Transient localization in crystalline organic semiconductors

A relation derived from the Kubo formula shows that optical conductivity measurements below the gap frequency in doped semiconductors can be used to probe directly the time-dependent quantum dynamics of charge carriers. This allows to extract fundamental quantities such as the elastic and inelastic scattering rates, as well as the localization length in disordered systems. When applied to crystalline organic semiconductors, an incipient electron localization caused by large dynamical lattice disorder is unveiled, implying a breakdown of semiclassical transport.Comment: Revised version, to appear in Phys. Rev. B Rapid Communication

2D-3D registration of CT vertebra volume to fluoroscopy projection: A calibration model assessment (doi:10.1155/2010/806094)

This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1?mm for displacements parallel to the fluoroscopic plane, and of order of 10?mm for the orthogonal displacement.<br/

Analytical evaluation of atomic form factors: application to Rayleigh scattering

Atomic form factors are widely used for the characterization of targets and specimens, from crystallography to biology. By using recent mathematical results, here we derive an analytical expression for the atomic form factor within the independent particle model constructed from nonrelativistic screened hydrogenic wavefunctions. The range of validity of this analytical expression is checked by comparing the analytically obtained form factors with the ones obtained within the Hartee-Fock method. As an example, we apply our analytical expression for the atomic form factor to evaluate the differential cross section for Rayleigh scattering off neutral atoms.Comment: 7 pages, 1 figur

The impacts in real estate of landscape values: Evidence from Tuscany (Italy)

Using spatial econometric techniques and local spatial statistics, this study explores the relationships between the real estate values in Tuscany with the individual perception of satisfaction by landscape types. The analysis includes the usual territorial variables such as proximity to urban centres and roads. The landscape values are measured through a sample of respondents who expressed their aesthetic-visual perceptions of different types of land use. Results from a multivariate local Geary highlight that house prices are not spatial independent and that between the variables included in the analysis there is mainly a positive correlation. Specifically, the findings demonstrate a significant spatial dependence in real estate prices. The aesthetic values influence the real estate price throughout more a spatial indirect effect rather than the direct effect. Practically, house prices in specific areas are more influenced by aspects such as proximity to essential services. The results seem to show to live close to highly aesthetic environments not in these environments. The results relating to the distance from the main roads, however, seem counterintuitive. This result probably depends on the evidence that these areas suffer from greater traffic jam or pollution or they are preferred for alternative uses such as for locating industrial plants or big shopping centres rather than residential use. Therefore, these effects decrease house prices

Material Flow in FSW of T-joints: Experimental and Numerical Analysis

In the paper the authors present the results of both an experimental and a numerical campaign focused on the analysis of the occurring material flow in the FSW of T joints of aluminum alloys. In particular to investigate the metal flow experimental tests and observations has been developed utilizing a thin foil of copper as marker placed between the skin and the stringer. In this way, the actual metal flow occurring during the FSW of T-joints has been highlighted together with the real bonding surface. The acquired information is definitively useful in order to choose effective set of process parameters, improving the process mechanics and avoiding the insurgence of defects

Enhancement of Wigner crystallization in quasi low-dimensional solids

The crystallization of electrons in quasi low-dimensional solids is studied in a model which retains the full three-dimensional nature of the Coulomb interactions. We show that restricting the electron motion to layers (or chains) gives rise to a rich sequence of structural transitions upon varying the particle density. In addition, the concurrence of low-dimensional electron motion and isotropic Coulomb interactions leads to a sizeable stabilization of the Wigner crystal, which could be one of the mechanisms at the origin of the charge ordered phases frequently observed in such compounds

An insight into friction stir consolidation process mechanics through advanced numerical model development

Friction stir consolidation (FSC) is a solid-state process adopted to recycle machining scraps with aim to reduce the adverse impact of obtaining metals from their primary source. FSC was also applied to offer plausible new routes for alloying and upcycling from powder and scrap metal and thus drew the attention of many researchers. During FSC process, a rotating tool with a certain force is applied to a given chips batch enclosed in a die chamber turning it into a consolidated billet. It is assumed that favorable process conditions for chips bonding are acquired by the combined effect of friction, stirring action, and pressure of the tool. However, the real process is quite complex, and it can be understood only by developing proper solid bonding criteria through numerical modeling that can forecast the consolidation process. Therefore, in this research, an attempt was made to implement different existing bonding criteria. Some of these were good enough to predict favorable conditions for sound bonding of particular case studies, however a uniform criteria with a single threshold value that is applicable to all case studies could not be achieved. Therefore, this study suggests for a new approach to accurately predict the bonding integrity of the FSC process

Fabrication of Billet from Aluminum Alloys AA 2011-T3/7075 Chips through Friction Stir Consolidation

Recently evolving Solid-State Recycling (SSR) techniques have shown promising features to recycle metals scraps more efficiently compared to remelting-based approaches. Among these SSR methods, Friction Stir Consolidation (FSC) has been successfully tested to transform metals chips directly into semi or final solid products. Therefore, researchers explored FSC critical process parameters and their subsequent effects on quality in terms of the mechanical and metallurgical properties of the billet. All the previous studies of FSC were limited to developing billet of mono materials. Therefore, in this research, an attempt was made to go beyond the idea of recycling; in fact, a billet of two dissimilar aluminum alloys AA 7075 and AA 2011-T3 out of chips was obtained. The mechanical and metallurgical properties were assessed through the Vickers hardness measurements and microstructure analysis. The experimental results of this research illustrate that the FSC process is a feasible approach to develop a billet of dissimilar materials with achieving quality closer to the corresponding billet of mono-material

Understanding formability and geometrical accuracy of SPIF process used as reshaping approach

Putting in place Circular Economy strategies is an urgent action to be undertaken. Manufacturing processes play a relevant role as efficient material reuse enabler. Scientists have to make an effort either to find new process or to rethink old process to reprocess End-of-life (EoL) components to recover both material and functions. In this paper, Single Point Incremental Forming (SPIF) process is used for reshaping sheet metal EoL components. Deep drawing process as well as uniaxial pre-straining (to imitate the End-of-Life component) followed by SPIF operations (to obtain the reshaped components) are set- up and implemented to form and reform aluminum sheet metal components. As the authors have already proved the technical feasibility of such an approach, the present paper aims at a better understanding of the formability and geometrical accuracy performance of SPIF process as used to reform components. Specifically, an experimental campaign varying kind and extent of restraining is developed and the formability and geometrical accuracy of the subsequent SIPF operations is analyzed. Results proves that SPIF process is a promising approach for reshaping purpose