351 research outputs found
An epimorphic subgroup arising from Roberts’ counterexample
No full textAbstractIn 1994, based on Roberts’ counterexample to Hilbert’s fourteenth problem, A’Campo-Neuen constructed an example of a linear action of a 12-dimensional commutative unipotent group H0 on a 19-dimensional vector space V such that the algebra of invariants k[V]H0 is not finitely generated. We consider a certain extension H of H0 by a one-dimensional torus and prove that H is epimorphic in SL(V). In particular, the homogeneous space SL(V)/H provides a new example of a homogeneous space with epimorphic stabilizer that admits no projective embeddings with small boundary
Preventing Sheet Metal Wrinkling in Coil Lines
No full textCoil lines are used in metal packaging facilities to treat the metal before forming the final product. As the sidewalls of cans are becoming thinner and thinner, one can see that the equipment has not been designed properly to feed up lighter plate weight metal. Thinner can walls cause the metal sheet to be fed into the machine crooked and results in a wrinkling of the first few feet of metal, which then needs to be thrown away. Because the current equipment is not working properly, operators have been feeding sheets of metal up a ten-foot ladder into the machine to feed the sheet in straight. This method puts the operator at a safety risk. The feed mechanism that is currently installed does work better with heavier plate weight metal. After talking with the operators and looking at the current equipment, a conceptual design test prototype was built to see if it would fix the problem. When running numerous tests with the prototype it was verified that the conceptual design would fix the problem. After the test prototype proved to be successful, a full design of the roller system was implemented. The design is currently finished and is in the process of being purchased. The expected installation date will be December 3-7th of this year
The Perception of F.D. E. Schleiermacher’s Concept in the Russian Philosophy of the First Half of the XIX century
No full textThe article deals with the perception of a personality and the concept of the German philosopher and theologian Fr. Schleiermacher in the Russian philosophy of the first half of the XIX th century. There is evidence of P.J. Chaadayev and I.V. Kireyevsky being aware of the texts by Fr. Schleiermacher as well as their evaluation of his personality and world view. Proceeding from the evidence, the author of this article reveals the main features of the first period of perceiving Fr. Schleiermacher’s ideas in Russia, and a conclusion follows that on the whole the novelty of his views was not understood and stayed underestimated
Investigation of K-modified P2-Na0.7Mn0.8Mg0.2O2 as a cathode material for sodium-ion batteries
No full textSodium-ion batteries (NIBs) are emerging as a potentially cheaper alternative to lithium-ion batteries (LIBs) due to the larger abundance of sodium and in some cases the similar intercalation chemistry to LIBs. Here we report the solid state synthesized K-modified P2 Na0.7Mn0.8Mg0.2O2 which adopts hexagonal P63/mmc symmetry. The second charge/discharge capacity for the as-prepared material is 115/111 mAh g-1 between 1.5-4.2 V at a current density of 15 mA g-1, which reduces to 61/60 mAh g-1 after 100 cycles. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDS) analysis shows a heterogeneous distribution of K and solid state 23Na NMR illustrates that the presence of K perturbs the local enivoronment of Na within the P2 Na0.7Mn0.8Mg0.2O2 crystal structure. Larger scale X-ray absorption near-edge structure (XANES) data on the K L-edge also illustrate that K is present on the surface of electrodes in preference to the bulk. In situ synchrotron X-ray diffraction (XRD) data illustrates that the P2 structural motif is preserved, featuring a solid solution reaction for most of charge-discharge except at the charged and discharged states where multiple phases are present. The K-modified sample of P2 Na0.7Mn0.8Mg0.2O2 is compared with the K-free samples in terms of both structural evolution and electrochemical performance
Aerodynamic Analysis and Drag Coefficient Evaluation of Time-Trial Bicycle Riders
No full textEvaluation of drag coefficient often requires wind tunnel experiments and can be prohibitively expensive if not impossible for large objects or systems. Computational Fluid Dynamics (CFD) aerodynamic analysis offers an alternative approach and can be used as a very effective design tool in many industries: automotive, aerospace, marine, etc. The main objective of this research is to investigate feasibility of using non-contact digitizers for developing finite element models of large objects for subsequent CFD analysis. The developed methodology is applied to investigation of time-trial bicycle rider efficiency. Companies competing in this class of racing spend millions trying to optimize bicycle and rider geometry in order to reduce aerodynamic drag. This project investigates an alternative way to optimize the aerodynamic efficiency of the rider, considering the rider contributes the majority of the drag force of the rider-bicycle system. If small riding position adjustments could be made to the rider's body during a race, drag may be significantly reduced. This idea, and the fact that the direction of wind impacting the rider can vary, influenced the concept of this project. It was hypothesized that adjusting the time-trial handlebars on the bicycle to stagger the fore-aft position of the rider's hands would influence the upper body to rotate slightly. This could then reduce the frontal area of the rider in the wind direction, therefore reducing the aerodynamic drag. To simulate this situation, the Konica Minolta VIVID 910 non-contact 3-D digitizer was used to scan two separate riders, each aboard a different bicycle, in several positions, as described above. The 3-D scans were then imported into the CFD software package Star-CCM+ and several simulations were run using each of the two rider-bicycle models. The initial simulations seemed to support the theory as the asymmetrical riding position experienced decreased drag at significant wind yaw angles while the normal riding position did not. A second study, using a different rider and bicycle, yielded less conclusive results. The two studies represent the groundwork for similar large system CFD analysis and provide useful recommendations for continued research into bicycle rider aerodynamics
Addressing Instability Issues in Microgrids Caused By Constant Power Loads Using Energy Storage Systems
No full textRenewable energy sources, the most reasonable fuel-shift taken over the naturally limited conventional fuels, necessarily deal with the self-functional microgrid system rather than the traditional grid distribution system. The study shows that the microgrid system, a comparatively low-powered system, experiences the challenge of instability due to the constant power load (CPL) from many electronic devices such as inverter-based systems. In this dissertation, as a methodical approach to mitigate the instability complication, AC microgrid stability is thoroughly investigated for each and every considerable parameter of the system. Furthermore, a specific loading limit is depicted by evaluating the stability margin from the small signal analysis of the microgrid scheme. After demonstrating all cases regarding the instability problem, the storage-based virtual impedance power compensation method is introduced to restore the system stability and literally extend the loading limit of the microgrid system. Here, a PID controller is implemented to maintain the constant terminal voltage of CPL via current injection method from storage. Since the system is highly nonlinear by nature, advanced nonlinear control techniques, such as Sliding Mode Control and Lyapunov Redesign Control technique, are implemented to control the entire nonlinear system. Robustness, noise rejection, and frequency variation are scrutinized rigorously in a virtual platform such as Matlab/Simulink with appreciable aftermaths. After that, a comparative analysis is presented between SMC and LRC controller robustness by varying CPL power. From this analysis, it is evident that Lyapunov redesign controller performs better than the previous one in retaining microgrid stability for dense CPL-loaded conditions. Finally, to ensure a robust storage system, Hybrid Energy Storage System is introduced and its advantages are discussed as extended research work.2017-02-2
OPTIMIZING SELF-HEALING WIND TURBINE BLADES UTILIZING VASCULAR IMPRINTED FIBER-REINFORCED EPOXY NANOCOMPOSITES
No full textWind energy, as a promising renewable resource, offers significant potential for clean, long-term power generation. This research aims to develop wind turbine blades with optimized autonomous self-healing capabilities which lead to reduced maintenance, repair, and energy compensation costs. The approach involves introducing self-healing capabilities into vacuum assisted resin transfer molding (VARTM) molded vascular imprinted fiber-reinforced epoxy composites (FREC), utilizing imprinting vascular networks, three-dimensional (3D) printing templates, infusing with dicyclopentadiene (DCPD), embedding into multilayer FREC, and wetted with first-generation Grubbs catalyst/epoxy mixture. The self-healing mechanism presented in this research utilizes the reaction between DCPD and the catalyst. DCPD is stored as a liquid in the vascular network, isolated from the catalyst until a damaging event triggers their combination. The two agents react and solidify upon damage to form the thermoset polydicyclopentadiene (PDCPD), effectively facilitating recovery from microcracks. This study proposed innovative modifications to these self-healing wind turbine blades to achieve cost-effective higher performance. These modifications include incorporating carbon nanotubes (CNTs) and replacing glass fiber sheets with carbon fiber sheets. This innovative approach enhances the durability and longevity of wind turbine blades, making them more efficient and cost-effective. Wind turbine blades are constantly subjected to bending forces, making self-healing crucial for their longevity. To demonstrate the self-healing capabilities of FREC material, three-point bending and tensile tests were conducted. The samples were tested before and after recovery. The maximum flexural and tensile strengths and percent recovery for the healed and non-healed FREC samples were calculated. Interestingly, in the first part of this study, the synergistic effects of epoxy resin, the PDCPD network, and reinforcement from glass fibers and CNTs result in enhanced mechanical properties for CNTs/DCPD/Glass FREC. Flexural stress (three-point bending) measurements demonstrated that the addition of epoxy resin with 0.6 wt% CNTs to the multilayer FREC to fabricate 0.4wt% CNTs self-healing wind turbine blades yields samples with a high recovery percentage of approximately 201.8%. This enhancement leads to wind turbine blades that are 24.3% stronger in flexural stress for non-healed samples and 27% more efficient in self-healing capabilities for healed samples compared to those without CNTs. Additionally, tensile strength improved by 13.8% for non-healed samples and 24.7% for healed samples, with a 107.9 % recovery percentage. In the second part of the study, the flexural strength of the non-healed DCPD/Hybrid glass-carbon FREC samples exhibited an enhancement by at least 14%, 17.7%, and 10% recorded concurrently with the replacement of glass fiber sheets with one, two, and three carbon fiber sheets. However, the flexural strength of the healed samples increased by at least 14.2%, 15.4%, 8%. At the same time, they showed stress recovery rates of 197.4%, 195%, and 194.3%, respectively. Furthermore, for the case of the replacement of glass fiber sheets with two carbon fiber sheets, the tensile strength improved by 6.9% for non-healed samples and 5.1% for healed samples, with a 96.8 % recovery percentage. Raman spectroscopy was conducted to assess the extent of the reaction between DCPD and the catalyst, resulting in the formation of PDCPD. Microstructure analysis demonstrated the comprehensive healing process in the sample, showing DCPD migration across multiple layers, enhancing the healing efficiency by addressing deeper and more extensive cracks. In the optimization part, the CNTs/DCPD/Hybrid glass-carbon FREC samples showed significant improvement, with 30.7% non-healed stress enhancement and 32.2% healed stress enhancement, with a 200% average recovery, indicating substantial structural enhancements. The tensile strength improved by 19.8% for non-healed samples and 27.1% for healed samples, with a 104.5 % recovery percentage.2026-08-2
Зміни показників ротової рідини дітей дошкільного віку з гінгівітом під впливом лікувально-профілактичних заходів
No full textSummary. The significant prevalence of inflammatory processes in periodontal tissues of children of different ages indicates insufficient effectiveness of preventive and therapeutic measures. Children of preschool age need special attention in the choice of therapeutic and prophylactic means.The aim of the study – a comparative evaluation of traditional treatment of children aged from 3–5 years with chronic catarrhal gingivitis with therapy with the use of anti-inflammatory gel with neovitin.Materials and Methods. 47 children with chronic catarrhal gingivitis were taken for dispensary observation and divided into groups: the main (23 children) and the comparative (24 children). All children underwent conventional therapy according to the protocols of medical care – basic therapy. In the main group, for a month, pathogenetic agents were used – an anti-inflammatory gel with neovitin, hygiene products were recommended. In the comparative group for local therapy, a 3 % hydrogen peroxide solution was used to rinse the oral cavity (during the first week of treatment) – Rotokan, a therapeutic and prophylactic toothpaste. Control examinations and examination with the definition of the hygienic state of the oral cavity using the hygienic index of Yu. A. Fedorov and V. V. Volodkina, the prevalence and intensity of the inflammatory process in the gums were assessed using the Schiller-Pisarev test and the PMA index, the oral fluid index (formation of oxyradical, urease activity, pH, viscosity, lysozyme content, degree of dysbiosis).Results and Discussion. After the treatment, elimination of gum inflammation in patients of the main group was accompanied by a 2.8-fold decrease in the PMA index; GI – 1.6 times. The reduction in the period of treatment of children was revealed in the application of the proposed treatment regimen. The effectiveness of the treatment was confirmed by a decrease in the formation of oxyradicals immediately after treatment by 15.67 % and 10.98 % (p<0.05), a decrease in urease activity was observed in 8.43 % and 5.47 %; the viscosity of the oral fluid decreased by 54.51 % and 50.51 % (p<0.05), the incidence of dysbiosis decreased by 22.49 % (p<0.05) and 10.36 % in children of the primary and comparative groups, respectively. After 0.5 years, the lysozyme content in the oral fluid of children increased by 21.12 % and 7.09 % (p<0.05), the pH increased by 1.39 % and 0.25 % (p>0.05) in children of the primary and comparative groups, respectively.Conclusions. The use of the proposed therapy with gel with neovitin contributed to the best results of treatment: a decrease in the degree of gingival inflammation by the PMA index by 2.8 times, a decrease in the number of visits to a doctor by 1.1, improvement of the oral fluid of children, and, to a greater extent, six months after the performed treatment.Резюме. Значительная распространенность воспалительных процессов в тканях пародонта детей разного возраста свидетельствует о недостаточной эффективности профилактических и лечебных мероприятий. В особом внимании по выбору лечебно-профилактических средств нуждаются дети дошкольного возраста.Цель исследования – сравнительная оценка традиционного лечения детей 3–5 лет с хроническим катаральным гингивитом с использованием противовоспалительного геля из неовитином.Материалы и методы. 47 детей, больных хроническим катаральным гингивитом, было взято под диспансерное наблюдение и разделено на группы: основную (23 ребенка) и сравнительную (24 ребенка). Всем детям проводилась общепринятая терапия согласно протоколов оказания медицинской помощи – базовая терапия. В основной группе в течение месяца применяли средства патогенетической направленности – противовоспалительный гель с неовитином, рекомендованы средства гигиены. В сравнительной группе для местной терапии был использован 3 % раствор перекиси водорода для полосканий полости рта (в течение первой недели лечения) – «Ротокан», лечебно-профилактическая зубная паста. Контрольные осмотры и обследование с определением гигиенического состояния полости рта с использованием гигиенического индекса Ю. А. Федорова и В. В. Володкиной, распространенность и интенсивность воспалительного процесса в деснах оценивали с помощью пробы Шиллера–Писарева и индекса РМА, показателей ротовой жидкости (образование оксирадикалов, уреазная активность, рН, вязкость, содержание лизоцима, степень дисбиоза).Результаты исследований и их обсуждение. После проведенного лечения ликвидация процесса воспаления десен у больных основной группы сопровождалась уменьшением индекса РМА в 2,8 раза; ГИ – в 1,6 раза. Установлено сокращение срока лечения детей при применении предложенной лечебной схемы. Эффективность проведенного лечения подтверждалась снижением образования оксирадикалов сразу после лечения на 15,67 и 10,98 % (р<0,05), происходило уменьшение уреазной активности на 8,43 и 5,47 %; снижалась вязкость ротовой жидкости на 54,51 и 50,51 % (р<0,05), уменьшалась степень дисбиоза на 22,49 % (р<0,05) и 10,36 % у детей основной и сравнительной групп соответственно. Через 0,5 года увеличивалось содержание лизоцима в ротовой жидкости детей на 21,12 и 7,09 % (р<0,05), увеличивалось рН на 1,39 и 0,25 % (р>0,05 ) у детей основной и сравнительной групп соответственно.Выводы. Применение предложенной терапии с использованием геля с неовитином способствовало лучшим результатам лечения: снижению степени воспаления десен по индексу РМА в 2,8 раза, уменьшению количества посещений врача на 1,1, улучшению показателей ротовой жидкости детей, причем, в большей степени через полгода после проведенного лечения.Резюме. Значна поширеність запальних процесів у тканинах пародонта дітей різного віку свідчить про недостатню ефективність профілактичних і лікувальних заходів. Особливої уваги щодо вибору лікувально-профілактичних засобів потребують діти дошкільного віку.