Updating the Option Implied Probability of Default Methodology

In this paper we ‘update’ the option implied probability of default (option iPoD) approach recently suggested in the literature. First, a numerically more stable objective function for the estimation of the risk neutral density is derived whose integrals can be solved analytically. Second, it is reasoned that the originally proposed approach for the estimation of the PoD has some serious drawbacks and hence an alternative procedure is suggested that is based on the Lagrange multipliers. Carrying out numerical evaluations and a practical application we find that the framework provides very promising results

Updating the Option Implied Probability of Default Methodology

In this paper we ‘update’ the option implied probability of default (option iPoD) approach recently suggested in the literature. First, a numerically more stable objective function for the estimation of the risk neutral density is derived whose integrals can be solved analytically. Second, it is reasoned that the originally proposed approach for the estimation of the PoD has some serious drawbacks and hence an alternative procedure is suggested that is based on the Lagrange multipliers. Carrying out numerical evaluations and a practical application we find that the framework provides very promising results.Option Implied Probability of Default; Risk Neutral Density; Cross Entropy

Space-charge distortion of transverse profiles measured by electron-based Ionization Profile Monitors and correction methods

Measurements of transverse profiles using Ionization Profile Monitors (IPMs) for high brightness beams are affected by the electromagnetic field of the beam. This interaction may cause a distortion of the measured profile shape despite strong external magnetic field applied to impose limits on the transverse movement of electrons. The mechanisms leading to this distortion are discussed in detail. The distortion itself is described by means of analytic calculations for simplified beam distributions and a full simulation model for realistic distributions. Simple relation for minimum magnetic field scaling with beam parameters for avoiding profile distortions is presented. Further, application of machine learning algorithms to the problem of reconstructing the actual beam profile from distorted measured profile is presented. The obtained results show good agreement for tests on simulation data. The performance of these algorithms indicate that they could be very useful for operations of IPMs on high brightness beams or IPMs with weak magnetic field

Untersuchungen zur Hufform und zum Hufhormwuchs beim Esel (Equus asinus)

folg

A modular framework for simulations of Ionization Profile Monitors - Implementation and Benchmarking

Simulations of electron and ion tracking in Ionization Profile Monitors are an important tool for specifying and designing new monitors. They are also essential for understanding the effects related to the ionization process, guiding field non-uniformities and influence of the beam fields which may lead to a distortion of measured beam profiles. Most of these effects cannot be treated analytically and therefore several simulation codes have been developed at different accelerator laboratories during the past years. Those existing codes are often tuned to the specific needs of a laboratory, are not well documented and lack a practical user interface. This work presents a novel, generic simulation tool with focus on the ability to test, maintain and extend the code. A complete documentation as well as facile usage were important aspects too. The application combines the features of existing codes in order to provide a common standard for IPM simulations. Because of its modular structure the application allows for exchanging the computational modules depending on the use case as well as for straightforward extensibility to new use cases. Future intended use cases are for example simulations of Beam Induced Fluorescence monitors based on gas jets or Electron Wire Scanners. The current set of algorithms includes several particle tracking methods (for instance Runge-Kutta 4th order or the Boris algorithm) and several bunch field evaluation algorithms (analytical solutions for specific cases as well as numerical Poisson solvers). The application and all involved methods have been tested and benchmarked against existing results. The code is well documented and includes a graphical user interface. It is publicly available as a git repository and as a Python package

A comparison of the real and non-archimedean Monge-Ampère operator

Let X be a proper algebraic variety over a non-archimedean, non-trivially valued field and L a line bundle on X. Given an algebraic model of L, a continuous semipositive metric on L^an induces a metric on the trivial line bundle which corresponds to a continuous function on X^an. If the model of L is defined on a strongly nondegenerate strictly polystable formal model of X^an, this function is convex on the faces of the corresponding skeleton. We show that if it additionally factorizes through the skeleton then on the maximal dimensional open faces its real Monge-Ampère measure is equal to the non-archimedean Monge-Ampère measure of the metric we started with up to multiplication by a constant. In order to prove this we generalize the definition of the non-archimedean Monge-Ampère measure from analytifications of proper algebraic varieties to a broader class of analytic spaces. It is then possible to formulate and prove the desired result locally by starting with a convex function on a maximal dimensional open face of some skeleton of X^an. As an application we can transfer regularity results for solutions of the real Monge-Ampère problem to the non-archimedean situation. In an appendix we examine an example which in the archimedean setting led to the insight that nef line bundles need not carry smooth semipositive metrics. We show that the non-archimedean analogue, which was a promising candidate for a similar result, does admit a semipositive metric in the sense of Zhang

Der Einfluss der präoperativen Darmvorbereitung bei Darmresektionen auf die postoperative Morbidität bei Patienten mit Morbus Crohn

In dieser retrospektiven Studie kamen wir zu dem Gesamtergebnis, dass eine präoperative orthograde mechanische Darmspülung (MBP) bei Patienten mit Morbus Crohn, die sich einer kolorektalen Resektion unterziehen, unbedingt in Betracht gezogen werden sollte. Die MBP war bis zur Einführung des Fast-Track Schemas Standard am Universitätsklinikum Regensburg und wurde aber in den Jahren 2004–2005 fast vollständig aufgegeben. Seit 2005 gab es jedoch einen offensichtlichen Anstieg der postoperativen Morbidität bei Patienten mit Morbus Crohn. Gründe, die dafür angenommen wurden, waren einerseits der vermehrte Einsatz moderner konservativer Behandlungsstrategien – auf welche scheinbar Patienten mit Morbus Crohn im Bereich des Kolons und strikturierender Erkrankung besser ansprechen als solche mit penetrierender Erkrankung – und die damit einhergehende Verlagerung hin zu mehr Operationen bei penetrierender Erkrankung und andererseits eine Verzögerung der Operation durch eine verlängerte konservative Behandlung vor allem bei Patienten mit penetrierender Erkrankung. Als Reaktion darauf wurde zunehmend eine zweizeitige ileokolische Resektion bei Hochrisikopatienten, meist bei Patienten mit penetrierender Erkrankung des distalen Ileums, durchgeführt. Es wurde jedoch bei Einführung des Fast-Track Schemas nicht berücksichtigt, dass kolorektale Resektionen bei Patienten mit Morbus Crohn, welche andere Grundvoraussetzungen für eine Operation liefern, nicht vergleichbar sind mit Patienten mit anderen Operationsindikationen, wie beispielsweise dem kolorektalen Karzinom. Daher reevaluierten wir die Bedeutung der MBP bei Patienten mit Morbus Crohn und kamen zu dem Ergebnis, dass Patienten mit präoperativer MBP am Tag vor der Operation im Vergleich zu Patienten ohne präoperative MBP ein signifikant verringertes Risiko für eine postoperative IASK (12 % vs. 24 %, p < 0,001), Anastomosenkomplikationen (12 % vs. 29,5 %, p < 0,001) und Gesamtkomplikationen (20 % vs. 37 %, p < 0,001) hatten. Patienten mit präoperativer MBP und präoperativer oraler Antibiose am Tag vor der Operation (= kombinierte Darmvorbereitung) erreichten eine IASK-Rate von 0 %, jedoch war die Zahl der Patienten mit kombinierter Darmvorbereitung zu gering, um einen statistisch signifikanten Einfluss auf die postoperative Morbidität nachzuweisen. Dieser Zusammenhang sollte in zukünftigen Studien erforscht werden. Weiterhin haben Patienten mit penetrierender Erkrankung des distalen Ileums ein hohes Risiko für postoperative IASK. Erstaunlicherweise profitierten Patienten mit ileokolischer Resektion bei penetrierender Erkrankung am meisten von einer präoperativen MBP hinsichtlich des postoperativen Outcomes im Vergleich zu Patienten mit Kolonresektionen bei Erkrankung des Kolons bei Morbus Crohn bzw. Patienten mit ileokolischer Resektion bei strikturierender Erkrankung. Warum genau der Einfluss der präoperativen MBP bei penetrierender Erkrankung des distalen Ileums am ausgeprägtesten war, sollte ebenfalls in weiteren Studien untersucht werden. Letztendlich konnte nach der Wiedereinführung der MBP ein offensichtlicher Rückgang der Häufigkeit postoperativer Anastomosenkomplikationen und zweizeitiger ileokolischer Resektionen verzeichnet werden. Ein zweizeitiges Verfahren konnte seit der Wiedereinführung der MBP hauptsächlich auf Notfälle reduziert werden

Nano-object release during machining of polymer-based nanocomposites depends on process factors and the type of nanofiller

We tested the nanomaterial release from composites during two different mechanical treatment processes, automated drilling and manual sawing. Polyurethane (PU) polymer discs (1-cm thickness and 11-cm diameter) were created using different nanomaterial fillers: multiwall carbon nanotubes (MWCNT), carbon black (CB), silicon dioxide (SiO2), and an unfilled PU control. Drilling generated far more submicron range particles than sawing. In the drilling experiments, none of the tested nanofillers showed a significant influence on particle number concentrations or sizes, except for the PU/MWCNT samples, from which larger particles were released than from control samples. Higher drilling speed and larger drill bit size were associated with higher particle counts. Differences between composites were observed during sawing: PU/CB released higher number concentrations of micro-sized particles compared to reference samples. When sawing PU/SiO2 more nanoparticle agglomerates were observed. Furthermore, polymer fumes were released during sawing experiments, which was attributed to the process heat. For both drilling and sawing, the majority of the aerosolized particles were polymer matrix materials containing nanofillers (or protruding from their surface), as evidenced by electron microscopic analysis. Results suggest that: (i) processes associated with higher energy inputs are more likely to result in higher particle release in terms of number concentration; (ii) nanofillers may alter release processes; and (iii) other types of released particles, in particular polymer fumes from high-temperature processes, must also be considered in occupational exposure and risk assessments