The Role of Sulfur Dioxide in Stratospheric Aerosol Formation Evaluated Using In-Situ Measurements in the Tropical Lower Stratosphere.

Stratospheric aerosols (SAs) are a variable component of the Earth's albedo that may be intentionally enhanced in the future to offset greenhouse gases (geoengineering). The role of tropospheric-sourced sulfur dioxide (SO2) in maintaining background SAs has been debated for decades without in-situ measurements of SO2 at the tropical tropopause to inform this issue. Here we clarify the role of SO2 in maintaining SAs by using new in-situ SO2 measurements to evaluate climate models and satellite retrievals. We then use the observed tropical tropopause SO2 mixing ratios to estimate the global flux of SO2 across the tropical tropopause. These analyses show that the tropopause background SO2 is about 5 times smaller than reported by the average satellite observations that have been used recently to test atmospheric models. This shifts the view of SO2 as a dominant source of SAs to a near-negligible one, possibly revealing a significant gap in the SA budget.

Organic aerosol formation downwind from the Deepwater Horizon oil spill.

A large fraction of atmospheric aerosols are derived from organic compounds with various volatilities. A National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft made airborne measurements of the gaseous and aerosol composition of air over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico that occurred from April to August 2010. A narrow plume of hydrocarbons was observed downwind of DWH that is attributed to the evaporation of fresh oil on the sea surface. A much wider plume with high concentrations of organic aerosol (>25 micrograms per cubic meter) was attributed to the formation of secondary organic aerosol (SOA) from unmeasured, less volatile hydrocarbons that were emitted from a wider area around DWH. These observations provide direct and compelling evidence for the importance of formation of SOA from less volatile hydrocarbons.

Reasoning about tasks, activities and technology to support collaboration.

An aspect of collaboration described as 'semi-synchronized activity' is discussed as a particular challenge for the task analysis (TA) of collaborative work. TA typically involves the decomposition of work systems into essentially independent component processes between which commodities (information or materials) pass. In collaborative work, people routinely violate the condition of independence by moving seemlessly in and out of synchronization with one another, allowing for both independent and varying levels of conjoint activity. The shift between joint and independent projects is not fixed but managed through more or less explicit awareness of the other people over time. A number of case studies of the effect of communication technologies in telemedical consultation are drawn upon to illustrate the relationship between awareness and synchronization in collaborative work. They show that an analysis of collaborative activity requires a consideration of: (1) the activities constituting work; (2) the interactions between participants required to carry out the activities; (3) who else has access to these activities besides the primary participants in the ongoing work; (4) the contemporaneity of activities; (5) the locations/environments in which the activities are carried out; and (6) the constraints that apply to accessibility and participation within and between these environments. The Comms Usage Diagram is described as a framing notation incorporating these characteristics for a broad, communications-level analysis of collaborative activity. It shows how particular technologies relate to particular phases of work, indexing their effects to collaborative activities in those contexts.

Telemedicine. What happens in remote consultation.

The results of a field study of three sites that used video to link primary care medical centers to hospitals are reported. The analysis was concerned with identifying the people involved, the tasks carried out in collaboration at each end of the link, and how the different communications facilities helped or hindered. The results are summarized as six task characteristics and their design implications for this model of telemedical consultation are discussed.

Pioneer imaging photopolarimeter optical system.

The imaging photopolarimeter aboard the Pioneer 10 spacecraft en route to the vicinity of Jupiter is described. This instrument is capable of moderate resolution spin-scan imaging and high precision polarimetric and photometric mapping of Jupiter in red and blue light. The field of view can be selectively changed from 0.50 mrad square to 40 mrad square to accommodate resolution and radiance combinations ranging from the zodiacal background to that of Jupiter. The dynamic range (radiance) of the instrument is greater than 10(8). Optical materials were chosen to survive, with minimum degradation, the rigors of a nearly 2-year journey to Jupiter including transit through the Jovian trapped radiation belts. The optics are described in detail, and the operational system is outlined. The procedures for preflight and in-flight calibration are described, and some performance characteristics and preliminary flight results are presented.

Molecular weights of aggregation states of Busycon hemocyanin.

Molecular weights of all hemocyanin aggregates which can be homogeneously isolated have been measured by sedimentation equilibrium. The larger aggregates, which are the ones present under physiological conditions, are, to a very close approximation, integral multiples of a 4.4 x 10(6)-dalton, 60 S species. Dissociation of the 60 S species at high pH gives heterogeneous samples in which the smallest species has a molecular weight of 300,000. The smallest subunit which can be produced in denaturing solvents also has a molecular weight of 300,000.

Radiation induced transmission loss in optical materials.

Results are presented for a number of window materials, color filter glasses, birefringent crystals, and optical fibers. The transmission loss caused by exposure to Co(60) gamma or 10-MeV electron radiation is tabulated over the 400-900-nm wavelength region. The transmission loss is greatest at the shorter wavelengths, and its rate is maximum for most materials at dosages greater than 10(5) rad (Si).