Results 1 - 10 of 600
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[en] We show how Cooper-pair-assisted transport, which describes the stimulated transport of electrons in the presence of Cooper-pairs, can be engineered and controlled with cold atoms, in regimes that are difficult to access for condensed matter systems. Our model is a channel connecting two cold atomic gases, and the mechanism to generate such a transport relies on the coupling of the channel to a molecular BEC, with diatomic molecules of fermionic atoms. Our results are obtained using a Floquet–Redfield master equation that accounts for an exact treatment of the interaction between atoms in the channel. We explore, in particular, the impact of the coupling to the BEC and the interaction between atoms in the junction on its transport properties, revealing non-trivial dependence of the produced particle current. We also study the effects of finite temperatures of the reservoirs and the robustness of the current against additional dissipation acting on the junction. Our work is experimentally relevant and has potential applications to dissipation engineering of transport with cold atoms, studies of thermoelectric effects, quantum heat engines, or Floquet Majorana fermions. (paper)
[en] Highlights: • The thermoelectric quantities perform the sensitivity to the inter-dot coupling strength. • Double Fano resonances can be created to largely enhance the thermoelectric effect at low-temperature. • Thermoelectric figure of merit can be improved due to the coexistence of local bipolar effect and Fano resonance. • Thermoelectric figure of merit can be optimized by adjusting the dot-lead coupling strengths. - Abstract: The thermoelectric transport properties of a parallel-coupled double quantum dot (PCDQD) system with side-coupled quantum dots (QDs) is investigated by using the Keldysh non-equilibrium Green's function technique. The thermoelectric quantities, including the thermal conductance, thermopower, and thermoelectric figure of merit denoted by ZT, are sensitive to the inter-dot coupling strength. With the help of side-coupled QD, unusual double Fano resonances are created in the conductance spectra to largely enhance the thermoelectric effect at low-temperature. Benefited from the coexistence of local bipolar effect and Fano resonance, the ZT can be improved by one-fold higher than that of original PCDQD system. Moreover, when the asymmetry parameter α, which indicates the geometric arrangement of coupled QDs with a given lead, takes appropriate value, the optimization of ZT can be achieved at high temperature. Our work suggests that the side-coupled QDs scheme holds promise for the designing of high-efficiency thermoelectric conversion devices.
[en] We investigate charge and energy transport in a three-terminal quantum Hall conductor. The peculiar properties of chiral propagation along the edges of the sample have important consequences on the response to thermal biases. Based on the separation of charge and heat flows, thermoelectric conversion and heat rectification can be manipulated by tuning the scattering at gate-modulated constrictions. Chiral motion in a magnetic field allows for a different behavior of left- and right-moving carriers giving rise to thermal rectification by redirecting the heat flows. We propose our system both as an efficient heat-to-work converter and as a heat diode. (paper)
[en] This article analyzes the financial impact of distributed energy resources (DERs) owned and operated by commercial customers on the load serving entities (LSEs). DERs reduce the customers' electricity bills and hence the revenues collected by their LSE. However, changes in customer demand profiles can potentially reduce the aggregated system demand profile, and therefore, reduce the LSE's costs in wholesale markets. Analysis of these financial impacts indicates that the LSE's lost revenue ultimately outweighs its reduced expenses. This is largely due to a significant reduction in revenue from demand charges. Dispatchable DERs, including energy storages and demand response, result in more financial losses for LSEs than photovoltaics. The financial losses LSEs face indicate that redesigning commercial customer tariffs is necessary in order for LSEs to accommodate customer owned DERs properly. Several suggestions on modifying commercial tariffs are presented. - Highlights: • We analyze the financial impacts on load serving entities of DERs owned by commercial customers. • Under the selected commercial tariff, load serving entities suffer economic losses. • Energy storages and demand response results in more financial losses for LSE than photovoltaics. • We provide some suggestions for tariff modifications.
