Structure evolution in tribological interfaces studied by multilayer model alloys

Recent studies of deformation mechanisms of metals and alloys pioneer the better investigation of the friction and wear behavior of materials with well-defined initial microstructures. Within this scope, in this work, the effect of sub-surface deformations on the resulting friction and wear behavior has been searched by means of a systematic experimental study on Au-Ni metallic multilayer model alloy system

Structure evolution in tribological interfaces studied by multilayer model alloys

Recent studies of deformation mechanisms of metals and alloys pioneer the better investigation of the friction and wear behavior of materials with well-defined initial microstructures. Within this scope, in this work, the effect of sub-surface deformations on the resulting friction and wear behavior has been searched by means of a systematic experimental study on Au-Ni metallic multilayer model alloy system

Structural lubricity under ambient conditions.

Despite its fundamental importance, physical mechanisms that govern friction are poorly understood. While a state of ultra-low friction, termed structural lubricity, is expected for any clean, atomically flat interface consisting of two different materials with incommensurate structures, some associated predictions could only be quantitatively confirmed under ultra-high vacuum (UHV) conditions so far. Here, we report structurally lubric sliding under ambient conditions at mesoscopic (∼4,000-130,000 nm(2)) interfaces formed by gold islands on graphite. Ab initio calculations reveal that the gold-graphite interface is expected to remain largely free from contaminant molecules, leading to structurally lubric sliding. The experiments reported here demonstrate the potential for practical lubrication schemes for micro- and nano-electromechanical systems, which would mainly rely on an atomic-scale structural mismatch between the slider and substrate components, via the utilization of material systems featuring clean, atomically flat interfaces under ambient conditions

Structure evolution in tribological interfaces studied by multilayer model alloys

Das Verständnis von Reibung und Verschleiß metallischer Oberflächen ist eine kontinuierliche Herausforderung für Ingenieure und Wissenschaftler – würde man die industriellen Prozesse des 21. Jahrhunderts insgesamt betrachten, ergäbe sich eine beachtlicher Energieaufwand durch Reibungsprozesse mit entsprechend großen wirtschaftlichen Auswirkungen. Es ist darüber hinaus sehr schwierig, Reibung und Verschleiß metallischer Oberflächen vorherzusagen, wenn der Einfluss der Randzonenverformung berücksichtigt werden soll. Studien zu den Verformungsmechanismen von Metallen und Legierungen ermöglichen ein besseres Verständnis der Reibungs- und Verschleißmechanismen von Werkstoffen mit genau definierten Ausgangsgefügen. In diesem Rahmen wurde in der vorliegenden Arbeit der Einfluss der Randzonenverformung auf das gemessene Reibungs- und Verschleißverhalten über eine systematische experimentelle Studie an einem Au-Ni-Multilagenmodellsystem untersucht. Die Reibexperimente, die an Au-Ni-Multilagenproben unter Ultrahochvakuumbedingungen (UHV) durchgeführt wurden, zeigten, dass die Dicke der einzelnen Schichten im Multilagensystem einen starken Einfluss auf die Reibung hat. Grund dafür ist der Übergang der vorherrschenden Verformungsmechanismen nahe der Oberfläche. Die Versuche geben auch einen neuen Ansatz vor für metallische Systeme in trockener und sauberer Umgebung vor: Die Verringerung der Reibkraft kann durch stabile Gefüge, z.B. über Legierungen, erreicht werden. Durch die ultrafeinen Körner, die durch mechanische Vermischung gebildet wurden, erhöht sich die Zahl der Korngrenzen. Die Verformung über die Korngrenzen ergibt einen niedrigen Reibungskoeffizienten. Mit zunehmender Zyklenzahl bildete sich ein metastabiles Gefüge aus Au und Ni, das bis zum Bruch der Triboschicht erhalten blieb. Um den Einfluss der Umgebung auf Reibung und Verschleiß metallischer Werkstoffe zu betrachten, wurde der zweite Teil der Versuche unter definierter Stickstoffatmosphäre durchgeführt. Wie bereits unter UHV-Bedingungen wurde ein deutlicher Anstieg des Reibungskoeffizienten mit zunehmender Schichtdicke gefunden. Die Reibungskräfte waren jedoch insgesamt höher als unter UHV-Bedingungen. Aufgrund der anderen Grenzflächeneigenschaften wurde verglichen zu den UHV-Bedingungen ein unterschiedliches Verschleißverhalten als auch eine andere Randzonengefügeentwicklung gefunden

Structure and nanotribology of thermally deposited gold nanoparticles on graphite

