Search Results (32)

Background: Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is one of the leading causes of chronic liver disease, affecting 30% of the global adult population and continuing to rise. Objective: We aimed to assess the effect of a two-year follow-up Mediterranean diet intervention on parameters of liver health in MASLD patients. Methods: Sixty-two people between 40 and 60 years of age, all diagnosed with MASLD, were enrolled in the two-year clinical trial, who were randomly assigned to one of three interventions following the Mediterranean diet pattern and the promotion of physical activity. After the intervention, the participants were categorized into two groups according to their progress in adhering to the Mediterranean diet (MedDiet), which was assessed at four follow-up time points, conducted at the start of this study and after 6, 12, and 24 months of intervention. A multivariate general linear model adjusted for age, sex, and intervention (diet and physical activity) was used. Bonferroni’s post hoc test identified differences between groups and sessions within the same group. Results: Participants in the highly adherent group showed significantly stronger improvement in anthropometric measures, lipid profile, and liver enzyme levels during the follow-up period, along with a reduction in the Dietary Inflammatory Index, intrahepatic fat content, the fatty liver index, and plasma cytokeratin-18 levels compared to baseline. The progress observed in several parameters at 12 months came to a standstill, likely because of the COVID-19 pandemic at that time. At 24 months, following the COVID-19 pandemic, these parameters improved as a result of better adherence to the Mediterranean diet. Conclusions: Greater adherence to the Mediterranean diet, along with increased physical activity, significantly enhances liver health markers in individuals with MASLD. These findings support the Mediterranean lifestyle as an effective non-pharmacological strategy to improve liver health and prevent liver-related complications in MASLD patients, potentially reducing the future public health burden. Full article

With their cost-effective manufacturing process, hybrid stepper motors (HSMs) are a popular choice for position control in low-power industrial applications. These versatile motors offer a compelling solution for reducing system costs and size since at standstill/low speeds, HSMs typically have higher torque density with respect to low-power permanent magnet (PM) motors. This higher torque density determines a reduced use of rare-earth PMs and, therefore, a lower environmental footprint. In practical applications, the commonly used microstepping control faces low efficiency, low dynamic performance, vibrations, and a variable maximum continuous torque depending on the working point. In this paper, the operating region of an HSM is extended in the field-weakening (FW) region, showing how field-oriented control (FOC) with FW allows one to strongly increase the drive performance with a slight cost increase thanks to the availability of low-cost magnetic encoders. Due to the fact that FOC provides only the requested current, the HSM faces lower temperatures, lower insulation degradation, and lower permanent magnet demagnetization issues. An experimental evaluation comparing the commonly used microstepping and the proposed FOC with FW is performed on four commercial HSMs with different DC voltage power supplies using an industrial test bench. In particular, the experimental campaign has a focus on steady-state conditions in the case of the maximum continuous torque, showing the advantages of FOC with FW because the advantages in transient conditions are well known. Full article

Experimental approaches for the identification of dynamic parameters in synchronous machines mainly include two methods, a three-phase sudden short-circuit (TPSSC) test and a standstill frequency response (SSFR) test. However, the former has significant safety risks, while the latter has a complex implementation process, resulting in insufficient adaptability to large-scale units. To overcome the above obstacles, this paper proposes an improved DC-decay test method that can be performed at an arbitrary rotor position so that the rotor pre-positioning process in the conventional DC-decay test can be neglected. Meanwhile, combining the transient analysis theory and particle swarm optimization algorithm, a semi-analytical parameter identification method is proposed. Finally, the proposed method is applied using a 172 MVA large synchronous machine. Compared to the results obtained by the TPSSC test using the Prony algorithm and other conventional type tests, the error of the parameter calculation results obtained with the conventional method reached a maximum of 16.6%, while that of the proposed method was merely 8.6%, and the experimental period could be shortened from 5 days to half a day. Full article

This paper addresses the challenge of developing a cost-effective and efficient soft-starting method for doubly fed induction machines (DFIMs), a critical requirement for various industrial applications, such as pumped-storage hydropower. The research aims to improve a previously developed starting method by introducing a rotor-side synchronization technique at standstill conditions, which simplifies the starting process and eliminates the need for additional equipment such as autotransformers, resistors, or auxiliary converters. The proposed method begins with the stator winding being fed directly from the power system, while the rotor-side converter adjusts the voltage and frequency to achieve synchronization. Once synchronized, the rotor frequency is gradually reduced by the converter, resulting in a smooth acceleration of the machine. The methodology is validated through a combination of simulations and experimental testing, demonstrating the effectiveness of the proposed approach. The results reveal smooth startup dynamics, with significant reductions in electrical stress, operational complexity, and converter sizing requirements compared to existing methods. Notably, the magnetizing current is supplied directly by the power system through the stator, reducing the burden on the rotor converter by 60% compared to the previous method. The conclusions highlight the method’s robustness and its potential as a superior alternative to existing DFIM starting techniques. Full article

Due to their exceptional operational versatility, doubly fed induction machines (DFIM) are widely employed in power systems comprising variable renewable energy-based electrical generation sources, such as wind farms and pumped-storage hydropower plants. However, their starting and grid synchronization methods require numerous maneuvers or additional components, making the process challenging. In this paper, a soft start method for DFIM, inspired by the traditional synchronization method of synchronous machines, is proposed. This method involves matching the frequencies, voltages, and phase angles on both sides of the main circuit breaker, by adjusting the excitation through the controlled power converter at standstill conditions. Once synchronization is achieved, the frequency is gradually reduced to the rated operational levels. This straightforward starting method effectively suppresses large inrush currents and voltage sags. The proposed method has been validated through computer simulations and experimental tests, yielding satisfactory results. Full article

In electric powertrain traction applications, the adopted trend to improve the performance and efficiency of electromechanical power conversion systems is to increase supply voltages and inverter switching frequencies. As a result, electrical machine conductors are subjected to ever-increasing electrical stresses, leading to premature insulation degradation and eventual short-circuits. Winding condition monitoring is crucial to prevent such critical failures. Based on the scientific literature, several methods can be used for early identification of aging. A first solution is to monitor partial discharges. This method requires the use of a specific measurement device and an undisturbed test environment. A second solution is to monitor the inter-turn winding capacitance, which is directly related to the condition of the insulation and can cause a change in the stator impedance behavior. Several approaches can be used to estimate or characterize this impedance behavior. They must be performed on a machine at standstill, which limits their application. In this paper, a new characterization method is proposed to monitor the high-frequency stator impedance evolution of voltage source inverter-fed machines. This method can be applied at any time without removing the machine from its operating environment. The range and accuracy of the proposed frequency characterization depend in particular on the supply voltage level and the bandwidth of the measurement probes. The effects of parameters such as temperature, switching frequency, and DC voltage amplitude on the impedance characteristic were also studied and will be presented. Tests carried out on an automotive traction machine have shown that the first two series and parallel resonances of the high-frequency impedance can be accurately identified using the proposed technique. Therefore, by monitoring these resonances, it is possible to predict the aging rate of the conductor. Full article

One main research area of the Competence Centre for Tribology is so-called standstill marks (SSMs) at roller bearings that occur if the bearing is exposed to vibrations or performs just micromovements. SSMs obtained from experiments are usually photographed, evaluated and manually categorized into six classes. An internal project has now investigated the extent to which this evaluation can be automated and objectified. Images of standstill marks were classified using convolutional neural networks that were implemented with the deep learning library Pytorch. With basic convolutional neural networks, an accuracy of 70.19% for the classification of all six classes and 83.65% for the classification of pairwise classes was achieved. Classification accuracies were improved by image augmentation and transfer learning with pre-trained convolutional neural networks. Overall, an accuracy of 83.65% for the classification of all six standstill mark classes and 91.35% for the classification of pairwise classes was achieved. Since 16 individual marks are generated per test run in a typical quasi standstill test (QSST) of the CCT and the deviation in the prediction of the classification is a maximum of one school grade, the accuracy achieved is already sufficient to carry out a reliable and objective evaluation of the markings. Full article

As the market for hybrid and electric vehicles expands, electric motor production and testing technology must be continuously improved to meet the cost and quality requirements of mass production. In order to detect faults in motors during the production process, a condition monitoring tool is used for the motor end line. During most condition monitoring, the motor operates in a static state where the speed of the motor remains constant and the voltage/current is recorded for a certain period. This process usually takes a long time and requires a loader to drag the motor to a standstill at a constant speed. In this paper, various transient process testing methods are introduced. For these processes, only transient operation of the motor, such as acceleration, loss, or a short circuit, is required. By analyzing the measurement results and simulation results of motor models, unhealthy motors can be detected more effectively. Full article

