Mechano-Chemical Modelling of Boundary Lubrication

Boundary lubrication is known to be significantly important in the design of machine parts. The decrease in the efficiency of the system as well as its durability when operating in boundary lubrication conditions highlights the importance of this regime. Boundary lubrication involves many different physical, chemical and mechanical phenomena which make it difficult to understand the real mechanisms of friction, wear and lubrication. Tribochemistry is undoubtedly one of the most important processes occurring in boundary lubrication. Modelling such a complicated process needs a robust physical and chemical modelling framework that is capable of capturing different phenomena. The majority of the modelling attempts in boundary lubrication covers the contact mechanics of rough surfaces with different numerical approaches. Despite the importance of the tribochemistry and its effect in reducing friction and wear of boundary lubricated contacts, there is no comprehensive modelling framework that considers tribochemistry into the boundary lubrication models. In this work, tribochemistry was implemented into the deterministic contact mechanics simulation for elastic-perfectly plastic contact of rough surfaces. A tribochemical model for the growth of the ZDDP antiwear additive was developed based on the thermodynamics of interfaces that combines formation and removal of the tribofilm. The tribochemical model was then coupled with the contact mechanics model which was developed based on potential energy principles. A modification to Archard’s wear equation was proposed which accounts for the role of ZDDP tribofilm in reducing the wear. This model was proposed based on the experimental observations of ZDDP in reducing wear. The numerical framework was then validated against experiments. The wear prediction capability of the model was validated against experiments from Mini-Traction Machine in a rolling/sliding contact. The model is able to predict changes in the topography of the surfaces and this was validated with experiments on a Micro Pitting Rig (MPR). The model shows a good potential in capturing the behaviours in boundary lubrication and opens new ways for further developments and testing the effect of different parameters in tribochemistry and wear. It can give insights in better understanding the real mechanisms of tribochemistry and also help in optimizing boundary lubricated contacts

An in vitro aerosolization efficiency comparison of generic and branded salbutamol metered dose inhalers

Background: Due to the high rate of pulmonary diseases, respiratory drug delivery systems have been attracted excessive attention for the past decades. Because of limitations and growing drug bill, physicians are encouraged to prescribe generically whenever possible. The purpose of this study was to evaluate whether there was any significant difference in aerosolization performance between a reference brand Salbutamol (A) Metered Dose Inhalers (MDIs) and two generic products (B and C). Methods: The aerosolization performance of MDIs was evaluated by calculating aerosolization indexes including fine particle fraction (FPF), fine particle dose (FPD), geometric standard deviation (GSD) and mass median aerodynamic diameters (MMAD) by using the next generation impactor. Results: Although aerosolization indexes of MDI A were superior than the Iranian brands, but the differences were not statistically significant. Conclusion: These results verified that generic MDIs deliver similar quantities of Salbutamol to the reference brand and aerosolization performance parameters of generic Salbutamol MDIs did not differ significantly from the reference brand

Correlation of Mandibular Second Molar Impaction with Third Molar Size, Angulation, Developmental Stage, and Bud Position

Objective: The present study assessed the association of size, axial angulation, developmental stage and bud position of the mandibular third molar with the second molar impaction in patients with mandibular second molar impaction.Methods: In this descriptive-analytical study (Case-Control Design), dental records of 5,420 patients in the age range of 12-15 years who underwent orthodontic treatment were assessed out of which 20 patients (14 females and 6 males) with lower second molar impaction were studied. Twenty control patients with erupted second molars were selected from the same centers and matched with the case group. Total sample size was 40 (Case and Control) and had normal distribution for the determined measurements. Third molar axial angulation towards the second molar, first molar and mandibular base, mesiodistal width of 3rd molar /2nd molar ratio, Nolla developmental stage and third molar bud position were measured and calculated in patients with impacted and erupted second molars and analyzed using student t and chi-square tests.Results: The mean degree of third molar angulation towards the second molar, first molar and mandibular base was 30.20, 53.6, and 51.3 degrees in cases and 21.4, 34.65 and 45.15 degrees in controls, respectively. Significant differences were found between the two groups in terms of third molar angulation towards the second molar (30.2 Vs 21.4 degrees p<0.047), and first molar (53.6 Vs34.65 degrees p<0.0001); while no differences were found between the two groups in terms of third molar angulation towards the mandibular base (51.3 Vs 45.15 degrees). The mean mesiodistal width of third molar/ second molar ratio was 0.99 in cases and 0.95 in controls with no significant difference. Nolla developmental stage and position of the marginal ridge of the third molar bud towards the second molar showed no definite relation with second molar impaction.Conclusion: It seems that angulation of third molar to the second and first molars is a major contributing factor to increase the risk of second molar impaction. Third molars size, developmental stages, and bud positions, do not show a significant relation to the second molar impaction

Near-Field Radar Microwave Imaging as an Add-on Modality to Mammography

According to global statistics, there is a high incidence of cancer in western countries; and, due to the limited resources available in most health care systems, it seems like one of the most feasible options to fight against cancer might be strict prevention policies—such as eliminating carcinogens in people’s daily lives. Nevertheless, early cancer detection and effective treatment are still necessary, and understanding their efficacy and limitations are important issues that need to be addressed in order to ultimately enhance patients’ survival rate. In the case of breast cancer, some of the problems faced by conventional mammography have been addressed in the literature; they include high rate of false-positive and false-negative results, as well as the possibility of overdiagnosis. New technologies, such as digital breast tomosynthesis (DBT), have been able to improve the sensitivity and specificity by using 3D imaging. However, the low contrast (1%) existing between tumors and healthy fibroglandular tissue at X-ray frequencies has been identified as one of the main causes of misdiagnosis in both conventional 2D mammography and DBT. Near-field radar imaging (NRI) provides a unique opportunity to overcome this problem, since the contrast existing between the aforementioned tissues is intrinsically higher (10%) at microwave frequencies. Moreover, the low resolution and highly complex scattering patterns of microwave systems can be enhanced by using prior information from other modalities, such as the DBT. Therefore, a multimodal DBT/NRI imaging system is proposed to exploit their individual strengths while minimizing their weaknesses. In this work, the foundation of this idea is reviewed, and a preliminary design and experimental validation of the NRI system, used as a DBT complement, is introduced

