bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the foundations of generalized Taylor dispersion theory
Authors: Frankel I. , Brenner H. 
Published: April 2006

Generalized Taylor dispersion theory extends the basic long-time, asymptotic scheme of Taylor and Aris greatly beyond the class of rectilinear duct and channel flow dispersion problems originally addressed by them. This feature has rendered it indispensable for studying flow and dispersion phenomena in porous media, chromatographic separation processes, heat transfer in cellular media, sedimentation of non-spherical Brownian particles, and transport of flexible clusters of interacting Brownian particles, to mention just a few examples of the broad class of non-unidirectional transport phenomena encompassed by this scheme. Moreover, generalized Taylor dispersion theory enjoys the attractive feature of conferring a unified paradigmatic structure upon the analysis of such apparently disparate physical problems. For each of the problems thus treated it provides an asymptotic, macroscale description of the original microscale transport process, being based upon a convective-diffusive ‘model’ problem characterized by a set of constant (position- and time-independent) phenomenological coefficients.The present contribution formally substantiates the scheme. This is accomplished by demonstrating that the coarse-grained (macroscale) transport ‘model’ equation leads to a solution which accords asymptotically with the leading-order behaviour of the comparable solution of the exact (microscale) convective–diffusive problem underlying the transport process. It is also shown, contrary to current belief, that no systematic improvement in the asymptotic order of approximation is possible through the incorporation of higher-order gradient terms into the model constitutive equation for the coarse-grained flux. Moreover, the inherent difference between the present rigorous asymptotic scheme and the dispersion models resulting from Gill–Subramanian moment-gradient expansions is illuminated, thereby conclusively resolving a long-standing puzzle in longitudinal dispersion theory.
Modal exchange mechanisms in Lapwood convection
Authors: Riley D. S. , Winters K. H. 
Published: April 2006

Techniques of bifurcation theory are used to study the porous-medium analogue of the classical Rayleigh-Bénard problem: Lapwood convection in a two-dimensional saturated porous cavity heated from below. Two particular aspects of the problem are focused upon: (i) the existence of multiple steady solutions and (ii) the influence of aspect ratio.Convection begins only when the applied temperature difference (say) exceeds a critical value defined by linear stability theory. The resulting convective flow pattern depends both on the magnitude of the temperature difference and on the aspect ratio of the cavity. A weakly nonlinear analysis reveals the roles played by so-called secondary bifurcations in determining the formation of further, anomalous patterns at fixed aspect ratio. In addition to giving rise to alternative stable flows for identical operating conditions, the secondary bifurcations are required for the modal exchanges which take place as the aspect ratio varies, a process which causes an abrupt change in preferred flow pattern at certain critical values of the aspect ratio.As a complement to and an extension of the weakly nonlinear analysis, numerical methods are used to determine the bifurcation processes and to elucidate the modal exchange mechanisms in both weakly and strongly convective flows. The effect of container size is studied by continuation methods to predict the variation of the critical Rayleigh number of the bifurcation points for aspect ratios in the range 0.5 to 2.0. In this way a stability map is obtained which shows the alternative patterns expected for particular operating conditions. The Nusselt number is computed and it is found that the alternative stable modes transfer significantly different amounts of heat through the medium.The study has provided new information on the existence and characteristics of, and interactions between, alternative steady modes of two-dimensional Lapwood convection. The results have important ramifications for the modelling and design of physical systems in which convective flow in a saturated porous medium is stimulated by an imposed unstable temperature gradient.
The turbulent near wake of a flat plate at low Reynolds number
Authors: Nakayama A. , Liu B. 
Published: April 2006

