The critical gas saturation in a porous medium in the presence of gravity

The critical gas saturation, S(gc), denotes the volume fraction of the gas phase at the onset of bulk gas flow during the depressurization of a supersaturated liquid in a porous medium. In the absence of gradients due to viscous or gravity forces, S(gc) is controlled by nucleation, capillary forces, and the rate of decline of the supersaturation. In this paper we address one important additional effect, that of buoyancy. We use 2-D pore-network simulations, based on invasion percolation in a gradient (IPG), and corresponding scaling relations to obtain the dependence of S(gc) on the gravity Bond number, B, under conditions of slow growth, namely when mass transfer is sufficiently fast. The critical gas saturation approaches two plateau values at low and high Bond numbers. In the in-between region it scales as a power law of B, which for a 2-D lattice is S(gc) approximately B(-0.91).     

Determination of hydrogen peroxide by using a flow injection system with immobilized peroxidase and long pathlength capillary spectrophotometry

The development of a highly sensitive method for the determination of nanomolar concentrations of hydrogen peroxide in the liquid phase is described. This paper demonstrates for the first time a flow injection analysis (FIA) system with immobilized enzyme reactor combined with a total internal reflective cell (a liquid waveguide capillary cell (LWCC)) and spectrophotometric detection, for the development of an improved procedure for the determination of hydrogen peroxide. Moreover, the newly synthesized 4-aminopyrazolone derivative, 4-amino-5-(p-aminophenyl)-1-methyl-2-phenyl-pyrazol-3-one (DAP), is used as a color coupler in its oxidative condensation with the sodium salt of N-ethyl-N-sulphopropylaniline sodium salt (ALPS) which acts as a hydrogen donor. Immobilization of peroxidase is achieved by coupling the periodate-treated enzyme to aminopropyl controlled-pore glass (CPG) beads. The determination of hydrogen peroxide is carried out in a 0.1 M phosphate buffer and the product is monitored at 590 nm with a charge-coupled device (CCD) detector equipped with fiber optics in a fully computerized system. The interference of different species, mainly ionic, was investigated.The method permits detection down to 4 nmol l⁻¹ hydrogen peroxide (signal-to-noise ratio=3). A linear calibration graph was obtained over the range 20-700 nmol l⁻¹. The relative standard deviation (R.S.D.) at 300 nmol l⁻¹ H₂O₂ is 1.7% (n=7). The method was successfully applied for the determination of hydrogen peroxide in samples from a vat-cleaning process.     

Effect of Immobilized Thiolated Glycosaminoglycans on Fibronectin Adsorption and Behavior of Fibroblasts

Glycosaminoglycans (GAGs) chondroitin sulfate, heparin, hyaluronan, and sulfated hyaluronan are lower and higher thiolated to enable a one?step covalent modification of gold or vinyl?terminated surfaces. Measurements of water contact angle and zeta potentials reveal that sulfated GAG?modified surfaces are more wettable and possess a negative surface potential. Additionally, higher thiolated GAGs (tGAGs) exhibit increased wettability and higher surface roughness. Fibronectin (FN) adsorption increases with sulfation degree of tGAGs. The tGAG?functionalized surfaces with higher degree of sulfation promote fibroblast adhesion most under serum‐free conditions. The preadsorption of FN allows for more cell adhesion on tGAG surfaces. Metabolic activity measurements show that cell growth is enhanced for tGAGs up to a certain thiolation degree. Overall, thiolation of GAGs does not hamper their bioactivity toward proteins and cells, which make them highly interesting for biomimetic surface modification of implants and tissue engineering scaffolds.     

Continuous-wave-controlled nonlinear x-wave generation

We demonstrate that the interaction between a two-dimensional localized wave packet and a continuous-wave background can lead to efficient x-wave generation in nonlinear bidispersive optical systems. This x-wave generation process was found to depend on both the relative phase and amplitude of the background with respect to the superimposed wave packet. Pertinent configurations that lead to such generation are considered.     

