Littérature scientifique sur le sujet « Stretch speed »
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Articles de revues sur le sujet "Stretch speed"
1
GRIFFITHS, R. I. « The Mechanics of the Medial Gastrocnemius Muscle in the Freely Hopping Wallaby (Thylogale Billardierii) ». Journal of Experimental Biology 147, no 1 (1 novembre 1989) : 439–56. http://dx.doi.org/10.1242/jeb.147.1.439.
Texte intégralRésumé :
Muscle force, electromyogram and length were monitored in the medial head of the gastrocnemius (MG) muscle in freely hopping wallabies (Thylogale billardierii Desmarest). During take-off hops from rest, MG muscle developed force with an isometric contraction. For constant-speed hops, force was produced in MG muscle during rapid stretch. The muscle resisted this stretch with a constant impedance that was independent of hopping speed. The rate of stretch of the muscle during high-speed hopping was as high as 1 ms−1 (5–6 muscle lengths per second) at the onset of stretch and slowed to no stretch at the peak of force. Since the mechanical impedance was constant while the stretch velocity changed, there was no significant viscosity present in the muscle. The tendon stretched by 3.2% at 7kmh−1 hopping and by 4.4% at 18kmh−1 hopping. Elastic energy storage in the tendons increased with hopping speed but the percentage of total work done by elastic recoil of the whole muscle did not increase at higher hopping speeds. The significance of the muscle stretch is in producing high forces rapidly and, in addition, there is considerable energy storage in the tend
2
Fasciano, Robert W., et Leslie Tung. « Factors governing mechanical stimulation in frog hearts ». American Journal of Physiology-Heart and Circulatory Physiology 277, no 6 (1 décembre 1999) : H2311—H2320. http://dx.doi.org/10.1152/ajpheart.1999.277.6.h2311.
Texte intégralRésumé :
Because stretch-induced activation may be important in generating clinically relevant arrhythmias in the heart, we delineated the ability of different types of stretches to activate ventricular tissue. Geometrically simple sheets of frog ( Rana catesbeiana) ventricular tissue were mounted to allow stretches to be applied perpendicular to one edge. Every heart could be activated by a stretch pulse ( n = 25), and several parameters were varied to determine their effects on mechanical activation threshold. At shorter coupling intervals, a larger stretch was needed to excite the tissue, and activation-recovery intervals were shorter, similar to previously published electrically probed strength-interval and restitution relations. Additionally, the tissue became easier to activate as the speed of the stretch increased from 0.09 to 2.6% length/ms. The increment in stretch needed for activation decreased as the baseline stretch increased from 0 to 6% length. Thus we show that mechanical activation is similar to electrical activation and that increasing uniquely mechanical parameters such as the speed of the applied stretch or baseline level of stretch can decrease the mechanical activation threshold.
3
Thiesset, F., F. Halter, C. Bariki, C. Lapeyre, C. Chauveau, I. Gökalp, L. Selle et T. Poinsot. « Isolating strain and curvature effects in premixed flame/vortex interactions ». Journal of Fluid Mechanics 831 (13 octobre 2017) : 618–54. http://dx.doi.org/10.1017/jfm.2017.641.
Texte intégralRésumé :
This study focuses on the response of premixed flames to a transient hydrodynamic perturbation in an intermediate situation between laminar stretched flames and turbulent flames: an axisymmetric vortex interacting with a flame. The reasons motivating this choice are discussed in the framework of turbulent combustion models and flame response to the stretch rate. We experimentally quantify the dependence of the flame kinematic properties (displacement and consumption speeds) to geometrical scalars (stretch rate and curvature) in flames characterized by different effective Lewis numbers. Whilst the displacement speed can be readily measured using particle image velocimetry and tomographic diagnostics, providing a reliable estimate of the consumption speed from experiments remains particularly challenging. In the present work, a method based on a budget of fuel on a well chosen domain is proposed and validated both experimentally and numerically using two-dimensional direct numerical simulations of flame/vortex interactions. It is demonstrated that the Lewis number impact neither the geometrical nor the kinematic features of the flames, these quantities being much more influenced by the vortex intensity. While interacting with the vortex, the flame displacement (at an isotherm close to the leading edge) and consumption speeds are found to increase almost independently of the type of fuel. We show that the total stretch rate is not the only scalar quantity impacting the flame displacement and consumption speeds and that curvature has a significant influence. Experimental data are interpreted in the light of asymptotic theories revealing the existence of two distinct Markstein numbers, one characterizing the dependence of flame speed to curvature, the other to the total stretch rate. This theory appears to be well suited for representing the evolution of the displacement speed with respect to either the total stretch rate, curvature or strain rate. It also explains the limited dependence of the flame displacement speed to Lewis number and the strong correlation with curvature observed in the experiments. An explicit relationship between displacement and consumption speeds is also given, indicating that the fuel consumption rate is likely to be altered by both the total stretch rate and curvature.
4
Ishikawa, M., et P. V. Komi. « The role of the stretch reflex in the gastrocnemius muscle during human locomotion at various speeds ». Journal of Applied Physiology 103, no 3 (septembre 2007) : 1030–36. http://dx.doi.org/10.1152/japplphysiol.00277.2007.
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In the present study, the fascicle length ( Lfa) of the human medial gastrocnemius (MG) muscle was monitored to evaluate possible input from the short-latency stretch reflex (SLR) during the stance phase of running and to examine its timing at various running speeds. Eight subjects ran at 2.0, 3.5, 5.0, and 6.5 m/s. The Lfa was measured with the high-speed ultrasound fascicle scanning together with kinematics and myoelectrical activities. The amplitudes and onset latency of SLR activities were determined. During ground contact, the sudden MG fascicle stretch occurred during the early contact at all running speeds. This was followed by the fascicle shortening. The timing of fascicle stretch depended on running speed and type of foot contact. In slower speed conditions (2.0, 3.5, 5 m/s), the MG fascicle stretch and the corresponding SLR activities occurred during the middle of the braking phase. In fast-speed running (6.5 m/s), however, the MG fascicle stretch occurred later compared with the lower speed. The corresponding SLR activities occurred significantly later at the end of the braking phase. In addition to the clear demonstration of the different timings of SLR in MG during ground contact of running, the results imply that the role of the MG SLR during the stance phase of running can be different between fast- and slow-speed running conditions.
