Supercritical fluid flow in porous media: modeling and simulation

The present work aims the modeling and simulation of supercritical fluid flow through porous media. This type of flow appears in several situations of interest in applied science and engineering, as the supercritical flow in porous materials employed in chromatography, supercritical extraction and petroleum reservoirs. The fluid is constituted of one pure substance, the flow is monophasic, highly compressible and isothermal. The porous media is isotropic, possibly heterogeneous, with rectangular format and the flow is two-dimensional. The heterogeneities of porous media are modeled by a simple power law, which describes the relationship between permeability and porosity. The modeling of the hydrodynamic phenomena incorporates the Darcy's law and the equation of mass conservation. Appropriated correlations are used to model, in a realistic form, the density and the viscosity of the fluid. A conservative finite-difference scheme is used in the discretization of the differential equations. The nonlinearity is treated by Newton method, together with the conjugate gradient method. The results of the simulation for pressure and mobility of supercritical and liquid propane flowing through porous media are presented, analyzed and graphically depicted.     

Comment on "Competition for consciousness among visual events: The psychophysics of reentrant visual processes" (Di Lollo, Enns & Rensink, 2000).

V. Di Lollo, J. T. Enns, and R. A. Rensink (2000) reported properties of masking that they claimed were inconsistent with all current models. The current authors show, through computer simulation, that many current models can account for V. Di Lollo et al.'s (2000) data. Although V. Di Lollo et al. (2000) argued that their data could be accounted for only with models that incorporate reentrant processing, the current authors show that reentrant processing is not necessary. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prognostic factors for the effects of two interventions for work-related neck-shoulder complaints: myofeedback training and ergonomic counselling

AIM: To explore prognostic factors for the effects of two interventions (myofeedback training in combination with ergonomic counselling (Mfb/EC) and ergonomic counselling alone (EC)) on discomfort and disability in work-related neck-shoulder complaints. METHODS: Thirty-six females completed the interventions. Discomfort and disability were assessed at baseline, immediately after the intervention, and at 3-month follow-up. Potential sociodemographic and psychological prognostic factors were assessed using questionnaires. Data were analysed using multiple regression and general linear modelling. RESULTS: Changes in discomfort were best predicted by baseline discomfort levels. Changes in disability were predicted by baseline disability levels, patient profile, and coping strategy 'ignoring sensations'. A significant difference between the Mfb/EC and EC group was found for coping strategy 'ignoring sensations', which appeared to be a predictor for changes in disability at 3-month follow-up in the Mfb/EC group only. CONCLUSIONS: Subjects with high levels of initial discomfort and disability and specific psychological patient profiles benefit most from interventions. Myofeedback training contributes a specific quality to those who ignore pain sensations.     

Affinity and Specificity for Binding to Glycosaminoglycans Can Be Tuned by Adapting Peptide Length and Sequence

Although glycosaminoglycan (GAG)–protein interactions are important in many physiological and pathological processes, the structural requirements for binding are poorly defined. Starting with GAG-binding peptide CXCL9(74-103), peptides were designed to elucidate the contribution to the GAG-binding affinity of different: (1) GAG-binding motifs (i.e., BBXB and BBBXXB); (2) amino acids in GAG-binding motifs and linker sequences; and (3) numbers of GAG-binding motifs. The affinity of eight chemically synthesized peptides for various GAGs was determined by isothermal fluorescence titration (IFT). Moreover, the binding of peptides to cellular GAGs on Chinese hamster ovary (CHO) cells was assessed using flow cytometry with and without soluble GAGs. The repetition of GAG-binding motifs in the peptides contributed to a higher affinity for heparan sulfate (HS) in the IFT measurements. Furthermore, the presence of Gln residues in both GAG-binding motifs and linker sequences increased the affinity of trimer peptides for low-molecular-weight heparin (LMWH), partially desulfated (ds)LMWH and HS, but not for hyaluronic acid. In addition, the peptides bound to cellular GAGs with differential affinity, and the addition of soluble HS or heparin reduced the binding of CXCL9(74-103) to cellular GAGs. These results indicate that the affinity and specificity of peptides for GAGs can be tuned by adapting their amino acid sequence and their number of GAG-binding motifs.     

