Search

Integrating wind power generators, whose frequency varies in a wide range due to varying wind speeds, into a grid is a formidable problem. At present, the use of permanent magnet synchronous generators (PMSG) and doubly fed induction generators (DFIG) as wind generators with suitable control is the best possible solution. However, a dual-field excited synchronous generator (DESG), which has two windings on the rotor, can also be used for the same purpose with appropriate control. A new control strategy, which essentially employs the d-axis and q-axis components of the alternator terminal voltage, is suggested here. This strategy essentially results in exciting the two field windings with a slip frequency. This eventually holds the stator frequency constant, irrespective of the rotor speed of the wind generator. The difference between the required frequency and the natural frequency, analogous to the rotor speed of the wind power generator, is the slip frequency. The ring modulator automatically adjusts the slip frequency depending on the actual speed of the generator's rotor. This paper uses the ANSYS MAXWELL 2022 R1 software to design a DESG and uses a ring modulator as the control function generator for feedback with ANSYS TWIN BUILDER 2022 R1. Simulations are carried out using transient–transient co-simulation by combining both of these software tools for cases of both a constant-speed input and of a variable-speed input to the rotor of the machine. Moreover, a mathematical model of the DESG as a wind generator with the proposed controlled strategy is used to perform the stability analysis of a nine-bus three-machine system, and the results are compared with those of conventional wind generators. [ABSTRACT FROM AUTHOR]

The most often used motor in commercial drives is the induction motor. While the induction motor is operating, electrical, thermal, mechanical, magnetic, and environmental stresses can result in defects. Therefore, many researchers who are involved in condition monitoring have been interested in the development of reliable and efficient fault diagnostic technologies. This paper's goal is to provide an overview of available fault detection methods for the broken rotor bar problem, one of several defects associated to induction motors. Despite the fact that it is less common than bearing or insulator failure, this fault may cause electrical machines to fail catastrophically. It can be quite harmful, especially in large motors, and it can develop as a result of manufacturing faults, repeated starting of the machine, mechanical stress, and thermal stress. Hence, a review on rotor defect diagnosis was conducted. In order to confirm rotor bar fracture, this research provides probable defect signatures that can be extracted from the current signal. Each defect signature is reported according to (a) loading level, (b) the number of BRBs, (c) validation, and (d) methodologies. [ABSTRACT FROM AUTHOR]

The impact on the stability of power systems is rising as the penetration level of renewable energy with sporadic natures rises rapidly on the grid. However, the impact of different types of renewable energy sources (wind, solar) and their combination on system stability varies even with the same penetration level. This paper concentrates mainly on the stability analysis of multi-machine systems connected to various types of renewable energy sources. The study presents a simple and novel control technique named automatic reactive power support (ARS) for both single and combinations of renewable sources by injecting the available reactive power into the system during fault through converters to enhance system stability. The permanent magnet synchronous generator (PMSG) and doubly fed induction generator (DFIG) are both considered as wind generators in this paper for comparison. In addition, transient stability enhancement is carried out by improving critical clearing time of a three-phase fault in the power system. With the creation of a 3-phase fault at various buses, stability analysis is carried out on the 9-bus WSCC test bus system and also on the 68-bus IEEE test system. Comparative analysis of six test case conditions is provided and the considered cases are without renewable source, with DFIG as a wind generator, PMSG as a wind generator, solar PV farm, wind farm with DFIG and solar PV in combination and the combination of wind farm with PMSG and solar PV. Moreover, the improvement in critical clearing time of the system is compared using conventional and proposed controls with all the aforementioned renewable sources. Comparative results show that the proposed control technique improves system stability and also that the combination of renewable energy sources ought to enhance the critical clearing time of system. [ABSTRACT FROM AUTHOR]

