1,069 research outputs found

    The distribution and modes of occurrence of impact melt at lunar craters

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    Numerous studies of the returned lunar samples as well as geologic and remote-sensing investigations have emphasized the importance of impact melts on the surface of the Moon. Information concerning the distribution and relative volumes is important for (1) an improved understanding of cratering processes, (2) kinetic energy estimates and energy partitioning studies, (3) the proper interpretation of melt-bearing lunar samples, and (4) comparative planetology studies. The identification of major flows of fluidized material associated with impact craters on the surface of Venus has increased interest in impact melt flows on the other terrestrial planets. For a number of years, we have been investigating the distribution, modes of occurrence, and relative and absolute amounts of impact melt associated with lunar craters as well as the manner in which melt volumes vary as a function of crater size, morphology, and target characteristics. The results of this effort are presented

    Asteroid amphitrite: Surface composition and prospects for the possible Galileo flyby

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    Studies of the trajectory of the Galileo mission to Jupiter recently revealed that the spacecraft can pass close to one of the largest asteroids (#29 Amphitrite). NASA has therefore altered the mission plan of the Galileo spacecraft to include a possible close flyby of Amphitrite in early December 1986, if the condition of the spacecraft allows. If this option is actually implemented, Amphitrite will become the only asteroid for which any high-spatial resolution images and reflection spectra will be available. To evaluate the value of this data and place Amphitrite in the context of the more than 600 asteroids for which some compositional information exists. Existing data was reexamined, new telescopic spectra of Amphitrite were obtained, and simulated Galileo data sets were constructed

    Facebook as a recruitment tool for adolescent health research: A systematic review

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    BACKGROUND: Researchers are increasingly using social media to recruit participants to surveys and clinical studies. However, the evidence of the efficacy and validity of adolescent recruitment through Facebook is yet to be established. OBJECTIVE: To conduct a systematic review of the literature on the use of Facebook to recruit adolescents for health research. DATA SOURCES: Nine electronic databases and reference lists were searched for articles published between 2004 and 2013. STUDY ELIGIBILITY CRITERIA: Studies were included in the review if: 1) participants were aged 10 to 18 years, 2) studies addressed a physical or mental health issue, 3) Facebook was identified as a recruitment tool, 4) recruitment details using Facebook were outlined in the methods section and considered in the discussion, or information was obtained by contacting the authors, 5) results revealed how many participants were recruited using Facebook, and 6) studies addressed how adolescent consent and/or parental consent was obtained. STUDY APPRAISALS AND SYNTHESIS METHODS: Titles, abstracts, and keywords were scanned and duplicates removed by 2 reviewers. Full text was evaluated for inclusion criteria, and 2 reviewers independently extracted data. RESULTS: The search resulted in 587 publications, of which 25 full-text papers were analyzed. Six studies met all the criteria for inclusion in the review. Three recruitment methods using Facebook was identified: 1) paid Facebook advertising, 2) use of the Facebook search tool, and 3) creation and use of a Facebook Page. CONCLUSIONS: Eligible studies described the use of paid Facebook advertising and Facebook as a search tool as methods to successfully recruit adolescent participants. Online and verbal consent was obtained from participants recruited from Facebook

    Preliminary results of spectral reflectance studies of tycho crater

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    The preliminary analysis and interpretation of near infrared spectra obtained for both the interior and exterior deposits associated with the Tycho crater is presented. Specific objectives were: (1) to determine the composition and stratigraphy of the highland crust in the Tycho target site; (2) to determine the likely composition of the primary ejecta which may be present in ray deposits; (3) to investigate the nature of spectral units defined in previous studies; (4) to further investigate the nature and origin of both the bright and dark haloes around the rim crest; and (5) to compare the compositions determined for the Tycho units with those of the Aristarchus crater as well as typical highland deposits. The spectra obtained for the interior areas exhibit similar spectral features. These include relatively strong 1 micron absorption bands whose minima are centered between 0.97 and 0.99 microns and shallow to intermediate continuum slopes. The spectra generally exhibit indications of a 1.3 micron feature consistent with the presence of Fe(2+) bearing plagioclase feldspar. The strong 1 micron absorption features indicate a dominant high Ca clinopyroxene component. Results obtained from the ejecta deposits show that the spectrum of the inner, bright halo is almost identical with those obtained for interior units. The spectrum of the dark halo exhibits a wide, relatively shallow absorption feature centered at 1.01 microns, a 1.3 micron absorption, and a steep continuum slope. This spectrum is interpreted as indicating the presence of pyroxene, Fe-bearing feldspar, and a significant component of Fe-bearing impact melt glass. Finally, the spectra of spots inside Tycho show similarity with certain spectra for Aristarchus. However, the suite of spectra obtained for Tycho exhibits a different trend in terms of band center versus width

    THE EFFECT OF SHOE TYPE ON VARIOUS KINETIC AND KINEMATIC VARIABLES DURING STEP-UP AND STEP-DOWN MOTIONS

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    The purpose of this study was to examine the effect of shoe type on the biomechanical responses to a stepping task. Participants (n = 8) performed six two minute stepping trials at a stepping rate of 72 bpm; 3 trials in hiking boots and 3 trials in hiking shoes. Lower limb joint angles and moments were calculated using Visual 3D. No significant differences were found in step down peak ground reaction forces (GRF), ankle, knee, and hip range of motion (ROM), joint moments, joint flexion at step down contact, or toe clearance height between footwear conditions. Due to the lack of differences found between footwear conditions, the use of either a hiking shoe or boot may not result in an increased risk of injury, therefore leaving the choice of footwear to the hiker’s personal preference

    JOINT ANGLES AND FORCES ON WRIST STRUCTURES DURING VARIATIONS OF YOGA POSES

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    The current study analysed joint angles of the wrists and forces on the structures in the hands and wrists in a hyperextended position and a neutral position during three different yoga poses. Participants (n = 9) performed three yoga poses (plank, side plank, and upward dog), with their wrists in a hyperextended position (H) and a neutral position (N). Each pose was completed three times for 10 seconds in H and N, for a total of six trials per pose. A two-way Repeated Measures ANOVA found significant differences in both wrist joint angles and GRF between H and N. Due to the suggested path transmission of forces, as well as the increased longitudinal loading that comes with wrist hyperextension, it is recommended that plank, side plank, and upward dog be performed in a neutral wrist position
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