5,060 research outputs found
Improving CubeSat downlink capacity with active phased array antennas
Master's Project (M.S.) University of Alaska Fairbanks, 2017Power budgets on small satellites are restricted by the limited surface area for solar panels. This limits the power available for radio communications, which constrains the downlink budget. The limited transmit power translates to low downlink data rates on small satellites. Antenna gain from directive antennas may be a power efficient way of improving the downlink budget, thereby increasing the downlink rate of small satellites. This project focuses on the design and development of a prototype low-power, electrically-steered S-band phased array RF front-end suitable for a CubeSat that could efficiently increase the EIRP, permitting higher data rates. A prototype of the array has been constructed and tested in an anechoic chamber. The four element array provides a minimum gain of 2.5 dB and average gain of 5 dB compared to a single patch antenna element with a 5W power envelope across a range of up to 60 degrees from broadside of the array
Discovery of kHz Fluctuations in Centaurus X-3: Evidence for Photon Bubble Oscillations (PBO) and Turbulence in a High Mass X-ray Binary Pulsar
We report the discovery of kHz fluctuations, including quasi-periodic
oscillations (QPO) at ~330 Hz and ~760 Hz and a broadband kHz continuum in the
power density spectrum of the high mass X-ray binary pulsar Centaurus X-3.
These observations of Cen X-3 were carried out with the Rossi X-ray Timing
Explorer (RXTE). The fluctuation spectrum is flat from mHz to a few Hz, then
steepens to behavior between a few Hz and ~100 Hz. Above a hundred Hz,
the spectrum shows the QPO features, plus a flat continuum extending to ~1200
Hz and then falling out to ~1800 Hz. These results, which required the
co-adding three days of observations of Cen X-3, are at least as fast as the
fastest known variations in X-ray emission from an accreting compact object
(kHz QPO in LMXB sources) and probably faster since extension to ~1800 Hz is
indicated by the most likely parameterization of the data.
Multi-dimensional radiation hydrodynamics simulations of optically thick
plasma flow onto the magnetic poles of an accreting neutron star show that the
fluctuations at frequencies above 100 Hz are consistent with photon bubble
turbulence and oscillations (PBO) previously predicted to be observable in this
source. For a polar cap opening angle of 0.25 radians, we show that the
spectral form above 100 Hz is reproduced by the simulations, including the
frequencies of the QPO and the relative power in the QPO and the kHz continuum.
This has resulted in the first model-dependent measurement of the polar cap
size of an X-ray pulsar.Comment: received ApJ: April 1, 1999 accepted ApJ: September 1, 199
Human-Centered Data Visualizations and Web Layouts for Life-Cycle Assessment Design Guides
User tests with 30 Dartmouth Engineering and STEM undergraduates were performed to investigate preferences toward a set of data visualizations and web layouts showing life-cycle assessment data and corresponding uncertainty. The data was collected and synthesized from academic papers, corporate manufacturers, and self-generated using the LCA software Sustainable Minds. A variety of visualizations were produced to accurately and aesthetically represent the data graphically, and especially understand how non-technical audiences interact with different displays of uncertainty, which is a key component of data visualization that is lacking from most LCA design guides. Web layouts were produced to present key information about the product and suggest sustainable design strategies in a digestible way end users.Ultimately, these learnings will be applied towards the creation of a free, user-friendly, online guide that provides useful recommendations for designers to reference when considering the assembly of products
Stocking Wilderness Lakes – There’s Something Fishy Going On?
The Wilderness Act of 1964 set aside lands to be managed and protected so as to preserve their natural conditions. Yet, many historically fishless lakes within designated wilderness continue to be stocked with native and non-native fish by state fish and game agencies in order to provide recreational fishing opportunities. This practice is controversial because stocking programs can compromise ecological and social values of Wilderness. Stocking is commonly accomplished without adequate cooperation and consultation between state and federal agencies. A better understanding of wilderness impacts from fish stocking, as well as improved cooperation between agencies may help balance opportunities for recreational fishing with wilderness values
An analysis of youth participation in athletics
School athletics has a significant impact on the development of youth. This study is an exploration of the differences between youth who participate in school athletics and those who do not. Specifically, the study examined youth academic performance and behavior referrals, and variables such as grade level, age, gender, and ethnicity. In addition, the study examined whether or not there was a relationship between participation in the school’s free or reduced lunch program and athletic participation.
