A numerical study on active control for tiltrotor whirl flutter stability augmentation

The use of active control to augment whirl flutter stability of tiltrotor aircraft is studied by means of a multibody simulation. The numerical model is based on a 1/5 scale semi-span aeroelastic wind tunnel model of a generic tiltrotor concept and possesses a gimballed, stiff-in-plane rotor that is windmilling. A single-input single-output controller and two types of multi-input multi-output algorithms, Linear Quadratic Gaussian Control and Generalized Predictive Control, are studied. They are using measured wing deflections in order to calculate appropriate swashplate input. Results on the closed-loop behavior of three wing and two gimbal natural modes are given. Robustness analyses with respect to major parameters like wing natural frequencies or structural damping are also briefly discussed. The rotor shear force is shown in the uncontrolled condition and in presence of a controller in order to illustrate the whirl flutter mechanism. The single-input single-output controller yielded substantial gain in stability and turned out to be most suitable for industrial application, whereas the Linear Quadratic Gaussian Regulator yielded even higher damping and still had good robustness characteristics

Economic Impact of the Mid-Term Review on Agricultural Production, Farm Income and Farm Survival: A Quantitative Analysis for Local Sub-Regions of Schleswig-Holstein in Germany

This study analyzes the impact of the Mid-Term Review (MTR) on the agricultural sector in Schleswig-Holstein, a federal state in Germany. First, a very detailed farm group linear programming model is built to quantify the effects on agricultural production and farm incomes. The production adjustment to the MTR and its impact on farm profit vary significantly between individual farms. These results depend mainly on the farm type and the resource endowments of the farms. Second, the impact on structural change is examined with a farm survival model. Although the MTR clearly reduces the incomes of several farm types, it accelerates the structural change only gradually.policy reform, modeling production adjustment, farm income, structural change, Community/Rural/Urban Development, Q12, Q18,

Documentation of Flexible Business Processes - A Healthcare Case Study

In many industries, such as manufacturing and logistics, semi-formal process models have become a common means to reason and communicate about business processes. However, in a dynamic and flexible environment the suitability of semiformal process models as an instrument of process documentation may be challenged. Hospital processes are typical examples of business processes that are characterized by both the existence of well-defined procedures and the need for operational flexibility. This research investigates the current practice of process documentation in healthcare by means of a case study in a German hospital. We aim at getting an understanding of how flexible processes may be documented to give medical staff effective guidance and how this documentation has to be managed in order to provide value in everyday routine. On the basis of our findings we give suggestions on how to effectively implement process documentations in similar settings

Quantum critical transport in clean graphene

We describe electrical transport in ideal single-layer graphene at zero applied bias. There is a crossover from collisionless transport at frequencies larger than k_B T/hbar (T is the temperature) to collision-dominated transport at lower frequencies. The d.c. conductivity is computed by the solution of a quantum Boltzmann equation. Due to a logarithmic singularity in the collinear scattering amplitude (a consequence of relativistic dispersion in two dimensions) quasi-particles and -holes moving in the same direction tend to an effective equilibrium distribution whose parameters depend on the direction of motion. This property allows us to find the non-equilibrium distribution functions and the quantum critical conductivity exactly to leading order in 1/|ln(alpha)| where alpha is the coupling constant characterizing the Coulomb interactions.Comment: 19 pages, 1 figure; (v2) added comment on hydrodynamic long-time tail

Toward Process Modeling in Creative Domains

Process modeling has emerged as a widely accepted approach in order to reduce organizational complexity in organizations. Process models are used for different purposes, including process analysis and redesign, risk management, and the implementation of software systems. However, the majority of existent approaches is restricted to processes that are wellstructured and predictable. Highly creative environments, such as the film industry or R&D departments, however, are characterized by high levels of flexibility. As existent approaches do not provide ample means to model such processes, this paper discusses the capabilities that a conceptual process modeling grammar for processes in creative environments must provide. Furthermore, we suggest an approach to process analysis that aims at the identification and specification of creativity in business processes. The study belongs to the design science paradigm; the discussion is grounded in a theory that explains the nature of processes that rely on creativity