The Effect of Strain Rate on Diffusion Flames

Several steady state and time-dependent solutions to the compressible conservation laws describing direct one-step near-equilibrium irreversible exothermic burning of initially unmixed gaseous reactants, with Lewis-Semenov number unity, are presented. The quantitative investigation first establishes the Burke-Schumann thin-flame solution using the Shvab-Zeldovich formulation. Real flames do not have the indefinitely thin reaction zone associated with the Burke-Schumann solution. Singular perturbation analysis is used to provide a modification of the thin-flame solution which includes a more realistic reaction zone of small but finite thickness. The particular geometry emphasized is the un bounded counterflow such that there exists a spatially constant rate of strain along the flame. While the solutions for diffusion flames under a finite tangential strain rate may be of interest in and of themselves for laminar flow, the problems are motivated by the authors' belief that they are pertinent to the study of diffusion-flame burning in transitional and turbulent shear flows

Extraction of silymarin compounds from milk thistle (Silybum marianum) seed using hot, liquid water as the solvent

High-value specialty chemicals are usually obtained from natural products by extracting with generally regarded as safe (GRAS) solvents. Because organic solvents are quite often used, high operating and disposal costs occur. When compared to traditional solvents, water is an interesting alternative because of its low operating and disposal costs. Milk thistle contains compounds (taxifolin, silychristin, silydianin, silybinin A, and silybinin B) that display hepatoxic protection properties. This paper examines the batch extraction of silymarin compounds from milk thistle seed meal in 50°C, 70°C, 85°C and 100°C water as a function of time. For taxifolin, silychristin, silybinin A, and silybinin B, extraction with 100°C water resulted in the highest yields. After 210 min of extraction at 100°C, the yield of taxifolin was 1.2 mg/g of seed while the yields of silychristin, silybinin A, and silybinin B were 5.0, 1.8 and 3.3 mg/g of seed, respectively. The ratios of the extracted compounds, and particularly the ratios at long extraction times, showed that the more polar compounds (taxifolin and silychristin) were preferentially extracted at 85°C, while the less polar silybinin was preferentially extracted at 100°C

Analytic studies on satellite detection of severe, two-cell tornadoes

It is argued that a two-cell structure is likely to be the unique property, and potentially satellite-accessible observable, of the exceptionally severe tornado. Analysis elucidating the dynamic, thermodynamic, and geometric properties of this two-cell structure is described. The analysis ultimately will furnish instrumentation requirements

Méthode de dimensionnement du réservoir dans les systèmes de pompage photovoltaïques

L'un des plus urgents problèmes auquel ont à faire face plusieurs pays en voie de développement est l'accès à l'eau potable. La plus grande partie de la population touchée par ce problème se retrouve en milieu rural, éloignée des grands réseaux de distribution d'électricité. Pour tenter de résoudre cette crise, l'introduction de systèmes de pompage photovoltaïques (PV), dans le cadre de programmes de pré-électrification rurale, offre une solution attrayante pour satisfaire les besoins en eau, en terme d'autonomie, de fiabilité et de performance.Un système de pompage photovoltaïque comprend un champ de modules PV qui transforme l'énergie solaire en électricité. Un onduleur (aussi appelé convertisseur) transforme ensuite le courant continu (CC) généré par le champ en courant alternatif (CA), ce dernier permettant d'alimenter un groupe moto-pompe (GMP) qui peut être immergé - dans un puits ou un forage - ou de surface (sur une rivière). II existe aussi des GMP à courant continu. Au lieu de stocker les surplus d'énergie produite dans de dispendieux accumulateurs (batteries), ce sont les surplus d'eau pompée que l'on emmagasine dans un réservoir. Ce système, dit « au fil du soleil », a obtenu d'excellentes performances en conditions réelles d'opération. Cependant, avec les méthodes de conception actuelles, la taille du réservoir est souvent grossièrement estimée.Dans le cas d'un réservoir trop petit, il en résulte une insatisfaction des usagers lorsque des débordements de réservoir se produisent. Ce gaspillaged'eau fait subir à la population des privations en ce qui concerne la consommation personnelle et affecte la rentabilité de l'opération quand les excédents d'eau sont habituellement vendus ou destinés à l'irrigation. Lorsque le réservoir est sur-dimensionné, les villageois ont alors à faire face à des coûts de construction trop élevés.La démarche entreprise dans cet article a pour but d'offrir une méthode de conception du réservoir qui ne se base pas uniquement sur le jugement et/ou les expériences passées.L'analyse du comportement des différentes composantes d'un système de pompage solaire a permis de mettre au point des modèles informatiques qui ont ensuite été validés grâce à des données obtenues sur le terrain au Sénégal. Le logiciel développé dans ce travail a pour but d'offrir une grande flexibilité pour la simulation de différents types d'équipement dans divers milieux d'opération. La qualité des résultats dépend étroitement de la précision des paramètres décrivant l'équipement et des données météorologiques.Grâce au logiciel, on pourra prédire le fonctionnement de nouvelles installations et assurer le suivi des systèmes déjà en place. La personne qui doit concevoir le système PV, de concert avec la communauté villageoise, sera capable de déterminer la taille optimale du réservoir (et peut-être valider les résultats obtenus avec les règles empiriques) permettant ainsi de mieux évaluer les coûts et les risques de pénurie qui sont liés à l'exploitation d'un système de pompage PV.Access to safe water supply is one of the must urgent problems in many developing countries. Most populations affected by this problem are in rural areas, where electricity distribution networks are not yet installed. In order to alleviate this crisis, the introduction of photovoltaic (PV) pumping systems provides an attractive solution to satisfy water needs, in terms of autonomy, reliability and performance.A solar pumping system consists of an array of PV modules that transform solar energy into electricity. An inverter converts the direct current (DC) generated by the array to alternating current (AC), that can then be used by a motor-pump unit, either submerged (in a borehole or a well) or an a river surface. DC motor-pump units can also be used. Instead of charging expansive batteries with the excess energy generated, the water is pumped and stored in a reservoir. This type of system yields excellent performances in real-time operating conditions. The site of the tank is, however, often roughly estimated in conventional design procedures.Consequently, problems such as the heavy financial burden of an over-sized tank or, on the contrary, a waste of water resources due to spillage in the case of a too-small tank are, unfortunately, quite common. These problems lead to dissatislaction among users when they have to deal with periods of personal water shortages and, in situations where the water is sold or used for irrigation, economic losses.The process introduced in this paper provides a design tool for sizing the water tank that goes further than mere « guestimates ».Analysis of the behaviour of the different components of a solar system was incorporated into computerized models, which were then validated with data gathered during field studies carried out in Senegal. The resulting software gives the designer flexibility to simulate different types of equipment under various operating conditions. The quality of the results depends closely an the accuracy of the parameters describing the equipment as well as on the reliability of the meteorological data.Different models are used in the software. The hourly climatic conditions (solar radiation and temperature) are simulated using the normal distribution. The model used to find the current-voltage (I-V) characteristics of the solar array has been developed by the Jet Propulsion Laboratory. The motor and centrifugal pump are modelled with a third order equation often used in practice. Finally, the optimal tank size is found with the volumetric method proposed by Al-Layla.From the climatic data the software enables the designer to study a typical day for a selected period of time, usually during the month with the lowest solar radiation. From the climatic data, the PV array output power for every hour of the day, the pumping flow-rate and finally the amount of water in the tank can be determined. Five scenarios of available sunshine have been calculated, allowing the designer to evaluate low-risk situations (low sunshine expected, thus larger equipment needed) and high-risk situations (higher sunshine, requiring smaller equipment).The software permits the prediction of performance for new systems as well as the diagnosis of existing ones. The system designer, in consultation with users, can then find the optimal size of the water tank (and possibly confirm the results obtained from the rule-of-thumb estimates) and better assess, with the help of a decision-making chart, the cost of a system and the risks of water shortages

Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions

Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes equations are considered for the case of the two-dimensional uniform flow past an impulsively-started circular cylinder. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions that can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

Incompressible viscous flow near the leading edge of a flat plate admitting slip

The shear stress at the leading edge, calculated on basis of the Navier-Stokes equations and the no-slip boundary condition, approaches infinity. However, taking into account the mean free path of the molecules, which implies admitting a certain slip, the shear stress becomes inversely proportional to the square root of the Knudsen number κ if κ→0. κ is defined as the ratio between the mean free path and the viscous length. The new boundary condition modifies the shear stress only within the Knudsen region of which the size is of the order of 3 to 4 times the mean free path.

Searching for solar-like oscillations in the delta Scuti star rho Puppis

Despite the shallow convective envelopes of delta Scuti pulsators, solar-like oscillations are theoretically predicted to be excited in those stars as well. To search for such stochastic oscillations we organised a spectroscopic multi-site campaign for the bright, metal-rich delta Sct star rho Puppis. We obtained a total of 2763 high-resolution spectra using four telescopes. We discuss the reduction and analysis with the iodine cell technique, developed for searching for low-amplitude radial velocity variations, in the presence of high-amplitude variability. Furthermore, we have determined the angular diameter of rho Puppis to be 1.68 \pm 0.03 mas, translating into a radius of 3.52 \pm 0.07Rsun. Using this value, the frequency of maximum power of possible solar-like oscillations, is expected at ~43 \pm 2 c/d (498 \pm 23 muHz). The dominant delta Scuti-type pulsation mode of rho Puppis is known to be the radial fundamental mode which allows us to determine the mean density of the star, and therefore an expected large frequency separation of 2.73 c/d (31.6 muHz). We conclude that 1) the radial velocity amplitudes of the delta Scuti pulsations are different for different spectral lines; 2) we can exclude solar-like oscillations to be present in rho Puppis with an amplitude per radial mode larger than 0.5 m/s.Comment: 14 pages, 12 figure, accepted for MNRA

Investigation of molluscan survivorship across the Cenomanian-Turonian Boundary Event using ecological niche modeling

In the beginning of the Late Cretaceous, the Western Interior Seaway experienced the effects of a global ocean anoxic event (OAE2, or the Bonarelli Event) across the Cenomanian-Turonian (C/T) boundary (~94 Ma). This event resulted in major environmental and biological disturbances creating significant biotic turnover, with recent research suggesting near mass extinction levels in some clades. In this study we utilize a paleobiological application of a modern ecological modeling technique (PaleoENM), to test whether changes in species’ survivorship and distribution patterns across this event relate to changes in their predicted suitable habitat area and abiotic niche dimensions. Results suggest that survivorship across the C/T is not strongly correlated with available suitable habitat. Additionally, a quarter of the taxa demonstrate significant abiotic niche stability across the C/T. These findings are consistent irrespective of higher taxonomic groups (i.e., genera), which suggests taxon-specific responses to environmental changes at the macroevolutionary scale of this study. This research supports the importance of biogeography in understanding and predicting species longevity and the maintenance of biodiversity. Application of the general principles described here to modern biological systems perturbed by human-induced anoxia may positively inform conservation efforts and predictions of modern extinction dynamics

An analysis of selected personality characteristics of guidance associates at North Texas State University

The problem under investigation was a description and analysis of change in selected personality characteristics of guidance associate students during the first and second year of training in the undergraduate curriculum designed for the Guidance Associate Degree at North Texas State University