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Arieira, Ana, Sara Madeira, Flávio Rodrigues und Filipe Silva. „Tribological Behavior of TiO2 PEEK Composite and Stainless Steel for Pediatric Crowns“. Materials 16, Nr. 6 (17.03.2023): 2420. http://dx.doi.org/10.3390/ma16062420.
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Dental decay still presents a major health problem among children. Its treatment usually requires the use of stainless steel crowns. This study compares the wear behavior of 316 L stainless steel and polyetheretherketone (PEEK) composite under identical test conditions. The wear tests were conducted in a reciprocating ball-on-plate tribometer (Plint TE67/R) using alumina balls as a counterface and artificial saliva as a lubricant at 37 °C to faithfully mimic oral conditions. The coefficient of friction (COF) and specific wear rate (k) values were determined and SEM/EDS examinations were performed to identify the predominant wear mechanisms. Results showed that PEEK exhibited a significantly lower coefficient of friction (COF = 0.094 ± 0.004) and thus lower wear volume (ΔV = 0.0078 ± 0.0125 mm3) and higher wear resistance, with an average value of specific wear rate of k = 9.07 × 10−6 mm3N−1m−1 when compared to stainless steel (COF = 0.32 ± 0.03, ΔV = 0.0125 ± 0.0029 mm3, k = 1.45 × 10−5 mm3N−1m−1). PEEK was revealed to be a potential material for use in pediatric crowns due to its high wear resistance while overcoming the disadvantages associated with steel at both an aesthetic and biological level.
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Carmona-Cervantes, Isabel Ariadna, Iván Campos-Silva, Ulises Figueroa-López und Andrea Guevara-Morales. „Effect of Recycled Polyvinyl Butyral (rPVB) Addition on the Tribological Performance of Glass–Fiber Reinforced Polyamide (PAGF) during Reciprocating Sliding Wear Conditions“. Polymers 15, Nr. 11 (05.06.2023): 2580. http://dx.doi.org/10.3390/polym15112580.
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Plastic recycling in the automotive industry is a priority. In this study, the effect of adding recycled polyvinyl butyral (rPVB) from automotive windshields on the coefficient of friction (CoF) and specific wear rate (k) of a glass–fiber reinforced polyamide (PAGF) is investigated. It was found that, at 15 and 20 wt.% of rPVB, it acts as a solid lubricant, reducing CoF and k up to 27% and 70%, respectively. Microscopical analysis of the wear tracks showed that rPVB spreads over the worn tracks, forming a lubricant layer, which protects the fibers from damage. However, at lower rPVB content, fiber damage cannot be prevented as the protective lubricant layer is not formed.
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da Cruz, Crislaine, Ivan Mathias, Mariza Veiga Senk, Gelson Biscaia de Souza und Francisco Carlos Serbena. „Effect of crystal size on the tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres“. Industrial Lubrication and Tribology 72, Nr. 9 (22.05.2020): 1109–16. http://dx.doi.org/10.1108/ilt-08-2019-0352.
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Purpose Lithium disilicate glass-ceramics (LS2 GC) are widely used as dental prosthetics and dental restorations. Based LS2 GC have hardness and translucency similar to that of natural teeth. This study aims to investigate the tribological features of LS2 GC with crystalline volume fraction of 64% and different crystal sizes from 8 µm to 34 µm for different counterparts. Design/methodology/approach The tribological behavior was investigated using a pin-on-disc tribometer with alumina and tungsten carbide (WC) spheres, applied load of 5 N and sliding speed of 5 cm/s at normal conditions. The coefficient of friction was measured continuously up to 10,000 sliding cycles. The specific wear rate was calculated from tribological and profile measurements. The wear mechanism was investigated by surface morphology analysis. Findings The coefficient of friction during running-in varied from 0.8 to 1.0 for the alumina counterpart, because of severe wear. Afterwards, it reduced and reached a stationary regime, characterized by a mild wear regime and the formation of a tribolayer formed by the debris. For the WC counterpart, the coefficient of friction curves increased initially with sliding cycles up to a stationary regime. The samples tested against WC presented the lowest specific wear rate (k), and no variation of wear rate with crystal size was observed. For samples tested against the alumina, crystallization and crystal size increased the wear resistance. Originality/value This study evaluated the effect of different counterfaces on the tribological properties of the LS2 GC, an important glass-ceramic base for many dental prosthetics and dental restorations, discussing results in light of the contact mechanics. Different specific wear rates, wear regimes and dependence on the glass-ceramic microstructure were observed depending on the counterpart. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0352/
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Hvizdoš, P., M. Besterci, P. Kulu und T. Kvačkaj. „Tribological Characteristics of Copper Based Composites with Al2O3 Particles at Various Temperatures“. High Temperature Materials and Processes 32, Nr. 5 (25.10.2013): 437–42. http://dx.doi.org/10.1515/htmp-2012-0161.
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AbstractTwo copper based composites: an experimental Cu-Al2O3 and commercial GlidCop AL-60 grade (with 1.1 wt.% Al2O3) with grains size approximately 1–2 µm were treated by Equal Channel Angular Pressure (ECAP) technique in order to induce severe plastic deformation and to reduce the grain size by about an order of magnitude. Microstructure of the as-received and ECAPed states of both systems were observed. Hardness of the experimental materials was measured by instrumented indentation. Tribological properties were studied by pin-on-disk technique in dry sliding against a steel ball at a various temperatures from room temperature up to 873 K. For all systems the coefficient of friction and specific wear rates were evaluated. Worn surfaces were studied by scanning electron microscopy and level of oxidation was measured using EDX spectrometry. It was found that between 473 K and 673 K the coefficient of friction decreased significantly. At lower temperatures the finer grained systems were more wear resistant than the as-received ones. The wear rate of all systems decreased down to zero at 673 K due to formation of hard oxide rich layers. Damage mechanisms were identified and their relationship with structural characteristics was inferred.
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Karim, Zailan, Mohd Zaki Nuawi, Jaharah A. Ghani, Shahrum Abdullah und Mariyam Jameelah Ghazali. „Wear Monitoring of Connecting Rod Bearing via Air-Borne Method Analyzed by Using I-KazTM Multi Level Value“. Advanced Materials Research 445 (Januar 2012): 941–46. http://dx.doi.org/10.4028/www.scientific.net/amr.445.941.
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Different techniques have been developed in the area of bearing wear monitoring. This paper proposes a different experimental study on bearing wear monitoring by using an airborne technique. The data captured in the airborne technique will be analyzed by using I-kazTM Multi Level (7Z) coefficient and then will be correlated with the conventional specific wear rates, K. The wear tests were carried out by using a pin-on-disc configuration at a sliding speed of 7.85 m/s. A set of sliding distance ranging from 20 160 km at a fixed load of 200 N was utilized and the K value was measured at every interval of 20 km for the speed. SAE40 type lubricant was used in the test to simulate the actual operation of the connecting rod bearing. The audio range frequency below 20 kHz in the airborne technique was obtained through a microphone 40SC type which was placed 10 mm from the pin-disc contact. The analysis result showed that the wear rate, K increased from 1.82 to 6.70x10-8 mm3/Nm as the sliding distance increased, indicating that a mild-abrasion wear regime had occurred. The curve fitting of K as a function of I-kazTM Multi Level coefficient showed a similarity to an established of Taylor Tool Life curve. Thus, it was possible to correlate the Taylor curve and worn bearing, mainly in monitoring and identifying the bearing condition with respect to the sliding distance. The trend of I-kazTM Multi Level coefficient was found to be consistent with the increase of sliding distance which indicates that the I-kazTM Multi Level value can positively be used as wear response indicator for bearing.
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Singh, Paramjit, Harish Pungotra und Nirmal S. Kalsi. „Parametric optimization of deep cryogenic treatment for the wear response of implant material UNS R56700: Taguchi’s approach“. Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 234, Nr. 1 (05.11.2019): 61–73. http://dx.doi.org/10.1177/0954411919884775.
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Using the Taguchi’s robust design of experiments methodology, this article presents the systematic identification and optimization of most influential parameters of deep cryogenic treatment process to minimize the specific wear rate of UNS R56700 (Ti6Al7Nb). In addition to the different soaking durations (0–96 h) at 77 K and different tempering temperatures (room temperature, 403–523 K), three commonly used variables of pin-on-disk test, namely, sliding speed (1.047–2.723 ms−1), contact pressure (0.641–1.282 MPa), and sliding time (600–2280 s) were chosen to conduct the tests. During dry sliding conditions, pin-on-disk tribo-tests were performed to slide Ti6Al7Nb on the surface of UNS 52986 (En31) material as per standardized ASTM G99 guidelines. Experimentally measured wear rate values were converted to signal–noise ratio to statistically analyze the influence of five control variables using pooled analysis of variance and F-test. Statistically found influential control variables are confirmed experimentally. The results show that sliding speed, contact pressure and soaking duration are the most significant factors influencing the wear rate. In contrast, the parameters, that is, tempering temperature and sliding time, exhibit a lower level of influence. Microstructural characterizations done using optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques suggested that deep cryogenic treatment favors the refinement of grain size of present phases with reduction in β-stabilization (β-phase) in Ti6Al7Nb. The possible reasons for the improvement in wear rate of Ti6Al7Nb underlying the morphological alterations have been explained.
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Pessolano Filos, Irene, Raffaella Sesana, Massimiliano Di Biase und Rocco Lupoi. „New Abrasive Coatings: Abraded Volume Measurements in Ceramic Ball Production“. Journal of Manufacturing and Materials Processing 5, Nr. 3 (27.07.2021): 81. http://dx.doi.org/10.3390/jmmp5030081.
