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PubMed2005

Transport of Mars-crossing asteroids from the quasi-Hilda region.

We employ set oriented methods in combination with graph partitioning algorithms to identify key dynamical regions in the Sun-Jupiter-particle three-body system. Transport rates from a region near the 3:2 Hilda resonance into the realm of orbits crossing Mars' orbit are computed. In contrast to common numerical approaches, our technique does not depend on single long term simulations of the underlying model. Thus, our statistical results are particularly reliable since they are not affected by a dynamical behavior which is almost nonergodic (i.e., dominated by strongly almost invariant sets).

Journal Article↗

PubMed1984

Effect of Photoperiod on Photosynthate Partitioning and Diurnal Rhythms in Sucrose Phosphate Synthase Activity in Leaves of Soybean (Glycine max L. [Merr.]) and Tobacco (Nicotiana tabacum L.).

Studies were conducted to identify the existence of diurnal rhythms in sucrose phosphate synthase (SPS) activity in leaves of three soybean (Glycine max L. [Merr.]) and two tobacco (Nicotiana tabacum L.) cultivars and the effect of photoperiod (15 versus 7 hours) on carbohydrate partitioning and the rhythm in enzyme activity. Acclimation of all the genotypes tested to a short day (7 hours) photoperiod resulted in increased rates of starch accumulation, whereas rates of translocation, foliar sucrose concentrations, and activities of SPS were decreased relative to plants acclimated to long days (15 hours). Under the long day photoperiod, two of the three soybean cultivars (;Ransom' and ;Jupiter') and one of the two tobacco cultivars (;22NF') studied exhibited a significant diurnal rhythm in SPS activity. With the soybean cultivars, acclimation to short days reduced the activity of SPS (leaf fresh weight basis) and tended to dampen the amplitude of the rhythm. With the tobacco cultivars, photoperiod affected the shape of the SPS-activity rhythm. The mean values for SPS activity (calculated from observations made during the light period) were correlated positively with translocation rates and were correlated negatively with starch accumulation rates. Overall, the results support the postulate that SPS activity is closely associated with starch/sucrose levels in leaves, and that acclimation to changes in photoperiod may be associated with changes in the activity of SPS.

Journal Article↗

PubMed1985

Genotypic variability of soybean response to agrobacterium strains harboring the ti or ri plasmids.

Twenty four diverse cultivars of soybean (Glycine max [L.] Merrill) and three lines of its annual wild progenitor Glycine soja Sieb and Zucc. were tested for their response to Agrobacterium strains harboring either the Ti (tumor-inducing) plasmid (pTi) from Agrobacterium tumefaciens or the Ri (root-inducing) plasmid (pRi) from Agrobacterium rhizogenes following uniform wounding and inoculation. Based upon gall weight at 8 weeks postinfection, three G. max cultivars (Biloxi, Jupiter, and Peking) and one G. soja line, Plant Introduction (PI) 398.693B, were judged highly susceptible to A. tumefaciens strain A348 (pTiA6), ten genotypes moderately susceptible, 11 weakly susceptible, and two nonsusceptible. Of 26 genotypes inoculated with strain R1000 (pRiA4b), only seven responded in a clearly susceptible fashion by forming small, fleshy roots at internodal infection sites. Cotyledons excised from 1- or 3-day old seedlings of Peking and Biloxi cultivars also formed galls when infected in vitro with agrobacteria carrying either the Ti or Ri plasmid. Tumor lines established from cotyledon and stem galls induced by A. tumefaciens A348 (pTiA6) exhibited the T-DNA borne traits of phytohormone-independent growth and octopine synthesis. Additionally, DNA isolated from cultured tumors hybridized with labeled T-DNA probe.

Journal Article↗

PubMed1988

Effect of the electrochemical proton gradient and anions on the ATPase activity of soybean submitochondrial particles.

Submitochondrial particles from soybean (Glycine max L. cv Jupiter) hypocotyls with an ATPase activity of 0.3 to 1.0 micromole per minute per milligram were prepared by sonication with Mg-ATP. The particles catalyzed ATP synthesis with NADH and succinate; the ratios of ATP/O with these substrates were 1.0 and 0.1, respectively. As monitored by oxonol-VI, the particles built up and maintained a membrane potential that was higher with NADH than with succinate or Mg-ATP. The ATPase activity of the particles increased two to threefold by preincubation with 50 millimolar phosphate at a temperature of 38 degrees C. The increase in ATPase activity became higher (five to sixfold) when particles were preincubated with Mg-ATP plus phosphate. Under the latter conditions, collapse of DeltamuH by carbonyl cyanide p-trifluoromethoxyphenylhydrazone prevented the activation. An increase in ATPase activity of the particles was also observed with NADH and succinate, although activation was lower with succinate. With these substrates, phosphate did not increase ATPase activation. When particles were preincubated with Mg-ATP, anions that stimulate ATP hydrolysis (malate, malonate, and bicarbonate) had an activating effect similar to that of phosphate. The data suggest that the soybean mitochondrial ATPase can be activated by DeltamuH but that this activation is increased by the binding of certain anions to a conformation of the enzyme that appears during hydrolytic cycles.

