Studies Comparing Results

There have been many more basis sets developed, but the list above enumerates the most widely used ones. Some of these sets were the work of many different authors and later improved. This sometimes results in different programs using the same name for two slightly different sets, ft is also possible to combine basis sets or modify them, which can result in either poor or excellent results, depending on how expertly it is done. How to customize basis sets is discussed in Chapter 28. 

Some of the basis sets discussed here are used more often than others. The STO-3G set is the most widely used minimal basis set. The Pople sets, particularly, 3 21G, 6 31G, and 6—311G, with the extra functions described previously are widely used for quantitative results, particularly for organic molecules. The correlation consistent sets have been most widely used in recent years for high-accuracy calculations. The CBS and G2 methods are becoming popular for very-high-accuracy results. The Wachters and Hay sets are popular for transition metals. The core potential sets, particularly Hay-Wadt, LANL2DZ, Dolg, and SBKJC, are used for heavy elements, Rb and heavier. 

Experience has shown that is better to obtain basis sets in electronic form than paper form since even slight errors in transposition will affect the calculation results. Some basis sets are included with most computer programs that require them. There is also a form page on the Web that allows a user to choose a basis and specify a format consistent with the input of several popular computational chemistry programs at http //www.emsl.pnl.gov 2080/forms/basisform.htm. The basis set is then sent to the user in the form of an e-mail message. 

For many projects, a basis set cannot be chosen based purely on the general rules of thumb listed above. There are a number of places to obtain a much more quantitative comparison of basis sets. The paper in which a basis set is published often contains the results of test calculations that give an indication of the accuracy of results. Several books, listed in the references below, contain extensive tabulations of results for various methods and basis sets. Every year, a bibliography of all computational chemistry papers published in the previous 

References to the individual basis sets have not been included here. Most can be readily found in the review articles. 

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No standardized approach has been devised, and again only conclusions drawn from studies comparing results within the same subject can be used with any confidence. 

In a few studies comparing results across countries (Bodur and Filiz 2009 Wagner et al. 2013), the general conclusion seems to be that the US tends to score higher than other countries on most of the survey s composites. However, one study in Taiwan found that staff results were higher than the US on many of the composites (Chen et al. 2010). 

Another issue of regioselectivity arises with meta-substituted arylhydrazones from which either 4- or 6-substitutcd indoles can be formed. Robinson has tabulated extensive data on this point[9]. A study comparing regioselectivity of cyclization as catalysed by HCl/EtOH and ZnClj was carried out for several m-substituted arylhydrazones of diethyl ketone[10]. The results given in Table 7.1 show some dependence on catalyst but mixtures are obtained under all conditions studied. 

Section 4.1 briefly describes some of the commonly employed experimental tools and procedures. Chaudhury et al., Israelachvili et al. and Tirrell et al. employed contact mechanics based approach to estimate surface energies of different self-assembled monolayers and polymers. In these studies, the results of these measurements were compared to the results of contact angle measurements. These measurements are reviewed in Section 4.2. The JKR type measurements are discussed in Section 4.2.1, and the measurements done using the surface forces apparatus (SFA) are reviewed in Section 4.2.2. 

Panagiotopoulos et al. [16] studied only a few ideal LJ mixtures, since their main objective was only to demonstrate the accuracy of the method. Murad et al. [17] have recently studied a wide range of ideal and nonideal LJ mixtures, and compared results obtained for osmotic pressure with the van t Hoff [17a] and other equations. Results for a wide range of other properties such as solvent exchange, chemical potentials and activity coefficients [18] were compared with the van der Waals 1 (vdWl) fluid approximation [19]. The vdWl theory replaces the mixture by one fictitious pure liquid with judiciously chosen potential parameters. It is defined for potentials with only two parameters, see Ref. 19. A summary of their most important conclusions include ... 

A study comparing the half-lives for hydrolysis of a variety of esters of 5 -0-acyl-uridines gave the following results ... 

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

Mooney Viscometer studies at 100°C and 120°C show lower viscosity of the Al-hlled gums. Lower viscosity compounds require less energy input for extrusion. Comparative results on the dynamic mechanical properties, measured using a rubber process analyzer (RPA), show that at the... 

