1,418 research outputs found
Design, theory, and measurement of a polarization insensitive absorber for terahertz imaging
We present the theory, design, and realization of a polarization-insensitive
metamaterial absorber for terahertz frequencies. We derive
geometrical-independent conditions for effective medium absorbers in general,
and for resonant metamaterials specically. Our fabricated design reaches and
absorptivity of 78% at 1.145 ThzComment: 6 Pages, 5 figures; figures update
Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388
We have undertaken a search for variable stars in the metal-rich globular
cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables
were found in this survey, increasing the total number of variables found near
NGC 6388 to ~57. A significant number of the variables are RR Lyrae (~14), most
of which are probable cluster members. The periods of the fundamental mode RR
Lyrae are shown to be unusually long compared to metal-rich field stars. The
existence of these long period RRab stars suggests that the horizontal branch
of NGC 6388 is unusually bright. This implies that the metallicity-luminosity
relationship for RR Lyrae stars is not universal if the RR Lyrae in NGC 6388
are indeed metal-rich. We consider the alternative possibility that the stars
in NGC 6388 may span a range in [Fe/H]. Four candidate Population II Cepheids
were also found. If they are members of the cluster, NGC 6388 would be the most
metal-rich globular cluster to contain Population II Cepheids. The mean V
magnitude of the RR Lyrae is found to be 16.85+/-0.05 resulting in a distance
of 9.0 to 10.3 kpc, for a range of assumed values of for RR Lyrae. We
determine the reddening of the cluster to be E(B-V)=0.40+/-0.03 mag, with
differential reddening across the face of the cluster. We discuss the
difficulty in determining the Oosterhoff classification of NGC 6388 and NGC
6441 due to the unusual nature of their RR Lyrae, and address evolutionary
constraints on a recent suggestion that they are of Oosterhoff type II.Comment: 35 pages, 16 figures, emulateapj5/apjfonts style. Astronomical
Journal, in press. We recommend the interested reader to download instead the
preprint with full-resolution figures, which can be found at
http://www.noao.edu/noao/staff/pritzl/clusters.htm
Limit theorems for weakly subcritical branching processes in random environment
For a branching process in random environment it is assumed that the
offspring distribution of the individuals varies in a random fashion,
independently from one generation to the other. Interestingly there is the
possibility that the process may at the same time be subcritical and,
conditioned on nonextinction, 'supercritical'. This so-called weakly
subcritical case is considered in this paper. We study the asymptotic survival
probability and the size of the population conditioned on non-extinction. Also
a functional limit theorem is proven, which makes the conditional
supercriticality manifest. A main tool is a new type of functional limit
theorems for conditional random walks.Comment: 35 page
The Globular Cluster M15. I. Identification, Discovery, and Period Determination of Variable Stars
We present new CCD photometry for variables in the globular cluster
M15. Our photometry was obtained using both the image subtraction package ISIS
and DAOPHOT/ALLFRAME. The data were acquired in 2001 on two observing runs on
11 observing nights using the 2-m telescope of the Bulgarian National
Astronomical Observatory ``Rozhen'' with a Photometrics CCD camera. For 40
previously known variables, we present a period for the first time, and
improved periods were obtained for many previously known variables. Fourteen
new variables are reported. We present updated Bailey diagrams for the cluster
and discuss its Oosterhoff classification. Although many of M15's RRab
pulsators fall at an intermediate locus between Oosterhoff types I and II in
the Bailey diagram, we argue that M15 is indeed a bona-fide Oosterhoff type IIComment: 48 pages, 7 figures, 3 table
Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS): Imaging and Tracking Capability
The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 microns, 6.0 to 4.4 microns) using two 128 128 detector arrays with a spectral resolution of 0.57/cm with a scan duration of approx. 11 seconds. From a geosynchronous orbit, the instrument will have the capability of taking successive measurements of such data to scan desired regions of the globe, from which atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., Earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept
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The validation of a computer-based food record for older adults: the Novel Assessment of Nutrition and Ageing (NANA) method
Dietary assessment in older adults can be challenging. The Novel Assessment of Nutrition and Ageing (NANA) method is a touch-screen
computer-based food record that enables older adults to record their dietary intakes. The objective of the present study was to assess
the relative validity of the NANA method for dietary assessment in older adults. For this purpose, three studies were conducted in which a
total of ninety-four older adults (aged 65–89 years) used the NANA method of dietary assessment. On a separate occasion, participants
completed a 4 d estimated food diary. Blood and 24 h urine samples were also collected from seventy-six of the volunteers for the analysis
of biomarkers of nutrient intake. The results from all the three studies were combined, and nutrient intake data collected using the NANA
method were compared against the 4 d estimated food diary and biomarkers of nutrient intake. Bland–Altman analysis showed
a reasonable agreement between the dietary assessment methods for energy and macronutrient intake; however, there were small, but
significant, differences for energy and protein intake, reflecting the tendency for the NANA method to record marginally lower energy intakes.
Significant positive correlations were observed between urinary urea and dietary protein intake using both the NANA and the 4 d estimated
food diary methods, and between plasma ascorbic acid and dietary vitamin C intake using the NANA method. The results demonstrate the
feasibility of computer-based dietary assessment in older adults, and suggest that the NANA method is comparable to the 4 d estimated
food diary, and could be used as an alternative to the food diary for the short-term assessment of an individual’s dietary intake
A temperate former West Antarctic ice sheet suggested by an extensive zone of bed channels
Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the icesheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods
Ground-Based Measurement Experiment and First Results with Geosynchronous-Imaging Fourier Transform Spectrometer Engineering Demonstration Unit
The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 microns, 6.0 to 4.4 microns) using two 128 x 128 detector arrays with a spectral resolution of 0.57 cm(exp -1) with a scan duration of approximately 11 seconds. From a geosynchronous orbit, the instrument will have the capability of taking successive measurements of such data to scan desired regions of the globe, from which atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., Earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept
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