Vibration-induced dynamical weakening of pyroclastic flows: Insights from rotating drum experiments

Pyroclastic flows are characterized by their high mobility, which is often attributed to gas fluidization of the usually fine and/or low-density particles. However, the physical mechanism that might drive sustained fluidization of pyroclastic flows over extraordinarily long runout distances is elusive. In this letter it is proposed that a powerful mechanism to weaken the frictional resistance of pyroclastic flows would arise from the prolonged and intense mechanical vibrations that commonly accompany these dense gravitational fluid-particle flows. The behavior of fine powders in a slowly rotating drum subjected to vibrations suggests that fluid-particle relative oscillations in granular beds can effectively promote the pore gas pressure at reduced shear rates. Dynamical weakening, as caused by the enhancement of pore fluid pressure, may be an important mechanism in any geophysical process that involves vibrations of granular beds in a viscous fluid. This is particularly relevant for granular flows involving large amounts of fine and/or light particles such as pyroclastic density currents.Ministerio de Economia y Competitividad CTQ2014-52763-C2-2-RJunta de Andalucía FQM-573

Dynamical weakening of pyroclastic flows by mechanical vibrations

Dynamical weakening of dense granular flows plays a critical role on diverse geological events such as seismic faulting and landslides. A common feature of these processes is the development of fluid-solid relative flows that could lead to fluidization by hydrodynamic viscous stresses. Volcanic ash landslides (pyroclastic flows) are characterized by their high mobility often attributed to fluidization of the usually fine and/or low-density particles by their interaction with the entrapped gas. However, the physical mechanism that might drive sustained fluidization of these dense granular flows over extraordinarily long runout distances is elusive. The behavior of volcanic ash in a slowly rotating drum subjected to mechanical vibrations shown in this work suggests that fluid-particle relative oscillations in dense granular flows present in volcanic eruption events can promote pore gas pressure at reduced shear rates as to sustain fluidization.Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-

Modeling the electrophoretic deposition of colloidal particles

This letter presents the results of numerical simulations of the buildup of a layer of colloidal particles on an electrode. In a low-frequency electric field, particles suspended in a low-conductivity liquid migrate to one electrode and then to the other. During each cycle, deposits are formed and dissipated. The current-voltage characteristics of the process reflect properties of the suspension and the deposited layer. Using a flux corrected transport (FCT) algorithm, the transport equation for the particle phase is solved simultaneously with equations describing the electric field. The model reproduces the main features of the current-voltage relation.Ministerio de Ciencia y Tecnología BFM2000-105

The charged bouncing ball: An experimental model for period-doubling bifurcation

This paper presents an experimental and theoretical study of the dynamics of a conducting ball in a poorly conducting liquid subjected to an electric field. When the applied voltage is constant the ball bounces regularly on the lower electrode. If an AC voltage is superimposed, with a period equal to the unperturbed time between impacts, the ball undergoes a period-doubling bifurcation when increasing the amplitude of the AC signal. The non-linear map which describes the dynamics of the ball is closely related to the standard map and to the classical problem of a bouncing ball on a moving table.Dirección General de Investigación Científica y Técnica (DGICYT) PB93-118

Mechanical Strength of Humidified Glass Beads

In this work we measure the mechanical strength of a bed of glass beads that has been previously subjected to a controlled flow of humid air by using a fluidized bed setup. The material is first initialized in a reproducible state by subjecting it to a high flow of dry air that drives the bed to bubbling. Then the gas flow is abruptly turned off and, once the bed is settled, it is subjected to a small flow of humid air during a certain period of time. Water moisture is added to the fluidizing air by bubbling it through water. The relative humidity and dew point of the air are monitored on-line by using humidity sensors upstream and downstream of the bed. After the stationary condition is reached, the bed is slowly tilted and the avalanche angle and depth are measured. From Coulomb’s wedge model and Rumpf’s equation using the attractive capillary force, the predicted angle of avalanche of the humidified samples is shown to be close to the experimental value.Ministerio de Ciencia y Tecnología (MCYT). España FIS2006-03645Junta de Andalucía FQM 42

