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Digitale Medien

Analysis of the transient behavior of kidney models (1978)

Stephenson, John L.

Springer

Bulletin of mathematical biology 40 (1978), S. 211-221

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ISSN: 1522-9602

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Mathematik

Notizen: Abstract Non-steady-state equations for kidney models are stated. General conservation relations for these equations are derived. Transient equations for the central core model of the renal medulla are developed. Solution of the equations by Laplace transform methods for time invariant volume flows is discussed. The general theory of solving models with time dependent flows by finite difference methods is developed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02461436

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2

Digitale Medien

Transient behaviour of the single loop solute cycling model of the renal medulla (1978)

Garner, Jackie B. ; Crump, Kenny S. ; Stephenson, John L.

Springer

Bulletin of mathematical biology 40 (1978), S. 273-300

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ISSN: 1522-9602

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Mathematik

Notizen: Abstract Transient solutions are developed for the buildup of a concentration gradient in the single loop solute cycling model of the renal medulla. The “pump” from ascending limb to descending limb is considered in both unsaturated and completely saturated modes of operation. Both analytic solutions and semianalytic solutions obtained from inverting Laplace transforms are considered. The classic representation of concentration buildup by the multiplication process is compared with calculated profiles. The “single effect” is found to vary both in time and space.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02461602

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3

Digitale Medien

Vitamin addition: an option for sustainable activated sludge process effluent quality (2000)

Burgess, J E ; Quarmby, J ; Stephenson, T

Springer

Journal of industrial microbiology and biotechnology 24 (2000), S. 267-274

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ISSN: 1476-5535

Schlagwort(e): Keywords: vitamins; activated sludge; industrial wastewater; porous pots; Amtox™

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: The process performance and metabolic rates of samples of activated sludge dosed with vitamin supplements have been compared. After initial screening, four vitamins and two metals as single supplements and in pairs, were dosed continuously into the mixed liquor of an activated sludge simulation. Toxicity, oxygen demand removal, respiration rates and suspended solids were measured to monitor the effect on process efficiency. It was confirmed experimentally that an industrial wastewater stream did not contain a sufficient supply of micronutrients for efficient biological treatment. This was concluded from the observation that control sludge batches (receiving no supplements) averaged chemical oxygen demand removal efficiency of 58%. Dosing micronutrients into the mixed liquor produced removal efficiencies of up to 69%. Some of the supplements increased the respiration rate of the sludge while some decreased it, indicating a range of stimulatory and inhibitory effects. Complex interactions between micronutrients that were dosed simultaneously were evident. Several positive effects led to the conclusion that micronutrients have the potential to optimise process performance of activated sludge plants treating industrial wastewater. The addition of phosphorus/niacin and molybdenum/lactoflavin removed wastewater components that were toxic to nitrifiers as indicated through toxicity testing, thus protecting downstream nitrification/denitrification treatment processes. Journal of Industrial Microbiology & Biotechnology (2000) 24, 267–274.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/sj.jim.2900817

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4

Digitale Medien

A mathematical model of proximal tubule absorption (1979)

Huss, Ronald E. ; Stephenson, John L.

Springer

The journal of membrane biology 47 (1979), S. 377-399

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ISSN: 1432-1424

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Chemie und Pharmazie

Notizen: Summary A previous model of the mechanisms of flow through epithelia was modified and extended to include hydrostatic and osmotic pressures in the cells and in the peritubular capillaries. The differential equations for flow and concentration in each region of the proximal tubule were derived. The equations were solved numerically by a finite difference method. The principal conclusions are: (i) Cell NaCl concentration remains essentially isotonic over the pressure variations considered; (ii) channel NaCl concentration varies only a few mosmol from isotonicity, and the hydrostatic and osmotic pressure differences across the cell wall are of the same order of magnitude; (iii) both reabsorbate osmolality and pressure-induced flow are relatively insensitive to the geometry of the system; (iv) a strong equilibrating mechanism exists in the sensitivity of the reabsorbate osmolality to luminal osmolality; this mechanism is far more significant than any other parameter change.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01869745

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5

Digitale Medien

The spike-strain test for polymeric liquids and its relevance for irreversible destruction of network connectivity by deformation (1979)

Wagner, M. H. ; Stephenson, S. E.

Springer

Rheologica acta 18 (1979), S. 463-468

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ISSN: 1435-1528

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Physik

Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Grundannahmen derLodgeschen Theorie der gummiartigen Flüssigkeit werden zusammengefaßt. Zwei weitere Annahmen sind notwendig, wenn man das Scher- und Dehnverhalten von Polymerschmelzen und konzentrierten Polymerlösungen bei finiten Deformationen beschreiben will: (1) die Annahme der Zerstörung des temporären Netzwerkes polymerer Flüssigkeiten mit zunehmender Deformation und (2) die Annahme, daß diese Zerstörung ein irreversibler Vorgang ist. Hier wird ein neuer Versuch, der sogenannte „Spike-Strain-Test“, vorgeschlagen. Damit ist es möglich, die Annahme einer irreversiblen Zerstörung des temporären Netzwerkes polymerer Flüssigkeiten mit zunehmender Deformation zu überprüfen. Die Bedeutung dieses Experimentes für eine größere Klasse von rheologischen Zustandsgleichungen wird diskutiert.

Notizen: Summary The basic assumptions ofLodge's rubberlike-liquid constitutive equation for polymer melts and concentrated solutions are summarized. By two additional assumptions — (i) the network disentanglement assumption and (ii) the irreversibility assumption — a modified rubberlike-liquid constitutive equation is obtained, which has been shown to be a valid description of material behaviour in shear and elongational flow. In this paper a novel test — the spikestrain test — is proposed. On the basis of this experiment the assumption of irreversible destruction of network connectivity by deformation can be examined. The significance of the spike-strain test for a larger class of constitutive equations is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01736952

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6

Digitale Medien

Assessing the conditions forin vivo electrical virtual biopsies in Barrett's oesophagus (2000)

González-Correa, C. A. ; Brown, B. H. ; Smallwood, R. H. ; [weitere]

Springer

Medical & biological engineering & computing 38 (2000), S. 373-376

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ISSN: 1741-0444

Schlagwort(e): Virtual biopsies ; Barrett's oesophagus ; Bio-electrical impedance

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Chemie und Pharmazie , Medizin

Notizen: Abstract It has previously been shown that it is possible to differentiate between squamous and columnar epithelia in rat and resected human tissues using an impedance probe to makein vitro measurements. This probe can be passed down an endoscope allowing measurements to be made in patients. However, the probe emerges parallel to the oesophageal wall, with little room to manoeuvre. The conditions of control required to give reliable readings have been investigated. The importance of pressure applied and the angle of approach to the oesophagus was assessed. Pressures in the range 26.6 Pa to 46.3 kPa and angles in the range 15–90 degrees were considered. Inin vitro studies it was observed that it was possible to obtain consistent readings with pressures greater than 2.9 kPa and with angles greater than 15 degrees between the probe and the oesophagus. These conditions can be achievedin vivo, and readings obtained from twelve patients are shown (45 readings on normal squamous, 34 on Barrett's oesophagus and 22 on stomach). At low frequencies (9.6–153.2 kHz), a Mann-Whitney test shows a significant difference (p〈0.001) when comparing the means from squamous and columnar, and also when readings from Barrett's and normal gastric epithelia are compared (p〈0.001).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02345004

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