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Technological progress in hybrid bearings developed high wear and abrasion resistant materials for rolling elements. The manufacturing process of bearing balls presents new challenges, as nowadays, it requires time-consuming and costly processes. In this frame, the bearing manufacturing industry is demanding improvements in materials, geometry, and processes. This work aims to investigate new abrasive coatings for grinding wheels for Si3N4 ball manufacturing. Tribological pin on disk tests are performed on samples of grinding materials (disk) versus a Si3N4 ball (pin). Two samples of specimens coated with an electrodeposited diamond and diamond-reinforced metal matrix composite are examined to measure the abrasion rate and the wear resistance of Silicon Nitride Si3N4 balls, considering the influence of sliding speed and the effect of coating deposition on diamond particle density and granulometry. The measurements estimated the specific wear coefficient k, the height wear surface h, and the wear rate u of the Si3N4 balls. The results pointed out that by increasing the sliding speed, the abraded volume increases for both the coatings. The parameters affecting the abrasion effectiveness of both the coatings are the surface roughness, the abrasive particle dimension, and the sliding speed.
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Osman, Omer, Necar Merah, Mohammed Abdul Samad, Amjad Al-Shaarawi und Meshari Alshalan. „Effects of Drilling Parameters and Mud Types on Wear Factors and Mechanisms of SM2535 Casings“. Lubricants 11, Nr. 10 (30.09.2023): 420. http://dx.doi.org/10.3390/lubricants11100420.
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This work aims to explore the impact of side loads, drill-pipe tool-joint (DP-TJ) speed (rpm), and mud type on the austenitic stainless steel SM2535-110 casing wear characteristics. Actual field drill pipe tool joints, casings, and drilling muds are used in this study. The results of the study show that under both types of lubrication, the wear volume increased with radial load and DP-TJ speed. SM2535-110 casing specimens tested under oil-based mud (OBM) lubrication had higher casing wear volumes than those obtained under water-based mud (WBM) lubrication. This unexpected behavior is mainly due to the increase in the surface hardness of the casing specimens tested under WBM. The results also show that the specific wear rate or wear factor (K) (which is defined as the volume loss per unit load per unit distance sliding) values of specimens tested under WBM are in general two to four times higher than those obtained under OBM. While K values under WBM increase with both the side load and rpm, those under OBM show a sharp decrease with rpm. This behavior under OBM is due to this lubricant’s higher viscosity and the change of lubrication regime from thin film to thick film lubrication at higher rpm. Scanning electron microscopy (SEM) and the digital microscopic imaging (DMI) of SM235-110 casing specimens show that an aggressive combination of adhesive, abrasive, and plastic deformation was observed under WBM, while the dominant wear mechanism under OBM is abrasive wear.
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Hernández-Sierra, M. T., R. Ortega-Álvarez, M. G. Bravo-Sánchez, L. D. Aguilera-Camacho, J. S. García-Miranda und K. J. Moreno. „Tribological improvement of hardened and tempered AISI 4140 steel against Al2O3 by using bio-lubricant“. MRS Advances 2, Nr. 62 (2017): 3873–81. http://dx.doi.org/10.1557/adv.2018.2.
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ABSTRACTAISI 4140 steel is a popular low alloy steel due to its wide applications as workpiece in the metal-mechanic industry; there are extensive research about surface modification to enhance its properties for specific applications. The focus of this study was to investigate the influence of the nature of lubricants, mineral and vegetable oils, on the tribological performance of the hardened and tempered AISI 4140 steel against alumina (Al2O3). For this purpose, friction tests were conducted in a pin on disc tribometer according to ASTM standard G 99-05, at room temperature of 25 °C and in air with about 30% relative humidity. Lubricants were selected to be commercial Holifa B22/2 oil as mineral oil and Castor Oil as bio-lubricant, with kinematic viscosity at 25 °C of 667 and 662 cSt respectively. The following conditions were settled for all the experiments: relative sliding speed of 0.05 ms-1, sliding distance of 1000 m and wear track radius of 2 mm. Friction behaviour was reported as the average kinetic friction coefficient (µK) while wear performance was evaluated as wear rate (K). In order to identify and determine wear mechanisms, worn surfaces were analyzed by optical microscopy and profilometry. It was found that, for these tribosystems, hardened and tempered AISI 4140 steel had the best friction and wear performance under lubrication with Castor Oil. The lowest µK achieved was 0.035, whereas the lowest K was 1.02x10-8 mm3/Nm. With this bio-lubricant, there were reductions in friction and wear up to 72% compared with those under mineral oil lubrication.
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Neamah, Z. J., und S. H. Mahdi. „Effect of zirconia addition on thermal and mechanical properties of poly-methyl methacrylate composites“. Digest Journal of Nanomaterials and Biostructures 18, Nr. 3 (Juli 2023): 927–32. http://dx.doi.org/10.15251/djnb.2023.183.927.
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The goal of this study was to improve the mechanical and thermal properties of PolyMethyl Meth Acrylate (PMMA) by adding Zirconia nanoparticles in various weight fraction percentages (0, 1, 1.5, 2, 2.5, 3)%. The cast technique was utilized of to prepare the (PMMA/zirconia) nanocomposites. The thermal and mechanical characterized of (PMMA/zirconia) nanocomposites were studied. Increased zirconia percentages in (PMMA/zirconia) nanocomposites lead to increase thermal conductivity (K), glass transition temperature, specific heat capacity (Cp), effusivity, impact strength, hardness, flexural strength, compressive strength and reduced wear rate, enhancing the thermal and mechanical properties of Poly-Methyl Meth Acrylate (PMMA).
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Korim, Nada S., Ayman Elsayed und Lianxi Hu. „Impacts of Lubricant Type on the Densification Behavior and Final Powder Compact Properties of Cu–Fe Alloy under Different Compaction Pressures“. Materials 15, Nr. 16 (20.08.2022): 5750. http://dx.doi.org/10.3390/ma15165750.
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A Cu–15Fe alloy was fabricated using a powder metallurgy (PM) route, with the addition of different solid lubricants (i.e., paraffin wax (PW) and stearic acid (SA) as well as their composites (PW+SA)). Green compacts were produced via cold compaction at different pressure levels of 50 MPa, 200 MPa, and 350 MPa, then sintered for 60 min under vacuum at 1050 °C. The systematic evolution of the densification, porosity, and pore-size behavior were studied. Vickers Hardness Tests were used to measure hardness. The analysis of the morphological alterations was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Moreover, under dry sliding conditions, pin-on-disk wear tests were conducted in order to determine tribological properties such as the coefficient of friction (µ), specific wear rate (K), and friction temperature gain. Results revealed that the lubrication process and compaction pressure play a crucial role in defining the characteristics of the final compact. Higher sintered densities and hardnesses were achieved at 50 MPa when PW was used as a solid lubricant, and became reduced as the compaction pressure increased. In contrast, in the case of SA, higher sintered densities and hardnesses were obtained at a compaction pressure of 350 MPa, and increased with increasing pressure. Moreover, PW samples exhibited lower coefficients of friction and wear properties. The addition of SA improves the wear loss of friction materials as well as their coefficients of friction. Compared to blank and PW samples, SA samples show a nearly 50% reduction in wear rate.
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Ibraheem Al-Tamimi, Jaafar Jaber, Rihab A. J. Altaii und Wedad K. Ali. „The Effect of Vitamin C and Antacid Tablets (SDI) on the Pharmacokinetics of Aspirin Tablets (SDI) in Human“. Al Mustansiriyah Journal of Pharmaceutical Sciences 16, Nr. 2 (01.12.2016): 99–104. http://dx.doi.org/10.32947/ajps.v16i2.116.
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The study explored the effect of vitamin c and antacid on the pharmacokinetics of aspirin in human subjects.
The study was conducted in 12 healthy adults volunteers who were asked to take in the first study, two tablets of aspirin (300 mg) alone. In a second study, the same subjects were given two tablets of aspirin (300 mg) together with one tablet of vitamin c 500 mg. Eventually, in the third study, the subjects were administered two tablets of aspirin (300 mg) and one capsule containing NaHCO3 (500 mg). The three studies were separated by one week wash out period.
In each study, urine was collected from each individual participated in the study at specific time intervals for up to24 hours post dosing to calculate the cumulative amount of salicylate excreted in urine. The excretion rate was plotted against the mid-time sampling time to calculate the elimination rate constant (K), and the elimination half-life (T0.5).
It was found from the current investigation that administration of vitamin c tablet with aspirin tablets reduce (K) values and elongate T0.5, whereas, NaHCO3 intake elevate K values and reduce T0.5 in all subjects participated in the study.
It can be concluded from the current investigation that administration of weak acid drugs like vitamin c, or weak base drugs like antacid have considerable effect on the residence of aspirin in the body and consequently its intensity and duration of clinical effect.
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Smajla, Darjan, Jure Žitnik und Nejc Šarabon. „Investigation of Inter-Limb Symmetry in Knee Extensors Using Different Strength Outcome Measures“. Diagnostics 11, Nr. 10 (12.10.2021): 1882. http://dx.doi.org/10.3390/diagnostics11101882.
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Muscle performance between contra-lateral knee extensors is most often assessed using maximal test for isometric/isokinetic torque evaluation. Recently, the rate of force development scaling factor (RFD-SF) has been used to evaluate neuromuscular capacity with a range of submaximal target peak torques, which could highlight other aspects of inter-limb (a)symmetry. The aim of our study was to investigate the differences, associations, and agreement between inter-limb symmetries of knee extensors using maximal torque (Tmax) rate of torque development (RTD), slope of the RFD-SF regression line (k), and theoretical peak of RTD (TPRTD). A total of 236 young, healthy athletes participated in the cross-sectional study. All participants performed unilateral knee extension (maximal voluntary contraction protocol and RFD-SF protocol) with both legs in the isometric knee dynamometer. Inter-limb symmetries were calculated for each outcome measure. Our results showed significant differences between all symmetry values (Tmax (91.7%), RTD (85.2%), k (94.2%), TPRTD (95.9%)). Significant strong correlations were found between symmetry values calculated from k and TPRTD (r = 0.88, p < 0.001), while weak correlation was found between Tmax and RTD (r = 0.17, p < 0.01. Fair agreement regarding leg dominance was found between Tmax and RTD values. Our results suggest that inter-limb (a)symmetries are metric- and task-specific.
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Kosolapov, Viktor. „Assessment of the influence of the working fluid production on the output parameters of the transmission hydraulic motor of the front loader“. Bulletin of Kharkov National Automobile and Highway University 1, Nr. 92 (04.03.2021): 167. http://dx.doi.org/10.30977/bul.2219-5548.2021.92.1.167.
