Isolation, notch

Samples may either be those in which the surface of interest has been exposed to the environment before analysis, or the surface to be examined is created in the UHV chamber of the instrument. The latter method is generally preferable, and also argon-ion bombardment is commonly used to clean sample surfaces in situ in the spectrometer. In metallurgical studies, the fracture sample is particularly important the sample is machined to fit the sample holder, and a notch is cut at the desired point for fracture. The fracture stage is isolated from the analytical chamber and is pumped down to UHV. Liquid nitrogen cooling is often provided, as this encourages... 

The water phase was extracted with further 15 L dichloromethane. The combined dichloromethane phases were dried with Na2S04 and were evaporated. The product was flushed off with 5 L acetone, 35 L acetone was added and the suspension was heated until reflux. The crystallised product did not dissolve completely. Heating was discontinued and the mixture was left over night with gentle cooling. The crystallised l-[2-[4-[5-chloro-l-(4-flourophenyl)-lH-indol-3-yl]-l-piperidinyl]ethyl]-2- imidazolidinone was isolated on a notch, washed with further 5 L acetone and dried over night under air stream at 60°C. Yield 4.90 kg (83.2%), melting point 154.7°C. 

This infarction never occurs in isolation (Zimmerman, 1968). In acute phase oflarge inferolateral infarctions or, less frequently, of anteroseptal infarctions, the presence of PR-segment deviations, atrial arrhythmias and/or abnormal P waves (notched, irregular shape) suggests that atrial involvement has occurred. This probably occurs rarely, although this has to be studied with new image techniques (CE-CMR). 

Etch-stop at dielectric interfaces is another common occurrence in surface micromachining, when the etch terminates on the sacrificial or isolation oxide beneath the active silicon layer. Notching effects appear in high-aspect ratio (narrow)... 

Katsanis N., Fitzgibbon J., Fisher E.M. (1996). Paralogy mapping identification of a region in the human MHC triplicated onto human chromosomes 1 and 9 allows the prediction and isolation of novel PBX and NOTCH loci. Genomics 35 101-108. 

WE working electrode, consisting of notched rod possibly isolated from the solution except at the notched position AE auxiliary electrode, consisting of circular platinum gauze around the working electrode L Luggin capillary to reference electrode RE G inlet for gas S seals. 

FIG U RE 15.17 The process of ion isolation is execnted seqnentiaUy. First, lower masses are ejected with a modified mass-selective axial instability scan that is, essentially, the same as normal analytical scanning. Second, higher masses are ejected resonantly with a broadband waveform. The ejection order may be reversed to avoid product ions of higher m/z-values. WFl is a notch waveform to eject unwanted ions during ionization and the post-ionization period WF2 is a broadband waveform to eject higher mass ions during higher mass isolation period. 

FIGURE 15.20 The basic concept of notch waveform isolation. In the isolation process, the working point of precursor ions is moved first to a j-value at which the secular frequency of precursor ions lies inside the window of the notch waveform. Subsequently, the notch waveform is turned on to eject all unwanted ions. Due to the limited duration of application of the notch waveform, the window is not a perfect box as is seen in the bottom picture of this figure. 

Schwartz and co-workers have proposed a modified notch isolation method that has somewhat higher resolution [39,40], The method combines a notch waveform with slow RF resonance ejection scanning. In the first step of the method, most of the unwanted ions, except the precursor and ions of mass/charge ratio similar to that of the precursor ions, are ejected by a notch waveform. The trapping RF is then scanned slowly down to eject ions with m/z-values higher than that of the precursor ions. Next, the trapping RF is ramped slowly up to eject ions with m/z-values lower than that of the precursor ions. An isolation resolution. Am, of ca 0.3 Th has been demonstrated with the technique. 

When the gas pressure in an isolated pore is different to that outside the compact, pore filling is either retarded with an excess internal pressure or accelerated with an excess external pressure. The former is due to entrapped insoluble gases and, in this case, pore filling is not complete and gas bubbles remain within liquid-filled pores. (Gas bubbles are, in fact, often observed in liquid phase sintered compacts.) Even in compacts with entrapped gases, pore filling can be critical because the possibility of formation of sharp internal notches at the pore surface during solidification of the liquid must be considerably reduced by liquid filling. 

FTICR-MS instruments operate on the principle of ion cyclotron resonance. As ions have resonant frequencies, these frequencies can be used to isolate the ions prior to further fragmentation or manipulation. For example, a resonant frequency pulse on the excite plates (E+/— in Figure 2.8b) will eject the ions at, or near, that frequency. Furthermore, frequency sweeps - carefully defined to not excite the ion of interest - can be used to eject unwanted ions. However, the most elegant method for ion isolation is that of Stored Waveform Inverse Fourier Transform (SWIFT) [86] in which an ion-exdtation pattern of interest is chosen, inverse Fourier-transformed, and the resulting time domain signal stored in memory. This stored signal is then clocked-out, amplified, and sent to the excite plates when needed. The typical isolation waveform in SWIFT uses a simple excitation box with a notch at the frequencies of the ion of interest, a few kHz. 

Transmitting several frequencies from a single broadband antenna system requires the use of combining networks. In general, a combiner can be categorized as one of three types runout, branched (star point), and balanced (constant impedance). Any of these types may employ band-reject (notch) or bandpass filters. Finally, components such as isolators can be added to a combiner network tailor the basic system to a specific application. This section discusses the use of filters, isolators, and other components in FM, UHF-TV, VHF-TV, and land mobile communication combiner networks. 

A disadvantage of using internal notch filters is that if the two filters in a module are not identically tuned, an imbalance occurs within the hybrid ring, reducing the isolation to a point where a spur can be generated within a transmitter. Once a spur has been generated, there are no filters within the system to reject that spur, since the filters are tuned only to the expected frequencies. Therefore, the spur is broadcast. 

Herrera and Almy described a simple continuous extraction apparatus (Fig. 5.20). The apparatus is constructed from a 50-mL beaker and a paper cone prepared from a 9-cm disk of filter paper (nonfluted), which rests on the lip of the beaker. A small notch is cut in the cone to allow solvent vapor to pass around it. The extraction solvent is placed in the beaker the solid material to be extracted is placed in the cone. A watch glass containing 2-3 g of ice is placed on top of the assembly to act as the condenser and to hold the paper cone in place. As the ice melts, the water is removed and replaced with fresh ice. The beaker is heated on a hot plate in the hood (some solvent evaporates during the extraction process and may need to be replaced). The concentrated solution collected in the beaker is then cooled and the soHd product is isolated by filtration or is recrystaUized. This system needs to be attended at aU times, but works reasonably well for brief extractions. 

Figure 17.2 Manifestations of superstmctural aspects of DOPC bilayers, observed by cryo-TEM on surfaces of unilamellar vesicles that were prepared in pure water [26]. Left column linear isolated membrane bends or folds. They are found as deep notches as in heart-shaped vesicles and also as extended overhangs on flat membranes. (The cushion-like contours indicate the presence of passages (overpasses) on the membrane.) The constrictions on the branched tube may be envisaged as lines of saddles. Right column two-dimensional grainy membrane textures. The graininess was observed on small vesicles as well as on planar membranes and may even coexist with smooth bilayer portions.

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