907 research outputs found
On the evolution of decoys in plant immune systems
The Guard-Guardee model for plant immunity describes how resistance proteins
(guards) in host cells monitor host target proteins (guardees) that are
manipulated by pathogen effector proteins. A recently suggested extension of
this model includes decoys, which are duplicated copies of guardee proteins,
and which have the sole function to attract the effector and, when modified by
the effector, trigger the plant immune response. Here we present a
proof-of-principle model for the functioning of decoys in plant immunity,
quantitatively developing this experimentally-derived concept. Our model links
the basic cellular chemistry to the outcomes of pathogen infection and
resulting fitness costs for the host. In particular, the model allows
identification of conditions under which it is optimal for decoys to act as
triggers for the plant immune response, and of conditions under which it is
optimal for decoys to act as sinks that bind the pathogen effectors but do not
trigger an immune response.Comment: 15 pages, 6 figure
A multiwavelength numerical model in support of quantitative retrievals of aerosol properties from automated lidar ceilometers and test applications for AOT and PM10 estimation
Abstract. The use of automated lidar ceilometer (ALC) systems for the
aerosol vertically resolved characterization has increased in recent
years thanks to their low construction and operation costs and their
capability of providing continuous unattended measurements. At the same time
there is a need to convert the ALC signals into usable geophysical
quantities. In fact, the quantitative assessment of the aerosol properties
from ALC measurements and the relevant assimilation in meteorological
forecast models is amongst the main objectives of the EU COST Action TOPROF
("Towards operational ground-based profiling with ALCs, Doppler lidars and
microwave radiometers for improving weather forecasts"). Concurrently, the E-PROFILE program of the European
Meteorological Services Network (EUMETNET) focuses on the harmonization of
ALC measurements and data provision across Europe. Within these frameworks,
we implemented a model-assisted methodology to retrieve key aerosol
properties (extinction coefficient, surface area, and volume) from elastic
lidar and/or ALC measurements. The method is based on results from a large
set of aerosol scattering simulations (Mie theory) performed at UV, visible,
and near-IR wavelengths using a Monte Carlo approach to select the input
aerosol microphysical properties. An average "continental aerosol type"
(i.e., clean to moderately polluted continental aerosol conditions) is
addressed in this study. Based on the simulation results, we derive mean
functional relationships linking the aerosol backscatter coefficients to the
abovementioned variables. Applied in the data inversion of single-wavelength
lidars and/or ALCs, these relationships allow quantitative determination of
the vertically resolved aerosol backscatter, extinction, volume, and surface
area and, in turn, of the extinction-to-backscatter ratios (i.e., the
lidar ratios, LRs) and extinction-to-volume conversion factor
(cv) at 355, 532, and 1064 nm. These variables provide valuable
information for visibility, radiative transfer, and air quality applications.
This study also includes (1) validation of the model simulations with real
measurements and (2) test applications of the proposed model-based ALC
inversion methodology. In particular, our model simulations were compared to
backscatter and extinction coefficients independently retrieved by Raman
lidar systems operating at different continental sites within the European
Aerosol Research Lidar Network (EARLINET). This comparison shows good
model–measurement agreement, with LR discrepancies below 20 %. The
model-assisted quantitative retrieval of both aerosol extinction and volume
was then tested using raw data from three different ALCs systems
(CHM 15k Nimbus), operating within the Italian Automated LIdar-CEilometer
network (ALICEnet). For this purpose, a 1-year record of the ALC-derived
aerosol optical thickness (AOT) at each site was compared to direct AOT
measurements performed by colocated sun–sky photometers. This comparison
shows an overall AOT agreement within 30 % at all sites. At one site, the
model-assisted ALC estimation of the aerosol volume and mass (i.e.,
PM10) in the lowermost levels was compared to values measured at
the surface level by colocated in situ instrumentation. Within this
exercise, the ALC-derived daily-mean mass concentration was found to
reproduce the corresponding (EU regulated) PM10 values measured by
the local air quality agency well in terms of both temporal variability and
absolute values. Although limited in space and time, the good performances of
the proposed approach suggest it could possibly
represent a valid option to extend the capabilities of ALCs to provide
quantitative information for operational air quality and meteorological
monitoring
Identification of Intermediates in the Reaction Pathway of SO on the CaO Surface: From Physisorption to Sulfite to Sulfate
The interaction of CaO and Ca(OH) with solvated or gaseous SO plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO with a CaO(001) single crystal. First, the surface chemistry of SO was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas
Phase transitions in the Potts spin glass model
We have studied the Potts spin glass with 2-state Ising spins and s-state
Potts variables using a cluster Monte Carlo dynamics. The model recovers the +-
J Ising spin glass (SG) for s=1 and exhibits for all s a SG transition at
T_{SG}(s) and a percolation transition at higher temperature T_p(s). We have
shown that for all values of at T_p(s) there is a thermodynamical
transition in the universality class of a ferromagnetic s-state Potts model.
