5,536 research outputs found
Correction: Theory of diffusion-influenced reactions in complex geometries
Correction for 'Theory of diffusion-influenced reactions in complex geometries' by Marta Galanti et al., Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/c6cp01147k
Lagrangian analysis of alignment dynamics for isentropic compressible magnetohydrodynamics
After a review of the isentropic compressible magnetohydrodynamics (ICMHD)
equations, a quaternionic framework for studying the alignment dynamics of a
general fluid flow is explained and applied to the ICMHD equations.Comment: 12 pages, 2 figures, submitted to a Focus Issue of New Journal of
Physics on "Magnetohydrodynamics and the Dynamo Problem" J-F Pinton, A
Pouquet, E Dormy and S Cowley, editor
Adaptive Basketball Shooter - Final Project Report
The Friday Club is a joint venture between the Cal Poly Kinesiology Department and the San Luis Obispo Special Olympics that offers people with varying degrees of disability the opportunity to meet weekly and learn various sports and games. At Friday Club, athletes in wheelchairs with limited arm strength use devices built by Cal Poly mechanical engineering students in order to participate in various sports. Many devices are designed to attach to the Universal Play Frame (UPF), a wheel-chair attachment. The purpose of this project was to design and build a UPF device that will launch a basketball, so that an athlete can participate in a game of “Horse.”
The project was worked on over the course of the 2013-2014 school year. To begin, the team developed a list of objectives for the device to meet and researched existing solutions for various facets of our design. The next step was to generate concepts of our device, and using Pugh matrices, proof of concept testing, and debate to narrow down to a single concept. Next, this concept was transformed into a fully-fledged design backed by engineering analysis. After design approval, all necessary parts and materials were ordered and a prototype was built over a 10 week period. The final prototype was tested with the Friday Club and displayed at the Senior Project Expo on May 31, 2014.
The final device that our team designed is a slingshot that launches the ball by releasing stretched elastic bands. Our design attaches to the UPF at two points, and can be aimed to shoot a basket from anywhere between 5 and 15 feet away. The athlete has the ability to control the direction, power, and release of each shot. The device can be set up in under five minutes by a single person and takes only 30 seconds to reset between shots.
Of all customer requirements that the device was to meet, it only failed to meet one of them. The first was that it should be able to shoot a three-pointer. Unfortunately, our device either did not have strong enough elastic, or did not have enough space to pull back the ball and carriage sufficiently. Therefore, our device can shoot a basket from a maximum of only 15 feet away, or a free throw. Other future recommendations are to strengthen some parts that take high impacts and to reduce the weight of some unnecessarily bulky parts.
Our budget for this project was 1,750. After analyzing our spending, we found that over 1,400.
In this report, our team’s entire design process is cataloged in detail. Also enclosed are detailed part drawings for each manufactured part of our final device, as well as a safety and operation manual
On the Structure of the Magnetic Field in a Kinematic ABC Flow Dynamo
The kinematic induction equation of MHD is solved numerically in the case of
the normal ``111'' ABC flow using a general staggered mesh method. Careful 3-D
visualizations of the topology of the magnetic field reveal that previous
conclusions about the modes of operation of this type of kinematic dynamo must
be revised. The two known windows of dynamo action at low and high magnetic
Reynolds number, correspond to two distinct modes, both relying crucially on
the replenishing of the magnetic field near a discontinuity at the beta-type
stagnation points in the flow. One of these modes display double magnetic
structures that were previously found only to obscure the physics of the
dynamo: They turn out, however, to play an important part in the process of
amplifying the magnetic field. Invariant properties of the mode in the second
magnetic Reynolds number window support the case for the normal ABC flow as a
fast dynamo.Comment: Associated webpage, see http://www.astro.su.se/~dorch/dynamo
Evidence for an axion-like particle from PKS 1222+216?
The surprising discovery by MAGIC of an intense, rapidly varying emission in
the energy range 70 - 400 GeV from the flat spectrum radio quasar PKS 1222+216
represents a challenge for all interpretative scenarios. Indeed, in order to
avoid absorption of \gamma rays in the dense ultraviolet radiation field of the
broad line region (BLR), one is forced to invoke some unconventional
astrophysical picture, like for instance the existence of a very compact (r\sim
10^{14} cm) emitting blob at a large distance (R \sim10^{18} cm) from the jet
base. We offer the investigation of a scenario based on the standard blazar
model for PKS 1222+216 where \gamma rays are produced close to the central
engine, but we add the new assumption that inside the source photons can
oscillate into axion-like particles (ALPs), which are a generic prediction of
several extensions of the Standard Model of elementary particle interactions.
