scholarly journals Unusual seismic signals associated with the activity at Galeras volcano, Colombia, from July 1992 to September 1994

1996 ◽  
Vol 39 (2) ◽  
Author(s):  
R. A. Torres C. ◽  
D. M. Gómez M. ◽  
L. Narvàez M.
Keyword(s):  
Gas Phase ◽  
Lava Dome ◽  
Solid Material ◽  
Seismic Signals ◽  
Free Gas ◽  
Source Characteristics ◽  
Cooling Crystallization ◽  
Impedance Contrast ◽  
Long Duration ◽  
Dominant Frequencies

After the emplacement of a lava dome at Galeras volcano in 1991, seven eruptions occurred from July 16, 1992, to September 23, 1994, six of which were preceded by quasi-monochromatic, long-duration seismic events with slowly decaying coda named «tornillos» (screws). The dominant frequencies of these unusual seismic signals are related to source characteristics and show temporal changes, diminishing and then tending to stabilize before an eruption. At the same time, the accumulated number and the duration of these signals increase several days prior to the eruption. The increase in the duration of the tornillo events and the decline of the dominant frequencies both suggest an increasing impedance contrast between the surrounding solid material and the fluid. These characteristics may be associated with an increase in the free gas phase in the magma produced by saturation of volatiles due to cooling, crystallization and partial solidification of the column of magma plugging the conduits. The solidified magma can contribute to sealing the conduits and preventing free gas escape, with consequent generation of overpressure. An eruption is initiated when the overpressure exceeds the resistance strength of the solid material.

Substrate-Free Gas-Phase Synthesis of Graphene Sheets

Nano Letters ◽  
2008 ◽  
Vol 8 (7) ◽  
pp. 2012-2016 ◽  
Author(s):  
Albert Dato ◽  
Velimir Radmilovic ◽  
Zonghoon Lee ◽  
Jonathan Phillips ◽  
Michael Frenklach
Keyword(s):  
Gas Phase ◽  
Graphene Sheets ◽  
Phase Synthesis ◽  
Free Gas ◽  
Gas Phase Synthesis

Growth of single crystalline GaN from chlorine-free gas phase

2008 ◽  
Vol 5 (6) ◽  
pp. 1543-1546 ◽  
Author(s):  
H.-J. Rost ◽  
D. Siche ◽  
K. Böttcher ◽  
D. Gogova ◽  
R. Fornari
Keyword(s):  
Gas Phase ◽  
Single Crystalline ◽  
Free Gas

scholarly journals Ultrasonic Detection of the Intravascular Free Gas Phase in Research on Diving

2020 ◽  
Vol 27 (2) ◽  
pp. 176-186
Author(s):  
Ryszard Kłos
Keyword(s):  
Gas Phase ◽  
Bayesian Approach ◽  
Research Work ◽  
Standard Form ◽  
Naval Academy ◽  
Ultrasonic Detection ◽  
Free Gas ◽  
Arterial Blood ◽  
Canadian Research ◽  
The Bayesian Approach

AbstractThe article presents a unique atypical application of the sonography technique and a methodological description of the introduction of this technique to research. The Bayesian approach applied to validation of the Doppler method for intravascular detection of the free gas phase instead of typical statistical inference has been demonstrated in the article. It describes the place of this method in the diving research work conducted in the Polish Naval Academy without any detailed analysis of the results achieved in the studies on decompression supported by ultrasonic detection of the free gas phase in venous vessels. It is a commonly held opinion that Doppler ultrasonic detection of the intravascular free gas phase is not a procedure that can be particularly useful in decompression research. The main objection is that detection of the free gas phase in venous vessels is a weak function to predict the presence of the free gas phase in tissues and arterial blood, so this method is not suitable for assessing the risk of decompression. Only a few countries disagree with this commonly held view and use this method to assess the risk of decompression in decompression studies. France has introduced detection of the free gas phase in venous vessels for diving research and then, together with Canada, improved this method, and developed it to a standard form. Based on the published results of the Canadian research, the technique was evaluated at the Naval Academy using statistical methods. The Academy accepted and adopted the results of this research and started to use this method in its own research on decompression over 25 years ago and continues to use it to great effect.

CO chemisorption on free gas phase metal clusters

1988 ◽  
Vol 88 (1) ◽  
pp. 111-119 ◽  
Author(s):  
D. M. Cox ◽  
K. C. Reichmann ◽  
D. J. Trevor ◽  
A. Kaldor
Keyword(s):  
Gas Phase ◽  
Metal Clusters ◽  
Co Chemisorption ◽  
Free Gas

Catalyst-Free Gas-Phase Epoxidation of Alkenes.

