Search results for "beam [positron]"

Measurement of gap between abutment and fixture in dental conical connection implants. A focused ion beam SEM observation

2020

Background The aim of the authors was to examine the abutment-fixture interface in Morse-type conical implants in order to verify gaps at this level using a new microscopical approach. Material and Methods In this in vitro study, 20 abutment-fixture complexes were prepared by sectioning (longitudinal and cross-sectional to the long axis) with a microtome and then with a focused ion beam (FIB). This is a micrometric machine tool that uses gallium ions to abrade circumscribed areas to dig deeper into the cuts obtained with the microtome in order to eliminate cut-induced artifacts. This is because the FIB abrasion is practically free from artifacts, which are normally generated by the action o…

Coronary artery anomalies: incidence, pathophysiology, clinical relevance and role of diagnostic imaging

2006

Conventional coronary angiography is the gold standard for the diagnosis of coronary artery anomalies. Coronary anomalies are relatively rare findings in patients undergoing conventional coronary angiography for suspected obstructive coronary artery disease. Recently, the increasing performance of diagnostic techniques, such as electron beam tomography (EBT), magnetic resonance (MR) and, more recently, multislice computed tomography (MSCT), has enabled their application to cardiac imaging. MSCT, in particular, has a prominent role in coronary imaging due to its spatial and temporal resolution and three-dimensional capabilities. We report the incidence and pathophysiology of coronary artery …

Mechanism of pulsed electron irradiation of the PLZT X/65/35 ceramics

2005

The comprehensive study of high-current pulsed electron irradiation effect on the structure and lattice dynamics as well as Atomic Force (AFM) and Laser Confocal Scanning microscope (LSCM) surface imaginaries of PLZT 8/65/35 ceramics have been performed. X-ray powder diffraction studies show the transformation of the cubic perovskite Pm-3m (Z = 1) into orthorhombic Pmmm (Z = 1) structure for the sample irradiated by one pulse (dose 6 × 1014 electrons/cm2) and into cubic Pm-3m with increased lattice volume and more ordered structure at irradiating by 10 and 100 pulses (dose 6 × 1015 and 6 × 1016 el/cm2). A consequence, the changes of number, intensity and phonon modes position occur in Raman…

Effect of Penetrating Irradiation on Polarization Reversal in PZT Thin Films

2006

Spatially non-uniform imprint behavior induced by X-ray synchrotron, electron, and neutron irradiation has been investigated in Pb(Zr,Ti)O3 thin films. The obtained effects have been explained as a result of acceleration of the bulk screening process induced by irradiation. It has been shown that the spatial distribution of the internal bias field is determined by the domain pattern existing during irradiation. The microstructural changes in the structural characteristics during fatigue cycling have been revealed by high resolution synchrotron X-ray diffraction experiments. Their correlation with the evolution of the switching characteristics has been revealed and discussed.

Broadband focused waves with compensated spatial dispersion: transverse versus axial balance.

2007

We determine the constraints an ABCD optical system must verify to achieve, at the focal region, broadband waves with compensated spatial dispersion either along the optical axis, called on-axis isodiffracting fields, or in the lateral direction, here named in-plane isodiffracting beams. An optical configuration is identified for generating both types of achromatic broadband focused wave fields. An experimental verification is also provided.

Optimization procedures for the bipartite unconstrained 0-1 quadratic programming problem

2014

The bipartite unconstrained 0-1 quadratic programming problem (BQP) is a difficult combinatorial problem defined on a complete graph that consists of selecting a subgraph that maximizes the sum of the weights associated with the chosen vertices and the edges that connect them. The problem has appeared under several different names in the literature, including maximum weight induced subgraph, maximum weight biclique, matrix factorization and maximum cut on bipartite graphs. There are only two unpublished works (technical reports) where heuristic approaches are tested on BQP instances. Our goal is to combine straightforward search elements to balance diversification and intensification in bot…

Measurement of the n-TOF beam profile with a micromegas detector

2004

A Micromegas detector was used in the neutron Time-Of-Flight (n_TOF) facility at CERN to evaluate the spatial distribution of the neutron beam as a function of its kinetic energy. This was achieved over a large range of neutron energies by using two complementary processes: at low energy by capture of a neutron via the 6Li(n,[alpha])t reaction, and at high energy by elastic scattering of neutrons on gas nuclei (argon+isobutane or helium+isobutane). Data are compared to Monte Carlo simulations and an analytic function fitting the beam profile has been calculated with a sufficient precision to use in neutron capture experiments at the n_TOF facility. http://www.sciencedirect.com/science/artic…

Compensation of missing wedge effects with sequential statistical reconstruction in electron tomography.

2014

Electron tomography (ET) of biological samples is used to study the organization and the structure of the whole cell and subcellular complexes in great detail. However, projections cannot be acquired over full tilt angle range with biological samples in electron microscopy. ET image reconstruction can be considered an ill-posed problem because of this missing information. This results in artifacts, seen as the loss of three-dimensional (3D) resolution in the reconstructed images. The goal of this study was to achieve isotropic resolution with a statistical reconstruction method, sequential maximum a posteriori expectation maximization (sMAP-EM), using no prior morphological knowledge about …

Patient-specific plan QA in active pencil beam scanning with proton and carbon ion beams: A new software solution to support treatment planning workf…

2016

Determination of boundaries between ranges of high and low gradient of beam profile

2016

Abstract Aim This work addresses the problem of treatment planning system commissioning by introducing a new method of determination of boundaries between high and low gradient in beam profile. Background The commissioning of a treatment planning system is a very important task in the radiation therapy. One of the main goals of this task is to compare two field profiles: measured and calculated. Applying points of 80% and 120% of nominal field size can lead to the incorrect determination of boundaries, especially for small field sizes. Materials and methods The method that is based on the beam profile gradient allows for proper assignment of boundaries between high and low gradient regions …