Pulse-to-pulse coupling in cylindrical discharges

Several filamentary discharges can be applied to a combustible mixture, which can then ignite. The energy density of this discharge is a vital parameter, as it directly influences the local temperature rise and radical production. The goal of this article is to investigate how a previous discharge affects the energy density of a second discharge. To investigate the pulse-to-pulse coupling of filamentary discharges a one-dimensional numerical model is developed. In the developed model, the compressible Navier-Stokes equations are coupled to a plasma model. The plasma model is used to estimate the local energy density, while the compressible Navier-Stokes equations model the reactive flow. As a first step, skeletal air plasma chemistry is used, which includes fast gas heating, slow gas heating and the rapid generation of radicals. The skeletal plasma chemistry is combined with a detailed hydrogen combustion mechanism. Simulations in both air and hydrogen/air are conducted at several discharge energies and pressures. From the analysis of these results, we conclude that the main mechanism of pulse-to-pulse coupling is the reduction in molar density due to temperature rise.</p

Numerical determination of iron dust laminar flame speeds with the counter-flow twin-flame technique

Iron dust counter-flow flames have been studied with the low-Mach-number combustion approximation. The model considers full coupling between the two phases, including particle/droplet drag. The dispersed phase flow strain relations are derived in the Stokes regime (Reynolds number much smaller than unity). The importance of solving a particle flow strain model is demonstrated by comparing three different cases: a free unstrained flame, a counter-flow flame where slip effects are neglected and a counter-flow flame where slip effects are included. All three cases show preferential diffusion effects, due to the lack of diffusion of iron in the fuel mixture, e.g. DFe,m= 0. The preferential diffusion effect causes a peak in the fuel equivalence ratio in the preheat zone. On the burned side, the combined effect of strain and preferential diffusion shows a decrease in fuel equivalence ratio. Inertia effects, which are only at play in the counter-flow case with slip, counteract this effect and result in an increase of the fuel equivalence ratio on the burned side. A laminar flame speed analysis is performed and a recommendation is given on how to experimentally determine the flame speed in a counter-flow set-up. Novelty &amp; Significance We introduce a novel model to include particle flow strain in a dispersed counter-flow set-up. For the first time, the impact of particle flow strain on the flame structure of iron dust is studied with a one-dimensional (1D) model. Two major effects that modify the flame structure and burning velocity are identified: preferential diffusion and inertia of the particles. Preferential diffusion effects are found to be always present in (iron) dust flames. Inertia effects play a role in the counter-flow case with slip. Due to the inertia of the particles, the particle flow strain is lower than the gas flow strain. As a consequence, higher particle concentrations are reached compared to the other cases. Furthermore, it is shown that each particle size experiences a different particle flow strain rate, which is important when doing experiments as it implies that the PSD at the flame front will be different than at the inlet.</p

Drought at the global scale in the 2nd part of the 20th century (1963-2001)

The large impacts of drought on society, economy and environment urge for a thorough investigation. A good knowledge of past drought events is important for both understanding of the processes causing drought, as well as to provide reliability assessments for drought projections for the future. Preferably, the investigation of historic drought events should rely on observations. Unfortunately, for a global scale these detailed observations are often not available. Therefore, the outcome of global hydrological models (GHMs) and off-line land surface models (LSMs) is used to assess droughts. In this study we have investigated to what extent simulated gridded time series from these large-scale models capture historic hydrological drought events. Results of ten different models, both GHMs and LSMs, made available by the WATCH project, were compared. All models are run on a global 0.5 degree grid for the period 1963-2000 with the same meteorological forcing data (WATCH forcing data). To identify hydrological drought events, the monthly aggregated total runoff values were used. Different methods were developed to identify spatio-temporal drought characteristics. General drought characteristics for each grid cell, as for example the average drought duration, were compared. These characteristics show that when comparing absolute values the models give substantially different results, whereas relative values lead to more or less the same drought pattern. Next to the general drought characteristics, some documented major historical drought events (one for each continent) were selected and described in more detail. For each drought event, the simulated drought clusters (spatial events) and their characteristics are given for one month during the event. It can be concluded that most major drought events are captured by all models. However, the spatial extent of the drought events differ substantially between the models. In general the models show a fast reaction to rainfall and therefore also capture drought events caused by large rainfall anomalies. More research is still needed, since here we only looked at a few selected number of documented drought events spread over the globe. To assess more in detail if these large-scale models are able to capture drought, additional quantitative analyses are needed together with a more elaborated comparison against observed drought events

Experimental and theoretical study of single iron particle combustion under low-oxygen dilution conditions

In the present study, a novel in situ particle sizing approach is proposed and used to measure the characteristic timescales of micron-sized iron particle combustion under low-oxygen (10–17 vol%) dilution conditions. The particle size is determined by probing the light emission intensity of a burning particle during melting, which is proportional to the cross-section area of the particle projected to the camera. Detailed descriptions of the calibration, validation, and characterization of the experimental method are elaborated. With systematic measurements, we obtain one-to-one correlations between combustion timescales and single particle diameters at various diluted oxygen concentrations. Furthermore, we formally derive a theoretical model for heterogeneous combustion of growing (iron) particles in the diffusion-limited regime. The model suggests that the diffusion-limited burn time scales with the initial particle diameter squared (i.e., a new, generalized d2-law). Owing to accounting for the particle growth, the newly derived model suggests a significantly (1.66 times) shorter combustion duration compared to the conventional d2-law for shrinking particle combustion. It turns out that the new model agrees well with the experiment. This agreement also suggests that under low-oxygen dilution conditions, the combustion regime of iron particles during the intensive burning stage (i.e., from ignition to the peak particle temperature) is limited by external oxygen diffusion.</p

