Condensazione di Bose-Einstein in trappole ottiche

Questo lavoro di tesi si occupa dello studio del fenomeno di condensazione di Bose-Einstein sia da un punto di vista teorico che, in maniera più accennata, da quello pratico-sperimentale; risulta pertanto strutturato in due parti. La prima è incentrata sull'analisi prettamente teorico-matematica dell'argomento, e si apre con l'introduzione dell'opportuno apparato formale atto alla trattazione della statistica quantistica; a tal proposito vengono definiti gli operatori di densità. Quindi viene affrontato il problema dell'indistinguibilità degli enti quantistici e del conseguente carattere di simmetria delle funzioni d'onda, individuando così la differenza tra particelle fermioniche e bosoniche. Di queste ultime vengono largamente studiate la statistica cui essere rispondono e le loro principali caratteristiche termodinamiche. Infine, viene analizzato il caso specifico del gas ideale di Bose, trattato nei limiti del continuo e termodinamico; è nel corso di questa trattazione che emerge il fenomeno di transizione chiamato condensazione di Bose-Einstein, di cui vengono ampiamente studiate le proprietà. La seconda parte, invece, è volta all'analisi delle tecniche sperimentali utilizzate per la realizzazione della condensazione, in particolare le trappole ottiche di dipolo; dopo averne studiato le caratteristiche, vengono illustrate alcune tecniche di raffreddamento di atomi intrappolati. Il lavoro si conclude con la trattazione delle principali tecniche diagnostiche e di riconoscimento del condensato.

Quantum Einstein gravity - advancements of heat kernel-based renormalization group studies

The asymptotic safety scenario allows to define a consistent theory of quantized gravity within the framework of quantum field theory. The central conjecture of this scenario is the existence of a non-Gaussian fixed point of the theory's renormalization group flow, that allows to formulate renormalization conditions that render the theory fully predictive. Investigations of this possibility use an exact functional renormalization group equation as a primary non-perturbative tool. This equation implements Wilsonian renormalization group transformations, and is demonstrated to represent a reformulation of the functional integral approach to quantum field theory.rnAs its main result, this thesis develops an algebraic algorithm which allows to systematically construct the renormalization group flow of gauge theories as well as gravity in arbitrary expansion schemes. In particular, it uses off-diagonal heat kernel techniques to efficiently handle the non-minimal differential operators which appear due to gauge symmetries. The central virtue of the algorithm is that no additional simplifications need to be employed, opening the possibility for more systematic investigations of the emergence of non-perturbative phenomena. As a by-product several novel results on the heat kernel expansion of the Laplace operator acting on general gauge bundles are obtained.rnThe constructed algorithm is used to re-derive the renormalization group flow of gravity in the Einstein-Hilbert truncation, showing the manifest background independence of the results. The well-studied Einstein-Hilbert case is further advanced by taking the effect of a running ghost field renormalization on the gravitational coupling constants into account. A detailed numerical analysis reveals a further stabilization of the found non-Gaussian fixed point.rnFinally, the proposed algorithm is applied to the case of higher derivative gravity including all curvature squared interactions. This establishes an improvement of existing computations, taking the independent running of the Euler topological term into account. Known perturbative results are reproduced in this case from the renormalization group equation, identifying however a unique non-Gaussian fixed point.rn

Investigations on asymptotic safety of metric, tetrad and Einstein-Cartan gravity

