879 research outputs found
Optical Communication Link Atmospheric Attenuation Model
The Space Communications and Navigation (SCaN) Center for Networking, Integration, and Communications (SCENIC) user interface, which provides web accessible space mission simulation and communication system analysis capabilities using verified and validated analysis algorithms, can execute analyses including, but not limited to, line-of-sight, orbit propagation, and dynamic link budget calculations between sets of missions and/or assets. SCENIC's purpose is to provide NASA civil servants and contractors a user-friendly tool, integrated with model data, that can simulate and analyze a range of space mission architectures without the need for repeated and redundant modeling. Given the abundance and further future development of free space optical (FSO) communication channels within modern space infrastructure, the availability of a reliable optical link analysis capability is crucial for SCENIC users. The efforts outlined in this paper aim to provide a model for atmospheric attenuation of FSO communication links, both due to absorption/scattering and turbulence, to increase the accuracy of SCENIC's optical link assessment capabilities. A previous model existed for optical absorption/scattering within the SCaN Link Budget Tool, but it was not location specific for the Earth ground-based nodes, nor was the model optimized for run-time. The new model utilizes years of National Oceanic and Atmospheric Administration (NOAA) visibility data from ground station locations around the world. Visibility, along with the wavelength of the optical signal, are input parameters to calculate the optical specific attenuation, which is a parameter in the calculation of the slant-path attenuation. A final FSO atmospheric attenuation value is comprised of the absorption/scattering attenuation and the turbulence attenuation. A run-time efficient algorithm for the model was then developed and programmed in MATLAB. Due to the simple model and vectorization possible in MATLAB, the algorithm has an average run-time of less than one fourth of the run-time of the previous implementation
Ariel - Volume 9 Number 2
Executive Editor
Emily Wofford
Business Manager
Fredric Jay Matlin
University News
John Patrick Welch
World News
George Robert Coar
Editorials Editor
Steve Levine
Features
Mark Rubin
Brad Feldstein
Photo
Rick Spade
Circulation
Victor Onufreiczuk
Lee Wugofsk
The Effects of Pictorial Realism, Delay of Visual Feedback, and Observer Interactivity on the Subjective Sense of Presence
Two experiments examined the effects of pictorial realism, observer interactivity, and delay of visual feedback on the sense of presence. Subjects were presented pairs of virtual enviornments (a simulated driving task) that differed in one or more ways from each other. After subjects had completed the second member of each pair they reported which of the two had produced the greater amount of presence and indicated the size of this difference by means of a 1-100 scale. As predicted, realism and interactivity increased presence while delay of visual feedback diminished it. According to subjects\u27 verbal responses to a postexperiment interview, pictorial realism was the least influential of the three variables examined. Further, although some subjects reported an increase in the sense of presence over the course of the experiment, most said it reamined unchanged or became weaker
Ariel - Volume 9 Number 5
Executive Editor
Seth B. Paul
Associate Editor
Warren J. Ventriglia
Business Manager
Fredric Jay Matlin
University News
John Patrick Welch
World News
George Robert Coar
Editorials Editor
Steve Levine
Features
Mark Rubin
Brad Feldstein
Sports Editor
Eli Saleeby
Photo Editor
Ken Buckwalter
Circulation
Victor Onufreiczuk
Lee Wugofski
Graphics and Art
Steve Hulkower
Commons Editor
Brenda Peterso
Subsidizing Religious Participation through Groups: A Model of the “Megachurch” Strategy for Growth
Either despite or because of their non-traditional approach, megachurches have grown significantly in the United States since 1980. This paper models religious participation as an imperfect public good which, absent intervention, yields suboptimal participation by members from the church’s perspective. Megachurches address this problem in part by employing secular-based group activities to subsidize religious participation that then translates into an increase in the attendees’ religious investment. This strategy not only allows megachurches to attract and retain new members when many traditional churches are losing members but also results in higher levels of an individual’s religious capital. As a result, the megachurch may raise expectations of members’ levels of commitment and faith practices. Data from the FACT2000 survey provide evidence that megachurches employ groups more extensively than other churches, and this approach is consistent with a strategy to use groups to help subsidize individuals’ religious investment. Religious capital rises among members of megachurches relative to members of non-megachurches as a result of this strategy
The level of carbonation of a sugar-sweetened beverage preload affects satiety and short-term energy and food intakes
Using NMR-based metabolomics to evaluate postprandial urinary responses following consumption of minimally processed wheat bran or wheat aleurone by men and women
Wheat bran, and especially wheat aleurone fraction, are concentrated sources of a wide
range of components which may contribute to the health benefits associated with higher consumption
of whole-grain foods. This study used NMR metabolomics to evaluate urine samples from baseline at
one and two hours postprandially, following the consumption of minimally processed bran, aleurone
or control by 14 participants (7 Females; 7 Males) in a randomized crossover trial. The methodology
discriminated between the urinary responses of control, and bran and aleurone, but not between
the two fractions. Compared to control, consumption of aleurone or bran led to significantly
and substantially higher urinary concentrations of lactate, alanine, N-acetylaspartate acid and
N-acetylaspartylglutamate and significantly and substantially lower urinary betaine concentrations
at one and two hours postprandially. There were sex related differences in urinary metabolite profiles
with generally higher hippurate and citrate and lower betaine in females compared to males. Overall,
this postprandial study suggests that acute consumption of bran or aleurone is associated with
a number of physiological effects that may impact on energy metabolism and which are consistent
with longer term human and animal metabolomic studies that used whole-grain wheat diets or
wheat fractions.peer-reviewe
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