30,363 research outputs found
On the Form of the Spitzer Leavitt Law and its Dependence on Metallicity
The form and metallicity-dependence of Spitzer mid-infrared Cepheid relations
are a source of debate. Consequently, Spitzer 3.6 and 4.5 um period-magnitude
and period-color diagrams were re-examined via robust routines, thus providing
the reader an alternative interpretation to consider. The relations (nearly
mean-magnitude) appear non-linear over an extensive baseline (0.45< logPo
<2.0), particularly the period-color trend, which to first-order follows
constant (3.6-4.5) color for shorter-period Cepheids and may transition into a
bluer convex trough at longer-periods. The period-magnitude functions can be
described by polynomials (e.g., [3.6 um]=Ko-(3.071+-0.059)
logPo-(0.120+-0.032)logPo^2), and Cepheid distances computed using 3.6 and 4.5
um relations agree and the latter provides a first-order consistency check (CO
sampled at 4.5 um does not seriously compromise those distances). The
period-magnitude relations appear relatively insensitive to metallicity
variations ([Fe/H]~0 to -0.75), a conclusion inferred partly from comparing
galaxy distances established from those relations and NED-D (n>700), yet a
solid conclusion awaits comprehensive mid-infrared observations for metal-poor
Cepheids in IC 1613 ([Fe/H] -1). The Cepheid-based distances were corrected for
dust obscuration using a new ratio (i.e., A(3.6)/E(B-V)=0.18+-0.06) deduced
from GLIMPSE (Spitzer) data.Comment: To appear in Ap
Applications of cluster analysis in natural resources research
There are no author-identified significant results in this report
Fast computation of effective diffusivities using a semi-analytical solution of the homogenization boundary value problem for block locally-isotropic heterogeneous media
Direct numerical simulation of diffusion through heterogeneous media can be
difficult due to the computational cost of resolving fine-scale
heterogeneities. One method to overcome this difficulty is to homogenize the
model by replacing the spatially-varying fine-scale diffusivity with an
effective diffusivity calculated from the solution of an appropriate boundary
value problem. In this paper, we present a new semi-analytical method for
solving this boundary value problem and computing the effective diffusivity for
pixellated, locally-isotropic, heterogeneous media. We compare our new solution
method to a standard finite volume method and show that equivalent accuracy can
be achieved in less computational time for several standard test cases. We also
demonstrate how the new solution method can be applied to complex heterogeneous
geometries represented by a grid of blocks. These results indicate that our new
semi-analytical method has the potential to significantly speed up simulations
of diffusion in heterogeneous media.Comment: 29 pages, 4 figures, 5 table
Turbulent Mixing in the Outer Solar Nebula
The effects of turbulence on the mixing of gases and dust in the outer Solar
nebula are examined using 3-D MHD calculations in the shearing-box
approximation with vertical stratification. The turbulence is driven by the
magneto-rotational instability. The magnetic and hydrodynamic stresses in the
turbulence correspond to an accretion time at the midplane about equal to the
lifetimes of T Tauri disks, while accretion in the surface layers is thirty
times faster. The mixing resulting from the turbulence is also fastest in the
surface layers. The mixing rate is similar to the rate of radial exchange of
orbital angular momentum, so that the Schmidt number is near unity. The
vertical spreading of a trace species is well-matched by solutions of a damped
wave equation when the flow is horizontally-averaged. The damped wave
description can be used to inexpensively treat mixing in 1-D chemical models.