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Singh, Sandeep, et . « Accident Study and Analysis of Selected Black Spots – A Case Study ». International Journal of Engineering & ; Technology 7, no 3.12 (20 juillet 2018) : 1254. http://dx.doi.org/10.14419/ijet.v7i3.12.17866.
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In the present study, accident statistics of 2011 to 2014 has resolved Vidya path as a black spot. In addition, attempt has been made to investigate the prevailing conditions of two V3 road stretches i.e. (Stretch – 1: road dividing sec – 14 and 15 and Stretch – 2: road dividing sec – 11 and 12) of Chandigarh for accidental risk. The moral of investigation has cleared that all the prime associated parties i.e. traffic, speed and users/driver are favoring the accidental risk; as during peak hour the road stretches were found short of capacity, speed of vehicles was over the legal speed and the users were ignoring the rules and regulation of driving. Consequently, the injury and life risk for pedestrians and cyclists are at the most. The preventive measures for the same are also incorporated.
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ALLESSIE, MAURITS. « Stretch and Speed : A Complicated Couple ». Journal of Cardiovascular Electrophysiology 22, no 4 (6 décembre 2010) : 402–4. http://dx.doi.org/10.1111/j.1540-8167.2010.01971.x.
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Cole, Daniel, Sungjin Im, Benjamin Moseley et Kirk Pruhs. « Speed scaling for stretch plus energy ». Operations Research Letters 40, no 3 (mai 2012) : 180–84. http://dx.doi.org/10.1016/j.orl.2012.02.003.
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Pinchak, Matthew, Timothy Ombrello, Campbell Carter, Ephraim Gutmark et Viswanath Katta. « The effects of hydrodynamic stretch on the flame propagation enhancement of ethylene by addition of ozone ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 373, no 2048 (13 août 2015) : 20140339. http://dx.doi.org/10.1098/rsta.2014.0339.
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The effect of O 3 on C 2 H 4 /synthetic-air flame propagation at sub-atmospheric pressure was investigated through detailed experiments and simulations. A Hencken burner provided an ideal platform to interrogate flame speed enhancement, producing a steady, laminar, nearly one-dimensional, minimally curved, weakly stretched, and nearly adiabatic flame that could be accurately compared with simulations. The experimental results showed enhancement of up to 7.5% in flame speed for 11 000 ppm of O 3 at stoichiometric conditions. Significantly, the axial stretch rate was also found to affect enhancement. Comparison of the flames for a given burner exit velocity resulted in the enhancement increasing almost 9% over the range of axial stretch rates that was investigated. Two-dimensional simulations agreed well with the experiments in terms of flame speed, as well as the trends of enhancement. Rate of production analysis showed that the primary pathway for O 3 consumption was through reaction with H, leading to early heat release and increased production of OH. Higher flame stretch rates resulted in increased flux through the H+O 3 reaction to provide increased enhancement, due to the thinning of the flame that accompanies higher stretch, and thus results in decreased distance for the H to diffuse before reacting with O 3 .
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Rassier, Dilson E., Eun-Jeong Lee et Walter Herzog. « Modulation of passive force in single skeletal muscle fibres ». Biology Letters 1, no 3 (28 juin 2005) : 342–45. http://dx.doi.org/10.1098/rsbl.2005.0337.
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In this study, we investigated the effects of activation and stretch on the passive force–sarcomere length relationship in skeletal muscle. Single fibres from the lumbrical muscle of frogs were placed at varying sarcomere lengths on the descending limb of the force–sarcomere length relationship, and tetanic contractions, active stretches and passive stretches (amplitudes of ca 10% of fibre length at a speed of 40% fibre length/s) were performed. The passive forces following stretch of an activated fibre were higher than the forces measured after isometric contractions or after stretches of a passive fibre at the corresponding sarcomere length. This effect was more pronounced at increased sarcomere lengths, and the passive force–sarcomere length relationship following active stretch was shifted upwards on the force axis compared with the corresponding relationship obtained following isometric contractions or passive stretches. These results provide strong evidence for an increase in passive force that is mediated by a length-dependent combination of stretch and activation, while activation or stretch alone does not produce this effect. Based on these results and recently published findings of the effects of Ca 2+ on titin stiffness, we propose that the observed increase in passive force is caused by the molecular spring titin.
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Wang, Haiou, Evatt R. Hawkes, Jacqueline H. Chen, Bo Zhou, Zhongshan Li et Marcus Aldén. « Direct numerical simulations of a high Karlovitz number laboratory premixed jet flame – an analysis of flame stretch and flame thickening ». Journal of Fluid Mechanics 815 (23 février 2017) : 511–36. http://dx.doi.org/10.1017/jfm.2017.53.
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This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: the positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed–curvature correlations and dominated in net by low probability highly curved regions. Flame thickening is demonstrated to be substantial on average, while local regions of flame thinning are also observed. The rate of change of the flame thickness (as measured by the scalar gradient magnitude) is demonstrated, analogously to flame stretch, to be a competition between straining tending to increase gradients and flame speed variations in the normal direction tending to decrease them. The flame stretch and flame thickness analyses are connected by the observation that high positive tangential strain rate regions generally correspond with low curvature regions; these regions tend to be positively stretched in net and are relatively thinner compared with other regions. High curvature magnitude regions (both positive and negative) generally correspond with lower tangential strain; these regions are in net negatively stretched and thickened substantially.
