Is there a Jordan geometry underlying quantum physics?

There have been several propositions for a geometric and essentially non-linear formulation of quantum mechanics. From a purely mathematical point of view, the point of view of Jordan algebra theory might give new strength to such approaches: there is a ``Jordan geometry'' belonging to the Jordan part of the algebra of observables, in the same way as Lie groups belong to the Lie part. Both the Lie geometry and the Jordan geometry are well-adapted to describe certain features of quantum theory. We concentrate here on the mathematical description of the Jordan geometry and raise some questions concerning possible relations with foundational issues of quantum theory.Comment: 30 page

Residue Formulas for the Large k Asymptotics of Witten's Invariants of Seifert Manifolds. The Case of SU(2)

We derive the large k asymptotics of the surgery formula for SU(2) Witten's invariants of general Seifert manifolds. The contributions of connected components of the moduli space of flat connections are identified. The contributions of irreducible connections are presented in a residue form. This form is similar to the one used by A. Szenes, L. Jeffrey and F. Kirwan. This similarity allows us to express the contributions of irreducible connections in terms of intersection numbers on their moduli spaces.Comment: 39 pages, no figures, LaTe

Defect healing at room temperature in pentacene thin films and improved transistor performance

We report on a healing of defects at room temperature in the organic semiconductor pentacene. This peculiar effect is a direct consequence of the weak intermolecular interaction which is characteristic of organic semiconductors. Pentacene thin-film transistors were fabricated and characterized by in situ gated four-terminal measurements. Under high vacuum conditions (base pressure of order 10E-8 mbar), the device performance is found to improve with time. The effective field-effect mobility increases by as much as a factor of two and mobilities up to 0.45 cm2/Vs were achieved. In addition, the contact resistance decreases by more than an order of magnitude and there is a significant reduction in current hysteresis. Oxygen/nitrogen exposure and annealing experiments show the improvement of the electronic parameters to be driven by a thermally promoted process and not by chemical doping. In order to extract the spectral density of trap states from the transistor characteristics, we have implemented a powerful scheme which allows for a calculation of the trap densities with high accuracy in a straightforward fashion. We show the performance improvement to be due to a reduction in the density of shallow traps <0.15 eV from the valence band edge, while the energetically deeper traps are essentially unaffected. This work contributes to an understanding of the shallow traps in organic semiconductors and identifies structural point defects within the grains of the polycrystalline thin films as a major cause.Comment: 13 pages, 13 figures, to be published in Phys. Rev.

HNS/Teflon, a new heat resistant explosive

HNS/Teflon (90/10) is a new pressed explosive developed for use in the Apollo program. The major advantages of HNS/Teflon are (1) excellent thermal stability at elevated temperatures, (2) superior resistance to sublimation at high temperatures and low pressures and (3) ease of molding powder preparation, pressing and machining. The impact sensitivity of HNS/Teflon is between that of Comp B and Comp A-3 while its explosive performance is about the same as TNT. Under the severe environmental conditions of the moon's surface, this explosive successfully performed its intended function of generating seismic waves in the Apollo ALSEP and LSPE experiments. (Modified author abstract

The Band Gap in Silicon Nanocrystallites

The gap in semiconductor nanocrystallites has been extensively studied both theoretically and experimentally over the last two decades. We have compared a recent ``state-of-the-art'' theoretical calculation with a recent ``state-of-the-art'' experimental observation of the gap in Si nanocrystallite. We find that the two are in substantial disagreement, with the disagreement being more pronounced at smaller sizes. Theoretical calculations appear to over-estimate the gap. Recognizing that the experimental observations are for a distribution of crystallite sizes, we proffer a phenomenological model to reconcile the theory with the experiment. We suggest that similar considerations must dictate comparisons between the theory and experiment vis-a-vis other properties such as radiative rate, decay constant, absorption coefficient, etc.Comment: 5 pages, latex, 2 figures. (Submitted Physical Review B

Oxygen-related traps in pentacene thin films: Energetic position and implications for transistor performance

