281 research outputs found
Tilt effects on moment tensor inversion in the near field of active volcanoes
Dynamic tilts (rotational motion around horizontal axes) change the projection of local gravity onto the horizontal components of seismometers. This causes sensitivity of these components to tilt, especially at low frequencies. We analyse the consequences of this effect onto moment tensor inversion for very long period (vlp) events in the near field of active volcanoes on the basis of synthetic examples using the station distribution of a real deployed seismic network and the topography of Mt. Merapi volcano (Java, Indonesia). The examples show that for periods in the vlp range of 10-30 s tilt can have a strong effect on the moment tensor inversion, although its effect on the horizontal seismograms is significant only for few stations. We show that tilts can be accurately computed using the spectral element method and include them in the Green's functions. The (simulated) tilts might be largely influenced by strain-tilt coupling (stc). However, due to the frequency dependence of the tilt contribution to the horizontal seismograms, only the largest tilt signals affect the source inversion in the vlp frequency range. As these are less sensitive to stc than the weaker signals, the effect of stc can likely be neglected in this application. In the converse argument, this is not necessarily true for longer periods, where the horizontal seismograms are dominated by the tilt signal and rotational sensors would be necessary to account for it. As these are not yet commercially available, this study underlines the necessity for the development of such instrument
Horizontal rotation signals detected by "G-Pisa" ring laser for the Mw=9.0, March 2011, Japan earthquake
We report the observation of the ground rotation induced by the Mw=9.0, 11th
of March 2011, Japan earthquake. The rotation measurements have been conducted
with a ring laser gyroscope operating in a vertical plane, thus detecting
rotations around the horizontal axis. Comparison of ground rotations with
vertical accelerations from a co-located force-balance accelerometer shows
excellent ring laser coupling at periods longer than 100s. Under the plane wave
assumption, we derive a theoretical relationship between horizontal rotation
and vertical acceleration for Rayleigh waves. Due to the oblique mounting of
the gyroscope with respect to the wave direction-of-arrival, apparent
velocities derived from the acceleration / rotation rate ratio are expected to
be always larger than, or equal to the true wave propagation velocity. This
hypothesis is confirmed through comparison with fundamental-mode, Rayleigh wave
phase velocities predicted for a standard Earth model.Comment: Accepted for publication in Journal of Seismolog
Influence of electron correlations on ground-state properties of III-V semiconductors
Lattice constants and bulk moduli of eleven cubic III-V semiconductors are
calculated using an ab initio scheme. Correlation contributions of the valence
electrons, in particular, are determined using increments for localized bonds
and for pairs and triples of such bonds; individual increments, in turn, are
evaluated using the coupled cluster approach with single and double
excitations. Core-valence correlation is taken into account by means of a core
polarization potential. Combining the results at the correlated level with
corresponding Hartree-Fock data, we obtain lattice constants which agree with
experiment within an average error of -0.2%; bulk moduli are accurate to +4%.
We discuss in detail the influence of the various correlation contributions on
lattice constants and bulk moduli.Comment: 4 pages, Latex, no figures, Phys. Rev. B, accepte
Not all parents are equal for MO-CMA-ES
International audienceThe Steady State variants of the Multi-Objective Covariance Matrix Adaptation Evolution Strategy (SS-MO-CMA-ES) generate one offspring from a uniformly selected parent. Some other parental selection operators for SS-MO-CMA-ES are investigated in this paper. These operators involve the definition of multi-objective rewards, estimating the expectation of the offspring survival and its Hypervolume contribution. Two selection modes, respectively using tournament, and inspired from the Multi-Armed Bandit framework, are used on top of these rewards. Extensive experimental validation comparatively demonstrates the merits of these new selection operators on unimodal MO problems
Opinion: A critical evaluation of the evidence for aerosol invigoration of deep convection
Deep convective updraft invigoration via indirect effects of increased aerosol number concentration on cloud microphysics is frequently cited as a driver of correlations between aerosol and deep convection properties. Here, we critically evaluate the theoretical, modeling, and observational evidence for warm- and cold-phase invigoration pathways. Though warm-phase invigoration is plausible and theoretically supported via lowering of the supersaturation with increased cloud droplet concentration in polluted conditions, the significance of this effect depends on substantial supersaturation changes in real-world convective clouds that have not been observed. Much of the theoretical support for cold-phase invigoration depends on unrealistic assumptions of instantaneous freezing and unloading of condensate in growing, isolated updrafts. When applying more realistic assumptions, impacts on buoyancy from enhanced latent heating via fusion in polluted conditions are largely canceled by greater condensate loading. Many foundational observational studies supporting invigoration have several fundamental methodological flaws that render their findings incorrect or highly questionable. Thus, much of the evidence for invigoration has come from numerical modeling, but different models and setups have produced a vast range of results. Furthermore, modeled aerosol impacts on deep convection are rarely tested for robustness, and microphysical biases relative to observations persist, rendering many results unreliable for application to the real world. Without clear theoretical, modeling, or observational support, and given that enervation rather than invigoration may occur for some deep convective regimes and environments, it is entirely possible that the overall impact of cold-phase invigoration is negligible. Substantial mesoscale variability of dominant thermodynamic controls on convective updraft strength coupled with substantial updraft and aerosol variability in any given event are poorly quantified by observations and present further challenges to isolating aerosol effects. Observational isolation and quantification of convective invigoration by aerosols is also complicated by limitations of available cloud condensation nuclei and updraft speed proxies, aerosol correlations with meteorological conditions, and cloud impacts on aerosols. Furthermore, many cloud processes, such as entrainment and condensate fallout, modulate updraft strength and aerosol–cloud interactions, varying with cloud life cycle and organization, but these processes remain poorly characterized. Considering these challenges, recommendations for future observational and modeling research related to aerosol invigoration of deep convection are provided.</p
Electron correlations for ground state properties of group IV semiconductors
Valence energies for crystalline C, Si, Ge, and Sn with diamond structure
have been determined using an ab-initio approach based on information from
cluster calculations. Correlation contributions, in particular, have been
evaluated in the coupled electron pair approximation (CEPA), by means of
increments obtained for localized bond orbitals and for pairs and triples of
such bonds. Combining these results with corresponding Hartree-Fock (HF) data,
we recover about 95 % of the experimental cohesive energies. Lattice constants
are overestimated at the HF level by about 1.5 %; correlation effects reduce
these deviations to values which are within the error bounds of this method. A
similar behavior is found for the bulk modulus: the HF values which are
significantly too high are reduced by correlation effects to about 97 % of the
experimental values.Comment: 22 pages, latex, 2 figure
Quantum computation with trapped polar molecules
We propose a novel physical realization of a quantum computer. The qubits are
electric dipole moments of ultracold diatomic molecules, oriented along or
against an external electric field. Individual molecules are held in a 1-D trap
array, with an electric field gradient allowing spectroscopic addressing of
each site. Bits are coupled via the electric dipole-dipole interaction. Using
technologies similar to those already demonstrated, this design can plausibly
lead to a quantum computer with qubits, which can perform CNOT gates in the anticipated decoherence time of s.Comment: 4 pages, RevTeX 4, 2 figures. Edited for length and converted to
RevTeX, but no substantial changes from earlier pdf versio
Measurement of p + d -> 3He + eta in S(11) Resonance
We have measured the reaction p + d -> 3He + eta at a proton beam energy of
980 MeV, which is 88.5 MeV above threshold using the new ``germanium wall''
detector system. A missing--mass resolution of the detector system of 2.6% was
achieved. The angular distribution of the meson is forward peaked. We found a
total cross section of (573 +- 83(stat.) +- 69(syst.))nb. The excitation
function for the present reaction is described by a Breit Wigner form with
parameters from photoproduction.Comment: 8 pages, 2 figures, corrected typos in heade
The geometry of nonlinear least squares with applications to sloppy models and optimization
Parameter estimation by nonlinear least squares minimization is a common
problem with an elegant geometric interpretation: the possible parameter values
of a model induce a manifold in the space of data predictions. The minimization
problem is then to find the point on the manifold closest to the data. We show
that the model manifolds of a large class of models, known as sloppy models,
have many universal features; they are characterized by a geometric series of
widths, extrinsic curvatures, and parameter-effects curvatures. A number of
common difficulties in optimizing least squares problems are due to this common
structure. First, algorithms tend to run into the boundaries of the model
manifold, causing parameters to diverge or become unphysical. We introduce the
model graph as an extension of the model manifold to remedy this problem. We
argue that appropriate priors can remove the boundaries and improve convergence
rates. We show that typical fits will have many evaporated parameters. Second,
bare model parameters are usually ill-suited to describing model behavior; cost
contours in parameter space tend to form hierarchies of plateaus and canyons.
Geometrically, we understand this inconvenient parametrization as an extremely
skewed coordinate basis and show that it induces a large parameter-effects
curvature on the manifold. Using coordinates based on geodesic motion, these
narrow canyons are transformed in many cases into a single quadratic, isotropic
basin. We interpret the modified Gauss-Newton and Levenberg-Marquardt fitting
algorithms as an Euler approximation to geodesic motion in these natural
coordinates on the model manifold and the model graph respectively. By adding a
geodesic acceleration adjustment to these algorithms, we alleviate the
difficulties from parameter-effects curvature, improving both efficiency and
success rates at finding good fits.Comment: 40 pages, 29 Figure
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