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Desde hace tiempo, la red trifásica eléctrica y otras composiciones trifásicas, sufren de diferentes fallos eléctricos los cuales deben ser controlados. En el caso de este TFM, el fruto de estudio es la falla eléctrica denominada cortocircuito. Estos cortocircuitos dan una problemática la cual se estudia en este proyecto. Uno de los más importantes es el incremento considerable de las corrientes, provocando así sobrecorrientes, en el momento en el que se produce del cortocircuito. Por eso, este TFM se basa en el estudio y entendimiento de los cortocircuitos y en como mitigar, mediante técnicas de control de limitación de corriente, el efecto de estos mismos. Para ello se ha construido una mr aislada la cual se compone a partir de seis inversores de potencia, seis transformadores y una serie de inductancias para modelizar el conexionado entre los inversores. En este sistema, durante un tiempo determinado, se fuerza la interconexión entre dos fases, para provocar así un cortocircuito entre fases. Posteriormente al fuerce del cortocircuito, y tras haber estudiado las tres diferentes técnicas de limitación de corriente que se aplican, estas son implementadas, junto a toda la mr, mediante el programa Matlab/Simulink. Con ello, se deducirán cuáles son los beneficios de cada una de las técnicas de control y se detallaran cuáles son los resultados de todas las técnicas utilizadas, para que puedan ser así comparadas. Para finalizar el proyecto, se realizara la pertinente conclusión, para de forma objetiva y basándose en los datos y resultados obtenidos, concluir en cuál es la técnica que presenta mayor beneficios en términos de mitigar los efectos del cortocircuito entre fases. For a long time, the three-phase electrical network and other three-phase compositions have been suffering from different electrical faults which must be controlled. In the case of this TFM, the object of study is the electrical fault called short-circuit. These short circuits give a problem which is studied in this project. One of the most important is the considerable increase in currents, thus causing overcurrents, at the moment when the short-circuit occurs. Therefore, this TFM is based on the study and understanding of short circuits and how to mitigate, by means of current limiting control techniques, the effect of these short circuits. For this purpose, an isolated microgrid has been built, which is composed of six power inverters, six transformers and a series of inductances to model the connections between the inverters. In this system, for a given time, the interconnection between two phases is forced, thus causing a short-circuit between phases. After forcing the shortcircuit, and after having studied the three different current limiting techniques that are used, these are implemented, together with the entire microgrid, using the Matlab/Simulink program. In this way, the benefits of each of the control techniques will be deduced and the results of all the techniques used will be detailed so that they can be compared. To close the project, the relevant conclusion will be drawn, in order to objectively and based on the data and results obtained, conclude which technique is the most beneficial in terms of mitigating the effects of shortcircuit between phases.

Orientador: Luis Roberto Marcondes Martins Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba Resumo: O objetivo neste estudo foi avaliar as propriedades físico-químicas de sistemas adesivos por meio dos testes de microdureza, estabilidade de cor, sorção, solubilidade e escoamento. Foram utilizados os sistemas adesivos Adper Single Bond 2 (Single Bond), Clearfil SE Bond (Clearfil) e Single Bond Universal Adhesive (Universal), seguindo de duas técnicas de aplicação, convencional (grupo controle) e aplicação de corrente elétrica (grupo experimental). A microdureza e estabilidade de cor foram avaliadas utilizando amostras de dentina de terceiros molares humanos recém extraídos, hígidos e livres de cáries (n=5). Para os testes de sorção e solubilidade (n=5) foram confeccionados corpos de prova (1,0 ±0,1 mm de espessura e 6,0±0,1 mm de diâmetro). E por fim, para o teste de escoamento foram utilizadas duas placas de vidro com área de 200 mm2 e 5 mm de espessura com massa de 15g cada uma delas (n=5). Após a coleta dos dados, os mesmos foram submetidos a análise de normalidade e homogeneidade dos valores e realizado teste estatístico paramétrico para os valores normais e homogêneos, apresentando nível de significância (?=0.05). A dentina tratada utilizando corrente elétrica apresentou menores valores de microdureza Knoop e manteve a estabilidade de cor, independentemente do método de aplicação. A sorção à água dos adesivos do grupo experimental apresentou redução nos valores, enquanto a solubilidade aumentou apenas utilizando o SB2. O escoamento apresentou maiores valores independente do sistema adesivo utilizado. O uso de corrente elétrica na aplicação do adesivo foi capaz de aumentar as propriedades de sorção e escoamento Abstract: The aim of this study was to evaluate the physicochemical properties of adhesive systems through microhardness, color stability, sorption, solubility and flow tests. Adper Single Bond 2 (Single Bond), Clearfil SE Bond (Clearfil) and Single Bond Universal Adhesive (Universal) adhesive systems were used, following two application techniques, conventional (control group) and electric current application (experimental group) . Microhardness and color stability were evaluated using dentin samples from freshly extracted, healthy and caries-free human third molars (n=5). For the sorption and solubility tests (n=5), specimens were made (1.0 ±0.1 mm thick and 6.0 ± 0.1 mm in diameter). Finally, for the flow test, two glass plates with an area of 200 mm2 and 5 mm thick with a mass of 15g each (n=5) were used. After data collection, they were subjected to analysis of normality and homogeneity of values and a parametric statistical test was performed for normal and homogeneous values, with a significance level (?=0.05). Dentin treated using electric current showed lower values of Knoop microhardness and maintained color stability, regardless of the application method. The sorption to water of the adhesives in the experimental group showed a reduction in values, while the solubility increased only using SB2. The flow showed higher values regardless of the adhesive system used. The use of electric current in the application of the adhesive was able to increase the sorption and flow properties Mestrado Dentística Mestra em Clínica Odontológica CAPES 88887.480726/2020-00

Combining non-invasive brain stimulation (NIBS) with resting-state functional magnetic resonance imaging (rs-fMRI) is a promising approach to characterize and potentially optimize the brain networks subtending cognition that changes as a function of age. However, whether multifocal NIBS approaches are able to modulate rs-fMRI brain dynamics in aged populations, and if these NIBS-induced changes are consistent with the simulated electric current distribution on the brain remains largely unknown. In the present investigation, thirty-one cognitively healthy older adults underwent two different multifocal real transcranial direct current stimulation (tDCS) conditions (C1 and C2) and a sham condition in a crossover design during a rs-fMRI acquisition. The real tDCS conditions were designed to electrically induce two distinct complex neural patterns, either targeting generalized frontoparietal cortical overactivity (C1) or a detachment between the frontal areas and the posteromedial cortex (C2). Data revealed that the two tDCS conditions modulated rs-fMRI differently. C1 increased the coactivation of multiple functional couplings as compared to sham, while a smaller number of connections increased in C1 as compared to C2. At the group level, C1-induced changes were topographically consistent with the calculated electric current density distribution. At the individual level, the extent of tDCS-induced rs-fMRI modulation in C1 was related with the magnitude of the simulated electric current density estimates. These results highlight that multifocal tDCS procedures can effectively change rs-fMRI neural functioning in advancing age, being the induced modulation consistent with the spatial distribution of the simulated electric current on the brain. Moreover, our data supports that individually tailoring NIBS-based interventions grounded on subject-specific structural data might be crucial to increase tDCS potential in future studies amongst older adults.

