Periodic Discontinuities in the Acceleration of Spheres in Free Flight

1978 ◽  
Vol 100 (1) ◽  
pp. 17-21 ◽  
Author(s):  
A. L. Tyler ◽  
D. L. Salt
Keyword(s):  
High Speed ◽  
Accurate Determination ◽  
Time Derivative ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Free Flight ◽  
Drag Coefficients ◽  
Abrupt Changes ◽  
Sufficient Precision

The trajectories of unrestrained spheres being accelerated from rest behind a normal shock wave in a shock tube have been recorded by high-speed stroboscopic photography, and precise measurements of the particle positions made with an optical comparator. Data of sufficient precision were obtained to permit the accurate determination of the second time derivative of the particle trajectories. The experiments were conducted in air with plastic spheres ranging in diameter from 0.7 to 2.4 mm and with specific gravities from 0.7 to 1.5. Particle Reynolds numbers from 1 × 104 to 5 × 104 were obtained, and absolute particle accelerations from 1 × 106 to 5 × 106 ± 0.16 × 106 cm/s2 were measured. The relative velocities were all subsonic; relative Mach numbers ranged from 0.3 to 0.6. The values of the particle acceleration, when plotted as a function of time, were found to contain periodic abrupt changes similar to a mathematical discontinuity. It is postulated that the associated abrupt changes in the forces exerted on the particles are caused by periodic detachment of low-pressure centers of vorticity which form behind the spheres. Values of the drag coefficients determined from the data similarly exhibit periodic abrupt changes. These changes appear, in the way they consistently increase during each cycle of the period and fall at the point of “discontinuity,” to be compatible with the postulate that the periodic behavior is caused by formation and abrupt detachment of low-pressure vortices in the wake. Values of the drag coefficients were found to vary from 10 percent to 30 percent above steady-state values at comparable Reynolds numbers—the range of the computed values of the drag coefficient being caused by the periodic nature of the quantity.

scholarly journals Die Dissoziation des C2-Moleküls durch Rotation

1967 ◽  
Vol 22 (12) ◽  
pp. 2023-2026b ◽  
Author(s):  
G. Messerle ◽  
L. Krauss
Keyword(s):  
Dissociation Energy ◽  
Accurate Determination ◽  
Low Pressure ◽  
Rotational Structure ◽  
Quantum Numbers ◽  
Very High

The C2-spectrum was excited i low pressure arc with an electrically heated tungstencathode. In this arc the rotational structure of the C2 bands could be followed up to very high rotational quantum numbers. In the c1IIg state a dissociation by rotation was observed. This effect yields D0(C2) = (6,11 ± 0,04) eV. The dissociation by rotation allows the accurate determination of the dissociation energy. Additionally the dissociation products of the IIg states could be fixed unambigously.

Factors affecting the accurate determination of cerebrovascular blood flow using high-speed droplet imaging

1998 ◽  
Author(s):  
Stephen Rudin ◽  
Afshin Divani ◽  
Ajay K. Wakhloo ◽  
Baruch B. Lieber ◽  
William Granger ◽  
...  
Keyword(s):  
Blood Flow ◽  
High Speed ◽  
Accurate Determination ◽  
Factors Affecting

scholarly journals NUMERICAL SIMULATION OF COOLING JET FROM HYDROGEN AND DEUTERIUM AS APPLICABLE TO INSTALLATIONS ON RECEIVING CRYOGENIC MONODISPERSE TARGETS

2019 ◽  
Vol 46 (1) ◽  
pp. 8-18
Author(s):  
A. V. Bukharov ◽  
A. F. Ginevsky ◽  
E. V. Vishnevsky
Keyword(s):  
High Speed ◽  
Low Pressure ◽  
Numerical Calculations ◽  
Liquid Jets ◽  
Temperature Changes ◽  
Working Chamber ◽  
Pressure Area ◽  
Speed Up ◽  
Determination Of Parameters

