From poorly-ordered precursors to crystals: Factors contributing to spherulitic growth of dolomite

2021 ◽  
Author(s):  
Juan Diego Rodriguez Blanco ◽  
Adrienn Maria Szucs
Keyword(s):  
Unified Model ◽  
Formation Mechanisms ◽  
Formation Processes ◽  
Ambient Conditions ◽  
Contributing Factors ◽  
Geological Record ◽  
Spherulitic Growth ◽  
Dolomite Problem ◽  
Dolomite Formation ◽  
Dolomite Precipitation

<p>Dolomite is one of the most abundant carbonate minerals in the geological record, yet it barely forms in the present. The contrast in the abundance of dolomite between geological and modern records combined with the impossibility of synthesizing stoichiometric dolomite in the laboratory at ambient conditions are known as the 'dolomite problem'. This enigma has been in the scope of research for decades, trying to understand dolomite formation, mechanisms and the contributing factors. Dolomite is known to form via two abiotic mechanisms; through (1) dolomitization or (2) dolomite cementation. Also, the contribution of microorganisms can result in biotic dolomite crystallization. The mechanisms of dolomite formation at the molecular and nanoscale in biotic and abiotic environments are relatively well-described, but we still struggle to develop a unified model of dolomite formation in modern and ancient settings. In this contribution, we summarize the development of research related to the dolomite formation processes and in particular the direct dolomite precipitation via spherulitic growth of proto-dolomite.</p>

scholarly journals Modern dolomite formation caused by seasonal cycling of oxygenic phototrophs and anoxygenic phototrophs in a hypersaline sabkha

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zach A. Diloreto ◽  
Sanchit Garg ◽  
Tomaso R. R. Bontognali ◽  
Maria Dittrich
Keyword(s):  
High Salinity ◽  
Atmospheric Oxygen ◽  
Microbial Composition ◽  
Anoxygenic Phototrophs ◽  
Geochemical Conditions ◽  
Exopolymeric Substances ◽  
Dolomite Problem ◽  
Dolomite Formation ◽  
Dolomite Precipitation ◽  
Oxygenic Phototrophs

AbstractThe “Dolomite Problem” has been a controversy for over a century, owing to massive assemblages of low-temperature dolomite in ancient rocks with little dolomite forming today despite favorable geochemical conditions. Experiments show that microbes and their exopolymeric substances (EPS) nucleate dolomite. However, factors controlling ancient abundances of dolomite can still not be explained. To decode the enigma of ancient dolomite, we examined a modern dolomite forming environment, and found that a cyclic shift in microbial community between cyanobacteria and anoxygenic phototrophs creates EPS suited to dolomite precipitation. Specifically, EPS show an increased concentration of carboxylic functional groups as microbial composition cycles from cyanobacterial to anoxygenic phototroph driven communities at low-and high- salinity, respectively. Comparing these results to other low-T forming environments suggests that large turnover of organic material under anoxic conditions is an important driver of the process. Consequently, the shift in atmospheric oxygen throughout Earth’s history may explain important aspects of “The Dolomite Problem”. Our results provide new context for the interpretation of dolomite throughout Earth’s history.

Using stable Mg isotopes to distinguish dolomite formation mechanisms: A case study from the Peru Margin

2014 ◽  
Vol 385 ◽  
pp. 84-91 ◽  
Author(s):  
Vasileios Mavromatis ◽  
Patrick Meister ◽  
Eric H. Oelkers
Keyword(s):  
Formation Mechanisms ◽  
Mg Isotopes ◽  
Dolomite Formation

scholarly journals Effect of annealing ambient conditions on crack formation mechanisms of bulk Bi-2212 ceramic systems

2021 ◽  
pp. 1-14
Author(s):  
U. Erdem ◽  
B. Akkurt ◽  
A.T. Ulgen ◽  
Y. Zalaoglu ◽  
T. Turgay ◽  
...  
Keyword(s):  
Crack Formation ◽  
Formation Mechanisms ◽  
Ambient Conditions

scholarly journals High contributions of fossil sources to more volatile organic aerosol

