Nonlinear thermoelectric response due to energy-dependent transport properties of a quantum dot

Quantum dots are useful model systems for studying quantum thermoelectric behavior because of their highly energy-dependent electron transport properties, which are tunable by electrostatic gating. As a result of this strong energy dependence, the thermoelectric response of quantum dots is expected to be nonlinear with respect to an applied thermal bias. However, until now this effect has been challenging to observe because, first, it is experimentally difficult to apply a sufficiently large thermal bias at the nanoscale and, second, it is difficult to distinguish thermal bias effects from purely temperature-dependent effects due to overall heating of a device. Here we take advantage of a novel thermal biasing technique and demonstrate a nonlinear thermoelectric response in a quantum dot which is defined in a heterostructured semiconductor nanowire. We also show that a theoretical model based on the Master equations fully explains the observed nonlinear thermoelectric response given the energy-dependent transport properties of the quantum dot.Comment: Cite as: A. Svilans, et al., Physica E (2015), http://dx.doi.org/10.1016/j.physe.2015.10.00

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

Multi-directional sorting modes in deterministic lateral displacement devices

Deterministic lateral displacement (DLD) devices separate micrometer-scale particles in solution based on their size using a laminar microfluidic flow in an array of obstacles. We investigate array geometries with rational row-shift fractions in DLD devices by use of a simple model including both advection and diffusion. Our model predicts novel multi-directional sorting modes that could be experimentally tested in high-throughput DLD devices containing obstacles that are much smaller than the separation between obstacles

Actitudes y prácticas de sexismo en los estudiantes de la escuela profesional de derecho y ciencias de la comunicación de la universidad privada Antenor Orrego. 2019

Con el objetivo de explorar y analizar las actitudes y prácticas de sexismo que se presentan en los estudiantes de la Escuela Profesional de Derecho y Ciencias de la comunicación de la Universidad Privada Antenor Orrego, 2019, se realizó una investigación de tipo cualitativo diseño fenomenológico en 40 estudiantes, los cuales fueron seleccionados a través de la estrategia bola de nieve, el total de la muestra se obtuvo por saturación teórica. Se aplicó una entrevista a profundidad, la cual estuvo dividida en dos secciones: Sección I: Actitudes de sexismo en los estudiantes; Sección II: Prácticas de sexismo en los estudiantes. Los resultados encontrados en Actitudes de sexismo en los estudiantes están dirigidos más al género femenino, donde la violencia verbal, los estudiantes la manifiestan como bromas pesadas, silbidos, piropos y hasta acoso; aparentemente relacionado al estereotipo actual de la imagen de la mujer. Las prácticas de sexismo se encuentran en la discriminación por género y procedencia de lugar de origen; se manifiesta mayormente dentro de las aulas, al conformar grupos de trabajo o en el desarrollo de la sesión educativa, incluso con inclusión de participación del docente. Así mismo los estudiantes señalan que tienen más ventaja en la vida universitaria las mujeres que tienen buen aspecto físico y son bellas. Las actitudes y prácticas de sexismo que se presentan de la Escuela Profesional de Derecho y Ciencias de la comunicación están dirigidas al género femenino, con connotaciones sobre su aspecto físico; se manifiesta en silbidos, piropos, bromas pesadas; estas prácticas se desarrollan en el aula al momento de las sesiones educativas; incluso con participación del docente. .In order to explore and analyze the attitudes and practices of sexism that are presented in the students of the Professional School of Law and Communication Sciences of the Antenor Orrego Private University, 2019, a qualitative phenomenological design research was conducted in 40 Students, who were selected through the snowball strategy, the total sample was obtained by theoretical saturation. An in-depth interview was applied, which was divided into two sections: Section I: Attitudes of sexism in students; Section II: Sexism practices in students. The results found in Attitudes of sexism in students are aimed more at the female gender, where verbal violence, students manifest as heavy jokes, whistles, compliments and even bullying; apparently related to the current stereotype of the image of women. Sexism practices are found in discrimination based on gender and origin of place of origin; It is manifested mostly in the classroom, when forming work groups or in the development of the educational session, even including teacher participation. Likewise, students point out that women who have good physical appearance and are beautiful have more advantage in university life. The attitudes and practices of sexism that are presented by the Professional School of Law and Communication Sciences are aimed at women, with connotations about their physical appearance; It manifests itself in whistles, compliments, heavy jokes; These practices are developed in the classroom at the time of the educational sessions; even with teacher participation.Tesi

