1,307 research outputs found
Foreground removal requirements for measuring large-scale CMB B-modes in light of BICEP2
The most convincing confirmation that the B-mode polarization signal detected
at degree scales by BICEP2 is due to the Cosmic Microwave Background (CMB)
would be the measurement of its large-scale counterpart. We assess the
requirements for diffuse component separation accuracy over large portions of
the sky in order to measure the large-scale B-mode signal corresponding to a
tensor to scalar ratio of r=0.1-0.2.
We use the method proposed by Bonaldi & Ricciardi (2011) to forecast the
performances of different simulated experiments taking into account noise and
foreground removal issues. We do not consider instrumental systematics, and we
implicitly assume that they are not the dominant source of error. If this is
the case, the confirmation of an r=0.1-0.2 signal is achievable by Planck even
for conservative assumptions regarding the accuracy of foreground cleaning. Our
forecasts suggest that the combination of this experiment with BICEP2 will lead
to an improvement of 25-45% in the constraint on r.
A next-generation CMB polarization satellite, represented in this work by the
COrE experiment, can reduce dramatically (by almost another order of magnitude)
the uncertainty on r. In this case, however, the accuracy of foreground removal
becomes critical to fully benefit from the increase in sensitivity.Comment: 8 pages, 3 figures, 1 table. Accepted by MNRA
Cosmological constraints from Sunyaev-Zeldovich cluster counts: an approach to account for missing redshifts
The accumulation of redshifts provides a significant observational bottleneck
when using galaxy cluster surveys to constrain cosmological parameters. We
propose a simple method to allow the use of samples where there is a fraction
of the redshifts that are not known. The simplest assumption is that the
missing redshifts are randomly extracted from the catalogue, but the method
also allows one to take into account known selection effects in the
accumulation of redshifts. We quantify the reduction in statistical precision
of cosmological parameter constraints as a function of the fraction of missing
redshifts for simulated surveys, and also investigate the impact of making an
incorrect assumption for the distribution of missing redshifts.Comment: 6 pages, 5 figures, accepted by Ap
CMB component separation in the pixel domain
We show that the popular ILC approach is unstable in respect to the division
of the sample of map pixels to the set of ``homogeneous'' subsamples. For
suitable choice of such subsamples we can obtain the restored CMB signal with
amplitudes ranged from zero to the amplitudes of the observed signal. We
propose approach which allows us to obtain reasonable estimates of at
and similar to WMAP for larger . With this
approach we reduce some anomalies of the WMAP results. In particular, our
estimate of the quadrupole is well consistent to theoretical one, the effect of
the ``axis of evil'' is suppressed and the symmetry of the north and south
galactic hemispheres increases. This results can change estimates of quadrupole
polarization and the redshift of reionization of the Universe. We propose also
new simple approach which can improve WMAP estimates of high power
spectrum.Comment: 7 pages, 5 figure
A reassessment of the evidence of the Integrated Sachs-Wolfe effect through the WMAP-NVSS correlation
We reassess the estimate of the cross-correlation of the spatial distribution
of the NRAO VLA Sky Survey (NVSS) radio sources with that of Cosmic Microwave
Background (CMB) anisotropies from the Wilkinson Microwave Anisotropy Probe
(WMAP). This re-analysis is motivated by the fact that most previous studies
adopted a redshift distribution of NVSS sources inconsistent with recent data.
