Miracle-dz/UniFAR-FTUs huggingface dataset:
Accurate and Efficient Estimation of Short-Circuit Current for MTDC Grids Considering MMC Control

DC short-circuit current calculation for the modular multilevel converter based multi-terminal direct current (MMC-MTDC) grid is critical and fundamental in equipment selection and protection setting. The existing MTDC grid short-circuit current calculation methods suffer from low efficiency, poor adaptability, and inflexibility. To address these issues, this paper proposes an efficient and general companion circuit-based method to estimate the short-circuit currents of asymmetric bipolar MTDC grids. First, an MMC is equivalent to an RLC series circuit in parallel with a time-dependent controlled current source. The equivalent model considers not only the discharge currents of the sub-module capacitors but also the ac in-feed current determined by MMC controllers. Then, the equivalent model for a bipolar MTDC grid with the dedicated metallic return is established by combing the equivalent MMC model with the lumped model of the dc transmission lines. Next, the companion circuit method is employed to efficiently and readily solve the equivalent model of the dc grid to obtain post-fault branch currents and node voltages. Both theoretical analyses and intensive tests on the CIGRE benchmark MTDC grid and Zhangbei bipolar MTDC grid verify the improved accuracy, efficiency, adaptability, and flexibility of the presented method.
All printed bio-sensing device

For the last few years giant strides have been made in the area of nanoscience. These strides will have a tremendous impact on many different areas such as drug-sensing, IC-industry and medicinal applications. Surface enhanced Raman spectroscopy is one aspect of this, were the signal from Raman scattering can be increased many times over. This is done by creating small structures in a material and coating it in a metal. During this work a chip was created using nano-imprint lithography techniques for the creation of nanostructures on a PET wafer. Physical vapor deposition was then used to apply a metal to these structures. Finally 3D-printing was used to integrate this wafer into a chip. Both the chip and the wafers were then tested using fluorescence and Raman spectroscopy. Mean signal to noise ratios as high as 557 were observed for 50 nm Ag on top of 50 nm pillars. The study thus show promising results in using these relatively cheap methods to build small highly sensitive and selective chips for use in the detection of trace amounts of molecules. Bachelors thesis in Physics at Umeå university Supervisor: Xueen Jia Examinator: Thomas Wågberg Max Bäckman (maba0152@student.umu.se) May 25, 2018
Review of Timber connections: Connector Plate, Cleats, Studies and Dovetail Connections

The strength of a building relies heavily upon the transfer of load from one connection to another [1,2]. A solid and reliable connection method must be utilized to increase the strength of timber panel and enable the structure to withhold an excessive amount of stress [3-5]. In wood buildings, an effective connection will provide the building with strength and ductility [6]. However, there are many connections needed in a wooden structure therefore an economical and durable connection is required to assemble a prefabricated panel quickly and inexpensively in mass production [6].
Evaluating the impact of lean practices on environmental performance: evidences from five manufacturing companies

Abstract Previous evidence suggests that lean practices help organizations to enhance environmental performance. However, the impact of lean practices on the environment is still unclear. This study, therefore, aims to analyse the relationship between lean and environmental performance in two main stages: first, a review of the relevant literature was developed, followed by a multiple case study analysis conducted in five manufacturing companies. Onsite data were collected from the firms during a 5 years’ time span of research and developing semi-structured interviews. Findings indicate that the environmental performance of the companies analysed is generally enhanced in the long-term after the implementation of lean. Moreover, the results suggest that the environmental performance of the firms investigated is mainly improved by using JIT and TQM practices in a lean transformation context. The research findings provide further results remarking the possible negative impact of Kanban deliveries, 5S and TPM on various environmental performance indicators.
Somatotype and body image: their sensitivity, specificity and validity to determine obesity

Se midió la sensibilidad y especificidad del somatotipo y de un cuestionario de imagen corporal para predecir obesidad. En un estudio transversal participaron 294 estudiantes universitarios del norte de México de ambos sexos (143 mujeres de 18 años a 35 años). Se midió el somatotipo por antropometría y se administró en cuatro ocasiones el cuestionario de imagen corporal de Gardner, adjuntando las siguientes preguntas: ¿Cómo me veo? ¿Cómo quisiera estar? ¿Cómo creo que me ven los demás? y ¿Cómo me ven los demás? El somatotipo y la imagen corporal predijeron de manera correcta entre el 90% y 95% de los casos con y sin obesidad; presentaron, además, ~86% de capacidad discriminante para determinar obesidad. La endomorfia, la ectomorfia y el ¿Cómo me ven los demás? presentaron la más alta sensibilidad y especificidad (~90%). Concluimos que el somatotipo y el cuestionario de imagen corporal son dos instrumentos válidos, sensibles y específicos para conocer el grado de obesidad.
Design and Optimization of Halbach-Array PM Rotor for High-Speed Axial-Flux Permanent Magnet Machine With Ironless Stator

