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Molecular modelling of the decomposition of NH₃ over CoO(100)

MATERIALS CHEMISTRY AND PHYSICS 2015年 156卷 141-149页

作者： Shojaee, Kambiz Haynes, Brian S. Montoya, Alejandro Univ Sydney Sch Chem & Biomol Engn Sydney NSW 2006 Australia

Spin-polarised density functional theory using the PBE + U approach are used to determine reaction pathways of successive NH3 dehydrogenation on the CoO(100) surface. NH3 dehydrogenation promotes noticeable displacements of the surface CoO sites, in particular due to the binding of NH2 and H species. Surface lattice O has low activity towards dehydrogenation, reflected in energy barriers that are in the range of 292 kJ mol(-1) to 328 kJ mol(-1). There is a preference of surface NH3 dehydrogenation to N-2 rather than towards NO, due to a high-energy penalty of surface O vacancy formation. The presence of CoO in cobalt oxide catalysts not only may decline the ammonia conversion but also alter the selectivity towards Ny rather than NO. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Oxides computer modelling and simulation Electronic structure Surface properties

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ESR studies of redox-active PMNT-PEG-PMNT polymer

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MATERIALS CHEMISTRY AND PHYSICS 2015年 161卷 250-255页

作者： Bednarowicz, M. Dobosz, B. Krzyminiewski, R. Halupka-Bryl, M. Deptula, T. Nagasaki, Y. Adam Mickiewicz Univ Dept Phys NanoBioMed Ctr Med Phys Div PL-61614 Poznan Poland Univ Tsukuba Grad Sch Pure & Appl Sci Dept Mat Sci Tsukuba Ibaraki 3058573 Japan Univ Tsukuba Grad Sch Comprehens Human Sci Masters Sch Med Sci Tsukuba Ibaraki 3058575 Japan Univ Tsukuba Natl Inst Mat Sci Int Ctr Mat Nanoarchitecton WPI MANA Satellite Lab Tsukuba Ibaraki 3058573 Japan

The paper presents the electron spin resonance (ESR) measurements of nitroxide radical-containing PMNT-PEG-PMNT triblock copolymer in different solvents: water, dimethyl formamide (DMF) and chloroform. Temperature dependence of electron spin resonance spectra were measured for each probe and several spectroscopic parameters describing physical properties, such as g-spectroscopic splitting factor value, resonance field (H-r), peak-to-peak line width (Delta H-pp) and correlation time (tau) were calculated and discussed. For the determination of the parameters characterizing the dynamics of TEMPO radicals in complex spectra the computer resolution enhancement method (CREM) and EasySpin software for ESR spectra simulations were used. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Electron paramagnetic resonance (EPR) Polymers Crystal structure computer modelling and simulation

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Lattice dynamics of binary and ternary phases in Ti-Si-C system: A combined Raman spectroscopy and density functional theory study

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MATERIALS CHEMISTRY AND PHYSICS 2015年 168卷 58-65页

作者： Wdowik, U. D. Twardowska, A. Medala-Wasik, M. Pedag Univ Inst Technol PL-30084 Krakow Poland

Results of the x-ray diffraction and the Raman spectroscopy experiments on the multiphase Ti-Si-C system containing Ti3SiC2 as the major phase and TiSi2, TiCx, and Ti5Si3/Ti5Si3C5 impurity phases are reported. Experimental studies are supported by the density functional theory calculations of the Raman spectra performed for the major and concomitant phases. The effect of carbon vacancies and impurities on the TiCx and Ti5Si3C5 Raman spectra is investigated. It is shown that identification and refinement of the phase composition of the multicomponent Ti-Si-C system based on the theoretical Raman spectroscopy can be achieved when both frequencies and intensities of the simulated Raman-active modes are simultaneously considered. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Ceramics Raman spectroscopy and scattering computer modelling and simulation Phonons

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Estimating skin blood saturation by selecting a subset of hyperspectral imaging data 13

Estimating skin blood saturation by selecting a subset of hy...

