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Three-body resonances in pionless effective field theory

Author: Dietz Sebastian
Hammer Hans-Werner
König Sebastian
Schwenk Achim
Publication venue: 'American Physical Society (APS)'
Publication date: 16/06/2022
Field of study

We investigate the appearance of resonances in three-body systems using pionless effective field theory at leading order. The Faddeev equation is analytically continued to the unphysical sheet adjacent to the positive real energy axis using a contour rotation. We consider both, the three-boson system and the three-neutron system. For the former, we calculate the trajectory of Borromean three-body Efimov states turning into resonances as they cross the three-body threshold. For the latter, we find no sign of three-body resonances or virtual states at leading order. This result is validated by exploring the level structure of three-body states in a finite volume approach.Comment: 18 pages, 10 figures, version published in Phys. Rev.

arXiv.org e-Print Archive

MPG.PuRe

A concept for quantitative characterization of the air balance in Bavarian forest soils

Author: Dietz Elke
Falk Wolfgang
Osenstetter Sebastian
Publication venue
Publication date: 01/02/2013
Field of study

Site-specific descriptions of soil water balance and soil air balance are important for tree species selection in forestry. We present a concept for describing the soil air balance for Bavaria. It is an enhancement of an empirical multiple linear regression model that explains soil oxygen deficiency in terms of topographic, climate and soil parameters. We modelled numerous combinations of site conditions with the hydrologic model LWF-Brook 90 to determine an estimator for soil oxygen deficiency. This estimator reflects water logging that persists for a certain length of time. In a second step we will develop a new regression model and combine this information with topographical information about additional water fluxes in a GIS. We aim to combine both steps in order to describe the air balance of forest soils for the entirety of Bavaria.Da neben der Beschreibung des Wasserhaushaltes auch die Kenntnis über Luftmangel für die standortgerechte Baumartenwahl wichtig ist, wird ein Konzept für die bayernweite Beschreibung des Lufthaushaltes vorgestellt. Es ist eine Weiterentwicklung eines empirischen Regressionsmodells, das die Staunässe mittels Geländeparametern, Klima und Bodendaten abschätzt. Dazu wurden mit dem Wasserhaushaltsprogramm LWF-Brook 90 zahlreiche Kombinationen von Standortsfaktoren simuliert und eine Schätzgröße für Luftmangel ausgegeben. Diese Größe beschreibt die Einschränkung des Lufthaushaltes über einen längeren Zeitraum. In einem weiteren Schritt wird dieser deterministische Luftmangelparameter über ein neues Regressionsmodell abgeleitet und mit zusätzlichen topographischen Informationen über Zu- und Abflüsse in einem GIS kombiniert. Ziel ist es, für ganz Bayern den Lufthaushalt von Waldböden zu beschreiben

Hochschulschriftenserver - Universität Frankfurt am Main

Big Data impacts on stochastic Forecast Models: Evidence from FX time series

Author: Sebastian Dietz
Publication venue: 'Pakistan Journal of Statistics and Operation Research'
Publication date: 01/12/2013
Field of study

With the rise of the Big Data paradigm new tasks for prediction models appeared. In addition to the volume problem of such data sets nonlinearity becomes important, as the more detailed data sets contain also more comprehensive information, e.g. about non regular seasonal or cyclical movements as well as jumps in time series. This essay compares two nonlinear methods for predicting a high frequency time series, the USD/Euro exchange rate. The first method investigated is Autoregressive Neural Network Processes (ARNN), a neural network based nonlinear extension of classical autoregressive process models from time series analysis (see Dietz 2011). Its advantage is its simple but scalable time series process model architecture, which is able to include all kinds of nonlinearities based on the universal approximation theorem of Hornik, Stinchcombe and White 1989 and the extensions of Hornik 1993. However, restrictions related to the numeric estimation procedures limit the flexibility of the model. The alternative is a Support Vector Machine Model (SVM, Vapnik 1995). The two methods compared have different approaches of error minimization (Empirical error minimization at the ARNN vs. structural error minimization at the SVM). Our new finding is, that time series data classified as “Big Data” need new methods for prediction. Estimation and prediction was performed using the statistical programming language R. Besides prediction results we will also discuss the impact of Big Data on data preparation and model validation steps. <!--[if gte mso 10]> <style>\ud /* Style Definitions */\ud table.MsoNormalTable\ud {mso-style-name:"Normale Tabelle";\ud mso-tstyle-rowband-size:0;\ud mso-tstyle-colband-size:0;\ud mso-style-noshow:yes;\ud mso-style-priority:99;\ud mso-style-parent:"";\ud mso-padding-alt:0cm 5.4pt 0cm 5.4pt;\ud mso-para-margin:0cm;\ud mso-para-margin-bottom:.0001pt;\ud mso-pagination:widow-orphan;\ud font-size:10.0pt;\ud font-family:"Times New Roman","serif";}\ud </style> <![endif]--

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Pakistan Journal of Statistics and Operation Research

Auf den Spuren von Macht und Herrschaft : Bericht eines Vernetzungsworkshops von Promovierenden der Theologien vom 31.03.–01.04.2022

Author: Dietz Sebastian
Publication venue: Institut für Christliche Sozialwissenschaften (ICS), Westfälische Wilhelms-Universität Münster
Publication date: 24/11/2022
Field of study

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Open Access-Zeitschriften an der WWU Münster (Westfälische Wilhelms-Universität)

Continuum structure of few-body systems

Author: Dietz Sebastian
Publication venue
Publication date: 01/01/2023
Field of study

The focus of this work is on the study of states on the unphysical sheets of the complex energy plane for few-particle systems using potentials derived from leading order pionless effective field theory. The aim is to obtain a statement about the continuum structure of the three-neutron system. For this purpose, various methods are applied. These allow the computation of observables on both, the physical and unphysical sheets. This group of methods is complemented by calculations in finite volume. On the basis of different two-particle test systems, methods for the calculation of the phase shifts and time delays, the analytical continuation in the coupling constant (ACCC) and the analytical continuation of the Lippmann-Schwinger equation to the unphysical sheet are compared with each other by the difficulty and possibilities of their application and the quality of their results. In the following, different three-particle system are considered. First, the method of analytical continuation is applied to a system of three spinless bosons. This offers the possibility to investigate resonances as well as virtual states on both unphysical sheets connected to the physical one. Furthermore, three-particle systems containing spin are considered. First, the phase shift anomaly of the neutron-deuteron system is investigated. Subsequently the three-neutron system is considered. For this purpose, first the phase shifts on the physical sheet are extracted by extrapolation from a bound to the physical dineutron. In the following, the pole structure of the three-neutron system on the unphysical sheet is investigated by analytical continuation. In both cases, no sign of a resonance or a virtual state is found. This result is supported by the calculation of the point production amplitude and its comparison with the predictions of the nonrelativistic conformal field theory. The point production amplitude is further derived for a four-neutron system as well as for the system of the three spinless bosons. The system of the three bosons serves here as a benchmark for the existence of a resonance. Finally, using the Lüscher formalism, the spectra of the dineutron-neutron as well as the dineutrondineutron scattering for unphysically bound dineutrons in finite volume are calculated. In both cases, it is shown that even for an unphysically increased interaction strength neither three- nor four-neutron resonances occur. In summary, this work shows using different methods, that the three-neutron system neither presents resonances nor virtual states. Furthermore, the non-existence of resonances in the four-neutron system is motivated by two methods

tuprints

Autoregressive Neuronale Netze - Univariate, Multivariate und Kointegrierte Modelle mit einer Anwendung aus dem Bereich der deutschen Automobilindustrie

Author: Dietz Sebastian
Publication venue
Publication date: 08/06/2011
Field of study

Prediction of economic variables is a basic component not only for economic models, but also for many business decisions. Nevertheless it is difficult to produce accurate predictions in times of economic crises, which cause nonlinear effects in the data. In this dissertation a nonlinear model for analysis of time series with nonlinear effects is introduced. Linear autoregressive processes are extended by neural networks to overcome the problem of nonlinearity. This idea is based on the universal approximation property of single hidden layer feedforward neural networks of Hornik (1993). Univariate Autoregressive Neural Network Processes (AR-NN) as well as Vector Autoregressive Neural Network Processes (VAR-NN) and Neural Network Vector Error Correction Models (NN-VEC) are introduced. Various methods for variable selection, parameter estimation and inference are discussed. AR-NN's as well as a NN-VEC are used for prediction and analysis of the relationships between 4 variables related to the German automobile industry: The US Dollar to Euro exchange rate, the industrial output of the German automobile industry, the sales of imported cars in the USA and an index of shares of German automobile manufacturing companies. Prediction results are compared to various linear and nonlinear univariate and multivariate models

Inferring functional modules of protein families with probabilistic topic models

Author: Dietz Laura
Konietzny Sebastian GA
McHardy Alice C
Publication venue: BioMed Central
Publication date: 01/01/2011
Field of study