In this article, a high-speed Halbach-array permanent magnet (PM) rotor for ironless stator axial-flux permanent magnet (AFPM) machine is proposed and researched with consideration of the multiphysics constraints, including the electromagnetic characteristics, mechanical strength, and rotor dynamics. Considering the severity of attractive force between twin rotors, the complex repulsive force among PM segments of Halbach-array and centrifugal force, the new hybrid sleeve, and PM fixation method are proposed to improve the rotor mechanical strength. Then, the rotor stress is analyzed by numerical analysis and three-dimensional (3-D) finite-element analysis (FEA). Furtherly, the sleeve thickness and interference fit are optimized by 3-D FEA. The rotor dynamics and bearing arrangement are analyzed to validate the effectiveness of the high-speed Halbach-array PM rotor. A 50-kW, 9000 r/min ironless stator AFPM machine prototype with Halbach-array PM rotor is manufactured and tested. The measured results show that the output power is up to 53.8 kW at 9000 r/min. The feasibility of high-speed Halbach-array PM rotor and accuracy of analysis method are validated by both simulated and measured results.
Measurement-Based Estimation of Inertia in AC Microgrids

This paper presents an improved method to estimate the available inertia in an islanded AC microgrid. Inertia estimation is carried out based on measured frequency response for any arbitrary disturbance that occurs in the system. Modifications are made to the conventional swing equation-based curve-fitting method to obtain an accurate estimate for a system with high penetration of renewable generations. A polynomial curve fit over the total power generation is introduced to estimate the size of the disturbance accurately. Additionally, a variable order polynomial fit is carried out over the measured frequency, which not only improves the estimate of inertia but also helps to refrain the influence of network topology and size/location of the disturbance. The test microgrid system considered is a modified Standard IEEE distribution network, which consists of radial feeders and distributed generations. Firstly, the proposed method is tested on a system with only synchronous generations to assess the accuracy of the estimate. This is followed by the integration of Type 3 and Type 4 wind turbines, and a PV array within the microgrid system. Virtual inertia control is then implemented in the wind turbines to obtain inertial support. Estimation study of the microgrid system with virtual inertia is then carried out. The developed estimation method can accurately estimate the inertia provided by the synchronous sources within the generation mix. Finally, from all the results and observations, the inertia estimation process in a microgrid system is segregated into synchronous and nonsynchronous inertia estimation.
Fault Ride-Through Enhancement of Grid Supporting Inverter-Based Microgrid Using Delayed Signal Cancellation Algorithm Secondary Control

The growing level of grid-connected renewable energy sources in the form of microgrids has made it highly imperative for grid-connected microgrids to contribute to the overall system stability. Consequently, secondary services which include the fault ride-through (FRT) capability are expected to be possessed characteristics by inverter-based microgrids. This enhances the stable operation of the main grid and sustained microgrid grid interconnection during grid faults in conformity with the emerging national grid codes. This paper proposes an effective FRT secondary control strategy to coordinate power injection during balanced and unbalanced fault conditions. This complements the primary control to form a two-layer hierarchical control structure in the microgrids. The primary level is comprised of voltage/power and current inner loops fed by a droop control. The droop control coordinates grid power-sharing amongst the voltage source inverters. When a fault occurs, the participating inverters operate to support the grid voltage, by injecting supplementary reactive power based on their droop gains. Similarly, under unbalanced voltage condition due to asymmetrical faults in the grid, the proposed secondary control ensures the positive sequence component compensation and negative and zero sequence components clearance using a delayed signal cancellation (DSC) algorithm and power electronic switched series impedance placed in-between the point of common coupling (PCC) and the main grid. While ensuring that FRT ancillary service is rendered to the main utility, the strategy proposed ensures relatively interrupted quality power is supplied to the microgrid load. Consequently, this strategy ensures the microgrid ride-through the voltage sag and supports the grid utility voltage during the period of the main utility grid fault. Results of the study are presented and discussed.
Systematic Synthesis and Derivation of Multilevel Converters Using Common Topological Structures With Unified Matrix Models

