965 research outputs found
Sort by
Calibrations of ROSINA-COPS and Observations at Comet 67P/Churyumov-Gerasimenko
Full text linkComets are thought to be the most pristine objects in the Solar System. Investigating comets will therefore shed light on the origin and formation of the Solar System. For this purpose the European Space Agency selected the Rosetta mission to carry out a study of the Jupiter family comet 67P/Churyumov-Gerasimenko at a close distance continuously for a period of more than two years around its closest approach to the Sun.
This work presents laboratory calibration and neutral gas coma measurements of the COmet Pressure Sensor (COPS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA). Following a brief introduction to the mission and the instrument, the data treatment principles are illustrated. Next, the laboratory calibrations to characterize COPS long term stability and to verify the data analysis methods are demonstrated. Finally, the results of COPS observations in the coma of comet 67P are shown and discussed in detail.
A few highlights are as follows: the peak total neutral gas production rate is slightly
shifted from perihelion passage and estimated to be approximately 4·1028 molecules/s;
neutral gas expansion velocities in October 2014 have been derived to be around 300 to 1200 m/s depending on illumination conditions on the surface and Rosetta’s location above the comet; though built to measure neutral gas, COPS surprisingly observed as well dust and plasma signatures.
All in all, COPS was working well throughout the Rosetta mission and has assisted to unravel a small section of the extensive puzzle about the formation of our Solar System
Physics of laser in contemporary visual arts
Full text linkIn Parallel with the latest scientific mutations and Technological developments, many contemporary artistic trends have emerged under the influence of the contemporary phase of the historical relationship between art, sciences, and technology. This relationship became able to change the methodology of the artistic creation processes totally to the extent that it represents separate artistic movements every one of them can actively refer to a new scientific approach to reinterpreting our understanding of the arts in our contemporary cultures.
One of the most significant artistic movements emerged since the middle of the 1960s until now is Laser-Art, in which light can reach its maximum values as a Hypermaterial that can independently constitute the artwork technically and conceptually simultaneously.
This thesis contextualizes laser art as an independent artistic trend has its history, classifications, criteria, philosophy, and aesthetical aspects. Via several analytical studies theoretically and practically, the thesis proves that laser art actively contributes, as an independent artistic trend, to change the conceptual definition of the artistic material. On the other hand, bridge the gap between the artistic context and the technical issues, in which the conceptual values became fully integrated into the physical properties of the medium (laser beam), therefore it became impossible to separate the idea and the material of the artwork from each other. Besides, the thesis reveals the potential hidden conceptual and philosophical dimensions of the holographic art as one of the most important branches of laser art. In advanced step, the research suggested a new model of interactive holographic art based on neural controlling, and how this advanced approach can lead us towards a new kind of the aesthetic values, in which participants effectively contribute neurologically to constituting the artwork itself
Physical coronary arteriogenesis of cardiac and extracardiac origin
Full text linkCoronary collaterals are pre-formed connections that provide an alternative route when regular antegrade blood flow to the heart muscle is compromised. In response to a coronary obstruction, coronary collaterals undergo gradual enlargement, variably compensating for impaired antegrade blood flow. As natural bypasses, sufficiently large coronary collaterals can preserve myocardial perfusion and viability in the acute and chronic phases of coronary artery disease.
