Size and albedo of Kuiper belt object 55636 from a stellar occultation.

The Kuiper belt is a collection of small bodies (Kuiper belt objects, KBOs) that lie beyond the orbit of Neptune and which are believed to have formed contemporaneously with the planets. Their small size and great distance make them difficult to study. KBO 55636 (2002 TX(300)) is a member of the water-ice-rich Haumea KBO collisional family. The Haumea family are among the most highly reflective objects in the Solar System. Dynamical calculations indicate that the collision that created KBO 55636 occurred at least 1 Gyr ago. Here we report observations of a multi-chord stellar occultation by KBO 55636, which occurred on 9 October 2009 ut. We find that it has a mean radius of 143 +/- 5 km (assuming a circular solution). Allowing for possible elliptical shapes, we find a geometric albedo of in the V photometric band, which establishes that KBO 55636 is smaller than previously thought and that, like its parent body, it is highly reflective. The dynamical age implies either that KBO 55636 has an active resurfacing mechanism, or that fresh water-ice in the outer Solar System can persist for gigayear timescales.

Repair of irradiation transforming deoxyribonucleic acid in wild type and a radiation-sensitive mutant of Micrococcus radiodurans.

The survival of biological activity in irradiated transforming deoxyribonucleic acid (DNA) has been assayed in the wild type and a radiation-sensitive mutant of Micrococcus radiodurans. The frequency of transformation with unirradiated DNA was lower in the mutant to about the same extent as the mutant's increased sensitivity to radiation. However, in both the wild type and the mutant, the irradiated DNA that was incorporated into the bacterial genome was repaired to the same extent as determined by the loss of transforming activity with increasing radiation dose. This applied to DNA irradiated either with ionizing or ultraviolet (UV) radiation. The rate of inactivation of biological activity after UV radiation was the same in any of the DNA preparations tested. For ionizing radiation, the rate of inactivation varied up to 40-fold, depending on the DNA preparation used, but for any one preparation was the same whether assayed in the wild type or the radiation-sensitive mutant. When recipient bacteria were irradiated with ionizing or UV radiation immediately before transformation, the frequency of transformation with unirradiated DNA fell, rapidly and exponentially in the case of the sensitive mutant but in a more complicated fashion in the wild type. The repair of DNA irradiated with ionizing radiation was approximately the same whether assayed in unirradiated or irradiated hosts. Thus, irradiation of the host reduced the integration of DNA but not its repair.

Prediction of uphill time-trial bicycling performance in humans with a scaling-derived protocol.

The present study sought to create a scaling-derived cycle ergometer protocol (SDP) that was derived theoretically and would correlate highly with actual uphill time-trial (TT) cycling performance. Local competitive cyclists each completed the SDP (an incremental test to exhaustion) using their own bicycle mounted on a stationary trainer, together with either a short (6.2 km, 2.9% grade; n = 8 men and 5 women) or long-course (12.5 km, 2.7% grade; n = 8 men) uphill TT. Maximal power output (Wmax) and power at the ventilatory threshold (WVT) were determined from the SDP results, as well as maximal oxygen uptake (VO2max), using standard indirect calorimetry procedures. Actual TT speed correlated very highly with both SDP completion time (r = 0.97-0.98) and relative Wmax (watts per kilogram; r = 0.92-0.97) for both uphill TT races. Correlations between TT speed and more demanding measurements (VO2max, WVT) (VO2max, WVT) were generally lower and more variable (r = 0.54-0.97). These results would indicate that two non-laboratory dependent measurements (SDP completion time and relative Wmax) derived from the SDP are valid markers for predicting actual uphill TT performance. This protocol may be useful to cycling coaches and athletes in identifying talented cyclists or for tracking changes in cycling performance outside of the sports science laboratory environment.

Repair of deoxyribonucleic acid in Haemophilus influenzae. I. X-ray sensitivity of ultraviolet-sensitive mutants and their behavior as hosts to ultraviolet-irradiated bacteriophage and transforming deoxyribonucleic acid.

Seven mutants of Haemophilus influenzae were isolated by the criterion of sensitivity to ultraviolet (UV) inactivation of colony formation. These mutants and the wild type were characterized with regard to X-ray inactivation of colony formation, UV induction of division inhibition, the ability of the eight strains to act as recipients to UV-irradiated H. influenzae phage and transforming deoxyribonucleic acid (DNA), and the influence of acriflavine on the survival of UV-irradiated transforming DNA with these strains as recipients. The photoreactivable sector of transforming DNA with yeast photoreactivating enzyme was measured for the most UV-sensitive mutant and was found to be greater than that of wild type. Judged by the above criteria, the order of the strains' sensitivities shows some, but by no means complete, correlation from one type of sensitivity characterization to another, indicating that a minimum of two variables is needed to explain the differences in the strains. Acriflavine increases the UV sensitivity of transforming DNA except in the most sensitive mutant. This effect is usually, but not always, more pronounced in the case of the more UV-resistant marker. The acriflavine effect is postulated to be the result of at least two factors: (i) interference with repair of transforming DNA in the host cell, and (ii) interference with the probability of recombination between transforming DNA and host DNA.