2019 ◽  
Vol 19 (15) ◽  
pp. 10405-10422 ◽  
Author(s):  
Haiyan Ni ◽  
Ru-Jin Huang ◽  
Junji Cao ◽  
Wenting Dai ◽  
Jiamao Zhou ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Elemental Carbon ◽  
Organic Aerosol ◽  
Formation Mechanisms ◽  
Formation Processes ◽  
Combustion System ◽  
Relative Contribution ◽  
Custom Made ◽  
Volatile Organic ◽  
Volatile Carbon

Abstract. Sources of particulate organic carbon (OC) with different volatility have rarely been investigated, despite the significant importance for better understanding of the atmospheric processes of organic aerosols. In this study we develop a radiocarbon-based (14C) approach for source apportionment of more volatile OC (mvOC) and apply to ambient aerosol samples collected in winter in six Chinese megacities. mvOC is isolated by desorbing organic carbon from the filter samples in helium (He) at 200 ∘C in a custom-made aerosol combustion system for 14C analysis. Evaluation of this new isolation method shows that the isolated mvOC amount agrees very well with the OC1 fraction (also desorbed at 200 ∘C in He) measured by a thermal–optical analyzer using the EUSAAR_2 protocol. The mvOC, OC and elemental carbon (EC) of 13 combined PM2.5 samples in six Chinese cities are analyzed for 14C to investigate their sources and formation mechanisms. The relative contribution of fossil sources to mvOC is 59±11 %, consistently larger than the contribution to OC (48±16 %) and smaller than that to EC (73±9 %), despite large differences in fossil contributions in different cities. The average difference in the fossil fractions between mvOC and OC is 13 % (range of 7 %–25 %), similar to that between mvOC and EC (13 %, with a range 4 %–25 %). Secondary OC (SOC) concentrations and sources are modeled based on the 14C-apportioned OC and EC and compared with concentrations and sources of mvOC. SOC concentrations (15.4±9.0 µg m−3) are consistently higher than those of mvOC (3.3±2.2 µg m−3), indicating that only a fraction of SOC is accounted for by the more volatile carbon fraction desorbed at 200 ∘C. The fossil fraction in SOC is 43 % (10 %–70 %), lower than that in mvOC (59 %, with a range of 45 %–78 %). Correlation between mvOC and SOC from nonfossil sources (mvOCnf vs. SOCnf) and from fossil sources (mvOCfossil vs. SOCfossil) is examined to further explore sources and formation processes of mvOC and SOC.

scholarly journals Expressive devices in the language of English- and Spanish-speaking youth

2011 ◽  
pp. 235 ◽  
Author(s):  
Félix Rodríguez González ◽  
Anna-Brita Stenström
Keyword(s):  
Word Formation ◽  
Formation Mechanisms ◽  
Formation Processes ◽  
Age And Gender ◽  
Spanish Speaking ◽  
Language Variety ◽  
Corpus Data ◽  
And Gender ◽  
Youth Language

The aim of this paper is threefold: first, to introduce the topic of youth slang by giving an overview of its main characteristics; second, to show the different word-formation processes that slang has to make the speaker’s message more expressive; and third, to study the extent to which these two aspects are reflected in two corpora representing London and Madrid youth language. The present study is based, primarily, on an inventory of the top ten ‘proper’ and ‘dirty’ slang words in each language variety with particular emphasis on the speakers’ age and gender, and, secondarily, on the entire corpus data, which showed great agreement with the features outlined in the overview of the main characteristics of youth slang, while the most obvious word-formation mechanisms turned out to be related to change of form and change of meaning.

