Design and Optimization of a Novel Monolithic Spring for High-Frequency Press-Pack SiC FET Modules

Silicon Carbide (SiC) Field-Effect Transistor (FET) modules lead the way in power electronics, being superior in efficiency and robustness for high-frequency applications. The shift towards SiC from traditional silicon (Si)-based devices is driven by its superior thermal conductivity, higher electric field strength, and operational efficiency at elevated temperatures. These features are critical for the development of next-generation, grid-oriented power converters aimed at enhancing the reliability and sustainability of power systems. This research focuses on high-frequency press-pack (HFPP) SiC FET modules, addressing the primary challenge of miniaturizing SiC FET dies without compromising performance, through an innovative press-contact design essential for increased high-frequency efficiency. The objective of the research is to develop and validate a novel monolithic spring (MS) for HFPP SiC FET modules, aiming to surpass conventional press-pack (PP) limitations. By machining airgap slits from a beryllium–copper block, the proposed MS design seeks to achieve optimal mechanical and electrical performance, targeting a linear spring constant, minimal stray inductance, and enhanced high-frequency body resistance. This approach combines theoretical modeling, finite element analysis (FEA) simulations, and experimental validation to overcome the inefficiencies of existing designs, thereby advancing HFPP SiC module technology and supporting the broader adoption of SiC FET in power systems. Additionally, FEA simulations are employed to contrast the novel MS design with traditional Si-based transistors, highlighting the MS\u27s advanced performance and efficiency in high-frequency applications. The research signifies a vital step towards improving the performance and sustainability of electrical grids worldwide, demonstrating the potential of SiC technology in transforming power conversion systems. Advisors: Liyan Qu and Jun Wan

Survey of general practitioners' knowledge about Helicobacter pylori infection

BACKGROUND: Helicobacter pylori, occurring throughout the world and causing gastroduodenal diseases, is one of the most common chronic bacterial agents in humans. The purpose of this study was to measure the general practitioners' (GPs) knowledge and practices pertaining to H. pylori infection. METHODS: A cross-sectional type questionnaire survey was conducted in all of 19 primary health care centres (PHCC) in Samsun, Turkey, between November 1 and December 31, 2003. The questionnaire was sent to 124 GPs and 109 (87.9 %) of those filled in. They were requested to answer the questions on the knowledge, sources of medical information, diagnostic tests and treatment to H. pylori. RESULTS: Medical journals were the most frequently used source of information on H. pylori, being cited by 86 (78.9%) of GPs. Ninety-two (84.4%) of the GPs reported having used one or more tests and 17 (15.6%) never used any test for the diagnosis of H. pylori infection. Only 9.8% had used stool antigen test for diagnosis. GPs reported that they would prescribe symptomatic treatment without ordering diagnostic tests for 29 (26.6%). 54.1% of the GPs explain that they sent patients with H. pylori infection to a specialist, and most used a triple drug regimen containing a PPI. Treatment duration varies between 7 to 28 days. 80.7 of the GPs treat patients for 14 days. CONCLUSION: GPs may not have enough knowledge about the importance of stool antigen test or possibility of usage of this test. GPs have not sufficient knowledge about the difference between symptomatic and asymptomatic individuals. It is thought that GPs preferred to treat the patients with suspected ulcer empirically or to send them to a specialist because of the limited diagnostic conditions. The efforts to educate the GPs about the algorithms regarding the management of H. pylori infection during post-graduation period should be improved in PHCCs

Effect of high temperature on sepiolite – hydraulic lime mortar

Sepiolite is a natural clay mineral consisting of magnesium hydrosilicate. High surface area and micropores which form micro structure of sepiolite play an important role for the sepiolite to be used as a binder in the construction sector. The adsorbed water molecules, which are located in the chemical composition of sepiolite, move away from the structure while temperature goes up. When the temperature reaches 950°C chemical structure of sepiolite becomes impaired. This behavior under high temperature of sepiolite supports the use in the construction industry. Pozzolans such as sepiolite have little binding effect on their own. Therefore lime or cement is used together. The use of lime and sepiolite together in the repair mortars for restoration of historic buildings is one of the recent studies. However authors didn’t encounter a study on high temperature resistance of mortars added with sepiolite. In this study to determine the behavior of mortars at high temperature, mixtures are designed at different rates of sand/binder and sepiolite/hydraulic lime. Specimens were exposed to 400°C and 700°C. The effect of high temperature on the lime mortar was determined, with respect to the loss in unit weight, ultrasonic pulse velocity, compressive strength and bending strength. At the end of the test results, there wasn’t any significant change in physical and mechanical properties of mortars up to 400°C. However above 400°C, negative effects were observed

UTILIZATION OF CHROME ORE CONCENTRATION PLANT TAILINGS AS FINE AGGREGATE IN READY-MIXED CONCRETE

Large amount of the chrome ore concentration plant tailings was discarded during chrome ore mining process. The accumulation of the tailings takes large areas of land for the storage and causes environmental and safety problems. When the annual consumption of the ready mixed concrete per person (approximately 1.5 m3/person) in Turkey is considered, employment of the tailings in the ready-mixed concrete may be a solution for the recovery of the tailings. In addition, using chrome tailings as a substitution for sand to produce ready-mixed concrete is a possible way to solve the resource problem of sand deficiency. The aim of this study is to investigate the utilization of the tailings taken from a chrome ore concentration plant in Eskisehir, Turkey as fine aggregate in ready-mixed concrete production. For this purpose, the tailings were partially replaced with the fine aggregate by the weight at 0, 10, 20 and 30% proportions by weight in the ready-mixed concrete mixtures. Standard curing is applied until the time of test to the 15x15x15 cm cube specimens taken from the mixtures.  The unit weight, compressive strength and ultrasonic pulse velocity values of the cubic specimens were investigated in this study. Performed tests showed that replacing sand to chrome ore tailings has a potential for further investigations. 

