Modelling thin film growth in the Ti-Ag system

With the aim to model the surface growth of Ti-Ag system over realistic time scales, two interatomic potential mixing rules for the Ti-Ag system were first investigated based on the embedded-atom method (EAM) elemental potentials. First principles calculations were performed using SIESTA for various configurations of the Ti-Ag system to see which model best fitted the ab initio results. The results showed that the surface energies, es- pecially that of Ti, were not well fitted by either model and the surface binding energies differed from the ab initio calculations. As a result, the modified embedded-atom method (MEAM) was investigated. In contrast to the other models, surface energies for pure Ti calculated by MEAM were in good agreement with the experimental data and the ab initio results. The MEAM mixing rule was used to investigate Ag adatoms on Ti and Ti adatoms on Ag. The results showed good agreement with SIESTA after parameter optimisation. Simulations of thin film growth in the Ag-Ti system are presented using an adaptive kinetic Monte Carlo method (AKMC). For the growth of Ti on Ag (100) and Ag (111) surfaces, the Ti adatoms prefer to exchange with the original surface layer atoms creating a mixed Ag/Ti surface. On a silver substrate, up to four mixed layers need to be formed before a pure Ti layer is obtained when the deposition energy is less than 20 eV. Conversely, the simulations of Ag on the Ti (0001) plane showed that the Ag adatoms repel each other on the Ti basal plane, before a complete first layer of Ag was obtained in a face-centred cubic structure. The implementations of a super-basin method within the adaptive ki- netic Monte Carlo method has allowed the simulation of 0.4s of surface growth on the Ag substrates. This work also compared two long time scale dynamics methods, namely AKMC and Parallel Trajectory Splicing (ParSplice) simulations. For these two configurations are considered on the Ag (111) substrate. The transitions and the associated energy barriers are identical for single atom diffusion but the diffusion rates differ. In the case of an adatom on an island, a super-basin system was created. The exit transitions found by a transition search algorithm and ParSplice were again the same whilst the mean exit time differed by a factor of two due to inaccurate prefactor calculations. The distribution of basin-exit times is also examined which obeys an exponential distribution

Development of an empirical interatomic potential for the Ag–Ti system

Two interatomic potential mixing rules for the Ti–Ag system were investigated based on the embedded-atom method (EAM) elemental potentials. First principles calculations were performed using SIESTA for various configurations of the Ti–Ag system to see which model best fitted the ab initio results. The results showed that the surface energies, especially that of Ti, were not well fitted by either model and the surface binding energies differed from the ab initio calculations. As a result, the modified embedded-atom method (MEAM) was investigated. In contrast to the other models, surface energies for pure Ti calculated by MEAM were in good agreement with the experimental data and the ab initio results. The MEAM mixing rule was used to investigate Ag ad-atoms on Ti and Ti ad-atoms on Ag. The results showed good agreement with SIESTA after parameter optimisation

Reaction pathways in atomistic models of thin film growth

The atomistic processes that form the basis of thin film growth often involve complex multi-atom movements of atoms or groups of atoms on or close to the surface of a substrate. These transitions and their pathways are often difficult to predict in advance. By using an adaptive kinetic Monte Carlo (AKMC) approach many complex mechanisms can be identified so that the growth processes can be understood and ultimately controlled. Here the AKMC technique is briefly described along with some special adaptions that can speed up the simulations when, for example, the transition barriers are small. Examples are given of such complex processes that occur in different material systems especially for the growth of metals and metallic oxides

Scaling from single-point sap velocity measurements to stand transpiration in a multispecies deciduous forest: Uncertainty sources, stand structure effect, and future scenarios

9 páginas.-- 5 figuras.-- 2 tablas.-- 58 referencias[EN] A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability on transpiration upscaling and explore the potential impacts of future shifts in species composition on the forest water budget. We measured sap velocity in five tree species (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton, and Betula papyrifera Marsh.) in a mature stand and a young stand in New Hampshire, USA. Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpiration will depend on the sap velocity, determined not only by radial variation and tree size, but also by the sapwood area distribution in the stand.[FR] Les études dont le but est d'estimer l'utilisation de l'eau a` l'échelle du peuplement dans les forêts mélangées font face a` un défi majeur : comment passer efficacement de l'échelle des arbres individuels a` l'échelle du peuplement. C'est le cas pour les écosystèmes forestiers dans le nord-est des États-Unis où les différences dans l'utilisation de l'eau entre les espèces et parmi les différentes catégories de taille n'ont pas fait l'objet d'études approfondies malgré leur pertinence pour une vaste gamme de services de l'écosystème. Nos objectifs consistaient a` évaluer l'importance des différentes sources de variation sur l'extrapolation de la transpiration et a` explorer les impacts potentiels des changements futurs dans la composition en espèces sur le bilan hydrique de la forêt. Nous avons mesuré la vitesse de la sève chez cinq espèces d'arbre (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton et Betula papyrifera Marsh.) dans un peuplement mature et dans un jeune peuplement au New Hampshire (É.-U.). Nos résultats ont montré que la plus grande source potentielle d'erreur était la variation radiale et que la vitesse de la sève était davantage déterminée par la taille des arbres que par l'espèce. La surface totale de bois d'aubier avait un effet très déterminant sur la transpiration qui variait selon la taille et l'espèce d'arbre. Nous concluons que l'effet des changements potentiels dans la composition en espèces sur la transpiration dépendra de la vitesse de la sève qui est principalement déterminée par la variation radiale et la taille des arbres mais aussi de la distribution de la surface de bois d'aubier dans le peuplement.This work was funded by the University of New Hampshire and the New Hampshire Agricultural Experiment Station. The Bartlett Experimental Forest is operated by the USDA Forest Service Northern Research Station. S. Mcgraw, P. Pellissier, C. Breton, S. Alvarado-Barrientos, R. Snyder, and Z. Aldag assisted in the field and in the lab. The 2011 stand inventory was led by S. Goswami. Tree heights were measured and compiled by C. Blodgett, T. Fahey, and L. Liu. A. Richardson shared meteorology and solar radiation data from the Bartlett Amerflux tower. The stands used in this experiment are maintained and monitored by the MELNHE project under the direction of R. Yanai and M. Fisk, with funding from NSF grants DEB 0235650 and DEB 0949324Peer reviewe

