5,858 research outputs found
On the transfer of resonant-line radiation in mesh simulations
The last decade has seen applications of Adaptive Mesh Refinement (AMR)
methods for a wide range of problems from space physics to cosmology. With the
advent of these methods, in which space is discretized into a mesh of many
individual cubic elements, the contemporary analog of the extensively studied
line radiative transfer (RT) in a semi-infinite slab is that of RT in a cube.
In this study we provide an approximate solution of the RT equation, as well as
analytic expressions for the probability distribution functions (pdfs) of the
properties of photons emerging from a cube, and compare them with the
corresponding slab problem. These pdfs can be used to perform fast
resonant-line RT in optically thick AMR cells where, otherwise, it could take
unrealistically long times to transfer even a handful of photons.Comment: 5 two-column pages, 2 figures; matches accepted version, to appear on
Ap
Enhanced transmission versus localization of a light pulse by a subwavelength metal slit: Can the pulse have both characteristics?
The existence of resonant enhanced transmission and collimation of light
waves by subwavelength slits in metal films [for example, see T.W. Ebbesen et
al., Nature (London) 391, 667 (1998) and H.J. Lezec et al., Science, 297, 820
(2002)] leads to the basic question: Can a light be enhanced and simultaneously
localized in space and time by a subwavelength slit? To address this question,
the spatial distribution of the energy flux of an ultrashort (femtosecond)
wave-packet diffracted by a subwavelength (nanometer-size) slit was analyzed by
using the conventional approach based on the Neerhoff and Mur solution of
Maxwell's equations. The results show that a light can be enhanced by orders of
magnitude and simultaneously localized in the near-field diffraction zone at
the nm- and fs-scales. Possible applications in nanophotonics are discussed.Comment: 5 figure
Lyman alpha line formation in starbursting galaxies II. Extremely Thick, Dustless, and Static HI Media
The Lya line transfer in an extremely thick medium of neutral hydrogen is
investigated by adopting an accelerating scheme in our Monte Carlo code to skip
a large number of core or resonant scatterings. This scheme reduces computing
time significantly with no sacrifice in the accuracy of the results. We applied
this numerical method to the Lya transfer in a static, uniform, dustless, and
plane-parallel medium. Two types of photon sources have been considered, the
midplane source and the uniformly distributed sources. The emergent profiles
show double peaks and absorption trough at the line-center. We compared our
results with the analytic solutions derived by previous researchers, and
confirmed that both solutions are in good agreement with each other. We
investigated the directionality of the emergent Lya photons and found that limb
brightening is observed in slightly thick media while limb darkening appears in
extremely thick media. The behavior of the directionality is noted to follow
that of the Thomson scattered radiation in electron clouds, because both Lya
wing scattering and Thomson scattering share the same Rayleigh scattering phase
function. The mean number of wing scatterings just before escape is in exact
agreement with the prediction of the diffusion approximation. The Lya photons
constituting the inner part of the emergent profiles follow the relationship
derived from the diffusion approximation. We present a brief discussion on the
application of our results to the formation of Lya broad absorption troughs and
P-Cygni type Lya profiles seen in the UV spectra of starburst galaxies.Comment: 24 papges, 12 figures, The revised version submitted to Ap
Liquid-liquid equilibrium for monodisperse spherical particles
A system of identical particles interacting through an isotropic potential
that allows for two preferred interparticle distances is numerically studied.
