Optimal Central Counterparty Risk Management

In order to protect themselves against the potential losses in case of a participant's default and to contain systemic risk, central counterparties (CCPs) need to maintain sufficient financial resources. Typically, these financial resources consist of margin requirements and contributions to a collective default fund. Based on a stylized model of CCP risk management, this article analyzes the main factors affecting the trade-off between margins and default fund. The optimal balance between these two risk management instruments is found to depend on collateral costs, participants' default probability, and the extent to which margin requirements are associated with risk-mitigating incentives. Given the increasing role of CCPs in financial markets in general and for financial stability in particular, these considerations are not only important for CCPs themselves, but also for financial regulators.Central counterparty, margin requirements, default fund, financial stability, incentives

Novel Analytical Hydrodynamic Modeling for Evaluating and Optimizing Alluvial Recharge: Principles, Model Approaches and Their Application for Water Resources Assessment in an Arid Region

This thesis presents a novel analytical solution strategy for the zero-inertia (ZI) equations of free surface flow. These equations are utilized herein for routing flood flow in open channels and for simulating excess rainfall runoff on overland planes. The novel solution approach is shown to be both accurate and robust, especially under the complicated and intricate conditions of infiltrating flow on initially dry river beds or soils, e.g., as present in arid and semiarid areas. This is underlain by comparing modeling results of the novel analytical procedure with those of validated numerical solutions. Furthermore, it is shown that the analytical ZI model can deliver a process-oriented portrayal of runoff concentration in the flood-generating parts of the catchment. Subsequently, the novel analytical ZI model is applied for a real-world water management problem in the Sultanate of Oman, Arabian Peninsula. Within an integrated flash flood routing model—which is also presented in this thesis—the novel analytical routing approach helps in accurately matching the dynamics of advancing and infiltrating ephemeral river flow, established as a consequence of release from a groundwater recharge dam. The integrated modeling system houses the aforementioned analytical downstream model and tailor-made, state-of-the-art modeling components to portray the upstream flow processes, dam operation (including evaporation), and spillway release flow. The proposed modeling system can aid in rendering a realistic image of transient transmission losses and dependent flow dynamics. This is of extremely high importance for water resources assessment, as well as for optimizing recharge dam operation strategies in order to maximize downstream transmission losses and, thus, groundwater recharge.:List of Figures List of Tables List of Algorithms List of Symbols and Acronyms 1 Introduction 1.1 The Role of Ephemeral River Flow for Groundwater Recharge 1.2 Methods for Estimating Groundwater Recharge 1.3 Groundwater Augmentation Techniques and the Involved Processes 1.4 The Role of Overland Flow for Flash Flood Formation 1.5 Objectives of the Thesis 1.6 Structure of the Work 2 Literature Review 2.1 Surface-Water Based Studies on the Estimation of Indirect Recharge 2.2 Review of Literature on Process-Oriented Overland Flow Modeling 2.3 Summary 3 Principles of Physically-Based Modeling of Infiltrating Free Surface Flows 3.1 Hydraulic Phases of an Infiltrating Flow Event 3.2 Hydrodynamic Models 3.2.1 The Saint-Venant Equations 3.2.2 Zero-Inertia Approximation 3.2.3 Kinematic Wave Approximation 3.2.4 Other Simplifications of the Full Hydrodynamic Model 3.3 Initial and Boundary Conditions 3.4 Relating Friction and Flow Properties 3.5 Accounting for Losses or Gains 3.6 Including Arbitrary Cross-Sectional Geometries 3.7 Discussion of the Reviewed Flow Models 3.7.1 Discussion of Modeling Approaches for Ephemeral River Routing 3.7.2 A Suitable Hydrodynamic Model for Overland Flow 3.7.3 On the Portrayal of Shocks with the Kinematic Wave Model 3.8 Summary 4 Solution Procedures for the Reviewed Flow Models 4.1 Method of Characteristics 4.2 Numerical Solution Procedures 4.2.1 Introduction to Finite Difference Methods 4.2.2 Mathematical