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Analysis of the blood flow behavior through microchannels by a confocal micro-PIV/PTV system

Lima, R.
Fonte: Tohoku University Publicador: Tohoku University
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
35.97%
Over the years, various experimental methods have been applied in an effort to understand the blood flow behavior in microcirculation. Most of our current knowledge in microcirculation is based on macroscopic flow phenomena such as Fahraeus effect and Fahraeus-Linqvist effect. The development of optical experimental techniques has contributed to obtain explanations on the way the blood flows through microvessels. Although the past results have been encouraging, detailed studies on the flow properties of blood in the microcirculation has been limited by several technical factors such as poor spatial resolution and difficulty to obtain quantitative detailed measurements at such small scales. Therefore, there is still a lack of knowledge on the microscale flow behavior of blood cells through microvessels. In recent years, due to advances in computers, optics, and digital image processing techniques, it has become possible to combine a particle image velocimetry (PIV) system with a conventional microscope. As a result, this combination, known as a micro-PIV, has greatly increased the resolution of the conventional PIV. Although the conventional micro-PIV technique has proven to be useful in measuring the flow behavior in microfluidics devices...

Aperfeiçoamento do método de elementos analíticos para simulação de escoamento em rochas porosas fraturadas; Improvement of the analytical element method for simulating of flow in fractured porous rocks

Marin, Ivan Silvestre Paganini
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/10/2011 PT
Relevância na Pesquisa
35.89%
Escoamento de água subterrânea em meios porosos fraturados é um problema de grande importância, principalmente nos contextos de petróleo, energia geotérmica e repositórios geológicos. Com o aquecimento da Terra, a geração de energia com baixa emissão de gases estufa torna-se imperativa, considerando o crescimento de uso de energia e o impacto do aquecimento global. Dentre as opções disponíveis para geração de energia, a energia nuclear apresenta-se como candidata. Entretanto, dentre os riscos do uso de energia nuclear, o destino do combustível usado e de materiais provenientes de descomissionamento é um problema em aberto. Repositórios geológicos surgem como uma alternativa para a estocagem de médio e longo prazo, por serem capazes de proporcionar isolamento em escalas geológicas de tempo. O principal vetor de propagação do material radioativo estocados em repositórios é a água subterrânea, e meios fraturados estão presentes na maioria dos domínios. Fraturas podem propagar a água subterrânea e, portanto, solutos com velocidades muito maiores que as do meio poroso. Além disso, fraturas são, geralmente, sistemas multiescala, em que diferentes escalas - de centímetros a kilômetros - podem ter um papel significativo. Métodos como elementos finitos...

Orff-Schulwerk approach and flow indicators in music education context: a preliminary study in Portugal

Cunha, João Cristiano; Carvalho, Sara
Fonte: International Journal Publicador: International Journal
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.94%
Extensive literature exists on Flow Theory. However there is a lack of published research investigating possible links between Orff-Schulwerk approach and Csikszentmihalyi’s concept of flow or optimal experience. Based on preliminary results from an ongoing research on Music / Music Pedagogy and (is links to) Musical Thought / Musical Cognition, the present paper aims to discuss the existence of optimal experiences / flow states boosted by Orff- Schulwerk approach activities / teaching music strategies in the context of Music Education in a Portuguese general public school (5th and 6th grades). Attempting to verify, analyze and understand these relationships, an empirical process was developed based on the Flow Theory - Optimal Experience (Csikszentmihalyi 1975, 1988, 1990) and consequently on FIMA - Flow Indicators in Musical Activity developed by Custodero (1998, 1999). Conventional flow methodology is adapted in order to define and to operacionalize cognitive strategies exhibited during Orff-Schulwerk approach activities in Music Eduction context. Results clearly validated this hipotesys and show how (and which) Orff-Schulwerk activities can provide children optimal experience /flow states in Music Education classes.

