IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Some remarks about the degree-one deformation of the Earth

Abstract: SUMMARY The degree-one deformation of the Earth (and the induced discrepancy between the figure centre and the mass centre of the Earth) is computed using a theoretical approach (Love numbers formalism) at short timescales (where the Earth has an elastic behaviour) as well as at long timescales (where the Earth has a viscoelastic or quasi-fluid behaviour). For a Maxwell model of rheology, the degree-one relaxation modes associated with the viscoelastic Love numbers have been investigated: the M, mode does not exist and there is only one transition mode (instead of two) generated by a viscosity discontinuity. The translations at each interface of the incompressible layers of the earth model [surface, 670 km depth discontinuity, core-mantle boundary (CMB) and inner-core boundary (ICB)] are computed. They are elastic with an order of magnitude of about 1 mm when the excitation source is the atmospheric continental loading or a magnetic pressure acting at the CMB. They are viscoelastic when the earth is submitted to Pleistocene deglaciation, with an order of magnitude of about 1 m. In a quasi-fluid approximation (Newtonian fluid) because of the mantle density heterogeneity their order of magnitude is about 100 m (except for the ICB, which is in quasi-hydrostatic equilibrium at this timescale). Degree-one deformation has particular characteristics related to geodesy as well as to mechanics: it is related to the centre of mass of the Earth and is strongly dependent on the choice of the origin of the reference frame. We have first to provide some precise definitions concerning these reference frames. We consider an initial undeformed reference sphere that is radially stratified. The geometric centre of the external spherical surface is coincident with that of each layer, and is identical to the centre of mass of the whole sphere. For a degree-one deformation, the external surface of the planet remains spherical but is translated with respect to the initial configuration; similarly, each internal layer of the planet is translated but the centre of mass does not change and remains fixed relative to the centre of the initial reference sphere. We define the figure centre as the geometric centre of the translated external spherical surface. The geometric centres of the various internal layers move in the deformed configuration and are different to the figure centre; they do not play any geodetic role and will not be given precisely (but they may be easily computed). The sources of degree-one deformation are essentially internal or external redistributed loads (including the atmosphere and the oceans), that is without net change in the total mass of the Earth. With respect to the reference configuration, a load is the expression of a mass transfer from a given hemisphere to the other one. This is observed for atmospheric and oceanic loading. For solid-mass anomalies, such as ice sheets, cool internal zones, surface tectonics, etc., the conservation of the centre of mass imposes a displacement of the particles in a direction opposite to that of the mass anomalies. This displacement is distributed within the whole planet.

Analog finite impulse response filter

Abstract: According to one embodiment of the invention, a programmable finite impulse response (FIR) filter is implemented with differential isolation circuits to isolate parasitic capacitance from attenuating an output signal at both a first and second differential output terminals of the FIR filter. The FIR includes a summing circuit that provides operational advantages to the FIR filter.

Geometry, percolation and transport properties of fracture networks derived from line data

Abstract: SUMMARY In most geological instances, 2-D or 3-D fracture distributions are not available from field data. We show here that when data relative to fractures are collected along a line such as a road or a well, estimations can be given to the major geometrical properties of the corresponding fracture networks, such as the volumetric density of fractures, their percolation character and their macroscopic permeability. All these formulae are analytical and can be split into two parts; the first one can be derived from the measured data, while the second one requires some assumption on the lateral extension of the fractures and on their permeability. All these techniques are applied to fractures located in the Baget watershed. They are also validated on a granite block whose structure is fully known. Extensions are proposed for networks with variable permeabilities and polydisperse fractures.

Quantitative Measurement of Paramagnetic Fe3+ in Kaolinite

Abstract: A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

The mechanism of solution of aluminum oxide in MgSiO3 perovskite

Abstract: We report 27Al and 29Si Nuclear Magnetic Resonance (NMR) spectra, collected at magnetic fields of 14.1 and 18.8 Tesla on samples as small as 1 mg, for Al-bearing MgSiO3 perovskite synthesized at 26–28 GPa. For Al, we find a 1∶1 ratio of two types of sites: a symmetrical, octahedral site and a low symmetry, distorted site that is most likely to be Al in modifications of normally eight-coordinated Mg sites. A charge coupled substitution of 2 Al for one Si and one Mg cation is strongly supported as the predominant mechanism in this pressure range.