4,678 research outputs found
An Overview of Redirected Walking Approaches and Techniques in Virtual Reality
One major obstacle to the ideal of virtual reality is the physical constraints of the user’s location, primarily its limited size. A commonly proposed solution is using redirected walking, defined as manipulation of the user’s experience to alter their walking path, to keep the user within a confined physical space without causing any perceivable sensory distortion for the user. This paper discusses various redirected walking approaches which have been proposed, including predictions of user movement via navigation meshes and simulated users, and subtle redirection techniques using blink-induced change blindness and avatar manipulation
Political Chemicals: Drugs, Rights, and the Good Life
Recreational drug use, whether publicly acknowledged or privately hidden, has long been a common activity within human societies. Though this comes with serious hazards, it also produces benefits, which often go unrecognized. Given the current prohibitory policies, it is important to consider whether such use ought to be restricted. I will do just that, focusing on whether recreational drug use can be part of a reasonable conception of the good life, as well as whether restrictions constitute an infringement on freedom. I will argue that, in moderation, recreational drug use constitutes a positive good for a large group of people, and that criminalization places an unfair burden upon these people, which breaches the liberal principle of neutrality
Detecting clinically meaningful biomarkers with repeated measurements in an Electronic Health Record
Electronic health record (EHR) data are becoming an increasingly common data
source for understanding clinical risk of acute events. While their
longitudinal nature presents opportunities to observe changing risk over time,
these analyses are complicated by the sparse and irregular measurements of many
of the clinical metrics making typical statistical methods unsuitable for these
data. In this paper, we present an analytic procedure to both sample from an
EHR and analyze the data to detect clinically meaningful markers of acute
myocardial infarction (MI). Using an EHR from a large national dialysis
organization we abstracted the records of 64,318 individuals and identified
5,314 people that had an MI during the study period. We describe a nested
case-control design to sample appropriate controls and an analytic approach
using regression splines. Fitting a mixed-model with truncated power splines we
perform a series of goodness-of-fit tests to determine whether any of 11
regularly collected laboratory markers are useful clinical predictors. We test
the clinical utility of each marker using an independent test set. The results
suggest that EHR data can be easily used to detect markers of clinically acute
events. Special software or analytic tools are not needed, even with irregular
EHR data.Comment: 23 pages, 3 figure
Scale-dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence
Under certain conditions, freely decaying magnetohydrodynamic (MHD) turbulence evolves in such a way that velocity and magnetic field fluctuations delta v and delta B approach a state of alignment in which delta v proportional to delta B. This process is called dynamic alignment. Boldyrev has suggested that a similar kind of alignment process occurs as energy cascades from large to small scales through the inertial range in strong incompressible MHD turbulence. In this study, plasma and magnetic field data from the Wind spacecraft, data acquired in the ecliptic plane near 1 AU, are employed to investigate the angle theta(tau) between velocity and magnetic field fluctuations in the solar wind as a function of the time scale tau of the fluctuations and to look for the scaling relation similar to tau(1/4) predicted by Boldyrev. We find that the angle appears to scale like a power law at large inertial range scales, but then deviates from power law behavior at medium to small inertial range scales. We also find that small errors in the velocity vector measurements can lead to large errors in the angle measurements at small time scales. As a result, we cannot rule out the possibility that the observed deviations from power law behavior arise from errors in the velocity measurements. When we fit the data from 2 x 10(3) s to 2 x 10(4) s with a power law of the form proportional to tau(p), our best fit values for p are in the range 0.27-0.36
Galactic Spiral Structure
We describe the structure and composition of six major stellar streams in a
population of 20 574 local stars in the New Hipparcos Reduction with known
radial velocities. We find that, once fast moving stars are excluded, almost
all stars belong to one of these streams. The results of our investigation have
lead us to re-examine the hydrogen maps of the Milky Way, from which we
identify the possibility of a symmetric two-armed spiral with half the
conventionally accepted pitch angle. We describe a model of spiral arm motions
which matches the observed velocities and composition of the six major streams,
as well as the observed velocities of the Hyades and Praesepe clusters at the
extreme of the Hyades stream. We model stellar orbits as perturbed ellipses
aligned at a focus in coordinates rotating at the rate of precession of
apocentre. Stars join a spiral arm just before apocentre, follow the arm for
more than half an orbit, and leave the arm soon after pericentre. Spiral
pattern speed equals the mean rate of precession of apocentre. Spiral arms are
shown to be stable configurations of stellar orbits, up to the formation of a
bar and/or ring. Pitch angle is directly related to the distribution of orbital
eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve
to form bars and rings. We show that orbits of gas clouds are stable only in
bisymmetric spirals. We conclude that spiral galaxies evolve toward grand
design two-armed spirals. We infer from the velocity distributions that the
Milky Way evolved into this form about 9 Gyrs ago.Comment: Published in Proc Roy Soc A. A high resolution version of this file
can be downloaded from http://papers.rqgravity.net/SpiralStructure.pdf. A
simplified account with animations begins at
http://rqgravity.net/SpiralStructur
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