3,170 research outputs found
A review of life cycle assessments of renewable energy systems
A review of life cycle assessments (LCAs) of wind energy published in the past few years are presented in this paper. The aim is to identify the differences of the developed methodologies, in particular, the factors such as methods used, energy performance and influence of uncertainty. Each of the factors is addressed to highlight the shortcomings and strengths of various approaches. Potential issues were identified regarding the way LCA is used for assessing environmental impact and energy performance of wind energy. It is found that the potential of incorporating the quantification of uncertainty in the manufacturing phase has not been studied elaborately. A framework methodology has been proposed in this paper to address this issue
A hybrid Data Quality Indicator and statistical method for improving uncertainty analysis in LCA of a small off-grid wind turbine
In Life Cycle Assessment (LCA) uncertainty analysis has been recommended when choosing sustainable products. Both Data Quality Indicator and statistical methods are used to estimate data uncertainties in LCA. Neither of these alone is however adequate enough to address the challenges in LCA of a complex system due to data scarcity and large quantity of material types. This paper applies a hybrid stochastic method, combining the statistical and Data Quality Indicator methods by using a pre-screening process based on Monte Carlo rank-order correlation sensitivity analysis, to improve the uncertainty estimate in wind turbine LCA with data limitations. In the presented case study which performed the stochastic estimation of CO2 emissions, similar results from the hybrid method were observed compared to the pure Data Quality Indicator method. Summarily, the presented hybrid method can be used as a possible alternative for evaluating deterministic LCA results like CO2 emissions, when results that are more reliable are desired with limited availability of data
Changing Impact of Fiscal Policy on Selected ASEAN Countries
This paper investigates the effectiveness of fiscal policy in five Association of Southeast Asian Nations (ASEAN) of Indonesia, Malaysia, the Philippines, Singapore and Thailand. Through a structural vector autoregression (VAR) model, government spending is found to have weak and largely insignificant impact on output, while taxes are found to have outcomes contrary to conventional theory. Extensions using a time-varying VAR model reveal the impact of taxes on output mainly reflect heightened concerns over public finances amid the Asian financial crisis and the recent global financial crisis. On the other hand, for Singapore and Thailand, there is evidence that government spending can at times be useful as a tool for countercyclical policy.ASEAN; fiscal policy; structural VAR; time-varying VAR
Are the Health of the Nation's targets attainable? Postal survey of general practitioners' views
The Health of the Nation's targets were introduced by the government in 1992 as part of a strategic approach to health.1 We aimed, in 1996, to elicit the views of general practitioners on the attainability of these targets
Precision Enhancement of 3D Surfaces from Multiple Compressed Depth Maps
In texture-plus-depth representation of a 3D scene, depth maps from different
camera viewpoints are typically lossily compressed via the classical transform
coding / coefficient quantization paradigm. In this paper we propose to reduce
distortion of the decoded depth maps due to quantization. The key observation
is that depth maps from different viewpoints constitute multiple descriptions
(MD) of the same 3D scene. Considering the MD jointly, we perform a POCS-like
iterative procedure to project a reconstructed signal from one depth map to the
other and back, so that the converged depth maps have higher precision than the
original quantized versions.Comment: This work was accepted as ongoing work paper in IEEE MMSP'201
Volumetric 3D Point Cloud Attribute Compression: Learned polynomial bilateral filter for prediction
We extend a previous study on 3D point cloud attribute compression scheme
that uses a volumetric approach: given a target volumetric attribute function
, we quantize and encode parameters
that characterize at the encoder, for reconstruction
at known 3D points at the decoder.