Journal Article↗

PubMed1993

Causal attributions and post-traumatic stress in adolescents.

The aim of the present study was to explore the relationship between causal attributions made by adolescent survivors of the Jupiter cruise ship sinking, and post-traumatic symptomatology in the year following disaster. Evidence is presented that more internal causal attributions for negative and uncontrollable events during the incident are associated with greater post-traumatic stress one year later. The findings are discussed with reference to an attributional model of shame.

Adolescent↗

PubMed2004

Long-term effects of psychological trauma on psychosocial functioning.

BACKGROUND: Most studies of the effects of trauma on mental health have generally not separately assessed psychosocial functioning, and in those that have key issues have received little attention, such as the relation between the time courses of the two kinds of outcome, and detailed assessment of social functioning in a range of domains. The present study made separate assessments with a view to testing four hypotheses. First, that the experience of trauma itself (independently of effects on mental health) has a negative effect on psychosocial functioning; second, that psychopathology following trauma is associated with poorer psychosocial functioning; third, that psychosocial functioning recovers when psychiatric conditions remit; fourth, that post-traumatic stress and depression have different associations with impairments of psycho-social functioning. METHOD: One hundred and fifteen young adults who had survived a shipping disaster (the sinking of the Jupiter in 1988) between 5 and 8 years previously, and 50 control participants were assessed for psychopathology, and for psychosocial functioning using the Adolescent to Adult Personality Functioning Assessment (ADAPFA). RESULTS: Results did not support the first hypothesis: survivors who, although experiencing a traumatic event, did not develop Post Traumatic Stress Disorder or other psychopathology warranting diagnosis, when compared with Controls who had no psychopathology since the time of the disaster, showed no significant differences on any ADAPFA domains or on total score. There was partial support for the second hypothesis: survivors with diagnosable disorder during the rating period showed poorer psychosocial functioning in total ADAPFA score and in the domains of Education/Work, Love Relationships, and Non-specific Social Contacts, though not in other domains. The third hypothesis was supported: recovered Survivors showed no psychosocial impairments compared with unaffected Controls. Results also supported the fourth hypothesis, showing differential effects of post traumatic stress and depression in relation to the extent and kind of psycho-social impairments. CONCLUSIONS: The results lend support to the general model that effects on psychosocial functioning following traumatic experience are mediated by psychopathology, though further research is needed to establish whether the present pattern of findings applies to other kinds of trauma.

Adolescent↗

PubMed1993

Crisis support in the aftermath of disaster: a longitudinal perspective.

Crisis support was assessed over an 18-month period with survivors of the Jupiter cruise ship disaster. It was found that the support received from family and friends decreased significantly over time. In addition, higher crisis support in the immediate aftermath was found to predict less post-traumatic symptomatology at a later period. The results are thought to have implications for the assessment and treatment of survivors at high risk of disturbance.

Adaptation, Psychological↗

PubMed2001

The early evolution of the inner solar system: a meteoritic perspective.

Formation of the solar system may have been triggered by a stellar wind. From then on, the solar system would have followed a conventional evolutionary path, including the formation of a disk and bipolar jets. The now extinct short-lived radionuclides beryllium-10 and, possibly, manganese-53 that were present in meteorites probably resulted from energetic particle irradiation within the solar system. Calcium-aluminum-rich inclusions (the oldest known solar system solids) and chondrules could have been produced by the bipolar jets, but it is more likely that they formed during localized events in the asteroid belt. The chondritic meteorites formed within the temperature range (100 to 400 kelvin) inferred for the midplane of classical T Tauri disks at 2 to 3 astronomical units from their central stars. However, these meteorites may retain a chemical memory of earlier times when midplane temperatures were much higher. Dissipation of the solar nebula occurred within a few million years of solar system formation, whereas differentiation of asteroidal-sized bodies occurred within 5 to 15 million years. The terrestrial planets took approximately 100 million years to form. Consequently, they would have accreted already differentiated bodies, and their final assembly was not completed until after the solar nebula had dispersed. This implies that water-bearing asteroids and/or icy planetesimals that formed near Jupiter are the likely sources of Earth's water.

Journal Article↗

PubMed2002

Observations of comet 19P/Borrelly by the miniature integrated camera and spectrometer aboard Deep Space 1.

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (</=345 kelvin, with no trace of water ice or hydrated minerals), consistent with approximately 10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.

Carbon↗

PubMed2003

Planetary science. The glitter of distant seas.

