28,971 research outputs found
Off-axis retrieval of orbital angular momentum of light stored in cold atoms
We report on the storage of orbital angu- lar momentum (OAM) of light of a
Laguerre-Gaussian mode in an ensemble of cold cesium atoms and its re- trieval
along an axis different from the incident light beam. We employed a
time-delayed four-wave mixing configuration to demonstrate that at small angle
(2o), after storage, the retrieved beam carries the same OAM as the one encoded
in the input beam. A calculation based on mode decomposition of the retrieved
beam over the Laguerre-Gaussian basis is in agreement with the experimental
observations done at small angle values. However, the calculation shows that
the OAM retrieving would get lost at larger angles, reducing the fidelity of
such storing-retrieving process. In addition, we have also observed that by
applying an external magnetic field to the atomic ensemble the retrieved OAM
presents Larmor oscillations, demonstrating the possibility of its manipulation
and off-axis retrieval.Comment: 9 pages, 4 figure
Novel techniques in VUV high-resolution spectroscopy
Novel VUV sources and techniques for VUV spectroscopy are reviewed.
Laser-based VUV sources have been developed via non-linear upconversion of
laser pulses in the nanosecond (ns), the picosecond (ps), and femtosecond (fs)
domain, and are applied in high-resolution gas phase spectroscopic studies.
While the ns and ps pulsed laser sources, at Fourier-transform limited
bandwidths, are used in wavelength scanning spectroscopy, the fs laser source
is used in a two-pulse time delayed mode. In addition a Fourier-transform
spectrometer for high resolution gas-phase spectroscopic studies in the VUV is
described, exhibiting the multiplex advantage to measure many resonances
simultaneously.Comment: 17 Pages, 8 figures, Conference proceedings of the VUV/X-ray 2013 at
Hefei, Chin
Dark/Visible Parallel Universes and Big Bang Nucleosynthesis
We develop a model for visible matter-dark matter interaction based on the
exchange of a massive gray boson called herein the Mulato. Our model hinges on
the assumption that all known particles in the visible matter have their
counterparts in the dark matter. We postulate six families of particles five of
which are dark. This leads to the unavoidable postulation of six parallel
worlds, the visible one and five invisible worlds. A close study of big bang
nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB)
bounds, galaxy dynamics, together with the Standard Model assumptions, help us
to set a limit on the mass and width of the new gauge boson. Modification of
the statistics underlying the kinetic energy distribution of particles during
the BBN is also discussed. The changes in reaction rates during the BBN due to
a departure from the Debye-Hueckel electron screening model is also
investigated.Comment: Invited talk at the Workshops "CompStar: the physics and astrophysics
of compact stars", Tahiti, June 4-8, 2012, "New Directions in Nuclear
Astrophysics", Castiglion Fiorentino, Italy, June 18-22, 2012, and
"Carpathian Summer School of Physics", Sinaia, Romania, June 24 - July 7,
2012. To be published in AIP Proceeding
Dinâmica da população e controle biológico da cigarrinha em pastagens de Brachiaria decumbens em Rondônia.
