Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cl”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectrum

We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg(exp 2) with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500 < l < 10,000. We fit a model for the lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from radio and infrared point sources, and clustered power from infrared point sources. At l = 3000, about half the power at 148 GHz comes from primary CMB after masking bright radio sources. The power from thermal and kinetic SZ is estimated to be Beta(sub 3000) is identical to 6.8 +/- 2.9 mu K (exp 2), where Beta (sub l) is identical to l(l + 1) C(sub l)/2pi. The IR Poisson power at 148 GHz is Bewta(sub 3000) 7.8 +/- 0.7 muK(exp 2) (C(sub l) = 5.5 +/- 0.5 nK(exp 2)), and a clustered IR component is required with Beta (sub 3000) = 4.6 +/- 0.9 muK(exp 2), assuming an analytic model for its power spectrum shape. At 218 GHz only about 15% of the power, approximately 27 mu K(exp 2), is CMB anisotropy at l = 3000. The remaining 85% is attributed to IR sources (approximately 50% Poisson and 35% clustered), with spectral index alpha = 3.69 +/- 0.14 for flux scaling as S(nu) varies as nu(sup alpha). We estimate primary cosmological parameters from the less contaminated 148 GHz spectrum, marginalizing over SZ and source power. The ACDM cosmological model is a good fit to the data (chi square/dof = 29/46), and ACDM parameters estimated from ACT+Wilkinson Microwave Anisotropy Probe (WMAP) are consistent with the seven-year WMAP limits, with scale invariant n(sub s) = 1 excluded at 99.7% confidence level (CL) (3 sigma). A model with no CMB lensing is disfavored at 2.8 sigma. By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6 sigma detection of primordial helium, with Y(sub p) = 0.313 +/- 0.044, and a 4 sigma detection of relativistic species, assumed to be neutrinos, with N(sub eff) = 5.3 +/- 1.3 (4.6 +/- 0.8 with BAO+H(sub 0) data). From the CMB alone the running of the spectral index is constrained to be d(sub s) / d ln k = -0,034 +/- 0,018, the limit on the tensor-to-scalar ratio is r < 0,25 (95% CL), and the possible contribution of Nambu cosmic strings to the power spectrum is constrained to string tension G(sub mu) < 1.6 x 10(exp -7) (95% CL),

Dunkley, J.↗
NASA NTRS2014

The Messy Aerosol Submodel MADE3 (v2.0b): Description and a Box Model Test

We introduce MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, 3rd generation), an aerosol dynamics submodel for application within the MESSy framework (Modular Earth Submodel System). MADE3 builds on the predecessor aerosol submodels MADE and MADE-in. Its main new features are the explicit representation of coarse particle interactions both with other particles and with condensable gases, and the inclusion of hydrochloric acid (HCl)chloride (Cl) partitioning between the gas and condensed phases. The aerosol size distribution is represented in the new submodel as a superposition of nine lognormal modes: one for fully soluble particles, one for insoluble particles, and one for mixed particles in each of three size ranges (Aitken, accumulation, and coarse mode size ranges). In order to assess the performance of MADE3 we compare it to its predecessor MADE and to the much more detailed particle-resolved aerosol model PartMC-MOSAIC in a box model simulation of an idealized marine boundary layer test case. MADE3 and MADE results are very similar, except in the coarse mode, where the aerosol is dominated by sea spray particles. Cl is reduced in MADE3 with respect to MADE due to the HClCl partitioning that leads to Cl removal from the sea spray aerosol in our test case. Additionally, aerosol nitrate concentration is higher in MADE3 due to the condensation of nitric acid on coarse particles. MADE3 and PartMC- MOSAIC show substantial differences in the fine particle size distributions (sizes about 2 micrometers) that could be relevant when simulating climate effects on a global scale. Nevertheless, the agreement between MADE3 and PartMC-MOSAIC is very good when it comes to coarse particle size distribution, and also in terms of aerosol composition. Considering these results and the well-established ability of MADE in reproducing observed aerosol loadings and composition, MADE3 seems suitable for application within a global model.

