174 research outputs found
Optical response of small silver clusters
The time-dependent local density approximation is applied to the optical
response of the silver clusters, Ag_2, Ag_3, Ag_8 and Ag_9^+. The calculation
includes all the electrons beyond the closed-shell Ag^{+11} ionic core, thus
including for the first time explicitly the filled d-shell in the response. The
excitation energy of the strong surface plasmon near 4 eV agrees well with
experiment. The theoretical transition strength is quenched by a factor of 4
with respect to the pure s-electron sum rule in Ag_8 due to the d-electrons. A
comparable amount of strength lies in complex states below 6 eV excitation. The
total below 6 eV, about 50% of the s sum rule, is consistent with published
experiments.Comment: 13 pages RevTex and 9 Postscript figure
Atributos microbianos do solo sob pastagens naturais com diferentes intensidades de pastejo
The soil microbial biomass is the living fraction of organic matter, being responsible for several biological and biochemical processes of the soil and influenced by the conditions imposed by the environment. To evaluate the effect of grazing on changes in soil microbial attributes we studied four grazing intensities based on natural grassland of Pampa Biome: 4, 8, 12 and 16 kg of dry matter per day per 100 kg of animal live weight, compared to an area without grazing. We used randomized block design with two replications. Samples were taken on 11/23/2011 and analyzed to determine the levels of soil organic matter (SOM), microbial biomass, nitrogen, respiration and metabolic quotient. The results showed that at intermediate grazing intensities, such as 12%, minor disturbances occur in soil microbial biomass compared to other intensities, emit less CO2 into the atmosphere for each animal unit produced. The levels of organic matter and soil microbial biomass systems are lower in grazed than in areas excluded from grazing for a long period.A biomassa microbiana do solo constitui a fração viva da matéria orgânica, sendo responsável por diversos processos biológicos e bioquímicos do solo e influenciada pelas condições impostas pelo meio. Visando avaliar o efeito do pastejo nas alterações dos atributos microbianos do solo, foram estudados 4 intensidades de pastejo baseados em pastagem natural do Bioma Pampa: 4, 8, 12 e 16% de oferta de forragem (kg de peso vivo em MS), comparados com uma área sem pastejo. Foi utilizado o delineamento em blocos casualizados com duas repetições. As amostras foram tomadas no dia 23/11/2011, sendo avaliados os teores de matéria orgânica do solo (MOS), biomassa microbiana, nitrogênio, respiração e quociente metabólico. Os resultados apontaram que em intensidades de pastejo intermediárias, como 12%, ocorrem menores distúrbios na biomassa microbiana do solo quando comparados às demais ofertas, emitindo menor quantidade de CO2 para a atmosfera para cada unidade animal produzida. Os teores de matéria orgânica e biomassa microbiana do solo em sistemas pastejados são inferiores àqueles de áreas excluídas do pastejo por um longo período
Observer study-based evaluation of TGAN architecture used to generate oncological PET images
The application of computer-vision algorithms in medical imaging has
increased rapidly in recent years. However, algorithm training is challenging
due to limited sample sizes, lack of labeled samples, as well as privacy
concerns regarding data sharing. To address these issues, we previously
developed (Bergen et al. 2022) a synthetic PET dataset for Head and Neck (H and
N) cancer using the temporal generative adversarial network (TGAN) architecture
and evaluated its performance segmenting lesions and identifying radiomics
features in synthesized images. In this work, a two-alternative forced-choice
(2AFC) observer study was performed to quantitatively evaluate the ability of
human observers to distinguish between real and synthesized oncological PET
images. In the study eight trained readers, including two board-certified
nuclear medicine physicians, read 170 real/synthetic image pairs presented as
2D-transaxial using a dedicated web app. For each image pair, the observer was
asked to identify the real image and input their confidence level with a
5-point Likert scale. P-values were computed using the binomial test and
Wilcoxon signed-rank test. A heat map was used to compare the response accuracy
distribution for the signed-rank test. Response accuracy for all observers
ranged from 36.2% [27.9-44.4] to 63.1% [54.8-71.3]. Six out of eight observers
did not identify the real image with statistical significance, indicating that
the synthetic dataset was reasonably representative of oncological PET images.
Overall, this study adds validity to the realism of our simulated H&N cancer
dataset, which may be implemented in the future to train AI algorithms while
favoring patient confidentiality and privacy protection
Origin of Shifts in the Surface Plasmon Resonance Frequencies for Au and Ag Nanoparticles
Origin of shifts in the surface plasmon resonance (SPR) frequency for noble
metal (Au, Ag) nanoclusters are discussed in this book chapter. Spill out of
electron from the Fermi surface is considered as the origin of red shift. On
the other hand, both screening of electrons of the noble metal in porous media
and quantum effect of screen surface electron are considered for the observed
blue shift in the SPR peak position.Comment: 37 pages, 14 Figures in the submitted book chapter of The Annual
Reviews in Plasmonics, edited by Professor Chris D. Geddes. Springer Scinec
SINFONI - Integral Field Spectroscopy at 50 milli-arcsecond resolution with the ESO VLT
SINFONI is an adaptive optics assisted near-infrared integral field
spectrometer for the ESO VLT. The Adaptive Optics Module (built by the ESO
Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed
for operations with natural or sodium laser guide stars. The near-infrared
integral field spectrometer SPIFFI (built by the Infrared Group of MPE)
provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral
resolving power of up to 3300. The adaptive optics module is in the phase of
integration; the spectrometer is presently tested in the laboratory. We provide
an overview of the project, with particular emphasis on the problems
encountered in designing and building an adaptive optics assisted spectrometer.Comment: This paper was published in Proc. SPIE, 4841, pp. 1548-1561 (2003),
and is made available as an electronic reprint with permission of SPIE.
Copyright notice added to first page of articl
Recria e terminação de novilhos de corte em diferentes sistemas alimentares.
Avaliou-se a influência de diferentes sistemas alimentares no desempenho de novilhos até o abate.Zootec
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
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