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131.
The mechanical properties of FeCr alloys rely heavily on atomic distribution and can be affected by phenomena such as Cr precipitation. While precipitation of FeCr alloys of various Cr concentrations has been studied before, dissolution of already existing Cr precipitates in FeCr alloys has not; this was the focus of this study. Our means of investigation was molecular dynamics computer simulation: we set up a number of configurations of FeCr alloys containing Cr precipitates of various sizes embedded in matrices of either pure Fe or with a 15% random Cr distribution, and examined their behaviour after thermal ageing at temperatures T ranging between 600 and 2000 K. The T range was selected so that it would include the (α+α′)?α transition in the standard FeCr phase diagram. High-T results provide insight into the mechanisms that govern the dissolution: Cr precipitates dissolve by vacancy exchange, leading to a random distribution of Cr atoms in an Fe matrix, as the short-range order parameter shifts from a positive value (clustering) to zero (random atomic arrangement). Precipitates at low T were found to be stable, as were those at intermediate T (~1000 K), in agreement with previous experimental and simulation studies that challenge the standard phase diagram's reliability. 相似文献
132.
Panagiotis D. Michailidis Konstantinos G. Margaritis 《Journal of Computational and Applied Mathematics》2011,236(3):326-341
Recent developments in high performance computer architecture have a significant effect on all fields of scientific computing. Linear algebra and especially the solution of linear systems of equations lie at the heart of many applications in scientific computing. This paper describes and analyzes three parallel versions of the dense direct methods such as the Gaussian elimination method and the LU form of Gaussian elimination that are used in linear system solving on a multicore using an OpenMP interface. More specifically, we present two naive parallel algorithms based on row block and row cyclic data distribution and we put special emphasis on presenting a third parallel algorithm based on the pipeline technique. Further, we propose an implementation of the pipelining technique in OpenMP. Experimental results on a multicore CPU show that the proposed OpenMP pipeline implementation achieves good overall performance compared to the other two naive parallel methods. Finally, in this work we propose a simple, fast and reasonably analytical model to predict the performance of the direct methods with the pipelining technique. 相似文献
133.
Trogadas P Parrondo J Ramani V 《Chemical communications (Cambridge, England)》2011,47(41):11549-11551
CeO(2), Pt/CeO(2) and MnO(2) additives were found to lower the rate of free radical induced polymer electrolyte membrane degradation in an operating fuel cell by over one order of magnitude. 相似文献
134.
Data envelopment analysis (DEA) is a linear programming methodology to evaluate the relative technical efficiency for each member of a set of peer decision making units (DMUs) with multiple inputs and multiple outputs. It has been widely used to measure performance in many areas. A weakness of the traditional DEA model is that it cannot deal with negative input or output values. There have been many studies exploring this issue, and various approaches have been proposed. 相似文献
135.
Scott N. Armstrong Panagiotis E. Souganidis 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2013
We study the asymptotic behavior of the principal eigenvalue of a weakly coupled, cooperative linear elliptic system in a stationary ergodic heterogeneous medium. The system arises as the so-called multigroup diffusion model for neutron flux in nuclear reactor cores, the principal eigenvalue determining the criticality of the reactor in a stationary state. Such systems have been well studied in recent years in the periodic setting, and the purpose of this work is to obtain results in random media. Our approach connects the linear eigenvalue problem to a system of quasilinear viscous Hamilton–Jacobi equations. By homogenizing the latter, we characterize the asymptotic behavior of the eigenvalue of the linear problem and exhibit some concentration behavior of the eigenfunctions. 相似文献
136.
Sakellarios AI Stefanou K Siogkas P Tsakanikas VD Bourantas CV Athanasiou L Exarchos TP Fotiou E Naka KK Papafaklis MI Patterson AJ Young VE Gillard JH Michalis LK Fotiadis DI 《Magnetic resonance imaging》2012,30(8):1068-1082
In this study, we present a novel methodology that allows reliable segmentation of the magnetic resonance images (MRIs) for accurate fully automated three-dimensional (3D) reconstruction of the carotid arteries and semiautomated characterization of plaque type. Our approach uses active contours to detect the luminal borders in the time-of-flight images and the outer vessel wall borders in the T(1)-weighted images. The methodology incorporates the connecting components theory for the automated identification of the bifurcation region and a knowledge-based algorithm for the accurate characterization of the plaque components. The proposed segmentation method was validated in randomly selected MRI frames analyzed offline by two expert observers. The interobserver variability of the method for the lumen and outer vessel wall was -1.60%±6.70% and 0.56%±6.28%, respectively, while the Williams Index for all metrics was close to unity. The methodology implemented to identify the composition of the plaque was also validated in 591 images acquired from 24 patients. The obtained Cohen's k was 0.68 (0.60-0.76) for lipid plaques, while the time needed to process an MRI sequence for 3D reconstruction was only 30 s. The obtained results indicate that the proposed methodology allows reliable and automated detection of the luminal and vessel wall borders and fast and accurate characterization of plaque type in carotid MRI sequences. These features render the currently presented methodology a useful tool in the clinical and research arena. 相似文献
137.
