The effects of contaminating noise on the calculation of active acoustic intensity for pressure gradient methods

2019 ◽  
Vol 145 (1) ◽  
pp. 173-184 ◽  
Author(s):  
Mylan R. Cook ◽  
Kent L. Gee ◽  
Tracianne B. Neilsen ◽  
Scott D. Sommerfeldt
Keyword(s):  
Pressure Gradient ◽  
Gradient Methods ◽  
Acoustic Intensity

Calculation of boundary-layer development using the turbulent energy equation: compressible flow on adiabatic walls

1971 ◽  
Vol 46 (1) ◽  
pp. 83-110 ◽  
Author(s):  
P. Bradshaw ◽  
D. H. Ferriss
Keyword(s):  
Pressure Gradient ◽  
Compressible Flow ◽  
Incompressible Flow ◽  
Gradient Methods ◽  
Turbulent Energy ◽  
Turbulence Structure ◽  
Flow Surface ◽  
Boundary Layer Development ◽  
Dimensional Boundary ◽  
Layer Development

The basic method described by Bradshaw, Ferriss & Atwell (1967) is extended to compressible flow in two-dimensional boundary layers in arbitrary pressure gradient (excluding shock waves and expansion fans) by invoking Morkovin's hypothesis (Favre 1964) that the turbulence structure is unaffected by compressibility. Using the same empirical functions as in incompressible flow, skin friction in zero pressure gradient is predicted to within 3% of Spalding & Chi's (1964) correlation for free-stream Mach numbers less than 5. Comparisons with experiments in pressure gradient are restricted by the lack of data, but, since Morkovin's hypothesis does not depend on pressure gradient, methods which use it (of which the present method seems to be the first) can be checked fairly adequately by comparisons with data in zero pressure gradient.No ‘compressibility transformations’ are needed, although the Crocco relation is used, provisionally, for the temperature: since the calculations take only about 20% longer than in incompressible flow, Morkovin's hypothesis does as much as any transformation could do. It is pointed out that, in supersonic flow, surface curvature which is large enough to induce a significant longitudinal pressure gradient is also large enough to have a very significant effect on the turbulence structure.

Pressure Drop During Condensation in Microchannels

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Hua Sheng Wang ◽  
Jie Sun ◽  
John W. Rose
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Void Fraction ◽  
Annular Flow ◽  
Gradient Methods ◽  
Pressure Gradients ◽  
High Quality ◽  
Friction Pressure ◽  
Flow Condensation ◽  
Approximate Equations

The paper reports calculations of friction pressure gradient for the special case of laminar annular flow condensation in microchannels. This is the only flow regime permitting theoretical solution without having recourse to experimental data. Comparisons are made with correlations based on experimental data for R134a. The correlations differ somewhat among themselves with the ratio of highest to lowest predicted friction pressure gradient typically around 1.4 and nearer to unity at high quality. The friction pressure gradients given by the laminar annular flow solutions are in fair agreement with the correlations at high quality and lower than the correlations at lower quality. Attention is drawn to the fact that the friction pressure gradient cannot be directly observed and its evaluation from measurements requires estimation of the nondissipative momentum or acceleration pressure gradient. Methods used to estimate the nondissipative pressure gradient require quality and void fraction together with equations which relate these and whose accuracy is difficult to quantify. Quality and void fraction can be readily found from the laminar annular flow solutions. Significant differences are found between these and values from approximate equations.

scholarly journals Plane-wave tube validation of bandwidth extension for energy-based quantities using pressure gradient methods

2017 ◽  
Author(s):  
Daxton Hawks ◽  
Tracianne B. Neilsen ◽  
Kent L. Gee ◽  
Scott D. Sommerfeldt
Keyword(s):  
Plane Wave ◽  
Pressure Gradient ◽  
Gradient Methods ◽  
Wave Tube ◽  
Bandwidth Extension

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.

Risk Factors for Hepatic Encephalopathy after Transjugular Intrahepatic Portosystemic Shunt in Patients with Hepatocellular Carcinoma and Portal Hypertension

2015 ◽  
Vol 24 (3) ◽  
pp. 301-307 ◽  
Author(s):  
Jiannan Yao ◽  
Li Zuo ◽  
Guangyu An ◽  
Zhendong Yue ◽  
Hongwei Zhao ◽  
...  
Keyword(s):  
Risk Factors ◽  
Hepatocellular Carcinoma ◽  
Portal Hypertension ◽  
Hepatic Encephalopathy ◽  
Pressure Gradient ◽  
Transjugular Intrahepatic Portosystemic Shunt ◽  
Meld Score ◽  
Portosystemic Shunt ◽  
Portal Flow ◽  
Intrahepatic Portosystemic Shunt

Aims: This study aimed at assessing the risk factors for hepatic encephalopathy (HE) after transjugular intrahepatic portosystemic shunt (TIPS) in patients with hepatocellular carcinoma (HCC) and portal hypertension. Method: Consecutive patients (n=279) with primary HCC who underwent TIPS between January 1997 and March 2012 at a single institution were retrospectively reviewed. Patients were followed up for 2 years. Pre-TIPS, peri-TIPS and post-TIPS clinical variables were reviewed using univariate and multivariate analyses to identify risk factors for HE after TIPS. Results: The overall incidence of HE was 41% (114/279). Multivariate analysis showed an increased odds for HE in patients with: >3 treatments with transcatheter arterial chemoembolization (TACE) and/or trans-arterial embolization (TAE) (odds ratio [OR], 4.078; 95% confidence interval [95%CI], 1.748-9.515); hepatopetal portal flow (OR, 2.362; 95%CI, 1.032-5.404); high portosystemic pressure gradient (OR, 1.198; 95%CI, 1.073-1.336) and high pre-TIPS MELD score (OR, 1.693; 95%CI, 1.390-2.062). Odds for HE were increased 1.693 fold for each 1-point increase in the MELD score, and 1.198 fold for each 1-mmHg decrease in the post-TIPS portosystemic pressure gradient. Conclusion: The identification of clinical variables associated with increased odds of HE may be useful for the selection of appropriate candidates for TIPS. Results suggest that an inappropriate decrease in the portosystemic pressure gradient might be associated with HE after TIPS. In addition, >3 treatments with TACE/TAE, hepatopetal portal flow, and high MELD score were also associated with increased odds of HE after TIPS. Key words:  –  –  – .

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