651 research outputs found
Driven Rydberg atoms reveal quartic level repulsion
The dynamics of Rydberg states of a hydrogen atom subject simultaneously to
uniform static electric field and two microwave fields with commensurate
frequencies is considered in the range of small fields amplitudes. In the
certain range of the parameters of the system the classical secular motion of
the electronic ellipse reveals chaotic behavior. Quantum mechanically, when the
fine structure of the atom is taken into account, the energy level statistics
obey predictions appropriate for the symplectic Gaussian random matrix
ensemble.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Non-resonant driving of H atom with broken time-reversal symmetry
The dynamics of atomic hydrogen placed in a static electric field and
illuminated by elliptically polarized microwaves is studied in the range of
small field amplitudes where perturbation calculations are applicable. For a
general configuration of the fields any generalized time-reversal symmetry is
broken and, as the classical dynamics is chaotic, the level statistics obeys
the random matrices prediction of Gaussian unitary ensemble.Comment: 4 pages, 2 figures, accepted for publication in J. Phys.
Visual Analytics for Network Security and Critical Infrastructures
A comprehensive analysis of cyber attacks is important for better understanding of their nature and their origin. Providing a sufficient insight into such a vast amount of diverse (and sometimes seemingly unrelated) data is a task that is suitable neither for humans nor for fully automated algorithms alone. Not only a combination of the two approaches but also a continuous reasoning process that is capable of generating a sufficient knowledge base is indispensable for a better understanding of the events. Our research is focused on designing new exploratory methods and interactive visualizations in the context of network security. The knowledge generation loop is important for its ability to help analysts to refine the nature of the processes that continuously occur and to offer them a better insight into the network security related events. In this paper, we formulate the research questions that relate to the proposed solution
Non-sequential triple ionization in strong fields
We consider the final stage of triple ionization of atoms in a strong
linearly polarized laser field. We propose that for intensities below the
saturation value for triple ionization the process is dominated by the
simultaneous escape of three electrons from a highly excited intermediate
complex. We identify within a classical model two pathways to triple
ionization, one with a triangular configuration of electrons and one with a
more linear one. Both are saddles in phase space. A stability analysis
indicates that the triangular configuration has the larger cross sections and
should be the dominant one. Trajectory simulations within the dominant symmetry
subspace reproduce the experimentally observed distribution of ion momenta
parallel to the polarization axis.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
As pessoas idosas e o regime de bens obrigatório: proteção ao idoso ou violação à autonomia da vontade?
O presente estudo tem o fito de analisar a vedação imposta aos idosos maiores de 70 anos de estipularem livremente o regime de bens para vigorar em seu casamento, positivada no art. 1641, II do Código Civil. O assunto é de grande relevância, tanto jurídica quanto social, porquanto comporta reflexões acerca do tratamento do Estado dado ao idoso e dos direitos a ele atinentes, bem como da posição que ele ocupa na sociedade e na família. O tema é tratado primeiramente em linhas gerais do direito de família e dos regimes de bens. Fornecendo em seguida um panorama da situação do
idoso, enquanto indivíduo e enquanto coletividade, dado que a população idosa brasileira proporcionalmente comparada à população mais jovem vem aumentando nos últimos anos. Utilizando-se da doutrina, analisando a jurisprudência, e ainda tratando o tema sob um ponto de vista interdisciplinar, buscando na filosofia, sociologia, ciência política e psicologia, subsídios para entender o papel do Estado. Tanto em sua atuação como protetor da moral, da ética e dos valores familiares, quanto no âmbito da autonomia e liberdade dos indivíduos de gerir suas relações privadas e patrimoniais e de
emitirem seus próprios juízos de valor. Busca-se também entender o papel do Estado de auxílio e proteção de subgrupos da sociedade que necessitam de tutela específica, como as crianças, adolescentes e idosos face ao que seria um ideal de isonomia. Permitindo-se deste modo que se tenha uma base solida para solucionar a questão que se apresenta: O regime de separação obrigatória de bens para as pessoas maiores de 70 anos: proteção ao idoso ou violação à autonomia da vontade
Localization of solitons: linear response of the mean-field ground state to weak external potentials
Two aspects of bright matter-wave solitons in weak external potentials are
discussed. First, we briefly review recent results on the Anderson localization
of an entire soliton in disordered potentials [Sacha et al. PRL 103, 210402
(2009)], as a paradigmatic showcase of genuine quantum dynamics beyond simple
perturbation theory. Second, we calculate the linear response of the mean-field
soliton shape to a weak, but otherwise arbitrary external potential, with a
detailed application to lattice potentials.Comment: Selected paper presented at the 2010 Spring Meeting of the Quantum
Optics and Photonics Section of the German Physical Society. V2: minor
changes, published versio
Simulations of core convection in rotating A-type stars: Differential rotation and overshooting
We present the results of 3--D simulations of core convection within A-type
stars of 2 solar masses, at a range of rotation rates. We consider the inner
30% by radius of such stars, thereby encompassing the convective core and some
of the surrounding radiative envelope. We utilize our anelastic spherical
harmonic (ASH) code, which solves the compressible Navier-Stokes equations in
the anelastic approximation, to examine highly nonlinear flows that can span
multiple scale heights. The cores of these stars are found to rotate
differentially, with central cylindrical regions of strikingly slow rotation
achieved in our simulations of stars whose convective Rossby number (R_{oc}) is
less than unity. Such differential rotation results from the redistribution of
angular momentum by the nonlinear convection that strongly senses the overall
rotation of the star. Penetrative convective motions extend into the overlying
radiative zone, yielding a prolate shape (aligned with the rotation axis) to
the central region in which nearly adiabatic stratification is achieved. This
is further surrounded by a region of overshooting motions, the extent of which
is greater at the equator than at the poles, yielding an overall spherical
shape to the domain experiencing at least some convective mixing. We assess the
overshooting achieved as the stability of the radiative exterior is varied, and
the weak circulations that result in that exterior. The convective plumes serve
to excite gravity waves in the radiative envelope, ranging from localized
ripples of many scales to some remarkable global resonances.Comment: 48 pages, 16 figures, some color. Accepted to Astrophys. J. Color
figures compressed with appreciable loss of quality; a PDF of the paper with
better figures is available at
http://lcd-www.colorado.edu/~brownim/core_convectsep24.pd
Pathways to double ionization of atoms in strong fields
We discuss the final stages of double ionization of atoms in a strong
linearly polarized laser field within a classical model. We propose that all
trajectories leading to non-sequential double ionization pass close to a saddle
in phase space which we identify and characterize. The saddle lies in a two
degree of freedom subspace of symmetrically escaping electrons. The
distribution of longitudinal momenta of ions as calculated within the subspace
shows the double hump structure observed in experiments. Including a symmetric
bending mode of the electrons allows us to reproduce the transverse ion
momenta. We discuss also a path to sequential ionization and show that it does
not lead to the observed momentum distributions.Comment: 10 pages, 10 figures; fig.6 and 7 exchanged in the final version
accepted for publication in Phys. Rev.
Condensate Heating by Atomic Losses
Atomic Bose-Einstein condensate is heated by atomic losses. Predicted
depletion ranges from 1% for a uniform 3D condensate to around 10% for a
quasi-1D condensate in a harmonic trap.Comment: 4 pages in RevTex, 1 eps figur
- …