Mechanical Damping of the Manometric System Used in the Pressure Gradient Technique

1974 ◽  
Vol BME-21 (1) ◽  
pp. 76-78 ◽  
Author(s):  
A. C. Lapointe ◽  
F. A. Roberge
Keyword(s):  
Pressure Gradient ◽  
Gradient Technique ◽  
Mechanical Damping

scholarly journals Hydrogen diffusion through polymer membranes

2020 ◽  
Vol 322 ◽  
pp. 01044
Author(s):  
Nicolas Gay ◽  
Takoua Lamouchi ◽  
Franck Agostini ◽  
Catherine A. Davy ◽  
Frédéric Skoczylas
Keyword(s):  
Experimental Study ◽  
Pressure Gradient ◽  
Concentration Gradient ◽  
High Density Polyethylene ◽  
Hydrogen Diffusion ◽  
Polymer Membranes ◽  
Gas Concentration ◽  
Classical Technique ◽  
Gradient Technique ◽  
Transfer Properties

This experimental study determines H2 transfer properties of High Density PolyEthylene (HDPE) or epoxy membranes. Two different techniques are compared. The pressure gradient technique is analyzed for permeability or diffusion. Results show that the main phenomenon involved is diffusion. The second technique involves a gas concentration gradient. Although implying significantly slower kinetics, this classical technique is consistent with results obtained with the faster pressure gradient technique.

Evaluation of Kolin type electromagnetic flowmeter and the pressure gradient technique

1962 ◽  
Vol 17 (2) ◽  
pp. 372-374 ◽  
Author(s):  
Joseph C. Greenfield ◽  
Dali J. Patel ◽  
Alexander J. Mallos ◽  
Donald L. Fry
Keyword(s):  
Pressure Gradient ◽  
Electromagnetic Flowmeter ◽  
Gradient Technique

Measurement errors in estimating aortic blood velocity by pressure gradient

1962 ◽  
Vol 17 (6) ◽  
pp. 1013-1019 ◽  
Author(s):  
Joseph C. Greenfield ◽  
Donald L. Fry
Keyword(s):  
Pressure Gradient ◽  
Measurement Errors ◽  
Differential Pressure ◽  
Optimum Pressure ◽  
Harmonic Content ◽  
Gradient Technique ◽  
Minimum Requirements ◽  
Special Measurement ◽  
Instantaneous Pressure ◽  
Pressure Catheter

The computed pressure-gradient technique is important in measuring instantaneous blood flow and velocity in man. Estimation of the instantaneous pressure gradient for this purpose presents many special problems. This study was designed to explore these special measurement problems and to establish certain minimum pressure-recording standards for application of the computed pressure-gradient technique to man. The nature of the functions to be measured was first explored by determining average values and harmonic content of typical pressure, flow, and pressure-gradient curves. In contrast to pressure and flow curves, the harmonic content of pressure-gradient curves was found to exceed the recording capabilities of currently available systems for measuring differential pressure. However, when velocity was computed from pressure gradient, the importance of errors related to higher frequencies is greatly diminished. To meet minimum requirements differential-pressure catheter-manometer systems should have a dynamic imbalance of less than 5% through frequencies of 15 cycles/sec, a single-ended dynamic response uniform (±5%) through 15 cycles/sec, and a static imbalance not greater than ±0.1% over the range 0–300 cm H2O. Although an optimum pressure tap separation could not be precisely defined, visual examination suggested that a tap separation of 8 cm should not be exceeded. Submitted on April 30, 1962

Instantaneous blood flow in the human aorta

1965 ◽  
Vol 20 (4) ◽  
pp. 691-695 ◽  
Author(s):  
Robert E. Snell ◽  
James M. Clements ◽  
Dali J. Patel ◽  
Donald L. Fry ◽  
Peter C. Luchsinger
Keyword(s):  
Blood Flow ◽  
Pressure Gradient ◽  
Flow Measurement ◽  
Regression Line ◽  
Human Aorta ◽  
Aortic Blood Flow ◽  
Mean Values ◽  
Gradient Technique ◽  
The Mean ◽  
Male Subjects

The computed pressure-gradient technique has been applied to the measurement of instantaneous aortic blood flow in 15 male subjects. The mean values of those curves obtained in the ascending aorta were compared with simultaneous measurements made by the dye-dilution technique. The correlation coefficient between the two methods was 0.85 and the slope of the regression line 0.80. The ability to measure flow by the pressure-gradient technique depends mainly on the accuracy of the catheter-manometer system, radius measurement, and the estimation of “zero flow.” pressure-gradient technique; methods of blood flow measurement Submitted on June 22, 1964

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

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