The Lateral Pressure Profile

Recently, the lateral pressure profile in a bilayer has been discussed in the context of partitioning of proteins in bilayers [100]. It is argued that this pressure profile can be used to rationalise the effects of additives on the membrane properties. Here a note of caution is necessary. It is not possible to define the lateral pressure profile through a bilayer unambiguously. The reason for this problem is that the local pressure not only has contributions that come from the local densities (this property is uniquely defined), but also from 

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R. S. Cantor, The lateral pressure profile in membranes a physical mechanism of general... 

Lateral pressure profile Measure of several counteracting forces exerted at different depths across the bilayer. 

Figure 16.3 Schematic representation of a lateral pressure profile in a vesicular bilayer. Only one monolayer is shown here, the same profile applies for the other monolayer. The lateral pressure n depends on the depth (Z) in the monolayer. From M. Kuiper, Azobenzene-substituted Phosphate Amphiphiles Effect of Ught-induced trans-cis Isomerisation on Vesicular Properties and the Channel Protein MscL, Ph. D. Thesis, University of Groningen, p 2, 2005...

For later use in heat and material balance calculations, plot these temperature points versus tray number on the tray-pressure profile. 

If a stroke patient receives intravenous (IV) thrombolysis, care often continues in the ED until the patient arrives in the ICU. Close monitoring must continue during this time, with special attention to the blood pressure. The blood pressure is most commonly checked via an arm cuff, since the placement of invasive lines (e.g., arterial catheterization) is relatively contraindicated once the patient has received intravenous thrombolysis (unless the situation is emergent and mandates such treatment). The systolic pressure must not exceed 185 mm Hg, and the diastolic pressure limit should be 110 mm Hg. Should the blood pressure exceed these limits, IV antihypertensive agents should be administered. IV pushes of labetolol (10-20 mg over 1-2 minutes) may be effective, but if patients are refractory to these initial measures then a continuous infusion of labetolol (0.5-2.0 mg/minute), nicardipine (5-15 mg/hour), or nitro-prusside (0.25-10 mg/kg/minute) may be necessary to keep the patient s blood pressure within the range. There will be a more detailed discussion of these antihypertensive agents, including their side effect profiles, later in this chapter. 

Comparison of McMillen s results with those for Newtonian fluids is instructive in two important respects. First, the non-Newtonian entrance loss was felt 40 diameters downstream from the entrance. Since the Reynolds number of the flow was only 50, the entrance loss for a Newtonian fluid (P3) would have only been felt downstream for a distance of 3 diameters. Second, comparison of the foregoing formula with the usually recommended procedure for Newtonian fluids (P3) indicates that the non-Newtonian pressure drop was approximately six times as great as that for Newtonian fluids under the same conditions. This figure was checked reasonably closely by the later work of Mooney and Black (M16), who found entrance losses of up to seven times those for comparable Newtonian fluids. Since this entrance loss (P3) is due to the energy required to set up the velocity profile, it might appear logical that... 

Prescott, Hudson, Foner, and Avery (60) extended the mass-spectrographic technique to the study of composition profiles across a low-pressure, propane-air flame under somewhat lean conditions. The appearance and disappearance of hydrogen, carbon monoxide, ethylene, and acetylene in the flame were demonstrated clearly. The proportion of acetylene was not high. Nonetheless, it is evident that the formation of acetylene is not just a result of pyrolysis of excess hydrocarbon by heat released in combustion of part of the gas. It is a result of reactions which must occur to some extent in all hydrocarbon combustion, but which would not be observable except by special techniques, or under conditions—such as rich flames or cool flames—where the later reactions of acetylene can l>e minimized. 

Figure 6.22 depicts schematically the flow configuration. Two identical rolls of radii R rotate in opposite directions with frequency of rotation N. The minimum gap between the rolls is 2H0. We assume that the polymer is uniformly distributed laterally over the roll width W. At a certain axial (upstream) location x = X2 (X2 < 0), the rolls come into contact with the polymeric melt, and start biting onto it. At a certain axial (downstream) location x A), the polymeric melt detaches itself from one of the rolls. Pressure, which is assumed to be atmospheric at X2, rises with x and reaches a maximum upstream of the minimum gap location (recall the foregoing discussion on the pressure profile between non-parallel plates), then drops back to atmospheric pressure at X. The pressure thus generated between the rolls creates significant separating forces on the rolls. The location of points A i and X2 depends on roll radius, gap clearance, and the total volume of polymer on the rolls in roll mills or the volumetric flow rate in calenders. 

Equation 6.4-11 implies that the pressure gradient is zero not only at x = X but also at x = X, where h also equals H, and where, as we shall see later, the pressure profile exhibits maximum. The pressure profile is obtained by integrating Eq. 6.4-11 with the boundary condition P(Xi) = 0. First, however, we must find a functional relationship between h and x. From plane geometry we get the following relationship... 

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