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 Excitonic lasing of strainfree InP(As) quantum dots in AlInAs microdisk (2017.03.20)
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 Optimal working conditions for thermoelectric generators with realistic thermal coupling (3739)
 Analytic model of effective screened Coulomb interactions in a multilayer system (3386)
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 Why the Speed of Light is not a Constant (2126)
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Bunching of numbers in a nonideal roulette: the key to winning strategies
 Uploaded:
 20.01.16
 Modified:
 20.01.16
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 2 MB
A. V. Kavokin, A. S. Sheremet and M. Yu. Petrov
Chances of a gambler are always lower than chances of a casino in the case of an ideal, mathematically perfect roulette, if the capital of the gambler is limited and the minimum and maximum allowed bets are limited by the casino. However, a realistic roulette is not ideal: the probabilities of realisation of different numbers slightly deviate. Describing this deviation by a statistical distribution with a width δ we find a critical δ that equalizes chances of gambler and casino in the case of a simple strategy of the game: the gambler always puts equal bets to the last N numbers. For upcritical δ the expected return of the roulette becomes positive. We show that the dramatic increase of gambler's chances is a manifestation of bunching of numbers in a nonideal roulette. We also estimate the critical starting capital needed to ensure the low risk game for an indefinite time.

From local forceflux relationships to internal dissipations and their impact on heat engine performance: The illustrative case of a thermoelectric generator
 Uploaded:
 04.09.13
 Modified:
 04.09.13
 File Size:
 269 KB
Y. Apertet, H. Ouerdane, C. Goupil and Ph. Lecoeur
We present an indepth analysis of the sometimes understated role of the principle of energy conservation in linear irreversible thermodynamics. Our case study is that of a thermoelectric generator (TEG), which is a heat engine of choice in irreversible thermodynamics, owing to the coupling between the electrical and heat fluxes. We show why Onsager’s reciprocal relations must be considered locally and how internal dissipative processes emerge from the extension of these relations to a global scale: The linear behavior of a heat engine at the local scale is associated with a dissipation process that must partake in the global energy balance. We discuss the consequences of internal dissipations on the socalled efficiency at maximum power, in the light of our comparative analyses of exoreversibility and endoreversibility on the one hand and of two classes of heat engines, autonomous and periodically driven, on the other hand. Finally, basing our analysis on energy conservation, we also discuss recent works which claim the possibility to overcome the traditional boundaries on efficiency imposed by finitetime thermodynamics in thermoelectric systems with broken timereversal symmetry; this we do by introducing a “thermal” thermopower and an “electrical” thermopower which permits an analysis of the thermoelectric response of the TEG considering a possible dissymmetry between the electrical/thermal and the thermal/electrical couplings.

On the efficiency at maximum cooling power
 Uploaded:
 04.09.13
 Modified:
 04.09.13
 File Size:
 424 KB
Y. Apertet, H. Ouerdane, A. Michot, C. Goupil and Ph. Lecoeur
The efficiency at maximum power (EMP) of heat engines operating as generators is one corner stone of finitetime thermodynamics, the CurzonAhlborn efficiency ηCA being considered as a universal upper bound. Yet, no valid counterpart to ηCA has been derived for the efficiency at maximum cooling power (EMCP) for heat engines operating as refrigerators. In this letter we analyse the reasons of the failure to obtain such a bound and we demonstrate that, despite the introduction of several optimisation criteria, the maximum cooling power condition should be considered as the genuine equivalent of maximum power condition in the finitetime thermodynamics frame. We then propose and discuss an analytic expression for the EMCP in the specific case of exoreversible refrigerators.

