Multifluid modelling of cometary coma for diverse range of parent volatile compositions

2021 ◽  
Author(s):  
Sana Ahmed ◽  
Kinsuk Acharyya
Keyword(s):  
Chemical Reactions ◽  
Fluid Model ◽  
Dissociative Recombination ◽  
Ionic Species ◽  
Volatile Composition ◽  
Diverse Range ◽  
Cometary Coma ◽  
Physico Chemical ◽  
Different Temperatures ◽  
Chemical Attributes

<p>Comets show a general diversity in their parent volatile composition, but in most cases H<sub>2</sub>O is observed to be the dominant volatile in terms of abundance. This is followed by CO and CO<sub>2</sub>, and trace amounts of other species such as CH<sub>4</sub>, CH<sub>3</sub>OH, O<sub>2</sub>, and NH<sub>3</sub> are also present. However, the observed ratio of n_x/H<sub>2</sub>O varies considerably from one comet to another (n_x represents any parent species other than water).</p><p>We aim to study how the chemistry and dynamics of the cometary coma changes for varying abundances of the major parent volatiles. We have constructed a fluid model, using the principles of conservation of mass, momentum and energy, for our study. Parent volatiles sublimating from the nucleus undergo photolytic reactions due to the solar UV radiation field, resulting in the formation of secondary neutral and ionic species and photoelectrons. Active chemistry occurs in the coma, and some of the chemical reactions taking place are ion-neutral rearrangement, charge exchange, dissociative recombination, electron impact dissociation and radiative de-excitation. The energy that is released due to these chemical reactions is non-uniformly distributed amongst all the species, resulting in different temperatures. Hence,  for a complete description of the coma, we have used a multifluid model whereby the neutrals, ions and electrons are considered as three separate fluids. Apart from chemical reactions, we have also considered the exchange of energy between the three fluids due to elastic and inelastic collisions.</p><p>We consider different initial compositions of the comet, and then use our model to generate the temperature and velocity profiles of the coma, for varying cometocentric distances. We also obtain the number density profiles of the different ionic and neutral species that are created in the coma. We see that changes in the initial parent volatile abundance will modify the temperature profile, and there are significant changes in the ionic abundances. Hence, the parent volatile composition of the comet drives the physico-chemical attributes of the coma.</p>

The deuterium interaction with tungsten and iridium in the UHV system

1985 ◽  
Vol 50 (12) ◽  
pp. 2656-2664
Author(s):  
Karel Kuchynka ◽  
Zlatko Knor
Keyword(s):  
Partial Pressure ◽  
Chemical Reactions ◽  
Pressure Range ◽  
Tungsten Filament ◽  
Different Temperatures ◽  
Pressure Changes

The behaviour of hydrogen, in its contact with the iridium and the tungsten filament kept at different temperatures, was studied in the pressure range 1.3 . 10-6 - 1.3 . 10-3 Pa, in a glass apparatus. The effects of adsorption, atomization, desorption, recombination of atoms and chemical reactions were investigated as a function of temperature of the filaments. The named individual processes were used for interpretation of the partial pressure changes in the apparatus. The significance of the above individual phenomena in the UHV experiments is pointed out in this paper.

An Approach of the Madeira Wine Chemistry

Beverages ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 12 ◽  
Author(s):  
Rosa Perestrelo ◽  
Catarina Silva ◽  
Carolina Gonçalves ◽  
Mariangie Castillo ◽  
José S. Câmara
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Least Squares ◽  
Partial Least Squares ◽  
Chemical Reactions ◽  
Ageing Process ◽  
Gas Chromatography Mass Spectrometry ◽  
Wine Aroma ◽  
Least Squares Regression ◽  
Volatile Composition

