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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.034 Byline: Sarah F. Newman (a), B.J. Buratti (a), R.H. Brown (b), R. Jaumann (c), J. Bauer (a), T. Momary (a) Keywords: Geological processes; Ices; IR spectroscopy; Saturn; Satellites Abstract: Saturn's satellite Dione is becoming an increasingly important object in the outer Solar System, as evidence for its current activity accumulates. Infrared observations of the surface can provide clues to the history of the body and currently active processes. Using data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS), we perform three sets of analyses that are sensitive to the ice state, temperature, thermal history, grain size and composition of surface ice. These are calculation of a 'crystallinity factor', spectral ratios and water ice band depths. In our analysis, we focus on the dichotomy between the wispy and dark terrain on Dione's trailing hemisphere, to better understand the source of the different materials and their current properties. Our results suggest two different scenarios: (1) the ice from the wispy region has a higher crystallinity and water ice content than the dark region or (2) the wispy region contains larger grains. Both of these models imply recent geologic activity on Dione. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 183-501, Pasadena, CA 91109, USA (b) Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., P.O. Box 210092, Tucson, AZ 85721-0092, USA (c) German Aerospace Center (DLR), Germany, RutherfordstraAe 2, 12489 Berlin, Germany Article History: Received 12 July 2007; Revised 23 February 2009; Accepted 9 April 2009

Amyotrophic lateral sclerosis (ALS) is a fatal degenerative motor neuron disorder. Ten percent of cases are inherited; most involve unidentified genes. We report here 13 mutations in the fused in sarcomo/translated in liposarcoma (FUS/TLS) gene on chromosome 16 that were specific for familial ALS. The FUS/TLS protein binds to RNA, functions in diverse processes, and is normally located predominantly in the nucleus. In contrast, the mutant forms of FUS/TLS accumulated in the cytoplasm of neurons, a pathology that is similar to that of the gene TAR DNA-binding protein 43 (TDP43), whose mutations also cause ALS. Neuronal cytoplasmic protein aggregation and defective RNA metabolism thus appear to be common pathogenic mechanisms involved in ALS and possibly in other neurodegenerative disorders.

Titan was once thought to have global oceans of light hydrocarbons on its surface (1-5), but after 40 close flybys of Titan by the Cassini spacecraft, it has become clear [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.04.019 Byline: Sarah F. Newman (a), B.J. Buratti (a), R.H. Brown (b), R. Jaumann (c), J. Bauer (a), T. Momary (a) Keywords: Enceladus; Geological processes; Ices; Saturn; satellites Abstract: Photometric and spectral analysis of data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) has yielded significant results regarding the properties and composition of the surface of Saturn's satellite Enceladus. We have obtained spectral cubes of this satellite, containing both spatial and spectral information, with a wavelength distribution in the infrared far more extensive than from any previous observations and at much higher spatial resolution. Using a composite mosaic of the satellite, we map the distribution of crystalline and amorphous ices on the surface of Enceladus according to a 'crystallinity factor' and also the depth of the temperature- and structure-dependent 1.65 micron water-ice band. These maps show the surface of Enceladus to be mostly crystalline, with a higher degree of crystallinity at the 'tiger-stripe' cracks and a larger amorphous signature between these stripes. These results suggest recent geological activity at the 'tiger stripe' cracks and an intriguing atmospheric environment over the south pole where amorphous ice is produced either through intense radiative bombardment, flash-freezing of cryovolcanic liquid, or rapid condensation of water vapor particles on icy microspherules or on the surface of Enceladus. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 183-501, Pasadena, CA 91109, USA (b) Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., P.O. Box 210092, Tucson, AZ 85721-0092, USA (c) German Aerospace Center (DLR), RutherfordstraAe 2, 12489 Berlin, Germany Article History: Received 15 November 2006; Revised 13 April 2007

Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350-5100 nm reflectance spectra and phase curves at 550-2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000-1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a fiat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm [H.sub.2]O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The C[O.sub.2] band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0[degrees]-144[degrees] range; Rhea shows an opposition surge at visible wavelengths in the 0.5[degrees]-1.17[degrees] interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping-despiking algorithm) are discussed in appendices. Keywords: Saturn, satellites; Spectroscopy; Infrared observations; Image processing

The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of < 90[degrees], resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible [sup.13]C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data. Keywords: Satellites; Galilean satellites; Jupiter system: Satellite surfaces: Surface composition; Space mission

During the Cassini-Jupiter flyby, VIMS observed Io at different phase angles, both in full sunlight and in eclipse. By using the sunlight measurements, we were able to produce phase curves in the visual through all the near infrared wavelengths covered by the VIMS instrument (0.85-5.1 [micro]m). The phase angle spanned from ~2[degrees] to ~120[degrees]. The measurements, done just after Io emerged from Jupiter's shadow, show an increase of about 15% in Io's reflectance with respect to what would be predicted by the phase curve. This behavior is observed at wavelengths > 1.2 [micro]m. Moreover, just after emergence from eclipse an increase of about 25% is observed in the depth of S[O.sub.2] frost bands at 4.07 and 4.35 [micro]m. At 0.879 < [lambda] < 1.04 [micro]m the brightening is 10-24%. Below [lambda] = 0.879 [micro]m the brightening, if present, should be less than the precision of our measurements (~5%). Apparently, these observations are not explained neither by a diverse spatial distribution of S[O.sub.2] on the Io' surface nor by atmospheric S[O.sub.2] condensation on the surface during the eclipse. Keywords: Io; Atmosphere; Infrared observations: Satellites of Jupiter

We present the results of spectral modeling of 17 Trojan asteroids. The surface composition of this group of objects (located just beyond the main belt, trapped in Jupiter's stable Lagrange points) remains uncertain due to an absence of diagnostic absorption features in their spectra. We quantitatively analyze spectra of these objects covering the range 0.34.0 [micro]m using the formulation for scattering in a particulate medium developed by Hapke. Since the widest spectral range possible is desired to provide the most robust results, recently measured near-IR spectra are combined with previously published visible and near-IR data. These composite spectra are converted to and modeled in terms of geometric albedo to provide the additional constraint of the absolute brightness of the asteroids. It is important that this modeling is performed for a large number of objects, and results are derived based on trends among best-fit models. Under this vigorous examination, we find that it is unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. Instead, anhydrous silicates adequately describe the spectral characteristics of this group of objects. A significant fraction of carbonaceous material is also likely present, but is not responsible for the red spectral slope in these models. Also, using these models, we estimate that these surfaces contain at most a few wt% of [H.sub.2]O ice and no more than 10-30 wt% of hydrated silicates. Keywords: Asteroids, composition; Kuiper belt objects; Radiative transfer; Spectroscopy; Surface, asteroids

Spectra of Asteroid 9969 Braille in the 1.25-2.6 [micro]m region returned by the Deep Space 1 (DS1) Mission show a ~ 10% absorption band centered at 2 [micro]m, and a reflectance peak at 1.6 [micro]m. Analysis of these features suggest that the composition of Braille is roughly equal parts pyroxene and olivine. Its spectrum between 0.4 and 2.5 [micro]m suggests that it is most closely related to the Q taxonomic type of asteroid. The spectrum also closely matches that of the ordinary chondrites, the most common type of terrestrial meteorite. The geometric albedo of Braille is unusually high ([p.sub.v] = 0.34), which is also consistent with its placement within the rarer classes of stony asteroids, and which suggests it has a relatively fresh, unweathered surface, perhaps due to a recent collision. Keywords: Asteroids NEOs; 9969 Braille; Deep Space 1

During the last two minutes before closest approach of Deep Space 1 to Comet 19P/Borrelly, a long exposure was made with the short-wavelength infrared (SWIR) imaging spectrometer. The observation yielded 46 spectra covering 1.3 2.6 [micro]m; the footprint of each spectrum was ~160 m x width of the nucleus. Borrelly's highly variegated and extremely dark 8-km-long nucleus exhibits a strong red slope in its short-wavelength infrared reflection spectrum. This slope is equivalent to J-K and H K colors of ~0.82 and ~0.43, respectively. Between 2.3-2.6 [micro]m thermal emission is clearly detectable in most of the spectra. These data show the nucleus surface to be hot and dry; no trace of [H.sub.2]O ice was detected. The surface temperature ranged continuously across the nucleus from [less than or equal to] 300 K near the terminator to a maximum of ~340 K, the expected sub-solar equilibrium temperature for a slowly rotating body. A single absorption band at ~2.39 [micro]m is quite evident in all of the spectra and resembles features seen in nitrogen-bearing organic molecules that are reasonable candidates for compositional components of cometary nuclei. However as of yet the source of this band is unknown. Keywords: Comet: Temperature: Thermal emission; Imaging spectrometer: Short-wavelength intfrared; SWIR: JHK color; Nitrogen-bearing organic molecules: H-K color: J-H color: Infrared spectra; Spectral absorption; Nucleus: Short-period comets: 19P/Borrelly; Borrelly: Deep Space 1