We find that the constraints on the bias-weighted redshift distribution,
b(z)xN(z), of NVSS sources, set by the observed angular correlation function,
w(theta), strongly mitigate the effect of the choice of N(z). If such
constraints are met, even highly discrepant redshift distributions yield
NVSS-WMAP cross-correlation functions consistent with each other within
statistical errors. The models favoured by recent data imply a bias factor,
b(z), decreasing with increasing z, rather than constant, as assumed by most
previous analyses. As a consequence, the function b(z)xN(z) has more weight at
z<1, i.e. in the redshift range yielding the maximum contribution to the ISW in
a standard LambdaCDM cosmology. On the whole, the NVSS turns out to be better
suited for ISW studies than generally believed, even in the absence of an
observational determination of the redshift distribution. The NVSS-WMAP
cross-correlation function is found to be fully consistent with the prediction
of the standard LambdaCDM cosmology.Comment: 6 pages, 2 figures, submitted to MNRA
Selective readout and back-action reduction for wideband acoustic gravitational wave detectors
We present the concept of selective readout for broadband resonant mass
gravitational wave detectors. This detection scheme is capable of specifically
selecting the signal from the contributions of the vibrational modes sensitive
to the gravitational waves, and efficiently rejecting the contribution from non
gravitationally sensitive modes. Moreover this readout, applied to a dual
detector, is capable to give an effective reduction of the back-action noise
within the frequency band of interest. The overall effect is a significant
enhancement in the predicted sensitivity, evaluated at the standard quantum
limit for a dual torus detector. A molybdenum detector, 1 m in diameter and
equipped with a wide area selective readout, would reach spectral strain
sensitivities 2x10^{-23}/sqrt{Hz} between 2-6 kHz.Comment: 9 pages, 4 figure
Inhomogeneous mechanical losses in micro-oscillators with high reflectivity coating
We characterize the mechanical quality factor of micro-oscillators covered by
a highly reflective coating. We test an approach to the reduction of mechanical
losses, that consists in limiting the size of the coated area to reduce the
strain and the consequent energy loss in this highly dissipative component.
Moreover, a mechanical isolation stage is incorporated in the device. The
results are discussed on the basis of an analysis of homogeneous and
non-homogeneous losses in the device and validated by a set of Finite-Element
models. The contributions of thermoelastic dissipation and coating losses are
separated and the measured quality factors are found in agreement with the
calculated values, while the absence of unmodeled losses confirms that the
isolation element integrated in the device efficiently uncouples the dynamics
of the mirror from the support system. Also the resonant frequencies evaluated
by Finite-Element models are in good agreement with the experimental data, and
allow the estimation of the Young modulus of the coating. The models that we
have developed and validated are important for the design of oscillating
micro-mirrors with high quality factor and, consequently, low thermal noise.
Such devices are useful in general for high sensitivity sensors, and in
particular for experiments of quantum opto-mechanics
STREPTOMYCETES AS BIOLOGICAL CONTROL AGENTS AND PLANT GROWTH-PROMOTING BACTERIA
Developing no-chemical strategies for the control of soil borne pathogens is one of the major issues for the cultivation of leafy vegetables. The application of Biological Control Agents (BCAs) represents a valuable approach and nowadays some biocontrol products are available on the market for greenhouse and field applications. However, these products often show lack of consistency and variable results mainly due to the poor knowledge about their biology and modes of applications and how the agroecosystem components modulate their efficacy.
Streptomycetes are soil inhabitants and have an important ecological role in the turn-over of organic matter; they can also establish beneficial relationships with plant roots enhancing host growth and protection against pathogens through the production of bioactive compounds, lytic enzymes, phytohormones and siderophores.
This PhD project aimed to study streptomycetes as BCA and Plant Growth Promoting Bacteria for their use to manage soil borne fungal epidemics in horticulture.
A collection of 200 endophytic streptomycete strains isolated from roots was used in this work. To be able to compare the activity of every strain against the pathogens, the dual culture assay was optimized for some representative fungal pathogens based on mycelium radial growth rate in vitro. Subsequently, the optimized method was applied to screen the collection. Some strains showed strong inhibitory activity, but it was specific for one target pathogen and in few cases comprised more than one pathogen. Based on the promising results obtained from the in vitro assays for Sclerotinia sclerotiorum, further studies were focused on the activity of ten strains used for biological control of lettuce drop in different conditions. In particular, it was studied the effect of the application timing of the antagonist and the pathogen, and the amount of the streptomycete used to improve lettuce drop protection. The survival analysis applied to the data of the growth chamber experiments showed that when lettuce was sown one week after the growth substrate inoculation with the pathogen and antagonists, disease control improved, and Streptomyces spp. FT05W, SW06W and SW29W reduced the risk of disease incidence by 42%. On the contrary, no beneficial effect was observed when lettuce was sown the same day of the growth substrate inoculation. Streptomycetes spore concentration significantly influenced lettuce drop protection, but this effect was strain-dependent.