Three dimensional model of a high temperature PEMFC using PBI doped phosphoric acid membranes. Study of the flow field effect on performance

Sousa, T.; Mamlouk, M.; Rangel, C. M.; Scott, K.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em 01/11/2011 ENG
Relevância na Pesquisa
35.82%
A three-dimensional isothermal model of a high temperature polymer membrane fuel cell equipped with polybenzimidazole (PBI) membrane is described. All major transport phenomena were taken into account except the species cross-over thought the membrane. The cathode catalyst layer was treated as spherical catalyst agglomerates with porous inter-agglomerate spaces. The inter-agglomerate spaces were filled with a mixture of electrolyte (hot phosphoric acid) and polytetrafluoroethylene (PTFE). This approach proved to be an essential requirement for accurate simulation. In this particular paper the influence of different flow field designs and dimensions on performance was intensely study. Traditional configurations were tested (straight, serpentine, pin-in and interdigitated), and a new designs were proposed. With these new designs we tried to maximize performance by providing homogeneous reactants distribution over the active area keeping low pressure drop and relatively high velocity. The dimension and position of the inlet and outlet manifolds were also analysed. From the obtained results was observed a massive influence of the manifolds position and dimension on performance. This fact leaded to an optimization of the manifolds which can give important guidelines for future bipolar plates production.

Effect of lateralized epileptic discharges on the thought flow

Mendonça,Paulo Bueno de; Piccinin,Lucy Campos; Capucho,Celso Medeiros; Campos,Carlos José Reis de
Fonte: Academia Brasileira de Neurologia - ABNEURO Publicador: Academia Brasileira de Neurologia - ABNEURO
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2001 EN
Relevância na Pesquisa
66.24%
PURPOSE: Pauses in verbal expression of thought flow in patients with partial epilepsy was studied in order to achieve a best comprehension of brain interhemispheric influences. METHOD: We studied thirty nine patients with partial epileptic seizures and twenty four volunteers (control group). Free association of ideas was used as a method to stablish the thought flow, starting with a stimulus word (subject name) that must be followed by spontaneous and consecutive word-phrase. Patients were instructed to say any thought that came to their minds without any kind of censoring. Subject responses were recorded through a PC keyboard and time intervals (pauses) between each word-phrase were processed by a software developed for this purpose. RESULTS: Time intervals reduction among associations in right lesional group were compared to left lesional, right non-lesional and control groups. An increase of associative time intervals was observed in the right non-lesional group compared to left non-lesional group. CONCLUSIONS: We suggest a possible inhibitory inter-hemispheric function of the right hemisphere modulating verbal expression of the thought flow. Considering the hypothesis of the inter-hemispheric inhibition by the right hemisphere on left hemisphere...

Formal Thought Disorder and language impairment in schizophrenia

Radanovic,Marcia; Sousa,Rafael T. de; Valiengo,L.; Gattaz,Wagner Farid; Forlenza,Orestes Vicente
Fonte: Academia Brasileira de Neurologia - ABNEURO Publicador: Academia Brasileira de Neurologia - ABNEURO
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
Relevância na Pesquisa
35.93%
Schizophrenia is a psychiatric illness in which disorders of thought content are a prominent feature. The disruption of normal flow of thought, or “Formal Thought Disorder” (FTD), has been traditionally assessed through the content and form of patients’ speech, and speech abnormalities in schizophrenia were considered as a by-product of the disruption in conceptual structures and associative processes related to psychosis. This view has been changed due to increasing evidence that language per se is impaired in schizophrenia, especially its semantic, discursive, and pragmatic aspects. Schizophrenia is currently considered by some authors as a “language related human specific disease” or “logopathy”, and the neuroanatomical and genetic correlates of the language impairment in these patients are under investigation. Such efforts may lead to a better understanding about the pathophysiology of this devastating mental disease. We present some current concepts related to FTD as opposed to primary neurolinguistic abnormalities in schizophrenia.

