Critical-volume hypothesis

Membrane conformational changes are observed on exposure to anesthetics, further supporting the importance of physical interactions that lead to perturbation of membrane macromolecules. For example, exposure of membranes to clinically relevant concentrations of anesthetics causes membranes to expand beyond a critical volume (critical volume hypothesis) associated with normal cellular function. Additionally, membrane structure becomes disorganized, so that the insertion of anesthetic molecules into the lipid membrane causes an increase in the mobility of the fatty acid chains in the phospholipid bilayer (membrane fluidization theory) or prevent the interconversion of membrane lipids from a gel to a liquid form, a process that is assumed necessary for normal neuronal function (lateral phase separation hypothesis). 

For example, EPA has developed safe standards for the toxicity of many emissions. Relative safety can then he defined in terms of safe emission levels of each. A method of accounting known as the critical volume method is used to estimate the volume of ambient air or water that would he required to dilute contaminants to acceptable safety standards. Athena EIE calculates and reports indices based on the worst offender—that is, the substance requiring the largest volume of air and water to achieve dilution to acceptable levels. 4 The hypothesis is that the same volume of air or water can contain a number of pollutants. 

This explains why there is no principal difference between the raw (doped) polyaniline and its dispersions, in whatever medium. The differences to be observed were only of quantitative, and not of qualitative nature, at least not in the direction, which was expected by most of those who still favor the fibril hypothesis. They believe that the chain is the primary active unit, which could also be dissolved and is believed to have conductive properties, even as a single chain. If that were the case, a dispersed (i.e., mechanically separated, in case of assumed fibrillar morphology, even destroyed) conductive polymer would not have the same conductivity and especially not the same transport properties in the dispersion medium above the critical volume concentration or after deposition from a low molecular weight liquid medium and drying. 

In 1954, Mullins, in a modification to the Overton hypothesis, proposed that besides the membrane concentration of the anesthetic, its volume, expressed as its volume fraction (mole fraction X partial molal volume), is important. This reasoning implied that the anesthetic, due to its solubility properties, expands the cell membrane, and that anesthesia occurs when a critical expansion value is reached, at about 0.3-0.5% of the original volume. 

IUPAC defines the lower limit of mesopores as 2 nm [1] which was considered as the limit below which the adsorption will occur by volume filling. However, in our recent article, based on the tensile stress hypothesis, we have shown that this limit is different than IUPAC limit. Using the mechanical stability criterion for the cylindrical meniscus (during adsorption), the critical size is obtained from... 

The model mouth was developed as part of the doctoral program of Saskia van Ruth at the Wageningen University in the Netherlands between 1992 and 1995. The hypothesis was that only those volatile compounds released under mouth conditions are relevant for aroma analysis. The volume of the mouth, temperature of the mouth, mastication, and salivation were thought to be critical parameters. Those pa-... 

There were other, less theoretical but no less persuasive objections. Some substances, such as ammonium chloride, dissociate in the vapor phase. That is, a single particle of vapor turns into two or more particles. Two or more particles occupy two or more times the volume that one particle does. That wreaks havoc with measurements of gas volumes and provides empirical evidence that fails to obey Gay-Lussac s law, making apparent nonsense of Avogadro s hypothesis. It was not until the phenomenon of dissociation was understood, and interpreted in terms of reaction kinetics, that this objection could be countered. Similar objections were raised against Dalton s laws of combining proportions, which work only for compounds of fixed composition. Metallic alloys and salt solutions, to take two of the most obvious exceptions, do seem to share some of the characteristics of chemical compounds, but they do not fit Daltons laws. The simplest way to avoid that objection was to say that only those substances that did fit Dalton s laws were true chemical compounds, but that is a circular argument that did not convince critics. 

As demonstrated throughout this volume, catalyst development is much more than just plant testing. Rejecting a hypothesis because of poor plant performance and not determining whether the catalyst was improperly prepared or treated can inhibit a breakthrough. Similarly, characterizing only the catalysts that give excellent performance so as to understand the system may cause researchers to miss the critical variable. 

If M=no. of molecules in unit volume, =const., pj/n=const., and this. holds also for the total pressurep—pe+pi. This is an application of Avogadro s hypothesis to liquids. Herz replaced Tb in Longinescu s equation by the critical temperature Te, and the density at 0°C. by the critical density Qc, finding... 

Ti-wadeite, but structural similarity in the case of Zr-wadeite. These differences/ similarities influence the energetics of nucleation, with the result that it is more difficult to form a critical nucleus of Ti-wadeite. Vessal and Dickinson (1994) have undertaken both constant volume and constant pressure molecular dynamics simulations to test this hypothesis. 

The MDA for a radioanalytical measurement process is defined as an estimate of the smallest true activity (or massic activity or volumic activity) in a sample with a specified probability 1-/3 that the net count rate will exceed the critical value, to conclude correctly that the sample contains the analyte. The probability /3 of a Type II error is defined as the error of failing to reject the null hypothesis when it is actually false. A Type II error is also called a false negative or false acceptance. It is common to choose a = p = 0.05, but other values of a and /3 can be selected. 

A comparison of the volume and enthalpy data substantiates this hypothesis. The second step of volume reduction is clearly related to the development of the specific heat peaks above Tg. The overshoots of enthalpy below the equilibrium value are moved from a lower temperature to a higher one if the Initial volume is decreased below a critical value. 

Hence, the results quoted above demonstrated clearly, that the transition of transesterification reaction kinetic curves from an autodecelerated regime to an autoaccelerated one was defined by a structural factor, namely, by reaching of fiactal-like molecule (reaction product) fractal dimension critical value, at which the number of reactive sites in volume and on the surface of molecule became equal. Within the fiamewoik of the fractal analysis the analytic relationship is obtained, confirming this hypothesis. 

Buzhinsky s hypothesis [384] is more universal. According to this, the failure condition occurs when the energy of deformation and a part of the energy of volume change reach definite critical values, being a linear function of a spheric d tensor. The design equation for the volumetric stressed state is... 

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