5,065 research outputs found
Background Rejection in Atmospheric Cherenkov Telescopes using Recurrent Convolutional Neural Networks
In this work, we present a new, high performance algorithm for background
rejection in imaging atmospheric Cherenkov telescopes. We build on the already
popular machine-learning techniques used in gamma-ray astronomy by the
application of the latest techniques in machine learning, namely recurrent and
convolutional neural networks, to the background rejection problem. Use of
these machine-learning techniques addresses some of the key challenges
encountered in the currently implemented algorithms and helps to significantly
increase the background rejection performance at all energies.
We apply these machine learning techniques to the H.E.S.S. telescope array,
first testing their performance on simulated data and then applying the
analysis to two well known gamma-ray sources. With real observational data we
find significantly improved performance over the current standard methods, with
a 20-25\% reduction in the background rate when applying the recurrent neural
network analysis. Importantly, we also find that the convolutional neural
network results are strongly dependent on the sky brightness in the source
region which has important implications for the future implementation of this
method in Cherenkov telescope analysis.Comment: 11 pages, 7 figures. To be submitted to The European Physical Journal
Quantum Hole Digging in Magnetic Molecular Clusters
Below 360 mK, Fe8 magnetic molecular clusters are in the pure quantum
relaxation regime. We showed recently that the predicted ``square-root time''
relaxation is obeyed, allowing us to develop a new method for watching the
evolution of the distribution of molecular spin states in the sample. We
measured the distribution P(H) of molecules which are in resonance at the
applied field H. Tunnelling initially causes rapid transitions of molecules,
thereby ``digging a hole'' in P(H). For small initial magnetisation values, the
hole width shows an intrinsic broadening which may be due to nuclear spins. We
present here hole digging measurements in the thermal activated regime which
may allow to study the effect of spin-phonon coupling.Comment: 3 pages, 2 figures, conference proceedings of LT22 (Helsinki,
Finland, August 4-11, 1999
On the origin of \gamma-ray emission in \eta\ Carina
\eta\ Car is the only colliding-wind binary for which high-energy \gamma\
rays are detected. Although the physical conditions in the shock region change
on timescales of hours to days, the variability seen at GeV energies is weak
and on significantly longer timescales. The \gamma-ray spectrum exhibits two
features that can be interpreted as emission from the shocks on either side of
the contact discontinuity. Here we report on the first time-dependent modelling
of the non-thermal emission in \eta\ Car. We find that emission from primary
electrons is likely not responsible for the \gamma-ray emission, but
accelerated protons interacting with the dense wind material can explain the
observations. In our model, efficient acceleration is required at both shocks,
with the primary side acting as a hadron calorimeter, whilst on the companion
side acceleration is limited by the flow time out of the system, resulting in
changing acceleration conditions. The system therefore represents a unique
laboratory for the exploration of hadronic particle acceleration in
non-relativistic shocks.Comment: 5 pages, 4 figures, 1 table, accepted for publication in MNRAS
Letter
Answer to the comment of Chudnovsky: On the square-root time relaxation in molecular nanomagnets
Answer to the comment of E. Chudnovsky concerning the following papers:
(1) N.V. Prokof'ev, P.C.E. Stamp, Phys. Rev. Lett.80, 5794 (1998).
(2) W. Wernsdorfer, T. Ohm, C. Sangregorio, R. Sessoli, D. Mailly, C.
Paulsen, Phys. Rev. Lett. 82, 3903 (1999).Comment: 1 page
Method for surmounting an obstacle by a robot vehicle
Surmounting obstacles in the path of a robot vehicle is accomplished by rotating the wheel forks of the vehicle about their transverse axes with respect to the vehicle body so as to shift most of the vehicle weight onto the rear wheels, and then driving the vehicle forward so as to drive the now lightly-loaded front wheels (only) over the obstacle. Then, after the front wheels have either surmounted or completely passed the obstacle (depending upon the length of the obstacle), the forks are again rotated about their transverse axes so as to shift most of the vehicle weight onto the front wheels. Then the vehicle is again driven forward so as to drive the now lightly-loaded rear wheels over the obstacle. Once the obstacle has been completely cleared and the vehicle is again on relatively level terrain, the forks are again rotated so as to uniformly distribute the vehicle weight between the front and rear wheels
Emergency response mobile robot for operations in combustible atmospheres
A mobile, self-powered, self-contained, and remote-controlled robot is presented. The robot is capable of safely operating in a combustible atmosphere and providing information about the atmosphere to the operator. The robot includes non-sparking and non-arcing electro-mechanical and electronic components designed to prevent the robot from igniting the combustible atmosphere. The robot also includes positively pressurized enclosures that house the electromechanical and electronic components of the robot and prevent intrusion of the combustible atmosphere into the enclosures. The enclosures are interconnected such that a pressurized gas injected into any one of the enclosures is routed to all the other enclosures through the interconnections. It is preferred that one or more sealed internal channels through structures intervening between the enclosures be employed. Pressure transducers for detecting if the pressure within the enclosures falls below a predetermined level are included. The robot also has a sensing device for determining the types of combustible substances in the surrounding atmosphere, as well as the concentrations of each type of substance relative to a pre-determined lower explosive limit (LEL). In addition, the sensing device can determine the percent level of oxygen present in the surrounding atmosphere
Readout of carbon nanotube vibrations based on spin-phonon coupling
We propose a scheme for spin-based detection of the bending motion in
suspended carbon-nanotubes, using the curvature-induced spin-orbit interaction.
We show that the resulting effective spin-phonon coupling can be used to
down-convert the high-frequency vibration-modulated spin-orbit field to
spin-flip processes at a much lower frequency. This vibration-induced
spin-resonance can be controlled with an axial magnetic field. We propose a
Pauli spin blockade readout scheme and predict that the leakage current shows
pronounced peaks as a function of the external magnetic field. Whereas the
resonant peaks allow for frequency readout, the slightly off-resonant current
is sensitive to the vibration amplitude.Comment: 3 pages(+), 3 figure
Tool actuation and force feedback on robot-assisted microsurgery system
An input control device with force sensors is configured to sense hand movements of a surgeon performing a robot-assisted microsurgery. The sensed hand movements actuate a mechanically decoupled robot manipulator. A microsurgical manipulator, attached to the robot manipulator, is activated to move small objects and perform microsurgical tasks. A force-feedback element coupled to the robot manipulator and the input control device provides the input control device with an amplified sense of touch in the microsurgical manipulator
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