Modeling for Active Control of Combustion and Thermally Driven Oscillations

Organized oscillations excited and sustained by high densities of energy release in combustion chambers have long caused serious problems in development of propulsion systems. The amplitudes often become sufficiently large to cause unacceptable structural vibrations. Because the oscillations are self-excited, they reach limiting amplitudes (limit cycles) only because of the action of nonlinear processes. Traditionally, satisfactory behavior has been achieved through a combination of trial-and-error design and testing, with control always involving passive means: geometrical modifications, changes of propellant composition, or devices to enhance dissipation of acoustic energy. Active control has been applied only to small-scale laboratory devices, but the limited success suggests the possibility of serious applications to full-scale propulsion systems. Realization of that potential rests on further experimental work, combined with deeper understanding of the mechanisms causing the oscillations and of the physical behavior of the systems. Effective design of active control systems will require faithful modeling of the relevant processes over broad frequency ranges covering the spectra of natural modes. This paper will cover the general character of the linear and nonlinear behavior of combustion systems, with special attention to acoustics and the mechanisms of excitation. The discussion is intended to supplement the paper by Doyle et al. concerned primarily with controls issues and the observed behavior of simple laboratory devices

Mol-CycleGAN - a generative model for molecular optimization

Designing a molecule with desired properties is one of the biggest challenges in drug development, as it requires optimization of chemical compound structures with respect to many complex properties. To augment the compound design process we introduce Mol-CycleGAN - a CycleGAN-based model that generates optimized compounds with high structural similarity to the original ones. Namely, given a molecule our model generates a structurally similar one with an optimized value of the considered property. We evaluate the performance of the model on selected optimization objectives related to structural properties (presence of halogen groups, number of aromatic rings) and to a physicochemical property (penalized logP). In the task of optimization of penalized logP of drug-like molecules our model significantly outperforms previous results

Discovery of Enhanced Germanium Abundances in Planetary Nebulae with FUSE

We report the discovery of Ge III $\lambda$1088.46 in the planetary nebulae (PNe) SwSt 1, BD+30$^{\rm o}$3639, NGC 3132, and IC 4593, observed with the Far Ultraviolet Spectroscopic Explorer. This is the first astronomical detection of this line and the first measurement of Ge (Z = 32) in PNe. We estimate Ge abundances using S and Fe as reference elements, for a range of assumptions about gas-phase depletions. The results indicate that Ge, which is synthesized in the initial steps of the s-process and therefore can be self-enriched in PNe, is enhanced by factors of > 3-10. The strongest evidence for enrichment is seen for PNe with Wolf-Rayet central stars, which are likely to contain heavily processed material.Comment: 11 pages, 1 figure, accepted for publication in ApJ Letter

Economic Analysis of Power Grid Interconnections Among Europe, North-East Asia, and North America With 100% Renewable Energy Generation

In this paper, we investigate whether the interconnection of power grids with 100% renewable energy generation can bring greater economic benefits now that the technology exists for high power, long distance Ultra High Voltage Direct Current transmission. Based on multi-year historical weather data and demand series, this study compares eight interconnection schemes for three regional grids in Europe, North-East Asia, and North America where there is around 8-hour time difference between any of the two regions. Sensitivity analyses are presented with respect to infrastructure capital cost and different weather year which show that interconnection yields a reduction of approximately 18% in the total annual system cost. The results in this paper also indicate that the regional levelized cost of electricity (LCOE) drops by 31%, 10%, and 10% for Europe, North-East Asia and North America, respectively. It is concluded that there is a strong incentive through both annual cost saving and regional LCOE drop in favour of full long-distance interconnections between the three regions in the context of the international drive towards a net-zero strategy

Global Electricity Interconnection With 100% Renewable Energy Generation

Under the United Nations ‘Net-Zero 2050’ target, transition towards a 100% renewable energy (RE) sourced power grid has become an ever more attractive pathway. However, the inherent fluctuations and intermittency of RE generation, particularly wind and solar, would inevitably pose great technical and economic barriers to their massive integration into the energy supply. A global interconnected electricity grid to utilize the complementarity of diverse demand patterns and RE sources provides an appealing solution. With detailed datasets, this paper is therefore to assess the economic benefits of such a global electricity grid with 100% RE generation using the state-of-the-art Ultra High Voltage Direct Current transmission technologies. The global electricity grid is split into 14 regions with 20 potential interconnection routes and regional geographical centroid is treated as equivalent node for inter-regional distance calculation. Global hourly meteorological re-analysis data of up to seven years with spatial resolution of ${0.25}^{\circ }\times {0.25}^{\circ }$ (approximate $28 \text {km}\times 28\text {km}$ ) is used to generate regional representative generation power series. With the minimum annual system cost for meeting demand in 2050, an integrated planning and power dispatch model is presented to determine the additional regional capacities of RE sources, storage systems, and the interconnectors from 2030, and in which load curtailment is incorporated and ‘ $N$ -1’ security are much stricter than those traditionally applied. The paper provides a comprehensive analysis with 24 cases based on different supply portfolios which show a 20% cost saving through specific global interconnections thereby lending support to the concept of a Global Electricity Grid