Dé juiste lezing bestaat niet! Hoe je vanuit een open houding tot dialogisch leesonderwijs komt

Vaak behandelen we teksten in de klas ten onrechte alsof er maar één mogelijke interpretatie is, waarbij leraren het als hun taak zien om hun leerlingen mee te nemen in die ene ‘ juiste lezing’. Vaak zijn er echter meerdere interpretaties mogelijk en kan de visie die uit de tekst spreekt kritisch benaderd worden. Dat zou leerzame gesprekken opleveren. Dit artikel bespreekt hoe een dialogische aanpak in het leesonderwijs ook al op basisscholen kan helpen om leraren en leerlingen gelijkwaardig en kritischer te laten nadenken over tekstbetekenissen. Hierbij is de benadering die leraren (en leerlingen) tegenover teksten aannemen cruciaal. Welke benadering stimuleert een goede dialoog over een tekst? En wat betekent dit voor de tekstkeuze en voor wat leraren moeten weten en kunnen

Tissue biopsy for the diagnosis of amyloidosis: experience from some centres

A reliable diagnosis of amyloidosis is usually based on a tissue biopsy. With increasing options for specific treatments of the different amyloid diseases, an exact and valid diagnosis including determination of the biochemical fibril nature is imperative. Biopsy sites as well as amyloid typing principles vary and this paper describes methods employed at some laboratories specialised in amyloidosis in Europe, Japan and USA

Text structure instruction in primary education: Effects on reading, summarization, and writing

Although knowledge of informational text structures can promote text comprehension, this topic receives little attention in the Dutch primary school curriculum. 201 Dutch students in grades 4-6 participated with their teachers (n = 10) in this quasi-experimental study with a switching-panels replication design. Students either first followed a text structure intervention (TOP) and then went back to business-as-usual, or the other way around. During the intervention, teachers taught their students about the characteristics of four informational text structures, and how to use structure-specific graphic organizers to organize main ideas for each structure. In addition, several writing tasks related to the different text structures were included. At three measurement occasions, students completed text structure tests, reading comprehension tests, summarization tasks, and writing tasks. Only the fourth graders in one iteration of the intervention showed immediate effects over and above the effect of business-as-usual lessons on the text structure test (d = 0.50), the reading comprehension test (d = 0.53), the summarization task (d = 0.48). In both iterations of the intervention, an immediate effect was found on writing (d = 0.33 and d = 0.39). These findings are discussed in the light of test-related issues and implementation fidelity data

External ureteric stent versus internal double J stent in kidney transplantation:a retrospective analysis on the incidence of urological complications and urinary tract infections

INTRODUCTION: Urologic complications (UCs) and urinary tract infections (UTIs) are common after kidney transplantation. Intraoperative stent placement at the vesicoureteric anastomosis reduces UC risk, but increases UTI risk.METHODS: In 2014 our stenting protocol changed from external ureteric stent (ES) to internal double J stent (DJ). We retrospectively studied the occurrence of UCs and UTIs in relation to ES or DJ in 697 kidney recipients.METHODS: An ES was used in 403 patients (57.8%), in 294 (42.2%) a DJ. ES was removed 7-12 days and DJ 3-4 weeks post-operative. Induction immunosuppression was the same in both groups. Primary outcomes at 6 months follow-up were UC (urinary leakage/ureter stenosis) and UTI; they were related to stenting procedure and clinical and transplant characteristics. The incidence of UCs was similar for ES (8.4%) and DJ (6.8%), p=0.389. ES use was a significant risk factor for UTI (OR 1.69 (1.15-2.50), p=0.008). Post-transplant hospitalization was significantly shorter in the DJ group. Despite more acute rejection episodes with ES (ES/DJ: 16.4%/6.1%, p&lt;0.001), no clinical relevant differences in graft outcomes existed.DISCUSSION: A DJ is, compared to ES, associated with a lower incidence of UTIs and comparable occurrence of UCs and is therefore the preferred technique for stenting the vesicoureteric anastomosis.</p

Global multimodel analysis of drought in runoff for the second half of the twentieth century

During the past decades large-scale models have been developed to simulate global and continental terrestrial water cycles. It is an open question whether these models are suitable to capture hydrological drought, in terms of runoff, on global scale. A multi-model ensemble analysis was carried out to evaluate if ten of such large-scale models agree on major drought events during the second half of the 20th century. Time series of monthly precipitation, monthly total runoff from ten global hydrological models, and their ensemble median have been used to identify drought. Temporal development of area in drought for various regions across the globe was investigated. Model spread was largest in regions with low runoff and smallest in regions with high runoff. In vast regions, correlation between runoff drought derived from the models and meteorological drought was found to be low. This indicated that models add information to the signal derived from precipitation and that runoff drought cannot directly be determined from precipitation data alone in global drought analyses with a constant aggregation period. However, duration and spatial extent of major drought events differed between models. Some models showed a fast runoff response to rainfall, which led to deviations from reported drought events in slowly responding hydrological systems. By using an ensemble of models, this fast runoff response was partly overcome and delay in drought propagating from meteorological drought to drought in runoff was included. Finally, an ensemble of models also allows to consider uncertainty associated with individual model structures