Does institutional context matter in building innovation capability?

Our study investigates whether changes in China's reform policies had an influence on the national innovation capability building. Specifically, our study empirically examines the relationship between national innovation capability and the roles of key drivers from 33 administrative regions across the two periods of the reform (1991-1998 and 1999-2005) with four types of domestic patents during 1992-2009. The data is drawn from government official statistics, using STATA for panel analysis. Overall findings demonstrate that the innovation environment was changed and consequently changed the impact of drivers on China's innovation capability differently between the two periods, which helps provide a better understanding of the effect of innovation system reform in each phase in China. We extend research on innovation capability to emerging economies and enhance our understanding of how the government policies shape a country's innovation capability through mechanisms of key innovation drivers in emerging economies

Openly Accessible Microfluidic Liquid Handlers for Automated High-Throughput Nanoliter Cell Culture

Cell culture is typically performed in Petri dishes, with a few million cells growing together, or in microwell plates with thousands of cells in each compartment. When the throughput of each experiment, especially of screening based assays, is increased, even using microliter solution per well will cost a considerable amount of cells and reagents. We took a rational approach to reduce the volume of each cell culture chamber. We designed and fabricated a poly­(dimethylsiloxane) based liquid pipet chip to deliver and transfer nanoliter (50–500 nL) samples and reagents with high accuracy and robustness. A few tens to a few hundreds of cells can be successfully seeded, transferred, passaged, transfected, and stimulated by drugs on a microwell chip using this pipet chip automatically. We have used this system to test the cell growth dynamically, observed the correlation between the culture conditions and cell viabilities, and quantitatively evaluated cell apoptosis induced by <i>cis</i>-diammineplatinum­(II) dichloride (cisplatin). This system shows great potential to facilitate large-scale screening and high-throughput cell-array based bioassays with the volume of each individual cell colony at the nanoliter level

Evolution of dispersal by memory and learning in integrodifference equation models

In this paper, we develop an integrodifference equation model that incorporates spatial memory and learning so that each year, a fraction of the population use the same dispersal kernel as the previous year, and the remaining individuals return to where they bred or were born. In temporally static environments, the equilibrium of the system corresponds to an ideal free dispersal strategy, which is evolutionarily stable. We prove local stability of this equilibrium in a special case, and we observe convergence towards this equilibrium in numerical computations. When there are periodic or stochastic temporal changes in the environment, the population is less able to match the environment, but is able to do so to some extent depending on the parameters. Overall, the mechanism proposed in this model shows a possible way for the dispersal kernel of a population to evolve towards an ideal free dispersal kernel.</p

Additional file 1: Table S1. of Years of life lost due to lower extremity injury in association with dementia, and care need: a 6-year follow-up population-based study using a multi-state approach among German elderly

ICDs used to identify dementia and lower extremity injury (ICD- 2010-GM). To list the concrete ICDs, which we used to identify dementia and lower extremity injury in our study. (DOCX 15 kb

Additional file 2: Table S2. of Years of life lost due to lower extremity injury in association with dementia, and care need: a 6-year follow-up population-based study using a multi-state approach among German elderly

Numbers and percentages of transitions and exposure of interest (LEI) by age. Differentiates Table 1 which is included in the main document by 5-year age groups. (DOCX 19 kb

Combined Fe₂O₃ and CaCO₃ Additives To Enhance the Immobilization of Pb in Cathode Ray Tube Funnel Glass

Cathode ray tube (CRT) funnel glass has posed an increasing threat to the environment due to its rapid replacement by new technology in recent years. In this study, a well-control thermal scheme was applied for synthesizing a specific crystalline phase, PbFe₁₂O₁₉, for Pb immobilization when reusing CRT funnel glass as raw materials for the ceramics industry. The Fourier transform infrared spectroscopy results show that introduction of CaCO₃ facilitated the breakage of strongly connected bonds between O–Si–O and Pb–O, which were firmly linked in the glass network. The X-ray diffraction results demonstrate that 30 wt % CaCO₃ loading effectively facilitated the transformation of Pb in CRT funnel glass to the stable-phase PbFe₁₂O₁₉. A higher sintering temperature increased Pb transformation efficiency while a longer dwelling time only showed a slight increase in PbFe₁₂O₁₉ formation. The prolonged toxic characteristic leaching procedure results show a substantial improvement in the acid resistance (approximately 2 mg/L) of the thermally treated product with 30 wt % CaCO₃ loading and sintering under 1000 °C for 5 h compared to the original CRT funnel glass (500 mg/L). The results of this study demonstrate that incorporation of CaCO₃ and Fe₂O₃ into CRT funnel glass can effectively promote Pb immobilization and provide a new strategy for stabilizing waste CRT funnel glass