Madeira wine is a fortified Portuguese wine, which has a crucial impact on the Madeira Island economy. The particular properties of Madeira wine result from the unique and specific winemaking and ageing processes that promote the occurrence of chemical reactions among acids, sugars, alcohols, and polyphenols, which are important to the extraordinary quality of the wine. These chemical reactions contribute to the appearance of novel compounds and/or the transformation of others, consequently promoting changes in qualitative and quantitative volatile and non-volatile composition. The current review comprises an overview of Madeira wines related to volatile (e.g., terpenes, norisoprenoids, alcohols, esters, fatty acids) and non-volatile composition (e.g., polyphenols, organic acids, amino acids, biogenic amines, and metals). Moreover, types of aroma compounds, the contribution of volatile organic compounds (VOCs) to the overall Madeira wine aroma, the change of their content during the ageing process, as well as the establishment of the potential ageing markers will also be reviewed. The viability of several analytical methods (e.g., gas chromatography-mass spectrometry (GC-MS), two-dimensional gas chromatography and time-of-flight mass spectrometry (GC×GC-ToFMS)) combined with chemometrics tools (e.g., partial least squares regression (PLS-R), partial least squares discriminant analysis (PLS-DA) was investigated to establish potential ageing markers to guarantee the Madeira wine authenticity. Acetals, furanic compounds, and lactones are the chemical families most commonly related with the ageing process.

scholarly journals Physico-chemical attributes of water of Hakaluki Haor, Sylhet, Bangladesh

2016 ◽  
Vol 3 (2) ◽  
pp. 67-72
Author(s):  
Md Tajul Islam ◽  
M Mahfuzur Rahman ◽  
Hassan Mahmud
Keyword(s):  
Water Quality ◽  
Seasonal Variation ◽  
Water Samples ◽  
Water Quality Assessment ◽  
Inorganic Pollutants ◽  
Chemical Parameters ◽  
Ph Values ◽  
Physico Chemical ◽  
Significant Seasonal Variation ◽  
Chemical Attributes

Water quality assessment has been carried out in the Hakaluki Haor of greater Sylhet district during May, 2013 to February, 2014. Water samples were collected from 5 spots during 4 seasons and a total of 15 physico-chemical parameters were studied. Significant seasonal variation was observed in all seasons among physico-chemical parameters. pH values varied from 5.9 - 7.1, water temperature varied from 23.7 – 26.7OC, transference varied from 23-53 cm, TSS varied from 18.1-192 mg/l, TDS varied 25-193.5 mg/l, EC varied from 30-680 ?s/cm , DO content of water varied from 4.6 - 5.6mg/l, BOD varied from 0.2-2.614 mg/l, COD varied from 38-312 mg/l, NO3-N varied from 0.1-30.4 mg/l, NH3 varied from 0.9-2.18 mg/l, alkalinity varied from 12-42 mg/l and PO4 varied from 0.9 -13.4 (mg/l). Agricultural and inorganic pollutants have been observed as the main causes of the Haor water pollution.Jahangirnagar University J. Biol. Sci. 3(2): 67-72, 2014 (December)

scholarly journals Diel dynamics of heleoplankton in relation to some physico-chemical attributes of water in an aquaculture tank in Guwahati, Assam

2012 ◽  
Vol 4 (1) ◽  
pp. 16-22
Author(s):  
Janardan Pathak ◽  
M. M. Goswami
Keyword(s):  
Water Temperature ◽  
T Test ◽  
Total Alkalinity ◽  
Diurnal Fluctuation ◽  
Total Hardness ◽  
Numerical Density ◽  
Physico Chemical ◽  
Free Carbon Dioxide ◽  
Chemical Attributes ◽  
Positive Correlations

