Mechanical improvement of hydroxyapatite by TiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles deposition

Deposition of Ti was carried out by laser ablation onto hydroxyapatite porous discs in an Ar atmosphere. Ti nanoparticles were deposited onto HAp surface in order to modify its roughness and morphology as it is observed by scanning electron microscopy (SEM) and scanning probe microscopy (SPM). A homogeneous distribution of Ti over the disc surface was corroborated by elemental mapping. A comparison of the hydroxyapatite hardness before and after deposition was performed using SPM nanoindentation. Transmission Electron Microscopy (TEM) showed that the Ti nanoparticles obtained were covered by an oxygen shell. It is shown that surface modifications of the covered HAp by Ti result in better mechanical properties, reducing the possible damage to the HAp ceramic by friction or impacts as it often happens in meniscus, bone junctions and the inclusion of prosthesis for human treatments.     

Multiple Testing Correction in Medical Image Analysis

We present a novel method for correcting the significance level of hypothesis testing that requires multiple comparisons. It is based on the spectral graph theory, in which the variables are seen as the vertices of a complete undirected graph and the correlation matrix as the adjacency matrix that weights its edges. The method increases the statistical power of the analysis by refuting the assumption of independence among variables, while keeping the probability of false positives low. By computing the eigenvalues of the correlation matrix, it is possible to obtain valuable information about the dependence levels among the variables of the problem, so that the effective number of independent variables can be estimated. The method is compared to other available models and its effectiveness illustrated in case studies involving high-dimensional sets of variables.     

Scientific and technological performance evaluation of the Spanish Council for Scientific Research (CSIC) in the field of Biotechnology

An evaluation of the Spanish CSIC performance in Biotechnology, as compared with those of the French CNRS and the Italian CNR, has been carried out to determine the balance between the generation of scientific knowledge and the transfer of technology. This study shows a high scientific productivity mostly in journals with moderate impact factor, a low generation of patents and an insufficient transfer of knowledge to the Spanish companies. Other indicators confirm the existence of competitive human resources in biotechnological research producing scientific knowledge of interest for the development of patents and that cooperates successfully at European level.     

Metric analysis of the information visibility and diffusion about the European Higher Education Area on Spanish University websites

The purpose of the study proposed in this paper is to evaluate the Spanish public university websites dedicated to the European Higher Education Area (EHEA). To do so, the quality of these resources has been analysed in the light of data provided by a series of indicators grouped in seven criteria, most of which were used to determine what information is made available and in what way. The criteria used in our analysis are: visibility, authority, updatedness, accesibility, correctness and completeness, quality assessment and navigability. All in all, the results allow us to carry out an overall diagnosis of the situation and also provide us with information about the situation at each university, thus revealing their main strengths, namely authority and navegability, and also their chief shortcomings: updatedness, accessibility and quality assessment. In this way it is possible to detect the best practices in each of the aspects evaluated so that they can serve as an example and guide for universities with greater deficiencies and thus help them to improve their EHEA websites.     

Effect of Crude Oil Composition and Blending on Flowing Properties

The effect of crude oil n-paraffin molecular weight distribution on wax crystallization risk was studied. Sixteen highly paraffinic crude oils from Eastern Venezuela were characterized, in terms of hydrocarbon family distribution, by High Temperature Simulate Distillation (HTSD), Gel Permeation Chromatography (GPC), and wax content. n-Paraffin chain length was correlated with crude oil cloud point and pour point. It was demonstrated that high molecular weight linear paraffins are responsible for crude oil wax precipitation. A quantitative correlation between molecular weight distribution and crude oil flowing properties was also obtained. It was found that the wider the molecular weight distribution, the lower is the wax crystallization risk. Blends of different paraffinic crude oils were prepared and their flowing properties were evaluated in comparison with the original crudes. Cloud points below the mean value were obtained. In some cases, a synergistic effect was observed (cloud points below the minimum of the two crude oils). Blends of some of these crudes with condensates afforded improvements on crude oil flow and a reduction of wax crystallization tendency (cloud point). This phenomenon can be attributed to a combination of two factors: I. increases in C24-n-paraffins, and II. a wider molecular weight distribution.     

Low temperature and strain rate dependence of fracture stress and fracture toughness on thin Fe40Ni40B20 amorphous ribbon

The fracture stress and the critical stress intensity factor of the Fe₄₀Ni₄₀B₂₀ amorphous metallic ribbons 20 μm thick were measured in the temperature range 4.2–300 K and at deformation rates from 3.3×10⁻⁶ to 1.25×10⁻³ m⁻¹ with the aim to obtain more information on the condition for the onset and development of the inhomogeneous plastic deformation and fracture.     

Efficient and accurate approach for powder compaction problems

 In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour; the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian (ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present spurious oscillations. Received: 20 March 2002 / Accepted: 15 October 2002 The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged.