515 research outputs found
Isolation of Bacteria with Potential Plant-Promoting Traits and Optimization of Their Growth Conditions
This research aimed at investigating the isolation and identification of bacterial strains with biological nitrogen-fixing capability and phosphate, potassium, and zinc solubilization activities from a durum wheat field under two different tillage practices including 10 years of conventional tillage (CT) and no-tillage (NT) practices. Attempts were also extended to estimate their relative abundances in the soil as well as to develop accurate mathematical models in determining the effect of different temperatures, NaCl concentrations and pH on the growth, and activity of selected isolates. Twelve effective bacterial strains, including Pseudomonas, Acinetobacter, and Comamonas genera, were identified with a great potential to solubilize the insoluble forms of phosphate (from 11.1 to 115.5 mg lâ1 at pH 8), potassium (from 32.2 to 35.6 mg lâ1 at pH 7), and zinc (from 1.11 to 389.90 mg lâ1 at pH 9) as well as to fix N2 gas (from 19.9 to 25.2 mg lâ1). To our knowledge, this is the first report of the ability of Comamonas testosteroni and Acinetobacter pittii to fix nitrogen and to solubilize insoluble potassium compound, respectively. Three families, Moraxellaceae, Pseudomonadaceae, and Comamonadaceae, showed a higher percentage of abundance in the NT samples as compared to the CT, but only significant difference was observed in the relative abundance of Pseudomonadaceae (P < 0.01). These strains could be definitively recommended as inoculants to promote plant growth in the wide ranges of pH, salinity levels (with maximum growth and complete inhibition of growth from 0.67â0.92% to 3.5â9.3% NaCl, respectively), and temperatures (2.1â45.1 °C)
The infrared emission of carbonaceous particles around C-rich IRAS sources
The IRAS spectra of 23 carbon-rich sources have been fitted by means of an improved theoretical model based on the Leung-Spagna radiative transfer code and using extinction data obtained in our laboratory for different types of amorphous carbon and silicon carbide submicron particles. The agreement between observations and theoretical spectra is rather good. However, a comparison between the IRAS
spectrum of the object 1244710425 (RU Vir) and that recently obtained at UKIRT, for the same object but with higher resolution, seems to open new problems
Measuring Polarization in microlensing events
We re-consider the polarization of the star light that may arise during
microlensing events due to the high gradient of magnification across the
atmosphere of the source star, by exploring the full range of microlensing and
stellar physical parameters. Since it is already known that only cool evolved
giant stars give rise to the highest polarization signals, we follow the model
by Simmons et al. (2002) to compute the polarization as due to the photon
scattering on dust grains in the stellar wind. Motivated by the possibility to
perform a polarization measurement during an ongoing microlensing event, we
consider the recently reported event catalog by the OGLE collaboration covering
the 2001-2009 campaigns (OGLE-III events), that makes available the largest and
more comprehensive set of single lens microlensing events towards the Galactic
bulge. The study of these events, integrated by a Monte Carlo analysis, allows
us to estimate the expected polarization profiles and to predict for which
source stars and at which time is most convenient to perform a polarization
measurement in an ongoing event. We find that about two dozens of OGLE-III
events (about 1 percent of the total) have maximum polarization degree in the
range 0.1 < P_{\rm max} <1 percent, corresponding to source stars with apparent
magnitude I < 14.5, being very cool red giants.This signal is measurable by
using the FORS2 polarimeter at VLT telescope with about 1 hour integration
time.Comment: Originally submitted to MNRAS on 01/07/2014. Present version with
minor changes as required by the Refere
Measuring polarization in microlensing events
We reconsider the polarization of the star light that may arise during microlensing events due to the high gradient of magnification across the atmosphere of the source star, by exploring the full range of microlensing and stellar physical parameters. Since it is already known that only cool evolved giant stars give rise to the highest polarization signals, we follow the model by Simmons etal. to compute the polarization as due to the photon scattering on dust grains in the stellar wind. Motivated by the possibility to perform a polarization measurement during an ongoing microlensing event, we consider the recently reported event catalogue by the Optical Gravitational Lensing Experiment (OGLE) collaboration covering the 2001-2009 campaigns (OGLE-III events), that makes available the largest and more comprehensive set of single-lens microlensing events towards the Galactic bulge. The study of these events, integrated by a Monte Carlo analysis, allows us to estimate the expected polarization profiles and to predict for which source stars and at which time is most convenient to perform a polarization measurement in an ongoing event. We find that about two dozens of OGLE-III events (about 1âperâcent of the total) have maximum polarization degree in the range 0.1<Pmax<1âperâcent, corresponding to source stars with apparent magnitude IâČ14.5, being very cool red giants. This signal is measurable by using the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT) telescope with about 1h integration tim
Discovery of a bright microlensing event with planetary features towards the Taurus region: a super Earth planet
The transient event labeled as TCP J05074264+2447555 recently discovered
towards the Taurus region was quickly recognized to be an ongoing microlensing
event on a source located at distance of only pc from Earth. Here, we
show that observations with high sampling rate close to the time of maximum
magnification revealed features that imply the presence of a binary lens system
with very low mass ratio components. We present a complete description of the
binary lens system which hosts an Earth-like planet with most likely mass of
M. Furthermore, the source estimated location and
detailed Monte Carlo simulations allowed us to classify the event as due to the
closest lens system, being at a distance of pc and mass M.Comment: Accepted for publication on MNRAS, 2018. 6 Pages, 5 Figures.
