Circumstellar disks and the search for neighbouring planetary systems

The recent discoveries of planets orbiting several 'mature' stars bring new life to the question of just how common other planetary systems might be. Observations of very young stars provide a way to address this question and suggest that a significant number of such stars harbour conditions appropriate for the formation of planetary systems like our own.     

Observations of the north polar region of Mars from the Mars orbiter laser altimeter

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.     

Water in Betelgeuse and Antares

Absorption lines of hot water have been identified in the infrared spectra of Betelgeuse (alpha Orionis) and Antares (alpha Scorpii) near 12.3 micrometers (811 to 819 wavenumbers). The water lines originate in the atmospheres of the stars, not in their circumstellar material. The spectra are similar in structure to umbral sunspot spectra. Pure rotation water lines of this type will occur throughout the spectra of cool stars at wavelengths greater than 10 micrometers. From the water spectra, the upper limit for the temperature in the line formation region in both stars is 2800 kelvin. The water column density in both stars is (3 +/- 2) x 10(18) molecules per square centimeter, yielding an abundance relative to atomic hydrogen of n(H2O)/n(H) approximately 10(-)7.     

Cloud Variations under Subtropical High Conditions

T The cloud variations under subtropical high (STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction. The results reveal that clouds mainly experience an isolated evolution in the STHs, which is designated in this study by the 1540 gpm geopotential lines at 850 hPa. In the STH domain throughout the Northern Hemisphere, the average amount of total clouds exceeds 30%. Low clouds dominate in the STH domain, contributing over 60% of total cloud amount within the Pacific subtropical high and over 40% within the Atlantic subtropical high. The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa, which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface. Furthermore, clouds present great geographical incoherence within the STH domain. In the eastern STHs, the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon, while the amount of high clouds remains stable throughout the day. Conversely, in the western STHs, the diurnal amplitude of low and middle clouds is less than three, while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening. Among the nine cloud categories, stratocumulus clouds with greater optical thickness account for the most under STH conditions, no matter their occurrence or amount, causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.     

Production of O2 on icy satellites by electronic excitation of low-temperature water ice

The signature of condensed molecular oxygen has been reported in recent optical-reflectance measurements of the jovian moon Ganymede, and a tenuous oxygen atmosphere has been observed on Europa. The surfaces of these moons contain large amounts of water ice, and it is thought that O2 is formed by the sputtering of ice by energetic particles from the jovian magnetosphere. Understanding how O2 might be formed from low-temperature ice is crucial for theoretical and experimental simulations of the surfaces and atmospheres of icy bodies in the Solar System. Here we report laboratory measurements of the threshold energy, cross-section and temperature dependence of O2 production by electronic excitation of ice in vacuum, following electron-beam irradiation. Molecular oxygen is formed by direct excitation and dissociation of a stable precursor molecule, rather than (as has been previously thought) by diffusion and chemical recombination of precursor fragments. The large cross-section for O2 production suggests that electronic excitation plays an important part in the formation of O2 on Ganymede and Europa.     

Structure and dynamics of amorphous water ice

Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.     

Transient clouds in Titan's lower atmosphere

The 1980 encounter by the Voyager 1 spacecraft with Titan, Saturn's largest moon, revealed the presence of a thick atmosphere containing nitrogen and methane (1.4 and approximately 0.05 bar, respectively). Methane was found to be nearly saturated at Titan's tropopause, which, with other considerations, led to the hypothesis that Titan might experience a methane analogue of Earth's vigorous hydrological cycle, with clouds, rain and seas. Yet recent analyses of Voyager data indicate large areas of super-saturated methane, more indicative of dry and stagnant conditions. A resolution to this apparent contradiction requires observations of Titan's lower atmosphere, which was hidden from the Voyager cameras by the photochemical haze (or smog) in Titan's stratosphere. Here we report near-infrared spectroscopic observations of Titan within four narrow spectral windows where the moon's atmosphere is ostensibly transparent. We detect pronounced flux enhancements that indicate the presence of reflective methane condensation clouds in the troposphere. These clouds occur at a relatively low altitude (15+/-10 km), at low latitudes, and appear to cover approximately 9 per cent of Titan's disk.     

