Elastic and elastic-perfectly plastic analysis of an axisymmetric sinusoidal surface asperity contact

ABSTRACT

Closed-form finite-element empirical models are available for elastic and elastic–plastic spherical and sinusoidal contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. Therefore this work has analysed and quantified the behaviour of an elastic and elastic- perfectly plastic axisymmetric sinusoidal surface in contact with a rigid flat for a wide range of material properties and different values of the amplitude to wavelength ratio from initial to complete contact (high load). The numerical results agreed well with the Hertz model and the Jackson–Green elastic–plastic spherical contact model at low loads. Empirical equations for elastic and also elastic-perfectly plastic cases are formulated for the contact pressure, contact area and surface separation. From the current analysis, it is found that it is not any single parameter, but different combinations of material properties and surface roughness that govern the whole contact behaviour. The critical value of the amplitude of the sinusoidal asperity below which it will deform completely elastically from initial to complete contact is established. At low values of amplitude normalized by the critical amplitude, it was found that the contact behaved similar to a spherical contact, with the average pressure (hardness) always remaining lower than three times the yield strength. However, at higher values the average pressure increased toward a value as high as six times the yield strength at complete contact. All of these equations should be useful in rough surface contact modelling, lubrication analysis, electrical contact modelling and in many other applications.     

Alumina supported copper nanoparticles for aziridination and cyclopropanation reactions

Alumina supported copper (Cu–Al₂O₃) nanoparticles were prepared and applied for the aziridination of olefins employing [N-(p-tolylsulfonyl)imino]phenyliodinane (PhI = NTs) as nitrene source to afford the corresponding 3-membered cyclic compounds in moderate to excellent yields. Cyclopropanation of several olefins was also carried out by using Cu–Al₂O₃ nanoparticles and ethyl diazoacetate as a carbene source. The catalyst was recovered by simple centrifugation and reused for four cycles.     

Effectiveness of sodium silicate as gangue depressants in iron ore slimes flotation

The recovery of iron from the screw classifier overflow slimes by direct flotation was studied.The relative effectiveness of sodium silicates with different silica-to-soda mole ratios as depressants for silica and silicate bearing minerals was investigated.Silica-to-soda mole ratio and silicate dosage were found to have significant effect on the separation efficiency.The results show that an increase of Fe content in the concentrate is observed with concomitant reduction in SiO2 and Al2O3 levels when a particular type of sodium silicate at a proper dosage is used.The concentrate of 58.89wt％ Fe,4.68wt％ SiO2,and 5.28wt％ Al2O3 with the weight recovery of 38.74％ and the metal recovery of 41.13％ can be obtained from the iron ore slimes with 54.44wt％ Fe,6.72wt％ SiO2,and 6.80wt％ Al2O3,when Na2SiO3 with a silica-to-soda mole ratio of 2.19 is used as a depressant at a feed rate of 0.2 kg/t.     

Angiogenic Effects and Crosstalk of Adipose-Derived Mesenchymal Stem/Stromal Cells and Their Extracellular Vesicles with Endothelial Cells

Adipose-derived mesenchymal stem/stromal cells (ASCs) are an adult stem cell population able to self-renew and differentiate into numerous cell lineages. ASCs provide a promising future for therapeutic angiogenesis due to their ability to promote blood vessel formation. Specifically, their ability to differentiate into endothelial cells (ECs) and pericyte-like cells and to secrete angiogenesis-promoting growth factors and extracellular vesicles (EVs) makes them an ideal option in cell therapy and in regenerative medicine in conditions including tissue ischemia. In recent angiogenesis research, ASCs have often been co-cultured with an endothelial cell (EC) type in order to form mature vessel-like networks in specific culture conditions. In this review, we introduce co-culture systems and co-transplantation studies between ASCs and ECs. In co-cultures, the cells communicate via direct cell–cell contact or via paracrine signaling. Most often, ASCs are found in the perivascular niche lining the vessels, where they stabilize the vascular structures and express common pericyte surface proteins. In co-cultures, ASCs modulate endothelial cells and induce angiogenesis by promoting tube formation, partly via secretion of EVs. In vivo co-transplantation of ASCs and ECs showed improved formation of functional vessels over a single cell type transplantation. Adipose tissue as a cell source for both mesenchymal stem cells and ECs for co-transplantation serves as a prominent option for therapeutic angiogenesis and blood perfusion in vivo.     

