Superlubricity of molybdenum disulfide subjected to large compressive strains

The friction between a molybdenum disulphide (MoS2) nanoflake and a MoS2 substrate was analyzed using a modified Tomlinson model based on atomistic force fields. The calculations performed in the study suggest that large deformations in the substrate can induce a dramatic decrease in the friction between the nanoflake and the substrate to produce the so-called superlubricity. The coefficient of friction decreases by 1–4 orders of magnitude when a high strain exceeding 0.1 is applied. This friction reduction is strongly anisotropic. For example, the reduction is most pronounced in the compressive regime when the nanoflake slides along the zigzag crystalline direction of the substrate. In other sliding directions, the coefficient of friction will reduce to its lowest value either when a high tensile strain is applied along the zigzag direction or when a high compressive strain is applied along the armchair direction. This anisotropy is correlated with the atomic configurations of MoS2.

Analysis of Chaotic Response of Frenkel-Kontorova-Tomlinson Model

The Frenkel-Kontorova-Tomlinson (FKT) model represents mechanical systems in which the atomic smooth surfaces of two bodies slide against each other. The model is very sensitive to changes of the system parameters, and ranges from simple stable harmonic to chaotic solutions. The design of the model between two bodies for the dynamic problem, following the network method rules, is explained with precision and run on standard electrical circuit simulation software. It provides the phase diagrams of atom displacement for each atom and the total friction force by the summation of all the atom displacements. This article is focused on studying the effect of the selected time step on the result and in the lack of sensitivity of Lyapunov exponents to assess chaotic behaviour.

Velocity-dependent friction enhances tribomechanical differences between monolayer and multilayer graphene

The influence of sliding speed in the nanoscale friction forces between a silicon tip and monolayer and multilayer graphene were investigated with the use of an atomic force microscope. We found that the friction forces increase linearly with the logarithm of the sliding speed in a highly layer-dependent way. The increase in friction forces with velocity is amplified at the monolayer. The amplification of the friction forces with velocity results from the introduction of additional corrugation in the interaction potential driven by the tip movement. This effect can be interpreted as a manifestation of local thermally induced surface corrugations in nanoscale influencing the hopping dynamics of the atoms at the contact. These experimental observations were explained by modeling the friction forces with the thermally activated Prandtl-Tomlinson model. The model allowed determination of the interaction potential between tip and graphene, critical forces, and attempt frequencies of slip events. The latter was observed to be dominated by the effective contact stiffness and independent of the number of layers.

Atomistic Origins of Friction

This chapter covers the current state of knowledge about how the shear strength (the force needed to slide one surface over another) originates at the atomic level. For adhesive friction, friction originates from the forces needed to move the atoms on one surface over the atomic structure of the opposing surface; the simplest model for adhesive friction is the cobblestone model. The Frenkel–Kontorova model, the Prandtl–Tomlinson model, and molecular dynamic simulations are typically used to show how the atomic structure of the surfaces leads to static friction. One exciting aspect of these friction models is the prediction of superlubricity or negligible friction for incommensurate sliding surfaces, which is now being realized in experiments. Also discussed is why superlubricity is not observed in real-life situations. As atoms and molecules slide over surfaces, kinetic friction originates from phonon and electronic excitations, which are typically studied using the quartz crystal microbalance (QCM).

APLIKASI MODEL PELLA-TOMLINSON PADA PENGELOLAAN SUMBER DAYA PERIKANAN KAKAP MERAH DI INDONESIA

ABSTRAKTujuan dari penelitian ini adalah memodelkan pengelolaan sumber daya perikanan kakap merah di Indonesiadengan menggunakan model Pella-Tomlinson. Penelitian ini dilakukan pada tahun 2016, dengan data perikanan kakap merah Indonesia. Model surplus produksi bio-ekonomi yang digunakan dalam penelitian ini adalah model Pella-Tomlinson. Hasil analisis mengindikasikan, pertama jumlah upaya tangkap aktual berada diatas jumlah jumlah upaya lestari (MSY). Jika pengelolaan perikanan dilakukan berdasarkan prinsip perikanan lestari, maka mulai tahun 2020 upaya tangkap di bawah jumlah upaya lestari (MSY). Kedua, dalam kondisi bussiness as ussual, terjadi kenaikan bio-massa ikan semenjak tahun 1980 sampai pada tahun 2000, akan tetapi dari tahun dari tahun 2000 sampai tahun 2014 terjadi penurunan bio-massa ikan. Jika tidak ada intervensi kebijakan untuk mengurangi laju degradasi sumber daya maka penurunan biomassa akan terus terjadi hingga tahun 2050. Jika pemerintah melakukan intervensi kebijakan pengelolaan perikanan secara berkelanjutan, akan terrjadi kenaikan biomassa dari tahun 2020 sampai dengan tahun 2050. Ketiga, sejalan dengan penurunan bio-massa karena tidak adanya intervensi kebijakan pengelolaan perikanan kakap merah secara berkelanjutan, maka keuntungan yang diterima nelayan akan menurun, karena terjadi penurunan hasil tangkapan. Tapi jika pemerintah mengeluarkan kebijakan pengelolaan perikanan kakap merah secara berkelanjutan seperti pembatasan upaya penangkapan, maka keuntungan yang diterima nelayan akan meningkat lagi dari tahun 2020 sampai dengan tahun 2050. Title: Pella-Tomlinson Model for Red Snapper Management in IndonesiaABSTRACT The purpose of this study to develop a management model for red snapper fishery using a Pella Tomlinson Model. The research was conducted in 2016, for the national snapper fisheries obtained from official yearly landing statisctic data to get the time series catches and efforts. Surplus production bioeconomic was utilized with modified Pella and Tomlinson model for the growth model. The analysis shows that first, total efforts deployed without any kind of management (e.g. stay as an open access) will yield higher effort than maximum efforts at maximum sustainable level yield (MSY). This is a consequence of the increasing rate of red snapper efforts between 1980-2014. If fishery management is kept at the sustainable level of total efforts, then in 2020, total efforts will be less than the MSY level. Second, biomass increased between 1980-2000 and then decreased after 2000 until 2014. If there will be no intervention to the depletion of fishery resources, the fishery will be completely depleted in 2050. Third, when the snapper biomass decreases, the cathes will decrease as well. Hence, that total profits from the fishery will decrease. However, some intervention and magement measures will be put in place, such as limiting the total efforts, the cathes and profits will bounce back and increase after 2020 and the years after.