405 research outputs found
General Rotorcraft Aeromechanical Stability Program (GRASP) version 1.03: User's manual
The Rotorcraft Dynamics Division, Aeroflightdynamics Directorate, U.S. Army Aviation Research and Technology Activity has developed the General Rotorcraft Aeromechanical Stability Program (GRASP) to perform calculations that will assess the stability of rotorcraft in hovering flight and ground contact conditions. The program is designed to be state-of-the-art, hybrid, finite-element/multibody code that can be applied to all existing and future helicopter configurations. While GRASP was specifically designed to solve rotorcraft stability problems, its innovative structure and formulation allow for application to a wide range of structures. This manual describes the preparation of the input file required by Version 1.03 of GRASP, the procedures used to invoke GRASP on the NASA Ames Research Center CRAY X-MP 48 computer, and the interpretation of the output produced by GRASP. The parameters used by the input file are defined, and summaries of the input file and the job control language are included
General Rotorcraft Aeromechanical Stability Program (GRASP): Theory manual
The general rotorcraft aeromechanical stability program (GRASP) was developed to calculate aeroelastic stability for rotorcraft in hovering flight, vertical flight, and ground contact conditions. GRASP is described in terms of its capabilities and its philosophy of modeling. The equations of motion that govern the physical system are described, as well as the analytical approximations used to derive them. The equations include the kinematical equation, the element equations, and the constraint equations. In addition, the solution procedures used by GRASP are described. GRASP is capable of treating the nonlinear static and linearized dynamic behavior of structures represented by arbitrary collections of rigid-body and beam elements. These elements may be connected in an arbitrary fashion, and are permitted to have large relative motions. The main limitation of this analysis is that periodic coefficient effects are not treated, restricting rotorcraft flight conditions to hover, axial flight, and ground contact. Instead of following the methods employed in other rotorcraft programs. GRASP is designed to be a hybrid of the finite-element method and the multibody methods used in spacecraft analysis. GRASP differs from traditional finite-element programs by allowing multiple levels of substructure in which the substructures can move and/or rotate relative to others with no small-angle approximations. This capability facilitates the modeling of rotorcraft structures, including the rotating/nonrotating interface and the details of the blade/root kinematics for various types. GRASP differs from traditional multibody programs by considering aeroelastic effects, including inflow dynamics (simple unsteady aerodynamics) and nonlinear aerodynamic coefficients
Diaphus taaningi Norman, the principal component of a shallow sound-scattering layer in the Cariaco Trench, Venezuela
A myctophid fish, Diaphus taaningi Norman, is the principal component of a distinct daytime sound-scattering layer lying near 250 m, well above the anoxic, hydrogen-sulfide zone of the Cariaco Trench. The scattering layer produced strong sonar echoes at 12, 25, and 50 kHz; mean sound-scattering strength at layer depth at 25 kHz was approximately --73 dB and at 50 kHz was approximately --67 dB...
Galaxy Star Formation as a Function of Environment in the Early Data Release of the Sloan Digital Sky Survey
We present in this paper a detailed analysis of the effect of environment on the star formation activity of galaxies within the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We have used the Halpha emission line to derive the star formation rate (SFR) for each galaxy within a volume-limited sample of 8598 galaxies with 0.05 less than or equal to z less than or equal to 0.095 and M (r*) less than or equal to 20.45. We find that the SFR of galaxies is strongly correlated with the local ( projected) galaxy density, and thus we present here a density-SFR relation that is analogous to the density-morphology relation. The effect of density on the SFR of galaxies is seen in three ways. First, the overall distribution of SFRs is shifted to lower values in dense environments compared with the field population. Second, the effect is most noticeable for the strongly star-forming galaxies (Halpha EW > 5 Angstrom) in the 75th percentile of the SFR distribution. Third, there is a break ( or characteristic density) in the density-SFR relation at a local galaxy density of similar to1 h(75)(-2) Mpc(-2). To understand this break further, we have studied the SFR of galaxies as a function of clustercentric radius from 17 clusters and groups objectively selected from the SDSS EDR data. The distribution of SFRs of cluster galaxies begins to change, compared with the field population, at a clustercentric radius of 3-4 virial radii (at the >1sigma statistical significance), which is consistent with the characteristic break in density that we observe in the density-SFR relation. This effect with clustercentric radius is again most noticeable for the most strongly star-forming galaxies. Our tests suggest that the density-morphology relation alone is unlikely to explain the density-SFR relation we observe. For example, we have used the ( inverse) concentration