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NASA NTRS2017

Synchronous Separation, Seaming, Sealing and Sterilization (S4) using Brazing for Sample Containerization and Planetary Protection

The potential return of samples back to Earth from other planetary bodies would be based on planetary protection requirements that vary depending on the type of body [1]. Potential Mars Sample Return would require the protection of our planet from backward contamination. To fulfill this requirement, it would be necessary to implement “break the chain of contact (BTC)” process, where any material reaching Earth would have to be inside a container that is sealed with an extremely high level of confidence. In order to accomplish this, it would be necessary to contain the acquired samples and destroy any potential biological materials that may have contaminated the external surface of the container, while protecting the samples for further analysis. Using brazing, a novel synchronous separation, seaming, sealing and sterilization (S4) process for sample containerization and planetary protection has been conceived and demonstrated. A prototype double-wall container with inner and outer shells and Earth clean interstitial space was used for this demonstration. For potential Mars sample return, the double wall container would be consist of two halves and prepared on Earth. The on-orbit execution would consist of inserting the sample into one of the halves and then mating to the other half and melt the braze material to perform the S4 process. The use of brazing material that melts at temperatures higher than 500OC would assure sterilization of the exposed areas due to pyrolysis since carbon bonds are broken at this temperature. The process consists of two-steps, Step-1: the double wall container halves are fabricated and brazed on Earth; and Step-2: Assembly and brazing the samples on orbit. To prevent potential jamming during the process of mating the two halves of the double-wall container and the extraction of the brazed inner container, a double cone-within-cone approach has been conceived. The results of this study are described and discussed in this manuscript.

Bar-Cohen, Yoseph↗
NASA NTRS1998

Advanced High Brilliance X-Ray Source

The possibility to dramatically increase the efficiency of laboratory based protein structure measurements through the use of polycapillary X-ray optics was investigated. This project initiated April 1, 1993 and concluded December 31, 1996 (including a no cost extension from June 31, 1996). This is a final report of the project. The basis for the project is the ability to collect X-rays from divergent electron bombardment laboratory X-ray sources and redirect them into quasiparallel or convergent (focused) beams. For example, a 0.1 radian (approx. 6 deg) portion of a divergent beam collected by a polycapillary collimator and transformed into a quasiparallel beam of 3 millradian (0.2 deg) could give a gain of 6(exp 2)/0.2(exp 2) x T for the intensity of a diffracted beam from a crystal with a 0.2 deg diffraction width. T is the transmission efficiency of the polycapillary diffraction optic, and for T=0.5, the gain would be 36/0.04 x O.5=45. In practice, the effective collection angle will depend on the source spot size, the input focal length of the optic (usually limited by the source spot-to-window distance on the x-ray tube) and the size of the crystal relative to the output diameter of the optic. The transmission efficiency, T, depends on the characteristics (fractional open area, surface roughness, shape and channel diameter) of the polycapillary optic and is typically in the range 0.2-0.4. These effects could substantially reduce the expected efficiency gain. During the course of this study, the possibility to use a weakly focused beam (0.5 deg convergence) was suggested which could give an additional 10-20 X efficiency gain for small samples . Weakly focused beams from double focusing mirrors are frequently used for macromolecular crystallography studies. Furthermore the crystals are typically oscillated by as much as 2 deg during each X-ray exposure in order to increase the reciprocal space (number of crystal planes) sampled and use of a slightly convergent beam could, in principle, provide a similar sampling benefit without oscillation. Although more problematic, because of complications in analyzing the diffraction patterns, it was also suggested that even more extreme beam convergence might be used to give another order of magnitude intensity gain and even smaller focused spot size which could make it possible to study smaller protein crystals than can be studied using standard laboratory based X-ray diffraction systems. This project represents the first systematic investigation of these possibilities. As initially proposed, the contract included requirements for design, purchase, evaluation and delivery of three polycapillary lenses to the Laboratory for Structural Biology at MSFC and demonstration of such optics at MSFC for selected protein crystal diffraction applications.

