702 research outputs found
Active Ground Optical Remote Sensing for Improved Monitoring of Seedling Stress in Nurseries
Active ground optical remote sensing (AGORS) devices mounted on overhead irrigation booms could help to improve seedling quality by autonomously monitoring seedling stress. In contrast to traditionally used passive optical sensors, AGORS devices operate independently of ambient light conditions and do not require spectral reference readings. Besides measuring red (590–670 nm) and near-infrared (>760 nm) reflectance AGORS devices have recently become available that also measure red-edge (730 nm) reflectance. We tested the hypothesis that the additional availability of red-edge reflectance information would improve AGORS of plant stress induced chlorophyll breakdown in Scots pine (Pinus sylvestris). Our results showed that the availability of red-edge reflectance information improved AGORS estimates of stress induced variation in chlorophyll concentration (r2 > 0.73, RMSE < 1.69) when compared to those without (r2 = 0.57, RMSE = 2.11)
First-principles study of (BiScO3){1-x}-(PbTiO3){x} piezoelectric alloys
We report a first-principles study of a class of (BiScO3)_{1-x}-(PbTiO3)_x
(BS-PT) alloys recently proposed by Eitel et al. as promising materials for
piezoelectric actuator applications. We show that (i) BS-PT displays very large
structural distortions and polarizations at the morphotropic phase boundary
(MPB) (we obtain a c/a of ~1.05-1.08 and P_tet of ~1.1 C/m^2); (ii) the
ferroelectric and piezoelectric properties of BS-PT are dominated by the onset
of hybridization between Bi/Pb-6p and O-2p orbitals, a mechanism that is
enhanced upon substitution of Pb by Bi; and (iii) the piezoelectric responses
of BS-PT and Pb(Zr_{1-x}Ti_x)O3 (PZT) at the MPB are comparable, at least as
far as the computed values of the piezoelectric coefficient d_15 are concerned.
While our results are generally consistent with experiment, they also suggest
that certain intrinsic properties of BS-PT may be even better than has been
indicated by experiments to date. We also discuss results for PZT that
demonstrate the prominent role played by Pb displacements in its piezoelectric
properties.Comment: 6 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/ji_bi/index.htm
Alteration of Multiple Leukocyte Gene Expression Networks is Linked with Magnetic Resonance Markers of Prognosis After Acute ST-Elevation Myocardial Infarction
Prognostic relevant pathways of leukocyte involvement in human myocardial ischemic-reperfusion injury are largely unknown. We enrolled 136 patients with ST-elevation myocardial infarction (STEMI) after primary angioplasty within 12 h after onset of symptoms. Following reperfusion, whole blood was collected within a median time interval of 20 h (interquartile range: 15-25 h) for genome-wide gene expression analysis. Subsequent CMR scans were performed using a standard protocol to determine infarct size (IS), area at risk (AAR), myocardial salvage index (MSI) and the extent of late microvascular obstruction (lateMO). We found 398 genes associated with lateMO and two genes with IS. Neither AAR, nor MSI showed significant correlations with gene expression. Genes correlating with lateMO were strongly related to several canonical pathways, including positive regulation of T-cell activation (p = 3.44 x 10(-5)), and regulation of inflammatory response (p = 1.86 x 10(-3)). Network analysis of multiple gene expression alterations associated with larger lateMO identified the following functional consequences: facilitated utilisation and decreased concentration of free fatty acid, repressed cell differentiation, enhanced phagocyte movement, increased cell death, vascular disease and compensatory vasculogenesis. In conclusion, the extent of lateMO after acute, reperfused STEMI correlated with altered activation of multiple genes related to fatty acid utilisation, lymphocyte differentiation, phagocyte mobilisation, cell survival, and vascular dysfunction
Almost Maximal Lepton Mixing with Large T Violation in Neutrino Oscillations and Neutrinoless Double Beta Decay
We point out two simple but instructive possibilities to construct the
charged lepton and neutrino mass matrices, from which the nearly bi-maximal
neutrino mixing with large T violation can naturally emerge. The two lepton
mixing scenarios are compatible very well with current experimental data on
solar and atmospheric neutrino oscillations, and one of them may lead to an
observable T-violating asymmetry between \nu_\mu --> \nu_e and \nu_e -->
\nu_\mu transitions in the long-baseline neutrino oscillation experiments.
Their implications on the neutrinoless double beta decay are also discussed.Comment: RevTex 15 pages (2 PS figures
Estudio de las funciones dieléctricas del semiconductor sulfuro de plomo
Hemos calculado la estructura electronica con la formulacion de Iii funcional densidad, del semiconductor PbS. A partir de ella, calculamos la variacion en frecuencia de las funciones dielectricas en el espectro comprendido entre 0 y 5 eV. Los picos obtenidos, asi como la forma general de las curvas correspondientes a las partes real epsilon1 e imaginaria epsilon2, resultan muy bien caracterizadas y entendidos en base a los diagram de bandas y densidades de estados calculados. El espectro dispersivo tiene su punto de inflexion en razonable acuerdo con la energia a la cual la absorcion aJcanza su maximo y comienza a disminuir, correspondiendo a un comportamiento metalico en el rango de las energfas mayores a 3 eV. Tambien presentamos resultados de la reflectividad de este material.We have performed a calculation of the electronic structure within the density functional formalism, of the semiconductor PbS. From it, the dependence in frecuency of the dielectric functions in the range between 0 and 5 eV, is calculated. The peaks, as well as the general shape of the curves corresponding to the real part Si and imaginary part s2, are very well described and understandable in terms of the calculated bands and density of states. The dispersive spectrum has its point of inflexion in reazonably agreement with the energy where the absorption is maximum, and starts decreasing in a metalic like behavior, for energies higher than 3 eV. Also we present results on the reflectivity of this material.Instituto de Física de Líquidos y Sistemas BiológicosFacultad de Ingenierí
Neutron production by cosmic-ray muons at shallow depth
The yield of neutrons produced by cosmic ray muons at a shallow depth of 32
meters of water equivalent has been measured. The Palo Verde neutrino detector,
containing 11.3 tons of Gd loaded liquid scintillator and 3.5 tons of acrylic
served as a target. The rate of one and two neutron captures was determined.
Modeling the neutron capture efficiency allowed us to deduce the total yield of
neutrons neutrons per muon
and g/cm. This yield is consistent with previous measurements at similar
depths.Comment: 12 pages, 3 figure
Neutrino mass spectrum and neutrinoless double beta decay
The relations between the effective Majorana mass of the electron neutrino,
, responsible for neutrinoless double beta decay, and the neutrino
oscillation parameters are considered. We show that for any specific
oscillation pattern can take any value (from zero to the existing
upper bound) for normal mass hierarchy and it can have a minimum for inverse
hierarchy. This means that oscillation experiments cannot fix in general
. Mass ranges for can be predicted in terms of oscillation
parameters with additional assumptions about the level of degeneracy and the
type of hierarchy of the neutrino mass spectrum. These predictions for
are systematically studied in the specific schemes of neutrino mass and flavor
which explain the solar and atmospheric neutrino data. The contributions from
individual mass eigenstates in terms of oscillation parameters have been
quantified. We study the dependence of on the non-oscillation
parameters: the overall scale of the neutrino mass and the relative mass
phases. We analyze how forthcoming oscillation experiments will improve the
predictions for . On the basis of these studies we evaluate the
discovery potential of future \znbb decay searches. The role \znbb decay
searches will play in the reconstruction of the neutrino mass spectrum is
clarified. The key scales of , which will lead to the discrimination
among various schemes are: eV and eV.Comment: 47 pages, 35 figure
Reactor-based Neutrino Oscillation Experiments
The status of neutrino oscillation searches employing nuclear reactors as
sources is reviewed. This technique, a direct continuation of the experiments
that proved the existence of neutrinos, is today an essential tool in
investigating the indications of oscillations found in studying neutrinos
produced in the sun and in the earth's atmosphere. The low-energy of the
reactor \nuebar makes them an ideal tool to explore oscillations with small
mass differences and relatively large mixing angles.
In the last several years the determination of the reactor anti-neutrino flux
and spectrum has reached a high degree of accuracy. Hence measurements of these
quantities at a given distance L can be readily compared with the expectation
at L = 0, thus testing \nuebar disappearance.
While two experiments, Chooz and Palo Verde, with baselines of about 1 km and
thus sensitive to the neutrino mass differences associated with the atmospheric
neutrino anomaly, have collected data and published results recently, an
ambitious project with a baseline of more than 100 km, Kamland, is preparing to
take data. This ultimate reactor experiment will have a sensitivity sufficient
to explore part of the oscillation phase space relevant to solar neutrino
scenarios. It is the only envisioned experiment with a terrestrial source of
neutrinos capable of addressing the solar neutrino puzzle.Comment: Submitted to Reviews of Modern Physics 34 pages, 39 figure
A search for low-mass WIMPs with EDELWEISS-II heat-and-ionization detectors
We report on a search for low-energy (E < 20 keV) WIMP-induced nuclear
recoils using data collected in 2009 - 2010 by EDELWEISS from four germanium
detectors equipped with thermal sensors and an electrode design (ID) which
allows to efficiently reject several sources of background. The data indicate
no evidence for an exponential distribution of low-energy nuclear recoils that
could be attributed to WIMP elastic scattering after an exposure of 113 kg.d.
For WIMPs of mass 10 GeV, the observation of one event in the WIMP search
region results in a 90% CL limit of 1.0x10^-5 pb on the spin-independent
WIMP-nucleon scattering cross-section, which constrains the parameter space
associated with the findings reported by the CoGeNT, DAMA and CRESST
experiments.Comment: PRD rapid communication accepte
Background studies for the EDELWEISS dark matter experiment
The EDELWEISS-II collaboration has completed a direct search for WIMP dark
matter using cryogenic Ge detectors (400 g each) and 384 kgdays of
effective exposure. A cross-section of pb is excluded at
90% C.L. for a WIMP mass of 85 GeV. The next phase, EDELWEISS-III, aims to
probe spin-independent WIMP-nucleon cross-sections down to a few
pb. We present here the study of gamma and neutron background
coming from radioactive decays in the set-up and shielding materials. We have
carried out Monte Carlo simulations for the completed EDELWEISS-II setup with
GEANT4 and normalised the expected background rates to the measured
radioactivity levels (or their upper limits) of all materials and components.
The expected gamma-ray event rate in EDELWEISS-II at 20-200 keV agrees with the
observed rate of 82 events/kg/day within the uncertainties in the measured
concentrations. The calculated neutron rate from radioactivity of 1.0-3.1
events (90% C.L.) at 20-200 keV in the EDELWEISS-II data together with the
expected upper limit on the misidentified gamma-ray events (), surface
betas (), and muon-induced neutrons (), do not contradict 5
observed events in nuclear recoil band. We have then extended the simulation
framework to the EDELWEISS-III configuration with 800 g crystals, better
material purity and additional neutron shielding inside the cryostat. The
gamma-ray and neutron backgrounds in 24 kg fiducial mass of EDELWEISS-III have
been calculated as 14-44 events/kg/day and 0.7-1.4 events per year,
respectively. The results of the background studies performed in the present
work have helped to select better purity components and improve shielding in
EDELWEISS-III to further reduce the expected rate of background events in the
next phase of the experiment.Comment: 15 pages, 9 figures, to be published in Astroparticle Physic
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