A density functional theory study of hydrogen dissociation and diffusion at the perimeter sites of Au/TiO2

<p>Reactivity of supported gold catalysts is a hot topic in catalysis for many years. This communication reports an investigation on the dissociation of molecular hydrogen at the perimeter sites of Au/TiO2 and the spillover of hydrogen atoms from the gold to the support using density functional theory calculations. It is found that the heterolytic dissociation is favoured in comparison with homolytic dissociation of molecular hydrogen at the perimeter sites. However, the surface oxygen of the rutile TiO2(110) surface at these sites can be readily passivated by the formed OH, suggesting that further dissociation of molecular hydrogen may occur at pure gold sites.</p>

Exchange between sub-surface and surface oxygen vacancies on CeO2(111):a new surface diffusion mechanism

<p>Using first principles calculations for O vacancy diffusion on CeO2(111), we locate a surface diffusion mechanism, the two-step O vacancy exchange one, which is more favored than the most common hopping mechanism. By analyzing the results, we identify quantitatively the physical origin of why the two-step exchange mechanism is preferred.</p>

Modifications of Surface Properties of Beta Ti by Laser Gas Diffusion Nitriding

Beta-type Ti-alloy is a promising biomedical implant material as it has a low Young���s modulus and is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapor deposition and chemical vapor deposition are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment. This paper will report the results achieved by a 100 W continuous wave (CW) fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using x-ray diffractometry, optical microscopy, three-dimensional surface profile and contact angle measurements, and nanoindentation test.

Diffusion coefficients in dense and supercritical fluids

Os coeficientes de difus��o (D 12) s��o propriedades fundamentais na investiga����o e na ind��stria, mas a falta de dados experimentais e a inexist��ncia de equa����es que os estimem com precis��o e confian��a em fases comprimidas ou condensadas constituem limita����es importantes. Os objetivos principais deste trabalho compreendem: i) a compila����o de uma grande base de dados para valores de D 12 de sistemas gasosos, l��quidos e supercr��ticos; ii) o desenvolvimento e valida����o de novos modelos de coeficientes de difus��o a dilui����o infinita, aplic��veis em amplas gamas de temperatura e densidade, para sistemas contendo componentes muito distintos em termos de polaridade, tamanho e simetria; iii) a montagem e teste de uma instala����o experimental para medir coeficientes de difus��o em l��quidos e fluidos supercr��ticos. Relativamente �� modela����o, uma nova express��o para coeficientes de difus��o a dilui����o infinita de esferas r��gidas foi desenvolvida e validada usando dados de din��mica molecular (desvio relativo absoluto m��dio, AARD = 4.44%) Foram tamb��m estudados os coeficientes de difus��o bin��rios de sistemas reais. Para tal, foi compilada uma extensa base de dados de difusividades de sistemas reais em gases e solventes densos (622 sistemas bin��rios num total de 9407 pontos experimentais e 358 mol��culas) e a mesma foi usada na valida����o dos novos modelos desenvolvidos nesta tese. Um conjunto de novos modelos foi proposto para o c��lculo de coeficientes de difus��o a dilui����o infinita usando diferentes abordagens: i) dois modelos de base molecular com um par��metro espec��fico para cada sistema, aplic��veis em sistemas gasosos, l��quidos e supercr��ticos, em que natureza do solvente se encontra limitada a apolar ou fracamente polar (AARDs globais na gama 4.26-4.40%); ii) dois modelos de base molecular biparam��tricos, aplic��veis em todos os estados f��sicos, para qualquer tipo de soluto dilu��do em qualquer solvente (apolar, fracamente polar e polar). Ambos os modelos d��o origem a erros globais entre 2.74% e 3.65%; iii) uma correla����o com um par��metro, espec��fica para coeficientes de difus��o em di��xido de carbono supercr��tico (SC-CO2) e ��gua l��quida (AARD = 3.56%); iv) nove correla����es emp��ricas e semi-emp��ricas que envolvem dois par��metros, dependentes apenas da temperatura e/ou densidade do solvente e/ou viscosidade do solvente. Estes ��ltimos modelos s��o muito simples e exibem excelentes resultados (AARDs entre 2.78% e 4.44%) em sistemas l��quidos e supercr��ticos; e v) duas equa����es preditivas para difusividades de solutos em SC-CO2, em que os erros globais de ambas s��o inferiores a 6.80%. No global, deve real��ar-se o facto de os novos modelos abrangerem a grande variedade de sistemas e mol��culas geralmente encontrados. Os resultados obtidos s��o consistentemente melhores do que os obtidos com os modelos e abordagens encontrados na literatura. No caso das correla����es com um ou dois par��metros, mostrou-se que estes mesmos par��metros podem ser ajustados usando um conjunto muito pequeno de dados, e posteriormente serem utilizados na previs��o de valores de D 12 longe do conjunto original de pontos. Uma nova instala����o experimental para medir coeficientes de difus��o bin��rios por t��cnicas cromatogr��ficas foi montada e testada. O equipamento, o procedimento experimental e os c��lculos anal��ticos necess��rios �� obten����o dos valores de D 12 pelo m��todo de abertura do pico cromatogr��fico, foram avaliados atrav��s da medi����o de difusividades de tolueno e acetona em SC-CO2. Seguidamente, foram medidos coeficientes de difus��o de eucaliptol em SC-CO2 nas gamas de 202 ��� 252 bar e 313.15 ��� 333.15 K. Os resultados experimentais foram analisados atrav��s de correla����es e modelos preditivos para D12.