Gibson, Walter M.↗
NASA NTRSDate not supplied

Stratigraphy of the Apollo 17 Landslide Core 73002 From FMR Maturity and VNIR and Mössbauer Spectroscopy

A suite of samples from the Apollo missions to the Moon (1969-1973) were set aside and stored under controlled conditions to have unexamined lunar samples available decades later for analyses that take advantage of evolved sample handling techniques, maturation of then existing instrumentation, and development of new analytical techniques and instrumentation [e.g., 1]. One preserved sample is the Apollo 17 double drive tube core (73001/2) that was driven into the lunar surface on the landslide deposit at Station 3 on the South Massif in the Taurus-Littrow valley [2]. The deeper section (73001) was stored frozen in a Core Sample Vacuum Container (CSVC) to maximize preservation of lunar volatiles. We report here, as a part of the Apollo Next Generation Sample Analysis (ANGSA) Initiative [1,3], stratigraphy for the upper core section (73002) with respect to maturity (ferromagnetic resonance (FMR) maturity index Is/FeO [4-6]), visible-near-IR (VNIR) spectroscopy, and, for representative samples, grain-size analysis and Mössbauer spectroscopy. Stratigraphy provides data to model the dynamics of lunar landslide deposits and their post-emplacement evolution in comparison to impact-driven mixing on an airless body and stratigraphic context for volatile and (if any) organic behavior. Reported by [7] are preliminary results for multispectral imaging and hyperspectral scanning of the first dissection pass of 73002.

R. V. Morris↗
NASA NTRS1996

Ulysses observations of double ion beams associated with coronal mass ejections

Coronal mass ejections (CME's) are thought to result from the loss of stability within a magnetically confined coronal structure leading to its radial expansion into interplanetary space. As the CME expands into the corona current sheets will form between the expanding CME and surrounding field lines in the ambient wind. This configuration may lead to reconnection between the CME and adjacemt field lines. Such reconnection may produce double ion beams as has been observed in the terrrestrial magnetosphere. We examine all 24 distinct signatures of CME's observed by Ulysses during the in-ecliptic portion of the mission. In 5 of these 24 cases the ion spectra were not clear and thus the presence of double ion beams could not be determined. In 13 of the remaining 19 CME's double ion beams were found on the leading and/or trailing edge of the CME but not in the interior of the CME. In 3 of the CME's double ion beams were found throughout the CME while in the remaining 3 CME's double ion beams were not present near or just inside of the CME. In contrast in a control sample of 19 randomly chosen intervals, double ion beams were present at the leading and/or trailing edges of the random intervals in only 3 of the 19 cases. There appears to be no correlation between probability of occurrence of double ion beams and a magnetic cloud or non-cloud configuration of the CME and no correlation between the presence of the double ion beams at the edges of the CME and the CME being a fast or slow CME.

Hammond, C. M.↗
NASA NTRS2003

Explosion Welding for Hermetic Containerization

A container designed for storing samples of hazardous material features a double wall, part of which is sacrificed during an explosion-welding process in which the container is sealed and transferred to a clean environment. The major advantage of this container sealing process is that once the samples have been sealed inside, the outer wall of what remains of the container is a clean surface that has not come into contact with the environment from which the samples were taken. Thus, there is no need to devise a decontamination process capable of mitigating all hazards that might be posed by unanticipated radioactive, chemical, and/or biological contamination of the outside of the container. The container sealing method was originally intended to be used to return samples from Mars to Earth, but it could also be used to store samples of hazardous materials, without the need to decontaminate its outer surface. The process stages are shown. In its initial double-wall form, the volume between the walls is isolated from the environment; in other words, the outer wall (which is later sacrificed) initially serves to protect the inner container from contamination. The sample is placed inside the container through an opening at one end, then the container is placed into a transfer dock/lid. The surfaces that will be welded together under the explosive have been coated with a soft metallic sacrificial layer. During the explosion, the sacrificial layer is ejected, and the container walls are welded together, creating a strong metallic seal. The inner container is released during the same event and enters the clean environment.

