62 research outputs found
Evidence for methane and ammonia in the coma of comet P/Halley
Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH_3 , and uniquely NH_3 , in coma gases in order to explain the data. A ratio of production rates Q(NH_3)/Q(H20) = 0.01-Q.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15.
The observations are fit best with Q(CH_4)/Q(H_20) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material
The Cassini Ion and Neutral Mass Spectrometer (INMS) Investigation
The Cassini Ion and Neutral Mass Spectrometer (INMS) investigation will determine the mass composition and number densities of neutral species and low-energy ions in key regions of the Saturn system. The primary focus of the INMS investigation is on the composition and structure of Titan’s upper atmosphere and its interaction with Saturn’s magnetospheric plasma. Of particular interest is the high-altitude region, between 900 and 1000 km, where the methane and nitrogen photochemistry is initiated that leads to the creation of complex hydrocarbons and nitriles that may eventually precipitate onto the moon’s surface to form hydrocarbon–nitrile lakes or oceans. The investigation is also focused on the neutral and plasma environments of Saturn’s ring system and icy moons and on the identification of positive ions and neutral species in Saturn’s inner magnetosphere. Measurement of material sputtered from the satellites and the rings by magnetospheric charged particle and micrometeorite bombardment is expected to provide information about the formation of the giant neutral cloud of water molecules and water products that surrounds Saturn out to a distance of ∼12 planetary radii and about the genesis and evolution of the rings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43764/1/11214_2004_Article_1408.pd
The distribution of ion acceptance in atmospheric pressure ion sources: Spatially resolved APLI measurements
Reactions of CH3OCH2+ with hydrocarbons and O, N, and S compounds: Applications for chemical ionization in selected ion flow tube studies
Use of a double resonance electron capture dissociation experiment to probe fragment intermediate lifetimes
The Positive Effects of Status Conflicts in Teams Where Members Perceive Status Hierarchies Differently
Near-Winners in Status Competitions: Neglected Sources of Dynamism in the Matthew Effect
Current research on status hierarchy dynamics focuses on the potential for, and constraints to, individual mobility. In this essay, I argue that Merton’s Matthew Effect incorrectly categorizes activity below a status threshold as linear. This misspecification calls into question existing models of competitions for social status. I argue for an improved theory of status tournaments as asymmetric, non-binary, and agentic. Through that new perspective, I raise questions for the legitimacy and power of stratifying institutions
Beyond high and low: Obstacles and opportunities associated with conceptualizing middle power and other middle‐range effects
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