A Sample-Efficient Algorithm for Episodic Finite-Horizon MDP with Constraints

Constrained Markov Decision Processes (CMDPs) formalize sequential decision-making problems whose objective is to minimize a cost function while satisfying constraints on various cost functions. In this paper, we consider the setting of episodic fixed-horizon CMDPs. We propose an online algorithm which leverages the linear programming formulation of finite-horizon CMDP for repeated optimistic planning to provide a probably approximately correct (PAC) guarantee on the number of episodes needed to ensure an $\epsilon$-optimal policy, i.e., with resulting objective value within $\epsilon$ of the optimal value and satisfying the constraints within $\epsilon$-tolerance, with probability at least $1-\delta$. The number of episodes needed is shown to be of the order $\tilde{\mathcal{O}}\big(\frac{|S||A|C^{2}H^{2}}{\epsilon^{2}}\log\frac{1}{\delta}\big)$, where $C$ is the upper bound on the number of possible successor states for a state-action pair. Therefore, if $C \ll |S|$, the number of episodes needed have a linear dependence on the state and action space sizes $|S|$ and $|A|$, respectively, and quadratic dependence on the time horizon $H$

A fast method for modelling skew and its effects in salient-pole synchronous generators

The general effects of implementing skewing techniques in electrical machines are well known and have been extensively studied over the years. An important aspect of such techniques is related to the identification of optimal methods for analyzing and modelling any skewed components. This paper presents a fast, finite-element-based method, able to accurately analyze the effects of skew on wound-field, salient-pole synchronous generators in a relatively shorter time than the more traditional methods. As vessel for studying the proposed technique, a 400kVA alternator is considered. Analytical and theoretical considerations on the benefits of skewing the stator in the generator under analysis are preliminary carried out. A finite-element model of the machine is built and the proposed method is then implemented to investigate the effects of the skewed stator. Comparisons against more traditional techniques are presented, with focus on the analysis of the voltage total harmonic distortion and the damper bars’ currents. Finally, experimental tests are performed at no-load and on-load operations for validation purposes, with excellent results being achieved

Analysis, modelling and design considerations for the excitation systems of synchronous generators

The traditional generating set is usually comprised of a classical, wound-field, salient-pole or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However due to the uncontrolled nature of this process, the rectified voltage available at the main generator’s rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite element analysis and with experimental results for a particular low-medium rated generating system in the 400kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical pre-sizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency

Impact of Fluid circulation in old oceanic Lithosphere on the seismicity of transfOrm-type plate boundaries: The FLOWS project (EU-COST ES1301)

Nuzzo, Marianne ... et. al.-- European Geosciences Union General Assembly 2014 (EGU2014), 27 april - 2 may 2014, Vienna, Austria.-- 1 pageThe recent occurrence of large earthquakes and the discovery of deep fluid seepage calls for a revision of the postulated hydrogeological inactivity and low seismic activity of old oceanic transform-type plate boundaries. Both processes are intrinsically associated. The COST Action FLOWS seeks to merge the expertise of a large number of research groups and supports the development of multidisciplinary knowledge on how seep fluid (bio)chemistry relates to seismicity. It aims to identify (bio)geochemical proxies for the detection of precursory seismic signals and to develop innovative physico-chemical sensors for deep-ocean seismogenic faults. At present, study areas include the Azores-Gibraltar Fracture Zone and the North Anatolian Fault which have generated some of the most devastating earthquakes in Europe. Here we present the latest results from recently-discovered deep-sea mud volcanoes (MVs) located at the rim of the Horseshoe Abyssal Plain, western Gulf of Cadiz (NE Atlantic Ocean). An analysis of the molecular and isotopic composition of hydrocarbon and noble gases is performed on fluids collected at the newly-discovered seeps and in MVs located across the active sedimentary wedge of the Gulf of Cadiz. The tectonic and seismic environments involved vary. However, all active seeps are located along crustal strike-slip faults, which clearly control the seepage of the deep-sourced fluids. Our results yield insights into the effects of the interplay of petroleum migration/trapping, deep sediment dewatering and gas hydrate formation on the geochemical signature of natural gas in deep marine sediments. The cross-disciplinary approach fostered by the FLOWS project yields first indications on the relations between tectonics and seismicity and the secondary processes that shape the geochemical compositions of the fluids transported from deeply buried sediments to the seafloor. It highlights the role of strike-slip faults as the locus of deep fluid transport to the surfacePeer Reviewe

Analysis of salient-pole synchronous generators operating in single-phase condition

The power generation industry has recently started to invest interest and focus on the single-phase operation of traditional three-phase, wound-field, synchronous generators. This is partially due to a combination of customer requirements and the need to understand the extent of flexibility in their current products. This paper deals with an in-detail analysis of a salient-pole, wound-field, three-phase synchronous generator operating in single-phase condition, at unity power factor. The particular 400kVA alternator is first analysed via the classical analytical equations and the results compared with finite-element and available experimental measurements for validation purposes. The tools developed in this stage are then used to analyse the generator under study when it operates in single-phase condition with different values of load. In this work, it can be observed how single-phase operation of synchronous generators can result in an increase of the power-per-phase performance and that, with the appropriate winding configuration, the machine can be used in single-phase operation with a reduced loading

sex differences in axial and limb distribution of melanocytic naevi

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Prediction of the voltage drop due to the diode commutation process in the excitation system of salient-pole synchronous generators

The commutation processes in uncontrolled diode rectifiers have been extensively studied and modelled. However, in some applications, such as electrical power generation, the effects of these processes are often neglected. In low to medium rated, field wound, synchronous generators, the excitation system makes up a significant percentage of the whole generating set. Thus, the voltage drop due to the diode commutations can be quite significant. It is therefore of critical importance that these are considered during all the design stages of the brushless excitation system of synchronous generators. In this paper, a detailed analysis of the commutation aspects related to the diode rectifier of a brushless exciter of a 400kVA synchronous generator is presented and an accurate voltage drop prediction model is proposed and validated

An integrated 2D/3D numerical methodology to predict the thermal field of electric motors

The present work aims at providing a predictive numerical methodology for the thermal characterization of electric motors. The methodology relies on a 2D -FE simulation for the estimation of the electromagnetic (iron and joule) losses. The latter are then exploited in a 3D-CFD Conjugate Heat Transfer analysis for the evaluation of the thermal field. The CFD model includes both the solid components and the fluid domains. The main novelty of the paper is represented by the copper coil modelling. In fact, copper, air, epoxy resin and enamel are synthetized in a single homogeneous body able to reproduce the thermal behaviour without including the single components, to reduce the computational cost. The methodology is validated against experimental data on a three-phase squirrel-cage induction motor. As for the experimental data (available at three different operating conditions), temperature distributions are measured by thermocouples at the test bench for the validation of the 3D-CFD CHT model. In addition, experimental estimations of the losses are available for the validation of the 2D electromagnetic simulations. The numerical results in terms of motor performance, electromagnetic losses and thermal field are discussed and are proved to be close to the experimental counterparts, for all the investigated conditions

An analytical and genetic-algorithm-based design tool for brushless excitation systems of low-medium rated synchronous generators

The sizing procedures adopted for the everyday design of electrical machines are well known and consolidated. However, for brushless exciters of field wound, synchronous generators, there is significant room for improvement as the impact of the diodes’ commutations in the rotating bridge rectifier are often neglected. This paper deals with the development of a fast analytical, genetic-algorithm-based design tool for the excitation systems of salient-pole, field wound synchronous generators. As vessel for this study, the exciter of a particular 400kVAis considered. The proposed tool is focused on achieving exciter designs that minimize the voltage drop due to the commutation processes in the rotating diode rectifier, with minimum impact on the overall efficiency

How soil microbial biodiversity is modified by soil chemical parameters in differently managed olive orchards

Soil restoration is an important challenge of the 21st century, facing the increasing soil degradation, characterized by decline in quality and decrease in ecosystem goods and services. Several studies confirmed that sustainable orchard management practices might sequester atmospheric CO2 into soil, tree biomass and litter, enhancing soil organic carbon (SOC) stock and biodiversity. Higher biodiversity in ecosystems leads to greater stability and multifunctionality. In bacteria-plant interactions, both the bacteria and the plant profit from each other. These interactions play an important role in agriculture, positively affecting plant status and improving product quality. This study aimed at evaluating soil N/C parameters and microbial communities in soil, leaf (aerial part) and xylem sap between olive trees managed under sustainable practices for 17 years (i.e., no-tillage, drip irrigation with urban wastewater and recycling of polygenic carbon sources, like cover crops and pruning material) and trees managed under conventional ones (i.e., soil tillage, burning of pruning residues, mineral fertilization, rainfed), in a mature olive grove located in Southern Italy. In March 2017, samples of soil, leaf and xylem sap were collected in both treatments for DNA extraction and metagenomic analysis of the microbial communities. Soil samples were also collected for chemical and metabolic analyses. Results revealed that the long-term adoption of sustainable agricultural practices increased SOC, organic-N, and microbial biodiversity, with positive effects on plant growth protection and crop quality of olive plants