84 research outputs found
Paying the forest for electricity: A modelling framework to market forest conservation as payment for ecosystem services benefiting hydropower generation
Published in PESC Special issue: Payments for ecosystem services in conservation: performance and prospectsThe operation and longevity of hydropower dams are
often negatively impacted by sedimentation. Forest
conservation can reduce soil erosion, and therefore
efforts to maintain upstream forest cover within a
watershed contribute to the economic life span of a
hydropower facility. The cost of forest conservation
can be viewed as an investment in hydropower and
be financed via a payment for ecosystem services
(PES) scheme. A novel modelling framework is used
to estimate payments for forest conservation consisting
of: (1) land-use change projection; (2)watershed erosion
modelling; (3) reservoir sedimentation estimation; (4)
power generation loss calculation; and (5) PES scheme
design. The framework was applied to a proposed dam
in Cambodia (Pursat 1). The estimated net present
value of forest conservation was US 6.4 million when considering droughts every eight
years. This can be remunerated with annual payments
ofUS 5.78ha-1, respectively, covering
forest protection costs estimated at US$ 0.9 ha-1 yr-1.
The application of this type of PES represents a rational
option that allows for conservation and development
of hydropower watersheds susceptible to erosion and
sedimentation
Paying the forest for electricity: A modelling framework to market forest conservation as payment for ecosystem services benefiting hydropower generation
Published in PESC Special issue: Payments for ecosystem services in conservation: performance and prospectsThe operation and longevity of hydropower dams are
often negatively impacted by sedimentation. Forest
conservation can reduce soil erosion, and therefore
efforts to maintain upstream forest cover within a
watershed contribute to the economic life span of a
hydropower facility. The cost of forest conservation
can be viewed as an investment in hydropower and
be financed via a payment for ecosystem services
(PES) scheme. A novel modelling framework is used
to estimate payments for forest conservation consisting
of: (1) land-use change projection; (2)watershed erosion
modelling; (3) reservoir sedimentation estimation; (4)
power generation loss calculation; and (5) PES scheme
design. The framework was applied to a proposed dam
in Cambodia (Pursat 1). The estimated net present
value of forest conservation was US 6.4 million when considering droughts every eight
years. This can be remunerated with annual payments
ofUS 5.78ha-1, respectively, covering
forest protection costs estimated at US$ 0.9 ha-1 yr-1.
The application of this type of PES represents a rational
option that allows for conservation and development
of hydropower watersheds susceptible to erosion and
sedimentation
Accurate hyperfine couplings for C59N
We identify the shortcomings of existing ab initio quantum chemistry
calculations for the hyperfine couplings in the recently characterized
azafullerene, C59N. Standard gaussian basis sets in the context of
all--electron calculations are insufficient to resolve the spin density near
the cores of the atoms. Using the Projector Augmented Wave method implemented
on top of a standard pseudopotential plane--wave density--functional framework,
we compute significantly more accurate values for the Fermi contact
interaction.Comment: 8 pages, 4 figure
Multiscale Computation with Interpolating Wavelets
Multiresolution analyses based upon interpolets, interpolating scaling
functions introduced by Deslauriers and Dubuc, are particularly well-suited to
physical applications because they allow exact recovery of the multiresolution
representation of a function from its sample values on a finite set of points
in space. We present a detailed study of the application of wavelet concepts to
physical problems expressed in such bases. The manuscript describes algorithms
for the associated transforms which, for properly constructed grids of variable
resolution, compute correctly without having to introduce extra grid points. We
demonstrate that for the application of local homogeneous operators in such
bases, the non-standard multiply of Beylkin, Coifman and Rokhlin also proceeds
exactly for inhomogeneous grids of appropriate form. To obtain less stringent
conditions on the grids, we generalize the non-standard multiply so that
communication may proceed between non-adjacent levels. The manuscript concludes
with timing comparisons against naive algorithms and an illustration of the
scale-independence of the convergence rate of the conjugate gradient solution
of Poisson's equation using a simple preconditioning, suggesting that this
approach leads to an O(n) solution of this equation.Comment: 33 pages, figures available at
http://laisla.mit.edu/muchomas/Papers/nonstand-figs.ps . Updated: (1) figures
file (figs.ps) now appear with the posting on the server; (2) references got
lost in the last submissio
Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum
This manuscript explores the apparent discrepancy between experimental data
and theoretical calculations of the lattice resistance of bcc tantalum. We
present the first results for the temperature dependence of the Peierls stress
in this system and the first ab initio calculation of the zero-temperature
Peierls stress to employ periodic boundary conditions, which are those best
suited to the study of metallic systems at the electron-structure level. Our ab
initio value for the Peierls stress is over five times larger than current
extrapolations of experimental lattice resistance to zero-temperature. Although
we do find that the common techniques for such extrapolation indeed tend to
underestimate the zero-temperature limit, the amount of the underestimation
which we observe is only 10-20%, leaving open the possibility that mechanisms
other than the simple Peierls stress are important in controlling the process
of low temperature slip.Comment: 12 pages and 9 figure
Simulating Physical Phenomena by Quantum Networks
Physical systems, characterized by an ensemble of interacting elementary
constituents, can be represented and studied by different algebras of
observables or operators. For example, a fully polarized electronic system can
be investigated by means of the algebra generated by the usual fermionic
creation and annihilation operators, or by using the algebra of Pauli
(spin-1/2) operators. The correspondence between the two algebras is given by
the Jordan-Wigner isomorphism. As we previously noted similar one-to-one
mappings enable one to represent any physical system in a quantum computer. In
this paper we evolve and exploit this fundamental concept in quantum
information processing to simulate generic physical phenomena by quantum
networks. We give quantum circuits useful for the efficient evaluation of the
physical properties (e.g, spectrum of observables or relevant correlation
functions) of an arbitrary system with Hamiltonian .Comment: 44 pages, 15 psfigur
Acceleration Schemes for Ab-Initio Molecular Dynamics and Electronic Structure Calculations
We study the convergence and the stability of fictitious dynamical methods
for electrons. First, we show that a particular damped second-order dynamics
has a much faster rate of convergence to the ground-state than first-order
steepest descent algorithms while retaining their numerical cost per time step.