Specifically, parameters are quantized coefficients of B-spline basis
vectors (for order ) that span the function space
at a particular resolution , which are coded from
coarse to fine resolutions for scalability. In this work, we focus on the
prediction of finer-grained coefficients given coarser-grained ones by learning
parameters of a polynomial bilateral filter (PBF) from data. PBF is a
pseudo-linear filter that is signal-dependent with a graph spectral
interpretation common in the graph signal processing (GSP) field. We
demonstrate PBF's predictive performance over a linear predictor inspired by
MPEG standardization over a wide range of point cloud datasets
Learned Nonlinear Predictor for Critically Sampled 3D Point Cloud Attribute Compression
We study 3D point cloud attribute compression via a volumetric approach:
assuming point cloud geometry is known at both encoder and decoder, parameters
of a continuous attribute function are quantized to and encoded, so that discrete
samples can be recovered at known 3D points
at the decoder. Specifically, we consider a
nested sequences of function subspaces , where is a family
of functions spanned by B-spline basis functions of order , is the
projection of on and encoded as low-pass coefficients
, and is the residual function in orthogonal subspace
(where ) and encoded as high-pass coefficients . In
this paper, to improve coding performance over [1], we study predicting
at level given at level and encoding of
for the case (RAHT()). For the prediction, we formalize RAHT(1) linear
prediction in MPEG-PCC in a theoretical framework, and propose a new nonlinear
predictor using a polynomial of bilateral filter. We derive equations to
efficiently compute the critically sampled high-pass coefficients
amenable to encoding. We optimize parameters in our resulting feed-forward
network on a large training set of point clouds by minimizing a rate-distortion
Lagrangian. Experimental results show that our improved framework outperformed
the MPEG G-PCC predictor by to in bit rate reduction
Photospheric Signatures of Granular-scale Flux Emergence and Cancellation at the Penumbral Boundary
We studied flux emergence events of sub-granular scale in a solar active
region. New Solar Telescope (NST) of Big Bear Solar Observatory made it
possible to clearly observe the photospheric signature of flux emergence with
very high spatial (0".11 at 7057{\AA}) and temporal (15 s) resolution. From TiO
observations with the pixel scale of 0".0375, we found several elongated
granule-like features (GLFs) stretching from the penumbral filaments of a
sunspot at a relatively high speed of over 4 km s-1. After a slender arched
darkening appeared at a tip of a penumbral filament, a bright point (BP)
developed and quickly moved away from the filament forming and stretching a
GLF. The size of a GLF was approximately 0.5" wide and 3" long. The moving BP
encountered nearby structures after several minutes of stretching, and a
well-defined elongated shape of a GLF faded away. Magnetograms from SDO/HMI and
NST/IRIM revealed that those GLFs are photospheric indicators of small-scale
flux emergence, and their disappearance is related to magnetic cancellation.
From two well-observed events, we describe detailed development of the
sub-structures of GLFs, and different cancellation processes that each of the
two GLFs underwent.Comment: Accepted for publication in The Astrophysical Journa
Constructing the Tree-Level Yang-Mills S-Matrix Using Complex Factorization
A remarkable connection between BCFW recursion relations and constraints on
the S-matrix was made by Benincasa and Cachazo in 0705.4305, who noted that
mutual consistency of different BCFW constructions of four-particle amplitudes
generates non-trivial (but familiar) constraints on three-particle coupling
constants --- these include gauge invariance, the equivalence principle, and
the lack of non-trivial couplings for spins >2. These constraints can also be
derived with weaker assumptions, by demanding the existence of four-point
amplitudes that factorize properly in all unitarity limits with complex
momenta. From this starting point, we show that the BCFW prescription can be
interpreted as an algorithm for fully constructing a tree-level S-matrix, and
that complex factorization of general BCFW amplitudes follows from the
factorization of four-particle amplitudes. The allowed set of BCFW deformations
is identified, formulated entirely as a statement on the three-particle sector,
and using only complex factorization as a guide. Consequently, our analysis
based on the physical consistency of the S-matrix is entirely independent of
field theory. We analyze the case of pure Yang-Mills, and outline a proof for
gravity. For Yang-Mills, we also show that the well-known scaling behavior of
BCFW-deformed amplitudes at large z is a simple consequence of factorization.
For gravity, factorization in certain channels requires asymptotic behavior
~1/z^2.Comment: 35 pages, 6 figure
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