Thèses sur le sujet "Stretch speed"
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Kochar, Yash N. « Laminar flame speed and stretch sensitivity of hydrocarbon fuels at high preheat, pressure and vitiation ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52216.
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This thesis investigates the laminar flame speed of C₁-C₃ alkanes and their binary mixtures at conditions of interest in natural gas based gas turbines viz. high temperature, pressure and dilution. Laminar flame speed has been found useful not only for validating chemical kinetics mechanisms but also for developing empirical scaling laws for practical combustion systems. The thesis addresses the lack of laminar flame speed data of C₁-C₃ alkanes at preheat (300-650 K), pressure (1-10 atm) and significant oxidizer dilution (15-21 vol% O₂). Over 400 measurements are reported over a wide range of conditions along with comparison to predictions from leading chemical mechanisms. Unstretched flame speed measurements were performed using a modified Bunsen flame technique based on reaction zone area from chemiluminescence imaging, whereas the strain sensitivity measurements were performed using a bluff-body stabilized stagnation flame with high resolution PIV. These measurements are used to: (i) discern the uncertainties associated with the measurements, (ii) understand the effect of fuel mixture and vitiation on flame speed, and (iii) validate the performance of the leading chemical kinetics mechanisms. Extensive testing shows the unstretched flame speed measurements from the modified Bunsen technique are reasonably accurate. Vitiation studies for methane and propane flames at high preheat show the reduction in flame speed results primarily from the thermal effect of the diluent and that the relative change in flame speed from the undiluted mixture is well correlated to the fractional change in the adiabatic flame temperature over a range of conditions. Significant difference in the measured and predicted flame speeds were observed for rich, atmospheric pressure, propane and lean, high pressure, methane/ethane mixtures with dilution. This highlights possible avenues for improvements in the chemical kinetics mechanisms. Systematic errors were also identified in the Bunsen flame measurements at certain conditions, such as for rich flames with dilution, indicating a need for better understanding of the Bunsen flame technique at these conditions. The difference in the measured and predicted flame speed does not show any clear correlation with the flame height or the strain sensitivity of the mixture. Finally previously proposed mixing rules for estimating flame speed of fuel mixtures from pure fuel components are shown to be reasonably accurate over a range of pressure, reactant temperature and dilution conditions.
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Senn, Daniel LeRoy. « Short-term Training Effects of Dynamic Warm Up Volume on Speed, Power, and Agility ». Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29320.
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This study examined the short-term training effects of two volumes of a dynamic warm up
performed 4 days per week over a 3 1/2-week period. A total of 25 Division III wrestlers
volunteered for the study. Three participants either dropped out or were unable to attend
post-testing, resulting in 22 total participants completing the study. Groups were divided
into control, low volume, and high volume groups. All participants completed pre and poststudy
performance tests including the standing long jump, proagility, start-stop-cut, and 30-
meter sprint. The low and high volume training groups each performed the same dynamic
warm up prior to each pre-season captain's practice. The control group did not participate
in an organized warm up. The low volume group performed one set of each warm up
exercise, and the high volume group performing two sets of each warm up exercise. Data
analysis indicated significant increases in performance for the standing long jump (p =
.011) and start-stop-cut (p = .000) measures among the entire sample population. However,
there was no significant difference between the groups in these measures. No significant
results were found either for the sample as a whole or between groups for the proagility and
30-meter measures. The increased performance of all groups, including the control group,
fails to provide evidence for the effectiveness of training with either warm up volume.
Further research is needed to address limitations of this study to determine effectiveness of
various warm up volumes.
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Hinton, Nathan Ian David. « Measuring laminar burning velocities using constant volume combustion vessel techniques ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:5b641b04-8040-4d49-a7e8-aae0b0ffc8b5.
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The laminar burning velocity is an important fundamental property of a fuel-air mixture at given conditions of temperature and pressure. Knowledge of burning velocities is required as an input for combustion models, including engine simulations, and the validation of chemical kinetic mechanisms. It is also important to understand the effect of stretch upon laminar flames, to correct for stretch and determine true (unstretched) laminar burning velocities, but also for modelling combustion where stretch rates are high, such as turbulent combustion models. A constant volume combustion vessel has been used in this work to determine burning velocities using two methods: a) flame speed measurements during the constant pressure period, and b) analysis of the pressure rise data. Consistency between these two techniques has been demonstrated for the first time. Flame front imaging and linear extrapolation of flame speed has been used to determine unstretched flame speeds at constant pressure and burned gas Markstein lengths. Measurement of the pressure rise during constant volume combustion has been used along with a numerical multi-zone combustion model to determine burning velocities for elevated temperatures and pressures as the unburned gas ahead of the spherically expanding flame front is compressed isentropically. This burning velocity data is correlated using a 14 term correlation to account for the effects of equivalence ratio, temperature, pressure and fraction of diluents. This correlation has been modified from an existing 12 term correlation to more accurately represent the dependence of burning velocity upon temperature and pressure. A number of fuels have been tested in the combustion vessel. Biogas (mixtures of CH4 and CO2) has been tested for a range of equivalence ratios (0.7–1.4), with initial temperatures of 298, 380 and 450 K, initial pressures of 1, 2 and 4 bar and CO2 fractions of up to 40% by mole. Hydrous ethanol has been tested at the same conditions (apart from 298 K due to the need to vaporise the ethanol), and for fractions of water up to 40% by volume. Binary, ternary and quaternary blends of toluene, n-heptane, ethanol and iso-octane (THEO) have been tested for stoichiometric mixtures only, at 380 and 450 K, and 1, 2 and 4 bar, to represent surrogate gasoline blended with ethanol. For all fuels, correlation coefficients have been obtained to represent the burning velocities over wide ranging conditions. Common trends are seen, such as the reduction in burning velocity with pressure and increase with temperature. In the case of biogas, increasing CO2 results in a decrease in burning velocity, a shift in peak burning velocity towards stoichiometric, a decrease in burned gas Markstein length and a delayed onset of cellularity. For hydrous ethanol the reduction in burning velocity as H2O content is increased is more noticeably non-linear, and whilst the onset of cellularity is delayed, the effect on Markstein length is minor. Chemical kinetic simulations are performed to replicate the conditions for biogas mixtures using the GRI 3.0 mechanism and the FlameMaster package. For hydrous ethanol, simulations were performed by Carsten Olm at Eötvös Loránd University, using the OpenSMOKE 1D premixed flame solver. In both cases, good agreement with experimental results is seen. Tests have also been performed using a single cylinder optical engine to compare the results of the hydrous ethanol tests with early burn combustion, and a good comparison is seen. Results from tests on THEO fuels are compared with mixing rules developed in the literature to enable burning velocities of blends to be determined from knowledge of that of the pure components alone. A variety of rules are compared, and it is found that in most cases, the best approximation is found by using the rule in which the burning velocity of the blend is represented by weighting by the energy fraction of the individual components.
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Marshall, Andrew. « Turbulent flame propagation characteristics of high hydrogen content fuels ». Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53859.
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Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors.
This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed.
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Das, Suma Rani. « Investigation of Design and Operating Parameters in Partially-Filled Rubber Mixing Simulations ». University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1479151141596147.
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Kabeš, Luboš. « Dopravní charakteristiky v uspořádání 2+1 ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227840.
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The thesis discusses the roads in lanes 2 + 1 arrangement in the country and abroad. It focuses primarily analogy of this type of arrangement in our situation, ie on stretches of roads I. classes with an increased number of lanes for slow vehicles to climb. Part of this work is to verify some of the traffic, including traffic flow characteristics compared to conventional two-lane roads, especially in terms of: sectional speed; overtaking; Accident and dependence longitudinal gradient. The work aims to evaluate the foreign experience and achievements of domestic communications options for application configuration 2 + 1 in the Czech Republic.
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Urs, Raksha. « Investigation of Accommodation and Presbyopia using Ultrasound Imaging during Ex Vivo Simulated Accommodation ». Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/360.
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The goal of this project is to obtain quantitative images of the lens and the ciliary body to validate EVAS-II (Second generation Ex Vivo Accommodation Simulator). To accomplish this goal it was necessary to develop methods, instrumentation and image processing techniques to acquire 3D images in EVAS-II, using UBM (Ultrasound Bio Microscope), and to apply these techniques to non-human primate eyes. The lens studies included measurement of speed of sound in the lens to reconstruct accurate images of the lens, development of instrumentation to measure the un-distorted lens shape and development of a mathematical model to quantify the whole lens shape. Speed measurements showed that the speed of sound exhibits a gradient profile in the equatorial plane, similar to refractive index and protein distributions in the lens. Lens shape measurements showed that the UBM can be used to accurately measure thickness, diameter, cross-sectional area, volume and surface area of the lens. The ciliary body studies included development of instrumentation and algorithms to obtain 3-D images of tissue in EVAS-II and development of methodology to quantify ciliary body movement during stretching. Studies showed that the accommodation process in young baboon eyes in EVAS-II is comparable to the in vivo process in rhesus monkeys. The UBM can be used to obtain reliable quantitative information about the lens and the ciliary body. 3-D UBM enables monitoring of ciliary body motion of the entire accommodative apparatus.
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Camara, Felipe Thomaz da [UNESP]. « Biodiesel de dendê em trator agrícola : desempenho em função do tempo de armazenamento e da proporção de mistura na operação de preparo do solo ». Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/100856.
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Funep
Biodiesel is a renewable fuel, biodegradable and produced from vegetable oil or from animal fat through transesterification. The viability of this product as a source of alternative energy depends on various factors, among which the mixture proportion and the stability during storage time stand out. This is because the availability of the raw material is seasonal and varies in accordance with the harvests of different cultures. The objective of the present work was to evaluate the operational performance of an agricultural tractor working with palm oil biodiesel while performing the operation of tillage with a chisel plow, also opacity, the density of the fuel and the outflow from the filling pump were studied regarding storage time and biodiesel/diesel mixture proportion. The experiment was conducted in the Department of Rural Engineering at UNESP, Jaboticabal, Brazil, in partnership with LADETEL/USP-Ribeirão Preto. Storage time was with new fuel (soon after production), three months and six months, and the percentage proportions used for biodiesel + diesel were B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). When comparing the treatments, we evaluated the fuel consumption, the real velocity of displacement, the sliding of the wheels, the strength of the traction bar, the fuel density, the outflow from the filling pump and the opacity of the fuel smoke. The results show an increase in consumption specific to a mixture starting from 25% biodiesel, although the storage time did not affect consumption. In relation to the opacity of smoke, there was a reduction, even with only 5% biodiesel in the mixture, again with the storage time having no influence.
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Camara, Felipe Thomaz da. « Biodiesel de dendê em trator agrícola : desempenho em função do tempo de armazenamento e da proporção de mistura na operação de preparo do solo / ». Jaboticabal : [s.n.], 2009. http://hdl.handle.net/11449/100856.
