Parametrically Excited Vibration in Rolling Element Bearings

A defect-free rolling element bearing has a varying stiffness. The variation of stiffness depends on number of rolling elements, their configuration and cage frequency. The time-varying characteristics of the stiffness results in a parametric excitation. This may lead to instability which is manifested as high vibration levels. An FEM simulation is performed to evaluate stiffness in each configuration of rolling elements and is used to study the variation of direct stiffness and cross coupled stiffness. The obtained stiffness variation is expanded into a Fourier series to form the equation of motion for the bearing vibration. As the stiffness varies with cage frequency, stiffness term in the equation of motion is periodic with parametric excitation. Hence, the equation of motion is a 2-DOF coupled Mathieu equation. Based on Mathieu parameters and cage frequency there exists unstable rpm ranges for a particular bearing. Floquet theory is employed to find out the stable and unstable regions. This involves finding out maximum Floquet exponent using Monodromy matrix. The results obtained through Floquet theory are in agreement with the numerical solution of the governing equations

Dynamic instability characteristics of rolling element bearings

The dynamics of bearing is a classical problem in machinery vibration. It is well known that rolling element bearings are susceptible to large vibration response at suitable parameter values arising due to instability. In the present work, we formulate the governing equations of motion of rolling element bearings. Herein, the rolling elements are modeled as lumped spring elements. With odd number of rolling elements, due to asymmetric effects of the bearing crosssection a parametric excitation effect is introduced in the system of governing equations. Further, due to the load zone effect this system represents a non-smooth dynamical system. The parametric stiffness term flips its sign depending on the sign of the displacement response. As such the governing equations of the system resemble the classical asymmetric Mathieu equation. In the literature, the method of Lyapunov-like exponents has been used to determine the stability boundaries of the asymmetric Mathieu equation. Herein, a positive Lyapunov-like exponent indicates instability whereas a stable response manifests as a negative Lyapunov-like exponent. In the present work, we use this method in detecting the stability and instability characteristics over the different bearing parameters. Stability diagrams are presented which can aid the designers and the user of the bearing in confirming the stability and instability zone. The method is validated by numerically integrating the governing equations. It is verified through numerical analysis that parameter combinations associated with an unstable zone manifest an exponential growth in response. Similarly, the parameter combinations associated with stable zone of the stability diagram shows bounded response

Application of combined omics platforms to accelerate biomedical discovery in diabesity

Diabesity has become a popular term to describe the specific form of diabetes that develops late in life and is associated with obesity. While there is a correlation between diabetes and obesity, the association is not universally predictive. Defining the metabolic characteristics of obesity that lead to diabetes, and how obese individuals who develop diabetes different from those who do not, are important goals. The use of large-scale omics analyses (e.g., metabolomic, proteomic, transcriptomic, and lipidomic) of diabetes and obesity may help to identify new targets to treat these conditions. This report discusses how various types of omics data can be integrated to shed light on the changes in metabolism that occur in obesity and diabetes

Synthesis, characterization and antibacterial activity studies of new 2‑pyrral‑L‑amino acid Schif base palladium (II) complexes.

Three new 2-pyrral amino acid Schif base palladium (II) complexes were synthesized, characterized and their activity against six bacterial species was investigated. The ligands: Potassium 2-pyrrolidine-L-methioninate (L1), Potassium 2-pyrrolidine-L-histidinate (L2) and Potassium 2-pyrrolidine-L-tryptophanate (L3) were synthesized and reacted with dichloro(1,5- cyclooctadiene)palladium(II) to form new palladium (II) complexes C1, C2 and C3, respectively. 1 NMR, FTIR, UV–Vis,elemental analysis and conductivity measurements were used to characterize the products. The antibacterial activities of the compounds were evaluated against Gram-positive Staphylococcus aureus (S. aureus, ATCC 25923), methicillin-resistant Staphylococcus aureus (MRSA, ATCC 33591), Staphylococcus epidermidis (S. epidermidis, ATCC 12228) and Streptococcus pyogenes (S. pyogenes, ATCC 19615) and, gram-negative Pseudomonas aeruginosa (P. aeruginosa, ATCC 27853) and Klebsiella pneumoniae (K. pneumoniae, ATCC 13883) using the agar well difusion assay and microtitre plate serial dilution method. The palladium complexes were active against the selected bacteria with the imidazole ring containing complex C2 and indole heterocyclic ring containing complex C3 showing the highest activity