Principles of Finite Difference Methods 4.3 Analytical Solution Procedures 4.4 Discussion of the Reviewed Solution Procedures 4.5 Summary and Conclusions 5 Novel Analytical Solution Approaches for the Zero-Inertia Equations 5.1 Novel Analytical Solution Approach for Zero-Inertia Open Channel Flow 5.1.1 Governing Equations 5.1.2 Including Nonprismatic Channel Geometries 5.1.3 Boundary and Initial Conditions 5.1.4 Analytical Solution of the Momentum Equation 5.1.5 Analytical Solution of the Continuity Equation 5.1.6 Algorithm for the Iterative Solution of the Nonlinear Problem 5.1.7 Coupling Surface Flow and Infiltration 5.1.8 Additional Remarks 5.2 Novel Analytical Solution Approach for Zero-Inertia Overland Flow 5.2.1 Governing Equations 5.2.2 Boundary and Initial Conditions 5.2.3 Analytical Solution 5.2.4 Algorithm for the Iterative Solution of the Nonlinear Problem 5.3 Summary 6 Comparative Studies with Generally Accepted Approaches 6.1 Open Channel Flow in Prismatic and Nonprismatic Permeable Open Channels 6.1.1 Test Setup 6.1.2 Comparison of Flow Dynamics 6.1.3 Analysis of the Geometry Parameter Sensitivity 6.1.4 Evaluating the Stability of the Analytical ZI Model 6.1.5 Summary 6.2 Overland Flow on a Plane 6.2.1 Test Setup 6.2.2 Comparison of Modeling Results 6.2.3 Summary 7 Flash Flood Routing under Transmission Losses and Dam Operation 7.1 Outline of the Structure of a Novel Integrated Modeling System 7.1.1 Wadi Flow Routing Models 7.1.2 Dam Simulation Model with Evaporation Component 7.2 Real-World Application of the Modeling System for an Arid Region 7.2.1 Study Area and Available Data 7.2.2 Parameter Sensitivity Analysis 7.2.3 Optimization-Based Process Parameter Estimation 7.2.4 Model Application for Wadi Ma\\\\\\\'awil 7.3 Summary 8 Summary and Conclusions 9 Outlook 9.1 The Modeling System for Improving Water Resources Assessment 9.2 The Modeling System for Optimizing Groundwater Recharge Bibliography A Mathematical Supplements A.1 Explicit First-Order Finite Difference Scheme for the Kinematic Wave Model A.2 Explicit Second-Order Finite Difference Scheme for the Kinematic Wave Model A.3 Implicit Finite Difference Scheme with Interior Point (Preissmann Scheme) A.4 Analytical Solution of the Kinematic Wave Model A.5 Details on the Derivation of the Iterative Procedure (5.47);(5.48) A.6 Details on the Evaluation of Equation (5.60) B Selected Publications of the Author B.1 Analytical Model of Surge Flow in Nonprismatic Permeable Channels B.2 Analytical Model of Surface Flow on Hillslopes B.3 Integrated Modeling System for Flash Flood Routing in Ephemeral RiversDiese Dissertation präsentiert einen neuartigen analytischen Lösungsansatz für das beschleunigungsfreie Wellenmodell (bzw. „Zero-Inertia-Modell“, „ZI-Modell“, oder „diffusives Wellenmodell“). Im Rahmen der Arbeit wird das hergeleitete hydrodynamische Modell sowohl zur Simulation von Freispiegelabflüssen in nichtprismatischen und durchlässigen Gerinnen, als auch für die Beschreibung von auf der Landoberfläche abfließendem Infiltrationsüberschuss eingesetzt. Es wird gezeigt, dass der neuartige analytische Ansatz — im Hinblick auf Massenerhaltung und die exakte Abbildung der Abflussdynamik — akkurate Ergebnisse liefert und gleichzeitig unter komplexen und verwickelten Prozessbedingungen anwendbar ist. So belegt eine vergleichende Analyse mit validierten numerischen Lösungsansätzen die Robustheit des analytischen ZI-Modells. Insbesondere die im Sinne der numerischen Mathematik stabile und genaue Modellierung der gekoppelten Abfluss- und Infiltrationsvorgänge in anfänglich trockenen Gerinnen ist dabei ein Novum. Weiterhin wird die Eignung und Anwendbarkeit des neuartigen Modellansatzes zur Beschreibung der Abflusskonzentrationsprozesse gezeigt. Der neuartige Lösungsansatz wird im Folgenden für ein reales Wassermanagementproblem im Sultanat Oman, Arabische Halbinsel eingesetzt. Als Bestandteil eines integrierten Modellsystems, welches ebenfalls im Rahmen der Dissertation vorgestellt wird, dient das analytische ZI-Modell zur Simulation von infiltrierendem Wadiabfluss, welcher unterstrom von Grundwasseranreicherungsdämmen starke Verluste von Masse und Impuls erfährt. Zusammen mit maßgeschneiderten und dem Stand der Technik entsprechenden Komponenten für die Betriebssimulation des Anreicherungsdammes (inklusive Verdunstung von der freien Seefläche) sowie für die Abbildung der oberstromigen hydrodynamischen Prozesse (ebenfalls inklusive Infiltration) wird