References update
The YSO Population in the Vela-D Molecular Cloud
We investigate the young stellar population in the Vela Molecular Ridge,
Cloud-D (VMR-D), a star forming (SF) region observed by both Spitzer/NASA and
Herschel/ESA space telescope. The point source, band-merged, Spitzer-IRAC
catalog complemented with MIPS photometry previously obtained is used to search
for candidate young stellar objects (YSO), also including sources detected in
less than four IRAC bands. Bona fide YSO are selected by using appropriate
color-color and color-magnitude criteria aimed to exclude both Galatic and
extragalactic contaminants. The derived star formation rate and efficiency are
compared with the same quantities characterizing other SF clouds. Additional
photometric data, spanning from the near-IR to the submillimeter, are used to
evaluate both bolometric luminosity and temperature for 33 YSOs located in a
region of the cloud observed by both Spitzer and Herschel. The
luminosity-temperature diagram suggests that some of these sources are
representative of Class 0 objects with bolometric temperatures below 70 K and
luminosities of the order of the solar luminosity. Far IR observations from the
Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to
obtain a band-merged photometric catalog of Herschel sources aimed to
independently search for protostars. We find 122 Herschel cores located on the
molecular cloud, 30 of which are protostellar and 92 starless. The global
protostellar luminosity function is obtained by merging the Spitzer and
Herschel protostars. Considering that 10 protostars are found in both Spitzer
and Herschel list it follows that in the investigated region we find 53
protostars and that the Spitzer selected protostars account for approximately
two-thirds of the total.Comment: 40 pages, 12 figures, accepted for publication in Ap
Characterizing the structure of diffuse emission in Hi-GAL maps
We present a study of the structure of the Galactic interstellar medium
through the Delta-variance technique, related to the power spectrum and the
fractal properties of infrared/sub-mm maps. Through this method, it is possible
to provide quantitative parameters which are useful to characterize different
morphological and physical conditions, and to better constrain the theoretical
models. In this respect, the Herschel Infrared Galactic Plane Survey carried
out at five photometric bands from 70 to 500 \mu m constitutes an unique
database for applying statistical tools to a variety of regions across the
Milky Way. In this paper, we derive a robust estimate of the power-law portion
of the power spectrum of four contiguous 2{\deg}x2{\deg} Hi-GAL tiles located
in the third Galactic quadrant (217{\deg} < l < 225{\deg}, -2{\deg} < b <
0{\deg}). The low level of confusion along the line of sight testified by CO
observations makes this region an ideal case. We find very different values of
the power spectrum slope from tile to tile but also from wavelength to
wavelength (2 < \beta < 3), with similarities between fields attributable to
components located at the same distance. Thanks to the comparison with models
of turbulence, an explanation of the determined slopes in terms of the fractal
geometry is also provided, and possible relations with the underlying physics
are investigated. In particular, an anti-correlation between ISM fractal
dimension and star formation efficiency is found for the two main distance
components observed in these fields. A possible link between the fractal
properties of the diffuse emission and the resulting clump mass function is
discussed.Comment: Accepted by Ap
- âŠ