1,721,005 research outputs found
Cement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent
No full textCement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent
No full textBound states in a superfluid vortex: A detailed study along the BCS-BEC crossover
No full textThe bound states that can occur in a superfluid vortex have recently called for attention owing to the capability
of detecting them experimentally. However, a detailed theoretical account for the presence of these vortex bound states is still lacking for all temperatures in the superfluid phase and couplings along the BCS-BEC crossover. Here, we fill this gap and present a systematic theoretical study based on the Bogoliubov–de Gennes equations for the bound states that occur over the two characteristic (inner and outer) spatial ranges in which the extension of a superfluid vortex can be partitioned. It is found that the total number of bound states decreases from the BCS (weak-coupling) side of the crossover toward the intermediate-coupling region where they are still present, whereas the bound states disappear upon entering the BEC (strong-coupling) side. A scaling relation is also obtained that connects the number of bound states in the inner spatial range of the vortex to the depth and width of the vortex itself. A criterion is finally provided in terms of the local density of states, to distinguish where a given fermionic superfluid is located in the coupling-temperature phase diagram of the BCS-BEC crossover
Quantitative comparison between theoretical predictions and experimental results for the BCS-BEC crossover
No full textTheoretical predictions for the Bardeen-Cooper-Schrieffer–Bose-Einstein condensation crossover of
trapped Fermi atoms are compared with recent experimental results for the density profiles of 6Li. The
calculations rest on a single theoretical approach that includes pairing fluctuations beyond mean-field.
Excellent agreement with experimental results is obtained. Theoretical predictions for the zerotemperature
chemical potential and gap at the unitarity limit are also found to compare extremely
well with Quantum Monte Carlo simulations and with recent experimental results
Optimizing the proximity effect along the BCS side of the BCS-BEC crossover
No full textThe proximity effect, which arises at the interface between two fermionic superfluids with different critical
temperatures, is examined with a nonlocal (integral) equation whose kernel contains information about the size
of Cooper pairs that leak across the interface. This integral approach avoids reference to the boundary conditions
at the interface that would be required with a differential approach. The temperature dependence of the pair
penetration depth on the normal side of the interface is determined over a wide temperature range also varying
the interparticle coupling along the BCS side of the BCS-BEC crossover independently on both sides of the
interface. In this way, the size of Cooper pairs evolves from being much larger than (BCS limit) the interparticle
distance to being comparable with (unitarity limit, halfway between the BCS and BEC limits) the interparticle
distance. Conditions are then found for which the proximity effect is optimized in terms of the extension
of the pair penetration depth
Nonlocal equation for the superconducting gap parameter
No full textThe properties are considered in detail of a nonlocal (integral) equation for the superconducting gap parameter, which is obtained by a coarse-graining procedure applied to the Bogoliubov-de Gennes (BdG) equations over the whole coupling-versus-temperature phase diagram associated with the superfluid phase. It is found that the limiting size of the coarse-graining procedure, which is dictated by the range of the kernel of this integral equation, corresponds to the size of the Cooper pairs over the whole coupling-versus-temperature phase diagram up to the critical temperature, even when Cooper pairs turn into composite bosons on the BEC side of the BCS-BEC crossover. A practical method is further implemented to solve numerically this integral equation in an efficient way, which is based on a novel algorithm for calculating the Fourier transforms. Application of this method to the case of an isolated vortex, throughout the BCS-BEC crossover and for all temperatures in the superfluid phase, helps clarifying the nature of the length scales associated with a single vortex and the kinds of details that are in practice disposed off by the coarse-graining procedure on the BdG equations
Entanglement between pairing and screening in the Gorkov-Melik-Barkhudarov correction to the critical temperature throughout the BCS-BEC crossover
Full text linkThe problem of the theoretical description of the critical temperature Tc of a Fermi superfluid dates back to
the work by Gorkov and Melik-Barkhudarov (GMB), who addressed it for a weakly coupled (dilute) superfluid
in what would today be referred to as the (extreme) BCS (weak-coupling) limit of the BCS-BEC crossover.
The point made in this context by GMB was that particle-particle (pairing) excitations, which are responsible
for superfluidity to occur below Tc, and particle-hole excitations, which give rise to screening also in a normal
system, get effectively disentangled from each other in the BCS limit, thus yielding a reduction by a factor of 2.2
of the value of Tc obtained when neglecting screening effects. Subsequent work on this topic, that was aimed at
extending the original GMB argument away from the BCS limit with diagrammatic methods, has tout court kept
this disentangling between pairing and screening throughout the BCS-BEC crossover, without realizing that the
conditions for it to be valid are soon violated away from the BCS limit. Here, we reconsider this problem from a
more general perspective and argue that pairing and screening are intrinsically entangled with each other along
the whole BCS-BEC crossover but for the BCS limit considered by GMB, with the particle-hole excitations soon
transmuting into particle-particle excitations away from this limit.We substantiate our argument by performing a
detailed numerical calculation of the GMB diagrammatic contribution suitably extended to the whole BCS-BEC
crossover, where the fullwave-vector and frequency dependence occurring in the repeated in-medium two-particle
scattering is duly taken into account. Our numerical calculations are tested against analytic results available in
both the BCS and BEC limits, and the contribution of the GMB diagrammatic term to the scattering length of
composite bosons in the BEC limit is highlighted. We calculate Tc throughout the BCS-BEC crossover and find
that it agrees quite well with quantum Monte Carlo calculations and experimental data available in the unitarity
regime
Analysis of volatile organic compounds in leather
No full textGas-chromatog./mass spectrometry combined with the purge and trap technique was used to det. the compn. of volatile emissions from various leather samples. The purge and trap technique consists on placing the leather sample in a hermetically closed vial at room temp. using inert gas flow to strip off and transport the volatile substances to an absorbent trap, to conc. the sample. The transfer of concd. sample to the gas-chromatog. column is accomplished by thermal desorption. Identification of alcs., aldehydes, ketones, hydrocarbons, benzene derivs., etc., was carried out by mass spectrometry. For an upholstery leather sample with strong odor, volatile compds. detected include terpenes, i.e., limonene, pinene, etc. The method is convenient and easy to implement for routine assessment of leather products to meet environmental stds. for indoor air related to furniture, upholstery, automobile interiors, as well as leather garments
Novel thermoplastic materials from wastes of the leather industry
No full textHydrolyzed collagen from leather industry is a natural polymer easily available at low cost and its use is not in competition with food industries or other main applications because it is a waste material and a by-product of the tanning process. In this work, polyethylene-collagen hydrolizate blends, at ratios of 100/0, 90/10 and 80/20, were processed using a blow film line equipped with a single screw extruder. Film blowing is a shaping technique used extensively to produce most plastics films and bags for packaging applications. The effect of processing parameters on the physical properties of blown films was investigated. The extruded films were characterized through mechanical testing, scanning electron microscopy, and thermal analysis. The manufactured films showed satisfactory mechanical and thermal properties, thus polyethylenecollagen hydrolizate blends appears as promising candidate for the production of innovative material suitable for production of thermoplastic items for applications in packaging and agricultural segments
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