196,063 research outputs found
Demonstration of extrinsic chirality of photoluminescence with semiconductor-metal hybrid nanowires
No full textChiral optical response is an inherent property of molecules and nanostructures, which cannot be superimposed on their mirror images. In specific cases, optical chirality can be observed also for symmetric structures. This so-called extrinsic chirality requires that the mirror symmetry is broken by the geometry of the structure together with the incident or emission angle of light. From the fabrication point of view, the benefit of extrinsic chirality is that there is no need to induce structural chirality at nanoscale. This paper reports demonstration extrinsic chirality of photoluminescence emission from asymmetrically Au-coated GaAs-AlGaAs-GaAs core-shell nanowires fabricated on silicon by a completely lithography-free self-assembled method. In particular, the extrinsic chirality of PL emission is shown to originate from a strong symmetry breaking of fundamental HE 11 waveguide modes due to the presence of the asymmetric Au coating, causing preferential emission of left and right-handed emissions in different directions in the far field
An MPC approach for grid-forming inverters: Theory and experiment
No full textMicrogrids (MGs) interest is growing very fast due to the environment urgency and their capability to integrate renewable energy in a flexible way. In particular, islanded MGs in which distributed energy resources (DERs) are connected to the infrastructure with power electronic converters have attracted the interest of many researchers of both academia and industry because management, control and protection of such systems is quite different from the case of traditional networks. According to their operation mode, MGs that power electronic converters can be divided into grid-forming, grid-feeding and grid-supporting inverters. In particular, grid forming inverters are asked to impose voltage and frequency in the MG. This paper aims to propose a model predictive control (MPC) based approach for grid-forming inverters in an islanded MG. The MPC strategy is implemented because of its capability to define the optimal control actions that contemporarily track the desired reference signals and accounts for equality and inequality constraints. The overall problem formulation (objective function and relevant constraints) is described step by step and considers the specificity of the considered DC source. The proposed approach allows for the obtaining of very good results in terms of readiness against disturbances, even if it requires being fed only by local measurements. In order to validate the developed method, this paper proposes an experimental validation of the designed MPC controller in order to show its correct operation on a real system in a power hardware in the loop set-up using a rapid control prototyping approach
VO2 phase change control of au nanorod emission enhancement of magnetic dipolar emitters
No full textIn this work, we combine the enhancement of the emitter efficiency due to the proximity of a resonant nanostructure, and the possibility to modulate it by means of a thin layer of a phase change material (PCM). PCMs have been used as active subwavelength elements that can switch between the phases that differ in electric and optical properties. The phase change results in a modulation of amplitude or phase of transmission or reflection over nanoscale propagation lengths, and it is compatible with fast optical systems [1,2]. Vanadium Dioxide (VO 2 ) is a promising candidate for nanoscale modulation since it shows dramatic contrast in its complex refractive index as it undergoes a structural phase transition from monoclinic (semiconductor) to rutile (metallic) phase at 68°C [3], induced thermally, electrically or optically. The proposed structure can be fabricated as follows: a thin V0 2 layer is deposited on a glass substrate, and covered by a thin spacer layer of silica, which is doped by luminescent ions; above the spacer, Au nanorods are added to provide the plasmonic resonant enhancement. Sandwiched magnetic dipoles feel strong resonance when V0 2 is metallic due to the strong magnetic field arising from the current loops between Au nanorod and V0 2 ; this resonance blue-shifts and decreases when V0 2 is dielectric. We first maximize the absorption change between the two phases at the emission line of Er 3+ , i.e. 1540 nm. With these optimized geometric parameters, we investigate emission of single dipoles in the layer under the nanorod, considering different positions, types, and orientations. We show the power emitted to the far-field by the magnetic dipole, averaged over the positions under the nanorod. We show that the emitted far-field follows the high contrast at the resonant wavelength of the optimized absorption, proving the control of the enhanced emission and its switching off. Finally, we investigate the influence of the periodicity, as the upper part of the design can be fabricated as a patterned 2D array of nanorods. We believe that such an approach can be of great importance for active modulation of efficient light sources at the nanoscale
Optimal Sizing of Battery Energy Storage Systems for Renewable Energy Integration in Energy Communities
No full textThe integration of renewable energy sources (RESs) into electrical grids has experienced significant growth in recent decades, propelled by the pursuit of a sustainable energy future. However, as the share of renewable electricity production rises, the likelihood of overloading network components and having overvoltages also increases. Battery Energy Storage Systems (BESSs) offer a promising solution for mitigating RESs curtailment. Therefore, this paper proposes an energy storage sizing strategy aimed at minimizing RESs curtailment in a distribution system with renewable energy communities (RECs). This approach, which leverages linear voltage drop relations, distinguishes itself for its simplicity. The constraints of the optimization problem are defined to prevent overload of the primary substation transformer, issues of undervoltage and overvoltage at network nodes, and overcurrent problems in the feeders. Simulation results on a test distribution network validate the proposed method, providing a practical approach to sizing BESSs in RECs and maximizing renewable energy utilization
Advances in photothermal science and techniques: a route for NDT from macro to nanoscale
No full textHeat transfer can differ distinctly at the nanoscale from that at the macroscale. Recent advancement in experimental techniques has enabled a large number of interesting observations and understanding of heat transfer processes at the nanoscale
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Photovoltaic Power Nowcasting Using Decision-Trees Based Algorithms and Neural Networks
No full textPrecise Photovoltaic (PV) power forecasting tools are needed to integrate PV into the new framework of the energy sector. Also, the related intermittent and random nature needs to be appropriately considered. In this context, this paper examines various machine learning algorithms used for one hour ahead forecasting of PV power production. Specifically, the performances of two Long Short-Term Memory (LSTM) recurrent neural networks, a Gradient Boost Machine (GBM) model and an Extreme Gradient Boosting (XGB) model, are compared. Six years of data are retrieved from the 81 kW PV power plant in the Savona campus of the University of Genoa and are used to train and test the algorithms. The performances of all the algorithms are compared over the original dataset, composed of meteorological variables linked with the PV production, a dataset using seasonal and trend decomposition (STL) of the meteorological variables, and some reduced datasets that mimic the situation in which some of the features are not available at least for some time steps. By comparing the results through different case studies, it can be justified that the XGB outperforms the other algorithms and the STL decomposition is helpful in increasing the performance of the model
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Control of Au nanoantenna emission enhancement of magnetic dipolar emitters by means of VO2 phase change layers
No full textActive, ultra-fast external control of the emission properties at the nanoscale is of great interest for chip-scale, tunable and efficient nanophotonics. Here we investigated the emission control of dipolar emitters coupled to a nanostructure made of an Au nanoantenna, and a thin vanadium dioxide (VO2) layer that changes from semiconductor to metallic state. If the emitters are sandwiched between the nanoantenna and the VO2 layer, the enhancement and/or suppression of the nanostructure’s magnetic dipole resonance enabled by the phase change behavior of the VO2 layer can provide a high contrast ratio of the emission efficiency. We show that a single nanoantenna can provide high magnetic field in the emission layer when VO2 is metallic, leading to high emission of the magnetic dipoles; this emission is then lowered when VO2 switches back to semiconductor. We finally optimized the contrast ratio by considering different orientation, distribution and nature of the dipoles, as well as the influence of a periodic Au nanoantenna pattern. As an example of a possible application, the design is optimized for the active control of an Er3+ doped SiO2 emission layer. The combination of the emission efficiency increase due to the plasmonic nanoantenna resonances and the ultra-fast contrast control due to the phase-changing medium can have important applications in tunable efficient light sources and their nanoscale integration
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