Stratified water columns: homogenization and interface evolution.

Stratified water columns are often found in lakes and oceans. Stratifications result from differences in density due to salt concentration, temperature, solid content and oxygenation. The stability of stratifications affects bioactivity, sedimentation, contaminant transport and environmental remediation. This study investigates the evolution of 6 stratified water columns created by differences in salinity, suspended minerals and the presence of a bottom heat source. We use acoustic wave reflection, photography, and both electrical conductivity and temperature profiles to track changes in stratification. Results show that multiple concurrent processes emerge across layers in otherwise quiescent water bodies. Dissimilar chemo-thermo conditions give rise to chemical and thermal diffusion, convection, and double-diffusion convection. When stratification involves suspended particles, interlayer processes include diffusiophoresis, flocculation/aggregation, sedimentation, osmosis, and chemo-consolidation; in this case, the specific surface and surface charge of suspended particles, and the salt concentration in contiguous layers determine aggregation-sedimentation-consolidation patterns. The interlayer transition zone acts as a high-pass filter that preferentially reflects low-frequency long-wavelength P-waves; invasive thermal and electrical conductivity probes provide complementary information and may identify stratification even when it is undetected by acoustic signals.

The capillary pressure vs. saturation curve for a fractured rock mass: fracture and matrix contributions.

The fractal topography of fracture surfaces challenges the upscaling of laboratory test results to the field scale, therefore the study of rock masses often requires numerical experimentation. We generate digital fracture analogues and model invasion percolation to investigate the capillarity-saturation Pc-Sw fracture response to changes in boundary conditions. Results show that aperture is Gaussian-distributed and the coefficient of variation is scale-independent. The aperture contraction during normal stress increments causes higher capillary pressures and steeper Pc-Sw curves, while shear displacement results in invasion anisotropy. The three-parameter van Genutchen model adequately fits the fracture capillary response in all cases; the capillary entry value decreases with fracture size, yet the fracture Pc-Sw curve normalized by the entry value is size-independent. Finally, we combine the fracture and matrix response to infer the rock mass response. Fracture spacing, aperture statistics and matrix porosity determine the rock mass capillarity-saturation Pc-Sw curve. Fractures without gouge control the entry pressure whereas the matrix regulates the residual saturation at high capillary pressure Pc.

Effect of grain dissolution on sloping ground.

The static and dynamic stability of natural or constructed slopes can be affected by dissolution or dissolution-like phenomena. Their underlying mechanisms, however, remain unclear. New experimental results and discrete element simulations provide particle-level and macroscale information on the consequences of mineral dissolution on slope behavior. At the microscale, load-carrying grain arches develop around dissolving particles, the porosity increases, and contact force chains evolve to form a honeycomb topology. At the macroscale, while vertical settlements are the prevailing deformation pattern, lateral granular movements that create mass wasting are prominent in sloping ground, even under the quasi-static granular loss. Horizontal grain displacement is maximum at the surface and decreases linearly with the distance from the slope surface to become zero at the bottom boundaries, much like vertical granular displacement along the depth. Sediments with smaller friction angles and steeper slopes experience greater displacement, both vertically and horizontally. Slopes become flatter after dissolution, with the reduction in slope angle directly related to the loss in ground elevation, ΔH/Ho. Yet, because of the porous fabric that results from dissolution, vertical shortening is less than the upper bound, estimated from the loss in the solid mass fraction, ΔH/Ho≈SF. Under water-saturated conditions, the post-dissolution fabric may lead to sudden undrained shear and slope slide.

Pore topology, volume expansion and pressure development in chemically-induced foam cements.

Foam cement is an engineered lightweight material relevant to a broad range of engineering applications. This study explores the effects of aluminum chips on cement-bentonite slurry expansion, pressure development, and the evolution of pore topology. The terminal volume expansion under free-boundary conditions or the pressure build up under volume-controlled conditions are a function of the aluminum mass ratio, bentonite mass ratio, and aluminum chip size. X-ray CT images show that finer aluminum chips create smaller pores but result in a larger volume expansion than when larger sized chips are used; on the other hand, large chip sizes result in unreacted residual aluminum. Time-lapse CT images clearly show the sequence of processes which lead to the development of foam cement: gas bubble nucleation, bubble growth, capillary-driven grain displacement enhanced by the presence of bentonite, coalescence, percolation, gas leakage and pore collapse. These results illustrate the potential to customize the mixture composition of chemically-induced gassy cement to control expansion and pressure build up, and to minimize percolating discontinuities and gas release.