A rotating disk of gas and dust around a young counterpart to beta Pictoris

beta Pictoris is the best known example of a main-sequence star encircled by a tenuous disk. Optical and infrared images of beta Pic suggest that the disk is composed of dust grains which have been interpreted as the debris generated by the disruption of the asteroid-sized remnants of planet-formation processes. The star itself is relatively old, with an age in excess of 100 Myr. Here we present high-resolution millimetre-wave images of continuum and molecular-line emission from dust and gas surrounding a much younger star, MWC480: the stellar properties of MWC480 are similar to those of beta Pic, but its age is just 6Myr. The morphology of the circumstellar material and a comparison with the predictions of kinematic modelling indicate the presence of a rotating disk, gravitationally bound to the star. Moreover, the mass of the disk is greater than the minimum required to form a planetary system like our own. We therefore suggest that the disk around the young star MWC480 could be a progenitor of debris disks of the type associated with older stars such as beta Pic, and so holds much promise for the study of both the origin of debris disks and the early stages of the formation of planetary systems.     

Thermal polymerization of amino acids under various atmospheres or at low pressures

The kinds and proportions of amino acids formed in two simulated prebiotic experiments or detected in hydrolyzed extracts of three extraterrestrial samples were found to polymerize thermally under various atmospheres or at low pressures. Yields, tested properties, and amino acid compositions of the polymers were not influenced by the type of enveloping atmosphere, including two simulated prebiotic atmospheres and five pure gases. However, polyamino acids prepared at low pressure (0.02, 10(-4) atm) were obtained in appreciably greater yield than those synthesized at 1 atm; amino acid composition was somewhat influenced by low pressure. The results indicate that polyamino acids could have been formed thermally under a variety of possible prebiotic atmospheres and on planetary bodies of low atmospheric pressure.     

Sensitive colorimetric determination of cholesterol in dairy products

Cholesterol can be determined colorimetrically in dairy products at levels of larger than or equal to 10 mug (coefficient of variation = 5.3%) with an o-phthalaldehyde reagent when non-cholesterol lipids are eliminated prior to color development. Absorbance for 2 mg tripalmitin was found to be equivalent to about 20 mug cholesterol. Saponification followed by hexane extraction removed interfering lipids. Using the described procedure, 238 individual raw milk samples were found to contain 144.4+/-37.9 mug cholesterol/ml, while their skim milk portions had 26.5+/-6.4 mug cholesterol/ml (mean +/- standard deviation). The o-phthalaldehyde cholesterol estimates agreed with those obtained by a gas-liquid chromatographic procedure when cheese and ice cream were analyzed by the colorimetric procedure with and without prior fat extraction.     

Detection of atomic deuterium in the upper atmosphere of Mars

High-resolution spectroscopy of Mars' atmosphere with the Hubble Space Telescope revealed the deuterium Lyman alpha line at an intensity of 23 +/- 6 rayleighs. This measured intensity corresponds to HD/H2 = 1.5 +/- 0.6 x 10(-4), which is smaller by a factor of 11 than HDO/H2O. This indicates that fractionation of HD/H2 relative to that of HDO/H2O is not kinetically controlled by the rates of formation and destruction of H2 and HD but is thermodynamically controlled by the isotope exchange HD + H2O left and right arrow HDO + H2. Molecular hydrogen is strongly depleted in deuterium relative to water on Mars because of the very long lifetime of H2 (1200 years). The derived isotope fractionation corresponds to an estimate of a planetwide reservoir of water ice about 5 meters thick that is exchangeable with the atmosphere.     

Unaltered cosmic spherules in a 1.4-Gyr-old sandstone from Finland

Micrometeorites-submillimetre-sized particles derived from asteroids and comets-occur in significant quantities in deep sea sediments, and the ice sheets of Greenland and Antarctica. The most abundant micrometeorites are cosmic spherules, which contain nickel-rich spinels that were crystallized and oxidized during atmospheric entry, therefore recording the oxygen content in the uppermost atmosphere. But the use of micrometeorites for detecting past changes in the flux of incoming extraterrestrial matter, and as probes of the evolution of the atmosphere, has been hampered by the fact that most objects with depositional ages higher than 0.5 Myr show severe chemical alteration. Here we report the discovery of unaltered cosmic spherules in a 1.4-Gyr-old sandstone (red bed) from Finland. From this we infer that red beds, a common lithology in the Earth's history, may contain substantial unbiased populations of fossil micrometeorites. The study of such populations would allow systematic research on variations in the micrometeorite flux from the early Proterozoic era to recent times (a time span of about 2.5 Gyr), and could help to better constrain the time when the atmospheric oxygen content was raised to its present level.     

Atmosphere-surface interactions on Mars: delta 17O measurements of carbonate from ALH 84001

Oxygen isotope measurements of carbonate from martian meteorite ALH 84001 (delta18O = 18.3 +/- 0.4 per mil, delta17O = 10.3 +/- 0.2 per mil, and Delta17O = 0.8 +/- 0.05 per mil) are fractionated with respect to those of silicate minerals. These measurements support the existence of two oxygen isotope reservoirs (the atmosphere and the silicate planet) on Mars at the time of carbonate growth. The cause of the atmospheric oxygen isotope anomaly may be exchange between CO2 and O(1D) produced by the photodecomposition of ozone. Atmospheric oxygen isotope compositions may be transferred to carbonate minerals by CO2-H2O exchange and mineral growth. A sink of 17O-depleted oxygen, as required by mass balance, may exist in the planetary regolith.     

Modeling and Forecasting of Bohai Sea Ice

The sea ice model for simulating ice growth, decay, and drift in the Bohai Sea was developed based on the ice conditions in the Sea and on existing sea ice models. Both dynamic and thermodynamic processes of sea ice are incorporated into the model. The viscous-plastic constitutive law is applied to estimate the internal ice stress. The thermodynamic growth rates are determined from the effect of thermodynamic forcing from atmosphere and ocean, which are parameterized according to the heat exchanges at the air∕ice, air∕water, and ice∕water interfaces. This model is coupled with an oceanic model and is linked to a numerical weather prediction model for forecasting ice conditions in the Bohai Sea and the northern Yellow Sea. Statistical verification was used to make an objective assessment of the model. This paper summarizes the development of the sea ice model and its application in Bohai Sea ice forecast.     

The influence of volume fraction of SiC particles on the properties of Al/SiC<Subscript>p</Subscript> nanocomposites produced by powder metallurgy with high energy ball milling

In this research, the objective is to investigate the effect of the volume percentage of SiC nanoparticles on the physical and mechanical properties of Al/SiC composite produced by powder metallurgy. For the mixing and the proper dispersion of SiC nanoparticles with 0, 1, 3 and 5% volume fraction of SiC in the aluminum matrix, a high energy planetary ball mill with the speed of 350 rpm and ball to powder weight ratio of 10: 1 was used under argon atmosphere. The powder samples were pressed in an onside template under a pressure of 500 MPa and sintered in a tube furnace under argon atmosphere for 2 h at 610°C. FE-SEM image and EDS analysis revealed that SiC nanoparticles represent uniformly dispersion in the aluminum matrix and the density of all the samples have increased while the porosity percentages have dramatically decreased after the sintering process. Furthermore, with the increase of the volume fraction of SiC nanoparticles the hardness also increases.     