A microscopic picture for the progressive leakage current growth in electrically stressed HfxSi1−xON∕SiON gate stacks in metal-oxide-semiconductor transistors based on the physics of mesoscopic conductors is proposed. The breakdown spot is modeled as a nanoconstriction connecting two electron reservoirs. We show that after eliminating the tunneling current component that flows through the nondamaged device area, the postbreakdown conductance exhibits levels of the order of the quantum unit 2e2∕h, where e is the electron charge and h the Planck’s constant, as is expected for atomic-sized contacts. Similarities and differences with previous studied systems are discussed.

The evolution of the electrical properties of HfO2/SiO2/Si dielectric stacks under electrical stress has been investigated using atomic force microscope-based techniques. The current through the grain boundaries (GBs), which is found to be higher than thorough the grains, is correlated to a higher density of positively charged defects at the GBs. Electrical stress produces different degradation kinetics in the grains and GBs, with a much shorter time to breakdown in the latter, indicating that GBs facilitate dielectric breakdown in high-k gate stacks.

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This paper presents a monopole antenna-based sensor for measuring different amounts and concentrations of salt and sugar in water. The proposed antenna sensor consists of a textile monopole antenna with circular-ring and partial ground plane. It is implemented by means of embroidery on a felt textile substrate and it resonates at 2.4 GHz. The textile substrate can absorb liquids through the sensing area incorporated within the monopole antenna structure. Therefore, the substrate dielectric properties are changed according to the liquid properties of the absorbed solution. The proposed antenna sensor uses microwave signals to track different amount and concentrations of salt and sugar in terms of the magnitude of the return loss and resonance frequency shift. The measurements are recorded and compared before and after applying different solutions. The rinsing reliability of the proposed antenna sensor has been also studied. The proposed antenna sensor demonstrates a high sensitivity of 800 MHz/mL with a good correlation with the linear fit ( R2=0.9737 ) and 550 MHz/mL with linear response ( R2=0.9135 ) for 5% salt and sugar concentration solutions, respectively. To the best of our knowledge, this article demonstrates for the first time the capability of a fully-textile antenna sensor to detect different amounts and concentrations of salt and sugar using microwave signals. This work was supported by the Spanish Goverment MINECO under Project TEC2016-79465-R.

An accurate procedure for coupling (time-dependent) driven electron tunneling and electromagnetic propagation at terahertz frequencies cannot be developed neither with equivalent electric-circuit approximations nor using standard electromagnetic solvers. Alternatively, in this work, a full-physical time-dependent self-consistent algorithm for such coupling is presented. In order to demonstrate the numerical viability of the algorithm and to show the great interest of driven electron tunneling devices for terahertz applications, a transistorlike tunneling device (coupled to lossy transmission lines) is designed for developing a rectifier, a harmonic generator, and an amplitude modulator at terahertz frequencies.

The relationship between electrical and structural characteristics of polycrystalline HfO2 films has been investigated by conductive atomic force microscopy under ultrahigh vacuum conditions. The results demonstrate that highly conductive and breakdown (BD) sites are concentrated mainly at the grain boundaries (GBs). Higher conductivity at the GBs is found to be related to their intrinsic electrical properties, while the positions of the electrical stress-induced BD sites correlate to the local thinning of the dielectric. The results indicate that variations in the local characteristics of the high-k film caused by its crystallization may have a strong impact on the electrical characteristics of high-k dielectric stacks.

Submitted by Julia CTC/B (julia.vieira@uerj.br) on 2021-11-30T20:49:58Z No. of bitstreams: 1 Dissertação - George Leandro dos Santos Pinto - 2020 - Completo.pdf: 8550860 bytes, checksum: 0e8ab26c15c218736fd00c7b7307fa30 (MD5) Made available in DSpace on 2021-11-30T20:49:58Z (GMT). No. of bitstreams: 1 Dissertação - George Leandro dos Santos Pinto - 2020 - Completo.pdf: 8550860 bytes, checksum: 0e8ab26c15c218736fd00c7b7307fa30 (MD5) Previous issue date: 2020-11-19 Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ This work presents a non-intrusive method to obtain information about damages caused by internal corrosion in AISI-304 stainless steel plates and to classify them according to their severity. By applying the Potential Drop technique, the mapping of the electric potential gradient is extracted, which is examined by image processing strategies such as operations for enhancement of edges and segmentation. With the use of Finite Element Modeling, simulations were carried out to generate examples of damaged plates, using four classes of defects that can be considered as part of pitting corrosion. The image processing stage acts as an extractor of features that, when presented to different regressors and classifiers, make it possible to know the damage depth estimate and the severity classification respectively. With the Random Forest regressor, the mean absolute error of 0.0575mm was obtained in the estimate of the depth of the defects. Additionally, with the application of a Convolutional Neural Network, the accuracy of 94.84% was achieved in the classification of the severity of the damages. Este trabalho apresenta um método não intrusivo para obtenção de informações sobre danos causados por corrosão interna em placas de aço inoxidável AISI-304 e classificá-los de acordo com sua severidade. Pela aplicação da técnica Potential Drop é extraído o mapeamento do gradiente de potencial elétrico, que é examinado por estratégias de processamento de imagens como operações para realce de bordas e segmentação. Com o emprego da Modelagem em Elementos Finitos foram realizadas simulações para gerar exemplos de placas danificadas, utilizando quatro classes de defeitos com geometria alveolar. O estágio de processamento de imagens atua como extrator de atributos que ao serem apresentados a diferentes regressores e classificadores possibilitam ser conhecidas a estimativa da profundidade dos danos e a classificação da sua severidade respectivamente. Com o regressor Random Forest foi obtido o erro absoluto médio de 0,0575 mm na estimativa da profundidade dos defeitos. Adicionalmente, com a aplicação de uma Rede Neural Convolucional foi alcançada a acurácia de 94,84% na classificação da gravidade dos danos.