der neuartige analytische Ansatz in einem Modellsystem zusammengefasst. Das Modellsystem ist in der Lage ein realistisches Bild der raumzeitlichen Dynamik des Abflusses sowie der Grundwasserneubildung aus infiltrierendem Wadiabfluss zu liefern. Damit stellt das Modellsystem ein wertvolles Werkzeug sowohl zur Wasserdargebotsermittlung, als auch für die Optimierung des Betriebes von Grundwasseranreicherungsdämmen dar.:List of Figures List of Tables List of Algorithms List of Symbols and Acronyms 1 Introduction 1.1 The Role of Ephemeral River Flow for Groundwater Recharge 1.2 Methods for Estimating Groundwater Recharge 1.3 Groundwater Augmentation Techniques and the Involved Processes 1.4 The Role of Overland Flow for Flash Flood Formation 1.5 Objectives of the Thesis 1.6 Structure of the Work 2 Literature Review 2.1 Surface-Water Based Studies on the Estimation of Indirect Recharge 2.2 Review of Literature on Process-Oriented Overland Flow Modeling 2.3 Summary 3 Principles of Physically-Based Modeling of Infiltrating Free Surface Flows 3.1 Hydraulic Phases of an Infiltrating Flow Event 3.2 Hydrodynamic Models 3.2.1 The Saint-Venant Equations 3.2.2 Zero-Inertia Approximation 3.2.3 Kinematic Wave Approximation 3.2.4 Other Simplifications of the Full Hydrodynamic Model 3.3 Initial and Boundary Conditions 3.4 Relating Friction and Flow Properties 3.5 Accounting for Losses or Gains 3.6 Including Arbitrary Cross-Sectional Geometries 3.7 Discussion of the Reviewed Flow Models 3.7.1 Discussion of Modeling Approaches for Ephemeral River Routing 3.7.2 A Suitable Hydrodynamic Model for Overland Flow 3.7.3 On the Portrayal of Shocks with the Kinematic Wave Model 3.8 Summary 4 Solution Procedures for the Reviewed Flow Models 4.1 Method of Characteristics 4.2 Numerical Solution Procedures 4.2.1 Introduction to Finite Difference Methods 4.2.2 Mathematical Principles of Finite Difference Methods 4.3 Analytical Solution Procedures 4.4 Discussion of the Reviewed Solution Procedures 4.5 Summary and Conclusions 5 Novel Analytical Solution Approaches for the Zero-Inertia Equations 5.1 Novel Analytical Solution Approach for Zero-Inertia Open Channel Flow 5.1.1 Governing Equations 5.1.2 Including Nonprismatic Channel Geometries 5.1.3 Boundary and Initial Conditions 5.1.4 Analytical Solution of the Momentum Equation 5.1.5 Analytical Solution of the Continuity Equation 5.1.6 Algorithm for the Iterative Solution of the Nonlinear Problem 5.1.7 Coupling Surface Flow and Infiltration 5.1.8 Additional Remarks 5.2 Novel Analytical Solution Approach for Zero-Inertia Overland Flow 5.2.1 Governing Equations 5.2.2 Boundary and Initial Conditions 5.2.3 Analytical Solution 5.2.4 Algorithm for the Iterative Solution of the Nonlinear Problem 5.3 Summary 6 Comparative Studies with Generally Accepted Approaches 6.1 Open Channel Flow in Prismatic and Nonprismatic Permeable Open Channels 6.1.1 Test Setup 6.1.2 Comparison of Flow Dynamics 6.1.3 Analysis of the Geometry Parameter Sensitivity 6.1.4 Evaluating the Stability of the Analytical ZI Model 6.1.5 Summary 6.2 Overland Flow on a Plane 6.2.1 Test Setup 6.2.2 Comparison of Modeling Results 6.2.3 Summary 7 Flash Flood Routing under Transmission Losses and Dam Operation 7.1 Outline of the Structure of a Novel Integrated Modeling System 7.1.1 Wadi Flow Routing Models 7.1.2 Dam Simulation Model with Evaporation Component 7.2 Real-World Application of the Modeling System for an Arid Region 7.2.1 Study Area and Available Data 7.2.2 Parameter Sensitivity Analysis 7.2.3 Optimization-Based Process Parameter Estimation 7.2.4 Model Application for Wadi Ma\\\\\\\'awil 7.3 Summary 8 Summary and Conclusions 9 Outlook 9.1 The Modeling System for Improving Water Resources Assessment 9.2 The Modeling System for Optimizing Groundwater Recharge Bibliography A Mathematical Supplements A.1 Explicit First-Order Finite Difference Scheme for the Kinematic Wave Model A.2 Explicit Second-Order Finite Difference Scheme for the Kinematic Wave Model A.3 Implicit Finite Difference Scheme with Interior Point (Preissmann Scheme) A.4 Analytical Solution of the Kinematic Wave Model A.5 Details on the Derivation of the Iterative Procedure (5.47);(5.48) A.6 Details on the Evaluation of Equation (5.60) B Selected Publications of the Author B.1 Analytical Model of Surge Flow in Nonprismatic Permeable Channels B.2 Analytical Model of Surface Flow on Hillslopes B.3 Integrated Modeling System for Flash Flood Routing in Ephemeral River

