159 research outputs found
The Traveling Salesman Problem Under Squared Euclidean Distances
Let be a set of points in , and let be a
real number. We define the distance between two points as
, where denotes the standard Euclidean distance between
and . We denote the traveling salesman problem under this distance
function by TSP(). We design a 5-approximation algorithm for TSP(2,2)
and generalize this result to obtain an approximation factor of
for and all .
We also study the variant Rev-TSP of the problem where the traveling salesman
is allowed to revisit points. We present a polynomial-time approximation scheme
for Rev-TSP with , and we show that Rev-TSP is APX-hard if and . The APX-hardness proof carries
over to TSP for the same parameter ranges.Comment: 12 pages, 4 figures. (v2) Minor linguistic change
Non-Destructive Testing Techniques for Corrosion Assessment in Reinforced Concrete Structures in Kenya
Deterioration of concrete structures is inevitable due to the fact that it is subjected to deterring environmental factors. Therefore, inspection and maintenance of these structures should be done to ensure their serviceability. Many concrete structures have been constructed in Kenya. A survey of some of the existing multi-storey buildings shows that even some of the old ones are in good condition; examples are the Norfork Hotel, Sarova Stanley Hotel and the railway bridges built in early 1900s. Yet, ageing structures require periodic monitoring to check their serviceability. Currently, inspection of most structures is done solely by simple visual means which is not always adequate. In order to enhance reliable assessment of structures, the present research introduces non-destructive testing (NDT) techniques for corrosion damage diagnosis in Kenyan concrete structures. Visual inspection is followed by half-cell potential measurements, carbonation tests and chloride tests. Laboratory analysis as well as field testing shows that NDT techniques provide safe, fast and reliable tools for the assessment of structural integrity. Keywords: Reinforced Concrete, Deterioration, Inspection, Non-destructive testin
Additions and corrections:Potential antitumor mitosenes: Relationship between in vitro DNA interstrand cross-link formation and DNA damage in Escherichia coli K-12 strains (Biochemical Pharmacology Vol. 48 (1994) 1371-1377)
Scheduling divisible loads with time and cost constraints
In distributed computing, divisible load theory provides an important system model for allocation of data-intensive computations to processing units working in parallel. The main task is to define how a computation job should be split into parts, to which processors those parts should be allocated and in which sequence. The model is characterized by multiple parameters describing processor availability in time, transfer times of job parts to processors, their computation times and processor usage costs. The main criteria are usually the schedule length and cost minimization. In this paper, we provide the generalized formulation of the problem, combining key features of divisible load models studied in the literature, and prove its NP-hardness even for unrestricted processor availability windows. We formulate a linear program for the version of the problem with a fixed number of processors. For the case with an arbitrary number of processors, we close the gaps in the study of special cases, developing efficient algorithms for single criterion and bicriteria versions of the problem, when transfer times are negligible
Potential antitumour mitosenes: Relationship between in vitro DNA interstrand cross-link formation and DNA damage in Escherichia coli K-12 strains
Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands
Grasslands are subject to considerable alteration due to human activities globally,
including widespread changes in populations and composition of large mammalian
herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and
these changes likely interact with increases in soil nutrient availability. Given the scale
of grassland soil fluxes, such changes can have striking consequences for atmospheric
C concentrations and the climate. Here, we use the Nutrient Network experiment
to examine the responses of soil C and N pools to mammalian herbivore exclusion
across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized
with NPK + micronutrients). We show that the impact of herbivore exclusion on soil
C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are
smaller upon herbivore exclusion. The highest mean soil C and N pools were found in
grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in
combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion
was contingent on temperature – herbivores likely cause losses of C and N in colder
sites and increases in warmer sites. Additionally, grasslands that contain mammalian
herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the
importance of conserving mammalian herbivore populations in grasslands worldwide.
We need to incorporate local-scale herbivory, and its interaction with nutrient enrichment and climate, within global-scale models to better predict land–atmosphere
interactions under future climate change.National Science Foundation Research Coordination Network,
Long Term Ecological Research,
Institute on the Environment,
Strategic Resources of the Netherlands Institute of Ecology,
Research Foundation Flanders,
VENI grant,
NWO-RUBICON grant,
NWO-VENI grant,
German Centre for Integrative Biodiversity Research,
German Research Foundation (FZT 118).http://wileyonlinelibrary.com/journal/gcbpm2021Mammal Research InstituteZoology and Entomolog
Optical detection of magnetic resonance in the photoexcited triplet state of a deep center in diamond
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