Among the different approaches for a construction of a fundamental quantum theory of gravity the Asymptotic Safety scenario conjectures that quantum gravity can be defined within the framework of conventional quantum field theory, but only non-perturbatively. In this case its high energy behavior is controlled by a non-Gaussian fixed point of the renormalization group flow, such that its infinite cutoff limit can be taken in a well defined way. A theory of this kind is referred to as non-perturbatively renormalizable. In the last decade a considerable amount of evidence has been collected that in four dimensional metric gravity such a fixed point, suitable for the Asymptotic Safety construction, indeed exists. This thesis extends the Asymptotic Safety program of quantum gravity by three independent studies that differ in the fundamental field variables the investigated quantum theory is based on, but all exhibit a gauge group of equivalent semi-direct product structure. It allows for the first time for a direct comparison of three asymptotically safe theories of gravity constructed from different field variables. The first study investigates metric gravity coupled to SU(N) Yang-Mills theory. In particular the gravitational effects to the running of the gauge coupling are analyzed and its implications for QED and the Standard Model are discussed. The second analysis amounts to the first investigation on an asymptotically safe theory of gravity in a pure tetrad formulation. Its renormalization group flow is compared to the corresponding approximation of the metric theory and the influence of its enlarged gauge group on the UV behavior of the theory is analyzed. The third study explores Asymptotic Safety of gravity in the Einstein-Cartan setting. Here, besides the tetrad, the spin connection is considered a second fundamental field. The larger number of independent field components and the enlarged gauge group render any RG analysis of this system much more difficult than the analog metric analysis. In order to reduce the complexity of this task a novel functional renormalization group equation is proposed, that allows for an evaluation of the flow in a purely algebraic manner. As a first example of its suitability it is applied to a three dimensional truncation of the form of the Holst action, with the Newton constant, the cosmological constant and the Immirzi parameter as its running couplings. A detailed comparison of the resulting renormalization group flow to a previous study of the same system demonstrates the reliability of the new equation and suggests its use for future studies of extended truncations in this framework.

Comparison of Roadside Crash Injury Metrics using Event Data Recorders

The occupant impact velocity (OIV) and acceleration severity index (ASI) are competing measures of crash severity used to assess occupant injury risk in full-scale crash tests involving roadside safety hardware, e.g. guardrail. Delta-V, or the maximum change in vehicle velocity, is the traditional metric of crash severity for real world crashes. This study compares the ability of the OIV, ASI, and delta-V to discriminate between serious and non-serious occupant injury in real world frontal collisions. Vehicle kinematics data from event data recorders (EDRs) were matched with detailed occupant injury information for 180 real world crashes. Cumulative probability of injury risk curves were generated using binary logistic regression for belted and unbelted data subsets. By comparing the available fit statistics and performing a separate ROC curve analysis, the more computationally intensive OIV and ASI were found to offer no significant predictive advantage over the simpler delta-V.

Human Resource Performance Metrics: Methods & Processes That Demonstrate You Care

Purpose – The purpose of the present analysis is to show that HR systems are not always designed in ways that consider the well-being of employees. In particular, performance metric methods seem to be designed with organizational goals in mind while focusing less on what employees need and desire. Design/methodology/approach – A literature review and multiple case-study method was utilized. Findings – The analysis showed that performance metrics should be revaluated by executives and HR professionals if they seek to develop socially responsible organizational cultures which care about the well-being of employees. Originality/value – The paper exposes the fact that performance appraisal techniques can be rooted in methodologies that ignore or deemphasize the value of employee well-being. The analysis provides a context in which all HR practices can be questioned in relation to meeting the standards of a social justice agenda in the area of corporate social responsibility.

Closed Time-like Curves and Inertial Frame Dragging: How to Time Travel via Spacetime Rotation

As the number of solutions to the Einstein equations with realistic matter sources that admit closed time-like curves (CTC's) has grown drastically, it has provoked some authors [10] to call for a physical interpretation of these seemingly exotic curves that could possibly allow for causality violations. A first step in drafting a physical interpretation would be to understand how CTC's are created because the recent work of [16] has suggested that, to follow a CTC, observers must counter-rotate with the rotating matter, contrary to the currently accepted explanation that it is due to inertial frame dragging that CTC's are created. The exact link between inertialframe dragging and CTC's is investigated by simulating particle geodesics and the precession of gyroscopes along CTC's and backward in time oriented circular orbits in the van Stockum metric, known to have CTC's that could be traversal, so the van Stockum cylinder could be exploited as a time machine. This study of gyroscopeprecession, in the van Stockum metric, supports the theory that CTC's are produced by inertial frame dragging due to rotating spacetime metrics.

