Discretization limits of lattice-Boltzmann methods for studying immiscible two-phase flow in porous media

Digital images of porous media often include features approaching the image resolution length scale. The behavior of numerical methods at low resolution is therefore important even for well-resolved systems. We study the behavior of the Shan-Chen (SC) and Rothman-Keller (RK) multicomponent lattice-Boltzmann models in situations where the fluid-fluid interfacial radius of curvature and/or the feature size of the medium approaches the discrete unit size of the computational grid. Various simple, small-scale test geometries are considered, and a drainage test is also performed in a Bentheimer sandstone sample. We find that both RK and SC models show very high ultimate limits: in ideal conditions the models can simulate static fluid configuration with acceptable accuracy in tubes as small as three lattice units across for RK model (six lattice units for SC model) and with an interfacial radius of curvature of two lattice units for RK and SC models. However, the stability of the models is affected when operating in these extreme discrete limits: in certain circumstances the models exhibit behaviors ranging from loss of accuracy to numerical instability. We discuss the circumstances where these behaviors occur and the ramifications for larger-scale fluid displacement simulations in porous media, along with strategies to mitigate the most severe effects. Overall we find that the RK model, with modern enhancements, exhibits fewer instabilities and is more suitable for systems of low fluid-fluid miscibility. The shortcomings of the SC model seem to arise predominantly from the high, strongly pressure-dependent miscibility of the two fluid components.     

Preclinical studies in normal canine prostate of a novel palladium-bacteriopheophorbide (WST09) photosensitizer for photodynamic therapy of prostate cancers

Photodynamic therapy (PDT) uses light to activate a photosensitizer to achieve localized tumor control. In this study, PDT mediated by a second-generation photosensitizer, palladium-bacteriopheophorbide WST09 (Tookad) was investigated as an alternative therapy for prostate cancer. Normal canine prostate was used as the animal model. PDT was performed by irradiating the surgically exposed prostate superficially or interstitially at 763 nm to different total fluences (100 or 200 J/cm2; 50, 100 or 200 J/cm) at 5 or 15 min after intravenous administration of the drug (2 mg/kg). Areas on the bladder and colon were also irradiated. The local light fluence rate and temperature were monitored by interstitial probes in the prostate. All animals recovered well, without urethral complications. During the 1 week to 3 month post-treatment period, the prostates were harvested for histopathological examination. The PDT-induced lesions showed uniform hemorrhagic necrosis and atrophy, were well delineated from the adjacent normal tissue and increased linearly in diameter with the logarithm of the delivered light fluence. A maximum PDT-induced lesion size of over 3 cm diameter could be achieved with a single interstitial treatment. There was no damage to the bladder or rectum caused by scattered light from the prostate. The bladder and rectum were also directly irradiated with PDT. At 80 J/cm2, a full-depth necrosis was observed but resulted in no perforation. At 40 J/cm2, PDT produced minimal damage to the bladder or rectum. On the basis of optical dosimetry, we have estimated that 20 J/cm2 is the fluence required to produce prostatic necrosis. Thus, the normal structure adjacent to the prostate can be safely preserved with careful dosimetry. At therapeutic PDT levels, there was no structural or functional urethral damage even when the urethra was within the treated region. Hence, Tookad-PDT appears to be a promising candidate for prostate ablation in patients with recurrent, or possibly even primary, prostate cancer.     

Measured solar ultraviolet radiation exposures of outdoor workers in Queensland in the building and construction industry

The risk to outdoor workers of exposure to solar ultraviolet radiation (UVR) has been known for some time, particularly in the building and construction industry, where workers often use little in the way of protection against solar UVR. In recent years there have been attempts by authorities in Australia and in Queensland in particular, where UVR levels in spring and summer are very high to extreme, to instigate and to encourage the use of personal UVR protection by outdoor workers. To quantify UVR exposure of building and construction industry workers involved in typical outdoor work, a study was conducted using UVR-sensitive polysulphone film badges. The results indicated that the doses were significant, often well in excess of recommended exposure limits. The measured exposures varied between trades. Data on the use of personal UVR-protective equipment and the skin type of workers were also collected. Many of the workers had skin types that were sensitive to UVR and showed signs of sunburn. In summary, the study found that at-risk individuals were exposed to extreme levels of UVR, in most cases without adequate and appropriate sun protection.     