Why the Expansion of the Universe Appears to Accelerate
 Uploaded:
 17.06.13
 Modified:
 17.06.13
 File Size:
 685 KB
Paul Smeulders
A Speed of Light falling over time inversely proportional to the expansion of the Universe leads to an experimentally observed exponential changing of the Red Shift over time. It is necessary to redefine the Angular Impulse Momentum in order to get a consistent expansion of space on all levels. Conservation of Energy and this newly defined Angular Impulse Momentum then leads to the requirement that all clocks slow down in time inversely proportional to the Red Shift, independent of whether the Speed of Light is constant or not. From the Lorentz equation it then follows that Ex pansion occurs over spacetime and not over space alone. A steady state expansion in true time is then transformed into an exponential expansion for an observer with a local clock. A finite lifetime of the Universe is transformed to an infi nite lifetime for these observers including elementary particles. 
Mesoscopic thermoelectric transport near zero transmission energies
 Uploaded:
 22.04.13
 Modified:
 22.04.13
 File Size:
 913 KB
YA. Abbout, H. Ouerdane and C. Goupil
We study the thermoelectric transport coefficients of a onedimensional (1D) electron waveguide connected to one and then two offchannel cavities, in the presence of dephasing phonons. The model system is that of a linear chain described as a 1Dlattice. For simplicitywe consider singlemode cavities, whichmay be tunedwith external gates. While the presence of only one offchannel cavity yields a nearly symmetric transmission profile, which is canceled around the cavity mode, an additional cavity modifies this profile strongly and results in an asymmetric shape characterized by oscillations. In both cases,we consider electronphonon interactions in our calculations and analyze their effects on the transmission function around the Fermi energy. Knowledge of the energydependent transmission function allows the numerical computation of thermoelectric transport coefficients, including the thermopower. In the presence of a second offchannel cavity, the sign of the thermopower depends on the relative position of this cavity energy level with respect to the Fermi energy: the thermopower is positive when lowenergy electrons in the vicinity of the Fermi level are not transmitted and becomes negative when the higherenergy electrons are not transmitted. 
Efficiency at maximum power of thermally coupled heat engines
 Uploaded:
 07.11.12
 Modified:
 07.11.12
 File Size:
 562 KB
Y. Apertet, H. Ouerdane, C. Goupil and Ph. Lecoeur
We study the efficiency at maximum power of two coupled heat engines, using thermoelectric generators (TEGs) as engines. Assuming that the heat and electric charge fluxes in the TEGs are strongly coupled, we simulate numerically the dependence of the behavior of the global system on the electrical load resistance of each generator in order to obtain the working condition that permits maximization of the output power. It turns out that this condition is not unique.We derive a simple analytic expression giving the relation between the electrical load resistance of each generator permitting output power maximization. We then focus on the efficiency at maximum power (EMP) of the whole system to demonstrate that the CurzonAhlborn efficiency may not always be recovered: The EMP varies with the specific working conditions of each generator but remains in the range predicted by irreversible thermodynamics theory. We discuss our results in light of nonideal Carnot engine behavior. 
Irreversibilities and efficiency at maximum power of heat engines: The illustrative case of a thermoelectric generator
 Uploaded:
 07.11.12
 Modified:
 07.11.12
 File Size:
 235 KB
Y. Apertet, H. Ouerdane, C. Goupil and Ph. Lecoeur
Energy conversion efficiency at maximum output power, which embodies the essential characteristics of heat engines, is the main focus of the present work. The socalled Curzon and Ahlborn efficiency η_{CA} is commonly believed to be an absolute reference for real heat engines; however, a different but general expression for the case of stochastic heat engines, η_{SS}, was recently found and then extended to lowdissipation engines. The discrepancy between η_{CA} and η_{SS} is here analyzed considering different irreversibility sources of heat engines, of both internal and external types. To this end, we choose a thermoelectric generator operating in the strongcoupling regime as a physical system to qualitatively and quantitatively study the impact of the nature of irreversibility on the efficiency at maximum output power. In the limit of pure external dissipation, we obtain η_{CA}, while η_{SS} corresponds to the case of pure internal dissipation. A continuous transition between from one extreme to the other, which may be operated by tuning the different sources of irreversibility, also is evidenced. 
Thermoelectric internal current loops inside inhomogeneous systems
 Uploaded:
 07.11.12
 Modified:
 07.11.12
 File Size:
 140 KB
Y. Apertet, H. Ouerdane, C. Goupil and Ph. Lecoeur
Considering a system composed of two different thermoelectric modules electrically and thermally connected in parallel, we demonstrate that the inhomogeneities of the thermoelectric properties of the materials may cause the appearance of an electrical current, which develops inside the system.We show that this current increases the effective thermal conductance of the whole system.We also discuss the significance of a recent finding concerning a reported new electrothermal effect in inhomogeneous bipolar semiconductors, in light of our results. 
Optimal working conditions for thermoelectric generators with realistic thermal coupling
 Uploaded:
 07.11.12
 Modified:
 07.11.12
 File Size:
 384 KB
Y. Apertet1, H. Ouerdane, O. Glavatskaya, C. Goupil and P. Lecoeur
We study how maximum output power can be obtained from a thermoelectric generator (TEG) with nonideal heat exchangers. We demonstrate with an analytic approach based on a forceflux formalism that the sole improvement of the intrinsic characteristics of thermoelectric modules including the enhancement of the figure of merit is of limited interest: the constraints imposed by the working conditions of the TEG must be considered on the same footing. Introducing an effective thermal conductance we derive the conditions which permit maximization of both efficiency and power production of the TEG dissipatively coupled to heat reservoirs. Thermal impedance matching must be accounted for as well as electrical impedance matching in order to maximize the output power. Our calculations also show that the thermal impedance does not only depend on the thermal conductivity at zero electrical current: it also depends on the TEG figure of merit. Our analysis thus yields both electrical and thermal conditions permitting optimal use of a thermoelectric generator. 
Interactions of neutral semipermeable shells in asymmetric electrolyte solutions
 Uploaded:
 17.10.12
 Modified:
 17.10.12
 File Size:
 423 KB
Vladimir Lobaskin, Artem N. Bogdanov and Olga I. Vinogradova
We study the ionic equilibria and interactions of neutral semipermeable spherical shells immersed in electrolyte solutions, including polyions. Although the shells are uncharged, only one type of ion of the electrolyte can permeate them, thus leading to a steric charge separation in the system. This gives rise to a charge accumulation inside the shell and a build up of concentrationdependent shell potential, which converts into a disjoining pressure between the neighboring shells. These are quantified using the Poisson–Boltzmann and integral equations theories. In particular, we show that in a case of low valency electrolytes, interactions between shells are repulsive and can be sufficiently strong to stabilize the shell dispersion. In contrast, the charge correlation effects in solutions of polyvalent ions result in attractions between the shells, with can lead to their aggregation.