Anomalously low friction of confined monolayer water with a quadrilateral structure

AbstractThe friction behavior of metals is directly linked to the mechanisms that accommodate deformation. We examine the links between mechanisms of strengthening, deformation, and the wide range of friction behaviors that are exhibited by shearing metal interfaces. Specifically, the focus is on understanding the shear strength of nanocrystalline and nanostructured metals, and conditions that lead to low friction coefficients. Grain boundary sliding and the breakdown of Hall–Petch strengthening at the shearing interface are found to generally and predictably explain the low friction of these materials. While the following is meant to serve as a general discussion of the strength of metals in the context of tribological applications, one important conclusion is that tribological research methods also provide opportunities for probing the fundamental properties and deformation mechanisms of metals.

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Comparative Analysis of Periodontal Pain According to the Type of Precision Orthodontic Appliances: Vestibular, Lingual and Aligners. A Prospective Clinical Study

Biology ◽

10.3390/biology10050379 ◽

2021 ◽

Vol 10 (5) ◽

pp. 379

Author(s):

Laura Antonio-Zancajo ◽

Javier Montero ◽

Daniele Garcovich ◽

Mario Alvarado-Lorenzo ◽

Alberto Albaladejo ◽

...

Keyword(s):

Clinical Study ◽

Pain Intensity ◽

Short Form ◽

Study Groups ◽

Mcgill Pain Questionnaire ◽

Prospective Clinical Study ◽

Orthodontic Appliances ◽

Low Friction ◽

Different Types ◽

Lower Arch

The objective of this prospective clinical study was to analyze the pain (intensity, location and type) that patients presented after the placement of different types of orthodontic appliances: conventional, low friction, lingual and aligners. The sample consisted of 120 patients divided into four groups: conventional (CON), low friction (LF), lingual (LO) and aligners (INV). The participants were given the Short-Form McGill Pain Questionnaire (Ortho-SF-MPQ), where they had to record the pain intensity (no pain, mild, moderate or intense) and the periodontal location at different time points, from the first 4 h to 7 days after the start of treatment. In all the study groups, the most frequent location was both anterior arches, with maximum values between 56.7% (CON group at 24 h) and 30% (LO group at 4 h). The “whole mouth” and “complete lower arch” locations were indicated only by the patients in the lingual group. Regarding pain intensity, the patients reported a higher percentage of mild–moderate pain during the first 3 days of treatment (96.7% in LO at 4 h, 86.7% in CON, 83.3% in LF and 90% in INV at 24 h); later, the reported pain decreased to no pain/mild pain, especially in the lingual group, until reaching values close to zero at 7 days post-treatment. The most frequent type of pain was acute in the low friction and lingual groups (with maxima of 60% and 46.7% at 24 h, respectively). On the contrary, in the conventional (36.7% at 4 h) and Invisalign (40% at 24 h) groups, the sensitive type was the most frequent. There are differences regarding periodontal pain in its intensity, location and type according to the use of different orthodontic techniques.

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Effect of Bias Voltage on Microstructure and Properties of Tantalum Nitride Coatings Deposited by RF Magnetron Sputtering

Coatings ◽

10.3390/coatings11080911 ◽

2021 ◽

Vol 11 (8) ◽

pp. 911

Author(s):

Wei Dai ◽

Yunzhan Shi

Keyword(s):

Magnetron Sputtering ◽

Bias Voltage ◽

Rf Magnetron Sputtering ◽

Amorphous Structure ◽

Tribological Performance ◽

Tantalum Nitride ◽

Growth Morphology ◽

Low Friction ◽

Nitride Coatings ◽

Overall Performance

TaNx coatings were deposited by RF magnetron sputtering with different bias voltages. The growth morphology, crystalline structure, chemical bond structure, hardness and elastic modulus, adhesion strength and tribological performance of the coatings were studied as a function of the bias voltage. The results showed that an increasing bias voltage refines the coating grains and facilitates structure densification. Simultaneously, the structure of the TaNx coatings transfers from a composite structure consisting of TaN and Ta2N crystals, through a single composite mainly composed of the Ta2N crystal, to an amorphous structure as the bias voltage increases from low to high, indicating that the phase composition of the TaNx coatings can be varied by the bias voltage. The coating composed of Ta2N crystal showed a good overall performance including enhanced hardness, enhanced adhesive strength, and good tribological performance with enhanced wear resistance and a low friction coefficient of 0.18.

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