Performance of convex underestimators in a branch-and-bound framework

The efficient determination of tight lower bounds in a branch-and-bound algorithm is crucial for the global optimization of models spanning numerous applications and fields. The global optimization method \(\alpha \)-branch-and-bound (\(\alpha \)BB, Adjiman et al. in Comput Chem Eng 22(9):1159–1179, 1998b, Comput Chem Eng 22(9):1137–1158, 1998a; Adjiman and Floudas in J Global Optim 9(1):23–40, 1996; Androulakis et al. J Global Optim 7(4):337–363, 1995; Floudas in Deterministic Global Optimization: Theory, Methods and Applications, vol. 37. Springer, Berlin, 2000; Maranas and Floudas in J Chem Phys 97(10):7667–7678, 1992, J Chem Phys 100(2):1247–1261, 1994a, J Global Optim 4(2):135–170, 1994), guarantees a global optimum with \(\epsilon \)-convergence for any \(\mathcal {C}^2\)-continuous function within a finite number of iterations via fathoming nodes of a branch-and-bound tree. We explored the performance of the \(\alpha \)BB method and a number of competing methods designed to provide tight, convex underestimators, including the piecewise (Meyer and Floudas in J Global Optim 32(2):221–258, 2005), generalized (Akrotirianakis and Floudas in J Global Optim 30(4):367–390, 2004a, J Global Optim 29(3):249–264, 2004b), and nondiagonal (Skjäl et al. in J Optim Theory Appl 154(2):462–490, 2012) \(\alpha \)BB methods, the Brauer and Rohn+E (Skjäl et al. in J Global Optim 58(3):411–427, 2014) \(\alpha \)BB methods, and the moment method (Lasserre and Thanh in J Global Optim 56(1):1–25, 2013). Using a test suite of 40 multivariate, box-constrained, nonconvex functions, the methods were compared based on the tightness of generated underestimators and the efficiency of convergence of a branch-and-bound global optimization algorithm.     

Determination of umbilical cord and maternal plasma concentrations of fentanyl by using novel spectrophotometric and chemiluminescence enzyme immunoassays

Two novel enzyme immunoassays of fentanyl have been developed using Horseradish Peroxidase (HRP) as an enzyme, 3,3′,5,5′tetramethylbenzidine (TMB) and luminol as its colorimetric and its chemiluminescence substrate, respectively. A fentanyl polyclonal antibody was used as a capture antibody for fentanyl and fentanyl-bovine serum albumin (BSA) conjugate. The latter was first biotinylated and then bound by streptavidin labeled with HRP, resulting in the development of two novel competitive immunoassays. The detection limits were 0.045 and 0.0048 ng ml⁻¹ for spectrophotometric and chemiluminescence detection, respectively, and were much lower than existing HRP-fentanyl based kits. Intra- and inter-assay CVs were 2.6-4.5 and 5.4-11.2%, respectively, at concentrations of 0.050-5.000 ng ml⁻¹ for the colorimetric assay, whilst for the chemiluminescent assay intra- and inter-assay CVs were 3.7-6.2 and 6.2-12.3%, respectively, for the linear range of the assay at concentrations of 0.008-0.800 ng ml⁻¹. The methods in this study were developed in order to measure maternal and neonatal fentanyl plasma samples during cesarean section, after the application of a novel subarachnoid analgesia technique. The 28 maternal and neonatal plasma samples were measured by both assays, providing data for subarachnoid administration of fentanyl that had never been presented before.     

Minimum distance regression-type estimates with rates under weak dependence

Under weak dependence, a minimum distance estimate is obtained for a smooth function and its derivatives in a regression-type framework. The upper bound of the risk depends on the Kolmogorov entropy of the underlying space and the mixing coefficient. It is shown that the proposed estimates have the same rate of convergence, in the L ₁-norm sense, as in the independent case.This work was partially supported by a research grant from the Natural Sciences and Engineering Research Council of Canada.     