Global nation product equity depending on a level of cultural diffusion

Purpose This paper aims to propose the global nation product equity model (GNPE) to measure global consumers��� equity of a product that a country produces, especially a nation���s cultural products (i.e. culducts). The model also examines the significant difference of GNPE depending on a cultural diffusion level. GNPE model proposes that depending on the level of people���s recognition/acceptance/preference of a culture from another country (i.e. cultural diffusion level), the equity of a product from that country could be different in different countries. As variables that affect GNPE, global nation product equity in general, global nation product equity of a product category and nation cultural equity are included in the model. Design/methodology/approach To test the model, this study developed Hallyu (Korean cultural diffusion)-related Korean culducts and measured global consumers��� equity for the Korean culducts. In all, 351 surveys were collected from China, France, England and the USA. Findings The results show the significantly different equities and relationships among equities depending on the level of Hallyu diffusion in each country. Therefore, Korea is suggested to focus on different equities in different countries. Originality/value This research proposed a new model that extends the previous brand equity models to non-branded products (i.e. cultural products). This model proposed new variables that affect equity of a product mentioned above and suggests different equities to improve in different countries depending on their level of cultural diffusion. Also, this cross-cultural study suggests a direction of culduct design, distribution and promotion strategies in the global market.

A Social Institutionalist Perspective on HR Diffusion: Histrorical and Cultural Receptivity to HRM in a Post-Comminist Context

This research considers cross-national diffusion of international human resource management (IHRM) ideas and practices by applying an emergent frame of sociological conceptualisation ��� ���social institutionalism��� (SI). We look at cultural filters to patterns of diffusion, assimilation and adoption of IHRM, using Romania as a case study. The paper considers the former Communist system of employment relations, suggesting that through institutionalisation former ways of thinking continued to influence definitions and practice of people management in post-Communist Eastern Europe. The paper provides a new perspective on HRM by discussing the value of SI as a general model for understanding cross-cultural receptivity to HR ideas, sensitising the HR practitioner and academic to institutionalised culture as a historical legacy influencing receptivity to international management ideas.

Dermic diffusion and stratum corneum: a state of the art review of mathematical models

Transdermal biotechnologies are an ever increasing ���eld of interest, due to the medical and pharmaceutical applications that they underlie. There are several mathematical models at use that permit a more inclusive vision of pure experimental data and even allow practical extrapolation for new dermal diffusion methodologies. However, they grasp a complex variety of theories and assumptions that allocate their use for speci���c situations. Models based on Fick's First Law found better use in contexts where scaled particle theory Models would be extensive in time-span but the reciprocal is also true, as context of transdermal diffusion of particular active compounds changes. This article reviews extensively the various theoretical methodologies for studying dermic diffusion in the rate limiting dermic barrier, the stratum corneum, and systematizes its characteristics, their proper context of application, advantages and limitations, as well as future perspectives.

Fractional control of heat diffusion systems

The concept of differentiation and integration to non-integer order has its origins in the seventeen century. However, only in the second-half of the twenty century appeared the first applications related to the area of control theory. In this paper we consider the study of a heat diffusion system based on the application of the fractional calculus concepts. In this perspective, several control methodologies are investigated and compared. Simulations are presented assessing the performance of the proposed fractional-order algorithms.

Analysis of diffusion process in fractured reservoirs using fractional derivative approach

The fractal geometry is used to model of a naturally fractured reservoir and the concept of fractional derivative is applied to the diffusion equation to incorporate the history of fluid flow in naturally fractured reservoirs. The resulting fractally fractional diffusion (FFD) equation is solved analytically in the Laplace space for three outer boundary conditions. The analytical solutions are used to analyze the response of a naturally fractured reservoir considering the anomalous behavior of oil production. Several synthetic examples are provided to illustrate the methodology proposed in this work and to explain the diffusion process in fractally fractured systems.