Objectives. Development of a model and carrying out numerical calculations for the cooling of thin jets of Hydrogen and Deuterium as applicable to installations on receiving cryogenic monodisperse targets.Methods. To achieve this purpose, the model of cryogenic jet outflow into the low pressure area was created and using PHOENICS software the temperature change of the surface and the interior of a jet over time for various external parameters is investigated through the numerical method.Result. The dependences of temperature changes of liquid Hydrogen and Deuterium jets along the jet surface and along the radius depending on the jet diameter, speed, initial jet temperature and pressure in the working chamber of installations for receiving cryogenic monodisperse targets were carried out.Conclusion. The principal possibility of creating high-speed cryogenic monodisperse targets is shown. According to the calculations, at input of thin liquid jets of Hydrogen or Deuterium with a speed up to 100 m/s into the working chamber with low pressure, jets at a distance of up to 1 mm do not have time to freeze and can be broken into monodisperse drops. Drops are cooled due to evaporation and become granules. The developed model, the program for determination of parameters of steady monodisperse disintegration of liquid cryogenic streams and results of numerical calculations can be used during creation of units for receiving high-speed cryogenic monodisperse targets.

scholarly journals Application of Low-Pressure Gas Chromatography/Tandem Mass Spectrometry to the Determination of Pesticide Residues in Tropical Fruits

2007 ◽  
Vol 90 (4) ◽  
pp. 1146-1164 ◽  
Author(s):  
Jos Luis Martnez Vidal ◽  
Jos Luis Fernndez Moreno ◽  
Francisco Javier Arrebola Libanas ◽  
Antonia Garrido Frenich
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Tandem Mass Spectrometry ◽  
Pesticide Residues ◽  
High Speed ◽  
Low Pressure ◽  
Tandem Mass ◽  
Tropical Fruits ◽  
Relative Standard

Abstract A multiresidue method has been developed for determining pesticide residues in the tropical fruits kiwi, custard apple, and mango. The intended purpose of the method is for regulatory analyses of commodities for pesticides that have established maximum residue limits. A fast and simple extraction method with cyclohexaneethyl acetate (1 + 1, v/v) and a high-speed homogenizer was optimized. Pressurized liquid extraction was evaluated as an alternative automated extraction technique. The pesticide residues were determined by using low-pressure gas chromatography coupled to tandem mass spectrometry. The proposed methodology was validated for each matrix. Pesticide recoveries ranged from 70 to 110%, with repeatability relative standard deviations of 18% at spiking levels of 12 and 50 g/kg. The limits of quantitation were in the range of 0.036.17 g/kg, and the limits of detection were between 0.01 and 3.75 g/kg. Mango can be selected as a representative matrix for calibration on the basis of the results of a potential matrix effect study. The method was successfully applied to the determination of pesticide residues in real samples in Spain.

Accurate Determination of the Cold Detection Threshold with High-Speed Cooling of the Skin

Pain Medicine ◽  
2020 ◽  
Vol 21 (12) ◽  
pp. 3428-3436
Author(s):  
Segolene Lithfous ◽  
Olivier Després ◽  
Thierry Pebayle ◽  
Claudia Casadio ◽  
Andre Dufour
Keyword(s):  
High Speed ◽  
Accurate Determination ◽  
Detection Threshold ◽  
Detection Thresholds ◽  
Temperature Ramp ◽  
Temperature Ramps ◽  
The Subject ◽  
Order Four ◽  
Healthy Participants

Abstract Objective This study used high-speed cooling of the skin and exact control of stimulus duration to measure the cold detection threshold in healthy participants. The objective was to compare the method of limits, in which the temperature is slowly and gradually increased/decreased until the subject perceives the stimulation, and the method of levels, in which the subject must detect brief thermal stimulations close to the threshold of perception. Methods Twenty healthy volunteers (nine women, 11 men) aged 20–30 years participated in the study. The method of limits and method of levels were performed in all subjects in a counterbalanced order. Four cold detection thresholds were measured with the method of levels, with a temperature ramp of 300°C/sec and stimulus durations of 50 ms, 100 ms, 300 ms, and 500 ms. Three thresholds were measured with the method of limits, with temperature ramps of 1°C/sec, 2°C/sec, and 4°C/sec. Results On average, the cold detection thresholds were −0.47°C below skin temperature with the method of levels and −1.67°C the method of limits. Interindividual variability was significantly lower with the method of levels than with the method of limits. Conclusions These results suggest that the method of levels is more accurate than the method of limits for measuring cold detection threshold. The improvement of cold detection threshold measurement may provide new perspectives to more precisely assess the function of A-delta fibers and the spino-thalamic pathway.