Hochwasserfrühwarnung für kleine Einzugsgebiete: Möglichkeiten und Grenzen im Lichte operationeller Anforderungen am Beispiel Sachsens

Endbericht zum Projektvorhaben „Konzeption, Umsetzung sowie Operationalisierung eines Systems zur Ableitung und Bereitstellung von Produkten zur Bewertung und Prognose der regionalen Hochwassergefährdung für kleine Einzugsgebiete in Sachsen” Redaktionsschluss: 31.12.201

Controlled DNA double-strand break induction in mice reveals post-damage transcriptome stability

DNA double-strand breaks (DSBs) and their repair can cause extensive epigenetic changes. As a result, DSBs have been proposed to promote transcriptional and, ultimately, physiological dysfunction via both cell-intrinsic and cell-non-autonomous pathways. Studying the consequences of DSBs in higher organisms has, however, been hindered by a scarcity of tools for controlled DSB induction. Here, we describe a mouse model that allows for both tissue-specific and temporally controlled DSB formation at ∼140 defined genomic loci. Using this model, we show that DSBs promote a DNA damage signaling-dependent decrease in gene expression in primary cells specifically at break-bearing genes, which is reversed upon DSB repair. Importantly, we demonstrate that restoration of gene expression can occur independently of cell cycle progression, underlining its relevance for normal tissue maintenance. Consistent with this, we observe no evidence for persistent transcriptional repression in response to a multi-day course of continuous DSB formation and repair in mouse lymphocytes in vivo. Together, our findings reveal an unexpected capacity of primary cells to maintain transcriptome integrity in response to DSBs, pointing to a limited role for DNA damage as a mediator of cell-autonomous epigenetic dysfunction

Trypanosoma brucei aquaglyceroporin 2 is a high-affinity transporter for pentamidine and melaminophenyl arsenic drugs and the main genetic determinant of resistance to these drugs.

