Scanning method

Bosworth used vacua of 10-4Pa, but that was all that was known (low pressure measuring devices not being available at that time) and it is likely that UHV conditions were not obtained (the surface was certainly in the form of tungsten oxide since it had a very high work function). However, recently, another group of workers has used the scanning photon beam method to look at the diffusion of caesium on tungsten surfaces under UHV conditions [232]. 

The secondary electron emission properties of surfaces have been used in combination with scanning techniques in this laboratory [45, 234]. 

Effects on the secondary electron emission can be assessed very simply by measuring the total drain current, /t, to the crystal surface 

Another novel method described recently involves the use of the electron-stimulated desorption (ESD, EID) of species from a surface. Lichtmann and Campuzano [239] used a scanning electron beam to induce desorption of F+ ions from a fluoridised molecule and obtained traces of F+ current (measured in a mass spectrometer) versus distance scanned across the sample. Only qualitative results were obtained but this again illustrates the strength of the scanning technique for boundary diffusion studies. 

Certainly the most common property of surfaces used in the area of surface diffusion studies is the field-induced emission of electrons. The property of field emission under vacuum conditions was first observed as early as 1897 [242] and in 1923 Schottky [243] attempted to explain field-emission from cold metals theoretically. The most significant practical advance came in 1937 with the invention of the field-emission microscope by Muller [7]. 

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There are a variety of possible linked scanning methods, but only those in more frequent use are discussed here. They differ from the linked scanning methods used in triple quadrupole instruments and ion traps in that two of the three fields (V, E, and B) are scanned simultaneously and automatically under computer control. The most common methods are listed in Table 34.1, which also defines the type of scanning with regard to precursor and product ions. 

Scanning method. The sequence of control over operating parameters of a mass spectrometer that results in a spectrum of masses, velocities, momenta, or energies. 

Field Scanning Methods In these techniques, the particles to be measured are examined collectively, and the signal from the assembly of particles is deconvulated to generate a size distribution. 

Nuclear medicine scans Method of body imaging that uses a radioactive tracer material (e.g., technetium and gallium) to produce body images. For example, bone scans detect uptake and cellular activity in areas of inflammation. 

It is possible to extend the line scanning method to two-dimensional scanning. In its simplest form, the display is made bright every time an X-ray photon is counted, thus generating a image of bright dots. The dot density provides a qualitative measure of the concentration of the element of interest. 

In the same way, spatial resolving power is a measure of the efficiency of distribution-analytical methods in micro- and surface analysis as well as scanning methods. From all the systematic representations of distribution-analytical problems given in Danzer et al. [1991], the mostly relevant are represented in Fig. 7.12. 

Gasser, R.B. (1997) Mutation scanning methods for the analysis of parasite genes. InternationalJournal for Parasitobgy 27, 1449-1463. 

Fig. 2.6. Schematic illustration of the experimental setup for pump-probe anisotropic reflectivity measurements with fast scan method. PBS denotes polarizing beam splitter, PD1 and PD2, a pair of matched photodiodes to detect p- and s-polarized components of the reflected probe beam, PD3 another photodiode to detect the interference pattern of He-Ne laser in a Michelson interferometer to calibrate the scanning of the pump path length...

The kinetics of homogeneous reaction of several reactive dyes of the vinylsulphone type with methyl-a-D-glucoside (7.9), selected as a soluble model for cellulose, were studied in aqueous dioxan solution. The relative reactivities of the various hydroxy groups in the model compound were compared by n.m.r. spectroscopy and the reaction products were separated by a t.l.c. double-scanning method [38]. The only sites of reaction with the vinylsulphone system were the hydroxy groups located at the C4 and C6 positions [39,40]. 

A highly substantive bluish red bis(sulphatoethylsulphone) structure (7.73) has been patented recently [29]. In a kinetic study using the t.l.c. double-scanning method, the condensation reactions between the bis(aminochlorotriazine) dye Cl Reactive Red 120 (7.48 X = Cl) and the two isomeric sulphatoethylsulphone anilines 7.38 and 7.39 to yield the two corresponding bis(sulphatoethylsulphone) isomeric dyes were compared. The rate constant of the reaction between Red 120 and the meta isomer 7.39 was about ten times as large as that for the para isomer 7.38 [64]. 

Note Mass accuracy is highly dependent on many parameters such as resolving power, scan rate, scanning method, signal-to-noise ratio of the peaks, peak shapes, overlap of isotopic peaks at same nominal mass, mass difference between adjacent reference peaks etc. An error of 5 mmu for routine applications is a conservative estimate and thus the experimental accurate mass should lie within this error range independent of the ionization method and the instrument used. [37] There is no reason that the correct (expected) composition has to be the composition with the smallest error. 

Jennings, K. R. Scanning Methods for Double-Focusing Mass Spectrometers. Almoster Ferreira, M. A. [118], 7-21. 1984. Dordrecht, D. Reidel Publishing. NATO ASI Series C Mathematical and Physical Sciences Ionic Processes Gas Phase. 

Robust peptide-derived approaches aim to identify a small drug-like molecule to mimic the peptide interactions. The primary peptide molecule is considered in these approaches as a tool compound to demonstrate that small molecules can compete with a given interaction. A variety of chemical, 3D structural and molecular modeling approaches are used to validate the essential 3D pharmacophore model which in turn is the basis for the design of the mimics. The chemical approaches include in addition to N- and C-terminal truncations a variety of positional scanning methods. Using alanine scans one can identify the key pharmacophore points D-amino-acid or proline scans allow stabilization of (i-turn structures cyclic scans bias the peptide or portions of the peptide in a particular conformation (a-helix, (i-turn and so on) other scans, like N-methyl-amino-acid scans and amide-bond-replacement (depsi-peptides) scans aim to improve the ADME properties." ... 

When performed with the rapid-scan method. 

Figure 6.7 Acyl region of IR spectra recorded with rapid-scan method after addition of 1-octene to HRh(CO)3P (P = tris(2-tert-butyl-4-methylphenyl) phosphite. = 1-octene. Reproduced from Ref [28] with permission.

Xu, B., Gunn, J. M., Dela Cruz, J. M., Lozovoy, V. V, and Dantus, M. 2006. Quantitative investigation of the multiphoton intrapulse interference phase scan method for simultaneous phase measurement and compensation of femtosecond laser pulses. J. Opt. Soc. Am. B Opt. Phys. 23(4) 750-59. 

A 2-D beam scanning system equipped with a set of magnets or electrostatic plates to deflect the beam horizontally and vertically is commonly used for uniform irradiation over a large area, e.g., > 10 x 10 cm. A schematic drawing of the 2-D beam scanning method is shown in Fig. 8. The scanning area may be varied by changing the excitation currents of the... 

The single and double scan methods allow estimation of the value of the characteristic parameters for both ionic and nonionic surfactants (see Table 1). The extrapolation of Eqs. 8 and 9 to SACN = 0 allows the classification of the head groups in some hydrophihcity scale. Inspection of Table 1 data indicates that the branching and isomeric structure does have quite an influence on the characteristic parameter, as it has been reported in the Hter-ature [12,27-32]. 

All ILs showed a rich photochemistry after UV photolysis leading to the buildup of various long-lived intermediate products as evidenced from the observation that ILs turn yellow upon continuous irradiation. On the other hand, exposing ILs to short excitation pulse (a rapid-scan method) significantly suppressed the formation of halides [22]. 

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