32,678 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
Maxometers (peak wind speed anemometers)
An instrument for measuring peak wind speeds under severe environmental conditions is described, comprising an elongated cylinder housed in an outer casing. The cylinder contains a piston attached to a longitudinally movable guided rod having a pressure disk mounted on one projecting end. Wind pressure against the pressure disk depresses the movable rod. When the wind reaches its maximum speed, the rod is locked by a ball clutch mechanism in the position of maximum inward movement. Thereafter maximum wind speed or pressure readings may be taken from calibrated indexing means
Industry views on water resources planning methods – prospects for change in England and Wales
This paper describes a qualitative study of practitioner perspectives on regulated water resources planning practice in England and Wales. The study focuses on strengths and weaknesses of existing practice and the case for change towards a risk-based approach informed by stochastic modelling assessments. In-depth, structured interviews were conducted to capture the views of planners, regulators and consultants closely involved in the planning process. We found broad agreement that the existing water availability assessment methods are fallible; they lack transparency, are often highly subjective and may fail to adequately expose problems of resilience. While most practitioners believe these issues warrant a more detailed examination of risk in the planning process, few believe there is a strong case for a fundamental shift towards risk-based planning informed by stochastic modelling assessments. The study identifies perceived business risks associated with change and exposes widespread scepticism of stochastic methods
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
The maxometer-dynamic and static tests
The ability to withstand extreme environmental conditions, such as the high flow velocities and extreme temperatures associated with the launch of aerospace vehicles, was considered in the developement of two maxometer models which are capable of measuring extremely high wind speeds (130 m/sec) and retaining a record of the peak speed over any given time period. The dynamic and static tests of these models are reported, along with pertinent results
Signal-to-noise ratio estimation in digital computer simulation of lowpass and bandpass systems with applications to analog and digital communications, volume 3
Techniques are developed to estimate power gain, delay, signal-to-noise ratio, and mean square error in digital computer simulations of lowpass and bandpass systems. The techniques are applied to analog and digital communications. The signal-to-noise ratio estimates are shown to be maximum likelihood estimates in additive white Gaussian noise. The methods are seen to be especially useful for digital communication systems where the mapping from the signal-to-noise ratio to the error probability can be obtained. Simulation results show the techniques developed to be accurate and quite versatile in evaluating the performance of many systems through digital computer simulation
NASA/MSFC FY-83 Atmospheric Research Review
Atmospheric research conducted at the Marshall Space Flight Center in FY 1983 is discussed. Clear air turbulence, gusts, and fog dispersal near airports is discussed. The use of Doppler Lidar signals in discussed, as are low level flow conditions that are hazardous to aircraft
Identifying Contaminated K-band Globular Cluster RR Lyrae Photometry
Acquiring near-infrared K-band (2.2 um) photometry for RR Lyrae variables in
globular clusters and nearby galaxies is advantageous since the resulting
distances are less impacted by reddening and metallicity. However, K-band
photometry for RR Lyrae variables in M5, Reticulum, M92, omega Cen, and M15
display clustercentric trends. HST ACS data imply that multiple stars in close
proximity to RR Lyrae variables located near the cluster core, where the
stellar density increases markedly, are generally unresolved in ground-based
images. RR Lyrae variables near the cluster cores appear to suffer from
photometric contamination, thereby yielding underestimated cluster distances
and biased ages. The impact is particularly pernicious since the contamination
propagates a systematic uncertainty into the distance scale, and hinders the
quest for precision cosmology. The clustercentric trends are probably
unassociated with variations in chemical composition since an empirical K-band
period-magnitude relation inferred from Araucaria/VLT data for RR Lyrae
variables in the Sculptor dSph exhibits a negligible metallicity dependence:
(0.059+-0.095)[Fe/H], a finding that supports prior observational results. A
future multi-epoch high-resolution near-infrared survey, analogous to the
optical HST ACS Galactic Globular Cluster Survey, may be employed to establish
K-band photometry for the contaminating stars discussed here.Comment: To appear in PAS
Documenting Antarctic Alteration of Eucrites
When meteorites were discovered in Antarctica, it was anticipated that terrestrial alteration would be at a minimum because of their deepfreeze storage where chemical reaction rates would be low. However, early compositional and petrologic studies established the presence of terrestrial alteration phases (e.g., [1, 2]). These were especially prevalent in chondrites because metal and troilite are most susceptible to terrestrial alteration [3]. Howardites, eucrites and diogenites (HEDs) are less prone to alteration because they have low abundances of metal and troilite. Nevertheless, investigations of HED meteorites document a wide array of mineralogical, compositional and isotopic effects of terrestrial alteration (e.g., [4-8]). Studies of the mineralogical effects of alteration [4] were done with old scanning electron microscope (SEM) technology which could only image small regions at a time. The micro-context of alteration phases was revealed, but larger-scale context was difficult to establish. Here we demonstrate the utility of wholethin-section X-ray mapping of eucrites by modern SEMs to document large-scale distributions of alteration materials which serve to evaluate sample freshness, highlight regions for detail study, and facilitate testing a hypothesis for alteration of eucrites [8
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