[en] The paper is devoted to the analysis of calibration results of thermoelectric voltage converter obtained by five participants of interlaboratory comparisons which ended in 2017. The analysis is accented on several aspects that led to inadequate deviation of results from the expected values. The attention is focused on the reasons for overestimation of measurement uncertainty reported by one of laboratories and the exceeding of the permissible value of criterion for assessing the competence of another laboratory at one observation point. Two variants of measurement schemes which were used by participants, are analyzed, main uncertainty sources are determined, uncertainty budgets are drawn up. The measurement model for a non-standardized measurement set-up is proposed, taking into account the drift of input and output signals. The logical conclusion of analysis is ascertainment of non-compliance with ISO/IEC 17025 recommendations and sufficient level lack of methodological support for these calibration laboratories. (author)
[en] The near field heat transfer between two finite size one-dimensional photonic crystals separated by a small vacuum gap and maintained in nonequilibrium thermal situation is theoretically investigated. The main features of this electromagnetic transfer are discussed and compared with what is generally observed with media that support surface polaritons. It is shown that the presence of surface Bloch waves can significantly enhance heat transfers beyond the far field limit for both polarization states of electromagnetic field at subwavelength separation distances. A specific attention is addressed to the consequence of the slopes of surface Bloch waves dispersion curves on the heat transfer. In particular, it is shown that the localization of surface Bloch waves close to the light line allows to observe a transfer exaltaion at larger separation distances than the Wien wavelength. These results could open new possibilities for the development of innovative near-field technologies such as near-field thermophotovoltaic conversion, plasmon assisted nanophotolitography or near-field spectroscopy.
[en] The close relationship between noise and thermoelectric conversion is studied in a quantum dot using a quantum approach based on the non-equilibrium Green function technique. We show that both the figure of merit and the efficiency can be written in term of noise and we highlight the central role played by the correlator between the charge current and the heat current that we call the mixed noise . After giving the expression of this quantity as an integral over energy, we calculate it, first in the linear response regime, next in the limit of small transmission through the barriers (Schottky regime) and finally in the intermediate regime. We discuss the notion of efficiency fluctuations and we also see here that the mixed noise comes into play. (special issue on unsolved problems of noise in physics, biology and technology)
[en] Thermal converters show significant ac–dc transfer differences at low frequencies due to nonlinearities of the heat transport mechanism and of the thermal-to-electric conversion. It is assumed that the ac–dc transfer differences at low frequencies are proportional to the input power. We have proved this assumption by an independent method with sampling techniques. A novel approach based on sine-wave fitting is used to calculate the RMS value of the sampled signal from the samples. It makes use of the low noise in a metrological environment. Expanded uncertainties in the order of 1.2 μV/V have been achieved. (paper)
[en] We examine the effective properties of a thermoelectric material in the vicinity of an arbitrarily shaped hole. Using complex variable methods, we establish closed-form representations of the electric and thermal fields in the matrix surrounding the hole. Specifically, we analyze the effective material parameters of a rectangular thermoelectric region containing an insulated macroscopic hole and determine that the effective electric and thermal conductivities depend strongly on the size and shape of the hole while the effective Seebeck coefficient always remains equal to that of the surrounding matrix. Perhaps most significantly, we conclude that since an insulated hole has almost the same effect on both the effective electric and thermal conductivities, its introduction does not affect the effective thermoelectric figure of merit in most thermoelectric materials. Consequently, we can conclude that, for the most part, an arbitrarily shaped hole can be inserted into a thermoelectric material without decreasing its maximum thermoelectric conversion efficiency. Our findings provide an important theoretical basis for the future design and development of thermoelectric devices.
[en] Highlights: • A new method for quick calculation of TEG length and cross-section is proposed. • There exist different optimal lengths and areas with different thermal boundaries. • Different combinations of lengths and areas can lead to same maximum power. • This method is approved to be accurate and time-efficient. - Abstract: A comprehensive mathematical model is proposed to calculate the optimal leg length and cross-section area of TEG unit to maximize the peak output power. The model shows that for a TEG unit, there exists an optimal ratio of leg length and leg cross-section area corresponding to the maximum peak output power with a convective thermal boundary condition, and the optimal leg length and cross-section area can be further calculated based on the optimal ratio. The mathematical model is also validated in this paper, and the corresponding error is within a reasonable range. Moreover, the effects of the leg length and leg area on the peak output power, the peak output power density and the efficiency of TEG unit with different thermal boundary conditions are also discussed. This study will provide guidance for the structure design optimization of TEG unit.