197,244 research outputs found
A comparative study on the cortico-hypoglossal connections in primates, using biotin dextranamine
No full textHow non-Darcy effects influence scaling laws in Hele-Shaw convection experiments
No full textWe examine experimentally the influence of non-Darcy effects on convective dissolution in Hele-Shaw cells. We focus on buoyancy-driven convection, where the flow is controlled by the Rayleigh-Darcy number, which measures the strength of convection compared to diffusion. The Hele-Shaw cell is suitable to mimic Darcy flows only under certain geometrical constraints, and a recent theoretical work (Letelier et al.J. Fluid Mech., vol. 864, 2019, pp. 746-767) demonstrated that a precise limit exists for the parameter - thickness-to-height ratio - beyond which the flow exhibits non-Darcy effects. In this work, we run experiments for solute convection in Rayleigh-Bénard-like configuration. We examine a wide range of the parameters space and we clearly identify the application limits of Darcy flow assumptions. Besides confirming previous theoretical predictions, current results are of relevance in the context of porous media flows - which are often studied experimentally with Hele-Shaw set-ups. Using our original datasets, we have been able to explain and reconcile the discrepancies observed between scaling laws previously proposed for Rayleigh-Bénard-like experiments and simulations in similar contexts. Specifically, we attribute an important role to the parameter, which clearly establishes thresholds beyond which Hele-Shaw experiment results are influenced by three-dimensional effects
Concentration-based velocity reconstruction in convective Hele–Shaw flows
No full textAbstract: We examine the process of convective dissolution in a Hele–Shaw cell. We consider a one-sided configuration and we propose a newly developed method to reconstruct the velocity field from concentration measurements. The great advantage of this Concentration-based Velocity Reconstruction (CVR) method consists of providing both concentration and velocity fields with a single snapshot of the experiment recorded in high resolution. We benchmark our method vis–à–vis against numerical simulations in the instance of Darcy flows, and we also include dispersive effects to the reconstruction process of non-Darcy flows. The absence of laser sources and the presence of one low-speed camera make this method a safe, accurate, and cost-effective alternative to classical PIV/PTV velocimetry processes. Finally, as an example of possible application, we employ the CVR method to analyse the tip splitting phenomena. Graphic abstract: [Figure not available: see fulltext.
Anterograde projections of the cortical tongue area of the tree shrew (Tupaia belangeri)
No full textIn altogether seven tree shrews, Tupaia belangeri, the anterograde projections of the motorcortical tongue area were investigated as part of a larger comparative study. Identification of the tongue area was carried out by electrical brain stimulation. Three different tracers were used: biotin-conjugated dextranamine (BDA), Phaseolus vulgaris leucoagglutinin (PHA-L) and 3H-leucine. Intracortical projections were found to the motor cortex around the injection site, the premotor cortex, supplementary motor area, the homologues of the primate frontoparietal operculum and insula, the anterior cingulate and agrannular retrosplenial cortex, the somatosensory and bordering inferior parietal cortex as well as to the perirhinal cortex. Except the very weak projections into the retrosplenial, posterior parietal and perirhinal region which were ipsilateral, all other projections were bilateral. Subcortically, there was a projection into the ventral putamen, rostrodorsal claustrum and, very sparsely, into the caudate nucleus. In the thalamus, terminal labeling was found in the nuclei reticularis, anteroventralis, anteromedialis, ventralis lateralis, ventralis posterior medialis, ventralis posterior inferior, medialis dorsalis, in the intralaminar nuclei paracentralis, centralis lateralis, centrum medianum and parafascicularis, in the midline thalamus and in the nuclei posterior and pulvinaris. Further diencephalic projections, however all of them wak, could be traced into the zona incerta, dorsolateral subthalamus, dorsomedial, lateral and supraoptic hypothalamus. In the midbrain, labeling was found in the deep layers of the lateral superior colliculus, in the bordering reticular formation and, very sparsely, in the periaqueductal grey. In the lower brain-stem, fibres ended in the griseum pontis, dorsolateral reticular formation, principal and spinal trigeminal nucleus and, sparsely, in the lateral parabrachial region, solitary tract nucleus, inferior olive and magnocellular reticular formation. No terminals were found in the hypoglossal nucleus. The projection system revealed with PHA-L was less extensive than that demonstrated with BDA and 3H-leucine, both of which were similar
