Experimental systems error structure

Laane has used MM2 to calculate the puckering in silacyclopent-2-ene and silacyclopent-3-ene. " " MM2 correctly predicts the planarity of sila-cyclopent-3-ene but incorrectly calls for silacyclopent-2-ene to be puckered. Laane attributes the error to an interaction between the silicon and the carbon TT system.The original MM2 parameters were modified such that the calculated minimum energy structure of silacyclopent-2-ene is consonant with the experimentally observed planar structure. 

By definition, the experimental unit is the smallest unit randomly allocated to a distinct level of a treatment factor. Note that if there is no randomization, there is no experimental unit and (in nearly all cases) no experiment. Although it is possible to perform experiments without randomization, it is difficult to do well, and risky unless the experimental system is very well understood (7). Randomization is important for several reasons. Randomization changes the sources of bias into sources of variation in general, a noisy assay is better than a biased assay. Further, randomization allows estimates of variation to represent variation in the population this in turn justifies statistical inference (standard errors, confidence intervals, etc.). A common practice in cell-culture bioassay is to rotate among a small collection of layouts rather than use random allocation. Whereas rotation among a collection of layouts is certainly better than a fixed layout, it is both possible and practical to use carefully structured randomization on a routine basis, particularly when using a robot. 

However, we have endless results that r = 1 in the vast majority of the experimental systems. Thus the wide applicability of the Frumkin isotherm is an indirect evidence that r = 1. Indeed, if we adopt r = 1, assume an adsorbed layer with a two-dimensional lattice structure and a random distribution of the adsorbed molecules, then statistical mechanics readily yields the Frumkin isotherm, Eq. (1). ° A direct indication that r is close to unity comes from the thermodynamic method we have proposed for the determination of This method is applicable to monolayers composed of solvent and constant orientated solute molecules. These conditions can be safely detected experimentally and if they are fulfilled, r can be obtained from surface pressure data by means of two extrapolations. Due to these extrapolations the method is extremely sensitive to experimental errors and for this reason it is applicable only to air / solution and liquid / liquid interfaces. All applications of this method gave the value r = 1 0.2, despite the considerable differences in the size of the adsorbates used. ... 

Recently we reported EXAFS results on bimetallic clusters of iridium and rhodium, supported on silica and on alumina (15). The components of this system both possess the fee structure in Efie metallic state, as do the components of the platinum-iridium system. The nearest neighbor interatomic distances in metallic iridium and rhodium are not very different (2.714A vs. 2.690A). From the results of the EXAFS measurements, we concluded that the interatomic distances corresponding to the various atomic pairs (i.e., iridium-iridium, rhodium-rhodium, and iridium-rhodium) in the clusters supported on either silica or alumina were equal within experimental error. Since the Interatomic distances of the pure metals differ by only 0.024A, the conclusion is not surprising. 

In the molecule of 4-methylene-3-borahomoadamantane derivative 79, the structure of which was determined by X-ray analysis, the six carbon atoms of the triene system, the two boron and two silicon atoms all lie in one plane within experimental error (mean deviation 1.4 pm). The boron atoms deviate from the trigonal-planar geometry, since the sum of bond angles around the atoms is only 355.8° instead of 360°, as usually encountered in triorganoboranes. Considerable distortions of the bond angles at the terminal C-C double bond occurs in the vicinity of the boron atoms B-C(4)-C(ll) 130.60(19)° and B-C(4)-C(5) 107.38(17)° <2002CEJ1537>. 

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