The influence of the spatial frequency content of discrete roughness distributions on the development of the crossflow instability

An experimental investigation on the influence of the spatial frequency content of roughness distributions on the development of crossflow instabilities has been carried out. From previous research it is known that micro roughness elements can have a large influence on the crossflow development. When the spanwise spacing is chosen such that it is the most unstable wavelength (following linear stability analysis), stationary crossflow waves are amplified. While in earlier studies the focus was on the height or spanwise spacing of roughness elements, in the present study it is chosen to vary the shape of the elements. Through the modification of the shape the forcing at the critical wavelength is increased, while the forcing at the harmonics of the critical wavelength is damped. Experiments were carried in the low turbulence wind tunnel at City University London (Tu=0.006%) on a swept flat plate in combination with displacement bodies to create a sufficiently strong favourable pressure gradient. Hot wire measurements across the plate tracked the development of stationary and travelling crossflow waves. Initially, stronger crossflow waves were found for the elements with stronger forcing, while further downstream the effect of forcing diminished. Spatial frequency spectra showed that the stronger forcing at the critical wavelength (via the roughness shape) dominates the response of the flow while low forcing at the harmonics has no notable effect. Additionally, high resolution streamwise hot wire scans showed that the onset of secondary instability is not significantly influenced by the spatial frequency content of the roughness distribution

Novel colorectal endoscopic in vivo imaging and resection practice: a short practice guide for interventional endoscopists

Colorectal cancer remains a leading cause of cancer death in the UK. With the advent of screening programmes and developing techniques designed to treat and stage colorectal neoplasia, there is increasing pressure on the colonoscopist to keep up to date with the latest practices in this area. This review looks at the basic principles behind endoscopic mucosal resection and forward to the potential endoscopic tools, including high-magnification chromoscopic colonoscopy, high-frequency miniprobe ultrasound and confocal laser scanning endomicroscopic colonoscopy, that may soon become part of routine colorectal cancer management

Boron isotopes in foraminifera : systematics, biomineralisation, and CO2 reconstruction

Funding: Fellowship from University of St Andrews, $100 (pending) from Richard Zeebe, UK NERC grants NE/N003861/1 and NE/N011716/1.The boron isotope composition of foraminifera provides a powerful tracer for CO2 change over geological time. This proxy is based on the equilibrium of boron and its isotopes in seawater, which is a function of pH. However while the chemical principles underlying this proxy are well understood, its reliability has previously been questioned, due to the difficulty of boron isotope (δ11B) analysis on foraminferal samples and questions regarding calibrations between δ11B and pH. This chapter reviews the current state of the δ11B-pH proxy in foraminfera, including the pioneering studies that established this proxy’s potential, and the recent work that has improved understanding of boron isotope systematics in foraminifera and applied this tracer to the geological record. The theoretical background of the δ11B-pH proxy is introduced, including an accurate formulation of the boron isotope mass balance equations. Sample preparation and analysis procedures are then reviewed, with discussion of sample cleaning, the potential influence of diagenesis, and the strengths and weaknesses of boron purification by column chromatography versus microsublimation, and analysis by NTIMS versus MC-ICPMS. The systematics of boron isotopes in foraminifera are discussed in detail, including results from benthic and planktic taxa, and models of boron incorporation, fractionation, and biomineralisation. Benthic taxa from the deep ocean have δ11B within error of borate ion at seawater pH. This is most easily explained by simple incorporation of borate ion at the pH of seawater. Planktic foraminifera have δ11B close to borate ion, but with minor offsets. These may be driven by physiological influences on the foraminiferal microenvironment; a novel explanation is also suggested for the reduced δ11B-pH sensitivities observed in culture, based on variable calcification rates. Biomineralisation influences on boron isotopes are then explored, addressing the apparently contradictory observations that foraminifera manipulate pH during chamber formation yet their δ11B appears to record the pH of ambient seawater. Potential solutions include the influences of magnesium-removal and carbon concentration, and the possibility that pH elevation is most pronounced during initial chamber formation under favourable environmental conditions. The steps required to reconstruct pH and pCO2 from δ11B are then reviewed, including the influence of seawater chemistry on boron equilibrium, the evolution of seawater δ11B, and the influence of second carbonate system parameters on δ11B-based reconstructions of pCO2. Applications of foraminiferal δ11B to the geological record are highlighted, including studies that trace CO2 storage and release during recent ice ages, and reconstructions of pCO2 over the Cenozoic. Relevant computer codes and data associated with this article are made available online.Publisher PDFPeer reviewe

