973 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
Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks
We present results of 2D and 3D PIC simulations of magnetic turbulence
production by isotropic cosmic-ray ions drifting upstream of SNR shocks. The
studies aim at testing recent predictions of a strong amplification of short
wavelength magnetic field and at studying the evolution of the magnetic
turbulence and its backreaction on cosmic rays. We observe that an oblique
filamentary mode grows more rapidly than the non-resonant parallel modes found
in analytical theory, and the growth rate of the field perturbations is much
slower than is estimated for the parallel plane-wave mode, possibly because in
our simulations we cannot maintain omega << Omega_i, the ion gyrofrequency, to
the degree required for the plane-wave mode to emerge. The evolved oblique
filamentary mode was also observed in MHD simulations to dominate in the
nonlinear phase. We thus confirm the generation of the turbulent magnetic field
due to the drift of cosmic-ray ions in the upstream plasma, but as our main
result find that the amplitude of the turbulence saturates at about dB/B~1. The
backreaction of the turbulence on the particles leads to an alignment of the
bulk-flow velocities of the cosmic rays and the background medium, which is an
essential characteristic of cosmic-ray modified shocks. It accounts for the
saturation of the instability at moderate field amplitudes. Previously
published MHD simulations have assumed a constant cosmic-ray current and no
energy or momentum flux in the cosmic rays, which excludes a backreaction of
the generated magnetic field on cosmic rays, and thus the saturation of the
field amplitude is artificially suppressed. This may explain the continued
growth of the magnetic field in the MHD simulations. A strong magnetic field
amplification to amplitudes dB >> B0 has not been demonstrated yet.Comment: revised version; accepted to ApJ; 36 pages, 13 figure
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
Central Asia: hotspot in the worldwide HIV epidemic
The HIV epidemic in central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) has accelerated since 2000. This expansion in the epidemic is largely attributable to escalating injection drug use, reflecting central Asia's geographic position along major drug trafficking routes. Although up to 75% of cumulative HIV cases have been among injection drug users (IDUs) so far, HIV infections are increasing in other population groups, including female sex workers and their clients, prisoners, and migrants. Among IDUs, risky injecting practices are highly prevalent, and the intersecting epidemic of sexually transmitted infections, particularly syphilis, highlights the potential for sexual transmission of HIV to bridging populations. Few HIV cases in children have been reported so far, with most resulting from nosocomial outbreaks in hospital settings. Some recent progress has been made towards scaling-up prevention, treatment, and care services, including harm reduction for IDUs, although key challenges remain
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
Angiotensin converting enzyme gene polymorphism is associated with severity of coronary artery disease in men with high total cholesterol levels
This study examines whether renin-angiotensin-aldosterone system gene polymorphisms: ACE (encoding for angiotensin converting enzyme) c.2306-117_404 I/D, AGTR1 (encoding for angiotensin II type-1 receptor) c.1080*86A>C and CYP11B2 (encoding for aldosterone synthase) c.-344C>T are associated with the extension of coronary atherosclerosis in a group of 647 patients who underwent elective coronary angiography. The extension of CAD was evaluated using the Gensini score. The polymorphisms were determined by PCR and RFLP assays. The associations between genotypes and the extent of coronary atherosclerosis were tested by the Kruskal-Wallis test, followed by pairwise comparisons using Wilcoxon test. The population has been divided into groups defined by: sex, smoking habit, past myocardial infarction, BMI (>, ≤ 25), age (>, ≤ 55), diabetes mellitus, level of total cholesterol (>, ≤ 200 mg/dl), LDL cholesterol (>, ≤ 130 mg/dl), HDL cholesterol (>, ≤ 40 mg/dl), triglycerides (>, ≤ 150 mg/dl). Significant associations between the ACE c.2306-117_404 I/D polymorphism and the Gensini score in men with high total cholesterol levels (PKruskal-Wallis = 0.008; Padjusted = 0.009), high level of LDL cholesterol (PKruskal-Wallis = 0.016; Padjusted = 0.028) and low level of HDL cholesterol (PKruskal-Wallis = 0.04; Padjusted = 0.055) have been found. No association between the AGTR1 c.1080*86A>C and CYP11B2 c.-344C>T and the Gensini score has been found. These results suggest that men who carry ACE c.2306-117_404 DD genotype and have high total cholesterol, high LDL cholesterol and low HDL cholesterol levels may be predisposed to the development of more severe CAD
Rapid changes in public perception toward a conservation initiative
Rapid, widespread changes in public perceptions and behaviors have the potential to influence conservation outcomes. However, few studies have documented whether and how such shifts occur throughout the span of a conservation initiative. We examined the 2020 ballot initiative to reintroduce wolves into Colorado, which passed with less support than prior surveys had estimated. We conducted a postelection survey of Colorado residents using the same methods as our preelection survey to compare responses between surveys and to official election results. Reported voting in favor of wolf reintroduction in the postelection survey decreased in comparison to voting intentions shared in the preelection survey, but not enough to reflect the actual vote. While bias from survey methods and/or sampling contributed to differences, we also found evidence that public perception changed. Specifically, beliefs about the potential for negative impacts of wolves increased, while beliefs about the potential for positive impacts of wolves decreased. Our findings highlight the need to conduct longitudinal monitoring of public perception given perceptions may be highly fluid as different entities attempt to sway voters. In addition, to better understand evolving perceptions, survey methods and sampling need to be improved
Cone beam computed tomography and intraoral radiography for diagnosis of dental abnormalities in dogs and cats
The development of veterinary dentistry has substantially improved the ability to diagnose canine and feline dental abnormalities. Consequently, examinations previously performed only on humans are now available for small animals, thus improving the diagnostic quality. This has increased the need for technical qualification of veterinary professionals and increased technological investments. This study evaluated the use of cone beam computed tomography and intraoral radiography as complementary exams for diagnosing dental abnormalities in dogs and cats. Cone beam computed tomography was provided faster image acquisition with high image quality, was associated with low ionizing radiation levels, enabled image editing, and reduced the exam duration. Our results showed that radiography was an effective method for dental radiographic examination with low cost and fast execution times, and can be performed during surgical procedures
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