Micro-abrasion-corrosion of cast CoCrMo-Effects of micron and sub-micron sized abrasives

The abrasion damage on retrieved CoCrMo based hip joints is reported to be influenced by the entrainment of micron and sub-micron sized debris/hard particles. This paper represents the first attempt to look into the effects of relatively soft abrasives with micron and sub-micron dimensions on the abrasion mechanisms and the abrasion-corrosion performance of the cast CoCrMo in simulated hip joint environments. A modified micro-abrasion tester incorporating a liquid tank and a three-electrode electrochemical cell was used. Al O (300 nm and 1 μm) and sub-micron sized BaSO abrasives were chosen as being comparable in the size and hardness to the wear particles found in vivo. Results show that the specific wear rates of cast CoCrMo are dependent on the abrasive particle size, hardness and volume concentration. Larger particle size, higher hardness and greater abrasive volume fractions gave greater wear rates. The wear-induced corrosion current generally increases with increasing wear rates, and the presence of proteins seems to suppress the wear-induced corrosion current especially when abrasive volume fractions were high. This study shows that the nature of abrasives and the test solutions are both important in determining the wear mechanisms and the abrasion-corrosion response of cast CoCrMo. These findings provide new and important insights into the in vivo wear mechanisms of CoCrMo. © 2009 Elsevier B.V. All rights reserved.

Coupled Effects of a Perturbation in a Complex Structure Observed with SDO/AIA, SDO/HMI and ROSA/HARDcam

We study properties of intensity fluctuations in NOAA Active Region 11250 observed on 13 July 2011 starting at UT 13:32. Included are data obtained in the EUV bands of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) as well as nearly simultaneous observations of the chromosphere made, at much higher spatial and temporal resolution, with the Rapid Oscillations in the Solar Atmosphere (ROSA) and Hydrogen-Alpha Rapid Dynamics camera (HARDcam) systems at the Dunn Solar Telescope. A complex structure seen in both the ROSA/HARDcam and SDO data sets comprises a system of loops extending outward from near the boundary of the leading sunspot umbra. It is visible in the ROSA Ca II K and HARDcam Hα images, as well as the SDO 304 Å, 171 Å and 193 Å channels, and it thus couples the chromosphere, transition region and corona. In the ground-based images the loop structure is 4.1 Mm long. Some 17.5 Mm, can be traced in the SDO/AIA data. The chromospheric emissions observed by ROSA and HARDcam appear to occupy the inner, and apparently cooler and lower, quarter of the loop. We compare the intensity fluctuations of two points within the structure. From alignment with SDO/HMI images we identify a point "A" near the loop structure, which sits directly above a bipolar magnetic feature in the photosphere. Point "B" is characteristic of locations within the loops that are visible in both the ROSA/HARDcam and the SDO/AIA data. The intensity traces for point A are quiet during the first part of the data string. At time ~ 19 min they suddenly begin a series of impulsive brightenings. In the 171 Å and 193 Å coronal lines the brightenings are localized impulses in time, but in the transition region line at 304 Å they are more extended in time. The intensity traces in the 304 Å line for point B shows a quasi-periodic signal that changes properties at about 19 min. The wavelet power spectra are characterized by two periodicities. A 6.7 min period extends from the beginning of the series until about 25 minutes, and another signal with period ~3 min starts at about 20 min. The 193 Å power spectrum has a characteristic period of 5 min, before the 20 min transition and a 2.5 min periodicity afterward. In the case of HARDcam Hα data a localized 4 min periodicity can be found until about 7 min, followed by a quiet regime. After ~20 min a 2.3 min periodicity appears. Interestingly a coronal loop visible in the 94 Å line that is centrally located in the AR, running from the leading umbra to the following polarity, at about time 20 min undergoes a strong brightening beginning at the same moment all along 15 Mm of its length. The fact that these different signals all experience a clear-cut change at time about 20 min suggests an underlying organizing mechanism. Given that point A has a direct connection to the photospheric magnetic bipole, we conjecture that the whole extended structure is connected in a complex manner to the underlying magnetic field. The periodicities in these features may favor the wave nature rather than upflows and interpretations will be discussed.

Predicting solvent effects on the structure of porous organic molecules

A computational approach for the prediction of the open, metastable, conformations of porous organic molecules in the presence of solvent is developed.

Reactions of atomic and molecular ions with acetone, 1,1,1- trifluoroacetone, and hexafluoroacetone: An investigation of the effects of molecular structure on the dynamics and kinetics of ion-molecule reactions

A selected ion flow tube study of the reactions of a series of gas-phase atomic cations (S⁺, Xe⁺, O⁺, Kr⁺, N⁺, Ar⁺ and Ne⁺) and molecular ions (SF _n⁺ (n = 1-5), CF_n⁺ (n = 1-3), CF₂Cl⁺, H₃O⁺, NO⁺, N ₂O⁺, CO₂⁺, CO⁺, and N₂⁺) spanning a large range of recombination energies (6.3-21.6 eV), with acetone, 1,1,1-trifluoroacetone, and hexafluoroacetone has been undertaken with the objective of exploring the nature of the reaction ion chemistry as the methyl groups in acetone are substituted for CF₃. The reaction rate coefficients and product ion branching ratios for all 66 reactions, measured at 298 K, are reported. The experimental reaction rate coefficients are compared to theoretically calculated collisional values. Several distinct reaction processes were observed among the large number of reactions studied, including charge transfer (non-dissociative and dissociative), abstraction, ion-molecule associations and, in the case of the reactions involving the reagent ion H₃O⁺, proton transfer. 

The Industrial Context of Occupational Mobility: Change in Structure

The neglect of a consideration of history has been a feature of mobility research. ‘History’ affects the results of analyses of social mobility by altering the occupational/industrial structure and by encouraging exchange mobility. Changes in industrial structure are rooted more directly in historical causes and can be seen as more fundamental than changes in occupational structure. Following a substantial review of the secondary literature on changes in industrial and occupational structure in Northern Ireland, loglinear analyses of intra- and intergenerational mobility tables for sociologically-derived cohort generations that incorporate occupational and industrial categories are presented. Structural and inheritance effects for industry are as significant as those for occupation. Given the well-established finding of ‘constant social fludity’ in mobility tables once structural effects are controlled, the inclusion of categorization by industry is necessary in order to reach an accurate understanding of occupational mobility and the role of historical change in mobility.

Structure and bioactivity of neuropeptide F from the human parasites Schistosoma mansoni and Schistosoma japonicum

The blood flukes Schistosoma mansoni and Schistosoma japonicum inflict immense suffering as agents of human schistosomiasis. Previous investigations have found the nervous systems of these worms contain abundant immunoreactivity to antisera targeting invertebrate neuropeptide Fs (NPFs) as well as structurally similar neuropeptides of the mammalian neuropeptide Y (NPY) family. Here, cDNAs encoding NPF in these worms were identified, and the mature neuropeptides from the two species differed by only a single amino acid. Both neuropeptides feature the characteristics common among NPFs; they are 36 amino acids long with a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide and Tyr residues at positions 10 and 17 from the carboxyl terminus. Synthetic S. mansoni NPF potently inhibits the forskolin-stimulated accumulation of cAMP in worm homogenates, with significant effects at 10(-11) M. This is the first demonstration of an endogenous inhibition of cAMP by an NPF, and because this is the predominant pathway associated with vertebrate NPY family peptides, it demonstrates a conservation of downstream signaling pathways used by NPFs and NPY peptides.

Bimetallic effects in the liquid phase hydrogenation of 2-butanone

A series of bimetallic Ru-containing monometallic and bimetallic catalysts were prepared and tested for their activity for the hydrogenation of 2-butanone to 2-butanol at 30 °C and 3 bar H2. RuPt bimetallic catalysts were the most active for the reaction, with a ratio of 5 wt% Ru:1 wt% Pt on activated carbon (AC) found to be optimum. The activity of this bimetallic catalyst was more than double that of the sum of the activities of the monometallic Ru and Pt catalysts, providing evidence of a “bimetallic” effect. Structural analysis of the bimetallic catalysts revealed that they consisted of clusters of particles of the order of 1–2 nm. Extended X-ray absorption fine structure analysis showed that there were two types of particle on the surface of the bimetallic RuPt catalyst, specifically monometallic Ru and bimetallic RuPt particles. For the bimetallic particles, it was possible to fit the data with a model in which a Ru core of 1.1 nm is enclosed by two Pt-rich layers, the outer layer containing only 13 at% Ru. Pretreatment of the monometallic and bimetallic catalysts in hydrogen had a significant effect on the activity. Both the bimetallic and monometallic Ru-based catalysts showed a trend of decreasing activity with increasing temperature of prereduction in hydrogen. This loss of activity was almost fully reversible by exposure of the catalysts to air after reduction. The changing activity with exposure to different gas phase environments could not be attributed to changes in particle size or surface composition. It is proposed that the introduction of hydrogen results in a gradual smoothing of the surface and loss of defect sites; this process being reversible on introduction of air. These defect sites are particularly important for the dissociative adsorption of hydrogen, potentially the rate-determining step in this reaction.

Theory of the near K-edge structure in electron energy loss spectroscopy

Arguments are given that lead to a formalism for calculating near K-edge structure in electron energy loss spectroscopy (EELS). This is essentially a one electron picture, while many body effects may be introduced at different levels, such as the local density approximation to density functional theory or the GW approximation to the electron self-energy. Calculations are made within the all electron LMTO scheme in crystals with complex atomic and electronic structures, and these are compared with experiment. (c) 2004 Elsevier B.V. All rights reserved.

Bandstructure approach to near edge structure

We review the current state of the art in EELS fingerprinting by computer simulation, focusing on the bandstructure approach to the problem. Currently calculations are made using a one electron theory, but we describe in principle the way to go beyond this to include final state effects. We include these effects within the one electron framework using the Slater transition state formula and assess the errors involved. Two examples are then given which illustrate the use of the one electron approximation within density functional theory. Our approach is to combine predicted atomic structure with predicted electronic structure to assist in fingerprinting of complex crystal structures.

Radiation damping effects on L-shell photoionization cross- sections of O-like Fe xix and N-like recombination rate coefficients for Fe xx

Photoionization cross-sections out of the fine-structure levels (2S(2)2p(4) P-3(2,0,1)) of the O-like Fe ion Fe XIX have been reinvestigated. Data for photoionization out of each of these finestructure levels have been obtained, where the calculations have been performed with and without the inclusion of radiation damping on the resonance structure in order to assess the importance of this process. Recombination rate coefficients are determined using the Milne relation, for the case of an electron recombining with N-like Fe ions (Fe XX) in the ground state to form O-like Fe (Fe XIX) existing in each of the fine- structure ground-state levels. Recombination rates are presented over a temperature range similar to 4.0 less than or equal to log T-e less than or equal to 7.0, of importance to the modelling of X-ray emission plasmas.

Solvation effects on equilibria: Triazoles and N-methyl piperidinol

We have performed calculations of the solvation effects on a number of equilibrium constants in water using a recently proposed hybrid quantum classical scheme in which the liquid environment is modelled using classical solvent molecules and the solute electronic structure is computed using modern quantum chemical methods. The liquid phase space is sampled from a fully classical simulation. We find that solvation effects on both triazole tautomeric equilibrium constants and piperidinol conformational equilibrium constants can be interpreted in terms of subtle differences in the local environment which can be seen in probability densities and radial distribution functions. Lower level calculations were performed for comparison and we conclude that the solvation thermodynamics can be predicted from a good classical model of solvent and solute molecules, but the implicit models that we tried are less successful.

On the structure and dynamics of ionic liquids

The structure and dynamics of the ionic liquid 1-ethyl-3-methylimidazolium nitrate is studied by molecular dynamics simulations. We find long-range spatial correlations between the ions and a three-dimensional local structure that reflects the asymmetry of the cations. The main contribution to the configurational energy comes from the electrostatic interactions which leads to charge-ordering effects. Radial screening and threedimensional distribution of charge are also analyzed. The motion of a single ion is studied via velocity and reorientational correlation functions. It is found that ions "rattle" in a long-lived cage, while the orientational structure relaxes on a time scale longer than 200 ps. As in a supercooled liquid, the mean square displacements reveal a subdiffusive dynamics. In addition, the presence of dynamic heterogeneities can be detected by analyzing the non-Gaussian behavior of the van Hove correlation function and the spatial arrangement of the most mobile ions. The short-time collective dynamics is also studied through the electric current time correlation function.

Simulation of the surface structure of butylmethylimidazolium ionic liquids

Molecular dynamics simulations of the liquid/vacuum surfaces of the room temperature ionic liquids [bmim][PF6], [bmim][BF4] and [bmim][Cl] have been carried out at various temperatures. The surfaces are structured with a top monolayer containing oriented cations and anions. The butyl side chains tend to face the vacuum and the methyl side chains the liquid. However, as the butyl chains are not densely packed, both anions and rings are visible from the vacuum phase. The effects of temperature and the anion on the degree of cation orientation is small, but the potential drop from the vacuum to the interior of the liquid is greater for liquids with smaller anions. We compare the simulation results with a range of experimental observations and suggest that neutron reflection from samples with protiated butyl groups would be a sensitive probe of the structure.

Self-cooling of a micro-mirror by radiation pressure

Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements, detection of gravitational waves and the study of the transition between classical and quantum behaviour of a mechanical system. Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror's oscillatory motion to the low-entropy cavity field. The crucial coupling between radiation and mechanical motion was made possible by producing free-standing micromirrors of low mass (m approximately 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q approximately 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback. We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.