Optic Flow Contribution to Locomotion Adjustments in Obstacle Avoidance

Locomotion generates a visual movement pattern characterized as optic flow. To explore how the locomotor adjustments are affected by this pattern, an experimental paradigm was developed to eliminate optic flow during obstacle avoidance. The aim was to investigate the contribution of optic flow in obstacle avoidance by using a stroboscopic lamp. Ten young adults walked on an 8m pathway and stepped over obstacles at two heights. Visual sampling was determined by a stroboscopic lamp (static and dynamic visual sampling). Three-dimensional kinematics data showed that the visual information about self-motion provided by the optic flow was crucial for estimating the distance from and the height of the obstacle. Participants presented conservative behavior for obstacle avoidance under experimental visual sampling conditions, which suggests that optic flow favors the coupling of vision to adaptive behavior for obstacle avoidance.

Turbulenttisen putkivirtauksen numeerinen mallinnus.

Numeerisella mallinnuksella on tavoitteena täydentää ja korvata kokeellista tutkimusta. Tässä tutkimuksessa on mallinnettu CFX 4.1- ja CFX 4.2-ohjelmien avulla lämmönsiirtoa putken sisäpinnalla. Virtausaineena putkessa on käytetty vettä ja vesi-monopropyleeniglykoliliuosta. Tarkasteltujen virtaustapausten Reynoldsin luku vaihtelee 200 - 30000. Kun glykolipitoisuus on suuri ja liuoksen lämpötila on pieni virtaus on laminaarista ja tällöin lämmönsiirtymiskerroin on pieni. Lämmönsiirron tehostamiseksi putkeen on asennettu turbulaattorilanka. Työssä on selvitetty edellytyksiä mallintaa hydraulisesti sileässä putkessa tapahtuvaa virtausta. Reynoldsin luvun ollessa alle 2300 mallinnuksessa on käytetty laminaarimallia. Reynoldsin luvuilla 2300-30000, turbulenttisella alueella, on käytetty pienten Reynoldsin luvun k-ɛ-mallia. Malli vaatii toimiakseen tiheän laskentaverkon putken seinämän läheisyydessä. Tarkastellulla alueella virtauksen ja lämmönsiirron mallinnuksen tulokset ovat vastaavat kuin teorian perusteella lasketut ja kokeellisista mittauksista saatavat tulokset. Lämmönsiirron tehostamiseksi putkeen on asennettu turbulaattorilanka. Tässä työssä on numeerisin menetelmin (pienten Reynoldsin luvun k-ɛ-malli ja k-ɛ-malli) suoritettu laskentaa yhdellä turbulaattorilankarakenteella. Laskennan vertailuaineistona on käytetty aikaisemmasta kokeellisesta tutkimuksesta saatua mittausdataa. Kokeellisessa tutkimuksessa turbulaattorirakenteena on käytetty putken seinämällä kiertyvää turbulaattorilankaa. Todellinen kolmiulotteinen geometria osoittautui vaikeaksi mallintaa. Toimivaa mallia ei ollut mahdollista toteuttaa aikataulun puitteissa ja mallin laskentakapasiteetin tarve kasvoi liian suureksi. Lankarakenne yksinkertaistettiin tasavälein toistuvaksi riparakenteeksi, joka on helpompi mallintaa aksisymmetriaa käyttäen kaksiulotteisena. Mallin tuloksista painehäviö asettuu kirjallisuudesta saatavan vertailuaineiston kanssa samalle tasolle, mutta lämmönsiirtymiskerroin on vertailuaineistoa huomattavasti suurempi.

Changes in cerebral hemodynamics and oxygenation induced by different speech tasks – an assessment by combining functional near‐infrared spectroscopy and capnography