T/A-analysis with or without measuring force: problems in the evaluation of normal limits

Turn/amplitude-analysis (TAA) has been applied to interference patterns of the right m. biceps brachii and the right m. rectus femoris of 33 healthy women aged 19 to 53 years. Interference patterns were recorded at 20, 40 and 60% +/- 10% of both muscles maximum force. The dependency of the turn/amplitude-parameters (T/A-parameters) on age, muscle and force is discussed. Normal limits for individual means of the T/A-parameters were calculated in form of the +/- 2 SD. Normal limits for single values were calculated in form of clouds. Both methods were applied to the values of each force level (20, 40 and 60%) and of all force levels together (10-70%). Clouds of the present study were clearly different from those of St?lberg. Evaluating individual means rates of false positive results were higher compared to those of single values. Rates of false positive results for single values and individual means of the parameters T/S and A/T were lower at the 20% force level than at the higher force levels and without measuring force. For the application of the TAA we advise every electrophysiological laboratory 1) to evaluate single values instead of individual means, 2) to use clouds instead of the +/- 2 SD as normal limits, 3) to measure force until a modified cloud-method will be applicable and 4) to elaborate its own normal limits.     

Results from the Mars Global Surveyor Thermal Emission Spectrometer

The Thermal Emission Spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase, together with about a 35 percent dust component provides the best fit to the spectrum. Qualitative upper limits can be placed on the concentration of carbonates (<10 percent), olivine (<10 percent), clay minerals (<20 percent), and quartz (<5 percent) in the limited regions observed. Limb observations in the northern hemisphere reveal low-lying dust hazes and detached water-ice clouds at altitudes up to 55 kilometers. At an aerocentric longitude of 224 degrees a major dust storm developed in the Noachis Terra region. The south polar cap retreat was similar to that observed by Viking.     

Health information processed under limited attention: Is it better to be "hot" or "cool?"

Introduction: The attentional myopia model (T. Mann & A. Ward, 2004) posits that under conditions of limited attention, individuals will be disproportionately influenced by highly salient cues. The "hot/cool" model (J. Metcalfe & W. Mischel, 1999) suggests that cues designed to activate "hot" emotional systems will typically dominate attention and promote relevant behavior more than cues designed to activate "cool" cognitive systems. Method: While under conditions of high or low cognitive load, participants heard information regarding the use of a zinc supplement and reported their intentions to try it. In Study 1, cool message cues that promoted the use of zinc were more salient than hot cues that discouraged its use. In Study 2, hot cues that discouraged the use of zinc were more salient than cool cues that promoted its use. Results: In both studies, the imposition of cognitive load increased the influence of salient cues, regardless of their motivational "temperature." Conclusions: Consistent with the attentional myopia model, either hot or cool health message cues can exert strong influence over individuals, depending on the relative salience of those cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modifications to the rate of wound contraction by allopurinol

The effect of allopurinol (50 mg/kg) on the rate of full thickness excisional wound contraction in the Hooded Lister rat was assessed by planimetric and histological examinations. Compared with control animals, those treated with allopurinol showed a significantly lower coefficient of wound area contraction for days 0-7 (p < 0.05) than those of control animals. Histologically, in the allopurinol treated wounds the granulation tissue was less cellular but appeared to contain more collagen. This inhibition by allopurinol of the contraction phase of wound healing associated with an increased quantity of granulation tissue suggests that mediation of the process may involve a complex interaction between the fibroblasts/myofibroblasts and free radicals.     

H3+ in dense and diffuse clouds

Interstellar H3+ has been detected in dense as well as diffuse clouds using three 3.7 microns infrared spectral lines of the nu 2 fundamental band. Column densities of H3+ from (1.7-5.5) x 10(14) cm-2 have been measured in dense clouds in absorption against the infrared continua of the deeply embedded young stellar objects GL2136, W33A, MonR2 IRS 3, GL961E, and GL2591. Strong and broad H3+ absorptions have been detected in dense and diffuse clouds towards GC IRS 3 and GCS3-2 in the region of the galactic center. A large column density of H3+, comparable to that of a dense cloud, has been detected towards the visible star Cygnus OB2 No. 12, which has a line of sight that crosses mostly diffuse clouds. The H3+ chemistry of dense and diffuse clouds are discussed using a very simple model. Some future projects and problems are discussed.