Band selection using variational mode decomposition applied in sparsity-based hyperspectral unmixing algorithms

In this work, a frequency-based dimensionality reduction technique using variational mode decomposition (VMD) is proposed. Dimensionality reduction is a very important aspect of preprocessing in case of hyperspectral image (HSI) analysis where this step helps in elimination of the lesser informative bands, thereby reducing the size of the data and making its processing computationally less challenging. In contrast to the standard dimensionality reduction methods such as inter-band block correlation (IBBC) where bands are eliminated based on their similarity with the consecutive bands, the proposed method uses frequency information of each band to categorize it as a less or more informative band. In this way, only the topmost informative bands of HSI are selected to form the reduced dataset. In our experiment, in order to verify the efficiency of VMD as a dimensionality reduction technique, the hyperspectral unmixed results obtained for IBBC reduced dataset is compared with those obtained for VMD reduced dataset. From the parametric measures such as classification accuracy, root-mean-square error (RMSE) and visual results obtained after unmixing for both IBBC and VMD reduced datasets, it is noticed that the VMD reduced dataset performs better by achieving higher classification accuracy and lower RMSE than that of the existing IBBC method.     

Characterisation and determination of in vitro antioxidant potential of betalains from Talinum triangulare (Jacq.) Willd.

Talinum triangulare (Jacq.) Willd is an erect, succulent, perennial herb belonging to the family Portulacaceae. Under extreme environmental conditions, the plant produces betalain pigments which get accumulated in the stem region. Hence, in the present study, the betaxanthin and betacyanin patterns from different samples of T. triangulare have been investigated by applying high-performance liquid chromatography photo-diode array detection (HPLC-PDA) coupled with positive ion electro-spray mass spectrometry. Two betacyanins and two betaxanthins were identified in aqueous methanolic extract of flower, stem and leaf. Betanin, isobetanin, immonium conjugates of betalamic acid with dopamine and tyrosine were elucidated. The total betalain content was estimated by photometric analysis. In vitro antioxidant activity for the betalain extract determined by various methods revealed potent scavenging ability. The current work may possibly be considered beneficial in utilisation of the plant T. triangulare as a natural colourant in food and beverage industries.     

Dry colour prediction of leather from its wet state

The present investigation describes the development of a regression model for dry colour prediction based on the colour of wet leather. Such a prediction will be useful in the colour matching of leather – the time delay in drying of wet leather and determination of the final colour can be avoided. The use of computer technology interfaced with a reflectance spectrophotometer provides a novel approach to the prediction of dry colour from wet colour. In this study, five different regression models, i.e. linear fit, log fit, quadratic fit, log quadratic fit and cubic fit, were developed, with the dry reflectance of the leather sample as a dependent variable and the wet reflectance of the leather as an independent variable. The relationship between moisture content and surface leather colour, a prerequisite for enabling prediction, was studied. The obtained log quadratic model can be used for accurate prediction of dry colour from wet colour.     

Cleaner tanning process for the manufacture of upper leathers

There is a growing need for eco-benign tanning systems owing to stringent environmental regulations. In this study, a combination tanning process based on henna and tetrakis hydroxymethyl phosphonium sulphate (THPS) for the production of upper leathers as a cleaner alternative is presented. Extract from the leaves of Lawsonia inermis (henna) has been evaluated for its tanning characteristics in a combination tanning system based on henna and THPS. Both tanning methodologies, henna followed by THPS (henna–THPS) and THPS followed by henna (THPS–henna), have been attempted. It has been observed that THPS–henna combination tanning, employing 20% henna and 1.5% THPS, provides a shrinkage temperature of 96°C. The characteristics of the leathers indicate that the THPS–henna combination system provides leathers with good organoleptic properties and comparable strength properties. The combination system provides significant reduction in the discharge of total dissolved solids in the wastewater. These leathers showed opened up, split compact fiber structure, indicating that the tanning process did not bring about any major change or destruction on the fiber structure of the leathers. The leathers have been further characterized for chemical analysis and scanning electron microscopy. The leathers obtained from the combination system are lighter in color compared to control leathers. Possibility of making upper leathers from THPS–henna combination system as an effective alternative cleaner tanning methodology is established in this work.     

F-SIFT and FUZZY-RVM based efficient multi-temporal image segmentation approach for remote sensing applications

Image segmentation plays a most important role in the remote sensing applications, for the efficient detection of the Earth surface. The main objective of the segmentation process is to modify and simplify the representation of an image into an easier form for efficient analysis. The performance of the image segmentation process reduces due to the occurrence of noise and disturbances in the image. Existing segmentation approaches suffer from the performance degradation in the segmentation accuracy owing to the quality of the acquired satellite image. To overcome these drawbacks, this paper proposes an efficient image segmentation process for the clear view of the multi-temporal satellite image. Gaussian Filter (GF) is used for filtering the image to remove the noises present in the image. PSO-Affine based image registration is applied for the extraction of the pixel points and registration of the multi-temporal image. Removal of cloud from the image is performed to get a clear view of the image. Feature extraction is performed by using the Fast-Scale Invariant Feature Transform (F-SIFT) approach. The feature points of the image are extracted to form the cluster including six different classes such as building area, road area, vegetation area, tree area, water area and land area. The classes of the cluster are recognized by using the Fuzzy-Relevance Vector Machine (F-RVM) algorithm. The proposed approach achieves better performance in the cloud removal and efficient image segmentation.