The Mark 4 VLBI correlator is a station‐based system designed to process data from up to 16 stations at an aggregate data rate of 1 Gbps/station. It is compatible with data recorded on Mark 3A, Mark 4, and VLBA tape‐based data‐acquisition systems, as well as the new disc‐based Mark 5 system which also supports both real‐time and quasi‐real‐time data‐transmission over high‐speed networks. The system incorporates an XF algorithm implemented in a custom‐VLSI chip that can be flexibly configured to cross‐correlate VLBI data from one to four baselines of a single 2‐bits/sample channel at 64 Mbps/channel/station. Each chip also incorporates integral phase generators, rotators and vernier‐delay management circuitry. Each of the sixteen Correlator Boards in the system contains 32 correlator chips and can process up to 8192 complex lags that can be flexibly traded off between baselines, lags and channels. Innovative algorithms allow station‐model information to be injected periodically into the data stream from each channel of each station to drive the correlation process. The correlator control software allows up to four independent multistation scans to be processed simultaneously to significantly improve processing efficiency.

Aims. The Atacama Large Millimeter Array (ALMA) is an international astronomy facility to be used for detecting and imaging all types of astronomical sources at millimeter and submillimeter wavelengths at a 5000-m elevation site in the Atacama Desert of Chile. Our main aims are: describe the correlator sub-system which is that part of the ALMA system that combines the signal from up to 64 remote individual radio antennas and forms them into a single instrument; emphasize the high spectral resolution and the configuration flexibility available with the ALMA correlator. Methods. The main digital signal processing features and a block diagram of the correlator being constructed for the ALMA radio astronomy observatory are presented. Tables of observing modes and spectral resolutions offered by the correlator system are given together with some examples of multi-resolution spectral modes. Results. The correlator is delivered by quadrants and the first quadrant is being tested while most of the other printed circuit cards required by the system have been produced. In its final version the ALMA correlator will process the outputs of up to 64 antennas using an instantaneous bandwidth of 8 GHz in each of two polarizations per antenna. In the frequency division mode, unrivalled spectral flexibility together with very high resolution (3.8 kHz) and up to 8192 spectral points are achieved. In the time division mode high time resolution is available with minimum data dump rates of 16 ms for all cross-products.Key words. techniques: interferometric -techniques: spectroscopic -instrumentation: interferometersinstrumentation: spectrographs IntroductionThe Atacama Large Millimeter Array (ALMA) is an international astronomy facility. ALMA is a partnership between Europe, North America and Japan, in cooperation with the Republic of Chile (see Alma Information and note at the end of this paper). ALMA will consist of a main array of up to 64 12-m diameter antennas supplied by Europe (ESO) and North America (NRAO/AUI) and a compact array of twelve 7-m plus four 12-m antennas supplied by Japan (NAOJ). The main goal of this paper is to describe the essential features of the ALMA correlator being constructed for the main array (64 antennas) and to emphasize its huge versatility making this correlator a key element of all future astronomy programs led with ALMA. The ALMA correlator is a very large digital system that combines the outputs of up to 64 array elements using an instantaneous bandwidth of 8 GHz in each of two polarizations per antenna, and produces a single astronomical telescope from the 64 movable antennas distributed within a diameter of about 150 m to an expanded configuration of maximum antenna separation 18.5 km.A digital correlator system is the heart of any modern radio astronomy system in which the signal power is detected by measuring (a) the cross-correlation of all antenna pairs in an array of antennas, and/or (b) the auto-correlation of one (or all) single antenna(s). Digital lags can easily be implemented...

A biosensor based on a conducting screen-printing ink for the direct amperometric measurement of glucose is described. Carbon electrode prints, containing the work, reference and auxiliary electrodes, are used as the substrate for the sensor. The active parts of the carbon ink are the redox enzyme glucose oxidase and the conducting polymer poty(pyrrole), which can communicate directly with each other. As a result, the biosensor is largely independent of the oxygen concentration. The feasibility of the described biosensor ink for screen printing is shown.

No abstract

No abstract