Saturn's largest moon, Titan, remains an enigma, explored only by remote sensing from Earth, and by the Voyager and Cassini spacecraft. The most puzzling aspects include the origin of the molecular nitrogen and methane in its atmosphere, and the mechanism(s) by which methane is maintained in the face of rapid destruction by photolysis. The Huygens probe, launched from the Cassini spacecraft, has made the first direct observations of the satellite's surface and lower atmosphere. Here we report direct atmospheric measurements from the Gas Chromatograph Mass Spectrometer (GCMS), including altitude profiles of the constituents, isotopic ratios and trace species (including organic compounds). The primary constituents were confirmed to be nitrogen and methane. Noble gases other than argon were not detected. The argon includes primordial 36Ar, and the radiogenic isotope 40Ar, providing an important constraint on the outgassing history of Titan. Trace organic species, including cyanogen and ethane, were found in surface measurements.

/pdf/the-abundances-of-constituents-of-titan-s-atmosphere-from-573eynu15u.pdf

The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe

目的 探讨CD25单抗在无血缘关系造血干细胞移植（UHSCT）中对干细胞植入和移植物抗宿主病（GVHD）的作用。方法 27例UHCST中，移植后1、4d给予CD25单抗1mg/kg。结果 27例中，除1例早期死亡外，26例患者造血全部重建。17例发生急性GVHD，其中Ⅱ度以上急性GVHD6例（23％）。复发3例，严重感染3例。26例可评价患者中，19例无病生存（73％）。结论 CD25单抗在UHSCT中对保证干细胞植入和预防GVHD有肯定的作用，白血病复发并不增加。此研究为UHCST和HLA不合的造血干细胞移植提供一个可选择的途径。

High resolution schemes for hyperbolic conservation laws

In northern Italy in 1997, two earthquakes of magnitudes 5.7 and 6 (separated by nine hours) marked the beginning of a sequence that lasted more than 30 days, with thousands of aftershocks including four additional events with magnitudes between 5 and 6. This normal-faulting sequence is not well explained with models of elastic stress transfer, particularly the persistence of hanging-wall seismicity that included two events with magnitudes greater than 5. Here we show that this sequence may have been driven by a fluid pressure pulse generated from the coseismic release of a known deep source of trapped high-pressure carbon dioxide (CO2). We find a strong correlation between the high-pressure front and the aftershock hypocentres over a two-week period, using precise hypocentre locations and a simple model of nonlinear diffusion. The triggering amplitude (10-20 MPa) of the pressure pulse overwhelms the typical (0.1-0.2 MPa) range from stress changes in the usual stress triggering models. We propose that aftershocks of large earthquakes in such geologic environments may be driven by the coseismic release of trapped, high-pressure fluids propagating through damaged zones created by the mainshock. This may provide a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow.

/pdf/aftershocks-driven-by-a-high-pressure-co2-source-at-depth-zdqs706kqs.pdf

Aftershocks driven by a high-pressure CO2 source at depth.

[1] Mud volcanism and diapirism have puzzled geoscientists for ∼2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000RG000093

Significance of mud volcanism

Numerous measurements of CO2 degassing from the soil, carried out with the accumulation chamber method, indicate that in the period April–July 1995 the upper part of the Fossa cone released a total output of 200 t d–1 of CO2, which corresponds to approximately 1000 t d–1 of steam. These large amounts of fluids are of the same order of magnitude as those released by the high temperature fumarolic field located inside the crater. The spatial distribution of soil gas fluxes shows that the main structures releasing CO2 are the inner slopes of the crater and a NW–SE line, located NE of the crater rim, which correspond to the main direction of Vulcano Island active faults. The comparison of the φCO2 maps with the soil temperature distribution, derived from both direct measurements and airborne infrared images, indicates the occurrence of extensive condensation of fumarolic steam within the upper part of the Fossa cone, whose total amount is comparable to the rainfall budget. Part of the condensate which originates from this process contributes to the recharge of the phreatic aquifer of Porto Plain, modifying the chemical and isotopic composition of the groundwater.

Diffuse emission of CO 2 from the Fossa crater, Vulcano Island (Italy)

Hydrothermal gas equilibria: the H2O-H2-CO2-CO-CH4 system

[1] We present a reliable methodology to estimate the energy associated with the subaerial diffuse degassing of volcanic-hydrothermal fluids. The fumaroles of 15 diffuse degassing structures (DDSs) located in eight volcanic systems in the world were sampled and analyzed. Furthermore, each area was measured for soil temperature gradients and for soil CO2 fluxes. The results show that each hydrothermal or volcanic system is characterized by a typical source fluid which feeds both the fumaroles and diffuse degassing through the soil. Experimental data and the results of physical numerical modeling of the process demonstrate that the heat released by condensation of steam at depth is almost totally transferred by conduction in the uppermost part of the soil. A linear relationship is observed between the log of the steam/gas ratio measured in the fumaroles and the log of the ratio between soil thermal gradient and soil-gas flux. The main parameter controlling this relation is the thermal conductivity of the soil (Kc). For each area, we computed the values of Kc which range from 0.4 to 2.3 W m−1 °C−1. Using the CO2 soil fluxes as a tracer of the deep fluids, we estimated that the total heat released by steam condensation in the systems considered varies from 1 to 100 MW.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004JB003542

Carbon dioxide diffuse degassing and estimation of heat release from volcanic and hydrothermal systems

[1] Phlegrean Fields is an active and densely populated caldera near Naples (Italy). Two major unrest episodes characterized its recent history, each leading to remarkable ground uplift and followed by slow subsidence. Fumaroles near the caldera centre underwent important chemical changes during these volcanic crises. Based on published data we show that a correlation exits between ground displacement and gas composition. Numerical modelling of hydrothermal circulation shows that periods of enhanced fluid injection at the base of the hydrothermal system, are consistent with the observed chemical variations. The model predicts an average increase in pore pressure and temperature within the system, suggesting potential effects on ground deformation. Literature data and simulation results show that periods of intense magmatic degassing could explain most of the features characterizing recent bradyseismic crises and should be considered a potential trigger for the unrest at Phlegrean Fields, as well as at other calderas in the world.

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Giovanni Chiodini

Papers

Diffuse emission of CO 2 from the Fossa crater, Vulcano Island (Italy)

Hydrothermal gas equilibria: the H2O-H2-CO2-CO-CH4 system

Carbon dioxide diffuse degassing and estimation of heat release from volcanic and hydrothermal systems

Magma degassing as a trigger of bradyseismic events: The case of Phlegrean Fields (Italy)

Quantification of deep CO2 fluxes from Central Italy. Examples of carbon balance for regional aquifers and of soil diffuse degassing