Stress distribution around kerogen particles as a measure of the initiation of bitumen-filled microfractures in organic-rich source rocks.

In this article, we present a method used to model the initiation of bitumen-filled microfractures in immature, organic-rich source rocks. The first part presents the method used to calculate the stress distribution around the kerogen particles. The second part explains the method used to calculate the pressure change as a function of the transformation ratio and the resulting overpressure.•The effective principal stresses acting on the kerogen boundary were calculated.•Kerogen geometries were determined using the measured aspect ratio of the kerogen traces obtained from the petrography observation.•To estimate overpressure, the increase in pressure due to the transformation of kerogen to bitumen was calculated.

Self-assembly of millimeter-scale magnetic particles in suspension.

Self-assembly is ubiquitous at all scales in nature. Most studies have focused on the self-assembly of micron-scale and nano-scale components. In this study, we explore the self-assembly of millimeter-scale magnetic particles in a bubble-column reactor to form 9 different structures. Two component systems (N-N and S-S particles) assemble faster than one-component systems (all particles have N-S poles) because they have more numerous bonding pathways. In addition, two-components add control to process initiation and evolution, and enable the formation of complex structures such as squares, tetrahedra and cubes. Self-assembly is collision-limited, thus, the formation time increases with the total number of bonds required to form the structure and the injected power. The dimensionless Mason number captures the interplay between hydrodynamic forces and magnetic interactions: self-assembly is most efficient at intermediate Mason numbers (the system is quasi-static at low Mason numbers with limited chances for particle interaction; on the other hand, hydrodynamic forces prevail over dipole-dipole interactions and hinder bonding at high Mason numbers). Two strategies to improve yield involve (1) the inclusion of pre-assembled nucleation templates to prevent the formation of incorrect initial structures that lead to kinetic traps, and (2) the presence of boundaries to geometrically filter unwanted configurations and to overcome kinetic traps through particle-wall collisions. Yield maximization involves system operation at an optimal Mason number, the inclusion of nucleation templates and the use of engineered boundaries (size and shape).

The effect of particle shape on discharge and clogging.

Granular flow is common across different fields from energy resource recovery and mineral processing to grain transport and traffic flow. Migrating particles may jam and form arches that span constrictions and hinder particle flow. Most studies have investigated the migration and clogging of spherical particles, however, natural particles are rarely spherical, but exhibit eccentricity, angularity and roughness. New experiments explore the discharge of cubes, 2D crosses, 3D crosses and spheres under dry conditions and during particle-laden fluid flow. Variables include orifice-to-particle size ratio and solidity. Cubes and 3D crosses are the most prone to clogging because of their ability to interlock or the development of face-to-face contacts that can resist torque and enhance bridging. Spheres arriving to the orifice must be correctly positioned to create stable bridges, while flat 2D crosses orient their longest axes in the direction of flowlines across the orifice and favor flow. Intermittent clogging causes kinetic retardation in particle-laden flow even in the absence of inertial effects; the gradual increase in the local particle solidity above the constriction enhances particle interactions and the probability of clogging. The discharge volume before clogging is a Poisson process for small orifice-to-particle size ratio; however, the clogging probability becomes history-dependent for non-spherical particles at large orifice-to-particle size ratio and high solidities, i.e., when particle-particle interactions and interlocking gain significance.

Self-assembled nanoparticle-coated interfaces: Capillary pressure, shell formation and buckling.

