Soil Chemistry: B. Physico-Chemical Models

Context. Disks around pre-main-sequence stars evolve over time by turbulent viscous spreading. The main contender to explain the strength of the turbulence is the magnetorotational instability model, whose efficiency depends on the disk ionization fraction. Aims. Our aim is to compute self-consistently the chemistry including polycyclic aromatic hydrocarbon (PAH) charge chemistry, the grain charging, and an estimate of an effective value of the turbulence α parameter in order to find observational signatures of disk turbulence. Methods. We introduced PAH and grain charging physics and their interplay with other gas-phase reactions in the physico-chemical code PRODIMO. Non-ideal magnetohydrodynamics effects such as ohmic and ambipolar diffusion are parametrized to derive an effective value for the turbulent parameter αeff. We explored the effects of turbulence heating and line broadening on CO isotopologue submillimeter lines. Results. The spatial distribution of αeff depends on various unconstrained disk parameters such as the magnetic parameter βmag or the cosmic ray density distribution inside the protoplanetary disk s. The inner disk midplane shows the presence of the so-called dead zone where the turbulence is almost inexistent. The disk is heated mostly by thermal accommodation on dust grains in the dead zone, by viscous heating outside the dead zone up to a few hundred astronomical units, and by chemical heating in the outer disk. The CO rotational lines probe the warm molecular disk layers where the turbulence is at its maximum. However, the effect of turbulence on the CO line profiles is minimal and difficult to distinguish from the thermal broadening. Conclusions. Viscous heating of the gas in the disk midplane outside the dead zone is efficient. The determination of α from CO rotational line observations alone is challenging.

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Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM III. Elemental depletion and shortcomings of the current physico-chemical models

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2016 ◽

2020 ◽

Vol 497 (2) ◽

pp. 2309-2319

Author(s):

V Wakelam ◽

W Iqbal ◽

J-P Melisse ◽

P Gratier ◽

M Ruaud ◽

...

Keyword(s):

Gas Phase ◽

Molecular Form ◽

Dense Medium ◽

Chemical Model ◽

Physical Conditions ◽

Dense Cores ◽

Chemical Models ◽

Physico Chemical ◽

Galactic Model ◽

Elemental Depletion

ABSTRACT We present a study of the elemental depletion in the interstellar medium. We combined the results of a Galactic model describing the gas physical conditions during the formation of dense cores with a full-gas-grain chemical model. During the transition between diffuse and dense medium, the reservoirs of elements, initially atomic in the gas, are gradually depleted on dust grains (with a phase of neutralization for those which are ions). This process becomes efficient when the density is larger than 100 cm−3. If the dense material goes back into diffuse conditions, these elements are brought back in the gas phase because of photo-dissociations of the molecules on the ices, followed by thermal desorption from the grains. Nothing remains on the grains for densities below 10 cm−3 or in the gas phase in a molecular form. One exception is chlorine, which is efficiently converted at low density. Our current gas–grain chemical model is not able to reproduce the depletion of atoms observed in the diffuse medium except for Cl, which gas abundance follows the observed one in medium with densities smaller than 10 cm−3. This is an indication that crucial processes (involving maybe chemisorption and/or ice irradiation profoundly modifying the nature of the ices) are missing.

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Repetitive inductions of bioluminescence of Pseudomonas putida TVA8 immobilised by adsorption on optical fibre

Chemical Papers ◽

10.1515/chempap-2016-0031 ◽

2016 ◽

Vol 70 (7) ◽

Cited By ~ 9

Author(s):

Jakub Zajíc ◽

Milan Bittner ◽

Tomáš Brányik ◽

Andrey Solovyev ◽

Stanislav Šabata ◽

...

Keyword(s):

Pseudomonas Putida ◽

Optical Fibre ◽

Contact Angles ◽

Solid Surfaces ◽

Zeta Potentials ◽

Chemical Models ◽

Physico Chemical

AbstractPhysico–chemical models of the interactions of cells with solid surfaces, which use contact angles and zeta potentials, indicated more facile adsorption of cells of

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Tracing the cold and warm physico-chemical structure of deeply embedded protostars: IRAS 16293−2422 vs. VLA 1623−2417

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731724 ◽

2018 ◽

Vol 617 ◽

pp. A120 ◽

Cited By ~ 17

Author(s):

N. M. Murillo ◽

E. F. van Dishoeck ◽

M. H. D. van der Wiel ◽

J. K. Jørgensen ◽

M. N. Drozdovskaya ◽

...