Influence of albumin on sorption kinetics in solid-phase microextraction: consequences for chemical analyses and uptake processes

Because of its simplicity, solid-phase microextraction (SPME) is an increasingly popular technique to use in experiments measuring freely dissolved concentrations of compounds in biological and environmental samples. However, a number of studies have shown that sorption kinetics of compounds in such SPME systems is dependent on the presence of a binding matrix. This affects the interpretability of nonequilibrium SPME data. In this study, this phenomenon was investigated by measuring the rate of depletion of pyrene from a "loaded" poly(dimethylsiloxane) fiber into surrounding cell culture medium containing different concentrations of bovine serum albumin (BSA). The rate of depletion was found to steadily increase with increasing concentrations of BSA. It was postulated that BSA facilitated the transport of pyrene through the medium. This phenomenon was modeled by considering diffusion of BSA-bound pyrene in addition to diffusion of unbound pyrene in the aqueous boundary layer (BL) around the fiber. The model closely fit the experimental data and illustrated that diffusion in the BL was rate limiting because the analyte's affinity for the fiber was high and the BL thickness significant. The concentration of binding matrix and the analyte's affinity for the matrix further determined the extent to which BSA-facilitated transport contributed to the kinetics of the system.     

Virus disinfection in water by biogenic silver immobilized in polyvinylidene fluoride membranes

The development of innovative water disinfection strategies is of utmost importance to prevent outbreaks of waterborne diseases related to poor treatment of (drinking) water. Recently, the association of silver nanoparticles with the bacterial cell surface of Lactobacillus fermentum (referred to as biogenic silver or bio-Ag⁰) has been reported to exhibit antiviral properties. The microscale bacterial carrier matrix serves as a scaffold for Ag⁰ particles, preventing aggregation during encapsulation. In this study, bio-Ag⁰ was immobilized in different microporous PVDF membranes using two different pre-treatments of bio-Ag⁰ and the immersion-precipitation method. Inactivation of UZ1 bacteriophages using these membranes was successfully demonstrated and was most probably related to the slow release of Ag⁺ from the membranes. At least a 3.4 log decrease of viruses was achieved by application of a membrane containing 2500 mg bio-Ag⁰_powder m⁻² in a submerged plate membrane reactor operated at a flux of 3.1 L m⁻² h⁻¹. Upon startup, the silver concentration in the effluent initially increased to 271 μg L⁻¹ but after filtration of 31 L m⁻², the concentration approached the drinking water limit ( = 100 μg L⁻¹). A virus decline of more than 3 log was achieved at a membrane flux of 75 L m⁻² h⁻¹, showing the potential of this membrane technology for water disinfection on small scale.     

Role of kinetics in acute lethality of nonreactive volatile organic compounds (VOCs)

OBJECTIVE: To introduce and test a standardized measurement protocol for DNA image cytometry into a newly developed LUCIA G system application program. Contribution to a discussion concerning the possibility of using the histology sections for DNA image cytometry. STUDY DESIGN: Routine biopsy material from 18 urinary bladder cancer cases was analyzed (Grade 1: n = 6, Grade 2: n = 6, Grade 3: n = 6), both in histological and in cytoseparated preparations. More than one hundred diagnostic and more than 30 reference cells were measured. DNA features (mean DNA value, 2cDI, B?cking's grade of malignancy) and histogram types in Auer's classification (AI-IV) were compared. RESULTS: Most carcinomas measured were aneuploid (two thirds G1, all G2, G3). The most common histogram type was A IV. Malignancy grade was mostly slightly higher in cytoseparated material, the shape of the histogram was analogous. Two carcinomas looking euploid in histology sections were proven aneuploid in cytoseparation. CONCLUSION: More convenient tissue section measurement provided useful DNA profile information in most cases. Those without proven aneuploidy should be additionally measured in cytoseparations. An experienced pathologist meeting strictly measurement protocol demands is an important part of the measurement system.