Dolgin, Benjamin↗
NASA NTRS2020

Analysis of Volatile Organic Compounds in the Apollo Next Generation Sample Analysis (ANGSA) 73002 Core Sample

Understanding the organic content of lunar regolith was an early priority upon the return of Apollo samples, with amino acids being of special interest because of their importance to life on Earth and their astrobiological relevance. Many initial studies focused on the detection of amino acids in these samples and attempts to determine the origin of those compounds. Although no consensus on the origin of the amino acids was reached in those early studies, more recent work determined that the detected amino acids originated from both terrestrial contamination and meteoritic or cometary in fall to the lunar surface. A majority of the amino acids in the Apollo samples studied originated from precursor molecules, either indigenous to the lunar samples or contaminants, that reacted during the water extraction and acid hydrolysis process for analysis in the laboratory, but the identities of the amino acid precursors still remain poorly understood. Such precursors could include hydrogen cyanide (HCN) and other volatile organic compounds such as amines, carboxylic acids, or aldehydes and ketones. The identities of these compounds, as well as the effects of years of curation on their abundances in lunar regolith samples stored at ambient temperature under nitrogen gas purge, are not clear. The specially curated samples available through the Apollo Next Generation Sample Analysis (ANGSA) program provide a unique opportunity to use state-of- the-art analytical techniques to examine previously unstudied lunar materials. The ANGSA samples include three types of samples: 1) samples stored frozen since <1 month after Earth arrival; 2) samples stored under helium; and 3) a double drive tube collected by Apollo 17 astronauts, with the bottom portion of the drive tube sealed under vacuum on the Moon and never opened. In contrast to the typically curated Apollo samples that have been kept for decades at room temperature under flowing nitrogen purge that may have significantly reduced the abundance of volatiles, the vacuum-sealed and frozen samples may have enhanced preservation of these volatiles. Our initial investigation examines amino acids and their potential volatile precursors, including hydrogen cyanide (HCN), aldehydes, ketones, amines, and mono-carboxylic acids, in a sample from the top portion of the Apollo 17 double drive tube. These results will aid in understanding the lunar abundances of these molecules and will also be compared to future analyses of other drive tube and frozen ANGSA samples.

Elsila, J. E.↗
NASA NTRS1977

Carotenoid diagenesis in a marine sediment

The major carotenoids at three levels (3, 40, and 175 m below the sediment-water interface) in a core from a marine sediment (Cariaco Trench, off Venezuela) have been examined. Mass and electronic spectral data have provided evidence for the onset of a progressive reduction of carotenoids in the geological column. The time scale of the process appears to depend on the particular carotenoid. Reduction of up to two double bonds is observed for the diol, zeaxanthin, in the oldest sediment (about 340,000 years old) but no reduction is observed in the younger samples (about 5000 and 56,000 years old). The diketone, canthaxanthin, shows evidence of reduction of up to two double bonds in the 56,000-yr sample and up to five double bonds in the oldest sample. No reduction of beta-carotene was observed in any of the samples.

Watts, C. D.↗
NASA NTRS1980

Circular-scan streak tube with solid-state readout

A circular-scan streak tube designed for use in a laser ranging system is described. Electrostatic focusing is used between the photocathode and a microchannel plate, and electrons from the microchannel plate are proximity focused onto an output phosphor screen. Electron beam deflection is achieved by driving two orthogonal sets of deflection plate assemblies in phase quadrature at a frequency of 200 MHz. The light intensity in the output beam trace is measured by using a circular Reticon array of 720 photodiodes, which is fiber-optically coupled to the output phosphor screen of the tube. Sample measurements of frequency-doubled Nd:YAG laser-pulse waveforms are given. Also the output beamwidth has been measured at the 200-MHz deflection frequency. The results suggest a limiting resolution of 33 psec for the circular-scan streak tube used for these tests.