In chronic stable coronary artery disease, medical therapy is complemented by established interventional therapies such as percutaneous coronary intervention and surgical coronary artery bypass grafting. However, new therapeutic options are needed for patients who are not candidates for conventional revascularization due to severe and/or diffuse obstructive coronary artery disease. Promotion of coronary collaterals represents such an alternative treatment option. However, while a multitude of interventions has been shown to be effective in collateral growth promotion, the effect of current interventions is only temporary and therefore recurrent application of the arteriogenic stimulus is necessary to sustain the level of collaterals. Historically, attempts to induce durable improvement of coronary collateral flow have already been made. Experimental and clinical studies examined the efficacy of distal ligation of the internal mammary artery (IMA) to augment blood flow to the coronary circulation. The basis of these studies was the clinical structural and experimental functional documentation of pre-formed connections between the internal mammary arteries and the coronary circulation - extracardiac collaterals. With the advent of coronary artery bypass grafting, the procedure was, however, abandoned. Notably, the clinical studies were based on crude outcome measures, such as symptomatic improvement. The function and in-vivo prevalence of internal mammary-to-coronary-anastomoses was therefore investigated in a clinical study (Project I) for the first time. 120 patients referred for elective coronary angiography for suspected or established coronary artery disease (CAD) underwent 180 pairs of coronary artery balloon occlusions, the first with and the second without simultaneous distal IMA occlusion (thought to augment flow via IMA-to-coronary connections). Collateral function was assessed during coronary balloon occlusion by collateral flow index (CFI), which is the ratio of coronary occlusive to aortic (effective perfusing) pressure, accounting for the back pressure (central venous pressure). Regional myocardial ischemia was assessed by the intracoronary electrocardiogram (ECG). With simultaneous distal IMA occlusion CFI was significantly higher during left IMA with left anterior descending coronary artery (LAD) occlusion and right IMA with right coronary artery (RCA) occlusion than during LAD or RCA occlusionalone. Conversely, during contralateral IMA occlusion, ie RCA with left IMA or LAD or left circumflex coronary artery (LCX) with right IMA occlusion, CFI was not different. Concordantly, myocardial ischemia by intracoronary ECG was lower during LAD or RCA occlusion with simultaneous ipsilateral IMA occlusion nd was not different during contralateral IMA occlusion or with LCX occlusion. In conclusion, it could be demonstrated that there was functional, ischemia-reducing collateral supply from the ipsilateral IMA to the right coronary and the left anterior descending coronary artery.
The effect of permanent distal right IMA on coronary collateral function was investigated or the first time in an open-label clinical trial (Project II). 50 patients with stable CAD underwent distal right IMA closure at baseline and determination of right and left coronary function (LAD or LCX) by CFI at baseline and at follow-up 6 weeks after right IMA device closure. CFI in the untreated RCA increased significantly from baseline to follow-up, while CFI in the untreated left coronary remained unchanged. Concordantly, regional myocardial ischemia determined by intracoronary ECG was reduced during a 1-minute coronary balloon occlusion in the RCA but not in the left coronary. In conclusion, permanent distal right IMA closure in this non-randomized study appeared to augment extracardiac right coronary collateral supply.
With acute myocardial ischemia, the mainstay of therapy lies in the antegrade technique of prompt percutaneous revascularization. However, a reopened epicardial conduit artery does not guarantee reperfusion of myocardial tissue, which can be impaired by microvascular dysfunction. In this situation of a failed antegrade approach, retrograde treatment approach has been proposed by an intervention in the coronary venous system - intermittent coronary sinus occlusion (CSO). Although the ischemia-relieving effect of CSO is thought to depend on coronary collaterals, its role of coronary collaterals has so far not been clearly defined in humans.
The role of coronary collaterals in the anti-ischemic effect of CSO was therefore investigated in a clinical study (Project III) and in a computer simulation (Project IV). In the clinical study, 35 patients with stable coronary artery disease underwent two 2-minute balloon occlusions of a major coronary artery to induce controlled ischemia. CSO was performed randomized to the first or second coronary balloon occlusion.Collateral function was assessed by CFI and regional myocardial ischemia was assessed by the ST-segment shift in the intracoronary ECG. Intermittent coronary sinus occlusion was shown to reduce myocardial ischemia depending on the extent of collateral function. With minimal collateral function, no ischemia-reducing effect of CSO was demonstrated. An anti-ischemic effect of CSO was seen with intermediate collateral function. High collateral function prevented myocardial ischemia in the first place and therefore, no additional effect of CSO was demonstrated.
The computer simulation (Project IV) consisted of a lumped-parameter model of a two-branch left coronary system circuit with arterial, capillary and venous compartments. As a key point, arterial collateral connections were an integral part of the model, in contrast to prior computer models. Importantly, the salient features of coronary pressure and flow during non-ischemic and ischemic conditions, as well as during CSO could be reproduced. In particular, the proposed main mechanism of CSO - retrograde flow from the venous to the venular and capillary compartment was reproduced by the model. As a key point, the model predicted retrograde flow to be dependent on the extent of collateral blood flow and contractility. With minimal collateral function, retrograde flow to an ischemic region was low, while it progressively increased with higher collateral function. Accounting for the combination of reduced contractility during ischemia and the level of collateral function, the effect on retrograde flow was much increased. Retrograde flow was predicted to be very low at zero to minimal collateral function and concomitantly severely reduced contractility. Conversely, retrograde flow increased steeply with increasing collateral function and more preserved contractility. In essence, the mathematical model provided a reasonable explanation for the findings from the clinical study (Project III) and could, for the first time, provide an explanation for the role of collaterals in the anti-ischemic effect of CSO
Funktionelle und strukturelle Analyse der primären ziliären Dyskinesie – Retrospektive auf 35 Jahre diagnostische Tätigkeit
Full text linkDie primäre ziliäre Dyskinesie (engl. Primary ciliary dyskinesia - PCD) ist eine seltene genetische Erkrankung, welche in erster Linie durch chronische pneumologische Probleme charakterisiert wird und pathophysiologisch Folge einer verminderten mukoziliären Clearance ist. Insbesondere besteht die Schwierigkeit bei dieser klinisch sich oft sehr früh und unspezifisch manifestierenden Erkrankung in der Diagnosestellung, weswegen wir auf zuverlässige diagnostische Methoden angewiesen sind.
