Search results for "Simulation."
showing 10 items of 4779 documents
QA of dynamic MLC based on EPID portal dosimetry.
2010
Abstract Purpose Dynamic delivery of intensity modulated beams (dIMRT) requires not only accurate verification of leaf positioning but also a control on the speed of motion. The latter is a parameter that has a major impact on the dose delivered to the patient. Time consumed in quality assurance (QA) procedures is an issue of relevance in any radiotherapy department. Electronic portal imaging dosimetry (EPID) can be very efficient for routine tests. The purpose of this work is to investigate the ability of our EPID for detecting small errors in leaf positioning, and to present our daily QA procedures for dIMRT based on EPID. Methods and materials A Varian 2100 CD Clinac equipped with an 80 …
Energy-Efficiency and Coverage Quality Management for Reliable Diagnostics in Wireless Sensor Networks
2020
International audience; The processing of data and signals provided by sensors aims at extracting rnrelevant features which can be used to assess and diagnose the health state rnof the monitored targets. Nevertheless, Wireless Sensor Networks (WSNs) present rna number of shortcomings that have an impact on the quality of the gathered rndata at the sink level, leading to imprecise diagnostics rnof the observed targets. To improve data accuracy, two main critical and related issues, namely the energy consumption and coverage quality, need to be considered. The goal is to maximize the network lifetime while guaranteeing the complete coverage of all the targets. Unfortunately, these performance…
Heterogeneity in general practitioners’ preferences for quality improvement programs: a choice experiment and policy simulation in France
2016
International audience; Despite increasing popularity, quality improvement programs (QIP) have had modest and variable impacts on enhancing the quality of physician practice. We investigate the heterogeneity of physicians’ preferences as a potential explanation of these mixed results in France, where the national voluntary QIP – the CAPI – has been cancelled due to its unpopularity. We rely on a discrete choice experiment to elicit heterogeneity in physicians’ preferences for the financial and non-financial components of QIP. Using mixed and latent class logit models, results show that the two models should be used in concert to shed light on different aspects of the heterogeneity in prefer…
A nanodosimetric model of radiation-induced clustered DNA damage yields
2010
International audience; We present a nanodosimetric model for predicting the yield of double strand breaks (DSBs) and non-DSB clustered damages induced in irradiated DNA. The model uses experimental ionization cluster size distributions measured in a gas model by an ion counting nanodosimeter or, alternatively, distributions simulated by a Monte Carlo track structure code developed to simulate the nanodosimeter. The model is based on a straightforward combinatorial approach translating ionizations, as measured or simulated in a sensitive gas volume, to lesions in a DNA segment of one-two helical turns considered equivalent to the sensitive volume of the nanodosimeter. The two model paramete…
Mechanical unfolding pathway of a model β-peptide foldamer.
2015
Foldamers constructed from oligomers of β-peptides form stable secondary helix structures already for small chain lengths, which makes them ideal candidates for the investigation of the (un)folding of polypeptides. Here, the results of molecular simulations of the mechanical unfolding of a β-heptapeptide in methanol solvent revealing the detailed unfolding pathway are reported. The unfolding process is shown to proceed via a stable intermediate even for such a small system. This result is arrived at performing non-equilibrium force ramp simulations employing different pulling velocities and also using standard calculations of the potential of mean force, i.e., the free energy as a function …
Structure and Matrix Isolation Infrared Spectrum of Formyl Fluoride Dimer: Blue-Shift of the C−H Stretching Frequency
2006
Infrared spectroscopy (IR) of formyl fluoride (HCOF) dimer is studied in low-temperature argon and krypton matrixes. New IR absorptions, ca. 17 cm(-1) blue shifted from the monomer C-H stretching fundamental, are assigned to the HCOF dimer. The MP2/6-311++G calculations were utilized to define structures and harmonic frequencies of various HCOF dimers. Among the four optimized structures, the dimer having two C-H...O hydrogen bonds possesses strongest intermolecular bonding. The calculated harmonic frequencies of this dimer structure are shifted from the monomer similarly as observed in the experiment. Thus, we suggest that the experimentally observed blue shifted C-H bands belong to the di…
Conformational Changes of a Single Semiflexible Macromolecule Near an Adsorbing Surface: A Monte Carlo Simulation
2009
The properties of a single semiflexible chain tethered to a planar surface with a long-ranged attractive potential are studied by means of Monte Carlo simulations. We employ the bond fluctuation lattice model and the Wang-Landau sampling technique. We present the diagram of states for semiflexible chains consisting of N = 64 and 128 monomer units as a function of temperature T and strength of the adsorption potential, epsilon(w), and also compare this with the diagram of states for flexible chains of these two lengths. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil, and quasi-two-dimensional solid globule with nematic bond ord…
Interface and Surface Properties of Short Polymers in Solution: Monte Carlo Simulations and Self-Consistent Field Theory
2000
We investigate the structure and thermodynamics of inhomogeneous polymer solutions in the framework of a coarse-grained off-lattice model. Properties of the liquidvapor interface and the packing of...
An approach to evaluation of sheet bending force under successive multiaxial stress condition
2009
A new bending under tension test is presented in this paper. This method tries to evaluate bending forces in sheet under successive multiaxial stress condition. This test is carried out in only one step with a pinned cylinder over a material that has been previously deformed to pure shear condition. Due to that, the bending process is made under higher back tension forces than the ones involved in the common methods previously studied in the literature. This entails high pressure values in the sheet-bending tool contact that affects the corresponding friction process. Material is strongly strengthened as a consequence of the deformation practiced in it, and as a result of that, bending forc…
Solvent-induced free energy landscape and solute-solvent dynamic coupling in a multielement solute
1999
AbstractMolecular dynamics simulations using a simple multielement model solute with internal degrees of freedom and accounting for solvent-induced interactions to all orders in explicit water are reported. The potential energy landscape of the solute is flat in vacuo. However, the sole untruncated solvent-induced interactions between apolar (hydrophobic) and charged elements generate a rich landscape of potential of mean force exhibiting typical features of protein landscapes. Despite the simplicity of our solute, the depth of minima in this landscape is not far in size from free energies that stabilize protein conformations. Dynamical coupling between configurational switching of the syst…