Mean-velocity and turbulence measurements have been made in the turbulent near wake of a flat plate at various Reynolds numbers in order to investigate the low-Reynolds-number effects in this region. The results indicate that the low-Reynolds-number effects are significant enough to partially explain the discrepancies in the existing mean-velocity data. It has been found that, while the Reynolds-number-independent, inner-law similarity of the boundary layers continues to exist, the width of the inner wake that develops within the inner-law region scales with the outer variable. Therefore, the mean velocity near the wake centreline depends on the Reynolds number. It is conjectured that this is due to the influence of the large eddies of the outer layer on the spreading of the inner wake.Measured turbulence quantities indicate that sudden changes occurring just downstream of the trailing edge are independent of the Reynolds number, but the subsequent development of the turbulent stress profiles depends on the Reynolds number. The Reynolds shear stress and the mean-velocity profiles within the inner wake show approximate similarity.
Radial spreading of viscous-gravity currents with solidifying crust
Authors: Fink Jonathan H. , Griffiths Ross W. 
Published: April 2006

We have investigated the effect of a solidifying crust on the dynamics and surface morphology of radial viscous-gravity currents. Liquid polyethylene glycol was admitted into the base of a tank filled with cold sucrose solution maintained at a temperature below the wax freezing point. As the radial current advanced away from the inlet, its surface solidified and deformed through a combination of folding and fracturing. For the warmest experiments, during which solidification did not occur, the radius of the current increased in proportion to the square root of time, as demonstrated both experimentally and theoretically for isothermal viscous fluids by Huppert (1982). When cooling was sufficiently rapid, solid crust formed and caused the spreading rate to decrease. A cooling model combining conduction in the wax with convection in the sucrose solution predicts the distance from the source at which the solid crust first appearedProgressively colder experiments revealed a sequence of surface morphologies which resembled features observed on cooling lava flows and lava lakes. Flows in which crust formed very slowly developed marginal levees which contained and channelled the main portion of the current. Colder flows with more rapid crust growth formed regularly spaced surface folds, multi-armed rift structures complete with shear offsets, and bulbous lobate forms similar to pillow lavas seen under the ocean. The same transitions between modes of surface deformation were also generated by keeping the ambient water temperature constant and decreasing the extrusion rate. This demonstration that surfaces can exhibit a well-defined sequence of morphologies which depend on the underlying flow conditions offers the prospect of more successful interpretation of natural lava flows.
Self-induced flow in a rotating tube
Authors: Gilham S. , Ivey P. C. , Owen J. M. , Pincombe J. R. 
Published: April 2006

When a tube, sealed at one end and open to a quiescent environment at the other, is rotated about its axis, fluid flows from the open end along the axis towards the sealed end and returns in an annular boundary layer on the cylindrical wall. This paper describes the first known study to be made of this self-induced flow. Numerical solutions of the Navier–Stokes equations are shown to be in mainly good agreement with experimental results obtained using flow visualization and laser–Doppler anemometry in a rotating glass tube.The self-induced flow in the tube can be described in terms of the length-to-radius ratio, G, and the Ekman number, E. However, for large values of G (G [ges ] 20), the flow outside the boundary layer on the endwall of the tube can be characterized by a single, modified, Ekman number, E*, where E* = GE. Although most of the fluid entering the open end of the tube is entrained into the annular (Stewartson-type) boundary layer, for small values of E* (E* < 0.2) some flow reaches the sealed end. For this so-called 'short-tube case’, the flow in the boundary layer on the endwall is shown to be similar to that associated with a disk rotating in a quiescent environment: the free disk. The self-induced flow for the short-tube case is believed to be responsible for the ’ hot-poker effect’ used, on some jet engines, to provide ice protection for the nose bullet.
On the evolution of a wave packet in a laminar boundary layer
Authors: Cohen Jacob , Breuer Kenneth S. , Haritonidis Joseph H. 
Published: April 2006

