Photodissociation of NO2 by pulsed laser light at 6943 A

Two photon absorption in photodissociation of nitrogen dioxide using pulsed laser at 6943

Model-independent inference of laser intensity

An ultrarelativistic electron beam passing through an intense laser pulse emits radiation around its direction of propagation into a characteristic angular profile. Here we show that measurement of the variances of this profile in the planes parallel and perpendicular to the laser polarization, and the mean initial and final energies of the electron beam, allows the intensity of the laser pulse to be inferred in way that is independent of the model of the electron dynamics. The method presented applies whether radiation reaction is important or not, and whether it is classical or quantum in nature, with accuracy of a few per cent across three orders of magnitude in intensity. It is tolerant of electron beams with broad energy spread and finite divergence. In laser-electron beam collision experiments, where spatiotemporal fluctuations cause alignment of the beams to vary from shot to shot, this permits inference of the laser intensity at the collision point, thereby facilitating comparisons between theoretical calculations and experimental data.Comment: 9 pages, 6 figures; merged supplementary material and main body, to appear in Phys Rev Accel Beam

Evaluation and implementation of Lie group integration methods for rigid multibody systems

As commonly known, standard time integration of the kinematic equations of rigid bodies modeled with three rotation parameters is infeasible due to singular points. Common workarounds are reparameterization strategies or Euler parameters. Both approaches typically vary in accuracy depending on the choice of rotation parameters. To efficiently compute different kinds of multibody systems, one aims at simulation results and performance that are independent of the type of rotation parameters. As a clear advantage, Lie group integration methods are rotation parameter independent. However, few studies have addressed whether Lie group integration methods are more accurate and efficient compared to conventional formulations based on Euler parameters or Euler angles. In this paper, we close this gap using the R3 x SO(3) Lie group formulation and several typical rigid multibody systems. It is shown that explicit Lie group integration methods outperform the conventional formulations in terms of accuracy. However, it turns out that the conventional Euler parameter-based formulation is the most accurate one in the case of implicit integration, while the Lie group integration method is computationally the more efficient one. It also turns out that Lie group integration methods can be implemented at almost no extra cost in an existing multibody simulation code if the Lie group method used to describe the configuration of a body is chosen accordingly

A comparison of Finite Elements for Nonlinear Beams: The absolute nodal coordinate and geometrically exact formulations

Two of the most popular finite element formulations for solving nonlinear beams are the absolute nodal coordinate and the geometrically exact approaches. Both can be applied to problems with very large deformations and strains, but they differ substantially at the continuous and the discrete levels. In addition, implementation and run-time computational costs also vary significantly. In the current work, we summarize the main features of the two formulations, highlighting their differences and similarities, and perform numerical benchmarks to assess their accuracy and robustness. The article concludes with recommendations for the choice of one formulation over the other

Evaluierung des Interesseninventars RIASEC-RRK anhand von Studenten und Absolventen der Sinologie und Japanologie sowie deren Kontrastierung

Ziel der Diplomarbeit war die Evaluation des neu entwickelten Interesseninventars RIASEC-RRK anhand von Studenten und Absolventen des Sinologie- und Japanologiestudiums. Für die Studienrichtung Sinologie konnte der Hollandcode AIS (Artistic, Investigative und Social) ermittelt werden. Der Dreiercode der Studienrichtung Japanologie lautet IAS. Ein Indiz für die Validität stellt die überwiegende Übereinstimmung der in dieser Stichprobe ermittelten Geschlechtsunterschiede mit den bereits in der Literatur vorhandenen Ergebnissen diesbezüglich dar. Weiters weist der RIASEC-RRK gute Reliabilitäten auf. Die von Holland postulierte hexagonale Struktur konnte in dieser Untersuchung nicht bestätigt werden. Zusätzlich wurden einige differentialpsychologische Betrachtungen angestellt

Rechtspopulismus in Westeuropa anhand der Beispiele Frankreich, Belgien, Dänemark und Österreich im Vergleich

In dieser Diplomarbeit werden vier verschiedene rechtspopulistische Parteien aus Frankreich, Belgien, Dänemark und Österreich durchleuchtet, ihre Geschichte als auch ihr Aufbau sind dabei genauso behandelt wie auch die Gründe für ihre electorale Erfolge, als auch Entgleisungen der einzelnen Funktionäre

Reliability Evaluation of Reinforcement Learning Methods for Mechanical Systems with Increasing Complexity

