A miniature CSTR cascade for continuous flow of reactions containing solids

Continuous handling of solids creates challenges for realizing continuous production of pharmaceuticals and fine chemicals. We present a new miniature continuous stirred-tank reactor (CSTR) cascade to handle solid-forming reactions in flow. Single-phase residence time distribution (RTD) measurements of the CSTR cascade reveal nearly ideal CSTR mixing behavior of the individual units. Consistency of experimental and predicted conversions of a Diels–Alder reaction further confirms the CSTR performance. Two solid-forming reactions, (i) glyoxal reacting with cyclohexylamine to form N,N′-dicyclohexylethylenediimine, (ii) sulfonylation of 2-octanol with methanesulfonyl chloride, demonstrate the ability of the reactor cascade to transport solid particles continuously for hours without significant signs of clogging

Growth of three-dimensional structures by atomic deposition on surfaces containing defects : simulations and theory

We perform a comprehensive study of the formation of three dimensional (pyramidal) structures in a large range of conditions, including the possible evaporation of adatoms from the surface and the presence of surface defects. We compare our computer simulations to theoretical calculations of the growth and find good agreement between them. This work clarifies precedent studies of three dimensional growth and predicts the island size distributions obtained in the different regimes. Finally, we show how our analysis can be used to interpret experimental data.Comment: 15 pages, Revtex. submitted to Surface Scienc

Aircraft measurements of microphysical properties of subvisible cirrus in the tropical tropopause layer

International audienceSubvisible cirrus (SVC) clouds are often observed within the tropical tropopause layer (TTL). Some studies suggest that SVC has a significant impact on the earth radiation budget. The Costa Rica Aura Validation Experiment (CR-AVE) sponsored by the National Aeronautics and Space Administration (NASA) took place near San Jose, Costa Rica from 14 January?15 February 2006. The NASA WB-57F sampled SVC in the TTL from ?75°C to ?90°C with an improved set of cloud particle probes. The first digital images of ice particles in the TTL are compared with replicator images of ice particles collected in 1973 by a WB-57F in the TTL. The newer measurements reveal larger particles, on the order of 100 ?m compared with <50 ?m from the earlier measurements, and also different particle shapes. The 1973 particles were mainly columnar and trigonal, whereas the newer measurements are quasi-spherical and hexagonal plates. The WB-57F also measured very high water vapor contents with some instruments, up to 4 ppmv, and aerosols with mixed organics and sulfates. It is unknown whether these ambient conditions were present in the 1973 studies, and whether such conditions have an influence on particle shape and the development of the large particles. A companion paper (Jensen et al., 2008) presents crystal growth calculations that suggest that the high water vapor measurements are required to grow ice particles to the observed sizes of 100 ?m and larger

The effect of monomer evaporation on a simple model of submonolayer growth

We present a model for thin film growth by particle deposition that takes into account the possible evaporation of the particles deposited on the surface. Our model focuses on the formation of two-dimensional structures. We find that the presence of evaporation can dramatically affect the growth kinetics of the film, and can give rise to regimes characterized by different ``growth'' exponents and island size distributions. Our results are obtained by extensive computer simulations as well as through a simple scaling approach and the analysis of rate equations describing the system. We carefully discuss the relationship of our model with previous studies by Venables and Stoyanov of the same physical situation, and we show that our analysis is more general.Comment: 41 pages including figures, Revtex, to be published in Physical Review

Stable unidimensional arrays of coherent strained islands

We investigate the equilibrium properties of arrays of coherent strained islands in heteroepitaxial thin films of bidimensional materials. The model we use takes into account only three essential ingredients : surface energies, elastic energies of the film and of the substrate and interaction energies between islands via the substrate. Using numerical simulations for a simple Lennard-Jones solid, we can assess the validity of the analytical expressions used to describe each of these contributions. A simple analytical expression is obtained for the total energy of the system. Minimizing this energy, we show that arrays of coherent islands can exist as stable configurations. Even in this simple approach, the quantitative results turn out to be very sensitive to some details of the surface energy.Comment: 24 pages, 7 figures. to be published in Surface Scienc

Draft final report of the LCM definition study

Life Cycle Management is a new framework to meet our present global challenges towards more sustainable patterns of production and consumption. In this context, LCM is offering a platform for the private and public sector. Thinking in systems and along product/service life cycles offers insights into how decisions should be made to improve a systems performance. The LCM concept has emerged out of industrial practice, but offers also opportunities for the public sector. In a new global understanding all market actors, policy makers, industry and consumers are essential players that need to find common platforms to achieve triple bottom line success - for all actors. In so far, LCM is rather opportunity driven as risk management or risk aversion driven. The LCM framework build on factual information and uses a variety of procedural and analytical tools, which themselves serve as underpinning of programs, management systems and, finally, corporate and policy strategies. The LCM Definition study positions existing tools, concepts and strategies in one overall framework, that allows sufficient flexibility to meet specific needs and thus also allows for flexibility for implementation. LCM is not a new “super”-tool that superimposes a new approach over existing successful practice. Opposite, LCM offers for the first time an umbrella framework, where tools that had been used in isolation before, can become mutually reinforcing and thus maximize their respective use. LCM is broad and flexible and reaches out to the public and private sector equally. The global challenges ahead of us require all market actors, and in particular industry and governments to align concepts and approaches to achieve the respective aims for all parties. Governments and the public sector need to provide the “right” framework and guidance under which the private sector then can realize its business objectives. Then this happens in a coordinated fashion

