300,333 research outputs found
Excitation and emission spectra of rubidium in rare-gas thin-films
To understand the optical properties of atoms in solid state matrices, the
absorption, excitation and emission spectra of rubidium doped thin-films of
argon, krypton and xenon were investigated in detail. A two-dimensional
spectral analysis extends earlier reports on the excitation and emission
properties of rubidium in rare-gas hosts. We found that the doped crystals of
krypton and xenon exhibit a simple absorption-emission relation, whereas
rubidium in argon showed more complicated spectral structures. Our sample
preparation employed in the present work yielded different results for the Ar
crystal, but our peak positions were consistent with the prediction based on
the linear extrapolation of Xe and Kr data. We also observed a bleaching
behavior in rubidium excitation spectra, which suggests a population transfer
from one to another spectral feature due to hole-burning. The observed optical
response implies that rubidium in rare-gas thin-films is detectable with
extremely high sensitivity, possibly down to a single atom level, in low
concentration samples.Comment: 7 pages, 5 figure
ZnS Cu-doped quantum dots
The paper presents a survey of literature on the structure and optical properties of ZnS and copper ion-doped ZnS quantum dots. The effect of other metal dopants on the spectral properties of ZnS:Cu quantum dots was also considered. The influence of such parameters as dopant concentration, temperature of the synthesis and compounds which form or modify the additional layer on dots on spectral properties of the quantum dots was described. Examples of application of ZnS:Cu quantum dots are also given
Studying the effect of concentration on spectral and optical properties of chitosan polymer
Due to its noteworthy physico-chemical behaviors, the chitosan (CS) biopolymer presents a compelling alternative to conventional biomaterials. By measuring the emission spectra at a spectrofluorophotometer in different concentrates (1x10-4, 1x10-5, and 1x10-6) M, the spectral characteristics of the CS polymer were obtained. The crystallinity of the CS polymer was determined by X-ray diffraction (XRD) analysis, which shows only one dominant peak indexed to the orthorhombic structure. With a drop in solution concentration, there was a shift toward the shorter wavelength and a decline in quantum yield. Using a UV-Vis spectrophotometer, the optical properties of the CS polymer, including its refractive index, absorption coefficient, energy band gap, extinction coefficient, and dielectric constant, have been studied. It was observed through the results that the optical parameters are linearly dependent with concentration. In contrast to the optical energy gap, which decreases with increasing concentration
Aerosol Characteristics at a high-altitude station Nainital during the ISRO-GBP Land Campaign-II
During the second land campaign (LC-II) organised by ISRO-GBP, extensive
ground-based measurements of aerosol characteristics were carried out over
Manora Peak (29.4oN; 79.5oE; 1951 metres above mean sea level), Nainital (a
high altitude station located in the Shivalik ranges of Central Himalayas)
during the dry, winter season (December) of 2004. These measurements included
the spectral aerosol optical depths (AOD), columnar water vapour content (W),
Total Columnar Ozone (TCO), total number concentration (NT) of near surface
aerosols, mass concentration of black carbon (MB), aerosol mass loading (MT),
and Global Solar Radiation. Based on these measured parameters, we present the
results on the near-surface and columnar properties of atmospheric aerosols at
Nainital.Comment: Published in the Proceedings of the ISRO-GBP Land-Campaign-II
meeting, Physical Research Laboratory, Ahmadabad (Inida), March 200
Detection of Edges in Spectral Data II. Nonlinear Enhancement
We discuss a general framework for recovering edges in piecewise smooth
functions with finitely many jump discontinuities, where . Our approach is based on two main aspects--localization using
appropriate concentration kernels and separation of scales by nonlinear
enhancement.
To detect such edges, one employs concentration kernels, ,
depending on the small scale . It is shown that odd kernels, properly
scaled, and admissible (in the sense of having small -moments of
order ) satisfy , thus recovering both the location and amplitudes of all edges.As
an example we consider general concentration kernels of the form
to detect edges from the first
spectral modes of piecewise smooth f's. Here we improve in
generality and simplicity over our previous study in [A. Gelb and E. Tadmor,
Appl. Comput. Harmon. Anal., 7 (1999), pp. 101-135]. Both periodic and
nonperiodic spectral projections are considered. We identify, in particular, a
new family of exponential factors, , with superior
localization properties.
The other aspect of our edge detection involves a nonlinear enhancement
procedure which is based on separation of scales between the edges, where
, and the smooth regions where . Numerical examples demonstrate that by coupling
concentration kernels with nonlinear enhancement one arrives at effective edge
detectors
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