The nucleus, coma, and dust jets of short-period Comet 19P/Borrelly were imaged from the Deep Space 1 spacecraft during its close flyby in September 2001. A prominent jet dominated the near-nucleus coma and emanated roughly normal to the long axis of nucleus from a broad central cavity. We show it to have remained fixed in position for more than 34 hr, much longer than the 26-hr rotation period. This confirms earlier suggestions that it is co-aligned with the rotation axis. From a combination of fitting the nucleus light curve from approach images and the nucleus' orientation from stereo images at encounter, we conclude that the sense of rotation is right-handed around the main jet vector. The inferred rotation pole is approximately perpendicular to the long axis of the nucleus, consistent with a simple rotational state. Lacking an existing IAU comet-specific convention but applying a convention provisionally adopted for asteroids, we label this the north pole. This places the sub-solar latitude at ~60[degrees] N at the time of the perihelion with the north pole in constant sunlight and thus receiving maximum average insolation. Keywords: Comet; Imaging; Nucleus; Topography; Coma; Dust jet; Short-period comets; 19P/Borrelly; Borrelly; Deep Space 1; Rotation axis; Rotation pole

We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a 'mirror' for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing technique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times. Keywords: Occultations; Jupiter; Infrared observations

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer coveting the wavelength range 0.3-5.2 [micro]m in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 [micro]m are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120[degrees]). Similarities in the center-to-limb profiles of [H.sup.+.sub.3] and C[H.sub.4] emissions indicate that the [H.sup.+.sub.3] ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian N[H.sub.3] absorption at 0.93 [micro]m is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 [micro]m, and a geometric albedo of 0.06 [+ or -] 0.01 at 2.2 [micro]m (assuming an 85-km radius). If the 3-[micro]m feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 [micro]m is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120[degrees] phase angle. Keywords: Jupiter; Jovian satellites; Jupiter's ring; Spectroscopy; Planetary atmospheres; Planetary surfaces; Cassini mission

We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95-2.5 [micro]m), 8 of these in L-band (2.8-4.0 [micro]m), and 14 in the range 0.82.5 [micro]m. These observations nearly double the number of published 0.8-2.5 [micro]m spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., [H.sub.2]O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface. Keywords: Asteroids, composition; Infrared observations; Organic chemistry; Spectroscopy; Surfaces, asteroids

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 ~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., Comets are thought to be frozen records of the ancient primordial material from which the planets formed 4500 million years ago. They delivered some of the inventory of water and [...]

We have observed the leading and trailing hemispheres of Phobos from 1.65 to 3.5 [micro]m and Deimos from 1.65 to 3.12 [micro]m near opposition. We find the trailing hemisphere of Phobos to be brighter than its leading hemisphere by 0.24 [+ or -] 0.06 magnitude at 1.65 [micro]m and brighter than Deimos by 0.98 [+ or -] 0.07 magnitude at 1.65 [micro]m. We see no difference larger than observational uncertainties in spectral slope between the leading and trailing hemispheres when the spectra are normalized to 1.65 [micro]m. We find no 3-[micro]m absorption feature due to hydrated minerals on either hemisphere to a level of ~5-10% on Phobos and ~20% on Deimos. When the infrared data are joined to visible and near-IR data obtained by previous workers, our data suggest the leading (Stickney-dominated) side of Phobos is best matched by T-class asteroids. The spectral slope of the trailing side of Phobos and leading side of Deimos are bracketed by the D-class asteroids. The best laboratory spectral matches to these Parts of Phobos are mature lunar soils and heated carbonaceous chondrites. The lack of 3-[micro]m absorption features on either side of Phobos argues against the presence of a large interior reservoir of water ice according to current models of Phobos' interior (F. P. Fanale and J. R. Salvail 1989, Geophys. Res. Lett. 16, 287-290; Icarus 88, 380-395). Key Words: satellites of Mars; asteroid composition; infrared observations; spectrophotometry.

