Filtration of the extracting agent in porous particles with entrapped gas at low-frequency pressure oscillations in the extractor

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aiming to suppress the oscillations while maintaining mechanical integrity of the device. An experimental verification demonstrated the validity of the model and showed a very stable operation of the modified dynamometer even at very low torque.

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Low-frequency arterial pressure fluctuations do not reflect sympathetic outflow: gender and age differences

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.274.4.h1194 ◽

1998 ◽

Vol 274 (4) ◽

pp. H1194-H1201 ◽

Cited By ~ 33

Author(s):

J. Andrew Taylor ◽

Todd D. Williams ◽

Douglas R. Seals ◽

Kevin P. Davy

Keyword(s):

Arterial Pressure ◽

Low Frequency ◽

Total Activity ◽

Sympathetic Outflow ◽

Pressure Oscillations ◽

Young Males ◽

Young Females ◽

Sympathetic Nervous ◽

Mayer Wave ◽

Older Males

Low-frequency arterial pressure oscillations (Mayer waves) have been proposed as an index of vascular sympathetic outflow. However, cross-sectional differences in these pressure oscillations may not reflect different levels of sympathetic nervous outflow in humans. Three groups of healthy subjects with characteristically different sympathetic nervous outflow were studied: young females ( n = 10, 18–28 yr), young males ( n = 11, 18–29 yr), and older males ( n = 13, 60–72 yr). Average R-R interval, arterial pressures, and systolic pressure variability at the Mayer wave frequency (0.05–0.15 Hz) did not differ among the three groups. Diastolic pressure Mayer wave variability was similar in young females vs. young males (39 ± 10 vs. 34 ± 5 mmHg2) and lower in older males vs. young males (14 ± 2 mmHg2; P < 0.05). In contrast, muscle sympathetic activity was lowest in young females (892 ± 249 total activity/min) and highest in older males (3,616 ± 528 total activity/min; both P < 0.05 vs. young males: 2,505 ± 285 total activity/min). Across the three groups, arterial pressure Mayer wave variability did not correlate with any index of sympathetic activity. Our results demonstrate that arterial pressure Mayer wave amplitude is not a surrogate measure of vascular sympathetic outflow.

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Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3078387 ◽

2009 ◽

Vol 131 (5) ◽

Cited By ~ 1

Author(s):

M. Madanmohan ◽

S. Pandey ◽

A. Kushari ◽

K. Ramamurthi

Keyword(s):

Heat Release ◽

Phase Angle ◽

Bluff Body ◽

Diffusion Flames ◽

Combustion Process ◽

Low Frequency ◽

Pressure Oscillations ◽

Pipe Length ◽

Entry Length ◽

Low Frequency Oscillations

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

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Amplitude-Limiting Feedback Control of Combustion Instability With a High-Momentum Air Jet

Noise Control and Acoustics ◽

10.1115/imece2004-60568 ◽

2004 ◽

Author(s):

Jong Ho Uhm ◽

Sumanta Acharya

Keyword(s):

Frequency Modulation ◽

Low Frequency ◽

Threshold Level ◽

Acoustic Mode ◽

Effective Control ◽

Pressure Amplitude ◽

High Momentum ◽

Pressure Oscillations ◽

Air Jet ◽

Duty Cycles

A new strategy that integrates low-frequency modulation of a high-momentum air-jet with amplitude feedback is presented for control of combustion oscillations in a swirl-stabilized spray combustor. The oscillations in the combustor of interest are dominated by an acoustic mode (235 Hz) with a low frequency (13 Hz) bulk-mode (of the upstream cavity) superimposed. An effective strategy for control is shown to be achieved through the use of a concept which utilizes low bandwidth modulation of a high-momentum air-jet that penetrates into the regions of positive Rayleigh index. It is shown that with a low frequency modulation (5 Hz) of the high momentum air-jet, the pressure oscillations can be reduced significantly (by a factor of nearly 6). Further improvement in control is achieved with an amplitude-limiting feedback strategy, in which, the valve opening and closing of the control air-jet is driven by the pressure amplitude relative to a specified threshold. The goal of the controller is to maintain pressure oscillations below the pre-set threshold level. With this strategy, the valve frequency and duty cycle are automatically adjusted based on the amplitude of the pressure signal. It is observed that modulation frequencies are typically in the range of 5–30 Hz (although higher frequencies, as high as 130 Hz, are needed occasionally). Duty cycles less than 50% are required for effective control. The amplitude-limiting feedback controller is shown to combine the benefits of low-bandwidth actuation, low-duty cycles, and greater reductions in pressure oscillations.

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Effect of area postrema lesion on low-frequency arterial pressure oscillations in dogs

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1987.253.3.h524 ◽

1987 ◽

Vol 253 (3) ◽

pp. H524-H530 ◽

Cited By ~ 1

Author(s):

F. E. Pollick ◽

K. L. Barnes ◽

C. M. Ferrario

Keyword(s):

Arterial Pressure ◽

Area Postrema ◽

Control Period ◽

Power Spectra ◽

Low Frequency ◽

Experimental Period ◽

Low Frequency Oscillation ◽

Pressure Oscillations ◽

Before And After ◽

Group A

To explore the possibility that chronic inactivation of the area postrema (AP) may alter the frequency distribution of oscillations in blood pressure, the power spectra for mean arterial pressure (MAP) were evaluated in conscious dogs before and after heat coagulation (n = 4) or sham lesions (n = 6) of the AP. No significant changes in MAP were observed in either group of dogs after surgery. Tachycardia was seen in AP-lesioned animals after surgery; no consistent changes in heart rate were found in sham-lesioned dogs. Spectra were averaged to provide a group spectral estimate for the AP-lesioned and sham-lesioned groups, respectively, for each experimental period. In the sham-lesioned group a variance peak was observed at approximately 0.03 Hz both before and after surgery. The same peak was seen in the AP-lesioned group during the control period but disappeared following AP lesion, apparently because a greater proportion of the variance was shifted toward frequencies below 0.03 Hz. In addition, a peak related to respiratory rate was present in both groups before surgery but was selectively abolished by AP lesion. AP lesion also substantially reduced the power associated with frequencies between 0.1 and 0.4 Hz. The use of spectral analysis has allowed us to demonstrate that a low-frequency oscillation of MAP in conscious, resting dogs requires the integrity of the AP and that the 0.1- to 0.4-Hz components of the variability of MAP are attenuated after removal of the AP.(ABSTRACT TRUNCATED AT 250 WORDS)

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