The Debrisoft ® monofilament debridement pad for use in acute or chronic wounds: A NICE medical technology guidance

As part of its Medical Technology Evaluation Programme, the National Institute for Health and Care Excellence (NICE) invited a manufacturer to provide clinical and economic evidence for the evaluation of the Debrisoft ® monofilament debridement pad for use in acute or chronic wounds. The University of Birmingham and Brunel University, acting as a consortium, was commissioned to act as an External Assessment Centre (EAC) for NICE, independently appraising the submission. This article is an overview of the original evidence submitted, the EAC’s findings and the final NICE guidance issued. The sponsor submitted a simple cost analysis to estimate the costs of using Debrisoft® to debride wounds compared with saline and gauze, hydrogel and larvae. Separate analyses were conducted for applications in home and applications in a clinic setting. The analysis took an UK National Health Service (NHS) perspective. It incorporated the costs of the technologies and supplementary technologies (such as dressings) and the costs of their application by a district nurse. The sponsor concluded that Debrisoft® was cost saving relative to the comparators. The EAC made amendments to the sponsor analysis to correct for errors and to reflect alternative assumptions. Debrisoft® remained cost saving in most analyses and savings ranged from £77 to £222 per patient compared with hydrogel, from £97 to £347 compared with saline and gauze, and from £180 to £484 compared with larvae depending on the assumptions included in the analysis and whether debridement took place in a home or clinic setting. All analyses were severely limited by the available data on effectiveness, in particular a lack of comparative studies and that the effectiveness data for the comparators came from studies reporting different clinical endpoints compared with Debrisoft®. The Medical Technologies Advisory Committee made a positive recommendation for adoption of Debrisoft® and this has been published as a NICE medical technology guidance (MTG17).The Birmingham and Brunel Consortium is funded by NICE to act as an External Assessment Centre for the Medical Technologies Evaluation Programme

The influence of groundwater abstraction on interpreting climate controls and extreme recharge events from well hydrographs in semi-arid South Africa

There is a scarcity of long-term groundwater hydrographs from sub-Saharan Africa to investigate groundwater sustainability, processes and controls. This paper presents an analysis of 21 hydrographs from semi-arid South Africa. Hydrographs from 1980 to 2000 were converted to standardised groundwater level indices and rationalised into four types (C1–C4) using hierarchical cluster analysis. Mean hydrographs for each type were cross-correlated with standardised precipitation and streamflow indices. Relationships with the El Niño–Southern Oscillation (ENSO) were also investigated. The four hydrograph types show a transition of autocorrelation over increasing timescales and increasingly subdued responses to rainfall. Type C1 strongly relates to rainfall, responding in most years, whereas C4 notably responds to only a single extreme event in 2000 and has limited relationship with rainfall. Types C2, C3 and C4 have stronger statistical relationships with standardised streamflow than standardised rainfall. C3 and C4 changes are significantly (p < 0.05) correlated to the mean wet season ENSO anomaly, indicating a tendency for substantial or minimal recharge to occur during extreme negative and positive ENSO years, respectively. The range of different hydrograph types, sometimes within only a few kilometres of each other, appears to be a result of abstraction interference and cannot be confidently attributed to variations in climate or hydrogeological setting. It is possible that high groundwater abstraction near C3/C4 sites masks frequent small-scale recharge events observed at C1/C2 sites, resulting in extreme events associated with negative ENSO years being more visible in the time series

Unconventional MBE Strategies from Computer Simulations for Optimized Growth Conditions

We investigate the influence of step edge diffusion (SED) and desorption on Molecular Beam Epitaxy (MBE) using kinetic Monte-Carlo simulations of the solid-on-solid (SOS) model. Based on these investigations we propose two strategies to optimize MBE growth. The strategies are applicable in different growth regimes: During layer-by-layer growth one can exploit the presence of desorption in order to achieve smooth surfaces. By additional short high flux pulses of particles one can increase the growth rate and assist layer-by-layer growth. If, however, mounds are formed (non-layer-by-layer growth) the SED can be used to control size and shape of the three-dimensional structures. By controlled reduction of the flux with time we achieve a fast coarsening together with smooth step edges.Comment: 19 pages, 7 figures, submitted to Phys. Rev.