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Conference on Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XIII

作者： Ewerlof, Maria Salerud, E. Goran Stromberg, Tomas Larsson, Marcus Linkoping Univ Dept Biomed Engn S-58183 Linkoping Sweden

ISBN: (纸本)9781628414189

Skin blood haemoglobin saturation (s(b)) can be estimated with hyperspectral imaging using the wavelength (lambda) range of 450-700 nm where haemoglobin absorption displays distinct spectral characteristics. Depending on the image size and photon transport algorithm, computations may be demanding. Therefore, this work aims to evaluate subsets with a reduced number of wavelengths for s(b) estimation. White Monte Carlo simulations are performed using a two-layered tissue model with discrete values for epidermal thickness (T-epi) and the reduced scattering coefficient (mu s'), mimicking an imaging setup. A detected intensity look-up table is calculated for a range of model parameter values relevant to human skin, adding absorption effects in the post-processing. Skin model parameters, including absorbers, are mu(s)' (lambda) T-epi, haemoglobin saturation (s(b)), tissue fraction blood (c(b)) and tissue fraction melanin (c(mel)). The skin model paired with the look-up table allow spectra to be calculated swiftly. Three inverse models with varying number of free parameters are evaluated: A(s(b), c(b)), B(s(b), c(b), c(mel)) and C(all parameters free). Fourteen wavelength candidates are selected by analysing the maximal spectral sensitivity to s(b) and minimizing the sensitivity to s(b). All possible combinations of these candidates with three, four and 14 wavelengths, as well as the full spectral range, are evaluated for estimating s(b) for 1000 randomly generated evaluation spectra. The results show that the simplified models A and B estimated.. b accurately using four wavelengths (mean error 2.2% for model B). If the number of wavelengths increased, the model complexity needed to be increased to avoid poor estimations.

关键词： Hyper spectral imaging skin blood saturation diffuse reflectance spectroscopy Monte Carlo skin optical properties computer modelling and simulation microcirculation

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Energetic investigation of the adsorption process of CH₄, C₂H₆ and N₂ on activated carbon: Numerical and statistical physics treatment

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PHYSICA B-CONDENSED MATTER 2014年第1期433卷 55-61页

作者： Ben Torkia, Yosra BenYahia, Manel Khalfaoui, Mohamed Al-Muhtaseb, Shaheen A. Ben Lamine, Abdelmottaleb Fac Sci Monastir Lab Quantum Phys Monastir 5019 Tunisia Qatar Univ Dept Chem Engn Doha Qatar

The adsorption energy distribution (AED) function of a commercial activated carbon (BDH-activatecl carbon) was investigated. For this purpose, the integral equation is derived by using a purely analytical statistical physics treatment. The description of the heterogeneity of the adsorbent is significantly clarified by defining the parameter N'(m)(E). This parameter represents the energetic density of the spatial density of the effectively occupied sites. To solve the integral equation, a numerical method was used based on an adequate algorithm. The Langmuir model was adopted as a local adsorption isotherm. This model is developed by using the grand canonical ensemble, which allows defining the physico-chemical parameters involved in the adsorption process. The AED function is estimated by a normal Gaussian [unction. This method is applied to the adsorption isotherms of nitrogen, methane and ethane at different temperatures. The development of the AED using a statistical physics treatment provides an explanation of the gas molecules behaviour during the adsorption process and gives new physical interpretations at microscopic levels. (C) 2013 Elsevier By. All rights reserved.

关键词： Interfaces computer modelling and simulation Adsorption Heterostructures

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Geometry dependent reaction response of Ta + Bi₂O₃ thermite powder filled linear cellular alloys

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MATERIALS CHEMISTRY AND PHYSICS 2014年第3期144卷 318-326页

作者： Fredenburg, D. A. Jakus, A. McCoy, T. Cochran, J. Thadhani, N. Los Alamos Natl Lab Los Alamos NM 87545 USA Northwestern Univ Evanston IL 60208 USA Spelman Coll Atlanta GA 30314 USA Georgia Inst Technol Atlanta GA 30332 USA

