112 research outputs found
High temperature phase transition in the coupled atom-light system in the presence of optical collisions
The problem of photonic phase transition for the system of a two-level atomic
ensemble interacting with a quantized single-mode electromagnetic field in the
presence of optical collisions (OC) is considered. We have shown that for large
and negative atom-field detuning a photonic field exhibits high temperature
second order phase transition to superradiant state under thermalization
condition for coupled atom-light states. Such a transition can be connected
with superfluid (coherent) properties of photon-like low branch (LB)
polaritons. We discuss the application of metallic cylindrical waveguide for
observing predicted effects.Comment: 8 pages, 2 figure
Solitons in cavity-QED arrays containing interacting qubits
We reveal the existence of polariton soliton solutions in the array of weakly
coupled optical cavities, each containing an ensemble of interacting qubits. An
effective complex Ginzburg-Landau equation is derived in the continuum limit
taking into account the effects of cavity field dissipation and qubit
dephasing. We have shown that an enhancement of the induced nonlinearity can be
achieved by two order of the magnitude with a negative interaction strength
which implies a large negative qubit-field detuning as well. Bright solitons
are found to be supported under perturbations only in the upper (optical)
branch of polaritons, for which the corresponding group velocity is controlled
by tuning the interacting strength. With the help of perturbation theory for
solitons, we also demonstrate that the group velocity of these polariton
solitons is suppressed by the diffusion process
Baryon Junction Loops in HIJING/B\=Bv2.0 and the Baryon/Meson Anomaly at RHIC
A new version, v2.0, of the HIJING/B\=B Monte Carlo nuclear collision event
generator is introduced in order to explore further the possible role of baryon
junctions loops in the baryon/meson anomaly (2 5 GeV/c) observed in
200A GeV Au+Au reactions at RHIC. We show that junction loops with an enhanced
intrinsic GeV/c transverse momentum kick may provide a partial
explanation of the anomaly as well as other important baryon stopping
observables.Comment: 27 pages, Latex(revtex), 8 figure
Thermalization of coupled atom-light states in the presence of optical collisions
The interaction of a two-level atomic ensemble with a quantized single mode
electromagnetic field in the presence of optical collisions (OC) is
investigated both theoretically and experimentally. The main accent is made on
achieving thermal equilibrium for coupled atom-light states (in particular
dressed states). We propose a model of atomic dressed state thermalization that
accounts for the evolution of the pseudo-spin Bloch vector components and
characterize the essential role of the spontaneous emission rate in the
thermalization process. Our model shows that the time of thermalization of the
coupled atom-light states strictly depends on the ratio of the detuning and the
resonant Rabi frequency. The predicted time of thermalization is in the
nanosecond domain and about ten times shorter than the natural lifetime at full
optical power in our experiment. Experimentally we are investigating the
interaction of the optical field with rubidium atoms in an ultra-high pressure
buffer gas cell under the condition of large atom-field detuning comparable to
the thermal energy in frequency units. In particular, an observed detuning
dependence of the saturated lineshape is interpreted as evidence for thermal
equilibrium of coupled atom-light states. A significant modification of
sideband intensity weights is predicted and obtained in this case as well.Comment: 14 pages, 12 figures; the content was edite
Merging Galaxies in the SDSS EDR
We present a new catalog of merging galaxies obtained through an automated
systematic search routine. The 1479 new pairs of merging galaxies were found in
approximately 462 sq deg of the Sloan Digital Sky Survey Early Data Release
(SDSS EDR; Stoughton et al. 2002) photometric data, and the pair catalog is
complete for galaxies in the magnitude range 16.0 <= g* <= 20.
The selection algorithm, implementing a variation on the original
Karachentsev (1972) criteria, proved to be very efficient and fast. Merging
galaxies were selected such that the inter-galaxy separations were less than
the sum of the component galaxies' radii.
We discuss the characteristics of the sample in terms of completeness, pair
separation, and the Holmberg effect. We also present an online atlas of images
for the SDSS EDR pairs obtained using the corrected frames from the SDSS EDR
database. The atlas images also include the relevant data for each pair member.