This study addresses the issue of construction stagnation affecting the adhesion and tensile properties of hydraulic asphalt concrete with acid aggregate. It investigates the impact of rest periods on the tensile characteristics of such materials under standard construction conditions. The influence of varying rest durations and asphalt temperatures on the tensile behavior of the concrete is assessed through indoor experiments. The bonding between asphalt and aggregate is examined, along with the tensile property variations of the concrete. The study found that the standstill time significantly affects the adhesion of asphalt, with the adhesion decreasing progressively with increased temperature and rest time, irrespective of the addition of anti-stripping agents. However, the inclusion of these agents can mitigate the reduction in adhesion. Furthermore, the study identified that rest duration has a more substantial impact on adhesion than temperature. The splitting tests demonstrate that the tensile properties of asphalt concrete are considerably affected by the resting time. Over a period of 0, 10, 20, and 30 days of rest, an increase in splitting strength and a decrease in splitting displacement were observed. The findings offer valuable insights for predicting the tensile performance of asphalt concrete in practical engineering applications after a period of rest. Full article

Despite continuous work on new power systems for vehicles, machines, and devices, the combustion engine is still the dominant system. The operation of the combustion engine is initiated during the starting process using starting devices. The most common starting system used is the electric starter. The starting process of an internal combustion engine depends on the following factors: the technical condition of the starting system, technical condition of the engine, battery charge level, lubricating properties, engine standstill time, engine and ambient temperature, type of fuel, etc. This article presents the results of laboratory tests of the electrical parameters of the starting process of a single-cylinder compression–ignition engine with variable fuel injection parameters and ambient temperature conditions. It was confirmed that for the increased fuel dose FD2, higher values of the measured electrical parameters (Imax, Pmax, and Pmed) were obtained compared to the series of tests with the nominal fuel dose. Knowledge of the values of the electrical parameters of the starting process is important not only for the user (vehicle driver, agricultural machinery operator, etc.), but above all for designers of modern starting systems for combustion engines and service personnel. The obtained results of testing the electrical parameters of the combustion engine during start-up may be helpful in designing new drive systems supported by a compression–ignition combustion engine. Full article

This paper applies the identified parameters of permanent magnet synchronous machines (PMSMs) for the maximum torque per ampere control (MTPA) under magnetic saturation. The variation in magnet flux with current is determined using a position offset approach while the variation in q-axis inductance with the current is estimated from the d-axis voltage equation afterward. In addition, the d-axis inductance is estimated at standstill by the injection of a small amplitude of high frequency d-axis current. The curve-fitted results of estimated parameters under different saturation conditions are then employed to aid the derivation of MTPA control law. The proposed method is experimentally verified on two prototype PMSMs. Experimental results show that compared with conventional MTPA schemes using fixed values of magnetic parameters, the proposed method can increase maximum output torque by 2.1% and 3.2% on two prototype PMSMs, respectively. Full article

The subject of polymer–polymer pair interaction is highly important, bearing in mind that such pairs are used in the construction of machines and equipment, among other uses. Considering that the characteristics of polymer–polymer sliding pairs (e.g., the load limit value and advantageous parameter, PV) differ from those of polymer–metal pairs, the subject is particularly interesting and has been little explored so far. Hence, the present study presents one of the areas of the effects of standstill time (intrinsically characteristic of polymeric materials) on the startup parameters in sliding pairs where the sample and the countersample were made of a polymeric material. Pairs of same-type polymers, POM–POM, PET–PET, and PA6–PA6, were subjected to tests. A test rig dedicated to static friction coefficient determination, whose principle of operation is based on the interdependences between the force characteristics of an inclined plane, was used for this purpose. The sliding pair was successively loaded with 25 N, 50 N, and 75 N, and the standstill time ranged from 0 to 10 min. The determined tribological characteristics were analysed with regard to the standstill time under load, unit pressure, and polymer pair material. An optical profilometer and a scanning electron microscope were used to qualitatively evaluate the effects of standstill time and unit pressure on the surfaces of the interacting elements. Complex interrelationships between the test results and the set experimental parameters were noted. SEM micrographs revealed post-friction changes in the sliding surfaces. Full article

