Databases are the fundamental component of an application for storing data. SQL (Structured Query Language) is a query language that is used to create, read, update, and remove records in most relational databases (CRUD operations). Because new relational database management systems have arisen, it is useful to compare some of them when linked to a Java application using Spring Data JPA. The time for each CRUD activity is analyzed for thousands and hundreds of thousands of entries. The motivation is to find the most performant combination for an application, considering its size (number of entries).
Local governments and battery manufacturers will have a serious problem once the batteries from first generation of electric vehicles will reach the End of Life. These batteries are retired because they do not comply with automotive safety regulations and transportation laws. Even so they still have about 80% of their initial capacity, which makes them suitable in other less demanding applications. However, they must first undergo an extensive evaluation to identify batteries with similar characteristics so that new battery packs can be made. This paper presents the development and testing of a multi-chemistry, multi-battery state of health screening system. The design is based on a bidirectional DC-DC cascaded Buck-Boost power converter that allows simultaneous testing of two or more cells, despite their chemistry.
The temperature regime of electronic modules is crucial for their reliable operation. This study deals with the implementation of a system for experimental investigation of the temperature field of electronic devices with the use of thermal camera. The main dependencies are described so that the pixel area can be obtained and the pixels can be classified into different temperature zones. Furthermore, an algorithm of the system has been developed, which describes the process of implementing an experimental investigation of the temperature field. The brain of the system is a microcontroller, which is responsible for obtaining the sensors readings and manipulating the heater and fan. It is connected with a personal computer, which allows to obtain and store the experimental data as time series for further analysis. The developed system could be used to implement planned experiments, the data from which is appropriate for creation and verification of thermal models of electronic devices.
Intracranial hemorrhage (ICH) is a common stroke type that requires an early and urgent diagnosis. The standard imaging modality for ICH diagnosis is computed tomography (CT). However, the type of hemorrhage must be identified by the neurologist to make an effective treatment decision. Although available traditional methods and deep learning-based algorithms for ICH detection can achieve excellent performance, the classification and segmentation of ICH images are difficult tasks since multiple types of ICH may exist within the CT image. Localizing ICH through a bounding box is a more straightforward task than the semantic segmentation task where the model tries to classify pixel-wise. In this work, the YOLOv3 model is proposed to localize mixed hemorrhages from CT images. Additionally, a pipeline for data augmentation was applied to address the problem of limited bounding box annotations for ICH detection. The YOLOv3 model has been evaluated and validated on the brain hemorrhage extended dataset. The proposed method achieved competitive results against state-of-the-art methods.
In this paper, the impact of different photovoltaic power plants (PVPPs) reactive power control strategies upon a microgrid operation are compared. The first strategies consist in operating the PVPPs at unitary or fixed power factor values, while a local load compensation strategy and an optimal reactive power control strategy, based on the Grey Wolf Optimizer (GWO), are also employed. The microgrid operation is simulated for a one-year period with a one-hour granulation for all considered strategies, and the active power losses, reactive power import and bus voltage levels are compared.
The sizing of earth grounding (EGR) is approached in the perspective of applying optimal criteria such as minimum footprint, conductive material consumption or investment costs. The soil resistivity, as a defining quantity for the dispersion resistance of the EGR, is analyzed to decide on the range of variation of its values and to estimate the maximum value, to be adopted in the design. The calculation relations are grouped in the sequence of their use, thus composing the complete physical model of the studied application. The known limited indications of the HEG utilization coefficient are compensated by proposing a linear relation for the calculation of this quantity as a function of the electrode length and the in-plane distance between neighboring parallel electrodes. Due to the non-linear physical model of HEG, it was necessary to develop an algorithm for the successive identification of the computational sizes, which is the basis for the determination of the triad electrode length-electrode number-distance between electrodes. The values of the dispersion resistance of the interconnecting conductor between the electrodes being important for the determination of the total dispersion resistance of the HEG, its calculation was included in the physical model of the EGR. Using the complete physical model of the HEG, a series of sizing runs are made to highlight the possibilities of applying the optimality criteria in setting the final values for the HEG specific quantities, under the mandatory condition of bringing the dispersion resistance of the EGR within the allowed range. Two of the optimal criteria represented by the minimum footprint area or mass of metallic materials were tested on a series of concrete data in order to determine areas of interest for future studies.
