905 research outputs found
Regional trends and controlling factors of fatal landslides in Latin America and the Caribbean
A new data set of landslides that caused loss of life in Latin America and the
Caribbean in the 10-year period from 2004 and 2013 inclusive has been
compiled, providing new insight into the impact of landslides in this key
part of the world. This data set indicates that in the 10-year period a total
of 11 631 people lost their lives across the region in 611 landslides. The
geographical distribution of the landslides is highly heterogeneous, with
areas of high incidence in parts of the Caribbean (most notably Haiti),
Central America, Colombia, and southeast Brazil. There is significant interannual
variation in the number of landslides, with the El Niño/La Niña cycle
emerging as a key control. Our analysis suggests that on a continental scale
the mapped factors that best explain the observed distribution are
topography, annual precipitation and population density. On a national basis
we have compared the occurrence of fatality-inducing landslide occurrence
with the production of locally authored research articles, demonstrating that
there is a landslide research deficit in Latin America and the Caribbean.
Understanding better the mechanisms, distribution causes and triggers of
landslides in Latin America and the Caribbean must be an essential first step
towards managing the hazard
The effect of heavy ions on the dispersion properties of kinetic Alfv\'en waves in astrophysical plasmas
Context. Spacecraft measurements have shown Kinetic Alfv\'en Waves
propagating in the terrestrial magnetosphere at lower wavenormal angles than
predicted by linear Vlasov theory of electron-proton plasmas. To explain these
observations, it has been suggested that the abundant heavy ion populations in
this region may have strong, non-trivial effects that allow Alfv\'enic waves to
acquire right-handed polarization at lower angles with respect to the
background magnetic field, as in the case of typical electron-proton plasma.
Aims. We study the dispersion properties of Alfv\'enic waves in plasmas with
stationary phase-space distribution functions with different heavy ion
populations. Our extensive numerical analysis has allowed us to quantify the
role of the heavy ion components on the transition from the left-hand polarized
electromagnetic ion-cyclotron (EMIC) mode to the right-hand polarized kinetic
Alfv\'en wave (KAW) mode. Methods. We used linear Vlasov-Maxwell theory to
obtain the dispersion relation for oblique electromagnetic waves. The
dispersion relation of Alfv\'en waves was obtained numerically by considering
four different oxygen ion concentrations ranging between 0.0 and 0.2 for all
propagation angles, as a function of both the wavenumber and the plasma beta
parameter. Results. The inclusion of the heavy O+ ions is found to considerably
reduce the transition angle from EMIC to KAW both as a function of the wave
number and plasma beta. With increasing O+ concentrations, waves become more
damped in specific wavenumber regions. However, the inclusion of oxygen ions
may allow weakly damped KAW to effectively propagate at smaller wave-normal
angles than in the electron-proton case, as suggested by observations.Comment: 11 pages, 8 figure
Landslides induced by the 2010 Chile megathrust earthquake: a comprehensive inventory and correlations with geological and seismic factors
The 2010 Mw=8.8 Maule earthquake, which occurred in the subduction contact between the Nazca and the South American tectonic plates off the coast of Chile, represents an important opportunity to improve understanding of the distribution and controls for the generation of landslides triggered by large megathrust earthquakes in subduction zones. This paper provides the analysis of the comprehensive landslide inventory for the Maule earthquake between 32.5° S and 38.5° S°. In total 1226 landslides were mapped over a total area of c.120,500 km2 , dominantly disrupted slides. The total landslide volume is c. 10.6 Mm3. The events are unevenly distributed in the study area, the majority of landslides located in the Principal Andean Cordillera and a very constrained region near the coast on the Arauco Peninsula, forming landslide clusters. Statistical analysis of our database suggests that relief and lithology are the main geological factors controlling coseismic landslides, while the seismic factor with higher correlation with landslide occurrence is the ratio between peak horizontal and peak vertical ground accelerations. The results and comparison with other seismic events elsewhere suggest that the number of landslides generated by megathrust earthquakes is lower than events triggered by shallow crustal earthquakes by at least one or two orders of magnitude, which is very important to consider in future seismic landslide hazard analysis
Microtesting of micro-injection molded parts
With the growth and demand for microinjection
moulded thermoplastic parts becoming ever so popular, an increased need for determination and understanding of material mechanical properties at the micro-scale level is observed. One of the most widespread mechanical characterization experiments is the tensile test. The use of miniaturised tensile apparatus is therefore a need. In this work we developed a novel universal microtesting apparatus for performing mechanical tests in micro-mouldigs. The influence of injection moulding processing conditions on the
