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

Reynolds-averaged Navier–Stokes simulation of hydrofoil effects on hydrodynamic coefficients of a catamaran in forced oscillation

2016 ◽  
Vol 231 (2) ◽  
pp. 364-383
Author(s):  
Amin Najafi ◽  
Mohammad Saeed Seif
Keyword(s):  
High Speed ◽  
Experimental Approach ◽  
Navier Stokes ◽  
Hydrodynamic Coefficients ◽  
Laboratory Equipment ◽  
Factors Affecting ◽  
High Frequencies ◽  
Frequency Independent ◽  
Reynolds Averaged Navier Stokes

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier–Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly efficient. In this study, the numerical results for hydrodynamic coefficients of a high-speed craft are verified against Troesch’s experimental results. In the following, after determination of hydrodynamic coefficients of a planing catamaran with and without foil, the foil effects on its hydrodynamic coefficients are evaluated. The results indicate that most of the coefficients are frequency-independent especially at high frequencies.

Factors affecting constancy of acetate concentration and correct determination of methanogenic activity in pH-stat experiments

2003 ◽  
Vol 48 (6) ◽  
pp. 111-118
Author(s):  
M. Mösche ◽  
U. Meyer
Keyword(s):  
Accurate Determination ◽  
Original Method ◽  
Experimental Conditions ◽  
Methanogenic Activity ◽  
Factors Affecting ◽  
Acetate Concentration ◽  
Correct Determination ◽  
Ph Stat ◽  
The Stability

The determination of methanogenic activity with a pH-stat titration bioassay is evaluated utilising a mathematical model of this system. For given kinetic parameters and experimental conditions the model calculates the development of titrant flow and acetate concentration during experiments. Simulations of experiments under various conditions are compared. They show that the original method inherently causes a strong drift of acetate concentration during the experiments and a misestimation of methanogenic activity. As a solution to these disadvantages the addition of sodium hydroxide to the titrant and a careful control of pH during flushing the reactor with gas prior to the experiment are recommended. In this way a better constancy of acetate concentration and a more accurate determination of methanogenic activity should be achievable. The accuracy of this method is limited by the stability of pH-electrode calibration parameters.

Factors affecting the stability and estimation of carotene in artificially dried grass and hays

1940 ◽  
Vol 30 (4) ◽  
pp. 622-638 ◽  
Author(s):  
S. K. Kon ◽  
S. Y. Thompson
Keyword(s):  
Chromatographic Analysis ◽  
Accurate Determination ◽  
Total Loss ◽  
Carotene Content ◽  
Factors Affecting ◽  
Ordinary Temperature ◽  
Initial Drop ◽  
The Difference ◽  
The Stability

1. The influence of storage in the light and in the dark at ordinary temperature and in a heated room at 70–80° F. on the carotene content of finely ground artificially dried grass stored in paper sacks and jute sacks was studied. There was an initial drop in carotene content from 61·1 to 46·5 mg./100 g., i.e. 23·9%, in the first month, and a total loss of 31·4% during 6 months' storage (August to February). No difference could be detected either between treatments or types of containers.2. There was a marked loss of carotene during 13 months' storage of baled artificially dried grass and of hays, amounting to 30–40% of the original value.3. Two methods of estimating carotene were compared. The method of Ferguson & Bishop (1936) gave higher results than the method of Peterson, Hughes & Freéman (1937). The difference is probably due to incomplete extraction in the latter method.4. Chromatographic analyses of “carotene” fractions from the above grasses showed the presence of coloured impurities amounting to 20·5–33·8% of the total recovered pigments.5. As these impurities are biologically inactive, chromatographic analysis or the use of special solvents are probably necessary for the accurate determination of carotene in forage.

A METHOD FOR COMPUTING THE TOTAL MAGNETIZATION VECTOR AND THE DIMENSIONS OF A RECTANGULAR BLOCK‐SHAPED BODY FROM MAGNETIC ANOMALIES

Geophysics ◽  
1966 ◽  
Vol 31 (1) ◽  
pp. 74-96 ◽  
Author(s):  
B. K. Bhattacharyya
Keyword(s):  
High Speed ◽  
Magnetization Vector ◽  
The Body ◽  
Total Field ◽  
Unknown Parameters ◽  
Factors Affecting ◽  
Vertical Derivative ◽  
Correct Location ◽  
Unit Of Length

In this paper is presented a new method for determining the following parameters of a uniformly magnetized body of rectangular prismatic shape: (i) horizontal dimensions, (ii) depths to the top and bottom of the body, and (iii) intensity and direction of magnetization. Accuracy in the computation of these parameters is highly dependent on the correct location of the center and on the determination of the major and minor axes of the body. An iterative method of calculations is used. This method is considerably aided not only by the second vertical derivative map of the observed total field but also by the total field reduced to the pole and its second vertical derivative map. The horizontal dimensions are determined by noting the location of the maximum of the odd component of the second vertical derivative about the center of the body. These dimensions are estimated with high accuracy when they are greater than the depth to the top of the body. The remaining unknown parameters of the body are calculated with the help of the first horizontal and vertical derivatives and the total field at the origin in the plane of observation which is directly above the center of the body. The present method also requires the total‐field value at the point one‐half unit of length above the origin. The factors affecting the accuracy in the calculation of the parameters are discussed in detail. With the help of high‐speed digital computers, this method can be used with great advantage for computation of the above parameters of magnetized bodies giving rise to a number of anomalies over a particular area.