Diurnal fluctuation of the phytoplankton and zooplankton population (numerical densities) and the physicochemical attributes of water are studied in an aquaculture pond at Guwahati, Assam. In the 24 hour diel cycle, the phytoplankton and zooplankton show significant (t-test, p < 0.01) variation in their numerical density at an interval of 4 hours. The studied physico-chemical parameters of water included Temperature, Total Alkalinity (TA), Total hardness (TH), Dissolved Oxygen (DO), Free Carbon dioxide (FCO2) and pH are analyzed concurrently, which reveals a significant fluctuation (t-test, p< .01) in the day and night hours. Multivariate correlation analysis portrays significant and positive correlations among the total population density of phytoplankton with respect to water temperature (r = 0.845, p<0.05) and pH (r = 0.881, p< 0.01) while it maintains significant negative correlations with TA (r = -0.837, p<0.05), TH (r = -0.768, p< 0.05) and FCO2 (r = -0.830, p<0.05). However, total numerical density of zooplankton reveals positive and significant correlations with TA (r = 0.842, p< 0.05) and FCO2 (r= 0.758, p< 0.05) while it shows significant negative correlations with water temperature (r = -0.906, p< 0.01) and pH (r =- 0.912, p< 0.01).

Thermodynamic of metal complexation of the macrocyclic antibiotic rifampicin

2001 ◽  
Vol 79 (1) ◽  
pp. 42-49
Author(s):  
I Shehatta ◽  
I Kenawy ◽  
A H Askalany ◽  
Ayman A Hassan
Keyword(s):  
Binding Sites ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Ligand Field ◽  
Water Medium ◽  
Acid Base ◽  
Distribution Diagram ◽  
Macrocyclic Antibiotic ◽  
Transition Series ◽  
Different Temperatures

The acid-base and complexation equilibria of rifampicin with H+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ were studied by means of potentiometry. The stoichiometric equilibrium constants were determined in 50% (v/v) methanol-water medium at different temperatures and constant ionic strength (0.05 M KCl). It was established that rifampicin has two proton-binding sites. The distribution diagram of the corresponding ionic species as a function of pH is given and indicated that rifampicin exists predominantly in the zwitterionic form at pH [Formula: see text] 5. The thermodynamic parameters of protonation and complexation were derived and discussed. The formation of the complexes is spontaneous, more favourable at lower temperatures, entropically unfavourable, and an enthalpy-driven process. The order of the changes in Gibbs energy and enthalpy accompanying the complexation was found to be Mn2+ < Co2+ < Ni2+ < Cu2+ > Pb2+ > Zn2+ > Cd2+ > Hg2+ in accordance with the well-known sequence of Irving and Williams. The transition series contraction energy (Er(Mn-Zn)), and the ligand field stabilization energy (δH) were calculated from the enthalpy changes.Key words: rifampicin, thermodynamics, potentiometry, and complexation.

The hydrolysis and biogas production of complex cellulosic substrates using three anaerobic biomass sources

2013 ◽  
Vol 67 (2) ◽  
pp. 293-298 ◽  
Author(s):  
C. Keating ◽  
D. Cysneiros ◽  
T. Mahony ◽  
V. O'Flaherty
Keyword(s):  
Biogas Production ◽  
Positive Role ◽  
Diverse Range ◽  
Factors Affecting ◽  
Rate Limiting Step ◽  
Solid Substrates ◽  
Different Temperatures ◽  
Anaerobic Biomass ◽  
Rate Limiting ◽  
Hydrolysis Of

In this study, the ability of various sludges to digest a diverse range of cellulose and cellulose-derived substrates was assessed at different temperatures to elucidate the factors affecting hydrolysis. For this purpose, the biogas production was monitored and the specific biogas activity (SBA) of the sludges was employed to compare the performance of three anaerobic sludges on the degradation of a variety of complex cellulose sources, across a range of temperatures. The sludge with the highest performance on complex substrates was derived from a full-scale bioreactor treating sewage at 37 °C. Hydrolysis was the rate-limiting step during the degradation of complex substrates. No activity was recorded for the synthetic cellulose compound carboxymethylcellulose (CMC) using any of the sludges tested. Increased temperature led to an increase in hydrolysis rates and thus SBA values. The non-granular nature of the mesophilic sludge played a positive role in the hydrolysis of solid substrates, while the granular sludges proved more effective on the degradation of soluble compounds.

Sign in / Sign up

Export Citation Format

Share Document