6,687 research outputs found
On the NP-Hardness of Approximating Ordering Constraint Satisfaction Problems
We show improved NP-hardness of approximating Ordering Constraint
Satisfaction Problems (OCSPs). For the two most well-studied OCSPs, Maximum
Acyclic Subgraph and Maximum Betweenness, we prove inapproximability of
and .
An OCSP is said to be approximation resistant if it is hard to approximate
better than taking a uniformly random ordering. We prove that the Maximum
Non-Betweenness Problem is approximation resistant and that there are width-
approximation-resistant OCSPs accepting only a fraction of
assignments. These results provide the first examples of
approximation-resistant OCSPs subject only to P \NP
Valuing mortality reductions in India : a study of compensating wage differentials
Conducting cost-benefit analyses of health and safety regulations requires placing a dollar value on reductions in health risks, including the risk of death. In the United States, mortality risks are often valued using compensating-wage differentials. These differentials measure what a worker would have to be paid to accept a small increase in his risk of death-which is assumed to equal what the worker would pay to achieve a small reduction in his risk of death. The authors estimate compensating-wage differentials for risk of fatal and nonfatal injuries in India's manufacturing industry. They estimate a hedonic wage equation using the most recent Occupational Wage Survey, supplemented by data on occupational injuries from the Indian Labour Yearbook. Their estimates of compensating-wage differentials imply a value of statistical life (VSL) in India of 6.4 million to 15 million 1990 rupees (roughly 360,000 at current exchange rates). This number is between 20 and 48 times forgone earnings-the human capital measure of the value of reducing the risk of death. The ratio of the VSL to forgone earnings implied by the study is larger than in comparable U.S. studies but smaller than the ratio implied by the only other compensating-wage study for India (Shanmugam 1997). The latter implies a ratio of VSL to forgone earnings of 73! The authors caution that in India, as in the United States, compensating-wage differentials in the labor market may overstate what individuals would themselves pay to reduce the risk of death. They suggest using their estimates as an upper boundon willingness to pay to reduce risk of death, and forgone earnings as a lower bound.Labor Policies,Water and Industry,Public Health Promotion,Environmental Economics&Policies,Banks&Banking Reform,Banks&Banking Reform,Health Monitoring&Evaluation,Health Economics&Finance,Water and Industry,Environmental Economics&Policies
High Order Upwind Schemes for Multidimensional Magnetohydrodynamics
A general method for constructing high order upwind schemes for
multidimensional magnetohydrodynamics (MHD), having as a main built-in
condition the divergence-free constraint \divb=0 for the magnetic field
vector \bb, is proposed. The suggested procedure is based on {\em
consistency} arguments, by taking into account the specific operator structure
of MHD equations with respect to the reference Euler equations of gas-dynamics.
This approach leads in a natural way to a staggered representation of the \bb
field numerical data where the divergence-free condition in the cell-averaged
form, corresponding to second order accurate numerical derivatives, is exactly
fulfilled. To extend this property to higher order schemes, we then give
general prescriptions to satisfy a order accurate \divb=0
relation for any numerical \bb field having a order interpolation
accuracy. Consistency arguments lead also to a proper formulation of the upwind
procedures needed to integrate the induction equations, assuring the exact
conservation in time of the divergence-free condition and the related
continuity properties for the \bb vector components. As an application, a
third order code to simulate multidimensional MHD flows of astrophysical
interest is developed using ENO-based reconstruction algorithms. Several test
problems to illustrate and validate the proposed approach are finally
presented.Comment: 34 pages, including 14 figure
2-D geoelectrical model for the Parnaiba Basin conductivity anomaly of northeast Brazil and tectonic implications
A magnetometer array study in the north-northeast of Brazil has revealed a roughly NE-SW-trending conductive structure in the southeastern part of the intracratonic ParnaĂba Basin. The magnetovariational response functions of this structure are numerically modelled to constrain its geometry to facilitate its geological and tectonic interpretation. The 2-D numerical model that incorporates the ocean effect and can account for the spatial and period dependence of the observed response locates the source regions of enhanced conductivity in a graben structure in the basement as well as in a block confined to the central part of the basin with an embedded resistive body. The anomalous electrical character of the sediments in the central part of the basin is consistent with the magnetotelluric data, the graben structure in the basement is corroborated by the aeromagnetic data. The formation of the graben structure is considered to be a manifestation of the extensional tectonics associated either with the Brasiliano orogeny or with the Jurassic–Cretaceous magmatic events. The diabase dikes intruded in the basin in association with the Jurassic-Cretaceous magmatic activity are shown to be accountable for the mapped resistive body entrapped in the conducting Paleozoic sediments. The thermal effects associated with magmatic activities are invoked to produce enhanced conductivity by the generation of carbon through the pyrolysis of hydrocarbon-saturated sediments
Results of the multicenter study of enhanced external counterpulsation (MUST-EECP): clinical benefits are sustained at a mean follow-up time of one year
Parallelizing Deadlock Resolution in Symbolic Synthesis of Distributed Programs
Previous work has shown that there are two major complexity barriers in the
synthesis of fault-tolerant distributed programs: (1) generation of fault-span,
the set of states reachable in the presence of faults, and (2) resolving
deadlock states, from where the program has no outgoing transitions. Of these,
the former closely resembles with model checking and, hence, techniques for
efficient verification are directly applicable to it. Hence, we focus on
expediting the latter with the use of multi-core technology.