Cohesion and Internal Friction of Fine Glass Beads as Affected by Small Intensity Vertical Vibration

We have used a novel centrifuge powder tester to obtain the angle of internal friction and cohesion of fine glass beads as affected by previous vibration in the vertical direction. In the experimental procedure we use a small amount of mass, typically between 2 and 4 grams, contained in a rectangular cell. The bed is initialized and subjected to low intensity vertical vibrations of controlled frequency and amplitude for a fixed period of time. By means of pre-vibration the material becomes compacted. Then the cell is taken to the centrifugal powder tester, in which it is rotated around its vertical axis at increasing values of the rotation velocity. At a critical point the shear stress caused by the action of the centrifugal force is large enough to drive material avalanches. From a theoretical analysis of these avalanches based on the Coulomb’s method of wedges we derive the angle of internal friction and cohesion of the glass beads. Measurements have been performed using different masses pre-vibrated at different frequencies and amplitudes. Results from the tests are fitted to a single trend when they are plotted as a function of the effective consolidation stress imposed on the bed by means of pre-vibration. Basically, the data indicate a significant increase of cohesion and a slight decrease of the angle of internal friction as the effective consolidation on the sample is increased. The interparticle cohesion force has been estimated from the cohesion measured, and using the averaging Rumpf’s equation. For the unconsolidated samples, the value estimated agrees with the expected force due to the sum of van der Waals and capillary forces for undeformed contacts between surface asperities. However, the interparticle cohesion force increases as pre-vibration intensity is increased, being this the main reason for the increase of cohesion at the bulk level. According to theoretical estimations, the increase of the interparticle cohesion force is attributable to the plastic yield of the surface asperities at contact. The rate of increase of the interparticle cohesion force with the interparticle consolidation force is in accordance with the results predicted by a theoretical model on plastic contacts between surface asperities. It can be concluded that fine powder flowability is seriously hindered by compaction due to pre-vibratio