Johnson, C. B.↗
NASA NTRS1993

Microwave digestion preparation and ICP determination of boron in human plasma

A microwave digestion procedure, followed by Inductively Coupled Argon Plasma Spectroscopy, is described for the determination of boron (B) in human plasma. The National Institute of Standards and Technology (NIST) currently does not certify the concentration of B in any substance. The NIST citrus leaves 1572 (CL) Standard Reference Material (SRM) and wheat flour 1567a (WF) were chosen to determine the efficacy of digestion. CL and WF values compare favorably to those obtained from an open-vessel, wet digestion followed by ICP, and by neutron activation and mass spectrometric measurements. Plasma samples were oxidized by doubled-distilled ultrapure HNO3 in 120 mL PFA Teflon vessels. An MDS-81D microwave digestion procedure allows for rapid and relatively precise determination of B in human plasma, while limiting handling hazards and sources of contamination.

Ferrando, A. A.↗
NASA NTRS1990

The environments of double radiogalaxies

Discussed here are simple methods by which the densities and pressures of the gas confining double radiogalaxies can be estimated from optical and x ray data. By applying these methods to an unbiased sample of nearby (z less than 0.5) double radiogalaxies, the author quantifies the empirical relation between the external confining pressure and the internal pressure of the lobes as inferred from the minimum energy argument. This relation is explained by an analytic model in which the lobes are statically confined by ambient material pre-heated in the bow-shock of the advancing radiosource. Such a model allows one to estimate source expansion speeds from a combination of radio and environmental data, and estimate properties of the environment from radio data alone, providing expansion speeds can be estimated from multifrequency observations.

Rawlings, Steve↗
NASA NTRSDate not supplied

Investigating Pyroclastic Volcanism in the Taurus-Littrow Valley (TLV) Using the Station 3 Double Drive Tube 73001-73002

Well over 100 pyroclastic deposits have been identified on the Moon. Eruptive processes such as represented by these deposits transported endogenous volatiles from the Moon’s mantle to its surface. Debris from pyroclastic deposits has been identified in all Apollo and Luna samples. The high-Ti pyroclastic de- posit sampled at Shorty Crater by the Station 4 double drive tube (74001-74002) is our best sampling of these types of deposits. Samples 78500 and 78526, NAC images of fissures in the Sculptured Hills, ash identified in 70001-7, and other green volcanic glass indicate that very low-Ti basalt (VLT) erup- tions also occurred in TLV. The double drive tube core being investigated by the ANGSA initiative provides an- other view of TLV pyroclastic eruptions. The regolith in 73001-73002 and the regolith breccias therein have nu- merous pyroclastic beads. Some individual regolith brec- cia fragments have abundant pyroclastic beads (>50 in a polished surface). In this work, we address the following questions. Do these glass beads overlap in composition with those sampled elsewhere in the TLV or do they rec- ord another episode of pyroclastic eruption? Are the magmas associated with pyroclastic eruptions petroge- netically related to the crystalline mare basalts in the TLV? Finally, is the volatile record of the pyroclastic eruptions better preserved in the newly opened and spe- cially contained Station 3 double drive tube core?

C.K. Shearer↗
NASA NTRSDate not supplied

From Apollo to Artemis: How Processing ANGSA Core Samples 73001/2 Can Help to Prepare for Future Sample Return Missions to the Moon and Beyond.