We present two approaches for parallelization by considering different design
choices. The first approach is based on the computation of equivalence classes
of program transitions (called group computation) that are needed due to the
issue of distribution (i.e., inability of processes to atomically read and
write all program variables). We show that in most cases the speedup of this
approach is close to the ideal speedup and in some cases it is superlinear. The
second approach uses traditional technique of partitioning deadlock states
among multiple threads. However, our experiments show that the speedup for this
approach is small. Consequently, our analysis demonstrates that a simple
approach of parallelizing the group computation is likely to be the effective
method for using multi-core computing in the context of deadlock resolution
Earthquake networks based on similar activity patterns
Earthquakes are a complex spatiotemporal phenomenon, the underlying mechanism
for which is still not fully understood despite decades of research and
analysis. We propose and develop a network approach to earthquake events. In
this network, a node represents a spatial location while a link between two
nodes represents similar activity patterns in the two different locations. The
strength of a link is proportional to the strength of the cross-correlation in
activities of two nodes joined by the link. We apply our network approach to a
Japanese earthquake catalog spanning the 14-year period 1985-1998. We find
strong links representing large correlations between patterns in locations
separated by more than 1000 km, corroborating prior observations that
earthquake interactions have no characteristic length scale. We find network
characteristics not attributable to chance alone, including a large number of
network links, high node assortativity, and strong stability over time.Comment: 8 pages text, 9 figures. Updated from previous versio
Directed Surfaces in Disordered Media
The critical exponents for a class of one-dimensional models of interface
depinning in disordered media can be calculated through a mapping onto directed
percolation (DP). In higher dimensions these models give rise to directed
surfaces, which do not belong to the directed percolation universality class.
We formulate a scaling theory of directed surfaces, and calculate critical
exponents numerically, using a cellular automaton that locates the directed
surfaces without making reference to the dynamics of the underlying interface
growth models.Comment: 4 pages, REVTEX, 2 Postscript figures avaliable from [email protected]
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Impacts of household sources on air pollution at village and regional scales in India
Approximately 3 billion people worldwide cook with solid fuels, such as wood, charcoal, and agricultural residues. These fuels, also used for residential heating, are often combusted in inefficient devices, producing carbonaceous emissions. Between 2.6 and 3.8 million premature deaths occur as a result of exposure to fine particulate matter from the resulting household air pollution (Health Effects Institute, 2018a; World Health Organization, 2018). Household air pollution also contributes to ambient air pollution; the magnitude of this contribution is uncertain. Here, we simulate the distribution of the two major health-damaging outdoor air pollutants (PM2:5 and O3) using state-of-thescience emissions databases and atmospheric chemical transport models to estimate the impact of household combustion on ambient air quality in India. The present study focuses on New Delhi and the SOMAARTH Demographic, Development, and Environmental Surveillance Site (DDESS) in the Palwal District of Haryana, located about 80 km south of New Delhi. The DDESS covers an approximate population of 200 000 within 52 villages. The emissions inventory used in the present study was prepared based on a national inventory in India (Sharma et al., 2015, 2016), an updated residential sector inventory prepared at the University of Illinois, updated cookstove emissions factors from Fleming et al. (2018b), and PM2:5 speciation from cooking fires from Jayarathne et al. (2018). Simulation of regional air quality was carried out using the US Environmental Protection Agency Community Multiscale Air Quality modeling system (CMAQ) in conjunction with the Weather Research and Forecasting modeling system (WRF) to simulate the meteorological inputs for CMAQ, and the global chemical transport model GEOS-Chem to generate concentrations on the boundary of the computational domain. Comparisons between observed and simulated O3 and PM2:5 levels are carried out to assess overall airborne levels and to estimate the contribution of household cooking emissions
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