F-14A aircraft high-speed flow simulations

A model of the Grumman/Navy F-14A aircraft was developed for analyses using the NASA/Grumman Transonic Wing-Body Code. Computations were performed for isolated wing and wing fuselage glove arrangements to determine the extent of aerodynamic interference effects which propagate outward onto the main wing outer panel. Additional studies were conducted using the full potential analysis, FLO 22, to calibrate any inaccuracies that might accrue because of small disturbance code limitations. Comparisons indicate that the NASA/Grumman code provides excellent flow simulations for the range of wing sweep angles and flow conditions that will be of interest for the upcoming F-14 Variable Sweep Flight Transition Experiment

Tensile failure criteria for fiber composite materials

The analysis provides insight into the failure mechanics of these materials and defines criteria which serve as tools for preliminary design material selection and for material reliability assessment. The model incorporates both dispersed and propagation type failures and includes the influence of material heterogeneity. The important effects of localized matrix damage and post-failure matrix shear stress transfer are included in the treatment. The model is used to evaluate the influence of key parameters on the failure of several commonly used fiber-matrix systems. Analyses of three possible failure modes were developed. These modes are the fiber break propagation mode, the cumulative group fracture mode, and the weakest link mode. Application of the new model to composite material systems has indicated several results which require attention in the development of reliable structural composites. Prominent among these are the size effect and the influence of fiber strength variability

X-ray Light Curves and Accretion Disk Structure of EX Hydrae

We present X-ray light curves for the cataclysmic variable EX Hydrae obtained with the Chandra High Energy Transmission Grating Spectrometer and the Extreme Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the shape and amplitude of the binary light curve and discuss a new feature: the phase of the minimum in the binary light curve, associated with absorption by the bulge on the accretion disk, increases with wavelength. We discuss several scenarios that could account for this trend and conclude that, most likely, the ionization state of the bulge gas is not constant, but rather decreases with binary phase. We also conclude that photoionization of the bulge by radiation originating from the white dwarf is not the main source of ionization, but that it is heated by shocks originating from the interaction between the inflowing material from the companion and the accretion disk. The findings in this paper provide a strong test for accretion disk models in close binary systems.Comment: 19 pages, 4 figures, accepted for publication in the Ap

The Effect of Layer Orientation on the Tensile Properties of Net Shape Parts Fabricated in Stereolithography

Stereolithographic technologies create parts in thermoset plastic polymeric mixtures of acrylates and epoxies. In order to predict the mechanical behavior of these parts, it is critical to understand the effects that build parameters have on the final properties of the polymer. Using a statistics based approach, the build parameters of layer orientation, layer thickness, and resin class are used as inputs. The response variables, peak stress, elongation at break and Young’s modulus (modulus of elasticity), are examined using the methodology specified in ASTM D638- 01 with modifications as noted. An initial test in Somos 8120 showed the surprising (and statistically significant) result that load bearing capability in the build direction was greater than in the in-layer direction. Additional tensile tests in Somos 8120 and Vantico SL-5510 were undertaken to verify this result, and determine if this effect is present across different classes of resin. This report details the rationale behind this experiment, presents the results to date, and outlines future efforts.Mechanical Engineerin

A Quantitative Non-radial Oscillation Model for the Subpulses in PSR B0943+10

In this paper, we analyze time series measurements of PSR B0943+10 and fit them with a non-radial oscillation model. The model we apply was first developed for total intensity measurements in an earlier paper, and expanded to encompass linear polarization in a companion paper to this one. We use PSR B0943+10 for the initial tests of our model because it has a simple geometry, it has been exhaustively studied in the literature, and its behavior is well-documented. As prelude to quantitative fitting, we have reanalyzed previously published archival data of PSR B0943+10 and uncovered subtle but significant behavior that is difficult to explain in the framework of the drifting spark model. Our fits of a non-radial oscillation model are able to successfully reproduce the observed behavior in this pulsar.Comment: 45 pages, 16 figures, accepted Ap