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

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.

scholarly journals An Evaluation of Errors in the Determination of Blood Flow by the Indicator Fractionation and Tissue Equilibration (Kety) Methods

1984 ◽  
Vol 4 (1) ◽  
pp. 47-60 ◽  
Author(s):  
Clifford S. Patlak ◽  
Ronald G. Blasberg ◽  
Joseph D. Fenstermacher
Keyword(s):  
Blood Flow ◽  
Accurate Determination ◽  
Timing Errors ◽  
Arterial Concentration ◽  
Fractionation Method ◽  
Time Courses ◽  
Infusion Schedule ◽  
The Impact ◽  
Experiment Duration

In this report, the effects of various errors and plasma time courses of indicator concentration on the accurate determination of cerebral blood flow ( F) are theoretically analyzed for the tissue equilibration and the indicator fractionation techniques. For the indicator fractionation technique, the impact of sample timing and tissue assaying errors and of indicator backflux were examined; for the tissue equilibration method, errors in the value of the partition coefficient (Λ), sample timing, and tissue assaying were considered. The recommended ways to decrease the effects of errors in the indicator fractionation technique are to administer the indicator by an intravenous bolus and to sample the tissue about 10 s thereafter. Possible errors in the assessment of F by the tissue equilibration technique are diminished by using an indicator infusion schedule which yields a continuous rise in arterial concentration and by selecting a 30-s experiment duration. Surprisingly, the impact of sample timing errors is greater on the determination of F with the tissue equilibration method than with the indicator fractionation technique. For the chosen plasma time courses, there is always a backflux error in an indicator fractionation estimation of F, and this error increases as the flow rate increases. Thus, provided the sample timing and tissue assay errors are small and the value of Λ is known, the tissue equilibration method is the more accurate of the two. If Λ is unknown, then the indicator fractionation technique should be used. In many cases, the indicator fractionation method will provide as accurate an estimate of F as will the tissue equilibration method.

Sagittal whole-spine magnetic resonance imaging in 750 consecutive outpatients: accurate determination of the number of lumbar vertebral bodies

2010 ◽  
Vol 12 (1) ◽  
pp. 47-55 ◽  
Author(s):  
Eric H. Hanson ◽  
Rahul K. Mishra ◽  
David S. Chang ◽  
Thomas G. Perkins ◽  
Daniel R. Bonifield ◽  
...  
Keyword(s):  
Lumbar Spine ◽  
Mr Imaging ◽  
High Speed ◽  
Imaging System ◽  
Accurate Determination ◽  
Outpatient Setting ◽  
Spine Mr ◽  
Vertebral Bodies ◽  
Whole Spine

Object When the number of lumbar and sacral vertebrae is being assessed, variations from typical lumbosacral anatomy may confuse the practitioner, potentially leading to significant clinical errors. In this study, the authors describe the statistical variation in lumbar spine anatomy in an outpatient imaging setting, evaluate the potential implications for clinical practice based on the variation in the number of lumbar-type vertebrae identified, and recommend a method for rapidly determining the number of lumbar spine vertebral bodies (VBs) in outpatients referred for lumbar spine MR imaging. Methods A total of 762 patients (male and female) who presented with low back–related medical conditions underwent whole-spine MR imaging in an outpatient setting. Results The high-speed whole-spine evaluation was successful for determining the number of lumbar-type VBs in 750 (98%) of 762 consecutive patients. The sagittal whole-spine 3-T MR imaging system images obtained between the beginning of January 2005 and the end of February 2007 were reviewed. The VBs were counted successively from the level of C-2 inferiorly to the intervertebral disc below the most inferior lumbar-type VB. Numbers of disc herniations were also evaluated in the context of the number of VBs. Conclusions One in 5 of these outpatients did not have 5 lumbar-type vertebrae: 14.5% had 6; 5.3% had 4; and 1 (0.13%) had the rare finding of 3 lumbar-type vertebrae. Two-thirds of the individuals with 6 lumbar-type vertebrae were male and two-thirds of the individuals with 4 lumbar-type vertebrae were female. Sagittal whole-spine MR imaging can be performed rapidly and efficiently in the majority of patients (98%), and provides improved accuracy for the determination of the number of lumbar-type VBs. A supplementary coronal MR, Ferguson view radiograph or intraoperative fluoroscopic determination for the presence of lumbosacral transitional vertebrae may add additional information when indicated for clinical treatment or surgical planning.

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