The transition process of a small-amplitude wave packet, generated by a controlled short-duration air pulse, to the formation of a turbulent spot is traced experimentally in a laminar boundary layer. The vertical and spanwise structures of the flow field are mapped at several downstream locations. The measurements, which include all three velocity components, show three stages of transition. In the first stage, the wave packet can be treated as a superposition of two- and three-dimensional waves according to linear stability theory, and most of the energy is centred around a mode corresponding to the most amplified wave. In the second stage, most of the energy is transferred to oblique waves which are centred around a wave having half the frequency of the most amplified linear mode. During this stage, the amplitude of the wave packet increases from 0.5 % to 5 % of the free-stream velocity. In the final stage, a turbulent spot develops and the amplitude of the disturbance increases to 27 % of the free-stream velocity.Theoretical aspects of the various stages are considered. The amplitude and phase distributions of various modes of all three velocity components are compared with the solutions provided by linear stability theory. The agreement between the theoretical and measured distributions is very good during the first two stages of transition. Based on linear stability theory, it is shown that the two-dimensional mode of the streamwise velocity component is not necessarily the most energetic wave. While linear stability theory fails to predict the generation of the oblique waves in the second stage of transition, it is demonstrated that this stage appears to be governed by Craik-type subharmonic resonances.
Dynamical analysis of electrochemical wall shear rate measurements
Authors: Van Steenhoven A. A. , Van De Beucken F. J. H. M. 
Published: April 2006

The performance of a circular electrochemical wall shear rate probe under unsteady flow conditions is analysed through a combined experimental, numerical and analytical approach. The experiments arc performed with a ferri- and ferrocyanide redox couple and compared to finite element analyses of the two-dimensional time-dependent convection—diffusion equation. The results are related to the analytical Lévêque solution for steady flow and for some cases to Pedley's model for heat transfer in reversing shear flow (Pedley 1976).The steady flow analyses showed that in our experiments axial diffusion is only of minor importance but that for the lower Péclet numbers (< 104) three-dimensional effects, like tangential diffusion, may not be neglected. A similar result is found for the oscillating case. A fair agreement is found between experimental and numerical data during flow acceleration, but during flow reversal remarkable (about 15%) deviations are found. The observed insensitivity of the transducer during flow reversal is quite well predicted by Pedley's model. Finally, the performance of the probe may be improved somewhat by a decrease in cathode length and cathode—anode distance.
Governance and Collaboration: Review Article
Authors: Durose Catherine , Rummery Kirstein 
Published: April 2006

Rod Rhodes (1997) Understanding Governance: Policy Networks, Governance, Reflexivity and Accountability, Open University Press 1997.Gerry Stoker (1998) ‘Governance as theory: five propositions’, International Journal of Social Sciences 50, 1, 17–28.Helen Sullivan and Chris Skelcher (2002) Working across Boundaries: Collaboration in Public Services, Palgrave.Janet Newman, Marion Barnes, Helen Sullivan, and A. Knops (2004) ‘Public participation and collaborative governance’, Journal of Social Policy 33, 203–223.From a term used largely within political science in the mid-1990s, ‘governance’ has become a key conceptual and analytical convention adopted by social policy, largely because of its usefulness in examining questions that are key to the discipline: citizenship; welfare rights and responsibilities; accountability; legitimacy and partnership working. Clarence and Painter (1998) have constructed a useful characterisation of public policy, identifying a shift in emphasis from hierarchies, to markets and now to collaboration. Networks, ‘joined up’ governance and partnership working are now central in both policy practice and analysis. These processes are not new, but New Labour have clearly expanded and accelerated them. For New Labour, collaborative working is now perceived as central in their response to key policy challenges: improving public services, tackling social exclusion and revitalising local democracy. These processes are now evident at all levels of policy making from supranational organisations such as the European Union down to neighbourhood-based initiatives. It appears that we are moving from the closed, unitary system of government of the Westminster model to a more open, decentralised system of governance. Our conceptions of citizenship have accordingly shifted, from one based on representation to one based on active participation, particularly within local communities. Governance is an issue which concerns all levels of government and citizen participation, from international-level World Bank concerns about commitment to efficiency and accountable government, to highly devolved localised urban regeneration partnerships.
Fresh Blood and Aged Stored Blood Are Equally Efficacious in Immediately Reversing Anemia-induced Brain Oxygenation Deficits in Humans
Authors: Weiskopf Richard B. , Feiner John , Hopf Harriet , Lieberman Jeremy , Finlay Heather E. , Quah Cheng , Kramer Joel H. , Bostrom Alan , Toy Pearl 
Published: April 2006

