5,018 research outputs found
Optical properties of Ge-oxygen defect center embedded in silica films
The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick
Ge-doped silica film on a pure silica substrate were investigated by looking at
the emission spectra and time decay detected under synchrotron radiation
excitation in the 10-300 K temperature range. This center exhibits two
luminescence bands centered at 4.3eV and 3.2eV associated with its
de-excitation from singlet (S1) and triplet (T1) states, respectively, that are
linked by an intersystem crossing process. The comparison with results obtained
from a bulk Ge-doped silica sample evidences that the efficiency of the
intersystem crossing rate depends on the properties of the matrix embedding the
Ge-oxygen defect centers, being more effective in the film than in the bulk
counterpart.Comment: 10 pages, 3 figures, in press on J. Non cryst. solids (2007
VIRTUAL REALITY FOR HISTORICAL ARCHITECTURE
Abstract. This article shows a first step in the development of an immersive virtual tour of the Cathedral of Palermo, entering the fields of Digital Cultural Heritage and Edutainment. Its purpose is to help people to gain knowledge about the site, highlighting the complex stratifications that have characterized its history.The development of the project has been possible thanks to different phases of work: surveys were initially carried out by laser scanning, then assembled and processed to obtain the 3D model of the current state; at the same time, the model of reconstruction was processed in several phases, based on historical, archival and iconographic sources; both models were, later, subject to post-processing, preparatory to the development of virtual navigation. The tour scenario includes options in order to make it attractive for the player, such as interactive elements, interfaces and animations.</p
The reaction on p-shell nuclei
This letter is concerned with the study of the reaction in p-shell nuclei, i.e., , ,
and . The emission rates are
reported as a function of . These rates are discussed in comparison with
previous findings. The ratio in p-shell nuclei is
found to depart largely from that on hydrogen, which provides support for large
in-medium effects possibly generated by the sub-threshold . The
continuum momentum spectra of prompt pions and free sigmas are also discussed
as well as the missing mass behavior and the link with the
reaction mechanism. The apparatus used for the investigation is the FINUDA
spectrometer operating at the DANE -factory (LNF-INFN, Italy).Comment: 14 pages, 5 figures, accepted for publication in Phys. Lett.
An Introduction to the Winograd Discrete Fourier Transform
This paper illustrates Winograd\u27s approach to computing the Discrete Fourier Transform (DFT). This new approach changes the DFT into a cyclic convolution of 2 sequences, and illustrates shortcuts for computing this cyclic convolution. This method is known to reduce the number of multiplies required to about 20% less than the number of multiplies used by the techniques of the Fast Fourier Transform. Three approaches are discussed, one for prime numbers, one for products of primes, and lastly one for powers of odd primes. For powers of 2 Winograd\u27s algorithm is, in general, inefficient and best if it is not used. A computer simulation is illustrated for the 35 point transform and its execution time is compared with that of the Fast Fourier Transform algorithm for 32 points
The relevance of point defects in studying silica-based materials from bulk to nanosystems
The macroscopic properties of silica can be modified by the presence of local microscopic modifications at the scale of the basic molecular units (point defects). Such defects can be generated during the production of glass, devices, or by the environments where the latter have to operate, impacting on the devices’ performance. For these reasons, the identification of defects, their generation processes, and the knowledge of their electrical and optical features are relevant for microelectronics and optoelectronics. The aim of this manuscript is to report some examples of how defects can be generated, how they can impact device performance, and how a defect species or a physical phenomenon that is a disadvantage in some fields can be used as an advantage in others
29Si Hyperfine Structure of the E'_\alpha Center in Amorphous Silicon Dioxide
We report a study by electron paramagnetic resonance (EPR) on the E'_\alpha
point defect in amorphous silicon dioxide (a-SiO2). Our experiments were
performed on gamma-ray irradiated oxygen-deficient materials and pointed out
that the 29Si hyperfine structure of the E'_alpha consists in a pair of lines
split by 49 mT. On the basis of the experimental results a microscopic model is
proposed for the E'_alpha center, consisting in a hole trapped in an oxygen
vacancy with the unpaired electron sp3 orbital pointing away from the vacancy
in a back-projected configuration and interacting with an extra oxygen atom of
the a-SiO2 matrix.Comment: 4 page
K- absorption in nuclei by two and three nucleons
It will be shown that the peaks in the (Lambda p) and (Lambda d) invariant
mass distributions, observed in recent FINUDA experiments and claimed to be
signals of deeply bound kaonic states, are naturally explained in terms of K-
absorption by two or three nucleons leaving the rest of the original nuclei as
spectator. For reactions on heavy nuclei, the subsequent interactions of the
particles produced in the primary absorption process with the residual nucleus
play an important role. Our analyses leads to the conclusion that at present
there is no experimental evidence of deeply bound K- state in nuclei. Although
the FINUDA experiments have been done for reasons which are not supported a
posteriori, some new physics can be extracted from the data.Comment: 6 pages, 5 figures. Talk presented at the International Conference on
Exotic Atoms "EXA 2008", Vienna, Austria, September 15-18, 200
Weak nonmesonic decay spectra of hypernuclei
We compute one- and two-nucleon kinetic-energy spectra and opening-angle
distributions for the nonmesonic weak decay of several hypernuclei, and compare
our results with some recent data. The decaymics is described by transition
potentials of the one-meson-exchange type, and the nuclear structure aspects by
two versions of the independent-particle shell model (IPSM). In version IPSM-a,
the hole states are treated as stationary, while in version IPSM-b the deep
hole states are considered to be quasi-stationary and are described by
Breit-Wigner distributions.Comment: 3 pages 2 figures. To be published in Nucl. Phys. A; Contribution to
the NN2009 International Conference, Beijing, China, August 200
Fruit Pest Events and Phenological Development According to Accumulated Heat Units
Mammals are "warm-blooded" and develop at a constant
rate regardless of the environmental temperature,
because they are able to maintain an internal temperature
that allows their biochemical reactions to progress normally.
Insects, which are "exothermic" (the same temperature as
their environment; there is no such thing as "cold-blooded"),
do not generate body heat, and are therefore limited in their
development to periods of favorable external temperature.
Below a certain temperature, which varies among species,
the insect's biochemical reactions cannot proceed, and
development stops. This temperature is known as the
insect's developmental threshold ordevelopmental base.
By charting the ambient temperature, it is possible to keep
track of insect development, which is directly proportional to
the amount of time accumulated above the developmental
threshold (up to some maximum not often reached during
the season). We arbitrarily divide this time into heat units,
or degree-days (DD)
Root Weevils
NYS IPM Type: Fruits IPM Fact SheetThere are more than 20 species of root weevils that attack strawberry in the United States. In New York, the three major species are the black vine weevil, Otiorhynchus sulcatus (Fabricius), the strawberry root weevil, 0. ovatus L., and the rough strawberry weevil, 0. rugostriatus Goeze. Root weevils are also pests of raspberries and rhododendrons
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