High-impedance fault detection is a recurring issue tackled by academics. The lack of publicly available manufacturers know-how, real measurements and logged data from electric utilities regarding their occurrence and the related protection schemes operation forces researchers to develop computational models resembling the contingencies present in power systems within the accuracy provided by peers’ previous validated work. This paper introduces a library comprised of built-in and user-defined blocks and subsystems that are necessary for: different high impedance fault conditions simulation, symmetrical component measurements, signal processing, feature extraction, and assessment of relay operation. The purpose of this paper is to provide researchers and technical practitioners with a user-friendly and straightforward framework that facilitates the simulation of a variety of high impedance fault conditions and the analysis of related protective relay behaviour.
Using a photovoltaic system to power a UAV allows it to fly longer distances and for longer periods of time. After conducting research on a solar UAV with a 151 cm wingspan that was powered by three different energy sources, a technical solution was developed to optimize the energy system and reduce the transient effects that were observed during the switching of electrical sources. By simulating a long-term aerial monitoring mission, the study demonstrated how an optimization algorithm based on the actual operating parameters of the UAV ensures a steady and efficient power supply to the power grid throughout the entire flight. As a result, the study's findings can be applied to the development of new UAVs with exceptional performance, ensuring that the process of selecting a suitable energy source for the flight conditions and supplying the electrical consumers is carried out optimally and efficiently, without any operational risks.
Telemedicine helps medical assistance based on the use of information and communication technology. The system we designed and developed at a laboratory prototype, i.e. Patient Tele-monitoring System is basically an application of Tele-medicine with the main purpose to streamline the diagnosis process, and so to reduce the waiting time of the patient in the waiting room of emergency or ambulatory medicine cabinet. Experiments we made in our laboratory concurred with the expectations of medicine specialists we consulted for advices. Further development of this work is also presented in the last chapter.
There are situations in practice when it is necessary to estimate the rotation speed of the heat engine of a car when its tachometer is not in a good health. In this case, a quick method of speed estimation, noninvasive if possible, even if it may not be very accurate, may be of help. The present paper proposes such a method for estimating the rotation speed of an internal combustion engine, utilizing the signals produced by the engine vibrations acquired with a mobile phone and supervised machine learning (ML) algorithms. The paper describes the complete process of the method, with details regarding the data acquisition and preprocessing, features building and ML algorithms implementation. An example of field deployment is also provided and an analysis is made about how a series of parameters influences the method and may be optimized in terms of two important criteria: accuracy and computation effort. Finally, a trade-off between the two criteria is carried out, specifying the optimal conditions for deploying the method in the field.
In this paper, the authors present a systematized methodology of modelling and analysis of the operating regimes of one of the two main components of pumping units with horizontal shaft - synchronous motor-centrifugal pump assembly - that equips high-power energy pumping stations in hydropower facilities with pumped storage. In this sense, for the centrifugal pumps seen as working machines in electric drive systems, the results obtained following a systematic methodology of modelling and analysis of operating regimes are presented. For solving, algorithms and calculation programs developed in the Mathcad programming environment were designed. For example, a representative case study of one of the three identical double-flow pumps from a high-power energy pumping station from a Hydropower Facility existing in our country (Romania), driven by a horizontal synchronous motor of 6 kV with electromagnetic excitation, was chosen.
Electricity is the most important product used in industry, commerce, education, and residential sector, whose quality must be maintained at the levels required by the EMC standards. Total harmonic distortion (THD) is an important indicator of power quality. The importance of issues of electrical power quality has recently increased due to the intensive use of electrical equipment. The article analyses an analogue THD-meter with notch filter, relatively simple and inexpensive, which can be used to measure the THD of voltage and current, made with linear integrated circuits and RC components. The analogue THD-meter is based on a notch filter that eliminates the frequency of 50 Hz, and signals with a frequency different from 50 Hz will be processed. The output of the analogue THD-meter is a voltage (in mV) proportional to the THD value. Simulations and experiments with a THD meter for voltage and current are presented and the errors are smaller when measuring THD for voltage (up to 4%) compared to measuring THD for current (up to 7%).
Results of a longitudinal research carried out within the Faculty of Electrical Engineering (University POLITEHNICA of Bucharest) to identify the dynamics of student preferences regarding the teaching-learning-assessment process are presented in this paper. The research was carried out throughout one full generation (four academic years) of students. The results showed that the academic maturity of the students (defined as the transition to a higher academic year) majorly impacts only the students' preferences regarding some aspects like the way of conducting the laboratory and project applications, the subject’s final evaluation procedure, the fining of academic deception and the mandatory evaluation of professors' activity by students. The studied generation (2016-2019) is the last one before the COVID-19 pandemic, before the paradigm shifts through the sudden transition to fully online activities highlighting the relevance of this research.