Background
Erythrocytes are transfused to treat or prevent imminent inadequate tissue oxygenation. 2,3-diphosphoglycerate concentration decreases and oxygen affinity of hemoglobin increases (P50 decreases) with blood storage, leading some to propose that erythrocytes stored for 14 or more days do not release sufficient oxygen to make their transfusion efficacious. The authors tested the hypothesis that erythrocytes stored for 3 weeks are as effective in supplying oxygen to human tissues as are erythrocytes stored for less than 5 h.

Methods
Nine healthy volunteers donated 2 units of blood more than 3 weeks before they were tested with a standard, computerized neuropsychological test (digit-symbol substitution test [DSST]) on 2 days, 1 week apart, before and after acute isovolemic reduction of their hemoglobin concentration to 7.4 and 5.5 g/dl. Volunteers randomly received autologous erythrocytes stored for either less than 5 h ("fresh") or 3 weeks ("stored") to return their hemoglobin concentration to 7.5 g/dl (double blinded). Erythrocytes of the alternate storage duration were transfused on the second experimental day. The DSST was repeated after transfusion.

Results
Acute anemia slowed DSST performance equivalently in both groups. Transfusion of stored erythrocytes with decreased P50 reversed the altered DSST (P < 0.001) to a time that did not differ from that at 7.4 g/dl hemoglobin during production of acute anemia (P = 0.88). The erythrocyte transfusion-induced DSST improvement did not differ between groups (P = 0.96).

Conclusion
Erythrocytes stored for 3 weeks are as efficacious as are erythrocytes stored for 3.5 h in reversing the neurocognitive deficit of acute anemia. Requiring fresh rather than stored erythrocytes for augmentation of oxygen delivery does not seem warranted.
Determination of Endotracheal Tube Size in a Perinatal Population
Authors: Fayoux Pierre , Devisme Louise , Merrot Olivier , Marciniak Bruno 
Published: April 2006

Background
This study aimed at correlating anatomical dimensions of the larynx and trachea to age and weight in a prenatal population. Endotracheal tube size determination was then proposed according to these considerations.

Methods
Anatomical measurements were obtained during 150 fetal and infant postmortem examinations. The optimal endotracheal tube size was determined by three methods: clinically, by a pressure method using calibrated inextensible balloons, and anatomically by comparing the laryngotracheal perimeter to the tube perimeters. Based on these results, recommended tube sizes were calculated.

Results
In premature babies before 37 weeks gestation, the optimal tube size according to pressure estimation was significantly greater than that determined by anatomical measurement alone. This difference was no longer valid after 40 weeks gestation.

Conclusions
This study identified the elasticity of laryngeal structures in premature babies, allowing intubation with tube sizes greater than predicted by anatomical measurements with an increasing injury risk located in the posterior part of the glottic plane. This elasticity disappears near 40 weeks gestation, and the injury risk then predominates in the subglottic region. These results lead the authors to recommend that the size of the endotracheal tube used in the perinatal population should be based on anatomical and experimental data to limit the injury risks.
Isoflurane Neuroprotection in Rat Hippocampal Slices Decreases with Aging
Authors: Zhan Xinhua , Fahlman Christian S. , Bickler Philip E. 
Published: April 2006

Background
Most in vitro neuroprotection studies with isoflurane have involved cells obtained during the embryonic or early postnatal period. However, in mature rodents, isoflurane neuroprotection does not persist. The authors determined whether neuroprotection of hippocampal slices with isoflurane decreases with aging and is due to decreased intracellular Ca regulation and survival protein phosphorylation.

