Matrix-independent Fe isotope ratio determination in silicates using UV femtosecond laser ablation     

Grit Steinhoefel  Ingo Horn  Friedhelm von Blanckenburg 《Chemical Geology》2009,268(1-2):67-73

UV femtosecond laser ablation coupled to MC-ICP-MS provides a promising in situ tool to investigate elemental and isotope ratios by non-matrix-matched calibration. In this study, we investigate Fe isotope composition in siliceous matrices including biotite, hornblende, garnet, fayalite and forsterite (San Carlos Olivine), and an oceanic Fe–Mn crust using the iron reference material IRMM-014 for calibration. To test the accuracy of the laser ablation data, Fe isotope compositions were obtained independently by solution ICP-MS after chromatographic separation of Fe. Sample materials with low Cr content, i.e. biotite, hornblende, fayalite and the Fe–Mn crust, reveal δ^56/54Fe and δ^57/54Fe values that agree with those from solution ICP-MS data within the measured precision. For high Cr concentration (⁵⁴Cr/⁵⁴Fe >0.0001), i.e. in the garnet and forsterite sample, δ^56/54Fe and δ^57/54Fe values were derived from ⁵⁷Fe/⁵⁶Fe ratios as correction of the isobaric interference of ⁵⁴Cr on ⁵⁴Fe is unsatisfactory. This approach provides accurate results for both minerals. Moreover, the garnet crystal exhibits isotopic zonation with differences of 0.3‰ in δ^56/54Fe showing that substantial heterogeneities exist in high-temperature metamorphic minerals. Multiple analyses of homogeneous sample materials reveal a repeatability of 0.1‰ (2 SD) for δ^56/54Fe and 0.2‰ (2 SD) for δ^57/54Fe, respectively. This study adds to the observations of Horn et al. (2006) who have shown that the determination of Fe isotope ratios in various matrices including iron alloys, iron oxides and hydroxides, iron sulfide and iron carbonates can be performed with high accuracy and precision at high spatial resolution using UV femtosecond laser ablation ICP-MS. These results demonstrate that femtosecond laser ablation ICP-MS is a largely matrix-independent method, which provides a substantial advantage over commonly employed nanosecond laser ablation systems.  相似文献   

An improved method for computer simulation of geochemical neutron activation experiments     

M. K. Horn 《Mathematical Geology》1970,2(2):131-139

A computer method has been developed that simulates gammaray spectra of geochemical thermal neutron activation experiments. The input for the simulation includes the designation of rock type, neutron flux, sample volume and density, irradiation time, time of detection start, duration of monitoring, and number of analyzer channels. The output of the simulation includes either two-or threedimensional computer drawn plots of the resulting (simulated) gammaray spectra. The threedimensional plots (energy vs counts per sec vs time of detection) allow the investigator to observe the apparent appearance and disappearance of photo peaks, annihilation peaks, and pair production peaks of the various isotopes as a function of time. Various combinations of irradiation, delay, and detection times result in various spectral patterns. The resultant patterns accurately simulate the real activation experiments run under the same time conditions. The simulated spectra are useful for identifying peaks obtained from real spectra, helping in radiochemical separation decisions, and, in general, in designing the neutron activation experiment.  相似文献   

Crossing the racial divide: a spatial-ecological perspective of offenders in the City of Tshwane Metropolitan Municipality, South Africa   总被引：1，自引：0，他引：1  

Gregory D. Breetzke  André Carl Horn 《GeoJournal》2006,67(3):181-194

Post-apartheid South Africa has been plagued by an increase in crime and a concomitant increase in the number of incarcerated offenders. Researchers have postulated many proximate causes for the insidious increase in crime, including the vast socio-economic inequalities existing in the country, a remnant of apartheid-era policies and post-apartheid migrations. This article focuses on the neglected field of the environmental criminology of offenders. Following a spatial-ecological approach the relationship between various socio-economic variables and offender rates in the City of Tshwane Metropolitan Municipality in South Africa is modelled. The GIS-based methodological procedure includes a crime offender index, correlational analysis and principal components analysis and produced five factors: social status and income, family characteristics, unskilled earner, residential mobility and ageing population. These five factors, accounted for almost 75% of the variance in the offender index. The findings of our research reject race as a determinant of crime, and rather highlight existing and emerging socio-economic inequalities in the globally connected post-industrial city in regions of political instability and economic uncertainty and its relationship with crime and crime prevention.  相似文献   

Magnetically tilted accretion disks     

Susanne Horn  Wolfgang Kundt 《Astrophysics and Space Science》1989,158(2):205-221

Accretion disks around magnetized, compact stars are expected to be tilted near their inner edges, due to the stresses exerted by the corotating magnetosphere of the inclined central rotator. We reassess numerically the results obtained analytically by Lipunovet al. (1981). Four qualitatively different situations occur, depending on the relative orientations of the outer accretion disk, the spin of the central rotator, and its magnetic dipole axis. In at least two of them, the inner part of the disk is expected to be decomposed into massive, magnetically confined clumps.  相似文献   

Biogeography Of Mesoamerica Symposium     

Sally P. Horn 《The Professional geographer》1985,37(4):482-483

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Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment     

A.L. Graps  A.L. Lane  L.J. Horn  K.E. Simmons 《Icarus》1984,60(2):409-415

The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas—the innermost satellite—the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous materials near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.  相似文献   

Using Video and GIS to Measure Two-dimensional Water Surface Elevations in the Swash Zone     