Metal-catalyzed phosphodiester cleavage: secondary 18O isotope effects as an indicator of mechanism

Information about the transition states of metal-catalyzed hydrolysis reactions of model phosphate compounds has been obtained through determination of isotope effects (IEs) on the hydrolysis reactions. Metal complexation has been found to significantly alter the transition state of the reaction from the alkaline hydrolysis reaction, and the transition state is quite dependent on the particular metal ion used. For the diester, ethyl p-nitrophenyl phosphate, the nonbridge 18O effect for the hydrolysis reactions catalyzed by Co(III) 1,5,9-triazacyclononane and Eu(III) were 1.0006 and 1.0016, respectively, indicative of a slightly associative transition state and little net change in bonding to the nonbridge oxygen. The reaction catalyzed by Zn(II) 1,4,7,10-tetraazacyclododecane had an 18O nonbridge IE of 1.0108, showing the reaction differs significantly from the reaction of the noncomplexed diester and resembles the reactions of triesters. Reaction with Co(III) 1,4,7,10-tetraazacyclododecane showed an inverse effect of 0.9948 reflecting the effects of bonding of the diester to the Co(III). Lanthanide-catalyzed hydrolysis has been observed to have unusually large 15N effects. To further investigate this effect, the 15N effect on the reaction catalyzed by Ce(IV) bis-Tris propane solutions at pH 8 was determined to be 1.0012. The 15N effects were also measured for the reaction of the monoester p-nitrophenyl phosphate by Ce(IV) bis-Tris propane (1.0014) and Eu(III) bis-Tris propane (1.0012). These smaller effects at pH 8 indicate that a smaller negative charge develops on the nitrogen during the hydrolysis reaction.     

Tailoring the trajectory of cell rolling with cytotactic surfaces

Cell separation technology is a key tool for biological studies and medical diagnostics that relies primarily on chemical labeling to identify particular phenotypes. An emergent method of sorting cells based on differential rolling on chemically patterned substrates holds potential benefits over existing technologies, but the underlying mechanisms being exploited are not well characterized. In order to better understand cell rolling on complex surfaces, a microfluidic device with chemically patterned stripes of the cell adhesion molecule P-selectin was designed. The behavior of HL-60 cells rolling under flow was analyzed using a high-resolution visual tracking system. This behavior was then correlated to a number of established predictive models. The combination of computational modeling and widely available fabrication techniques described herein represents a crucial step toward the successful development of continuous, label-free methods of cell separation based on rolling adhesion.     

Screening and determination of polycyclic aromatic hydrocarbons in seafoods using QuEChERS-based extraction and high-performance liquid chromatography with fluorescence detection

A rapid, sensitive, and accurate method for the screening and determination of polycyclic aromatic hydrocarbons (PAHs) in edible seafood is described. The method uses quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based extraction and HPLC with fluorescence detection (FLD). The method was developed and validated in response to the massive Deepwater Horizon oil spill in the Gulf of Mexico. Rapid and highly sensitive PAH screening methods are critical tools needed for oil spill response; they help to assess when seafood is safe for harvesting and consumption. Sample preparation involves SPE of edible seafood portions with acetonitrile, followed by the addition of salts to induce water partitioning. After centrifugation, a portion of the acetonitrile layer is filtered prior to analysis via HPLC-FLD. The chromatographic method uses a polymeric C18 stationary phase designed for PAH analysis with gradient elution, and it resolves 15 U.S. Environmental Protection Agency priority parent PAHs in fewer than 20 min. The procedure was validated in three laboratories for the parent PAHs using spike recovery experiments at PAH fortification levels ranging from 25 to 10 000 microg/kg in oysters, shrimp, crab, and finfish, with recoveries ranging from 78 to 99%. Additional validation was conducted for a series of alkylated homologs of naphthalene, dibenzothiophene, and phenanthrene, with recoveries ranging from 87 to 128%. Method accuracy was further assessed based on analysis of National Institute of Standards and Technology Standard Reference Material 1974b. The method provides method detection limits in the sub to low ppb (microg/kg) range, and practical LOQs in the low ppb (microg/kg) range for most of the PAH compounds studied.     

