5,092 research outputs found
Magnetic phase transition in coherently coupled Bose gases in optical lattices
We describe the ground state of a gas of bosonic atoms with two coherently
coupled internal levels in a deep optical lattice in a one dimensional
geometry. In the single-band approximation this system is described by a
Bose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating
phase which can be either paramagnetic or ferromagnetic. We characterize the
quantum phase transitions at unit filling by means of a density matrix
renormalization group technique and compare it with a mean-field approach. The
presence of the ferromagnetic Ising-like transition modifies the Mott lobes. In
the Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ
model in a transverse field and the numerical results compare very well with
the analytical results obtained from the spin model. In the superfluid regime
quantum fluctuations strongly modify the phase transition with respect to the
well established mean-field three dimensional classical bifurcation.Comment: 6 pages, 3 figure
Excitations and S-matrix for su(3) spin chain combining and ${3^{*}}
The associated Hamiltonian for a su(3) spin chain combining and
representations is calculated. The ansatz equations for this chain
are obtained and solved in the thermodynamic limit, and the ground state and
excitations are described. Thus, relations between the number of roots and the
number of holes in each level have been found . The excited states are
characterized by means of these quantum numbers. Finally, the exact S matrix
for a state with two holes is found.Comment: 17 pages, plaintex, harvmac (to be published in J. of Phys. A
A Vaccine Against Group B Streptococcus: Recent Advances
Group B streptococcus (GBS) causes a high burden of neonatal and infant disease globally. Implementing a vaccine for pregnant women is a promising strategy to prevent neonatal and infant GBS disease and has been identified as a priority by the World Health Organisation (WHO). GBS serotype-specific polysaccharide – protein conjugate vaccines are at advanced stages of development, but a large number of participants would be required to undertake Phase III clinical efficacy trials. Efforts are therefore currently focused on establishing serocorrelates of protection in natural immunity studies as an alternative pathway for licensure of a GBS vaccine, followed by Phase IV studies to evaluate safety and effectiveness. Protein vaccines are in earlier stages of development but are highly promising as they might confer protection irrespective of serotype. Further epidemiological, immunological and health economic studies are required to enable the vaccine to reach its target population as soon as possible
Wavelength de-multiplexing properties of a single aperture flanked by periodic arrays of indentations
In this paper we explore the transmission properties of single subwavelength
apertures perforated in thin metallic films flanked by asymmetric
configurations of periodic arrays of indentations. It is shown how the
corrugation in the input side can be used to transmit selectively only two
different wavelengths. Also, by tuning the geometrical parameters defining the
corrugation of the output side, these two chosen wavelengths can emerge from
the structure as two very narrow beams propagating at well-defined directions.
This new ability of structured metals can be used as a base to build
micron-sized wavelength de-multiplexers.Comment: Accepted for publication in Photonics and Nanostructure
Efficiency of encounter-controlled reaction between diffusing reactants in a finite lattice: topology and boundary effects
The role of dimensionality (Euclidean versus fractal), spatial extent,
boundary effects and system topology on the efficiency of diffusion-reaction
processes involving two simultaneously-diffusing reactants is analyzed. We
present numerically-exact values for the mean time to reaction, as gauged by
the mean walklength before reactive encounter, obtained via application of the
theory of finite Markov processes, and via Monte Carlo simulation. As a general
rule, we conclude that for sufficiently large systems, the efficiency of
diffusion-reaction processes involving two synchronously diffusing reactants
(two-walker case) relative to processes in which one reactant of a pair is
anchored at some point in the reaction space (one walker plus trap case) is
higher, and is enhanced the lower the dimensionality of the system. This
differential efficiency becomes larger with increasing system size and, for
periodic systems, its asymptotic value may depend on the parity of the lattice.
Imposing confining boundaries on the system enhances the differential
efficiency relative to the periodic case, while decreasing the absolute
efficiencies of both two-walker and one walker plus trap processes. Analytic
arguments are presented to provide a rationale for the results obtained. The
insights afforded by the analysis to the design of heterogeneous catalyst
systems are also discussed.Comment: 15 pages, 8 figures, uses revtex4, accepted for publication in
Physica
Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics
© 2016. American Geophysical Union. All Rights Reserved. Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow characteristics. Three-dimensional velocities were measured during two different events—a near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops
Theory of extraordinary transmission of light through quasiperiodic arrays of subwavelength holes
By using a theoretical formalism able to work in both real and k-spaces, the
physical origin of the phenomenon of extraordinary transmission of light
through quasi-periodic arrays of holes is revealed. Long-range order present in
a quasiperiodic array selects the wavevector(s) of the surface electromagnetic
mode(s) that allows an efficient transmission of light through subwavelength
holes.Comment: 4 pages, 4 figure
Development of encapsulation strategies and composite edible films to maintain lactoferrin bioactivity: A review
Lactoferrin (LF) is a whey protein with various and valuable biological activities. For this reason, LF has been used as a supplement in formula milk and functional products. However, it must be considered that the properties of LF can be affected by technological treatments and gastrointestinal conditions. In this article, we have revised the literature published on the research done during the last decades on the development of various technologies, such as encapsulation or composite materials, to protect LF and avoid its degradation. Multiple compounds can be used to con-duct this protective function, such as proteins, including those from milk, or polysaccharides, like alginate or chitosan. Furthermore, LF can be used as a component in complexes, nanoparticles, hy-drogels and emulsions, to encapsulate, protect and deliver other bioactive compounds, such as essential oils or probiotics. Additionally, LF can be part of systems to deliver drugs or to apply certain therapies to target cells expressing LF receptors. These systems also allow improving the detection of gliomas and have also been used for treating some pathologies, such as different types of tu-mours. Finally, the application of LF in edible and active films can be effective against some con-taminants and limit the increase of the natural microbiota present in meat, for example, becoming one of the most interesting research topics in food technology. © 2021 by the authors. Li-censee MDPI, Basel, Switzerland
Integrability of a t-J model with impurities
A t-J model for correlated electrons with impurities is proposed. The
impurities are introduced in such a way that integrability of the model in one
dimension is not violated. The algebraic Bethe ansatz solution of the model is
also given and it is shown that the Bethe states are highest weight states with
respect to the supersymmetry algebra gl(2/1)Comment: 14 page
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