Classification of flora data is a high complexity problem due to the similarity of plants. Identification and determination of plant species is a task that most of the general public is unable to do and it can be a challenge even for the expertise of qualified individuals. This paper studies the possibility of using lightweight convolutional neural networks on resources constrained devices or platforms to accurately classify leaves of plants. Several low complexity convolutional neural networks are considered for the problem of leaves recognition in terms of accuracy, precision, latency and complexity. A novel scheme for enhancement and augmentation of the leaf’s images is proposed and demonstrated as capable to improve performance. MobileNet, L-CNN and NL-CNN models with Android implementations in Tensorflow Lite1 are considered, demonstrating the capability to build a portable intelligent instrument capable to identify plants by their leaves with an accuracy of 95.3%.
The purpose of this paper is to highlight the advantages of applying a preventive and corrective maintenance method in relation to the life of the insulation system of the transformers in operation. This paper proposes a maintenance method based on the revitalization of the insulation of power transformers, in order to extend their life. Two case studies are presented, and the results of the measurements made before and after the revitalization process support the requirements of a preventive and corrective maintenance method.
Given the timeliness of this thematic, we propose an automatic system with the help of which the user complies certain conditions so that the hours spent at the computer do not affect his health, taking into account the right distance from the monitor, the correct body position, the brightness of the ambient environment, as well as warning the user about the time optimal working time at the computer, office or reading time and recommending breaks at a certain time interval.
Over the last years, solar energy has become of great interest regarding new solutions of energy harvesting, especially when it comes to the global warming topic. Hence, photovoltaic cells have gained a lot of popularity and have grabbed the attention of multiple industries that are looking to expand their energy harvesting applications, whether it means powering up certain systems or storing the energy for later usage. This paper describes a possibility of maximizing the solar energy harvesting capability of a photovoltaic system, employing light sensors for maximum power point tracking, and adjusting the position of the photovoltaic panels. Even though the efficiency of this technology is able to sustain the power consumption on a large scale, improvement methods are always researched.
The analysis of the behavior of non-linear elements in electrical equipment is particularly important, especially in the non-sinusoidal regime. In this case, the non-linearity of the circuit elements generates additional current and voltage harmonics that worsen the energy quality and become dangerous for the normal operation of electrical equipment. There are specialized classical software tools for the analysis of these circuits that do not provide all the necessary information about the new harmonic content of the circuit and about the contributions of non-sinusoidal regime and non-linearity. This deficiency is solved by the method proposed by the authors. The method uses a mathematical model based on the multinomial theorem and the nonlinear characteristic i(u) of the circuit element. An original symbolic algorithm determines both the new content of the current harmonics for different operating regimes as well as the contributions of the voltage harmonics and the coefficients of the approximation polynomial i(u) to the current harmonics. The results obtained on two studied cases are compared with traditional simulation techniques and validated by their accuracy.
The degradation of electrical contacts is closely related to contact resistance. Contact resistance in electrical connections is a consequence of numerous factors interlinked, e.g., oxidation, temperature, mechanical vibration, narrowing of electrical current as it passes through the interface, and other contaminants from the surrounding environment. This paper presents an experimental study of the degradation of electrical contacts by performing accelerated thermal aging of fabricated physical samples and evaluating the contact resistance in the low current and voltage range. The electrical contact sample used in this study was prepared by depositing ZrCu (Zirconium Copper) alloy coatings on a copper-clad laminate using cathodic arc deposition. The experimental results indicate that the contact resistance increases as the contacts degrade over time and the size of the contact load improves the total contact area between the samples.
A microcontroller-based architecture of a DC voltage calibrator is presented in the paper and its performance is analyzed. The voltage calibrator is used as a basic measurement, test and adjustment technique for setting and checking measurement instrumentation. The voltage provided is used to achieve optimal performance of the device or process under test. The proposed calibrator is built around the PIC 18F452 microcontroller, using its PWM output signal generator facility. Both 8 bits and 10 bits resolution have been used and studied along this work. The advantages of using a microcontroller are: the possibility to display useful information (number, duty cycle, and voltage), communication with a computer and easy operation with buttons. The experiments revealed also the importance of the used components (for example, by changing the output operational amplifier with a quality one, it was possible to reduce the output residual voltage from 39 mV to 0.9 mV). Aspects regarding errors and their correction are analyzed. The designed calibrator can be used for the calibration of measuring instruments, in other measurement applications and for educational purposes.