Keyword(s):

Chemical Structure ◽

Cavity Wall ◽

Key Factors ◽

Chemical Complexity ◽

Chemical Structures ◽

Chemical Models ◽

Physico Chemical ◽

Envelope Material ◽

Low Mass ◽

Dust Distribution

Context. Much attention has been placed on the dust distribution in protostellar envelopes, but there are still many unanswered questions regarding the physico-chemical structure of the gas. Aims. Our aim is to start identifying the factors that determine the chemical structure of protostellar regions, by studying and comparing low-mass embedded systems in key molecular tracers. Methods. The cold and warm chemical structures of two embedded Class 0 systems, IRAS 16293−2422 and VLA 1623−2417 were characterized through interferometric observations. DCO+, N2H+, and N2D+ were used to trace the spatial distribution and physics of the cold regions of the envelope, while c-C3H2 and C2H from models of the chemistry are expected to trace the warm (UV-irradiated) regions. Results. The two sources show a number of striking similarities and differences. DCO+ consistently traces the cold material at the disk-envelope interface, where gas and dust temperatures are lowered due to disk shadowing. N2H+ and N2D+, also tracing cold gas, show low abundances toward VLA 1623−2417, but for IRAS 16293−2422, the distribution of N2D+ is consistent with the same chemical models that reproduce DCO+. The two systems show different spatial distributions c-C3H2 and C2H. For IRAS 16293−2422, c-C3H2 traces the outflow cavity wall, while C2H is found in the envelope material but not the outflow cavity wall. In contrast, toward VLA 1623−2417 both molecules trace the outflow cavity wall. Finally, hot core molecules are abundantly observed toward IRAS 16293−2422 but not toward VLA 1623−2417. Conclusions. We identify temperature as one of the key factors in determining the chemical structure of protostars as seen in gaseous molecules. More luminous protostars, such as IRAS 16293−2422, will have chemical complexity out to larger distances than colder protostars, such as VLA 1623−2417. Additionally, disks in the embedded phase have a crucial role in controlling both the gas and dust temperature of the envelope, and consequently the chemical structure.

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Special kinetic models of selection processes in biomacromolecular systems

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19883220 ◽

1988 ◽

Vol 53 (12) ◽

pp. 3220-3239

Author(s):

Vladimír Kvasnička

Keyword(s):

Kinetic Models ◽

Jacobi Matrix ◽

Selection Process ◽

Linearization Method ◽

Qualitative Theory ◽

Chemical Models ◽

Selection Processes ◽

Physico Chemical ◽

Special Cases ◽

The Given

Physico-chemical models of selection processes on biomacromolecules - replicators are investigated. Three special cases are considered: 1) Replicators are selfreproduced with mutations, 2) selection process involving two or more substrates, and 3) selection process is controlled by external positive inflows of replicators. Simple tools of qualitative theory of differential equations are used, in particular the so-called linearization method based on the eigenvalues of Jacobi matrix evaluated at the given stationary state.

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Physico-chemical models of galena flotation system

World Journal of Engineering ◽

10.1260/1708-5284.11.5.447 ◽

2014 ◽

Vol 11 (5) ◽

pp. 447-456

Author(s):

M. Chettibi ◽

A. Abramov ◽

A. Boutrid

Keyword(s):

Main Idea ◽

Oxidation Products ◽

Lead Sulphide ◽

Flotation Process ◽

Chemical Reagents ◽

Ph Values ◽

Chemical Models ◽

Sorption Layer ◽

Physico Chemical ◽

Automation Systems

Main idea to prevent the ground contamination by heavy metals is to extract them maximally with minimum consumption of chemical reagents. So, a perfect studying of pulp ionic structure, an adjustment of the sulphuric ores flotation parameters and modelling of minerals selectivity variables, by using the thermodynamic method of analysis, the behavior of lead xanthenes surface state in solution and experimental investigation results, allow obtaining quantitative physico-chemical models of minimum necessary xanthenes concentration of lead sulphide complete flotation.The optimal pH values, ensuring a complete flotation of galena agree with the potential of zero or minimum charge of its surface, and the optimal composition of the collector sorption layer consisting both of chemisorbed xanthenes and physically adsorbed dixanthenes.In additional, it was obtained quantitative models for the necessary xanthenes concentration of lead sulphide complete flotation in the case of different oxidation products from the galena surface in pH values from 7,0 up to 12,0.The models derived can be used as the criteria for functional units of automation systems to control and regulate the flotation process in mineral processing plants. All these should conduct to increasing of metals extraction degree with minimum chemical reagents consumption and providing good environmental protection.

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