HYPOTHESIS: Particle accumulation at liquid-liquid or liquid-gas interfaces can significantly alter capillary behavior and give rise to unusual interfacial phenomena including the asymmetric macroscopic mechanical response of the interface. EXPERIMENTS: This study explores the accumulation of cetyltrimethylammonium bromide-modified nanoparticles at fluid interfaces and the subsequent mechanical response of nanoparticle-coated droplets during contraction and expansion. Droplet tests involve the simultaneous recording of the droplet shape and the capillary pressure. Complementary single-pore experiments examine the response of particle-coated interfaces as they traverse a pore constriction. FINDINGS: Interfaces promote order. The time-dependent nanoparticle accumulation at the interface is diffusion-controlled. The nanoparticle coated droplets can sustain negative capillary pressure before they buckle. Buckling patterns strongly depend on the boundary conditions: non-slip boundary conditions lead to crumples while slip boundary conditions result in just a few depressions. The particle-coated interface exhibits asymmetric behavior in response to particle-level capillary forces: an "oil droplet in a nanofluid bath" withstands a significantly higher capillary pressure difference than a "nanofluid droplet in an oil bath". A first-order equilibrium analysis of interaction forces explains the asymmetric response. Single-constriction experiments show that the formation of particle-coated interfaces has a pronounced effect on fluid displacement in porous media.

The critical role of pore size on depth-dependent microbial cell counts in sediments.

Cell counts decrease with sediment depth. Typical explanations consider limiting factors such as water availability and chemistry, carbon source, nutrients, energy and temperature, and overlook the role of pore size. Our analyses consider sediment self-compaction, the evolution of pore size with depth, and the probability of pores larger than the microbial size to compute the volume fraction of life-compatible pores. We evaluate cell counts vs. depth profiles gathered at 116 sites worldwide. Results confirm the critical role of pore size on cell counts in the subsurface and explain much of the data spread (from ~ 9 orders of magnitude range in cell counts to ~ 2 orders). Cells colonize pores often forming dense biofilms, thus, cell counts in pores are orders of magnitude higher than in the water column. Similar arguments apply to rocks.

Electrification at water-hydrophobe interfaces.

The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. A clear understanding of these mechanisms could, for instance, aid the rational design of triboelectric generators and micro- and nano-fluidic devices. Here, we investigate the origins of the excess positive charges incurred on water droplets that are dispensed from capillaries made of polypropylene, perfluorodecyltrichlorosilane-coated glass, and polytetrafluoroethylene. Results demonstrate that the magnitude and sign of electrical charges vary depending on: the hydrophobicity/hydrophilicity of the capillary; the presence/absence of a water reservoir inside the capillary; the chemical and physical properties of aqueous solutions such as pH, ionic strength, dielectric constant and dissolved CO2 content; and environmental conditions such as relative humidity. Based on these results, we deduce that common hydrophobic materials possess surface-bound negative charge. Thus, when these surfaces are submerged in water, hydrated cations form an electrical double layer. Furthermore, we demonstrate that the primary role of hydrophobicity is to facilitate water-substrate separation without leaving a significant amount of liquid behind. These results advance the fundamental understanding of water-hydrophobe interfaces and should translate into superior materials and technologies for energy transduction, electrowetting, and separation processes, among others.

Haines jumps: Pore scale mechanisms.

Haines instabilities are sudden jumps of the fluid interface accompanied by fluid redistribution and a transient pressure response. Haines jumps affect global displacement patterns in porous media, promote fingered invasion, increase fluid trapping, and contribute to hysteretic saturation. Detailed analyses and experimental results show that jumps take place when the pressure-volume response is multivalued across the pore throat, during either advancing or receding tests. This situation emerges in "soft systems" such as liquids with entrapped gas bubbles, compliant substrates, and when multiple menisci interact across the porous networks. Elastic deformations and capillarity combine to form the dimensionless elastocapillary number N_{ec} for a given pore geometry and fluid mixture: a system with elastocapillary number N_{ec}<1 is prone to Haines instabilities. Therefore, Haines jumps are more likely to occur not only in soft porous systems, but also when the network topology is characterized by pronounced pore constrictions, and the fluids form small contact angles and generate high interfacial tension.

