Direct numerical simulations of interface dynamics to link capillary pressure and total surface energy

The flow of two immiscible fluids through a porous medium depends on the complex interplay between gravity, capillarity, and viscous forces. The interaction between these forces and the geometry of the medium gives rise to a variety of complex flow regimes that are difficult to describe using continuum models. Although a number of pore-scale models have been employed, a careful investigation of the macroscopic effects of pore-scale processes requires methods based on conservation principles in order to reduce the number of modeling assumptions. In this work we perform direct numerical simulations of drainage by solving Navier-Stokes equations in the pore space and employing the Volume Of Fluid (VOF) method to track the evolution of the fluid-fluid interface. After demonstrating that the method is able to deal with large viscosity contrasts and model the transition from stable flow to viscous fingering, we focus on the macroscopic capillary pressure and we compare different definitions of this quantity under quasi-static and dynamic conditions. We show that the difference between the intrinsic phase-average pressures, which is commonly used as definition of Darcy-scale capillary pressure, is subject to several limitations and it is not accurate in presence of viscous effects or trapping. In contrast, a definition based on the variation of the total surface energy provides an accurate estimate of the macroscopic capillary pressure. This definition, which links the capillary pressure to its physical origin, allows a better separation of viscous effects and does not depend on the presence of trapped fluid clusters.

Gravity-driven slug motion in capillary tubes

The velocity of a liquid slug falling in a capillary tube is lower than predicted for Poiseuille flow due to presence of menisci, whose shapes are determined by the complex interplay of capillary, viscous, and gravitational forces. Due to the presence of menisci, a capillary pressure proportional to surface curvature acts on the slug and streamlines are bent close to the interface, resulting in enhanced viscous dissipation at the wedges. To determine the origin of drag-force increase relative to Poiseuille flow, we compute the force resultant acting on the slug by integrating Navier-Stokes equations over the liquid volume. Invoking relationships from differential geometry we demonstrate that the additional drag is due to viscous forces only and that no capillary drag of hydrodynamic origin exists (i.e., due to hydrodynamic deformation of the interface). Requiring that the force resultant is zero, we derive scaling laws for the steady velocity in the limit of small capillary numbers by estimating the leading order viscous dissipation in the different regions of the slug (i.e., the unperturbed Poiseuille-like bulk, the static menisci close to the tube axis and the dynamic regions close to the contact lines). Considering both partial and complete wetting, we find that the relationship between dimensionless velocity and weight is, in general, nonlinear. Whereas the relationship obtained for complete-wetting conditions is found in agreement with the experimental data of Bico and Quere [J. Bico and D. Quere, J. Colloid Interface Sci. 243, 262 (2001)], the scaling law under partial-wetting conditions is validated by numerical simulations performed with the Volume of Fluid method. The simulated steady velocities agree with the behavior predicted by the theoretical scaling laws in presence and in absence of static contact angle hysteresis. The numerical simulations suggest that wedge-flow dissipation alone cannot account for the entire additional drag and that the non-Poiseuille dissipation in the static menisci (not considered in previous studies) has to be considered for large contact angles.

Biochemical identification of three sympatric Apodemus species by protein electrophoresis of blood samples

The allelic pattern of seralbumine and general protein 1 of the three sympatric Apodemus species Apodemus sylvaticus, A. flavicollis, and A. alpicola, were studied using electrophoretic analysis of blood samples, This method appears to be a sensitive tool for distinguishing the three Apodemus species in the Alps, Their identification on the basis of external characteristics in the field is sometimes extremely difficult, even more so for juvenile specimens. Compared to previously described methods the electrophoretic analysis does not require killing animals and can be used on juveniles.

Prognostic significance of nailfold capillary microscopy in patients with Raynaud's phenomenon and scleroderma-pattern abnormalities. A six-year follow-up study.