Anterograde projections of the cortical tongue area of the tree shrew (Tupaia belangeri)
No full textIn altogether seven tree shrews, Tupaia belangeri, the anterograde projections of the motorcortical tongue area were investigated as part of a larger comparative study. Identification of the tongue area was carried out by electrical brain stimulation. Three different tracers were used: biotin-conjugated dextranamine (BDA), Phaseolus vulgaris leucoagglutinin (PHA-L) and 3H-leucine. Intracortical projections were found to the motor cortex around the injection site, the premotor cortex, supplementary motor area, the homologues of the primate frontoparietal operculum and insula, the anterior cingulate and agrannular retrosplenial cortex, the somatosensory and bordering inferior parietal cortex as well as to the perirhinal cortex. Except the very weak projections into the retrosplenial, posterior parietal and perirhinal region which were ipsilateral, all other projections were bilateral. Subcortically, there was a projection into the ventral putamen, rostrodorsal claustrum and, very sparsely, into the caudate nucleus. In the thalamus, terminal labeling was found in the nuclei reticularis, anteroventralis, anteromedialis, ventralis lateralis, ventralis posterior medialis, ventralis posterior inferior, medialis dorsalis, in the intralaminar nuclei paracentralis, centralis lateralis, centrum medianum and parafascicularis, in the midline thalamus and in the nuclei posterior and pulvinaris. Further diencephalic projections, however all of them wak, could be traced into the zona incerta, dorsolateral subthalamus, dorsomedial, lateral and supraoptic hypothalamus. In the midbrain, labeling was found in the deep layers of the lateral superior colliculus, in the bordering reticular formation and, very sparsely, in the periaqueductal grey. In the lower brain-stem, fibres ended in the griseum pontis, dorsolateral reticular formation, principal and spinal trigeminal nucleus and, sparsely, in the lateral parabrachial region, solitary tract nucleus, inferior olive and magnocellular reticular formation. No terminals were found in the hypoglossal nucleus. The projection system revealed with PHA-L was less extensive than that demonstrated with BDA and 3H-leucine, both of which were similar
Influence of Reynolds number on the dynamics of rigid, slender and non-axisymmetric fibres in channel flow turbulence
No full textWe investigate experimentally the dynamics of non-axisymmetric fibres in channel flow turbulence, focusing specifically on the importance of the fibre size relative to the flow scales. To this aim, we maintain the same physical size of the fibres and we increase the shear Reynolds number. Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. Fibres are slender - length to diameter ratio of 120 - rigid, curved and neutrally buoyant particles and their shape ranges from low curvature - almost straight fibres - to moderate curvature. In all cases, fibre size remains small compared with the channel height (≤1.5%). Three-dimensional and time-resolved recordings of the laser-illuminated measurement region are obtained from four high-speed cameras and used to infer fibre dynamics. With the aid of multiplicative algebraic reconstruction techniques, fibre position, orientation, velocity and rotation rates are determined. Our measurements span over the half-channel height, from wall to centre, and allow a complete characterisation of the fibre dynamics in all regions of the flow. Specifically, we measure fibre preferential distribution and orientation. We observe that the fibre dynamics is always influenced by their curvature. Through a comparison between measurements of the near-wall dynamics of the fibres and the near-wall dynamics of the flow, we identify a causal relationship between fibre velocity and orientation, and the near-wall turbulence dynamics. Finally, we have been able to provide original measurements of the tumbling rate of the fibres, for which we report the influence of fibre curvature. We underline that our measurements confirm previous findings obtained in numerical and experimental works
Non-carbonaceous supported platinum electrocatalyst as alternative to carbon base materials toward oxygen reduction reaction for low-temperature fuel cells