Instalado na area experimental da EMBRAPA-UEPAE Porto Velho, visando controlar o ataque das cigarrinhas-das-pastagens em Rondonia. Foi iniciado em jan./1977, com seis piquetes de 1ha cada um, com pastagens de brachiaria decumens. Tres piquetes foram adubados com fosforo, 100kg/ha, e tres nao adubados. Cada piquete comportou tres garrotes de dois anos de idade.As ninfas foram contadas atraves de um quadro de madeira medindo 0,25m de lado, jogado 10 vezes ao acaso por piquete. O processo de contagem dos adultos foi feito atravesde uma rede entomologica de 0,4m de diametro. Conclui-se que: apos seis meses de aplicacao ainda encontrou-se cigarrinhas mortas; o fungo atinte jovens e adultos; apos aplicacao do fungo houve rapida recuperacao das pastagem, embora tenha ocorrido a presenca de animais. A formulacao do molhavel mostrou-se mais eficiente; recomenda-se duas aplicacoes: l - inicio das chuvas, 2 - epoca do aparecimento da primeira geracao; O efeito do Metharrhizium anisopliae de um ano para outro ainda nao forneceu dados suficientes; o novo isolado recebel a sigla K19 - 1976.bitstream/item/46844/1/COT-7-19790001.pd
Cluster size entropy in the Axelrod model of social influence: small-world networks and mass media
We study the Axelrod's cultural adaptation model using the concept of cluster
size entropy, that gives information on the variability of the cultural
cluster size present in the system. Using networks of different topologies,
from regular to random, we find that the critical point of the well-known
nonequilibrium monocultural-multicultural (order-disorder) transition of the
Axelrod model is unambiguously given by the maximum of the
distributions. The width of the cluster entropy distributions can be used to
qualitatively determine whether the transition is first- or second-order. By
scaling the cluster entropy distributions we were able to obtain a relationship
between the critical cultural trait and the number of cultural
features in regular networks. We also analyze the effect of the mass media
(external field) on social systems within the Axelrod model in a square
network. We find a new partially ordered phase whose largest cultural cluster
is not aligned with the external field, in contrast with a recent suggestion
that this type of phase cannot be formed in regular networks. We draw a new
phase diagram for the Axelrod model in regular networks.Comment: 21 pages, 7 figure
Irreversible Opinion Spreading on Scale-Free Networks
We study the dynamical and critical behavior of a model for irreversible
opinion spreading on Barab\'asi-Albert (BA) scale-free networks by performing
extensive Monte Carlo simulations. The opinion spreading within an
inhomogeneous society is investigated by means of the magnetic Eden model, a
nonequilibrium kinetic model for the growth of binary mixtures in contact with
a thermal bath. The deposition dynamics, which is studied as a function of the
degree of the occupied sites, shows evidence for the leading role played by
hubs in the growth process. Systems of finite size grow either ordered or
disordered, depending on the temperature. By means of standard finite-size
scaling procedures, the effective order-disorder phase transitions are found to
persist in the thermodynamic limit. This critical behavior, however, is absent
in related equilibrium spin systems such as the Ising model on BA scale-free
networks, which in the thermodynamic limit only displays a ferromagnetic phase.
The dependence of these results on the degree exponent is also discussed for
the case of uncorrelated scale-free networks.Comment: 9 pages, 10 figures; added results and discussion on uncorrelated
scale-free networks; added references. To appear in PR
Structural and dynamical properties of a quasi-one-dimensional classical binary system
The ground state configurations and the \lq{}\lq{}normal\rq{}\rq{} mode
spectra of a -one-dimensional (Q1D) binary system of charged particles
interacting through a screened Coulomb potential are presented. The minimum
energy configurations were obtained analytically and independently through
molecular dynamic simulations. A rich variety of ordered structures were found
as a function of the screening parameter, the particle density, and the ratio
between the charges of the distinct types of particles. Continuous and
discontinuous structural transitions, as well as an unexpected symmetry
breaking in the charge distribution are observed when the density of the system
is changed. For near equal charges we found a disordered phase where a mixing
of the two types of particles occurs. The phonon dispersion curves were
calculated within the harmonic approximation for the one- and two-chain
structures.Comment: 11 pages, 11 fig
Study of the Fully Frustrated Clock Model using the Wang-Landau Algorithm
Monte Carlo simulations using the newly proposed Wang-Landau algorithm
together with the broad histogram relation are performed to study the
antiferromagnetic six-state clock model on the triangular lattice, which is
fully frustrated. We confirm the existence of the magnetic ordering belonging
to the Kosterlitz-Thouless (KT) type phase transition followed by the chiral
ordering which occurs at slightly higher temperature. We also observe the lower
temperature phase transition of KT type due to the discrete symmetry of the
clock model. By using finite-size scaling analysis, the higher KT temperature
and the chiral critical temperature are respectively estimated as
and . The results are in favor of the double
transition scenario. The lower KT temperature is estimated as .
Two decay exponents of KT transitions corresponding to higher and lower
temperatures are respectively estimated as and
, which suggests that the exponents associated with the KT
transitions are universal even for the frustrated model.Comment: 7 pages including 9 eps figures, RevTeX, to appear in J. Phys.
- …