We studied the influence of oxygen on the electronic trap states in a pentacene thin film. This was done by carrying out gated four-terminal measurements on thin-film transistors as a function of temperature and without ever exposing the samples to ambient air. Photooxidation of pentacene is shown to lead to a peak of trap states centered at 0.28 eV from the mobility edge, with trap densities of the order of 10(18) cm(-3). These trap states need to be occupied at first and cause a reduction in the number of free carriers, i.e. a consistent shift of the density of free holes as a function of gate voltage. Moreover, the exposure to oxygen reduces the mobility of the charge carriers above the mobility edge. We correlate the change of these transport parameters with the change of the essential device parameters, i.e. subthreshold performance and effective field-effect mobility. This study supports the assumption of a mobility edge for charge transport, and contributes to a detailed understanding of an important degradation mechanism of organic field-effect transistors. Deep traps in an organic field-effect transistor reduce the effective field-effect mobility by reducing the number of free carriers and their mobility above the mobility edge.Comment: 13 pages, 14 figures, to be published in Phys. Rev.

Regional variation in the flexural properties of the equine hoof wall

The equine hoof wall is a hard, keratinous structure that transmits forces generated when the hoof connects the ground to the skeleton of the horse. During locomotion the hoof capsule is known to deform, resulting in an inward curvature of the dorsal wall and expansion of the heels. However, while researchers have studied the tensile and compressive properties, there is a lack of data on the flexural properties of the hoof wall in different locations around the hoof capsule. In this study, the flexural properties and hydration status of the hoof wall were investigated in two orthogonal directions, in different locations around the hoof capsule. The hoof was divided into three regions: the dorsal-most aspect (toe), the medial and lateral regions (quarters) and the heels caudally. Beams were cut both perpendicular (transverse) and parallel (longitudinal) to the orientation of the tubules. Differences in the mechanical properties were then investigated using three-point bending tests. There were considerable differences in the flexural properties around the hoof capsule; transverse beams from the heel were 45% more compliant than those from the toe region. This corresponded with changes in the hydration of the hoof wall; beams from the heel region were more hydrated (28.2 ± 0.60%) than those from the toe (24.2 ± 0.44%; P < 0.01). Regional variation in the water content is thought to help explain differences in the flexural properties. Mechanical data are further discussed in relation to variation in the structure and loading of the hoof wall

\u27Mini-interval gait\u27 switching: Understanding the positive implications of a novel training regime

The neuromechanical reorganization required to change gaits imposes an energetic cost 75% greater than either a walking or running step at the same speed. By combining walking and running with the requisite gait switching transition steps, an exercise protocol can be generated with virtually any desired metabolic output even at relatively slow treadmill speed. Gait switching increases metabolic demand through discrete events, which can be tolerated more easily by individuals recovering from health problems, just as interval training allows greater work production for healthy individuals. In addition to cardio-respiratory benefits, ‘mini-intervals’ with frequent gait switching also provides positive effects and attributes such as distributing muscle group activation, re-training neural coordination, and avoiding repetitive joint overloading. It has the added benefit of developing stability during transitions while a safety hand rail is present which can lead to greater stability in more complex natural environments. Finally, increased mental focus may help avoid the monotony of usual treadmill workouts, aiding adherence to an exercise program. We review evidence for the cost increase of the gait transition step and explain the mechanisms involved. We also discuss literature supporting the range of benefits for mini-interval gait switching as a training and rehabilitation tool

Historical experiences: A framework for encountering complex historical sources

We encounter information about the past in everyday life through films, books and complex historical sources – such as historic sites or eyewitness accounts. Investigations of how visitors and learners engage with these complex historical sources have mainly focused on the ‘something special’ of the encounter on the one hand and on the clear cognitive engagement on the other. Yet, we know little about what and how learners and visitors learn from these complex historical sources and the resultant historical experiences. However, it is an important precondition for further theoretical and empirical research to fully understand these experiences. This article takes the first step in building an integrated model to understand from a situated embodied perspective the historical experiences derived from encounters with complex historical sources. Drawing on Germanand English-language literature across related disciplines, we conceptualized the experience within an interplay of cognitive, affective and physical engagement. Within these dimensions, we identified responses that indicate the different elements of the historical experience and discuss limitations and avenues for further research