Introduction In several studies, we found that during guided rhythmic speech exercises, a decrease in cerebral hemodynamics and oxygenation occurred as the result of a decrease in the partial pressure of carbon dioxide in the arterial blood (PaCO2) during speaking. To further explore the effect of PaCO2 variations on cerebral hemodynamics and oxygenation, the aim of the present study was to investigate the impact of spoken, inner and heard speech tasks on these parameters. Material and Methods Speech tasks included recitation or inner recitation or listening to hexameter, alliteration, prose, or performing mental arithmetic. The following physiological parameters were measured: tissue oxygen saturation (StO2) and absolute concentrations of oxyhemoglobin, deoxyhemoglobin, total hemoglobin (over the left and right anterior prefrontal cortex, using an ISS OxiplexTS frequency domain near-infrared spectrometer) and end-tidal CO2 (PETCO2; using Nellcor N1000 and Datex NORMOCAP capnographs). Statistical analysis was applied to the differences between baseline, 2 tasks, and 3 post-baseline periods. Data of 3 studies with 24, 7 and 29 healthy subjects, respectively, were combined, and linear regression analyses were calculated. Results Linear regression analyses revealed significant relations between changes in oxyhemoglobin, deoxyhemoglobin, total hemoglobin or StO2 and the participants’ age, the baseline PETCO2 or certain speech tasks. While hexameter verses affected changes during the tasks, alliteration verses only affected changes during the recovery phase. Discussion and Conclusion The observed effects in hemodynamics and oxygenation indicate a combination of neurovascular coupling (increased neuronal activity leading to an increase in the cerebral metabolic rate of oxygen resulting in an increase in cerebral flood flow/volume) and CO2 reactivity (increased breathing during speech tasks causing a decrease in PaCO2 leading to vasoconstriction and decrease in cerebral blood flow). The neurovascular coupling characteristics are task-dependent. References Scholkmann F, Gerber U, Wolf M, Wolf U. End-tidal CO2: An important parameter for a correct interpretation in functional brain studies using speech tasks. Neuroimage 2013;66:71-79. Scholkmann F, Wolf M, Wolf U. The effect of inner speech on arterial CO2, cerebral hemodynamics and oxygenation – A functional NIRS study. Adv Exp Med Biol 2013;789:81-87.

Slip ratio in dispersed viscous oil-water pipe flow

In this article, dispersed flow of viscous oil and water is investigated. The experimental work was performed in a 26.2-mm-i.d. 12-m-long horizontal glass pipe using water and oil (viscosity of 100 mPa s and density of 860 kg/m(3)) as test fluids. High-speed video recording and a new wire-mesh sensor based on capacitance (permittivity) measurements were used to characterize the flow. Furthermore, holdup data were obtained using quick-closing-valves technique (QCV). An interesting finding was the oil-water slip ratio greater than one for dispersed flow at high Reynolds number. Chordal phase fraction distribution diagrams and images of the holdup distribution over the pipe cross-section obtained via wire-mesh sensor indicated a significant amount of water near to the pipe wall for the three different dispersed flow patterns identified in this study: oil-in-water homogeneous dispersion (o/w H), oil-in-water non-homogeneous dispersion (o/w NH) and Dual continuous (Do/w & Dw/o). The phase slip might be explained by the existence of a water film surrounding the homogeneous mixture of oil-in-water in a hidrofilic-oilfobic pipe. (C) 2010 Elsevier Inc. All rights reserved.

Vasopressin-dependent coupling between sodium transport and water flow in a mouse cortical collecting duct cell line.

Water balance is achieved through the ability of the kidney to control water reabsorption in the connecting tubule and the collecting duct. In a mouse cortical collecting duct cell line (mCCD(c11)), physiological concentrations of arginine vasopressin increased both electrogenic, amiloride-sensitive, epithelial sodium channel (ENaC)-mediated sodium transport measured by the short-circuit current (Isc) method and water flow (Jv apical to basal) measured by gravimetry with similar activation coefficient K(1/2) (6 and 12 pM, respectively). Jv increased linearly according to the osmotic gradient across the monolayer. A small but highly significant Jv was also measured under isoosmotic conditions. To test the coupling between sodium reabsorption and water flow, mCCD(c11) cells were treated for 24 h under isoosmotic condition with either diluent, amiloride, vasopressin or vasopressin and amiloride. Isc, Jv, and net chemical sodium fluxes were measured across the same monolayers. Around 30% of baseline and 50% of vasopressin-induced water flow is coupled to an amiloride-sensitive, ENaC-mediated, electrogenic sodium transport, whereas the remaining flow is coupled to an amiloride-insensitive, nonelectrogenic sodium transport mediated by an unknown electroneutral transporter. The mCCD(c11) cell line is a first example of a mammalian tight epithelium allowing quantitative study of the coupling between sodium and water transport. Our data are consistent with the 'near isoosmotic' fluid transport model.

Impaired chemical coupling of cerebral blood flow is compatible with intact neurological outcome in neonates with perinatal risk factors.