Absolute rate coefficient determination and reaction mechanism investigation for the reaction of Cl atoms with CH2I2 and the oxidation mechanism of CH2I radicals

The gas-phase reaction of atomic chlorine with diiodomethane was studied over the temperature range 273-363 K with the very low-pressure reactor (VLPR) technique. The reaction takes place in a Knudsen reactor at pressures below 3 mTorr, where the steady-state concentration of both reactants and stable products is continuously measured by electron-impact mass spectrometry. The absolute rate coefficient as a function of temperature was given by k = (4.70 +/- 0.65) x 10-11 exp[-(241 +/- 33)/T] cm3molecule-1s-1, in the low-pressure regime. The quoted uncertainties are given at a 95% level of confidence (2sigma) and include systematic errors. The reaction occurs via two pathways: the abstraction of a hydrogen atom leading to HCl and the abstraction of an iodine atom leading to ICl. The HCl yield was measured to be ca. 55 +/- 10%. The results suggest that the reaction proceeds via the intermediate CH2I2-Cl adduct formation, with a I-Cl bond strength of 51.9 +/- 15 kJ mol-1, calculated at the B3P86/aug-cc-pVTZ-PP level of theory. Furthermore, the oxidation reactions of CHI2 and CH2I radicals were studied by introducing an excess of molecular oxygen in the Knudsen reactor. HCHO and HCOOH were the primary oxidation products indicating that the reactions with O2 proceed via the intermediate peroxy radical formation and the subsequent elimination of either IO radical or I atom. HCHO and HCOOH were also detected by FT-IR, as the reaction products of photolytically generated CH2I radicals with O2 in a static cell, which supports the proposed oxidation mechanism. Since the photolysis of CH2I2 is about 3 orders of magnitude faster than its reactive loss by Cl atoms, the title reaction does not constitute an important tropospheric sink for CH2I2.     

Review on the electrochemical oxidation of endocrine-disrupting chemicals using BDD anodes

The application of synthetic diamond-based electrodes in water treatment has been shown to be promising, especially for boron-doped diamond (BDD). With a wide potential window and high overpotential for oxygen evolution among many more excellent qualities, BDD anodes surpass the capabilities of conventional electrodes. Currently, the synthesis and fabrication of low-cost BDD anodes are still in the primary stages of development. Electrochemical oxidation of EDCs on BDD anodes in water samples have been shown to be effective with very high removal efficiencies. The presence of this group of pollutants in wastewater effluents and various water matrices causes environmental concerns and requires an immediate solution due to their persistence and threat for both humas and wildlife. Extensive research on BDD continues to be carried out with various EDCs, such as parabens and pesticides, to determine the most suitable parameters, possible mechanisms of the degradation process, and its viability in large-scale applications. These efforts remain imperative as the presence of EDCs could severely affect human health and the surrounding environment. Although significant progress has been achieved, the advanced technology is unable to achieve feasible application in a large scale due to major hindrances. In this mini review, the focus was on the recent applications of electrochemical oxidation using BDD thin-film anodes (2019 to present) for the removal of a range of EDCs. The main factors that affect the performance of BDD anodes in the electrochemical oxidation of EDCs were discussed and evaluated, highlighting some ways to overcome the issues that prevent the technology from moving onto the next stage of development.     

pH and ionic strength effect on single fibrinogen molecule adsorption on mica studied with AFM

Although several investigations have been reported on the effect of pH or ionic strength on protein adsorption, most of them have been carried out with protein monolayers and not with single molecules. We have used atomic force microscopy to image, in phosphate buffer, single fibrinogen molecules adsorbed on mica and compare the surface coverage at variable pH (7.4, 5.8, 3.5) or ionic strength (15, 150, 500 mM) conditions. The images obtained and the statistical analysis of the surface coverage indicate adsorption enhancement at the IEP of fibrinogen (pH 5.8) and minimum adsorption at pH 3.5. On the other hand, more protein was adsorbed when the salt concentration of the buffer at pH 7.4 was increased from 15 to 150 mM. However, further increase of salt concentration up to 500 mM resulted in decreased adsorption. To confirm the aforementioned results an approaching bare Si(3)N(4) tip was used as an electrostatic analogue to a protein molecule and interaction force curves between it and the substrate were recorded. The results were in consistence with the double layer theory which justifies the screening of electrostatic repulsion as the salt concentration increases.