Methods
Hippocampal slices from 5-day-old, 1-month-old, and 19- to 23-month-old rats were deprived of oxygen and glucose for 5-30 min in media bubbled with 1% isoflurane. Cell death was assessed in the CA1, CA3, and dentate regions, and intracellular Ca concentration was measured in CA1 neurons. N-methyl-d-aspartate receptor (NMDAR)-dependent Ca influx was measured and the phosphorylation of NMDARs, and the survival proteins Akt and mitogen-activated protein kinase p42/44 were quantified.

Results
Twenty minutes of oxygen and glucose deprivation killed approximately 40-60% of neurons in CA3 and dentate in all age groups. Isoflurane, 1%, reduced death of CA1, CA3, and dentate neurons in slices from 5-day-old rats but not those from 23-month-old rats. In 5-day slices, isoflurane attenuated NMDAR-mediated Ca influx, whereas in aging slices, Ca influx was increased protein kinase C. In aging slices, isoflurane did not increase the phosphorylation of Akt and p42/44.

Conclusions
Isoflurane neuroprotection of hippocampal slices during oxygen and glucose deprivation decreases with age. Isoflurane does not prevent large increases in intracellular Ca concentration during oxygen and glucose deprivation and does not induce the phosphorylation of the prosurvival proteins in aging slices. A protein kinase C-mediated increase in NMDAR activity may result in increased excitotoxicity and decreased neuroprotection by volatile anesthetics in the aging brain.
Infarct-remodeled Myocardium Is Receptive to Protection by Isoflurane Postconditioning
Authors: Feng Jianhua , Fischer Gregor , Lucchinetti Eliana , Zhu Min , Bestmann Lukas , Jegger David , Arras Margarete , Pasch Thomas , Perriard Jean-Claude , Schaub Marcus C. , Zaugg Michael 
Published: April 2006

Background
Postinfarct remodeled myocardium exhibits numerous structural and biochemical alterations. So far, it is unknown whether postconditioning elicited by volatile anesthetics can also provide protection in the remodeled myocardium.

Methods
Myocardial infarct was induced in male Wistar rats by ligation of the left anterior descending coronary artery. Six weeks later, hearts were buffer-perfused and exposed to 40 min of ischemia followed by 90 min of reperfusion. Anesthetic postconditioning was induced by 15 min of 2.1 vol% isoflurane. In some experiments, LY294002 (15 microM), a phosphatidylinositol 3-kinase inhibitor, was coadministered with isoflurane. Masson's trichrome staining, immunohistochemistry, Western blot analysis, and reverse-transcription polymerase chain reaction served to confirm remodeling. In buffer-perfused hearts, functional recovery was recorded, and acute infarct size was measured using 1% triphenyltetrazolium chloride staining and lactate dehydrogenase release during reperfusion. Western blot analysis was used to determine phosphorylation of reperfusion injury salvage kinases including protein kinase B/Akt and its downstream targets after 15 min of reperfusion.

Results
Infarct hearts exhibited typical macroscopic and molecular changes of remodeling. Isoflurane postconditioning improved functional recovery and decreased acute infarct size, as determined by triphenyltetrazolium (35 +/- 5% in unprotected hearts vs. 8 +/- 3% in anesthetic postconditioning; P < 0.05) and lactate dehydrogenase release. This protection was abolished by LY294002, which inhibited phosphorylation of protein kinase B/Akt and its downstream targets glycogen synthase kinase 3beta, endothelial nitric oxide synthase, and p70S6 kinase.

Conclusions
Infarct-remodeled myocardium is receptive to protection by isoflurane postconditioning via protein kinase B/Akt signaling. This is the first time to demonstrate that anesthetic postconditioning retains its marked protection in diseased myocardium.