Die Vitalanalyse mittels Lichtmikroskop (high speed video microscopy analysis [HSVA]) gewann dabei im Verlauf, umso mehr als die technische Verfügbarkeit von schnellen Aufnahmesystemen zu akzeptablen Preisen eine detaillierte Analyse der Motilität erlaubte, an Bedeutung gegenüber der zuvor als Goldstandard angesehenen Transmissionselektronenmikroskopie [TEM].
In der vorliegenden Arbeit soll die Erfahrung im Bereich funktionell-strukturelle PCD Analytik, die in den letzten 35 Jahre am Institut für Anatomie gesammelt werden konnte, systematisch zusammengetragen und analysiert, sowie ein Leitfaden für das technische Prozedere präsentiert werden
Empirically-Grounded Construction of Bug Prediction and Detection Tools
Full text linkThere is an increasing demand on high-quality software as software bugs have an economic impact not only on software projects, but also on national economies in general. Software quality is achieved via the main quality assurance activities of testing and code reviewing. However, these activities are expensive, thus they need to be carried out efficiently.
Auxiliary software quality tools such as bug detection and bug prediction tools help developers focus their testing and reviewing activities on the parts of software that more likely contain bugs. However, these tools are far from adoption as mainstream development tools. Previous research points to their inability to adapt to the peculiarities of projects and their high rate of false positives as the main obstacles of their adoption.
We propose empirically-grounded analysis to improve the adaptability and efficiency of bug detection and prediction tools. For a bug detector to be efficient, it needs to detect bugs that are conspicuous, frequent, and specific to a software project. We empirically show that the null-related bugs fulfill these criteria and are worth building detectors for. We analyze the null dereferencing problem and find that its root cause lies in methods that return null. We propose an empirical solution to this problem that depends on the wisdom of the crowd. For each API method, we extract the nullability measure that expresses how often the return value of this method is checked against null in the ecosystem of the API. We use nullability to annotate API methods with nullness annotation and warn developers about missing and excessive null checks.
For a bug predictor to be efficient, it needs to be optimized as both a machine learning model and a software quality tool. We empirically show how feature selection and hyperparameter optimizations improve prediction accuracy. Then we optimize bug prediction to locate the maximum number of bugs in the minimum amount of code by finding the most cost-effective combination of bug prediction configurations, i.e., dependent variables, machine learning model, and response variable. We show that using both source code and change metrics as dependent variables, applying feature selection on them, then using an optimized Random Forest to predict the number of bugs results in the most cost-effective bug predictor.
Throughout this thesis, we show how empirically-grounded analysis helps us achieve efficient bug prediction and detection tools and adapt them to the characteristics of each software project
Three essays on career concerns
Full text linkThis dissertation consists of three essays dealing with the concept of career concerns. Exhibiting the desire to be perceived favorably by others is at the core of this concept. For over three decades researchers have been investigating this concept in theory and in practice. This thesis contributes to the theoretical strand of literature with three models. While each essay highlights a different organizational issue, the common ground of all three is the relationship between a principal (she) and a career concerned agent (he).
Essay 1 studies the effect of career concerns with respect to one of the fundamental organizational questions arising naturally in business: how should a job consisting of two sequential tasks be allocated among the employees? Should the same agent be in charge (integration), or should different agents be in charge (separation)? We find a well-known rent-saving effect favoring integration and a novel shirking effect favoring separation. This shirking effect is purely due to the career concerns of the agent. A project, which is always successful might undermine the contribution of the agent in charge. The agent then has an incentive to shirk in one stage of the project, just to show that the project’s success is due to the agent’s contribution. In case of separation, the agent has one task only to signal his ability, and hence is well incentivized.