However, even in calculations reaching a statistical steady state, the
concentration at any given time varies substantially over horizontal planes,
due to fluctuations in the rate and direction of the transport. In addition to
mixing species that are formed under widely varying conditions, the turbulence
intermittently forces the nebula away from local chemical equilibrium. The
different transport rates in the surface layers and interior may affect
estimates of the grain evolution and molecular abundances during the formation
of the Solar system.Comment: To appear in the Astrophysical Journal; 20 pages, 9 figure
Paleoseismic and Slip-Rate Observations along the Honey Lake Fault Zone, Northeastern California, USA
The Honey Lake fault is a major strike-slip fault in northeastern California that accommodates northwest-directed right-lateral shear in the northern Walker Lane. We reexamine the fault’s paleoseismic history and slip rate by evaluating a natural stream bank exposure of the fault and offset terrace riser. Structural and stratigraphic relations within the modern stream cut, radiocarbon ages, and a detailed topographic survey of the offset terrace riser are used to estimate a Holocene fault slip rate of 1.7–0.6 mm/yr or more. We also interpret the occurrence of at least four surface-rupturing earthquakes during the last 7025 calendar years before present (B.P.). Three of the surface-rupturing earthquakes occurred prior to 4670 calendar years B.P. and have interevent times that range between 730 and 990 yr. The stratigraphic record is limited after ~4670 calendar years B.P., and records evidence for at least one more subsequent surface-rupturing earthquake
Atmospheric observations for STS-4 landing
A summary of synoptic weather conditions existing over the western United States is given for the time of Shuttle descent into Edwards Air Force Base, California. The techniques and methods used to furnish synoptic atmospheric data at the surface and aloft for flight verification of the STS-4 Orbiter during its descent into Edwards Air Force Base are specified. Examples of the upper level data set are given
Development of computer software to analyze entire LANDSAT scenes and to summarize classification results of variable-size polygons
The Forest Pest Management Division (FPMD) of the Pennsylvania Bureau of Forestry has the responsibility for conducting annual surveys of the State's forest lands to accurately detect, map, and appraise forest insect infestations. A standardized, timely, and cost-effective method of accurately surveying forests and their condition should enhance the probability of suppressing infestations. The repetitive and synoptic coverage provided by LANDSAT (formerly ERTS) makes such satellite-derived data potentially attractive as a survey medium for monitoring forest insect damage over large areas. Forest Pest Management Division personnel have expressed keen interest in LANDSAT data and have informally cooperated with NASA/Goddard Space Flight Center (GSFC) since 1976 in the development of techniques to facilitate their use. The results of this work indicate that it may be feasible to use LANDSAT digital data to conduct annual surveys of insect defoliation of hardwood forests
Alessi 95 and the short period Cepheid SU Cassiopeiae
The parameters for the newly-discovered open cluster Alessi 95 are
established on the basis of available photometric and spectroscopic data, in
conjunction with new observations. Colour excesses for
spectroscopically-observed B and A-type stars near SU Cas follow a reddening
relation described by E(U-B)/E(B-V)=0.83+0.02*E(B-V), implying a value of
R=Av/E(B-V)~2.8 for the associated dust. Alessi 95 has a mean reddening of
E(B-V)_(B0)=0.35+-0.02 s.e., an intrinsic distance modulus of Vo-Mv=8.16+-0.04
s.e. (+-0.21 s.d.), d=429+-8 pc, and an estimated age of 10^8.2 yr from ZAMS
fitting of available UBV, CCD BV, NOMAD, and 2MASS JHKs observations of cluster
stars. SU Cas is a likely cluster member, with an inferred space reddening of
E(B-V)=0.33+-0.02 and a luminosity of =-3.15+-0.07 s.e., consistent with
overtone pulsation (P_FM=2.75 d), as also implied by the Cepheid's light curve
parameters, rate of period increase, and Hipparcos parallaxes for cluster
stars. There is excellent agreement of the distance estimates for SU Cas
inferred from cluster ZAMS fitting, its pulsation parallax derived from the
infrared surface brightness technique, and Hipparcos parallaxes, which all
agree to within a few percent.Comment: Accepted for Publication (MNRAS
Atmospheric environment for space shuttle (STS-8) launch
Selected atmospheric conditions observed near Space Shuttle STS-8 launch time on August 30, 1983, at Kennedy Space Center, Florida are summarized. Values of ambient pressure, temperature, moisture, ground winds, visual observations (cloud), and winds aloft are included. The sequence of prelaunch Jimsphere measured vertical wind profiles is given. Also presented are wind and thermodynamic parameters representative of surface and aloft conditions in the SRB descent/impact ocean area. Final meteorological tapes, which consist of wind and thermodynamic parameters versus altitude, for STS-8 vehicle ascent and SRB descent/impact were constructed. The STS-8 ascent meteorological data tape was constructed
The Value of Salt Marsh Edge vs Interior as a Habitat for Fish and Decapod Crustaceans in a Louisiana Tidal Marsh
Flume nets of various lengths and a 3-m seine were used to sample the fishes and macrocrustaceans using a flooded Louisiana salt marsh and the adjacent tidal creek. The experiment allowed for species-specific comparisons of the flooded marsh at the creek edge versus the interior. Of the 37,667 organisms collected in flume nets from January through November 1989, 89% were decapods (nine species) and 11% were fish (29 species). An additional 18,539 organisms (75% decapods and 25% fish) were collected from concurrent seine samples taken from July through November. Comparison of catches among different flume lengths and low tide versus high tide seine collections revealed distinct patterns of marsh habitat utilization. Densities of most organisms were highest within 3 m of the water’s edge, but significant numbers of marsh-resident fish species used the interior marshes. The edge marshes appeared to be used by both transient and resident species; however, the interior marshes were used primarily by marsh-resident species (Cyprinodontiformes and Palaemonetes sp.) that are excellent food sources for adult transient-species. Four zonations of marsh use are described for transients, residents, and rare species
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