No full textAbstract This dissertation is focused on investigation of comparative evaluation of structure, composition and electrochemical performance of new electrocatalysts approach Platinum (Pt) supported on metal oxides which are specifically Titanium suboxide and Titanium nanotube suboxide (TNTS). The Pt/MOx (M: Nb, Ti, Mn, Cu and Ni…) and Pt/TixO2x-1 with intrinsic electrocatalytic activity, conductivity and excellent stability are studied in acidic media toward the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Specifically, a Pt thin layer (monolayer) is homogeneously deposited on the surface of TixO2x-1-Mo and TNTS supports by using different methods. For almost all applied methods the Pt atoms utilization, involved in the reactions, is very high. These efforts indicate that both the Pt morphology and the support structure can significantly enhance the catalytic activity and stability of electrocatalysts toward ORR and MOR. The interest in ORR and MOR is motivated by the application of these novel electrocatalysts at the cathodes and anode side, respectively, of proton exchange membrane fuel cells (PEMFCs). In fact, PEMFCs are extensively considered as potential highly efficient devices for clean energy production in many different applications, from portable to transportation and stationary. The mechanism of PEMFCs is to convert directly the chemical energy of hydrogen (or methanol) fuel and oxygen (air) oxidant into usable electrical energy. At the cathode (the positive electrode), a considerable amount of platinum is generally required to catalyse the sluggish ORR, because of its slow kinetics. Due to the excellent conductivity and high specific surface area, carbon materials are extensively employed in both the anode and cathode to support Pt electrocatalyst in PEMFCs. A major drawback of Pt/C electrocatalyst is at the cathodic site in which the electrode potential and pH are relatively high: carbon materials suffer corrosion (C + H2O → CO2 + 4H+ + 4e-, 0.207 V vs NHE at 25 °C) with consequent dissolution of Pt metal catalyst. Such a dissolution, which is an anodic reaction, causes problems of mixed potential formation at cathodic side with subsequent decreasing of the long-term stability of the Pt electrocatalyst performance and shifting the ORR reversible potential to lower values. This drawback is one of major technical barriers to the widespread commercialization of PEMFCs as energy source. Apart from carbon corrosion, in case of methanol as fuel, DMFCs suffer from methanol cross-over through the polymeric membrane, which causes a further reduction in electroactivity performance. In fact, the oxidation of methanol at the cathode involves the formation of intermediate products, mainly CO, which are strongly adsorbed to the surface of Pt-based catalysts reducing the number of active sites of Pt and consequently the ORR activity. These phenomena, together with the high cost of Pt, are considered the primary limiting factors to the developing the large-scale commercialization of DMFCs and PEMFCs. In order to overcome the problems associated to carbon corrosion and alleviate CO poisoning, this PhD thesis demonstrates the application of metal oxides, in particular the sub-oxide TixO2x-1-M, as a potential electrocatalyst support, promoting the electrocatalytic activity, stability and poison resistance of Pt electrocatalysts. TixO2x-1, which is a non-carbonaceous material with high conductivity, stability and durability in acidic media, has great potential to be an alternative promising material to carbon supports for Pt electrocatalyst in order to further boost PEMFCs and DMFCs applicatio
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
Long non-axisymmetric fibres in turbulent channel flow
No full textIn this work, we investigate the dynamics of long non-axisymmetric fibres in turbulent channel flow. The experimental facility is the TU Wien Turbulent Water Channel, consisting of a closed water channel (aspect ratio of 10), and the experiments are performed at a shear Reynolds number of 360. Fibres are neutrally buoyant rods that are curved and characterised by a length-to-diameter ratio of 120. Illumination is provided by a laser sheet and the motion of fibres is recorded by four high-speed cameras in a fully developed flow section. We apply multiplicative algebraic reconstruction techniques to the recorded images from four high-speed cameras to identify the three-dimensional location, shape and orientation of the fibres. The fibres are also tracked in time to obtain their three-dimensional vectors of velocity and rotation rate. We investigate the behaviour of the fibres, from the near-wall region to the channel centre, and we produce original statistics on the effect of curvature of the fibres on their orientation and rotation rate. Specifically, we measured the orientation and rotation rate of the fibres, and we can confirm that in the centre, the most homogeneous part of the channel, statistics, although influenced by the curvature, bear similarities to those obtained in previous investigations in homogeneous isotropic turbulence. In addition, we have been able to compare the tumbling rate of our long non-axisymmetric fibres with previous solutions for curved ellipsoids in simple shear flow
"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
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