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Problem. During the operation of the volumetric hydraulic drive of the front loader, as the surfaces of the movable interfaces of the hydraulic drive elements wear out, the gaps increase, and as a result, the leaks of the working fluid (WF) increase, and, therefore, the performance of the machine as a whole decreases. The resource of the hydraulic drive units is largely determined by the physicochemical properties of the WF, and in particular, the ability of the WF to reduce the specific load in the contact of the surfaces of the movable joints. During the operation of the transmission hydraulic drive, the aging of the fluid occurs. As a result, its operational properties deteriorate, including a decrease in the bearing capacity of the WF lubricant film. This leads to an increase in the wear of the interface surfaces of the volumetric hydraulic drive of the transmission (VHDT) and a decrease in the productivity of the machine. Goal. Experimental studies of the influence of the working fluid production on the rate of change of the volumetric efficiency of the hydraulic motor of the volumetric hydraulic drive of the front loader transmission have been carried out. Methodology. The tests of the MP-90 hydraulic motor were carried out at the stand. The object of the study was the hydraulic motor of the MP-90 frontal loader. Hydraulic oil MANITOU HUILE HYDRAULIQUE ISO HV46 with different operating time was used as the WF. Samples were taken from the transmission drive system of the PMTS-1200 front loader. The experimental ones were carried out under the following conditions: WF temperature, t = 323 K; rotational speed of the pump drive shaft, n = 25 s ; the operating time of the WF varied within the range of T = 0–720 motor-hours with a step of 200 motor-hours; the purity of RZ is not less than 10 class according to GOST 17216-2001; the test time was taken equal to 40 hours; pressure in the discharge line 26.5 MPa, vibration amplitude 6 MPa, vibration frequency 0.2 s. Results. It is shown that an increase in the operating time of the WF during the operation of the machine determines, other things being equal, an increase in the rate of change in the volumetric efficiency of the VHDT hydraulic motor. Originality. To prevent increased wear of the moving surfaces of the VHDT interfaces during the operation of the front-end loader, it is necessary to use WF the bearing capacity of the lubricating film which is higher than the maximum permissible value. Practical value. The use of the results of the study will increase the VHDT of the hydraulic drive elements of the front loader and reduce the rate of decrease in its productivity during its operation.
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Hierholzer, J., M. Cordes, H. B. Straub, U. Keske, H. J. Meencke, H. Eichstädt, R. Felix und S. Venz. „Quantitative Estimation of I-123-Iomazenil Receptor Binding in Temporal Lobe Epilepsies Using Two SPECT Acquisitions – Comparison with the Regional Cerebral Blood Flow and a Compartment Model“. Nuklearmedizin 37, Nr. 02 (1998): 49–56. http://dx.doi.org/10.1055/s-0038-1629792.
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Summary Aim: To compare published fractional rate constants of I-123-lomazenil (IMZ) and C-11-Flumazenil (three-compartment/four-parameter model) with a I-123-lomazenil receptor index calculated from two SPECT acquisitions and to compare the receptor index of the epileptogenic area with the contralateral side in patients with unilateral temporal lobe epilepsies. Methods: 28 patients were studied. 13/28 patients had a drug-resistant unilateral temporal lobe epilepsy with a successful focus localisation performed by an extensive video/EEG monitoring. 15 other patients with clinically suspected focal epilepsy and a normal MRI and IMZ SPECT scanning were used as controls. SPECT scanning was performed in all patients 15 and 100 min after intravenous injection of 111 MBq IMZ and 10 min after application of 740 MBq Tc-99m-HMPAO. Quantification of the regional uptake was performed using ROI-technique and the specific and non-specific binding of IMZ was calculated. The receptor index was calculated by the difference of the specific binding from 15 to 100 min p. i. divided by the time interval. Results: The receptor index showed a linear correlation with recently published fractional rate constants k 3 (r = 0.69 and 0.67; p = 0.15) and a moderate correlation with the k 4 constant (-0.53 and -0.43; p = 0.28) by the means of C-11 -Flumazenil PET and 1-123-lomazenil SPECT studies, respectively. However, statistical significance was not reached due to the few data points available from the published reports. Furthermore, the IMZ receptor index was lower in the epileptogenic area of patients with unilateral temporal lobe epilepsies compared with their contralateral side (p = 0.02; Wilcoxon-test). The IMZ receptor index showed a weak correlation with the regional cerebral blood flow independent of the evaluated region (r <0.4; p <0.05). Conclusion: The IMZ receptor index indicated to be a simple routine approach to estimate the fractional rate constant k 3 (r = 0.67). The lower value of the receptor index within the epileptogenic area might be due to a lower receptor density. However in further studies, IMZ might be a helpful tool to find out subtle changes of the receptor affinity due to its approximately 30-fold higher ligand-receptor affinity compared to C-11-Flumazenil.
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Żak, Andrzej, Anna Dańczak und Włodzimierz Dudziński. „Low-temperature martensite relaxation in Co–Ni–Ga shape memory alloy monocrystal revealed using in situ cooling, transmission electron microscopy and low rate calorimetry“. Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, Nr. 4 (08.07.2020): 563–71. http://dx.doi.org/10.1107/s2052520620006794.
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This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been limited to specific heating and cooling rates, which could lead to an incomplete description of the resulting phenomena. Differential scanning calorimetry (DSC) performed with different heating/cooling rates enabled the precise determination of enthalpy values, which deviate from literature values. Weak and previously unnoticed thermal phenomena at temperatures below 190 K were also observed. Their presence was confirmed by low-temperature in situ transmission electron microscopy (TEM). Through DSC measurements and TEM observations, a model of the discovered phenomenon was proposed, which may have an impact on a better understanding of the physics of magnetic shape memory materials.
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Woodcock, Leslie V. „Global Warming by Geothermal Heat from Fracking: Energy Industry’s Enthalpy Footprints“. Entropy 24, Nr. 9 (19.09.2022): 1316. http://dx.doi.org/10.3390/e24091316.
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Hypothetical dry adiabatic lapse rate (DALR) air expansion processes in atmosphere climate models that predict global warming cannot be the causal explanation of the experimentally observed mean lapse rate (approx.−6.5 K/km) in the troposphere. The DALR hypothesis violates the 2nd law of thermodynamics. A corollary of the heat balance revision of climate model predictions is that increasing the atmospheric concentration of a weak molecular transducer, CO2, could only have a net cooling effect, if any, on the biosphere interface temperatures between the lithosphere and atmosphere. The greenhouse-gas hypothesis, moreover, does not withstand scientific scrutiny against the experimental data. The global map of temperature difference contours is heterogeneous with various hotspots localized within specific land areas. There are regional patches of significant increases in time-average temperature differences, (∆<T>) = 3 K+, in a ring around the arctic circle, with similar hotspots in Brazil, South Africa and Madagascar, a 2–3 K band across central Australia, SE Europe centred in Poland, southern China and the Philippines. These global-warming map hotspots coincide with the locations of the most intensive fracking operational regions of the shale gas industry. Regional global warming is caused by an increase in geothermal conductivity following hydraulic fracture operations. The mean lapse rate (d<T>/dz)z at the surface of the lithosphere will decrease slightly in the regions where these operations have enhanced heat transfer. Geothermal heat from induced seismic activity has caused an irreversible increase in enthalpy (H) input into the overall energy balance at these locations. Investigating global warming further, we report the energy industry’s enthalpy outputs from the heat generated by all fuel consumption. We also calculate a global electricity usage enthalpy output. The global warming index, <∆T-biosphere> since 1950, presently +0.875 K, first became non-zero in the early 1970’s around the same time as natural gas usage began and has increased linearly by 0.0175 K/year ever since. Le Chatelier’s principle, applied to the dissipation processes of the biosphere’s ΔH-contours and [CO2] concentrations, helps to explain the global warming statistics.
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Januś, Marta, Karol Kyzioł, Stanisława Kluska, Witold Jastrzębski, Anna Adamczyk, Zbigniew Grzesik, Sławomir Zimowski, Marek Potoczek und Tomasz Brylewski. „Plasmochemical Modification of Crofer 22APU for Intermediate-Temperature Solid Oxide Fuel Cell Interconnects Using RF PA CVD Method“. Materials 15, Nr. 12 (08.06.2022): 4081. http://dx.doi.org/10.3390/ma15124081.
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The results of plasmochemical modification on Crofer 22APU ferritic stainless steel with a SiCxNy:H layer, as well as the impact of these processes on the increase in usability of the steel as intermediate-temperature solid oxide fuel cell (IT-SOFC), interconnects, are presented in this work. The layer was obtained using Radio-Frequency Plasma-Activated Chemical Vapor Deposition (RF PA CVD, 13.56 MHz) with or without the N+ ion modification process of the steel surface. To determine the impact of the surface modification on the steel’s resistance to high-temperature corrosion and on its mechanical properties, the chemical composition, atomic structure, and microstructure were investigated by means of IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Microhardness, Young’s modulus, wear rate, as well as electrical resistance, were also determined. Micromechanical experiments showed that the plasmochemical modification has a positive influence on the surface hardness and Young’s modulus of the investigated samples. High-temperature oxidation studies performed for the samples indicate that N+ ion modification prior to the deposition of the SiCxNy:H layer improves the corrosion resistance of Crofer 22APU steel modified via CVD. The area-specific resistance of the studied samples was 0.01 Ω·cm2, which is lower than that of bare steel after 500 h of oxidation at 1073 K. It was demonstrated that the deposition of the SiCxNy:H layer preceded by N+ ion modification yields the best properties.
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Rigin, B. V., E. V. Zuev, I. I. Matvienko und A. S. Andreeva. „Molecular labeling of <i>Vrn</i>, <i>Ppd</i> genes and vernalization response of the ultra-early lines of spring bread wheat <i>Triticum aestivum</i> L.“ Plant Biotechnology and Breeding 4, Nr. 3 (23.12.2021): 26–36. http://dx.doi.org/10.30901/2658-6266-2021-3-o2.
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Background. The knowledge of genetic control of vernalization response in the ultra-early accessions can facilitate bread wheat breeding for a high adaptive capacity. Materials and methods. The study involved the ultra-early lines Rico (k-65588) and Rimax (k-67257) as the earliest maturing lines in the VIR bread wheat collection, as well as 10 Rifor lines (k-67120, k-67121, k-67250-67256) with a high rate of development before heading. A late ripening accession ‘Forlani Roberto’ (k-42641) and ‘Leningradskaya 6’ variety (k-64900), regionally adapted to Northwestern Russia, were also studied. The alleles of the Vrn and Ppd genes were identified by the PCR analysis using the allele-specific primers published in literature sources. The response to vernalization (30 days at 3°C) and a short 12-hour day were determined using a methodology accepted at VIR. Results. The ultra-early lines respond to a short 12-hour day and 30-day vernalization very poorly. The genotype of ultra-early wheat lines is mainly represented by three genes, Vrn-A1, Vrn-B1a, and Vrn-D1, which ensure insensitivity to vernalization alongside with the expression of Ppd-D1a, which controls the response to photoperiod. The ultra-early lines Rifor 4 and Rifor 5 have a recessive allele vrn-A1a, like the original ‘Forlani Roberto’ accession. The lines Rifor 4 and Rifor 5 are vernalization-insensitive under the long day and have a very weak response under the short day (3.5±0.42 days and 4.0±0.61 days, respectively). However, ‘Forlani Roberto’ with the vrn-A1a gene responds to vernalization in the same way under any photoperiod (12.3±1.58 days and 12.2±0.74 days). Conclusion The ultra-early lines of bread wheat Rifor 4 and Rifor 5 with the vrn-A1a gene can have no response to vernalization or have a low level response. This effect can be a reason for the formation of a complex of modifier genes along with the dominant gene Vrn-D1, which forms during the hybridization of F7-8 Rico × Forlani Roberto. The ultra-early lines of bread wheat Rico, Rimax and Rifor (k-67120, k-67121, k-67250-67256) can serve as effective sources of genes for earliness in common wheat breeding.
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Pendergrass, Angeline G., und Dennis L. Hartmann. „The Atmospheric Energy Constraint on Global-Mean Precipitation Change“. Journal of Climate 27, Nr. 2 (15.01.2014): 757–68. http://dx.doi.org/10.1175/jcli-d-13-00163.1.
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Abstract Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) robustly predict that the rate of increase in global-mean precipitation with global-mean surface temperature increase is much less than the rate of increase of water vapor. The goal of this paper is to explain in detail the mechanisms by which precipitation increase is constrained by radiative cooling. Changes in clear-sky atmospheric radiative cooling resulting from changes in temperature and humidity in global warming simulations are in good agreement with the multimodel, global-mean precipitation increase projected by GCMs (~1.1 W m−2 K−1). In an atmosphere with fixed specific humidity, radiative cooling from the top of the atmosphere (TOA) increases in response to a uniform temperature increase of the surface and atmosphere, while atmospheric cooling by exchange with the surface decreases because the upward emission of longwave radiation from the surface increases more than the downward longwave radiation from the atmosphere. When a fixed relative humidity (RH) assumption is made, however, uniform warming causes a much smaller increase of cooling at the TOA, and the surface contribution reverses to an increase in net cooling rate due to increased downward emission from water vapor. Sensitivity of precipitation changes to lapse rate changes is modest when RH is fixed. Carbon dioxide reduces TOA emission with only weak effects on surface fluxes, and thus suppresses precipitation. The net atmospheric cooling response and thereby the precipitation response to CO2-induced warming at fixed RH are mostly contributed by changes in surface fluxes. The role of clouds is discussed. Intermodel spread in the rate of precipitation increase across the CMIP5 simulations is attributed to differences in the atmospheric cooling.
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Brezina, V., B. Bank, E. C. Cropper, S. Rosen, F. S. Vilim, I. Kupfermann und K. R. Weiss. „Nine members of the myomodulin family of peptide cotransmitters at the B16-ARC neuromuscular junction of Aplysia“. Journal of Neurophysiology 74, Nr. 1 (01.07.1995): 54–72. http://dx.doi.org/10.1152/jn.1995.74.1.54.
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1. Neuromodulation by multiple related peptides with different spectra of physiological effects appears an effective way to integrate complex physiological functions. A good opportunity to examine this issue occurs in the accessory radula closer (ARC) neuromuscular circuit of Aplysia, where, extensive previous work has shown, acetylcholine-induced contractions of the muscle are variously modulated by several families of peptide cotransmitters released under appropriate behavioral circumstances from the muscle's own two motor neurons. 2. In this work we focused on the myomodulins (MMs) released from motor neuron B16. Previous work has characterized MMA (PMSMLRLamide) and MMB (GSYRMMRLamide). We now similarly purified from ARC neuromuscular material and sequenced MMC (GWSMLRLamide), MMD (GLSMLRLamide), MME (GLQMLRLamide), and MMF (SLNMLRLamide). Three additional MMs, MMG (TLSMLRLamide), MMH (GLHMLRLamide), and MMI (SLSMLRLamide), are encoded by a known MM gene. B16 probably synthesizes, and coreleases, all nine MMs. Further MMs have been found in other mollusks. All evidence indicates that the MMs are a major, widely distributed family of molluscan neuropeptides important as neuromuscular modulators and probably also central transmitters or modulators. 3. MM effects on motor neuron B16-elicited ARC muscle contractions were best analyzed as the sum of three distinct actions: potentiation, depression of the amplitude of the contractions, and acceleration of their relaxation rate. We compared the effectiveness of all nine MMs in these respects. We correlated this with their effectiveness in enhancing the L-type Ca current and activating a specific K current in voltage-clamped dissociated ARC muscle fibers, effects we previously proposed to underlie, respectively, the potentiation and the depression of contractions. 4. All nine MMs were similarly effective in enhancing the Ca current and, as far as it was possible to determine, potentiating the amplitude as well as accelerating the relaxation rate of the contractions. 5. In contrast, the MMs' ability to activate the K current and depress the contractions varied greatly. MMB and MMC, in particular, were weak, whereas the other seven MMs were considerably more effective in both respects. 6. Altogether, we were able to explain the potentiating and depressing strengths of the MMs by the magnitude of their modulation of the Ca and K currents, providing further support for our hypothesis that the effects on contraction amplitude are mediated by the effects on the two currents. 7. The net effect on contraction amplitude was determined by the balance between the potentiation and depression. Although most MM concentrations had both potentiating and depressing actions, potentiated contractions predominated at low and depressed contractions (but with accelerated relaxation rate) at high concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)
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Zolotnitskaya, Anna, und Lisa M. Satlin. „Developmental expression of ROMK in rat kidney“. American Journal of Physiology-Renal Physiology 276, Nr. 6 (01.06.1999): F825—F836. http://dx.doi.org/10.1152/ajprenal.1999.276.6.f825.
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The apical secretory K+(SK) channel in the principal cell represents the rate-limiting step for K+ secretion across the cortical collecting duct (CCD). Patch clamp analysis of maturing rabbit principal cells identifies an increase in number of conducting SK channels after the 2nd week of life [L. M. Satlin and L. G. Palmer. Am. J. Physiol. 272 ( Renal Physiol. 41): F397–F404, 1997], ∼1 wk after an increase in activity of the amiloride-sensitive epithelial Na+channel (ENaC) is detected. To correlate the postnatal increase in channel activity with developmental expression of ROMK, the molecular correlate of the SK channel, we used gene-specific probes to show a developmental increase in abundance of renal ROMK mRNA and a ROMK-specific antibody to examine the nephron distribution, localization, and abundance of this protein in developing rat kidney. Using antibodies directed against aquaporin-3 (AQP-3) and Tamm-Horsfall protein (THP), we confirmed that ROMK was expressed along the apical membranes of principal cells and thick ascending limbs of Henle (TALH) in adult kidney. Within the midcortex of the neonatal kidney, ROMK-positive segments revealed weak coincident staining with the TALH-specific antibody but did not colabel with an antibody directed against distal and connecting tubule (CNT)-specific kallikrein or the lectin Dolichos biflorus agglutinin (DBA), which labels proximal tubules and collecting ducts. In inner cortex and outer medulla of kidneys from 1-wk-old animals, ROMK protein was identified in medullary TALH (MTALH) and DBA-positive collecting ducts. By 3 wk of age, coincident ROMK and DBA expression was detected in midcortical and outer cortical CNTs and CCDs. Immunoblot analysis of plasma membrane-enriched fractions of maturing rat kidney revealed a developmental increase in a ∼40-kDa band, the expected size for ROMK. Immunolocalization of α-ENaC showed apical staining of a majority of cells in distal nephron segments after the 1st week of postnatal life. The β- and γ-ENaC subunit expression was routinely detected in a mostly cytoplasmic distribution immediately after birth, albeit in low abundance; γ-ENaC showed some apical polarization. These results suggest that the postnatal increases in a principal cell apical SK and Na+channel activity are mediated, at least in part, by increases in abundance of ROMK message and protein and ENaC subunit proteins.
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Halgamuge, Malka N. „Supervised Machine Learning Algorithms for Bioelectromagnetics: Prediction Models and Feature Selection Techniques Using Data from Weak Radiofrequency Radiation Effect on Human and Animals Cells“. International Journal of Environmental Research and Public Health 17, Nr. 12 (26.06.2020): 4595. http://dx.doi.org/10.3390/ijerph17124595.
