Raman and fluorescence investigations on retrieved Biolox® delta femoral heads

Since the introduction of ceramic‐on‐ceramic couplings in total hip arthroplasty, continuous efforts have been performed to improve the performance of the prosthetic components. To expand the applications of ceramics, in 2000 an innovative alumina–zirconia composite was introduced in the market. The present study represents the first investigation aimed at characterising at the molecular level Biolox® delta retrievals implanted between 1999 and 2009. Fluorescence and Raman results showed that a progressive improvement of the material properties has occurred in the period between 1999 and 2009. Raman spectroscopy showed that wear was the main cause of the in vivo tetragonal‐to‐monoclinic zirconia transformation. Our findings validated the in vitro accelerated ageing protocols proposed in the literature to simulate the effects of the in vivo wear, because the mechanism operating in vivo was found to be the same active in vitro. The in vitro fracture of a new femoral head appeared to be an extreme wear condition that determined the most significant changes in the residual stress state and monoclinic content both in the section of the fragments and on their surface. The micro‐Raman mapping of the fractured articulating surface showed that the tetragonal‐to‐monoclinic transformation involved a region much more extended than as reported in the literature. Copyright © 2012 John Wiley & Sons, Ltd.     

Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient β on the excited state ( 2³ P ₂) and metastable state ( 2³ S ₁) populations is also investigated. From these results we infer a rather uniform rate constant K _sp = (1±0.4)×10^-7 cm³/s. Received 8 September 2000 and Received in final form 19 December 2000     

Evolution of Classical and Quantum States in the Groupoid Picture of Quantum Mechanics

The evolution of states of the composition of classical and quantum systems in the groupoid formalism for physical theories introduced recently is discussed. It is shown that the notion of a classical system, in the sense of Birkhoff and von Neumann, is equivalent, in the case of systems with a countable number of outputs, to a totally disconnected groupoid with Abelian von Neumann algebra. The impossibility of evolving a separable state of a composite system made up of a classical and a quantum one into an entangled state by means of a unitary evolution is proven in accordance with Raggio’s theorem, which is extended to include a new family of separable states corresponding to the composition of a system with a totally disconnected space of outcomes and a quantum one.     

用于BNCT-SPECT的帕维亚TRIGA MARK II反应堆热柱优化设计

针对坐落于意大利帕维亚大学的TRIGA Mark II反应堆热柱结构进行优化设计,从而满足面向硼中子俘获治疗(BNCT)的单光子发射计算机断层成像(SPECT)研究要求。为提高计算效率并减小统计误差,对比分析使用SSW/SSR方法与直接使用反应堆为源项时热柱内照射位置处中子能谱,其结果基本一致,从而验证了SSW/SSR方法的可靠性。为在该反应堆开展BNCT中SPECT实验,热柱中子束需准直为笔形束。对比分析四种热柱优化方案下束流口处及探测器处热中子和光子通量：40 cm长石墨(射束口5 cm3 cm);0.5 cm厚硼包裹40 cm长石墨(射束口5 cm3 cm);30 cm长天然锂聚乙烯(射束口直径4 cm);30 cm长天然锂聚乙烯(20 cm长射束口直径5 cm,5 cm长射束口直径4 cm,5 cm长射束口直径2 cm)。结果显示,射束口处热中子通量分别为1.05108,2.52107,6.08107和5.10 107 #/(cm2s)。综合考虑中子准直效果及光子污染,方案三具有最优性能。为后续进行BNCT-SPECT理论和实验研究提供了基础,从而有效促进BNCT剂量准确评估方法的研究进程。     

Derivation of a new class of distributions for the microcanonical ensemble

A new class of distributions for the microcanonical ensemble, which are shown to be stable laws, are derived by applying the central limit theorem to the canonical ensemble. This opens up a whole new host of phenomena that can be treated from a unified thermodynamic point of view. Pressure broadening of line shapes is used as an illustration.1. Work supported, in part, by contributions from the Consiglio Nazionale di Ricerche and the Ministero dell'Università e della Ricerca Scientifica e Tecnologica.2. The interaction parameterC is proportional to the mean square dipole moment. As an order of magnitude of the dipole moment, we can take it as the product of the electric charge and a typical atomic radius for a moderately excited state, which is several times the Bohr radius. Multiplication by the fine structure constant converts the Bohr radius into the Compton wavelength, thereby reducing the magnitude of the interaction by 1/137.     

Exsolution of Nickel Nanoparticles from Mixed-Valence Metal Oxides: A Quantitative Evaluation by Magnetic Measurements

A fast and accurate experimental method is demonstrated to assess the fraction of exsolved metallic nanoparticles using magnetic measurements. As a benchmark, nanometric metallic nickel exsolved from (La_1−xSr_x)(Cr_1−yNi_y)O_3−δ is used for its high relevance as a solid oxide fuel cell component. The method is based on the difference in the magnetic response of the exsolved metallic nickel (ferromagnetic) and Sr-doped lanthanum chromite ceramic matrix (paramagnetic). The exsolved nickel results in coherent nanoparticles pinned on the surface of the Sr-doped lanthanum chromite ceramic matrix, as evidenced by electron microscopy analyses. The results obtained indicate the procedure as a fast and sensitive method to study the exsolution of ferromagnetic nanoparticles.     

Impedance spectroscopy study of the sintering of yttria-stabilized zirconia/magnesia composites

In the present study, the sintering of (ZrO₂:8 mol%Y₂O₃)_1 ? m–(MgO)_m, YSZ–mMg composites, with m in the 0–30 mol% range, has been investigated by impedance spectroscopy (IS), dilatometry, and X-ray diffraction. Impedance diagrams were collected at 400 °C after heating the green compacts up to a selected sintering temperature, which was increased stepwise from 800 to 1400 °C. The combined experimental results revealed that the samples can be separated in two categories: below and above the solubility limit of MgO in the YSZ (m ~ 10). Moreover, important microstructural features associated with both the sintering process and solid solution formation of YSZ–mMgO samples were correlated to the electrical properties inferred by IS.