Pacientes con adenopatías calcificadas / Patient with calcified lymph nodes

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Paciente con bronquiectasias y litoptisis / Patient with bronchiectasis and lithoptysis

La broncolitiasis (cálculos bronquiales) es una afección rara. Se originan por la erosión bronquial de calcificaciones hiliares o parenquimatosas, que por lo general son secundarias a infecciones, como la tuberculosis o la histoplasmosis1. Presentamosel caso de una paciente con bronquiectasias bilaterales secundarias a tuberculosis y que durante el seguimientoha presentado varios episodios de litoptisis

The broncolithiasis (bronchial stones) is a rare affection. They are produced by the bronchial erosion of hili or parenchymatose calcifications, that are generally secondary to infections like the tuberculosis or histoplasmosis1. We report the case of a patient with bilateral bronchiectasis due to tuberculosis and that during the following she presented severalepisodes of lithoptysis (AU)

¿Está cambiando la etiología de las bronquiectasias? / Is the etiology of bronchiectasis changing?

Introducción: Las bronquiectasias (BQ) constituyen el estadio final de una heterogénea variedad de procesos patológicos.Objetivo: Valorar la etiología de las BQ de los pacientes derivados a una consulta monográfica de esta patología de un hospital terciario, durante el período comprendido entre julio 2002 a septiembre 2005.Pacientes y métodos: Se incluyeron todos los pacientes que fueron remitidos a la consulta con el diagnóstico de BQ mediante tomografía axial computarizada de tórax. Se les realizaron una historia clínica detallada, microbiología de esputo, espirometría, Mantoux y, en determinados casos, determinación de inmunoglobulinas IgE, IgG, IgA, IgM, IgG e IgE específicas a Aspergillus, proteinograma, anticuerpos antinucleares, test del sudor, estudio genético para fibrosis quística,radiografía de senos, espermiograma y estudio gastroduodenal.Resultados: Fueron evaluados 171 enfermos, 85 mujeres, con una edad media de 63,97 años (rango: 19-94). Presentaron una espirometría con porcentajes sobre el valor teórico de FVC: 69,83%, (19,92) y FEV1 67,01% (25,44). Se determinaron las siguientes etiologías causantes de las bronquiectasias: en el 38% fueron secundarias a tuberculosis, el 15,5%a enfermedad pulmonar obstructiva crónica, el 11,9% a asma, el 4,8% a enfermedad del tejido conectivo, el 4,2% a neumonía necrotizante, el 2,4% a enfermedad del cilio inmóvil, déficit de alfa 1 antitripsina y a inmunodeficiencias, el resto de las etiologías fueron inferiores al 2%. En 20 casos la etiología fue desconocida.Conclusión: Los protocolos diagnósticos de una consulta monográfica ayudan a establecer la causa primaria de las bronquiectasias. En nuestro medio las etiologías más frecuentes fueron la tuberculosis, la EPOC y asma

Objective: To evaluate the aetiology of bronchiectasis of patients from a monographic consult in an University hospital, from july 2002 to september 2005.Methods: All the patients with bronchiectasis diagnose confirmed by high resolution computed tomography (HRCT) were included. We made a clinical history, sputum microbiology, pulmonary function test, Mantoux test, and in certain cases: inmunoglobulins E, G, A, M, Aspergillus inmunoglobulins G and E, proteinogram, autoantibodies, sweat chloride test, CF genotyping, sinus radiology,spermiogram, and barium swallow/oesophageal imaging.Results: 171 patients were evaluated, 85 women, with a mean age of 63.97 years (range 19-94). They had a spirometry with FVC 69.83 % (19.92) and FEV 1 67.01 %(25.44). The causes of bronchiectasis ere: 38% due to tuberculosis, 15,5% to chronic obstructive pulmonary disease (COPD), 11.9% to asthma, 4.8% to collagen diseases, 4.2% to necrotizing pneumonia, 2.4% to inmotile cilia syndrome; other aetiologies were less than 2%. In 20 cases the aetiology was unknown.Conclusion: The diagnostic guidelines in a monographic consult help to determinate the mean cause of the bronchiectasis. In our area the most frequent causes were the tuberculosis, the COPD and the asthma

Diagnóstico de atresia bronquial en una mujer adulta / Diagnosis of bronchial atresia in an adult woman

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[Lumbar disc disease in adolescents]. / Hernia discal lumbar en adolescentes.

