LDEF Materials Workshop 1991, part 2

The LDEF Materials Workshop 1991 was a follow-on to the Materials Sessions at the First LDEF Post-Retrieval Symposium held in Kissimmee, Florida, June 1991. The workshop comprised a series of technical sessions on materials themes, followed by theme panel meetings. Themes included materials, environmental parameters, and data bases; contamination; thermal control and protective coating and surface treatments; polymers and films; polymer matrix composites; metals, ceramics, and optical materials; lubricants adhesives, seals, fasteners, solar cells, and batteries. This document continues the LDEF Space Environmental Effects on Materials Special Investigation Group (MSIG) pursuit to investigate the effects of LEO exposure on materials which were not originally planned to be test specimens. Papers from the technical sessions are presented

Photographic Observations of the Hayabusa Re-entry

We analyzed photographic observations of the re-entry of the Hayabusa spacecraft and capsule over Southern Australia on June 13, 2010, 13:52 UT. Radiometric measurements of the brightness of the associated fireball were obtained as well. We derived the trajectories and velocities of the spacecraft, its four fragments and the capsule. The capsule trajectory was within a few hundred meters of the trajectory predicted by JAXA prior the re-entry. The spacecraft trajectory was about 1 km higher than the capsule trajectory. Two major fragments separated from the spacecraft at a height of about 62 km with mutual lateral velocity of 250 m/s. The maximum absolute magnitude of the fireball of -12.6 was reached at a height of 67 km. The dynamic pressures acting on the spacecraft at the fragmentation points were only 1 - 50 kPa. No spacecraft fragment was seen to survive below the height of 47 km. The integral luminous efficiency of the event was 1.3%. As expected, the capsule had a very low luminous efficiency and very low ablation coefficient. The ablation coefficients and masses of the major spacecraft fragments are discussed.Comment: Accepted for publication in PASJ, 16 pages, 8 figures, 5 table

The Escape of Ionizing Photons from the Galaxy

The Magellanic Stream and several high velocity clouds have now been detected in optical line emission. The observed emission measures and kinematics are most plausibly explained by photoionization due to hot, young stars in the Galactic disk. The highly favorable orientation of the Stream allows an unambiguous determination of the fraction of ionizing photons, F_esc, which escape the disk. We have modelled the production and transport of ionizing photons through an opaque interstellar medium. Normalization to the Stream detections requires F_esc = 6%, in reasonable agreement with the flux required to ionize the Reynolds layer. Neither shock heating nor emission within a hot Galactic corona can be important in producing the observed H-alpha emission. If such a large escape fraction is typical of L_* galaxies, star-forming systems dominate the extragalactic ionizing background. Within the context of this model, both the three-dimensional orientation of the Stream and the distances to high-velocity clouds can be determined by sensitive H-alpha observations.Comment: 4 pages; LaTeX2e, emulateapj.sty, apjfonts.sty; 4 encapsulated PS figures. For correct labels, may need to print Fig. 3 separately due to psfig limitation. Astrophysical Journal (Letters), accepte

Ionizing Photons and EUV Excesses in Clusters of Galaxies

Observations with the Extreme Ultraviolet Explorer satellite are purported to show extreme ultraviolet (EUV) and soft X-ray excesses in several clusters of galaxies (Bonamente, Lieu & Mittaz 2001). If interpreted as thermal emission, this would imply the presence of warm (T\sim 10^6 K) gas in these clusters with a mass comparable to that of gas at coronal temperatures. If true, this would have profound implications for our understanding of galaxy clusters and the distribution of baryons in the universe. Here we show that because of the large ionizing photon emissivities of gas at such low temperatures, the ionizing photon fluxes seen by disk galaxies in the observed clusters can be very large, resulting in minimum emission measures from neutral gas in such disks as high as 100 cm^(-6) pc. This result is essentially independent of the mechanism actually responsible for producing the alleged EUV excesses. The predicted emission measures in Abell 1795 (z=0.063) are about an order of magnitude larger than seen in the Reynolds layer of the Galaxy, providing a straightforward observational test of the reality of the EUV excess. New tunable filter H alpha images and WFPC images from the Hubble Space Telescope archive do not support the existence of the claimed EUV excess.Comment: To appear in ApJ Letters; 11 pages, 3 figure

Proceedings of the LDEF Materials Data Analysis Workshop

The 5-year, 10-month flight of the Long Duration Exposure Facility (LDEF) greatly enhanced the potential value of most LDEF materials, compared to the original 1-year flight plan. NASA recognized this potential by forming the LDEF Space Environmental Effects on Materials Special Investigation Group in early 1989 to address the expanded opportunities available in the LDEF structure and on experimental trays, so that the value of all LDEF materials to current and future space missions would be assessed and documented. The LDEF Materials Data Analysis Workshop served as one step toward the realization of that responsibility and ran concurrently with activities surrounding the successful return of the spacecraft to the NASA Kennedy Space Center. A compilation of visual aids utilized by speakers at the workshop is presented. Session 1 summarized current information on analysis responsibilities and plans and was aimed at updating the workshop attendees: the LDEF Advisory Committee, Principle Investigators, Special Investigation Group Members, and others involved in LDEF analyses or management. Sessions 2 and 3 addressed materials data analysis methodology, specimen preparation, shipment and archival, and initial plans for the LDEF Materials Data Base. A complementary objective of the workshop was to stimulate interest and awareness of opportunities to vastly expand the overall data base by considering the entire spacecraft as a materials experiment

