Physical Science: New Insights and Developments Vol. 2

Statistical Cluster and Regression Evaluation of Friction Coefficient in Extremely Thin Diamond-Like Carbon Films

2025-08-18T10:53:48+00:00

Extremely thin diamond-like carbon (DLC) films are commonly used for nanotribological applications as a protective film. Atomic-scale wear and minute fluctuations in friction degrade equipment performance. Thus, improving the nanotribology of these protective films is crucial for realising higher reliability in nano-systems. The tribological properties of extremely thin DLC films at high temperature were studied. The films were deposited on nickel phosphorus (NiP) or Si substrates using filtered cathodic vacuum arc (FCVA) or plasma chemical vapour deposition (P-CVD). The nanotribological properties of the films were investigated using AFM. To evaluate how the friction durability properties of the film depend on load, the friction coefficient was measured using a load-increase and decrease type friction tester. Cluster analysis of the dependence of the friction coefficient on load and number of reciprocating cycles was performed on the data from the friction test using statistical analysis. The nanoindentation hardness values and elastic moduli of the films were lower on NiP than on Si. The nanofriction force of the FCVA-DLC film on NiP was low at room temperature, but very high at high temperatures. In this hard film, the lubricous adsorbate was removed by sliding at high temperature, making it easily damaged through the large deformation of NiP. In contrast, the friction force of the P-CVD-DLC films on both substrates was low at high temperatures. In this case, the lubricous tribochemical products from the P-CVD-DLC film reduced friction and wear. The friction map dependencies on load and number of reciprocating cycles were evaluated using a friction test and statistical cluster analysis. In contrast to the FCVA-DLC film, the friction coefficient of the P-CVD-DLC film is relatively high at room temperature; however, the friction coefficient decreases at high temperature, associated with an increase in durability and critical load. The friction durability of both films depended more strongly on load on NiP than on Si, with the friction coefficients on Si being almost independent of load. At high temperatures and loads, the durability of the FCVA-DLC film on NiP decreased, and this film was easily damaged. Low friction and better durability at high temperature can be obtained for this P-CVD-DLC film; this is evident in the superior nanofriction and wear properties of the film at high temperature.

A Comprehensive Overview of Atmospheric and Spaceflight Operation

2025-08-18T10:57:32+00:00

The limit of the atmosphere and the beginning of space are considered to be at 100 km altitude. Microgravity is the term used to characterise the very low acceleration level encountered inside a spacecraft in LEO (Low Earth Orbit). The study aims to monitor atmospheric operations and their applications. Chemical composition in the lower layers: 78% of nitrogen, 21% of oxygen, 1% of argon, and < 0.1% others and then a very small amount of other molecules, mainly water vapour and carbon dioxide, are present, which are in fact greenhouse gases, so they are important although they are small in quantity in the atmosphere compared to the other components. In terms of temperature evolution towards the atmosphere, at the level of the ground, with a temperature of 288 K, or 15°C. As one goes up in the mesosphere, about 50 km altitude, the temperature decreases again, and then above 80-90 km altitude it starts to increase again, because of the ionisation of the oxygen, mainly, and somewhat nitrogen atoms in the so-called thermosphere. Microgravity: these are the conditions that one can have in free fall. If someone has pure free fall, they are going to have zero-g or weightlessness, but in fact, there are always perturbing forces. The Hohmann transfer is a special kind of transfer from one circular orbit to another circular orbit. First of all, manoeuvring in orbit is basically ΔV vectorial that, if applied at some point in the orbit of a satellite or spacecraft that one will change the orbit. Here is an example of an initial circular orbit, and if velocity is added in the direction of the circular velocity. At some point, ΔV, if added, it will change the orbit to an elliptical orbit of high energy. Basically, energy was added to the orbit, kinetic energy was also added, so a larger value of the semi-major axis can be obtained instead of the radius r of the initial circular orbit. An elliptical orbit appears, which has a semi-major axis larger than the radius of the initial circular orbit. Now, only instantaneous ΔV will be considered. This is the simplification. Most of the time, the initial conditions are a spacecraft on the ground, called the chaser, which is active and another spacecraft in orbit, the target, which is passive.

Convectional Onset in Ferrofluid Layer Through a Darcy-brinkman Porous Medium

2025-08-18T11:02:53+00:00

This chapter considers the analysis of the instabilities of convection through a porous medium in a layer of incompressible ferrofluid when the layer is subjected to a uniform magnetic field along with an external heat source. The Darcy-Brinkman model is used to study porous media. The perturbation method is used in combination with the normal mode method to analyse the influence of various integrated factors involved in the stability/instability of the considered system. The case of exponential variation in stratification is considered, and the dependence of the growth rate on the kinematic viscosity, medium porosity, medium permeability, heat source, Darcy-Brinkman number, and Alfvén squared velocity is also analytically demonstrated. The cases of stable stratification and unstable stratification are also analysed to determine the stabilisation as well as destabilisation effects of the system under certain constraints.

Symmetry Breaking Model of Volume Pulsating Walking Droplets: A Study of Critical Aspects

2025-08-18T11:06:31+00:00

In the last fifteen years, the classical study of hydrodynamical Faraday waves has attracted renewed interest since the discovery of walking droplets and the more general discovery of hydrodynamical pilot wave models. Notwithstanding that many papers have cleared and rationalised a lot of phenomena with similarities to quantum mechanics (wave/particle duality, discrete orbits, tunnelling effect, statistical properties, etc. The study proposes a generalised model describing the dynamics of extended pulsating walking droplets. The first section provides a brief overview of the open problems of walking droplets. The second section analyses some critical issues of the general stroboscopic models. The third section elaborates on the proposed generalised model of pulsating droplets. Finally, a link is shown between walking droplets and the acoustic gravity wave induced on the surface of the vibrating bath.