Reinforcement learning (RL) is one of the emerging fields of artificial intelligence (AI) intended for designing agents that take actions in the physical environment. RL has many vital applications, including robotics and autonomous vehicles. The key characteristic of RL is its ability to learn from experience without requiring direct programming or supervision. To learn, an agent interacts with an environment by acting and observing the resulting states and rewards. In most practical applications, an environment is implemented as a virtual system due to cost, time, and safety concerns. Simultaneously, multibody system dynamics (MSD) is a framework for efficiently and systematically developing virtual systems of arbitrary complexity. MSD is commonly used to create virtual models of robots, vehicles, machinery, and humans. The features of RL and MSD make them perfect companions in building sophisticated, automated, and autonomous mechatronic systems. The research demonstrates the use of RL in controlling multibody systems. While AI methods are used to solve some of the most challenging tasks in engineering, their proper understanding and implementation are demanding. Therefore, we introduce and detail three commonly used RL algorithms to control the inverted N-pendulum on the cart. Single-, double-, and triple-pendulum configurations are investigated, showing the capability of RL methods to handle increasingly complex dynamical systems. We show 2D state space zones where the agent succeeds or fails the stabilization. Despite passing randomized tests during training, blind spots may occur where the agent’s policy fails. Results confirm that RL is a versatile, although complex, control engineering approach.Publishers versio

A novel director-based Bernoulli–Euler beam finite element in absolute nodal coordinate formulation free of geometric singularities

Abstract. A three-dimensional nonlinear finite element for thin beams is proposed within the absolute nodal coordinate formulation (ANCF). The deformation of the element is described by means of displacement vector, axial slope and axial rotation parameter per node. The element is based on the Bernoulli–Euler theory and can undergo coupled axial extension, bending and torsion in the large deformation case. Singularities – which are typically caused by such parameterizations – are overcome by a director per element node. Once the directors are properly defined, a cross sectional frame is defined at any point of the beam axis. Since the director is updated during computation, no singularities occur. The proposed element is a three-dimensional ANCF Bernoulli–Euler beam element free of singularities and without transverse slope vectors. Detailed convergence analysis by means of various numerical static and dynamic examples and comparison to analytical solutions shows the performance and accuracy of the element.</jats:p

Real-Time State Estimation of Hydraulically-Driven Systems Based on Unscented Kalman Filter and Low-Fidelity Models

Abstract The algorithms identifying machine health and predicting maintenance needs require accurate information about the machine’s state. Because of the great amount of collected data and limited data buffering and data transfer capabilities in many hydraulic machinery applications, the data should be processed in real time. The real-time requirement demands computationally efficient simulation models, while the self-correcting nature of estimation algorithms allows models with lower precision to be used. The study combines the novel low-fidelity surrogate models with an Unscented Kalman Filter (UKF) for the real-time state estimation of the coupled mechanical systems. The surrogate-assisted modeling approach reduces the model complexity and improves computational efficiency while maintaining high accuracy. A hydraulic forestry crane case study is investigated, and the computational efficiency and numerical accuracy of the developed observers are evaluated. The encoder measurements are provided by the high-fidelity model. The high-fidelity model introduces imperfections in the form of the frictional forces in the hydraulic cylinders, which induce approximately 2 % error in actuated force. The case study results demonstrate that the surrogate-based state observer delivers estimations within the real-time computational range. It shows a maximum accuracy deviation of 7.31 % for unmeasured states compared to the high-fidelity model-based observer.Abstract The algorithms identifying machine health and predicting maintenance needs require accurate information about the machine’s state. Because of the great amount of collected data and limited data buffering and data transfer capabilities in many hydraulic machinery applications, the data should be processed in real time. The real-time requirement demands computationally efficient simulation models, while the self-correcting nature of estimation algorithms allows models with lower precision to be used. The study combines the novel low-fidelity surrogate models with an Unscented Kalman Filter (UKF) for the real-time state estimation of the coupled mechanical systems. The surrogate-assisted modeling approach reduces the model complexity and improves computational efficiency while maintaining high accuracy. A hydraulic forestry crane case study is investigated, and the computational efficiency and numerical accuracy of the developed observers are evaluated. The encoder measurements are provided by the high-fidelity model. The high-fidelity model introduces imperfections in the form of the frictional forces in the hydraulic cylinders, which induce approximately 2 % error in actuated force. The case study results demonstrate that the surrogate-based state observer delivers estimations within the real-time computational range. It shows a maximum accuracy deviation of 7.31 % for unmeasured states compared to the high-fidelity model-based observer

Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration (μ 500 MeV) with an intense laser pulse (a0>10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy >30 MeV