Copyright of Acta Oto-Laryngologica is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article investigates the overvoltage occurring during switching states in the line cooperating with the local subsystem. It discusses the possibilities of determining extreme values of overvoltage of all kinds by means of simulation tests. In particular, special attention was paid to the need to faithfully representation of components in power system i.e. transmission line, voltage transformer and surge arrester for correct reproduce electromagnetic waveforms on the primary as well as secondary side of voltage transformers. Overvoltages appearing in the line connected to the local subsystem during switching operations are forced by the change of network operating conditions. Electromagnetic transients in the unloaded line were tested after its sudden disconnection from the power supply. In the research, particular attention was paid to the conditions of switching off the line (moment and disconnection unity), the influence of surge protection devices, the type of the voltage transformer and the short-circuit power of the power subsystems. Simulation tests have shown that under certain conditions overvoltages with dangerously high values (e.g. 2.25x400 kV) may occur. [ABSTRACT FROM AUTHOR]

Salivary gland tumours represent about 6% of head and neck neoplasms and about 0.5% of all malignancies in humans. Tumour growth and malignant transformation are complex processes involving various actions of molecules. Furthermore, some malignant salivary gland tumours are deemed to be caused by dedifferentiation or malignant transformation of benign tumours. The mechanisms of this transformation depend on a variety of different elements, such as cell cycle regulators, oncogenes, proteins, angiogenesis factors, and adipocytokines. The authors used PubMed, Medline, and Google websites to find and review the most significant papers related to malignant transformation in benign salivary gland tumours. [ABSTRACT FROM AUTHOR]

Objectives The aim of this study was to evaluate serum levels of adiponectin, leptin, visfatin and IL-6 in patients with pleomorphic adenoma, Warthin’s tumor and acinic cell carcinoma of the parotid gland. Materials and methods Venous blood samples were collected from 30 patients with pleomorphic adenoma, 21 patients with Warthin’s tumor and 8 patients with acinic cell carcinoma. Serum adiponectin, leptin, visfatin, IL-6 and CRP concentrations were determined. Results Our results revealed significantly lower adiponectin serum levels in patients with malignant tumors compared to benign tumor individuals. Moreover, in benign cases the level was significantly higher compared to controls. Furthermore, serum leptin concentrations of benign tumor patients were higher compared to controls. Those differences, however, were observed only in males. The serum visfatin level was elevated in all tumor subjects compared to healthy individuals, whereas the serum IL-6 concentration was similar. Conclusions We anticipate that adiponectin may play a potential protective role in salivary gland tumors. Also leptin and visfatin seem to play an important role in salivary gland tumor pathology, although in males and females leptin may act or be regulated in a different manner. The influence of visfatin on salivary gland tumors is probably independent of IL-6 production. [ABSTRACT FROM AUTHOR]

Salivary gland tumors account for 3–6% of tumors of the head and neck. About 80% of salivary gland tumors occur in parotid glands. Oxidative stress (OS) is implicated in the origin, development, and whole-body effects of various tumors. There are no data on the occurrence of OS in the parotid gland tumors. The aim of this study was to ascertain if whole-body OS accompanies parotid gland tumors, based first of all on oxidative modifications of blood serum proteins and other markers of OS in the serum of the patients. The group studied included 17 patients with pleomorphic adenoma, 9 patients with Warthin’s tumor, 8 patients with acinic cell carcinoma, and 24 age-matched controls. We found increased concentration of interleukin 4 in patients with acinic cell carcinoma, decreased plasma thiols, increased AOPP concentration, and decreased FRAP of blood serum in all groups of the patients while protein oxidative modifications assessed fluorimetrically, protein carbonyls, protein nitration, malondialdehyde concentration, and serum ABTS⁎-scavenging capacity were unchanged. These data indicate the occurrence of OS in patients with parotid gland tumors and point to various sensitivities of OS markers. [ABSTRACT FROM AUTHOR]

Objectives: In Poland, no national registry of MS patients has yet been introduced. So far, no demographic studies have been conducted in patients with MS in Upper Silesia. The aim of the present study was to evaluate, for the first time, a selected demographic and clinical parameters in MS patients from the Upper Silesia region and compare these characteristics with previously published data from other regions of Poland. Materials & Methods: 640 patients with clinically defined MS, were prospectively and randomly selected for the study. Social, socio-economic, and demographic data were obtained through a questionnaire study. All subjects performed a self-assessment of their health condition using EQ-5D and EQ-VAS version questionnaires. Results: The ratio of women to men was 2.18. The average age of onset was 29.6 ± 11.1 years; the disease duration was 7.9 ± 4.5 years. The relapsing-remitting form of MS was diagnosed in 73.12%. In 71.25% the onset was monofocal and in 28.75% multifocal disease onset was observed. Among the studied population 339 (52.97%) patients were still employed. A mean EQ-VAS score of 66.11 ± 20.12 was calculated. Conclusions: Results from our study identify for the first time the demographic and clinical characteristics of the Upper Silesia MS population. [ABSTRACT FROM AUTHOR]