Consequences of late breeding on moult and recovery rate of a long-distance migrant, the Wheatear (Oenanthe oenanthe)

Unsere Studie hat am Steinschmätzer die Folgen einer verlängerten Brutzeit durch zusätzliche Spätbruten für das Zeitmanagement von Weitstreckenziehern untersucht. Wir fragten, ob der Zeitverlauf der Mauser verändert wird, ob saisonale Aktivitäten verschachtelt werden und ob die Geschlechter unterschiedlich auf spätes Brüten reagieren. Zudem erwarteten wir eine verminderte Rückkehrrate von Spätbrütern. Die Ergebnisse zeigen, dass Steinschmätzer beider Geschlechter ohne Spätbruten kurz nach dem Ausfliegen der Jungen gleichzeitig mit der Mauser beginnen, während spät brütende Steinschmätzer den Mauserbeginn verzögern. Die Verzögerung ist bei den Weibchen (23 Tage) viel ausgeprägter als bei den Männchen (6 Tage). Infolgedessen überlappten spätbrütende Männchen häufig Brut und Mauser, während die Weibchen möglicherweise vor dem Zugbeginn in Zeitdruck gerieten. Trotz des späten Mauserbeginns wechselten Spätbrüter beider Geschlechter ihr Gefieder tendenziell um etwa eine Woche langsamer und konnten somit ihre Verspätung nicht kompensieren. Obwohl zwei Bruten für den Steinschmätzer sicher eine höhere Belastung darstellen, zeigten die Rückkehrraten keine Benachteiligung auf. Unabhängig von Alter, Geschlecht und Anzahl der Bruten lag die Rate im Populationsmittel bei 23,5 %. Vermutlich ziehen nur Steinschmätzer in ausgezeichneter körperlicher Verfassung Spätbruten auf und gleichen die zusätzliche Belastung aus.The present study investigates consequences of late breeding for the seasonal time management of long-distance migrants, as exemplified by the Wheatear. We examined whether the time course of moult was changed, whether seasonal activities were overlapped, and whether the sexes differed in the ways they modified seasonal behaviour when breeding late. Furthermore, we expected that late breeders would incur a cost of additional late breeding by reduced return rates. The results of the study showed that in Wheatears without late clutches both sexes initiated moult simultaneously soon after fledging of the clutch. Late breeders, in contrast, delayed moult onset. The delay was much more pronounced in females (23 days) than males (6 days). As a consequence, late breeding males but not females frequently overlapped breeding and moult, while females may have incurred time pressure to finish moult in time for migration. Despite the late onset of moult, its duration was extended by approximately one week, and therefore, late breeders did not compensate for their seasonal delay. Yet although double clutches are most likely to be demanding, late-breeding Wheatears showed no signs of decreased, but instead, tentatively elevated return rates. Return rates were independent of age, sex, and number of clutches and averaged 23.5 %. We propose that only Wheatears in excellent physical condition initiate additional late clutches and are able to compensate for any arising costs

A novel vacuum ultra violet lamp for metastable rare gas experiments

We report on a new design of a vacuum ultra violet (VUV) lamp for direct optical excitation of high laying atomic states e.g. for excitation of metastable rare gas atoms. The lamp can be directly mounted to ultra high vacuum vessels (p <= 10^(-10) mbar). It is driven by a 2.45 GHz microwave source. For optimum operation it requires powers of approximately 20 W. The VUV light is transmitted through a magnesium fluoride window, which is known to have a decreasing transmittance for VUV photons with time. In our special setup, after a run-time of the VUV lamp of 550 h the detected signal continuously decreased to 25 % of its initial value. This corresponds to a lifetime increase of two orders of magnitude compared to previous setups or commercial lamps