11,210 research outputs found
Closed Expressions for Lie Algebra Invariants and Finite Transformations
A simple procedure to obtain complete, closed expressions for Lie algebra
invariants is presented. The invariants are ultimately polynomials in the group
parameters. The construction of finite group elements require the use of
projectors, whose coefficients are invariant polynomials. The detailed general
forms of these projectors are given. Closed expressions for finite Lorentz
transformations, both homogeneous and inhomogeneous, as well as for Galilei
transformations, are found as examples.Comment: 34 pages, ps file, no figure
Network conduciveness with application to the graph-coloring and independent-set optimization transitions
We introduce the notion of a network's conduciveness, a probabilistically
interpretable measure of how the network's structure allows it to be conducive
to roaming agents, in certain conditions, from one portion of the network to
another. We exemplify its use through an application to the two problems in
combinatorial optimization that, given an undirected graph, ask that its
so-called chromatic and independence numbers be found. Though NP-hard, when
solved on sequences of expanding random graphs there appear marked transitions
at which optimal solutions can be obtained substantially more easily than right
before them. We demonstrate that these phenomena can be understood by resorting
to the network that represents the solution space of the problems for each
graph and examining its conduciveness between the non-optimal solutions and the
optimal ones. At the said transitions, this network becomes strikingly more
conducive in the direction of the optimal solutions than it was just before
them, while at the same time becoming less conducive in the opposite direction.
We believe that, besides becoming useful also in other areas in which network
theory has a role to play, network conduciveness may become instrumental in
helping clarify further issues related to NP-hardness that remain poorly
understood
Intensificação da bovinocultura de corte: estratégias de manejo reprodutivo e sanitário.
Manejo reprodutivo em gado de corte; Sincronizacao do estro em bovinos; Manejo sanitario em sistemas intensivos de producao de carne; Novos metodos de avaliacao da capacidade reprodutiva de touros.bitstream/CPPSE/12479/1/PROCIDoc26RTB636.0824LV.pd
Convex Independence in Permutation Graphs
A set C of vertices of a graph is P_3-convex if every vertex outside C has at
most one neighbor in C. The convex hull \sigma(A) of a set A is the smallest
P_3-convex set that contains A. A set M is convexly independent if for every
vertex x \in M, x \notin \sigma(M-x). We show that the maximal number of
vertices that a convexly independent set in a permutation graph can have, can
be computed in polynomial time
Anomalies in a waterlike model confined between plates
Using molecular dynamic simulations we study a waterlike model confined
between two fixed hydrophobic plates. The system is tested for density,
diffusion and structural anomalous behavior and compared with the bulk results.
Within the range of confining distances we had explored we observe that in the
pressure-temperature phase diagram the temperature of maximum density (TMD
line), the temperature of maximum and minimum diffusion occur at lower
temperatures when compared with the bulk values. For distances between the two
layers below a certain threshold ,, only two layers of particles are
formed, for three or more layers are formed. In the case of three
layers the central layer stays liquid while the contact layers crystallize.
This result is in agreement with simulations for atomistic models
Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at
We perform a detailed analysis of the statistical significance of a
concentration of Lyman break galaxies at recently discovered by
Steidel et al. (1997), using a series of N-body simulations with
particles in a (100\himpc)^3 comoving box. While the observed number density
of Lyman break galaxies at implies that they correspond to systems
with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of
such objects on average is not strong enough to be reconciled with the
concentration if it is fairly common; we predict one similar concentration
approximately per () fields in three representative cold dark matter
models. Considering the current observational uncertainty of the frequency of
such clustering at , it would be premature to rule out the models, but
the future spectroscopic surveys in a dozen fields could definitely challenge
all the existing cosmological models a posteriori fitted to the universe.Comment: the final version which matchs that published in ApJ Letters (Feb
1998); compared with the previous versions, the predictions for the SCDM
model are slightly changed; Latex, 11 pages, including 3 ps figure
Experimental analysis of lateral impact on planar brittle material: spatial properties of the cracks
The breakup of glass and alumina plates due to planar impacts on one of their
lateral sides is studied. Particular attention is given to investigating the
spatial location of the cracks within the plates. Analysis based on a
phenomenological model suggests that bifurcations along the cracks' paths are
more likely to take place closer to the impact region than far away from it, i.