To determine the differences and relationships of youth that participate in school athletics and those who do not participate, an existing dataset of 4,078 students was used from a mid-sized Midwestern school district. The data was provided from a local nonprofit organization that gathers data from the school district and offers the data to other nonprofit organizations to measure participant outcomes.
The study found that there was a significant difference between youth who participate in school athletics and those who do not based on academic performance (GPA), behavior referrals, age and grade level. The study found that there was a significant relationship between youth who participate in school athletics and those who do not based on participation in the school’s free or reduced lunch program and their ethnicity. There was no significant relationship between youth who participate in school athletics and those who do not based on gender.
The results suggest that youth should be actively involved with school athletics because the findings have demonstrated to have a significant impact on the study participant’s GPA and behavior. A reason that this may occur is athletes may be held to a higher standard by their coaches because if they do not achieve a certain grade or they are misbehaving, then they may not be able to participate in athletics
Stimulus-invariant processing and spectrotemporal reverse correlation in primary auditory cortex
The spectrotemporal receptive field (STRF) provides a versatile and
integrated, spectral and temporal, functional characterization of single cells
in primary auditory cortex (AI). In this paper, we explore the origin of, and
relationship between, different ways of measuring and analyzing an STRF. We
demonstrate that STRFs measured using a spectrotemporally diverse array of
broadband stimuli -- such as dynamic ripples, spectrotemporally white noise,
and temporally orthogonal ripple combinations (TORCs) -- are very similar,
confirming earlier findings that the STRF is a robust linear descriptor of the
cell. We also present a new deterministic analysis framework that employs the
Fourier series to describe the spectrotemporal modulations contained in the
stimuli and responses. Additional insights into the STRF measurements,
including the nature and interpretation of measurement errors, is presented
using the Fourier transform, coupled to singular-value decomposition (SVD), and
variability analyses including bootstrap. The results promote the utility of
the STRF as a core functional descriptor of neurons in AI.Comment: 42 pages, 8 Figures; to appear in Journal of Computational
Neuroscienc
Minimal Universal Extra Dimensions
Highly degenerate spectra associated with universal extra dimensions (UED)
provide an interesting phenomenology not only from the point of view of
cosmology and astrophysics, but also for colliders. We study these exotic
signals for the simplest case, called minimal UED, where it is natural to find
slow charged particles, displaced vertices, tracks with non-vanishing impact
parameters, track kinks, and even vanishing charged tracks.Comment: 6 pages, 3 figures. Contributed to XXIII International Symposium on
Lepton and Photon Interactions at High Energy, Aug 13-18, 2007, Daegu, Kore
Mapping a Course for Improved Student Learning: How Innovative Schools Systematically Use Student Performance Data to Guide Improvement
To be useful to teachers and school leaders, test data must provide more than just a destination. Student performance results must also provide guidance that informs educators that they are moving in the right direction, while providing interactive and recursive feedback for mid-course adjustments. In order for student performance data to be useful to teachers and school leaders, and to make it worthwhile for them to make the extensive efforts necessary to learn to interpret and act upon what they learn, data feedback systems must rely on multiple sources of data collected and analyzed at regular intervals.
This report is about building better roadmaps for teachers and school leaders in order to guide their instructional decision-making. The data required for more precise decision-making come from systematically exploiting a variety of student performance data at both the individual classroom and school levels. Rather than just relying on one individual test to provide guidance, innovative school leaders are building more comprehensive systems of assessments that provide better interim information from multiple perspectives. Through more sophisticated data systems, teachers and school leaders can foster a more inquiryoriented approach that involves ongoing and sustained investigations into the kinds of teaching that produce more powerful student learning. In this report, we show how innovative teachers and school leaders are creatively using their data to help guide their strategic decisions. Through their examples, we develop and describe a theory of what a system of school data use might look like
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