Analysis of Cortical Flow Models In Vivo

Benink, Hélène A.; Mandato, Craig A.; Bement, William M.
Fonte: The American Society for Cell Biology Publicador: The American Society for Cell Biology
Tipo: Artigo de Revista Científica
Publicado em /08/2000 EN
Relevância na Pesquisa
25.97%
Cortical flow, the directed movement of cortical F-actin and cortical organelles, is a basic cellular motility process. Microtubules are thought to somehow direct cortical flow, but whether they do so by stimulating or inhibiting contraction of the cortical actin cytoskeleton is the subject of debate. Treatment of Xenopus oocytes with phorbol 12-myristate 13-acetate (PMA) triggers cortical flow toward the animal pole of the oocyte; this flow is suppressed by microtubules. To determine how this suppression occurs and whether it can control the direction of cortical flow, oocytes were subjected to localized manipulation of either the contractile stimulus (PMA) or microtubules. Localized PMA application resulted in redirection of cortical flow toward the site of application, as judged by movement of cortical pigment granules, cortical F-actin, and cortical myosin-2A. Such redirected flow was accelerated by microtubule depolymerization, showing that the suppression of cortical flow by microtubules is independent of the direction of flow. Direct observation of cortical F-actin by time-lapse confocal analysis in combination with photobleaching showed that cortical flow is driven by contraction of the cortical F-actin network and that microtubules suppress this contraction. The oocyte germinal vesicle serves as a microtubule organizing center in Xenopus oocytes; experimental displacement of the germinal vesicle toward the animal pole resulted in localized flow away from the animal pole. The results show that 1) cortical flow is directed toward areas of localized contraction of the cortical F-actin cytoskeleton; 2) microtubules suppress cortical flow by inhibiting contraction of the cortical F-actin cytoskeleton; and 3) localized...

Stimulation of osmotic water flow in toad bladder by prostaglandin E1. Evidence for different compartments of cyclic AMP.

Flores, J; Witkum, P A; Beckman, B; Sharp, G W
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1975 EN
Relevância na Pesquisa
26.17%
The effect of prostaglandin E1 (PGE1) on osmotic water flow across toad bladder and cyclic AMP content of the mucosal epithelial cells has been determined under basal conditions and in the presence of either theophylline or antidiuretic hormone (ADH); Under basal conditions and with PGE1 concentrations from 10(-8) to 10(-5) M no evidence of stimulation of water flow was observed, and with 10(-7) M PGE1 a significant inhibition was foundmcyclic AMP content under control conditions was 8 pmol/mg protein. It was 9 at 10(-8) M PGE1, 13 at 10(-7) M, 16 at 10(-6) M, and 23 at 10(-5) M. In the presence of theophylline, 10(-8) and 10(-7) M PGE1 inhibited the theophylline-induced water flow as expected. In contrast, 10(-6) and 10(-5) M PGE1 enhanced the rate of water flow. Theophylline increased cyclic AMP content from 8 to 18 pmol/mg protein. PGE1 in the presence of theophylline caused marked increases in cyclic AMP content; The content was 23 at 10(-7) M, 41 at 10(-6) M, and 130 at 10(-5) M; Thus PGE1 stimulates theophylline-induced water flow at cyclic AMP concentrations somewhere between 23 and 41 pmol/mg. Further evidence along these lines was obtained from experiments in which the effects of PGE1 on ADH-induced water flow were studied. Inhibitory effects of PGE1 were not observed at concentrations of PGE1 which raised the level of intracellular cyclic AMP to 30 pmol/mg protein or higher. These results were obtained despite the fact that all four concentrations of PGE1 tested were found capable of inhibiting ADH-induced water flow under appropriate conditions or...

