Rates of production of super 24 Na and super 28 Mg in the atmosphere by cosmic radiation
Production rates determination for Na 24 and Mg 28 isotopes in Ar exposed to cosmic rays
Bhandari, N.↗
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Continuous propagation of microalgae. III.
Data are presented which give the specific photosynthetic rate and the specific utilization rates of urea and carbon dioxide as functions of specific growth rate for Chlorella. A mathematical model expresses a set of mass balance relations between biotic and environmental materials. Criteria of validity are used to test this model. Predictive procedures are complemented by a particular model of microbial growth. Methods are demonstrated for predicting substrate utilization rates, production rates of extracellular metabolites, growth limiting conditions, and photosynthetic quotients from propagator variables.
Hanson, D. T.↗
Radar image interpretation techniques applied to sea ice geophysical problems
The geophysical science problems in the sea ice area which at present concern understanding the ice budget, where ice is formed, how thick it grows and where it melts, and the processes which control the interaction of air-sea and ice at the ice margins is discussed. The science problems relate to basic questions of sea ice: how much is there, thickness, drift rate, production rate, determination of the morphology of the ice margin, storms feeling for the ice, storms and influence at the margin to alter the pack, and ocean response to a storm at the margin. Some of these questions are descriptive and some require complex modeling of interactions between the ice, the ocean, the atmosphere and the radiation fields. All involve measurements of the character of the ice pack, and SAR plays a significant role in the measurements.
Carsey, F. D.↗
Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter
There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx. 10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10 were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.
Reedy, Robert C.↗
Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter
There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx.10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10, were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.
Reedy, Robert C.↗
Comet C/2013 V5 (Oukaimeden): Evidence for Depleted Organic Volatiles and Compositional Heterogeneity as Revealed through Infrared Spectroscopy
We obtained high-resolution (lambda divided by delta times lambda equals approximately 25,000) pre-perihelion spectra of Comet C/2013 V5 (Oukaimeden) using NIRSPEC at Keck II on UT 2014 September 5-6, and CSHELL (Cryogenic Echelle Spectrograph) at the NASA-Infrared Telescope Facility on September 11-13, altogether spanning a range in heliocentric distance R (sub h) equals 0.789-0.698 astronomical units. We report water production rates, and production rates and abundance ratios relative to co-measured H2O for eight trace molecules: CO, H2CO, CH3OH, CH4, C2H2, C2H6, HCN, and NH3. Our measured water production rates from NIRSPEC ( Near Infra-Red Spectrograph) and CSHELL observations remained relatively constant and were close to those from SOHO (Solar and Heliospheric Observatory) / Solar Wind Anisotropies observations that encompassed our dates, suggesting H2O production dominated by release directly from or within approximately 2000 kilometers of the nucleus. All trace volatiles were depleted relative to their respective median abundances among comets, excepting NH3, which was consistent with its median abundance. Most surprising were pronounced increases in abundance ratios for CH3OH (by 51 percent relative to simultaneously measured H2O) and especially C2H6 (by 87 percent) between September 5 and 6. On September 5, C2H6 was severely depleted, consistent with its lowest abundance yet measured for any comet. It also tracked the spatial profile of H2O, suggesting C2H6 was associated with a polar ice phase dominating gas production. On September 6, C2H6 was only moderately depleted and was spatially distinct from H2O, suggesting both polar- and nonpolar-dominated ice phases contributed to the activity then. Our results are consistent with a nonhomogeneous volatile composition for C/2013V5, implying differential processing of its constituent ices.
DiSanti, Michael A.↗
Beam efflux measurements
Measurements have been made of the high energy thrust ions, (Group I), high angle/high energy ions (Group II), and high angle/low energy ions (Group IV) of a mercury electron bombardment thruster in the angular divergence range from 0 deg to greater than 90 deg. The measurements have been made as a function of thrust ion current, propellant utilization efficiency, bombardment discharge voltage, screen and accelerator grid potential (accel-decel ratio) and neutralizer keeper potential. The shape of the Group IV (charge exchange) ion plume has remained essentially fixed within the range of variation of the engine operation parameters. The magnitude of the charge exchange ion flux scales with thrust ion current, for good propellant utilization conditions. For fixed thrust ion current, charge exchange ion flux increases for diminishing propellant utilization efficiency. Facility effects influence experimental accuracies within the range of propellant utilization efficiency used in the experiments. The flux of high angle/high energy Group II ions is significantly diminished by the use of minimum decel voltages on the accelerator grid. A computer model of charge exchange ion production and motion has been developed. The program allows computation of charge exchange ion volume production rate, total production rate, and charge exchange ion trajectories for "genuine" and "facilities effects" particles. In the computed flux deposition patterns, the Group I and Group IV ion plumes exhibit a counter motion.
