Uncertainty analysis for rolling contact fatigue failure probability of silicon nitride ball bearings

Uncertainty analysis and parametric studies are presented for estimating the fatigue failure probability of surface cracks in silicon nitride ball bearings subjected to rolling contact fatigue. Uncertainty quantification of input parameters are presented first based on experimental data, inspection capability, and geometric reasoning. Surrogate models for equivalent stress intensity factors are then used for uncertainty propagation, which are built upon high fidelity finite element modeling with half-penny-shaped surface cracks. Instead of black-box type surrogate modeling, physical observations are employed to decompose the high dimensional surrogate model into multiple one-dimensional models. The cross-validation technique is used to find the best surrogate that has the smallest prediction variance. The probability of failure is estimated using Monte Carlo simulation and surrogate models. The parametric studies show that reducing the maximum crack size (by limiting inspection threshold) and increasing the fatigue threshold (by improving fracture toughness of a material) are the most effective ways of reducing the probability of failure. For example, decreasing the maximum crack size by 4.4% and increasing the lowest fracture threshold by 2.8% results in the reduction of probability of failure by 40%. Ball survivability increases with decreasing ball diameter, for a given peak Hertzian stress. In order to apply the current study to hybrid ball bearing design, the survivability results are generalized through non-dimensionalization.     

The Relative UV Sensitizer Activity of Purified Advanced Glycation Endproducts

Abstract— The oxidation products of ascorbic acid react with lens proteins to form advanced glycation endproducts (AGE) that are capable of generating reactive oxygen species when irradiated with UVA light. L-Threose, the most active of these oxidation products, was reacted with N -acetyl lysine and six AGE peaks were isolated by RP-HPLC. Each peak exhibited fluorescence and generated superoxide anion and singlet oxygen in response to UV light. Solutions of these AGE peaks (50 μg/mL) generated5–10 nmol/mL of superoxide anion during a 30 min irradiation. This activity was 100-fold less than the superoxide anion generated by kynurenic acid and 400-fold less than riboflavin.
Ultraviolet irradiation generated from 1.2 to 2.7 μmol/mL of singlet oxygen with the purified threose AGE compounds. This activity was similar to that seen with other purified AGE compounds (pentosidine, LM-1 and Ac-FTP) and with kynurenine and 3-OH kynurenine. This considerable singlet oxygen formation, however, was still 40-fold less than that obtained with kynurenic acid and 100-fold less than riboflavin under the same irradiation conditions. In spite of this lower sensitizer efficiency, the purified AGE generated20–60-fold more singlet oxygen on a weight basis than either crude ascorbic acid glycated proteins or a preparation of water-insoluble proteins from aged normal human lenses. On a molar basis, therefore, AGE could account for the sensitizer activity in these protein preparations if they represented less than 1% of the total amino acids.     

Mass spectra of t-butyloxycarbonyl (BOC)-protected peptides

Analytically useful mass spectra of t-butyloxycarbonyl protected tetra- and pentapeptides can be obtained under chemical ionization conditions at a source temperature of 250-270 °C without the use of a reagent gas. The mass spectrum of die thermally labile amino acid arginine could also be recorded under the same conditions.     

Solution phase synthesis of alamethicin I

The total synthesis of alamethicin I by solution phase methods is reported.     

Synthesis and biological study of novel methylene‐bis‐chalcones and substituted methylene‐bis‐pyrimidines/pyrimidinones

A series of novel methylene‐bis‐chalcones was prepared by the reaction of 5,5′‐methylene‐bis‐salicylaldehyde with different acetophenones, subsequent treatment of methylene‐bis‐chalcones with urea/thiourea gave the corresponding methylene‐bis‐pyrimidinones/methylene‐bis‐mercaptopyrimidines in good yields. Characterization of the new compounds has been done by means of IR, ¹H NMR, MS and elemental analysis. The antibacterial, antitubercular and antifungal activity of the compounds has also been evaluated.     

