Nitrogen and Oxygen Photochemistry following SL9

The collision of Shoemaker Levy 9 (SL9) with Jupiter caused many new molecular species to be deposited in the Jovian stratosphere. We use a photochemical model to follow the evolution of the impact derived species. Our results regarding the nitrogen and oxygen compounds are presented here. NH3 photolysis initiates the nitrogen photochemistry. Much of the nitrogen ends up in N2, nitrogen-sulfur compounds, and HCN, but NH3 and nitriles such as C2H3CN may also exist in observable quantities for a year or so after the impacts. Oxygen species survive for a long time in the Jovian stratosphere. The only major oxygen containing compounds that exhibit dramatic changes in the lower stratosphere in the first year following the impacts are SO, SO2, and OCS - H2O, CO2, and CO are comparatively stable. We discuss the important photochemical processes operating on the nitrogen and oxygen species in the Jovian stratosphere, make prediction concerning the temporal variation of the major species, and identify molecules that might act as good tracers for atmospheric dynamics

Third-Order Nonlinearity Measurement Techniques

To measure the degenerate (single-frequency) optical nonlinearities, third-order nonlinearity measurement and their related techniques were employed. When a laser beam is induced on a nonlinear (NL) medium, a phase change is easily identified using third-order nonlinearity measurement techniques (Z-scan). When the sample material is scanned on Z-axis, the phase change is denoted by sign and magnitude, the refractive index which is directly related to the change in the index of refraction. The nonlinear absorption from the absorption coefficient is independent of the index of refraction which is a required parameter for calculating nonlinear refraction. Further, the change in transmission caused by nonlinear absorption of the subjected material is related to the change in absorption coefficient which is easily determined by the Z-scan technique. From Z-scan responses, real and imaginary parts of third-order nonlinear susceptibility (χ3) can be determined. The Z-scan technique is an interesting process that leads to optical power limiting and nonlinear optical propagation

The Deep Water Abundance on Jupiter: New Constraints from Thermochemical Kinetics and Diffusion Modeling

We have developed a one-dimensional thermochemical kinetics and diffusion model for Jupiter's atmosphere that accurately describes the transition from the thermochemical regime in the deep troposphere (where chemical equilibrium is established) to the quenched regime in the upper troposphere (where chemical equilibrium is disrupted). The model is used to calculate chemical abundances of tropospheric constituents and to identify important chemical pathways for CO-CH4 interconversion in hydrogen-dominated atmospheres. In particular, the observed mole fraction and chemical behavior of CO is used to indirectly constrain the Jovian water inventory. Our model can reproduce the observed tropospheric CO abundance provided that the water mole fraction lies in the range (0.25-6.0) x 10^-3 in Jupiter's deep troposphere, corresponding to an enrichment of 0.3 to 7.3 times the protosolar abundance (assumed to be H2O/H2 = 9.61 x 10^-4). Our results suggest that Jupiter's oxygen enrichment is roughly similar to that for carbon, nitrogen, and other heavy elements, and we conclude that formation scenarios that require very large (>8 times solar) enrichments in water can be ruled out. We also evaluate and refine the simple time-constant arguments currently used to predict the quenched CO abundance on Jupiter, other giant planets, and brown dwarfs.Comment: 42 pages, 7 figures, 4 tables, with note added in proof. Accepted for publication in Icarus [in press

Hydrogen and Deuterium Loss from the Terrestrial Atmosphere: A Quantitative Assessment of Nonthermal Escape Fluxes

A comprehensive one-dimensional photochemical model extending from the middle atmosphere (50 km) to the exobase (432 km) has been used to study the escape of hydrogen and deuterium from the Earth's atmosphere. The model incorporates recent advances in chemical kinetics as well as atmospheric observations by satellites, especially the Atmosphere Explorer C satellite. The results suggest: (1) the escape fluxes of both H and D are limited by the upward transport of total hydrogen and total deuterium at the homopause (this result is known as Hunten's limiting flux theorem); (2) about one fourth of total hydrogen escape is thermal, the rest being nonthermal; (3) escape of D is nonthermal; and (4) charge exchange and polar wind are important mechanisms for the nonthermal escape of H and D, but other nonthermal mechanisms may be required. The efficiency to escape from the terrestrial atmosphere for D is 0.74 of the efficiency for H. If the difference between the D/H ratio measured in deep-sea tholeiite glass and that of standard sea water, δD = −77‰, were caused by the escape of H and D, we estimate that as much water as the equivalent of 36% of the present ocean might have been lost in the past

Neptune's visual albedo variations over a solar cycle: A pre-Voyager look at ion-induced nucleatlon and cloud formation in Neptune's troposphere

High-energy galactic cosmic rays can penetrate to deep levels within Neptune's atmosphere to form a substantial ionospheric layer in the lower stratosphere and upper troposphere of the planet. Because cosmic-ray modulation in the interplanetary medium creates an inverse relationship between cosmic-ray intensity and solar activity, the ionization rate in the lower atmosphere will vary with the 11-year solar cycle in such a way that maximum ionization will occur at sunspot minimum and minimum ionization at sunspot maximum. This variable ionization may, by the process of ion-induced nucleation, regulate the formation and optical properties of an upper tropospheric haze in the atmosphere of Neptune and could thus provide a mechanism for modulating the planet's visual brightness over a solar cycle. We estimate the rates of cosmic-ray ionization at solar maximum and minimum for a range of proposed Neptune dipole magnetic field strengths; discuss the physics of formation of ion clusters and eventual aerosol particles; and, using a simple radiative transfer model, discuss the ways in which this variable aerosol formation can modulate the geometric albedo of Neptune over a solar cycle. If Voyager spacecraft observations reveal that Neptune's dipole magnetic field is about 1 Gauss or less, then our modeling indicates that variations in an aerosol layer due to differences in cosmic ray ionization may help explain some of the observed brightness variation of Neptune over a solar cycle

Atmospheric Entry Studies for Venus Missions: 45 Sphere-Cone Rigid Aeroshells and Ballistic Entries

The present study considers direct ballistic entries into the atmosphere of Venus using a 45deg sphere-cone rigid aeroshell, a legacy shape that has been used successfully in the past in the Pioneer Venus Multiprobe Mission. For a number of entry mass and heatshield diameter combinations (i.e., various ballistic coefficients) and entry velocities, the trajectory space in terms of entry flight path angles between skip out and -30deg is explored with a 3DoF trajectory code, TRAJ. From these trajectories, the viable entry flight path angle space is determined through the use of mechanical and thermal performance limits on the thermal protection material and science payload; the thermal protection material of choice is entry-grade carbon phenolic, for which a material thermal response model is available. For mechanical performance, a 200 g limit is placed on the peak deceleration load experienced by the science instruments, and 10 bar is assumed as the pressure limit for entry-grade carbon-phenolic material. For thermal performance, inflection points in the total heat load distribution are used as cut off criteria. Analysis of the results shows the existence of a range of critical ballistic coefficients beyond which the steepest possible entries are determined by the pressure limit of the material rather than the deceleration load limit

Community participation to improve health services for children: a methodology for a community dialogue intervention in Uganda

Background: Like other developing countries, Uganda still struggles to meaningfully reduce child mortality. A strategy of giving information to communities to spark interest in improving child survival through inducing responsibility and social sanctioning in the health workforce was postulated. By focusing on diarrhea, pneumonia and malaria, a Community and District Empow- erment for Scale up (CODES) undertaking used “community dialogues” to arm communities with health system performance information. This empowered them to monitor health service provision and demand for quality child-health services.Methods: We describe a process of community dialoguing through use of citizen report cards, short-text-messages, media and post-dialogue monitoring. Each community dialogue assembled 70-100 members including health workers and community leaders. After each community dialogue, participants implemented activities outlined in generated community contracts. Radio messages promoted demand for child-health services and elicited support to implement accepted activities.Conclusion: The perception that community dialoging is “a lot of talk” that never advances meaningful action was debunked since participant-initiated actions were conceived and implemented. Potential for use of electronic communication in real-time feedback and stimulating discussion proved viable. Post-dialogue monitoring captured in community contracts facilitated pro- cess evaluation and added plausibility for observed effects. Capacitated organizations during post-dialogue monitoring guaran- teed sustainability.Keywords: Community dialogues, post-dialogue monitoring, sustainability, strategy, community, child survival

Couples' voluntary counselling and testing and nevirapine use in antenatal clinics in two African capitals: a prospective cohort study

<p>Abstract</p> <p>Background</p> <p>With the accessibility of prevention of mother to child transmission (PMTCT) services in sub-Saharan Africa, more women are being tested for HIV in antenatal care settings. Involving partners in the counselling and testing process could help prevent horizontal and vertical transmission of HIV. This study was conducted to assess the feasibility of couples' voluntary counseling and testing (CVCT) in antenatal care and to measure compliance with PMTCT.</p> <p>Methods</p> <p>A prospective cohort study was conducted over eight months at two public antenatal clinics in Kigali, Rwanda, and Lusaka, Zambia. A convenience sample of 3625 pregnant women was enrolled. Of these, 1054 women were lost to follow up. The intervention consisted of same-day individual voluntary counselling and testing (VCT) and weekend CVCT; HIV-positive participants received nevirapine tablets. In Kigali, nevirapine syrup was provided in the labour and delivery ward; in Lusaka, nevirapine syrup was supplied in pre-measured single-dose syringes. The main outcome measures were nurse midwife-recorded deliveries and reported nevirapine use.</p> <p>Results</p> <p>In eight months, 1940 women enrolled in Kigali (984 VCT, 956 CVCT) and 1685 women enrolled in Lusaka (1022 VCT, 663 CVCT). HIV prevalence was 14% in Kigali, and 27% in Lusaka. Loss to follow up was more common in Kigali than Lusaka (33% vs. 24%, p = 0.000). In Lusaka, HIV-positive and HIV-negative women had significantly different loss-to-follow-up rates (30% vs. 22%, p = 0.002). CVCT was associated with reduced loss to follow up: in Kigali, 31% of couples versus 36% of women testing alone (p = 0.011); and in Lusaka, 22% of couples versus 25% of women testing alone (p = 0.137). Among HIV-positive women with follow up, CVCT had no impact on nevirapine use (86-89% in Kigali; 78-79% in Lusaka).</p> <p>Conclusions</p> <p>Weekend CVCT, though new, was feasible in both capital cities. The beneficial impact of CVCT on loss to follow up was significant, while nevirapine compliance was similar in women tested alone or with their partners. Pre-measured nevirapine syrup syringes provided flexibility to HIV-positive mothers in Lusaka, but may have contributed to study loss to follow up. These two prevention interventions remain a challenge, with CVCT still operating without supportive government policy in Zambia.</p