Resolution improving

Laminographical approaches can be used for layer-by-layer visualization of the internal microstructure for the flat objects (multilayers, PCBs etc.), that caimot be reconstructed by computerized tomography because of the limited possibilities in rotation. Depth and lateral spatial resolutions are limited by the tube, camera and rotation accuracy. Microfocus X-ray tubes and digital registration techniques with static cameras allow improving resolution. Precision object manipulations and more effective distortion corrections can do further improvement. 

From (1) it is clear that the phase contrast can be interpreted simply in terms of tbe variation (second order derivative) of the projected image density, and increases with improving resolution of the system, in agreement with the findings of [3]. 

Molecular beam sample introduction (described in section (Bl.7.2)). followed by the orthogonal extraction of ions, results in improved resolution in TOP instruments over eflfrisive sources. The particles in the molecular beam typically have translational temperatures orthogonal to the beam path of only a few Kelvin. Thus, there is less concern with both the initial velocity of the ions once they are generated and with where in the ion source they are fonned (since the particles are originally confined to the beam path). 

Wiley W C and McLaren I H 1955 Time-of-flight mass spectrometer with improved resolution Rev. Sc/. Instrum. 26 1150-7... 

Equations 12.21 and 12.22 contain terms corresponding to column efficiency, column selectivity, and capacity factor. These terms can be varied, more or less independently, to obtain the desired resolution and analysis time for a pair of solutes. The first term, which is a function of the number of theoretical plates or the height of a theoretical plate, accounts for the effect of column efficiency. The second term is a function of a and accounts for the influence of column selectivity. Finally, the third term in both equations is a function of b, and accounts for the effect of solute B s capacity factor. Manipulating these parameters to improve resolution is the subject of the remainder of this section. 

One of the simplest ways to improve resolution is to adjust the capacity factor for solute B. If all other terms in equation 12.21 remain constant, increasing k improves resolution. As shown in Figure 12.11, however, the effect is greatest when the... 

Adjusting the capacity factor to improve resolution between one pair of solutes may lead to an unacceptably long retention time for other solutes. For example, improving resolution for solutes with short retention times by increasing... 

A second approach to improving resolution is to adjust alpha, a. In fact, when a is nearly 1, it usually is not possible to improve resolution by adjusting ki or N. Changes in a often have a more dramatic effect on resolution than k. For example, changing a from 1.1 to 1.5 improves resolution by 267%. 

Another approach to improving resolution is to use thin films of stationary phase. Capillary columns used in gas chromatography and the bonded phases commonly used in HPLC provide a significant decrease in plate height due to the reduction of the Hs term in equation 12.27. 

By use of an electrostatic ion mirror called a reflectron, arrival times of ions of the same m/z value at the detector can be made more nearly equal. The reflectron improves resolution of m/z values. 

As PWB technology is refined to provide greater integration using finer conductor lines, there is renewed interest in hquid resists. The absence of a cover sheet and the abihty to apply thinner films both contribute to improved resolution and to an intrinsically lower consumables cost (16,17). 

A second approach modifies the CA resist chemistry. Eor example, researchers have introduced basic additives into the resist formulation to minimize the impact of surface contamination of the resist film (82,83). A resist that already contains added base (and consequendy requites a larger imaging dose) should be less affected by the absorption of small amounts of basic contaminants. Systems of this type have been claimed to have improved resolution as well. The rationalization here is that the acid that diffuses into the unexposed regions of the resist film is neutralized and does not contribute to image degradation (84,85). 

From the early 1980s to present, infrared sensitive two dimensional arrays were mated to integrated circuits for signal processing and sensitivity to better than 0.03 K (see Photodetectors). These focal plane arrays of some 500 by 500 elements eliminate the need for scanning and provide good spatial resolution. Some versions have no special cooling requirements. The development trend is to increase the number of pixels to improve resolution, increase the field of view and keep the size and cost of the optics within acceptable bounds. 

Contaminant by-products depend upon process routes to the product, so maximum impurity specifications may vary, eg, for CHA produced by aniline hydrogenation versus that made by cyclohexanol amination. Capillary column chromatography has improved resolution and quantitation of contaminants beyond the more fliUy described packed column methods (61) used historically to define specification standards. Wet chemical titrimetry for water by Kad Eisher or amine number by acid titration have changed Httle except for thein automation. Colorimetric methods remain based on APHA standards. 

Although energy resolution is rarely employed in positron camera systems, scatter is not normally a problem. This is because of the very short time window within which two photons must arrive in order to be counted. At low decay rates, the incidence of accidental events is very low, rising only slightly for those that occur as the result of scatter. Some systems employ time-of-flight measurements of the time difference between the arrival of the two photons to obtain additional information about the location of an annihilation along the line. This has been used to improve resolution and statistical accuracy. Resolution is in the range of 3—4 mm and is less dependent on position than is SPECT (16). 

Along with, and closely connected to, the developments in precise impact techniques is the development of methods to carry out time-resolved materials response measurements of stress or particle velocity wave profiles. With time resolutions approaching 1 ns, these devices have enabled study of mechanical responses not possible in the early period of the 1960s. The improved time-resolutions have resulted from direct measurement of stress or particle velocity, rather than from improved accuracy and resolution in measurement of position and time. In a continuation of this trend, capabilities are being developed to provide direct measurements of the rate-of-change of stress. With the ability to measure such a derivative function, detailed study of new phenomena and improved resolution and accuracy in descriptions of known rate-dependent phenomena seem possible. 

For mechanical wave measurements, notice should be taken of the advances in technology. It is particularly notable that the major advances in materials description have not resulted so much from improved resolution in measurement of displacement and/or time, but in direct measurements of the derivative functions of acceleration, stress rate, and density rate as called for in the theory of structured wave propagation. Future developments, such as can be anticipated with piezoelectric polymers, in which direct measurements are made of rate-of-change of stress or particle velocity should lead to the observation of recognized mechanical effects in more detail, and perhaps the identification of new mechanical phenomena. 

Figure 4.21 demonstrates the effect of temperature on the resolution of PEOs on a TSK-GEL G6000PWxi. and G3000PWxl in series. Increased temperature will decrease mobile phase viscosity and improve diffusion, which will improve resolution. 

The optimum flow rate for most SEC separations using conventional PLgel column dimensions (internal diameter 7.5 mm) is 1.0 ml/min. It may be of some benefit to work with lower flow rates, particularly for the analysis of higher molecular weight polymers where the reduced flow rate improves resolution through enhanced mass transfer and further reduces the risk of shear... 

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