Brain neural network, development, microbiome, microbial toxins and COVID-19

Although almost 2 years have passed since the beginning of the coronavirus disease 2019 (COVID-19) pandemic in the world, there is still a threat to the health of people at risk and patients. Specialists in various sciences conduct various researches in order to eliminate or reduce the problems caused by this disease. Neural network science plays a vital role in this regard. It is important to note the key points of neuro-microbial involvement in the diagnosis and management of COVID-19 therapy by physicians and patients whose nervous systems are challenged. The relationship between COVID-19, microbiome and the profile of microbial toxins in the body is one of the factors that can directly or indirectly play a key role in the body's resistance to Covid-19 and changes in the neural network of the brain. In this article, we introduce the relationship and behavioral and mood problems that can result from neuronal changes. In linking the components of this network, artificial intelligence (AI), machine learning (ML) and data mining (DM) can be important strategies to assist health providers to choose best decision based on patient’s history.

Development of a new mechano-chemical model in boundary lubrication

A newly developed tribochemical model based on thermodynamics of interfaces and kinetics of tribochemical reactions is implemented in a contact mechanics simulation and the results are validated against experimental results. The model considers both mechanical and thermal activation of tribochemical reactions instead of former thermal activation theories. The model considers tribofilm removal and is able to capture the tribofilm behaviour during the experiment. The aim of this work is to implement tribochemistry into deterministic modelling of boundary lubrication and study the effect of tribofilms in reducing friction or wear. A new contact mechanics model considering normal and tangential forces in boundary lubrication is developed for two real rough steel surfaces. The model is developed for real tribological systems and is flexible to different laboratory experiments. Tribochemistry (e.g. tribofilm formation and removal) and also mechanical properties are considered in this model. The amount of wear is calculated using a modified Archard’s wear equation accounting for local tribofilm thickness and its mechanical properties. This model can be used for monitoring the tribofilm growth on rough surfaces and also the real time surface roughness as well as changes in the λ ratio. This model enables the observation of in-situ tribofilm thickness and surface coverage and helps in better understanding the real mechanisms of wear

A Semi-deterministic Wear Model Considering the Effect of Zinc Dialkyl Dithiophosphate Tribofilm

Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded contacts under boundary lubrication conditions. Previous works have mainly reported contact mechanics simulations for capturing the boundary lubrication regime, but the real mechanism in which tribofilms reduce wear is still unclear. In this paper, the wear prediction capabilities of a recently published mechanochemical simulation approach (Ghanbarzadeh et al. in Tribol Int, 2014) are tested. The wear model, which involves a time- and spatially dependent coefficient of wear, was tested for two additive concentrations and three temperatures at different times, and the predictions are validated against experimental results. The experiments were conducted using a mini-traction machine in a sliding/rolling condition, and the spacer layer interferometry method was used to measure the tribofilm thickness. Wear measurements have been taken using a white-light interferometry. Good agreement is seen between simulation and experiment in terms of tribofilm thickness and wear depth predictions

Comparison of Tensile, Permeability and Color Properties of Starch-based Bionanocomposites Containing Two Types of Fillers: Sodium Montmorilonite and Cellulose Nanocrystal

The objective of this research was to compare the tensile, permeability, solubility and color properties of plasticized starch-polyvinyl alcohol-Montmo-rillonite (PS-PVA-MMT) and plasticized starch-polyvinyl alcohol-cellulose nanocrystal (PS-PVA-NCC) bionanocomposite flms. The results showed that adding MMT (7%), increased the ultimate tensile strenght from 4.2 MPa to 4.61 MPa, however, NCC (7%) did not show signifcant (p < 0.5) effect on the ultimate tensile strength. Addition of MMT decreased while NCC  increased  the  strain-to-break of  the flms. The solubility in water decreased from 23.56% to 18.77% and 11.75% for the flms containing NCC and MMT, respectively. Similarly, water vapor permeability value of 7.41 ×10-7 g/m.h.Pa was dropped to 7.05×10-7 g/m.h.Pa and 6.19×10-7 g/m.h.Pa in flms containing NCC and MMT, respectively. The results showed that the effects of MMT on tensile and permeability were higher than NCC, which can be attributed to differences in the structure and hydrophilicity of two nanoparticles

A Numerical Model for Investigating the Effect of Viscoelasticity on the Partial Slip Solution

To investigate the effects of viscoelasticity on the stick-slip behaviour, a new model reproducing the partial slip of viscoelastic materials under fully coupled conditions is developed in this paper. The ratio of retardation time to relaxation time is employed to characterize the rheological property of a viscoelastic material. It is found that materials with higher ratios exhibit more fluid-like behaviours while those with lower ratios perform more like solid. As long as the contact input (load or displacement) is constant, the stick ratio (ratio of stick area to contacting area) is found to be insensitive to the viscoelasticity of materials. However, the separation pattern of the stick and slip regions varies with time when different contact phenomena (creep or stress relaxation) are encountered in the lateral and normal directions. The transition process from partial slip to gross sliding of viscoelastic materials, unlike the elastic response, tends to be abrupt when fully coupled conditions between shear tractions and pressure are introduced. When identical contact parameters are specified for different viscoelastic materials, the more fluid-like material always experiences a quicker transition from partial slip to gross sliding