3,995 research outputs found
Combination of 13 C/ 113 Cd NMR, potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter
International audienceThis work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid– base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/ basic site ratios: 0.15 for Phytagel and 0.76 for polyga-lacturonic acid. Spectroscopic techniques (13 C/ 113 Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactiv-ity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d'Optimisation et de Speci-ation Chimique dans l'Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd 2+ /H
Dynamical localization of matter wave solitons in managed barrier potentials
The bright matter wave soliton propagation through a barrier with a rapidly
oscillating position is investigated. The averaged over rapid oscillations
Gross-Pitaevskii (GP) equation is derived. It is shown that the soliton is
dynamically trapped by the effective double-barrier.
The analytical predictions for the soliton effective dynamics is confirmed by
the numerical simulations of the full GP equation.Comment: 10 pages, 6 figure
Symmetry breaking induced by random fluctuations for Bose-Einstein condensates in a double-well trap
This paper is devoted to the study of the dynamics of two weakly-coupled
Bose-Einstein condensates confined in a double-well trap and perturbed by
random external forces. Energy diffusion due to random forcing allows the
system to visit symmetry-breaking states when the number of atoms exceeds a
threshold value. The energy distribution evolves to a stationary distribution
which depends on the initial state of the condensate only through the total
number of atoms. This loss of memory of the initial conditions allows a simple
and complete description of the stationary dynamics of the condensate which
randomly visits symmetric and symmetry-breaking states.Comment: 12 pages, 6 figure
Transmission of matter wave solitons through nonlinear traps and barriers
The transmissions of matter wave solitons through linear and nonlinear
inhomogeneities induced by the spatial variations of the trap and the
scattering length in Bose-Einstein condensates are investigated. New phenomena,
such as the enhanced transmission of a soliton through a linear trap by a
modulation of the scattering length, are exhibited. The theory is based on the
perturbed Inverse Scattering Transform for solitons, and we show that radiation
effects are important. Numerical simulations of the Gross-Pitaevskii equation
confirm the theoretical predictions.Comment: 6 pages, 4 figure
Work fluctuation theorems for harmonic oscillators
The work fluctuations of an oscillator in contact with a thermostat and
driven out of equilibrium by an external force are studied experimentally and
theoretically within the context of Fluctuation Theorems (FTs). The oscillator
dynamics is modeled by a second order Langevin equation. Both the transient and
stationary state fluctuation theorems hold and the finite time corrections are
very different from those of a first order Langevin equation. The periodic
forcing of the oscillator is also studied; it presents new and unexpected short
time convergences. Analytical expressions are given in all cases
Western Mediterranean precipitation over the last 300 years from instrumental observations
The paper reports the results of the analysis of the 14 longest precipitation
instrumental series, covering the last 300 years, that have been recovered in six subareas
of the Western Mediterranean basin, i.e., Portugal, Northern and Southern Spain, Southern
France, Northern and Southern Italy. This study extends back by one century our knowledge
about the instrumental precipitation over theWestern Mediterranean, and by two centuries in
some specific subareas. All the time series show repeated swings. No specific trends have been found over the whole period, except in a few cases, but with modest time changes and
sometimes having opposite tendency. The same can be said for the most recent decades
although with some more marked departures from the average. The correlation between the
various Mediterranean subareas is generally not significant, or almost uncorrelated. The
Wavelet Spectral Analysis applied to the precipitation identifies only a minor 56-year cycle
in autumn, i.e., the same return period that has been found in literature for the Sea Surface
Temperature over North Atlantic. A comparison with a gridded dataset reconstruction based on
mixed multiproxy and instrumental observations, shows that the grid reconstruction is in good
agreement with the observed data for the period after 1900, less for the previous period
Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
Recently strong evidence has been found in favor of a BCS-like condensation
of excitons in 1\textit{T}-TiSe. Theoretical photoemission intensity maps
have been generated by the spectral function calculated within the excitonic
condensate phase model and set against experimental angle-resolved
photoemission spectroscopy data. Here, the calculations in the framework of
this model are presented in detail. They represent an extension of the original
excitonic insulator phase model of J\'erome \textit{et al.} [Phys. Rev. {\bf
158}, 462 (1967)] to three dimensional and anisotropic band dispersions. A
detailed analysis of its properties and further comparison with experiment are
also discussedComment: Submitted to PRB, 11 pages, 7 figure
Evaluation of fatigue life of recycled opaque PET from household milk bottle wastes
Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide
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