Systematic mesh development for 3D CFD simulation of fixed beds: Single sphere study

To develop and validate meshes for computational fluid dynamics (CFD) simulations of transport in fixed beds, a single particle is often used as a test case. We present results for drag coefficient (C_D) and heat transfer Nusselt number (Nu) for flow past a sphere, focusing on high flow rates typical of industrial steam reformers (400 < Re < 20,000). Over this range, good predictions of C_D were obtained using large eddy simulation (LES) to capture vortex shedding and wake dynamics, with a mesh refined downstream from the sphere. The small time-steps and high cell count required make this too expensive for fixed beds. Nu can be accurately calculated using a Reynolds-averaged Navier-Stokes (RANS) method with shear-stress transport (SST) k-ω closure provided the mesh at the particle surface is fine enough and covers most of the boundary layer. Single sphere simulations of heat transfer are more useful for fixed bed mesh development than drag coefficient calculations.     

Second gene expression in bicistronic constructs using short synthetic intercistrons and viral IRES sequences

The authors addressed 5 issues bearing on the validity of the construct of depressive personality disorder (DPD): its relationship with the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987) mood and personality disorders and normal personality dimensions of negative and positive affectivity, its stability over 30-months, and its impact on the course of Axis I depressive disorders. Two samples were used: 156 outpatients with mood disorders, personality disorders, or both, and 267 of their 1st-degree relatives. The association between DPD and dysthymia was fairly modest, whereas the associations with major depression and the personality disorders were quite low. DPD was moderately correlated with both negative and positive affectivity; however, it contributed unique information beyond that available from the 2 emotional superfactors. Finally, DPD was moderately stable over a 30-month period and was associated with a poorer course of depression.     

Multidirectional Subspace Expansion for One-Parameter and Multiparameter Tikhonov Regularization

Tikhonov regularization is a popular method to approximate solutions of linear discrete ill-posed problems when the observed or measured data is contaminated by noise. Multiparameter Tikhonov regularization may improve the quality of the computed approximate solutions. We propose a new iterative method for large-scale multiparameter Tikhonov regularization with general regularization operators based on a multidirectional subspace expansion. The multidirectional subspace expansion may be combined with subspace truncation to avoid excessive growth of the search space. Furthermore, we introduce a simple and effective parameter selection strategy based on the discrepancy principle and related to perturbation results.     

The pressure drop experiment to determine slug lengths in multiphase monoliths

The length of the liquid slugs, that separate the elongated bubbles in Taylor flow, is an important parameter for mass transfer, flow stability and pressure drop in capillary microchannels. In this work, pressure drop measurements are used to determine the length of slug in Taylor flow in downflow monoliths. The method is sensitive if the slugs are relatively short, less than 10 times the channel diameter. The pressure drop measurements are a cheap and fast alternative to tomographic or electric methods. Experiments using different distributors indicate that the slug length varies significantly with changes in the hydrodynamics in the feed section of the monoliths. Slug length correlations that are based on parameters inside the channels can therefore not safely be used for a different setup. As a result, the slug length should be measured in each experimental setup, which makes a inexpensive and robust method to do so very welcome.     

Time-lapse,three-dimensional in situ imaging of ice crystal growth in a colloidal silica suspension

The freezing of colloidal suspensions is encountered in many natural and engineering processes such as the freezing of soils, food engineering and cryobiology. It can also be used as a bio-inspired, versatile and environmentally friendly processing route for porous materials and composites. Yet, it is still a puzzling phenomenon with many unexplained features, owing to the complexity of the system and the space and time scales at which the process should be investigated. This study demonstrates the interest in fast X-ray computed tomography for providing time-lapse, three-dimensional, in situ imaging of ice crystal growth in a colloidal silica suspension. The experimental measurements show that the local increase in colloid concentration does not affect the growth kinetics of the crystals until the colloidal particles become closely packed. For particles much smaller than ice crystals, the concentrated colloidal suspension is equivalent to a simple liquid phase with higher viscosity and a freezing point determined by the concentration of colloidal particles.     

Science and technology of catalytic diesel particulate filters

During the last few decades, concerns have grown on the negative effects that diesel particulate matter has on health. Because of this, particulate emissions were subjected to restrictions and various emission-reduction technologies were developed. It is ironic that some of these technologies led to reductions in the legislated total particulate mass while neglecting the number of particles. Focusing on the mass is not necessarily correct, because it might well be that not the mass but the number of particles and the characteristics of them (size, composition) have a higher impact on health. To eliminate the threat of diesel particulate matter, essentially absolute filtration in combination with the oxidation of all emitted hydrocarbons is what will be required.

After two decades of development, the first filters will soon be introduced on a large scale. Many different problems had to be overcome; it was especially important that the filter was robust and its regeneration was controllable. The key technology to controllable regeneration is oxidation catalysis, which is the main area of focus in this review. Catalytic filter regeneration is very complex, something which is apparent in the main aspects of catalysis (i.e., activity, stability, and selectivity). Complications are that the process conditions can be very transient and that the temperatures are usually low. It is shown that the oxidation catalyst cannot be examined isolated from the total system. Within the margins of size restrictions and an engine's service life, essentially all particulate matter should be trapped, the filter should be regenerated safely, no toxic by-products should be formed, and the catalyst should not alter the filtration characteristics, and vice versa.

The exhaust conditions of passenger cars are not favorable for continuous regeneration strategies, because the best strategy seems to be periodic regeneration with the aid of a catalyst. This concept is not passive, which makes it complex and expensive. The best technology for filter regeneration with trucks and buses seems to be continuous regeneration. Using the NO_x present in the exhaust gas for soot oxidation amounts to a simple and robust concept. A future limitation might be the minimal required NO_x:soot ratio; it is not sure if this will be met in future engines. Alternatively, a low-temperature catalyst may be developed that does not require NO_x. Developing such an advanced catalytic trap will be one of the major challenges of catalytic filter engineering.     

The Impact of Software Growth on the Electronics Industry

Software growth has significantly impacted the computer industry and is changing many other electronics industries. It is not a question of whether intellectual property will be sold in the form of software, but which companies will do it successfully. The actions electronics companies take today will ultimately determine how large a role they will play in a world increasingly dominated by software     

The value of site-based observations complementary to naturalistic driving observations: A pilot study on the right turn manoeuvre

Naturalistic driving studies are increasingly applied in different shapes and sizes. The European project PROLOGUE has investigated the value and feasibility of a large-scale naturalistic driving study in Europe. Within PROLOGUE several pilot studies have been conducted in different countries. The Dutch field trial investigated the value and feasibility of adding site-based observations to in-vehicle observations.     

Chemical analysis of heat treated softwoods

Heat treatment of wood has been found an effective method to improve dimensional stability and durability against biodegradation. A two-stage heat treatment of wood at relatively mild conditions (<200 °C) was investigated by using different chemical analysing methods, such as a wood chemical component analysis, CHNO-elemental analysis, UV-spectroscopy, and analysis of the acetyl and free hydroxyl group content. The results of this study contribute to a better understanding of the typical reaction mechanisms occurring and of the effect of heat treatment on the properties of wood, as described in previous 13C-NMR and FTIR studies of heat treated wood.