Multilevel converters (MLCs) have been increasingly adopted in both low-power low-voltage systems and high-power high-voltage applications. In recent years, many new topologies have been proposed, and a few of them have been successfully implemented in industry. While searching for new topologies, synthesis and derivation principles of multilevel topologies are critical for converter design. In this article, a generalized synthesizing approach of multilevel topologies is proposed and analyzed with the considerations of the voltage source, current source, and matrix-type MLCs. Based on the proposed method, the topological relationship among these three types MLCs is revealed through the stage-based common circuit structure. In addition to the graphic-based approach, a mathematical approach is proposed for representing the MLC topologies in this work. The matrix-based model is utilized to unify and verify the derivation and simplification process in a systematic way through many MLC examples in this article. Finally, demonstration examples are presented to show how the proposed principles can be used to derive new topologies covering five-level to nine-level converters. With the ever-increasing research efforts on MLCs, it is hoped that this article can provide a new approach that inspires the development of more interesting and practical MLC topologies for various applications.
Students’ Attitude Toward Physical Education: Relations With Physical Activity, Physical Fitness, and Self-Concept

This study investigated the relation between students’ attitude toward physical education (PE) and its correlates by simultaneously considering age, sex, enjoying physical activity (PA), self-perceived physically active lifestyle (PAL), self-perception of physical competence, PA, and cardiovascular fitness (CF). This cross-sectional study included 235 students (M = 15.2 ± 2.5 years). All correlates of students’ attitude toward PE were assessed via questionnaires. CF was assessed by via Fitnessgram. Pearson correlation coefficients confirmed a large positive correlation between attitude toward PE and PA enjoyment (r = .71, p < .001) and PAL (r = .52, p < .001). Moderate positive correlations were found for self-perception of physical competence, nonorganized PA, organized PA, and CF (.24 ≥ r ≤ .48, ps < .001) . Multiple linear regression showed that enjoying PA (β = .62, p < .001) was the only significant predictor when all variables were considered simultaneously. The model explained 55% of explained variance on students’ attitude toward PE. Binary logistic regressions showed that students who reported enjoying PA were 9.3 times more likely to report a positive attitude toward PE. In contrast, students who did not enjoy PA and those who overperformed in the CF test were 4.2 and 1.1 , respectively, more likely to report a negative attitude toward PE. Coherently across all analyses, from all the predictors studied, PA enjoyment seems to be the most powerful, showing the highest contribution in explaining students’ attitude toward PE. Subscribe to TPE
Low-Power, Low-Phase-Noise Gm-Boosted 10-GHz VCO With Center-Tap Transformer and Stacked Transistor

This brief presents a low-power-consuming and low-phase-noise 10 GHz voltage-controlled oscillator (VCO) using the 65 nm CMOS technology. We propose a new structure for the VCO using a center-tap transformer and stacked transistor, which realizes negative $g_{m}$ -boosting to improve the phase noise and start-up conditions. The measured output frequency range of the designed VCO with a binary-weighted 3 bit capacitor bank is 9.66 to 11.07 GHz. The proposed VCO demonstrates a measured phase noise of −115.4 dBc/Hz at a 1 MHz offset frequency. To the best of our knowledge, compared to previously reported 10 GHz VCOs, the proposed circuit achieves the lowest phase noise. The proposed VCO achieves a power consumption of 2.7 mW, which reveals figure of merit and figure of merit with frequency tuning values as low as −191.4 and −194.1 dBc/Hz, respectively, and also the lowest value among state-of-the-art 10 GHz VCOs.
A Real-Time Entropy Estimation Algorithm for Lithium Batteries Based on a Combination of Kalman Filter and Nonlinear Observer

This article proposes a novel real-time entropy estimation algorithm based on a Kalman filter combined with a nonlinear observer. The proposed algorithm requires the thermodynamic profile of the battery to be extracted in the laboratory from fresh batteries beforehand, which is piecewise linearly approximated by mean of B-Splines of the first order. Then, a nonlinear observer is used to estimate in real time the open-circuit voltage of the battery. Finally, using the linearized thermodynamic profile as a model and the estimated open-circuit voltage as input, a Kalman filter is designed to determine the entropy of the battery from the measured battery temperature. The proposed algorithm is embedded into a conventional 8 b 16 MHz microcontroller and, under standard constant current, constant-voltage charging conditions, estimates the entropy with less than 0.60 J<inline-formula><tex-math notation="LaTeX">$\cdot$</tex-math></inline-formula>K<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> of error for three different types of lithium-ion batteries and less than 3 J<inline-formula><tex-math notation="LaTeX">$\cdot$</tex-math></inline-formula>K<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> of error for one type of lithium-polymer batteries, while requiring less than 1 ms of computation time per iteration.
Quantitative Research of Photobioreactor Performance Based on an Improved Surface Fitting Method

