42,786 research outputs found
Photon reabsorption in fluorescent solar collectors
Understanding photon transport losses in fluorescence solar collectors is very important for increasing optical efficiencies. We present an analytical expression to characterize photon reabsorption in fluorescent solar collectors, which represent a major source of photon loss. A particularly useful universal form of this expression is found in the limit of high reabsorption, which gives the photon reabsorption probability in a simple form as a function of the absorption coefficient and the optical étendue of the emitted photon beam. Our mathematical model predicts fluorescence spectra emitted from the collector edge, which are in excellent agreement with experiment and provide an effective characterization tool for photon transport in light absorbing media
Orbital Dependent Phase Control in Ca2-xSrxRuO4
We present first-principles studies on the orbital states of the layered
perovskites CaSrRuO. The crossover from antiferromagnetic (AF)
Mott insulator for to nearly ferromagnetic (FM) metal at is
characterized by the systematic change of the orbital occupation. For the
AF side (), we present firm evidence for the ferro-orbital
ordering. It is found that the degeneracy of (or ) states is
lifted robustly due to the two-dimensional (2D) crystal-structure, even without
the Jahn-Teller distortion of RuO. This effect dominates, and the
cooperative occupation of orbital is concluded. In contrast to recent
proposals, the resulting electronic structure explains well both the observed
X-ray absorption spectra and the double peak structure of optical conductivity.
For the FM side (), however, the orbital with half filling opens a
pseudo-gap in the FM state and contributes to the spin =1/2 moment (rather
than =1 for =0.0 case) dominantly, while states are itinerant
with very small spin polarization, explaining the recent neutron data
consistently.Comment: 17 pages, 5 figure
Fermionization of a strongly interacting Bose-Fermi mixture in a one-dimensional harmonic trap
We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture
confined in a harmonic trap. It consists of a Tonks-Girardeau (TG) gas (1D Bose
gas with repulsive hard-core interactions) and of a non-interacting Fermi gas
(1D spin-aligned Fermi gas), both species interacting through hard-core
repulsive interactions. Using a generalized Bose-Fermi mapping, we determine
the exact particle density profiles, momentum distributions and behaviour of
the mixture under 1D expansion when opening the trap. In real space, bosons and
fermions do not display any phase separation: the respective density profiles
extend over the same region and they both present a number of peaks equal to
the total number of particles in the trap. In momentum space the bosonic
component has the typical narrow TG profile, while the fermionic component
shows a broad distribution with fermionic oscillations at small momenta. Due to
the large boson-fermion repulsive interactions, both the bosonic and the
fermionic momentum distributions decay as at large momenta, like in
the case of a pure bosonic TG gas. The coefficient is related to the
two-body density matrix and to the bosonic concentration in the mixture. When
opening the trap, both momentum distributions "fermionize" under expansion and
turn into that of a Fermi gas with a particle number equal to the total number
of particles in the mixture.Comment: revised version; 8 pages, 7 figure
Chinese users’ preference for web browser icons.
This paper compares the perspicacity, appropriateness and preference of web browser icons from leading software providers with those of a culture-specific design. The history and future direction of web browsers is outlined, together with the implications for the future growth of Chinese internet users. China, with its rapidly expanding young netizens has now overtaken the USA in terms of the number of internet users (253 million) and we predict it will reach saturation (≈70% internet penetration rate) by 2012.
If correct, this will have a dramatic effect on the use of English as the ‘Lingua Franca’ of the Internet. This online study was conducted in Taiwan and involved 103 participants (mean age 21 years), who were given three sets of web browser icons to review, namely Microsoft Internet Explorer 7.0, Macintosh Safari 3.0, and culturally specific icons created using the Culture-Centred Design methodology. The findings of the study show that all three sets have generally high recognition rates, but that some icon functions (e.g. Go/Visit and Favourite) in all three sets have poor recognition rates and are considered inappropriate. Furthermore, some significant differences were found when we analysed the level of user experience amongst several icons
James River slack water data report : temperature, salinity, dissolved oxygen, 1971 - 1980
The slack water survey program, which has been supp orted by the State Water Control Board and the Virginia Institute of Marine Science under the Cooperative State Agencies program, provides an extended series of tem perature, salinity, dissolved oxygen and nutrient measurements along the James River. These have been used to: 1) establish, verify, and update mathe matical and physical hydraulic models; 2) provide a baseline against which effects of unusual events have been measured; and could be used to: 3) es tablish annu al and longer period 11 climatological trends in response to changing natural phenomena and man-made modifica tions to the estuary; 4) provide a basis against which fluctuations in biota could be compared. This report contains station locations, survey schedules, field procedures, sample handling procedures, and data reduction and storage procedures. In addition, 10 years of contoured temperature, salinity, and dissolved oxygen data is presented. The primary purpose of this report is to provide the data in a format which we believe will be useful to others. Analysis and interpretation of the data is underway and this will be the subject of a later report
Anisotropic Optic Conductivities due to Spin and Orbital Orderings in LaVO3 and YVO3: First-Principles Studies
