Pulsatile pressure measurements via harmonics-based orthogonal projection of noisy pressure gradients

2006 ◽  
Author(s):  
Yuehuan Wang ◽  
Abbas N. Moghaddam ◽  
Geoffrey Behrens ◽  
Nasser Fatouraee ◽  
Juan Cebral ◽  
...  
Keyword(s):  
Orthogonal Projection ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Pulsatile Pressure

The Study of Evaporation from Small Surfaces by the Direct Measurement of Water Vapour Pressure Gradients

1970 ◽  
Vol 53 (3) ◽  
pp. 753-762
Author(s):  
JOHN MACHIN
Keyword(s):  
Water Vapour ◽  
Direct Measurement ◽  
Vapour Pressure ◽  
Point Method ◽  
Dew Point ◽  
Water Vapour Pressure ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Wind Speeds ◽  
Experimental Values

1. The construction, maintenance and calibration of a sensitive instrument capable of making numerous vapour-pressure measurements within humidity gradients by the dew-point method is described. 2. Coefficients of diffusion of water vapour in air, calculated from observed vapour-pressure gradients and measured rates of evaporation agree with theoretical and other experimental values in still air. 3. Apparent coefficients in wind speeds between 10 and 100 cm/s were significantly lower than those in still air. 4. This finding, together with the performance of the dew-point probe, is discussed in relation to its possible use in the study of evaporation from animals and plants.

CFD Challenge: Solutions Using the In-House Finite-Element-Based Solver NEWTETR

2012 ◽  
Author(s):  
Yiemeng Hoi ◽  
David A. Steinman
Keyword(s):  
Steady State ◽  
Pressure Measurements ◽  
Surface Geometry ◽  
Flow Rates ◽  
Pressure Drops ◽  
Or Groups ◽  
Giant Cerebral Aneurysm ◽  
Pulsatile Pressure ◽  
Nominal Surface

Briefly, this Challenge aims to test the sensitivity of steady and pulsatile pressure drops as predicted by different CFD solvers or groups, and ultimately against in vitro pressure measurements. The current study focuses on the Phase I of the Challenge. We simulated steady state and pulsatile pressure drops based on the nominal surface geometry and specific inlet flow rates on a giant cerebral aneurysm with proximal stenosis.

Diurnal Cycle of Thermally Driven Cross-Basin Winds in Arizona’s Meteor Crater

2011 ◽  
Vol 50 (3) ◽  
pp. 729-744 ◽  
Author(s):  
Manuela Lehner ◽  
C. David Whiteman ◽  
Sebastian W. Hoch
Keyword(s):  
Diurnal Cycle ◽  
Inversion Layer ◽  
Crater Floor ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Westerly Winds ◽  
Thermally Driven ◽  
Temperature And Pressure ◽  
The Cross

Abstract Cross-basin winds produced by asymmetric insolation of the crater sidewalls occur in Arizona’s Meteor Crater on days with weak background winds. The diurnal cycle of the cross-basin winds is analyzed together with radiation, temperature, and pressure measurements at the crater sidewalls for a 1-month period. The asymmetric irradiation causes horizontal temperature and pressure gradients across the crater basin that drive the cross-basin winds near the crater floor. The horizontal temperature and pressure gradients and wind directions change as the sun moves across the sky, with easterly winds in the morning and westerly winds in the evening. A case study of 12 October 2006 further illustrates the obtained relation between these parameters for an individual day. The occurrence of an elevated cross-basin flow on 23 October 2006 is shown to relate to the presence of an elevated inversion layer.

Dural sinus stent placement for idiopathic intracranial hypertension

2012 ◽  
Vol 116 (3) ◽  
pp. 538-548 ◽  
Author(s):  
David A. Kumpe ◽  
Jeffrey L. Bennett ◽  
Joshua Seinfeld ◽  
Victoria S. Pelak ◽  
Ashish Chawla ◽  
...  
Keyword(s):  
Intracranial Hypertension ◽  
Stent Placement ◽  
Idiopathic Intracranial Hypertension ◽  
Venous Pressure ◽  
Dural Sinus ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Junction Region ◽  
Hemodynamic Deterioration

Object The use of unilateral dural sinus stent placement in patients with idiopathic intracranial hypertension (IIH) has been described by multiple investigators. To date there is a paucity of information on the angiographic and hemodynamic outcome of these procedures. The object of this study was to define the clinical, angiographic, and hemodynamic outcome of placement of unilateral dural sinus stents to treat intracranial venous hypertension in a subgroup of patients meeting the diagnostic criteria for IIH. Methods Eighteen consecutive patients with a clinical diagnosis of IIH were treated with unilateral stent placement in the transverse-sigmoid junction region. All patients had papilledema. All 12 female patients had headaches; 1 of 6 males had headaches previously that disappeared after weight loss. Seventeen patients had elevated opening pressures at lumbar puncture. Twelve patients had opening pressures of 33–55 cm H2O. All patients underwent diagnostic cerebral arteriography that showed venous outflow compromise by filling defects in the transverse-sigmoid junction region. All patients underwent intracranial selective venous pressure measurements across the filling defects. Follow-up arteriography was performed in 16 patients and follow-up venography/venous pressure measurements were performed in 15 patients. Results Initial pressure gradients across the filling defects ranged from 10.5 to 39 mm Hg. Nineteen stent procedures were performed in 18 patients. One patient underwent repeat stent placement for hemodynamic failure. Pressure gradients were reduced in every instance and ranged from 0 to 7 mm Hg after stenting. Fifteen of 16 patients in whom ophthalmological follow-up was performed experienced disappearance of papilledema. Follow-up arteriography in 16 patients at 5–99 months (mean 25.3 months, median 18.5 months) showed patency of all stents without in-stent restenosis. Two patients had filling defects immediately above the stent. Four other patients developed transverse sinus narrowing above the stent without filling defects. One of these patients underwent repeat stent placement because of hemodynamic deterioration. Two of the other 3 patients had hemodynamic deterioration with recurrent pressure gradients of 10.5 and 18 mm Hg. Conclusions All stents remained patent without restenosis. Stent placement is durable and successfully eliminates papilledema in appropriately selected patients. Continuing hemodynamic success in this series was 80%, and was 87% with repeat stent placement in 1 patient.

