3,503 research outputs found
Non-classical transport with angular-dependent path-length distributions. 1: Theory
This paper extends a recently introduced theory describing particle transport
for random statistically homogeneous systems in which the distribution function
p(s) for chord lengths between scattering centers is non-exponential. Here, we
relax the previous assumption that p(s) does not depend on the direction of
flight \Omega; this leads to an extended generalized linear Boltzmann equation
that includes angular-dependent cross sections, and to an extended generalized
diffusion equation that accounts for anisotropic behavior resulting from the
statistics of the system.Comment: 22 pages; Version 3: shortened title; corrected typo
Non-classical transport with angular-dependent path-length distributions. 2: Application to pebble bed reactor cores
We describe an analysis of neutron transport in the interior of model pebble
bed reactor (PBR) cores, considering both crystal and random pebble
arrangements. Monte Carlo codes were developed for (i) generating random
realizations of the model PBR core, and (ii) performing neutron transport
inside the crystal and random heterogeneous cores; numerical results are
presented for two different choices of material parameters. These numerical
results are used to investigate the anisotropic behavior of neutrons in each
case and to assess the accuracy of estimates for the diffusion coefficients
obtained with the diffusion approximations of different models: the atomic mix
model, the Behrens correction, the Lieberoth correction, the generalized linear
Boltzmann equation (GLBE), and the new GLBE with angular-dependent path-length
distributions. This new theory utilizes a non-classical form of the Boltzmann
equation in which the locations of the scattering centers in the system are
correlated and the distance-to-collision is not exponentially distributed; this
leads to an anisotropic diffusion equation. We show that the results predicted
using the new GLBE theory are extremely accurate, correctly identifying the
anisotropic diffusion in each case and greatly outperforming the other models
for the case of random systems.Comment: 24 pages, 11 figures; Version 3: shortened title, corrected typo
The role of bipartite structure in R&D collaboration networks
A number of real-world networks are, in fact, one-mode projections of
bipartite networks comprised of two types of nodes. For institutions engaging
in collaboration for technological innovation, the underlying network is
bipartite with institutions (agents) linked to the patents they have filed
(artifacts), while the projection is the co-patenting network. Projected
network topology is highly affected by the underlying bipartite structure,
hence a lack of understanding of the bipartite network has consequences for the
information that might be drawn from the one-mode co-patenting network. Here,
we create an empirical bipartite network using data from 2.7 million patents.
We project this network onto the agents (institutions) and look at properties
of both the bipartite and projected networks that may play a role in knowledge
sharing and collaboration. We compare these empirical properties to those of
synthetic bipartite networks and their projections in order to understand the
processes that might operate in the network formation. A good understanding of
the topology is critical for investigating the potential flow of technological
knowledge. We show how degree distributions and small cycles affect the
topology of the one-mode projected network - specifically degree and clustering
distributions, and assortativity. We propose new network-based metrics to
quantify how collaborative agents are in the co-patenting network. We find that
several large corporations that are the most collaborative agents in the
network, however such organisations tend to have a low diversity of
collaborators. In contrast, the most prolific institutions tend to collaborate
relatively little but with a diverse set of collaborators. This indicates that
they concentrate the knowledge of their core technical research, while seeking
specific complementary knowledge via collaboration with smaller companies.Comment: 23 pages, 12 figures, 2 table
Nonclassical Particle Transport in 1-D Random Periodic Media
We investigate the accuracy of the recently proposed nonclassical transport
equation. This equation contains an extra independent variable compared to the
classical transport equation (the path-length ), and models particle
transport taking place in homogenized random media in which a particle's
distance-to-collision is not exponentially distributed. To solve the
nonclassical equation one needs to know the -dependent ensemble-averaged
total cross section, , or its corresponding path-length
distribution function, . We consider a 1-D spatially periodic system
consisting of alternating solid and void layers, randomly placed in the
-axis. We obtain an analytical expression for and use this result
to compute the corresponding . Then, we proceed to numerically
solve the nonclassical equation for different test problems in rod geometry;
that is, particles can move only in the directions . To assess the
accuracy of these solutions, we produce "benchmark" results obtained by (i)
generating a large number of physical realizations of the system, (ii)
numerically solving the transport equation in each realization, and (iii)
ensemble-averaging the solutions over all physical realizations. We show that
the numerical results validate the nonclassical model; the solutions obtained
with the nonclassical equation accurately estimate the ensemble-averaged scalar
flux in this 1-D random periodic system, greatly outperforming the widely-used
atomic mix model in most problems.Comment: 50 pages; 7 Tables; 21 Figures. This is an expanded version (full
journal article) of the conference paper listed in arXiv:1412.338
Gil Vicente e os sexos
O espectáculo Serviço D’Amores, encenado por Maria Emília Correia, que é igualmente a autora da dramaturgia, ao emergir na programação do Teatro Nacional D. Maria II como um espectáculo acessível, apelativo, vivo, colorido e aparentemente mais exercício visual e lúdico do que especulação filosófica (o que não é senão parcialmente verdade mas, mesmo que o fosse, tinha a sustentar tal opção numa leitura exegética da obra vicentina que nela vê a criação plástica mais do “ourives” do que do poeta que Vicente também foi), esconde, porém, para quem quiser atentar, uma leitura disfórica do amor, como que anunciando a posteridade vicentina no que há-de vir a ser, no final do Renascimento, com Camões, o período perturbante a que se chamou Maneirismo
Reflexões sobre escritas [de teatro] um problema sem território
A presente reflexão visa colocar lado a lado, sem preocupações de continuidade ou exaustividade, duas tentativas de se romper com os cânones da dramaturgia convencional e de construir vias que hão-de ter posteridade justamente na construção das escritas cénicas da contemporaneidade. Um desses caminhos de indagação é estrangeiro e funda-se em experimentações seminais levadas a cabo por estrangeirados de língua materna inglesa; outro, é português, não tem programa identitário e tem sede provisória na, marginalizada, escrita cénica para teatro das mulheres no nosso país
O teatro português e o 25 de Abril: uma história ainda por contar
Este artigo visa apresentar uma panorâmica da evolução e mudanças estruturais no teatro em Portugal.A 25 de Abril de 1974, uma nova era começa no historial do depauperado teatro português. Após quase cinquenta anos de obscurantismo e de Censura o teatro português vai, finalmente, tentar recuperar décadas de atraso e abrir-se ao mundo através de uma propedêutica de emergência na actualização das linguagens estéticas e na aceleração da divulgação de dramaturgias até aí proibidas ou ignoradas. Nos anos imediatos à Revolução, o teatro foi, entre nós, fundamentalmente, um teatro à procura do diálogo com o tempo e a circunstância, um teatro colectivista e de agitação e propaganda, e, o que é muito importante, um teatro à procura de uma nova geografia estrutural e de uma cada vez mais sistemática e alargada intervenção social
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