Mixing state↗
NASA NTRS2016

Hydrogen Isotopic Composition of Apatite in Northwest Africa 7034: A Record of the "Intermediate" H-Isotopic Reservoir in the Martian Crust?

Northwest Africa (NWA) 7034 and its pairings comprise a regolith breccia with a basaltic bulk composition [1] that yields a better match than any other martian meteorite to visible-infrared reflectance spectra of the martian surface measured from orbit [2]. The composition of the fine-grained matrix within NWA 7034 bears a striking resemblance to the major element composition estimated for the martian crust, with several exceptions. The NWA 7034 matrix is depleted in Fe, Ti, and Cr and enriched in Al, Na, and P [3]. The differences in Al and Fe are the most substantial, but the Fe content of NWA 7034 matrix falls within the range reported for the southern highlands crust [6]. It was previously suggested by [4] that NWA 7034 was sourced from the southern highlands based on the ancient 4.4 Ga ages recorded in NWA 7034/7533 zircons [4, 5]. In addition, the NWA 7034 matrix material is enriched in incompatible trace elements by a factor of 1.2-1.5 [7] relative to estimates of the bulk martian crust. The La/Yb ratio of the bulk martian crust is estimated to be approximately 3 [7], and the La/Yb of the NWA 7034 matrix materials ranges from approximately 3.9 to 4.4 [3, 8], indicating a higher degree of LREE enrichment in the NWA 7034 matrix materials. This elevated La/Yb ratio and enrichment in incompatible lithophile trace elements is consistent with NWA 7034 representing a more geochemically enriched crustal terrain than is represented by the bulk martian crust, which would be expected if NWA 7034 represents the bulk crust from the southern highlands. Given the similarities between NWA 7034 and the martian crust, NWA 7034 may represent an important sample for constraining the composition of the martian crust, particularly the ancient highlands. In the present study, we seek to constrain the H isotopic composition of the martian crust using Cl-rich apatite in NWA 7034. Usui et al., [9] recently proposed that a H isotopic reservoir exists within the martian crust that has a H-isotopic composition that is intermediate (δD of 1000-2000per mille) between an isotopically light mantle (Delta D is less than 275per mille [10]) and an isotopically heavy atmosphere (δD of 2500-6100per mille [11, 12]). Apatites in NWA 7034 occur in a number of lithologic domains, however apatites across all lithologic domains have been affected by a Pb-loss event at about 1.5 Ga before present [5], so they are unlikely to have retained a primary composition and are more likely to have equilibrated with fluids within the martian crust that may or may not have exchanged with the martian atmosphere. Equilibration of apatite with crustal fluids is further supported by the chlorine-rich compositions exhibited by apatites in NWA 7034 in comparison to apatites from other martian meteorites (Figure 1; [13]). Cl is more hydrophilic than F, which promotes formation of Cl-rich apatite compositions in fluid-rich systems [e.g., 14, 15-17].

McCubbin, F. M.↗
NASA NTRS2016

A Giant Radio Halo in a Low-Mass Sz-selected Galaxy Cluster: ACT-CLJ0256.5+0006

We present the detection of a giant radio halo (GRH) in the Sunyaev-Zel'dovich (SZ)- selected merging galaxy cluster ACT-CL J0256.5+ 0006 (z = 0.363), observed with the Giant Metrewave Radio Telescope at 325 and 610 MHz. We find this cluster to host a faint (S610 = 5.6 +/- 1.4mJy) radio halo with an angular extent of 2.6 arcmin, corresponding to 0.8 Mpc at the cluster redshift, qualifying it as a GRH. J0256 is one of the lowest mass systems, M500, SZ = (5.0 +/- 1.2) × 10(exp14) M, found to host a GRH. We measure the GRH at lower significance at 325 MHz (S325 = 10.3 +/- 5.3mJy), obtaining a spectral index measurement of α610 325 = 1.0+ 0.7 − 0.9. This result is consistent with the mean spectral index of the population of typical radio haloes, alpha = 1.2 +/- 0.2. Adopting the latter value, we determine a 1.4 GHz radio power of P1.4 GHz = (1.0 +/- 0.3) × 10(exp 24)W/Hz, placing this cluster within the scatter of known scaling relations. Various lines of evidence, including the intracluster medium morphology, suggest that ACT-CL J0256.5+ 0006 is composed of two subclusters. We determine a merger mass ratio of 7:4, and a line-of-sight velocity difference of v⊥ = 1880 +/- 210 km/s. We construct a simple merger model to infer relevant time-scales in the merger. From its location on the P1.4GHz-LX scaling relation, we infer that we observe ACT-CL J0256.5+ 0006 just before first core crossing.

