Thermal-EHD contacts lubricated with oil/refrigerant solutions: a new cavitation modeling approach based on refrigerant solubility

A first cavitation modeling with thermal effects for oil/refrigerant solutions lubricated ElastoHydroDynamic (EHD) point contacts is reported in this work. The solubility of the oil/refrigerant system is introduced into the Generalized Reynolds equation coupled with the elasticity equation and the energy conservation equation. The numerical results show a very good agreement with the published experimental results concerning film thickness prediction. Moreover, the present model describes the cavitation region on a physical basis. A discussion with other cavitation models from the literature is proposed. It puts into light the necessity of taking into account the solubility of the refrigerant into oil for such problems. Compared to pure oil, oil/refrigerant solutions can potentially reduce the amount of liquid oil for the next contact due to its higher cavitation intensity.

Cylindrical model of electrochromic colouration of hydrated vanadium pentoxide thin films with point contacts

This article analyses experiments on the kinetics of the internal electrochromism of thin (micron) films of hydrated vanadium pentoxide xerogel with point contacts. It describes a cylindrical model of electrochromic colouration, which was used to evaluate the concentration of the colour centres in the initial film and after additional hydrogenation of this film by plasmaimmersion ion implantation.When we compared the calculated values of the concentration of colour centres with the equilibrium concentration of protons in the xerogel, we saw that the mobility of the protons migrating from the depth of the film to the cathode region, which are involved in the electrochemical reaction, was not a determinant of the electrochromism kinetics.The rate of electrochromic colouration could be increased by the formation of layered film structures based on hydrated vanadium pentoxide, which have increased overall electron conductivity and, as a consequence, low faradaic resistance of the electrochromic cathodic reaction.

Film thickness interrelationship of base oil and grease lubricated compliant and hard non-conformal contacts

The interfaces of plastic components are often operated as self-lubricating or lubricated with greases close to the piezoviscous-elastic lubrication regime. However, current basic tribological knowledge about grease-lubricated compliant contacts is still very limited. This experimental study provides insight into relations between film thicknesses of grease and its base oil in compliant polymethylmethacrylate–steel and stiff glass–steel point contacts at different speeds and loads. The results are compared with predictions. The ratio between grease and its base oil film thickness was found to be significantly influenced by the interplay of load and the non-Newtonian response of grease, especially for the compliant contact, while the effect of speed and the slide-to-roll ratio was considerably lower. The role of viscoelasticity and grease thickener concentration is discussed.

Resistive properties of Janson’s point contacts in the conditions of polarization inversion

The sensitive element of a new quantum sensor generation is the Janson dendritic point contact. Analytes that are in the space surrounding the sensitive element are able to interact with the freshly formed surface of the conduction channel of the Janson quantum point contact, as well as with the surface of the dendrite during its growth. This interaction provides the influence of the substances under study on the configuration of the output characteristic of the sensor, represented by the system conductivity histogram. The conductivity histogram is built on the basis of the chrono-resistogram of the self-oscillating point-contact cyclic switchover effect, which is directly recorded under self-oscillation conditions. In the structure of the sensor element, Janson's dendritic point contact is immersed in an electrolyte and in an electric field forms a chrono-resistogram, which depends on the environment composition. The paper considers one of the aspects of such chrono-resistograms formation. The features of a gapless electrochemical system in the process of realizing the point-contact cyclic switchover effect are analyzed. Modeling the sensitive element in the form of a gapless electrode system allowed explaining the mechanism and dynamics of the transition “Janson point contact – dendrite and counter electrode in the electrolyte”. The most important parameter of the gapless electrode system is the coordinate of the polarization inversion boundary. It is shown that the idea of the coordinate of the polarization inversion boundary plays a fundamental role in modeling the resistive properties of a point-contact system and its lifetime. The synthesized mathematical models describe well the experimentally obtained dependences of the resistance on the exposure time of the nanostructure in an electric field. It was found that the dependence of the contact resistance on the exposure time, obtained under the assumption of a linear distribution of the anodic polarization along the main axis of the conduction channel, is described by a differential equation in which the growth rate of resistance is directly proportional to the cube of this resistance. The materials obtained make it possible to purposefully optimize the design parameters and operating conditions of sensor devices based on Janson point contacts for the analysis of complex gaseous and liquid mixtures.

Differential thermopower images as a probe of many-body effects in quantum point contacts

Mesoscopic circuit elements such as quantum dots and quantum point contacts (QPCs) offer a uniquely controllable platform for engineering complex quantum devices, whose tunability makes them ideal for generating and investigating interacting quantum systems. However, the conductance measurements commonly employed in mesoscopics experiments are poorly suited to discerning correlated phenomena from those of single-particle origin. Here, we introduce non-equilibrium thermopower measurements as a novel approach to probing the local density of states (LDOS), offering an energy-resolved readout of many-body effects. We combine differential thermopower measurements with non-equilibrium density functional theory (DFT) to both confirm the presence of a localized state at the saddle point of a QPC and reveal secondary states that emerge wherever the reservoir chemical potential intersects the gate-induced potential barrier. These experiments establish differential thermopower imaging as a robust and general approach to exploring quantum many-body effects in mesoscopic circuits.