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Orientador: Afonso LopesBanca: Wilson José Oliveira de Souza
Banca: Carlos Alberto Alves de Oliveira
Banca: Newton La Scala Junior
Banca: Carlos Eduardo Angeli Furlani
Resumo:Biodiesel é um combustível renovável, biodegradável e produzido a partir de óleo vegetal ou de gordura animal por meio de transesterificação. A viabilidade desse produto como fonte alternativa de energia depende de vários fatores, entre os quais se destacam a proporção de mistura e a estabilidade durante o período de armazenamento, uma vez que a disponibilidade de matéria-prima é sazonal e varia de acordo com a safra de cada cultura. O presente trabalho teve como objetivo avaliar o desempenho operacional realizando a operação de preparo do solo com escarificador e a opacidade da fumaça de um trator agrícola funcionando com biodiesel de dendê, a densidade do combustível e a vazão da bomba de abastecimento, cujos fatores estudados foram o tempo de armazenamento e a proporção de mistura biodiesel/diesel. O experimento foi conduzido no Departamento de Engenharia Rural, da UNESPJaboticabal, em parceria com o LADETEL/USP-Ribeirão Preto. O tempo de armazenamento foi combustível novo (logo após ser produzido), três e seis meses, e as proporções percentuais de biodiesel + diesel foram B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). Para comparar os tratamentos, foram avaliados o consumo de combustível, a força de tração na barra, a velocidade real de deslocamento, a patinagem das rodas, a potência na barra de tração, a densidade do combustível, a vazão da bomba de abastecimento e a opacidade da fumaça de combustão. Os resultados evidenciaram aumento no consumo específico a partir da mistura com 25% de biodiesel, entretanto o tempo de armazenamento não influenciou no consumo. Com relação a opacidade da fumaça, houve redução, mesmo com apenas 5% de biodiesel na mistura, com o tempo de armazenamento não influenciando.
Abstract: Biodiesel is a renewable fuel, biodegradable and produced from vegetable oil or from animal fat through transesterification. The viability of this product as a source of alternative energy depends on various factors, among which the mixture proportion and the stability during storage time stand out. This is because the availability of the raw material is seasonal and varies in accordance with the harvests of different cultures. The objective of the present work was to evaluate the operational performance of an agricultural tractor working with palm oil biodiesel while performing the operation of tillage with a chisel plow, also opacity, the density of the fuel and the outflow from the filling pump were studied regarding storage time and biodiesel/diesel mixture proportion. The experiment was conducted in the Department of Rural Engineering at UNESP, Jaboticabal, Brazil, in partnership with LADETEL/USP-Ribeirão Preto. Storage time was with new fuel (soon after production), three months and six months, and the percentage proportions used for biodiesel + diesel were B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). When comparing the treatments, we evaluated the fuel consumption, the real velocity of displacement, the sliding of the wheels, the strength of the traction bar, the fuel density, the outflow from the filling pump and the opacity of the fuel smoke. The results show an increase in consumption specific to a mixture starting from 25% biodiesel, although the storage time did not affect consumption. In relation to the opacity of smoke, there was a reduction, even with only 5% biodiesel in the mixture, again with the storage time having no influence.
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Hallgren, Adam. « Det avlastande bärsystemets påverkan på att bära en sjukbår : en studie baserad på prov och försök ». Thesis, Försvarshögskolan, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-9881.
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For a wounded soldier to have as good a chance of survival as possible, an important variable during care is the time it takes for the wounded to get to a high-quality medical facility where there is expertise in surgery. If the injured person is to be transported with a stretcher carried by other soldiers, the speed for which this can be done is limited by the strength of the bearer in the hands and forearms.This study aims to explore how the speed and perceived ergonomics of those who carry a stretcher can change for a group if it is issued a relieving carrying system that redistributes the load of the stretcher to the hips, back and legs. The study is largely based on a study by Knapik et al (2000) where similar tests were done in a controlled indoor environment but where this study was done in a field environment with groups of 2 or 4 people carrying a stretcher.The study is done in the form of tests and experiments with conscripts from Skaraborg Wing, F 7. The conscripts carried a stretcher in a field-like environment where speed, comfort and usability were in focus. The study was also done with a questionnaire belonging to the experiments to value the experience.The study resulted in a relieving carrying system integrated in the Swedish Armed Forces' combat vest 2000 having an increased average speed with the median 30.7% when carrying a stretcher loaded with 100 kg. The analysis shows that it is above all women who benefit greatly from not carrying a stretcher with their hands. Something they are statistically worse at than men. The study also shows that there are tendencies that the comfort is improved for a soldier.För att en sårad soldat ska ha så goda chanser till överlevnad som möjligt är en viktig variabel under omhändertagandet tiden det tar för den sårade att komma till en högkvalitativ sjukvårdsinrättning, där det finns expertis inom kirurgi. Om den skadade ska transporteras med sjukbår som bärs av andra soldater, är hastigheten för vilket detta kan göras begränsad av de bärandes styrka i händer och underarmar.Denna studie syftar till att utforska hur hastigheten samt den upplevda ergonomin för de som bär en sjukbår kan förändras för en grupp om den tillförs ett avlastande bärsystem som omfördelar lasten till höfter, rygg och benen. Studien baseras till stor del på en studie av Knapik med flera (2000) där liknande tester gjordes i en kontrollerad inomhusmiljö, men där denna studie är gjord i en fältmiljö med grupper om 2 eller 4 personer som bär en sjukbår.Studien är gjord i form av prov och försök med värnpliktiga ur Skaraborgs Flygflottilj, F 7, som bär en bår i en fältliknande miljö där hastigheten, komforten och användbarheten stod i fokus. Studien är även gjord med en enkätundersökning tillhörande försöken i syfte att skatta upplevelsen.Studien resulterade i att ett avlastande bärsystem integrerat i Försvarsmaktens stridsväst 2000 medförde en ökad snitthastighet, med medianen 30,7%, vid bärande av en sjukbår 2 lastad med 100 kg. Analysen påvisar att det framför allt är kvinnor som har stor nytta av att inte bära en sjukbår med händerna, något de statistiskt sett är sämre på än män. Studien visar även att det finns tendenser för att komforten förbättras för en soldat men användbarheten är oförändrad.
Livres sur le sujet "Stretch speed"
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K, Rahmouni. Speedy, Stumpy, Stretch and Swimmer. Independently Published, 2019.