Knowles, Kendra↗
NASA NTRS2017

Experimental Study into the Partitioning Behavior of Fluorine, Chlorine, Hydroxyl, and Sulfur (S2-) Between Apatite and a Synthetic Kreep Basalt Melt

The mineral apatite (Ca5 (PO4)3(F, Cl, OH)) is known for its ability to constrain the petrogenesis of the rock in which it is hosted and for its ubiquity throughout the Solar System, as it is found in lunar, martian, and terrestrial rocks alike (McCubbin et. al, 2015). The abundance of volatile elements, and for this particular study, the elevated abundance of sulfur (S2-) in high-Al basalt samples bearing apatite, could provide more insight for inquiries posed about the behavior of volatiles in lunar and martian magmatic systems (Boyce et. al, 2010). Oxygen fugacity will be an important parameter for these experiments, as the Moon, Mars, and Earth have different redox states (Herd, 2008). The objective of this experimental endeavor is to determine apatite-melt partition coefficients for the volatile elements (F-, Cl-, OH-, S2-) that make up the X-site (i.e., the typically monovalent anion site) in the mineral apatite in a lunar melt composition under lunar oxygen fugacity conditions approx.1-2 log units below the iron-wüstite buffer). All experiments will be conducted at NASA, Johnson Space Center in the High Pressure Experimental Petrology Laboratory. In order to conduct apatite-melt partition experiments with oxygen fugacity as an additional parameter, we will create a synthetic mix of the lunar KREEP basalt 15386, a sample retrieved during Apollo 15 that is believed to represent an indigenous volcanic melt derived from the lunar interior (Rhodes, J.M et. al, 2006). Other geochemically significant elements including C, Co, Ni, Mo, and rare earth elements will be included in the mix at trace abundances in order to assess their partitioning behavior without effecting the overall behavior of the system. The synthetic mix will then be loaded into a piston cylinder, an apparatus used to simulate high-pressure/high-temperature conditions of planetary interiors, and exposed to 0.5 GPa of pressure, the pressure observed in the upper mantle of the Moon, and heated to the melting temperature of the materials. To make sure crystals grow large enough for the necessary analyses, the sample will be kept at the crystallization temperature for 8 hours. This extended run time should also allow the sample to achieve a steady state which is necessary to accurately assess the partitioning of these elements between apatite and melt. The results from this experimental study will allow us to determine the fate of F-, Cl-, OH-, and S2- during the magmatic evolution of the Moon.

