Cluster sampling

Cluster sampling methods, which first identify a set of compound clusters, followed by the selection of several compounds from each cluster [73]. Grid-based sampling, which places all the compounds into a low-dimensional descriptor space divided into many cells and then chooses a few compounds from each cell [74]. 

It is now fairly well established that atomic and few-atom cluster arrays can be generated and trapped in weakly interacting matrices 91), and subsequently scrutinized by various forms of spectroscopy. Up to this time, IR-Raman-UV-visible absorption and emission-esr-MCD-EXAFS-Mossbauer methods have been successfully applied to matrix-cluster samples. It is self-evident that an understanding of the methods of generating and identifying these species is a prerequisite for... 

The next available full-shell cluster that has been investigated by MoBbauer spectroscopy was the four-shell cluster Pt309phen 3603o+io (phen = 4,7-p-C6H4S03Na substituted 1,10-phenanthroline) [17]. Its inner core consists of 147 atoms. However, since platinum is not MoBbauer-active, the cluster sample had to be irradiated with thermal neutrons to transfer a fraction of the Pt... 

At the other extreme, although very large maps offer the maximum opportunity for samples to spread out, biggest is not always best, as we noted with artificial neural networks. The aim of the SOM is both to cluster samples and... 

Table 1. The observed cluster sample reddening from [5], metallicities, abundance ratios and heliocentric radial velocities from [7], [8], [9]...

Fig. 1. Mean Li abundance as a function of age. Li abundances are in the usual notation log n(Li)= N(Li)/N(H)+12. Different symbols indicate stars in different mass bins, namely 1 0.02 M0 (circles), 1.05 0.02 M0 (squares) and 1.1 0.02 M0 (triangles). The Sun is also shown. The horizontal line denotes the initial log n(Li). The following clusters have been considered 120 Myr Pleiades 600 Myr Hyades 2 Gyr IC 4651, NGC 3680, NGC 752 4.5 Gyr M 67 (only the upper envelope of the Li vs. Teff distribution -see text) 7 Gyr NGC 188. The cluster samples have all been analysed with the same method. Error bars correspond to lcr deviations from the mean.

Cluster emission, 27 305 Cluster glass transitions, 74 469 Clustering techniques, 6 16-17 Cluster sampling, 26 1018 C-Methylcalix[4]resorcinarene, 74 165 CMOS image sensors, fabrication... 

Co2(CO)g has been used to obtain encapsulated cobalt clusters in Y-faujasite, which have been used as model catalysts for methane homologation [152]. The gas phase adsorption of Co2(CO)8 under N2 rendered predominately encaged Co4(CO)i2 species whereas Co,s(CO)iis was obtained when the impregnation of Co2(CO)8 was carried out under a CO/H2 atmosphere [152, 155], Samples were oxidized at 80°C, subsequently reduced at 400 °C and then structurally characterized by EXAFS. Clusters of two and three cobalt atoms were formed from encaged Co4(CO)i2 and COis(CO)iis, respectively. Higher methane conversion and selectivity to C2+ products in the CH4 homologation reaction have been obtained for the two atoms-size cluster sample the results were discussed using a DFT model [152]. 

If a point sampled happened to be an active point, it is counted as an individual hit. Thus, the number of active points sampled by a particular method is defined as the individual hit rate obtained by that method. On the other hand, in order to characterize the representativeness of a sampling, we define the concept of a cluster hit as follows. If one or more points are sampled from an active cluster, we define that this active cluster is sampled and counted as a cluster hit. Therefore, the number of active clusters sampled by a particular method is defined as the cluster hit rate obtained by that method. 

Results of Curve-Fitting Analysis of Rh K-Edge EXAFS Data Obtained at 300 K for NaY-Entrapped Rh Cluster Samples"... 

In cluster sampling, the pool is already divided into numerous separate groups (such as bottles of tablets). 

The formation of CO2 is then measured for the mixed cluster samples and compared to the formation on pure Au clusters. Fig. 1.76 shows the one cycle TPR spectra for the clean MgO and gold films as well as for selected cluster sizes, which are discussed in detail below for understanding the impurity doping and the size effects. Whereas the pure gold tetramer is inert, the strontium-doped AusSr cluster produces CO2 at 250 and 500 K. These... 

Fig. 1.97. Formation of CO2 (a) and N2 (b) for Pd4, Pds, and Pdso measured by a temperature programmed reaction (TPR) experiment. In these experiments, the cluster samples were first dosed at 90 K to CO (1 Langmuir) and snbseqnently to NO (1 Langmuir). The reactivities for various clusters, expressed as the normahzed number of product molecules per cluster, are shown in the insets...

Figure 14.13 shows a TEM image of soot clusters sampled from an acetylene-in-air diffusion flame. Analysis shows these clusters are fractals with D — 1.8 and a = 23 nm (thus for X= 514.5 nm a= 0.28). This is typical of carbonaceous soot formed in a variety of flames. 

Pineri et al have performed a series of investi-gations " " " on the structural properties of Nafion polymers and have derived a three-phase model in which fluorocarbon crystallites, ionic hydrophilic clusters, and an amorphous hydro-phobic region of lower ionic content coexist. The microcrystallites can be eliminated by heating the Nafion-Na sample to 330°C, and then quenching it to room temperature." They showed that at high water content (>15wt%) the quenched Nafion membranes are essentially two-phase systems." These phases are rather well separated and most of the water is in the ionic clusters. Samples of lower water content (8 wt %) show deviations from two-phase behavior." ... 

Figure 1. Absorption spectra of several representative CdS cluster samples. The 60-A CdS is made inside an ionic polymer film. The 20-A CdS is a free-standing cluster capped with thiophenolate on the surfaces. The 10-A sample is a monodisperse 55-atom CdS cluster (not counting the peripheral phenyl groups). The spectra are scaled arbitrarily. (Taken from reference 31 with permission.)...

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