Monitoring and Analysis of Frozen Debris Lobes, Phase I

INE/AUTC 12.2

Determination of the Telluric Water Vapor Absorption Correction for Astronomical Data Obtained from the Kuiper Airborne Observatory

The amount of telluric water vapor along the line of sight of the Kuiper Airborne Observatory telescope as obtained concommitantly on 23 flights is compared with the NASA-Ames Michelson interferometer and with the NOAA-Boulder radiometer. A strong correlation between the two determinations exists, and a method for computing the atmospheric transmission for a given radiometer reading is established

Vacuum-UV negative photoion spectroscopy of gas-phase polyatomic molecules

This Review describes recent experiments to detect anions following vacuum-UV photoexcitation of gas-phase polyatomic molecules. Using synchrotron radiation in the range 10-35 eV at a resolution down to 0.02 eV, negative ions formed are detected by mass spectrometry. The molecules studied in detail include CF$_4$, SF$_6$ and CH$_4$; the CF$_3$X series where X = Cl,Br,I; the CH$_3$Y series where Y = F,Cl,Br; and SF$_5$Z where Z = CF$_3$,Cl. Spectra and raw data only are reported for other members of the CH$_x$F$_y$, CH$_x$Cl$_y$ including CCl$_4$, and CF$_x$Cl$_y$ series where ($x$+$y$) = 4; and saturated and unsaturated members of the C$_m$H$_n$ and C$_m$F$_n$ series up to m = 3. Anions detected range from atomic species such as H-, F- and Cl- through to heavier polyatomics such as SF$_5^-$, CF$_3^-$ and CH$_2$Cl$^-$. The majority of anions display a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation, generically written as ABC + h$v$ $\rightarrow$ D$^-$ + E$^+$ + neutral(s). In a few cases, the anion signal increases much more rapidly than a linear dependence with pressure, suggesting that anions now form via a multi-step process such as dissociative electron attachment. Cross sections for ion-pair formation can be put on to an absolute scale by calibrating the signal strength with those of F$^-$ from SF$_6$ and CF$_4$, although there are difficulties associated with the determination of H$^-$ cross sections from hydrogen-containing molecules unless this anion is dominant. Following normalisation to total vacuum-UV absorption cross sections (where data are available), quantum yields for anion production are obtained. Cross sections in the range ca. 10$^{-23}$ to 10$^{-19}$ cm$^2$ , and quantum yields in the range ca. 10$^{-6}$ to 10$^{-3}$ are reported. The Review describes the two ion-pair mechanisms of indirect and direct formation and their differing characteristics, and the properties needed for anion formation by dissociative electron attachment. From this huge quantity of data, attempts are made to rationalise the circumstances needed for favourable formation of anions, and which anions have the largest cross section for their formation. Since most anions form indirectly via predissociation of an initially-excited Rydberg state of the parent molecule by an ion-pair continuum, it appears that the dynamics of this curve crossing is the dominant process which determines which anions are formed preferentially. The thermochemistry of the different exit channels and the microscopic properties of the anion formed do not appear to be especially significant. Finally, for the reaction ABC + h$v$ $\rightarrow$ A$^-$ + BC$^+$ , the appearance energy of A$^-$ can be used to determine an upper limit to the bond dissociation energy of AB (to A + BC), or an upper limit to that of ABC$^+$ (to A + BC$^+$). Where known, the data are in excellent agreement with literature values

Vacuum-Ultraviolet negative photoion spectroscopy of SF5Cl

Using vacuum-UV radiation from a synchrotron, gas-phase negative ions are detected by mass spectrometry following photoexcitation of SF$_5$Cl. F$^-$, Cl$^-$ and SF$_5^-$are observed, and their ion yields recorded in the range 8-30 eV. F$^-$ and Cl$^-$ show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation, generically written AB + h$v$ $\rightarrow$ C$^-$ + D$^+$ (+ neutral(s)). F$^-$ is the strongest signal, and absolute cross sections are determined by calibrating the signal intensity with that of F$^-$ from SF$_6$ and CF$_4$. Resonances are observed, and assigned to transitions to Rydberg states of SF$_5$Cl. The Cl$^-$ signal is much weaker, despite the S-Cl bond being significantly weaker than the S-F bond. Appearance energies for F$^-$ and Cl$^-$ of 12.7 ± 0.2 and 10.6 ± 0.2 eV are determined. The spectra suggest that these ions form indirectly by crossing of Rydberg states of SF$_5$Cl onto an ion-pair continuum

Near-infrared and X-ray obscuration to the nucleus of the Seyfert 2 galaxy NGC 3281

We present the results of a near-infrared and X-ray study of the Seyfert 2 galaxy NGC 3281. Emission from the Seyfert nucleus is detected in both regions of the electromagnetic spectrum, allowing us to infer both the equivalent line of sight hydrogen column density, N_H = 71.0(+11.3,-12.3)e26/m^2 and the extinction due to dust, A_V = 22+/-11 magnitudes (90% confidence intervals). We infer a ratio of N_H/A_V which is an order of magnitude larger than that determined along lines of sight in the Milky Way and discuss possible interpretations. We consider the most plausible explanation to be a dense cloud in the foreground of both the X-ray and infrared emitting regions which obscures the entire X-ray source but only a fraction of the much larger infrared source.Comment: 23 pages including 9 figure

Overview of the Main Propulsion System for a Nuclear Thermal Propulsion Flight Demonstrator

A demonstration of a Nuclear Thermal Propulsion (NTP) engine has not been conducted in over 50 years. Several tests were conducted during the NERVA program but no NTP engine was ever flown in space. In the last several years there has been a considerable amount of conceptual design work on NTP engines conducted. With the prospect of human Mars missions in the 2030s there has been a renewed interest in NTP engines. A concept design study was conducted with the intent to design 2 flight demonstrator vehicles that would buy down programmatic and technical risks associated with launching and operating nuclear reactors in space. The intent of the first demonstrator mission would be to employ a simplified NTP engine and buy down programmatic risks whereas the second demonstrator would buy down technical risks with a NTP engine designed to be similar to an operational NTP model. The results of the study showed that a simplified NTP engine demonstrator could be feasibly built and flown in the near term with mostly high TRL, commercial off-the-shelf components

Fuselage shell and cavity response measurements on a DC-9 test section

A series of fuselage shell and cavity response measurements conducted on a DC-9 aircraft test section are described. The objectives of these measurements were to define the shell and cavity model characteristics of the fuselage, understand the structural-acoustic coupling characteristics of the fuselage, and measure the response of the fuselage to different types of acoustic and vibration excitation. The fuselage was excited with several combinations of acoustic and mechanical sources using interior and exterior loudspeakers and shakers, and the response to these inputs was measured with arrays of microphones and accelerometers. The data were analyzed to generate spatial plots of the shell acceleration and cabin acoustic pressure field, and corresponding acceleration and pressure wavenumber maps. Analysis and interpretation of the spatial plots and wavenumber maps provided the required information on modal characteristics, structural-acoustic coupling, and fuselage response

UHB demonstrator interior noise control flight tests and analysis

The measurement and analysis of MD-UHB (McDonnell Douglas Ultra High Bypass) Demonstrator noise and vibration flight test data are described as they relate to passenger cabin noise. The analyses were done to investigate the interior noise characteristics of advanced turboprop aircraft with aft-mounted engines, and to study the effectiveness of selected noise control treatments in reducing passenger cabin noise. The UHB Demonstrator is an MD-80 test aircraft with the left JT8D engine replaced with a prototype UHB engine. For these tests, the UHB engine was a General Electric Unducted Fan, with either 8x8 or 10x8 counter-rotating propeller configurations. Interior noise level characteristics were studied for several altitudes and speeds, with emphasis on high altitude (35,000 ft), high speed (0.75 Mach) cruise conditions. The effectiveness of several noise control treatments was evaluated based on cabin noise measurements. The important airborne and structureborne transmission paths were identified for both tonal and broadband sources using the results of a sound intensity survey, exterior and interior noise and vibration data, and partial coherence analysis techniques. Estimates of the turbulent boundary layer pressure wavenumber-frequency spectrum were made, based on measured fuselage noise levels

An algorithm for determining program feasibility of a multi-mode PAM commutator telemetry system Technical report no. 10

Algorithm formulation for evaluation of strapping arrangement programs for PAM multimode commutation system of Saturn telemetry syste