A quantum-dot heat engine operating close to the thermodynamic efficiency limits

Cyclical heat engines are a paradigm of classical thermodynamics, but are impractical for miniaturization because they rely on moving parts. A more recent concept is particle-exchange (PE) heat engines, which uses energy filtering to control a thermally driven particle flow between two heat reservoirs. As they do not require moving parts and can be realized in solid-state materials, they are suitable for low-power applications and miniaturization. It was predicted that PE engines could reach the same thermodynamically ideal efficiency limits as those accessible to cyclical engines, but this prediction has not been verified experimentally. Here, we demonstrate a PE heat engine based on a quantum dot (QD) embedded into a semiconductor nanowire. We directly measure the engine's steady-state electric power output and combine it with the calculated electronic heat flow to determine the electronic efficiency $\eta$. We find that at the maximum power conditions, $\eta$ is in agreement with the Curzon-Ahlborn efficiency and that the overall maximum $\eta$ is in excess of 70$\%$ of the Carnot efficiency while maintaining a finite power output. Our results demonstrate that thermoelectric power conversion can, in principle, be achieved close to the thermodynamic limits, with direct relevance for future hot-carrier photovoltaics, on-chip coolers or energy harvesters for quantum technologies

Single-electron transport in InAs nanowire quantum dots formed by crystal phase engineering

We report electrical characterization of quantum dots formed by introducing pairs of thin wurtzite (WZ) segments in zinc blende (ZB) InAs nanowires. Regular Coulomb oscillations are observed over a wide gate voltage span, indicating that WZ segments create significant barriers for electron transport. We find a direct correlation of transport properties with quantum dot length and corresponding growth time of the enclosed ZB segment. The correlation is made possible by using a method to extract lengths of nanowire crystal phase segments directly from scanning electron microscopy images, and with support from transmission electron microscope images of typical nanowires. From experiments on controlled filling of nearly empty dots with electrons, up to the point where Coulomb oscillations can no longer be resolved, we estimate a lower bound for the ZB-WZ conduction-band offset of 95 meV.Comment: 9 pages 9 figure

Electron-hole interactions in coupled InAs-GaSb quantum dots based on nanowire crystal phase templates

We report growth and characterization of a coupled quantum dot structure that utilizes nanowire templates for selective epitaxy of radial heterostructures. The starting point is a zinc blende InAs nanowire with thin segments of wurtzite structure. These segments have dual roles: they act as tunnel barriers for electron transport in the InAs core, and they also locally suppress growth of a GaSb shell, resulting in coaxial InAs-GaSb quantum dots with integrated electrical probes. The parallel quantum dot structure hosts spatially separated electrons and holes that interact due to the type-II broken gap of InAs-GaSb heterojunctions. The Coulomb blockade in the electron and hole transport is studied, and periodic interactions of electrons and holes are observed and can be reproduced by modeling. Distorted Coulomb diamonds indicate voltage-induced ground-state transitions, possibly a result of changes in the spatial distribution of holes in the thin GaSb shell.Comment: 8 pages, 7 figure

Spectroscopy and level detuning of few-electron spin states in parallel InAs quantum dots

We use tunneling spectroscopy to study the evolution of few-electron spin states in parallel InAs nanowire double quantum dots (QDs) as a function of level detuning and applied magnetic field. Compared to the much more studied serial configuration, parallel coupling of the QDs to source and drain greatly expands the probing range of excited state transport. Owing to a strong confinement, we can here isolate transport involving only the very first interacting single QD orbital pair. For the (2,0)-(1,1) charge transition, with relevance for spin-based qubits, we investigate the excited (1,1) triplet, and hybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits the (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet, we clearly resolve transport through all triplet states near the avoided singlet-triplet crossings. Transport calculations, based on a simple model with one orbital on each QD, fully replicate the experimental data. Finally, we observe an expected mirrored symmetry between the 1-2 and 2-3 electron transitions resulting from the two-fold spin degeneracy of the orbitals.Comment: 17 pages, 8 figure

Electrical control of spins and giant g-factors in ring-like coupled quantum dots

Emerging theoretical concepts for quantum technologies have driven a continuous search for structures where a quantum state, such as spin, can be manipulated efficiently. Central to many concepts is the ability to control a system by electric and magnetic fields, relying on strong spin-orbit interaction and a large g-factor. Here, we present a new mechanism for spin and orbital manipulation using small electric and magnetic fields. By hybridizing specific quantum dot states at two points inside InAs nanowires, nearly perfect quantum rings form. Large and highly anisotropic effective g-factors are observed, explained by a strong orbital contribution. Importantly, we find that the orbital and spin-orbital contributions can be efficiently quenched by simply detuning the individual quantum dot levels with an electric field. In this way, we demonstrate not only control of the effective g-factor from 80 to almost 0 for the same charge state, but also electrostatic change of the ground state spin