e., the bifurcation probability seems to lower as the perpendicular distance
from the impacted lateral in- creases. It is also found that many observables
are not sensitive to the plate material used in this work, as long as the
fragment multiplicities corresponding to the fragmentation of the plates are
similar. This gives support to the universal properties of the fragmentation
process reported in for- mer experiments. However, even under the just
mentioned circumstances, some spatial observables are capable of distinguishing
the material of which the plates are made and, therefore, it suggests that this
universality should be carefully investigated
The Stellar Content of Obscured Galactic Giant HII Regions. VI: W51A
We present K-band spectra of newly born OB stars in the obscured Galactic
giant H II region W51A and ~ 0.8'' angular resolution images in the J, H and
K_S-bands. Four objects have been spectroscopically classified as O-type stars.
The mean spectroscopic parallax of the four stars gives a distance of 2.0 \pm
0.3 kpc (error in the mean), significantly smaller than the radio recombination
line kinematic value of 5.5 kpc or the values derived from maser propermotion
observations (6--8 kpc). The number of Lyman continuum photons from the
contribution of all massive stars (NLyc ~ 1.5 x 10^{50} s^{-1}) is in good
agreement with that inferred from radio recombination lines (NLyc = 1.3 x
10^{50} s^{-1}) after accounting for the smaller distance derived here.
We present analysis of archival high angular resolution images (NAOS CONICA
at VLT and T-ReCS at Gemini) of the compact region W51 IRS2. The K_S--band
images resolve the infrared source IRS~2 indicating that it is a very young
compact HII region. Sources IRS2E was resolved into compact cluster (within 660
AU of projected distance) of 3 objects, but one of them is just bright extended
emission. W51d1 and W51d2 were identified with compact clusters of 3 objects
(maybe 4 in the case of W51d1) each one. Although IRS~2E is the brightest
source in the K-band and at 12.6 \micron, it is not clearly associated with a
radio continuum source. Our spectrum of IRS~2E shows, similar to previous work,
strong emission in Br and HeI, as well as three forbidden emission
lines of FeIII and emission lines of molecular hydrogen (H_2) marking it as a
massive young stellar object.Comment: 31 pages and 9 figures, submitted to A
Sistemas mistos de produção de leite e carne bovina.
Tanto do ponto de vista biológico quanto econômico, a pecuária bovina e uma atividade de produção conjunta porque produz, ao mesmo tempo. leite e carne (GOMES. 1993). O que varia é a ênfase ou a importância relativa dada a cada um dos produtos. 0 que proporciona a obtenção de varias classes de sistemas de produção. cujo número depende fundamentalmente do nível de especificidade desejado. Essa característica da pecuária bovina dificulta a conceituação exata dos sistemas mistos de produção de leite e carne, mas é importante no processo de tomada de decisões em todos os níveis deplanejamento (estratégico, tático, operacional). O objetivo deste artigo é apresentar, de forma resumida, o estado da arte sobre os sistemas mistos de produção de leite e carne bovina, considerando alguns aspectos importantes, com a conceituação a caracterização, a importância, as relações de natureza genética entre as produções de leite e de carne, os resultados experimentais e o potencial desses sistemas de produção no Brasil
Early appraisal of the fixation probability in directed networks
In evolutionary dynamics, the probability that a mutation spreads through the
whole population, having arisen in a single individual, is known as the
fixation probability. In general, it is not possible to find the fixation
probability analytically given the mutant's fitness and the topological
constraints that govern the spread of the mutation, so one resorts to
simulations instead. Depending on the topology in use, a great number of
evolutionary steps may be needed in each of the simulation events, particularly
in those that end with the population containing mutants only. We introduce two
techniques to accelerate the determination of the fixation probability. The
first one skips all evolutionary steps in which the number of mutants does not
change and thereby reduces the number of steps per simulation event
considerably. This technique is computationally advantageous for some of the
so-called layered networks. The second technique, which is not restricted to
layered networks, consists of aborting any simulation event in which the number
of mutants has grown beyond a certain threshold value, and counting that event
as having led to a total spread of the mutation. For large populations, and
regardless of the network's topology, we demonstrate, both analytically and by
means of simulations, that using a threshold of about 100 mutants leads to an
estimate of the fixation probability that deviates in no significant way from
that obtained from the full-fledged simulations. We have observed speedups of
two orders of magnitude for layered networks with 10000 nodes
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