Our damped dynamics has efficiency comparable to that of conjugate gradient
methods in typical electronic minimization problems. Then, we analyse the
factors that limit the size of the integration time step in approaches based on
plane-wave expansions. The maximum allowed time step is dictated by the highest
frequency components of the fictitious electronic dynamics. These can result
either from the large wavevector components of the kinetic energy or from the
small wavevector components of the Coulomb potential giving rise to the so
called {\it charge sloshing} problem. We show how to eliminate large wavevector
instabilities by adopting a preconditioning scheme that is implemented here for
the first-time in the context of Car-Parrinello ab-initio molecular dynamics
simulations of the ionic motion. We also show how to solve the charge-sloshing
problem when this is present. We substantiate our theoretical analysis with
numerical tests on a number of different silicon and carbon systems having both
insulating and metallic character.Comment: RevTex, 9 figures available upon request, to appear in Phys. Rev.
Non-Equilibrium Electron Transport in Two-Dimensional Nano-Structures Modeled by Green's Functions and the Finite-Element Method
We use the effective-mass approximation and the density-functional theory
with the local-density approximation for modeling two-dimensional
nano-structures connected phase-coherently to two infinite leads. Using the
non-equilibrium Green's function method the electron density and the current
are calculated under a bias voltage. The problem of solving for the Green's
functions numerically is formulated using the finite-element method (FEM). The
Green's functions have non-reflecting open boundary conditions to take care of
the infinite size of the system. We show how these boundary conditions are
formulated in the FEM. The scheme is tested by calculating transmission
probabilities for simple model potentials. The potential of the scheme is
demonstrated by determining non-linear current-voltage behaviors of resonant
tunneling structures.Comment: 13 pages,15 figure
FGF receptor genes and breast cancer susceptibility: results from the Breast Cancer Association Consortium
Background:Breast cancer is one of the most common malignancies in women. Genome-wide association studies have identified FGFR2 as a breast cancer susceptibility gene. Common variation in other fibroblast growth factor (FGF) receptors might also modify risk. We tested this hypothesis by studying genotyped single-nucleotide polymorphisms (SNPs) and imputed SNPs in FGFR1, FGFR3, FGFR4 and FGFRL1 in the Breast Cancer Association Consortium.
Methods:Data were combined from 49 studies, including 53 835 cases and 50 156 controls, of which 89 050 (46 450 cases and 42 600 controls) were of European ancestry, 12 893 (6269 cases and 6624 controls) of Asian and 2048 (1116 cases and 932 controls) of African ancestry. Associations with risk of breast cancer, overall and by disease sub-type, were assessed using unconditional logistic regression.
Results:Little evidence of association with breast cancer risk was observed for SNPs in the FGF receptor genes. The strongest evidence in European women was for rs743682 in FGFR3; the estimated per-allele odds ratio was 1.05 (95 confidence interval=1.02-1.09, P=0.0020), which is substantially lower than that observed for SNPs in FGFR2.
Conclusion:Our results suggest that common variants in the other FGF receptors are not associated with risk of breast cancer to the degree observed for FGFR2. © 2014 Cancer Research UK
The methodological quality is insufficient in clinical practice guidelines in the context of COVID-19 : systematic review
Objectives
The number of published clinical practice guidelines related to COVID-19 has rapidly increased. This study explored if basic methodological standards of guideline development have been met in the published clinical practice guidelines related to COVID-19.
Study Design and Setting
Rapid systematic review from February 1 until April 27, 2020 using MEDLINE [PubMed], CINAHL [Ebsco], Trip and manual search, including all types of healthcare workers providing any kind of healthcare to any patient population in any setting.
Results
There were 1342 titles screened and 188 guidelines included. The highest average AGREE II domain score was 89% for scope and purpose, the lowest for rigor of development (25%). Only eight guidelines (4%) were based on a systematic literature search and a structured consensus process by representative experts (classified as the highest methodological quality). The majority (156; 83%) was solely built on an informal expert consensus. A process for regular updates was described in 27 guidelines (14%). Patients were included in the development of only one guideline.
Conclusion
Despite clear scope, most publications fell short of basic methodological standards of guideline development. Clinicians should use guidelines that include up-to-date information, were informed by stakeholder involvement, and employed rigorous methodologies
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