A New Approach to Mixed/Boundary Friction Prediction Using the Logistics Curve

There is a strong focus on improving the energy efficiency of machines. Over the last 20-30 years, one way to improve energy efficiency has been to reduce lubricant viscosity. This also has the effect of leading to thinner oil films between the machine’s moving surfaces and is likely to lead to increased mixed/boundary friction. Accurately predicting friction in the mixed/boundary friction regime is therefore becoming of great importance. The work reported here suggests that commonly used asperity friction models significantly underestimate friction in the mixed/boundary friction, and a new model, based on a logistic curve fit, gives a better estimate of mixed/boundary friction, provides good agreement with experimental friction data (from Mini Traction Machine experiments), and is much more straightforward for engineers and tribologists to apply for the estimation of mixed/boundary friction losses.

Hyperspectral Remote Sensing Detection of Marine Oil Spills Using an Adaptive Long-Term Moment Estimation Optimizer

Marine oil spills can damage marine ecosystems, economic development, and human health. It is important to accurately identify the type of oil spills and detect the thickness of oil films on the sea surface to obtain the amount of oil spill for on-site emergency responses and scientific decision-making. Optical remote sensing is an important method for marine oil-spill detection and identification. In this study, hyperspectral images of five types of oil spills were obtained using unmanned aerial vehicles (UAV). To address the poor spectral separability between different types of light oils and weak spectral differences in heavy oils with different thicknesses, we propose the adaptive long-term moment estimation (ALTME) optimizer, which cumulatively learns the spectral characteristics and then builds a marine oil-spill detection model based on a one-dimensional convolutional neural network. The results of the detection experiment show that the ALTME optimizer can store in memory multiple batches of long-term oil-spill spectral information, accurately identify the type of oil spills, and detect different thicknesses of oil films. The overall detection accuracy is larger than 98.09%, and the Kappa coefficient is larger than 0.970. The F1-score for the recognition of light-oil types is larger than 0.971, and the F1-score for detecting films of heavy oils with different film thicknesses is larger than 0.980. The proposed optimizer also performs well on a public hyperspectral dataset. We further carried out a feasibility study on oil-spill detection using UAV thermal infrared remote sensing technology, and the results show its potential for oil-spill detection in strong sunlight.

Zein-Based Films Containing Monolaurin/Eugenol or Essential Oils with Potential for Bioactive Packaging Application

Zein is renewable plant protein with valuable film-forming properties that can be used as a packaging material. It is known that the addition of natural cross-linkers can enhance a film’s tensile properties. In this study, we aimed to prepare antimicrobial zein-based films enriched with monolaurin, eugenol, oregano, and thyme essential oil. Films were prepared using the solvent casting technique from ethanol solution. Their physicochemical properties were investigated using structural, morphological, and thermal techniques. Polar and dispersive components were analyzed using two models to evaluate the effects on the surface free energy values. The antimicrobial activity was proven using a disk diffusion method and the suppression of bacterial growth was confirmed via a growth kinetics study with the Gompertz function. The films’ morphological characteristics led to systems with uniform distribution of essential oils or eugenol droplets combined with a flat-plated structure of monolaurin. A unique combination of polyphenolic eugenol and amphiphilic monoglyceride provided highly stretchable films with enhanced barrier properties and efficiency against Gram-positive and Gram-negative bacteria, yeasts, and molds. The prepared zein-based films with tunable surface properties represent an alternative to non-renewable resources with a potential application as active packaging materials.

Development and Characterization of Active Native and Cross-Linked Pearl Millet Starch-Based Film Loaded with Fenugreek Oil

In this study, cross-linked pearl millet starch and fenugreek oil was used to develop active starch edible films to overcome the limitations of native starch and to substitute artificial preservatives with natural one. The starch was cross-linked at three levels (1%, 3% and 5%) using sodium trimetaphosphate (STMP), and physicochemical properties were studied. Moreover, a comparative study was conducted among four samples of films prepared using native starch, cross-linked starch, and native and cross-linked starch loaded with fenugreek oil for physical, thermal, mechanical, morphological, and antibacterial properties. The solubility, swelling, and amylose content of native and modified starch varied from 11.25–12.75%, 12.91–15.10 g/g, and 8.97–16.55%, respectively. The values of these parameters were reduced as the concentration of STMP increased. Cross-linked starch films showed lower moisture, solubility, water vapor permeability(WVP), and elongation at break (EB) values while having higher thickness, opacity, thermal, and tensile strength values. The microscopic images of cross-linked starch films showed smooth surfaces and the absence of ridges, pores, and cracks. The films loaded with fenugreek oil showed different results; the moisture content, water solubility, and tensile strength were decreased while thickness, opacity, WVP, and EB were increased. The onset temperature and peak temperature were lower, while enthalpy of gelatinization was increased to a greater extent than films without oil. The addition of fenugreek oil to films showed a good inhibition area of 40.22% for native+oil films and 41.53% for cross-linked+oil films % against Escherichia coli. This study confirmed the successful utilization of fenugreek oil as a very effective antimicrobial agent in preparing edible films.

Nonlinear stability analysis and numerical continuation of bifurcations of a rotor supported by floating ring bearings

Floating ring bearings have been widely used, over the last decades, in rotors of automotive turbochargers because of their improved damping behavior and their good emergency-operating capabilities. They also offer a cost-effective design and have good assembly properties. Nevertheless, rotors with floating ring bearings show vibration effects of nonlinear nature induced by self-excited oscillations originating from the bearing oil films (oil whirl/whip phenomena) and may exhibit various nonlinear vibration effects which may cause damage to the rotor. In order to investigate these dynamic phenomena, this paper has developed a nonlinear model of a perfectly balanced rigid rotor supported by two identical floating ring bearings with consideration of their vibration behavior mainly governed by fluid dynamics. The dimensionless hydrodynamic forces of floating ring bearings have been derived based on the short bearing theory and the half Sommerfeld solution. Using the numerical continuation approach, different bifurcations are detected when a control parameter, the journal speed, is varied. Depending on the system’s physical parameters, the rotor can show stable or unstable limit cycles which themselves may collapse beyond a certain rotor speed to exhibit a fold bifurcation. Bifurcation analysis is performed to investigate the occurring instabilities and nonlinear phenomena. Such results explain the instabilities characteristics of the floating ring bearing in high-speed applications. It has also been found that the selection of the bearing modulus plays an important role in the characterization of the rotor stability threshold speed and bifurcation sequences. An understanding of the system’s nonlinear behavior serves as the basis for new and rational criteria for the design and the safe operation of rotating machines.