Development of Scale-down system for perfusion precesses

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Increasing integrative negotiation in European organizations through trustworthiness and trust

Integrative negotiation in which employers and employees create value is a major necessity in the current challenging context. Collective labor negotiations in organizations are traditionally focused on mostly distributive issues, such as pay, working hours, and holidays. However, the current situation demands the inclusion of other issues of a potentially more integrative nature, such as telework, sustainability, and risk prevention, the enhancement of which is a major challenge for organizations. In this study, we explore the negotiation process between management and employee representatives (ERs), analyzing the roles of trust and trustworthiness. We collected data from 614 human resources managers from different organizations in 11 European countries. The results confirm that ERs who management perceive to be trustworthy have a greater influence on negotiation, particularly with regard to integrative as opposed to distributive issues, and that trust partially mediates this relationship

Thermoelectric characterization of the Kondo resonance in nanowire quantum dots

We experimentally verify hitherto untested theoretical predictions about the thermoelectric properties of Kondo correlated quantum dots (QDs). The specific conditions required for this study are obtained by using QDs epitaxially grown in nanowires, combined with a recently developed method for controlling and measuring temperature differences at the nanoscale. This makes it possible to obtain data of very high quality both below and above the Kondo temperature, and allows a quantitative comparison with theoretical predictions. Specifically, we verify that Kondo correlations can induce a polarity change of the thermoelectric current, which can be reversed either by increasing the temperature or by applying a magnetic field

La mediación: una herramienta de gestión constructiva del conflicto en el lugar de trabajo

Mediation becomes relevant nowadays as a way to manage conflicts in the workplace in a nonjudicial way, preventing costly, extensive, and unsatisfying legal procedures. This study tries to systematize the more recent research about mediation, showing the main challenges, questions, and findings. Research suggests the importance of integrating the organizational and societal context in the study of mediation, the use of efficiency, equity, and voice objectives for evaluating mediation effectiveness, and taking into account a contingency approach in mediator strategies. There is an important gap between the large development of professional practice in mediation and the few systematic studies on this topic. This paper offers a model that considers current research and practice for mediation effectiveness. This model could be used to focus the orientation of scholars, practitioners, and governments in search of new developments in the design of mediation. Future research could explore specific combinations of these dimensions to analyze sectors, organizations, or cases of mediation.La mediación está adquiriendo relevancia hoy en día como una forma extrajudicial de gestionar los conflictos, evitando procedimientos legales costosos, largos e insatisfactorios. Este estudio trata de sistematizar la investigación más reciente sobre la mediación, mostrando los principales retos, cuestiones y conclusiones. La investigación sugiere la importancia de integrar el contexto organizativo y social en el estudio de la mediación, el uso de objetivos de eficiencia, equidad y voz para evaluar la eficacia de la mediación y tener en cuenta un enfoque contingente en las estrategias de las personas mediadoras. Existe una importante brecha entre el gran desarrollo de la práctica profesional de la mediación y la escasez de estudios sistemáticos sobre este tema. Este artículo ofrece un modelo que tiene en cuenta tanto la investigación como el ejercicio práctico para entender cómo se producen las mediaciones eficaces. Este modelo podría utilizarse para orientar a la academia, el ejercicio profesional y a los gobiernos en la búsqueda de nuevos desarrollos en el diseño de la mediación. Las investigaciones futuras podrían explorar combinaciones específicas de estas dimensiones para analizar sectores, organizaciones o casos de mediación

Multidimensional engineering of Chymosin for efficient cheese production by machine learning guided directed evolution

The global cheese market today exceeds $100B/year. Chymosin (a.k.a. rennin) is an aspartic endopeptidase produced by the stomach lining of new-born mammals. During cheese production chymosin is added to the milk where it cleaves the glycomacropeptide (GMP) from the surface of casein micelles to initiate milk coagulation. Current commercial recombinant chymosin enzymes derived from Bos taurus (cow) or Camelus dromedarius (camel) are limited in their proteolytic specificity leading to incomplete milk-to-cheese conversion. Increasing the chymosin specificity for GMP cleavage would significantly decrease the amount of milk needed for cheese production thereby reducing cost and decreasing environmental footprint of the dairy industry. Separate from milk coagulation, chymosin dependent release of N-terminal peptides from alphaS1 casein during cheese ripening leads to unwanted softening, accompanied with cheese loss during industrial processing such as slicing and shredding. Furthermore, chymosin dependent cleavage of the C-terminal end of beta casein contributes to unwanted bitterness of the cheese. Improvement of chymosin proteolytic specificity in both milk coagulation and cheese ripening is consequently of high commercial relevance. Please click Additional Files below to see the full abstract