This catalog will be useful for conducting studies of the general
characteristics of merging galaxies, their environments, and their component
galaxies. The redshifts for a subset of the interacting and merging galaxies
and the distribution of angular sizes for these systems indicate the SDSS
provides a much deeper sample than almost any other wide-area catalog to date.Comment: 58 pages, which includes 15 figures and 6 tables. Figures 2, 8, 9,
10, 11, 13, and 14 are provided as JPEG files. For online atlas, see
http://home.fnal.gov/~sallam/MergePair/ . Accepted for publication in A
Josephson dynamics for coupled polariton modes under the atom-field interaction in the cavity
We consider a new approach to the problem of Bose-Einstein condensation (BEC)
of polaritons for atom-field interaction under the strong coupling regime in
the cavity. We investigate the dynamics of two macroscopically populated
polariton modes corresponding to the upper and lower branch energy states
coupled via Kerr-like nonlinearity of atomic medium. We found out the
dispersion relations for new type of collective excitations in the system under
consideration. Various temporal regimes like linear (nonlinear) Josephson
transition and/or Rabi oscillations, macroscopic quantum self-trapping (MQST)
dynamics for population imbalance of polariton modes are predicted. We also
examine the switching properties for time-averaged population imbalance
depending on initial conditions, effective nonlinear parameter of atomic medium
and kinetic energy of low-branch polaritons.Comment: 10 pages, 6 postscript figures, uses svjour.cl
The Conformal Anomaly of M5-Branes
We show that the conformal anomaly for N M5-branes grows like . The
method we employ relates Coulomb branch interactions in six dimensions to
interactions in four dimensions using supersymmetry. This leads to a relation
between the six-dimensional conformal anomaly and the conformal anomaly of N=4
Yang-Mills. Along the way, we determine the structure of the four derivative
interactions for the toroidally compactified (2,0) theory, while encountering
interesting novelties in the structure of the six derivative interactions.Comment: 38 pages, LaTeX; references adde
Preliminary survey of backdrivable linear actuators for humanoid robots
This paper presents a preliminary survey of the use of direct drive linear motors for joint actuation of a humanoid robot. Their prime asset relies on backdrivability, a significant feature to properly cushion high impacts between feet and ground during dynamic walking or running. Our long-term goal is the design of high performance human size bipedal walking robots. However, this paper focuses on a preliminary feasibility study: the design and experimentation of a mono-actuator lower limb
One maternal lineage leads the expansion of Thaumastocoris peregrinus (Hemiptera: Thaumastocoridae) in the new and old worlds.
The bronze bug, Thaumastocoris peregrinus, an Australian native insect, has become a nearly worldwide invasive pest in the last 16 years and has been causing signifcant damage to eucalypts (Myrtaceae), including Eucalyptus spp. and Corymbia spp. Its rapid expansion leads to new questions about pathways and routes that T. peregrinus used to invade other continents and countries. We used mtDNA to characterize specimens of T. peregrinus collected from 10 countries where this species has become established, including six recently invaded countries: Chile, Israel, Mexico, Paraguay, Portugal, and the United States of America. We then combined our mtDNA data with previous data available from South Africa, Australia, and Europe to construct a world mtDNA network of haplotypes. Haplotype A was the most common present in all specimens of sites sampled in the New World, Europe, and Israel, however from Australia second more frequently. Haplotype D was the most common one from native populations in Australia. Haplotype A difers from the two major haplotypes found in South Africa (D and G), confrming that at least two independent invasions occurred, one from Australia to South Africa, and the other one from Australia to South America (A). In conclusion, Haplotype A has an invasion success over many countries in the World. Additionally, analyzing data from our work and previous reports, it is possible to suggest some invasive routes of T. peregrinus to predict such events and support preventive control measures
A model for net-baryon rapidity distribution
In nuclear collisions, a sizable fraction of the available energy is carried
away by baryons. As the baryon number is conserved, the net-baryon
retains information on the energy-momentum carried by the incoming nuclei. A
simple and consistent model for net-baryon production in high energy
proton-proton and nucleus-nucleus collisions is presented. The basic
ingredients of the model are valence string formation based on standard PDFs
with QCD evolution and string fragmentation via the Schwinger mechanism. The
results of the model are presented and compared with data at different
centre-of-mass energies and centralities, as well as with existing models.
These results show that a good description of the main features of net-baryon
data is possible in the framework of a simplistic model, with the advantage of
making the fundamental production mechanisms manifest.Comment: 9 pages, 12 figures; in fig. 11 a) the vertical scale was correcte
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