887 research outputs found
Cosmic-ray Acceleration at Ultrarelativistic Shock Waves: Effects of a "Realistic" Magnetic Field Structure
First-order Fermi acceleration processes at ultrarelativistic shocks are
studied with Monte Carlo simulations. The accelerated particle spectra are
derived by integrating the exact particle trajectories in a turbulent magnetic
field near the shock. ''Realistic'' features of the field structure are
included. We show that the main acceleration process at superluminal shocks is
the particle compression at the shock. Formation of energetic spectral tails is
possible in a limited energy range only for highly perturbed magnetic fields,
with cutoffs occuring at low energies within the resonance energy range
considered. These spectral features result from the anisotropic character of
particle transport in the downstream magnetic field, where field compression
produces effectively 2D perturbations. Because of the downstream field
compression, the acceleration process is inefficient in parallel shocks for
larger turbulence amplitudes, and features observed in oblique shocks are
recovered. For small-amplitude turbulence, wide-energy range particle spectra
are formed and modifications of the process due to the existence of long-wave
perturbations are observed. In both sub- and superluminal shocks, an increase
of \gamma leads to steeper spectra with lower cut-off energies. The spectra
obtained for the ``realistic'' background conditions assumed here do not
converge to the ``universal'' spectral index claimed in the literature. Thus
the role of the first-order Fermi process in astrophysical sources hosting
relativistic shocks requires serious reanalysis.Comment: submitted to Ap
OpenMutt - 3D Printed Robotic Quadruped
Embry-Riddle Aeronautical University is seeking a robotic dog as a research avenue for different biomechanical designs, control systems, and robotic designs for experimentation and study. The quadruped is based on several open-source platforms including James Bruton’s openDogV3, the MIT Mini-Cheetah, and the NYU Open Dynamic Robot Initiative. The implementation of this research will begin with a quarter model, consisting of a singular leg from the hip to the foot. The leg will be mounted on a benchtop test stand that allows for controlled movement and accessible experimentation. The leg will be separate from the full-model quadruped strictly for experimentation and any full-model revisions. The OpenMutt’s quarter model uses 3 Brushless DC Electric Motors (BLDC) attached to 3 cycloidal gearboxes as its main form of actuation. The majority of parts were manufactured using Polylactic Acid (PLA). Some leg testing has already been completed, but a synchronized movement is yet to be completed
OpenMutt - 3D Printed Robotic Quadruped
The objective of the OpenMutt project is to build a modular, open-source quadruped as a multidisciplinary research testbed for students and faculty. The design is based on proven models, including the MIT Mini-Cheetah, NYU Open Dynamic Robot, and Bruton’s openDogV3, with modifications to decrease manufacturing time and cost. OpenMutt utilizes 12 brushless motors, each attached to a cycloidal gearbox for actuation. The quarter model has three degrees of freedom, translational and rotational. A remote control will be used for general movement with impedance and PID controllers for torque and joint control. The majority of parts were additively manufactured with Fused Deposition Modeling(FDM) printers using Polylactic Acid(PLA) and Thermoplastic Polyurethane(TPU). A power supply will be used for quarter model testing, while the full model will use an onboard battery with the battery-management system (BMS). Due to the 13:1 gear ratio of the cycloidal gearbox, motors like the ones selected are adaptable to the model. The purpose behind the application of these methods is to ensure a platform that is easy to construct, iterate and learn with
Mixed quark-nucleon phase in neutron stars and nuclear symmetry energy
The influence of the nuclear symmetry energy on the formation of a mixed
quark-nucleon phase in neutron star cores is studied. We use simple
parametrizations of the nuclear matter equation of state, and the bag model for
the quark phase. The behavior of nucleon matter isobars, which is responsible
for the existence of the mixed phase, is investigated. The role of the nuclear
symmetry energy changes with the value of the bag constant B. For lower values
of B the properties of the mixed phase do not depend strongly on the symmetry
energy. For larger B we find that a critical pressure for the first quark
droplets to form is strongly dependent on the nuclear symmetry energy, but the
pressure at which last nucleons disappear is independent of it.Comment: 12 pages, 16 figures, Phys. Rev. C in pres
A Process for Co-Designing Educational Technology Systems for Refugee Children
There is a growing interest in the potential for technology to facilitate emergency education of refugee children. However, designing in this space requires knowledge of the displaced population and the contextual dynamics surrounding it. Design should therefore be informed by both existing research across relevant disciplines, and from the practical experience of those who are on the ground facing the problem in real life. This paper describes a process for designing appropriate technology for these settings. The process draws on literature from emergency education, student engagement and motivation, educational technology, and participatory design. We emphasise a thorough understanding of the problem definition, the nature of the emergency, and of socio-cultural aspects that can inform the design process. We describe how this process was implemented leading to the design of a digital learning space for children living in a refugee camp in Greece. This drew on involving different groups of participants such as social-workers, parents, and children
Performance of a small size telescope (SST-1M) camera for gamma-ray astronomy with the Cherenkov Telescope Array
The foreseen implementations of the Small Size Telescopes (SST) in CTA will
provide unique insights into the highest energy gamma rays offering fundamental
means to discover and under- stand the sources populating the Galaxy and our
local neighborhood. Aiming at such a goal, the SST-1M is one of the three