The aim of this study was to assess the prognostic significance of scleroderma capillary pattern (SD-pattern) in patients with Raynaud's phenomenon. Thirty patients with a capillaroscopy examination suggestive of scleroderma (megacapillaries and/or avascularity) but without clinical criteria of scleroderma (ARA criteria) were reevaluated 6 years after the initial clinical and capillaroscopy examinations. SD-pattern abnormalities were classified according to a semiquantitative method. Eight out of the 28 evaluated patients (28%) developed a scleroderma spectrum disorder (SDS). The presence of avascularity and/or a mean of more than two megacapillaries digit greatly enhanced the percentage of evolution toward SDS (70%/88% respectively). Most of the patients with few enlarged capillaries and no capillary rarefaction at entry had primary acrocyanosis (11/15). None of them developed SDS. The microangiopathy disappeared during the follow-up period in most of these patients (14/15). These results confirm the prognostic value of SD-pattern capillary abnormalities for SDS. Primary acrocyanosis, a benign clinical entity should be considered in presence of few megacapillaries and without capillary rarefaction.

Novel FOXF1 Mutations in Sporadic and Familial Cases of Alveolar Capillary Dysplasia with Misaligned Pulmonary Veins Imply a Role for its DNA Binding Domain.

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV) is a rare and lethal developmental disorder of the lung defined by a constellation of characteristic histopathological features. Nonpulmonary anomalies involving organs of gastrointestinal, cardiovascular, and genitourinary systems have been identified in approximately 80% of patients with ACD/MPV. We have collected DNA and pathological samples from more than 90 infants with ACD/MPV and their family members. Since the publication of our initial report of four point mutations and 10 deletions, we have identified an additional 38 novel nonsynonymous mutations of FOXF1 (nine nonsense, seven frameshift, one inframe deletion, 20 missense, and one no stop). This report represents an up to date list of all known FOXF1 mutations to the best of our knowledge. Majority of the cases are sporadic. We report four familial cases of which three show maternal inheritance, consistent with paternal imprinting of the gene. Twenty five mutations (60%) are located within the putative DNA-binding domain, indicating its plausible role in FOXF1 function. Five mutations map to the second exon. We identified two additional genic and eight genomic deletions upstream to FOXF1. These results corroborate and extend our previous observations and further establish involvement of FOXF1 in ACD/MPV and lung organogenesis.

Graphitized carbon black in quartz tubes for the sampling of indoor air nicotine and analysis by microwave thermal desorption-capillary gas chromatography

Nicotine in a smoky indoor air environment can be determined using graphitized carbon black as a solid sorbent in quartz tubes. The temperature stability, high purity, and heat absorption characteristics of the sorbent, as well as the permeability of the quartz tubes to microwaves, enable the thermal desorption by means of microwaves after active sampling. Permeation and dynamic dilution procedures for the generation of nicotine in the vapor phase at low and high concentrations are used to evaluate the performances of the sampler. Tube preparation is described and the microwave desorption temperature is measured. Breakthrough volume is determined to allow sampling at 0.1-1 L/min for definite periods of time. The procedure is tested for the determination of gas and paticulate phase nicotine in sidestream smoke produced in an experimental chamber.

Screening for wound-induced oxylipins in Arabidopsis thaliana by differential HPLC-APCI/MS profiling of crude leaf extracts and subsequent characterisation by capillary-scale NMR

A simple non-targeted differential HPLC-APCI/MS approach has been developed in order to survey metabolome modifications that occur in the leaves of Arabidopsis thaliana following wound-induced stress. The wound-induced accumulation of metabolites, particularly oxylipins, was evaluated by HPLC-MS analysis of crude leaf extracts. A generic, rapid and reproducible pressure liquid extraction procedure was developed for the analysis of restricted leaf samples without the need for specific sample preparation. The presence of various oxylipins was determined by head-to-head comparison of the HPLC-MS data, filtered with a component detection algorithm, and automatically compared with the aid of software searching for small differences in similar HPLC-MS profiles. Repeatability was verified in several specimens belonging to different series. Wound-inducible jasmonates were efficiently highlighted by this non-targeted approach without the need for complex sample preparation as is the case for the 'oxylipin signature' procedure based on GC-MS. Furthermore this HPLC-MS screening technique allowed the isolation of induced compounds for further characterisation by capillary-scale NMR (CapNMR) after HPLC scale-up. In this paper, the screening method is described and applied to illustrate its potential for monitoring polar and non-polar stress-induced constituents as well as its use in combination with CapNMR for the structural assignment of wound-induced compounds of interest

