23,251 research outputs found
A novel low complexity local hybrid pseudo-SSIM-SATD distortion metric towards perceptual rate control
The front-end block-based video encoder applies an Image Quality Assessment (IQA) as part of the distortion metric. Typically, the distortion metric applies uniform weighting for the absolute differences within a Sub-Macroblock (Sub-MB) at any given time. As video is predominately designed for Humans, the distortion metric should reflect the Human Visual System (HVS). Thus, a perceptual distortion metric (PDM), will lower the convex hull of the Rate-Distortion (R-D) curve towards the origin, by removing perceptual redundancy and retaining perceptual clues. Structured Similarity (SSIM), a perceptual IQA, has been adapted via logarithmic functions to measure distortion, however, it is restricted to the Group of Picture level and hence unable to adapt to the local Sub-MB changes. This paper proposes a Local Hybrid Pseudo-SSIM-SATD (LHPSS) Distortion Metric, operating at the Sub-MB level and satisfying the Triangle Equality Rule (≤). A detailed discussion of LHPSS's Psuedo-SSIM model will illustrate how SSIM can be perceptually scaled within the distortion metric space of SATD using non-logarithmic functions. Results of HD video encoded across different QPs will be presented showing the competitive bit usage under IbBbBbBbP prediction structure for similar image quality. Finally, the mode decision choices superimposed on the Intra frame will illustrate that LHPSS lowers the R-D curve as homogeneous regions are represented with larger block size
Review of standard traditional distortion metrics and a need for perceptual distortion metric at a (sub) macroblock level
Within a video encoder the distortion metric performs an Image Quality Assessment (IQA). However, to exploit perceptual redundancy to lower the convex hull of the Rate-
Distortion (R-D) curve, a Perceptual Distortion Metric (PDM)
modelling of the Human Visual System (HVS) should be used. Since block-based video encoders like H.264/AVC operate at the Sub-Macroblock (Sub-MB) level, there exists a need to produce a locally operating PDM. A locally operating PDM must meet the requirements of Standard Traditional Distortion Metrics (STDMs), in that it must satisfy the Triangle Equality Rule. Hence, this paper presents a review of STDMs of SSE, SAD and SATD against the perceptual IQA of Structural Similarity (SSIM) at the Sub-MB level. Furthermore, this paper illustrates the Universal Bounded Region (UBR) by block size that supports the triangle equality rule within the Sub-MB level, between SSIM and STDMs like SATD at the prediction stage
Structural and magnetic properties of Pr-alloyed MnBi nanostructures
The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr)
nanostructures with a range of Pr concentrations have been investigated. The
nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9
atomic percent and melt-spun ribbons having Pr concentrations 0, 2, 4 and 6
percent respectively. Addition of Pr into the MnBi lattice has produced a
significant change in the magnetic properties of these nanostructures including
an increase in coercivity and structural phase transition temperature, and a
decrease in saturation magnetization and anisotropy energy. The highest value
of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe.
The observed magnetic properties are explained as the consequences of competing
ferromagnetic and antiferromagnetic interactions
Qualitative properties of -fair policies in bandwidth-sharing networks
We consider a flow-level model of a network operating under an -fair
bandwidth sharing policy (with ) proposed by Roberts and
Massouli\'{e} [Telecomunication Systems 15 (2000) 185-201]. This is a
probabilistic model that captures the long-term aspects of bandwidth sharing
between users or flows in a communication network. We study the transient
properties as well as the steady-state distribution of the model. In
particular, for , we obtain bounds on the maximum number of flows
in the network over a given time horizon, by means of a maximal inequality
derived from the standard Lyapunov drift condition. As a corollary, we
establish the full state space collapse property for all . For the
steady-state distribution, we obtain explicit exponential tail bounds on the
number of flows, for any , by relying on a norm-like Lyapunov
function. As a corollary, we establish the validity of the diffusion
approximation developed by Kang et al. [Ann. Appl. Probab. 19 (2009)
1719-1780], in steady state, for the case where and under a local
traffic condition.Comment: Published in at http://dx.doi.org/10.1214/12-AAP915 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Molecular clouds and clumps in the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO)
Galactic Ring Survey (GRS) of 13 CO (1-0) emission covers Galactic longitudes
18 deg < l < 55.7 deg and Galactic latitudes |b| <= 1 deg. Using the SEQUOIA
array on the FCRAO 14m telescope, the GRS fully sampled the 13 CO Galactic
emission (46 arcsec angular resolution on a 22 arcsec grid) and achieved a
spectral resolution of 0.21 km/s. Because the GRS uses 13 CO, an optically thin
tracer, rather than 12 CO, an optically thick tracer, the GRS allows a much
better determination of column density and also a cleaner separation of
velocity components along a line of sight. With this homogeneous, fully-sampled
survey of 13 CO, emission, we have identified 829 molecular clouds and 6124
clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we
present details of the catalog and a preliminary analysis of the properties of
the molecular clouds and their clumps. Moreover, we compare clouds inside and
outside of the 5 kpc ring and find that clouds within the ring typically have
warmer temperatures, higher column densities, larger areas, and more clumps
compared to clouds located outside the ring. This is expected if these clouds
are actively forming stars. This catalog provides a useful tool for the study
of molecular clouds and their embedded young stellar objects.Comment: 29 pages. ApJ in pres
Non-degenerate four-wave mixing in rubidium vapor: transient regime
We investigate the transient response of the generated light from Four-Wave
Mixing (FWM) in the diamond configuration using a step-down field excitation.
The transients show fast decay times and oscillations that depend on the
detunings and intensities of the fields. A simplified model taking into account
the thermal motion of the atoms, propagation, absorption and dispersion effects
shows qualitative agreement with the experimental observations with the energy
levels in rubidium (5S1/2, 5P1/2, 5P3/2 and 6S1/2). The atomic polarization
comes from all the contributions of different velocity classes of atoms in the
ensemble modifying dramatically the total transient behavior of the light from
FWM.Comment: 11 pages, 11 figures, to be published in Physical Review
Coherence Length of Excitons in a Semiconductor Quantum Well
We report on the first experimental determination of the coherence length of
excitons in semiconductors using the combination of spatially resolved
photoluminescence with phonon sideband spectroscopy. The coherence length of
excitons in ZnSe quantum wells is determined to be 300 ~ 400 nm, about 25 ~ 30
times the exciton de Broglie wavelength. With increasing exciton kinetic
energy, the coherence length decreases slowly. The discrepancy between the
coherence lengths measured and calculated by only considering the acoustic
phonon scattering suggests an important influence of static disorder.Comment: 4 Pages, 4 figure
Scaling and Formulary cross sections for ion-atom impact ionization
The values of ion-atom ionization cross sections are frequently needed for
many applications that utilize the propagation of fast ions through matter.
When experimental data and theoretical calculations are not available,
approximate formulas are frequently used. This paper briefly summarizes the
most important theoretical results and approaches to cross section calculations
in order to place the discussion in historical perspective and offer a concise
introduction to the topic. Based on experimental data and theoretical
predictions, a new fit for ionization cross sections is proposed. The range of
validity and accuracy of several frequently used approximations (classical
trajectory, the Born approximation, and so forth) are discussed using, as
examples, the ionization cross sections of hydrogen and helium atoms by various
fully stripped ions.Comment: 46 pages, 8 figure
Optimizing farmyard manure and cattle slurry applications for intensively managed grasslands based on UK-DNDC model simulations
Fertilizer applications can enhance soil fertility, pasture growth and thereby increase production. Nitrogen fertilizer
has, however, been identified as a significant source of nitrous oxide (N2O) emissions fromagriculture if not used correctly and can thereby increase the environmental damage costs associatedwith agricultural production.
The optimumuse of organic fertilizers requires an improved understanding of nutrient cycles and their controls.
Against this context, the objective of this research was to evaluate the scope for reducing N2O emissions from grassland using a number of manure management practices including more frequent applications of smaller doses and differentmethods of application.We used amodified UK-DNDCmodel and N2O emissions from grasslands at Pwllpeiran (PW), UK during the calibration period in autumn, were 1.35 kg N/ha/y (cattle slurry) and 0.95 kgN/ha/y (farmyardmanure), and 2.31 kg N/ha/y (cattle slurry) and 1.08 kgN/ha/y (farmyardmanure) during validation period in spring, compared to 1.43 kg N/ha/y (cattle slurry) and 0.29 kgN/ha/y (farmyard manure)
during spring at NorthWyke (NW), UK. The modelling results suggested that the time period between fertilizing and sampling (TPFA), rainfall and the daily average air temperature are key factors for N2O emissions. Also, the
emission factor (EF) varies spatio-temporally (0–2%) compared to uniform 1% EF assumption of IPCC. Predicted N2O emissions were positively and linearly (R2≈1) related with N loadings under all scenarios. During the scenario analysis, the use of high frequency, lowdose fertilizer applications compared to a single one off application was predicted to reduce N2O peak fluxes and overall emissions for cattle slurry during the autumn and spring seasons at the PWand NW experimental sites by 17% and 15%, respectively. These results demonstrated that an optimized application regime using outputs from the modelling approach is a promising tool for supporting
environmentally-friendly precision agriculture
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