index of SDSS galaxies to classify late-type galaxies and show that the distribution of the star-forming (EW Halpha > 5Angstrom) late-type galaxies is different in dense regions ( within 2 virial radii) compared with similar galaxies in the field. However, at present, we are unable to make definitive statements about the independence of the density-morphology and density-SFR relation. We have tested our work against potential systematic uncertainties including stellar absorption, reddening, SDSS survey strategy, SDSS analysis pipelines, and aperture bias. Our observations are in qualitative agreement with recent simulations of hierarchical galaxy formation that predict a decrease in the SFR of galaxies within the virial radius. Our results are in agreement with recent 2dF Galaxy Redshift Survey results as well as consistent with previous observations of a decrease in the SFR of galaxies in the cores of distant clusters. Taken together, these works demonstrate that the decrease in SFR of galaxies in dense environments is a universal phenomenon over a wide range in density (from 0.08 to 10 h(75)(-2) Mpc(-2)) and redshift (out to z similar or equal to 0.5)
Measurement of the Condensation Coefficient of Water in the UMR Simulation Chamber
The UMR Cloud Simulation Facility is described. The facility is designed to provide a controlled environment simulating the conditions of natural atmospheric processes. It consists of two cooled-wall expansion cloud chambers and peripheral instrumentation for generation and characterization of aerosols used for cloud formation studies. Results of initial studies of the growth of warm cloud droplets and inferred measurements of the condensation coefficient are described
Measurement of the Condensation Coefficient of Water in the UMR Cloud Simulation Chamber
Measurements of the condensation coefficient of water under conditions closely approximating those in natural atmospheric cloud have been made in the cooled-wall UMR cloud simulation chamber. Current measurements disclose a value of condensation coefficient near unity at the outset of the experiment, generally decreasing to lower values (~ .01) as the experiment progresses. The significance of the magnitude of condensation coefficient in atmospheric cloud is briefly discussed
Binary Quasars at High Redshift I: 24 New Quasar Pairs at z ~ 3-4
The clustering of quasars on small scales yields fundamental constraints on
models of quasar evolution and the buildup of supermassive black holes. This
paper describes the first systematic survey to discover high redshift binary
quasars. Using color-selection and photometric redshift techniques, we searched
8142 deg^2 of SDSS imaging data for binary quasar candidates, and confirmed
them with follow-up spectroscopy. Our sample of 27 high redshift binaries (24
of them new discoveries) at redshifts 2.9 < z < 4.3 with proper transverse
separations 10 kpc < R_{\perp} < 650 kpc increases the number of such objects
known by an order of magnitude. Eight members of this sample are very close
pairs with R_{\perp} 3.5.
The completeness and efficiency of our well-defined selection algorithm are
quantified using simulated photometry and we find that our sample is ~ 50%
complete. Our companion paper uses this knowledge to make the first measurement
of the small scale clustering (R < 1 Mpc/h comoving) of high-redshift quasars.
High redshift binaries constitute exponentially rare coincidences of two
extreme (M >~ 10^9 Msun) supermassive black holes. At z ~ 4 there is about one
close binary per 10 Gpc^3, thus these could be the highest sigma peaks, the
analogs of superclusters, in the early Universe.Comment: Submitted to Ap
Eight-Dimensional Mid-Infrared/Optical Bayesian Quasar Selection
We explore the multidimensional, multiwavelength selection of quasars from
mid-IR (MIR) plus optical data, specifically from Spitzer-IRAC and the Sloan
Digital Sky Survey (SDSS). We apply modern statistical techniques to combined
Spitzer MIR and SDSS optical data, allowing up to 8-D color selection of
quasars. Using a Bayesian selection method, we catalog 5546 quasar candidates
to an 8.0 um depth of 56 uJy over an area of ~24 sq. deg; ~70% of these
candidates are not identified by applying the same Bayesian algorithm to
4-color SDSS optical data alone. Our selection recovers 97.7% of known type 1
quasars in this area and greatly improves the effectiveness of identifying
3.5<z<5 quasars. Even using only the two shortest wavelength IRAC bandpasses,
it is possible to use our Bayesian techniques to select quasars with 97%
completeness and as little as 10% contamination. This sample has a photometric
redshift accuracy of 93.6% (Delta Z +/-0.3), remaining roughly constant when
the two reddest MIR bands are excluded. While our methods are designed to find
type 1 (unobscured) quasars, as many as 1200 of the objects are type 2
(obscured) quasar candidates. Coupling deep optical imaging data with deep
mid-IR data could enable selection of quasars in significant numbers past the
peak of the quasar luminosity function (QLF) to at least z~4. Such a sample
would constrain the shape of the QLF and enable quasar clustering studies over
the largest range of redshift and luminosity to date, yielding significant
gains in our understanding of quasars and the evolution of galaxies.Comment: 49 pages, 14 figures, 7 tables. AJ, accepte
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