Komatsu, G. K.↗
Observations and analysis of O(1D) and NH2 line profiles for the coma of comet P/Halley
A set of high-resolution Fabry-Perot measurements of the coma of comet P/Halley was acquired in the (O I) 6300 A and NH2 6298.62 A emission lines. These high-resolution measurements provide the first optical observations capable of studying directly the photochemical kinetics and dynamic outflow of the coma. The observations were analyzed by a Monte Carlo Particle Trajectory Model. The agreement of the model and observed line profiles was excellent and verified the underlying dynamics, exothermic photodissociative chemistry, and collisional thermalization in the coma. The somewhat wider intrinsic line profile width for the O(1D) emission in 1986 January compared to 1986 May, is, for example, produced by the larger outflow speeds and gas temperatures nearer perihelion in January. The January O(1D) profile, which is wider than the January NH2 profile, is indicative of the photochemical kinetics in the dissociation of the parent molecules H2O and OH in the coma. The absolute calibration of the observations in 1986 January allowed the production rates for H2O and the NH2-parent molecules to be determined. The average daily water production rates derived from the O(1D) emission data for January 16 and 17 are presented. These very large water production rates are consistent with the extrapolated (and 7.6 day time variable) water production rates determined from the analysis of lower spectral resolution observations for O(1D) and H-alpha emissions that covered the time period up to January 13. The large production rates on January 16 and 17 establish that the maximum water production rate for comet Halley accurred pre-perihelion in January. Implications drawn from comparison with 18 cm radio emission data in January suggest that the peak water production rate was even larger. The average production rate for NH3 determined from the NH2 emission data for January 17 was (1.48 +/- 0.10) x 10(exp 28) molecules/s, yielding an NH3/H2O production rate ratio of 0.55%.
Smyth, William H.↗
Comet Giacobini-Zinner - A normal comet?
Observations of Comet Giacobini-Zinner were obtained during its 1985 apparition using an IDS spectrograph at McDonald Observatory. Column densities and production rates were computed. The production rates were compared to observations of other 'normal' comets. Giacobini-Zinner is shown to be depleted in C2 and C3 relative to CN. These production rates are down by a factor of 5.
Cochran, Anita L.↗
Cosmogenic Production of Be-7 and Be-10 in Water Targets
We have measured Be-10(t(sub 1/2) = 1.5 x 10(exp 6) years) and Be-7 (t(sub 1/2) = 53.28 days) concentrations in water targets exposed for 1 to 2 years at Echo Lake, Colorado (elevation = 3246 m) and at La Jolla, California (140 m). Neutron monitor data were used to normalize the measured concentrations in order to calculate production rates equivalent to the cosmic ray flux averaged over four solar cycles (43 years). The Be-7 production rates thus obtained correspond to 6.03 +/- 0.07 x 10(exp -6) atom/g.O/s at Echo Lake and 5.06 +/- 0.20 x 10(exp -7) atom/g.O/ s at La Jolla. The Be-10 production rates correspond to 3.14 +/- 0.18 x 10(exp -6) atom/g.O/s at Echo Lake and 2.68 +/- 0.47 x 10(exp -7) atom/g.O/s at La Jolla. When compared with Be-10 production rates determined in Be-10-saturated rocks from the Antarctic and with theoretical calculations based on meteorite and lunar sample data, we find that the million-year average production rate is about 14 - 17% greater than the present production rate averaged over the last four solar cycles. Comparison with production rates determined by measuring glacially polished rocks from the Sierra Nevada in California indicates that average production (based on a revised 13,000-year deglaciation age and a geographic latitude correction) is a about 11% greater than the average over the last four solar cycles. The measured Be-10/Be-7 production ratio in oxygen is 0.52 +/- 0.03 at Echo Lake and 0.55 +/- 0.07 at La Jolla.
Nishiizumi, K.↗
Submillimetric Spectroscopic Observations of Volatiles in Comet C-2004 Q2 (Machholz)
Submillimeter spectroscopic observations of comets provide an important tool for understanding their chemical composition and enable a taxonomic classification. Aims. We aim to determine the production rates of several parent- and product volatiles and the C-12/C-13 isotopic carbon ratio in the long-period comet C/2004 Q2 (Machholz), which is likely to originate from the Oort Cloud. Methods. The line emission from several molecules in the coma was measured with high signal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU by means of high-resolution spectroscopic observations using the Submillimeter Telescope (SMT) at the Arizona Radio Observatory (ARO). Results. We have obtained production rates of several volatiles (CH3OH, HCN, H(sup 13)CN, HNC, H2CO, CO, and CS) by comparing the observed and simulated line-integrated intensities. We calculated the synthetic profiles using a radiative transfer code that includes collisions between neutrals and electrons, and the effects of radiative pumping of the fundamental vibrational levels by solar infrared radiation. Furthermore, multiline observations of the CH3OH J = 7-6 series allow us to estimate the rotational temperature using the rotation diagram technique. We find that the CH3OH population distribution of the levels sampled by these lines can be described by a rotational temperature of 40 +/- 3 K. Derived mixing ratios relative to hydrogen cyanide are CO/CH3OH/H2CO/CS/HNC/HC-13N/HCN= 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a pointing offset of 8" due to the uncertain ephemeris at the time of the observations and the telescope pointing error. Conclusions. The measured relative molecular abundances in C/2004 Q2 (Machholz) are between low- to typical values of those obtained in Oort Cloud comets, suggesting that it has visited the inner solar system previously and undergone thermal processing. The HNC/HCN abundance ratio of approx 3.1% is comparable to that found in other comets, accounting for the dependence on the heliocentric distance, and could possibly be explained by ion-molecule chemical processes in the low-temperature atmosphere. From a tentative HC-13N detection, the measured value of 97 +/- 30 for the HC-12N/HC-13N isotopologue pair is consistent with a telluric value. The outgassing variability observed in the HCN production rates over a period of two hours is consistent with the rotation of the nucleus derived using different observational techniques.
chemical composition↗
A composition comparison between comets P/Halley and P/Brorsen-Metcalf
The appearance of comet Brorsen-Metcalf in 1989 following only a few years on the heels of comet Halley in 1986 gave an unusual opportunity to compare two comets of similar orbital elements but potentially different physical and chemical characteristics. Photometric spectral data were acquired for Brorsen-Metcalf on two dates: 13 July 1989 and 2 August 1989. The observations were performed with the 154 cm Catalina Telescope of the University of Arizona Observatories. The spectrum for 13 July 1989 is compared to a Halley spectrum. The general appearance of the spectra is very similar, both comets showing emission due to C2, NH2, OI(D-1), and CN. Neither displays any emission features that are exclusive to only one of the two. Since water is now reasonably well established as the major driving force in the activity of a comet, the H2O production rate for comet Brorsen-Metcalf was calculated. The relative ratios between the production rates of the various species obtained from the data are presented. Results are summarized in tabular form. All species are compared to the H2O production rate of the two comets. The results indicate that C2 originates from an extended source of dust particles or small polymers in addition to parent molecules. The lower production rates of C2 and CN in Brorsen-Metcalf correlate well with both the lower dust production and their smaller increase as the comet approaches the sun. Even without a mode, the spectroscopic observations of Brorsen-Metcalf allowed significant compositional conclusions to be drawn. The NH2 abundance is lower by about a factor of three which appears to be independent of heliocentric distance. Both C2 and CN are less abundant in Brorsen-Metcalf than in Halley and do not seem to participate as much in the strong increase as the comet approaches the sun. The lower H2O production rate implies that the active surface area of the comet Brorsen-Metcalf is much smaller, or equivalently the comet as a whole is much smaller. The substantially lower continuum level for Brorsen-Metcalf cannot readily be explained by smaller or larger active surface area, and must be intrinsic to the comet's embedded dust-to-ice ratio, or to an overall smaller-sized dust grain population.
Disanti, Michael A.↗
IUE observations of comets P/Brorsen-Metcalf and Okazaki-Levy-Rudenko
Comet P/Brorsen-Metcalf (1989c) was observed with the International Ultraviolet Explorer (IUE) on several dates from 27 July 1989 through 5 August 1989; comet Okazaki-Levy-Rudenko (1989r) was observed in low dispersion with IUE on 2 and 22 December 1989. The water production rates for P/Brorsen-Metcalf were derived from OH measurements using the vectorial model of Festou (1981). Included also are the water production rates for Okazaki-Levy-Rudenko. Two estimates of the water production rate from the O I emission around 1304 A(octogons) are included. The ultraviolet continuum was not reliably measurable in comet P/Brorsen-Metcalf in most of the spectra, but Afp is approximately 30 cm for 2 August. For the comet Okazaki-Levy-Rudenko, an Afp = 50 cm was derived for 22 December. Both comets have very little dust compared to other recently observed comets. The ratio of CS to water production rates are presented. Relative to water, both comets had less CS than P/Halley in the same range of heliocentric distances. The CS production rates were obtained from a Haser model, assuming a short-lived parent (CS2). Because the dynamic range of the IUE spectrographs are limited, not all species can be measured in each spectrum. The P/Brorsen-Metcalf spectra from 31 July and 3 August were obtained from the NSSDC Archives. Due to the observing technique used for these spectra, the exposure time and hence, the brightnesses and derived quantities have a small uncertainty associated with them.