When the parameters of the interaction potential are adequately chosen, the
system exhibits coexistence between two different liquid phases (in addition to
the usual liquid-gas coexistence). It is shown that this coexistence can occur
at equilibrium, namely, in the region where the liquid is thermodynamically
stable.Comment: 6 pages, 8 figures. Published versio
99mTc-labelled StealthÂź liposomal doxorubicin (CaelyxÂź) in glioblastomas and metastatic brain tumours
British Journal of Cancer (2002) 86, 659â660. DOI: 10.1038/sj/bjc/6600093 www.bjcancer.co
Now the wars are over: The past, present and future of Scottish battlefields
Battlefield archaeology has provided a new way of appreciating historic battlefields. This paper provides a summary of the long history of warfare and conflict in Scotland which has given rise to a large number of battlefield sites. Recent moves to highlight the archaeological importance of these sites, in the form
of Historic Scotlandâs Battlefields Inventory are discussed, along with some of the problems associated with the preservation and management of these important
cultural sites
Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer
We present new abundance analyses of six blue metal-poor (BMP) stars with
very low iron abundances ([Fe/H] < -2), based on new high resolution echelle
spectra. Three are spectroscopic binaries and three have constant radial
velocities. The chemical compositions of these two groups are very different,
as the binary BMP stars have large enhancements of carbon and neutron-capture
elements that are products of s-process nucleosynthesis. One star, CS
29497-030, has an extreme enhancement of lead, [Pb/Fe] = +3.7, the largest
abundance in any star yet discovered. It probably also has an oxygen
overabundance compared to the other BMP stars of our sample. The binary BMP
stars must have attained their status via mass transfer during the asymptotic
giant branch (AGB) evolutions of their companion stars, which are now unseen
and most likely are compact objects. We have not found any examples of AGB mass
transfer among BMP binaries with [Fe/H] > -2.Comment: 34 pages, 9 figures, 7 tables; To appear in the Astrophysical Journa
Astrometric Methods and Instrumentation to Identify and Characterize Extrasolar Planets: A Review
I present a review of astrometric techniques and instrumentation utilized to
search for, detect, and characterize extra-solar planets. First, I briefly
summarize the properties of the present-day sample of extrasolar planets, in
connection with predictions from theoretical models of planet formation and
evolution. Next, the generic approach to planet detection with astrometry is
described, with significant discussion of a variety of technical, statistical,
and astrophysical issues to be faced by future ground-based as well as
space-borne efforts in order to achieve the required degree of measurement
precision. After a brief summary of past and present efforts to detect planets
via milli-arcsecond astrometry, I then discuss the planet-finding capabilities
of future astrometric observatories aiming at micro-arcsecond precision.
Lastly, I outline a number experiments that can be conducted by means of
high-precision astrometry during the next decade, to illustrate its potential
for important contributions to planetary science, in comparison with other
indirect and direct methods for the detection and characterization of planetary
systems.Comment: 61 pages, 8 figures, PASP, accepted (October 2005 issue
Nearby low-mass triple system GJ795
We report the results of our optical speckle-interferometric observations of
the nearby triple system GJ795 performed with the 6-m BTA telescope with
diffraction-limited angular resolution. The three components of the system were
optically resolved for the first time. Position measurements allowed us to
determine the elements of the inner orbit of the triple system. We use the
measured magnitude differences to estimate the absolute magnitudes and spectral
types of the components of the triple: =7.310.08,
=8.660.10, =8.420.10, K5,
K9, K8. The total mass of the system is
equal to =1.69. We show
GJ795 to be a hierarchical triple system which satisfies the empirical
stability criteria.Comment: 6 pages, 2 figures, published in Astrophysical Bulleti
Foreign Direct Investments in Business Services: Transforming the VisegrĂĄd Four Region into a Knowledge-based Economy?
Foreign direct investments (FDIs) in the service sector are widely attributed an important role in bringing more skill-intensive activities into the Visegrad Four (V4). This regionâcomprising Poland, the Czech Republic, Hungary and Slovakiaârelied heavily on FDIs in manufacturing, which was often found to generate activities with limited skill content. This contribution deconstructs the chaotic concept of âbusiness servicesâ by analysing the actual nature of service sector activities outsourced and offshored to the V4. Using the knowledge-based economy (KBE) as a benchmark, the paper assesses the potential of service sector outsourcing in contributing to regional competitiveness by increasing the innovative capacity. It also discusses the role of state policies towards service sector FDI (SFDI). The analysis combines data obtained from case studies undertaken in service sector outsourcing projects in V4 countries. Moreover, it draws on interviews with senior employees of investment promotion agencies and publicly available data and statistics on activities within the service sector in the region. It argues that the recent inward investments in business services in the V4 mainly utilize existing local human capital resources, and their contribution to the development of the KBE is limited to employment creation and demand for skilled labour
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