808 research outputs found
Conformal Predictive Safety Filter for RL Controllers in Dynamic Environments
The interest in using reinforcement learning (RL) controllers in
safety-critical applications such as robot navigation around pedestrians
motivates the development of additional safety mechanisms. Running RL-enabled
systems among uncertain dynamic agents may result in high counts of collisions
and failures to reach the goal. The system could be safer if the pre-trained RL
policy was uncertainty-informed. For that reason, we propose conformal
predictive safety filters that: 1) predict the other agents' trajectories, 2)
use statistical techniques to provide uncertainty intervals around these
predictions, and 3) learn an additional safety filter that closely follows the
RL controller but avoids the uncertainty intervals. We use conformal prediction
to learn uncertainty-informed predictive safety filters, which make no
assumptions about the agents' distribution. The framework is modular and
outperforms the existing controllers in simulation. We demonstrate our approach
with multiple experiments in a collision avoidance gym environment and show
that our approach minimizes the number of collisions without making
overly-conservative predictions
Frequency of Participation in an Employee Fitness Program and Health Care Expenditures
Regular physical activity is strongly linked to prevention of costly chronic health conditions. However, there has been limited examination of the impact that level of participation in physical activity promotion programs has on health care costs. This study examined a fitness reimbursement program (FRP) offered to small employers. FRP participants received 6.14 (2.6%) for low-moderate (P?=?0.60), 20.01 (8.4%) for high (P?=?0.08). With high-cost outliers included, significant monthly cost savings were observed for the moderate-high ($43.52, P?Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140192/1/pop.2015.0102.pd
CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass and radius
We study the components of cool and warm/hot gas in the circumgalactic medium
(CGM) of simulated galaxies and address the relative production of OVI by
photoionization versus collisional ionization, as a function of halo mass,
redshift, and distance from the galaxy halo center. This is done utilizing two
different suites of zoom-in hydro-cosmological simulations, VELA (6 halos;
) and NIHAO (18 halos; to ), which provide a broad theoretical basis
because they use different codes and physical recipes for star formation and
feedback. In all halos studied in this work, we find that collisional
ionization by thermal electrons dominates at high redshift, while
photoionization of cool or warm gas by the metagalactic radiation takes over
near . In halos of and above, collisions become
important again at , while photoionization remains significant down to
for less massive halos. In halos with , at most of the photoionized OVI is in a
warm, not cool, gas phase (~K). We also find that
collisions are dominant in the central regions of halos, while photoionization
is more significant at the outskirts, around , even in massive
halos. This too may be explained by the presence of warm gas or, in lower mass
halos, by cool gas inflows
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Perceptual thresholds for foot slipping in animated characters
The computer game industry continues to progress toward realistic-looking character motion. However, even in state-of-the-art games, the use of motion capture data in character animation may result in errors such as “foot slipping,” where the feet do not match up with the floor properly during translation. Various algorithms have been proposed to minimize foot slipping, including one which changes limb lengths. While foot slipping decreases the realism of character motion, there must be some threshold below which this error is imperceptible; devoting further processor time in these cases is wasteful. We apply the classical method of perception threshold determination using a set of motion clips with parameterized slipping error. From this experiment, we develop guidelines for acceptable error. Furthermore, we show that introducing simple camera motion may increase the perceptual threshold, and thus could be used to “mask” foot slipping errors
Constructing Finite Frames of a Given Spectrum and Set of Lengths
When constructing finite frames for a given application, the most important consideration is the spectrum of the frame operator. Indeed, the minimum and maximum eigenvalues of the frame operator are the optimal frame bounds, and the frame is tight precisely when this spectrum is constant. Often, the second-most important design consideration is the lengths of frame vectors: Gabor, wavelet, equiangular and Grassmannian frames are all special cases of equal norm frames, and unit norm tight frame-based encoding is known to be optimally robust against additive noise and erasures. We consider the problem of constructing frames whose frame operator has a given spectrum and whose vectors have prescribed lengths. For a given spectrum and set of lengths, the existence of such frames is characterized by the Schur-Horn Theorem---they exist if and only if the spectrum majorizes the squared lengths---the classical proof of which is nonconstructive. Certain construction methods, such as harmonic frames and spectral tetris, are known in the special case of unit norm tight frames, but even these provide but a few examples from the manifold of all such frames, the dimension of which is known and nontrivial. In this paper, we provide a new method for explicitly constructing any and all frames whose frame operator has a prescribed spectrum and whose vectors have prescribed lengths. The method itself has two parts. In the first part, one chooses eigensteps---a sequence of interlacing spectra---that transform the trivial spectrum into the desired one. The second part is to explicitly compute the frame vectors in terms of these eigensteps; though nontrivial, this process is nevertheless straightforward enough to be implemented by hand, involving only arithmetic, square roots and matrix multiplication
An Emergency Room Decision-Support Program That Increased Physician Office Visits, Decreased Emergency Room Visits, and Saved Money
The objective of this study was to evaluate an Emergency Room having a Decision-Support (ERDS) program designed to appropriately reduce ER use among frequent users, defined as 3 or more visits within a 12-month period. To achieve this, adults with an AARP Medicare Supplement Insurance plan insured by UnitedHealthcare Insurance Company (for New York residents, UnitedHealthcare Insurance Company of New York) were eligible to participate in the program. These included 7070 individuals who elected to enroll in the ERDS program and an equal number of matched nonparticipants who were eligible but either declined or were unreachable. Program-related benefits were estimated by comparing the difference in downstream health care utilization and expenditures between engaged and not engaged individuals after using propensity score matching to adjust for case mix differences between these groups. As a result, compared with the not engaged, engaged individuals experienced better care coordination, evidenced by a greater reduction in ER visits (P=0.033) and hospital admissions (P=0.002) and an increase in office visits (P<0.001). The program was cost-effective, with a return on investment (ROI) of 1.24, which was calculated by dividing the total program savings (2.75 million). The ROI implies that for every dollar invested in this program, $1.24 was saved, most of which was for the federal Medicare program. In conclusion, the decrease in ER visits and hospital admissions and the increase in office visits may indicate the program helped individuals to seek the appropriate levels of care. (Population Health Management 2014;17:257?264)Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140184/1/pop.2013.0117.pd
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