Spin-polarized transport through weakly coupled double quantum dots in the Coulomb-blockade regime

We analyze cotunneling transport through two quantum dots in series weakly coupled to external ferromagnetic leads. In the Coulomb blockade regime the electric current flows due to third-order tunneling, while the second-order single-barrier processes have indirect impact on the current by changing the occupation probabilities of the double dot system. We predict a zero-bias maximum in the differential conductance, whose magnitude is conditioned by the value of the inter-dot Coulomb interaction. This maximum is present in both magnetic configurations of the system and results from asymmetry in cotunneling through different virtual states. Furthermore, we show that tunnel magnetoresistance exhibits a distinctively different behavior depending on temperature, being rather independent of the value of inter-dot correlation. Moreover, we find negative TMR in some range of the bias voltage.Comment: 9 pages, 7 figures, accepted in Phys. Rev.

Molecular states in carbon nanotube double quantum dots

We report electrical transport measurements through a semiconducting single-walled carbon nanotube (SWNT) with three additional top-gates. At low temperatures the system acts as a double quantum dot with large inter-dot tunnel coupling allowing for the observation of tunnel-coupled molecular states extending over the whole double-dot system. We precisely extract the tunnel coupling and identify the molecular states by the sequential-tunneling line shape of the resonances in differential conductance.Comment: 5 pages, 4 figure

Defining and controlling double quantum dots in single-walled carbon nanotubes

We report the experimental realization of double quantum dots in single-walled carbon nanotubes. The device consists of a nanotube with source and drain contact, and three additional top-gate electrodes in between. We show that, by energizing these top-gates, it is possible to locally gate a nanotube, to create a barrier, or to tune the chemical potential of a part of the nanotube. At low temperatures we find (for three different devices) that in certain ranges of top-gate voltages our device acts as a double quantum dot, evidenced by the typical honeycomb charge stability pattern.Comment: 9 pages, 3 figure

Expression of 3q oncogene SEC62 in atypical fibroxanthoma-immunohistochemical analysis of 41 cases and correlation with clinical, viral and histopathologic features

Atypical fibroxanthoma (AFX) is a rare mesenchymal tumor with predominance in older male patients located mainly in chronically UV-exposed skin. Differentiation from clinically more aggressive pleomorphic dermal sarcoma (PDS) is still under debate and immunohistochemical markers are not available yet. An immunohistochemical study, including 41 cases of AFX was conducted to investigate the expression of 3q encoded oncogene SEC62 in AFX and determine the associations with histomorphologic, clinical and viral parameters. Our cohort displayed a mean of 79.9 years at the onset of the disease. In total, 90.2% (37/41) AFXs were located in the head and neck area, whereas, four were located at the extremities (9.7%). Tumor diameter ranged between 0.06 and 40 cm2 with a mean of 5.7 cm2. SEC62 expression was markedly increased in lesional tissue compared with the adjacent healthy squamous epithelium. We found significantly higher expression of SEC62 in cases of AFX with tumor necrosis. Tendency of higher Sec62-IRS-scores were found for tumors with higher Clark levels and a tumor size >5 cm2. Sec62 is involved in endoplasmic reticulum stress tolerance and cell migration, and has been identified as a novel prognostic marker for non-small cell lung cancer as well as head and neck squamous cell carcinoma. For the first time, to the best of our knowledge, we suggest a role of 3q oncogene SEC62 in AFX and discuss a potential prognostic relevance in cases of disputable AFX with unfavorable histomorphologic features and may initiate a discussion on Sec62 serving as discriminating marker between AFX and PDS

Epidemiologie akuter Verletzungen und Überlastungsschäden im Unterwasser-Rugby

Fragestellung: Unterwasser-Rugby (UWR) ist ein anspruchsvoller Mannschaftssport; Athleten benötigen dabei ein hohes Maß an Kraft, Ausdauer, Schnelligkeit und Koordination. Intensive Zweikämpfe sind ein wesentlicher Bestandteil des Sports und können zu Verletzungen führen. Derzeit gibt es nur wenig Daten bzgl. des Auftretens von Verletzungen im UWR-Sport. Ziel der vorliegenden Studie war es daher, die Art und Häufigkeit von Verletzungen im UWR-Sport zu untersuchen. Methodik: Zwischen 11/2020 und 03/2021 wurden UWR-Athleten mittels Online-Fragebogen (SurveyMonkey) zu Trainingsgewohnheiten, Verletzungen und chronischen Beschwerden befragt. Der Fragebogen (n = 32 bis 111 Fragen, abhängig von der Anzahl zurückliegender Verletzungen) umfasste: allgemeine und gesundheitsbezogene Daten (n = 10 Fragen), Trainingsgewohnheiten (n = 15 Fragen), Informationen über chronische Beschwerden (n = 9 Fragen) und akute Verletzungen (n = 21 bis 77 Fragen). Zur Bewertung chronischer Überlastungsschäden wurde der Oslo Sports Trauma Research Centre (OSTRC) Score verwendet. Ergebnisse und Schlussfolgerung: Insgesamt wurden 161 aktive Sportler (Ø 36,1 Jahre; Ø180,7 cm, 82,7 kg; männlich: 119, weiblich 39) in die Studie aufgenommen. Das Leistungsniveau war: 1. deutsche Bundesliga: 73x, 2. Bundesliga: 46x, Landesliga: 17x, Bezirksliga: 1x, keine Liga: 24x. Das sportartspezifische Trainingspensum betrug Ø 5,6 Stunden pro Woche, darunter UWR-Training, zusätzliches Schwimmtraining (n = 71), Krafttraining (n = 70) oder Ausdauertraining (n = 102). Zurückliegende akute Verletzungen mit einer Trainingspause und/oder einem Arztbesuch wurden bei 78,8% der Athleten festgestellt. Es handelte sich dabei um Hand/Finger- (42,2%), Hand/Ohr- (Gehirnerschütterung, gerissenes Trommelfell; 18,1%), Handgelenk- (5,5%) oder Halswirbelsäulenverletzungen (5,0%). Chronische Beschwerden wurden von 42,8% der Teilnehmer angegeben, vor allem an Hand/Finger (18,8%), Schulter/Schlüsselbein (14,1%), Halswirbelsäule und Handgelenk (je 10,7%), Kopf/Gesicht (8,7%), Sprunggelenk und Knie (je 6,7%). Die vorliegende Studie an Athleten unterschiedlicher Leistungsstufen analysiert die Verteilung von Verletzungen bei UWR. Führende Verletzungsregionen sind Hand-/Fingerverletzungen, Kopf-/Ohrverletzungen, Handgelenk- und Halswirbelsäulenverletzungen. Die gewonnenen Erkenntnisse können als Grundlage für Präventionskonzepte dienen