Essay 2 considers an agent who serves as an expert. He investigates the circumstances for an investment. Depending on the underlying state of the world, a risky or a safe project should be executed. His career concerns, contrary to the ones in Essay 1, target at the correctness of his evaluation. We examine the role of information an outside party has access to as an incentive instrument for a career concerned expert. Two distinguished degrees of information are considered, intransparency and transparency. The latter allows the market to have access to additional relevant information with respect to the agent’s evaluation. Making an organization transparent comes at a cost, but nevertheless we find instances where transparency is optimal due to the expert’s career concerns. His incentives are increased once the market has superior inference capability, i.e. once the organization is made transparent.
Finally, Essay 3 examines the interplay between explicit and implicit incentives of a career concerned agent. Akin to Essay 2 the agent is modeled as an expert who investigates the nature of a project whose outcome depends on the underlying state of the world. While the modeling of the career concerns is similar to Essay 2, the focus is different. This time the principal has two instruments at hand to incentivize the career concerned agent, namely offering a bonus contingent on a well performed project and secondly, a double-check after a rejected project. The latter generates the information about the correctness of the agent’s decision. We find that the principal prefers to offer a bonus if the prior probability of implementing correctly is sufficiently low. The use of double-checks is preferred, otherwise
Applications of Mathematical Programming in Personnel Scheduling
Full text linkIn the few decades of its existence, mathematical programming has evolved into an important branch of operations research and management science. This thesis consists of four papers in which we apply mathematical programming to real-life personnel scheduling and project management problems. We develop exact mathematical programming formulations. Furthermore, we propose effective heuristic strategies to decompose the original problems into subproblems that can be solved effciently with tailored mathematical programming formulations. We opt for solution methods that are based on mathematical programming, because their advantages in practice are a) the exibility to easily accommodate changes in the problem setting, b) the possibility to evaluate the quality of the solutions obtained, and c) the possibility to use general-purpose solvers, which are often the only software available in practice
4D laboratory experiments of oblique extension and scissor tectonics, structural inheritance and sedimentation: implications for rift evolution, rift propagation and rift segment interaction
Full text linkExtension of the continental lithosphere leads to the formation of continental rift basins. When extension persists, continental break-up and oceanic spreading ensue, creating conjugate passive margins on both sides of a new oceanic basin. Rifts and passive margins have been intensely studied by geologists because of their vast hydrocarbon potential, representing the bulk of the global proven oil and gas resources and are of great importance for human society, housing a considerable share of the world’ s population. Passive margins, as their name suggest represent the remainders of a successful rifting event leading to continental break-up and have since ceased to experience active extension. In contrast, many continental rifts are still actively deforming. These rift basins are prone to various types of natural hazards but also provide economic opportunities for geothermal energy production.
However, despite the numerous geological studies, the complex tectonic evolution and structural frameworks of rifts and passive margins remain poorly understood; most rifts and passive margins have experienced oblique extension and/or scissor extension as well as the reactivation of pre-existing structures and significant syn-tectonic sedimentation during their history.
The aim of this Thesis, funded by the Swiss National Science Foundation and carried out at the University of Bern, is to improve our understanding of rifting processes using state- of-the-art analogue model experiments. These analogue models simulate the development and propagation of young continental rifts and the interaction between individual rift segments in the context of oblique extension and scissor extension settings, and aslo investigates the role of structural inheritance and sedimentation on the system. In addition, this thesis includes a comparison of various experimental methods involving foam, rubber and base plate set-ups, commonly used for simulations of extensional tectonics. The models are among others analysed with cutting-edge X-Ray computed tomography (XRCT or CT) and digital volume correlation (DVC) techniques for unparalleled 4D visualisation and quantification of internal model evolution.
The experimental method comparison illu- strates that structural inheritance is key to focus deformation leading to rift development. In the rubber and foam base set-ups, a viscous basal layer facilitates localization as it buffers distributed deformation, and reduces coupling, allowing the brittle cover to behave as rigid blocks, whereas it prevents the strong and probably exaggerated concentration of faulting along the edge of the base plates that develops in the rigid plate models. The experiments illustrate furthermore that the standard brittle-ductile foam set-up with a seed focussing deformation produces the least amount of boundary effects and is thus respresents best of the set-ups tested for studies of rift basin development. A rubber base setting could in theory be similarly efficient, yet a rubber or foam sidewall will be necessary to reduce boundary effects. The brittle-ductile base plate models for instance develop too much friction along the sidewalls, a problem that may be solved with the use of a lubricant.
