Semiclassical transport in nearly symmetric quantum dots. I. Symmetry breaking in the dot

We apply the semiclassical theory of transport to quantum dots with exact and approximate spatial symmetries; left-right mirror symmetry, up-down mirror symmetry, inversion symmetry, or fourfold symmetry. In this work—the first of a pair of articles—we consider (a) perfectly symmetric dots and (b) nearly symmetric dots in which the symmetry is broken by the dot's internal dynamics. The second article addresses symmetry-breaking by displacement of the leads. Using semiclassics, we identify the origin of the symmetry-induced interference effects that contribute to weak localization corrections and universal conductance fluctuations. For perfect spatial symmetry, we recover results previously found using the random-matrix theory conjecture. We then go on to show how the results are affected by asymmetries in the dot, magnetic fields, and decoherence. In particular, the symmetry-asymmetry crossover is found to be described by a universal dependence on an asymmetry parameter gamma_asym. However, the form of this parameter is very different depending on how the dot is deformed away from spatial symmetry. Symmetry-induced interference effects are completely destroyed when the dot's boundary is globally deformed by less than an electron wavelength. In contrast, these effects are only reduced by a finite amount when a part of the dot's boundary smaller than a lead-width is deformed an arbitrarily large distance

Semiclassical transport in nearly symmetric quantum dots II: symmetry-breaking due to asymmetric leads

In this work - the second of a pair of articles - we consider transport through spatially symmetric quantum dots with leads whose widths or positions do not obey the spatial symmetry. We use the semiclassical theory of transport to find the symmetry-induced contributions to weak localization corrections and universal conductance fluctuations for dots with left-right, up-down, inversion and four-fold symmetries. We show that all these contributions are suppressed by asymmetric leads, however they remain finite whenever leads intersect with their images under the symmetry operation. For an up-down symmetric dot, this means that the contributions can be finite even if one of the leads is completely asymmetric. We find that the suppression of the contributions to universal conductance fluctuations is the square of the suppression of contributions to weak localization. Finally, we develop a random-matrix theory model which enables us to numerically confirm these results.Comment: (18pages - 9figures) This is the second of a pair of articles (v3 typos corrected - including in equations

The Broad-Band Spectrum and Infrared Variability of the Magnetar AXP 1E1048.1-5937

We present photometry of the Anomalous X-ray pulsar 1E1048.1-5937 in the infrared and optical, taken at Magellan and the VLT. The object is detected in the I, J and Ks bands under excellent conditions. We find that the source has varied greatly in its infrared brightness and present these new magnitudes. No correlation is found between the infrared flux and spin-down rate, but the infrared flux and X-ray flux may be anti-correlated. Assuming nominal reddening values, the resultant spectral energy distribution is found to be inconsistent with the only other AXP SED available (for 4U0142+61). We consider the effect of the uncertainty in the reddening to the source on its SED. We find that although both the X-ray and infrared fluxes have varied greatly for this source, the most recent flux ratio is remarkably consistent with what is is found for other AXPs. Finally, we discuss the implications of our findings in the context of the magnetar model.Comment: 21 pages, 5 eps figures. Submitted to Ap

Platform-independent Dynamic Reconfiguration of Distributed Applications

The aim of dynamic reconfiguration is to allow a system to evolve incrementally from one configuration to another at run-time, without restarting it or taking it offline. In recent years, support for transparent dynamic reconfiguration has been added to middleware platforms, shifting the complexity required to enable dynamic reconfiguration to the supporting infrastructure. These approaches to dynamic reconfiguration are mostly platform-specific and depend on particular implementation approaches suitable for particular platforms. In this paper, we propose an approach to dynamic reconfiguration of distributed applications that is suitable for application implemented on top of different platforms. This approach supports a platform-independent view of an application that profits from reconfiguration transparency. In this view, requirements on the ability to reconfigure components are expressed in an abstract manner. These requirements are then satisfied by platform-specific realizations

Model-driven Development for User-centric Well-being Support: From Dynamic Well-being Domain Models to Context-aware Applications

Applications that can use information obtained through device sensors to alter their behavior are called context-aware. Design and development of such applications is currently done by modeling the application's context or by using novel requirements engineering methods. If the application is to support the user's well-being, these methods fall short due to their technical focus. We propose a model-driven approach that deals with the specifics of the well-being domain by using a DSL that captures the user's personal well-being context. The development method is user-centric, rather than technology focused. Initial user experiments show promising results

Incorporating medical knowledge in the design process of context-aware well-being systems

The concept of self-adapting applications delivering enriched end-user services is highly promising. These context-aware applications can be seen in increasing numbers in a wide range of fields, including that of health and well-being. Using sensors to collect context data and smart reasoning algorithms to deduce higher-level information, they have the potential to adapt their behavior in real time to better suit the context at hand. However, the development process for these types of systems is challenging, as the user needs and preferences in different contexts are not easy to anticipate at design time. If services offered by the application do not align with the user needs in some situations, the user may disregard the application altogether. In order to address this challenge, we propose to use medical knowledge related to well-being in the development process of context-aware well-being systems. We believe that this approach allows for improved identification and design of effective context-aware services for well-being support

Psychophysiological correlates of peritraumatic dissociative responses in survivors of life-threatening cardiac events

The psychophysiological startle response pattern associated with peritraumatic dissociation (DISS) was studied in 103 survivors of a life-threatening cardiac event (mean age 61.0 years, SD 13.95). Mean time period since the cardiac event was 37 (79 IQD) months. All patients underwent a psychodiagnostic evaluation (including the Peritraumatic Dissociative Experiences Questionnaire) and a psychophysiological startle experience which comprised the delivery of 15 acoustic startle trials. Magnitude and habituation to trials were measured by means of electromyogram (EMG) and skin conductance responses (SCR). Thirty-two (31%) subjects were indexed as patients with a clinically significant level of DISS symptoms. High-level DISS was associated with a higher magnitude of SCR (ANOVA for repeated measures p = 0.017) and EMG (p = 0.055) and an impaired habituation (SCR slope p = 0.064; EMG slope p = 0.005) in comparison to subjects with no or low DISS. In a subgroup analysis, high-level DISS patients with severe post-traumatic stress disorder (PTSD; n = 11) in comparison to high-level DISS patients without subsequent PTSD (n = 19) exhibited higher EMG amplitudes during all trials (repeated measures analysis of variance IF = 5.511, p = 0.026). The results demonstrate exaggerated startle responses in SCR and EMG measures - an abnormal defensive response to high-intensity stimuli which indicates a steady state of increased arousal. DISS patients without PTSD exhibited balanced autonomic responses to the startle trials. DISS may, therefore, unfold malignant properties only in combination with persistent physiological hyperarousability. Copyright (C) 2002 S. Karger AG, Basel