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The emergence of new technologies to incorporate and analyze data with high-performance computing has expanded our capability to accurately predict any incident. Supervised Machine learning (ML) can be utilized for a fast and consistent prediction, and to obtain the underlying pattern of the data better. We develop a prediction strategy, for the first time, using supervised ML to observe the possible impact of weak radiofrequency electromagnetic field (RF-EMF) on human and animal cells without performing in-vitro laboratory experiments. We extracted laboratory experimental data from 300 peer-reviewed scientific publications (1990–2015) describing 1127 experimental case studies of human and animal cells response to RF-EMF. We used domain knowledge, Principal Component Analysis (PCA), and the Chi-squared feature selection techniques to select six optimal features for computation and cost-efficiency. We then develop grouping or clustering strategies to allocate these selected features into five different laboratory experiment scenarios. The dataset has been tested with ten different classifiers, and the outputs are estimated using the k-fold cross-validation method. The assessment of a classifier’s prediction performance is critical for assessing its suitability. Hence, a detailed comparison of the percentage of the model accuracy (PCC), Root Mean Squared Error (RMSE), precision, sensitivity (recall), 1 − specificity, Area under the ROC Curve (AUC), and precision-recall (PRC Area) for each classification method were observed. Our findings suggest that the Random Forest algorithm exceeds in all groups in terms of all performance measures and shows AUC = 0.903 where k-fold = 60. A robust correlation was observed in the specific absorption rate (SAR) with frequency and cumulative effect or exposure time with SAR×time (impact of accumulated SAR within the exposure time) of RF-EMF. In contrast, the relationship between frequency and exposure time was not significant. In future, with more experimental data, the sample size can be increased, leading to more accurate work.
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Maragkoudakis, A., C. Boersma, P. Temi, J. D. Bregman und L. J. Allamandola. „Linking Characteristics of the Polycyclic Aromatic Hydrocarbon Population with Galaxy Properties: A Quantitative Approach Using the NASA Ames PAH IR Spectroscopic Database“. Astrophysical Journal 931, Nr. 1 (01.05.2022): 38. http://dx.doi.org/10.3847/1538-4357/ac666f.
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Abstract Utilizing the data and tools provided through the NASA Ames PAH IR Spectroscopic Database (PAHdb), we study the PAH component of over 900 Spitzer-IRS galaxy spectra. Employing a database-fitting approach, the average PAH size, the PAH size distribution, and PAH ionization fraction are deduced. In turn, we examine their connection with the properties of the host galaxy. We found that PAH population within galaxies consists of middle-sized PAHs with an average number of carbon atoms of N C ¯ = 55, and a charge state distribution of ∼40% ionized—60% neutral. We describe a correlation between the 6.2/11.2 μm PAH ratio with the ionization parameter ( γ ≡ ( G 0 / n e ) ( T gas / 1 K ) 0.5 ), a moderate correlation between the 8.6/11.2 μm PAH ratio and specific star formation rate, and a weak anticorrelation between γ and M *. From the PAHdb decomposition, we provide estimates for the 3.3 μm PAH band, not covered by Spitzer observations, and establish a correlation between the 3.3/11.2 μm PAH ratio with N C. We further deliver a library of mid-IR PAH template spectra parameterized on PAH size and ionization fraction, which can be used in galaxy spectral energy distribution fitting codes for the modeling of the mid-IR PAH emission component in galaxies.
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Lhymn, C., und S. V. Pepper. „On the specific wear rate of polymer composites“. Advances in Polymer Technology 9, Nr. 1 (1989): 41–49. http://dx.doi.org/10.1002/adv.1989.060090105.
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Zhang, H., und Wu Yi Chen. „Rapid Selection of Milling Tools Based on the Initial Wear“. Advanced Materials Research 188 (März 2011): 416–22. http://dx.doi.org/10.4028/www.scientific.net/amr.188.416.
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In this paper, tool life, tool wear criteria, initial wear and cutting length at initial wear are picked out from 295 milling tool wear curves to calculate initial wear rate K0, final wear rate K1 and the ratio K between the two. By statistic analysis of K0, K1 and K, a statistical regularity between K0 and K1 is found, which indicates that the faster the initial wear, the shorter the tool life would be. Based on the statistical regularity, a milling tool rapid selection method is proposed, and an experiment on selecting the best tools for machining TC4 is carried out to verify the method. The results show that the method can reduce the consumption of material and time significantly, which confirm the efficiency of the method.
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Kailas, Satish V., und S. K. Biswas. „Sliding Wear of Copper Against Alumina“. Journal of Tribology 121, Nr. 4 (01.10.1999): 795–801. http://dx.doi.org/10.1115/1.2834137.
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OFHC copper pins with 10 ppm oxygen were slid against alumina at a load of 50 N and sliding speeds of 0.1 ms−1 to 4.0 ms−1. The wear characteristics of copper were related to the strain rate response of copper under uniaxial compression between strain rates of 0.1 s−1 and 100 s−1 and temperatures in the range of 298 K to 673 K. It is seen that copper undergoes flow banding at strain rates of 1 s−1 up to a temperature of 523 K, which is the major instability in the region tested. These flow bands are regions of crack nucleation. The strain rates and temperatures existing in the subsurface of copper slid against alumina are estimated and superimposed on the strain rate response map of copper. The superposition shows that the subsurface of copper slid at low velocities is likely to exhibit flow band instability induced cracking. It is suggested that this is the reason for the observed high wear rate at low velocities. The subsurface deformation with increasing velocity becomes more homogeneous. This reduces the wear rate. At velocities >2 ms−1 there is homogeneous flow and extrusion of thin (10 μm) bands of material out of the trailing edge. This results in the gradual increase of wear rate with increasing velocity above 2.0 ms−1.
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Mueller, Barbara. „Results of the First Improvement Step Regarding Removal Efficiency of Kanchan Arsenic Filters in the Lowlands of Nepal—A Case Study“. Water 13, Nr. 13 (26.06.2021): 1765. http://dx.doi.org/10.3390/w13131765.
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In Nepal as well as in other countries in Southeast Asia, the World Health Organization drinking water guideline of 10 µg/L concerning arsenic concentrations in ground water hosted in Quaternary alluvial sediments is often regionally exceeded. The commonly accepted theories include that arsenic in ground water stems from reductive dissolution of As-rich Fe(III)hydr(oxides) including microbial degradation of sedimentary organic matter. On the contrary, the influence of clay minerals in the sediments as hosts for As was clearly underestimated, as geochemical analysis depicted that As was generally associated with specific elements such as Na, K, Al, and Li. Moreover, there was a very weak correlation or decoupling between As and Fe in the ground water in Nepal, and this fact points to consequences for water treatment. The so-called Kanchan filters, used for the removal of As, installed in the lowlands of Nepal often exhibited effluent As concentrations well above Nepal’s drinking water quality standard value (i.e., 50 μg/L). Ground water concentrations of Fe and As proved to be the most important geochemical factors regarding the performance of the filters. Moreover, the flow rate as well as the contact time to the rusty nails in the filter, intended to adsorb As on their surface, influenced the removal efficiency. The removal rate was severely influenced by the handling of the filters, too. This short communication provides an overview of the removal efficiency of 30 filters, their drawbacks, the influence of the aging material in the filters as well as measures of improvements to enhance the efficiency of the filters. Proper instruction for users of Kanchan filters is a major point that needs to be addressed in the future.
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Mohammed, Abdul Jawad, Anwaruddin Siddiqui Mohammed und Abdul Samad Mohammed. „Prediction of Tribological Properties of UHMWPE/SiC Polymer Composites Using Machine Learning Techniques“. Polymers 15, Nr. 20 (11.10.2023): 4057. http://dx.doi.org/10.3390/polym15204057.
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Polymer composites are a class of material that are gaining a lot of attention in demanding tribological applications due to the ability of manipulating their performance by changing various factors, such as processing parameters, types of fillers, and operational parameters. Hence, a number of samples under different conditions need to be repeatedly produced and tested in order to satisfy the requirements of an application. However, with the advent of a new field of triboinformatics, which is a scientific discipline involving computer technology to collect, store, analyze, and evaluate tribological properties, we presently have access to a variety of high-end tools, such as various machine learning (ML) techniques, which can significantly aid in efficiently gauging the polymer’s characteristics without the need to invest time and money in a physical experimentation. The development of an accurate model specifically for predicting the properties of the composite would not only cheapen the process of product testing, but also bolster the production rates of a very strong polymer combination. Hence, in the current study, the performance of five different machine learning (ML) techniques is evaluated for accurately predicting the tribological properties of ultrahigh molecular-weight polyethylene (UHMWPE) polymer composites reinforced with silicon carbide (SiC) nanoparticles. Three input parameters, namely, the applied pressure, holding time, and the concentration of SiCs, are considered with the specific wear rate (SWR) and coefficient of friction (COF) as the two output parameters. The five techniques used are support vector machines (SVMs), decision trees (DTs), random forests (RFs), k-nearest neighbors (KNNs), and artificial neural networks (ANNs). Three evaluation statistical metrics, namely, the coefficient of determination (R2-value), mean absolute error (MAE), and root mean square error (RMSE), are used to evaluate and compare the performances of the different ML techniques. Based upon the experimental dataset, the SVM technique was observed to yield the lowest error rates—with the RMSE being 2.09 × 10−4 and MAE being 2 × 10−4 for COF and for SWR, an RMSE of 2 × 10−4 and MAE of 1.6 × 10−4 were obtained—and highest R2-values of 0.9999 for COF and 0.9998 for SWR. The observed performance metrics shows the SVM as the most reliable technique in predicting the tribological properties—with an accuracy of 99.99% for COF and 99.98% for SWR—of the polymer composites.
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Parthasarathi, N. L., Utpal Borah und Shaju K. Albert. „Influence of Interfacial Oxides Formed During Dry Sliding Wear of NiCrBSiCFe Plasma Coating on AISI 316 Steel Substrates“. High Temperature Materials and Processes 33, Nr. 1 (01.02.2014): 27–39. http://dx.doi.org/10.1515/htmp-2013-0017.
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AbstractRecent thermal spray processes such as plasma spraying are usually employed to deposit Nickel–Chromium coatings onto the AISI 316 steel substrates to improve the wear resistance. Ni-base alloys, which are widely used to obtain wear resistant coatings, are usually heat treated after thermal spraying to improve their tribological properties. The dry sling wear experiments were carried out in pin on disc tribometer at room temperature 35 °C (308 K), 150 °C (423 K), 250 °C (523 K) and 350 °C (623 K) against medium carbon steel (EN8). The worn surfaces were examined by X-ray diffraction and SEM (Scanning Electron Microscopy) with EDS (Energy dispersive spectroscopy). The applied load was 40 N and sliding speed was 2 m/s. In 350 °C, the wear rate was marginally lesser than the rest of the temperatures due to the initiation of oxide layer formation, which was also substantiated by SEM and EDS. Fe peaks and O peaks were found scarcely. Few Fe peaks were also predominantly noticed by EDS analysis. The presence of Fe3O4 in the tribolayers formed during sliding wear acted as a protective film to retard the wear rate in terms of mass loss.