Various factors are shown to be of influence on the evolution of a rift basin. Firstly, the application of a linear viscous seed, simulating a linear weak zone in the upper crust, produces a narrow rift basin, where previous authors have often applied wider patches of viscous material or rubber sheets to create a wider rift zone. Furthermore, the rate of extension is shown to control the degree of brittle-ductile coupling, either producing a localized rift along the seed or multiple rift basins throughout the model. Also the amount of extension determines the type of structures present in a rift: a small amount of extension only results in minor deformation along the boundary faults whereas a large amount of extension produces additional faulting within the rift wedge, accompanied by a rising viscous layer. The amount of extension itself is depends on the degree of extension obliquity, as increasing oblique extension results in progressively narrower basins, with steeper boundary faults and oblique internal structures.
Moreover, along-strike variations in extension rate in both time and space may lead to a complex structural configuration, as illustrated by scissor extension models. It appears that such gradients in the rate (and thus amount) of extension are a crucial factor controlling rift propagation.
A final influence on rift basin development is syn-rift sedimentation. The presence of sediments in the rift basin does not affect the initial rift configuration set by large-scale tectonic forces, but its additional weight does influence the structural style within the rift basin, concentrating deformation along a set of major faults instead of a myriad of minor faults and causing increased total subsidence, preventing the viscous layer from rising. High syn-rift sediment influx might even delay continental break-up, but larger-scale plate tectonic processes determine whether a continent is actually broken up in the end.
Most of the factors that influence the evolution of individual rift segments, affect the interaction and linkage between them as well. For instance, a weak seed may localize deformation, but a high extension rate and associated brittle-ductile coupling results in the development of multiple rift basins with little amounts of extension in each, limiting their capacity to interact. Instead, low extension rates focus deformation in a single rift, allowing it to propagate and interact with other segments.
Furthermore, the models illustrate that large rift offsets hinder rift linkage, especially when the extension direction is such that the segments propagate parallel to each other or even apart, although in some cases a strike- slip transfer zone may develop. The interplay between initial seed geometry and extension direction proves to be a crucial factor for rift linkage establishment.
Within this context, secondary structural weaknesses, connecting the main rifts, are of minor importance and are only activated when oriented favourably to the regional extension direction. Syn-rift sedimentation, although of importance for internal rift structures, does not significantly affect the large-scale rift linkage zone formation, especially since these zones experience relatively little subsidence, thus less accommodation space is available for sediment deposition. In contrast to the situation with large-scale rift structures, along- strike extension gradients associated with scissor extension have no strong impact on rift interaction zones, since the extension gradient between the two rift segments is generally minor.
Although top view photographs and CT data allow a thorough insight into the 3D external and internal model evolution, 4D DVC analysis has provided an unprecedented understanding of 3D internal displacement and deformation within the brittle and viscous parts of the models. These results illustrate the strong difference between brittle and viscous behaviour, the sand acting as rigid blocks interrupted by discrete zones of faulting, floating on the viscous layer that shows a distributed flow pattern. Not only does the DVC analysis capture the rising viscous material beneath the rift basins, it also reveals out-of-plane motion of both brittle and viscous material due to interacting rift segments. This last observation is crucial for 2D structural reconstructions of orthogonal extension settings, as both viscous and brittle material can move out of section.
The models are compared with natural examples of continental rifts and rift interaction structures, resembling various structures observed in e.g. the East African Rift System, the North Sea Viking Graben and the Cenozoic European Rift System. However, a comparison with previous models and natural examples also shows a reasonable fit with the geometries of oceanic spreading centres, suggesting that these brittle-viscous set-ups can also be used for the modelling of mid-oceanic ridge settings
Data sources:
BORIS Portal Bern Open Repository and I...BAF-Online: Proceedings of the Berner Al...HASBonline – Hefte zur Archäologie des M...Informationswissenschaft: Theorie, Metho...Jahrbuch Diakonie SchweizJournal of Eye Movement ResearchJournal of Radiation Oncology Informatic...BOP SerialsVersants. Revista suiza de literaturas r...
BORIS Theses
BORIS ThesesAccess Repository Dashboard
Do you manage BORIS Theses? Access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard!