Influence of ion implantation on titanium surfaces for medical applications

The implantation of ions into the near surface layer is a new approach to improve the osseointegration of metallic biomaterials like titanium. Meanwhile it is well known that surface topography and surface physico-chemistry as well as visco-elastic properties influence the cell response after implantation of implants into the human body. To optimize the cell response of titanium, ion implantation techniques have been used to integrate calcium and phosphorus, both elements present in the inorganic bone phase. In this context, the concentration profile of the detected elements and their chemical state have been investigated using X-ray photoelectron spectroscopy and Auger electron spectroscopy depth profiling. Ion implantation leads to strong changes of the chemical composition of the near surface region, which are expected to modify the biofunctionality as observed in previous experiments on the cell response. The co-implantation of calcium and phosphorus samples, which showed best results in the performed tests (biological and physical), leads to a strong modification of the chemical surface composition.     

Impact of multiple re-use of anion-exchange chromatography media on virus removal

We evaluated viral clearance in multiply-cycled anion-exchange media run in flow-through mode. We found that anion-exchange columns do not lose viral clearance capacity after extensive re-use, if they are cleaned with recommended buffers that do not chemically degrade the media. In contrast, anion-exchange (AEX) columns that are not cleaned or are cleaned with buffers that chemically degrade the media lost viral clearance capacity after extended use. In these cases, other performance attributes that changed at the same time were increased band spreading, decreased DNA clearance and accumulating backpressure that prevented re-use past 80-120 cycles. Thus, our data suggests that flow through mode anion-exchange columns that are cleaned with recommended cleaning buffers, and periodically monitored for band spreading, DNA clearance and/or backpressure need not be re-evaluated for viral clearance at the end of the validated media lifetime.     

Measuring the change in the intermolecular Raman spectrum during dipolar solvation

We demonstrate a method to directly measure the change in the spectrum of intermolecular solvent fluctuations as a function of time after electronic excitation of a solute, and this method is applied to the dye Coumarin 102 (C102) in acetonitrile. The complete intermolecular response is captured following resonant excitation with time domain third-order Raman spectroscopy. In a previous report, we introduced this method and used it to probe one point in the intermolecular response as a function of time after solute excitation (Underwood, D. F., Blank, D. A. J. Phys. Chem. A 2003, 107 (7), 956). Here we extend this approach to recover the change in the entire intermolecular response as a function of time. To our knowledge the results provide the first direct measurement of the difference in the equilibrated intermolecular response after excitation of a solute and its evolution during a dipolar solvation event. Excitation of C102 results in a significant increase in the solvent-solute interaction due to a large increase in the dipole moment. The observed change in the intermolecular response is consistent with a rapid change in local solvent density, with intermolecular kinetic energy transfer changing the response on longer time scales. Evolution of the response exhibits a strong frequency dependence and suggests changes over longer distances at longer delay times. The measured change in the spectrum of solvent fluctuations represents a direct experimental confirmation of the breakdown of linear response and confirms predictions from molecular dynamics simulations.     

Study of light proton-rich nuclei by complete kinematics measurements

Light proton-rich bound and unbound nuclei were produced by means of stripping reactions of secondary beams of ²⁰Mg and ¹⁸Ne. The decays of the unbound nuclei ^18,19Na have been measured by detecting their decay products ^17,18Ne and one proton and by performing an invariant-mass reconstruction. For ¹⁸Na, the present work is the first measurement of its decay. As the decay scheme of this nucleus could not be determined, two possible scenarios are proposed and discussed. In addition, the decay of excited states in ¹⁷Ne via two-proton emission was observed. The proton-proton angular distribution is isotropic for the first two-proton-emitting states, whereas higher-lying states seem to decay by a correlated two-proton emission, consistent with a ²He emission pattern for part of the decay strength.Received: 30 September 2003, Revised: 27 November 2003, Published online: 2 June 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 23.40.-s decay; double decay; electron and muon capture - 23.50. + z Decay by proton emissionM. Chartier: Present address: Physics Department, University of Liverpool, Liverpool, UK.M. Fallot: Present address: SUBATECH, Ecole des Mines, BP 20722, F-44307 Nantes Cedex, France.A. Shrivastava: Permanent address: Bhabha Atomic Research Center, Mumbai, India.Experiment performed at the GANIL facility, Caen, France.     