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Zhang, Jianyou, Guangcheng Zhou, Lifeng Fei, Lifan Chen, Lei Sun, Fei Lyu und Yuting Ding. „Study on Purification and Characterization of Polyphenol Oxidase from Acetes chinensis“. Molecules 26, Nr. 24 (13.12.2021): 7545. http://dx.doi.org/10.3390/molecules26247545.
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Acetes chinensis (belonging to the Decapoda Sergestidae genus) is widely distributed in East Asian waters and is extremely widespread and present in the shallow coastal areas of China. Polyphenol oxidase (PPO), which was extracted from Acetes chinensis, was purified in a four-step procedure involving phosphate-buffered saline treatment, ammonium sulphate precipitation, DEAE-Cellulose chromatography, and Phenyl-Sepharose HP chromatography, and then, its biochemical characterization was measured. The specific activity of the purified enzyme was increased to 643.4 U/mg, which is a 30.35 times increase in purification, and the recovery rate was 17.9%. L-dopa was used as the substrate, the enzymatic reactions catalyzed by PPO conformed to the Michaelis equation, the maximum reaction velocity was 769.23 U/mL, and the Michaelis constant Km was 0.846 mmol/L. The optimal pH of PPO from Acetes chinensis was 7.5, and the optimal temperature was 35 °C. The metal ions experiment showed that Mn2+ and K+ could enhance the activity of PPO; that Ba2+ and Ca2+ could inhibit the activity of PPO; and that Cu2+ had a double effect on PPO, increasing the PPO activity at low concentrations and inhibiting the PPO activity at high concentrations. The inhibitor experiment showed that the inhibitory effects of EDTA and kojic acid were weak and that ascorbic acid and sodium pyrophosphate had good inhibitory effects. The purification and characterization of Acetes chinensis serve as guidelines for the prediction of enzyme behavior, leading to effective prevention of enzymatic browning during processing.
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Lhymn, C. „Statistical Analysis of Wear Rate Data“. Journal of Tribology 109, Nr. 4 (01.10.1987): 594–97. http://dx.doi.org/10.1115/1.3261514.
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The wear rate data of glass fiber reinforced polyethylene terephthalate (PET) has been analyzed statistically using the wear lifetime model together with the two-parameter Weibull distribution function. The specific wear rate versus normal load curve has been given a theoretical explanation, the empirical model being derived from the concepts of crack propagation and delamination physics.
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Adebayo, B., und W. A. Bello. „Property Analysis for Correlation of Specific Energy with Penetration Rate and Bit Wear Rate“. Advanced Materials Research 367 (Oktober 2011): 547–53. http://dx.doi.org/10.4028/www.scientific.net/amr.367.547.
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This study evaluates rock properties for correlation of specific energy with penetration rate and bit wear rate. In order to achieve these objectives five rock samples were obtained from the study area. These samples were tested in the laboratory for uniaxial compressive strength and tensile strength using 1100kN compression machine and point load tester respectively. Also, the mineral composition of the samples was determined by thin section examination. Bit deterioration was measured with digital vernier calliper at regular intervals. The specific energy was determined from field data using empirical equations. The results of the uniaxial compressive strength of the five rock samples varied from 165-320 MPa and were classified as having very high compressive strength characteristics. The point load strength index of the samples had values ranging from 5.50 – 10.67 MPa representing the tensile strength. The result of the statistical correlation matrix revealed that penetration rate and bit wear rate are dominant factors affecting the prediction of specific energy having high coefficient of correlation. The regression model had multiple coefficient of correlation of R2 = 0.893 which means that 89.3% of variation in specific energy could be attributed to variation in penetration rate and bit wear rate. Ultimately, computer programme DRILLING PROFESSIONAL 2009 was developed to compute penetration rate, wear rate and specific energy when necessary inputs are supplied. This gives quarry operators advance information on time of drilling and bit consumption.
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Trenholm, L. E., R. N. Carrow und R. R. Duncan. „Wear Tolerance, Growth, and Quality of Seashore Paspalum in Response to Nitrogen and Potassium“. HortScience 36, Nr. 4 (Juli 2001): 780–83. http://dx.doi.org/10.21273/hortsci.36.4.780.
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Damage from traffic can seriously injure athletic field turfgrass, although fertility regimes can influence wear tolerance. While excess nitrogen (N) can reduce wear tolerance, moderate N has improved tolerance and hastened recovery from injury. Potassium (K) may enhance wear tolerance through regulation of turgor potential. This research was undertaken to determine shoot growth and wear tolerance of seashore paspalum (Paspalum vaginatum Swartz) to N and K application. Field studies were conducted in 1998 at the Univ. of Georgia Experiment Station, Griffin. Grasses were established on U.S. Golf Association specification greens in 1996. Fertility treatments were applied at annual N rates of 196 and 392 kg·ha-1 and K rates of 92 and 392 kg·ha-1. The higher N rate increased wear tolerance, shoot growth, shoot density, visual quality, and color of the two ecotypes, AP 10 and AP 14, but reduced their visible range spectral reflectance, indicating greater absorption of photosynthetically active radiation (PAR). Measured responses to K were minimal and no enhancement of wear tolerance in response to K treatment was noted.
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Baker, S. N., R. Spinks, A. Jackson und R. N. Lemon. „Synchronization in Monkey Motor Cortex During a Precision Grip Task. I. Task-Dependent Modulation in Single-Unit Synchrony“. Journal of Neurophysiology 85, Nr. 2 (01.02.2001): 869–85. http://dx.doi.org/10.1152/jn.2001.85.2.869.
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Neural synchronization in the cortex, and its potential role in information coding, has attracted much recent attention. In this study, we have recorded long spike trains (mean, 33,000 spikes) simultaneously from multiple single neurons in the primary motor cortex (M1) of two conscious macaque monkeys performing a precision grip task. The task required the monkey to use its index finger and thumb to move two spring-loaded levers into a target, hold them there for 1 s, and release for a food reward. Synchrony was analyzed using a time-resolved cross-correlation method, normalized using an estimate of the instantaneous firing rate of the cell. This was shown to be more reliable than methods using trial-averaged firing rate. A total of 375 neurons was recorded from the M1 hand area; 235 were identified as pyramidal tract neurons. Synchrony was weak [mean k′ = 1.05 ± 0.04 (SD)] but widespread among pairs of M1 neurons (218/1359 pairs with above-chance synchrony), including output neurons. Synchrony usually took the form of a broad central peak [average width, 18.7 ± 8.7 (SD) ms]. There were marked changes during different phases of the task. As a population, synchrony was greatest during the steady hold period in striking contrast to the averaged cell firing rate, which was maximal when the animal was moving the levers into target. However, the modulation of synchrony during task performance showed considerable variation across individual cell pairs. Two types of synchrony were identified: oscillatory (with periodic side lobes in the cross-correlation) and nonoscillatory. Their relative contributions were quantified by filtering the cross-correlations to exclude either frequencies from 18 to 37 Hz or all higher and lower frequencies. At the peak of population synchrony during the hold period, about half (51.7% in one monkey, 56.2% in the other) of the synchronization was within this oscillatory bandwidth. This study provides strong support for assemblies of neurons being synchronized during specific phases of a complex task with potentially important consequences for both information processing within M1 and for the impact of M1 commands on target motoneurons.
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Kolev, Mihail, Ludmil Drenchev und Veselin Petkov. „Wear Analysis of an Advanced Al–Al2O3 Composite Infiltrated with a Tin-Based Alloy“. Metals 11, Nr. 11 (24.10.2021): 1692. http://dx.doi.org/10.3390/met11111692.
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In this study, a hybrid material is produced, and the effect of different loads varying from 40 to 60 N against an EN-31 steel counter disk on its wear behavior under dry sliding conditions at room temperature is studied. The tribological behavior is studied via the pin-on-disk method and analyzed using primary wear parameters, such as the coefficient of friction (COF), mass wear, and specific wear rate. The obtained results are compared with the results for B83 babbitt under the same wear test conditions. Microstructural observation with scanning electron microscopy (SEM) is performed along with X-ray energy dispersive spectroscopy (EDX) for chemical analysis conduction. The results from the wear experiments indicate that the hybrid material possesses a lower COF, mass wear, and specific wear rate as well as a higher wear resistance in comparison to the B83 babbitt specimen when subjected to the same test conditions. The results from the wear experiments indicate that by applying different loads of 40, 50, and 60 N, the hybrid material possesses a lower mass wear, specific wear rate, and COF specifically at a load of 40 N in comparison to the B83 babbitt specimen under the same test conditions. It was also observed that by increasing the load under dry sliding friction, the hybrid material increases its mass wear and specific wear rate.
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van de Wal, R. S. W., W. Greuell, M. R. van den Broeke, C. H. Reijmer und J. Oerlemans. „Surface mass-balance observations and automatic weather station data along a transect near Kangerlussuaq, West Greenland“. Annals of Glaciology 42 (2005): 311–16. http://dx.doi.org/10.3189/172756405781812529.
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AbstractSurface mass-balance data from the Kangerlussuaq transect (K-transect) located on the western part of the Greenland ice sheet near 67° N are presented. The series covers the period 1990-2003 and is the longest series of surface mass-balance measurements in Greenland. The surface mass-balance measurements cover an altitude range of 390-1850 m and show a linear increase of the specific mass balance, with a mass-balance gradient of 3.7 × 10–3 m m–1 and a mean equilibrium-line altitude of 1535 ma.s.l. Interannual variability shows a weak 4 yearly periodicity. In addition to the surface mass-balance data, automatic weather station data at an elevation of approximately 1010m are available for the period 1997-2002. These data are used to explain observed surface mass-balance anomalies over the same 5 years. It is shown that variations in shortwave radiation dominate interannual variability. The mean annual cycle of temperature is characterized by a maximum in summer around the melting point, leading to a mean summer outgoing longwave radiation of approximately 314 W–2. The mean annual cycle in wind speed shows a maximum in winter (on average around 8 m s–1) and a minimum in summer (on average around around 5 m s–1), which is characteristic for a katabatic forcing. During summer the net radiation is on average about 61 Wm–2, which is used for ice melting at a rate of typically 2 cm w.e.d-1. Net radiation contributes 84% of the total energy used for summer melting averaged over the 5 years.