Turner, Amber↗
NASA NTRS2016

Measurements of Oxychlorine species on Mars

Mars landed and orbiter missions have instrumentation capable of detecting oxychlorine phases (e.g. perchlorate, chlorate) on the surface. Perchlorate (~0.6 wt%) was first detected by the Wet Chemistry Laboratory in the surface material at the Phoenix Mars Landing site. Subsequent analyses by the Thermal Evolved Gas Analyser aboard the same lander detected an oxygen release (~465°C) consistent with the thermal decomposition of perchlorate. Recent thermal analysis by the Mars Science Laboratory’s Sample Analysis at Mars instrument has also indicated the presence of oxychlorine phases (up to 1.2 wt%) in Gale Crater materials. Despite being at detectable concentrations, the Chemistry and Mineralogy (CheMin) X-ray diffractometer has not detected oxychlorine phases. This suggests that Gale Crater oxychlorine may exist as poorly crystalline phases or that perchlorate/chlorate mixtures exist, so that individual oxychlorine concentrations are below CheMin detection limits (~1 wt%). Although not initially designed to detect oxychlorine phases, reinterpretation of Viking Gas Chromatography/Mass Spectrometer data also suggest that oxychlorine phases are present in the Viking surface materials. Remote near-infrared spectral analyses by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument indicate that at least some martian recurring slope lineae (RSL) have spectral signatures consistent with the presence of hydrated perchlorates or chlorates during the seasons when RSL are most extensive. Despite the thermal emission spectrometer, Thermal Emission Imaging System, Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité and CRISM detection of hundreds of anhydrous chloride (~10–25 vol%) deposits, expected associated oxychlorine phases (>5–10 vol%) have not been detected. Total Cl and oxychlorine data sets from the Phoenix Lander and the Mars Science Laboratory missions could be used to develop oxychlorine versus total Cl correlations, which may constrain oxychlorine concentrations at other locations on Mars by using total Cl determined by other missions (e.g. Viking, Pathfinder, MER and Odyssey). Development of microfluidic or ‘lab-on-a-chip’ instrumentation has the potential to be the next generation analytical capability used to identify and quantify individual oxychlorine species on future landed robotic missions to Mars.

Perchlorate↗
NASA NTRS2003

Confirmation of a radio-selected galaxy overdensity at z = 1.11¹

We report the discovery of a galaxy overdensity at z = 1.11 associated with the z = 1.110 high-redshift radio galaxy MG1 J04426+0202 (hereafterMG0442+0202). The group, Cl 0442+0202, was found in a near-infrared survey of z > 1 radio galaxies undertaken to identify spatially coincident regions with a high density of objects red in I-K' color, typical of z > 1 elliptical galaxies. Spectroscopic observations from the Keck I telescope reveal five galaxies within 3500 of MG 0442+0202 at 1.10 < z < 1.11. These member galaxies have broadband colors and optical spectra consistent with passively evolving elliptical galaxies formed at high redshift. Archival ROSAT observations reveal a 3 detection of soft X-ray emission coincident with Cl 0442+0202 at a level 5 times greater than expected for the radio galaxy. These data suggest a rich galaxy cluster and inspired a 45 ks Chandra X-Ray Observatory observation. As expected, the radio galaxy is unresolved by Chandra but is responsible for approximately half the observed X-ray flux. The remaining ROSAT flux is resolved into four point sources within 1500 of the radio galaxy, corresponding to a surface density 2 orders of magnitude higher than average for X-ray sources at these flux levels [S(0.5–2 keV) > 5 X 10¯16 ergs cm¯² s¯¹]. One of these point sources is identified with a radio-quiet type II quasar at z = 1.863, akin to sources recently reported in deep Chandra surveys. The limit on an extended hot intracluster medium in the Chandra data is S(1–6 keV) < 1.9 X 10¯15 ergs cm¯² s¯¹ (3 σ, 30˝ radius aperture). Though the X-ray observations do not confirm the existence of a massive bound cluster at z > 1, the success of the optical=near-infrared targeting of early-type systems near the radio galaxy validates searches using radio galaxies as beacons for highredshift large-scale structure.We interpret Cl 0442+0202 as a massive cluster in the process of formation.

Spinard, Hyron↗
NASA NTRSDate not supplied

Formation of Fe(III) (hydr)oxides from Fe(II) sulfides: Implications for akaganeite detection on Mars