scholarly journals Accuracy and Uncertainty of Gradient Based Leak Localization Procedure for Liquid Transmission Pipelines

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5080
Author(s):  
Pawel Ostapkowicz ◽  
Andrzej Bratek
Keyword(s):  
Measurement Data ◽  
Uncertainty Assessment ◽  
Laboratory Model ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Low Intensity ◽  
Measuring Devices ◽  
Gradient Based ◽  
Leak Localization ◽  
Transmission Pipelines

This paper describes issues of leakage localization in liquid transmission pipelines. It focuses on the standard leak localization procedure, which is based on the calculation of pressure gradients using pressure measurements captured along a pipeline. The procedure was verified in terms of an accuracy and uncertainty assessment of the resultant coordinate of a leak spot. An important aim of the verification was to assess the effectiveness of the procedure in the case of localization of low intensity leakages with a level of 0.25–2.00% of the nominal flow rate. An uncertainty assessment was carried out according to the GUM convention. The assessment was based on the metrological characteristics of measuring devices and measurement data obtained from the laboratory model of the pipeline.

Oscillating Flow in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Barton L. Smith ◽  
Kristen V. Mortensen ◽  
Spencer Wendel
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Displacement Amplitude ◽  
Oscillating Flow ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Piv Measurements ◽  
Separated Shear Layer ◽  
Minor Losses ◽  
Increasing Function

Separating oscillating flow in an internal adverse pressure gradient geometry is studied experimentally. Phase-locked PIV measurements and simultaneous pressure measurements reveal that during the accelerating portion of the cycle, the flow remains attached in spite of a very large adverse pressure gradient. During the decelerating portion of the cycle, the flow is more prone to separation. The duration and extent of the separation depend strongly on the oscillation displacement amplitude relative to the cross-stream dimension. In some cases, the flow separates but reattaches as the separated shear layer is accelerated temporally. The time-varying pressure measurements are used to determine the resultant minor losses for the flow in each direction. These are found to be an increasing function of displacement amplitude and independent of the Reynolds number.

MR measurement of pulsatile pressure gradients

1994 ◽  
Vol 4 (6) ◽  
pp. 829-836 ◽  
Author(s):  
Steven N. Urchuk ◽  
Donald B. Plewes
Keyword(s):  
Pressure Gradients ◽  
Pulsatile Pressure

Comparison of venous sinus manometry gradients obtained while awake and under general anesthesia before venous sinus stenting

2016 ◽  
Vol 9 (10) ◽  
pp. 990-993 ◽  
Author(s):  
Kyle M Fargen ◽  
Alejandro M Spiotta ◽  
Madison Hyer ◽  
Jonathan Lena ◽  
Raymond D Turner ◽  
...  
Keyword(s):  
General Anesthesia ◽  
Venous Sinus ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Outflow Obstruction ◽  
Variable Effect ◽  
Significant Difference ◽  
Venous Outflow Obstruction ◽  
A Site ◽  
Sinus Pressure

IntroductionVenous sinus stenting is a popular treatment strategy for patients with high venous sinus pressure gradients across a site of outflow obstruction. Little is known about the effect of anesthesia on venous sinus pressure measurements.ObjectiveTo compare venous manometry performed in patients under general anesthesia and while awake.MethodsA prospective database was accessed to retrospectively identify patients who had undergone venous sinus stenting. Pressure gradients were compared between those patients who underwent manometry while awake and before stenting under general anesthesia.ResultsThirty patients with both general anesthesia and awake pressure recordings were identified. Pressure measurements were highly variable but overall were higher under general anesthesia by an average of 5.8 mm Hg (1.7; p=0.002). A significant difference between awake and general anesthesia pressure measurements was detected in the sigmoid sinus (5.8 mm Hg (2.0); p=0.005) and the jugular vein (8.1 mm Hg (3.9); p=0.040). Only 11/30 (36.7%) pressure gradients remained within 5 mm Hg of the original awake gradient when repeated under general anesthesia; 9/30 (30%) patients had gradients that were at least 10 mm Hg different across procedures.ConclusionsCalculated pressure gradients were markedly affected by anesthesia. These findings suggest that candidacy for stenting should be determined with venous manometry while patients are awake owing to the unpredictable and highly variable effect of general anesthesia on pressure measurements and an apparent tendency to underestimate the degree of venous outflow obstruction.

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