Esta dissertação de mestrado propõe desenvolver um sistema de monitoramento de desgaste de ferramenta durante o processo de usinagem através da medição da potência elétrica do motor de fuso. Os métodos diretos de medição são mais confiáveis, mas só podem ser utilizados quando a ferramenta está fora de operação. As soluções para monitoramento online do desgaste podem ser as medições dos seguintes itens: força de corte, emissão acústica, vibração, corrente elétrica, temperatura de corte, dimensões da peça, sinais ultrassônicos e óticos, acabamento superficial, que podem ser utilizados individualmente ou de forma conjunta, para um melhor monitoramento do processo. Inicialmente é realizada uma revisão sobre o processo de fresamento, o desgaste da ferramenta, os métodos de medição do desgaste, de forma especial, o monitoramento através da medição da potência elétrica. Posteriormente, são evidenciados o método para o cálculo da potência elétrica, os princípios de funcionamento de um motor de indução, o controle de velocidade de motores, o processamento digital de sinais e as redes neurais artificiais (RNAs). Em seguida, é apresentada a metodologia de trabalho, ou seja, como foi desenvolvida a placa de aquisição de dados, quais foram os materiais, equipamentos e métodos utilizados nos ensaios. Os resultados experimentais apresentam a construção e calibração do sistema de aquisição de dados, os ensaios para determinação da potência elétrica consumida pelo motor de fuso em função do desgaste utilizando diferentes condições de usinagem. De posse desses dados, é realizado o treinamento da RNA e a verificação dos resultados são feitos, comparando o valor de desgaste medido com aquele estimado pela rede. A RNA utilizada é uma Feed-Forward, com treinamento através do algoritmo de BackPropagation Levenberg-Marquardt. Este processo obteve resultados satisfatórios e promissores, identificando um potencial grandioso da utilização desta medição da potência elétrica para predição do desgaste da ferramenta de usinagem. This master's thesis proposes to develop a tool wear monitoring system during the machining process by measuring the electrical power of the spindle motor. Direct measurement methods are more reliable, but can only be used when the tool is out of operation. The solutions for online wear monitoring can be the measurements of the following items: cutting force, acoustic emission, vibration, electric current, cutting temperature, part dimensions, ultrasonic and optical signals, surface finish, which can be used individually or jointly, for better monitoring of the process. Initially, a review is carried out on the milling process, tool wear, wear measurement methods, in particular, monitoring by measuring the electrical power. Subsequently, the method for calculating electrical power, the operating principles of an induction motor, the control of motor speeds, digital signal processing and artificial neural networks (ANNs) are highlighted. Then, the work methodology is presented, that is, how the data acquisition board was developed, what were the materials, equipment and methods used in the tests. The experimental results show the construction and calibration of the data acquisition system, the tests to determine the electrical power consumed by the spindle motor as a function of wear using different machining conditions. With these data in hand, ANN training is carried out and the results are checked, comparing the measured wear value with that estimated by the network. The ANN used is a Feed-Forward, with training through the BackPropagation algorithm Levenberg-Marquardt. This process obtained satisfactory and promising results, identifying a great potential for the use of this measurement of electrical power to predict the wear of the machining tool.

Auroral substorms and solar flares are basically various manifestations of electromagnetic energy dissipation, so that it is useful to consider both phenomena in terms of a chain of processes, consisting of power supply (dynamo), transmission (currents/circuits) and dissipation (auroral substorms, solar flares), the electric current approach. In this short review, we briefly describe both phenomena together on the basis of the chain process. It is shown that the introduction of a dynamo process in this consideration provides a step-by-step way of studying both phenomena. It is shown: (a) Both the solar wind-magnetosphere dynamo and a photospheric dynamo proposed by Lee et al. (1995) have enough power to accumulate enough energy for the explosive features of both phenomena, respectively. (b) For substorms, the power is accumulated in the inner magnetosphere and inflates it, and for flares the power is likely to be accumulated in a loop current along and above two-ribbon flares. (c) For substorms, the energy release (unloading) process deflates the inner magnetosphere, resulting in an earthward electric field, and for flares the disruption of the loop current suggested by Alfven (1950) may be responsible for the energy release. (d) The processes in (c) are responsible for the explosive features of both phenomena.

Acompanha: Atividades experimentais de eletrodinâmica para deficientes visuais Esta dissertação teve como objetivo elaborar, aplicar e avaliar um material destinado ao ensino de eletrodinâmica para deficientes visuais. Para tanto, utilizamos como referencial teórico, a teoria da Aprendizagem Significativa, Atividades Experimentais Investigativas, Sequência Didática e o Ensino de Física, dando ênfase à Eletrodinâmica. Além disso, realizamos, também, uma pesquisa qualitativa, aplicada a um aluno deficiente visual e a dois alunos videntes, considerando o material viável para os demais alunos sem deficiência visual, a fim de desenvolver um trabalho significativo a todos. Após a elaboração da sequência didática e da sua aplicação, coletamos os dados por meio do registro com gravação de áudio, observações e questionários relacionados aos resultados e à usabilidade do material selecionado. Por conseguinte, com a análise dos questionários e por meio de um comparativo do antes e depois, percebemos que houve um avanço em relação ao conceito de Eletrodinâmica e que os alunos conseguiram avançar, significativamente, em todas as atividades, constituindo uma linguagem científica. Assim, diante dos resultados e da troca de experiência, utilizando os pressupostos da Aprendizagem Significativa, concluímos que os objetivos foram alcançados. Desse modo, esperamos com este trabalho, contribuir com a divulgação e o debate da inclusão dos deficientes visuais no Ensino de Física, a fim de assegurar, dessa forma, oportunidades iguais a todos This dissertation had as objective to elaborate, to apply and to evaluate a material destined to the teaching of electrodynamics for visually impaired. We used as a theoretical reference the theory of Significant Learning, Investigative Experimental Activities, Didactic Sequence and Physics Teaching with emphasis on Electrodynamics. We conducted a qualitative research, applied to a visually impaired student and two visionary students, considering the material feasible for the other students without visual impairment, seeking to develop meaningful work for all. After the elaboration of the didactic sequence and its application, we sought to collect the data through the recording with audio recording, observations and questionnaires related to the results and usability of the material used. With the analysis of the questionnaires and making a comparison of before and after, we realized that there was an advance in relation to the concept of Electrodynamics and that in all activities the students managed to advance significantly, constituting a scientific language. In view of the results and the exchange of experience using the assumptions of Meaningful Learning, we conclude that the objectives have been achieved. With this work we hope to contribute to the dissemination and discussion of the inclusion of the visually impaired in Physics Education, guaranteeing equal opportunities for all.