The effects of a 5-HT2A receptor antagonist on blood flow in lumbar disc herniation : application of nucleus pulposus in a canine model

Sekiguchi, Miho; Konno, Shin-ichi; Kikuchi, Shin-ichi
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
25.95%
Blood vessel clots are found around the nerve root in patients with lumbar disc herniation. Thrombosis formation in the experimental application of nucleus pulposus to the nerve root has been shown in histological studies. In addition, reduction of blood flow and nerve conduction velocity are induced by the application of nucleus pulposus, which mimics lumbar disc herniation. In patients with lumbar disc herniation, nerve root block, which is thought to increase nerve blood flow, improves radiculopathy. 5-HT2A receptor antagonists are used in chronic arterial occlusive diseases to improve blood flow and have been reported to work as well as nonsteroidal anti-inflammatory drugs in improving radiculopathy due to lumbar disc herniation in clinical studies. This study investigated the effects of a 5-HT2A receptor antagonist on blood vessel diameter and blood flow in a canine experimental model of lumbar disc herniation. A total of 13 dogs were used. The animals were divided into three experimental groups and surgery was performed 1 week before measurements. In the nucleus pulposus group (NP; n = 5), the nucleus pulposus was applied to the nerve roots from the ventral side. In the sham group (n = 5), nucleus pulposus was not applied. In the naïve group (n = 3)...

Flow regulation of collecting duct endothelin-1 production

Lyon-Roberts, Brianna; Strait, Kevin A.; van Peursem, Evan; Kittikulsuth, Wararat; Pollock, Jennifer S.; Pollock, David M.; Kohan, Donald E.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
25.95%
Collecting duct (CD) endothelin-1 (ET-1) is an important autocrine inhibitor of CD Na+ reabsorption. Salt loading is thought to increase CD ET-1 production; however, definitive evidence of this, as well as understanding of the mechanisms transducing this effect, is lacking. Tubule fluid flow increases in response to Na+ loading; hence, we studied flow modulation of CD ET-1 production. Three days of a high-salt diet increased mouse and rat inner medullary CD (IMCD) ET-1 mRNA expression. Acute furosemide infusion increased urinary ET-1 excretion in anesthetized rats. Primary cultures of mouse or rat IMCD detached in response to flow using a closed perfusion chamber, consequently a CD cell line (mpkCCDcl4) was examined. Flow increased ET-1 mRNA at shear stress rates exceeding 1 dyne/cm2, with the maximal effect seen between 2 and 10 dyne/cm2. Induction of ET-1 mRNA was first evident after 1 h, and most apparent after 2 h, of flow. Inhibition of calmodulin or dihydropyridine-sensitive Ca2+ channels did not alter the flow response; however, chelation of intracellular Ca2+ or removal of extracellular Ca2+ largely prevented flow-stimulated ET-1 mRNA accumulation. Downregulation of protein kinase C (PKC) using phorbol 12-myristate 13-acetate...

Flow parsing and heading perception show similar dependence on quality and quantity of optic flow

Foulkes, Andrew J.; Rushton, Simon K.; Warren, Paul A.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 19/06/2013 EN
Relevância na Pesquisa
25.96%
Here we examine the relationship between the perception of heading and flow parsing. In a companion study we have investigated the pattern of dependence of human heading estimation on the quantity (amount of dots per frame) and quality (amount of directional noise) of motion information in an optic flow field. In the present study we investigated whether the flow parsing mechanism, which is thought to aid in the assessment of scene-relative object movement during observer movement, exhibits a similar pattern of dependence on these stimulus manipulations. Finding that the pattern of flow parsing effects was similar to that observed for heading thresholds would provide some evidence that these two complementary roles for optic flow processing are reliant on the same, or similar, neural computation. We found that the pattern of flow parsing effects observed does indeed display a striking similarity to the heading thresholds. As with judgements of heading, there is a critical value of around 25 dots per frame; below this value flow parsing effects rapidly deteriorate and above this value flow parsing effects are stable [see Warren et al. (1988) for similar results for heading]. Also, as with judgements of heading, when there were 50 or more dots there was a systematic effect of noise on the magnitude of the flow parsing effect. These results are discussed in the context of different possible schemes of flow processing to support both heading and flow parsing mechanisms.

Novel multiparameter flow cytometry techniques for the detection of leukaemia associated phenotypes and minimal residual disease monitoring in acute myeloid leukaemia.