Early detection of pathophysiological factors associated with permanent brain damage is a major issue in neonatal medicine. The aim of our study was to evaluate the significance of the CO2 reactivity of cerebral blood flow (CBF) in neonates with perinatal risk factors. Fourteen ventilated neonates with perinatal risk factors (pathological cardiotocogramm, low cord pH, postpartal encephalopathy) were enrolled into this prospective study. The study was performed 18-123 h after birth. CBF was measured using the noninvasive intravenous 133Xe method. Two measurements were taken with a minimal PaCO2-difference of 5 mm Hg. From the two CBF values the CO2 reactivity was calculated. Outcome was evaluated 1 year after birth. The CBF values at a lower PaCO2 ranged from 6.6 to 115. 2 ml/100 g brain issue/min (median = 18.2) and at a higher PaCO2 level from 7.1 to 125.7 ml/100 g brain tissue/min (median = 18.75). The calculated CO2 reactivity ranged from -9.6 to 6.6% (median 1.1%) change in CBF/mm Hg change in PaCO2. CO2 reactivity correlated with lowest pH (r2 = 0.35, p = 0.02). Two infants died, one of neonatal sepsis, the other of heart failure. Neurological outcome at the age of 1 year was normal in 11 patients, 1 had severe cerebral palsy. From the 12 surviving patients the patient with severe neurological deficit showed the highest CBF values (125.7 ml/100 g/min). Impaired chemical coupling of cerebral blood flow is compatible with intact neurological outcome in neonates with perinatal risk factors. CO2 reactivity in these newborns correlates with the lowest pH and may reflect the severity of perinatal asphyxia.

Coupling an aerosol box model with one-dimensional flow: a tool for understanding observations of new particle formation events

Field observations of new particle formation and the subsequent particle growth are typically only possible at a fixed measurement location, and hence do not follow the temporal evolution of an air parcel in a Lagrangian sense. Standard analysis for determining formation and growth rates requires that the time-dependent formation rate and growth rate of the particles are spatially invariant; air parcel advection means that the observed temporal evolution of the particle size distribution at a fixed measurement location may not represent the true evolution if there are spatial variations in the formation and growth rates. Here we present a zero-dimensional aerosol box model coupled with one-dimensional atmospheric flow to describe the impact of advection on the evolution of simulated new particle formation events. Wind speed, particle formation rates and growth rates are input parameters that can vary as a function of time and location, using wind speed to connect location to time. The output simulates measurements at a fixed location; formation and growth rates of the particle mode can then be calculated from the simulated observations at a stationary point for different scenarios and be compared with the ‘true’ input parameters. Hence, we can investigate how spatial variations in the formation and growth rates of new particles would appear in observations of particle number size distributions at a fixed measurement site. We show that the particle size distribution and growth rate at a fixed location is dependent on the formation and growth parameters upwind, even if local conditions do not vary. We also show that different input parameters used may result in very similar simulated measurements. Erroneous interpretation of observations in terms of particle formation and growth rates, and the time span and areal extent of new particle formation, is possible if the spatial effects are not accounted for.

Automatic Classification of Three-Phase Flow Patterns of Heavy Oil in a Horizontal Pipe Using Support Vector Machines

The pipe flow of a viscous-oil-gas-water mixture such as that involved in heavy oil production is a rather complex thereto-fluid dynamical problem. Considering the complexity of three-phase flow, it is of fundamental importance the introduction of a flow pattern classification tool to obtain useful information about the flow structure. Flow patterns are important because they indicate the degree of mixing during flow and the spatial distribution of phases. In particular, the pressure drop and temperature evolution along the pipe is highly dependent on the spatial configuration of the phases. In this work we investigate the three-phase water-assisted flow patterns, i.e. those configurations where water is injected in order to reduce friction caused by the viscous oil. Phase flow rates and pressure drop data from previous laboratory experiments in a horizontal pipe are used for flow pattern identification by means of the 'support vector machine' technique (SVM).

A new approach for determining stability constants of metal ion complexes in aquatic systems based on flow injection-ion exchange-flame atomic absorption spectrometry coupling

A method based an ion exchange(IE)-atomic absorption spectrometry(AAS) coupled by flow techniques, allowing the determination of formation constants of, at least, the first species of complex systems, in aqueous solution, was developed.The IE-AAS coupling reduces significantly the number of experimental steps in comparison with IE batch methods, resulting in an important increase in analytical rate. The method is simple both from experimental and computational points of view, making possible its utilization by workers without special expertise in the field of complex equilibria in solution. on the other hand, taking into account mainly the amount of hollow cathode lamps available to date, the developed procedure may be applied, within certain limitations, to the study of many systems whose features prevent the use of traditional approaches.

Water-assisted Flow of Heavy Oil in a Vertical Pipe: Pilot-scale Experiments

The use of the core-annular flow pattern, where a thin fluid surrounds a very viscous one, has been suggested as an attractive artificial-lift method for heavy oils in the current Brazilian ultra-deepwater production scenario. This paper reports the pressure drop measurements and the core-annular flow observed in a 2 7/8-inch and 300 meter deep pilot-scale well conveying a mixture of heavy crude oil (2000 mPa.s and 950 kg/m3 at 35 C) and water at several combinations of the individual flow rates. The two-phase pressure drop data are compared with those of single-phase oil flow to assess the gains due to water injection. Another issue is the handling of the core-annular flow once it has been established. High-frequency pressure-gradient signals were collected and a treatment based on the Gabor transform together with neural networks is proposed as a promising solution for monitoring and control. The preliminary results are encouraging. The pilot-scale tests, including long-term experiments, were conducted in order to investigate the applicability of using water to transport heavy oils in actual wells. It represents an important step towards the full scale application of the proposed artificial-lift technology. The registered improvements in terms of oil production rate and pressure drop reductions are remarkable.