Performance analysis of real-time and general-purpose operating systems for path planning of the multi-robot systems

In general, modern operating systems can be divided into two essential parts, real-time operating systems (RTOS) and general-purpose operating systems (GPOS). The main difference between GPOS and RTOS is the system istime-critical or not. It means that; in GPOS, a high-priority thread cannot preempt a kernel call. But, in RTOS, a low-priority task is preempted by a high-priority task if necessary, even if it’s executing a kernel call. Most Linux distributions can be used as both GPOS and RTOS with kernel modifications. In this study, two Linux distributions, Ubuntu and Pardus, were analyzed and their performances were compared both as GPOS and RTOS for path planning of the multi-robot systems. Robot groups with different numbers of members were used to perform the path tracking tasks using both Ubuntu and Pardus as GPOS and RTOS. In this way, both the performance of two different Linux distributions in robotic applications were observed and compared in two forms, GPOS, and RTOS

Statistical Analysis of Chemical Admixtures Usage for Concrete: A Survey of Eskisehir city, Turkey

AbstractNowadays, the concrete admixtures are widely used in the construction projects. The main types of chemical admixtures can be summarized as plasticizers, accelerating/retarding agents, air entraining agents, waterproofing additives and others such as corrosion inhibitors and colouring agents etc. The benefits derived from the use of chemical admixtures include improved durability, strength, chemical resistance, colouring, reduction in water and cement requirement and enhanced working properties of concrete. Turkey is one of the major consumers in developing countries regarding chemical admixtures. Therefore, this study set out to determine general utilization and consciousness about admixtures through a survey in Eskisehir, Turkey. The survey was performed by 153 construction professionals. The questions about reasons for preference of admixtures, types of preferred admixtures and dosage, beneficial and adverse effects of admixtures, impacts on cost and judicious use of admixtures are included in the survey. A number of statistical analyses are carried out using SPSS on data obtained. According to results, chemical admixtures are used over 70% of the total annual concrete production. The initial expectation of the participants in the use of the admixtures is to improve the properties of the fresh concrete. Additionally, the most preferred admixtures are plasticizers. The ensuing types of admixtures are agents affecting the setting time of concrete. Although the participants’ interest to using chemical admixtures is very remarkable, the awareness on this subject is very deficient. The similar studies can be suggested to apply more comprehensively. Professionals, at any level in the construction sector, need to be informed about the accurate consumption of these agents in order to avoid inappropriate results

Utilization of ceramic waste in the production of Khorasan mortar

Khorasan mortar was used in almost all of the historical structures in the geographical area of turkey. It is still used in the renovation of these structures. Water, lime, baked clay is used in the production of Khorasan by breaking and grinding. Crushed brick and tiles are preferred as baked clay. In this study, the usability of ceramic wastes as baked clay was investigated. An important part of ceramic production is made especially in Eskişehir and its vicinity. 10% of ceramic production shows up as wastes because of various reasons. These wastes which are under 20 mm are crushed in the jaw breakers and these which are under 150 mm are grinned in grinders, transformed to powder and then mixed with hydrated lime and water in various proportions, in this way Khorasan mortars are obtained. In mortar production, crushed ceramic-ceramic powder ratio, ceramic-lime ratio were changed and the most suitable ratios were tried to be found. Samples taken from these mortars which are 4 cm x 4 cm x 16 cm in size are removed after a day from the mold and kept in humid environment. Physical and mechanical properties such as unit weight, ultrasonic pulse velocity, bending strength, compressive strength of the mortar were determined. As a result of the experiments, the unit weights range was between 1.5–1.65 kg/dm3, the ultrasonic pulse velocity rates range from 1.3–1.9 km/h, the range of bending strengths was from 0.25–1.05 MPa, and compressive strength has changed in the range of 7.5–10.5 MPa. With the work done, it is recommended to use a high percentage of lime while using ceramic wastes in the process of producing Khorasan mortar

Evaluation of risk management practices: data analysis of NHS England hospitals

Risk management practices are applied in the National Health Service (NHS) England hospitals to reduce harm rates and to ensure safety. This study evaluates current risk management practices in the NHS England hospitals through highlighting non-compliance issues within the practice and through explaining board level risk priorities. All data were collected for selected (N=34) NHS England hospitals. Data were gathered from the NHS Litigation Authority (NHSLA) reports to reveal risk management problems and from Board Assurance Frameworks (BAF) to define top risks. Results from an external authority of the NHSLA show that local induction of staff is a major non-compliance issue for risk management practice with more than half of the hospitals having difficulties. Following that supervision of medical staff in training is the second highly observed deficiency. Results from hospitals’ board level demonstrate that top risks in hospitals were regarding quality and performance issues. Additionally, most of the board level defined top risks were categorized as organizational and clinical-related risks. Within these, workforce issues and non-compliance with requirements are highlighted as top risks for organizational-related risks while Accident and Emergency (A&E) targets and treatment delays are prioritized as part of clinical-related risks. Financial deficit is also frequently defined at board level as a top risk for financial-related risks. Both the NHSLA and hospital board level assessments show that workforce related issues are still a major concern in hospital risk management practices. It is therefore a slight influence of an external authority (NHSLA) has been recognized on prioritization of board level defined risks