scholarly journals Dolomite genesis in bioturbated marine zones of an early-middle Miocene coastal mud volcano outcrop (Kuwait)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ammar Alibrahim ◽  
Michael J. Duane ◽  
Maria Dittrich
Keyword(s):  
Middle Miocene ◽  
Saturation Index ◽  
Mud Volcano ◽  
Microbial Consortia ◽  
Charged Fluids ◽  
Ce Anomaly ◽  
Eu Anomaly ◽  
Dolomite Formation ◽  
Reducing Bacteria ◽  
Dolomite Precipitation

AbstractThe origin of spheroidal dolomitized burrow from Al-Subiya sabkha in Kuwait was previously described as enigmatic as no evidence of precursor calcium carbonate was found in the siliciclastic sediment. An assumption for the genesis of spheroidal dolomite from the same area was attributed to hydrocarbon seepage but no evidence was provided. Here, we investigated a recently discovered early-middle Miocene coastal mud volcano outcrop in Al-Subiya sabkha where dolomitized burrows and spheroidal dolomite are found in bioturbated marine zones, and associated with traces of salt. Conversely, the continental zone lacks bioturbation features, dolomite and traces of salt, which together contrast with bioturbated rich marine zones. Geochemical signatures of Rare Earth Elements + Yttrium show a true positive Ce anomaly (Ce/Ce* > 1.2) and positive Eu/Eu* anomaly of spheroidal dolomite indicating strictly anoxic conditions, and sulphate reduction to sulphide, respectively. Our results are suggestive of a relationship between dolomite formation and interdependent events of hydrocarbon seepage, flux of hypersaline seawater, bioturbation, and fluid flow in the marine zones of the mud volcano. The bioturbation activity of crustaceans introduced channels/burrows in the sediment–water interface allowing for the mixing of seeped pressurized hydrocarbon-charged fluids, and evaporitic seawater. In the irrigated channels/burrows, the seeped pressurized hydrocarbon-charged fluids were oxidized via microbial consortia of methanotrophic archaea and sulphate-reducing bacteria resulting in elevated alkalinity and saturation index with respect to dolomite, thus providing the preferential geochemical microenvironment for dolomite precipitation in the bioturbated sediment.

scholarly journals High contributions of fossil sources to more volatile organic carbon

2019 ◽  
Author(s):  
Haiyan Ni ◽  
Ru-Jin Huang ◽  
Junji Cao ◽  
Wenting Dai ◽  
Jiamao Zhou ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Elemental Carbon ◽  
Formation Mechanisms ◽  
Formation Processes ◽  
Combustion System ◽  
Relative Contribution ◽  
Volatile Organic Carbon ◽  
Custom Made ◽  
Volatile Organic ◽  
Volatile Carbon

Abstract. Sources of particulate organic carbon (OC) with different volatility have rarely been investigated despite the significant importance for better understanding of the atmospheric processes of organic aerosols. In this study we develop a radiocarbon (14C) based approach for source apportionment of more volatile OC (mvOC) and apply to ambient aerosol samples collected in winter in six Chinese megacities. mvOC is isolated by desorbing organic carbon from the filter samples in He at 200 °C in a custom-made aerosol combustion system for 14C analysis. Evaluation of this new isolation method shows that the isolated mvOC amount agrees very well with the OC1 fraction (also desorbed at 200 °C in He) measured by a thermal optical analyzer using the EUSAAR_2 protocol. The mvOC, OC and elemental carbon (EC) of thirteen combined PM2.5 samples in six Chinese cities are analyzed for 14C to investigate their sources and formation mechanisms. The relative contribution of fossil sources to mvOC is 59 ± 11 %, consistently larger than the contribution to OC (48 ± 16 %) and smaller than that to EC (73 ± 9 %), despite large differences in fossil contributions in different cities. The average difference in the fossil fractions between mvOC and OC is 13 % (7 %–25 %; range), similar to that between mvOC and EC (13 %; 4 %–25 %). SOC concentrations and sources are modelled based on the 14C-apportioned OC and EC, and compared with concentrations and sources of mvOC. SOC concentrations (15.4 ± 9.0 μg m-3) are consistently higher than those of mvOC (3.3 ± 2.2 μg m-3), indicating that only a fraction of SOC is accounted for by the more volatile carbon fraction desorbed at 200 °C. The fossil fraction in SOC is 43 % (10 %–70 %), lower than that in mvOC (59 %; 45 %–78 %). Correlation between mvOC and SOC from non-fossil sources (mvOCnf vs. SOCnf) and from fossil sources (mvOCfossil vs. SOCfossil) are examined to further explore sources and formation processes of mvOC and SOC.