Diffusion characteristics of ethylene glycol in skeletal muscle

Part of the optical clearing study in biological tissues concerns the determination of the diffusion characteristics of water and optical clearing agents in the subject tissue. Such information is sufficient to characterize the time dependence of the optical clearing mechanisms���tissue dehydration and refractive index (RI) matching. We have used a simple method based on collimated optical transmittance measurements made from muscle samples under treatment with aqueous solutions containing different concentrations of ethylene glycol (EG), to determine the diffusion time values of water and EG in skeletal muscle. By representing the estimated mean diffusion time values from each treatment as a function of agent concentration in solution, we could identify the real diffusion times for water and agent. These values allowed for the calculation of the correspondent diffusion coefficients for those fluids. With these results, we have demonstrated that the dehydration mechanism is the one that dominates optical clearing in the first minute of treatment, while the RI matching takes over the optical clearing operations after that and remains for a longer time of treatment up to about 10 min, as we could see for EG and thin tissue samples of 0.5 mm.

The characteristic time of glucose diffusion measured for muscle tissue at optical clearing

The study of agent diffusion in biological tissues is very important to understand and characterize the optical clearing effects and mechanisms involved: tissue dehydration and refractive index matching. From measurements made to study the optical clearing, it is obvious that light scattering is reduced and that the optical properties of the tissue are controlled in the process. On the other hand, optical measurements do not allow direct determination of the diffusion properties of the agent in the tissue and some calculations are necessary to estimate those properties. This fact is imposed by the occurrence of two fluxes at optical clearing: water typically directed out of and agent directed into the tissue. When the water content in the immersion solution is approximately the same as the free water content of the tissue, a balance is established for water and the agent flux dominates. To prove this concept experimentally, we have measured the collimated transmittance of skeletal muscle samples under treatment with aqueous solutions containing different concentrations of glucose. After estimating the mean diffusion time values for each of the treatments we have represented those values as a function of glucose concentration in solution. Such a representation presents a maximum diffusion time for a water content in solution equal to the tissue free water content. Such a maximum represents the real diffusion time of glucose in the muscle and with this value we could calculate the corresponding diffusion coefficient.

A technology diffusion perspective of Enterprise Resource Planning across European Small and Medium Enterprises: from determinants to Use to Value

Tese apresentada como requisito parcial para obten����o do grau de Doutor em Gest��o de Informa����o

Alveolar echinococcosis of the liver: Diffusion-weighted MRI findings and potential role in lesion characterisation

PURPOSE: To report the diffusion-weighted MRI findings in alveolar echinococcosis (AE) of the liver and evaluate the potential role of apparent diffusion coefficients (ADCs) in the characterisation of lesions. MATERIALS AND METHODS: We retrospectively included 22 patients with 63 AE liver lesions (&#8805;1cm), examined with 3-T liver MRI, including a free-breathing diffusion-weighted single-shot echo-planar imaging sequence (b-values=50, 300 and 600s/mm(2)). Two radiologists jointly assessed the following lesion features: size, location, presence of cystic and/or solid components (according to Kodama's classification system), relative contrast enhancement, and calcifications (on CT). The ADCtotal, ADCmin and ADCmax were measured in each lesion and the surrounding liver parenchyma. RESULTS: Three type 1, 19 type 2, 17 type 3, three type 4 and 21 type 5 lesions were identified. The mean (��SD) ADCtotal, ADCmin and ADCmax for all lesions were 1.73��0.50, 0.76��0.38 and 2.63��0.76��10(-3)mm(2)/s, respectively. The mean ADCtotal for type 1, type 2, type 3, type 4 and type 5 lesions were 1.97��1.01, 1.76��0.53, 1.73��0.41, 1.15��0.42 and 1.76��0.44��10(-3)mm(2)/s, respectively. No significant differences were found between the five lesion types, except for type 4 (p=0.0363). There was a significant correlation between the presence of a solid component and low ADCmin (r=0.39, p=0.0016), whereas an inverse correlation was found between the relative contrast enhancement and ADCtotal (r=-0.34, p=0.0072). CONCLUSION: The ADCs of AE lesions are relatively low compared to other cystic liver lesions, which may help in the differential diagnosis. Although ADCs are of little use to distinguish between the five lesion types, their low value reflects the underlying solid component.

An introduction to model-independent diffusion magnetic resonance imaging.

ABSTRACT: q-Space-based techniques such as diffusion spectrum imaging, q-ball imaging, and their variations have been used extensively in research for their desired capability to delineate complex neuronal architectures such as multiple fiber crossings in each of the image voxels. The purpose of this article was to provide an introduction to the q-space formalism and the principles of basic q-space techniques together with the discussion on the advantages as well as challenges in translating these techniques into the clinical environment. A review of the currently used q-space-based protocols in clinical research is also provided.