Akaganeite (β-FeO(OH,Cl)) is a Fe(III) (hydr)oxide with a tunnel structure typically occupied by chloride. This mineral was first proposed to be present in Meridiani Planum and Gusev crater on Mars and akaganeite was subsequently detected by X-ray diffraction in Yellowknife Bay and Vera Rubin Ridge locations in Gale crater. Akaganeite in Gale crater has been proposed to form from Fe(II) sulfides but formation conditions remain unconstrained. We investigated akageneite formation by oxidative alteration of natural Fe(II) sulfide pyrrhotite exposed to HCl and oxidation-hydrolysis of Fe(II) HCl-leached from pyrrhotite at initial pH0 1.5, 2, 3, and 4. X-ray diffraction and Mössbauer analyses revealed formation of poorly-crystallized akageneite in oxidative alteration experiments. Air-exposure of the HCl-reacted dry pyrrhotite led to an increase in akageneite formation and precipitation of Fe(II) hydrated sulfates, goethite, and hydronium jarosite. Iron(II) oxidation-hydrolysis was sensitive to Si dissolved from phyllosilicates in one pyrrhotite sample. Akaganeite and goethite formed at pH0 1.5 and 2 with akageneite more abundant at dissolved Si/Fe ratio of 0.08 and goethite more abundant at Si/Fe of 0.01. Akaganeite formed together with hematite, ferrihydrite, and goethite at pH0 3, and formation was suppressed at pH0 4. Well-crystallized akageneite precipitated at pH0 1.5 while akaganeite of poorer crystallinity formed at pH0 2 and 3. Akageneite in Gale crater could form from sulfides by both mechanisms: oxidative alteration of sulfide minerals and oxidation-hydrolysis of leached Fe(II). The processes likely occurred during late diagenetic events triggered by interactions of acidic Cl-bearing groundwater with Fe(II) sulfides. Akaganeite in Yellowknife Bay, Gale crater could have formed by Fe(II) oxidation-hydrolysis either as a sole Fe(III) (hydr)oxide at pH<2 or along with ferrihydrite and hematite at 2<pH<4 in Si-enriched conditions. Akaganeite formation at Vera Rubin Ridge, Gale crater could have occurred through oxidative alteration of sulfides in Cl-bearing pH 1.2-1.5 solutions. The presence of well-crystalline akageneite in Vera Rubin Ridge indicates that Fe(II) oxidation-hydrolysis contributed to akageneite formation.

Mars gale crater akaganeite↗
NASA NTRS2023

On the Origin of Fluorine-Poor Apatite in Chondrite Parent Bodies

We conducted a petrologic study of apatite within one LL chondrite, six R chondrites, and six CK chondrites. These data were combined with previously published apatite data from a broader range of chondrite meteorites to determine that chondrites host either chlorapatite or hydroxylapatite with ≤33 mol% F in the apatite X-site (unless affected by partial melting by impacts, which can cause F-enrichment of residual apatite). These data indicate that either fluorapatite was not a primary condensate from the solar nebula or that it did not survive lower temperature nebular processes and/or parent body processes. Bulk-rock Cl and F data from chondrites were used to determine that the solar system has a Cl/F ratio of 10.5 ± 1.0 (3σ). The Cl/F ratios of apatite from chondrites are broadly reflective of the solar system Cl/F value, indicating that apatite in chondrites is fluorine poor because the solar system has about an order of magnitude more Cl than F. The Cl/F ratio of the solar system was combined with known apatite-melt partitioning relationships for F and Cl to predict the range of apatite compositions that would form from a melt with a chondritic Cl/F ratio. This range of apatite compositions allowed for the development of a crude model to use apatite X-site compositions from achondrites (and chondrite melt rocks) to determine whether they derive from a volatile-depleted and/or differentiated source, albeit with important caveats that are detailed in the manuscript. This study further highlights the utility of apatite as a mineralogical tool to understand the origin of volatiles (including H 2 O) and the diversity of their associated geological processes throughout the history of our solar system, including at its nascent stage.

