Partitioning of Ni2+, Co2+, Fe2+, Mn2+ and Mg2+ between olivine and silicate melts: compositional dependence of partition coefficient

Partitioning of Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺ between olivine and silicate melts has been determined near the join (Mg_0.5·-Fe_0.5)₂SiO₄-K₂O 4SiO₂ and for seven different basaltic compositions. The experiments were made at 1 atm total pressure, 1500-1100°C, and under moderate to reducing oxygen fugacities. The concentration factor, defined as K^MO = (MO)^ol/(MO)^liq (molar ratio), increases markedly for all the cations studied as the olivine component of the liquid decreases. Much of the increase in K^MO is considered as due to the compositional effect of the coexisting liquid: the temperature effect on K^MO is probably opposite to the compositional effect (K^MO decreases as temperature decreases).The partition coefficient K^MO-MgO = (MO/MgO)^ol/(MO/MgO)^liq for the reaction, M_ol²⁺ + Mg_liq²⁺ = M_liq²⁺ + Mg_ol²⁺. is relatively constant over a wide range of SiO₂ content of the liquid, except in the case of Ni²⁺. The partition coefficients have similar ranges both in synthetic and natural rock systems: K^NiO-MgO = 1.8–3.0, K^CoO-MgO = 0.6–0.8, K^FeO-MgO = 0.27–0.38, and K^MnO-MgO = 0.23–0.32. There is a systematic variation in the partition coefficient K^MO-MgO with the composition of liquid; K^MO-MgO increases with increasing SiO₂ content of melt. The partition coefficients for Co²⁺, Fe²⁺ and Mn²⁺ are useful to test the equilibration of olivine with magma of a wide compositional range.     

Resonance capacity method for earthquake response analysis of hysteretic structures

The Resonance Capacity Method is proposed for the earthquake response analysis of hysteretic structures. Resonance Capacity is a physical quantity of structures which is related to the hysteretic energy absorbed by structures in one cycle and is equated to the acceleration, velocity and displacement amplitudes α₀, d₀ and d₀ of earthquake ground motions at resonance.¹ According to the idealized trapezoidal approximation of earthquake ground motions in the logarithmic period–velocity plane as proposed by Veletsos and Newmark,⁸ the Resonance Capacity property applies in each period range, short, medium and long, where α₀, v₀ and d₀ respectively are approximately constant. In the medium range of periods, the energy dissipated in hysteretic loops and the deformation amplitudes of a single-degree system with elasto–plastic force–deformation relationships are calculated for the case of El Centro 1940, 18 May earthquake, by this Resonance Capacity Method. The result is compared with results from conventional numerical response analyses obtained by Berg and Thomaides,¹⁴ Kato and Akiyama¹² and Veletsos and Newmark,⁸ and the general agreement is seen to be good. Therefore, it may be possible to apply this Resonance Capacity Method over the entire range of periods. By means of this method the earthquake response analysis of hysteretic systems can be performed easily, and the hysteretic energy and fatigue characteristics of structures may be taken into account directly, up to the point of fracture.     

Fast Oxidation Reaction of Nitrite by Dissolved Oxygen in the Freezing Process in the Tropospheric Aqueous Phase

Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10^-10 mol dm^-3), ca. 10 hr in oxidation by H₂O₂ (2×10^-4 mol dm^-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase.     

ESR diagram: a method to distinguish vitrinite macerals

It has been found that samples consisting of a homogeneous vitrinite show a good ESR correlation of spin concentration with geothermal parameters and that a graph of ESR line width vs g-value can be useful in the identification of the maceral and the determination of the coalification rank.     

The theory of the nutation for the rigid earth model at the second order

We perform a complete reconstruction of the series of the nutation for a rigid Earth model with the use of the very accurate theories ELP2000 and VSOP82 for the motion of the Moon and the planets respectively, in such a way that all the individual contributions up to 0.005 mas should be taken. This implies the introduction of the planetary effects, of the influence of second-order parts of the potential of the Earth (J3, triaxiality), and some improvements due to an extension of the theory at the second order. All this increase notably the number of coefficients to be taken in account, and modifies also in a significant way the value of some of them.     

The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter

In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 ±0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 ±2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.     

From an initial transient-state to a steady-state in metamorphic reactions: An experimental approach in the system dolomite-quartz-H2O

Abstract We carried out hydrothermal experiments in the system dolomite‐quartz‐H₂O to track the temporal change in reaction rates of simultaneous reactions during the development of reaction zones. Two types of configurations for the starting materials were prepared: dolomite single crystals + quartz powder + water and quartz single crystals + dolomite powder + water, both sealed separately in gold capsules. Runs at 0.1GPa and 600°C with cold seal pressure vessels gave the following results. (i) In short duration (45–71 h) runs metastable layer sequences involving wollastonite and talc occur in the reaction zone, whereas they disappear in longer duration (168–336 h) runs. (ii) The layer sequence of the reaction zones in short duration runs differs from place to place on the dolomite crystal even in the same run. (iii) The diversity of layer sequences in the short duration runs merges into a unique layer sequence in the longer duration runs. (iv) The reaction zone develops locally on the dolomite crystal, but no reaction zone was observed on the quartz crystal in any of the runs. The lines of evidence (i)–(iii) show that the system evolves from an initial transient‐ to a steady‐state and that the kinetic effect is important in the development of reaction zones. A steady diffusion model for the unique layer sequence Qtz/Di/Fo + Cal/Dol + Cal/Dol shows that the Dol + Cal layer cannot be formed by diffusion‐controlled process and that the stability of the layer sequence Qtz/Di/Fo + Cal/Dol depends not only on L‐ratios (a = /L_CaOCaO and b = /L_MgOMgO) but also on the relative rate P = (−2ξ₁ − ξ₂)/(–ξ₁ − 2ξ₂) of competing reactions: Dol + 2Qtz = Di + 2CO₂ (ξ₁) and 2Dol + Qtz = Fo + 2Cal + 2CO₂ (ξ₂). For smaller P the stability field will shift to higher values of a and b. The steady diffusion model also shows that the apparent‐non‐reactivity on the quartz surface can be attributed to void formation in a large volume fraction in the diopside layer.