©2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Transformer Rectifier Units (TRUs) are a reliable way for DC generation in several electric applications. These units are formed by multiple three-phase uncontrolled bridge rectifiers connected according to two main topologies (parallel and series), and fed by a phase-shifting transformer, which can have different configurations. Fault diagnosis of the uncontrolled bridge rectifier diodes is one of the most important concerns on the electronic devices, nonetheless, rectifier units are inherently not protected in front of Open-Circuit (O/C) faults, which cause malfunction and performance deterioration. In order to solve this drawback, the proposed fault diagnosis method is based on the O/C fault signature observed in the DC-link output voltage of TRUs rectifier. It allows detecting the O/C diodes of parallel and series TRUs with different phase-shifting transformer configurations and for the most usual fault scenarios. Moreover, it also helps the prediction of diodes that could be exposed to failure after the fault, which provides corrective maintenance for the TRU development. The proposed method is illustrated from MATLABTM numerical simulations of a 12-pulse TRU, and is validated with experimental tests. This work supported in part by the Research Project Estabilidad de Redes MVdc Integrando Tecnologias de Energias Renovables, Almacenamiento de Energia y Convertidores de Fuente de Impedancia, RTI2018-095720-B-C33, in part by the Ministerio de Ciencia, Innovación y Universidades, and in part by the European Union.

A crescente demanda por sensoriamento remoto para previsões meteorológicas, amplificadores de telecomunicações e monitoramento de voos longos tem gerado demanda por fontes alternativas de energia. Consequentemente, isso leva a uma micro fonte de auto-alimentação no local, para evitar a substituição desnecessária de baterias e a transmissão da linha de energia. Uma fonte comum de energia é o vento ou as ondas que são colhidas usando transdutores de vibração, agindo assim em geradores e sensores. Nesta dissertação, uma estrutura de estrutura de portal com material piezoelétrico usando ondas como fonte de energia vibratória. Primeiro, foi feita uma caracterização dinâmica inicial para excitação senoidal e pulsante. Segundo, uma análise de sensibilidade paramétrica foi realizada e um processo de otimização foi realizado usando o Particle Swarm Optimization (PSO). Terceiro, para melhorar ainda mais o desempenho do controlador da Equação de Riccati Dependente do Estado (SDRE), foi usada para variar a carga externa. Os resultados mostram que o PSO não escolheu o mesmo parâmetro presente na literatura com um pequeno ganho (0,5%) em desempenho. No entanto, o controlador SDRE mostrou um aumento de 0.59 para 3 em um periodo de 200 . The growing demand for remote sensing for weather forecasts, telecommunication amplifiers, and monitoring long flights, has been generating demand for alternative power sources. Consequently, this leads to a micro self-power source on site, to avoid unnecessary batteries replacement and power line transmission. A common source of energy is wind or waves that are harvested using vibration transducer, thus actuating as generators and sensors. In this dissertation, a portal frame structure with piezoelectric material using waves as a source of vibration energy. First, an initial dynamic characterization was made for sine and beating excitation. Second, a parametric sensibility analysis was made and an optimization process was carried out using Particle Swarm Optimization (PSO). Third, to further improve the performance the State-Dependent Riccati Equation (SDRE) controller was used varying the external load. The results shows that the PSO did not choose the same parameter as present on the literature with an small gain (.5%) in performance. However, the SDRE controller shown an increase of 0.59 to 3 in a period of 200 .

Multispacecraft missions such as Cluster, Themis, Swarm, and MMS contribute to the exploration of geospace with their capability to produce gradient and curl estimates from sets of spatially distributed in situ measurements. This paper combines all existing estimators of the reciprocal vector family for spatial derivatives and their errors. The resulting framework proves to be robust and adaptive in the sense that it works reliably for arrays with arbitrary numbers of spacecraft and possibly degenerate geometries. The analysis procedure is illustrated using synthetic data as well as magnetic measurements from the Cluster and Swarm missions. An implementation of the core algorithm in Python is shown to be compact and computationally efficient so that it can be easily integrated in the various free and open source packages for the Space Physics and Heliophysics community.

We study Coulomb correlation effects and their role in superconductivity of ϵ-iron under pressure from 12 to 33 GPa by using a combination of density functional and dynamical mean-field theory. Our results indicate a persistence of the Fermi-liquid behavior below the temperature ∼1000K. The Coulomb correlations are found to substantially renormalize the density of states, reducing the distance from the peak to the Fermi level to 0.4 eV compared to 0.75 eV obtained in DFT calculations. We find significant antiferromagnetic correlations, which are accompanied by the formation of short-lived local magnetic moments. We use the obtained results as a starting point for construction of the multiband Bethe-Salpeter equation, which eigenvalues indicate that antiferromagnetic spin fluctuations may result in the superconducting pairing in ϵ-Fe. Moreover, the tendency to superconducting instability becomes weaker with the increase of pressure, which may explain the disappearance of superconductivity at ∼30GPa. © 2020 American Physical Society. The DFT DMFT calculations and solution of the BSE were supported by Russian Science Foundation (project 19-12-00012). The calculations of the particle-hole bubble were supported by the Ministry of Science and Higher Education of the Russian Federation (theme Electron No. AAAA-A18-118020190098-5).

We present a density-functional-theory-based study of a two-dimensional phase of chromium bismuthate (CrBi), a previously unknown material with exceptional magnetic and magneto-optical characteristics. Monolayer CrBi is a ferromagnetic metal with strong spin-orbit coupling induced by the heavy bismuth atoms, resulting in a strongly anisotropic Ising-type magnetic ordering with the Curie temperature estimated to be higher than 300 K. The electronic structure of the system is topologically nontrivial, giving rise to a nonzero Berry curvature in the ground magnetic state, leading to the anomalous Hall effect with a conductivity plateau of about 1.5e2/h at the Fermi level. Remarkably, the Hall conductivity and the magneto-optical constant are found to be strongly dependent on the direction of magnetization. Besides, monolayer CrBi demonstrates the polar magneto-optical Kerr effect in the visible and near-ultraviolet spectral ranges with the maximum rotation angles of up to 10 mrad. Our findings suggest that monolayer CrBi is a promising system for practical applications in magneto-optical and spintronic devices. © 2021 American Physical Society. The authors acknowledge the Ankara University for high performance computing facility through the AYP under Grant No. 17A0443001. This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No. 119F361. The numerical calculations reported in this paper were partially performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources).