Cataloged from PDF version of article.Forming a complete understanding of the physical mechanisms that govern friction on the nanometer and atomic scales is an ongoing endeavor for scientists from various disciplines. While atomic force microscopy (AFM) has proven to be invaluable for the detailed study of nano-scale frictional properties associated with various surfaces, issues related to the precise characterization of the contact formed by the probe tip and the sample surface remain largely unsolved. In recent years, an alternative approach to nanotribology experiments has involved the lateral manipulation of well-characterized nanoparticles on sample surfaces via AFM and the measurement of associated frictional forces. In line with this idea, ambient-condition structural/nanotribological characterization and nano-manipulation experiments involving gold nanoparticles (AuNP) thermally deposited on highly oriented pyrolytic graphite (HOPG) are presented in this thesis. The effect of deposition amount on thin film morphology is discussed and post- deposition annealing procedure in terms of different annealing temperatures and times are tackled in order to characterize AuNP formation on HOPG. The morphology and distribution of AuNPs on HOPG are studied via scanning electron microscopy (SEM) while the confirmation of AuNP crystallinity via transmission electron microscopy (TEM) is also described. Topographical characterization of the resulting AuNP/HOPG material system performed via contact-mode AFM is demonstrated. Lateral force measurements are also presented, in terms of the dependence of friction force on normal load as well as the dependence of friction force increase at AuNP edges on normal load and particle height. Subsequent to comprehensive structural and frictional characterization, the results of nano-manipulation experiments performed on AuNPs on the HOPG substrate are reported and it is observed that AuNPs experience remarkably low frictional forces during sliding. A detailed study of friction with respect to contact area firmly confirms the occurrence of structurally lubric sliding under ambient conditions for this material system. This result constitutes the first observation of structurally lubric sliding under ambient conditions between different materials in the scientific literature.Cihan, EbruM.S

Diyabetik albino Balb/ c farelerdea aminoguanidinin böbrek üzerindeki etkisi

Bu çalışmanın amacı, uyarılabilir nitrik oksit sentaz (iNOS) aktivasyonunun ve nitrik oksidin streptozotos in (STZ) ile uyarılmış diyabetik farelerde böbrek dokusunu nasıl etkilediğini ve etkisinin spesifik bir iNOS inhibitörü olan a minoguanidin (AG) ile önlenip önlenemediğini öğrenmektir. Yirmi dört erkek fare, 90 gün boyunca günlük 100 mg. kg - 1 AG (AG Grubu), tek doz 150 mg. kg- 1 STZ (STZ Grubu),tek doz 150 mg. kg - 1 STZyi takiben 90 gün boyunca günlük 100 mg. kg - 1 AG (STZ - AG Grubu) ve sadece intraperitonal fizyolojik tuzlu su (Kontrol Grubu) alan dört gruba ayrılmıştır. NADPH - diaforez (NADPH -d) dağılımı, STZ uygulanmış hayvanların böbrek kesitlerinde kontrolle karşılaştırıldığında daha fazlaydı. STZ uygulaması proksimal tübüllerde fırç a kenarların devamlılığının bozulmasına, glomerulus endotelinde hasara ve juks taglomerular hücrelerde renin granüllerinin daha fazla olmasına yol açmıştır . STZ uygulamasını takiben verilen AG, böbrek korteksindeki histolojik ve sitolojik değişiklikleri kıs men önlemiştir ve renin dağılımı kontrol hayvanlardakine benzer şekilde olmuştur. Uyarılabilir nitrik oksit (iNO) artışıyla böbrekte meydana gelen bozulmanın AG uygulamasıyla kısmen önlenebildiği bulunmuştur. Diyabette, artan iNOS ile jukstaglomerular hücr elerde reningranülleri dağılımı arasında olası bir ilişki vardırThe aim of this study is to find out how activated inducible nitric oxide synthase (iNOS) and nitric oxide (NO) affect kidney tissue in streptozotocin (STZ)-induced diabetic mice and whether its influence can be prevented by aminoguanidine (AG), a specific iNOS inhibitor. Twenty-four male mice were divided into four study groups (n=6) receiving a daily dose of 100 mg.kg-1 AG for 90 days (Group AG), a single dose of 150 mg.kg-1 STZ (Group STZ), a single dose of 150 mg.kg-1 STZ followed by daily administration of 100 mg.kg-1 AG for 90 days (Group STZ-AG), and intraperitoneally injections of saline only (Group Control) for 90 days. Dispersion of NADPH-diaphorase (NADPH-d) was stronger in the kidney sections of STZ-treated animals compared with the controls. STZ treatment caused disruption of continuity of the brush borders in proximal tubules, glomerular endothelial damage, and considerable renin granules in the juxtaglomerular cells. AG administration following STZ treatment partly prevented histological and cytological changes in kidney cortex, and renin dispersion was similar to that in control animals. We found that increased inducible nitric oxide (iNO) caused kidney tissue degeneration that could be prevented to some extent by AG treatment. There is a possible relationship between increased iNOS and dispersion of renin granules in juxtaglomerular cells in diabetes