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Dixit, Tulika, und K. Eswar Prasad. „Effect of Temperature and Sliding Velocity on the Dry Sliding Wear Mechanisms of Boron Modified Ti-6Al-4V Alloys“. Lubricants 10, Nr. 11 (04.11.2022): 296. http://dx.doi.org/10.3390/lubricants10110296.
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The dry sliding wear behavior of as-cast pristine and boron-modified Ti-6Al-4V (Ti64) alloys (having 0.3 and 0.55 wt% B) is investigated using pin-on-disc experiments with the pin being Ti64 alloy and the EN31 steel disc. Experiments are performed at sliding speeds (s) of 1, 2, and 4 m/s and temperatures 300 and 573 K. A mixed response in wear behavior is observed. At the lowest sliding speed, all three alloys (except 0.55B alloy at 300 K) exhibit similar wear rates, with abrasive wear being the dominant wear mechanism. At 2 m/s, temperature and s increase, and adhesive wear takes over along with delamination wear. Here, the 0.55B sample shows the highest wear rate due to the debonding of more TiB particles, which increases three body abrasion wear. With further increase in s to 4 m/s, delamination and oxidation wear are observed for all the samples. XRD evaluation shows traces of TiO2 and Fe2O3, which imply the formation of MML in samples tested at s = 4 m/s, which is also validated through subsurface microstructure analysis. It is found that MML having more TiB particles has more stability, because of which 0.3B samples show higher wear rate.
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Chinchanikar, Satish, Amol Barade und Abhijeet Deshpande. „Sliding Wear Characteristics of Carbon Filled Polytetrafluoroethylene (PTFE) Composite against AISI 304 Stainless Steel Counterface“. Materials Science Forum 1034 (15.06.2021): 51–60. http://dx.doi.org/10.4028/www.scientific.net/msf.1034.51.
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In the present work, dry sliding wear characteristics of polytetrafluoroethylene (PTFE) composite reinforced with 35% by weight carbon fiber against AISI 304 stainless steel counterface is investigated with a view to consider PTFE composite as an alternative material for automotive applications. Dry sliding experiments were performed on pin-on-disk wear testing machine varying the normal load on pin, disk rotation (rpm) and temperature correlating with the range of pressure, sliding velocity and temperature variation at reciprocating conditions of compressor. A mathematical model to predict specific wear rate in terms of pressure and temperature was developed to understand parametric effect on wear rate. Specific wear rate has been observed to decrease with increase in pressure and temperature. Although, pressure (normal load) has been observed as more significant in lowering specific wear rate than temperature, no significant benefit was observed at higher ranges of pressure. Decrease in specific wear rate with increase in normal load (pressure) can be attributed to formation of transfer film at sliding interfaces. However, it is necessary to characterize transition of formation of transfer film varying with normal load and temperature respectively.
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Sheshegova, Т. К., und I. N. Shchennikova. „SOURCES OF BARLEY RESISTANCE TO HELMINTHOSPORIOTIC DISEASES AND THEIR USE IN THE NORTH-EAST FARC“. Bulletin of NSAU (Novosibirsk State Agrarian University), Nr. 2 (15.07.2020): 76–83. http://dx.doi.org/10.31677/2072-6724-2020-55-2-76-83.
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The paper explores 70 samples of spring barley from the collection of WIR under conditions of rather rigid natural infectious helminthosporioses (striped, reticulated and dark brown spotting) in FARC of the North-East in 2018-2019. The spotting was investigated 4-5 times during plants ontogenesis every 10-12 days since the phase 29 on the Cadox scale. The methodology suggested by O.S. Afanasenko (2005) was used to assess the diseases. The nature of vegetative-microbial interactions was evaluated by SCDP (square under the curve of disease progress) and IS (stability index) indicators. During immunological experiment, the authors observed 11 samples resistant to dark brown spotting with lesion rate 10.0-13.0%, SCDP parameters equal 167-223, DUT was 0.18-0.25; 18 samples resistant to reticular spotting (6.0-10.0%, PCRB - 53-103, DUT - 0.18-0.35), and 29 samples characterized by immunity and high resistance to stripe spotting (0-5.0%, SCDP - 10-75). IS - 0.01-0.09). Only 4 samples (Makbo, Kalkul, Buyan and Forward) are characterized by group non-specific resistance to reticulate and dark brown spotting and striate immunity. The longest occurrence period (2-7 days) of dark brown spotting was observed in 8 samples, and reticulum spotting (2-13 days) - in 16 samples. The paper finds out that NCL 95098 (Argentina) had the relatively long occurrence period in terms of dark brown spotting, and varieties from Afghanistan (k-5983) and China (k-2929) to reticulate spotting. Badiory, Makbo, Rodos, and Buyan varieties have equal dynamics of both spotting and slow rusting of diseases in ontogenesis. There is a weak (r = -0.33 - reticulate) and medium (r = -0.58 - dark brown) negative correlation between the latent period and the defeat. The regression equations (y = -0,6071x+6,8571; R2 = 0,917 - dark brown; y = -0,3941x+11,35; R2 = 0,733 - reticulated) show that from infection to the first disease symptoms, their daily increase in trend is 0,61 and 0,39%. Kalkul, NCL 95098, Badioryi and Buyan varieties are seen as effective promising for selection programs to produce high yield adaptive varieties under the conditions of the region. Apart from stability, they are distinguished by the number of productive stems, long, well-grained ears and high productivity.
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Datta, Ananya, Erin S. Tomiyama und Kathryn Richdale. „MICROBIAL BIOBURDEN OF ORTHOKERATOLOGY AND HYDROGEL CONTACT LENSES AND STORAGE CASES USING A HYDROGEN-PEROXIDE DISINFECTING SYSTEM“. Journal of Contact lens Research and Science 5, Nr. 1 (26.10.2021): e19-e31. http://dx.doi.org/10.22374/jclrs.v5i1.43.
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Background and objective: The fitting of orthokeratology (ortho-k) and multifocal soft contact lenses (SCL) is becoming increasingly popular worldwide for reducing the rate of myopia progression. However, overnight wear use of lenses and microbial contamination of contact lenses and storage vials has been shown to increase the risk of corneal inflammatory and infiltrative events (CIEs). Therefore, we conducted a pilot study to compare the rate, level, and type of microbial contamination of contact lenses and storage vialswhen participants wear ortho-k and SCL in combination with a hydrogen-peroxide disinfecting system.
Material and Methods: A prospective, single-centre, randomized, crossover study was conducted to evalu-ate the rate and level of contact lens and storage vials contamination during the use of ortho-k and SCL along with a hydrogen-peroxide disinfecting solution over two 10 day wearing periods. Ocular signs and symptoms were assessed during lens wear at baseline and after each wearing period. In addition, contact lens and storage vials were collected, and the type and amount of microbial contamination were evaluated using viable culture and standard identification methods.Results: Twenty-five adults were enrolled, and 21 completed the study. One (5%) ortho-k lens, five (24%) ortho-k storage vials, one (5%) SCL and one (5%) SCL storage vial were contaminated (P > 0.05), predominantly with Gram-positive bacteria. None of the participants had contamination with both ortho-k and SCL. No significant differences were found between the ocular signs, including conjunctival redness and roughness, or conjunctival or corneal staining (all P > 0.05), irrespective of using ortho-k or SCL.
Conclusion: This study provides the first data that directly compares microbial contamination of ortho-K versus SCL in patients using a hydrogen-peroxide disinfection system. However, the overall microbial contamination rate of contact lens storage vials was much lower (30%) than the previously reported study with ortho-k lens wear. The results support conducting a larger clinical trial designed to understand differences in microbial contamination with different lens materials and modalities.
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Stojanovic, Blaza, Jasmina Blagojevic, Miroslav Babic, Sandra Velickovic und Slavica Miladinovic. „Optimization of hybrid aluminum composites wear using Taguchi method and artificial neural network“. Industrial Lubrication and Tribology 69, Nr. 6 (13.11.2017): 1005–15. http://dx.doi.org/10.1108/ilt-02-2017-0043.
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Purpose This research aims to describe the influence of weight per cent of graphite (Gr), applied load and sliding speed on the wear behavior of aluminum (Al) alloy A356 reinforced with silicon carbide (SiC) (10 Wt.%) and Gr (1 Wt.% and 5 Wt.%) particles. The objective is to analyze the effect of the aforementioned parameters on a specific wear rate. Design/methodology/approach These hybrid composites are obtained by means of the compo-casting process. Tribological analyses were conducted on block-on-disc tribometer at three different loads (10, 20 and 30 N) and three different sliding speeds (0.25, 0.5 and 1 m/s), at the sliding distance of 900 m, in dry sliding wear conditions. Optimization of the tribological behavior was conducted via the Taguchi method, and ANOVA was used for the analysis of the specific wear rate. Confirmation tests are used to foresee and check the experimental results. Examined samples were analyzed via a scanning electron microscope (SEM). Regression models for predicting specific wear rate were developed with Taguchi and ANN (artificial neural network) methods. Findings The biggest impact on value of specific wear rate has the load (43.006%), while the impact of Wt.% Gr (31.514%) was less. After comparison of the results, i.e. regression models, for predicting the specific wear rate, it was observed that ANN was more efficient than the Taguchi method. The specific wear rate of Al alloy A356 with SiC (10 Wt.%) and Gr (1 Wt.% and 5 Wt.%) decreases with a decrease in the load and weight per cent of Gr-reinforcing material, as well as with a decrease in sliding speed. Originality/value The results obtained in this paper using the Taguchi method and the ANN method are useful for improving and further investigating the wear behavior of the SiC- and Gr-reinforced Al alloy A356.