Matthew Foote  & Diane Horn 《Transactions in GIS》2002,6(1):43-68

This paper describes initial research into the use of video imaging technologies to provide high-resolution hydrodynamic measurements of two-dimensional cross-shore swash water surfaces. Data collected from a laboratory-based video system and a manual digitisation technique using a desktop GIS are compared with the results from a widely used kinematic model of run-up and backwash. A GIS is then used to produce water surfaces using the kinematic model and then to compare the two graphically. The two-dimensional video technique is believed to provide a novel application of video data for measurement of the swash zone water surface.  相似文献   

Complex concentric granitoid intrusions in the coastal mobile belt,Espírito Santo,Brazil: The Santa Angélica Pluton — an example     

Dipl-Geol. P. Bayer  Dipl-Geol. R. Schmidt-Thomé  Prof. Dr. K. Weber-Diefenbach  Dipl-Geol. H. A. Horn 《International Journal of Earth Sciences》1987,76(2):357-371

The Brazilian Coastal Mobile Belt in southern Espírito Santo consists of Archean to Upper Proterozoic units which have been metamorphosed and deformed to a gneiss, migmatite and granulite-facies rock assemblage during Archean and Proterozoic tectono-thermal events.Several tectonic phases and an amphibolite-facies metamorphism are attributed to the Brasiliano-Event (680-450 Ma).Towards the end of the Brasiliano-Cycle diapirically ascending basic to intermediate and acid magmas intruded the lower crust, forming numerous concordant plutons.A model is presented for the Santa Angélica intrusion: A mantle derived basic magma, probably a fractionated alkali or transitional basalt, intruded the lower crust and induced anatectic melting and production of granitic melts. Intensive mechanical mixing of basic and granitic magma during ascent through buoyant and/or forced convection led to a wide variety of hybrid rocks. The structures suggest liquid-solid and liquid-liquid, or mushy-mushy interaction of the contrasting magmas. Different stages of mechanical mixing and homogenization are preserved, now representing »frozen-in« magma mixing features.

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Zusammenfassung Der Brasilianische Küstenfaltengürtel im südlichen Espírito Santo beinhaltet archaische bis oberproterozoische Einheiten, die durch tektono-thermale Ereignisse des Archaikums und Proterozoikums in hochdeformierte Gneise und Migmatite umgewandelt wurden.Dem Brasiliano-Ereignis (680–450 Ma) werden mehrere tektonische Phasen unter amphibolitfaziellen Metamorphosebedingungen zugeordnet.Gegen Ende des Brasiliano-Zyklus' erfolgte der diapirische Aufstieg basisch/intermediärer bis saurer Magmen in tiefere Krustenstockwerke unter Bildung konkordanter Plutone.Für den Santa Angélica Pluton wird ein Intrusionsmodell vorgestellt: Basisches Magma aus dem Mantel, das als Fraktionierungsprodukt eines Alkalioder Transitionalbasaltes angesehen wird, induziert anatektische Granitschmelzen in der Unterkruste. Intensive mechanische Durchmischung während des Aufstieges infolge »buoyant« und/oder »forced convection« führt zur Bildung eines weiten Spektrums von Hybridgesteinen. Die darin beobachteten Strukturen sind auf »Flüssig-Fest«- und »Flüssig-Flüssig«-Reaktionen zwischen den beiden verschiedenen Magmen zurückzuführen. Es sind die verschiedensten Stadien der mechanischen Durchmischung und Homogenisierung erhalten. Auf diese Weise ist die Magmenmischung heute in »eingefrorenem« Zustand erhalten.

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Resumen El cinturon orogénico costero brasilero en el sur del estado de Espírito Santo contiene unidades arcaicas hasta proterozoicas superiores, las cuales fueron transformados en gneises, migmatitas y rocas de la facies granulita y altamente deformadas por eventos téctono-termales del Arcaico y Proterozoico.Al Evento Brasiliano (680-450 Ma) se le atribuyen varias fases tectónicas bajo condiciones de metamorfismo de facies de anfibolita.Hacia el final del Ciclo Brasiliano se efectuó la ascensión diapírica de magmas básicos/intermedios a ácidos bajo la formación de varios plutones concordantes en profundos niveles de la corteza.Se presenta un modelo de intrusión para el plutón de Santa Angélica: Magma básico proveniente del manto induce magma granítico anatéctico en la corteza inferior. El magma básico es considerado un producto de cristallisación fraccionada de un basalto alcalino o transicional. La intensiva mezcla mecánica durante la ascensión a consecuencia de »buoyant« y/o »forced convection« condujo a la formación de rocas híbridas en su mas amplo espectro. Las estructuras observadas en estas rocas se deben a reacciones líquidosólido, líquido-líquido y »mushy-mushy« entre ambos magmas.Los mas diversos estadios de la mezcla mecánica y de la homogeneisación fueron conservados.Actualmente se encuentra el »magma-mixing« en un estadio de »congelamiento«.

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Espirito Santo , - . Brasiliano (680–450 Ma ) . - , , . Santa Angelica : , , ; «» (buoyant) / « » (forced convection) . « — » « — » , . « ».

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Biochemische Charakteristika des Sestons. Teil 2: Aktivität     

W. Stelzer  A. Benndorf  J. Benndorf  W. Horn 《洁净——土壤、空气、水》1977,5(2):135-140

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Zur Beeinflussung von Planktonpopulationen durch Butonat,Trichlorfon und Dichlorvos     

K. Grahl  H. Horn  R. Hallebach 《洁净——土壤、空气、水》1981,9(2):147-161

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