Mid-infrared images of beta Pictoris and the possible role of planetesimal collisions in the central disk

When viewed in optical starlight scattered by dust, the nearly edge-on debris disk surrounding the A5V star beta Pictoris (distance 19.3 pc; ref. 1) extends farther than 1,450 au from the star. Its large-scale complexity has been well characterized, but the detailed structure of the disk's central approximately 200-au region has remained elusive. This region is of special interest, because planets may have formed there during the star's 10-20-million-year lifetime, perhaps resulting in both the observed tilt of 4.6 degrees relative to the large-scale main disk and the partial clearing of the innermost dust. A peculiarity of the central disk (also possibly related to the presence of planets) is the asymmetry in the brightness of the 'wings', in which the southwestern wing is brighter and more extended at 12 microm than the northeastern wing. Here we present thermal infrared images of the central disk that imply that the brightness asymmetry results from the presence of a bright clump composed of particles that may differ in size from dust elsewhere in the disk. We suggest that this clump results from the collisional grinding of resonantly trapped planetesimals or the cataclysmic break-up of a planetesimal.     

Ergonomic Evaluation on Taxi Drivers Compartment

Driving involves long hours of physical work within c onfined compartment. Taxi drivers usually work with prolonged working hours, add itional stress may likely be induced on particular body limbs. Occupational heal th may occur and working efficiency may potentially be affected resulting fr om fatigues, pains or diseases. These problems, however, could be remedied if mo re attention is paid on seating design, the workplace and driving postures adopt ed. Ergonomics design can provide better understanding...     

Pre-training Assessment Through the Web

Web-based training is growing quickly in popularit y for professionals in industrial organizations and large enterprises. The savings in cost and time are significant. The instructor-led trainings are bounded by time and place, not to mention the cost involved in traveling, accommodation and training venue. However, in the most online training courses, all trainees are given same training materials and teaching paradigms. The problem of differentia ting the trainees‘ abilities is the main concern. We n...