It has long been known that Saturn's largest moon, Titan, has a thick nitrogen atmosphere, which obscures the underlying surface. In his Perspective, Lorenz highlights the report by Campbell et al., who have used the giant Arecibo and Green Bank radio telescopes as a radar to probe Titan's hidden surface. The surface appears to be distinct from those of the icy satellites of Jupiter, in both brightness and polarization. The new data show sharp spikes in the reflected microwave spectrum, indicating large, smooth areas of radar-dark material. These features suggest the widespread existence of lakes or seas of liquid hydrocarbons on Titan.

Astronomical Phenomena↗

PubMed2004

Discovery of mass anomalies on Ganymede.

We present the discovery of mass anomalies on Ganymede, Jupiter's third and largest Galilean satellite. This discovery is surprising for such a large icy satellite. We used the radio Doppler data generated with the Galileo spacecraft during its second encounter with Ganymede on 6 September 1996 to model the mass anomalies. Two surface mass anomalies, one a positive mass at high latitude and the other a negative mass at low latitude, can explain the data. There are no obvious geological features that can be identified with the anomalies.

Journal Article↗

PubMed2004

Ultraviolet imaging spectroscopy shows an active saturnian system.

Neutral oxygen in the saturnian system shows variability, and the total number of oxygen atoms peaks at 4 x 10(34). Saturn's aurora brightens in response to solar-wind forcing, and the auroral spectrum resembles Jupiter's. Phoebe's surface shows variable water-ice content, and the data indicate it originated in the outer solar system. Saturn's rings also show variable water abundance, with the purest ice in the outermost A ring. This radial variation is consistent with initially pure water ice bombarded by meteors, but smaller radial structures may indicate collisional transport and recent renewal events in the past 10(7) to 10(8) years.

Extraterrestrial Environment↗

PubMed2004

Temperatures, winds, and composition in the saturnian system.

Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.

Atmosphere↗

PubMed2006

A thick cloud of Neptune Trojans and their colors.

The dynamical and physical properties of asteroids offer one of the few constraints on the formation, evolution, and migration of the giant planets. Trojan asteroids share a planet's semimajor axis but lead or follow it by about 60 degrees near the two triangular Lagrangian points of gravitational equilibrium. Here we report the discovery of a high-inclination Neptune Trojan, 2005 TN(53). This discovery demonstrates that the Neptune Trojan population occupies a thick disk, which is indicative of "freeze-in" capture instead of in situ or collisional formation. The Neptune Trojans appear to have a population that is several times larger than the Jupiter Trojans. Our color measurements show that Neptune Trojans have statistically indistinguishable slightly red colors, which suggests that they had a common formation and evolutionary history and are distinct from the classical Kuiper Belt objects.

Evolution, Planetary↗

PubMed2006

Exotic Earths: forming habitable worlds with giant planet migration.

Close-in giant planets (e.g., "hot Jupiters") are thought to form far from their host stars and migrate inward, through the terrestrial planet zone, via torques with a massive gaseous disk. Here we simulate terrestrial planet growth during and after giant planet migration. Several-Earth-mass planets also form interior to the migrating jovian planet, analogous to recently discovered "hot Earths." Very-water-rich, Earth-mass planets form from surviving material outside the giant planet's orbit, often in the habitable zone and with low orbital eccentricities. More than a third of the known systems of giant planets may harbor Earth-like planets.

Astronomical Phenomena↗

PubMed2006

Discovery of a young planetary-mass binary.

We have identified a companion to the young planetary-mass brown dwarf Oph 162225-240515. This pair forms a resolved binary consisting of two objects with masses comparable to those of extrasolar giant planets. Several lines of evidence confirm the coevality and youth of the two objects, suggesting that they form a physical binary. Models yield masses of approximately 14 and approximately 7 times the mass of Jupiter for the primary and the secondary object, respectively, at an age of approximately 1 million years. A wide ( approximately 240-astronomical unit) binary in the ultra-low-mass regime poses a challenge to some popular models of brown dwarf formation.

Journal Article↗

PubMed2006

The phase-dependent infrared brightness of the extrasolar planet upsilon Andromedae b.

The star upsilon Andromedae is orbited by three known planets, the innermost of which has an orbital period of 4.617 days and a mass at least 0.69 that of Jupiter. This planet is close enough to its host star that the radiation it absorbs overwhelms its internal heat losses. Here, we present the 24-micrometer light curve of this system, obtained with the Spitzer Space Telescope. It shows a variation in phase with the orbital motion of the innermost planet, demonstrating that such planets possess distinct hot substellar (day) and cold antistellar (night) faces.

Astronomical Phenomena↗

PubMed1995

Infrared spectrum of the cool brown dwarf Gl 229B.

Spectroscopic measurements of a cool brown dwarf, Gl 229B, reveal absorption features attributable to methane in the near infrared much like those of Jupiter. These features are not seen in any star. The presence of methane indicates that the surface temperature of Gl 229B is below 1000 kelvin. Features attributed to water vapor also indicate that Gl 229B is much cooler than any known star.

Extraterrestrial Environment↗