Image Leaks: Dierk Schmidt’s Critical Opening of a Permeable Medium

2012 ◽  
Vol 29 ◽  
pp. 123-130
Author(s):  
Christian Höller
Keyword(s):  
Critical Opening

Determination of the critical opening of a concentrator of finite radius from a stress-strain curve

1986 ◽  
Vol 18 (5) ◽  
pp. 664-668
Author(s):  
M. V. Shakhmatov ◽  
V. V. Erofeev ◽  
V. A. Lupin ◽  
A. A. Ostsemin
Keyword(s):  
Strain Curve ◽  
Stress Strain Curve ◽  
Finite Radius ◽  
Stress Strain ◽  
Critical Opening

scholarly journals Modeling the dynamics of recruitment and derecruitment in mice with acute lung injury

2008 ◽  
Vol 105 (6) ◽  
pp. 1813-1821 ◽  
Author(s):  
Christopher B. Massa ◽  
Gilman B. Allen ◽  
Jason H. T. Bates
Keyword(s):  
Acute Lung Injury ◽  
Lung Injury ◽  
Lung Recruitment ◽  
Mechanically Ventilated ◽  
Critical Opening ◽  
Injured Lung ◽  
Order Of Magnitude ◽  
Opening And Closing ◽  
Air Liquid Interface ◽  
Insight Into

Lung recruitment and derecruitment contribute significantly to variations in the elastance of the respiratory system during mechanical ventilation. However, the decreases in elastance that occur with deep inflation are transient, especially in acute lung injury. Bates and Irvin ( 8 ) proposed a model of the lung that recreates time-varying changes in elastance as a result of progressive recruitment and derecruitment of lung units. The model is characterized by distributions of critical opening and closing pressures throughout the lung and by distributions of speeds with which the processes of opening and closing take place once the critical pressures have been achieved. In the present study, we adapted this model to represent a mechanically ventilated mouse. We fit the model to data collected in a previous study from control mice and mice in various stages of acid-induced acute lung injury ( 3 ). Excellent fits to the data were obtained when the normally distributed critical opening pressures were about 5 cmH2O above the closing pressures and when the hyperbolically distributed opening velocities were about an order of magnitude greater than the closing velocities. We also found that, compared with controls, the injured mice had markedly increased opening and closing pressures but no change in the velocities, suggesting that the key biophysical change wrought by acid injury is dysfunction of surface tension at the air-liquid interface. Our computational model of lung recruitment and derecruitment dynamics is thus capable of accurately mimicking data from mice with acute lung injury and may provide insight into the altered biophysics of the injured lung.

The effect of repeated cold exposure of the hand on the reactivity of digital vessels

1969 ◽  
Vol 47 (3) ◽  
pp. 261-265 ◽  
Author(s):  
Peter Gaskell ◽  
Kathleen L. Long
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Cold Exposure ◽  
Opening Pressure ◽  
Relative Flow Rate ◽  
Opposite Hand ◽  
Critical Opening ◽  
Before And After ◽  
Relative Change ◽  
Relative Flow

One hand of each of 10 subjects was immersed in stirred water at 4 °C for 1 h per day, 5 days per week, for 3 weeks, to produce local acclimatization to cold. The opposite hand was immersed at the same time in water at 32 °C. The reactivity of digital vessels in a finger of each hand was measured as the increase in the critical opening pressure of the vessels in response to an intravenous infusion of noradrenaline at 2 and 5 μg/min. The reactivity of digital vessels in the test hand was compared with that in the control hand both before and after the repeated cold exposure of the test hand to see whether the cold exposure altered the reactivity of vessels in the test hand relative to that in the control hand. No evidence of such a relative change was obtained. Resting blood flow at 21 and 32 °C in the test hand was compared with that in the control hand both before and after the repeated cold exposure. No change in the relative flow rate in the two hands was observed as a result of the cold exposure. Roentgen studies of the hands did not reveal any effect of the repeated cold exposure on the mineralization of the bones of the hands.

Critical opening pressure and reactivity of tail vessels in conscious hypertensive rats

1976 ◽  
Vol 54 (3) ◽  
pp. 314-321
Author(s):  
A. C. Darke ◽  
P. G. Nair ◽  
P. Gaskell
Keyword(s):  
Blood Pressure ◽  
Renovascular Hypertension ◽  
Vascular Reactivity ◽  
Experimental Hypertension ◽  
Hypertensive Rats ◽  
Opening Pressure ◽  
Critical Opening ◽  
Resistance Vessels ◽  
Before And After ◽  
Desoxycorticosterone Acetate

The possible role of increased vascular reactivity in the mechanism of experimental hypertension was studied by measurements of the critical opening pressure (COP) of tail vessels in conscious rats. In hypertension induced by administration of desoxycorticosterone acetate (DOCA) and replacement of the drinking water by 1% NaCl solution (DOCA–NaCl hypertension), and in one-kidney Goldblatt renovascular hypertension, the raised level of blood pressure was associated with an increased COP of the tail vessels when measured both before and after ganglionic blockade. In rats treated with either DOCA alone or 1% NaCl alone there was no significant increase in systolic blood pressure (SBP) or COP relative to the corresponding controls. In all four experimental series intravenous infusion of angiotensin or norepinephrine in conscious ganglion-blocked rats produced dose-dependent increases in SBP and COP. In DOCA–NaCl hypertensive rats but not in renovascular hypertensives, nor in rats treated with DOCA alone or 1% NaCl alone, the increase in COP for a given increment in dose of angiotensin or norepinephrine was significantly greater than in the control rats. It is concluded that in DOCA–NaCl hypertension there is a true increase in the reactivity of the smooth muscle of the resistance vessels to angiotensin and norepinephrine. In renovascular hypertension this is not the case and other factors must therefore be involved in causing the increased blood pressure and COP.

