Performance of hydrodynamic journal bearing under the combined influence of textured surface and journal misalignment: A numerical survey

A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to $0\mathrm{°}$ or $180\mathrm{°}$.     

Theoretical and vibrational spectroscopic analysis of the CO stretching mode of cholesteryl alkanoates: the particular case of the cholesteryl acetate

Structural and vibrational properties of the CO stretching bond of cholesteryl acetate and related steroids are investigated theoretically and by Micro-Raman spectroscopy. In this work, an analysis of the CO stretching mode for the cholesteryl acetate is presented. Experimental results in crystalline, isotropic liquid and liquid crystal phases are compared with quantum chemical calculations using semi empirical hamiltonians (AM1 and PM3) and the density functional theory. The calculations were performed on isolated molecules with different conformations as found on previous investigations giving strong evidence of their existence. Calculated frequencies are found to be very close to experiments and suggest the possible existence of the predicted conformers.     

New figuring model based on surface slope profile for grazing‐incidence reflective optics

Surface slope profile is widely used in the metrology of grazing‐incidence reflective optics instead of surface height profile. Nevertheless, the theoretical and experimental model currently used in deterministic optical figuring processes is based on surface height, not on surface slope. This means that the raw slope profile data from metrology need to be converted to height profile to perform the current height‐based figuring processes. The inevitable measurement noise in the raw slope data will introduce significant cumulative error in the resultant height profiles. As a consequence, this conversion will degrade the determinism of the figuring processes, and will have an impact on the ultimate surface figuring results. To overcome this problem, an innovative figuring model is proposed, which directly uses the raw slope profile data instead of the usual height data as input for the deterministic process. In this paper, first the influence of the measurement noise on the resultant height profile is analyzed, and then a new model is presented; finally a demonstration experiment is carried out using a one‐dimensional ion beam figuring process to demonstrate the validity of our approach.     

Automatic alignment of a Kirkpatrick-Baez active optic by use of a soft-x-ray Hartmann wavefront sensor

We present what we believe to be the first automatic alignment of a synchrotron beamline by the Hartmann technique. Experiments were performed, in the soft-x-ray range (E=3 keV, lambda=0.414 nm), by using a four-actuator Kirkpatrick-Baez (KB) active optic. A system imaging the KB focal spot and a soft-x-ray Hartmann wavefront sensor were used alternatively to control the KB optic. The beam corrected with the help of the imaging system was used to calibrate the wavefront sensor. With both closed loops, we focused the beam into a 6.8 microm x 9 microm FWHM focal spot.     

A damage identification technique for beam-like and truss structures based on FRF and Bat Algorithm

In this paper, a Structural Health Monitoring (SHM) technique for damage identification in beam-like and truss structures using Frequency Response Function (FRF) data coupled with optimization techniques is presented. Genetic Algorithm (GA) and Bat Algorithm (BA) are used to estimate the location and severity of damage. The damage in the structures is simulated by reduction in rigidity of specific members. Both optimization techniques are coupled with modelled structures using Finite Element Method (FEM). The approach is based on minimizing an objective function by comparing measured and calculated FRFs. The results show that better accuracy is obtained using BA than using GA in terms of precision and computational time. Furthermore, it is found that the proposed approach provides faster solution than other approaches in the literature.     

The Human Melanocyte as a Particular Target for UVA Radiation and an Endpoint for Photoprotection Assessment

The induction of DNA breaks by UVA (320-400 nm) in the nucleus of normal human melanocytes in culture was investigated using single cell gel electrophoresis, also called the comet assay. Endogenous pigment and/or melanin-related molecules were found to enhance DNA breakage: comets were more intense in melanocytes than in fibroblasts, in cells with high melanin content or after stimulation of melanogenesis by supplying tyrosine in the culture medium. After UVA doses where strong comets were observed, neither cytotoxicity nor stimulation of tyrosinase activity were detected. However, the accumulation of p53 protein suggested that cells reacted to genotoxic stress under these experimental conditions. The same approach was used to compare two sunscreens with identical sun protection factors but different UVA protection factors. The results presented in this paper suggest that human melanocytes may be used as a target cell to evidence broadspectrum photoprotection. Moreover, these data appear to be helpful in getting a better understanding of the role of sunlight in the initiating steps of melanocyte transformation.     

Polyvinylpyrrolidone Behavior in Water/Ethanol Mixed Solvents: Comparison of Modeling Predictions with Experimental Results

The objective of this work is to study the behavior of a neutral polymer, polyvinylpyrrolidone (PVP), in a mixture of water and ethanol. A comparison of the experimental results with a theoretical model of effective solvent interaction with polymer (ESIP) was made. To do so, dynamic light scattering experiments were used to measure the hydrodynamic radius of PVP (M _w = 3.6 × 10⁵ g·mol^?1) as a function of the ethanol fraction, x _A, in the medium at 25 °C. We show that the polymer adopts an ideal chain–globule–coil conformation transition as the ethanol molar fraction varies. This transition is attributed to the change of the solvent quality which results from water and ethanol complex formation. On the other hand, the ternary PVP/water/ethanol system was described by the ESIP model. From the polymer–effective solvent interaction, the second virial coefficient of the polymer/effective solvent and the preferential adsorption parameter were calculated. The obtained results are in agreement with the reported experiments.     

Passivation of TiO2 by ultra-thin Al-oxide

The passivation of sol–gel TiO₂ by ultra-thin layers of Al-oxide has been investigated using transient and spectral photovoltage (PV) techniques. The ultra-thin layers of Al-oxide were prepared by the ion-layer gas reaction (ILGAR) technique and modified by thermal treatments in air, vacuum or Ar/H₂S atmosphere. The samples where characterized by elastic recoil detection analysis (ERDA), X-ray photoelectron spectroscopy (XPS), and contact potential difference (CPD) technique. Without an Al-oxide surface layer, electronic states in the forbidden gap of TiO₂ are formed during thermal treatments in vacuum and Ar/H₂S. The trap density is strongly reduced at the TiO₂/Al-oxide interface. The formation of electronic defects is prevented by a closed ultra-thin layer of Al-oxide.     

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.     

Hartmann wave-front measurement at 13.4 nm with lambdaEUV/120 accuracy

We report, for the first time to our knowledge, experimental demonstration of wave-front analysis via the Hartmann technique in the extreme ultraviolet range. The reference wave front needed to calibrate the sensor was generated by spatially filtering a focused undulator beam with 1.7- and 0.6-microm-diameter pinholes. To fully characterize the sensor, accuracy and sensitivity measurements were performed. The incident beam's wavelength was varied from 7 to 25 nm. Measurements of accuracy better than lambdaEUV/120 (0.11 nm) were obtained at lambdaEUV = 13.4 nm. The aberrations introduced by an additional thin mirror, as well as wave front of the spatially unfiltered incident beam, were also measured.