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Utzschneider, Cathy. Mastering Running. Human Kinetics, 2014. http://dx.doi.org/10.5040/9781718219137.
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Run faster, stronger, and longer—and remain injury free. With Mastering Running, regardless of your age, optimal performance and new personal bests await. Cathy Utzschneider, highly accomplished and renowned masters runner and coach, has created the definitive guide for runners, athletes, and fitness buffs. Runners from 30 to 100 will benefit from the targeted approach that covers these aspects: • Evaluating and refining running form to improve speed and endurance • Exercises, stretches, and routines to prevent common age-related injuries • Training programs for the mile, 5K, 10K, half marathon, and full marathon • Proven strategies, used by today’s top runners, that shave seconds off your time Mastering Running contains all the advice and instruction you’d expect from an elite-level coach. With details on segmenting, front running, tapering, recovering, and fueling, Mastering Running is the one guide you’ll rely on time and again to achieve your potential.
Chapitres de livres sur le sujet "Stretch speed"
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Guzererler, Ahmet, William R. Provancher et Cagatay Basdogan. « Perception of Skin Stretch Applied to Palm : Effects of Speed and Displacement ». Dans Haptics : Perception, Devices, Control, and Applications, 180–89. Cham : Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-42321-0_17.
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Manasrah, Ahmad, et Shahnaz Alkhalil. « A 2-DoF Skin Stretch Display on Palm : Effect of Stimulation Shape, Speed and Intensity ». Dans Haptics : Science, Technology, Applications, 12–24. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-58147-3_2.
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Rizzi, Arthur, Charles J. Purcell et J. Thomas McMurray. « Numerical Experiment with Inviscid Vortex-Stretched Flow around a Cranked Delta Wing : Transonic Speed ». Dans Turbulent Shear-Layer/Shock-Wave Interactions, 283–98. Berlin, Heidelberg : Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-642-82770-9_23.
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Devare, Medha, Elizabeth Arnaud, Erick Antezana et Brian King. « Governing Agricultural Data : Challenges and Recommendations ». Dans Towards Responsible Plant Data Linkage : Data Challenges for Agricultural Research and Development, 201–22. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-13276-6_11.
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AbstractThe biomedical domain has shown that in silico analyses over vast data pools enhances the speed and scale of scientific innovation. This can hold true in agricultural research and guide similar multi-stakeholder action in service of global food security as well (Streich et al. Curr Opin Biotechnol 61:217–225. Retrieved from https://doi.org/10.1016/j.copbio.2020.01.010, 2020). However, entrenched research culture and data and standards governance issues to enable data interoperability and ease of reuse continue to be roadblocks in the agricultural research for development sector. Effective operationalization of the FAIR Data Principles towards Findable, Accessible, Interoperable, and Reusable data requires that agricultural researchers accept that their responsibilities in a digital age include the stewardship of data assets to assure long-term preservation, access and reuse. The development and adoption of common agricultural data standards are key to assuring good stewardship, but face several challenges, including limited awareness about standards compliance; lagging data science capacity; emphasis on data collection rather than reuse; and limited fund allocation for data and standards management. Community-based hurdles around the development and governance of standards and fostering their adoption also abound. This chapter discusses challenges and possible solutions to making FAIR agricultural data assets the norm rather than the exception to catalyze a much-needed revolution towards “translational agriculture”.
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Syam, Nirmalya. « Robust Patent Examination or Deep Harmonization ? Cooperation and Work Sharing Between Patent Offices ». Dans Access to Medicines and Vaccines, 241–76. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-83114-1_9.
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AbstractPatent laws and regulations in many countries have utilized the flexibility available under the WTO TRIPS Agreement to apply nationally appropriate standards to define the patentability criteria of novelty, inventive step and industrial applicability, in order to ensure the grant of high-quality patents for genuine inventions. Robust search and examination are crucial for the application of this flexibility to ensure the grant of patents for genuine inventions, e.g., for secondary pharmaceutical patent applications which could lead to patent evergreening and adversely impact access to medicines by restraining generic competition. However, limited examination resources of patent offices have been stretched by the tremendous surge in the number of patent applications to be processed, leading to delays and backlogs. This has led patent offices to prioritize efficient and speedy processing of patent applications with their limited resources by using the search and examination work of other patent offices, sometimes to the extent of granting a patent on the basis of a corresponding grant by another patent office. This chapter discusses how work sharing has been driven by the major patent offices as part of a global patent harmonization agenda, both within the WIPO Patent Cooperation Treaty and through technical assistance and cooperation with other patent offices, and suggests how patent offices in developing countries could best harness the advantages of work sharing, particularly in a South-South cooperation framework, while safeguarding the ability to apply in practice the patentability requirements under their national laws through a robust search and examination of patent claims.
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Cuccaroni, A., P. Veyron, A. Lacroix et M. Russo. « Second phase of the Eastern European High speed railway line : Stretch 47 and the Saverne Tunnel ». Dans Underground. The Way to the Future, 217–24. CRC Press, 2013. http://dx.doi.org/10.1201/b14769-32.
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Shroff, Gautam. « Correct ». Dans The Intelligent Web. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199646715.003.0011.