Wolff M Pálsson GK Korelis PT Dura JA Majkrzak C Hj?rvarsson B 《J Phys Condens Matter》2012,24(25):255306
The distribution of hydrogen in Nb/Ta superlattices has been investigated by combined neutron reflectivity and x-ray scattering. We provide evidence to support that strain modulations determined with x-ray diffraction can be interpreted as modulations in hydrogen content. We show that the hydrogen concentration is modulated and favors Nb, in agreement with previous studies. We measure the concentration directly using neutron reflectivity and demonstrate no detectable change in the distribution of hydrogen with temperature, in stark contrast to previous studies. 相似文献
138.
Yechun Wang Panagiotis Dimitrakopoulos 《Theoretical and Computational Fluid Dynamics》2012,26(1-4):361-379
In this study, we investigate computationally the low-Reynolds-number droplet motion in a square micro-channel, a problem frequently encountered in microfluidic devices, enhanced oil recovery and coating processes. The droplet deformation and motion are determined via a three-dimensional spectral boundary element method for wall-bounded flows. The effects of the flow rate, viscosity ratio and droplet size on the interfacial dynamics are identified for droplets smaller and larger than the channel size and for a wide range of viscosity ratio. Owing to the stronger hydrodynamic forces in the thin lubrication film between the droplet interface and the solid walls, large droplets exhibit larger deformation and smaller velocity. Under the same average velocity, a droplet in a channel shows a significantly smaller deformation and higher velocity than in a cylindrical tube with the same size, owing to the existence of the corners’ area in the channel which permits flow of the surrounding fluid. A suitable periodic boundary implementation for our spectral element method is developed to study the dynamics of an array of identical droplets moving in the channel. In this case, the droplet deformation and velocity are reduced as their separation decreases; the reduction is influenced by the flow rate, viscosity ratio and more significantly the droplet size. 相似文献
139.
Serdar Durdagi Manthos G. Papadopoulos Panagiotis G. Zoumpoulakis Catherine Koukoulitsa Thomas Mavromoustakos 《Molecular diversity》2010,14(2):257-276
When X-ray structure of a ligand-bound receptor is not available, homology models of the protein of interest can be used to
obtain the ligand-binding cavities. The steroelectronic properties of these cavities are directly related to the performed
molecular model coordinates. Thus, the use of different template structures for homology may result in variation of ligand-binding
modes. We have recently reported the MD simulations of a potent CB ligand at bovine rhodopsin-based CB1 and CB2 receptors
(Durdagi et al., Bioorg Med Chem 16:7377–7387, 2008). In this present study, a homology modeling study based on the β2-adrenergic receptor for both CB1 and CB2 receptors was performed, and the results were compared with rhodopsin-based models.
In addition, the role of membrane bilayers to the adopted conformations of potent AMG3 CB ligand has been analyzed for receptor-free
and membrane-associated receptor systems. The performed MD trajectory analysis results have shown that gauche conformations at the terminal segment of the alkyl side chain of AMG3 are not favored in solution. Different adopting dihedral
angles defined between aromatic and dithiolane rings at the active sites of the CB1 and CB2 receptors, which are adapted lead
to different alkyl side chain orientations and thus, may give clues to the medicinal chemists to synthesize more selective
CB ligands. The binding sites of receptors derived by rhodopsin-based models have been regenerated using the β2-adrenergic based template receptors. The re-obtained models confirmed the ligand-binding pockets that were derived based
on rhodopsin. 相似文献
140.
Aikaterini Sakellari Sotirios Karavoltsos Dimitra Tagkouli Christiana Rizou Vassilia J. Sinanoglou Panagiotis Zoumpoulakis 《Analytical letters》2019,52(17):2692-2709
AbstractMushrooms are efficient accumulators of essential and toxic elements. Although oyster (Pleurotus spp.) mushrooms are widely commercialized and consumed, few data exist regarding trace elements content and bioaccumulation in cultivated P. ostreatus and P. eryngii, while no data are available for P. nebrodensis. The contents of Al, As, Ba, Cd, Co, Cr, Cs, Cu, Fe, K, Mn, Na, Ni, Pb, Rb, Sr, V, and Zn were monitored using inductively coupled plasma-mass spectrometry (ICP-MS) and atomic emission spectrometry (AES) in P. ostreatus, P. eryngii, and P. nebrodensis mushrooms and their cultivation substrates that include wheat straw (WHS), grape marc (GMC), olive leaves (OLV), and two-phase olive mill wastes (OMW), separately or in mixtures. Bioaccumulation factors (BAFs) less than 0.3 were obtained for Al, Ba, Co, Cr, Fe, Mn, Ni, Pb, Sr, and V; BAFs exceeding 1 for K?>?Zn?>?Cd?>?Cr?>?Rb?>?As, while the BAFs for Na were less 0.7. Mushrooms grown on OLV and OMW presented lower BAFs than those grown on WHS and GMC for all elements except for K, Cd, and Cu. P. ostreatus was an effective accumulator for Cr, Fe, and Zn; P. eryngii for Al, Cs, Ni, and V; and P. nebrodensis for As and Cd. The estimated daily intakes (μg kg?1 body weight) from mushroom consumption were less than 0.010 for As, Cd, Co, Cs, Pb, and V, 0.010–0.10 for Ba, Cr, Ni, and Sr, 0.10–5.0 for Al, Cu, Fe, Mn, Rb, and Zn, 65–83 for Na, and 858–1030 for K. Overall, the mushrooms studied provide significant amounts of K, adequate amounts of Mn and Zn and low amounts of Na and toxic elements. 相似文献