ChemInform ◽  
2005 ◽  
Vol 36 (36) ◽  
Author(s):  
Torsten Berndt ◽  
Olaf Boege
Keyword(s):  
Gas Phase ◽  
Free Gas ◽  
Catalyst Free ◽  
Epoxidation Of Alkenes

The seismic sound of deep volcanic processes

2020 ◽  
Author(s):  
Simone Cesca ◽  
Torsten Dahm ◽  
Sebastian Heimann ◽  
Martin Hensch ◽  
Jean Letort ◽  
...  
Keyword(s):  
Progressive Failure ◽  
Low Frequency ◽  
Moho Depth ◽  
Seismic Signals ◽  
Magma Intrusion ◽  
Long Period ◽  
First Case ◽  
Long Duration ◽  
Volcanic Processes ◽  
Fluid Transfer

<p>Deep volcanic processes and magma intrusion episodes through the crust are typically accompanied by a variety of seismic signals, including volcano-tectonic (VT) seismicity, very long period (VLP) signals and deep low-frequency (DLF) events. These signals can reveal the migration of magma batches and the resonance of magma reservoirs and dikes. The recent 2018-2019 unrest offshore the island of Mayotte, Comoros archipelago, represents the first case of a geophysically monitored magmatic intrusion from a deep sub-Moho reservoir through the whole crust reaching the surface. At Mayotte, a huge magma movement and the following drainage of a deep reservoir were accompanied by a complex seismic sequence, including a massive VT swarm and energetic long-duration very long period (VLP) signals recorded globally. The identification and characterization of ~7000 VTs and ~400 VLPs by applying waveforms-based seismological methods allowed us to reconst the unrest phases: early VTs, migrating upward, were driven by the ascent of a magmatic dike, and tracked its propagating from Moho depth to the seafloor, while later VTs marked the progressive failure of the reservoir’s roof, triggering its resonance and the generation of long-duration VLPs. At the Eifel, Germany, weak DLFs earthquakes have been recorded over the last decades and located along a deep channel-like structure, extending from sub-Moho depth (~40-45 km) to the upper crust (~5-10 km). While not showing any clear migration, they reveal a different way of fluid transfer from depth towards the surface, possibly marking intermediate small reservoirs along a feeding channel. Here, brittle failure occurring in the vicinity of the reservoirs may cause their resonance. The Mayotte and Eifel observations are example of end member models for deep fluid transfer processes through the crust. These examples show that, by listening to seismic signals at different distances and by analysing them with modern waveform based methods, we can provide a detailed picture of deep magmatic processes and enable future eruption early warning.</p>

From disk midplanes to exoplanet atmospheres. The volatile chemical link.

2020 ◽  
Author(s):  
Christian Eistrup
Keyword(s):  
Chemical Composition ◽  
Gas Phase ◽  
Chemical Reactions ◽  
Chemical Evolution ◽  
Protoplanetary Disks ◽  
Solid Material ◽  
Comprehensive Treatment ◽  
Large Network ◽  
Grain Interaction ◽  
Grain Surface

<p>Exoplanetary science is now pushing to constrain the atmospheric compositions of exoplanets. This quest will be further aided by the next generation of facilities, such as the JWST and ground-based ELTs. Linking the observed composition of exoplanet atmospheres to where and how these atmospheres formed in their natal protoplanetary disks often involves comparing the observed exoplanetary atmospheric carbon-to-oxygen (C/O) ratio to a model of a disk midplane with a fixed chemical composition. In this scenario, chemical evolution in the midplane prior to and during the planet formation era is not considered. The C/O ratios of gas and ice in the disk midplane are simply defined by icelines of volatile molecules such as water and CO in the midplane. However, kinetic chemical evolution during the lifetime of the gaseous disk can change the relative abundances of volatile molecules, thus altering the C/O ratios of the planet-forming material. In my chemical evolution models, I utilize a large network of gas-phase, grain-surface and gas-grain interaction reactions, thus providing a comprehensive treatment of chemistry. In my talk, I will outline how such chemical reactions can cause the chemical composition in the disk midplane to evolve, how this affects the C/O ratios of the gas and solid material that form planets, and how such changes to the midplane chemical composition can lead to differences in exoplanet atmospheric compositions. These differences in exoplanet atmospheric compositions may be discernible with JWST observations.</p>

Hydrogen-Free Gas-Phase Deoxydehydration of 2,3-Butanediol to Butene on Silica-Supported Vanadium Catalysts

ChemCatChem ◽  
2017 ◽  
Vol 9 (13) ◽  
pp. 2443-2447 ◽  
Author(s):  
Kelvin Mingyao Kwok ◽  
Catherine Kai Shin Choong ◽  
Daniel Sze Wei Ong ◽  
Joy Chun Qi Ng ◽  
Chuandayani Gunawan Gwie ◽  
...  
Keyword(s):  
Gas Phase ◽  
Free Gas ◽  
Vanadium Catalysts
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