scholarly journals New high-speed centre of mass method incorporating background subtraction for accurate determination of fluorescence lifetime

2016 ◽  
Vol 24 (7) ◽  
pp. 6899 ◽  
Author(s):  
Simon P. Poland ◽  
Ahmet T. Erdogan ◽  
Nikola Krstajić ◽  
James Levitt ◽  
Viviane Devauges ◽  
...  
Keyword(s):  
Fluorescence Lifetime ◽  
Background Subtraction ◽  
High Speed ◽  
Accurate Determination ◽  
Centre Of Mass

Hot-Film Measurements on a Low Pressure Turbine Linear Cascade With Bypass Transition

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Stephan Stotz ◽  
Franz Blaim ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Accurate Determination ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
The State ◽  
Bypass Transition ◽  
Laminar Separation ◽  
Linear Cascade ◽  
Air Jet ◽  
Hot Film

Transition of the state of the boundary layer from laminar to turbulent plays an important role in the aerodynamic loss generation on turbine airfoils. An accurate simulation of the transition process and of the state of the boundary layer is therefore crucial for prediction of the aerodynamic efficiency of components in rotating machines. A lot of the research in the past years dealt with the transition over laminar separation bubbles, especially concerning flows in low pressure turbines (LPTs) of air jet engines. Nevertheless, bypass transition is also frequent in turbomachines at higher Reynolds numbers as well as for properly designed profiles. Compared with transition over a laminar separation bubble, a bypass transition is experimentally much more difficult to detect with standard measurement techniques. In such cases it becomes necessary to use more sophisticated techniques, such as hot-film anemometry, hot wires, or Preston probes in order to obtain accurate information on the state of the boundary layer. The study presented is carried out using a linear cascade with a LPT blade profile with strong front loading and gentle flow deceleration at the rear suction side of the blade. Measurements were performed at the high-speed cascade wind tunnel of the Institute of Jet Propulsion at engine relevant Mach and Reynolds numbers. Emphasis is put on the evaluation of the different transition processes at midspan and its influence on profile losses. The data postprocessing was adapted for compressible flows, which allows a more accurate determination of the transition area as well as qualitatively better distributions of the wall shear stress. Finally, comparisons with simulations, using computational fluid dynamics (CFD) tools, are performed and fields for improvement of the turbulence and transition models are identified.

Experimental device for the accurate determination of wood-water relations on micro-samples

Holzforschung ◽  
2007 ◽  
Vol 61 (4) ◽  
pp. 419-429 ◽  
Author(s):  
Patrick Perré
Keyword(s):  
Moisture Content ◽  
Water Relations ◽  
High Speed ◽  
Growth Ring ◽  
Accurate Determination ◽  
Longitudinal Direction ◽  
Experimental Device ◽  
Normal Wood ◽  
Diamond Wire Saw

Abstract This paper describes an experimental device designed for the accurate determination of wood/water relations on micro-samples. The moisture content of the sample is measured with a highly sensitive electronic microbalance. Moreover, the dimensions of the sample in tangential and longitudinal direction are collected continuously without contact by means of two high-speed laser scan micrometers. The device is placed in a climatic chamber. The micro-samples investigated were prepared with a diamond wire saw. A sample thickness of less than 1 mm allows the moisture content to be almost uniform during the test. The data obtained are of excellent quality and accuracy, in spite of the very small mass and dimensions of the samples. The device provides a perfect tool for investigating the dynamic interaction between relative humidity, moisture content, and shrinkage. Results collected for beech, spruce and eucalyptus are presented. Important findings include: deviation from a linear relation between shrinkage and moisture content in beech; uniqueness of the shrinkage versus moisture content curve during desorption/adsorption cycles; evidence of cell collapse in eucalyptus, especially for tension wood; and property variations within the growth ring of normal wood and compression wood of spruce.

