Diagnosis of Mechanism

A chart for vibration diagnosis is presented in Table 19-9. While this is a general criterion or rough guideline for diagnosis of mechanical problems, it can be developed into a very powerful diagnostic system when specific problems and their associated frequency domain vibration spectra are... 

Differentiation of vascular-related liver diseases Detection of alterations regarding the bile ducts Differential diagnosis of mechanical jaundice Assessment of portal hypertension Extent of collateral vessels Unclarified diffuse alterations of the liver parenchyma... 

A more elegant and convincing demonstration of the ylid mechanism is accomplished by tracer studies. In the ylid mechanism, the trimethylamine produced contains one deuterium atom per molecule if the beta hydrogen atom is labelled in the substrate (47), whereas the E2 mechanism yields unlabelled material. Analysis by mass spectroscopy or nuclear magnetic resonance affords a convenient diagnosis of mechanism. Tracer studies confirm the absence of the ylid mechanism for the Hofmann reactions of a series of quaternary ammonium salts (51) , (52) . 

PIatinum(ii).—General. Activation volumes are often useful guides to the diagnosis of mechanism, frequently permitting distinction between associative and dissociative mechanisms and sometimes permitting more subtle distinctions, as between /a and/) or 7a and A alternatives. Reactions of a series of complexes [Pt(dien)X]+ (X = Cl, Br, I, or N3) with a range of incoming nucleophiles Nu (Nu = OH, I", Ng-, NO2 , SCN, or py) follow the usual rate law (1) characteristic of substitution at square-planar species. Activation volumes have been determined, in aqueous solution, both... 

Solvents. Solvent transfer parameters have been used from time to time in diagnosis of mechanisms of organic reactions. Now their first use in an inorganic system has been discussed. Comparisons between kinetic results and solvent transfer activity coefficients for solvolysis of [Cr(NCS)e] in DMSO, DMF, and dimethylacetamide have been considered in terms of a dissociative mechanism. The DMSO results can be accommodated by a dissociative model for the transition state, but those in DMF and dimethylacetamide fit less well. It is interesting to compare these conclusions with, for instance, the dissociative mechanism proposed by the same authors for anation of the [Cr(DMSO)e] + and [Cr(DMF)6] + cations, and the associative mechanism suggested on the basis of the determined activation volume for exchange of DMSO with [Cr(DMSO)e +. ... 

The aims and coverage of this chapter are similar to those of the analogous chapters in Volumes 1 and 3. Reactions in pure, Le. single, solvents and in mixed solvents are dealt with in the first and second sections. The final section includes references to non-classical effects of electrolytes on rates of reactions in aqueous salt solutions. Within each section two aspects of solvent effects on reactivities are covered. The first is the use of reactivity trends in various solvents or solvent mixtures for the diagnosis of mechanisms of substitution. This remains a popular exercise despite the numerous hazards in interpretation. The second is the understanding of reactivities in terms of the established properties of the solvents and their interactions with the initial and transition states. References which merely state kinetic results in non-aqueous or mixed solvents are in general not included. Insofar as such references concentrate on the compound rather than the solvent they are more appropriately mentioned elsewhere in this Report. 

The use of activation volumes in the diagnosis of mechanism has continued to provide much valuable information. Activation volumes for substitution at octahedral complexes have formed the subject of a well-referenced review,in which the importance both of intrinsic and of solvation contributions is recognized. The topics of most relevance to this chapter include isomerization and racemization reactions of cobalt(III) complexes, aquation of cobalt(III) and of iron(II) complexes, and base hydrolysis of cobalt(III) complexes. Merbach s continuing investigations into the effects of pressure on rates of solvent exchange at 2-h and 3+ transition metal cations, while not being always strictly... 

The correlation of reaction rates with dielectric properties is a well-established approach to the diagnosis of mechanism. Most recent examples of this deal with mixed aqueous solvents (see below), but logarithms of second-order rate constants for oxidative addition of methyl iodide or of oxygen to rraw-[IrCl(CO)(PPh3)2] have been found to correlate with the dielectric constant function (D —l)/(2i) + 1). However, the correlation of these rate constants with the empirical Ex values for the respective solvents, mentioned above, is better. 

If the activity coefficient term on the right of equation (13) stays constant with changing medium, then a linear correlation of log kx with -H0 should follow for the A-l mechanism. The above diagnosis of the A-l mechanism is known as the Zucker-Hammett hypothesis3. 

While the ECG is an invaluable tool for the observation of heart rate and rhythm, as well as for the diagnosis of conduction abnormalities, ischaemia, and infarcts, its detailed interpretation is not without pitfalls. One reason for this is that different changes in cardiac cellular behaviour may give rise to very similar effects on the ECG. This makes it difficult to draw conclusions from a patient s ECG to the underlying (sub-)cellular mechanisms. This issue is usually referred to as the inverse problem. ... 

Shafqat S, Kelly PJ, Furie KL. Holier monitoring in diagnosis of stroke mechanism. Inter Med J 2004 34 305-309. 

C. H. Giles, T. H. MacEwan, S. N. Natchwa and D. Smith, Studies in Adsorption, Part XI A System of Classification of Solution Adsorption Isotherms and its Use in Diagnosis of Adsorption Mechanism and its Measurement of Specific Surface Area of Solids, J. Chem. Soc., p. 3973,1960. 

The patient has been transferred from the CT scanner to the surgical intensive care unit for mechanical ventilation, blood pressure support, and surgical evaluation. A diagnosis of acute pancreatitis with pancreatic necrosis is made. 

The exact mechanism of action of these drugs is unknown, but both agents are fairly well tolerated. Hydroxychloroquine or sulfasalazine may be initiated on diagnosis of mild disease. Owing to their slow onset of action, each drug must be given at... 

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