INTRODUCTION: Intervertebral disc herniation is a very common neurosurgical pathology. Most commonly disc disease occurs in adults and series published in children are only few and each reports only few cases. A genetic factor has been considered but in none of our patients there was a family history of disc disease. PATIENTS AND METHODS: We report ten patients with disc herniations in adolescents occurring among 1920 patients operated of herniated discs between 1988 and 1998. These herniations in adolescents were all related to some sport activities, and they occurred in the age range of 12 to 16 years. Symptoms were back pain and lower extremities pains of roots L5 or S1. All were studied with magnetic resonance imaging and in all patients the herniated disc was either in L4 L5 or L5 S1 intervertebral spaces. All disc were subligamental and 81.5% were posterolateral in position. Pathological studies of the herniated discs showed elastic consistency with high water content without degenerative changes. RESULTS: After microscopic removal of the herniated discs pain disappeared and remained so in the follow up. It was not necessary to reoperate in any of these patients and the postoperative follow up was between 2 and 5 years. CONCLUSIONS: Herniated disc disease is very infrequent in adolescents and all recovered completely after surgery, and the localization is posterolateral and subligamental.

Parasites and pathologic conditions of the cockle Cerastoderma edule populations of the coast of Galicia (NW Spain).

A survey of pathological conditions affecting cockle populations of the most economically important natural beds of Galician estuaries in NW Spain was performed. Samples of 30 adult cockles were collected from each of 34 natural beds in the spring of 1999 and processed by histological techniques. Disseminated neoplasia were seen in samples from most of the natural beds, in some cases with a high prevalence. The gregarine Nematopsis sp., larval trematode stages, and branchial extracellular large cysts enclosing bacteria-like microorganisms were the most prevalent parasites. Paravortex cardii, intracellular colonies of rickettsiae-like organisms in digestive and gill epithelium, Pseudoklossia sp. coccidians, Trichodina sp., and other ciliates were frequently seen in the samples. Copepods in gills and intestine and unidentified gregarines in intestine epithelia and surrounding connective tissue were less prevalent and were observed in samples of some natural beds. Large foci of heavy hemocytic infiltration were detected in a few sites only. Cysts of Steinhausia sp. and plasmodia and spores of a haplosporidian were seen in cockles from two localities. Inflammation was frequently observed in the samples. Some of the parasites and pathological conditions could be associated with mortality.

[Septic thrombophlebitis of the portal vein associated with reversible portal hypertension]. / Tromboflebitis séptica de la vena porta asociada a hipertension portal reversible.

Septic thrombophlebitis of the portal vein is an unusual and serious complication of abdominal infection. We present a patient with thrombophlebitis of the portal vein of unknown origin, suffering from fever, abdominal pain, jaundice, abnormal liver test function and bacteremia related to Bacteroides fragilis. Ultrasonography, with doppler of the portal vein, was performed which showed thrombosis of the portal vein together with signs of portal hypertension. The patient underwent six weeks of antibiotic treatment. The evolution was favourable, the infection was overcome and the portal vein was de-obstructed as a consequence of which the signs of portal hypertension disappeared.

Tromboflebitis séptica de la vena porta asociada a hipertension portal reversible. / [Septic thrombophlebitis of the portal vein associated with reversible portal hypertension]

Septic thrombophlebitis of the portal vein is an unusual and serious complication of abdominal infection. We present a patient with thrombophlebitis of the portal vein of unknown origin, suffering from fever, abdominal pain, jaundice, abnormal liver test function and bacteremia related to Bacteroides fragilis. Ultrasonography, with doppler of the portal vein, was performed which showed thrombosis of the portal vein together with signs of portal hypertension. The patient underwent six weeks of antibiotic treatment. The evolution was favourable, the infection was overcome and the portal vein was de-obstructed as a consequence of which the signs of portal hypertension disappeared.