The impact initiated reaction response of a Ta + Bi2O3 thermite powder mixture encapsulated in two different maraging steel geometric structures was investigated. Experiments were performed on the Ta + Bi2O3 mixture initially compressed to similar to 40% theoretical maximum density in a hollow cylinder and 9-Cell linear cellular alloy (LCA) structure, both of equivalent relative solid density. The powder filled structures were impacted against a rigid high-strength anvil over the velocity range of 60-204 m s(-1). Reactions were observed in the powder mixture at velocities as low as 60 m s(-1) in the 9-Cell LCA structure, and at 105 m s(-1) for the hollow cylinder geometry. Three dimensional simulations of the powder filled structures impacting a rigid anvil were carried out at velocities near the reaction threshold conditions. Continuous measurements of pressure and strain were recorded in the simulation at several locations within the powder filler and solid walls of the maraging steel LCA structures. Comparison of calculated results with experimental findings suggested that reaction of the powder filler in both encapsulating geometries occurred at late times as a result of an activated microstructure and elevated temperatures. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Compaction High strain-rate test computer modelling and simulation Finite element analysis Phase transition

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Tris (pentafluorophenyl) phosphine: A dual functionality additive for flame-retarding and sacrificial Oxidation on LiMn₂O₄ for lithium ion battery

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MATERIALS CHEMISTRY AND PHYSICS 2014年第3期143卷 1048-1054页

作者： Xu, Mengqing Liang, Ying Li, Bin Xing, Lidan Wang, Yong Li, Weishan S China Normal Univ Sch Chem & Environm Guangzhou 510006 Guangdong Peoples R China S China Normal Univ Guangdong High Educ Inst Key Lab Electrochem Technol Energy Storage & Powe Guangzhou 510006 Guangdong Peoples R China S China Normal Univ Engn Res Ctr Mat & Technol Electrochem Energy Sto Guangzhou 510006 Guangdong Peoples R China Dongying Hitech Spring Chem Ind Co Ltd Dongying 257081 Peoples R China

Tris (pentafluorophenyl) phosphine (TPFPP) additive possesses a dual functionality. The first of which is aimed at decreasing the flammability of the electrolyte, while the second is directed at the inhibition of the oxidative decomposition of electrolyte on cathode materials in lithium-ion batteries. The properties of the electrolyte containing TPFPP and the enhancements of cycling performance of Li/LiMn2O4 cells are investigated via a combination of electrochemical methods, self-extinguishing time (SET), differential scanning calorimeter (DSC), as well as density functional theory (DFT) computations. It is found that the incorporation of TPFPP to 1.0 M LiPF6 in 1:1:1 (v/v/v) ethylene carbonate/dimethyl carbonate/diethyl carbonate improves the thermal stability and decrease the flammability of the electrolyte. In addition, the initial discharge capacity and cycling stability of Li/LiMn2O4 is improved as well. The improved cycling performance with TPFPP added can be ascribed to the participation in surface layer formation process with incorporation of TPFPP. DFT theoretical computations are in good agreement with the modified cyclic voltammetry behavior of electrolyte with and without TPFPP additive on LiMn2O4 and graphite electrodes. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Interfaces computer modelling and simulation X-ray photo-emission spectroscopy (XPS) Surface properties

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FT-Raman and FTIR spectra of photoactive aminobenzazole derivatives in the solid state: A combined experimental and theoretical study

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MATERIALS CHEMISTRY AND PHYSICS 2014年第3期148卷 833-840页

作者： Alves, Rodrigo Martins Rodembusch, Fabiano Severo Habis, Charles Moreira, Eduardo Ceretta Univ Fed Pampa Grp Pesquisa Espectroscopia Mat Foton BR-96400970 Bage RS Brazil Univ Fed Rio Grande do Sul Grp Pesquisa Fotoquim Organ Aplicada BR-91501970 Porto Alegre RS Brazil No Virginia Community Coll Manassas VA USA

