. The hydrogenation process
presented here can be easily implemented in any RIE plasma system.Comment: 7 page
seasonal behaviour of keratinophilic fungi isolated from parks soil in milan
Soil samples collected from 10 parks in Milan were examined for the presence of keratinophilic fungi by the Orr's hair baiting technique. The organisms isolated and their frequency were as follows: Arthroderma uncinatum and its anamorph Keratinomyces ajelloi were dominant and recovered from 22.5% - 43.7% and 40% - 50% of the soil samples collected in summer and winter respectively. Myceliophthora vellerea was isolated in 31.2% of the samples, particularly in winter, Microsporum gypseum in winter (20%) and Trichophyton terrestre (10%) in summer. Chrysosporium keratinophilum (16.2% in summer and 18.7% in winter) C. indicum (15% s- 23.7% w), C. pannicola (5% s - 37% w). Aphanoascus fulvescens was isolated in summer (23.7%). Among the cycloheximide-resistant keratinophilic fungi Alternaria alternata (27.5% s – 33.7% w), Paecilomyces lilacinus (26.2% s - 18.7% w) and Acremonium strictum (8.7% s - 20% w) also were observed. The distribution of the different species is discussed
A Quantitative Evaluation of the Galaxy Component of COSMOS and APM Catalogs
We have carried out an independent quantitative evaluation of the galaxy
component of the "COSMOS/UKST Southern Sky Object Catalogue" (SSC) and the
"APM/UKST J Catalogue" (APM). Using CCD observations our results corroborate
the accuracy of the photometry of both catalogs, which have an overall
dispersion of about 0.2 mag in the range 17 <= b_J <= 21.5. The SSC presents
externally calibrated galaxy magnitudes that follow a linear relation, while
the APM instrumental magnitudes of galaxies, only internally calibrated by the
use of stellar profiles, require second-order corrections. The completeness of
both catalogs in a general field falls rapidly fainter than b_J = 20.0, being
slightly better for APM. The 90% completeness level of the SSC is reached
between b_J = 19.5 and 20.0, while for APM this happens between b_J = 20.5 and
21.0. Both SSC and APM are found to be less complete in a galaxy cluster field.
Galaxies misclassified as stars in the SSC receive an incorrect magnitude
because the stellar ones take saturation into account besides using a different
calibration curve. In both cases, the misclassified galaxies show a large
diversity of colors that range from typical colors of early-types to those of
blue star-forming galaxies. A possible explanation for this effect is that it
results from the combination of low sampling resolutions with properties of the
image classifier for objects with characteristic sizes close to the
instrumental resolution. We find that the overall contamination by stars
misclassified as galaxies is < 5% to b_J = 20.5, as originally estimated for
both catalogs. Although our results come from small areas of the sky, they are
extracted from two different plates and are based on the comparison with two
independent datasets.Comment: 14 pages of text and tables, 8 figures; to be published in the
Astronomical Journal; for a single postscript version file see
ftp://danw.on.br/outgoing/caretta/caretta.p
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