Hybrid Quantum Dot-2D Electron Gas Devices for Coherent Optoelectronics

We present an inverted GaAs 2D electron gas with self-assembled InAs quantum dots in close proximity, with the goal of combining quantum transport with quantum optics experiments. We have grown and characterized several wafers -- using transport, AFM and optics -- finding narrow-linewidth optical dots and high-mobility, single subband 2D gases. Despite being buried 500 nm below the surface, the dots are clearly visible on AFM scans, allowing precise localization and paving the way towards a hybrid quantum system integrating optical dots with surface gate-defined nanostructures in the 2D gas.Comment: 4 pages, 5 figures (color

A scalable optical detection scheme for matter wave interferometry

Imaging of surface adsorbed molecules is investigated as a novel detection method for matter wave interferometry with fluorescent particles. Mechanically magnified fluorescence imaging turns out to be an excellent tool for recording quantum interference patterns. It has a good sensitivity and yields patterns of high visibility. The spatial resolution of this technique is only determined by the Talbot gratings and can exceed the optical resolution limit by an order of magnitude. A unique advantage of this approach is its scalability: for certain classes of nano-sized objects, the detection sensitivity will even increase significantly with increasing size of the particle.Comment: 10 pages, 4 figure

Structural and magnetic properties of Fe/ZnSe(001) interfaces

We have performed first principles electronic structure calculations to investigate the structural and magnetic properties of Fe/ZnSe(001) interfaces. Calculations involving full geometry optimizations have been carried out for a broad range of thickness of Fe layers(0.5 monolayer to 10 monolayers) on top of a ZnSe(001) substrate. Both Zn and Se terminated interfaces have been explored. Total energy calculations show that Se segregates at the surface which is in agreement with recent experiments. For both Zn and Se terminations, the interface Fe magnetic moments are higher than the bulk bcc Fe moment. We have also investigated the effect of adding Fe atoms on top of a reconstructed ZnSe surface to explore the role of reconstruction of semiconductor surfaces in determining properties of metal-semiconductor interfaces. Fe breaks the Se dimer bond formed for a Se-rich (2x1) reconstructed surface. Finally, we looked at the reverse growth i.e. growth of Zn and Se atoms on a bcc Fe(001) substrate to investigate the properties of the second interface of a magnetotunnel junction. The results are in good agreement with the theoretical and experimental results, wherever available.Comment: 7 pages, 8 figures, accepted for publication in PR

Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors

We measured the single-photon detection efficiency of NbN superconducting single photon detectors as a function of the polarization state of the incident light for different wavelengths in the range from 488 nm to 1550 nm. The polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good agreement with numerical calculations. We use an optical-impedance model to describe the absorption for polarization parallel to the wires of the detector. For lossy NbN films, the absorption can be kept constant by keeping the product of layer thickness and filling factor constant. As a consequence, we find that the maximum possible absorption is independent of filling factor. By illuminating the detector through the substrate, an absorption efficiency of ~70% can be reached for a detector on Si or GaAs, without the need for an optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic

Numerical study of the strongly screened vortex glass model in an external field

The vortex glass model for a disordered high-T_c superconductor in an external magnetic field is studied in the strong screening limit. With exact ground state (i.e. T=0) calculations we show that 1) the ground state of the vortex configuration varies drastically with infinitesimal variations of the strength of the external field, 2) the minimum energy of global excitation loops of length scale L do not depend on the strength of the external field, however 3) the excitation loops themself depend sensibly on the field. From 2) we infer the absence of a true superconducting state at any finite temperature independent of the external field.Comment: 6 pages RevTeX, 5 eps-figures include

Comparison of the scintillation noise above different observatories measured with MASS instruments

Scintillation noise is a major limitation of ground base photometric precision. An extensive dataset of stellar scintillation collected at 11 astronomical sites world-wide with MASS instruments was used to estimate the scintillation noise of large telescopes in the case of fast photometry and traditional long-exposure regime. Statistical distributions of the corresponding parameters are given. The scintillation noise is mostly determined by turbulence and wind in the upper atmosphere and comparable at all sites, with slightly smaller values at Mauna Kea and largest noise at Tolonchar in Chile. We show that the classical Young's formula under-estimates the scintillation noise.The temporal variations of the scintillation noise are also similar at all sites, showing short-term variability at time scales of 1 -- 2 hours and slower variations, including marked seasonal trends (stronger scintillation and less clear sky during local winter). Some correlation was found between nearby observatories.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 11 figure

Adaption eines elektronischen Laborbuchs (Elab) an ein objektorientiertes Datenbank-Management-System