different implementations that are being prototyped and tested for CTA. SST-1M
is a Davies-Cotton single mirror telescope equipped with a unique camera
technology based on SiPMs with demonstrated advantages over classical
photomultipliers in terms of duty-cycle. In this contribution, we describe the
telescope components, the camera, and the trigger and readout system. The
results of the commissioning of the camera using a dedicated test setup are
then presented. The performances of the camera first prototype in terms of
expected trigger rates and trigger efficiencies for different night-sky
background conditions are presented, and the camera response is compared to
end-to-end simulations.Comment: All CTA contributions at arXiv:1709.0348
Development of a strategy for calibrating the novel SiPM camera of the SST-1M telescope proposed for the Cherenkov Telescope Array
CTA will comprise a sub-array of up to 70 small size telescopes (SSTs) at the
southern array. The SST-1M project, a 4 m-diameter Davies Cotton telescope with
9 degrees FoV and a 1296 pixels SiPM camera, is designed to meet the
requirements of the next generation ground based gamma-ray observatory CTA in
the energy range above 3 TeV. Silicon photomultipliers (SiPM) cameras of
gamma-ray telescopes can achieve good performance even during high night sky
background conditions. Defining a fully automated calibration strategy of SiPM
cameras is of great importance for large scale production validation and online
calibration. The SST-1M sub-consortium developed a software compatible with CTA
pipeline software (CTApipe). The calibration of the SST-1M camera is based on
the Camera Test Setup (CTS), a set of LED boards mounted in front of the
camera. The CTS LEDs are operated in pulsed or continuous mode to emulate
signal and night sky background respectively. Continuous and pulsed light data
analysis allows us to extract single pixel calibration parameters to be used
during CTA operation.Comment: All CTA contributions at arXiv:1709.0348
Control Software for the SST-1M Small-Size Telescope prototype for the Cherenkov Telescope Array
The SST-1M is a 4-m Davies--Cotton atmospheric Cherenkov telescope optimized
to provide gamma-ray sensitivity above a few TeV. The SST-1M is proposed as
part of the Small-Size Telescope array for the Cherenkov Telescope Array (CTA),
the first prototype has already been deployed. The SST-1M control software of
all subsystems (active mirror control, drive system, safety system,
photo-detection plane, DigiCam, CCD cameras) and the whole telescope itself
(master controller) uses the standard software design proposed for all CTA
telescopes based on the ALMA Common Software (ACS) developed to control the
Atacama Large Millimeter Array (ALMA). Each subsystem is represented by a
separate ACS component, which handles the communication to and the operation of
the subsystem. Interfacing with the actual hardware is performed via the OPC UA
communication protocol, supported either natively by dedicated industrial
standard servers (PLCs) or separate service applications developed to wrap
lower level protocols (e.g. CAN bus, camera slow control) into OPC UA. Early
operations of the telescope without the camera were already carried out. The
camera is fully assembled and is capable to perform data acquisition using
artificial light source.Comment: In Proceedings of the 35th International Cosmic Ray Conference
(ICRC2017), Busan, Korea. All CTA contributions at arXiv:1709.0348
Modeling the Emission Processes in Blazars
Blazars are the most violent steady/recurrent sources of high-energy
gamma-ray emission in the known Universe. They are prominent emitters of
electromagnetic radiation throughout the entire electromagnetic spectrum. The
observable radiation most likely originates in a relativistic jet oriented at a
small angle with respect to the line of sight. This review starts out with a
general overview of the phenomenology of blazars, including results from a
recent multiwavelength observing campaign on 3C279. Subsequently, issues of
modeling broadband spectra will be discussed. Spectral information alone is not
sufficient to distinguish between competing models and to constrain essential
parameters, in particular related to the primary particle acceleration and
radiation mechanisms in the jet. Short-term spectral variability information
may help to break such model degeneracies, which will require snap-shot
spectral information on intraday time scales, which may soon be achievable for
many blazars even in the gamma-ray regime with the upcoming GLAST mission and
current advances in Atmospheric Cherenkov Telescope technology. In addition to
pure leptonic and hadronic models of gamma-ray emission from blazars,
leptonic/hadronic hybrid models are reviewed, and the recently developed
hadronic synchrotron mirror model for TeV gamma-ray flares which are not
accompanied by simultaneous X-ray flares (``orphan TeV flares'') is revisited.Comment: Invited Review at "The Multimessenger Approach to Gamma-Ray Sources",
Barcelona, Spain, July 2006; submitted to Astrophysics and Space Science. 10
pages, including 6 eps figures. Uses Springer's ApSS macro
Using muon rings for the optical throughput calibration of the SST-1M prototype for the Cherenkov Telescope Array
Imaging Atmospheric Cherenkov Telescopes (IACTs) are ground-based instruments
devoted to the study of very high energy gamma-rays coming from space. The
detection technique consists of observing images created by the Cherenkov light
emitted when gamma rays, or more generally cosmic rays, propagate through the
atmosphere. While in the case of protons or gamma-rays the images present a
filled and more or less elongated shape, energetic muons penetrating the
atmosphere are visualised as characteristic circular rings or arcs. A
relatively simple analysis of the ring images allows the reconstruction of all
the relevant parameters of the detected muons, such as the energy, the impact
parameter, and the incoming direction, with the final aim to use them to
calibrate the total optical throughput of the given IACT telescope. We present
the results of preliminary studies on the use of images created by muons as
optical throughput calibrators of the single mirror small size telescope
prototype SST-1M proposed for the Cherenkov Telescope Array.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
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