5,635 research outputs found
Space disposal of nuclear wastes. Volume 1: Socio-political aspects
The history and interpretation of radioactive waste management in the U.S., criteria for choosing from various options for waste disposal, and the impact of nuclear power growth from 1975 to 2000 are discussed. Preconditions for the existence of high level wastes in a form suitable for space disposal are explored. The role of the NASA space shuttle program in the space disposal of nuclear wastes, and the impact on program management, resources and regulation are examined
The Growth in Size and Mass of Cluster Galaxies since z=2
We study the formation and evolution of Brightest Cluster Galaxies starting
from a population of quiescent ellipticals and following them to .
To this end, we use a suite of nine high-resolution dark matter-only
simulations of galaxy clusters in a CDM universe. We develop a scheme
in which simulation particles are weighted to generate realistic and
dynamically stable stellar density profiles at . Our initial conditions
assign a stellar mass to every identified dark halo as expected from abundance
matching; assuming there exists a one-to-one relation between the visible
properties of galaxies and their host haloes. We set the sizes of the luminous
components according to the observed relations for massive quiescent
galaxies. We study the evolution of the mass-size relation, the fate of
satellite galaxies and the mass aggregation of the cluster central. From ,
these galaxies grow on average in size by a factor 5 to 10 of and in mass by 2
to 3. The stellar mass growth rate of the simulated BCGs in our sample is of
1.9 in the range consistent with observations, and of 1.5 in the
range . Furthermore the satellite galaxies evolve to the present day
mass-size relation by . Assuming passively evolving stellar populations,
we present surface brightness profiles for our cluster centrals which resemble
those observed for the cDs in similar mass clusters both at and at .
This demonstrates that the CDM cosmology does indeed predict minor and
major mergers to occur in galaxy clusters with the frequency and mass ratio
distribution required to explain the observed growth in size of passive
galaxies since . Our experiment shows that Brightest Cluster Galaxies can
form through dissipationless mergers of quiescent massive galaxies,
without substantial additional star formation.Comment: submitted to MNRAS, 10 pages, 8 figures, 2 table
Lin-Kernighan Heuristic Adaptations for the Generalized Traveling Salesman Problem
The Lin-Kernighan heuristic is known to be one of the most successful
heuristics for the Traveling Salesman Problem (TSP). It has also proven its
efficiency in application to some other problems. In this paper we discuss
possible adaptations of TSP heuristics for the Generalized Traveling Salesman
Problem (GTSP) and focus on the case of the Lin-Kernighan algorithm. At first,
we provide an easy-to-understand description of the original Lin-Kernighan
heuristic. Then we propose several adaptations, both trivial and complicated.
Finally, we conduct a fair competition between all the variations of the
Lin-Kernighan adaptation and some other GTSP heuristics. It appears that our
adaptation of the Lin-Kernighan algorithm for the GTSP reproduces the success
of the original heuristic. Different variations of our adaptation outperform
all other heuristics in a wide range of trade-offs between solution quality and
running time, making Lin-Kernighan the state-of-the-art GTSP local search.Comment: 25 page
They watch and wonder. Public attitudes toward advanced technology
The relationship of technological development to individual and community response was investigated to provide a general conceptual, as well as empirical basis, for an understanding of the impact of advanced technologies on social life. Results of the surveys are presented in tables and graphs
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Resource constrained routing and scheduling: Review and research prospects
In the service industry, it is crucial to efficiently allocate scarce resources to perform tasks and meet particular service requirements. What considerably complicates matters is when these resources, for example skilled technicians, nurses, and home carers have to visit different customer locations. This paper provides a comprehensive survey on resource constrained routing and scheduling that unveils the problem characteristics with respect to resource qualifications, service requirements and problem objectives. It also identifies the most effective exact and heuristic algorithms for this class of problems. The paper closes with several research prospects
Evidence for a novel shift-symmetric universality class from the functional renormalization group
Wetterich's equation provides a powerful tool for investigating the existence
and universal properties of renormalization group fixed points exhibiting
quantum scale invariance. Motivated by recent works on asymptotically safe
scalar-tensor theories, we develop a novel approximation scheme which projects
the functional renormalization group equation onto functions of the kinetic
term. Applying this projection to scalars and gauge fields, our analysis
identifies a new universality class with a very special spectrum of stability
coefficients. The implications of our findings in the context of asymptotically
safe gravity-matter systems are discussed.Comment: 10 pages, 3 figure
Environment of the submillimeter-bright massive starburst HFLS3 at z∼6.34
We describe the search for Lyman break galaxies (LBGs) near the submillimeter-bright starburst galaxy HFLS3 at z = 6.34 and a study on the environment of this massive galaxy during the end of reionization. We performed two independent selections of LBGs on images obtained with the Gran Telescopio Canarias (GTC) and the Hubble Space Telescope (HST) by combining nondetections in bands blueward of the Lyman break and color selection. A total of 10 objects fulfilling the LBG selection criteria at z > 5.5 were selected over the 4.54 and 55.5 arcmin^2 covered by our HST and GTC images, respectively. The photometric redshift, UV luminosity, and star formation rate of these sources were estimated with models of their spectral energy distribution. These z ~ 6 candidates have physical properties and number densities in agreement with previous results. The UV luminosity function at z ~ 6 and a Voronoi tessellation analysis of this field show no strong evidence for an overdensity of relatively bright objects (m_(F105W) < 25.9) associated with HFLS3. However, the overdensity parameter deduced from this field and the surface density of objects cannot exclude definitively the LBG overdensity hypothesis. Moreover, we identified three faint objects at less than 3'' from HFLS3 with color consistent with those expected for z ~ 6 galaxies. Deeper data are needed to confirm their redshifts and to study their association with HFLS3 and the galaxy merger that may be responsible for the massive starburst
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