Introduction: Apollo Sample 73001/2 is a ~71cm long double drive tube consisting of an upper part (73002) and a lower part (73001) that contains regolith collected near Lara Crater at the Apollo 17 site, Station 3. The double drive tube is believed to have penetrated a lunar landslide deposit that was transported from the slope of the South Massif into the Taurus-Littrow Valley [1]. As part of the ANGSA (Apollo Next Generation Sample Analyses) initiative, preparing a preliminary examination (PE) catalog of 73001/2 is a crucial first step for the early identification of material types such as rock fragments and potential stratigraphy within the core. Many new curation and scientific tools such as X-ray computed tomography (XCT) [3], multi-spectral imaging [4], and gas extraction manifold with piercing tool [5-7], have been applied to the ANGSA core to benefit curation strategy, PE efforts, sample allocation to the planetary science community, and ultimately help to prepare for future sample return missions like Artemis. 73001/2 Preliminary Examination and Processing: Sample 73002 was successfully opened and extruded in Nov. 2019 and fully dissected at the end of 2021. Sample 73001 (Fig. 1) was successfully extruded in March 2022 after careful planning before opening the Core Sample Vacuum Container (CSVC) that was holding the drive tube of 73001. XCT, as part of PE, was used to scan the bottom and top part of the 73001 core tube within the CSVC prior to opening it to 1) facilitate non-destructive, rapid detection of any contamination potentials due to piercing of the CSVC during gas extraction [7]; and 2) to aid in the Artemis sample tool development and provide data on the knife edge seal of the CSVC. This knowledge will help us connect the mechanics of the implemented design (i.e., XCT data) to the performance of the seal (i.e., data on the gas samples will tell us how well the seal preserved the volatile record of lunar samples). Both type of information will feed forward into Artemis tool and storage strategies for future samples. Results and Lessons learned: The XCT data of the CSVC and core tube within showed that the bottom Teflon cap was not pierced during gas extraction (Fig. 1c) and thus, the sample integrity remained guaranteed during piercing and subsequent gas extraction. However, the XCT scan of the top of the core (Fig. 1b) revealed that the drive tube was overfilled with lunar soil and the tool that keeps the soil constrained within the drive tube was not fully deployed. These preliminary data allowed us to implement the necessary steps to prevent loss of sample integrity, including any potential stratigraphy shifts during extrusion. Processing Apollo core 73001/2, creating an informative PE catalog, and applying new and refined tools and technologies for sample analyses are invaluable activities that will assist in circumventing any potential pitfalls, aid in the characterization of samples, and help in the assessment of how well any lunar material has been collected and preserved in the past. This will aid in designing future sample collections and curation procedures and help to prepare for future human exploration and sampling missions such as Artemis. References: [1] Schmitt H. (2017) Icarus 298, 2-33. [3] Zeigler et al. (2021) LPSC 52nd, #2632; [4] Sun et al. (2021), LPSC 52nd, #1789; [5] Parai et al. (2021), LPSC 52nd #2665; [6] Schild et al. (2021) LPSC 52nd #1888; [7] McDonald (2022) ESL 2022.

ANGSA↗
NASA NTRS1994

Near-infrared imaging of Markarian 231: Evidence for a double nucleus

Near-infrared (1.2-2.4 micrometers) images are presented for the central 10 arcsec of the Seyfert 1 galaxy Markarian 231. We find a faint, but intrinsically luminous (M(sub k) approximately -20.7) secondary peak in the near-infrared light distribution approximately 3.5 arcsec (2.7 kpc) south of the primary Seyfert 1 nucleus. Since there is no optical or infrared evidence for ongoing star formation at the location of this secondary peak, and its near-infrared luminosity and color are comparable to slightly reddened spiral bulges or elliptical nuclei, we identify this peak with the stripped nucleus of the companion galaxy involved in the Mrk 231 merger event. Depending upon the exact ratio of the masses of the primary and secondary nucleus in the Mrk 231 system we estimate a merger time scale of less than or equal to 10(exp 9) yr. The morphology of the southern nucleus suggests that it may have recently survived a close passage (r less than 200 pc) with the Seyfert 1 nucleus on a highly elliptical orbit, in which case the merger time scale may be significantly shorter (approximately 10(exp 7) yr. We re-calculate the average merger time scale for the seven ultraluminous infrared galaxies with double nuclei in the Bright Galaxy Sample (the BGS) of Soifer et al. (AJ, 98, 766 (1989)) and derive a value of approximately 10(exp 8) yr. Since seven of ten of the ultraluminous infrared galaxies in the BGS are now known to be double, we estimate the ultraluminous 'phase' may be close to this value. Along with Arp 220 and Mrk 273, Mrk 231 is the third member of the class to possess a high brightness temperature non-thermal radio core and a double nucleus, suggesting the time scale for the generation or fueling of the active nucleus can be much less than the dynamical time scale for the merger of the progenitor nuclei.