OBJECTIVES: Trypanosoma brucei drug transporters include the TbAT1/P2 aminopurine transporter and the high-affinity pentamidine transporter (HAPT1), but the genetic identity of HAPT1 is unknown. We recently reported that loss of T. brucei aquaglyceroporin 2 (TbAQP2) caused melarsoprol/pentamidine cross-resistance (MPXR) in these parasites and the current study aims to delineate the mechanism by which this occurs. METHODS: The TbAQP2 loci of isogenic pairs of drug-susceptible and MPXR strains of T. brucei subspecies were sequenced. Drug susceptibility profiles of trypanosome strains were correlated with expression of mutated TbAQP2 alleles. Pentamidine transport was studied in T. brucei subspecies expressing TbAQP2 variants. RESULTS: All MPXR strains examined contained TbAQP2 deletions or rearrangements, regardless of whether the strains were originally adapted in vitro or in vivo to arsenicals or to pentamidine. The MPXR strains and AQP2 knockout strains had lost HAPT1 activity. Reintroduction of TbAQP2 in MPXR trypanosomes restored susceptibility to the drugs and reinstated HAPT1 activity, but did not change the activity of TbAT1/P2. Expression of TbAQP2 sensitized Leishmania mexicana promastigotes 40-fold to pentamidine and >1000-fold to melaminophenyl arsenicals and induced a high-affinity pentamidine transport activity indistinguishable from HAPT1 by Km and inhibitor profile. Grafting the TbAQP2 selectivity filter amino acid residues onto a chimeric allele of AQP2 and AQP3 partly restored susceptibility to pentamidine and an arsenical. CONCLUSIONS: TbAQP2 mediates high-affinity uptake of pentamidine and melaminophenyl arsenicals in trypanosomes and TbAQP2 encodes the previously reported HAPT1 activity. This finding establishes TbAQP2 as an important drug transporter

Towards a methodical framework for comprehensively assessing forest multifunctionality

Funded by Deutsche Forschungsgemeinschaft. Grant Number: DFG FOR 891/1-3 National Natural Science Foundation of China. Grant Numbers: 30710103907, 30930005, 31170457, 31210103910 Swiss National Science Foundation (SNSF) Sino-German Centre for Research Promotion in Beijing. Grant Number: GZ 986Peer reviewedPublisher PD

“Dogged” Search of Fresh Nakhla Surfaces Reveals New Alteration Textures

Special Issue: 74th Annual Meeting of the Meteoritical Society, August 8-12, 2011, London, U.K.International audienceCarbonaceous chondrites are considered as amongst the most primitive Solar System samples available. One of their primitive characteristics is their enrichment in volatile elements.This includes hydrogen, which is present in hydrated and hydroxylated minerals. More precisely, the mineralogy is expected to be dominated by phyllosilicates in the case of CM chondrites, and by Montmorillonite type clays in the case of CI. Here, in order to characterize and quantify the abundance of lowtemperature minerals in carbonaceous chondrites, we performed thermogravimetric analysis of matrix fragments of Tagish Lake, Murchison and Orgueil

Trypanosoma brucei aquaglyceroporin 2 is a high-affinity transporter for pentamidine and melaminophenyl arsenic drugs and the main genetic determinant of resistance to these drugs

Objectives Trypanosoma brucei drug transporters include the TbAT1/P2 aminopurine transporter and the high-affinity pentamidine transporter (HAPT1), but the genetic identity of HAPT1 is unknown. We recently reported that loss of T. brucei aquaglyceroporin 2 (TbAQP2) caused melarsoprol/pentamidine cross-resistance (MPXR) in these parasites and the current study aims to delineate the mechanism by which this occurs. Methods The TbAQP2 loci of isogenic pairs of drug-susceptible and MPXR strains of T. brucei subspecies were sequenced. Drug susceptibility profiles of trypanosome strains were correlated with expression of mutated TbAQP2 alleles. Pentamidine transport was studied in T. brucei subspecies expressing TbAQP2 variants. Results All MPXR strains examined contained TbAQP2 deletions or rearrangements, regardless of whether the strains were originally adapted in vitro or in vivo to arsenicals or to pentamidine. The MPXR strains and AQP2 knockout strains had lost HAPT1 activity. Reintroduction of TbAQP2 in MPXR trypanosomes restored susceptibility to the drugs and reinstated HAPT1 activity, but did not change the activity of TbAT1/P2. Expression of TbAQP2 sensitized Leishmania mexicana promastigotes 40-fold to pentamidine and >1000-fold to melaminophenyl arsenicals and induced a high-affinity pentamidine transport activity indistinguishable from HAPT1 by Km and inhibitor profile. Grafting the TbAQP2 selectivity filter amino acid residues onto a chimeric allele of AQP2 and AQP3 partly restored susceptibility to pentamidine and an arsenical. Conclusions TbAQP2 mediates high-affinity uptake of pentamidine and melaminophenyl arsenicals in trypanosomes and TbAQP2 encodes the previously reported HAPT1 activity. This finding establishes TbAQP2 as an important drug transporte