Al-Mawali, Adhra Hilal Nasser
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2008
Relevância na Pesquisa
35.86%
Despite high remission rate in acute myeloid leukaemia (AML) after chemotherapy, relapse of the underlying disease remains a major challenge and one of the most frequent causes of treatment failure. In this study, the presence of leukaemiaassociated phenotypes (LAPs) was first studied retrospectively using our standard diagnostic protocol with 3-colour flow cytometry. LAPs were present in 54 (64%) of 84 AML patients analysed between 2002 to 2004. The presence of LAPs was correlated with failure to respond to induction chemotherapy (p <0.05) in univariate analysis. Presence of LAPs was shown to be an independent predictor for failure to respond to induction chemotherapy with a relative risk ratio of 1.6 (p < 0.05, 95% CI, 1.0-2.6) in multivariate analysis. Subsequently, in a prospective study, we used 5-colour multiparametric flow cytometry (MFC) for detection of LAPs to determine if LAPs could be detected in a greater proportion of leukaemic patients and minimal residual disease (MRD) detection could therefore be applied in more patients. In 54 consecutive, newly diagnosed AML patients from 2005 to 2007, LAPs were identified in 51 (94%). Thus, MRD studies were potentially applicable to virtually all patients. The sensitivity and specificity of MFC technique was improved by analysing 10 normal and 5 regenerating bone marrows (BM) for the presence of these LAPs and by determining maximum log difference (LD). CD7...

The significance and lag-time of deep through flow: an example from a small, ephemeral catchment with contrasting soil types in the Adelaide Hills, South Australia

Bestland, E.; Milgate, S.; Chittleborough, D.; van Leeuwen, J.; Pichler, M.; Soloninka, L.
Fonte: European Geosciences Union Publicador: European Geosciences Union
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
26.07%
The importance of deep throughflow in a small (3.4 km2) ephemeral catchment in the Adelaide Hills of South Australia was investigated by detailed hydrochemical analysis of soil water and stream flow during autumn and early winter rains. In this Mediterranean climate with strong summer moisture deficits, several significant rainfalls are required to generate soil throughflow and stream flow (in ephemeral streams). During Autumn 2007, a large (127 mm) drought-breaking rain occurred in April followed by significant May rains; most of this precipitation occurred prior to the initiation of stream flow in late May. These early events, especially the 127 mm event, had low (depleted) stable water isotope values compared with both later rains and average winter precipitation. Thus, this large depleted early rain event provided an excellent natural tracer. During the June and July rainfall events, daily stream and soil water samples were collected and analysed. Results from major and trace elements, water isotopes (δ18O, δD), and dissolved organic carbon analysis clearly demonstrate that a large component of this early April and May rain was stored and later pushed out of deep soil or regolith zones. This pre-event water was identified in the stream as well as identified in deeper soil horizons due to its different isotopic signature which contrasted sharply with the June–July event water. Based on this data...

Differential roles of adhesion receptors during neutrophil adhesion to endothelial cells under flow conditions

Gopalan, Priya Kadambi
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
25.99%
Neutrophil emigration from the vasculature is an essential part of the primary immune response to infections. It is a multi-step process of cell interaction with the endothelium (capture, rolling, arrest and transmigration) that involves several classes of receptors. Neutrophils are captured (tethered) and then roll on the endothelial surface. This initial interaction is thought to involve the selectin family of cell adhesion molecules. Cell arrest (firm adhesion) follows neutrophil activation. Activated CD18 integrins and ICAM-1, a member of the immunoglobulin gene superfamily, mediate arrest. Finally, the neutrophils transmigrate beneath the endothelial cells, a process also thought to be dependent on the CD18 integrins and ICAM-1. We used a parallel plate flow chamber to simulate laminar flow along vessel walls in the vasculature. We demonstrate that L-selectin can activate the adhesive function the CD18 integrins. In this work, we show for the first time that L-selectin can activate LFA-1. We also show that two of the members of the CD18 integrin family, LFA-1 and Mac-1, are both sufficient to mediate neutrophil arrest and transmigration across endothelial cells stimulated for 4 hr with IL-$1eta .$ We provide evidence for the existence of a pathway independent of the CD18 integrins that can mediate arrest and transmigration. Neutrophils utilizing this pathway are able to transmigrate with a rate comparable to CD18-dependent transmigration. We provide some preliminary data that demonstrates that PECAM-1 ligation does not activate neutrophil CD18 integrin-mediated arrest...

