A small scale regularly packed circulating fluidized bed. Part II: Mass transfer

The underlying objective of the present study is to increase gas¿solids contact in a circulating fluidized bed by the introduction of obstacles in the riser portion. The presence of such obstacles leads to suppression of radial inhomogeneities in the solids mass flux and concentration, and break-up of solids clusters. At ambient conditions, gas¿solids mass transfer was investigated for cocurrent upward flow of air and microsize solid particles (FCC, 70 ¿m diameter) over a regularly structured inert packing introduced into the riser part of a circulating fluidized bed unit. The packed section has a height of 0.48 m, a cross-sectional area of 0.06 × O.06 m2, and contains regularly stacked 0.01 m diameter Perspex bars as the obstacles meant to enhance the gas¿solids contact. Gas mass fluxes used were 1.4 and 2.7 kg m¿2 s¿1. Solids mass fluxes were varied in the range 0Gs 12 kg m¿2 s¿1. Experimental mass transfer data were obtained by applying the method of adsorption of naphthalene vapor on FCC particles. A conservative estimate of the apparent gas¿solids mass transfer coefficient kg* could be derived from the naphthalene vapor concentration profile along the packed section on the basis of a plug-flow-model interpretation, while assuming single-particle behaviour and neglecting intraparticle diffusion effects. Such kg* values appear to increase with increasing gas mass flux, but decrease with increasing solids mass flux (and consequently increasing solids volume fraction) probably due to the corresponding increase in particle shielding. Comparison of the present results with available literature data for similar solid materials suggests that the effect of the packing inserted into the CFB is significant: the Sherwood numbers derived from the present study are relatively high

A small scale regularly packed circulating fluidized bed. Part I: Hydrodynamics.

The present investigation is based on the idea of intensifying the gas¿solids contact in a circulating fluidized bed by introducing obstacles into it. Such obstacles may effectively suppress radial inhomogeneities in the solids flux and concentration, increase the dynamic solids hold-up, and break up solids clusters. This article (Part I) deals with the hydrodynamics (pressure drop and solids hold-up) investigated at ambient conditions, for cocurrent upward flow of air and microsize solid particles (FCC, 70 µm diameter) over a regularly structured inert packing introduced into the riser part of a circulating fluidized bed unit. The packed section has a height of 0.48 m, a cross-sectional area of 0.06 × 0.06 m2 and contains regularly-stacked 0.01 m diameter Perspex bars as the obstacles meant to enhance the gas¿solids contact. Slide-valves mounted above and below the packed section can be used to trap the solids inventory and determine the (dynamic) solids hold-up. Gas and solids mass fluxes have been varied in the range of 0.7 < Gg < 4.4 and O < Gs < 15 kg m-2s-2, respectively. Part II will report on the results of gas¿solids mass transfer measurements, which have been carried out in the same set-up at comparable experimental conditions. Results of this work show that: (i) the pressure gradient over the packed section increases linearly with increasing solids mass flux, but faster than linearly with increasing applied gas mass flux, (ii) the dynamic solids volume fraction can be described quite well by the correlation ß dyn = 0.0084 GsGg-1.22 for almost the entire range of applied gas and solids mass fluxes, (iii) the value for the solids friction factor derived for the gas flux range 0.7 < Gg < 3.7 kg (m-2s-1) varies from 1.4 to 2.5 and is linear with the solids volume fraction. These fs values are about 2 to 3 decades higher than those obtained from fs correlations derived for dilute-phase pneumatic conveying lines operated under the same experimental conditions

Optimization of layered double hydroxide stability and adsorption capacity for anionic surfactants

Low cost adsorption technology offers high potential to clean up laundry rinsing water. From an earlier selection of adsorbents (Schouten et al. 2007), layered double hydroxide (LDH) proved to be an interesting material for the removal of anionic surfactant, linear alkyl benzene sulfonate (LAS) which is the main contaminant in rinsing water. The main research question was to identify the effect of process parameters of the LDH synthesis on the stability of the LDH structure and the adsorption capacity of LAS. LDH was synthesized with the co-precipitation method of Reichle (1986); a solution of M2+(NO3)2 and M3+(NO3)3 and a second solution of NaOH and Na2CO3 were pumped in a beaker and mixed. The precipitate that was formed was allowed to age and was subsequently washed, dried and calcined. The process parameters that were investigated are the concentration of the initial solutions, M2+/M3+ ratio and type of cations. The crystallinity can be improved by decreasing the concentration of the initial solutions; this also decreases the leaching of M3+ from the brucite-like structure into the water. The highest adsorption capacity is obtained for Mg2+/Al3+ with a ratio 1 and 2 because of the higher charge density compared to ratio 3. Storing the LDH samples in water resulted in a reduction of adsorption capacity and a decrease in surface area and pore volume. Therefore, LDH is not applicable in a small device for long term use in aqueous surroundings. The adsorption capacity can be maintained during storage in a dry N2 atmosphere

Giant deer (Megaloceros giganteus) diet from Mid-Weichselian deposits under the present North Sea inferred from molar-embedded botanical remains

