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The scheduling of a school, where students, teachers, rooms and lessons are to be assigned according the curriculum, is a large combinatorial optimization problem. It appears that there are many solutions for a medium‐sized Dutch secondary school, of the order of 102400. We have developed a computational method to find good solutions.

We report on an extension of earlier work to search the archival database of the Differential Microwave Radiometers (DMR) aboard the COBE satellite for evidence of transient events at microwave wavelengths associated with cosmic gamma-ray bursts (GRBs). Over its four-year lifetime the DMR experiment repeatedly surveyed the sky to measure fluctuations in the cosmic microwave background. On a number of occasions at least one of the horns of the DMR was also serendipitously pointing in the direction of a cosmic gamma-ray burst at the moment of burst occurrence. Our original investigation covered the eight-month period April–December 1991 when a number of GRBs were observed by the COBE/DMR at or within a few seconds of the CGRO/BATSE trigger time. Upper limits only were obtained for any simultaneous microwave flux from these events, in the range 7–42 kJy. Most recently, we have extended our search using the additional 24 months of COBE DMR data now publicly available, covering the time period January 1992 thr...

We report on the status of our ongoing project to search the database of the COBE Differential Microwave Radiometer (DMR) experiment for transient signals at microwave wavelengths simultaneous with cosmic gamma-ray bursts (GRBs). To date we have carried out a complete search of the DMR database using burst positions taken from the original BATSE 1B catalog for the eight-month period of overlap (May–December 1991) corresponding to the first public release of COBE data. We are currently repeating our original search of the COBE DMR database using the revised burst positions of the newly-released BATSE 3B catalog. Using BATSE 1B positions, at least two apparent simultaneous observations of GRBs by the COBE DMR occurred in 1991, along with a number of “near misses” within 30 seconds in time. At present, only upper limits to burst microwave emission are indicated. Even in the event of a non-detection of a GRB by the COBE DMR, unprecedented observational limits will still be obtained, constraining the predictio...