mechanical behaviour of Polypropylene (PP) and Methyl Methacrylate-Butadiene-Styrene (MABS) microinjection moulded specimens is studied
Development of a flexible pressure sensor for measurement of endotension
An aneurysm is a bulge in a weakened portion of a blood vessel wall much like the bulge that
results from over-inflating an inner tube. If left untreated, it may burst or rupture causing shock and/or death
due to massive blood loss. Endovascular aneurysm repair (EVAR) is one of the treatments available for aortic
aneurysms but, in spite of major advances in the operating techniques, complications still occur and lifelong
surveillance is recommended. Current surveillance protocols are based on medical imaging exams that
besides being expensive are time consuming. After a brief introduction to EVAR and its complications, this
paper reviews post-EVAR surveillance protocols and the current devices to measure endotension. Finally, are
introduced two new concepts for a flexible pressure sensor with passive telemetry.The first author wishes to thank FCT-Fundacao para a Ciencia e Tecnologia, in Portugal, for the financial support provided by the grant SFRH/BD/42967/2008.This work is supported by FCT under the project MIT-Pt/EDAM-EMD/0007/2008
Study of pressure sensors placement using an Abdominal Aortic Aneurysm (AAA) model
An Abdominal Aortic Aneurysm (AAA) model for post-EVAR (endovascular aneurysm repair)
analysis, including the blood flow, the bifurcated stent-graft, the aorta aneurysm wall motion and the stagnant
blood inside the aneurysm sac, was built and solved using a Fluid Structure Interaction (FSI) code. The
post-EVAR analysis aims to check the feasibility of EVAR surveillance using a remote pressure sensor, and
the study of the pressure variations inside the aneurysm sac to determine the best placement position for the
pressure sensor(s). First results suggest that aneurysm sac pressure measurement is feasible and can be a
good indicator of aneurysms post-EVAR evolution.This work is supported by FCT under the project MIT-Pt/EDAM-EMD/0007/2008
Chaos and Noise in a Truncated Toda Potential
Results are reported from a numerical investigation of orbits in a truncated
Toda potential which is perturbed by weak friction and noise. Two significant
conclusions are shown to emerge: (1) Despite other nontrivial behaviour,
configuration, velocity, and energy space moments associated with these
perturbations exhibit a simple scaling in the amplitude of the friction and
noise. (2) Even very weak friction and noise can induce an extrinsic diffusion
through cantori on a time scale much shorter than that associated with
intrinsic diffusion in the unperturbed system.Comment: 10 pages uuencoded PostScript (figures included), (A trivial
mathematical error leading to an erroneous conclusion is corrected
A Uniform Approximation for the Fidelity in Chaotic Systems
In quantum/wave systems with chaotic classical analogs, wavefunctions evolve
in highly complex, yet deterministic ways. A slight perturbation of the system,
though, will cause the evolution to diverge from its original behavior
increasingly with time. This divergence can be measured by the fidelity, which
is defined as the squared overlap of the two time evolved states. For chaotic
systems, two main decay regimes of either Gaussian or exponential behavior have
been identified depending on the strength of the perturbation. For perturbation
strengths intermediate between the two regimes, the fidelity displays both
forms of decay. By applying a complementary combination of random matrix and
semiclassical theory, a uniform approximation can be derived that covers the
full range of perturbation strengths. The time dependence is entirely fixed by
the density of states and the so-called transition parameter, which can be
related to the phase space volume of the system and the classical action
diffusion constant, respectively. The accuracy of the approximations are
illustrated with the standard map.Comment: 16 pages, 4 figures, accepted in J. Phys. A, special edition on
Random Matrix Theor
Characteristic distributions of finite-time Lyapunov exponents
We study the probability densities of finite-time or \local Lyapunov
exponents (LLEs) in low-dimensional chaotic systems. While the multifractal
formalism describes how these densities behave in the asymptotic or long-time
limit, there are significant finite-size corrections which are coordinate
dependent. Depending on the nature of the dynamical state, the distribution of
local Lyapunov exponents has a characteristic shape. For intermittent dynamics,
and at crises, dynamical correlations lead to distributions with stretched
exponential tails, while for fully-developed chaos the probability density has
a cusp. Exact results are presented for the logistic map, . At
intermittency the density is markedly asymmetric, while for `typical' chaos, it
is known that the central limit theorem obtains and a Gaussian density results.
Local analysis provides information on the variation of predictability on
dynamical attractors. These densities, which are used to characterize the {\sl
nonuniform} spatial organization on chaotic attractors are robust to noise and
can therefore be measured from experimental data.Comment: To be appear in Phys. Rev
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