Diphenic acid as a general conformational lock in the design of bihelical structures

The bihelical (figure of "infinity") topology was examined from vantages of design, crystal structures, chirality, circular dichroism (CD) studies and molecular-orbital calculations. The minimalistic design envisaged the sequential linking of cystine to the anchor diphenic acid, which proved to be a general conformational lock. The bihelical compound 4 was obtained in two steps from diphenic anhydride 1 and cystine di-OMe. The chirality of 4 arises largely from the L-cystine. The bihelical compound 5 obtained from D-cystine di-OMe was found, by X-ray crystallography, CD studies, and optical rotation, to be the perfect mirror image of 4 prepared from L-cystine. The crystal structure of prototype 8, prepared by protocols used for 4 from the achiral cystine analogue cystamine, had a "U"-shaped conformation held together by intramolecular hydrogen bonds. Analysis of 4 and 5 show that the pairs of nine-membered beta-turn-like constructs made compact through hydrogen bonding with DMSO hold the key for the bihelical conformation. Another factor is the need for the presence of a ligand at the Calpha position. The absence of this, as in 8, allows major flexibility in the torsional angles around this critical region, promoting flexible alternatives. The CD analysis of 4, confirmed to be bihelical by X-ray crystallography, showed a typical negative band at about 210 A attributed to the beta-turn-like motif, and in the positive-band region a peak at about 227 A, generally related to the twist of the biphenyl unit. The cystamine analogue 8, which showed a "U"-type structure, presented a CD spectrum with no typical features. The total energy, derived from theoretical calculations by using the X-ray structure data, support the bihelical structure for 4 and a "U"-shaped one for 8. The limited utility of such calculations was tested with composite 9. Composite 9, in which the anchor diphenic acid is linked to cystamine on the one hand and to cystine on the other, showed a CD spectrum similar to that of 4, and this coupled with molecular-orbital calculations, using data from 4 and 8, predict a bihelical structure for this compound.     

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarising optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system. On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single-handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 μm to 15 μm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/μm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.     

Synthesis and electron transfer kinetics of a surfactant–cobalt(III) complex: effects of micelles, β-cyclodextrin, and ionic liquids

A surfactant–cobalt(III) complex, cis-[Co(en)₂(4AMP)(DA)](ClO₄)₃, (en = ethylenediamine, 4AMP = 4-aminopyridine, DA = dodecylamine), was synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) value of this surfactant–cobalt(III) complex in aqueous solution was obtained from conductance measurements. Conductivity data were used for evaluation of the temperature-dependent CMC and the thermodynamics of micellization ( $ \Updelta {\text{G}}_{\text{m}}^{ 0} $ Δ G m 0 , $ \Updelta {\text{H}}_{\text{m}}^{0} $ Δ H m 0 , and $ \Updelta {\text{S}}_{\text{m}}^{0} $ Δ S m 0 ). The kinetics of reduction of this surfactant–cobalt(III) complex by ion(II) in micelles, β-cyclodextrin (β-CD), and ionic liquid (IL) were studied. The reaction was found to be second order, and the electron transfer is postulated as outer sphere. The second-order rate constant for the electron transfer reaction was found to increase with increasing concentration of IL, but inclusion of the long aliphatic chain of the surfactant complex into β-CD decreases the rate of the reaction. The results have been interpreted in terms of the amphiphilicity of the surfactant complex.     

Synthesis of some novel methylene‐bis‐pyrimidinyl‐spiro‐4‐thiazolidinones as biologically potent agents

A series of novel methylene‐bis‐pyrimidinyl‐spiro‐4‐thiazolidinones 6a‐h have been synthesized by cyclocondensation of thioglycolic acid with methylene‐bis‐(N‐cyclohexylidene‐N‐pyrimidine) 5a‐h , which in turn have been prepared by the reaction of cyclohexanone with methylene‐bis‐2‐aminopyrimidines 4a‐h , which are prepared by the reaction of guanidine hydrochloride with methylene‐bis‐chalcones 3a‐h . The compounds 3a‐h have been synthesized by the reaction of 5‐(3‐formyl‐4‐hydroxybenzyl)‐2‐hydroxybenzaldehyde 2 with various acetophenones in presence of KOH. The compound 2 is prepared by the reported method. The structures of the compounds synthesized have been confirmed by their elemental analysis and spectral data. Their antibacterial and antifungal activities have also been evaluated.