The purpose of this study was to analyze Japanese secondary science curriculum materials to determine their potential for supporting secondary teacher learning. In the study, curriculum materials for “Electric Currents” provided by five secondary science textbook publishers were analyzed from the viewpoint of design heuristics for educative curriculum materials. The research questions that guided this study are: (1) What kind of professional knowledge contents for teacher learning are supported intensively in the curriculum materials; and (2) what kind of forms of support for teacher learning are contained in the curriculum materials. Based on the results, some characteristics of Japanese secondary science curriculum materials were identified. First, there was strong support for pedagogical content knowledge of science topics, especially, support for teachers in using scientific phenomena. However, there was only weak support for pedagogical content knowledge for scientific inquiry. Second, the materials contained several forms of support that helps teachers know how to use instructional approaches and activities in productive ways, i.e. implementation guidance. But the materials contained only a few forms of support that present explicit justification for using particular instructional approaches by explaining why these approaches are pedagogically and scientifically appropriate, i.e. rationales.

The active and reactive powers, P and Q, are crucial variables in the parallel operation of single-phase inverters using the droop method, introducing proportional droops in the inverter output frequency and voltage amplitude references. P and Q, or P-Q, are calculated as the product of the inverter output voltage and its orthogonal version with the output current, respectively. However, when sharing nonlinear loads these powers, Pav and Qav, should be averaged by low-pass filters (LPFs) with a very low cut-off frequency to avoid the high distortion induced by these loads. This forces the droop method to operate at a very low dynamic velocity and degrades the system stability. Then, different solutions have been proposed in literature to increase the system velocity, but only considering linear loads. Therefore, this work presents a method to calculate Pav and Qav using second-order generalized integrators (SOGI) to face this problem with nonlinear loads. A double SOGI (DSOGI) approach is applied to filter the nonlinear load current and provide its fundamental component to the inverter, leading to a faster dynamic velocity of the droop-based load sharing capability and improving the stability. The proposed method is shown to be faster than others in the literature when considering nonlinear loads, while smoothly driving the system with low distortion levels. Simulations, hardware-in-loop (HIL) and experimental results are provided to validate this proposal.

Background Capacitive-resistive electric transfer (CRET) is a non-invasive therapeutic strategy that applies radiofrequency electric currents within the 400–600 kHz range to tissue repair and regeneration. Previous studies by our group have shown that 48 h of intermittent exposure to a 570 kHz CRET signal at a subthermal density of 50 μA/mm2 causes significant changes in the expression and activation of cell cycle control proteins, leading to cycle arrest in human cancer cell cultures. The present study investigates the relevance of the signal frequency in the response of the human neuroblastoma cell line NB69 to subthermal electric treatment with four different signal frequency currents within the 350–650 kHz range. Methods Trypan blue assay, flow cytometry, immunofluorescence and immunoblot were used to study the effects of subthermal CRET currents on cell viability, cell cycle progression and the expression of several marker proteins involved in NB69 cell death and proliferation. Results The results reveal that among the frequencies tested, only a 448 kHz signal elicited both proapoptotic and antiproliferative, statistically significant responses. The apoptotic effect would be due, at least in part, to significant changes induced by the 448 kHz signal in the expression of p53, Bax and caspase-3. The cytostatic response was preceded by alterations in the kinetics of the cell cycle and in the expression of proteins p-ERK1/2, cyclin D1 and p27, which is consistent with a potential involvement of the EGF receptor in electrically induced changes in the ERK1/2 pathway. This receives additional support from results indicating that the proapototic and antiproliferative responses to CRET can be transiently blocked when the electric stimulus is applied in the presence of PD98059, a chemical inhibitor of the ERK1/2 pathway. Conclusion The understanding of the mechanisms underlying the ability of slowing down cancer cell growth through electrically-induced changes in the expression of proteins involved in the control of cell proliferation and apoptosis might afford new insights in the field of oncology.

El estudio de las resonancias en circuitos eléctricos es fundamental puesto que este fenómeno puede llevar a valores de voltaje o corriente elevados que podrían llegar a dañar el circuito o la instalación eléctrica. Existen diferentes métodos para analizar dicho fenómeno, pero su aplicación no es sencilla. A la hora de estudiar la resonancia, las respuestas a las siguientes preguntas podrían revelar información importante que sería de gran ayuda: ¿Cuál es la frecuencia a la cual ocurre la resonancia? ¿Cuál es la zona del circuito más sensible a la resonancia? ¿Desde qué punto del circuito se puede observar mejor el fenómeno? ¿Cuál es el elemento del circuito que más influye en la resonancia? Las repuestas a muchas de estas preguntas no se pueden determinar fácilmente con los métodos tradicionales para el estudio de las resonancias. Recientemente, ha aparecido el método modal de análisis que, aplicado junto con del método de los nudos, es capaz de resolver todas las cuestiones anteriores. Este trabajo estudia el fenómeno de la resonancia a partir del método modal de análisis. En primer lugar, se presenta su deducción desde el método de los nudos y luego se explica cómo localiza y analiza el fenómeno de la resonancia en circuitos eléctricos. Tras el estudio de este método, el trabajo concluye con la creación de un programa en Matlab que aplica el método modal de análisis a cualquier circuito eléctrico y sistemáticamente nos devuelve los parámetros relevantes para el estudio de la resonancia.

Este trabalho propõe duas técnicas de controle baseadas em razão cíclica variável para o retificador boost entrelaçado em série. O objetivo das estratégias de controle é aumentar o fator de potência e eficiência do retificador ao eliminar a distorção harmônica de corrente na entrada, característica deste conversor por ser constituído de dois boosts operando em modo de condução descontínua. É apresentada primeiramente uma revisão bibliográfica sobre soluções utilizadas em topologias semelhantes, bem como trabalhos recentes que utilizam este retificador. Na sequência, para cada estratégia proposta é feita uma avaliação do modo de operação, bem como análise matemática, metodologia de projeto e validação dos resultados via simulações e testes em bancada. Os resultados são comparados com as exigências da norma IEC 61000-3-2 e com o retificador sem nenhuma técnica de correção. As duas técnicas de controle propostas são de fácil aplicação e apresentaram grande melhoria na distorção harmônica de corrente em comparação ao conversor clássico, passando com folga pela exigência da norma utilizada. This work proposes two control techniques based on variable duty-cycle for the serial interleaved boost rectifier. The purpose of the control strategies is to increase the power factor and efficiency of the rectifier by eliminating the harmonic distortion of the input current, which is characteristic of this converter as it consists of two boosts operating in discontinuous conduction mode. At first, it is presented a bibliographic review about solutions used in similar topologies, as well as recent works that used this rectifier. Next, for each strategy, an evaluation of the operation is performed, as well as mathematical analysis, design methodology and validation of results through simulations and bench tests. The results are compared with the requirements of IEC 61000-3-2 and with the rectifier without any correction technique. The two control techniques proposed are simple to implement and presented great improvement in current harmonic distortion compared to the classical converter, easily complying with the requirement of the standard used.