Synthesis and Study of Olefin Metathesis Catalysts Supported by Redox-Switchable Diaminocarbene 3 Ferrocenophanes

A redox-switchable ligand, N,N'-dimethyldiaminocarbene[3]ferrocenophane (5), was synthesized and incorporated into a series of Ir- and Ru-based complexes. Electrochemical and spectroscopic analyses of (5) Ir(CO)(2)Cl (15) revealed that 5 displayed a Tolman electronic parameter value of 2050 cm(-1) in the neutral state and 2061 cm(-1) upon oxidation. Moreover, inspection of X-ray crystallography data recorded for (5) Ir(cis,cis-1,5-cyclooctadiene)Cl (13) revealed that 5 was sterically less bulky (%V-Bur = 28.4) than other known diaminocarbene[3]ferrocenophanes, which facilitated the synthesis of (5)(PPh3)Cl2Ru-(3-phenylindenylid-1-ene) (18). Complex 18 exhibited quasi-reversible electrochemical processes at 0.79 and 0.98 V relative to SCE, which were assigned to the Fe and Ru centers in the complex, respectively, based on UV-vis and electron pair resonance spectroscopic measurements. Adding 2,3-dichloro-5,6-dicyanoquinone over the course of a ring-opening metathesis polymerization of cis, cis-1,5-cyclooctadiene catalyzed by 18 ([monomer](0)/[18](0) = 2500) reduced the corresponding rate constant of the reaction by over an order of magnitude (pre-oxidation: k(obs) = 0.045 s(-1); post-oxidation: k(obs) = 0.0012 s(-1)). Subsequent reduction of the oxidized species using decamethylferrocene restored catalytic activity (post-reduction: k(obs) = up to 0.016 s(-1), depending on when the reductant was added). The difference in the polymerization rates was attributed to the relative donating ability of the redox-active ligand (i.e., strongly donating 5 versus weakly donating 5(+)) which ultimately governed the activity displayed by the corresponding catalyst.U. S. Army Research Office W911NF-09-1-0446Chemistr

Phenomenology of loop quantum cosmology

After introducing the basic ingredients of Loop Quantum Cosmology, I will briefly discuss some of its phenomenological aspects. Those can give some useful insight about the full Loop Quantum Gravity theory and provide an answer to some long-standing questions in early universe cosmology.Comment: 16 pages, 3 figures; Invited talk in the First Mediterranean Conference on Classical and Quantum Gravity (Crete, Greece

ORFEUS II and IUE Spectroscopy of EX Hydrae

Using ORFEUS-SPAS II FUV spectra, IUE UV spectra, and archival EUVE deep survey photometry, we present a detailed picture of the behavior of the magnetic cataclysmic variable EX Hydrae. Like HUT spectra of this source, the FUV and UV spectra reveal broad emission lines of He II, C II-IV, N III and V, O VI, Si III-IV, and Al III superposed on a continuum which is blue in the UV and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI doublet is resolved into broad and narrow emission components. Consistent with its behavior in the optical, the FUV and UV continuum flux densities, the FUV and UV broad emission line fluxes, and the radial velocity of the O VI broad emission component all vary on the spin phase of the white dwarf, with the maximum of the FUV and UV continuum and broad emission line flux light curves coincident with maximum blueshift of the broad O VI emission component. On the binary phase, the broad dip in the EUV light curve is accompanied by strong eclipses of the UV emission lines and by variations in both the flux and radial velocity of the O VI narrow emission component. The available data are consistent with the accretion funnel being the source of the FUV and UV continuum and the O VI broad emission component, and the white dwarf being the source of the O VI narrow emission component.Comment: 21 pages, 10 Postscript figures; LaTeX format, uses aaspp4.sty; table2.tex included separately because it must be printed sideways - see instructions in the file; accepted on 1999 Feb 20 for publication in The Astrophysical Journa