DAC converter

Deacetoxy/deacetylcephalosporin C synthase (DAOC/DACS), the enzyme isolated from Cephalosporium acremonium catalysing587 the ring expansion of penicillin N, 473, to deacetoxycephalosporin (DAOC), 474, and the hydroxylation of 474 to deacetylcephalosporin C(DAC), 475, which in vivo is acetylated by a different enzyme to give cephalosporin C, 476 (equation 284), converts also the unnatural substrate exomethylene cephalosporin C, 477a, directly to DAC, 475 (equation 285). 

Asynchronous Pitch Shifting. Asynchronous pitch shifting, the simplest pitch shifting method, simply changes the clock rate of each output digital to analog converter (DAC) to vary the pitch. Each channel requires a separate DAC. Each DAC has its own clock whose rate is determined by the requested frequency for that channel. When a DAC clock occurs, the DAC issues a request to a memory controller that supplies a waveform sample to the DAC. The earliest samplers had a separate memory for each DAC. 

A typical example of subtractive dither use in an A/D converter can be found in a Teac patent [Nakahashi and Ono, 1990], Notable features include the use of limiting and overload detectors as well as the ability to control the dither amplitude. A clever example of non-subtractive dither [Frindle, 1995][Frindle, 1992] separates the input signal into two paths. One of the paths is now inverted and then both paths are added to a random noise source. After the DAC, the two analog signals are subtracted the result is the sum of the conversion errors and twice the input signal. 

The final step in the biosynthesis of CPC (Fig. 1) is catalyzed by acetyl CoA deacetylcephalosporin C O-acetyltransferase (DAC-AT). Fujisawa et al. [48] showed that cell-free extracts of a CPC-producing strain readily converted DAC and acetyl-1-[14C]-CoA to labeled CPC. They utilized this novel assay system to characterize several mutants that accumulated DAC and correctly proposed that... 

A scan controller provides several functions under computer control, namely detector coordinate redefinition, position and command display, ADC selection, and diagnostic analysis of interface subassemblies. Coordinate redefinition was necessary because the format of the 12-bit word presented to the X or Y DAC is straight binary, whereas the 12-bit computer employs offset binary (two s complement arithmetic). Thus, the word outputted to the X or Y DAC from the computer is converted from offset binary to straight binary. The scan coordinate specified by the computer is displayed in a 12-bit LED register. The load X, load... 

Fig. 8.8 Successive approximation converter (DAC digital-to-analog converter, SAR successive approximation register).

The biosynthesis of CPC is well known. The first step of CPC synthesis is the formation of the tripeptide S-(L-a-aminoadipyl)-L-cysteinlyl-D-valine (LLD-ACV) from L-a-aminoadipinic acid (AAA), L-cystein (CYS ) and D-valine (VAL) by the LLD-ACV synthetase (ACVS). LLD-ACV is converted with the enzyme isopenicillin AT-synthetase (cyclase) to isopenicillin N (IPN) and then with isopenicillin N-epimerase to penicillin N (PEN). The 6-ring is formed by deacetoxycephalosporin C-synthase (expandase). Deacetoxycephalosporin C (DAOC) is converted with deacetoxycephalosporin C-hydroxylase to decacetylcephalosporin C (DAC) and the latter with deacetylcephalosporin C-acyltransferase to CPC (Fig. 1). Except the amino acid and ACV, all others were monitored by on-line HPLC. 

It is possible to record data in different time windows after the application of a pulse to obtain time-resolved spectra. The pulses are applied to the sample rod externally using a digital-to-analog converter (DAC), and the photoelectrons are amplified and counted for a given period. The kinetic energy axis of the spectrometer is also controlled by the DAC. Each measurement starts by setting the kinetic energy to the first point with application of +10V to the sample rod. 

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