Fast network configuration in Software Defined Networking

Software Defined Networking (SDN) provides a framework to dynamically adjust and re-program the data plane with the use of flow rules. The realization of highly adaptive SDNs with the ability to respond to changing demands or recover after a network failure in a short period of time, hinges on efficient updates of flow rules. We model the time to deploy a set of flow rules by the update time at the bottleneck switch, and formulate the problem of selecting paths to minimize the deployment time under feasibility constraints as a mixed integer linear program (MILP). To reduce the computation time of determining flow rules, we propose efficient heuristics designed to approximate the minimum-deployment-time solution by relaxing the MILP or selecting the paths sequentially. Through extensive simulations we show that our algorithms outperform current, shortest path based solutions by reducing the total network configuration time up to 55% while having similar packet loss, in the considered scenarios. We also demonstrate that in a networked environment with a certain fraction of failed links, our algorithms are able to reduce the average time to reestablish disrupted flows by 40%

On nonlinear conservation laws with a nonlocal diffusion term

AbstractScalar one-dimensional conservation laws with a nonlocal diffusion term corresponding to a Riesz–Feller differential operator are considered. Solvability results for the Cauchy problem in L∞ are adapted from the case of a fractional derivative with homogeneous symbol. The main interest of this work is the investigation of smooth shock profiles. In the case of a genuinely nonlinear smooth flux function we prove the existence of such travelling waves, which are monotone and satisfy the standard entropy condition. Moreover, the dynamic nonlinear stability of the travelling waves under small perturbations is proven, similarly to the case of the standard diffusive regularisation, by constructing a Lyapunov functional

Impact of snow state variation for design flood simulations in glacierized catchments

A continuously running hydrological energy balance model was used to analyse the influence of different snow covers on the formation of large floods within glacierized catchments. Model outputs from three different catchments in the Austrian Alps with glacierizations ranging from 30 to 39% were statistically interpreted to cover a wide range of possible combinations of areal snow cover distribution and mean snow water equivalent (SWE_m) and to define initialisation values for extreme runoff scenarios. These model states consider snow conditions between less than 10% snow coverage up to almost complete snow coverage, with different snow depths represented by minimum, mean or maximum levels of SWE_m. For the utilization of extreme runoffs, these snow cover states were combined with design storm input data. An analysis of the resulting flood hydrographs showed that the maximum runoff values occur with minimal snow cover conditions. With increasing snow coverage and SWE_m, flow magnitudes tend to decrease while the relevant precipitation time increases significantly. The influence of topographical catchment features, snow cover and SWE_m on the simulated scenario discharge is discussed. The contribution of the different runoff components to the modelled peak flows confirms the assumption that floods in glacierized catchments are a combination of directly discharging rain and ice melt

Performance of foundation-owned firms in Germany: The role of foundation purpose, stock market listing, and family involvement

To address succession issues, the owners of family firms increasingly transfer their equity to family and charitable foundations, thereby creating so-called foundation-owned firms. This form of succession has become increasingly common in various European countries. A small yet insightful stream of research has emerged comparing the performance of foundation-owned firms against the performance of nonfoundation-owned firms. Our study goes one step further and accounts for the heterogeneous nature of foundation-owned firms. We investigate the role of foundation purpose (family versus charitable foundation), stock market listing, and family involvement. Our results show that firms owned by a family foundation have better accounting performance than firms owned by a charitable foundation. We further find a performance-enhancing effect of family involvement in the firm's management or supervisory board. Contrary to our expectations, we did not observe significant performance differences between private and stock market-listed foundation-owned firms. Our study advances the emergent stream of the foundation-owned (family) firm literature by integrating research on foundation-owned firms with research on family firms. Furthermore, we contribute to the corporate governance literature on ownership effects and blockholder ownership

Hydrological modelling of glacierized catchments focussing on the validation of simulated snow patterns – applications within the flood forecasting system of the Tyrolean river Inn

The catchment of the river Inn is located in the Swiss and Austrian Alps. In the frame of the flood forecasting system "HoPI" (Hochwasserprognose für den Tiroler Inn), the Austrian part of the river Inn and its tributaries are covered within a hybrid numerical model. The runoff from the glacierized headwaters of the south-western Inn tributaries is calculated using the Snow- and Icemelt Model "SES" which utilizes a spatially-distributed energy balance approach; within SES, the accumulation and melting processes for snow, firn, and ice are considered. It is of great importance that such a type of model is used in the simulation of alpine areas since in these regions stream flow is influenced by the accumulation and melt of snow and ice and snow-free glaciers have also the potential to increase or even induce flood flow. For a prototype of the forecast system, SES was calibrated using the snow depletion of a glacier, but later, following the first results during the operational mode, the model was recalibrated and validated using remotely-sensed data covering all 13 glacierized catchments. Using the final snow-parameter setting, a simulation run of 15 hydrological years without any state corrections achieved overall agreements between observed and simulated snow cover ranging from 68% to 88% for all individual catchments. Runoff was calibrated and validated using the data from three different gauges. A parameter set, including both validated snow and runoff parameters, was applied for the modelling of a fourth gauged catchment and also achieved accurate results. This final unique parameterization was transferred to the remaining, ungauged watersheds

Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach

Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east–west direction

Hacia un cambio en el paradigma del manejo y modelación de sistemas de drenaje urbano en países en desarrollo

En países en vía de desarrollo, la falta de infraestructura de saneamiento básico y el número creciente de habitantes en sus centros urbanos han venido aumentando las demandas sobre los recursos hídricos disponibles. En el contexto de Bogotá (Colombia), este artículo emplea un marco de modelación integrada y presenta una revisión de estudios que han buscado una mejora en el manejo de los sistemas de drenaje urbano. Es sabido que hay una necesidad de evaluar estos sistemas como una única entidad cuando se busca propender por el control de la contaminación, su manejo y operación óptima. Esta visión holística ofrece la oportunidad de estudiar las interacciones entre los sub-sistemas y el impacto de la totalidad del sistema en la calidad del agua de los cuerpos receptores

Boltzmann and Fokker-Planck equations modelling the Elo rating system with learning effects

In this paper we propose and study a new kinetic rating model for a large number of players, which is motivated by the well-known Elo rating system. Each player is characterised by an intrinsic strength and a rating, which are both updated after each game. We state and analyse the respective Boltzmann type equation and derive the corresponding nonlinear, nonlocal Fokker-Planck equation. We investigate the existence of solutions to the Fokker-Planck equation and discuss their behaviour in the long time limit. Furthermore, we illustrate the dynamics of the Boltzmann and Fokker-Planck equation with various numerical experiments