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.

Amorphous materials: Properties, structure, and durability: Quantification of the kinetics of iron oxidation in silicate melts using Raman spectroscopy and assessment of the role of oxygen diffusion

Abstract: A diopside composition silicate glass containing 8 wt% Fe2O3 was prepared from melt equilibrated at 1500 °C and different redox conditions in the range log f O2 = −0.7 (air) to log f O2 = −6. The Fe2+/FeT was measured using Mossbauer spectroscopy. The Mossbauer data were used to calibrate Raman-scattering intensity variations of the same samples as a function of oxidation state, providing a simple empirical method to determine the redox ratio of this glass. This new Micro-Raman-based method has been used to quantify redox profiles across partially oxidized samples. No significant Fe2+/FeT gradients were found (values were constant from the surface to the center), although the average oxidation state was observed to increase as a function of time. The former result contrasts with O self-diffusion profiles measured with the ion microprobe on diopside glasses prepared at similar experimental conditions, for which strong isotopic gradients were found at the sample scale (corresponding to a self-diffusion coefficient for O at 1450 °C of 1 × 10−11 m2/s). Local oxidation of Fe in the melt therefore appears to occur independently of long-range diffusion of O from the sample surface. A mechanism capable of explaining this observation is proposed based upon the fact that redox gradients result in the generation of electromotive forces. This results in a powerful driving force to wipe out redox gradients through fast electron transfer. However, migration of electrons alone would result in unfavorable charge gradients, in particular at the surface of the sample. At the temperature of our experiments, the local mobility of O is apparently sufficient to compensate the migration of electrons. Despite rapid charge transfer, the bulk oxidation state of our sample is nevertheless limited by the addition of external O. The time dependence of the bulk oxidation state of our samples can be modeled by a constant rate of O diffusion across the interface of 2.1 10−7 m/s. However, the bulk oxidation state of the liquid is also found to be concordant with variations calculated assuming that diffusion of O is the rate-limiting mechanism. This apparent paradox may be explained if the characteristic time-scales of O self-diffusion in the sample volume and of O incorporation at the sample surface are similar. We suggest that this is indeed the case, given that both of these processes are likely to be limited by the frequency of bond-breaking and bond-forming events in the liquid.

Quantitative analysis of ammonium in biotite using infrared spectroscopy

Abstract: The present paper provides a calibration of the Beer-Lambert law allowing the determination of the ammonium (NH4) content of biotite using infrared (IR) spectroscopy. Single biotite crystals were analyzed by Fourier Transform Infrared spectroscopy. Using a linear correlation between the NH4 infrared absorption band intensity and the NH4 content as determined by vacuum techniques, the NH4 molar absorption coeffi cient at 1430 cm -1 was found to be 441 ± 31 L/mol·cm. After having calibrated the biotite thickness to Si-O absorption band, the NH4 content of biotite can be calculated directly from its IR spectrum by the relation: (NH4 1249 , A 1430 , and A 2395 are absorbances corresponding to wavenumbers 1249 cm -1 (Si-O vibration peak), 1430 cm -1 (NH4 bending), and 2395 cm -1 (spectrum baseline), respectively. The analysis of biotites having different chemical compositions suggests that, to a fi rst approximation, the calibration is independent of biotite chemical composition. An infrared determination of NH4 partitioning between muscovite and biotite coexisting in the same rocks shows good agreement with results of previous studies and further validates the method.

Anatomy of a laminar starting thermal plume at high Prandtl number

Abstract: We present an experimental study of the dynamics of a plume generated from a small heat source in a high Prandtl number fluid with a strongly temperature-dependent viscosity. The velocity field was determined with particle image velocimetry, while the temperature field was measured using differential interferometry and thermochromic liquid crystals. The combination of these different techniques run simultaneously allows us to identify the different stages of plume development, and to compare the positions of key-features of the velocity field (centers of rotation, maximum vorticity locations, stagnation points) respective to the plume thermal anomaly, for Prandtl numbers greater than 103. We further show that the thermal structure of the plume stem is well predicted by the constant viscosity model of Batchelor (Q J R Met Soc 80: 339–358, 1954) for viscosity ratios up to 50.

Contemporaneous convective and collapsing eruptive dynamics: The transitional regime of explosive eruptions

Abstract: [1] Two contrasting eruptive regimes have been classically postulated to describe the behavior of explosive eruptions: convective and collapsing. Early studies have recognized that many eruptions evolve from the first to the second regime and have assumed the existence of a sharp boundary between them. Consequently, the dynamics of such transition has never been investigated in detail. Here, we present results of integrated deposit analyses and numerical simulations which demonstrate univocally that both dynamics can, and often do, coexist for hours in a new intermediate transitional regime of explosive eruptions. The study elucidates the features of the new regime in terms of mass partitioning, pyroclastic current dynamics and interplay among convective and collapsing styles.