2,554 research outputs found
Green's function of a dressed particle
We present a new, highly efficient yet accurate approximation for the Green's
functions of dressed particles, using the Holstein polaron as an example.
Instead of summing a subclass of diagrams (e.g. the non-crossed ones, in the
self-consistent Born approximation (SCBA)), we sum all the diagrams, but with
each diagram averaged over its free propagators' momenta. The resulting Green's
function satisfies exactly the first six spectral weight sum rules. All higher
sum rules are satisfied with great accuracy, becoming asymptotically exact for
coupling both much larger and much smaller than the free particle bandwidth.
Possible generalizations to other models are also discussed.Comment: 4 pages, 3 figure
Giant proximity effect in a phase-fluctuating superconductor
When a tunneling barrier between two superconductors is formed by a normal
material that would be a superconductor in the absence of phase fluctuations,
the resulting Josephson effect can undergo an enormous enhancement. We
establish this novel proximity effect by a general argument as well as a
numerical simulation and argue that it may underlie recent experimental
observations of the giant proximity effect between two cuprate superconductors
separated by a barrier made of the same material rendered normal by severe
underdoping.Comment: 4 pages, 3 figures; version to appear in PRL (results of simulations
in 3d added). For related work and info visit
http://www.physics.ubc.ca/~fran
The effect of the Abrikosov vortex phase on spin and charge states in magnetic semiconductor-superconductor hybrids
We explore the possibility of using the inhomogeneous magnetic field carried
by an Abrikosov vortex in a type-II superconductor to localize spin-polarized
textures in a nearby magnetic semiconductor quantum well. We show how
Zeeman-induced localization induced by a single vortex is indeed possible, and
use these results to investigate the effect of a periodic vortex array on the
transport properties of the magnetic semiconductor. In particular, we find an
unconventional Integer Quantum Hall regime, and predict directly testable
experimental consequences due to the presence of the periodic spin polarized
structure induced by the superconducting vortex lattice in the magnetic
semiconductor.Comment: 12 pages, 15 figure
NANO-VESICLES OF SALBUTAMOL SULPHATE IN METERED DOSE INHALERS: FORMULATION, CHARACTERIZATION AND IN VITRO EVALUATION
Objective: The present work was aimed to prepare niosomes entrapping salbutamol sulphate (SS) using reversed phase evaporation method (REV).Methods: Niosomes were prepared by mixing span 60 and cholesterol in 1:1 molar ratio in chloroform, SS in water was then added to organic phase to form niosomal SS. Formulations after evaporation of chloroform, freeze centrifuged then lyophilized, were evaluated for particles size, polydispersity index (Pdi), zeta-potential, morphology, entrapment efficiency (EE%) and in vitro release. For pulmonary delivery; metered dose inhalers (MDI) were prepared by suspending SS niosomes equivalent to 20 mg SS in hydrofluoroalkane (HFA). The metered valve was investigated for leakage rate, the total number of puffs/canister, weight/puff, dose uniformity and particle size.Results: The results showed spherical niosomes with 400-451 nm particles that entrapped 66.19% of SS. 76.54±0.132% SS release from niosomes that showed a controlled release profile for 8h. The leakage test was not exceeding 4 mg/3 d, the number of puffs were up to 200puffs/canister, the dose delivered/puff was 0.1 mg and 0.64-4.51μm niosomal aerosol.Conclusion: The results indicate an encouraging strategy to formulate a controlled drug delivery by entrapping (SS) in niosomes which could be packaged into (MDI) that met the requirements of (USP) aerosols guidelines which offering a novel approach to respiratory delivery
Chaotic behavior of a coupled system of the Riccati map
In this paper, We present the equivalent discrete system of coupled Riccati map. We study some the dynamic behavior such as (xed points and their asymptotic stability, the lyapunov exponents, chaos and bifurcation) of the system. Numerical simulation is presented to ensure the analytical results
Single polaron properties of the breathing-mode Hamiltonian
We investigate numerically various properties of the one-dimensional (1D)
breathing-mode polaron. We use an extension of a variational scheme to compute
the energies and wave-functions of the two lowest-energy eigenstates for any
momentum, as well as a scheme to compute directly the polaron Greens function.
We contrast these results with results for the 1D Holstein polaron. In
particular, we find that the crossover from a large to a small polaron is
significantly sharper. Unlike for the Holstein model, at moderate and large
couplings the breathing-mode polaron dispersion has non-monotonic dependence on
the polaron momentum k. Neither of these aspects is revealed by a previous
study based on the self-consistent Born approximation
Momentum average approximation for models with boson-modulated hopping: Role of closed loops in the dynamical generation of a finite quasiparticle mass
We generalize the momentum average approximation to study the properties of
single polarons in models with boson affected hopping, where the fermion-boson
scattering depends explicitly on both the fermion's and the boson's momentum.
As a specific example, we investigate the Edwards fermion-boson model in both
one and two dimensions. In one dimension, this allows us to compare our results
with exact diagonalization results, to validate the accuracy of our
approximation. The generalization to two-dimensional lattices allows us to
calculate the polaron's quasiparticle weight and dispersion throughout the
Brillouin zone and to demonstrate the importance of Trugman loops in generating
a finite effective mass even when the free fermion has an infinite mass.Comment: 15 pages, 14 figure
Hybrid TUI Abacus Model: An Advance Tool for Learning Math
In the world of changing technology, the speed of development using new technology has increased and so has the learning rate. Modern software helps new generation of kids learn new things easily but lack the practicality of touch and feel, and kids also become less physically and socially interactive. There always has been an argument about which way is better for learning for kids. Hence, a test was conducted to evaluate whether practical learning or learning through software resulted in faster learning. The test involved 20 kids of the 4-7 year age group, where kids were divided into two sets, each set consisting of 10 kids. One set of kids where taught mathematical operations such as addition, subtraction, multiplication and division using a physical abacus tool while the other set was given a mobile application of the Abacus Tool. Both the sets of students were given one week learning time and a paper pen test was conducted for both the set of kids. They were allowed to use the same version of Abacus on which they were trained for a week. The results of the kids that used the mobile application surpassed those who were given the physical Abacus tool. Thus, we may conclude that learning Abacus virtually using software helps kids learn faster and much better but makes kids physically and socially inactive. We propose a hybrid model where kids experience the physical touch and feel, socialize more, while also getting the motivation of self-praise and leveraging modern software Abacus. This hybrid model is implemented in the form of Abacus
Evolution of a barotropic shear layer into elliptical vortices
When a barotropic shear layer becomes unstable, it produces the well known
Kelvin-Helmholtz instability (KH). The non-linear manifestation of KH is
usually in the form of spiral billows. However, a piecewise linear shear layer
produces a different type of KH characterized by elliptical vortices of
constant vorticity connected via thin braids. Using direct numerical simulation
and contour dynamics, we show that the interaction between two
counter-propagating vorticity waves is solely responsible for this KH
formation. We investigate the oscillation of the vorticity wave amplitude, the
rotation and nutation of the elliptical vortex, and straining of the braids.
Our analysis also provides possible explanation behind the formation and
evolution of elliptical vortices appearing in geophysical and astrophysical
flows, e.g. meddies, Stratospheric polar vortices, Jovian vortices, Neptune's
Great Dark Spot and coherent vortices in the wind belts of Uranus.Comment: 7 pages, 4 figures, Accepted in Physical Review
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