8,895 research outputs found
Earthquake-induced ground failures in Italy from a reviewed database
Abstract. A database (Italian acronym CEDIT) of earthquake-induced ground failures in Italy is presented, and the related content is analysed. The catalogue collects data regarding landslides, liquefaction, ground cracks, surface faulting and ground changes triggered by earthquakes of Mercalli epicentral intensity 8 or greater that occurred in the last millennium in Italy. As of January 2013, the CEDIT database has been available online for public use (http://www.ceri.uniroma1.it/cn/gis.jsp ) and is presently hosted by the website of the Research Centre for Geological Risks (CERI) of the Sapienza University of Rome. Summary statistics of the database content indicate that 14% of the Italian municipalities have experienced at least one earthquake-induced ground failure and that landslides are the most common ground effects (approximately 45%), followed by ground cracks (32%) and liquefaction (18%). The relationships between ground effects and earthquake parameters such as seismic source energy (earthquake magnitude and epicentral intensity), local conditions (site intensity) and source-to-site distances are also analysed. The analysis indicates that liquefaction, surface faulting and ground changes are much more dependent on the earthquake source energy (i.e. magnitude) than landslides and ground cracks. In contrast, the latter effects are triggered at lower site intensities and greater epicentral distances than the other environmental effects
The Structure of Isothermal, Self-gravitating Gas Spheres for Softened Gravity
A theory for the structure of isothermal, self-gravitating gas spheres in
pressure equilibrium in a softened gravitational field is developed. The one
parameter spline softening proposed by Hernquist & Katz (1989) is used. We show
that the addition of this extra scale parameter implies that the set of
equilibrium solutions constitute a one-parameter family, rather than the one
and only one isothermal sphere solution for Newtonian gravity. We demonstrate
the perhaps somewhat surprising result that for any finite choice of softening
length and temperature, it is possible to deposit an arbitrarily large mass of
gas in pressure equilibrium and with a non-singular density distribution inside
of r_0 for any r_0 > 0. The theoretical predictions of our models are compared
with the properties of the small, massive, quasi-isothermal gas clumps which
typically form in numerical Tree-SPH simulations of 'passive' galaxy formation
of Milky Way sized galaxies. We find reasonable agreement despite the neglect
of rotational support in the models. We comment on whether the hydrodynamical
resolution in our numerical simulation of galaxy formation is sufficient, and
finally we conclude that one should be cautious, when comparing results of
numerical simulations involving gravitational softening and hydrodynamical
smoothing, with reality.Comment: 22 pages Latex + 12 figure
Casimir energy and black hole pair creation in Schwarzschild-de Sitter spacetime
Following the subtraction procedure for manifolds with boundaries, we
calculate by variational methods, the Schwarzschild-de Sitter and the de Sitter
space energy difference. By computing the one loop approximation for TT tensors
we discover the existence of an unstable mode even for the non-degenerate case.
This result seems to be in agreement with the sub-maximal black hole pair
creation of Bousso-Hawking. The instability can be eliminated by the boundary
reduction method. Implications on a foam-like space are discussed.Comment: 19 pages,RevTeX with package epsf and four eps figures. Added other
references. Accepted for publication in Classical and Quantum Gravit
Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes
This paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F gâ1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F gâ1), electrochemically reduced GO (EC-rGO) (27.6 F gâ1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F gâ1)-based electrodes.© 2013, Springer Science+Business Media Dordrecht
Casimir stress on parallel plates in de Sitter space
The Casimir stress on two parallel plates in de Sitter background for
massless scalar field satisfying Robin boundary conditions on the plates is
calculated. The metric is written in conformally flat form to make maximum use
of the Minkowski space calculations. Different cosmological constants are
assumed for the space between and outside of the plates to have general results
applicable to the case of domain wall formations in the early universe.Comment: 6 page
Casimir Forces for Robin Scalar Field on Cylindrical Shell in de Sitter Space
The Casimir stress on a cylinderical shell in background of conformally flat
space-time for massless scalar field is investigated. In the general case of
Robin (mixed) boundary condition formulae are derived for the vacuum
expectation values of the energy-momentum tensor and vacuum forces acting on
boundaries. The special case of the dS bulk is considered then different
cosmological constants are assumed for the space inside and outside of the
shell to have general results applicable to the case of cylindrical domain wall
formations in the early universe.Comment: 10 pages, no figur
Casimir effect for scalar fields with Robin boundary conditions in Schwarzschild background
The stress tensor of a massless scalar field satisfying Robin boundary
conditions on two one-dimensional wall in two-dimensional Schwarzschild
background is calculated. We show that vacuum expectation value of stress
tensor can be obtained explicitly by Casimir effect, trace anomaly and Hawking
radiation.Comment: 10 pages, no figure
Dynamical Generation of Spacetime Signature by Massive Quantum Fields on a Topologically Non-Trivial Background
The effective potential for a dynamical Wick field (dynamical signature)
induced by the quantum effects of massive fields on a topologically non-trivial
dimensional background is considered. It is shown that when the radius of
the compactified dimension is very small compared with (where
is a proper-time cutoff), a flat metric with Lorentzian signature is
preferred on . When the compactification radius
becomes larger a careful analysis of the 1-loop effective potential indicates
that a Lorentzian signature is preferred in both and and that these
results are relatively stable under metrical perturbations
Dynamical Determination of the Metric Signature in Spacetime of Nontrivial Topology
The formalism of Greensite for treating the spacetime signature as a
dynamical degree of freedom induced by quantum fields is considered for
spacetimes with nontrivial topology of the kind , for varying . It is shown that a dynamical origin for the Lorentzian
signature is possible in the five-dimensional space with small torus radius (periodic boundary conditions), as well as in
four-dimensional space with trivial topology. Hence, the possibility exists
that the early universe might have been of the Kaluza-Klein type, \ie
multidimensional and of Lorentzian signature.Comment: 10 pages, LaTeX file, 4 figure
The evolution of gravitationally unstable protoplanetary disks: fragmentation and possible giant planet formation
We carry out a large set of very high resolution, three dimensional smoothed
particle hydrodynamics (SPH) simulations describing the evolution of
gravitationally unstable gaseous protoplanetary disks. We consider a broad
range of initial disk parameters. Disk masses out to 20 AU range from 0.075 to
0.125 , roughly consistent with the high-end of the mass
distribution inferred for disks around T Tauri stars. The initial disks span
minimum parameters between 0.8 and 2, with most models being around . The disks are evolved assuming either a locally isothermal equation of
state or an adiabatic equation of state with varying . When
overdensities above a specific threshold appear as a result of gravitational
instability in a locally isothermal calculation, the equation of state is
switched to adiabatic to account for the increased optical depth. We show that
when a disk has a minimum parameter less than 1.4 strong trailing spiral
instabilities, typically three or four armed modes, form and grow until
fragmentation occurs along the arms after about 5 mean disk orbital times. The
resulting clumps contract quickly to densities several orders of magnitude
higher than the initial disk density, and the densest of them survive even
under adiabatic conditions. These clumps are stable to tidal disruption and
merge quickly, leaving 2-3 protoplanets on fairly eccentric orbits (the mean
eccentricity being around 0.2) with masses between 0.7 and more than , well in agreement with those of detected extrasolar planets.after
years. Fragmentation is not strongly dependent on whether the disk
starts from a marginally unstable state or gradually achieves it, as shown by a
test where the disk gradually achieves the critical by growing in mass.Comment: 48 pages, 18 figures, submitted to ApJ. Abstract considerably
reduced, see paper. PostScript file including hi-res figures and movies of
the simulations can be dowloaded at http://www.astro.washington.edu/mayer
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