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.

Pre‐ and syn‐eruptive geochemistry of volcanic gases from Soufriere Hills of Montserrat, West Indies

Abstract: Soufriere Hills fumaroles contained magma-derived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal composition. Chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at Galway's Soufriere, the most active fumarolic field. Hydrothermal buffering of the fumaroles has been favoured by their remote location (1–2 km) from the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater. High temperature (720°C) gas collected from the extruding lava dome in Feb. 1996 was chemically and isotopically representative of the magmatic gas stream. Its composition allows assessment of average eruptive fluxes of H2O, CO2 and HCl which require the degassing of only 2.5–3 times more magma than erupted.

Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems

Abstract: –Raman spectra were acquired on a series of natural and synthetic sulfideminerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr 2 FeS 4 ). Natural samplescome from three enstatite chondrites, three aubrites, and one anomalous ungroupedenstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) tocomplex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285,360, and 470 cm 1 for the Mg-rich sulfides; at 185, 205, and 285 cm 1 for the Ca-richsulfides; at 250, 370, and 580 cm 1 for the Mn-rich sulfides; at 255, 290, and 365 cm 1 for the Cr-rich sulfides; and at 290 and 335 cm 1 for troilite with, occasionally, an extrapeak at 240 cm 1 . A peak at 160 cm 1 is present in all Raman spectra and cannot beused to discriminate between the different sulfide compositions. According to grouptheory, none of the cubic monosulfides oldhamite, niningerite, or alabandite shouldpresent first-order Raman spectra because of their ideal rocksalt structure. The occurrenceof broad Raman peaks is tentatively explained by local breaking of symmetry rules.Measurements compare well with the infrared frequencies calculated from first-principlescalculations. Raman spectra arise from activation of certain vibrational modes due toclustering in the solid solutions or to coupling with electronic transitions in semiconductorsulfides.INTRODUCTIONRecently, particular effort was put intounderstanding the occurrence of sulfur-rich phases inmagmatic systems and meteorites as well as in materialscience and metallurgy (e.g., Sinyakavo and Kosyakov2001; Holzheid and Grove 2002; Keil 2007; Liu et al.2007). The degassing of sulfur from volcanoes plays animportant role in the present and past atmosphereproperties, and in the geochemical cycle of sulfur in theEarth system (e.g., Farquhar et al. 2002; Moretti andOttonello 2005; Liu et al. 2007). Sulfur can take a largenumber of oxidation states, from 2 to 6+, and itoccurs in several gaseous and crystallized forms.Because of this large range of possible oxidation states,it remains a difficult element to study.The sulfide compounds are important phases inmeteorites (e.g., Keil 1989, 2007). Specifically, the majorpart of sulfur in meteorites is found either in troilite;FeS; or in other sulfides like oldhamite, CaS,

Giant nonadiabatic effects in layer metals: raman spectra of intercalated graphite explained.

Abstract: The occurrence of nonadiabatic effects in the vibrational properties of metals has been predicted since the 1960s, but hardly confirmed experimentally. We report the first fully ab initio calculations of nonadiabatic frequencies of a number of conventional (hcp Ti and Mg) and layered metals (MgB2, CaC6, and other intercalated graphites). Nonadiabatic effects can be spectacularly large (up to 30% of the phonon frequencies) in both cases, but they can only be experimentally observed in the Raman spectra of layered compounds. In layered metals nonadiabatic effects are crucial to explaining the observed Raman shifts and linewidths. Moreover, we show that those quantities can be used to extract the electron momentum-relaxation time.