Observational constraints on interstellar dust models

No single model has been able to account for all of the observed spectroscopic properties of interstellar or circumstellar dust. The reason for this is that, despite the agreement that the grains are composed of silicaceous/metal oxide and carbonaceous material, there is strong disagreement as to their exact structure and composition. This led Draine and Lee (1984) to use interstellar extinction data to define an interstellar graphitic material; new observational findings have made even that identification uncertain. But the great advantage of their approach is that they used observations at all of the wavelengths available to define the material. Here, the authors attempt a variation of that approach. They examine recent UV and IR data and attempt to put constraints on the possible types of interstellar grain composition, and to connect these constraints with grain models. A summary of some of the important constraints imposed by the observations is given

Si3N4 emissivity and the unidentified infrared bands

Infrared spectroscopy of warm (about 150 to 750 K), dusty astronomical sources has revealed a structured emission spectrum which can be diagnostic of the composition, temperature, and in some cases, even size and shape of the grains giving rise to the observed emission. The identifications of silicate emission in oxygen rich objects and SiC in carbon rich object are two examples of this type of analysis. Cometary spectra at moderate resolution have similarly revealed silicate emission, tying together interstellar and interplanetary dust. However, Goebel has pointed out that some astronomical sources appear to contain a different type of dust which results in a qualitatively different spectral shape in the 8 to 13 micron region. The spectra shown make it appear unlikely that silicon nitride can be identified as the source of the 8 to 13 micron emission in either NGC 6572 or Nova Aql 1982. The similarity between the general wavelength and shape of the 10 micron emission from some silicates and that from the two forms of silicon nitride reported could allow a mix of cosmic grains which include some silicon nitride if only the 8 to 13 micron data are considered

Aerobrake assembly with minimum Space Station accommodation

The minimum Space Station Freedom accommodations required for initial assembly, repair, and refurbishment of the Lunar aerobrake were investigated. Baseline Space Station Freedom support services were assumed, as well as reasonable earth-to-orbit possibilities. A set of three aerobrake configurations representative of the major themes in aerobraking were developed. Structural assembly concepts, along with on-orbit assembly and refurbishment scenarios were created. The scenarios were exercised to identify required Space Station Freedom accommodations. Finally, important areas for follow-on study were also identified

Evaluation of the Advanced Subsonic Technology Program Noise Reduction Benefits

This report presents a detailed evaluation of the aircraft noise reduction technology concepts developed during the course of the NASA/FAA Advanced Subsonic Technology (AST) Noise Reduction Program. In 1992, NASA and the FAA initiated a cosponsored, multi-year program with the U.S. aircraft industry focused on achieving significant advances in aircraft noise reduction. The program achieved success through a systematic development and validation of noise reduction technology. Using the NASA Aircraft Noise Prediction Program, the noise reduction benefit of the technologies that reached a NASA technology readiness level of 5 or 6 were applied to each of four classes of aircraft which included a large four engine aircraft, a large twin engine aircraft, a small twin engine aircraft and a business jet. Total aircraft noise reductions resulting from the implementation of the appropriate technologies for each class of aircraft are presented and compared to the AST program goals

Dinosaur tracks in Triassic Molteno sediments: the earliest evidence of dinosaurs in South Africa?

A fossil tracksite containing well-preserved tridactyl footprints of bipedal theropod dinosaurs is reported from fluvial overbank deposits of Molteno age (Stormberg Group: Triassic) in the northeastern Cape Province, South Africa. They occur stratigraphically below the mudrocks of the Elliot Formation, in which dinosaur remains are comparatively common, and are taken to represent the earliest evidence for dinosaurs in South Africa. They also represent the earliest unequivocal evidence of tetrapods in Molteno deposits.Foundation for Research Development; Trustees of the Port Elizabeth Museu

AMPA Receptor Phosphorylation and Synaptic Colocalization on Motor Neurons Drive Maladaptive Plasticity below Complete Spinal Cord Injury.

Clinical spinal cord injury (SCI) is accompanied by comorbid peripheral injury in 47% of patients. Human and animal modeling data have shown that painful peripheral injuries undermine long-term recovery of locomotion through unknown mechanisms. Peripheral nociceptive stimuli induce maladaptive synaptic plasticity in dorsal horn sensory systems through AMPA receptor (AMPAR) phosphorylation and trafficking to synapses. Here we test whether ventral horn motor neurons in rats demonstrate similar experience-dependent maladaptive plasticity below a complete SCI in vivo. Quantitative biochemistry demonstrated that intermittent nociceptive stimulation (INS) rapidly and selectively increases AMPAR subunit GluA1 serine 831 phosphorylation and localization to synapses in the injured spinal cord, while reducing synaptic GluA2. These changes predict motor dysfunction in the absence of cell death signaling, suggesting an opportunity for therapeutic reversal. Automated confocal time-course analysis of lumbar ventral horn motor neurons confirmed a time-dependent increase in synaptic GluA1 with concurrent decrease in synaptic GluA2. Optical fractionation of neuronal plasma membranes revealed GluA2 removal from extrasynaptic sites on motor neurons early after INS followed by removal from synapses 2 h later. As GluA2-lacking AMPARs are canonical calcium-permeable AMPARs (CP-AMPARs), their stimulus- and time-dependent insertion provides a therapeutic target for limiting calcium-dependent dynamic maladaptive plasticity after SCI. Confirming this, a selective CP-AMPAR antagonist protected against INS-induced maladaptive spinal plasticity, restoring adaptive motor responses on a sensorimotor spinal training task. These findings highlight the critical involvement of AMPARs in experience-dependent spinal cord plasticity after injury and provide a pharmacologically targetable synaptic mechanism by which early postinjury experience shapes motor plasticity

Can insertion length for a double-lumen endobronchial tube be predicted?

Publisher's copy made available with the permission of the publisherIt has been suggested that the appropriate length of insertion for double-lumen tubes can be estimated by external measurement. This study examined the accuracy of external measurement in estimating the actual length of insertion required in 130 patients. It also examined the relationship between the length inserted and the patient’s height in 126 patients and their weight in 125 patients. Although there was a fair correlation between the measured external length and the final inserted length (r=0.61), the 95% confidence intervals of slope and intercept allowed a large variation and the prediction was too wide to be clinically useful. Height was reasonably well correlated with the final length (r=0.51) but an equally wide 95% confidence interval rendered it of little clinical value. There was no correlation between weight and final tube length. It is concluded that external measurement alone is not adequate to predict a clinically acceptable position of the double-lumen tube.R.A. Dyer, S.A.M. Heijke, W.J. Russell, M.B. Bloch, M.F.M. Jameshttp://www.aaic.net.au/Article.asp?D=200004

Rotating flux-focusing eddy current probe for flaw detection

A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks about circular fasteners and other circular inhomogeneities in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil, The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal. By rotating the probe in a path around a circular fastener such as a rivet while maintaining a constant distance between the probe and the center of a rivet, the signal due to current flow about the rivet can be held constant. Any further changes in the current distribution, such as due to a fatigue crack at the rivet joint, can be detected as an increase in the output voltage above that due to the flow about the rivet head