32,858 research outputs found
Optimization of Occlusion-Inducing Depth Pixels in 3-D Video Coding
The optimization of occlusion-inducing depth pixels in depth map coding has
received little attention in the literature, since their associated texture
pixels are occluded in the synthesized view and their effect on the synthesized
view is considered negligible. However, the occlusion-inducing depth pixels
still need to consume the bits to be transmitted, and will induce geometry
distortion that inherently exists in the synthesized view. In this paper, we
propose an efficient depth map coding scheme specifically for the
occlusion-inducing depth pixels by using allowable depth distortions. Firstly,
we formulate a problem of minimizing the overall geometry distortion in the
occlusion subject to the bit rate constraint, for which the depth distortion is
properly adjusted within the set of allowable depth distortions that introduce
the same disparity error as the initial depth distortion. Then, we propose a
dynamic programming solution to find the optimal depth distortion vector for
the occlusion. The proposed algorithm can improve the coding efficiency without
alteration of the occlusion order. Simulation results confirm the performance
improvement compared to other existing algorithms
On the use of an explicit chemical mechanism to dissect peroxy acetyl nitrate formation.
Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model--Master Chemical Mechanism (MCM) model--to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities
Computing Optical Properties of Ultra-thin Crystals
An overview is given of recent advances in experimental and theoretical
understanding of optical properties of ultra-thin crystal structures (graphene,
phosphorene, silicene, MoS2, MoSe2 , WS2 , WSe2 , h-AlN, h-BN, fluorographene,
graphane). Ultra-thin crystals are atomically-thick layered crystals that have
unique properties which differ from their 3D counterpart. Because of the
difficulties in the synthesis of few-atom-thick crystal structures, which are
thought to be the main building blocks of future nanotechnology, reliable
theoretical predictions of their electronic, vibrational and optical properties
are of great importance. Recent studies revealed the reliable predictive power
of existing theoretical approaches based on density functional theory (DFT)
Signatures of Self-Interacting Dark Matter in the Matter Power Spectrum and the CMB
We consider a self-interacting dark matter model in which the massive dark
photon mediating the self-interaction decays to light dark fermions to avoid
over-closing the universe. We find that if the model is constrained to explain
the dark matter halos inferred for spiral galaxies and galaxy clusters
simultaneously, there is a strong indication that dark matter is produced
asymmetrically in the early universe. It also implies the presence of dark
radiation, late kinetic decoupling for dark matter, and a suppressed linear
power spectrum due to dark acoustic damping. The Lyman- forest power
spectrum measurements put a strong upper limit on the damping scale and the
model has little room to reduce the abundances of satellite galaxies. Future
observations in the matter power spectrum and the CMB, in tandem with the
impact of self-interactions in galactic halos, makes it possible to measure the
gauge coupling and masses of the dark sector particles even when signals in
conventional dark matter searches are absent.Comment: 5 pages, 7 figures, published version in PL
Using microlensed quasars to probe the structure of the Milky Way
This paper presents an investigation into the gravitational microlensing of
quasars by stars and stellar remnants in the Milky Way. We present predictions
for the all-sky microlensing optical depth, time-scale distributions and event
rates for future large-area sky surveys. As expected, the total event rate
increases rapidly with increasing magnitude limit, reflecting the fact that the
number density of quasars is a steep function of magnitude. Surveys such as
Pan-STARRS and LSST should be able to detect more than ten events per year,
with typical event durations of around one month. Since microlensing of quasar
sources suffers from fewer degeneracies than lensing of Milky Way sources, they
could be used as a powerful tool for recovering the mass of the lensing object
in a robust, often model-independent, manner. As a consequence, for a subset of
these events it will be possible to directly `weigh' the star (or stellar
remnant) that is causing the lensing signal, either through higher order
microlensing effects and/or high-precision astrometric observations of the lens
star (using, for example, Gaia or SIM-lite). This means that such events could
play a crucial role in stellar astronomy. Given the current operational
timelines for Pan-STARRS and LSST, by the end of the decade they could
potentially detect up to 100 events. Although this is still too few events to
place detailed constraints on Galactic models, consistency checks can be
carried out and such samples could lead to exciting and unexpected discoveries.Comment: 11 pages, 8 figures. MNRAS (in press). Minor revisions according to
referee's report; mainly presentational issues and clarification of a few
items in the discussion; results and conclusions remain unchange
English versus Swahili: language choice in Bongo Flava as expression of cultural and economic changes in Tanzania
Since around 2011, Bongo Flava musicians use significantly more English in their lyrics than in the previous years, particularly in love songs. This article documents and describes this new trend and discusses the reasons for the change in language use. It reveals that the new development is indicative of a transformation of Bongo Flava towards pop, caused by changes in the domestic market on the one hand and by a growing outward-looking market orientation on the other. These changes are demanding new ways of constructing identities through the use of language.Tangu mnamo mwaka 2011, wasanii wa Bongo Flava walio wengi hutumia kiasi kikubwa cha Kiinge¬reza katika nyimbo zao ukilinganisha na miaka ya nyuma. Hali hiyo inajionyesha zaidi katika nyimbo za mapenzi. Makala hii inaeleza mwelekeo huo mpya na kujadili sababu zake. Inatoa hoja ya kwamba mwelekeo huo umesababishwa hasa na mabadiliko katika soko la muziki ndani na nje ya Tanzania, hasa katika bara la Afrika. Mabadiliko hayo ndiyo yanayosababisha kutumia zaidi lugha ya Kiingereza
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