Search results for "chemical evolution"

Prebiotic Evolution and the Origin of Life: Chemical and Biochemical Aspects

1988

Evolution, as the term is used here, signifies any development or change adapting to the environment. Chemical evolution connotes changes of chemical substances, it thus signifies that changes occur fundamentally in the molecules. Frequently “chemical evolution” is used synonymously for “abiotic” or “prebiotic formation” of organic molecules in a cosmic system, usually on the prebiotic (or primitive) Earth. It is then assumed that the organic molecules were formed from the constituents of the primitive atmosphere, hydrosphere, and — in part — lithospere.

Studies on mechanism and physico-chemical parameters at the origin of the cement setting. I. The fundamental processes involved during the cement set…

1995

Abstract The mechanical evolution and the structure of the cement paste have been analysed in relation with the chemical evolution of the system. The setting process can be described as following two fundamental steps: the coagulation of cement grains during the first minutes following the mixing, and the rigidification of the coagulated structure which arises simultaneously with the acceleration of the hydrates formation During the coagulation step, the structure formed is proved to be mechanically reversible. The rigidification of the coagulated structure is provided by the hydrates formation in the contact zone. The increase of the paste cohesion at this stage is proportional to the quan…

Combined Nontargeted Analytical Methodologies for the Characterization of the Chemical Evolution of Bottled Wines

2015

Three-dimensional Simulations from Supernovae to Their Supernova Remnants: The Dynamical and Chemical Evolution of Supernova 1987A

2020

Chemical Evolution of Nitrogen-based Compounds in Mozzarella Cheeses

2018

This Brief evaluates the consequences of protein modifications in cheeses, with special emphasis on mozzarella cheeses. It explains the influence of biogenic amines on food quality and safety. As certain biogenic amines display a toxic potential to humans, considerable research has been undertaken in recent years to evaluate their presence in fermented foods, such as cheeses. This Brief summarizes how the presence of amines is influenced by different factors such as cheese variety, seasoning and microflora. The authors compare typical profiles of different products, e.g. ripe vs. unripe cheeses, focusing also on the different types of mozzarella cheeses. The Brief also introduces several an…

Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate

1994

This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resu…

ORIGIN: metal creation and evolution from the cosmic dawn

2012

Herder, Jan-Willem den et al.

The Hamburg/ESO R-process Enhanced Star survey (HERES):XI. The highly r-process-enhanced star CS 29497-004

2017

We report an abundance analysis for the highly r-process-enhanced (r-II) star CS 29497-004, a very metal-poor giant with Teff = 5013K and [Fe/H]=-2.85, whose nature was initially discovered in the course of the HERES project. Our analysis is based on high signal-to-noise, high-resolution (R~75000) VLT/UVES spectra and MARCS model atmospheres under the assumption of local thermodynamic equilibrium, and obtains abundance measurements for a total of 46 elements, 31 of which are neutron-capture elements. As is the case for the other 25 r-II stars currently known, the heavy-element abundance pattern of CS 29497-004 well-matches a scaled Solar System second peak r-process-element abundance patter…

Chemical Evolution of Interstellar Methanol Ice Analogs upon Ultraviolet Irradiation: The Role of the Substrate

2018

An important issue in the chemistry of interstellar ices is the role of dust materials. In this work, we study the effect of an amorphous water-rich magnesium silicate deposited onto ZnSe windows on the chemical evolution of ultraviolet-irradiated methanol ices. For comparison, we also irradiate similar ices deposited onto bare ZnSe windows. Silicates are produced at relatively low temperatures exploiting a sol-gel technique. The chemical composition of the synthesized material reflects the forsterite stoichiometry. Si-OH groups and magnesium carbonates are incorporated during the process. The results show that the substrate material does affect the chemical evolution of the ice. In particu…

Rapid chemical evolution of tropospheric volcanic emissions from Redoubt Volcano, Alaska, based on observations of ozone and halogen-containing gases

2013

Abstract We report results from an observational and modeling study of reactive chemistry in the tropospheric plume emitted by Redoubt Volcano, Alaska. Our measurements include the first observations of Br and I degassing from an Alaskan volcano, the first study of O 3 evolution in a volcanic plume, as well as the first detection of BrO in the plume of a passively degassing Alaskan volcano. This study also represents the first detailed spatially-resolved comparison of measured and modeled O 3 depletion in a volcanic plume. The composition of the plume was measured on June 20, 2010 using base-treated filter packs (for F, Cl, Br, I, and S) at the crater rim and by an instrumented fixed-wing a…