4,519 research outputs found
Dissipative Effects on the Superfluid to Insulator Transition in Mixed-dimensional Optical Lattices
We study the superfluid to Mott insulator transition of a mixture of heavy
bosons and light fermions loaded in an optical lattice. We focus on the effect
of the light fermions on the dynamics of the heavy bosons. It is shown that,
when the lattice potential is sufficiently deep to confine the bosons to one
dimension but allowing the fermions to freely move in three dimensions (i.e. a
mixed-dimensionality lattice), the fermions act as an ohmic bath for bosons
leading to screening and dissipation effects on the bosons. Using a
perturbative renormalization-group analysis, it is shown that the
fermion-induced dissipative effects have no appreciable impact on the
transition from the superfluid to the Mott-insulator state at integer filling.
On the other hand, dissipative effects are found to be very important in the
half-filled case near the critical point. In this case, in the presence of a
finite incommensurability that destabilizes the Mott phase, the bosons can
still be localized by virtue of dissipative effects.Comment: 10 pages, 8 figure
Model Wavefunctions for the Collective Modes and the Magneto-roton Theory of the Fractional Quantum Hall Effect
We construct model wavefunctions for the collective modes of fractional
quantum Hall systems. The wavefunctions are expressed in terms of symmetric
polynomials characterized by a root partition and a "squeezed" basis, and show
excellent agreement with exact diagonalization results for finite systems. In
the long wavelength limit, the model wavefunctions reduce to those predicted by
the single-mode approximation, and remain accurate at energies above the
continuum of roton pairs.Comment: 4 pages, 3 figures, minor changes for the final prl versio
Multiphase transport model for heavy ion collisions at RHIC
Using a multiphase transport model (AMPT) with both partonic and hadronic
interactions, we study the multiplicity and transverse momentum distributions
of charged particles such as pions, kaons and protons in central Au+Au
collisions at RHIC energies. Effects due to nuclear shadowing and jet quenching
on these observables are also studied. We further show preliminary results on
the production of multistrange baryons from the strangeness-exchange reactions
during the hadronic stage of heavy ion collisions.Comment: 4 pages, 4 figures, espcrc1.sty included, presented at 15th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(QM2001), Long Island, New York, January 200
Partonic effects on higher-order anisotropic flows in relativistic heavy-ion collisions
Higher-order anisotropic flows and in heavy ion collisions at
the Relativistic Heavy Ion Collider are studied in a multiphase transport model
that has previously been used successfully for describing the elliptic flow
in these collisions. We find that the same parton scattering cross
section of about 10 \textrm{mb} used in explaining the measured can also
reproduce the recent data on and from Au + Au collisions at
\textrm{AGeV}. It is further found that the is a more
sensitive probe of the initial partonic dynamics in these collisions than
. Moreover, higher-order parton anisotropic flows are nonnegligible and
satisfy the scaling relation , which
leads naturally to the observed similar scaling relation among hadron
anisotropic flows when the coalescence model is used to describe hadron
production from the partonic matter.Comment: 5 pages, 3 figures, version to appear in PRC as a Rapid Communicatio
Enhanced transmission of optically thick metallic films at infrared wavelengths
For an optically thick metallic film, the transmission for both s- and
p-polarized waves is extremely low. If the metallic film is coated on both
sides with a finite dielectric layer, light transmission for -polarized
waves can be enhanced considerably. This enhancement is not related to surface
plasmon-polaritions. Instead, it is due to the interplay between Fabry-Perot
interference in the coated dielectric layer and the existence of the Brewster
angle at the dielectric/metallic interface. It is shown that the coated
metallic films can act as excellent polarizers at infrared wavelengths.Comment: 3 pages, 4 figures. Submitted to Appl. Phys. Let
Late-Time Optical Afterglow Observations with LBT and MDM
Using the 2.4m MDM and 8.4m Large Binocular Telescope, we observed nine GRB
afterglows to systematically probe the late time behaviors of afterglows
including jet breaks, flares, and supernova bumps. In particular, the LBT
observations have typical flux limits of 25-26 mag in the Sloan r' band, which
allows us to extend the temporal baseline for measuring jet breaks by another
decade in time scale. We detected four jet breaks (including a "textbook" jet
break in GRB070125) and a fifth candidate, all of which are not detectable
without deep, late time optical observations. In the other four cases, we do
not detect the jet breaks either because of contamination from the host galaxy
light, the presence of a supernova bump, or the intrinsic faintness of the
optical afterglow. This suggests that the basic picture that GRBs are
collimated is still valid and that the apparent lack of Swift jet breaks is due
to poorly sampled afterglow light curves, particularly at late times. Besides
the jet breaks, we also detected late time flares, which could attribute to
late central engine activities, and two supernova bumps.Comment: 5 pages, 5 figures, 2008 NANJING GAMMA-RAY BURST CONFERENCE. AIP
Conference Proceedings, Volume 1065, pp. 93-97 (2008), Eds. Y.F. Huang, Z.G.
Dai, B. Zhan
Ecological surveys of certain plant communities around urban areas of Karachi
A phytosociological study was conducted as an initial assessment of the vegetation on different sites to determine the community structure and how the communities were related based on their species composition and edaphic characteristics. The communities were distinct types ranging from halophytes to xerophytes withdisturbed in nature. Plant communities based on first leading dominant species (Prosopis, Avicennia, Gynandropis, Salvadora, Ipomea, Halopyrum, Limonium, Abutilon and Calotropis) were explored in the study area. Out of thirtynine plant species, Prosopis juliflora attained the highest total importance value index (I.V.I.) followed by Avicenniamarina, Suaeda fruticosa and Gynandropsis gynandra. Nine species attained first leading position. Thirteen species attained second dominant position. However, twelve species attained third dominant position in all stands. P. juliflora was the only species that was found six times as a first dominant, three times as second and one time as a thirddominates species. None of the other species was in a position to get first, second and third position as a leading dominant in all stands. The communities were of heterogeneous type, with low species diversity and ranged from 1.36 to 4.54. Most of the plant communities showed less than 50% CMI values. However, Prosopis in association with Pasplidium and Cenchrus community showed highest CMI value (70.00). The soils of the study areas were sandy loam, loamy sand, loamy silt, sandy and silty. The soils are alkaline in nature. An appreciable amount of calcium carbonate (13-26%) with moderate percentage of maximum water holding capacity (19-41%) and high soilEC (593 s/cmì) were recorded. It was also observed that certain edaphic and human activity, discharge of pollutants with out any pretreatment was found responsible for variation in the nature, structure and composition of vegetation. The plant growth and their continuity was in danger in many disturb areas, especially in some coastal areas where salinity and the incident of Tasman spirit oil spillage was occurred just few months before the survey carried out.Construction of flyover, expansion of the roads and cut down of the natural vegetation producing additional losses to flora of the region
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