Thermodynamic stability of nanosized multicomponent bubbles/droplets: The square gradient theory and the capillary approach

Formation of nanosized droplets/bubbles from a metastable bulk phase is connected to many unresolved scientific questions. We analyze the properties and stability of multicomponent droplets and bubbles in the canonical ensemble, and compare with single-component systems. The bubbles/droplets are described on the mesoscopic level by square gradient theory. Furthermore, we compare the results to a capillary model which gives a macroscopic description. Remarkably, the solutions of the square gradient model, representing bubbles and droplets, are accurately reproduced by the capillary model except in the vicinity of the spinodals. The solutions of the square gradient model form closed loops, which shows the inherent symmetry and connected nature of bubbles and droplets. A thermodynamic stability analysis is carried out, where the second variation of the square gradient description is compared to the eigenvalues of the Hessian matrix in the capillary description. The analysis shows that it is impossible to stabilize arbitrarily small bubbles or droplets in closed systems and gives insight into metastable regions close to the minimum bubble/droplet radii. Despite the large difference in complexity, the square gradient and the capillary model predict the same finite threshold sizes and very similar stability limits for bubbles and droplets, both for single-component and two-component systems.

Information transfer between large and small two-dimensional polyacrylamide gel electrophoresis.

To determine the feasibility of data transfer, an interlaboratory comparison was conducted on colon carcinoma cell line (DLD-1) proteins resolved by two-dimensional polyacrylamide gel electrophoresis either on small (6 x 7 cm) or large (16x18 cm) gels. The gels were silver-stained and scanned by laser densitometry, and the image obtained was analyzed using Melanie software. The number of spots detected was 1337+/-161 vs. 2382+/-176 for small vs. large format gels, respectively. After gel calibration using landmarks determined using pl and Mr markers, large- and small-format gels were matched and 712+/-36 proteins were found on both types of gels. Having performed accurate gel matching it was possible to acquire additional information after accessing a 2-D PAGE reference database (http://www.expasy.ch/ cgibin/map2/def?DLD1_HUMAN). Thus, the difference in gel size is not an obstacle for data transfer. This will facilitate exchanges between laboratories or consultation concerning existing databases.

Capillary thermal desorption unit for near real-time analysis of VOCs at sub-trace levels. Application to the analysis of environmental air contamination and breath samples

A capillary microtrap thermal desorption module is developed for near real-time analysis of volatile organic compounds (VOCs) at sub-ppbv levels in air samples. The device allows the direct injection of the thermally desorbed VOCs into a chromatographic column. It does not use a second cryotrap to focalize the adsorbed compounds before entering the separation column so reducing the formation of artifacts. The connection of the microtrap to a GC–MS allows the quantitative determination of VOCs in less than 40 min with detection limits of between 5 and 10 pptv (25 °C and 760 mmHg), which correspond to 19–43 ng m−3, using sampling volumes of 775 cm3. The microtrap is applied to the analysis of environmental air contamination in different laboratories of our faculty. The results obtained indicate that most volatile compounds are easily diffused through the air and that they also may contaminate the surrounding areas when the habitual safety precautions (e.g., working under fume hoods) are used during the manipulation of solvents. The application of the microtrap to the analysis of VOCs in breath samples suggest that 2,5-dimethylfuran may be a strong indicator of a person's smoking status

Metodologias analíticas para determinação das fumonisinas em milho e alimentos à base de milho

Fumonisins are mycotoxins occurring worldwide, mainly in maize and maize-based food products, which could affect animal and human health. This paper reviews analytical methodologies for the determination of these fungal toxins in foods. It includes extraction, cleanup, derivatization procedures, detection, quantification, and confirmation procedures. Initial attempts at gas chromatographic methods and thin layer chromatography were supplanted by liquid chromatographic methods, mainly performed with fluorometric detection, or mass spectrometry detection, enabling the analysis of polar and thermolabile chemicals without chemical derivatization, which results in lower limits of detection. Alternative methods, such as enzyme linked immunosorbent assay or zone capillary zone electrophoresis, are also described.