Control of flow over a backward facing step

Woolman, Scott G.
Fonte: Monterey, California: Naval Postgraduate School Publicador: Monterey, California: Naval Postgraduate School
Tipo: Tese de Doutorado Formato: x, 81 p.
EN_US
Relevância na Pesquisa
35.82%
Approved for public release; distribution unlimited.; The poor aerodynamic design of the superstructures of today's Navy ships create a highly turbulent airwake that can make shipboard helicopter operations quite hazardous. This study is part of a longer-term project to tailor airflow over a ship's helicopter deck in order to improve the poor quality of the airflow. This airflow is thought to be largely responsible for several costly blade strike mishaps involving H-46 helicopters during start-up and shut down. Numerous computer simulations were conducted using the Phoenics Computational Fluid Dynamics code to simulate airflow over a backward-facing- step. The latter represents a simple 2-d model of flow behind a typical hangar flight deck combination. In each run a deflector of different size, orientation or porosity was placed in a specific location in an attempt to reduce the size of the recirculation zone, the velocities and the turbulence levels. Of the studies involved, a vertical deflector offset downstream with its lower edge at the top of the step produced the best overall results.; Lieutenant, United States Coast Guard

METABOREFLEX-INDUCED FLOW IMPROVEMENT IS ABSENT IN OLDER MALES WITH TYPE II DIABETES

BRAVO, MICHAEL FRANCIS
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.08%
Background: Exercise is widely recognized as the cornerstone of management of type II diabetes (T2D). However, it is also known that people with T2D have poor adherence to exercise regimens, which is largely thought to be because of poor exercise tolerance. Recent studies have suggested that this exercise intolerance may be caused by a reduction in exercising muscle blood flow. One physiological mechanism which could potentially contribute is the muscle metaboreflex (MMR). This mechanism is thought to be a pressure-based flow-improving mechanism, but as a result of reduced efficacy of vasodilators and sympatholytic agents, might in fact be restraining the flow-improvement in persons with T2D. Hypothesis: Persons with T2D would not improve exercising muscle blood flow upon MMR activation. This absence of flow-improvement will be due to an augmented vasoconstriction in the exercising muscle. Methods: T2D (n=7) and CTL (n=6) participants performed rhythmic forearm handgrip exercise at an intensity equivalent to 20% MVC for 9 minutes with and without the application of ischemic plantar flexion (IPF). Forearm blood flow (FBF), mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), total peripheral resistance (TPR) and forearm vascular conductance (FVK) were quantified for the last thirty seconds of each of four time points during the protocol. Plasma norepinephrine was measured via deep venous and arterialized venous blood sampling. Results: Steady state exercising FBF was increased in CTL but not in T2D during MMR activation (mean ± SE mL/min: CTLControl 161.16 ± 5.95...

Scaling relations of branching pulsatile flow

Silva, Carla; Reis, A. Heitor
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.92%
Apparently complex flow structures obey to scaling relations that enable to make it viable the study of their configuration and flow dynamics. This is the case of flow structures that exhibit several branching levels and are thought to perform optimally. Here we present scaling relations of diameters and lengths of branching cylindrical channels with pulsatile flows, and compare them with other relations published in the literature. It is shown that, under constant global volume of the flow tree, and for zero pulse frequency these scaling relations reduce to Murrays's law of consecutive diameters. Optimal scaling depends on pulse frequency, distensibility of the channel walls, and asymmetry of the daughter vessels. In case that in addition to global volume of the flow tree, the pressure head is also kept constant, a similar scaling law of channel lengths emerges that holds together with the law of diameter scaling. The effect of channel distensibility is shown to be somehow important, such that for achieving optimal performance (lowest impedance) channels with lower relative distensibility must have their diameter increased. Results are compared with those of other models for the case of some arteries.

