Chip protection methods

Another class of readout measures RNA expression levels, with the three most common methods being chip-based hybridization/fluorescence techniques, realtime polymerase chain reaction (RT-PCR) and quantitative nuclease protection assays (QNPA) [48, 49]. Chip-based methods are widely used for whole-genome scans (discussed in more detail below), but have a disadvantage that they are relatively expensive and so are not really high throughput. The quantitative reproducibility and dynamic range of these chip-based methods are also lower than for the other RNA readout techniques. RT-PCR is a more quantitative technique for measuring transcript levels, and is typically run for up to 40 transcripts at a time. QNPA is another... 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

The resolution of the photolithographic process determines the maximum achievable density of the array (i. e. the amount of sequence information encoded on the chip). Table 2 shows the relationship between the resolution, in terms of smallest feature size, and the maximum density at which an array can be printed . Application of the photolithographic process using photolabile protecting groups currently provides a spatial resolution that allows arrays to be fabricated with densities on the order of 106 sequences/cm2, which corresponds to an individual feature size of 10 X 10 m. This feature size is near the limit of resolution that can be achieved by this method using standard photolithography equipment. 

Although the surface of most IC chips has been passivated with a layer of inorganic dielectric material such as silicon dioxide or silicon nitride (polyimides have also been used as final passivating layers), the protection provided by such layers is not sufficient to ensure reliable operation throughout the lifetime of the device. The three basic methods of protection are... 

Ultrapure silicon has largely supplanted germanium in micro- and power-electronics (integrated circuits, microchips, thyristors, transistors, rectifiers etc.). Silicon accounts for more than 90% of the semiconductor market. There are a number of reasons for the dominance of silicon. Silicon forms stable Si02-protective layers, which can be removed by simple etch processes. This is the basis on which the etch and doping methods are developed, which permit an extremely high density of electronic components e.g. in microprocessors or memory chips. 64 MB memory chips can be currently produced in this way. 

In this process the arc is struck between a flux-covered consumable electrode and tbe work. Thus method is the most widely used form of arc welding and is used on all materials with the exception of aluminium The flux produces gas which shields the surface of the molten metal and leaves behind a slag which protects the hot metal from the atmosphere while cooling and has to be chipped off when cool. 

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