Das Elektronische Laborbuch Elab ist ein Softwarewerkzeug zur Unterstützung der Entwicklung von Herstellungsprozessen von Mikrosystemen. Es dient der Darstellung und dem Modifizieren von Prozessen und Prozeßreihen. Dabei wird auch die Variantenbildung unterstützt. Elab ist ein objektorientiert aufgebautes System. Mehrbenutzerbetrieb, Zugriffsberechtigungen und Versionsverwaltung machen die Anbindung an ein objektorientiertes Datenbank-Management-System erforderlich. Aus diesem Grund wurde das Datenbanksystem ObjectStore mit Sprachanbindung zu Smalltalk (OSST) ausgewählt. Der parallele Zugriff von verschiedenen Applikationen auf den persistenten Datenbestand erfordert spezielle Sperrmechanismen auf der Grundlage einfacherer Mechanismen der ObjectStore Datenbanken. Durch die Implementierung von semantischen Sperren kann objektweises Sperren erreicht werden. Im Mehrbenutzerbetrieb gehören die Benutzer bestimmten Projektgruppen an, die nur Zugriff auf die Daten ihres Projekts haben. Ein Superuser übernimmt die Aufgaben der Benutzerverwaltung

‘Midwives Overboard!’ Inside their hearts are breaking, their makeup may be flaking but their smile still stays on

PROBLEM: Midwifery practice is emotional and, at times, traumatic work. Cumulative exposure to this, in an unsupportive environment can result in the development of psychological and behavioural symptoms of distress. BACKGROUND: As there is a clear link between the wellbeing of staff and the quality of patient care, the issue of midwife wellbeing is gathering significant attention. Despite this, it can be rare to find a midwife who will publically admit to how much they are struggling. They soldier on, often in silence. AIM: This paper aims to present a narrative review of the literature in relation to work-related psychological distress in midwifery populations. Opportunities for change are presented with the intention of generating further conversations within the academic and healthcare communities. METHODS: A narrative literature review was conducted. FINDINGS: Internationally, midwives experience various types of work-related psychological distress. These include both organisational and occupational sources of stress. DISCUSSION: Dysfunctional working cultures and inadequate support are not conducive to safe patient care or the sustained progressive development of the midwifery profession. New research, revised international strategies and new evidence based interventions of support are required to support midwives in psychological distress. This will in turn maximise patient, public and staff safety. CONCLUSIONS: Ethically, midwives are entitled to a psychologically safe professional journey. This paper offers the principal conclusion that when maternity services invest in the mental health and wellbeing of midwives, they may reap the rewards of improved patient care, improved staff experience and safer maternity services

Autoinducers act as biological timers in Vibrio harveyi

Quorum sensing regulates cell density-dependent phenotypes and involves the synthesis, excretion and detection of so-called autoinducers. Vibrio harveyi strain ATCC BAA-1116 (recently reclassified as Vibrio campbellii), one of the best-characterized model organisms for the study of quorum sensing, produces and responds to three autoinducers. HAI-1, AI-2 and CAI-1 are recognized by different receptors, but all information is channeled into the same signaling cascade, which controls a specific set of genes. Here we examine temporal variations of availability and concentration of the three autoinducers in V. harveyi, and monitor the phenotypes they regulate, from the early exponential to the stationary growth phase in liquid culture. Specifically, the exponential growth phase is characterized by an increase in AI-2 and the induction of bioluminescence, while HAI-1 and CAI-1 are undetectable prior to the late exponential growth phase. CAI-1 activity reaches its maximum upon entry into stationary phase, while molar concentrations of AI-2 and HAI-1 become approximately equal. Similarly, autoinducer-dependent exoproteolytic activity increases at the transition into stationary phase. These findings are reflected in temporal alterations in expression of the luxR gene that encodes the master regulator LuxR, and of four autoinducer-regulated genes during growth. Moreover, in vitro phosphorylation assays reveal a tight correlation between the HAI-1/AI-2 ratio as input and levels of receptor-mediated phosphorylation of LuxU as output. Our study supports a model in which the combinations of autoinducers available, rather than cell density per se, determine the timing of various processes in V. harveyi populations

A Social Service Measurement Model

The development and implementation of a measurement model for a system of social service agenci.es is discussed. The system, the Jewish Community Federation of Cleveland, is a voluntary association of a full range of human service agencies. Design and workings of the project team, analysis and structuring of the organizational system, and overall goals of the research are first presented. The measurement model itself is then delineated. Essentially, the model is a device for assembling and synthesizing information on system throughput, priorities, and indicators of quality of service. Finally, the information system which supports the model is examined and other issues relating to implementation are discussed. [Likely published circa 1972.