Saturn's moon Enceladus emits a plume of water vapour and micro-metre-sized ice particles from a series of warm fissures located near its south pole (1-10). This geological activity could be powered or controlled by variations in the tidal stresses experienced by Enceladus as it moves around its slightly eccentric orbit. The specific mechanisms by which these varying stresses are converted into heat, however, are still being debated (11-16). Furthermore, it has proved difficult to find a clear correlation between the predicted tidal forces and measured temporal variations in the plume's gas content (17-19) or the particle flux from individual sources (20,21). Here we report that the plume's horizontally integrated brightness is several times greater when Enceladus is near the point in its eccentric orbit where it is furthest from Saturn (apocentre) than it is when near the point of closest approach to the planet (pericentre). More material therefore seems to be escaping from beneath Enceladus' surface at times when geophysical models predict its fissures should be under tension (12,15,16) and therefore may be wider open., This analysis focuses on 252 images of the Enceladus plume at wavelengths of 0.88-1.56 µm obtained by the Cassini spacecraft's Visual and Infrared Mapping Spectrometer (VIMS) (22) between 2005 and [...]

We have observed in the laboratory that nitrogen condenses initially as a transparent layer if the deposition rate is less than about 3 [[micro]meter]/hr. To correlate our laboratory results with the Voyager observations of Triton and ground-based observations of Pluto, we have calculated the nitrogen deposition rates on these bodies. The maximum deposition rate for Pluto (with 40 K icy surface temperature) is calculated to be about 1.65 [[micro]meter]/hr and for Triton is [approximately equal to]1.38 [[micro]meter]/hr at 38 K. This implies that nitrogen on these bodies may preferentially condense as a transparent layer. Voyager 2 observations in August 1989 revealed that Triton's northern hemisphere had an overall lower albedo than the southern hemisphere. This was surprising since at that time deposition of fresh [N.sub.2] frost should have taken place over most of Triton's northern hemisphere (subsolar point was 45 [degrees] S). In contrast, the subliming southern cap was seen as a bright feature. Our new approach to this problem is based on the combination of the energy balance calculations and the laboratory results. We explain the darker northern hemisphere by the condensation of an initially transparent layer on a dark substrate, which might be dark organics produced by UV photolysis of C[H.sub.4] ice. The bright southern cap can be a result of [N.sub.2] shattering due to the earlier passage of the cubic-hexagonal phase transition fronts. If there is a similar puzzling north/south albedo asymmetry on Pluto, as indicated by two independent sets of observations (M. W. Buie, D. J. Tholen, and K. Horne, 1992, Icarus 97, 211-227; E. F. Young and R. P. Binzel, 1993, Icarus 102, 134-149), our results offer an explanation for it. We also infer an original grain size of [N.sub.2] ice on Triton and, possibly, on Pluto. The role of impurities is discussed.

A coupled Finite Element-State Space (CFE-SS) model of switched reluctance motor (SRM) drive systems is used to evaluate the impact of chopping on the machine performance characteristics. The model is used to predict the impact of chopping on the machine inductance profiles, armature currents, and core losses. The modeling environment utilizes an iterative approach which includes the full impact of nonlinearities on the machine magnetic circuit, that results in the nonsinusoidal flux density waveforms in the different parts of the machine. The modeling approach is applied to a four phase SRM. Furthermore, the predicted results are verified by comparison to experimental data.

Transpiration efficiency (TE) is the weight of dry matter produced per unit of transpiration. If mineral nutrients are taken up in proportion to transpiration, then the concentration of minerals in dry matter may be predictive of TE. It has recently been reported that specific leaf weight (SLW) is also correlated with TE. Since both mineral concentration and SLW are easily and inexpensively measured, they may be valuable predictors of TE. Five experiments with 7 to 19 genotypes of peanut (Arachis hypoguea L.; [C.sub.3] species) and four experiments with 9 or 10 genotypes of pearl millet [Pennisetum glaucum (L.) R. Br.; C4 species] were conducted to assess the predictive value of mineral concentration and SLW for TE. In peanut experiments, samples were also analyzed for C isotope discrimination (Δ). Plants were grown in pots in the greenhouse in sand, soil, and solution culture. Specific leaf weight, Δ, ash, and mineral element concentrations were determined at the end of the experiments. There was a strong negative correlation between Δ and TE in the four peanut experiments in which Δ was determined. Leaf ash concentration was negatively correlated with TE in four out of six comparisons for each of the species (r = -0.55 to -0.88). In peanut, Ca and Mg were negatively correlated with TE. No other elements were consistently related to TE in either peanut or pearl millet. The SLW was positively correlated with TE. Thus, both leaf ash and SLW were predictive of TE, but further research is needed to determine the physiological bases for the relationships and their general applicability., Transpiration efficiency is an important characteristic in environments deficient in water. Variation among cultivars in TE has been demonstrated for several crop species (Hubick et al., 1986; Hubick and Farquhar, [...]

