21,222 research outputs found
Use and Perceived Value of Class Forums
Numerous studies have illustrated the ability of online class discussion forums to support college-level student learning and performance. Yet few instructors incorporate forums into their courses. Many believe that students will fail to find value in or even use class forums or they are concerned about increasing their instructional workloads. Herein we address these concerns via a mixed-methods study of our own students\u27 experiences with class forums
The NANOGrav 11 yr Data Set: Limits on Gravitational Wave Memory
The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays, the nonoscillatory GW memory effect is detectable. Further, any burst of GWs will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11 yr data set for GW memory. This data set is sensitive to very low-frequency GWs of ~3 to 400 nHz (periods of ~11 yr–1 month). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of 2.5 × 10⁻¹⁴, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at <0.4 yr⁻¹. That strain corresponds to an SMBHB merger with reduced mass of ηM ~ 2 × 10¹⁰ M_⊙ and inclination of ι = π/3 at a distance of 1 Gpc. As a test of our analysis, we analyzed the NANOGrav 9 yr data set as well. This analysis found an anomolous signal, which does not appear in the 11 yr data set. This signal is not a GW, and its origin remains unknown
An investigation of Fe XVI emission lines in solar and stellar EUV and soft X-ray spectra
New fully relativistic calculations of radiative rates and electron impact
excitation cross sections for Fe XVI are used to determine theoretical
emission-line ratios applicable to the 251 - 361 A and 32 - 77 A portions of
the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A
comparison of the EUV results with observations from the Solar
Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals
excellent agreement between theory and experiment. However, for emission lines
in the 32 - 49 A portion of the soft X-ray spectral region, there are large
discrepancies between theory and measurement for both a solar flare spectrum
obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and
observations of Capella from the Low Energy Transmission Grating Spectrometer
(LETGS) on the Chandra X-ray Observatory. These are probably due to blending in
the solar flare and Capella data from both first order lines and from shorter
wavelength transitions detected in second and third order. By contrast, there
is very good agreement between our theoretical results and the XSST and LETGS
observations in the 50 - 77 A wavelength range, contrary to previous results.
In particular, there is no evidence that the Fe XVI emission from the XSST
flare arises from plasma at a much higher temperature than that expected for Fe
XVI in ionization equilibrium, as suggested by earlier work.Comment: 6 pages, 4 tables, 1 figure, MNRAS in pres
Positional estimation techniques for an autonomous mobile robot
Techniques for positional estimation of a mobile robot navigation in an indoor environment are described. A comprehensive review of the various positional estimation techniques studied in the literature is first presented. The techniques are divided into four different types and each of them is discussed briefly. Two different kinds of environments are considered for positional estimation; mountainous natural terrain and an urban, man-made environment with polyhedral buildings. In both cases, the robot is assumed to be equipped with single visual camera that can be panned and tilted and also a 3-D description (world model) of the environment is given. Such a description could be obtained from a stereo pair of aerial images or from the architectural plans of the buildings. Techniques for positional estimation using the camera input and the world model are presented
On the stability constraints and oscillatory behavior of coupled systems
Stability constraints for two general forms of coupled systems of second order nonlinear differential equation
PriPeARL: A Framework for Privacy-Preserving Analytics and Reporting at LinkedIn
Preserving privacy of users is a key requirement of web-scale analytics and
reporting applications, and has witnessed a renewed focus in light of recent
data breaches and new regulations such as GDPR. We focus on the problem of
computing robust, reliable analytics in a privacy-preserving manner, while
satisfying product requirements. We present PriPeARL, a framework for
privacy-preserving analytics and reporting, inspired by differential privacy.
We describe the overall design and architecture, and the key modeling
components, focusing on the unique challenges associated with privacy,
coverage, utility, and consistency. We perform an experimental study in the
context of ads analytics and reporting at LinkedIn, thereby demonstrating the
tradeoffs between privacy and utility needs, and the applicability of
privacy-preserving mechanisms to real-world data. We also highlight the lessons
learned from the production deployment of our system at LinkedIn.Comment: Conference information: ACM International Conference on Information
and Knowledge Management (CIKM 2018
Effect of type of load on stress analysis of thin-walled ducts
The standard procedure for qualifying the design of duct (pipe) systems in the Space Shuttle Main Engine (SSME) has been fairly well defined. However, since pipe elbows are quite common and important in the SSME duct systems, a clear understanding of the detailed stress profile of the components is necessary for accurate structural and life assessments. This study was initiated to predict the stress profile at/near the tangent point along the cross section of the duct under various types of loads. Also, this study was further extended to understand the stiffening effect on stresses due to pressure at the tangent point. The intention of this study was to identify the importance of selecting proper locations for mounting strain gauges and to utilize the obtained results to anchor dynamic models for accurate structural and life assessments of the SSME ducts under a dynamic environment. The finite element method was utilized in this study
Some remarks on the stability of time-varying systems
Stability of linear time varying system
Event-by-Event Search for Charged Neutral Fluctuations in Pb - Pb Collisions at 158-A-GeV
Results from the analysis of data obtained from the WA98 experiment at the
CERN SPS have been presented. Some events have been filtered which show photon
excess in limited zones within the overlap region of the charged
particle and photon multiplicity detectors.Comment: 6 pages, 4 figure
Protein adsorption on heterogeneous surfaces
The adsorption of the protein bovine serum albumin from an aqueous solution onto substrata made from pure silica, pure zirconia, and a mixture of the two has revealed that the adsorption behavior of the protein onto the mixture very significantly diverges from the corresponding mean of the behaviors with the pure substrata. A tentative explanation in terms of matching substratum heterogeneity with protein surface heterogeneity is offered
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