Enhancing Cubosome Functionality by Coating with a Single Layer of Poly-epsilon-lysine

We report the preparation and characterization of monoolein cubosomes that can be easily surface modified through adsorption of a single layer of cationic poly-epsilon-lysine. Poly-epsilon-lysine coated cubosomes show remarkable stability in serum solution, are nontoxic and, are readily internalized by HeLa cells. The poly-epsilon-lysine coating provides chemical handles for further bioconjugation of the cubosome surface. We also demonstrate that the initial release rate of a hydrophilic drug, Naproxen sodium, from the cubosomes is retarded with just a single layer of polymer. Interestingly, cubosomes loaded with Naproxen sodium, recently shown to have anticancer properties, cause more apoptosis in HeLa cells when compared to free unencapsulated drug

Redox Decomposition of Silver Citrate Complex in Nanoscale Confinement: An Unusual Mechanism of Formation and Growth of Silver Nanoparticles

We demonstrate for the first time the intrinsic role of nanoconfinement in facilitating the chemical reduction of metal ion precursors with a suitable reductant for the synthesis of metal nanoparticles, when the identical reaction does not occur in bulk solution. Taking the case of citrate reduction of silver ions under the unusual condition of [citrate]/[Ag+] >> 1, it has been observed that the silver citrate complex, stable in bulk solution, decomposes readily in confined nanodomains of charged and neutral matrices (ion-exchange film and porous polystyrene beads), leading to the formation of silver nanoparticles. The evolution of growth of silver nanoparticles in the ion-exchange films has been studied using a combination of Ag-110m radiotracer, small-angle X-ray scattering (SAXS) experiments, and transmission electron microscopy (TEM). It has been observed that the nanoconfined redox decomposition of silver citrate complex is responsible for the formation of Ag seeds, which thereafter catalyze oxidation of citrate and act as electron sink for subsequent reduction of silver ions. Because of these parallel processes, the particle sizes are in the bimodal distribution at some stages of the reaction. A continuous seeding with parallel growth mechanism has been revealed. Based on the SAXS data and radiotracer kinetics, the growth mechanism has been elucidated as a combination of continuous autoreduction of silver ions on the nanoparticle surfaces and a sudden coalescence of nanoparticles at a critical number density. However, for a fixed period of reduction, the size, size distribution, and number density of thus-formed Ag nanoparticles have been found to be dependent on physical architecture and chemical composition of the matrix

Nafion membrane incorporated with silver nanoparticles as optical test strip for dissolved hydrogen peroxide: Preparation, deployment and the mechanism of action

We report the preparation of an optical test strip for quantitative assay of hydrogen peroxide (H2O2) in aqueous solution. Silver nanoparticles(AgNPs) with good optical quality are synthesized by in-situ reduction of silver ions in Nafion-117 membrane previously absorbed with ascorbate ion (HA(-)). The nanocomposite membrane exhibits a narrow Localized Surface Plasmon Resonance (LSPR) band at 413 nm. The extent of decrease in intensity of the LSPR band in presence of H2O2 solution gives quantitative estimate of H2O2 concentration. The detector has been found to show a good analytical response towards H2O2 detection at pH 7 over a wide concentration range. The detection limit has been calculated to be 2.6 x 10(-8) mol L-1, which is lower than the conventional enzyme based biosensors. The present test strip has been succesfully employed for the quantitative assay of H2O2 in milk. The mechanism of change in LSPR in presence of H2O2 (1.0 x 10(-3) mol L-1) has been explored for the first time using time resolved Small-Angle X-ray Scattering and radiotracer techniques. The results show that at this concentration of H2O2, its sharp oxidative sawing action is responsible for cutting off the nanoparticles into smaller fragments resulting in rapid reduction of absorption crossection. (C) 2017 Elsevier B.V. All rights reserved