2,030 research outputs found
Mixtures of Bose gases confined in concentrically coupled annular traps
A two-component Bose-Einstein condensate confined in an axially-symmetric
potential with two local minima, resembling two concentric annular traps, is
investigated. The system shows a number of quantum phase transitions that
result from the competition between phase coexistence, and radial/azimuthal
phase separation. The ground-state phase diagram, as well as the rotational
properties, including the (meta)stability of currents in this system, are
analysed.Comment: 6 pages, 5 figures, minor revision
Final-state read-out of exciton qubits by observing resonantly excited photoluminescence in quantum dots
We report on a new approach to detect excitonic qubits in semiconductor
quantum dots by observing spontaneous emissions from the relevant qubit level.
The ground state of excitons is resonantly excited by picosecond optical
pulses. Emissions from the same state are temporally resolved with picosecond
time resolution. To capture weak emissions, we greatly suppress the elastic
scattering of excitation beams, by applying obliquely incident geometry to the
micro photoluminescence set-up. Rabi oscillations of the ground-state excitons
appear to be involved in the dependence of emission intensity on excitation
amplitude.Comment: 4 pages, 4 figures, to appear in Appl. Phys. Let
AdS3 Gravitational Instantons from Conformal Field Theory
A conformal field theory on the boundary of three-dimensional asymptotic
anti-de Sitter spaces which appear as near horizon geometry of D-brane bound
states is discussed. It is shown that partition functions of gravitational
instantons appear as high and low temperature limits of the partition function
of the conformal field theory. The result reproduces phase transition between
the anti-de Sitter space and the BTZ black hole in the bulk gravity.Comment: 22 pages, minor correction
Wettability influences cell behavior on superhydrophobic surfaces with different topographies
Surface wettability and topography are recognized as critical factors influencing cell behavior on biomaterials. So far only few works have reported cell responses on surfaces exhibiting extreme wettability in combination with surface topography. The goal of this work is to study whether cell behavior on superhydrophobic surfaces is influenced by surface topography and polymer type. Biomimetic superhydrophobic rough surfaces of polystyrene and poly(l-lactic acid) with different micro/nanotopographies were obtained from smooth surfaces using a simple phase-separation based method. Total protein was quantified and showed a less adsorption of bovine serum albumin onto rough surfaces as compared to smooth surfaces of the same material. The mouse osteoblastic MC3T3-E1 cell line and primary bovine articular chondrocytes were used to study cell attachment and proliferation. Cells attached and proliferate better in the smooth surfaces. The superhydrophobic surfaces allowed cells to adhere but inhibited their proliferation. This study indicates that surface wettability, rather than polymer type or the topography of the superhydrophobic surfaces, is a critical factor in determining cell behavior
Chitosan membranes exhibiting shape memory capability by the action of controlled hydration
Chitosan membranes can undergo a glass transition at room temperaturetriggered by hydration. The mechanical properties of the membranes were followed by atension test and dynamic mechanical analysis (DMA), with the sample in wet conditionsafter being immersed in varying compositions of water/ethanol mixtures. Results show thatwith the increasing of water content, the Young’s and storage modulus decreasesystematically. For water contents of ca. 35 vol%, chitosan (CHT) exhibits a glasstransition, showing an elastomeric plateau in the elastic modulus above this hydration leveland the occurrence of a peak in the loss factor. Due to the semi-crystalline nature of CHT,membranes of this biomaterial present a shape memory capability induced by water uptake.By fixation of the permanent shape by further covalent cross-linking, the membranes canhave different permanent shapes appropriate for different applications, including in thebiomedical area.This work was supported by the Portuguese Foundation for Science and Technology Foundation (FCT) through project PTDC/FIS/115048/2009
Charged black holes: Wave equations for gravitational and electromagnetic perturbations
A pair of wave equations for the electromagnetic and gravitational
perturbations of the charged Kerr black hole are derived. The perturbed
Einstein-Maxwell equations in a new gauge are employed in the derivation. The
wave equations refer to the perturbed Maxwell spinor and to the shear
of a principal null direction of the Weyl curvature. The whole
construction rests on the tripod of three distinct derivatives of the first
curvature of a principal null direction.Comment: 12 pages, to appear in Ap.
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