196,216 research outputs found
Rôle des forces de portance et diffusion hydrodynamique dans le processus de séparation par la technique de SPLITT
No full textLa séparation ou le tri des particules et des cellules sanguines peut être réalisée au moyen d'une technique appelée Splitt-Flow Thin Fractionation (SPLITT). Les espèces sont entraînées par un liquide vecteur dans une cellule mince et la séparation dépend fortement de la migration des espèces perpendiculaire à l'écoulement. Nous étudions expérimentalement les forces de portance hydrodynamique, et la diffusion hydrodynamique induite par cisaillement, en tant que mécanismes de transport transversal de particules en écoulement. Par comparaison d'expériences réalisées au sol et en micropesanteur, nous montrons l'influence de la gravité dans le processus de séparation à travers les forces de portance. En faisant varier les paramètres de l'écoulement, nous montrons également l'influence de la diffusion hydrodynamique dans le processus de séparation par la technique de SPLITT
Extraktion von Diatomeenschalen mittels SPLITT-Fraktionierung. Ein neues Verfahren zur Abtrennung von Diatomeenschalen aus limnischen Sedimenten
No full textDiatom frustules are an interesting tool for climatic and ecological research and they have for some time been employed in isotope research work as a paleothermometer. Diatom frustules are Said to be very stable over a long period of time, and thus the stable oxygen isotopes within the frustule's SiO can under certain conditions represent a good proxy for climatic or ecological reconstructions (Juillet, 1980; Juillet & Labeyrie, 1987; Shemesh et al., 1992). Especially in those cases where carbonates are not available for climate research, diatoms seem to be a very promising alternative. This is for example the situation in the high resolution sedimentary sequences of Westeifel Maar lakes. The sedimentary sequences consist of turbidites, siderit-laminites and annually laminated diatomaceous gyttja but mostly lack any carbonates (Negendank & Brauer & Zolitschka, 1990). The problem, however, is to get highly purified diatom material for reliable oxygen isotope investigations. This implies that minerogenic impurities have to be separated since they can easily alter the isotope signal of a diatom layer and, thus, lead to wrong results. Additionally it is in many cases desirable to distinguish between diatom fractions of different sizes, i.e. to distinguish between different diatom species. It therefore was the aim of this work to develop a new method for separating quantitatively diatom frustules from lake sediments for investigations of the stable oxygen isotope composition in diatom SiO. This method uses a new technique for separating particles depending an their sinking velocity in a liquid, streaming through a narrow channel. The technique to be used splits particles hydrodynamically into different size classes, a procedure which is called SPLITT-fractionation (split-flow lateral-transport thin Separation cells) and was first presented by Giddings (1985). As with field-flow fractionation (FFF) techniques, thin flow channels in conjunction with a field (gravitation) applied perpendicular to the flow are used for SPLITT-fractionation. A sample suspension containing the particles to be separated is continuously introduced through one inlet into the cell while Sediment-free liquid is introduced into the cell through a second inlet. Within the cell the two flows merge smoothly, the suspension overlying the sediment-free carrier flow, resulting in a laminar flow in which the Separation of particles takes place. Within the laminar current grains migrate according to their density, shape and ABSTRACT size towards either of two outlets. As a result the sample will be divided into two fractions around a cut-off diameter, which is controlled by the ratio of the two outlet flow rates. As diatoms behave hydrodynamically different compared with mineral grains, the described method provides a tool to separate them by SPLITT-fractionation. The advantages of SPLITT-fractionation over other separating methods for diatoms are reproducibility, high throughput by continuous flow, minimum losses, fast procedure and minimum contamination of the sample. The SPLITT cell used in this study has a length of 20 cm, a breadth of 4 cm, and a height of 371 m. The Sample concentration used was below 1 weight percent to minimise particle-particle interaction which spoils resolution. Sediment samples of different origin, age, compaction and diatom amount were tested. In a first step a method was established to suspend the material in water with HO (30%). In this process also most of the organic matter was removed, to prevent agglomeration in the sample suspension. Afterwards the samples were sieved into fractions of > 80m, 20 - 80m and < 20 m. The fractions < 80 m were used for SPLITT-fractionation. The fraction 20 - 80 m was fractionated in one step. Because of the small amount of grains with hydrodynamical properties similar to diatom skeletons, it was relatively easy to get a clean diatom fraction. The fraction < 20 m was treated several times to enrich a sample fraction with diatoms. Because of the high amount of mineral grains (especially grains with equal sinking velocities) it wasn't possible to get an entirely clean sample of diatom frustules. To avoid problems related therewith an additional step was introduced by dividing the corresponding samples with 5 and 10 m sieves. The resulting fractions do no more contain minerals with hydrodynamical properties of diatoms and therefore a separation of diatom frustules is again possible. In addition a method was developed for analysing grain distribution and amount of diatom frustules using image processing methods. For each SPLITT-fractionation subsamples from the two outlets were collected and photographed under the microscope. The pictures were then evaluated using image processing software. The photographs represented the particle size distribution of the fractions, the amount of frustules and gave a cut-off diameter at different in- and outlet flowrates
SPLITT cell analytical separation of silica particles. Non-specific crossover effects: Does the shear-induced diffusion play a role?
No full textThe gravitational split-flow lateral transport thin fractionation is known to be a fast, simple, theoretically tractable and tunable tool for the binary separation of molecular or particulate samples into different dimensional fractions. This fractionation is performed in a so-called SPLITT cell and is due to the combined effect of the gravitational force field and the flow rates inside the separation channel. It is known that separation performance is strongly dependent on the flow rate conditions and feed flow concentration, however, to date, few studies have been conducted to investigate the effect non-specific crossover has on separation. The aim of this work is to establish whether diffusive processes stemming from hydrodynamic effects contribute in any way to the quality of separation. A silica sample of known ranule size distribution was chosen for this study which has nvironmental applications
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
- …