Effect of Environment on Microstructure Evolution and Friction of Au–Ni Multilayers

We present results from a systematic investigation of environmental effects on the frictional behavior of Au–Ni multilayer films of varying interlayer spacing. The current results, sliding against ruby spheres in a dry N2 atmosphere, are compared to prior work on the tribological behavior of these materials under ultra-high vacuum (UHV) (Cihan et al. in Sci Rep 9:1–10, 2019). Under both conditions, there is a regime of high friction when the interlayer spacing is large and a regime of low friction when the spacing is small. The low friction regime is associated with a critical grain size below which grain bound-ary sliding is expected to be the dominant mechanism of deformation. A shear-induced alloy formation (60–65 at.% Ni in Au) and a concomitant low friction coefficient was observed with multilayer spacings of 20 nm and lower under UHV. A distinct microstructure was found in dry N2, and is attributed to different interfacial characteristics due to adsorbed species; rather than mixing between Au and Ni layers, only the uppermost Au layers were affected by shearing. These observations are coupled with the friction and wear behavior of multilayer samples sliding under different environments

Carbon nanotube neurotransistors with ambipolar memory and learning functions

In recent years, neuromorphic computing has gained attention as a promising approach to enhance computing efficiency. Among existing approaches, neurotransistors have emerged as a particularly promising option as they accurately represent neuron structure, integrating the plasticity of synapses along with that of the neuronal membrane. An ambipolar character could offer designers more flexibility in customizing the charge flow to construct circuits of higher complexity. We propose a novel design for an ambipolar neuromorphic transistor, utilizing carbon nanotubes as the semiconducting channel and an ion-doped sol-gel as the polarizable gate dielectric. Due to its tunability and high dielectric constant, the sol-gel effectively modulates the conductivity of nanotubes, leading to efficient and controllable short-term potentiation and depression. Experimental results indicate that the proposed design achieves reliable and tunable synaptic responses with low power consumption. Our findings suggest that the method can potentially provide an efficient solution for realizing more adaptable cognitive computing systems.Comment: 16 pages, 6 pages of supporting information at the end, 6 main figures, 10 supporting figure

Antioxidant and anti-inflammatory activities of a commercial noni juice revealed by carrageenan-induced paw edema

This study aimed to investigate antioxidant and anti-inflammatory activities of a commercial product of noni (Morinda citrifolia) juice. Carrageenan-induced rat paw edema was employed as inflammatory model. One control and three experimental groups were formed. Experimental groups were administered noni juice alone, noni juice+carrageenan, and carrageenan alone. Oxidant and antioxidant capacity were determined by d-ROMs test and BAP test, respectively. Plasma concentrations of endothelin-1 and leptin were measured by ELISA. Measurements were performed at zero time and 2nd hour of inflammation. Oxidant capacity decreased in noni-received groups at 2nd hour (p=0.019). Antioxidant capacity of the group which received noni alone was found to be higher at 2nd hour (p=0.036). Plasma concentrations of endothelin-1 and leptin were notably lower in noni-received groups (p=0.001 and p=0.021, respectively). The results show that the commercial noni juice investigated has pronounced antioxidant and anti-inflammatory activities

Low friction of metallic multilayers by formation of a shear-induced alloy

During sliding of metallic surfaces, the near surfaces undergo significant changes in terms of topography, composition and microstructure. Since friction and wear behavior of the materials are strongly influenced by sub-surface deformations, it is fundamental to investigate these effects. Therefore, the present study aims towards a better understanding of the behavior of friction depending on well-defined initial microstructures. By performing sliding experiments on Au-Ni multilayer samples under ultrahigh vacuum (UHV) conditions, we observe that the individual layer thickness of multilayer systems has a strong influence on friction behavior due to the transition in the dominant deformation mechanism near the surface. The experiments reported here provide a new route for lowering the friction force of metallic material systems in dry contact by providing more stable microstructures and alloy formation. Through ultrafine grains present in the alloy formed by mechanical mixing the number of grain boundaries strongly increases and hence, grain boundary-mediated deformation results in the low friction coefficient