Tris(hydroxymethyl)aminomethane (Tris) has been used as the buffer in bioactivity testing for over two decades and has become a standard choice for the scientific community. While it is believed to ...be non-interacting, the extent of its interactions with titanium oxide surfaces has not been systematically studied. Here, we use experimental (zeta potential measurements) and computational (molecular dynamics) approaches to evaluate the interaction of Tris with a rutile surface and how it affects the adsorption of other molecules relevant in biomedical in vitro testing. We show that the interaction of Tris with the rutile surface is strong and significantly affects the interaction of other organic residues with the surface. These strong interactions are compounded by the Tris concentration in the in vitro testing protocol, which is much higher compared to other components. Our findings indicate that the kinetics observed in in vitro tests will be strongly influenced by the presence of Tris as a buffering agent when compared to the natural CO2 buffer in blood. These results reveal that considering the so-far neglected active role of Tris in in vitro testing is critically needed and that in vitro protocols using CO2 partial pressure as the buffering agent should yield more reliable results.
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•We examine the interaction of Tris and amino acids with a rutile surface.•Our findings reveal that the affinity of Tris for the surface is not negligible.•When present, Tris inhibits the interaction of amino acids with the surface.•One must rethink the use of Tris as the buffering agent for in vitro testing.
Synthesis and Sintering of ZnO Nanopowders Aimable, Anne; Goure Doubi, Hervé; Stuer, Michael ...
Microsystem technologies : sensors, actuators, systems integration,
06/2017, Letnik:
5, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulating their development: sufficient low-cost, high throughput ...synthesis methods which lead to a production with well-defined and reproducible properties; and for ceramics specifically, the conservation of the powders’ nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv50~60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a “scale-out” concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 °C and 1100 °C, and Spark Plasma Sintering (SPS) at 900 °C. The performance of the synthesized nanopowder was compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 min at 900 °C, while also limiting the grain growth, thus leading to a nanostructured material.
For many organizations, Information Technology (IT) enabled business initiatives and IT infrastructure constitute major investments that, if not managed properly, may impair rather than enhance the ...organization's competitive position. Especially since the advent of Sarbanes–Oxley (SOX), both management and IT professionals are concerned with design, implementation, and assessment of IT governance strategies to ensure that technology truly serves the needs of the business. Via an in-depth study within one organisation, this research explores the factors influencing IT governance structures, processes, and outcome metrics. Interview responses to open-ended questions indicated that more effective IT governance performance outcomes are associated with a shared understanding of business and IT objectives; active involvement of IT steering committees; a balance of business and IT representatives in IT decisions; and comprehensive and well-communicated IT strategies and policies. IT governance also plays a prominent role in fostering project success and delivering business value.
Portlandite is an important constituent of cementitious materials. Consequently the growth of portlandite is of great interest to fully understand the hydration of cement, a process still posing many ...scientific challenges. In this paper the growth of portlandite in aqueous systems is studied by simulating the adsorption of Ca2+ and OH− at different portlandite surfaces. For the simulation an adapted version of the Freeman (Freeman et al., 2007) in combination with the TIP4P/2005 (Abascal and Vega, 2005) force field was used for both molecular dynamics, conventional and well-tempered metadynamics calculations. Depending on the structure of the portlandite–water interface, different adsorption sites were observed. Based on these we were able to propose an atomistic mechanism of portlandite growth in different crystallographic directions. The proposed mechanism indicates that different species control the growth in different directions, consistent with experimental observations reported in literature (Arnold, 2004).
Our work investigates the precipitation mechanism of a seeded calcium carbonate reaction, by using cryogenic TEM to observe the early stages of the reaction. The early precipitation of a hydrated ...phase is proposed as an intermediate phase before transformation into calcite. Thermodynamic modeling in conjunction with pH, surface potential measurements, and colloidal stability modeling demonstrate that calcite growth is dominated by agglomeration. This is in agreement with the cryogenic TEM observations, which suggest oriented attachment dominates early aggregation. The final stage of the reaction is described by a ripening mechanism that is significantly inhibited when high concentrations of polyacrylic acid (PAA) are used. The different concentrations of PAA lead to significant differences in the final particle substructure observed using cross section TEM. At low PAA concentrations, single crystal particles result, coherent with the proposed early oriented attachment mechanism and interfacial energy calculations. A core shell model is proposed for high PAA concentrations, whereas internal ripening of nanosized pores has been observed for low PAA concentrations, suggesting trapped solvent during the rapid initial particle formation at the relatively high supersaturations (S = 30) investigated.