The efficiency of the cluster dynamics is compared with that of standard spin
flip dynamics.Comment: 8 pages, Latex, with 8 EPS fig
Percolation transition and the onset of non exponential relaxation in fully frustrated models
We numerically study the dynamical properties of fully frustrated models in 2
and 3 dimensions. The results obtained support the hypothesis that the
percolation transition of the Kasteleyn-Fortuin clusters corresponds to the
onset of stretched exponential autocorrelation functions in systems without
disorder. This dynamical behavior may be due to the ``large scale'' effects of
frustration, present below the percolation threshold. Moreover these results
are consistent with the picture suggested by Campbell et al. in space of
configurations.Comment: 8 pages, 11 figures, revised versio
The Potts Fully Frustrated model: Thermodynamics, percolation and dynamics in 2 dimensions
We consider a Potts model diluted by fully frustrated Ising spins. The model
corresponds to a fully frustrated Potts model with variables having an integer
absolute value and a sign. This model presents precursor phenomena of a glass
transition in the high-temperature region. We show that the onset of these
phenomena can be related to a thermodynamic transition. Furthermore this
transition can be mapped onto a percolation transition. We numerically study
the phase diagram in 2 dimensions (2D) for this model with frustration and {\em
without} disorder and we compare it to the phase diagram of the model with
frustration {\em and} disorder and of the ferromagnetic model.
Introducing a parameter that connects the three models, we generalize the exact
expression of the ferromagnetic Potts transition temperature in 2D to the other
cases. Finally, we estimate the dynamic critical exponents related to the Potts
order parameter and to the energy.Comment: 10 pages, 10 figures, new result
an inclusive view of saharan dust advections to italy and the central mediterranean
Abstract We address observations of physical and chemical properties of Saharan dust advections (SDA) as observed in the Central Mediterranean basin, within the framework of the LIFE+10, DIAPASON project ( www.diapason-life.eu ). DIAPASON aimed at the definition of best practices and tools to detect and evaluate the contribution of Saharan dust to ground particulate matter (PM) loads. Polarization-sensitive, automated lidar-ceilometers (PLC) are one of the tools prototyped and used in the Rome area to reach this goal. The results presented in this study focus on: 1) the effectiveness of various observational tools at detecting and characterizing atmospheric dust plumes, and 2) processes and properties of Saharan dust advections reaching the central Mediterranean region. In this respect, the combination of numerical model forecasts and time-resolved (at least hourly) PLC or chemical observations was found to constitute an efficient way to predict and confirm the presence of Saharan dust. In the period 2011–2014, Saharan dust advections were observed to reach over Rome on about 32% of the days. In some 70% of these days the dust reached the ground in dry conditions, while 30% of advection days involved wet deposition. Dry (wet) deposition was found to maximize (minimize) in summer. The northern Sahara between Algeria and Tunisia (Grand Erg Oriental), was confirmed as the most frequent region of origin of the dust mobilized towards central Italy. Secondary source regions include northern Morocco and Libya. On a statistical basis, Saharan advections to Rome were preceded by increasing atmospheric pressure and stability. These conditions were found to favor the accumulation of aerosols related to local emission sources before the SDA reached the ground. Meteorology (precipitation and turbulence in primis) resulted to be an important modulator of PM concentrations during SDAs. Magnitude and timing of these factors should be well considered to correctly evaluate the dust share in PM loads or the related health effects. Saharan advections observed during DIAPASON affected particle concentrations down to diameters of about 0.6–1 μm, with number concentrations peaking at the 2.5 μm diameter range. These advections were associated with a significant increase in Si-rich particles containing a non-negligible fraction of water. Rainfall was observed to preferentially remove dust particles larger than 2 μm, causing a significant depletion in the Ca-rich fraction with respect to the Si-rich one. The increase in PLC depolarization ratios above 5%, as well as the hourly PIXE records of the Si/Ca ratio increasing above 1 were found to represent good markers for the actual presence of Saharan dust particulate matter, when Saharan advection conditions are occurring
Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c
Two-particle correlation functions of negatively charged hadrons from Pb-Pb
collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment
at the CERN SPS. A Coulomb correction procedure that assumes an expanding
source has been implemented. Within the framework of an expanding thermalized
source model the size and dynamical state of the collision fireball at
freeze-out have been reconstructed as a function of the centrality of the
collision. Less central collisions exhibit a different dynamics than central
ones: both transverse and longitudinal expansion velocities are slower, the
expansion duration is shorter and the system freezes out showing smaller
dimensions and higher temperature.Comment: 22 pages, 11 figures, Te
Strangeness enhancements at central rapidity in 40 A GeV/c Pb-Pb collisions
Results are presented on neutral kaon, hyperon and antihyperon production in
Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern
follows the same hierarchy as seen in the higher energy data - the enhancement
increases with the strangeness content of the hyperons and with the centrality
of collision. The centrality dependence of the Pb-Pb yields and enhancements is
steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness
enhancements at mid-rapidity is discussed.Comment: 15 pages, 10 figures and 3 tables. Presented at International
Conference on Strangeness in Quark Matter (SQM2009), Buzios, Rio de Janeiro,
Brazil, 27 Sept - 2 Oct 2009. Submitted to J.Phys.G: Nucl.Part.Phys, one
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