1,459 research outputs found
Falloff of the Weyl scalars in binary black hole spacetimes
The peeling theorem of general relativity predicts that the Weyl curvature
scalars Psi_n (n=0...4), when constructed from a suitable null tetrad in an
asymptotically flat spacetime, fall off asymptotically as r^(n-5) along
outgoing radial null geodesics. This leads to the interpretation of Psi_4 as
outgoing gravitational radiation at large distances from the source. We have
performed numerical simulations in full general relativity of a binary black
hole inspiral and merger, and have computed the Weyl scalars in the standard
tetrad used in numerical relativity. In contrast with previous results, we
observe that all the Weyl scalars fall off according to the predictions of the
theorem.Comment: 7 pages, 3 figures, published versio
DEVELOPMENT OF CASE STUDIES FOR THE NAVAL ACADEMY NE 203 ETHICS AND MORAL REASONING FOR NAVAL LEADERS COURSE
This thesis reviews the structure and teaching methods used in the United States Naval Academy’s NE 203 Ethics and Moral Reasoning for Naval Leaders course. We begin with a broad overview of the utility and effectiveness of the case method as a means of instructing undergraduate students in the field of ethics. We then focus on its current implementation in the Naval Academy’s NE 203 course, using interviews with senior faculty to understand the importance of the case method in teaching practical ethics. The culminating products created within this thesis are two ethical case studies, with associated teaching plans, designed for instruction by Naval Academy faculty in the NE 203 ethics course. The first case study narrates the story of Michael Izbicki, a 2008 Naval Academy graduate and designated submarine officer who petitioned for discharge as a conscientious objector upon considering the possibility that his military duty may include launching nuclear-armed weapons against American adversaries. The case study examines the moral tension that one experiences when facing a contradiction between the special obligation incurred by taking the military Oath of Office, and one’s deeply held religious views. The second case study is on when USS Mason was attacked in 2016.Lieutenant, United States NavyCaptain, United States Marine CorpsApproved for public release. Distribution is unlimited
Letter from Henrietta J. Goodale, 1903-09-20, Shelburne, N.H., to Anne Whitney, Plymouth, Mass.
https://repository.wellesley.edu/whitney_correspondence/2573/thumbnail.jp
Co-observing the Weather, Co-predicting the Climate: Human Factors in Building Infrastructures for Crowdsourced Data
This paper investigates the embodied performance of 'doing citizen science'. It examines how 'citizen scientists' produce scientific data using the resources available to them, and how their socio-technical practices and emotions impact the construction of a crowdsourced data infrastructure. We found that conducting citizen science is highly emotional and experiential, but these individual experiences and feelings tend to get lost or become invisible when user-contributed data are aggregated and integrated into a big data infrastructure. While new meanings can be extracted from big data sets, the loss of individual emotional and practical elements denotes the loss of data provenance and the marginalisation of individual efforts, motivations, and local politics which might lead to disengaged participants and unsustainable communities of citizen scientists. The challenges of constructing a data infrastructure for crowdsourced data therefore lie in the management of both technical and social issues which are local as well as global
Automatic correction of hand pointing in stereoscopic depth
In order to examine whether stereoscopic depth information could drive fast automatic correction of hand pointing, an experiment was designed in a 3D visual environment in which participants were asked to point to a target at different stereoscopic depths as quickly and accurately as possible within a limited time window (≤300 ms). The experiment consisted of two tasks: "depthGO" in which participants were asked to point to the new target position if the target jumped, and "depthSTOP" in which participants were instructed to abort their ongoing movements after the target jumped. The depth jump was designed to occur in 20% of the trials in both tasks. Results showed that fast automatic correction of hand movements could be driven by stereoscopic depth to occur in as early as 190 ms.This work was supported by the Grants from the National Natural Science Foundation of China (60970062 and 61173116) and the Doctoral Fund of Ministry of Education of China (20110072110014)
Binary neutron-star mergers with Whisky and SACRA: First quantitative comparison of results from independent general-relativistic hydrodynamics codes
We present the first quantitative comparison of two independent
general-relativistic hydrodynamics codes, the Whisky code and the SACRA code.
We compare the output of simulations starting from the same initial data and
carried out with the configuration (numerical methods, grid setup, resolution,
gauges) which for each code has been found to give consistent and sufficiently
accurate results, in particular in terms of cleanness of gravitational
waveforms. We focus on the quantities that should be conserved during the
evolution (rest mass, total mass energy, and total angular momentum) and on the
gravitational-wave amplitude and frequency. We find that the results produced
by the two codes agree at a reasonable level, with variations in the different
quantities but always at better than about 10%.Comment: Published on Phys. Rev.
Shape-specific activation of occipital cortex in an early blind echolocation expert
We have previously reported that an early-blind echolocating individual (EB) showed robust occipital activation when he identified distant, silent objects based on echoes from his tongue clicks (Thaler, Arnott, & Goodale, 2011). In the present study we investigated the extent to which echolocation activation in EB's occipital cortex reflected general echolocation processing per se versus feature-specific processing. In the first experiment, echolocation audio sessions were captured with in-ear microphones in an anechoic chamber or hallway alcove as EB produced tongue clicks in front of a concave or flat object covered in aluminum foil or a cotton towel. All eight echolocation sessions (2 shapes×2 surface materials×2 environments) were then randomly presented to him during a sparse-temporal scanning fMRI session. While fMRI contrasts of chamber versus alcove-recorded echolocation stimuli underscored the importance of auditory cortex for extracting echo information, main task comparisons demonstrated a prominent role of occipital cortex in shape-specific echo processing in a manner consistent with latent, multisensory cortical specialization. Specifically, relative to surface composition judgments, shape judgments elicited greater BOLD activity in ventrolateral occipital areas and bilateral occipital pole. A second echolocation experiment involving shape judgments of objects located 20° to the left or right of straight ahead activated more rostral areas of EB's calcarine cortex relative to location judgments of those same objects and, as we previously reported, such calcarine activity was largest when the object was located in contralateral hemispace. Interestingly, other echolocating experts (i.e., a congenitally blind individual in Experiment 1, and a late blind individual in Experiment 2) did not show the same pattern of feature-specific echo-processing calcarine activity as EB, suggesting the possible significance of early visual experience and early echolocation training. Together, our findings indicate that the echolocation activation in EB's occipital cortex is feature-specific, and that these object representations appear to be organized in a topographic manner
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