591 research outputs found
Simulation of shock induced vapor condensation flows in the Lennard-Jones fluid by microscopic and continuum models
No full textThe vapor condensation onto a thin liquid film, induced by the reflection of a weak shock wave, is studied by molecular dynamics atomistic simulations of a simple Lennard-Jones fluid. Molecular dynamics results provide reference flowfields for two models. The first one adopts a hybrid continuum-kinetic description in which the liquid phase is described by hydrodynamic equations, whereas the vapor is described by the Boltzmann equation. The structureless liquid-vapor interface is replaced by a classical kinetic boundary condition. The second model is based on the diffuse interface full continuum description of the Lennard-Jones fluid liquid, vapor, and interface regions. For both models, the required fluid thermodynamic and transport properties have been prescribed according to those of the Lennard-Jones fluid. Not unexpectedly, the results show that the continuum-kinetic model provides a good description of molecular dynamics results when the vapor is close to ideal conditions, increasingly deviating from reference data when the vapor non-ideality increases. The opposite behavior is found for the diffuse interface model. It is observed that flow conditions exist where both models fail to provide a reasonably accurate description of reference flow properties
Multiphase Baer-Nunziato type models for the simulation of self-pressurizing tanks
No full textSelf-pressurizing tank dynamics is modeled using a Baer-Nunziato type multiphase model, with relaxation source terms that account for the exchange of momentum, energy and matter among the phases. Numerical results for nitrous oxide are compared to experimental results available in literature. Since the source terms have an infinite relaxation speed, local thermodynamic equilibrium is reached and the model cannot reproduce the initial pressure and temperature drop observed in experimental results. However it well approximates the subsequent linear decrease of pressure with respect to time. Future work will investigate the effects of finite relaxation speed of the source terms
Elemental speciation analysis, from environmental to biochemical challenge
No full textInformation regarding the distribution of
metallic/metalloid chemical species in biological compartments is required
for understanding their biochemical impact on living organisms. To obtain
such information implies the use of a dedicated measurement approach, namely
speciation analysis. The current trend in (elemental) speciation analysis regards bioinorganic
applications. New analytical methodologies are therefore necessary for
identification, detection and characterization of metal(loids) complexed or
incorporated into biomolecules. The established element-speciation
approaches developed for the determination of low molecular mass metal(loid)
species (e.g. organometallic compounds) in environmental, food,
toxicological and health sciences are presently being adapted for the
determination of high molecular mass metal-species, generally related to
biological processes. This is one of the newest approaches in terms of
element speciation and is called metallomics; this concept refers to the totality of
metal species in a cell and covers the inorganic element content and the
ensemble of its complexes with biomolecules, particularly proteins,
participating in the organisms' response to beneficial or harmful
conditions. Compared to conventional elemental speciation analysis, the
approach applied to bioinorganic analysis is challenging, particularly given
the difficulties in identification/characterization of the organic (e.g.
protein) content of such species. In addition, quantification is not
feasible with the conventional approaches, which led to the exploitation of
the unique feature of (post-column) online isotope dilution-mass
spectrometry for species quantification in metallomics
Towards an improved qualitative and quantitative determination of glutathione peroxidase, selenoprotein P and selenoalbumin in human serum by HPLC coupled to ICP-MS
No full textThis paper deals primarily with the validation of a clean-up procedure based on anion exchange solid-phase extraction for the accurate determination of glutathione peroxidase (GPx), selenoprotein P (SelP) and selenoalbumin (SeAlb) in human serum by affinity HPLC (AF-HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). In addition, the identification and the purity assessment of the GPx, SelP and SeAlb peak fractions separated by AF-HPLC is addressed by their analysis using matrix assisted laser desorption ionization-time of flight mass spectrometry. © 2010 The Royal Society of Chemistry
Simultaneous speciation analysis of glutathione peroxidase, selenoprotein P and selenoalbumin in human serum by tandem anion exchange-affinity HPLC and on-line isotope dilution ICP-quadrupole MS
No full textA method based on anion exchange (AE) and
affinity (AF)-HPLC (AE-AF-HPLC) hyphenated to inductively
coupled plasma-(quadrupole) mass spectrometry (ICP-QMS)
was developed for the speciation analysis of selenoprotein P
(SelP), glutathione peroxidase (GPx) and selenoalbumin
(SeAlb) in human serum. AE-HPLC is proposed here for the
on-line alleviation of Cl and Br spectral interferences on 77Se
(40Ar37Cl) and 82Se (81Br1H). Separation of GPx, SelP and
SeAlb by AE-AF-HPLC was obtained within a total
chromatographic runtime of <20 min. On-line (post-column)
isotope dilution (ON-ID) and on-line external calibration (ONEC)-
ICP-QMS were used for the quantification of Se in GPx,
SelP and SeAlb. ON-EC using a Se-L-cystine standard was
shown to be a suitable approach for the routine simultaneous
speciation analysis of serum GPx, SelP and SeAlb. The
method validation was carried out by direct ICP-sector field
MS determination of Se in GPx, SelP and SeAlb fractions
collected after AE-AF-HPLC separation. In addition, the
method accuracy for the determination of total protein-bound
Se was assessed by analyzing a human serum reference
material (BCR-637) certified for total Se content
Direct simulation Monte Carlo applications to liquid-vapor flows
No full textThe paper aims at presenting Direct Simulation Monte Carlo (DSMC) extensions and applications to dense fluids. A succinct review of past and current research topics is presented, followed by a more detailed description of DSMC simulations for the numerical solution of the Enskog-Vlasov equation, applied to the study of liquid-vapor flows. Results about simulations of evaporation of a simple liquid in contact with a dense vapor are presented as an example
Changes in the occurrence of heavy metals in polar ice during the last climatic cycles, with special emphasis on the possible link between cosmic dust accretion rate and the 100 kyr cycle
No full text
Controllo di qualità delle procedure di campionamento nello studio della distribuzione di metalli in tracce in matrici ambientali.
No full textDifferential pulse anodic stripping voltammetry for ultratrace determination of cadmium and lead in Antarctic snow.
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