For the first time the role of the internal heat source, due to radioactive decay in Triton's core, is investigated with respect to geyser-like plumes. Triton is one of only three known objects in the Solar System (the other two are Earth and the jovian satellite Io) where eruptive activity has been definitely observed. A new mechanism of energy supply to the Tritonian eruptive plumes is proposed. This mechanism is based on heat transport in the solid-nitrogen polar caps due to thermal convection, in addition to conduction. The conductive-convective model shows that a 1 K increase in the [N.sub.2] ice subsurface temperature over the surface value is reached much closer to the surface in the region of an upwelling subsurface plume compared with a pure conductive case. This temperature rise is sufficient to double the nitrogen vapor pressure. Therefore, it is enough to drive the atmospheric plumes to the observed height of [approximately equal to]8 km, provided 1 K warmer nitrogen ice encounters a vent and hence is exposed to the [approximately equal to]15-[micro]bar Tritonian atmosphere. Solid-state convection onsets if a nitrogen layer is sufficiently thick and the average solid [N.sub.2] grain size is small enough. Critical values of these parameters are presented for Triton. A possible origin of the subsurface vents on Triton is also suggested.

Selection in 'Pensacola' bahiagrass (Paspalum notatum Flugge var. 'saurae' Parodi) has resulted in populations with higher forage yields. This research was conducted to study physiological and morphological traits that might be related to the yield increases. Plants of populations representing selection Cycles 0 (Pensacola), 9 ('Tifton 9') and 14 (T14) were grown in the greenhouse and leaf photosynthesis and plant growth were measured. Height and diameter were measured and rhizomes were counted on spaced plants of the same populations in the field. One field experiment was established with seedlings, and another with seedlings and plants taken from plots mowed to 3.5 cm every 2 wk for 2 yr. Leaf photosynthesis was higher for Pensacola than for Tifton 9 and T14. Dry weights of greenhouse-grown plants were similar at 84 d of age, but for older plants of Tifton 9 and T14 weights were 31 and 58% greater, respectively, than for Pensacola. Tifton 9 and T14 were 26 and 60% taller, respectively, than Pensacola at 84 d of age, and height/diameter ratios of field-grown plants were greater for Tifton 9 and T14, Pensacola had more rhizomes than Tifton 9 and T14. Plants of T14 from mowed plots were more prostrate and had 2.8 times more rhizomes than those from seedlings, but for Tifton 9 and Pensacola the source of plants had no effect. Winter survival at this location was greater than 90% for Pensacola, but it was 51 and 64% for T14 in two experiments. It appears that selection for increased yield in bahiagrass resulted in taller plants with fewer rhizomes, a greater tendency for winter injury, and a greater susceptibility to population shifts under close, frequent mowing.

Yields of bahiagrass (Paspalum notatum Flugge) have been increased over that of 'Pensacola' through several cycles of selection. To determine factors contributing to the increased yields, a field experiment was conducted for 3 yr to examine yields, biomass, and leaf area index of three populations representing Cycles 0 (Pensacola, original population), 9 ('Tifton 9') and 14 (T14). Plots were mowed every 2 wk at 3.5- and 10-cm heights and quadrat samples were taken to estimate dry weights of stubble after mowing plus rhizomes. In the first harvest year, T14 yielded more than the other two populations when mowed at 3.5 cm, but less when mowed at 10 cm. Yields averaged across the second and third years and across cutting heights were 20 and 25% higher for Tifton 9 and T14, respectively, than for Pensacola. Total biomass (excluding roots) was higher in July of the first year for Pensacola than for Tifton 9 and T14, and for the latter two, harvested yield made up a larger percentage of the total. However, in July of the third year neither biomass nor percentage of the biomass harvested differed among the populations. Stubble plus rhizome weights increased throughout the 3-yr period and were higher for Pensacola than Tifton 9 and T14 because of its more prostrate growth habit. If the annual increase in weight of stubble plus rhizomes were added to harvested yields, then biomass production by Tifton 9 and T14 was 12.4 and 12.9 t [ha.sup.-1] [yr.sup.-1], respectively, compared with 10.4 t [ha.sup.-1] [yr.sup.-1] for Pensacola. Thus, it appears that selection for increased yield has resulted in increased allocation of dry matter to harvestable foliage and possibly a greater production of non-root biomass.