Francis M. McCubbin↗
NASA NTRSDate not supplied

The Impact of Atmospheric Dynamics and Anthropogenic Very Short-Lived Chlorine Species on the Recovery of Extra-Polar Ozone

The successful implementation of the Montreal Protocol has led to a decrease in the atmospheric abundance of ozone-depleting substances and a slowing in the destruction of the ozone layer. Previous studies have suggested that atmospheric dynamics, or a rise in compounds not regulated by the Montreal Protocol, such as very short-lived chlorine species (VSL Cl), may lead to a slower than expected recovery of the ozone layer. In this presentation, we examine the expected recovery of total column ozone (TCO) and stratospheric column ozone (SCO) to values observed in 1980 using a novel multiple linear regression (MLR) model that involves a month-by-month regression. The MLR model is trained to TCO anomalies from six data records (SBUV v8.7 MOD, SBUV v8.6 COH, WOUDC, GSG, GTO-ECV, MSR-2) over 1979 to 2021 for the Northern Hemisphere (35N – 60N), the Southern Hemisphere (60S – 35S) and the Tropics (20S – 20N), and SCO anomalies from ML-TOMCAT for these same zonal bands. The MLR includes the effect of halogens (equivalent effective stratospheric chlorine (EESC)), total solar irradiance, stratospheric aerosol optical depth, quasi-biennial oscillation, and the El Niño Southern Oscillation as regressors. We also include the effect of atmospheric dynamics such as the Brewer-Dobson Circulation, Arctic Oscillation, and the Antarctic Oscillation, and VSL Cl species in the formulation of EESC. We use a novel approach to the MLR framework, by separating the observed and regressor time series into the respective months (separating all of the Januarys, Februarys, etc.). Then we conduct a regression for each month from 1979 to 2021 for the three zonal bands denoted above. The model results for each month are combined together to achieve a full monthly time series from 1979 to 2021. We use this novel approach to ascertain the effect of atmospheric dynamics on TCO and SCO, since the dynamical proxies affect ozone in a distinctly different manner for various months. In this presentation, we will quantify the role of both the inclusion of VSL Cl species in the formulation of EESC as well as atmospheric dynamics in explaining the slower than expected recovery of extra-polar TCO and SCO over the past decade.

Laura A. McBride↗
NASA NTRS1971

Fundamental limitations on V/STOL terminal guidance due to aircraft characteristics

A review is given of limitations on approach flight paths of V/STOL aircraft, including limits on descent angle due to maximum drag/lift ratio. A method of calculating maximum drag/lift ratio of tilt-wing and deflected slipstream aircraft is presented. Derivatives and transfer functions for the CL-84 tilt-wing and X-22A tilt-duct aircraft are presented. For the unaugmented CL-84 in steep descents the transfer function relating descent angle to thrust contains a right-half plane zero. Using optimal control theory, it is shown that this zero causes a serious degradation in the accuracy with which steep flight paths can be followed in the presence of gusts.

Wolkovitch, J.↗
NASA NTRS1971

Research and investigation of gas dynamic lasers

Chemical mixing laser investigations were conducted (1) to investigate the properties of a bimolecular exchange laser system pumped by the H + Cl2 yields HCl(v) + Cl reaction, initiated by arc-dissociated H2, with lasing occurring between wavelengths of 3.4 and 4.0 microns, and (2) to establish the feasibility of an atom recombination-transfer laser employing recombination of arc-dissociated nitrogen with subsequent transfer of vibrational energy to CO2 for lasing at 10.6 microns. One-dimensional analytical results indicate higher results should be obtained with up to v = 3 to 2 transitions participating. Diagnostic and analytical results show that the reaction mechanism during mixing, a back reaction of HCl(v) with H atoms, reaction of Cl with H2(v), moderately fast V-V, V-T processes, and possible HCl(o) initial contaminant level may explain the low performance. N2-CO2 thermal mixing laser studies were extended to measure the efficiency of transfer of recombination energy in such a nonequilibrium N2 source to 10.6 microns optical energy. The low level of efficiency suggests that V-T decay processes may prevent vibrational energy freezing until much lower temperatures are achieved and that trapping of energy in long-lived electronic excitation of N2 may be a factor.

Boedeker, L. R.↗
NASA NTRS1972

SCC of Ti-6Al-4V foil by methanol - Effect of treatments with 2,4-pentanedione and its metal complexes.

The susceptibility of Ti-6Al-4V foil to stress corrosion cracking (SCC) by methanol can be decreased by treatment of the foil with 2,4-pentanedione prior to its immersion in the corroding media. It is assumed that such treatments remove from the protective film formed on the foil by exposure to the atmosphere, certain metal ions whose oxides are more readily penetrated by the ions, Na + and Cl- or Fe(3+) and Cl-, present in the corroding media.

