269 research outputs found
Sustaining the Internet with Hyperbolic Mapping
The Internet infrastructure is severely stressed. Rapidly growing overheads
associated with the primary function of the Internet---routing information
packets between any two computers in the world---cause concerns among Internet
experts that the existing Internet routing architecture may not sustain even
another decade. Here we present a method to map the Internet to a hyperbolic
space. Guided with the constructed map, which we release with this paper,
Internet routing exhibits scaling properties close to theoretically best
possible, thus resolving serious scaling limitations that the Internet faces
today. Besides this immediate practical viability, our network mapping method
can provide a different perspective on the community structure in complex
networks
Ab initio coupled-cluster theory for open-shell nuclei
We develop a new method to describe properties of truly open-shell nuclei.
This method is based on single-reference coupled-cluster theory and the
equation-of-motion method with extensions to nuclei with nucleons
outside a closed shell. We perform proof-of-principle calculations for the
ground states of the helium isotopes He and the first excited
state in He. The comparison with exact results from matrix diagonalization
in small model spaces demonstrates the accuracy of the coupled-cluster methods.
Three-particle--one-hole excitations of He play an important role for the
accurate description of He. For the open-shell nucleus He, the
computational cost of the method is comparable with the coupled-cluster
singles-and-doubles approximation while its accuracy is similar to
coupled-cluster with singles, doubles and triples excitations
Diagonalization of multicomponent wave equations with a Born-Oppenheimer example
A general method to decouple multicomponent linear wave equations is presented. First, the Weyl calculus is used to transform operator relations into relations between c-number valued matrices. Then it is shown that the symbol representing the wave operator can be diagonalized systematically up to arbitrary order in an appropriate expansion parameter. After transforming the symbols back to operators, the original problem is reduced to solving a set of linear uncoupled scalar wave equations. The procedure is exemplified for a particle with a Born-Oppenheimer-type Hamiltonian valid through second order in h. The resulting effective scalar Hamiltonians are seen to contain an additional velocity-dependent potential. This contribution has not been reported in recent studies investigating the adiabatic motion of a neutral particle moving in an inhomogeneous magnetic field. Finally, the relation of the general method to standard quantum-mechanical perturbation theory is discussed
Small denominators, frequency operators, and Lie transforms for nearly integrable quantum spin systems
Based on the previously proposed notions of action operators and of quantum integrability, frequency operators are introduced in a fully quantum-mechanical setting. They are conceptually useful because another formulation can be given to unitary perturbation theory. When worked out for quantum spin systems, this variant is found to be formally equivalent to canonical perturbation theory applied to nearly integrable systems consisting of classical spins. In particular, it becomes possible to locate the quantum-mechanical operator-valued equivalent of the frequency denominators that may cause divergence of the classical perturbation series. The results that are established here link the concept of quantum-mechanical integrability to a technical question, namely, the behavior of specific perturbation series
A visĂŁo dos professores quanto ao processo de ensino e de aprendizagem do Basquetebol nas aulas de Educação FĂsica: A realidade de Volta Redonda/RJ
A presente pesquisa teve como objetivo geral investigar a visĂŁo dos professores acerca do processo de ensino e de aprendizagem do basquetebol nas aulas de Educação FĂsica em ambiente escolar. Participaram da pesquisa docentes das instituiçÔes pĂșblicas e privadas do municĂpio de Volta Redonda/RJ/Brasil em turmas do 6Âș ao 9Âș ano do ensino fundamental. Tratou-se de um estudo quanti-qualitativo com anĂĄlise de conteĂșdo e, como procedimento de coleta de dados, foram entrevistados sessenta docentes que opinaram acerca da questĂŁo investigada. Verificou-se a realidade do desenvolvimento do basquetebol nĂŁo somente na condição de conteĂșdo das aulas da Educação FĂsica, mas tambĂ©m numa dimensĂŁo que transpĂ”e os limites escolares, onde o esporte representa significativo papel na sociedade. AçÔes conjuntas no sentido de oportunizar o crescimento do basquetebol como conteĂșdo das aulas de Educação FĂsica podem representar um caminho para a descrição da sua aplicação em todos os contextos, embora nĂŁo se deva abrir mĂŁo da relevĂąncia da disciplina no cenĂĄrio escolar em favor da obtenção de resultados em competiçÔes esportivas
An importance sampling algorithm for generating exact eigenstates of the nuclear Hamiltonian
We endow a recently devised algorithm for generating exact eigensolutions of
large matrices with an importance sampling, which is in control of the extent
and accuracy of the truncation of their dimensions. We made several tests on
typical nuclei using a correlated basis obtained from partitioning the shell
model space. The sampling so implemented allows not only for a substantial
reduction of the shell model space but also for an extrapolation to exact
eigenvalues and E2 strengths.Comment: A compressed file composed of a text in latex of 19 pages and 9
figures in p
Two-Center Integrals for r_{ij}^{n} Polynomial Correlated Wave Functions
All integrals needed to evaluate the correlated wave functions with
polynomial terms of inter-electronic distance are included. For this form of
the wave function, the integrals needed can be expressed as a product of
integrals involving at most four electrons
Association study between genetic monoaminergic polymorphisms and OCD response to clomipramine treatment
Global Networks of Trade and Bits
Considerable efforts have been made in recent years to produce detailed
topologies of the Internet. Although Internet topology data have been brought
to the attention of a wide and somewhat diverse audience of scholars, so far
they have been overlooked by economists. In this paper, we suggest that such
data could be effectively treated as a proxy to characterize the size of the
"digital economy" at country level and outsourcing: thus, we analyse the
topological structure of the network of trade in digital services (trade in
bits) and compare it with that of the more traditional flow of manufactured
goods across countries. To perform meaningful comparisons across networks with
different characteristics, we define a stochastic benchmark for the number of
connections among each country-pair, based on hypergeometric distribution.
Original data are thus filtered by means of different thresholds, so that we
only focus on the strongest links, i.e., statistically significant links. We
find that trade in bits displays a sparser and less hierarchical network
structure, which is more similar to trade in high-skill manufactured goods than
total trade. Lastly, distance plays a more prominent role in shaping the
network of international trade in physical goods than trade in digital
services.Comment: 25 pages, 6 figure
Computational Nuclear Physics and Post Hartree-Fock Methods
We present a computational approach to infinite nuclear matter employing
Hartree-Fock theory, many-body perturbation theory and coupled cluster theory.
These lectures are closely linked with those of chapters 9, 10 and 11 and serve
as input for the correlation functions employed in Monte Carlo calculations in
chapter 9, the in-medium similarity renormalization group theory of dense
fermionic systems of chapter 10 and the Green's function approach in chapter
11. We provide extensive code examples and benchmark calculations, allowing
thereby an eventual reader to start writing her/his own codes. We start with an
object-oriented serial code and end with discussions on strategies for porting
the code to present and planned high-performance computing facilities.Comment: 82 pages, to appear in Lecture Notes in Physics (Springer), "An
advanced course in computational nuclear physics: Bridging the scales from
quarks to neutron stars", M. Hjorth-Jensen, M. P. Lombardo, U. van Kolck,
Editor
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