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Johnsy, Arputhavalli, S. Agilan, S. Jebasingh und Joseph Vijay. „Effect of sintering temperature on the mechanical properties of vacuum sintered Co-(Zn)-Ni-Al alloys“. Science of Sintering 52, Nr. 3 (2020): 329–38. http://dx.doi.org/10.2298/sos2003327j.
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In the present study, the wear resistance behavior and the microhardness of the Co38Ni35Al27 and Co35Zn10Ni32Al23 ferromagnetic shape memory alloys (FSMAs) were investigated. The alloy samples were prepared by powder metallurgy method along with the vacuum sintering technique. The major aim is to prepare an alloy with high wear resistance having remarkable microhardness suitable for the sustainable shape memory alloy. The wear test report shows that the wear resistance is high for the sample sintered at 673 K and it gradually reduces when the sintering temperature decreases. The result also shows that the inclusion of zinc in the alloy increases the wear rate. The maximum hardness value of 126 HV was observed in Co38Ni35Al27 sample sintered at 673 K for 8 hrs because of its minimal porosity.
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Wang, Yanjiang, Sixiang Zhao, Zhi Jia, Jinjin Ji, Dexue Liu, Tingbiao Guo und Yutian Ding. „Study on Friction and Wear Behavior of Inconel 625 Superalloy during Hot Extrusion“. Advances in Materials Science and Engineering 2020 (27.02.2020): 1–11. http://dx.doi.org/10.1155/2020/5453703.
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Friction during the hot extrusion of Inconel 625 superalloy tubes causes severe wear of the mold and plays a decisive role in the quality of the workpieces. In this paper, a ball-to-disk method was utilized to investigate the tribological behavior of Inconel 625 using two different tribological pairs, i.e., GCr15 and Si3N4, at room and elevated temperatures. Friction coefficient, specific wear rate, and morphology of worn surfaces were systematically characterized. It was found that the friction coefficients for both tribological pairs generally increased as the testing temperature increased, while the specific wear rate increased firstly and then decreased with the rise of temperature. Along with the increasing sliding speed, the friction coefficient between Inconel 625 and Si3N4 decreased monotonically, while the specific wear rate increased firstly and then decreased. Under any given testing condition, the friction coefficient and specific wear rate of the Inconel 625 for Inconel/Si3N4 pair are less than those of the Inconel/GCr15 pair. The main wear mechanisms between GCr15 and Inconel 625 are adhesive and fatigue wear at all testing temperatures. The wear mechanisms between Si3N4 and Inconel 625 are adhesive and abrasive wear at room temperature but fatigue wear at 500°C. Our findings indicate that the use of ceramic molds in the hot extrusion of Inconel 625 may significantly improve the surface qualities of the product and reduce the wear of the mold.
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Vakharia, V., S. Pandya und P. Patel. „Tool wear rate prediction using discrete wavelet transform and K-Star algorithm“. Life Cycle Reliability and Safety Engineering 7, Nr. 3 (17.07.2018): 115–25. http://dx.doi.org/10.1007/s41872-018-0057-5.
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Kim, Yeon Wook, Jae Hoon Kim, Bo Hwi Seo, Hoon Seok Choi, Sung Han Park und Hwan Kyu Lee. „Mathematical Model to Evaluate Wear Rate of Graphite as Sealing Materials“. Advanced Materials Research 871 (Dezember 2013): 200–205. http://dx.doi.org/10.4028/www.scientific.net/amr.871.200.
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The dry sliding wear behavior of graphite (HK-6) that is used as the sealing material to cut off hot gas was evaluated as a function of applied load, sliding speed and temperature. The reciprocating wear tests were carried out at room temperature and elevated temperatures. An attempt has been made to develop a mathematical model by response surface methodology (RSM) and an analysis of variance (ANOVA) technique was applied to confirm the validity of the developed model. Also, the effect of applied load, sliding speed and temperature on wear the behavior of graphite was investigated. The wear mechanism was compared through the observation of the worn surface by SEM analysis. The specific wear rate was dependent on the interaction between temperature, applied load and sliding speed. A developed model can be used to effectively predict the specific wear rate of graphite as a sealing material within the range of variables studied.
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Murakami, Takashi, und Kunio Matsuzaki. „Friction and Wear Properties of Fe7Mo6-Based Alloy under Various Sliding Conditions“. Materials Science Forum 706-709 (Januar 2012): 1083–88. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1083.
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In this study, the friction and wear properties of the Fe7Mo6-based alloy/Al2O3 tribopair were investigated at high temperatures in air and at 298 K in water. The Fe7Mo6-based alloy/Al2O3 tribopair exhibited friction coefficients as low as 0.5 at 298 K and 873 K in air. On the other hand, this tribopair exhibited higher friction coefficients at 573 K than at 298 K and 873 K. It was also found that the friction coefficients of this tribopair were approximately 0.5 in water. The Fe7Mo6-based alloy disk specimens and their paired Al2O3 ball specimens exhibited the highest specific wear rates at 873 K in air. Oxygen-rich phase was observed on the worn surfaces of all the disk specimens. Concerning the friction and wear tests at high temperatures in air, the amount of the oxygen-rich phase increased with increasing the testing temperature. In addition, a little larger amount of the oxygen-rich phase was observed on the worn surface formed at 298 K in water than that formed at 298 K in air.
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Sharath, B. N., K. S. Madhu und C. V. Venkatesh. „Experimental Study on Dry Sliding Wear Behaviour of Al-B4C-Gr Metal Matrix Composite at Different Temperatures“. Applied Mechanics and Materials 895 (November 2019): 96–101. http://dx.doi.org/10.4028/www.scientific.net/amm.895.96.
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In the present scenario aluminium is an useful metal due its admirable properties such as light weight, low cost and excellent thermal conductivity.In order to take advantages of these properties aluminium is being used to make the metal matrix composites for tribological application, In this present investigation effort has been made to assess the wear properties of Al–B4C–Gr metal matrix composite at various temperatures such as 323° K, 373° K and 423° K. Al–B4C–Gr Hybrid metal matrix composites were fabricated by stir casting technique. The influence of parameters like load, speed, distance and temperature on the wear rate was investigated. A plan of experiments, based on Taguchi model with L27 orthogonal array and analysis of variance was employed to investigate the influence of process parameters on the wear behaviour of these hybrid metal matrix composites. The wear resistance increased with increasing temperature, but wear resistance decreased at higher loads. It was observed that the abrasive wear is dominates while sliding as observed by SEM analysis of worn out specimens.
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Arhaim, Y. H., A. Shalwan und B. F. Yousif. „Correlation between Frictional Force, Interface Temperature and Specific Wear Rate of Fibre Polymer Composites“. Advanced Materials Research 685 (April 2013): 45–49. http://dx.doi.org/10.4028/www.scientific.net/amr.685.45.
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Friction is classified as the main dominant element having an adverse influence on materials' lifespan and performance. Friction between any sliding contacts is continually accompanied by heat generation and shear force. The surface deterioration produces destruction in the component and reduced the life expectancy of the components. The shear force and/or the frictional heat areseen to be the main reasonscausing occurrence of the wear on surfaces and the wear removal during adhesion wear loading. In the current paper, a comprehensive experiments and observation were made to correlate the three main elements of tribology (friction, temperature, and weight loss) to epoxy and its composites based on glass and kenaf fibres. The tests were conducted in adhesive wear loading conditions against stainless steel counterface under dry contact conditions. SEM was performed to categorize the damage features of both composites. The results revealed that the interface temperature has more influence on the wear behaviour of both composites than the friction coefficient. Different destructive features were observed.
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St. Maurice, Martin, Nunilo Cremades, Matthew A. Croxen, Gary Sisson, Javier Sancho und Paul S. Hoffman. „Flavodoxin:Quinone Reductase (FqrB): a Redox Partner of Pyruvate:Ferredoxin Oxidoreductase That Reversibly Couples Pyruvate Oxidation to NADPH Production in Helicobacter pylori and Campylobacter jejuni“. Journal of Bacteriology 189, Nr. 13 (27.04.2007): 4764–73. http://dx.doi.org/10.1128/jb.00287-07.
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ABSTRACT Pyruvate-dependent reduction of NADP has been demonstrated in cell extracts of the human gastric pathogen Helicobacter pylori. However, NADP is not a substrate of purified pyruvate:ferredoxin oxidoreductase (PFOR), suggesting that other redox active enzymes mediate this reaction. Here we show that fqrB (HP1164), which is essential and highly conserved among the epsilonproteobacteria, exhibits NADPH oxidoreductase activity. FqrB was purified by nickel interaction chromatography following overexpression in Escherichia coli. The protein contained flavin adenine dinucleotide and exhibited NADPH quinone reductase activity with menadione or benzoquinone and weak activity with cytochrome c, molecular oxygen, and 5,5′-dithio-bis-2-nitrobenzoic acid (DTNB). FqrB exhibited a ping-pong catalytic mechanism, a k cat of 122 s−1, and an apparent Km of 14 μM for menadione and 26 μM for NADPH. FqrB also reduced flavodoxin (FldA), the electron carrier of PFOR. In coupled enzyme assays with purified PFOR and FldA, FqrB reduced NADP in a pyruvate- and reduced coenzyme A (CoA)-dependent manner. Moreover, in the presence of NADPH, CO2, and acetyl-CoA, the PFOR:FldA:FqrB complex generated pyruvate via CO2 fixation. PFOR was the rate-limiting enzyme in the complex, and nitazoxanide, a specific inhibitor of PFOR of H. pylori and Campylobacter jejuni, also inhibited NADP reduction in cell-free lysates. These capnophilic (CO2-requiring) organisms contain gaps in pathways of central metabolism that would benefit substantially from pyruvate formation via CO2 fixation. Thus, FqrB provides a novel function in pyruvate metabolism and, together with production of superoxide anions via quinone reduction under high oxygen tensions, contributes to the unique microaerobic lifestyle that defines the epsilonproteobacterial group.