scholarly journals Determination of digesta flow entering the omasal canal of dairy cows using different marker systems

2003 ◽  
Vol 90 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Seppo Ahvenjärvi ◽  
Aila Vanhatalo ◽  
Kevin J. Shingfield ◽  
Pekka Huhtanen
Keyword(s):  
Particulate Matter ◽  
Liquid Phase ◽  
Dairy Cows ◽  
High Speed ◽  
Volatile Fatty Acids ◽  
Accurate Determination ◽  
Water Soluble ◽  
Neutral Detergent Fibre ◽  
Inorganic Matter

Four studies were conducted to compare the effect of four indigestible markers (LiCoEDTA, Yb-acetate, Cr-mordanted straw and indigestible neutral-detergent fibre (INDF)) and three marker systems on the flow of digesta entering the omasal canal of lactating dairy cows. Samples of digesta aspirated from the omasal canal were pooled and separated using filtration and high-speed centrifugation into three fractions defined as the liquid phase, small particulate and large particulate matter. Co was primarily associated with the liquid phase, Yb was concentrated in small particulate matter, whilst Cr and INDF were associated with large particles. Digesta flow was calculated based on single markers or using the reconstitution system based on combinations of two (Co + Yb, Co + Cr and Co + INDF) or three markers (Co + Yb + Cr and Co + Yb + INDF). Use of single markers resulted in large differences between estimates of organic matter (OM) flow entering the omasal canal suggesting that samples were not representative of true digesta. Digesta appeared to consist of at least three phases that tended to separate during sampling. OM was concentrated in particulate matter, whilst the liquid phase consisted mainly of volatile fatty acids and inorganic matter. Yb was intimately associated with nitrogenous compounds, whereas Cr and INDF were concentrated in fibrous material. Current data indicated that marker systems based on Yb in combination with Cr or INDF are required for the accurate determination of OM, N and neutral-detergent fibre flow. In cases where the flow of water-soluble nutrients entering the omasal canal is also required, the marker system should also include Co.

Effect of Roughness and Unsteadiness on the Performance of a New Low Pressure Turbine Blade at Low Reynolds Numbers

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Francesco Montomoli ◽  
Howard Hodson ◽  
Frank Haselbach
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Beneficial Effect ◽  
High Speed ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Lift ◽  
Wake Passing

This paper presents a study of the performance of a high-lift profile for low pressure turbines at Reynolds numbers lower than in previous investigations. By following the results of Coull et al. (2008, “Velocity Distributions for Low Pressure Turbines,” ASME Paper No. GT2008-50589) on the design of high-lift airfoils, the profile is forward loaded. The separate and combined effects of roughness and wake passing are compared. On a front loaded blade, the effect of incidence becomes more important and the consequences in terms of cascade losses, is evaluated. The experimental investigation was carried out in the high speed wind tunnel of Whittle Laboratory, University of Cambridge. This is a closed-circuit continuous wind tunnel where the Reynolds number and Mach number can be fixed independently. The unsteadiness caused by wake passing in front of the blades is reproduced using a wake generator with rotating bars. The results confirm that the beneficial effect of unsteadiness on losses is present even at the lowest Reynolds number examined (Re3=20,000). This beneficial effect is reduced at positive incidence. With a front loaded airfoil and positive incidence, the transition occurs on the suction side close to the leading edge and this results in higher losses. This has been found valid for the entire Reynolds range investigated (20,000≤Re3≤140,000). Roughening the surface also had a beneficial effect on the losses but this effect vanishes at the lower Reynolds numbers, i.e., (Re3≤30,000), where the surface becomes hydraulically smooth. The present study suggests that a blade with as-cast surface roughness has a lower loss than a polished one.

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