The relationship between performance and working conditions in photobioreactor hydrogen production systems illuminated by a variable intensity light source has been described quantitatively using relational expressions. First, based on the finite volume method and the Michaelis-Menten model, the hydrogen production process of a photobioreactor (PBR) system was simulated numerically. Then, the performance of the PBR system was evaluated considering the hydrogen production rate, dimensionless hydrogen production rate, hydrogen production thrust coefficient and conversion efficiency of light energy to hydrogen energy rate as performance parameters, and the relationship between these parameters and working conditions was studied. Finally, the improved quantum-behaved particle swarm optimization (IQPSO) and surface fitting technique based on the curve fitting method were used to obtain relational expressions about the performance and working conditions of the PBR. All of the results show that the method can obtain accurately relational expressions for the performance optimization and forecasts of the PBR system.
Model Verification and Justification Study of Spirally Corrugated Pipes in a Ground-Air Heat Exchanger Application

Ground-air heat exchangers have become an important topic in recent years due to their contributions to the market growth of the ground source heat pump industry. This paper provides a comprehensive study and recommends suggestions on the selection process of a suitable pipe for an air-to-water heat pump (AWHP). Parametric studies including material, turbulent plate quantity, and pipe type were performed to identify an optimal pipe design for high-performance AWHP. Both numerical and experimental studies were carried out to validate current pipe models. Overall, there was good agreement between the numerical model and experimental results. It was determined that a spirally corrugated pipe exhibited excellent thermal power generation with little compromising pressure drop. Finally, a pipe selection example was demonstrated as a design guideline to size an optimal pipe for AWHP application.
Visible Range Characterization of Au/Graphene-GaAs Schottky Junctions in MESFET

We report the simulated visible range characteristics of gold (Au)/graphene-GaAs Schottky junctions in MESFET (Metal–Semiconductor Field Effect Transistor) under photovoltaic, forward bias, and reverse bias conditions. The devices exhibit high photoresponse in zero bias conditions, moderate response under applied reverse bias, and zero photoresponse in forward bias conditions. We discuss in detail the factors involved in the attained response and provide comparative analysis of the studied devices with our previously published work on ultraviolet (UV) characterization demonstrating moderate response under both zero bias and reverse bias, and z ero response under forward bias. We also perform comparison of our theoretical results with the literature showing enhanced or comparable performance. The simulation model is validated with the experimental results reported elsewhere as well as with the commercially available software (Visual TCAD) simulations. The GaAs MESFET Schottky junctions will serve good purpose in UV-visible applications.
Dynamics and control of a 3-DOF planar parallel manipulator using visual servoing resolved acceleration control

This paper proposes the visual servoing resolved acceleration control scheme applied to a 3-degree of freedom (DOF) planar manipulator, which aims to reduce computational loads of the feedback control loop and the tracking errors of the end-effector in the conventional resolved acceleration control scheme. The computation loads are increased due to the calculations of the direct kinematics and the velocity inversion in the feedback control loop. The tracking errors of the end-effector are increased due to low-accuracy encoders, gearbox backlashes, and manipulator flexibility, etc. The proposed scheme incorporates a visual system, which directly captures the position of the end-effector instead of calculating the direct kinematics and the velocity inversion. Due to the requirement of inverse dynamics in the proposed scheme, the transformation of the Jacobian matrices between the passive and active links is imposed to the Euler-Lagrange’s equation so as to derive dynamic equations. In order to show the control performances, three existing torque-based control schemes are also applied to the manipulator. This study investigates the numerical simulations and the experimental validations, and the results show that the proposed scheme can reduce the computation loads and the tracking errors of the end-effector to compare with the three existing schemes.
Principles of Bone Biology

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Near-Optimal Scheduling in Day-Ahead Markets: Pricing Models and Payment Redistribution Bounds

Near-optimal unit commitment (UC) scheduling is a practical reality in wholesale electricity markets. This paper revisits previous work that has found that minor differences in cost among near-optimal schedules can result in a large redistribution of market payments (i.e., changes in generator profits and consumer surplus). It has been believed that this instability is unavoidable, but previous studies have only calculated prices using what we call the Restricted pricing model. This paper compares previous results to three additional models that are based on integer relaxation, and which we call the Partial, Tight, and Loose Dispatchable pricing models. Results are presented for a suite of test cases, including four ISO-scale cases. Similar to previous findings, the Restricted and Partial Dispatchable models both result in large payment redistributions among alternative solutions. In contrast, theoretical and experimental results for the Tight and Loose Dispatchable models show that pricing models with unconditional integer relaxation will have bounded payment redistributions, and, further, this bound can become quite small by tightening the UC problem's convex relaxation. In the presence of market power, stable financial outcomes may improve market efficiency by reducing incentives to bid strategically.