(Re)Mapping Mother Earth: A Geographical Perspective on Environmental Feminisms

1993 ◽  
Vol 11 (4) ◽  
pp. 379-394 ◽  
Author(s):  
C Nesmith ◽  
S A Radcliffe
Keyword(s):  
Environmental Issues ◽  
Global Development ◽  
Critical Engagement ◽  
Critical Opening ◽  
Geographical Perspective ◽  
And Gender ◽  
Mother Earth ◽  
Further Development

The emerging set of discourses around women, nature, and the environment can be identified with the umbrella term environmental or ecological feminisms. In developing a geographical approach to environmental issues, a critical engagement with the questions raised by environmental feminisms is suggested. After a brief introduction to the principles of environmental feminisms for a geographical audience, three broad fields for future geographical work are outlined, namely: nature, culture, and gender; gendered relations of global development and environments; and gendered landscapes and identities. In particular it is argued that feminist and cultural geographical writing provides a critical opening for the further development of environmental feminist approaches.

scholarly journals The influence of channel width and inflow rate on the critical opening-size of granular flow in two-dimensional channels

2003 ◽  
Vol 52 (4) ◽  
pp. 875
Author(s):  
Xu Guang-Lei ◽  
Hu Guo-Qi ◽  
Zhang Xun-Sheng ◽  
Bao De-Song ◽  
Chen Wei ◽  
...  
Keyword(s):  
Granular Flow ◽  
Channel Width ◽  
Two Dimensional ◽  
Inflow Rate ◽  
Critical Opening

The Influence of Lysine-8-vasopressin, Oxytocin, and Adrenaline on Vascular Smooth Muscle in the Human Finger

1973 ◽  
Vol 51 (4) ◽  
pp. 284-290 ◽  
Author(s):  
Peter Gaskell
Keyword(s):  
Blood Pressure ◽  
Smooth Muscle ◽  
Vascular Resistance ◽  
Young Women ◽  
Systemic Blood Pressure ◽  
Apparent Effect ◽  
Opening Pressure ◽  
Systemic Blood ◽  
Critical Opening ◽  
Human Finger

Lysine-8-vasopressin, oxytocin, or adrenaline was administered by intravenous infusion to young women, and their effect on the critical opening pressure (COP) of digital vessels, vascular resistance in the finger, and systemic blood pressure was measured. All doses of lysine-8-vasopressin between 0.001 and 0.08 U/min increased the COP of digital vessels but only the largest dose raised blood pressure slightly. A dose of 0.04 U/min had little if any effect on overall vascular resistance in the finger. Nevertheless the smallest dose given (0.001 U/min), which is within the physiological range of secretion rate by the pituitary gland, increased the COP of digital vessels substantially. Oxytocin at doses of 5–160 mU/min had no apparent effect on COP or vascular resistance of digital vessels or on blood pressure. Adrenaline at 4 μg/min increased the COP of digital vessels substantially. The latter observation is consistent with the absence of β receptors in vessels of the skin of the fingers.

THE MEASUREMENT OF BLOOD PRESSURE, THE CRITICAL OPENING PRESSURE, AND THE CRITICAL CLOSING PRESSURE OF DIGITAL VESSELS UNDER VARIOUS CIRCUMSTANCES

1965 ◽  
Vol 43 (6) ◽  
pp. 979-993 ◽  
Author(s):  
Peter Gaskell
Keyword(s):  
Blood Pressure ◽  
Nerve Block ◽  
Spectroscopic Method ◽  
Spectroscopic Technique ◽  
Opening Pressure ◽  
Small Vessels ◽  
Critical Opening ◽  
Critical Closing Pressure ◽  
Digital Nerve Block ◽  
Closing Pressure

A spectroscopic technique for the estimation of the critical opening pressure (COP) or critical closing pressure (CCP) of small vessels in the finger is described. The spectroscopic method of estimation of the systolic blood pressure, which is part of the technique and which involves the detection of reappearance of oxyhemoglobin absorption bands in the spectrum of reflected light from the skin distal to a blood pressure cuff that is slowly deflated, was compared to the auscultatory technique in 38 subjects on 53 occasions and gave the same results. The COP of small vessels in the finger estimated by the spectroscopic technique was decreased by body heating and by digital nerve block as had been previously shown by the microscopical method. The COP of vessels in the finger after digital nerve block in 43 normotensive young women between the ages of 18 and 22 years ranged from 2 to 19 mm Hg with a mean of 9.5 ± 4.6 (S.D.) mm Hg. When the COP was estimated in many of the same subjects after preparation as for measurement of the basal metabolic rate, in most cases it fell within the range of values obtained after nerve block. The COP in 26 subjects ranged from 1 to 22 mm Hg with a mean of 10.9 ± 5.0 (S.D.). The values for CCP estimated by the spectroscopic method in 81 individuals were not significantly different from those for COP estimated on the same occasion.

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