High Power Piezoelectric Characterization System (HiPoCS™)

2025-08-20T10:50:52+00:00

Piezoelectric materials have been widely used in the automotive, medical instrument, information and telecommunication industry as sensors, actuators, frequency controlling devices, and high voltage and power sources. Piezoelectric devices make use of direct and inverse piezoelectric effects to perform a function. Both these piezoelectric effects are found in the crystal structures of some materials. The bottleneck of the piezoelectric devices in miniaturization is the heat generation owing to the losses. There are three losses in a piezoelectric material: dielectric, elastic and piezoelectric losses. The development of high-power-density piezoelectrics is directly relevant to the clarification of the loss mechanisms in such materials. This study describes the characterization methodologies of high-power piezoelectrics, in particular, in determining the three losses separately. ‘Intensive’ and ‘extensive’ losses are introduced in this study. Two broad categories of measurement techniques are discussed: (1) electrical excitation method, and (2) mechanical excitation method. The former is basically admittance/impedance measurement via the output current over the input voltage, further classified into four methods: (a) constant voltage, (b) constant current, (c) constant vibration velocity, and (d) constant input energy. To the contrary, the latter is basically the transient mechanical vibration ring-down measurement under various electrical constraint conditions. The key is to obtain precise values of both mechanical quality factors at resonance Q_A and at antiresonance Q_B, regardless of measuring techniques, so that we can determine the piezoelectric loss precisely. The difference of Q_M between the resonance and antiresonance originates from the electromechanical coupling factor k² loss, \((\frac{k^{2''}}{k{2'}})\) = (2 tan \(\theta\)' - tan \(\delta\)' - tan \(\phi\)') Depending on the sign of the k² loss, more efficient driving frequency can be derived rather than the conventional “resonance’ frequency. Recent studies on the loss determination methodology were also added in this study.

An Analytic Approximation for the Bohm Plasma Sheath Potential

2025-09-22T11:20:00+00:00

The plasmas in physics are characterised by quasi-neutrality, which means that the number of ions and electrons is nearly equal. This property is lost near the walls containing the plasma. The classic treatment for this region, called Bohm Sheath model, leads to the idea that there are two regions: a long one denoted as presheath, where the quasi-neutrality is still preserved, and the sheath region, where there are a few electrons, and the ions are those fed by the plasma, whose velocity is determined by the wall potential and plasma density. Here, a new analytic approximation for the Bohm Sheath Potential is presented, which is valid for any value of the characteristic parameter K, measuring the mean ion velocity. The procedure to obtain this approximation is different to those used by previous authors, because now, the characteristic exponential parameter \(\lambda\), depends on the parameter K, as well as the wall potential \(\phi\)w. In previous works, that parameter used to be a function of K only, and all the approximations used to fail for K \(\le\)\(\frac{1}{2}\)^,which is not the case now. The proposed method is shown to remain valid even at K=1/2, a regime where earlier approximations fail, and numerical comparisons confirm improved accuracy.

An Analytic Approximation for the Modified Bessel Function of Negative Fractional Order I−2\(_{/3}\)(x)

2025-09-22T11:29:08+00:00

The modified Bessel functions appear in Electrodynamics and other areas of Physics. In the present work, an analytic approximation to the modified Bessel function of negative fractional order I_-2/3(x) is presented. The validity of the approximation is for every positive value of the independent variable. The accuracy is high in spite of the small number (4) of parameters used. The approximation is a combination of elementary functions with rational ones. Power series and asymptotic expansions are simultaneously used to obtain the approximation.

Triple-Shock Configurations in High-Speed Flows Over Plane and Cylinder Bodies in Different Gases

2025-09-22T11:36:08+00:00

Flow control is crucial for refining the quality of high-speed flows and improving the performance and safety of fast aircraft. Unsteady flow control through external energy deposition has been widely discussed in the literature. Such processes often involve complex shock wave interactions, including the occurrence of triple shock configurations. This сhapter considers the issues of controlling supersonic flow past aerodynamic bodies under the action of external energy supply. The mechanism of interaction of the bow shock wave with an oblique shock wave formed by the refraction of the bow shock wave on the outer surface of the energy source is revealed. Unsteady triple-shock configurations near the surface of compound cylindrical bodies "hemisphere-cylinder" and "hemisphere-cone-cylinder" under the action of external energy supply for gaseous media with an adiabatic index of 1.4 and 1.2 are investigated at freestream Mach number M = 4. The studies are carried out numerically based on the Euler equations. Complex-conservative difference schemes are used in the simulations. The influence of the triple-shock configuration on the surface pressure is investigated and the formation of local spatio-temporal regions of the increased pressure is established. It is shown that the mechanism of pressure growth at the boundary, together with the local increase in the drag force, is associated with the action of the vortex flow, as well as with the action of the resulting shock wave structures. The dependences of the angles of the three-shock configuration on the rarefaction coefficient in the energy input region and on the angle of the incident shock wave are obtained. A comparison with the plane case is made. Obtained results can be used for organization of flow control with the use of external energy deposition by means of laser, microwave or electrical discharge.