International audience; We present a metallic mirror-based resonant cavity-enhanced InAlAs/InGaAs metal-semiconductor-metal (InAlAs/InGaAs-MSM) photodetector driven by a 1550 nm wavelength illumination. The device shows a quantum efficiency higher than 30%, a cut-off frequency higher than 100 GHz, and a saturation current density above 40 kA/cm2 . As a proof of concept, we demonstrate the generation of 0.25 mW of continuous wave output power at a frequency of 100 GHz via the photomixing of an optical beatnote. This result underlines the potential of InAlAs/InGaAs-MSM for subterahertz and terahertz optoelectronic applications driven by telecom lasers.

In this study, the use of polymer inclusion membrane under constant electric current for the removal of Cr(VI) from water has investigated for the first time. Transport of Cr(VI) is performed by an electric current from the donor phase to the acceptor phase with a constant electric current of 0.5 A. The optimized membrane includes of 12.1% 2-nitrophenyl octyl ether (2-NPOE), 77.6% cellulose triacetate (CTA), 10.3% tricapryl-methylammonium chloride (Aliquat 336) as a carrier. We tested the applicability of the selected membrane for Cr(VI) removal in real environmental water samples and evaluated its reusability. Electro membrane experiments were carried out under various parameters, such as the effect of electro membrane voltage at constant DC electric current; electro membrane current at constant voltage, acceptor phase pH, and stable electro membrane; and a comparison of polymer inclusion membrane and electro membrane transport studies. The Cr(VI) transport was achieved 98.33% after 40 min under optimized conditions. An alternative method has been employed that eliminates the changing of electrical current by the application of constant electric current for higher reproducibility of electro membrane extraction experiments by combining the excellent selective and long-term use features of polymer inclusion membrane. © 2016 Elsevier B.V.

A new three-dimensional (3D) electric field enhanced generation model has been developed to describe the electric field effects on the thermal electron–hole pair generation rate. The originality of this model lies in the full three-dimensional description of the synergetic mechanism between the Poole–Frenkel barrier lowering and the phonon-assisted tunneling mechanism. To do this, a classical one-dimensional (1D) model has been integrated over all possible directions of emission of the carriers. The 3D model has been implemented in a Monte Carlo tool devoted to the simulation of the dark current increase induced by radiations in image sensors. Our three-dimensional simulation has been compared to one-dimensional electric field effects’ simulations and experimental data found in the literature in the context of gold contamination. The consequence of using a three-dimensional electric field enhanced generation (EFEG) model is the reduction of the dispersive effect on the dark current distribution of the electric field; hence, each dark current peak is narrower and shows a higher peak's amplitude. The three-dimensional model needs to slightly change the cross-sectional parameters used for a 1D EFEG case to keep a realistic description of each dark current peak of the histogram. In the rest of the paper, we extended our work on constraints relative to space applications. The histograms of the simulated dark current taking into account one- and three-dimensional electric field enhancement effects have been estimated and compared to experimental data acquired after a proton irradiation at room temperature. The use of a three-dimensional model tends to give a more realistic prediction of the dark current non-uniformity in an irradiated pixel array.

International audience; Current noise fluctuations have been investigated in terahertz (THz) quantum well photodetectors embedded in antenna-coupled photonic architectures and compared with standard substrate-coupled mesa detectors. The noise measurements give a value of the photoconductive gain that is in excellent agreement with that extracted from previous responsivity calibrations. Moreover, our results confirm that the noise equivalent power (NEP) of the antenna-coupled devices is of the order of 0.2 pW/Hz0.5. This low NEP value and the wide band frequency response (∼GHz) of the detectors are ideal figures for the development of heterodyne receivers that are, at present, a valuable technological solution to overcome the current limitation of THz sensors.

International audience; The Ionization by Radial Electron Neat Adaptation (IRENA) ion source has been designed to operate under extreme radiation conditions. Based on the electron beam generated plasma concept, the ion source is specifically adapted for thick target exploitation under intense irradiation. A validation prototype has been already designed and tested offline. The design of a new optimized prototype for online difficult beams production with ISOL facilities will be presented and discussed. In particular, simulation activities for thermionic emission, ions confinement and extraction will be presented and results discussed.

We investigate the anisotropic magnetoresistance (AMR) of ferromagnetic CoNi microhelices fabricated by electrodeposition and laser printing. We find that the geometry of the three-dimensional winding determines a characteristic angular and field-dependence of the AMR due to the competition between helical shape anisotropy and external magnetic field. Moreover, we show that there is an additional contribution to the AMR that scales proportionally to the applied current and depends on the helix chirality. We attribute this contribution to the self magnetic field induced by the current, which modifies the orientation of the magnetization relative to the current flow along the helix. Our results underline the interest of three-dimensional curved geometries to tune the AMR and realize tubular magnetoresistive devices., Comment: 5 pages, 5 figures, journal article

The popularization of multicopter drones opens new possibilities for investigations of the atmospheric potential. The method of directly measuring of the electric potential drop of the lower part of the atmosphere has been conducted in the past by means of tethered balloons. In this paper, we investigate the possibility of using multicopter drones to deploy conductive wires to measure the atmospheric potential. Drones provide the advantage to hold the potential probe vertically reaching stable geometry. The main disadvantage of the drone is the short-limited time of flight that does not allow continues measurements. Here we present the results of our first five flights reaching altitudes of 300 m. The potential measurements show linearity and are consistent with previous works until an altitude of 200 m. At that altitude, the occurrence of corona starts to significantly affect. The resulted system impedance resulted be in the range of ~0.7 1010 O which is consistent with previous works. The paper provides guidance for future investigations. This work was supported by research grants from the Spanish Ministry of Economy and the European Regional Development Fund (FEDER): ESP2013-48032-C5-3-R, ESP2015-69909-C5-5-R and ESP2017-86263-C4-2-R

