1,463 research outputs found
Turbulent heat transfer in spacer-filled channels: Experimental and computational study and selection of turbulence models
Heat transfer in spacer-filled channels of the kind used in Membrane Distillation was studied in the Reynolds number range 100–2000, encompassing both steady laminar and early-turbulent flow conditions. Experimental data, including distributions of the local heat transfer coefficient h, were obtained by Liquid Crystal Thermography and Digital Image Processing. Alternative turbulence models, both of first order (k-ε, RNG k-ε, k-ω, BSL k-ω, SST k-ω) and of second order (LRR RS, SSG RS, ω RS, BSL RS), were tested for their ability to predict measured distributions and mean values of h. The best agreement with the experimental results was provided by first-order ω-based models able to resolve the viscous/conductive sublayer, while all other models, and particularly ε-based models using wall functions, yielded disappointing predictions
Two-body bound and edge states in the extended SSH Bose-Hubbard model
We study the bosonic two-body problem in a Su-Schrieffer-Heeger dimerized
chain with on-site and nearest-neighbor interactions. We find two classes of
bound states. The first, similar to the one induced by on-site interactions,
has its center of mass on the strong link, whereas the second, existing only
thanks to nearest-neighbors interactions, is centered on the weak link. We
identify energy crossings between these states and analyse them using exact
diagonalization and perturbation theory. In the presence of open boundary
conditions, novel strongly-localized edge-bound states appear in the spectrum
as a consequence of the interplay between lattice geometry, on-site and
nearest-neighbor interactions. Contrary to the case of purely on-site
interactions, such EBS persist even in the strongly interacting regime.Comment: 12 pages, 8 figures; Submitted to EPJ Special Topics, Quantum Gases
and Quantum Coherenc
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Ultracold fermions in a one-dimensional bipartite optical lattice: metal-insulator transitions driven by shaking
We describe the behavior of a system of fermionic atoms loaded in a bipartite
one-dimensional optical lattice that is under the action of an external
time-periodic driving force. By using Floquet theory, an effective model with
renormalized hopping coefficients is derived. The insulating behavior
characterizing the system at half-filling in the absence of driving is
dynamically suppressed and for particular values of the driving parameter the
system becomes either a standard metal or an unconventional metal with four
Fermi points. We use the bosonization technique to investigate the effect of
on-site Hubbard interactions on the four Fermi-point metal-insulator phase
transition. Attractive interactions are expected to enlarge the regime of
parameters where the unconventional metallic phase arises, whereas repulsive
interactions reduce it. This metallic phase is known to be a Luther-Emery
liquid (spin gapped metal) for both, repulsive and attractive interactions,
contrarily to the usual Hubbard model which exhibits a Mott insulator phase for
repulsive interactions. Ultracold fermions in driven one-dimensional bipartite
optical lattices provide an interesting platform for the realization of this
long studied four Fermi-point unconventional metal.Comment: 11 pages, 6 figure
Particle-hole character of the Higgs and Goldstone modes in strongly-interacting lattice bosons
We study the low-energy excitations of the Bose-Hubbard model in the
strongly-interacting superfluid phase using a Gutzwiller approach and extract
the single-particle and single-hole excitation amplitudes for each mode. We
report emergent mode-dependent particle-hole symmetry on specific arc-shaped
lines in the phase diagram connecting the well-known Lorentz-invariant limits
of the Bose-Hubbard model. By tracking the in-phase particle-hole symmetric
oscillations of the order parameter, we provide an answer to the long-standing
question about the fate of the pure amplitude Higgs mode away from the
integer-density critical point. Furthermore, we point out that out-of-phase
oscillations are responsible for a full suppression of the condensate density
oscillations of the gapless Goldstone mode. Possible detection protocols are
also discussed.Comment: 6 pages, 3 figure
Optimization of net power density in Reverse Electrodialysis
Reverse Electrodialysis (RED) extracts electrical energy from the salinity difference between two solutions using selective ion exchange membranes. In RED, conditions yielding a large net power density (NPD) are generally desired, due to the still large cost of the membranes. NPD depends on a large number of physical and geometric parameters. Some of these, for example the inlet concentrations of concentrate and diluate, can be regarded as “scenario” variables, imposed by external constraints (e.g., availability) or chosen by different criteria than NPD maximization. Others, namely the thicknesses HCONC, HDIL and the velocities UCONC, UDIL in the concentrate and diluate channels, can be regarded as free design parameters and can be chosen so as to maximize NPD. In the present study, a simplified model of a RED stack was coupled with an optimization algorithm in order to determine the conditions of maximum NPD in the space of the variables HCONC, HDIL,UCONC, UDIL for different sets of “scenario” variables. The study shows that an optimal choice of the free design parameters for any given scenario, as opposed to the adoption of standard fixed values for the same parameters, may provide significant improvements in NPD
Quantum simulation of correlated-hopping models with fermions in optical lattices
By using a modulated magnetic field in a Feshbach resonance for ultracold
fermionic atoms in optical lattices, we show that it is possible to engineer a
class of models usually referred to as correlated-hopping models. These models
differ from the Hubbard model in exhibiting additional density-dependent
interaction terms that affect the hopping processes. In addition to the
spin-SU(2) symmetry, they also possess a charge-SU(2) symmetry, which opens the
possibility of investigating the -pairing mechanism for superconductivity
introduced by Yang for the Hubbard model. We discuss the known solution of the
model in 1D (where states have been found in the degenerate manifold of
the ground state) and show that, away from the integrable point, quantum Monte
Carlo simulations at half filling predict the emergence of a phase with
coexisting incommensurate spin and charge order.Comment: 10 pages, 9 figure
Characterizing pre-transplant and post-transplant kidney rejection risk by B cell immune repertoire sequencing.
Studying immune repertoire in the context of organ transplant provides important information on how adaptive immunity may contribute and modulate graft rejection. Here we characterize the peripheral blood immune repertoire of individuals before and after kidney transplant using B cell receptor sequencing in a longitudinal clinical study. Individuals who develop rejection after transplantation have a more diverse immune repertoire before transplant, suggesting a predisposition for post-transplant rejection risk. Additionally, over 2 years of follow-up, patients who develop rejection demonstrate a specific set of expanded clones that persist after the rejection. While there is an overall reduction of peripheral B cell diversity, likely due to increased general immunosuppression exposure in this cohort, the detection of specific IGHV gene usage across all rejecting patients supports that a common pool of immunogenic antigens may drive post-transplant rejection. Our findings may have clinical implications for the prediction and clinical management of kidney transplant rejection
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