This study reports the experimental investigation of two photoactive aminobenzazole derivatives in the solid state by FT-Raman and Infrared Spectroscopies (FTIR) and its comparison with theoretical models. The optimized molecular structure, vibrational frequencies, and corresponding vibrational assignments of these compounds have been investigated experimentally and theoretically using Spanish Initiative for Electronic simulations with Thousands of Atoms (SIESTA) and Gaussian03 Software Package. The FT-Raman and FTIR spectra were acquired with high resolution and emission frequencies identified by simulating the vibrational modes. The most intense peak observed in the FT-Raman spectra is the in-plane deformation vibrational of O-H bond that could be related to the vibrational region responsible for the stabilization of the enol conformer in the ground state which undergoes ESIPT to form a keto tautomer in the excited state. Additionally, the position of the amino group played an important role on the vibrational characteristics of the studied compounds. Also, the simulations proved to be a good approach in undertaking the FTIR and FT-Raman experiments. The use of graphic correlations helps us to determine the method and basis that best fit the experimental results. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Optical materials Organic compounds Chemical synthesis ab initio calculations computer modelling and simulation Infrared spectroscopy (IR)

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Characterization of solvent-filled polyurethane/urea-formaldehyde core-shell composites

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MATERIALS CHEMISTRY AND PHYSICS 2014年第3期143卷 1018-1025页

作者： Neuser, S. Manfredi, E. Michaud, V. Ecole Polytech Fed Lausanne Inst Mat Lab Technol Composites & Polymeres LTC CH-1015 Lausanne Switzerland

Encapsulation of liquid phases is a crucial step in many self-healing material systems where a healing agent has to be protected during processing and then released during a damage event. In this work, the mechanical properties of polyurethane (PU) reinforced urea-formaldehyde (UF) shells are characterized. It was found that shell thickness is both a function of PU content in the core phase and of the microcapsule diameter. Furthermore, a saturation thickness was found for high PU contents or high capsule diameters and this phenomenon had direct implications on the bursting force under compression of single microcapsules. With help of an analytical model, the Young's modulus of the hybrid PU/UF was determined and in general, PU-reinforced shells had a lower modulus but higher ductility in terms of elongation at break, leading to more resistant microcapsules overall. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Polymers Compression and shear Mechanical testing computer modelling and simulation

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Structural dependence of threshold displacement energies in rutile, anatase, and brookite TiO₂

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MATERIALS CHEMISTRY AND PHYSICS 2014年第1-2期147卷 311-318页

作者： Robinson, M. Marks, N. A. Lumpkin, G. R. Curtin Univ Nanochem Res Inst Perth WA 6845 Australia Australian Nucl Sci & Technol Org Kirrawee Dc NSW 2232 Australia Curtin Univ Discipline Phys & Astron Perth WA 6845 Australia

Systematic molecular dynamics simulations of low energy cascades have been performed to examine how threshold displacement events are effected by changes in crystal structure. Exploiting the structural proximity of the rutile, anatase and brookite polymorphs of TiO2, a quantitative examination of defect production has been carried out including detailed defect analysis and the determination of values of the threshold displacement energy (E-d). Across all polymorphs comparable values of E-d are reported for oxygen at around 20 eV, with the value for Ti in rutile (73 +/- 2 eV) significantly higher than that in brookite (34 +/- 1 eV) and anatase (39 +/- 1 eV). Quantifying defect formation probability as a function of Primary Knock-on Atom (PKA) energy, simulations in rutile indicate a consistent reduction in defect formation at energies higher than E-d relative to anatase and brookite. Defect cluster analysis reveals a significant proportion of di-Frenkel pairs in anatase at Ti PKA energies around E-d. These clusters, which are stabilised by the localisation of two Frenkel pairs, are associated with a recombination barrier of approximately 0.19 eV. As such, annihilation is likely under typical experimental conditions which suggests an expected increase in the measured Ti value of E-d. Identical O defect populations produced at the threshold by the O PKA in both rutile and anatase explain the comparable values of E-d. At higher O PKA energies, the commencement of defect production on both sublattices in anatase is observed in contrast to the confinement of defects to the O sublattice in rutile. The overall trends reported are consistent with in-situ irradiation experiments and thermal spike simulations, suggesting the contrasting radiation response of the polymorphs of TiO2 is apparent during the initial stages of defect production. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Radiation damage computer modelling and simulation Microstructure Oxides

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