Armus, L.↗
NASA NTRS2008

Fast Offset Laser Phase-Locking System

Figure 1 shows a simplified block diagram of an improved optoelectronic system for locking the phase of one laser to that of another laser with an adjustable offset frequency specified by the user. In comparison with prior systems, this system exhibits higher performance (including higher stability) and is much easier to use. The system is based on a field-programmable gate array (FPGA) and operates almost entirely digitally; hence, it is easily adaptable to many different systems. The system achieves phase stability of less than a microcycle. It was developed to satisfy the phase-stability requirement for a planned spaceborne gravitational-wave-detecting heterodyne laser interferometer (LISA). The system has potential terrestrial utility in communications, lidar, and other applications. The present system includes a fast phasemeter that is a companion to the microcycle-accurate one described in High-Accuracy, High-Dynamic-Range Phase-Measurement System (NPO-41927), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 22. In the present system (as in the previously reported one), beams from the two lasers (here denoted the master and slave lasers) interfere on a photodiode. The heterodyne photodiode output is digitized and fed to the fast phasemeter, which produces suitably conditioned, low-latency analog control signals which lock the phase of the slave laser to that of the master laser. These control signals are used to drive a thermal and a piezoelectric transducer that adjust the frequency and phase of the slave-laser output. The output of the photodiode is a heterodyne signal at the difference between the frequencies of the two lasers. (The difference is currently required to be less than 20 MHz due to the Nyquist limit of the current sampling rate. We foresee few problems in doubling this limit using current equipment.) Within the phasemeter, the photodiode-output signal is digitized to 15 bits at a sampling frequency of 40 MHz by use of the same analog-to-digital converter (ADC) as that of the previously reported phasemeter. The ADC output is passed to the FPGA, wherein the signal is demodulated using a digitally generated oscillator signal at the offset locking frequency specified by the user. The demodulated signal is low-pass filtered, decimated to a sample rate of 1 MHz, then filtered again. The decimated and filtered signal is converted to an analog output by a 1 MHz, 16-bit digital-to-analog converters. After a simple low-pass filter, these analog signals drive the thermal and piezoelectric transducers of the laser.

Shaddock, Daniel↗
NASA NTRS2012

In Situ Potassium-Argon Geochronology Using Fluxed Fusion and a Double Spike

A document highlights an Li-based fluxing agent that enables sample fusion and quantitative Ar-release at relatively low temperatures (900-1,000 C), readily achievable with current flight resistance furnace designs. A solid, double spike containing known quantities of Ar-39 and K-41 was developed that, when added in known amounts to a sample, enables the extraction of a Ar-40/K-40 ratio for age estimation without a sample mass measurement. The use of a combination of a flux and a double spike as a means of solving the mechanical hurdles to an in situ K-Ar geochronology measurement has never been proposed before. This methodology and instrument design would provide a capability for assessing the ages of rocks and minerals on the surfaces of planets and other rocky terrestrial bodies in the solar system.

Hurowitz, Joel A.↗
NASA NTRS1980

Multiple-creep-test apparatus

Simplified, compact apparatus uses fixtures that can test three samples at once for flexure, compression, or double-shear creep. Each fixture uses series of rods and plates to divide one load equally among three samples. Fixtures could be expanded to carry more samples by adding more rods and plates.

