Tam T. Nguyen

Nitric oxide (NO.) is a physiological messenger formed by several cell types. Reaction with O2 forms oxides that nitrosate amines at pH values near 7. We now report experiments in which NO. was added to intact human cells and to aerobic solutions of DNA, RNA, guanine, or adenine. TK6 human lymphoblastoid cells were mutated 15- to 18-fold above background levels at both the HPRT and TK gene loci. Xanthine and hypoxanthine, from deamination of guanine and adenine, respectively, were formed in all cases. NO. induced dose-responsive DNA strand breakage. Yields of xanthine ranged from nearly equal to about 80-fold higher than those of hypoxanthine. Yields of xanthine and hypoxanthine from nucleic acids were higher than those from free guanine and adenine. This was most pronounced for xanthine; 0.3 nmol/mg was formed from free guanine vs. 550 nmol/mg from calf thymus RNA. Nitric oxide added to TK6 cells produced a 40- to 50-fold increase in hypoxanthine and xanthine in cellular DNA. We believe that these results, plus the expected deaminations of cytosine to uracil and 5-methylcytosine to thymine, account for the mutagenicity of nitric oxide toward bacteria and mammalian cells.

The Microrover Flight Experiment (MFEX) is a NASA OACT (Office of Advanced Concepts and Technology) flight experiment which, integrated with the Mars Pathfinder (MPF) lander and spacecraft system, landed on Mars on July 4, 1997. In the succeeding 30 sols (1 sol=1 Martian day), the Sojourner microrover accomplished all of its primary and extended mission objectives. After completion of the originally planned extended mission, MFEX continued to conduct a series of technology experiments, deploy its alpha proton X-ray spectrometer (APXS) on rocks and soil, and image both terrain features and the lander. This mission was conducted under the constraints of a once-per-sol opportunity for command and telemetry transmissions between the lander and Earth operators. As such, the MFEX rover was required to carry out its mission, including terrain navigation and contingency response, under supervised autonomous control. For example, goal locations were specified daily by human operators; the rover then safely traversed to these locations. During traverses, the rover autonomously detected and avoided rock, slope, and drop-off hazards, changing its path as needed before turning back towards its goal. This capability to operate in an unmodeled environment, choosing actions in response to sensor input to accomplish requested objectives, is unique among robotic space missions to date.

We report the detection of a transiting planet around π Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V = 5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered planet has a size of 2.04 ± 0.05 R⊕ and an orbital period of 6.27 days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays a 6.27-day periodicity, confirming the existence of the planet and leading to a mass determination of 4.82±0.85 M⊕. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter-McLaughlin effect, astrometry, and direct imaging.

<div class="htmlview paragraph">On July 4, 1997, the Mars Pathfinder spacecraft successfully landed on Mars in the Ares Vallis landing site and deployed an 11.5-kilogram microrover named Sojourner. This microrover accomplished its primary mission objectives in the first 7 days, and continued to operate for a total of 83 sols (1 sol = Mars day = 1 Earth day + ∼24 mins) until the lander lost communication with Earth, probably due to lander battery failure. The microrover navigated to many sites surrounding the lander, and conducted various science and technology experiments using its on-board instruments.</div> <div class="htmlview paragraph">In this paper, the rover navigation performance is analyzed on the basis of received rover telemetry, rover uplink commands and stereo images captured by the lander cameras. Its physical traversal path is redrawn from the stereo images containing tracks and is compared with the rover-recorded path and the driver-planned path. Implications for next-generation planetary rovers are described, including the sub-1-Kg Nanorover being built by NASA to conduct asteroid exploration as part of the Japanese MUSES-C sample return mission and the large rover with the Athena payload which will be used as part of the Mars sample return program.</div>

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of primary processes in the pyrolysis of cyclopentanes and cyclohexanesTrevor C. Brown, Keith D. King, and Tam T. NguyenCite this: J. Phys. Chem. 1986, 90, 3, 419–424Publication Date (Print):January 1, 1986Publication History Published online1 May 2002Published inissue 1 January 1986https://pubs.acs.org/doi/10.1021/j100275a013https://doi.org/10.1021/j100275a013research-articleACS PublicationsRequest reuse permissionsArticle Views209Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts