Q-factor inversion using reconstructed source spectral consistency

Seismic waves propagating in an anelastic medium undergo phase and amplitude distortions. Although these effects may be compensated for during imaging processes, a background [Formula: see text]-model is generally required for their successful application. We have developed a new approach to the [Formula: see text]-estimation problem, which is fundamentally related to the basic physical principle of time reversal. It is based on back-propagating recorded traces to their known source location using the reverse tomographic equation. This equation is a ray approximation of viscoelastic wave propagation. It is applied assuming a known and correct velocity model. We subsequently measure consistency between spectral shapes of traces that were back-propagated using the tomographic equation. We formulate an inverse problem using this consistency as an objective function. In conventional inversion, on the contrary, the discrepancy between modeled and recorded data, or some data characteristics, is minimized. The inverse problem is solved by ant-colony optimization, a global optimization approach, to avoid local minima present in the objective function. This method does not require knowledge of the source function and uses the full spectrum rather than its parametric reduction. Through synthetic and field cross-hole examples, we illustrate its accuracy and sensitivity in inverting for complex attenuation models. In the synthetic case, we also compare reconstructed source consistency with the conventional centroid frequency shift objective function. The latter displays poor resolution when recovering complex [Formula: see text] structures. We determine that the reconstructed source-consistency approach should be used as a part of an iterative workflow, possibly yielding initial models for a joint velocity and [Formula: see text] inversion.

Self-organization into ferroelectric and antiferroelectric crystals via the interplay between particle shape and dipolar interaction

Ferroelectricity and antiferroelectricity are widely seen in various types of condensed matter and are of technological significance not only due to their electrical switchability but also due to intriguing cross-coupling effects such as electro-mechanical and electro-caloric effects. The control of the two types of dipolar order has practically been made by changing the ionic radius of a constituent atom or externally applying strain for inorganic crystals and by changing the shape of a molecule for organic crystals. However, the basic physical principle behind such controllability involving crystal–lattice organization is still unknown. On the basis of a physical picture that a competition of dipolar order with another type of order is essential to understand this phenomenon, here we develop a simple model system composed of spheroid-like particles with a permanent dipole, which may capture an essence of this important structural transition in organic systems. In this model, we reveal that energetic frustration between the two types of anisotropic interactions, dipolar and steric interactions, is a key to control not only the phase transition but also the coupling between polarization and strain. Our finding provides a fundamental physical principle for self-organization to a crystal with desired dipolar order and realization of large electro-mechanical effects.

Multi-Photon Excitation Microscopy: An Old Idea in Quantum Theory Applied to Modern Scientific Problems

Multi-photon excitation microscopy provides attractive advantages over confocal microscopy for three-dimensionalry resolved fluorescence imaging and photochemistry. The most commonly used type of multi-photon excitation is two-photon excitation where simultaneous absorption of two photons leads to a single quantitized event. The powerful advantages of using two-photon excitation microscopy arise from the basic physical principle that the absorption depends on the square of the excitation intensity. In practice, two-photon excitation is generated by focusing a single pulsed laser through the microscope. As the laser beam is focused, the photons become more crowded, but the only place at which they are crowded enough to generate an appreciable amount of two-photon excitation is at the focus. Above and below the focus, the photon density is not high enough for two of them to interact with a single fluorophore at the same time. This dramatic difference between confocal and two-photon excitation microscopy is shown in Fig. 1.

Berichte: Mach's Principle - A Critical Review

After a short historical introduction it is discussed how far Mach's principle is incorporated into general relativity. The possible role of Mach's principle as a selection rule for the solutions of Einstein's field equations is summarized. Then follows a discussion of Math's principle in theories of gravitation other than Einstein's, mainly the Brans-Dicke theory. Finally the experiments on the isotropy of inertial mass and their consequence for Mach's principle are described. The conclusion is that Mach's principle, though an extremely stimulating thought, has at present little claim to be a basic physical principle.