Background: COVID-19 was an infection that was capable of bringing the entire world to a standstill position within a period of days to months. Despite the advancements in the medical sector, the contagion was difficult to control and costed the lives of millions of people worldwide. Many short- and long-term effects are witnessed even to date in people that contracted the disease. Pregnant females had to suffer not only the devastating effects of the virus, but also the psycho-social impact of the lockdown. The impact of COVID-19 infection during pregnancy causing decreased antenatal care or hypoxemic episodes due to severe respiratory distress and whether it could lead to the appearance of congenital gastrointestinal malformation in neonates is still unclear. The aim of our study was to analyze if COVID-19 infection during pregnancy could increase the incidence of gastric malformations in neonates born from these women. Materials and Methods: We sifted the files of all neonates admitted into our hospital between January 2022 and December 2022, and based on inclusion and exclusion criteria, we included the cases having gastrointestinal congenital malformations during the COVID-19 pandemic. We performed a single-center, retrospective, observational descriptive study. We further divided the patients based on the anatomical location of the malformation. We also took down details of the evolution of pregnancy and whether the mother had contracted a SARS-CoV-2 infection during the pregnancy. Details regarding the Apgar score, days of intensive care admission, sex, and nutrition were the key findings studied. Results: A total of 47 neonates were found to have digestive anomalies, among which, based on the anatomical locations, the number of malformation cases found at the level of the esophagus were 15, while 16 occurred at the level of the pylorus; we found 12 cases of malformation of the duodenum, and four cases had malformation of the rectum. Out of these 47 neonates, 38.3% were females and 61.7% were males. A total of 58% were preemies, among which 9% had intra-uterine growth retardation (IUGR), and 42% were full-term newborns, among which 4% had intra-uterine growth retardation (IUGR). A total of 45% of the births were primiparous pregnancies and 55% were from multiparous females. A total of 14 mothers were found to have tested positive for COVID-19 during the course of pregnancy (p-value = 0.23); many had mild symptoms but were not tested. Conclusions: COVID-19 can affect the wellbeing of the pregnant female and their fetus. Larger studies can help gain extensive knowledge as to whether COVID-19 also has the potential to result in congenital gastrointestinal anomalies in children born from COVID-19 positive mothers. In our study, only a few infants born with this pathology were found to be born from COVID-19 positive mothers. Hence, it is difficult to conclude or exclude a direct correlation between the infection and the congenital malformations. Full article

Magnetic levitation can reduce particulate contamination that occurs during wafer transportation in the semiconductor manufacturing process. This technology radically eliminates contact between the wafer and the transport system, reducing friction, wear, and particle generation. Therefore, it is suitable for achieving high cleanliness in the ultra-fine line-width semiconductor production process and solving the need for particle removal in a vacuum environment. In this study, the roller and linear motion guide components of the wafer transfer system were replaced with a magnetic levitation module, and a robot arm was installed on top to transport a single wafer. A posture controller and a current controller were designed, and test equipment simulating the wafer transfer system was also manufactured and tested. Regarding mover and system identification, a sine sweep test was performed on the motion axis of the five degrees of freedom. Through the obtained system identification, it was possible to design the posture controller more precisely. Moreover, through levitation in standstill experiments and high-speed operation experiments, the wafer transport system can be used to verify dust-free high-speed transport and accurate positioning performance. Full article

Rolling bearings operated at small oscillation angles or exposed to vibrations during standstill show typical damage after only a short period of operation. This can be false brinelling damage, so-called standstill marks or classic fretting damage (fretting corrosion, tribo-oxidation). It is important to differentiate here according to the amplitude-ratio x/2b, which indicates the ratio between the rolling element Motion (x) and the Hertzian contact half-axis (b). Depending on this ratio, suitable laboratory test methods must be used to test the lubricating grease practically for the particular application. For this purpose, the Fafnir wear test, according to the standard of the American Society for Testing and Materials ASTM D4170, is also listed in the current high-performance multi-use specification of the National Lubricating Grease Institute (NLGI) as a release test for lubricating greases. In Europe, the SNR-FEB2 test is frequently used, which is also required to release greases in the blade bearings of wind turbines, among other things. In the case of standstill marks due to very small oscillation angles or vibrations, the Mannheim Tribology Competence Center (KTM) has developed a special test now established in the industry. The oscillating angles vary in these three different standard tests in the range from ±6° in the Fafnir test to ±3° in the SNR-FEB2 test to ±0.5° in the KTM standstill marking test; the x-to-2b ratios range from 5.5 (Fafnir) to 3.4 (SNR) to 0.5 (KTM). This paper will explain the scientific basis for these special operating and test conditions and compare test results of specially prepared model greases in these three standard rolling bearing tests, two test variations and a classical fretting test under oscillating sliding friction (ASTM D7594). The paper’s main objective is to show that the suitability of grease for such an application depends strongly on the prevailing operating conditions. Different tests in this field are, therefore, not interchangeable. Good results in one test do not automatically mean good results in a similar test at first glance. Therefore, selecting the right test for the application is important. Full article