LDEF Materials Workshop 1991, part 1

The workshop comprised a series of technical sessions on materials themes, followed by theme panel meetings. Themes included materials, environmental parameters, and data bases; contamination; thermal control and protective coatings and surface treatments; polymers and films; polymer matrix composites; metals, ceramics, and optical materials; lubricants adhesives, seals, fasteners, solar cells, and batteries. This report contains most of the papers presented at the technical sessions. It also contains theme panel reports and visual aids. This document continues the LDEF Space Environmental Effects on Materials Special Investigation Group (MSIG) pursuit of its charter to investigate the effects of LEO exposure on materials which where not originally planned to be test specimens and to integrate this information with data generated by principal investigators into an LDEF materials data base

A geochemical study of the winonaites: Evidence for limited partial melting and constraints on the precursor composition

The winonaites are primitive achondrites which are associated with the IAB iron meteorites. Textural evidence implies heating to at least the Fe, Ni–FeS cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. Oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. Here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-IAB parent asteroid. Modal mineralogy and geochemical data are presented for eight winonaites. Textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (Northwest Africa 1463) reached the Fe, Ni–FeS cotectic. However, only one (Tierra Blanca) shows geochemical evidence for silicate melting processes. Tierra Blanca is interpreted as a residue of small-degree silicate melting. Our sample of Winona shows geochemical evidence for extensive terrestrial weathering. All other winonaites studied here (Fortuna, Queen Alexander Range 94535, Hammadah al Hamra 193, Pontlyfni and NWA 1463) have chondritic major-element ratios and flat CI-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. The majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the Fe, Ni–FeS cotectic temperature) and ∼1370 K (the basaltic partial melting temperature). Silicate inclusions in the IAB irons demonstrate partial melting did occur in some parts of the parent body (Ruzicka and Hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. Together, this indicates that melting was the result of internal heating by short-lived radionuclides. The brecciated nature of the winonaites suggests that the parent body was later disrupted by a catastrophic impact, which allowed the preservation of the largely unmelted winonaites. Despite major-element similarities to both ordinary and enstatite chondrites, trace-element analysis suggests the winonaite parent body had a carbonaceous chondrite-like precursor composition. The parent body of the winonaites was volatile-depleted relative to CI, but enriched compared to the other carbonaceous classes. The closest match are the CM chondrites; however, the specific precursor is not sampled in current meteorite collections

The Genetic and Functional Role of ABCA12 in Harlequin Ichthyosis

Harlequin Ichthyosis (HI) is the most severe disorder in the family of autosomal recessive congenital ichthyosis (ARCI). Recessive mutations in the ABC transporter ABCA12 were found to be causative in HI. Loss of ABCA12 leads to defective transport of ceramides, impaired transportation of proteases, premature terminal differentiation, transepidermal water loss (TEWL) and the retention of squames, which leads to the characteristic clinical phenotype of thickened hyperkeratotic plates overlying the skin. This thesis focuses on the genetic and functional role of ABCA12 in the skin and how loss of ABCA12 leads to the HI epidermis. Several molecular genetic techniques were utilised to ascertain and evaluate possible causative mutations for HI in the gene ABCA12. The identification of novel and known, point and complex mutations give molecular diagnostics a greater reservoir to help identify possible causative mutations in future cases. The spectrum of ABCA12 mutations, which have been attributed to different diseases within ARCI, was discussed. A HI immortalised cell line was derived from a patient with a compound heterozygote mutation in ABCA12, with a nonsense p.Glu2264X and c.5382-2a/g, a complex splice site mutation of the putative acceptor site (AG) preceding exon 35. Further investigations assessed the use of low affinity acceptor sites by the spliceosome. Immunohistochemistry of the patient biopsy showed an absence of ABCA12 and a reduction of ABCA1 proteins. Knockdown of ABCA12 in control K17 immortalised keratinocytes decreased expression levels of ABCA1 and LXRβ proteins. Functional studies of the HI patient derived cell line validated a HI cellular phenotype in monolayer. The expression levels of involucrin, TGM1 and K10 proteins showed how the patient derived HI cell line under calcium shift initiated premature terminal differentiation in vitro, compared to controls. The activation of nuclear hormone receptors PPARβ/δ and LXRβ by the application of their agonists on the HI cell line increased the transcript and protein levels of the reduced ABCA1. The same agonists reduced specific markers of differentiation, which were activated prematurely in the HI cell line under calcium shift, suggesting a potential therapeutic strategy to explore.Samuel Hardgrave Harlequin Ichthyosis Research Trust charity studentshi