Matrix-assisted laser desorption/ionisation mass spectrometric response factors of peptides generated using different proteolytic enzymes

Matrix-assisted laser desorption/ionisation (MALDI) mechanisms and the factors that influence the intensity of the ion signal in the mass spectrum remain imperfectly understood. In proteomics, it is often necessary to maximise the peptide response in the mass spectrum, especially for low abundant proteins or for proteolytic peptides of particular significance. We set out to determine which of the common proteolytic enzymes give rise to peptides with the best response factors under MALDI conditions. Standard proteins were enzymatically digested using four common proteases. We assessed relative response factors by coanalyzing the resulting digests. Thus, when tryptic peptides were added in equimolar quantities to their corresponding Asp-N, chymotrypsin and Glu-C digests, tryptic peptide signals were always predominant in the resulting MALDI mass spectra. Observable peaks attributable to non-tryptic peptides generally contained a terminal basic residue. It was proposed that a terminal basic residue has a disproportionate influence upon gas-phase basicity, and this hypothesis was supported by experiments with model isotopically labelled peptides. Experiments applying Cook's kinetic method showed that the peptide with a C-terminal arginine residue was more basic than the equivalent peptide with an N-terminal arginine, which was more basic than the peptide in which the arginine was mid-chain. Thus, the observation of the higher MALDI mass spectrometry response factors of tryptic peptides in comparison with peptides derived using other proteolytic enzymes corresponds with higher gas-phase basicities and may, along with other factors such as the complexity of the digest, influence the choice of enzyme in "bottom-up" proteomic experiments.     

Reveal E. coli 2.0 method for detection of Escherichia coli O157:H7 in raw beef

Reveal E. coli 2.0 is a new lateral-flow immunodiagnostic test for detection of E. coli O157:H7 and O157:NM in raw beef trim and ground beef. Compared with the original Reveal E. coli O157:H7 assay, the new test utilizes a unique antibody combination resulting in improved test specificity. The device architecture and test procedure have also been modified, and a single enrichment protocol was developed which allows the test to be performed at any point during an enrichment period of 12 to 20 h. Results of inclusivity and exclusivity testing showed that the test is specific for E. coli serotypes O157:H7 and O157:NM, with the exception of two strains of O157:H38 and one strain of O157:H43 which produced positive reactions. In internal and independent laboratory trials comparing the Reveal 2.0 method to the U.S. Department of Agriculture-Food Safety and Inspection Service reference culture procedure for detection of E. coli O157:H7 in 65 and 375 g raw beef trim and ground beef samples, there were no statistically significant differences in method performance with the exception of a single internal trial with 375 g ground beef samples in which the Reveal method produced significantly more positive results. There were no unconfirmed positive results by the Reveal assay, for specificity of 100%. Results of ruggedness testing showed that the Reveal test produces accurate results even with substantial deviation in sample volume or device incubation time or temperature. However, addition of the promoter reagent to the test sample prior to introducing the test device is essential to proper test performance.     

Recent trends in carbon nanomaterial-based electrochemical sensors for biomolecules: A review

Carbon nanomaterials are advantageous for electrochemical sensors because they increase the electroactive surface area, enhance electron transfer, and promote adsorption of molecules. Carbon nanotubes (CNTs) have been incorporated into electrochemical sensors for biomolecules and strategies have included the traditional dip coating and drop casting methods, direct growth of CNTs on electrodes and the use of CNT fibers and yarns made exclusively of CNTs. Recent research has also focused on utilizing many new types of carbon nanomaterials beyond CNTs. Forms of graphene are now increasingly popular for sensors including reduced graphene oxide, carbon nanohorns, graphene nanofoams, graphene nanorods, and graphene nanoflowers. In this review, we compare different carbon nanomaterial strategies for creating electrochemical sensors for biomolecules. Analytes covered include neurotransmitters and neurochemicals, such as dopamine, ascorbic acid, and serotonin; hydrogen peroxide; proteins, such as biomarkers; and DNA. The review also addresses enzyme-based electrodes that are used to detect non-electroactive species such as glucose, alcohols, and proteins. Finally, we analyze some of the future directions for the field, pointing out gaps in fundamental understanding of electron transfer to carbon nanomaterials and the need for more practical implementation of sensors.