The molar of a giant deer, Megaloceros giganteus (Blumenbach, 1799), was discovered in sandy deposits of the North Sea, about 10 km west of the present shoreline of the Netherlands. Compacted masticated plant remains were preserved in the molar's deep folds. A palaeoecological analysis of these plant remains shows the complete dominance of pollen from Artemisia (sage) and other Asteraceae Tubuliflorae (Compositae), indicating that the animal foraged in a steppe environment, and may have preferred to eat Artemisia, which contain a high level of nutrients such as calcium and phosphorous components, which are important for antler building. Radiocarbon dating indicates that the plant remains are of mid‐Weichselian age [38 570 (+300, −290) 14C a BP, Greenland Interstadial‐11]. This is the first study of the food choice of M. giganteus based on palaeoecological evidence. We hypothesize about links between the extirpation of M. giganteus at the onset of the Holocene in North‐West Europe and the transition from a landscape with highly dynamic geomorphological processes and consequently prevalence of immature and nutrient‐rich soils, to a less dynamic landscape with stable, leached and acidifying soils, and the decline of Artemisia and other calciphilous plants

Functional performance of mobile versus fixed bearing total knee prostheses: a randomised controlled trial

PURPOSE: The primary goal of this study was to assess the difference in active flexion between patients with a mobile versus a fixed bearing, cruciate retaining, and total knee arthroplasty. The study was designed as a randomised controlled multi-centre trial. METHODS: Participants were assigned to interventions by using block-stratified, random allocation. Outcome parameters were active flexion, passive flexion, and Knee Society Score (KSS). Outcome parameters were assessed preoperatively and at 3, 6, and 12 months postoperatively by an independent nurse. RESULTS: Ninety-two patients from one centre were included, 46 in each group. Active flexion was comparable for the two groups, 99.9° for the mobile bearing group and 101° for the fixed bearing group with a baseline controlled difference of 1.0 (95% CI −3.9 to 5.8, n.s.). The Clinical KSS was comparable between the two bearing groups (Mobile 90.0 vs. fixed 92.4, n.s.). The functional KSS showed a difference that was attributable to the stair climbing subscore, which showed a difference in favour of the fixed bearing design between preoperative and 3 months (7.3 point difference; 95% CI 2.3–12.5; P = 0.005) as well as 12 months (4.8 point difference; 95% CI 0.1–9.6; P = 0.045). CONCLUSIONS: There were no short-term differences in active flexion between fixed bearing and mobile bearing total knee arthroplasty. LEVEL OF EVIDENCE: I

The mucosal adjuvant cholera toxin B instructs non-mucosal dendritic cells to promote IgA production via retinoic acid and TGF-β

It is currently unknown how mucosal adjuvants cause induction of secretory immunoglobulin A (IgA), and how T cell-dependent (TD) or -independent (TI) pathways might be involved. Mucosal dendritic cells (DCs) are the primary antigen presenting cells driving TI IgA synthesis, by producing a proliferation-inducing ligand (APRIL), B cell activating factor (BAFF), Retinoic Acid (RA), TGF-beta or nitric oxide (NO). We hypothesized that the mucosal adjuvant Cholera Toxin subunit B (CTB) could imprint non-mucosal DCs to induce IgA synthesis, and studied the mechanism of its induction. In vitro, CTB-treated bone marrow derived DCs primed for IgA production by B cells without the help of T cells, yet required co-signaling by different Toll-like receptor (TLR) ligands acting via the MyD88 pathway. CTB-DC induced IgA production was blocked in vitro or in vivo when RA receptor antagonist, TGF-beta signaling inhibitor or neutralizing anti-TGF-beta was added, demonstrating the involvement of RA and TGF-beta in promoting IgA responses. There was no major involvement for BAFF, APRIL or NO. This study highlights that synergism between CTB and MyD88-dependent TLR signals selectively imprints a TI IgA-inducing capacity in non-mucosal DCs, explaining how CTB acts as an IgA promoting adjuvant

Galactose inhibition of the constitutive transport of hexoses in Saccharomyces cerevisiae

The relationship between the pathways of glucose and galactose utilization in Saccharomyces cerevisiae has been studied. Galactose (which is transported and phosphorylated by inducible systems) is a strong inhibitor of the utilization of glucose, fructose and mannose (which have the same constitutive transport and phosphorylation systems). Conversely, all these three hexoses inhibit the utilization of galactose, though with poor efficiency. These cross-inhibitions only occur in yeast adapted to galactose or in galactose-constitutive mutants. The efficiency of galactose as inhibitor is even greater than the efficiencies of each of the other three hexoses to inhibit the utilization of each other. Phosphorylation is not involved in the inhibition and transport of sugars is the affected step. The cross-inhibitions between galactose and either glucose, fructose or mannose do not implicate utilization of one hexose at the expense of the other, as it occurs in the mutual interactions between the latter three sugars. it seems that, by growing the yeast in galactose, a protein component is synthesized, or alternatively modified, that once bound to either galactose or any one of the other three hexoses (glucose, fructose or mannose), cross-interacts respectively with the constitutive or the inducible transport systems, impairing their function.This work was supported by a grant (PB87-0206) from the DGICYT, Promoción General del Conocimiento.Peer Reviewe