Over the last years a new type of tubular plug flow reactor, the segmented flow tubular reactor (SFTR), has proven its versatility and robustness through the water-based synthesis of precipitates as ...varied as CaCO3, BaTiO3, Mn(1-x)NixC2O4·2H2O, YBa oxalates, copper oxalate, ZnS, ZnO, iron oxides, and TiO2 produced with a high powder quality (phase composition, particle size, and shape) and high reproducibility. The SFTR has been developed to overcome the classical problems of powder production scale-up from batch processes, which are mainly linked with mass and heat transfer. Recently, the SFTR concept has been further developed and applied for the synthesis of metals, metal oxides, and salts in form of nano- or micro-particles in organic solvents. This has been done by increasing the working temperature and modifying the particle carrying solvent. In this paper we summarize the experimental results for four materials prepared according to the polyol synthesis route combined with the SFTR. CeO2, Ni, Ag, and Ca3(PO4)2 nanoparticles (NPs) can be obtained with a production rate of about 1-10 g per h. The production was carried out for several hours with constant product quality. These findings further corroborate the reliability and versatility of the SFTR for high throughput powder production.
Data models provide a map of the components of an information system. Prior research has indicated that more expressive conceptual data models (despite their increased size) result in better ...performance for problem solving tasks. An initial experiment using logical data models indicated that more expressive logical data models also enhanced end-user performance for information retrieval tasks. However, the principles of parsimony and bounded rationality imply that, past some point, increases in size lead to a level of complexity that results in impaired performance. The results of this study support these principles. For a logical data model of increased but still modest size, users composing queries for the more expressive logical data model did not perform as well as users composing queries for the corresponding less expressive but more parsimonious logical data model. These results indicate that, when constructing logical data models, data modelers should consider tradeoffs between parsimony and expressiveness.
•Construction professionals’ work-life conflict experience is bi-directional in nature.•Work demands affect work-to-family conflict both directly, and indirectly through role blurring.•Construction ...professionals are more susceptible to work demands compared to family demands.•Construction professionals’ work-family conflict experience varies according to job position and work authority.
The demanding work environment of the construction industry has spawned many studies on construction professionals’ experiences of work-to-family conflict. Relatively less attention has been placed on family-to-work conflict. Many employees in modern organizations play a role in both work and family domains and juggle between work and family responsibilities, underscoring the need to holistically understand work-family experiences of construction professionals. This study considered the bi-directional nature of work-family conflict and proposed an integrated research model to examine the work-family interface among South African construction professionals. Data (n = 864) were collected through an online survey administered to construction professionals registered with their respective statutory councils. Structural equation modelling (SEM) was employed to test the research hypotheses. Within the work domain, work demands (i.e., work pressure and work hours) affect work-to-family conflict, both directly and indirectly, through the boundary-spanning demand of role blurring. Regarding workplace social support, only co-worker support is negatively associated with work-to-family conflict but not supervisor support. Within the family domain, the number of young children living at home and household task demands are positively associated with family-to-work conflict, while partner support is negatively associated with family-to-work conflict. Work-to-family conflict positively affects family-to-work conflict, but not the reverse. Work demands and role blurring experienced by professionals are likely to be affected by their job position and level of work authority. The findings suggest that organizations in the construction industry should protect their employees from experiencing excessive work-family conflict through creating a socially-supportive workplace environment, providing work-family programmes that foster greater boundary flexibility, and implementing effective work design characterised by reasonable workloads and work hours.
Two complementary topics are discussed: (i) the continuous production of silver nanoparticles (AgNPs) and (ii) the measurement of reaction yield by X-ray absorption near-edge spectroscopy (XANES). ...The continuous polyol synthesis of AgNPs in grams amount and in the size range of 7–104 nm was carried out in the segmented flow tubular reactor (SFTR). Particle size was tailored by controlling the synthesis parameters such as temperature, reactant concentrations, and polyvinylpyrrolidone (PVP) molecular weight. The continuous production was tested for 4 h, and the product has shown constant particle size distribution over the whole production time. Reliable continuous production of 2.3 g h–1 of ∼100 nm AgNPs can be achieved with a lab-scale SFTR. The produced particles were fully characterized with respect to size, size distribution, and chemical purity. To better understand the growth mechanism, synchrotron-radiation high-resolution X-ray diffraction, and X-ray absorption spectroscopy data were collected directly on the AgNPs suspension. In particular, from XANES experiments, the conversion yield of Ag+ to Ag0 was measured. The results are consistent with a two-step process where PVP controls the particle nucleation while growth is ensured by thermally induced ethylene glycol oxidation.
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