Experimentelle Untersuchung zu Stabilitaet und Transition in dreidimensionalen Grenzschichten mit Absaugung Teil I: Entwicklung, Konzeption und Aufbau einer Absaugeeinrichtung fuer das Prinzipmodell der schiebenden ebenen Platte

Es wird ausgefuehrt, auf welche Weise experimentelle Windkanaluntersuchungen mit Absaugung am DLR-Prinzipexperiment der schiebenden Platte einen Beitrag zur Loesung von aktuellen Problemen bei der Hybrid-Laminarfluegeltechnik liefern koennen. Die Konzeption und Herstellung eines Absaugesystems fuer die ebene Platte wird beschrieben. Vorversuche zum Nachweis der gewuenschten Spezifikation deuten an, da die "receptivity" von Laengswirbeln, deren Entwicklung besonders unter Flugbedingungen ueber die Transitionslage entscheidet, das zentrale Problem bei der gewuenschten Stabilisierung von Grenzschichtstroemungen mit Absaugung darstellt

Studies on the Absorption of Pyridostigmine: the Application of a Spectrophotometric Method for the Determination of Pyridostigmine in Plasma

Peer Reviewe

Einfluß der äußeren Strömungsbedingungen auf den Transitionsprozeß einer dreidimensionalen Grenzschicht

Der laminar-turbulente Übergang durch Querströmungsinstabilität wird in einer inkompressiblen, beschleunigten 3-d Grenzschicht experimentell untersucht. Da die beobachtete Instabilitätsentwicklung wesentlich von den äußeren Strömungsbedingungen abhängt, muß zuerst die Gültigkeit der zum Vergleich herangezogenen, primären, linearen und lokalen Stabilitätstheorie in bezug auf instationäre Störwellen überprüft werden. Die mit der Oberflächenheißfilmtechnik ermittelten Ausbreitungsrichtungen und Phasengeschwindigkeiten stimmen dabei im Gegensatz zu den Gruppengeschwindigkeiten sehr gut mit der Theorie überein. Dann wird der Einfluß von Turbulenzgrad, Schall, Variationen der mittleren Wirbelstärke in der Anströmung und Oberflächenrauhigkeiten auf die Instabilitätsentwicklung untersucht. Es zeigt sich, daß Anströmturbulenz die Initialisierung laufender Störwellen bestimmt,während kleinste 3-d Rauhigkeiten die Entwicklung stationärer Längswirbel fördern. Die von der linearen Theorie nicht erfaßbare Abhängigkeit der Transitions-Reynoldszahlen bzw. N-Faktoren von verschiedenen äußeren Strömungsbedingungen wird diskutiert. Danach finden sich maximale N-Faktoren nicht wie in 2-d Grenzschichten für Tu - 0, sondern bei etwas größeren Turbulenzgraden

Experiment und lokale Stabilitaetstheorie in Grenzschichten mit Laengswirbelartigen Stoerungen

Mit Hilfe von experimentellen Ergebnissen aus der Untersuchung des Transitionsprozesses in dreidimensionalen Grenzschichten an ebenen und gekruemmten Flaechen wird die Gueltigkeit der lokalen linearen Stabilitaetstheorie bei Querstroemungs- und Zentrifugalinstabilitaet diskutiert. In beiden Faellen bilden sich Laengswirbel als primaere Instabilitaet. Bei Querstroemungsinstabilitaet wird vor allem die Abhaengigkeit von den Anfangsbedingungen, vorgegeben durch Turbulenzgrad und Oberflaechenrauhigkeit, aufgezeigt, waehrend bei Zentrifugalinstabilitaet der Einfluss konkaver und konvexer Kruemmung verdeutlicht wird. Die Vergleiche zwischen Experiment und Theorie lassen erkennen, dass die lokale lineare Stabilitaetstheorie die Entwicklung der Stoerstroemung nicht beschreiben kann. Auf die Folgerung fuer die Anwendung der eN- Methode wird hingewiesen