April 8th 1997; revised May 24th 1999 Update to DCDT for the MAC This version can be obtained from: [ANONYMOUS.RASMB.SPIN.MAC.DCDT-STAFFORD]dcdt_mac.hqx or: ftp://bbri.harvard.edu/RASMB/SPIN/MAC/DCDT-STAFFORD/dcdt_mac.hqx It is capable of processing the XL-I files from the Rayleigh system. There are three versions of the application, one for 680x0 mac's, one for PPC's and one for all non FPU machines. Also included with dcdt is a conversion utility that converts XL-I Rayleigh files from ASCII to a binary format that can be read by dcdt. It compresses the ascii files by 90% making it 10 time faster to read them in to DCDT. It is recommended that you zip the files on the PC, tranfer them to the mac and unzip them on the mac. Then convert them to binary and process the binary files. Keep the zipped archives but delete the ascii files. You can always recover them from the zip archive later if you need to. The convert utility is somewhat brutish - be careful. Put the files you want to convert into a separate folder; put the convert utility in the same folder and double click it. It looks for any file with a name having the format 00nnn.IPn and converts it to a binary file named B0nnn.ipn. It loops through from 00001.ip1 to 00999.ip8. The list file should be composed of names with the format 00nnn.ipn. It can be used to read either the ascii or the corresponding binary files. There is an option called "Fine adjust" which you should choose for aligning the scans. Click in the air-air space in a relatively flat spot. [Try to match your menisci as closely as possible when you load the cell. The Rayleigh system is not as forgiving as the scanner. If the menisci are not carefully matched, you won't get good cancellation of the buffer redistribution and you will get skewed baselines that get worse with time.] [By the way, if you have strongly absorbing buffer components, you must match the menisci to get proper buffer subtraction because the buffer will redistribute somewhat during the run. This occurs most noticeably at the meniscus and the base; therefore, the column heights must be closely matched to get good cancellation between the two sectors.] Then choose option (3) for taking care of integral fringe shifts. You will know whether or not you've done these two operations correctly (Fine adjust and (3)) if you have nice, small error bars in the g(s*) plot. Please note: Rayleigh data should be taken over the *entire* CCD camera frame. It has been suggested that data be acquired starting just inside the meniscus. BUT the meniscus and data from the air-air space MUST be included in the data set to do the g(s) analysis. The dcdt software is smart enough to deal with fringe jumps across the meniscus. If you have any questions or problems, email me: stafford@bbri.org Walter Stafford