Radiator design system computer programs

Minimum weight space radiator subsystems which can operate over heat load ranges wider than the capabilities of current subsystems are investigated according to projected trends of future long duration space vehicles. Special consideration is given to maximum heat rejection requirements of the low temperature radiators needed for environmental control systems. The set of radiator design programs that have resulted from this investigation are presented in order to provide the analyst with a capability to generate optimum weight radiator panels or sets of panels from practical design considerations, including transient performance. Modifications are also provided for existing programs to improve capability and user convenience

Nonperiodic echoes from mushroom billiard hats

Mushroom billiards have the remarkable property to show one or more clear cut integrable islands in one or several chaotic seas, without any fractal boundaries. The islands correspond to orbits confined to the hats of the mushrooms, which they share with the chaotic orbits. It is thus interesting to ask how long a chaotic orbit will remain in the hat before returning to the stem. This question is equivalent to the inquiry about delay times for scattering from the hat of the mushroom into an opening where the stem should be. For fixed angular momentum we find that no more than three different delay times are possible. This induces striking nonperiodic structures in the delay times that may be of importance for mesoscopic devices and should be accessible to microwave experiments.Comment: Submitted to Phys. Rev. E without the appendi

Geometric Analysis of Particular Compactly Constructed Time Machine Spacetimes

We formulate the concept of time machine structure for spacetimes exhibiting a compactely constructed region with closed timelike curves. After reviewing essential properties of the pseudo Schwarzschild spacetime introduced by A. Ori, we present an analysis of its geodesics analogous to the one conducted in the case of the Schwarzschild spacetime. We conclude that the pseudo Schwarzschild spacetime is geodesically incomplete and not extendible to a complete spacetime. We then introduce a rotating generalization of the pseudo Schwarzschild metric, which we call the the pseudo Kerr spacetime. We establish its time machine structure and analyze its global properties.Comment: 14 pages, 3 figure

Lifshitz and Excited State Quantum Phase Transitions in Microwave Dirac Billiards

We present experimental results for the density of states (DOS) of a superconducting microwave Dirac billiard which serves as an idealized model for the electronic properties of graphene. The DOS exhibits two sharp peaks which evolve into van Hove singularities with increasing system size. They divide the band structure into regions governed by the \emph{relativistic} Dirac equation and by the \emph{non-relativistic} Schr\"odinger equation, respectively. We demonstrate that in the thermodynamic limit a topological transition appears as a neck-disrupting Lifshitz transition in the number susceptibility and as an excited state transition in the electronic excitations. Furthermore, we recover the finite-size scaling typical for excited state quantum phase transitions involving logarithmic divergences and identify a quasi-order parameter

Rabi Oscillations at Exceptional Points in Microwave Billiards

We experimentally investigated the decay behavior with time t of resonances near and at exceptional points, where two complex eigenvalues and also the associated eigenfunctions coalesce. The measurements were performed with a dissipative microwave billiard, whose shape depends on two parameters. The t^2-dependence predicted at the exceptional point on the basis of a two-state matrix model could be verified. Outside the exceptional point the predicted Rabi oscillations, also called quantum echoes in this context, were detected. To our knowledge this is the first time that quantum echoes related to exceptional points were observed experimentally.Comment: 10 pages, 3 figure

Machine learning for shaft power prediction and analysis of fouling related performance deterioration

Improving operational performance and reducing fuel consumption is increasingly important for shipping companies. Ship performance degrades over time due to hull and propeller fouling; therefore assessing when fouling effects are significant enough to warrant cleaning is critical. Advancements in onboard data logging systems, combined with machine learning techniques, unlock the potential to predict fouling effects accurately and determine when to clean. This study evaluates five models for shaft power prediction: Multiple Linear Regression, Decision Tree (AdaBoost), K – Nearest Neighbours, Artificial Neural Network and Random Forest. The importance of pre-processing is highlighted, contributing to the creation of a model with lower errors than previous studies. The significance of environmental parameters was explored, with the novel integration of wave statistics to the operational dataset, and simulated power-speed curves created from predictions to identify performance deterioration due to fouling. The Random Forest model was most effective in predicting shaft power, with an error of 1.17%. The addition of ‘Days Since Clean’ and ‘Significant Wave Height’ increased prediction accuracy by 0.07% and 0.12% respectively. Simulated power-speed curves revealed a 5.2% increase in shaft power due to fouling. This study provides operators with a method to determine when to conduct hull and propeller cleaning