Convergence of Rothe's method for fully nonlinear parabolic equations

Convergence of Rothe's method for the fully nonlinear parabolic equation u_t+F(D²u, Du, u, x, t)=0 is considered under some continuity assumptions on F. We show that the Rothe solutions are Lipschitz in time, Hölder in space, and they solve the equation in the viscosity sense. As an immediate corollary we get Lipschitz behavior in time of the viscosity solutions of our equation.     

pi bonding in second and third row molecules: testing the strength of Linus's blanket

The flexibility of valence bond (VB) theory provides a new method of calculating pi-bond energies in the double-bonded species H(m)A=BH(n), where A, B = C, N, O, Si, P, S. This new method circumvents the problems usually associated with obtaining pi-bond strengths by targeting only the pi bond, while all other factors remain constant. In this manner, a clean separation between sigma- and pi effects can be achieved which highlights some expected trends in bond strength upon moving from left to right and up and down the Periodic Table. Intra-row pi bonds conform to the classic statement by Pauling [L. Pauling, The Natiure of the Chemical Bond, Cornell University Press, Ithaca, 1960, 3rd edition] regarding the relationship of heteronuclear bond strengths to their homonuclear constituents whereas inter-row pi bonds do not. This variance with Pauling's statement is shown to be due to the constraining effect of the underlying sigma bonds which prevents optimal p(pi)-p(pi) overlap. While Pauling's statement was based on the assumption that the resonance energy (RE) would be large for heteronuclear and small for homonuclear bonds, we have found large REs for all bonds studied herein; this leads to the conclusion that REs are dependent not only on the electronegativity difference but also the electronegativity sum of the constituent atoms. This situation where the bond is neither covalent nor ionic but originates in the covalent-ionic mixing has been termed charge shift (CS) bonding [S. Shaik, P. Maitre, G. Sini, P. C. Hiberty, J. Am. Chem. Soc. 1992, 114, 7861]. We have shown that CS bonding extends beyond single sigma bonds in first row molecules, thus supporting the idea that CS-bonding is a ubiquitous bonding form.     

Discovery of doubly magic 48Ni

In an experiment at the SISSI/LISE3 facility of GANIL, we used the projectile fragmentation of a primary 58Ni26+ beam at 74.5 MeV/nucleon with an average current of 3 &mgr;A on a natural nickel target to produce very neutron-deficient isotopes. In a 10-day experiment, 287 42Cr isotopes, 53 45Fe isotopes, 106 49Ni isotopes, and 4 48Ni isotopes were unambiguously identified. The doubly magic nucleus 48Ni, observed for the first time, is the most proton-rich isotope ever identified with an isospin projection T(z) = -4. It is probably the last doubly magic nucleus with "classical" shell closures accessible for present-day facilities. Its observation allows us to deduce a lower limit for the half-life of 48Ni of 0.5 &mgr;s.     

One-neutron knockout from individual single-particle states of 11Be

The structure of the halo nucleus 11Be has been studied using the reaction 9Be(11Be,10Be+gamma)X at 60 MeV/nucleon. The ground state structure of 11Be is determined by comparing the experimental cross sections to a calculation combining spectroscopic factors from the shell model with l-dependent single-particle cross sections obtained in an eikonal model. This experiment shows the dominant 1s single-particle character of the 11Be ground state and indicates a small contribution of 0d admixture in the wave function. After correction for the approximately 22% intensity to excited levels, a clean and precise distribution of parallel momentum for knockout from the 1s halo wave function is obtained for the first time.     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.