ABSTRACT
Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z approximately 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.39 - 0.12 + 0.11 (refs 5-7). Subsequently, it was measured spectroscopically to be z = 6.29 +/- 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.
ABSTRACT
A model was developed to identify the characteristics of long jumping technique that determine the distance of the jump. The performances of the finalists in the TAC (U.S. national) Championships were recorded cinematographically and the best trials analyzed. The results indicated that the relative lengths of the last two strides of the approach are poor indicators of success in the event. Maximum horizontal velocities were usually attained at takeoff into the third- or second-last stride and not exclusively during the second-last stride, as previously reported. None of the subjects had either a zero or upward vertical velocity of the center of gravity at touchdown of the foot for takeoff into the jump, contrary to an argument occasionally advanced. The greatest percentages of the variance in the distance of the jump were accounted for by the horizontal velocity at takeoff into the fourth-last stride, the change in horizontal velocity during the next support phase, the horizontal and resultant velocities at takeoff and the flight distance.