The anisotropy of low energy (05eV) optical excitations in strongly
correlated transition-metal oxides is closely related to the spin and orbital
orderings. The recent successes of LDA+ method in describing the magnetic
and electronic structures enable us to calculate the optical conductivity from
first-principles. The LaVO and YVO, both of which have
configuration and have various spin and orbital ordered phases at low
temperature, show distinct anisotropy in the optical spectra. The effects of
spin and orbital ordering on the anisotropy are studied in detail based on our
first-principles calculations. The experimental spectra of both compounds at
low temperature phases can be qualitatively explained with our calculations,
while the studies for the intermediate temperature phase of YVO suggest the
substantial persistence of the low temperature phase at elevated temperature.Comment: 6 pages, 3 figures, accepted by PR
A Differential X-Ray Gunn-Peterson Test Using a Giant Cluster Filament
Using CCD detectors onboard the forthcoming X-ray observatories Chandra and
XMM, it is possible to devise a measurement of the absolute density of heavy
elements in the hypothetical warm gas filling intercluster space. This gas may
be the largest reservoir of baryonic matter in the Universe, but even its
existence has not been proven observationally at low redshifts. The proposed
measurement would make use of a unique filament of galaxy clusters spanning
over 700 Mpc (0.1<z<0.2) along the line of sight in a small area of the sky in
Aquarius. The surface density of Abell clusters there is more than 6 times the
sky average. It is likely that the intercluster matter column density is
enhanced by a similar factor, making its detection feasible under certain
optimistic assumptions about its density and elemental abundances. One can
compare photoabsorption depth, mostly in the partially ionized oxygen edges, in
the spectra of clusters at different distances along the filament, looking for
a systematic increase of depth with the distance. The absorption can be
measured by the same detector and through the same Galactic column, hence the
differential test. A CCD moderate energy resolution (about 100 eV) is adequate
for detecting an absorption edge at a known redshift.Comment: Latex, 4 pages, 3 figures, uses emulateapj.sty. ApJ Letters in pres
Coherent States on Hilbert Modules
We generalize the concept of coherent states, traditionally defined as
special families of vectors on Hilbert spaces, to Hilbert modules. We show that
Hilbert modules over -algebras are the natural settings for a
generalization of coherent states defined on Hilbert spaces. We consider those
Hilbert -modules which have a natural left action from another
-algebra say, . The coherent states are well defined in this
case and they behave well with respect to the left action by .
Certain classical objects like the Cuntz algebra are related to specific
examples of coherent states. Finally we show that coherent states on modules
give rise to a completely positive kernel between two -algebras, in
complete analogy to the Hilbert space situation. Related to this there is a
dilation result for positive operator valued measures, in the sense of Naimark.
A number of examples are worked out to illustrate the theory
Global exponential stability of classical solutions to the hydrodynamic model for semiconductors
In this paper, the global well-posedness and stability of classical solutions
to the multidimensional hydrodynamic model for semiconductors on the framework
of Besov space are considered. We weaken the regularity requirement of the
initial data, and improve some known results in Sobolev space. The local
existence of classical solutions to the Cauchy problem is obtained by the
regularized means and compactness argument. Using the high- and low- frequency
decomposition method, we prove the global exponential stability of classical
solutions (close to equilibrium). Furthermore, it is also shown that the
vorticity decays to zero exponentially in the 2D and 3D space. The main
analytic tools are the Littlewood-Paley decomposition and Bony's para-product
formula.Comment: 18 page
Warm-Hot Gas in and around the Milky Way: Detection and Implications of OVII Absorption toward LMC X-3
X-ray absorption lines of highly-ionized species such as OVII at about zero
redshift have been firmly detected in the spectra of several active galactic
nuclei. However, the location of the absorbing gas remains a subject of debate.
To separate the Galactic and extragalactic contributions to the absorption, we
have obtained Chandra LETG-HRC and FUSE observations of the black hole X-ray
binary LMC X--3. A joint analysis of the detected OVII and Ne IX Kalpha lines,
together with the non-detection of the OVII Kbeta and OVIII Kalpha lines, gives
the measurements of the temperature, velocity dispersion, and hot oxygen column
density. The X-ray data also allow us to place a 95% confidence lower limit to
the Ne/O ratio as 0.14. The OVII line centroid and its relative shift from the
Galactic OI Kalpha absorption line, detected in the same observations, are
inconsistent with the systemic velocity of LMC X--3 ().
The far-UV spectrum shows OVI absorption at Galactic velocities, but no OVI
absorption is detected at the LMC velocity at significance. Both
the nonthermal broadening and the decreasing scale height with the increasing
ionization state further suggest an origin of the highly-ionized gas in a
supernova-driven galactic fountain. In addition, we estimate the warm and hot
electron column densities from our detected OVII Kalpha line in the LMC X--3
X-ray spectra and from the dispersion measure of a pulsar in the LMC vicinity.
We then infer the O/H ratio of the gas to be ,
consistent with the chemically-enriched galactic fountain scenario. We conclude
that the Galactic hot interstellar medium should in general substantially
contribute to zero-redshift X-ray absorption lines in extragalactic sources.Comment: 11 pages, accepted for publication in Ap
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