3,486 research outputs found
Coordinated Multi-Agent Imitation Learning
We study the problem of imitation learning from demonstrations of multiple
coordinating agents. One key challenge in this setting is that learning a good
model of coordination can be difficult, since coordination is often implicit in
the demonstrations and must be inferred as a latent variable. We propose a
joint approach that simultaneously learns a latent coordination model along
with the individual policies. In particular, our method integrates unsupervised
structure learning with conventional imitation learning. We illustrate the
power of our approach on a difficult problem of learning multiple policies for
fine-grained behavior modeling in team sports, where different players occupy
different roles in the coordinated team strategy. We show that having a
coordination model to infer the roles of players yields substantially improved
imitation loss compared to conventional baselines.Comment: International Conference on Machine Learning 201
Dickkopf-3 is upregulated in osteoarthritis and has a chondroprotective role
Objective Dickkopf-3 (Dkk3) is a non-canonical member of the Dkk family of Wnt antagonists and its upregulation has been reported in microarray analysis of cartilage from mouse models of osteoarthritis (OA). In this study we assessed Dkk3 expression in human OA cartilage to ascertain its potential role in chondrocyte signaling and cartilage maintenance. Methods Dkk3 expression was analysed in human adult OA cartilage and synovial tissues and during chondrogenesis of ATDC5 and human mesenchymal stem cells. The role of Dkk3 in cartilage maintenance was analysed by incubation of bovine and human cartilage explants with interleukin-1 (IL1) and oncostatin-M (OSM). Dkk3 expression was measured in cartilage following murine hip avulsion. Whether Dkk3 influenced Wnt, TGF and activin cell signaling was assessed in primary human chondrocytes and SW1353 chondrosarcoma cells using RT-qPCR and luminescence assays. Results Increased gene and protein levels of Dkk3 were detected in human OA cartilage, synovial tissue and synovial fluid. DKK3 expression was decreased during chondrogenesis of both ATDC5 cells and humans MSCs. Dkk3 inhibited IL1 and OSM-mediated proteoglycan loss from human and bovine cartilage explants and collagen loss from bovine cartilage explans. Cartilage DKK3 expression was decreased following hip avulsion injury. TGF signaling was enhanced by Dkk3 and Wnt3a and activin signaling were inhibited. Conclusions We provide evidence that Dkk3 is upregulated in OA and may have a protective effect on cartilage integrity by preventing proteoglycan loss and helping to restore OA-relevant signaling pathway activity. Targeting Dkk3 may be a novel approach in the treatment of OA
A spectrograph instrument concept for the Prime Focus Spectrograph (PFS) on Subaru Telescope
We describe the conceptual design of the spectrograph opto-mechanical concept
for the SuMIRe Prime Focus Spectrograph (PFS) being developed for the SUBARU
telescope. The SuMIRe PFS will consist of four identical spectrographs, each
receiving 600 fibers from a 2400 fiber robotic positioner at the prime focus.
Each spectrograph will have three channels covering in total, a wavelength
range from 380 nm to 1300 nm. The requirements for the instrument are
summarized in Section 1. We present the optical design and the optical
performance and analysis in Section 2. Section 3 introduces the mechanical
design, its requirements and the proposed concepts. Finally, the AIT phases for
the Spectrograph System are described in Section 5.Comment: 8 pages, 5 figures, submitted to "Ground-based and Airborne
Instrumentation for Astronomy IV, Ian S. McLean, Suzanne K. Ramsay, Hideki
Takami, Editors, Proc. SPIE 8446 (2012)
Theory of pixel lensing towards M31 I: the density contribution and mass of MACHOs
POINT-AGAPE is an Anglo-French collaboration which is employing the Isaac
Newton Telescope (INT) to conduct a pixel-lensing survey towards M31. In this
paper we investigate what we can learn from pixel-lensing observables about the
MACHO mass and fractional contribution in M31 and the Galaxy for the case of
spherically-symmetric near-isothermal haloes. We employ detailed pixel-lensing
simulations which include many of the factors which affect the observables. For
a maximum MACHO halo we predict an event rate in V of up to 100 per season for
M31 and 40 per season for the Galaxy. However, the Einstein radius crossing
time is generally not measurable and the observed full-width half-maximum
duration provides only a weak tracer of lens mass. Nonetheless, we find that
the near-far asymmetry in the spatial distribution of M31 MACHOs provides
significant information on their mass and density contribution. We present a
likelihood estimator for measuring the fractional contribution and mass of both
M31 and Galaxy MACHOs which permits an unbiased determination to be made of
MACHO parameters, even from data-sets strongly contaminated by variable stars.