Мета дослідження – порівняльна оцінка традиційного лікування дітей 3–5 років із хронічним катаральним гінгівітом з використанням протизапального гелю з неовітином.Матеріали і методи. 47 дітей, хворих на хронічний катаральний гінгівіт, було взято під диспансерне спостереження та поділено на групи: основну (23 дитини) і порівняльну (24 дитини). Усім дітям проводили загальноприйняту терапію згідно з протоколами надання медичної допомоги – базова терапія. В основній групі протягом місяця застосовували засоби патогенетичної спрямованості – протизапальний гель з неовітином, рекомендовані засоби гігієни. В порівняльній групі для місцевої терапії було використано 3 % розчин пероксиду водню; для полоскань ротової порожнини (протягом першого тижня лікування) – «Ротокан», лікувально-профілактична зубна паста. Контрольні огляди та обстеження із визначенням гігієнічного стану порожнини рота за гігієнічним індексом Ю. А. Федорова і В. В. Володкіної, поширеності та інтенсивності запального процесу в яснах оцінювали за допомогою проби Шіллера–Писарєва та індексу РМА, показників ротової рідини (утворення оксирадикалів, уреазна активність, рН, в’язкість, вміст лізоциму, ступінь дисбіозу).Результати досліджень та їх обговорення. Після проведеного лікування ліквідація процесу запалення ясен у хворих основної групи супроводжувалась зменшенням індексу РМА у 2,8 раза; ГІ – в 1,6 раза. Встановлено скорочення терміну лікування дітей при застосуванні запропонованої лікувальної схеми. Ефективність проведеного лікування підтверджувалася зменшенням утворення оксирадикалів одразу після лікування на 15,67 та 10,98 % (р<0,05); відбувалося зниження уреазної активності на 8,43 та 5,47 %; зменшувалася в’язкість ротової рідини на 54,51 та 50,51 % (р<0,05); знижувався ступінь дисбіозу на 22,49 % (р<0,05) та 10,36 % у дітей основної і порівняльної груп відповідно. Через 0,5 року збільшувався вміст лізоциму в ротовій рідині дітей на 21,12 та 7,09 % (р<0,05), збільшувалось рН на 1,39 та 0,25 % (р>0,05) у дітей основної і порівняльної груп відповідно.Висновки. Застосування запропонованої терапії із використанням гелю з неовітином сприяло кращим результатам лікування: зниженню ступеня запалення ясен за індексом РМА у 2,8 раза, зменшенню кількості відвідувань лікаря на 1,1, поліпшенню показників ротової рідини дітей, причому, більшою мірою через півроку після проведеного лікування
Cation disorder in NaW2O6+δ·nH2−zO post-ion exchange with K, Rb, Sr, and Cs
No full textThe structure of the defect pyrochlore NaW(2)O(6+delta)center dot nH(2-z)O after ion exchange with K, Rb, Sr or Cs for Na has been investigated using thermal analysis, solid-state nuclear magnetic resonance, laboratory X-ray and neutron diffraction methods. Neutron diffraction studies show that both the A-type cations (Na(+), K(+), Rb(+), and/or Cs(+)) and the water molecules reside within the channels that form in the 111 direction of the W(2)O(6) framework and that these strongly interact. The analytical results suggest that the water and A-type cations compete for space in the tunnels within the W(2)O(6) pyrochlore framework, with the total number of water molecules and cations being approximately constant in the six samples investigated. The interplay between the cations and water explains the non-linear dependence of the a lattice parameter on the choice of cation. It appears that the ion-exchange capacity of the material will be controlled by the amount of water initially present in the sample
High-pressure structural behavior and equation of state of NaZnF3.
No full textWe report the results of density functional theory ab-initio calculations and monochromatic synchrotron X-ray diffraction study carried out for orthorhombic NaZnF3 in the pressure range 0-40 GPa. Perovskite-to-postperovskite phase transition was anticipated by first-principles computations and then observed in high-pressure diamond anvil cell synchrotron diffraction experiment between 14 and 22 GPa. Above 25 GPa postperovskite structure (CaIrO3 type, space group Cmcm) coexists with another phase, yet unidentified. On decompression, pure postperovskite-type structure was found to be stable down to 4 GPa: below this pressure sample contained both perovskite and postperovskite modifications. Fit of experimental P-V data to the third-order Birch-Murnaghan equation of state gave bulk moduli, K-P,K-0 64.98 +/- 2.67 and 69.88 +/- 3.69 GPa for perovskite and postperovskite modifications, respectively. Both phases demonstrated strong anisotropy of compressibility. For postperovskite NaZnF3, the highest compression was observed along the direction perpendicular to the planes of ZnF6 octahedra arrangement. © 2009, Elsevier Ltd
- …