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Last summer I took my family on a driving holiday in the American south-western desert covering many national parks. While driving along some of the long tracts of razor-straight highways, such as between Las Vegas and St George, Utah, I often fought drowsiness, not because of lack of sleep, but from the sheer monotony. A familiar experience for many, no doubt. Hardly any conscious thought is needed during such drives. It must be one’s ‘System’, as per Kahneman, which is most certainly doing what ever work is needed. Nevertheless, sleep is not an option. In spite of all the marvellous features embedded in the modern car, the ability to drive itself is, sadly, still missing. The cruise control button helps a bit, allowing one’s feet torelax as the car’s speed remains on an even keel. But the eyes and mind must remain awake and alert. When, if ever, one wonders, will cars with a ‘drive’ button become as common as those with an automatic transmission? Is driving along a perfectly straight stretch of highway really that difficult? After all, we all know that a modern jetliner can fly on autopilot, allowing even a single pilot to read a novel while ‘flying’ the aircraft on a long transcontinental flight. In fact, the jetliner would fly itself perfectly even if the pilot dozed off for many minutes or even hours. We insist that at least one pilot be awake and alert only for our own peace of mind, so as to be able to adequately respond to any emergency situation that might arise. First of all, the ubiquitous autopilot is itself quite a complex piece of equipment. Even to get a plane to fly perfectly straight along a desired heading at a fixed altitude takes a lot of work. The reason, as you must have guessed, is that nature, in the guise of the air on which our jetliner rides, can be quite unpredictable. Wind speeds and directions change continuously, even ever so slightly, requiring constant adjustments to the plane’s engine power, ailerons, flaps, and rudder. In the absence of such adjustments, our jetliner would most certainly veer off course, or lose or gain speed, even dangerously enough to trigger a powered dive or a stall.
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Beerling, David. « Leaves, genes, and greenhouse gases ». Dans The Emerald Planet. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780192806024.003.0009.
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The Galileo spacecraft, named after the Italian astronomer Galileo Galilei (1564–1642), who launched modern astronomy with his observations of the heavens in 1610, plunged to oblivion in Jupiter’s crushing atmosphere on 21 September 2003. Launched in 1989, it left behind a historic legacy that changed the way we view the solar system. Galileo’s mission was to study the planetary giant Jupiter and its satellites, four of which Galileo himself observed, to his surprise, moving as ‘stars’ around the planet from his garden in Pardu, Italy. En route, the spacecraft captured the first close-up images of an asteroid (Gaspra) and made direct observations of fragments of the comet Shoemaker–Levy 9 smashing into Jupiter. Most remarkable of all were the startling images of icebergs on the surface of Europa beamed backed in April 1997, after nearly eight years of solar system exploration. Icebergs suggested the existence of an extraterrestrial ocean, liquid water. To the rapt attention of the world’s press, NASA’s mission scientists commented that liquid water plus organic compounds already present on Europa, gave you ‘life within a billion years’. Whether this is the case is a moot point; water is essential for life on Earth as we know it, but this is no guarantee it is needed for life elsewhere in the Universe. Oceans may also exist beneath the barren rocky crusts of two other Galilean satellites, Callisto and Ganymede. Callisto and Ganymede probably maintain a liquid ocean thanks to the heat produced by natural radioactivity of their rocky interiors. Europa, though, lies much closer to Jupiter, and any liquid water could be maintained by heating due to gravitational forces that stretch and squeeze the planet in much the same way as Earth’s moon influences our tides. To reach Jupiter, Galileo required two slingshots (gravitational assists) around Earth and Venus. Gravitational assists accelerate the speed and adjust the trajectory of the spacecraft without it expending fuel. The planets doing the assisting pay the price with an imperceptible slowing in their speed of rotation. In Galileo’s case, the procedure fortuitously permitted close observations of Earth from space, allowing a control experiment in the search for extraterrestrial life, never before attempted.
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« Figure 2. The 10-m acceleration times for the different warm-up protocols. * significantly faster than the No stretch condition. Figure 3. The 20-m maximum speed times for the different warm-up protocols. * significantly faster than the No stretch condition. » Dans Science and Football V, 411. Routledge, 2005. http://dx.doi.org/10.4324/9780203412992-154.
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Jacobs, Harriet. « XXIII. Still in Prison ». Dans Incidents in the Life of a Slave Girl. Oxford University Press, 2015. http://dx.doi.org/10.1093/owc/9780198709879.003.0024.
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When spring returned, and I took in the little patch of green the aperture commanded, I asked myself how many more summers and winters I must be condemned to spend thus. I longed to draw in a plentiful draught of fresh air, to stretch...
Actes de conférences sur le sujet "Stretch speed"
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Bosworth, Bryan T., et Mark A. Foster. « High-speed spectral shearing contrast time-stretch microscopy ». Dans CLEO : Science and Innovations. Washington, D.C. : OSA, 2016. http://dx.doi.org/10.1364/cleo_si.2016.sm1o.3.
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Lo, Michelle C. K., Kelvin C. M. Lee, Dickson M. D. Siu, Edmund Y. Lam et Kevin K. Tsia. « Augmented multiplexed asymmetric-detection time-stretch optical microscopy by generative deep learning ». Dans High-Speed Biomedical Imaging and Spectroscopy VI, sous la direction de Keisuke Goda et Kevin K. Tsia. SPIE, 2021. http://dx.doi.org/10.1117/12.2582985.
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Venkateswaran, Prabhakar, Andrew D. Marshall, David R. Noble, Jerry M. Seitzman et Tim C. Lieuwen. « Turbulent Consumption Speed Scaling of H2/CO Blends ». Dans ASME 2011 Turbo Expo : Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45401.
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This paper describes measurements and analysis of global turbulent consumption speeds, ST,GC, of hydrogen/carbon monoxide (H2/CO) mixtures. The turbulent flame properties of such mixtures are of fundamental interest because of their strong stretch sensitivity and of practical interest since they are the primary constituents of syngas fuels. Data are analyzed at mean flow velocities and turbulence intensities of 4 < U0 < 50 m/s and 1 < u′rms/SL,0 < 100, respectively, for H2/CO blends ranging from 30–90% H2 by volume. Data from two sets of experiments are reported. In the first, fuel blends ranging from 30–90% H2 and mixture equivalence ratio, Φ, were adjusted at each fuel composition to have nominally the same un-stretched laminar flame speed, SL,0. In the second set, equivalence ratios were varied at constant H2 levels. The data clearly corroborate results from other studies that show significant sensitivity of ST,GC to fuel composition. For example, at a fixed u′rms, ST,GC of a 90% H2 case (at Φ = 0.48) is a factor of three times larger than the baseline Φ = 0.9, CH4/air mixture that has the same SL,0 value. We also describe physics-based correlations of these data, using leading points concepts and detailed kinetic calculations of their stretch sensitivities. These results are used to develop an inequality for negative Markstein length flames that bounds the turbulent flame speed data and show that the data can be collapsed using the maximum stretched laminar flame speed, SL,max, rather than SL,0.