Based on these results we planned appropriate field experiment to confirm the results obtained, however, in the field we did not observed significant differences in lettuce protection. Therefore we
speculated that moving from controlled to a more complex agroecosystem environment the streptomycete antagonistic activity could fade away probably due to unfavorable interaction in a more complex microflora.
Indole-3-acetic acid and the siderophore production were observed for Streptomyces spp. CVM02R and SW29W in in vitro assays, but in field experiments no significant PGP effect on lettuce was obtained at harvest assessing the head weights of plants.
The colonization of lettuce rhizosphere and root tissues was investigated using the EGFP labelled strain Streptomyces sp. ZEA17I. This strain showed both rhizospheric and endophytic competences, characters necessary for its successful use for biological control. In addition we showed that applying the strains as spore suspension in the growth substrate resulted in significantly higher roots and rhizosphere colonization than when delivered as seed coating.
In conclusion, the results obtained in this study showed that bacteria of the genus Streptomycetes appear valuable candidates for the biological control of soil borne fungal pathogens. However, the complex interactions among the host plant, the antagonist and the pathogen occurring in the agroecosystem are mostly unknown and could generate contradictory results for different environments. Therefore, we think that further studies on simplified models are necessary in order to understand the mechanism on which biological control is based, in order to improve streptomycete activity as BCA for the management of fungal soil borne epidemics
Detection of weak stochastic force in a parametrically stabilized micro opto-mechanical system
Measuring a weak force is an important task for micro-mechanical systems,
both when using devices as sensitive detectors and, particularly, in
experiments of quantum mechanics. The optimal strategy for resolving a weak
stochastic signal force on a huge background (typically given by thermal noise)
is a crucial and debated topic, and the stability of the mechanical resonance
is a further, related critical issue. We introduce and analyze the parametric
control of the optical spring, that allows to stabilize the resonance and
provides a phase reference for the oscillator motion, yet conserving a free
evolution in one quadrature of the phase space. We also study quantitatively
the characteristics of our micro opto-mechanical system as detector of
stochastic force for short measurement times (for quick, high resolution
monitoring) as well as for the longer term observations that optimize the
sensitivity. We compare a simple, naive strategy based on the evaluation of the
variance of the displacement (that is a widely used technique) with an optimal
Wiener-Kolmogorov data analysis. We show that, thanks to the parametric
stabilization of the effective susceptibility, we can more efficiently
implement Wiener filtering, and we investigate how this strategy improves the
performance of our system. We finally demonstrate the possibility to resolve
stochastic force variations well below 1% of the thermal noise
An ultra-low dissipation micro-oscillator for quantum opto-mechanics
Generating non-classical states of light by opto-mechanical coupling depends
critically on the mechanical and optical properties of micro-oscillators and on
the minimization of thermal noise. We present an oscillating micro-mirror with
a mechanical quality factor Q = 2.6x10^6 at cryogenic temperature and a Finesse
of 65000, obtained thanks to an innovative approach to the design and the
control of mechanical dissipation. Already at 4 K with an input laser power of
2 mW, the radiation-pressure quantum fluctuations become the main noise source,
overcoming thermal noise. This feature makes our devices particularly suitable
for the production of pondero-motive squeezing.Comment: 21 pages including Supplementary Informatio
Harmonic damped oscillators with feedback. A Langevin study
We consider a system in direct contact with a thermal reservoir and which, if
left unperturbed, is well described by a memory-less equilibrium Langevin
equation of the second order in the time coordinate. In such conditions, the
strength of the noise fluctuations is set by the damping factor, in accordance
with the Fluctuation and Dissipation theorem. We study the system when it is
subject to a feedback mechanism, by modifying the Langevin equation
accordingly. Memory terms now arise in the time evolution, which we study in a
non-equilibrium steady state. Two types of feedback schemes are considered, one
focusing on time shifts and one on phase shifts, and for both cases we evaluate
the power spectrum of the system's fluctuations. Our analysis finds application
in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.Comment: 17 page
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