[Alban Köhler (1874-1947): Inventor of grid therapy]

Grid (or sieve) therapy ("Gitter-" oder "Siebtherapie"), spatially fractionated kilo- and megavolt X-ray therapy, was invented in 1909 by Alban Köhler, a radiologist in Wiesbaden, Germany. He tested it on several patients before 1913 using approximately 60-70kV Hittorf-Crookes tubes. Köhler pushed the X-ray tube's lead-shielded housing against a stiff grid of 1 mm-square iron wires woven 3.0-3.5mm on center, taped tightly to the skin over a thin chamois. Numerous islets unshielded by iron in the pressure-blanched skin were irradiated with up to about 6 erythema doses (ED). The skin was then thoroughly cleansed, disinfected, and bandaged; delayed punctate necrosis healed in several weeks. Although grid therapy was disparaged or ignored until the 1930s, it has been used successfully since then to shrink bulky malignancies. Also, advanced cancers in rats and mice have been mitigated or ablated using Köhler's concept since the early 1990s by unidirectional or stereotactic exposure to an array of nearly parallel microplanar (25-75μm-wide) beams of very intense, moderately hard (median energy approximately 100 keV) synchrotron-generated X rays spaced 0.1-0.4mm on center. Such beams maintain sharp edges at high doses well beneath the skin yet confer little toxicity. They could palliate some otherwise intractable malignancies, perhaps in young children too, with tolerable sequelae. There are plans for such studies in larger animals.

Augmenting Static Source Views in IDEs with Dynamic Metrics

Mainstream IDEs such as Eclipse support developers in managing software projects mainly by offering static views of the source code. Such a static perspective neglects any information about runtime behavior. However, object-oriented programs heavily rely on polymorphism and late-binding, which makes them difficult to understand just based on their static structure. Developers thus resort to debuggers or profilers to study the system's dynamics. However, the information provided by these tools is volatile and hence cannot be exploited to ease the navigation of the source space. In this paper we present an approach to augment the static source perspective with dynamic metrics such as precise runtime type information, or memory and object allocation statistics. Dynamic metrics can leverage the understanding for the behavior and structure of a system. We rely on dynamic data gathering based on aspects to analyze running Java systems. By solving concrete use cases we illustrate how dynamic metrics directly available in the IDE are useful. We also comprehensively report on the efficiency of our approach to gather dynamic metrics.

Senseo: Enriching Eclipse's Static Source Views with Dynamic Metrics

Maintaining object-oriented systems that use inheritance and polymorphism is difficult, since runtime information, such as which methods are actually invoked at a call site, is not visible in the static source code. We have implemented Senseo, an Eclipse plugin enhancing Eclipse's static source views with various dynamic metrics, such as runtime types, the number of objects created, or the amount of memory allocated in particular methods.

Mechanische Ersatzmodelle zum Nachweis der Realisierbarkeit minimaler Restbeschleunigungen während der Freifallphase im Einstein-Elevator

Der Einstein-Elevator entspricht einer deutlichen Abwandlung eines klassischen Fallturms. In Falltürmen werden wissenschaftliche Experimente unter Schwerelosigkeit durchgeführt. In großen Vakuumkammern werden dazu die Experimente, ohne das Einleiten externer Kräfte, fallengelassen. Die klassische Fallturmtechnik hat den Nachteil einer geringen Wiederholrate durch einen hohen Zeitaufwand bei der Herstellung des Vakuums. Der Einstein-Elevator schafft durch sein weltweit einzigartiges Führungs- und Antriebskonzept den Zeitaufwand für die Versuchsdurchführung drastisch zu verkürzen und die Qualität der Schwerelosigkeit zu verbessern. Um die benötigte Qualität in der Versuchsumgebung zu erzielen, wurde das Konzept mithilfe einer Mehrkörpersimulation hinsichtlich der im Experiment in der Freifallphase zu erwartenden minimalen Restbeschleunigungen untersucht.