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Afkhami, Behdad, Yanyu Wang, Scott A. Miers et Jeffrey D. Naber. « Experimental Study of Flame Stretch Under Engine-Like Conditions ». Dans ASME 2017 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/icef2017-3636.
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Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.
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Yang, Kuojun, Shulin Tian et Jinpeng Song. « A high speed random equivalent sampling method based on time-stretch ». Dans 2013 2nd International Symposium on Instrumentation & Measurement, Sensor Network and Automation (IMSNA). IEEE, 2013. http://dx.doi.org/10.1109/imsna.2013.6743241.
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Siu, Dickson M. D., Anson H. L. Tang, Kelvin C. M. Lee, Kenneth K. Y. Wong et Kevin K. Tsia. « Ultralarge-scale spinning time-stretch quantitative phase imaging system for label-free cell and tissue imaging (Conference Presentation) ». Dans High-Speed Biomedical Imaging and Spectroscopy IV, sous la direction de Keisuke Goda et Kevin K. Tsia. SPIE, 2019. http://dx.doi.org/10.1117/12.2508354.
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Bosworth, Bryan, et Mark A. Foster. « High-speed quantitative phase imaging using time-stretch spectral shearing contrast (Conference Presentation) ». Dans High-Speed Biomedical Imaging and Spectroscopy II : Toward Big Data Instrumentation and Management, sous la direction de Keisuke Goda et Kevin K. Tsia. SPIE, 2017. http://dx.doi.org/10.1117/12.2253106.
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Kutkan, Halit, Alberto Amato, Giovanni Campa, Giulio Ghirardo, Luis Tay Wo Chong et Eirik Æsøy. « Modelling of Turbulent Premixed CH4/H2/Air Flames Including the Influence of Stretch and Heat Losses ». Dans ASME Turbo Expo 2021 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59063.
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Abstract This paper presents a RANS turbulent combustion model for CH4/H2/air mixtures which includes the effect of heat losses and flame stretch. This approach extends a previous model concept designed for methane/air mixtures and improves the prediction of flame stabilization when hydrogen is added to the fuel. Heat loss and stretch effects are modelled by tabulating the consumption speed of laminar counter flow flames in a fresh-to-burnt configuration with detailed chemistry at various heat loss and flame stretch values. These computed values are then introduced in the turbulent combustion model by means of a turbulent flame speed expression which is derived as a function of flame stretch, heat loss and H2 addition. The model proposed in this paper is compared to existing models on experimental data of spherical expanding turbulent flame speeds. The performance of the model is further validated by comparing CFD predictions to experimental data of an atmospheric turbulent premixed bluff-body stabilized flame fed with CH4/H2/air mixtures ranging from pure methane to pure hydrogen.
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Wu, Jianglai, Yiqing Xu, Andy K. S. Lau, Anson H. L. Tang, Antony C. S. Chan, Kenneth K. Y. Wong et Kevin K. Tsia. « Optical time-stretch microscopy enabled by free-space angular-chirp-enhanced delay (Conference Presentation) ». Dans High-Speed Biomedical Imaging and Spectroscopy II : Toward Big Data Instrumentation and Management, sous la direction de Keisuke Goda et Kevin K. Tsia. SPIE, 2017. http://dx.doi.org/10.1117/12.2251377.
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Marshall, Andrew, Julia Lundrigan, Prabhakar Venkateswaran, Jerry Seitzman et Tim Lieuwen. « Measurements of Stretch Statistics at Flame Leading Points for High Hydrogen Content Fuels ». Dans ASME Turbo Expo 2014 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-26420.
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Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high speed particle image velocimetry (PIV) in a low swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.
Rapports d'organisations sur le sujet "Stretch speed"
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Brodie, Katherine, Brittany Bruder, Richard Slocum et Nicholas Spore. Simultaneous mapping of coastal topography and bathymetry from a lightweight multicamera UAS. Engineer Research and Development Center (U.S.), août 2021. http://dx.doi.org/10.21079/11681/41440.
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A low-cost multicamera Unmanned Aircraft System (UAS) is used to simultaneously estimate open-coast topography and bathymetry from a single longitudinal coastal flight. The UAS combines nadir and oblique imagery to create a wide field of view (FOV), which enables collection of mobile, long dwell timeseries of the littoral zone suitable for structure-from motion (SfM), and wave speed inversion algorithms. Resultant digital surface models (DSMs) compare well with terrestrial topographic lidar and bathymetric survey data at Duck, NC, USA, with root-mean-square error (RMSE)/bias of 0.26/–0.05 and 0.34/–0.05 m, respectively. Bathymetric data from another flight at Virginia Beach, VA, USA, demonstrates successful comparison (RMSE/bias of 0.17/0.06 m) in a secondary environment. UAS-derived engineering data products, total volume profiles and shoreline position, were congruent with those calculated from traditional topo-bathymetric surveys at Duck. Capturing both topography and bathymetry within a single flight, the presented multicamera system is more efficient than data acquisition with a single camera UAS; this advantage grows for longer stretches of coastline (10 km). Efficiency increases further with an on-board Global Navigation Satellite System–Inertial Navigation System (GNSS-INS) to eliminate ground control point (GCP) placement. The Appendix reprocesses the Virginia Beach flight with the GNSS–INS input and no GCPs.