99 research outputs found
Long range mediated interactions in a mixed dimensional system
We present a mixed-dimensional atomic gas system to unambiguously detect and
systematically probe mediated interactions. In our scheme, fermionic atoms are
confined in two parallel planes and interact via exchange of elementary
excitations in a three-dimensional background gas. This interaction gives rise
to a frequency shift of the out-of-phase dipole oscillations of the two clouds,
which we calculate using a strong coupling theory taking the two-body
mixed-dimensional scattering into account exactly. The shift is shown to be
easily measurable for strong interactions and can be used as a probe for
mediated interactions.Comment: 7 pages, 5 figure
An electronic ratchet is required in nanostructured intermediate band solar cells
We investigate in this letter the intrinsic properties that have limited the
efficiency of nanostructured intermediate band solar cells. Those devices take
advantage of intra-band transitions, which occur on narrow energy width, and
present low radiative recombination efficiency. We derive the minimum
requirements in terms of those two characteristics to achieve efficiencies in
excess of the Shockley-Queisser limit, and show that compatible nanostructures
are challenging to obtain. Especially, we evidence that currently
experimentally considered materials cannot overcome the best single junction
cells. In order to solve those issues, we consider devices including an
electronic ratchet mechanism. Firstly, such devices are shown to be much less
sensitive on the limitations of the nanostructures characteristics, so that
requirements for high efficiencies can be met. Secondly, we show that quantum
well devices present advantages over their quantum dots counterparts, although
they have attracted much less interest so far
d13C pattern of dissolved inorganic carbon in a small granitic catchment: the Strengbach case study (Vosges mountains, France)
The transfers and origins of dissolved inorganic carbon DIC. were studied for a year in a soil–spring–stream system in
the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side
of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80%.. Brown acid and
podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO2 generated by oxidation
of soil organic matter. The d13CDIC. in catchment waters is highly variable, from about y22‰ in the springs and
piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of
d13C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d13DIC 2 C of about y24‰ in winter and
y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular
diffusion of soil CO2 in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on
average. is a result of isotopic equilibration of the aqueous CO2 with atmospheric CO2
Analog Simulation of Weyl Particles with Cold Atoms
We study theoretically, numerically, and experimentally the relaxation of a
collisionless gas in a quadrupole trap after a momentum kick. The
non-separability of the potential enables a quasi thermalization of the single
particle distribution function even in the absence of interactions.
Suprinsingly, the dynamics features an effective decoupling between the strong
trapping axis and the weak trapping plane. The energy delivered during the kick
is redistributed according to the symmetries of the system and satisfies the
Virial theorem, allowing for the prediction of the final temperatures. We show
that this behaviour is formally equivalent to the relaxation of massless
relativistic Weyl fermions after a sudden displacement from the center of a
harmonic trap
Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment, Vosges mountains, France)
Strontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members
Beneficial impact of a thin tunnel barrier in quantum well intermediate-band solar cell
Based on electronic quantum transport modeling, we study the transition between the intermediate-band and the conduction-band in nano-structured intermediate-band solar cell. We show that a tunnel barrier between the quantum well (QW) and the host material could improve the current. The confinement generated by such a barrier favors the inter-subband optical coupling in the QW and then changes the excitation-collection trade-off. More surprisingly, we also show that tunneling impacts the radiative recombination and then the voltage. Using a detailed balance model we explain and we propose a broadening factor for this Voc modification. Finally we show that a thin tunnel barrier is beneficial for both current and voltage
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