Haney, E. G.↗
NASA NTRS1973

Ionic migration and weathering in frozen Antarctic soils

Soils of continental Antarctica are forming in one of the most severe terrestrial environments. Continuously low temperatures and the scarcity of water in the liquid state result in the development of desert-type soils. In an earlier experiment to determine the degree to which radioactive Na(Cl-36) would migrate from a shallow point source in permafrost, movement was observed. To confirm this result, a similar experiment involving (Na-22)Cl was conducted. Significantly less movement of the Na-22 ion was observed. Ionic movement in the unfrozen interfacial films at mineral surfaces in frozen ground is held to be important in chemical weathering in Antarctic soils.

Ugolini, F. C.↗
NASA NTRS1973

A spectroscopic study of CW chemical lasers.

A subsonic transverse-flow chemical laser has been instrumented to permit measurements of vibration-rotation state populations and laser output spectra under flow conditions typical of present CW hydrogen halide laser operation. Measurements are presented for the F + HI, F + HBr, F + CH4, F + HCl, F + H2, Cl + HI, and Cl + HBr atom-exchange reaction systems. CW operation was found to be characterized by relatively modest departures from Maxwell-Boltzmann vibrational energy distributions at all stages of reaction in contrast to pulsed operation based on similar reactions.

Rosen, D. I.↗
NASA NTRS1973

Volatile trace elements and the characterization of the Cayley Formation and the primitive lunar crust

Two types of highland terrain appear to be present at the Apollo 16 landing site. The Plains Formation called Cayley is ubiquitous and blankets even those regions that were presumably a part of the mountainous Descartes Formation. The second type of terrain is that associated with the ejectae from North and South Ray craters. The stratigraphy sampled by the ejectae underlays the Cayley layer as characterized above and may permit a redefinition of Descartes Formation as that which underlays the smooth Plains deposits. These conclusions are based on the concentrations and chemical coherence between elements such as Cl-F-P2O5 and Ru-Os. The primitive lunar crust may be characterized by the type of feldspathic rocks which are enriched in trace elements, such as Cl, Br, U, Te, Ru, and Os, as found in 'rusty' rock 66095 and in 61016; other feldspathic rocks are depleted and may be of secondary origin.

Jovanovic, S.↗
NASA NTRS1973

The applicability and effectiveness of cluster analysis

An insight into the characteristics which determine the performance of a clustering algorithm is presented. In order for the techniques which are examined to accurately cluster data, two conditions must be simultaneously satisfied. First the data must have a particular structure, and second the parameters chosen for the clustering algorithm must be correct. By examining the structure of the data from the Cl flight line, it is clear that no single set of parameters can be used to accurately cluster all the different crops. The effectiveness of either a noniterative or iterative clustering algorithm to accurately cluster data representative of the Cl flight line is questionable. Thus extensive a prior knowledge is required in order to use cluster analysis in its present form for applications like assisting in the definition of field boundaries and evaluating the homogeneity of a field. New or modified techniques are necessary for clustering to be a reliable tool.

Ingram, D. S.↗
NASA NTRS1975

Psychophysical Models for Signal Detection with Time Varying Uncertainty

Psychophysical models for the behavior of the human operator in detection tasks which include change in detectability, correlation between observations and deferred decisions are developed. Classical Signal Detection Theory (SDT) is discussed and its emphasis on the sensory processes is contrasted to decision strategies. The analysis of decision strategies utilizes detection tasks with time varying signal strength. The classical theory is modified to include such tasks and several optimal decision strategies are explored. Two methods of classifying strategies are suggested. The first method is similar to the analysis of ROC curves, while the second is based on the relation between the criterion level (CL) and the detectability. Experiments to verify the analysis of tasks with changes of signal strength are designed. The results show that subjects are aware of changes in detectability and tend to use strategies that involve changes in the CL's.

Gai, E.↗