If M31 does not have a significant population of MACHOs in the mass range
0.001-1 Solar masses strong limits will result from the first season of INT
observations. Simulations based on currently favoured density and mass values
indicate that, after three seasons, the M31 MACHO parameters should be
constrained to within a factor four uncertainty in halo fraction and an order
of magnitude uncertainty in mass (90% confidence). Interesting constraints on
Galaxy MACHOs may also be possible. For a campaign lasting ten years,
comparable to the lifetime of current LMC surveys, reliable estimates of MACHO
parameters in both galaxies should be possible. (Abridged)Comment: 21 pages, 14 figures. Submitted to MNRA
The Hyperfine Molecular Hubbard Hamiltonian
An ultracold gas of heteronuclear alkali dimer molecules with hyperfine
structure loaded into a one-dimensional optical lattice is investigated. The
\emph{Hyperfine Molecular Hubbard Hamiltonian} (HMHH), an effective low-energy
lattice Hamiltonian, is derived from first principles. The large permanent
electric dipole moment of these molecules gives rise to long range
dipole-dipole forces in a DC electric field and allows for transitions between
rotational states in an AC microwave field. Additionally, a strong magnetic
field can be used to control the hyperfine degrees of freedom independently of
the rotational degrees of freedom. By tuning the angle between the DC electric
and magnetic fields and the strength of the AC field it is possible to control
the number of internal states involved in the dynamics as well as the degree of
correlation between the spatial and internal degrees of freedom. The HMHH's
unique features have direct experimental consequences such as quantum
dephasing, tunable complexity, and the dependence of the phase diagram on the
molecular state
Visible camera cryostat design and performance for the SuMIRe Prime Focus Spectrograph (PFS)
We describe the design and performance of the SuMIRe Prime Focus Spectrograph
(PFS) visible camera cryostats. SuMIRe PFS is a massively multi-plexed
ground-based spectrograph consisting of four identical spectrograph modules,
each receiving roughly 600 fibers from a 2394 fiber robotic positioner at the
prime focus. Each spectrograph module has three channels covering wavelength
ranges 380~nm -- 640~nm, 640~nm -- 955~nm, and 955~nm -- 1.26~um, with the
dispersed light being imaged in each channel by a f/1.07 vacuum Schmidt camera.
The cameras are very large, having a clear aperture of 300~mm at the entrance
window, and a mass of 280~kg. In this paper we describe the design of the
visible camera cryostats and discuss various aspects of cryostat performance
Learning Online Smooth Predictors for Realtime Camera Planning using Recurrent Decision Trees
We study the problem of online prediction for realtime camera planning, where the goal is to predict smooth trajectories that correctly track and frame objects of interest (e.g., players in a basketball game). The conventional approach for training predictors does not directly consider temporal consistency, and often produces undesirable jitter. Although post-hoc smoothing (e.g., via a Kalman filter) can mitigate this issue to some degree, it is not ideal due to overly stringent modeling assumptions (e.g., Gaussian noise). We propose a recurrent decision tree framework that can directly incorporate temporal consistency into a data-driven predictor, as well as a learning algorithm that can efficiently learn such temporally smooth models. Our approach does not require any post-processing, making online smooth predictions much easier to generate when the noise model is unknown. We apply our approach to sports broadcasting: given noisy player detections, we learn where the camera should look based on human demonstrations. Our experiments exhibit significant improvements over conventional baselines and showcase the practicality of our approach
SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at
the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE
is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns
to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2
above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the
burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle
Physic
A method for improving the performance of gradient systems for diffusion-weighted MRI
The MR signal is sensitive to diffusion. This effect can be increased by the use of large, balanced bipolar gradients. The gradient systems of MR scanners are calibrated at installation and during regular servicing visits. Because the measured apparent diffusion constant (ADC) depends on the square of the amplitude of the diffusion sensitizing gradients, errors in the gradient calibration are exaggerated. If the error is varying among the different gradient axes, it will affect the estimated degree of anisotropy. To assess the gradient calibration accuracy in a whole-body MRI scanner, ADC values were calculated for a uniform water phantom along each gradient direction while monitoring the temperature. Knowledge of the temperature allows the expected diffusion constant of water to be calculated independent of the MRI measurement. It was found that the gradient axes (±x, ±y, ±z) were calibrated differently, resulting in offset ADC values. A method is presented to rescale the amplitude of each of the six principal gradient axes within the MR pulse sequence. The scaling factor is the square root of the ratio of the expected and observed diffusion constants. In addition, fiber tracking results in the human brain were noticeably affected by improving the gradient system calibration. Magn Reson Med 58:763â768, 2007. © 2007 Wiley-Liss, Inc
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