A Study of Burr Formation Processes Using the Finite Element Method: Part II—The Influences of Exit Angle, Rake Angle, and Backup Material on Burr Formation Processes

1999 ◽  
Vol 122 (2) ◽  
pp. 229-237 ◽  
Author(s):  
I. W. Park ◽  
D. A. Dornfeld
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Metal Cutting ◽  
Rake Angle ◽  
Plastic Work ◽  
Burr Formation ◽  
Formation Mechanisms ◽  
Exit Angle ◽  
Formation Processes ◽  
Burr Size

Finite element models in orthogonal cutting are presented in order to examine the influences of exit angles of the workpiece, tool rake angles, and backup materials on burr formation processes in 304 L stainless steel in particular. Based on the metal-cutting simulation procedure proposed by the authors, a series of stress and strain contours and final burr/breakout configurations are obtained. The burr formation mechanisms with respect to five different exit angles are found, and duration of the burr formation process increases with an increase of exit angle, resulting in different burr/breakout configurations. Based on the development of negative shear stress in front of the tool tip, the tool tip damage, what is called “chipping,” is investigated. Also, with fixed cutting conditions and workpiece exit geometry, the influence of the rake angle is found to be closely related to the rate of plastic work in steady-state cutting because the larger the rate of plastic work in steady-state cutting, the earlier the burr initiation commences. Furthermore, in order to effectively minimize the burr size, three cases of backup material influences on burr formation processes are examined. It is found that the burr size can be effectively minimized when the backup material supports the workpiece only up to the predefined machined surface. [S0094-4289(00)01402-X]

scholarly journals Processes used in the creation of anthroponyms in Old Hungarian

Onomastica ◽  
2020 ◽  
Vol 64 ◽  
Author(s):  
Evelin Mozga
Keyword(s):  
Middle Ages ◽  
Morphological Structure ◽  
Formation Mechanisms ◽  
Formation Processes ◽  
The Creation ◽  
The Given ◽  
The Middle Ages ◽  
Naming Practices

In the Middle Ages, several name-formation processes played a role in the creation of the anthroponyms in Hungarian. The main name-formation mechanisms were: 1. Semantic name-formation. Within this mechanism, the anthroponym develops through the use of internal elements of the language in such a way that the anthroponymic meaning is created without any change in morphological structure. In Old Hungarian naming practices, the most frequent types of semantic name-formation were: a. metaphoric name-giving (e.g. farkas ʽfarkas’ [wolf] > anthroponym Farkas), b. metonymic name-giving (e.g. when an “instrument” of a profession becomes the name of the person practising the given profession; ökör ʽökör’ [ox] > anthroponym Ökör as the name of a butcher), c. semantic split: e.g. ethnonyms, names of professions, etc., often become anthroponyms without the use of any morphological tool (kovács ʽkovács’ [smith] > anthroponym Kovács). 2. Morphematic construction. In the Old Hungarian period, several suffixes  contributed to the creation of anthroponyms, among which the most common ones were: -d(i) ~ -t(i), -s, -a/-e etc. This  morphological solution was the most important tool for adapting foreign names in the Middle Ages: Petrus in Latin > Petr-i, Pet-e, Pet-i, Pet-es in Hungarian.  3. Syntagmatic construction. This process, through the combination of two existing lexemes, creates an anthroponym composed of two constituents, in which both elements provide a certain  information about the named person. In this essay I provide an overview of the typical name-formation processes characterising the formation of anthroponyms in Old Hungarian. 

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