Avaliação da composição química de águas do Sistema Guarapiranga: estudo de caso nos anos de 2002 e 2003

The supply of drinking water in the Metropolitan Area of São Paulo City has been a great and serious challenge in the latest years. This work demonstrates the viability of the evaluation of the degree of contamination of the water reservoirs using analytical procedures, which allow the analysis of several compounds at relatively low cost: stripping square wave voltammetry (SSWV) and capillary zone electrophoresis with contactless conductivity detection (CZE-CCD). The results of ionic composition indicated significant contamination of the Guarapiranga water system by human activities on the reservoir banks. In fact, the Guavirutuba and Itupu streams presented high concentrations of phosphate and ammonium ions. This can be directly related to misuse and unruled occupation of the soil and precarious sanitary infrastructure.

Determination of cocaine in brazilian paper currency by capillary gas chromatography/mass spectrometry

The presence of illicit drugs such as cocaine and marijuana in US paper currency is very well demonstrated. However, there is no published study describing the presence of cocaine and/or other illicit drugs in Brazilian paper currency. In this study, Brazilian banknotes were collected from nine cities, extracted and analyzed by capillary gas chromatography/mass spectrometry, in order to investigate the presence of cocaine. Bills were extracted with deionized water followed by ethyl acetate. Results showed that 93% of the bills presented cocaine in a concentration range of 2.38-275.10 µg/bill.

Typing of Enterococcus faecium by polymerase chain reaction and pulsed field gel electrophoresis

Polymerase chain reaction (PCR) with JB1 or REP consensus oligonucleotides and pulsed field gel electrophoresis (PFGE) were used to study genomic DNA extracted from 31 strains of enterococci. Eleven ATCC strains, representative of 11 species of Enterococcus, were initially tested by JB1-PCR, revealing that Enterococcus malodoratus and Enterococcus hirae presented identical banding patterns. Eight Enterococcus faecium isolates from Stanford University and 12 from São Paulo Hospital were studied by JB1-PCR, REP-PCR 1/2R and PFGE. Among the isolates from Stanford University, 5 genotypes were defined by JB1-PCR, 7 by REP-PCR 1/2R and 4 by PFGE. Among the isolates from São Paulo Hospital, 9 genotypes were identified by JB1-PCR, 6 by REP-PCR and 5 by PFGE. The three methods identified identical genotypes, but there was not complete agreement among them.

Evaluation by blue native polyacrylamide electrophoresis colorimetric staining of the effects of physical exercise on the activities of mitochondrial complexes in rat muscle

Blue native polyacrylamide electrophoresis (BN-PAGE) is a technique developed for the analysis of membrane complexes. Combined with histochemical staining, it permits the analysis and quantification of the activities of mitochondrial oxidative phosphorylation enzymes using whole muscle homogenates, without the need to isolate muscle mitochondria. Mitochondrial complex activities were measured by emerging gels in a solution containing all specific substrates for NADH dehydrogenase and cytochrome c oxidase enzymes (complexes I and IV, respectively) and the colored bands obtained were measured by optique densitometry. The objective of the present study was the application of BN-PAGE colorimetric staining for enzymatic characterization of mitochondrial complexes I and IV in rat muscles with different morphological and biochemical properties. We also investigated these activities at different times after acute exercise of rat soleus muscle. Although having fewer mitochondria than oxidative muscles, white gastrocnemius muscle presented a significantly higher activity (26.7 ± 9.5) in terms of complex I/V ratio compared to the red gastrocnemius (3.8 ± 0.65, P < 0.05) and soleus (9.8 ± 0.9, P < 0.001) muscles. Furthermore, the complex IV/V ratio of white gastrocnemius muscle was always significantly higher when compared to the other muscles. Ninety-five minutes of exhaustive physical exercise induced a decrease in complex I/V and complex IV/V ratios after all resting times (0, 3 and 6 h) compared to control (P < 0.05), probably reflecting the oxidative damage due to increasing free radical production in mitochondria. These results demonstrate the possible and useful application of BN-PAGE-histochemical staining to physical exercise studies.