Geometrical and kinematic properties of interfacial waves in stratified oil-water flow in inclined pipe

The stratified oil-water flow pattern is common in the petroleum industry, especially in offshore directional wells and pipelines. Previous studies have shown that the phenomenon of flow pattern transition in stratified flow can be related to the interfacial wave structure (problem of hydrodynamic instability). The study of the wavy stratified flow pattern requires the characterization of the interfacial wave properties, i.e., average shape, celerity and geometric properties (amplitude and wavelength) as a function of holdup, inclination angle and phases' relative velocity. However, the data available in the literature on wavy stratified flow is scanty, especially in inclined pipes and when oil is viscous. This paper presents new geometric and kinematic interfacial wave properties as a function of a proposed two-phase Froude number in the wavy-stratified liquid-liquid flow. The experimental work was conducted in a glass test line of 12 m and 0.026 m id., oil (density and viscosity of 828 kg/m(3) and 0.3 Pa s at 20 degrees C, respectively) and water as the working fluids at several inclinations from horizontal (-20 degrees, -10 degrees, 0 degrees, 10 degrees, 20 degrees). The results suggest a physical relation between wave shape and the hydrodynamic stability of the stratified liquid-liquid flow pattern. (C) 2011 Elsevier Inc. All rights reserved.

Drag reduction phenomenon in viscous oil-water dispersed pipe flow: Experimental investigation and phenomenological modeling

An experimental study on drag-reduction phenomenon in dispersed oil-water flow has been performed in a 26-mm-i.d. Twelve meter long horizontal glass pipe. The flow was characterized using a novel wire-mesh sensor based on capacitance measurements and high-speed video recording. New two-phase pressure gradient, volume fraction, and phase distribution data have been used in the analysis. Drag reduction and slip ratio were detected at oil volume fractions between 10 and 45% and high mixture Reynolds numbers, and with water as the dominant phase. Phase-fraction distribution diagrams and cross-sectional imaging of the flow suggested the presence of a higher amount of water near to the pipe wall. Based on that, a phenomenology for explaining drag reduction in dispersed flow in a flow situation where slip ratio is significant is proposed. A simple phenomenological model is developed and the agreement between model predictions and data, including data from the literature, is encouraging. (c) 2011 American Institute of Chemical Engineers AIChE J, 2012

Stability of the tunnel face reinforced by bolts under seepage flow conditions

Il presente lavoro tratta la stabilità del fronte di scavo, rinforzato con barre di consolidamento ed interessato da drenaggi in avanzamento, di gallerie sotto falda in rocce tenere o terreni. Tale studio è stato sviluppato dal progetto di Tesi attraverso l’analisi all’equilibrio limite che approssima il fronte di scavo con un rettangolo e considera un meccanismo di rottura composto da un cuneo, a tergo del fronte, caricato da un prisma. Il metodo descritto consente di tenere conto dell’effetto stabilizzante delle barre, mediante una distribuzione della pressione di supporto non uniforme. Nel caso di gallerie sotto falda, lo stesso metodo permette inoltre di considerare l’effetto destabilizzante dei gradienti idraulici. Sono state ricavate soluzioni analitiche per la valutazione della stabilità, ed implementate successivamente nel software di analisi numerica MATLAB. Dalle analisi condotte è emerso che il numero minimo di barre per garantire la stabilità del fronte di scavo è in molti casi elevato e risulta impossibile da porre in opera in terreni scarsamente coesivi o in gallerie sotto elevati battenti d’acqua. Per risolvere questa situazione si può prevedere l’inserimento di drenaggi in avanzamento, con lo scopo di diminuire i gradienti idraulici nei pressi del fronte della galleria. Il modello che descrive il nuovo andamento dei carichi idraulici, considerando la presenza di dreni, è stato realizzato con il software commerciale agli elementi finiti COMSOL. Una volta determinati gli andamenti dei carichi idraulici, sono stati condotti studi parametrici sull’effetto dei dreni combinato con gli elementi di rinforzo. Dopo tali analisi sono stati ricavati nomogrammi adimensionali che tengano conto della presenza contemporanea delle barre e dei dreni. Tali diagrammi costituiscono uno strumento utile e valido per la progettazione del rinforzo del fronte di scavo. Infine sono stati realizzati confronti fra casi di studio reali e risultati ottenuti dal modello.