Electron microscopy, to determine

The activity loss measured here is caused by recrystallizations. This was demonstrated by using scanning electron microscopy to determine nickel crystallite size in the same catalyst samples. These tests revealed that the catalyst used in demonstration plants has only a slight tendency to recrystallize or sinter after steam formation and loss of starting activity. 

DNA, since proximity eflfects demand that the DNA or nascent RNA closest to the histones at the point of disruption will be the polyanion for which those histones will preferentially reassociate. Ten Heggeler-Bordier et al. [95] have verified these observations. They used immuno-electron microscopy to determine what happens to histones after transcription with T7 RNA polymerase of a multi-nucleosomal template and also observed transfer to the nascent RNA. In contrast, Kirov et al. [96] have reported that no histones displace during transcription with this polymerase. However, as described above, transcriptional efficiency and ultimately histone displacement is not efficient in very low ionic strength conditions. 

Finally, the surfaces of the cores are examined both optically and by secondary electron microscopy to determine the extent of microstructural changes that are occuring due to atmospheric exposure. Energy dispersive analysis of x-rays (EDAX) also serves to detect atmospheric particles which have deposited onto the core surface. All this information can then be used to at least qualitatively identify deterioration processes that may be occuring. 

In S. hexapraecingula, amphiesmal vesicle membranes in the motile cells and the plasma membrane in the nonmotile cells were examined by freeze-fracture electron microscopy to determine whether they contained cellulose-synthesizing TCs (Sekida et al. 2004). According to Sekida et al. (2004), no microfibril impression was found in the protoplasmic face (PF) and the extracellular face (EF) of either the inner or outer amphiesmal vesicle membranes in the motile cells. No particle... 

Viral particles of HCMV and Kaposi s sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) have recently been examined. During the her-pesviral replicative cycle, different viral particles are formed. For HCMV, this includes mature, infectious virions, noninfectious enveloped particles, and dense bodies [6]. Similarly for KSHV, only a portion of the produced virus particles is infectious [40]. Therefore, analysis of infectious virions requires their separation from the noninfectious and immature forms. Density ultacentrifugation gradients are typically used to separate the various forms. Each fraction can be analyzed by electron microscopy to determine the level of purity [6,41] or by assaying for viral DNA and an envelope glycoprotein [40]. 

A second group of nanocomposites mentioned earlier is characterized by exhibiting negative deviations from the tortuous path model. These account for another significant number of composites. In these composites this negative deviation can be explained by one of two possible mechanisms. The first is the one mentioned in the previous example where tactoids predominate in the composite. In these cases the aspect ratio of the tactoids has not been determined but the data is compared to the tortuous path equation predictions utilizing the aspect ratio of the completely exfoliated clay. The solution in these cases is to utilize X-ray diffraction and electron microscopy to determine the true aspect ratio of the tactoids. This was done in the previous example. 

Opsin, which loops back and forth across the cell membrane, and rhodopsin are transmembrane proteins. Unwin and Henderson used electron microscopy to determine the structure of bacterial rhodopsin at 7 A resolution. More recently, the crystal structure of bovine rhodopsin at 2.8 A resolution was solved by Palczewski and colleagues. 

The range of applicability of the above theoretical approaches and numerical results can be estimated by comparing them with experimental results obtained, mostly, by direct optical microscope observation and for monodisperse polystyrene latex particles [8-10, 13, 14, 19, 21, 22, 34—36]. Several sets of experimental data have also been gathered using the AFM for latex [17, 20], colloid gold [62] or dendrimer suspensions [26]. One can also apply electron microscopy to determine particle... 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

The characterization of evaporated alloy films can be carried out at widely different levels of sophistication. At the very least, it is necessary to determine the bulk composition, probably after the film has been used for an adsorption or catalytic experiment. Then various techniques can be applied, e.g., X-ray diffraction, electron diffraction, and electron microscopy, to investigate the homogeneity or morphology of the film. The measurement of surface area by chemisorption presents special problems compared with the pure metals. Finally, there is the question of the surface composition (as distinct from the bulk or overall composition), and a brief account is given of techniques such as Auger electron spectroscopy which might be applied to alloy films. 

The mass versus particle size distribution of several polymer latices with diameters in the range of 30 nm to 1500 nm was determined in less than 20 minutes using an integrated hydrodynamic chromatograph. Distributions obtained were compared with those found by other particle sizing techniques such as electron microscopy to verify validity of the technique. The instrument employed was able to analyze latices re-producibly with different optical properties, even though some of the injected particles may have been trapped within the column. Latex properties were correlated with particle size distribution data to illustrate the benefit of this particle sizing technique. 

Some complications were introduced into the system in this composition region by Ricken et al. and Riess et al., who confirmed the previously suggested stoichiomeU ies at n=7,10 and 11 but also found stable phases at an oxygen-cerium ratios of 1.808 (P,) and 1.79 (Pj). At the same time, Knappe and Eyring confirmed the existence of phases at n=7 and II (not 9 and 10) by electron microscopy and determined two new phases at n=19 (CeiyOj4) and n=62 (Ce Oi,2) as well as a series of other less clearly defined phases in the range CeO, 1.76[Pg.30]

Drugs. Farkas et al. " have used a combination of polarizing microscopy, SANS, and transmission electron microscopy to characterize the liquid crystalline phases produced by the non-ionic surfactants, Syn-peronic A7 (PEG7-C13.15), alone and in the presence of two chlorhexidine species, chlorhexidine base, and its diacetate salt. Polarizing microscopy and electron microscopy were used to examine the nature of the liquid crystals formed, while SANS was used to determine their interlayer spacing. For the SANS studies. 

Among the established instrumental methods for determining metal dispersion, electron microscopy appears to be finding increasing favour and recent advances include the application of high-resolution and controlled-atmosphere electron microscopy to supported metal catalysts (Section 3). Recently, attempts have been made to estimate crystallite size from XPS intensities EXAFS also promises a still more complete description of the... 

Low temperature ashing techniques were employed to reduce the oxidation and decomposition of the minerals which would occur under normal ashing conditions. Mineralogical analyses were performed using X-ray powder diffraction, infra-red spectroscopy, optical petrography, and scanning electron microscopy. Elemental determinations were performed using atomic absorption spectroscopy. 

Carbon blacks with specific surface areas of up to 100 m /g can be regarded as essentially nonporous [15] since they give reversible Type II isotherms in the lUPAC classification [10]. Early physisorption measurements on carbon blacks [1] were designed to test the validity of surfiice areas determined the BET method [6]. Carbon blacks were considered [5] to be especially suitable for this purpose because the discrete nature of their spheroidal particles allowed electron microscopy to be used for the evaluation of the particle size distribution. Certain well-characterized carbon blacks are still extremely useful as reference adsorbents [11, 16]. 

The application of hi resolution electron microscopy to the determination of structures in systems with actual or potential use in selective oxidation catalysis is discussed. Problems of image interpretation, arising from instrumental aberrations and multiple scattering, are outlined, and exan les of its use are given in the systems Bi-Mo-W-0, Bi-Mo-Nb-0 and Bi-W-Nb-0. In all three, intermediate phases are revealed which show either potential or actual structural adaptability to varying stoichiometry, particularly with regard to oxygen content. 

---