As a result, a considerable fraction of very-high-energy photons can escape
absorption from the BLR through the mechanism of photon-ALP oscillations much
in the same way as they largely avoid absorption from extragalactic background
light when propagating over cosmic distances in the presence of large-scale
magnetic fields in the nG range. In addition we show that the above MAGIC
observations and the simultaneous Fermi/LAT observations in the energy range
0.3 - 3 GeV can both be explained by a standard spectral energy distribution
for experimentally allowed values of the model parameters. In particular, we
need a very light ALP just like in the case of photon-ALP oscillations in
cosmic space. Moreover, we find it quite tantalizing that the most favorable
value of the photon-ALP coupling happens to be the same in both situations.
Although our ALPs cannot contribute to the cold dark matter, they are a viable
candidate for the quintessential dark energy. [abridged]Comment: 32 pages, 10 figures, accepted for publication in Physical Review
Coherent vortex structures and 3D enstrophy cascade
Existence of 2D enstrophy cascade in a suitable mathematical setting, and
under suitable conditions compatible with 2D turbulence phenomenology, is known
both in the Fourier and in the physical scales. The goal of this paper is to
show that the same geometric condition preventing the formation of
singularities - 1/2-H\"older coherence of the vorticity direction - coupled
with a suitable condition on a modified Kraichnan scale, and under a certain
modulation assumption on evolution of the vorticity, leads to existence of 3D
enstrophy cascade in physical scales of the flow.Comment: 15 pp; final version -- to appear in CM
Estimation of the susceptibility of a road network to shallow landslides with the integration of the sediment connectivity
Abstract. Landslides cause severe damage to the road network of the hit zone, in terms of
both direct (partial or complete destruction of a road or blockages) and
indirect (traffic restriction or the cut-off of a certain area) costs. Thus, the
identification of the parts of the road network that are more susceptible to
landslides is fundamental to reduce the risk to the population potentially
exposed and the financial expense caused by the damage. For these reasons,
this paper aimed to develop and test a data-driven model for the
identification of road sectors that are susceptible to being hit by shallow
landslides triggered in slopes upstream from the infrastructure. This model was
based on the Generalized Additive Method, where the function relating
predictors and response variable is an empirically fitted smooth function
that allows fitting the data in the more likely functional form, considering
also non-linear relations. This work also analyzed the importance, on the
estimation of the susceptibility, of considering or not the sediment
connectivity, which influences the path and the travel distance of the
materials mobilized by a slope failure until hitting a potential barrier such as a road.
The study was carried out in a catchment of northeastern Oltrepò Pavese
(northern Italy), where several shallow landslides affected roads in the last
8 years. The most significant explanatory variables were selected by a random
partition of the available dataset in two parts (training and test subsets),
100 times according to a bootstrap procedure. These variables (selected
80 times by the bootstrap procedure) were used to build the final
susceptibility model, the accuracy of which was estimated through a 100-fold
repetition of the holdout method for regression, based on the training and test
sets created through the 100 bootstrap model selection. The presented
methodology allows the identification, in a robust and reliable way, of the
most susceptible road sectors that could be hit by sediments delivered by
landslides. The best predictive capability was obtained using a model in
which the index of connectivity was also calculated according to a linear
relationship, was considered. Most susceptible road traits resulted to be
located below steep slopes with a limited height (lower than 50 m), where
sediment connectivity is high. Different land use scenarios were considered in
order to estimate possible changes in road susceptibility. Land use classes
of the study area were characterized by similar connectivity features. As a
consequence, variations on the susceptibility of the road network according
to different scenarios of distribution of land cover were limited. The
results of this research demonstrate the ability of the developed methodology
in the assessment of susceptible roads. This could give the managers of
infrastructure information about the criticality of the different road traits,
thereby allowing attention and economic budgets to be shifted towards the
most critical assets, where structural and non-structural mitigation measures
could be implemented
Juno spacecraft gravity measurements provide evidence for normal modes of Jupiter
The Juno spacecraft has been collecting data to shed light on the planet’s origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter’s zonal gravitational field. Here, we analyze 22 Juno’s gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10–50 cm/s at 900–1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions
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