11,783 research outputs found
Near-linear Time Algorithm for Approximate Minimum Degree Spanning Trees
Given a graph , we wish to compute a spanning tree whose maximum
vertex degree, i.e. tree degree, is as small as possible. Computing the exact
optimal solution is known to be NP-hard, since it generalizes the Hamiltonian
path problem. For the approximation version of this problem, a
time algorithm that computes a spanning tree of degree at most is
previously known [F\"urer \& Raghavachari 1994]; here denotes the
minimum tree degree of all the spanning trees. In this paper we give the first
near-linear time approximation algorithm for this problem. Specifically
speaking, we propose an time algorithm that
computes a spanning tree with tree degree for any constant .
Thus, when , we can achieve approximate solutions with
constant approximate ratio arbitrarily close to 1 in near-linear time.Comment: 17 page
Voltage modulated electro-luminescence spectroscopy and negative capacitance - the role of sub-bandgap states in light emitting devices
Voltage modulated electroluminescence spectra and low frequency ({\leq} 100
kHz) impedance characteristics of electroluminescent diodes are studied.
Voltage modulated light emission tracks the onset of observed negative
capacitance at a forward bias level for each modulation frequency. Active
participation of sub-bandgap defect states in minority carrier recombination
dynamics is sought to explain the results. Negative capacitance is understood
as a necessary dielectric response to compensate any irreversible transient
changes in the minority carrier reservoir due to radiative recombinations
mediated by slowly responding sub-bandgap defects. Experimentally measured
variations of the in-phase component of modulated electroluminescence spectra
with forward bias levels and modulation frequencies support the dynamic
influence of these states in the radiative recombination process. Predominant
negative sign of the in-phase component of voltage modulated
electroluminescence signal further confirms the bi-molecular nature of light
emission. We also discuss how these states can actually affect the net density
of minority carriers available for radiative recombination. Results indicate
that these sub-bandgap states can suppress external quantum efficiency of such
devices under high frequency operation commonly used in optical communication.Comment: 21 pages, 4 sets of figure
Dataplane Specialization for High-performance OpenFlow Software Switching
OpenFlow is an amazingly expressive dataplane program-
ming language, but this expressiveness comes at a severe
performance price as switches must do excessive packet clas-
sification in the fast path. The prevalent OpenFlow software
switch architecture is therefore built on flow caching, but
this imposes intricate limitations on the workloads that can
be supported efficiently and may even open the door to mali-
cious cache overflow attacks. In this paper we argue that in-
stead of enforcing the same universal flow cache semantics
to all OpenFlow applications and optimize for the common
case, a switch should rather automatically specialize its dat-
aplane piecemeal with respect to the configured workload.
We introduce ES WITCH , a novel switch architecture that
uses on-the-fly template-based code generation to compile
any OpenFlow pipeline into efficient machine code, which
can then be readily used as fast path. We present a proof-
of-concept prototype and we demonstrate on illustrative use
cases that ES WITCH yields a simpler architecture, superior
packet processing speed, improved latency and CPU scala-
bility, and predictable performance. Our prototype can eas-
ily scale beyond 100 Gbps on a single Intel blade even with
complex OpenFlow pipelines
Barrier modification in sub-barrier fusion reactions using Wong formula with Skyrme forces in semiclassical formalism
We obtain the nuclear proximity potential by using semiclassical extended
Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), and use
it in the extended -summed Wong formula under frozen density
approximation. This method has the advantage of allowing the use of different
Skyrme forces, giving different barriers. Thus, for a given reaction, we could
choose a Skyrme force with proper barrier characteristics, not-requiring extra
``barrier lowering" or ``barrier narrowing" for a best fit to data. For the
Ni+Mo reaction, the -summed Wong formula, with effects of
deformations and orientations of nuclei included, fits the fusion-evaporation
cross section data exactly for the force GSkI, requiring additional barrier
modifications for forces SIII and SV. However, the same for other similar
reactions, like Ni+Ni, fits the data best for SIII force.
Hence, the barrier modification effects in -summed Wong expression
depends on the choice of Skyrme force in extended ETF method.Comment: INPC2010, Vancouver, CANAD
Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses
The mixed-alkali effect on the cation dynamics in silicate glasses is
analyzed via molecular dynamics simulations. Observations suggest a description
of the dynamics in terms of stable sites mostly specific to one ionic species.
As main contributions to the mixed--alkali slowdown longer residence times and
an increased probability of correlated backjumps are identified. The slowdown
is related to the limited accessibility of foreign sites. The mismatch
experienced in a foreign site is stronger and more retarding for the larger
ions, the smaller ions can be temporarily accommodated. Also correlations
between unlike as well as like cations are demonstrated that support
cooperative behavior.Comment: 10 pages, 12 figures, 1 table, revtex4, submitted to Phys. Rev.