Abstract Background Genome and metagenome studies have identified thousands of protein families whose functions are poorly understood and for which techniques for functional characterization provide only partial information. For such proteins, the genome context can give further information about their functional context. Results We describe a Bayesian method, based on a probabilistic topic model, which directly identifies functional modules of protein families. The method explores the co-occurrence patterns of protein families across a collection of sequence samples to infer a probabilistic model of arbitrarily-sized functional modules. Conclusions We show that our method identifies protein modules - some of which correspond to well-known biological processes - that are tightly interconnected with known functional interactions and are different from the interactions identified by pairwise co-occurrence. The modules are not specific to any given organism and may combine different realizations of a protein complex or pathway within different taxa.</p

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Global Determination of Snow Cover using Remote Sensing and a Near Real Time Processing Chain

Author: Dietz Andreas
Rößler Sebastian
Publication venue
Publication date: 09/06/2021
Field of study

Remote sensing offers the best prerequisites for obtaining comprehensive information on global snow cover. Although microwave remote sensing can provide limited information about the thickness of the snowpack and the water stored (i.e. snow water equivalent), its geometric resolution is not sufficient for an accurate spatial analysis. Optical remote sensing provides the required spatial resolution, but it is often compromised by clouds or at high geographical latitudes by the polar night. In order to obtain cloud-free information on daily snow cover from optical data, the German Aerospace Center developed the already established product Global SnowPack (GSP). It is based on the daily MODIS snow products originating from Terra and Aqua platforms and provided by NSIDC. With the help of sequential algorithms and additional data (digital elevation model, land cover classifications), pixels with clouds or polar night are continuously eliminated. While the Global SnowPack has so far only been calculated retrospectively for the entire hydrological year, there will now also be a near real time product (NRT-GSP). The latest MODIS data (these are available after approx. 2 days) are interpolated on a daily basis using the previous days. The product will be available in the future on the GeoService of the Earth Observation Center. We see an application of this product, for example, in the prediction of extreme hydrological events. In a recently published study, the development of the snow cover of various catchment areas of nival rivers derived from Global SnowPack was incorporated into a snowmelt runoff model. It was found that extreme high and low water events during the annual spring flood were reflected early in the development of the snow cover extent. With the help of the NRT-GSP product, such a development would be recognizable at an early stage and preparations could be made

Institute of Transport Research:Publications

DLR Global SnowPack - possible applications of the near real-time product

Author: Dietz Andreas
Rößler Sebastian
Publication venue
Publication date: 03/06/2022
Field of study

For over 20 years, the MODIS sensors on Terra and Aqua have been providing data on global snow coverage. The daily data provided by the National Snow and Ice Data Center (NSIDC) (currently in version 6.1) is already of very high quality and serves as input data for the DLR Global SnowPack processor. There, remaining data gaps (e.g. due to clouds or polar night) are filled in 4 interpolation steps and cloud-free data is thus provided daily. So far this has only happened retrospectively after the end of a hydrological year (end of the meteorological summer). This data is now made available daily in near real time with a time lag of 3 days in the EOC GeoService Portal. This enables the use of this data in time-critical issues, such as with regard to flood hazards. At the conference we will present the product, the access options and possible applications

Institute of Transport Research:Publications

Detection of Snow Cover from Historical and Recent AVHHR Data - A Thematic TIMELINE Processor

Author: Dietz Andreas
Rößler Sebastian
Publication venue: 'MDPI AG'
Publication date: 01/03/2022
Field of study

Global snow cover forms the largest and most transient part of the cryosphere in terms of area. On the local and regional scale, small changes can have drastic effects such as floods and droughts, and on the global scale is the planetary albedo. Daily imagery of snow cover forms the basis of long-term observation and analysis, and only optical sensors offer the necessary spatial and temporal resolution to address decadal developments and the impact of climate change on snow availability. The MODIS sensors have been providing this daily information since 2000; before that, only the Advanced Very High-Resolution Radiometer (AVHRR) from the National Oceanographic and Atmospheric Administration (NOAA) was suitable. In the TIMELINE project of the German Aerospace Center, the historic AVHRR archive in HRPT (High Resolution Picture Transmission) format is processed for the European area and, among other processors, one output is the thematic product 'snow cover' that will be made available in 1 km resolution since 1981. The snow detection is based on the Normalized Difference Snow Index (NDSI), which enables a direct comparison with the MODIS snow product. In addition to the NDSI, ERA5 re-analysis data on the skin temperature and other level 2 TIMELINE products are included in the generation of the binary snow mask. The AVHRR orbit segments are projected from the swath projection into LAEA Europe, aggregated into daily coverages, and from this, the 10-day and monthly snow covers are finally calculated. In this publication, the snow cover algorithm is presented, as well as the results of the first validations and possible applications of the final product

Institute of Transport Research:Publications

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