We have examined the role of melatonin receptor MT2 and quinone reductase II in the regulation of the redox status of preadipocytes (3T3-L1) in vitro. 3T3-L1 cells were treated with melatonin at a physiological concentration (10−9 mol/L) and a supraphysiological (pharmacological) concentration (10−3 mol/L) for 24 h. Luzindole (10−4 mol/L), an antagonist of MT2 receptor, and prazosin (10−5 mol/L), an inhibitor of quinone reductase II, were added 30 min before subsequent exposure of the cells to melatonin. The level of oxidative stress was determined by the analysis of activities of enzymes neutralising reactive oxygen species, and determination of the malondialdehyde (MDA) content. Melatonin increased activities of manganese and copper-zinc superoxide dismutase (MnSOD, Cu/ZnSOD) and catalase (CAT) at both a physiological concentration (10−9 mol/L) and a pharmacological concentration (10−3 mol/L). MDA content was unchanged, whereas activities of glutathione peroxidase (GSH-Px) and glutathione reductase (GSSG-Rd) were increased only by the physiological concentration. Both effects were partially inhibited by luzindole, but not prazosin. These observations suggest that melatonin, acting at least partially via MT2 receptors, can increase antioxidant enzymes activities in 3T3-L1 preadipocytes. [ABSTRACT FROM AUTHOR]

Despite knowledge of classical coronary artery disease (CAD) risk factors, the morbidity and mortality associated with this disease remain high. Therefore, new factors that may affect the development of CAD, such as the gut microbiome, are extensively investigated. This study aimed to evaluate gut microbiome composition in CAD patients in relation to the control group. We examined 169 CAD patients and 166 people in the control group, without CAD, matched in terms of age and sex to the study group. Both populations underwent a detailed health assessment. The microbiome analysis was based on the V3–V4 region of the 16S rRNA gene (NGS method). Among 4074 identified taxonomic units in the whole population, 1070 differed between study groups. The most common bacterial types were Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Furthermore, a higher Firmicutes/Bacteroidetes ratio in the CAD group compared with the control was demonstrated. Firmicutes/Bacteroidetes ratio, independent of age, sex, CAD status, LDL cholesterol concentration, and statins treatment, was related to altered phosphatidylcholine concentrations obtained in targeted metabolomics. Altered alpha-biodiversity (Kruskal–Wallis test, p = 0.001) and beta-biodiversity (Bray–Curtis metric, p < 0.001) in the CAD group were observed. Moreover, a predicted functional analysis revealed some taxonomic units, metabolic pathways, and proteins that might be characteristic of the CAD patients' microbiome, such as increased expressions of 6-phospho-β-glucosidase and protein-N(pi)-phosphohistidine-sugar phosphotransferase and decreased expressions of DNA topoisomerase, oxaloacetate decarboxylase, and 6-beta-glucosidase. In summary, CAD is associated with altered gut microbiome composition and function. [ABSTRACT FROM AUTHOR]

Practical successes have been achieved with neural network models in a variety of domains, including energy-related industry. The large, complex design space of electrical power systems (EPS) is only minimally explored in current practice. The satisfactory results that nevertheless have been obtained testify that neural networks are a robust modeling technology; at the same time, however, the lack of a systematic design approach implies that the best neural network models generally remain undiscovered for most applications. This paper presents an approach to an adaptive protective systems problem in the complex power generating units. First, we demonstrate the complex interdependencies between various parameters of EPS protection systems. We then present an approach, based on protection and adaptation criteria, for designing a neural network based adaptive protection system. © 2000 John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]