The best-studied system is Pb(CHj)4. This can easily be prepared using 22-yr Pb, which decays to °Bi by branched jS-emission—maximum j3-energies 15 keV (81%) and 61 keV (19%). The crossover y-transition is 14% converted. The results of various studies 22, 21) show retention of bonding in some 70-80% of the °Bi formed in the gas phase, and a similarly high yield in dilute solutions. Curiously, the yield of °Bi(CH3)4 fell to 18% at a mole fraction of 0.05 and rose again on further dilution (21). Adloff (2) has studied the f decay of PbPh4, with comparable results. 

Even though recent progress in hardware and software development has made it possible to study quite large molecules, systems of the size considered here do not lend themselves to studies with any ab initio technique. The Hartree-Fock method has the advantage of being size consistent, which Is a necessity for this type of study when results for molecules of vastly different size are to be compared. In addition, the method is technically and economically feasible for these large systems. 

Comparative Toxicokinetics. In humans, the targets for trichloroethylene toxicity are the liver, kidney, cardiovascular system, and nervous system. Experimental animal studies support this conclusion, although the susceptibilities of some targets, such as the liver, appear to differ between rats and mice. The fact that these two species could exhibit such different effects allows us to question which species is an appropriate model for humans. A similar situation occurred in the cancer studies, where results in rats and mice had different outcomes. The critical issue appears to be differences in metabolism of trichloroethylene across species (Andersen et al. 1980 Buben and O Flaherty 1985 Filser and Bolt 1979 Prout et al. 1985 Stott et al. 1982). Further studies relating the metabolism of humans to those of rats and mice are needed to confirm the basis for differences in species and sex susceptibility to trichloroethylene s toxic effects and in estimating human heath effects from animal data. Development and validation of PBPK models is one approach to interspecies comparisons of data. 

A number of other studies of AB cements have used X-ray diffraction. For example, Sorrell (1977) and Sorrell Armstrong (1976) employed the technique in the study of oxychloride cements formed in aqueous solution by interaction of oxides and chlorides of either zinc or magnesium. Individual phases were identified, again using Cu K radiation, this time comparing results with those previously obtained for pure compounds. Results from these two studies are described in detail in Sections 7.2 and 7.3 respectively. 

This chapter will review some recently completed studies on the long-term effects of MDMA in nonhuman primates. The goals of these studies were to (1) determine if the neurotoxic effects of MDMA, which have been well documented in the rodent (see below), generalize to the primate (2) compare the relative sensitivity of primates and rodents to the neurotoxic effects of MDMA (3) ascertain if the toxic effects of MDMA in the monkey are restricted to nerve fibers (as they are in the rat), or if they involve cell bodies as well (4) evaluate how closely toxic doses of MDMA in the monkey approximate those used by humans and (5) examine whether 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF) can be used to detect MDMA-induced serotonergic damage in the CNS of primates. Before presenting the results of these studies, previous results in the... 

The extraction efficiencies using a blender and a shaker were compared and both methods gave similar results. A corn sample treated with radiolabeled carfentrazone-ethyl and collected from a metabolism study was used for comparison. Multiple samples can be extracted simultaneously if extraction is performed by shaking. In addition, since the extraction procedures in the residue study closely followed the extraction scheme in the metabolism study, the resulting extraction efficiencies from both studies were almost identical. 

First we compare the results for clinopyroxene which was the only phase common to both of these studies. The results from the pure H2O experiments are somewhat inconsistent. Keppler (1996) found that Th was more mobile than U, contrary to all observations, whereas Brenan et al. (1995) found the reverse. However, subduction zone fluids are almost certain to contain solutes like Na and Cl derived from seawater and Keppler and Wyllie (1990) showed that the solubility of U, but not Th, is enhanced by the presence of Cl, although the salinities used by Keppler (1996) were very high. Both Brenan et al. (1995) and Keppler (1996) found that U was an order of magnitude more fluid mobile than Th when NaCl was present, although, in the Brenan et al. (1995) experiments, the absolute D "opyroxene/flu.d lower in the presence of NaCl than... 

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