Pro-poor policies and improvements in maternal health outcomes in India
BACKGROUND: Since 2005, India has experienced an impressive 77% reduction in maternal mortality compared to the global average of 43%. What explains this impressive performance in terms of reduction in maternal mortality and improvement in maternal health outcomes? This paper evaluates the effect of household wealth status on maternal mortality in India, and also separates out the performance of the Empowered Action Group (EAG) states and the Southern states of India. The results are discussed in the light of various pro-poor programmes and policies designed to reduce maternal mortality and the existing supply side gaps in the healthcare system of India. Using multiple sources of data, this study aims to understand the trends in maternal mortality (1997-2017) between EAG and non EAG states in India and explore various household, economic and policy factors that may explain reduction in maternal mortality and improvement in maternal health outcomes in India. METHODS: This study triangulates data from different rounds of Sample Registration Systems to assess the trend in maternal mortality in India. It further analysed the National Family Health Surveys (NFHS). NFHS-4, 2015-16 has gathered information on maternal mortality and pregnancy-related deaths from 601,509 households. Using logistic regression, we estimate the association of various socio-economic variables on maternal deaths in the various states of India. RESULTS: On an average, wealth status of the households did not have a statistically significant association with maternal mortality in India. However, our disaggregate analysis reveals, the gains in terms of maternal mortality have been unevenly distributed. Although the rich-poor gap in maternal mortality has reduced in EAG states such as Bihar, Odisha, Assam, Rajasthan, the maternal mortality has remained above the national average for many of these states. The EAG states also experience supply side shortfalls in terms of availability of PHC and PHC doctors; and availability of specialist doctors. CONCLUSIONS: The novel contribution of the present paper is that the association of household wealth status and place of residence with maternal mortality is statistically not significant implying financial barriers to access maternal health services have been minimised. This result, and India's impressive performance with respect to maternal health outcomes, can be attributed to the various pro-poor policies and cash incentive schemes successfully launched in recent years. Community-level involvement with pivotal role played by community health workers has been one of the major reasons for the success of many ongoing policies. Policy makers need to prioritise the underperforming states and socio-economic groups within the states by addressing both demand-side and supply-side measures simultaneously mediated by contextual factors
Naval Ship Maintenance: An Analysis of the Dutch Shipbuilding Industry Using the Knowledge Value Added, Systems Dynamics, and Integrated Risk Management Methodologies
Sponsored Report (for Acquisition Research Program)Initiatives to reduce the cost of ship maintenance have not yet realized the normal cost-reduction learning curve improvements. One explanation is the lack of recommended technologies. Damen, a Dutch shipbuilding and service firm, has incorporated similar technologies and is developing others to improve its operations. The research team collected data on Dutch ship maintenance operations and used them to build three types of computer simulation models of ship maintenance and technology adoption. The results were analyzed and compared with previously developed modeling results of U.S. Navy ship maintenance and technology adoption. Adopting 3D PDF alone improves ROI significantly more than adopting a logistics package alone and adding both technologies improves ROI more than adding either technology alone. Adoption of the technologies would provide cost benefits far in excess of not using the technologies and there were marginal benefits in sequentially implementing the technologies over immediately implementing them. There are a number of issues in comparing the results with previous research but the potential benefits of using the technologies are very high in both cases. Implications for acquisition practice include the need for careful analysis and selection from among a variety of available information technologies and the recommendation for a phased development and implementation approach to manage uncertainty.Acquisition Research Progra
The Decay of Disease Association with Declining Linkage Disequilibrium: A Fine Mapping Theorem
Several important and fundamental aspects of disease genetics models have yet to be described. One such property is the relationship of disease association statistics at a marker site closely linked to a disease causing site. A complete description of this two-locus system is of particular importance to experimental efforts to fine map association signals for complex diseases. Here, we present a simple relationship between disease association statistics and the decline of linkage disequilibrium from a causal site. Specifically, the ratio of Chi-square disease association statistics at a marker site and causal site is equivalent to the standard measure of pairwise linkage disequilibrium, r2. A complete derivation of this relationship from a general disease model is shown. Quite interestingly, this relationship holds across all modes of inheritance. Extensive Monte Carlo simulations using a disease genetics model applied to chromosomes subjected to a standard model of recombination are employed to better understand the variation around this fine mapping theorem due to sampling effects. We also use this relationship to provide a framework for estimating properties of a non-interrogated causal site using data at closely linked markers. Lastly, we apply this way of examining association data from high-density genotyping in a large, publicly-available data set investigating extreme BMI. We anticipate that understanding the patterns of disease association decay with declining linkage disequilibrium from a causal site will enable more powerful fine mapping methods and provide new avenues for identifying causal sites/genes from fine-mapping studies
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