Gas Flow Rates through Inert and Chemically Reactive Porous Beds

Baker, Jonathan; Champneys, Alan; Correia, Joaquim; Ceseri, Maurizio; Curtis, John; Hicks, Peter D.; Hinch, John; Lacey, Andrew; Lawn, Heather; Ockendon, John; Please, Colin; Tsardakas, Michael
Fonte: Study Groups with Industry, Mathematics in Industry Publicador: Study Groups with Industry, Mathematics in Industry
Tipo: Aula
ENG
Relevância na Pesquisa
35.77%
The study group was tasked to investigate: 1. how gas ows through irregularly shaped particles, and whether the Kozeny-Carman equation (relating the Kozeny-Carman constant K, porosity \phi and specific surface area S_k), could be improved to extend the usual spherical particle geometries to account for cylindrical, tetrahedral, ellipsoid and rhombic particle geometries; 2. the critical pressure for the collapse of bed; 3. the rate of reaction and build up in pressure in energetic porous beds; 4. "chuffing" - a periodic phenomenon observed in the later stages of some experiments, thought to be due to incomplete ignition of reactants in the initial phase of the reaction.

Oriented calcite concretions in Upper Miocene carbonate rocks of Menorca, Spain : evidence for fluid flow through a heterogeneous porous system

Pomar, Luis; Westphal, H.; Obrador i Tudurí, Antoni
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2004 ENG
Relevância na Pesquisa
35.86%
Elongate calcite concretions in Upper Miocene dolomitic, shallow-marine grainstones and packstones of Menorca document fluid flow through heterogeneous systems. These post-dolomitization concretions are thought to have grown with elongation axes parallel to groundwater flow direction, and to reflect the hydraulic gradient and the anisotropy of the hydraulic conductivity. Differences in shape, size and orientation of concretions, as well as the spatial and crosscutting relationships reflect two phases of calcite-cementing fluids. This is in contrast to most examples in the literature that distinguish just one phase of precipitating fluids. The first phase of cementing fluids flowed horizontally, most likely in the phreatic zone, across hydraulic high-conductivity layers that resulted from sediment-packing heterogeneities and preferential dissolution during dolomitization. These first-phase fluids were most likely injected into the host rock through fracture zones and probably originated in deeper settings. The second phase of cementing fluids was downward directed and possibly of meteoric origin. First-generation concretions, acting as permeability barriers, partly controlled the fluid pathways, precipitation patterns, and concretion type and loci.

High Momentum Flow Region and Central Recirculation Zone Interaction in Swirling Flows

Vigueras-Zuniga,Marco Osvaldo; Valera-Medina,Agustin; Syred,Nick; Bowen,Phil
Fonte: Sociedad Mexicana de Ingeniería Mecánica Publicador: Sociedad Mexicana de Ingeniería Mecánica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
Relevância na Pesquisa
35.93%
'Fuel-flexible' gas turbines will be required over the next 20 years at least. However, this contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in the fuel supply. Swirl stabilized combustion, being the most widely spread technology to control combustion in gas turbines, will be a technology needed for dynamic stabilization of the flow field. However, the features of the recirculation zone are highly complex, three dimensional and time dependent, depending on a variety of parameters. A high momentum flow region inherent to swirling flows has attracted the attention of several groups interested in blowoff and stretch flame phenomena. Therefore, this study focuses on experimental results obtained to characterise the relation between the central recirculation zone and the high momentum flow region under moderate swirl levels using a well-studied tangential swirl burner for power generation applications. As to be expected the recirculation zone and the high momentum flow region rotate together about the central axis. Moreover, the interaction between them produces high, intense local velocities. This region of High Momentum (shearing flow) also presents a complex geometry that seems to be based on the geometrical features of the burner...