Orientador: Cristiano Monteiro de Barros Cordeiro Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: No trabalho aqui apresentado, fibras ópticas especiais foram fabricadas e estudadas para fins de sensoriamento de corrente elétrica e campo magnético. Primeiramente, propusemos e fabricamos uma fibra óptica especial com dois tipos de birrefringência: linear e circular. Para a adição de birrefringência linear, um padrão de buracos levemente assimétrico, de modo a produzir um núcleo elíptico, foi empregado. Para a adição de birrefringência circular, adotamos a estratégia de imprimir uma torção na fibra durante sua fabricação. Essa fibra óptica especial foi modelada, fabricada e analisada teórica (método dos elementos finitos) e experimentalmente (modos guiados, perda, birrefringência) A aplicação da fibra especial com taxa de torção como sensor de corrente elétrica se baseou no efeito Faraday, em que a luz tem seu estado de polarização alterado ao atravessar uma região sob a influência de um campo magnético. Para o estabelecimento do sensor foi utilizado um método de interrogação polarimétrico com luz linearmente polarizada. Obtivemos uma sensibilidade de (1,00 ± 0,04) x 10-5 A-1 e, mais importante, demonstramos que o procedimento de adicionar birrefringência circular à fibra torna-a menos sensível a perturbações externas, em especial, ao efeito da birrefringência linear induzida pela curvatura da fibra. Ainda no âmbito de sensoriamento de corrente elétrica e campo magnético, discutimos alguns sensores utilizando fibras convencionais, com redes de Bragg e filmes finos de terfenol-D (material magnetostritivo). Por fim, desenvolvemos um sensor de temperatura empregando uma fibra capilar com núcleo imerso na parede (embedded-core fiber) e preenchida com material metálico (índio). Com este sensor, obtivemos uma sensibilidade de (8,40 ± 0,06) nm.°C-1, valor comparável aos mais elevados encontrados na literatura Abstract: In this work, specialty optical fibers were developed and studied for electric current and magnetic field sensing. First we proposed and fabricated an optical fiber with linear and circular birefringences. To create the linear birefringence a slightly asymmetric pattern of air holes was used to produce an elliptical core. In order to add circular birefringence to the fiber we developed a mechanism to spun the fiber during its fabrication. This specialty optical fiber was theoretically (finite elements method) and experimentally (guided modes, loss and birefringences) analyzed. Using the spun fiber as an electric current sensor was based on the Faraday effect, where light has its polarization changed when travelling through a region under the influence of a magnetic field. To establish the sensor we used a polarimetric interrogation system with linearly polarized light. Here we obtained a sensitivity of (1,00 ± 0,04) x 10-5 A-1 and, most importantly, we demonstrated that the procedure of adding circular birefringence to the fiber makes it less sensitive to external perturbations, such as the effect of the linear birefringence induced by curvature. Regarding electric current and magnetic field sensing, we studied some configurations using a conventional optical fiber, with an inscripted FBG and a thin film of magnetosctrictiv material, terfenol-D. Finally, we developed a temperature sensor by employing a embedded-core fiber filled with índium. With this sensor we obtained a sensitivity of (8,40 ± 0,06) nm.°C-1, which is comparable to the highest reported values Doutorado Física Doutor em Ciências CAPES 797088/2009

Lightning striking tall towers is mainly of the upward lightning type, which is characterized by the absence of a first return stroke and the presence of an initial continuous current (ICC) with or without superimposed pulses. The Säntis Tower is 124 m tall and it is located on the top of the Säntis Mountain (2502 m ASL) in the eastern Swiss Alps. The Tower location exhibited the highest lightning flash density in Switzerland during the period from 1999 to 2006. The Tower was instrumented in May 2010 for the measurement of lightning current parameters. In order to complement these data, a Lightning Mapping Array (LMA) was deployed around the Tower during the Summer 2017. The LMA system locates the sources of radio emissions in the very high frequency range (VHF, 60-66 MHz) in three dimensions by a time-of-arrival analysis. The LMA system allows detailed analysis of individual flashes, through the mapping of the lightning channels in the cloud with sufficient time resolution and spatial precision to locate the origin and propagation of each flash. With the help of the LMA, we intend to further investigate the initiation and propagation characteristics of upward lightning emerging from the Tower. From June 29 to August 15, 2017, 33 upward flashes initiated from the Säntis tower were registered by the LMA network. These records are the first set of VHF total lightning mapping obtained in Switzerland. Preliminary results of the campaign are presented in this paper. © 2018 IEEE.

In this work, we performed EME experiments under a constant direct electric current with PIM. The method not only offered working opportunities with very low potential values (50-70 V), but also highlighted the suitability of PIM applications under constant current in EME. The donor solution is containing the target analyte while in the right chamber there is an acceptor solution to transport the target analyte. Cr(VI) transported from sample solution to an acceptor solution with a high efficiency and recovery 99.75% in 50 minutes. We worked applied electric current constant, platinum wire thickness, membrane stability and life through EME-PIM process, selectivity and applicability of EME-PIM process to the real samples. The Scanning Electron Microscopy also used to elucidate the morphology and structure of PIMs. The membrane's stability and the EME's reproducibility greatly improved by using a constant electric current instead of constant voltage, which can further lower transport times and enhance economical aspects of large-scale applications. © 2018 The Electrochemical Society.

The determination of the specific resistance of representative soils taken from tthe surface strata of the Salt Lake Valley, with varying water contents, was the problem confronting the writers at the beginning of the investigation. In the following thesis an attempt is made to explain the methods used in the exact solution of the problem stated above, together with the data obtained relative to the variation of soil resistance with the water content, physical structure and chemical composition.

Nous avons présenté dans ce travail le contrôle de la Génératrice à Réluctance Variable (GRV) connectée au réseau alternatif monophasé pour une application éolienne. La régulation de la vitesse de rotation est assurée par le convertisseur coté génératrice et le couple est imposé par la machine à courant continu utilisée ici pour simuler la turbine éolienne. La connexion de la génératrice au réseau est réalisée par un convertisseur DC-AC qui assure le maintien de la tension du bus DC par un correcteur PI. Un correcteur résonant est utilisé pour suivre la consigne de courant sinusoïdale.

Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in affects strongly the electric resistivity and its temperature dependence $\rho(T)$, while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in $\rho(T)$ near the Curie temperature $T_C$. At $T < T_C$, the $\rho(T)$ behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of the normal and anomalous Hall effect were determined. It was shown that the latter coefficient, $R_S$, is related to the residual resistivity $\rho_0$ by a power law $R_S \sim \rho_0^k/M_S$ with $M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for Co$_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co$_2$YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The temperature dependence of resistivity at low temperatures is analyzed and discussed in the framework of the two-magnon scattering theory., Comment: Invited Report on the Moscow International Symposium on Magnetism MISM-2017, pdf only, 6 pages, J. Magn. Magn. Mater., in press

This paper studies different circulating current references for the modular multilevel converter. The circulating current references are obtained from the instantaneous values of the output current and modulation signal of the phase leg. Therefore, the determination of the amplitude and phase of the output current is not needed, which is a significant improvement compared to other methods such as those based on injecting specific harmonics in the circulating currents. Among the different methods studied in this paper, a new method is introduced, which is able to reduce the capacitor voltage ripples compared to the other methods. A closed-loop control is also proposed which is able to track the circulating current references. With the discussed methods, the average values of the capacitor voltages are maintained at their reference while the voltage ripples are kept low. Experimental results are presented to demonstrate the effectiveness of the proposed and discussed methods.

The electrical conductivity (T) and thermoelectric power S(T) measurements of Sr2InV3O11 showed the insulating state and the change of sign of thermopower from p to n at Tn􀀀p = 400 K. The I–V characteristics provided the evidence of symmetrical and non-linear behaviour typical of strong emission of charge carriers induced by temperature and voltage. Relative dielectric permittivity "r as well as loss tangent (tan ) strongly depend both on the temperature in the range of 295–400 K and the frequency in the range of 5 102 to 1 106 Hz, showing the broad maximum at 320 K. These effects are considered as a relaxation process like in the Maxwell–Wagner or Jonscher model as well as the conduction of electric current, as determined by the Joule–Lenz law[…]

CNPq Este trabalho apresenta um retificador trifásico isolado com correção do fator de potência utilizando um autotransformador Scott e utilizando dois retificadores monofásicos isolados com correção do fator de potência de estágio único (S2). O autotransformador Scott faz uma redução de fases permitindo que se utilizem dois retificadores de estágio único. Os conversores monofásicos utilizados são do tipo Full-Bridge Flyback. O conversor proposto pode operar como elevador ou abaixador de tensão dependendo da relação entre as tensões de entrada e saída do conversor. O controle do conversor foi feito via MCU modelo TMS320F28335. Este trabalho apresenta a análise teórica do conversor operando em modo de condução contínua (CCM), bem como os resultados experimentais baseado em um protótipode 4kw. This work presents a three-phase isolated rectifier with power factor correction using a Scott autotransformer and two isolated single-phase single-stage (S2) rectifiers. The Scott autotransformer provides a phase reduction allowing the use of two single-phase rectifiers. The single-phase converters used are the Full-Bridge Flyback type. The proposed converter can operate as a step-down or a step-up voltage, according to the relation between input andoutput voltage. The control of the converter was made in a MCU model TMS320F28335. This paper presents the theoretical analysis of the converter for continuous conduction mode (CCM) as well as experimental results based on a 4 kW prototype.

Electron and hole transport properties of the organic small molecule N,N0 -Di(1-naphthyl)-N,N0 - diphenyl-(1,10 -biphenyl)-4,40 -diamine are investigated by space-charge-limited current measurements. The hole transport shows trap-free behavior with a mobility of 2.3 108m2 /Vs at vanishing carrier density and electric field. The electron transport, on the other hand, shows heavily trap-limited behavior, which leads to highly unbalanced transport. A trap concentration of 1.3 1024m3 was found by modeling the electron currents, similar to the universal trap concentration found in conjugated polymers. This indicates that electron trapping is a generic property of organic semiconductors, ranging from vacuum-deposited small-molecules to solution-processed conjugated polymers.

In order to understand the physics mechanism of a negative ion extraction in negative ion sources, an emission surface of the negative ions around an aperture at a plasma grid, so-called a meniscus, has been analyzed by an inverse calculation of the negative ion trajectory in a two dimensional beam analysis code. In this method, the meniscus is defined as the final position of the negative ion trajectories which are inversely calculated from the measured beam profile to the plasma grid. In a case of the volume-produced negative ions, the calculated meniscus by the inverse calculation was similar to that obtained in conventional beam simulation codes for positive ion extractions such as BEAMORBT and SLACCAD. The negative ion current density was uniform along the meniscus. This indicates that the negative ions produced in the plasma are transported to the plasma grid uniformly as considered in the transportation of the positive ions. However, in a surface production case of negative ions, where the negative ions are generated near the plasma grid with lower work function by seeding cesium, the current density in the peripheral region of the meniscus close to the plasma grid surface was estimated to be 2 times larger than the center region, which suggested that the extraction process of the surface-produced negative ions was much different with that for the positive ions. Because this non-uniform profile of the current density made the meniscus shape strongly concave, the beam extracted from the peripheral region could have a large divergence angle, which might be one of origins of so-called beam halo. This is the first results of the determination of the meniscus based on the experiment, which is useful to improve the prediction of the meniscus shape and heat loads based on the beam trajectories including beam halo.

The field emission (FE) properties of carbon nanotube (CNT)-based cathodes have been investigated on nanostructured surfaces grown by plasma enhanced chemical vapor deposition. The FE angular properties and temporal stability of the emergent electron beam have been determined using a dedicated apparatus for cathodes of various architectures and geometries, characterized by scanning electron microscopy and I-V measurements. The angular electron beam divergence and time instability at the extraction stage, which are crucial parameters in order to obtain high brilliance of FE-based-cathode electron sources, have been measured for electrons emitted by several regular architectures of vertically aligned arrays and critically compared to conventional disordered cathodes. The measured divergences strongly depend on the grid mesh. For regular arrays of individual CNT, divergences from 2° to 5° have been obtained; in this specific case, measurements together with ray-tracing simulations suggest that the maximum emission angle is of the order of ±30° about the tube main axis. Larger divergences have been measured for electron beams emitted from honeycomb-structured cathodes (6°) and significantly broader angle distributions (10°) from disordered CNT surfaces. Emission current instabilities of the order of 1% for temporal stability studies conducted across a medium time scale (hours) have been noted for all cathodes consisting of a high number (10$^{4}$ and larger) of aligned CNTs, with the degree of stability being largely independent of the architecture.

We present a simplified, rapid, and accurate method for the measurement of the thermoelectric Thomson coefficient by the dynamical heating of a suspended wire by an alternating current. By applying a temperature gradient across the wire, we find that the response at the second harmonic of the excitation frequency is directly proportional to the Thomson coefficient. The absolute thermoelectric coefficient of a single material can therefore be extracted with high precision by a phase sensitive detector. We test our method on platinum and nickel wires and develop both analytical and numerical models to determine the leading sources of error., Comment: 10 pages, 7 figures and 1 table