Roettger, E. E.↗
Rocket observation of the ultraviolet spectrum of Comet Halley
An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on Feb. 26, 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 x 10 to the 29th/s and the volume mixing ratio of CO to H2O is 21 percent. The predicted brightness distribution from a radial outflow model with H2O and CO as parent molecules are in accordance with the measured spatial profiles of O I and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker C I emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3 percent of the water production rate is included in the model.
Woods, T. N.↗
On the calculation of cosmic-ray exposure ages of stone meteorites
Abundances of cosmic ray-produced noble gases and Al-26, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages less than 3,000,000 yr. Concentrations of cosmogenic He, Ne, and Ar in these meteorites have been corrected for differences in target element abundances by normalization to L-chondrite chemistry. Combined noble gas measurements in depth samples of the Keyes and St. Severin chondrites are utilized to derive equations for normalizing the production rates of cosmogenic He-3, Ne-21, and Ar-38 in chondrites to an adopted 'average' shielding. The measured unsaturated AL-26 concentrations and the calculated equilibrium Al-26 for these meteorites are combined to estimate exposure ages. These exposure ages are statistically compared with chemistry- and shielding-corrected concentrations of cosmogenic He, Ne, and Ar to derive absolute production rates for these nuclides, which are found to be roughly 25% higher than production rates used in the past. From these production rates and relative chemical correction factors, production rates for other classes of stone meteorites are derived.
Cressy, P. J., Jr.↗
Modeling of the silane FBR system
Development of a mathematical model for fluidized bed pyrolysis of silane that relates production rate and product properties (size, size distribution, presence or absence of fines) with bed size and operating conditions (temperature, feed concentration, flow rate, seed size, etc.) and development of user oriented algorithm for the model are considered. A parameter sensitivity study of the model was also developed.
Dudokovic, M. P.↗
Spectroscopy of Comet P/Encke in 1980 - 1981
Digital spectroscopic scans of P/Comets Encke, Stephan-Oterma, and Gunn were obtained with a sky-subtraction scanner system. Quantiative fluxes for the cometary emission bands of CN, C3, C2, NH2, and the 'D OI red auroral line are presented for P/Encke. The most straight-forward and model-independent line flux to interpret is the lambda lambda 6300, 6364 forbidden oxygen doublet. After an NH2 blending correction, the oxygen production rate may be directly measured from the Lick small-aperture fluxes. The oxygen production rates increased rapidly with decreasing heliocentric distance for both P/Encke and P/Stephan-Oterma. A rough power-law exponent in r with n = approximately -2.5 describes the change in oxygen production for P/Encke. Compared to the water production rates inferred from IUE satellite spectra showing the lambda 3080 OH band, these oxygen production rates are consistently lower by a factor of 11. This implies a common origin for the two species; H2O is the likely sole OI ID parent.
Spinrad, H.↗
The 15 years of comet photometry: A comparative analysis of 80 comets
In 1976, a program of narrowband photometry of comets was initiated that has encompassed well over 400 nights of observations. To date, the program has provided detailed information on 80 comets, 11 of which were observed during multiple apparitions. The filters (initially isolating CN, C2, and continuum and later including C3, OH, and NH) as well as the detectors used for the observations were changed over time, and the parameters adopted in the reduction and modeling of the data have likewise evolved. Accordingly, we have re-reduced the entire database and have derived production rates using current values for scalelengths and fluorescence efficiencies. Having completed this task, the results for different comets can now be meaningfully compared. The general characteristics that are discussed include ranges in composition (molecular production rate ratios) and dustiness (gas production compared with Af(rho)). Additionally an analysis of trends on how the production rates vary with heliocentric distance and on pre- and post-perihelion asymmetries in the production rates of individual comets. Possible taxonomic groupings are also described.
Osip, David J.↗