Haehner, C. L.↗
NASA NTRS1980

Measurements of the sampling volume of an infrared laser doppler velocimeter for the study of feasibility of simultaneous three-dimensional velocity profile mapping

High resolution incoherent mapping of the sampling volume was performed to determine the three dimensional profile of the volume of the beam from which information can be obtained by scattering. The incoherent sampling volume of the infrared laser Doppler velocimeter was found to be heavily dependent upon the configuration of the outgoing laser beam. In general when only half the beam is allowed to focus at the focal plane, the x, y traverses indicate a broader beam with nominal side lobes. However, if the total beam is permitted to impinge on the focal plane there is substantial narrowing of the beam with increased maximum intensity and an increase in side lobes. The double maximum indicated by the coherent sampling volume appears to be an artifact of the scanning process not a fundamental entity of the sampling volume.

Bond, R. L.↗
NASA NTRS1994

An IUE survey of interstellar H I Ly alpha absorption. 2: Interpretations

We present an analysis of interstellar neutral hydrogen column densities obtained from archival Ly alpha absorption line data toward the complete sample of B2 and hotter stars observed at high spectral resolution with the IUE satellite. The full sample includes 554 stars and more than doubles the number of lines of sight previously observed. Many of the B2 and B1.5 stars exhibit contamination from stellar Ly alpha absorption, and were excluded from the subsequent analysis. The final working sample includes 393 stars. We present statistical averages for a number of quantities derived for the sample. The stars range in distance from 0.12 to 11 kpc with an average distance of 2.1 kpc. Values for average sight-line density range from 0.017 to 8.62 atoms cm(exp -3), with an overall average of 0.23 atoms cm(exp -3). Neutral hydrogen and dust are well correlated, with N(H I)/E(B - V) = 4.93 x 10(exp 21) cm(exp -2) mag(exp -1), and N(H I)/E(Bump) = 2.17 x 10(exp 21) cm(exp -2) mag(exp -1). There is an increase in the H I to dust ratios for the densest sight lines. Evidently, the H I to dust ratios in dense clouds are higher than in the lower density medium between the clouds and in interarm directions. The effect is probably an indication of dust modification in the dense clouds. The H I to dust ratios are approx. 17% smaller for the sight lines to O stars compared to the ratios found toward B stars. We have identified sight lines with anomalously large and small values of N(H I)/E(B - V) and H(H I)/E(Bump). Some of these sight lines are well-known examples of peculiar extinction (i.e., HD 147933 and HD 37061 (NU Ori)). Others are less well known and may provide important new examples of regions with highly modified dust. The number of stars with anomalously low H I to dust ratios is disproportionately larger than the number of stars with anomalously high H I to dust ratios. The distribution of the gas away form the Galactic plane for the sample of objects is complex. For the subset of 375 stars whose lines of sight have a statistically low probablility of intersecting a large cloud, the distribution may be roughly approximated by an exponential density distribution, with a midplane density of 0.366 atoms cm(exp -3), a scale height of 195 pc, and a random logarithmic scattering parameter sigma (sub p) of 0.159 dex. For the same sample of stars, interstellar dust is found to be confined closer to the plane than the H I, with (E(B - V)/r)(sub 0) = 0.257 mag kpc(exp -1), scale height h = 152 pc, and sigma(sub p) = 0.263 dex. The dust distribution is more inhomogeneous than the gas distribution. The observed distribution of H I away from the Galactic plane can also be fitted with a two-component exponential model including the effects of patchiness. Unfortunately, the foreground contamination produced by the cloudy and more confined component of H I makes it difficult to estimate the scale height of the extended component without invoking an independent estimate of its midplane density. Assuming n(sub 2)(0) = 0.16 cm(exp -3) from the Copernicus satellite H I/H(sub 2) survey, we obtain n(sub 1)(0) = 0.247 cm(exp -3), h(sub 1) = 73 PC, and h(sub 2) + 357 pc.

Diplas, Athanassios↗