Validity and worth in the science curriculum: learning school science outside the laboratory

It is widely acknowledged that there are problems with school science in many developed countries of the world. Such problems manifest themselves in a progressive decline in pupil enthusiasm for school science across the secondary age range and the fact that fewer students are choosing to study the physical sciences at higher levels and as careers. Responses to these developments have included proposals to reform the curriculum, pedagogy and the nature of pupil discussion in science lessons. We support such changes but argue from a consideration of the aims of science education that secondary school science is too rooted in the science laboratory; substantially greater use needs to be made of out-of-school sites for the teaching of science. Such usage should result in a school science education that is more valid and more motivating and is better at fulfilling defensible aims of school science education. Our contention is that laboratory-based school science teaching needs to be complemented by out-of-school science learning that draws on the actual world (e.g. through fieldtrips), the presented world (e.g. in science centres, botanic gardens, zoos and science museums) and the virtual worlds that are increasingly available through information and communications technologies (ICT)

Electric Field Control of Spin Transport

Spintronics is an approach to electronics in which the spin of the electrons is exploited to control the electric resistance R of devices. One basic building block is the spin-valve, which is formed if two ferromagnetic electrodes are separated by a thin tunneling barrier. In such devices, R depends on the orientation of the magnetisation of the electrodes. It is usually larger in the antiparallel than in the parallel configuration. The relative difference of R, the so-called magneto-resistance (MR), is then positive. Common devices, such as the giant magneto-resistance sensor used in reading heads of hard disks, are based on this phenomenon. The MR may become anomalous (negative), if the transmission probability of electrons through the device is spin or energy dependent. This offers a route to the realisation of gate-tunable MR devices, because transmission probabilities can readily be tuned in many devices with an electrical gate signal. Such devices have, however, been elusive so far. We report here on a pronounced gate-field controlled MR in devices made from carbon nanotubes with ferromagnetic contacts. Both the amplitude and the sign of the MR are tunable with the gate voltage in a predictable manner. We emphasise that this spin-field effect is not restricted to carbon nanotubes but constitutes a generic effect which can in principle be exploited in all resonant tunneling devices.Comment: 22 pages, 5 figure

A major electronics upgrade for the H.E.S.S. Cherenkov telescopes 1-4

The High Energy Stereoscopic System (H.E.S.S.) is an array of imaging atmospheric Cherenkov telescopes (IACTs) located in the Khomas Highland in Namibia. It consists of four 12-m telescopes (CT1-4), which started operations in 2003, and a 28-m diameter one (CT5), which was brought online in 2012. It is the only IACT system featuring telescopes of different sizes, which provides sensitivity for gamma rays across a very wide energy range, from ~30 GeV up to ~100 TeV. Since the camera electronics of CT1-4 are much older than the one of CT5, an upgrade is being carried out; first deployment was in 2015, full operation is planned for 2016. The goals of this upgrade are threefold: reducing the dead time of the cameras, improving the overall performance of the array and reducing the system failure rate related to aging. Upon completion, the upgrade will assure the continuous operation of H.E.S.S. at its full sensitivity until and possibly beyond the advent of CTA. In the design of the new components, several CTA concepts and technologies were used and are thus being evaluated in the field: The upgraded read-out electronics is based on the NECTAR readout chips; the new camera front- and back-end control subsystems are based on an FPGA and an embedded ARM computer; the communication between subsystems is based on standard Ethernet technologies. These hardware solutions offer good performance, robustness and flexibility. The design of the new cameras is reported here.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July- 6 August, 2015, The Hague, The Netherland

Double quantum dot with integrated charge sensor based on Ge/Si heterostructure nanowires

Coupled electron spins in semiconductor double quantum dots hold promise as the basis for solid-state qubits. To date, most experiments have used III-V materials, in which coherence is limited by hyperfine interactions. Ge/Si heterostructure nanowires seem ideally suited to overcome this limitation: the predominance of spin-zero nuclei suppresses the hyperfine interaction and chemical synthesis creates a clean and defect-free system with highly controllable properties. Here we present a top gate-defined double quantum dot based on Ge/Si heterostructure nanowires with fully tunable coupling between the dots and to the leads. We also demonstrate a novel approach to charge sensing in a one-dimensional nanostructure by capacitively coupling the double dot to a single dot on an adjacent nanowire. The double quantum dot and integrated charge sensor serve as an essential building block required to form a solid-state spin qubit free of nuclear spin.Comment: Related work at http://marcuslab.harvard.edu and http://cmliris.harvard.ed