1,937 research outputs found
Ultracold atom-molecule collisions with fermionic atoms
Elastic and inelastic properties of weakly bound s- and p-wave molecules of
fermionic atoms that collide with a third atom are investigated. Analysis of
calculated collisional properties of s-wave dimers of fermions in different
spin states permit us to compare and highlight the physical mechanisms that
determine the stability of s-wave and p-wave molecules. In contrast to s-wave
molecules, the collisional properties of p-wave molecules are found to be
largely insensitive to variations of the p-wave scattering length and that
these collisions will usually result in short molecular lifetimes. We also
discuss the importance of this result for both theories and experiments
involving degenerate Fermi gases.Comment: 6 pages, 2 figure
Uses Genres and Media Ensembles : A Conceptual Roadmap for Research of Convergent Audiences
This chapter tackles one of the main methodological and conceptual challenges to current audience research: fragmentation of viewers’ practices of reception. The use of digital and networked media and the consequent multiplication of screens, distribution channels and content sources have further complicated the notion of “watching television” and, along with that, academic and applied audience research. The chapter reintroduces Maria Bakardjieva’s concept of uses genres and connects it with the concept of media ensemble, suggesting that for research on the domestic consumption of films and TV series, the application of these concepts in qualitative (ethnographic) research and in audience surveys comes with strong advantages. Firstly, the concepts help to identify distinct types of consumption practices linked with specific technological objects, with specific audiovisual content and with typical everyday situations, and they enable us to analyze consumption explicitly within the contexts of the spatiotemporal and social organization of everyday life. Secondly, in cases of small- and peripheral-market audiences, the concepts enable us to identify specifics in audiences’ practices linked with the characteristics of these markets (e.g., with localized and non-localized content, with domestic and global production, etc.). And thirdly, the concepts explicitly acknowledge power both involved in and shaping the analyzed practices by emphasizing the “generative process of technology,” i.e., the transformative role of users’ practices in shaping technological and economic systems
Low-energy three-body dynamics in binary quantum gases
The universal three-body dynamics in ultra-cold binary Fermi and Fermi-Bose
mixtures is studied. Two identical fermions of the mass and a particle of
the mass with the zero-range two-body interaction in the states of the
total angular momentum L=1 are considered. Using the boundary condition model
for the s-wave interaction of different particles, both eigenvalue and
scattering problems are treated by solving hyper-radial equations, whose terms
are derived analytically. The dependencies of the three-body binding energies
on the mass ratio for the positive two-body scattering length are
calculated; it is shown that the ground and excited states arise at and ,
respectively. For m/m_1 \alt \lambda_1 and m/m_1 \alt \lambda_2, the
relevant bound states turn to narrow resonances, whose positions and widths are
calculated. The 2 + 1 elastic scattering and the three-body recombination near
the three-body threshold are studied and it is shown that a two-hump structure
in the mass-ratio dependencies of the cross sections is connected with arising
of the bound states.Comment: 16 page
Evolution of spectral properties along the O(6)-U(5) transition in the interacting boson model. II. Classical trajectories
This article continues our previous study of level dynamics in the
[O(6)-U(5)]O(5) transition of the interacting boson model
[nucl-th/0504016] using the semiclassical theory of spectral fluctuations. We
find classical monodromy, related to a singular bundle of orbits with infinite
period at energy E=0, and bifurcations of numerous periodic orbits for E>0. The
spectrum of allowed ratios of periods associated with beta- and
gamma-vibrations exhibits an abrupt change around zero energy. These findings
explain anomalous bunching of quantum states in the E0 region, which
is responsible for the redistribution of levels between O(6) and U(5)
multiplets.Comment: 11 pages, 7 figures; continuation of nucl-th/050401
Evolution of spectral properties along the O(6)-U(5) transition in the interacting boson model. I. Level dynamics
We investigate the evolution of quantal spectra and the corresponding wave
functions along the [O(6)-U(5)]O(5) transition of the interacting
boson model. The model is integrable in this regime and its ground state passes
through a second-order structural phase transition. We show that the whole
spectrum as a function of the Hamiltonian control parameter, as well as
structures of all excited states, exhibit rather organized and correlated
behaviors, that provide deeper insight into the nature of this transitional
path.Comment: 10 pages, 8 figure
Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments
The processes with three or more charged particles in the final state exhibit
particular threshold behavior, as inferred by the famous Wannier law for (2e +
ion) system. We formulate a general solution which determines the threshold
behavior of the cross section for multiple fragmentation. Applications to
several systems of particular importance with three, four and five leptons
(electrons and positrons) in the field of charged core; and two pairs of
identical particles with opposite charges are presented. New threshold
exponents for these systems are predicted, while some previously suggested
threshold laws are revised.Comment: 40 pages, Revtex, scheduled for the July issue of Phys.Rev.A (1998
Three-Body Halos in Two Dimensions
A method to study weakly bound three-body quantum systems in two dimensions
is formulated in coordinate space for short-range potentials. Occurrences of
spatially extended structures (halos) are investigated. Borromean systems are
shown to exist in two dimensions for a certain class of potentials. An
extensive numerical investigation shows that a weakly bound two-body state
gives rise to two weakly bound three-body states, a reminiscence of the Efimov
effect in three dimensions. The properties of these two states in the weak
binding limit turn out to be universal.
PACS number(s): 03.65.Ge, 21.45.+v, 31.15.Ja, 02.60NmComment: 9 pages, 2 postscript figures, LaTeX, epsf.st
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