Metástasis orales y maxilares: análisis clínico retrospectivo de 21 casos

Retrospective descriptive study of 21 oral soft tissue and/or maxillary bone metastatic cases. Materials and methods: Hospital records of our own department are reviewed for a 12-year period. Lymphoproliferative diseases, skin metastases, salivary glands, other craniofacial bones and cervical lymph-nodes are excluded. Epidemiologic, personal health, clinical, treatment and follow-up data are recollected and analysed in frequency statistics. Results: Male:Female ratio is 1.3:1, year-old range 52-82 and ethnic group 100 % white-caucasian. 19.0 % have carcinogenic occupational exposure, 52.4 % tobacco abuse, 61.9 % some kind of alcohol use, 57.1 % cardiovascular risk, 19.0 % cardiologic records, 28.6 % pulmonary, 19.0 % gastrointestinal, 19.0 % endocrine, 14.3 % genitourinary, 9.5 % other primary malignancy and 23.8% a first-degree relative with a neoplasm. 33.3 % patients have taken osteonecrosis-related drugs or received craniofacial radiotherapy. Metastasis is the debut in 7 patients while it corresponds to infirmity progression in 14. The chief reason for consultation is a mass. 8 lesions affect soft tissue and 13 the bone. 81.0 % have epithelial neoplasm lineages. The organ of origin is: 23.8 % lung, 23.8 breast, 23.8 % kidney, 9.5 % skin, 9.5 % soft parts, 4.8 % prostate and 4.8 % thyroid. 100 % have other location metastases. 14.3 % patients undergo surgery, 38.1 % receive radiotherapy, 47.6 % chemo- or targeted therapy, and 28.6 % symptomatic treatment. After a 1-124 months range of follow-up, 17 patients die and 4 are alive. Conclusions: Craniomaxillofacial metastases, usually with multiple visceral or axial skeleton lesions, have an ominous prognosis. Multidisciplinary management could benefit the patient status and lead to more favourable outcomes. There are exceptional cases of long-term survival.Estudio descriptivo retrospectivo de 21 casos de metástasis en tejidos blandos orales y/o huesos maxilares. Material y métodos: Revisión a 12 años de actas de nuestro departamento, excluyendo procesos linfoproliferativos, metástasis cutáneas, glándulas salivales, otros huesos craneofaciales y ganglios cervicales. Se recopilan datos epidemiológicos, antecedentes, clínicos, tratamiento y seguimiento, y analizan mediante estadísticos de frecuencia. Resultados: La proporción varón:mujer es 1,3:1, entre 52-82 años y todos de etnia blanco-caucásica. El 19,0 % tiene exposición laboral carcinógena, el 52,4 % tabaquismo, el 61,9 % consumo de alcohol, el 57,1 % riesgo cardiovascular, el 19,0 % patología cardiaca, el 28,6 % pulmonar, el 19 % gastrointestinal, el 19 % endocrina, el 14,3 % genitourinaria, el 9,5 % otro tumor maligno primario y el 23,8 % un familiar de primer grado con una neoplasia, el 33,3 % ha tomado fármacos asociados a osteonecrosis o recibido radioterapia craneofacial. Siete pacientes debutan con la metástasis y 14 como progresión de neoplasia conocida. El motivo de consulta principal es una masa. Ocho lesiones afectan a tejidos blandos y 13 al hueso. El 81 % son tumores de estirpe epitelial. El origen es: 23,8 % pulmón, 23,8 % mama, 23,8 % renal, 9,5 % piel, 9,5 % partes blandas, 4,8 % próstata y 4,8 % tiroides. El 100 % tiene metástasis en otras localizaciones. El 14,3% pacientes son tratados con cirugía, el 38,1 % con radioterapia, el 47,6 % con quimio- o terapia dirigida, y el 28,6 % con tratamiento sintomático. 17 pacientes fallecidos y 4 vivos con rango 1-124 meses de seguimiento. Conclusiones: Las metástasis craneomaxilofaciales, habitualmente con múltiples lesiones viscerales o en esqueleto axial, tienen pronóstico infausto. El manejo multidisciplinar podría beneficiar el estado basal del paciente y llevar a mejores resultados. Existen casos excepcionales de supervivencia a largo plazo

Multi-species simulation of Trichel pulses in oxygen

A multi-species model consisting of seven species has been implemented to simulate the generation and development of Trichel pulses in oxygen between a sphere (the cathode) and a plane (the anode). The spatial and temporal evolution of species is obtained by solving the continuity equations of species using a classical one-dimensional model of negative corona discharge. The chemical kinetics of corona discharge includes electron impact reactions (ionization, dissociative and non-dissociative electron attachment, molecular dissociation, etc.), charge transfer reactions and reactions between neutral species

Actividad antidiabética de un extracto de hexane de Prosthechea michuacana en ratas diabéticas inducidas por estreptozotocina

En este estudio se determinaron los efectos antidiabéticos, antihiperlipidemico y glicación (AGEs) de algunos extractos de Prosthechea michuacana (PM) en ratas normoglucémicas y con diabetes inducida por estreptozotocina (STZ). Se probó el efecto de los extractos de hexano, cloroformo, metanol de PM sobre la actividad hipoglucemiante, la carga de glucosa, los parámetros bioquímicos tales como triglicéridos, niveles de colesterol total, peroxidación lipídica, glucógeno del hígado, los niveles de glucógeno muscular, niveles de superoxide dismutase, catalasa, glutation reductasa and glutation peroxidasa en ratas normales y diabéticas. También se determinó la glucosa 6 Phosphatasa y las actividades de GK en el hígado, la inhibición de la insulina y la glicosilación de las proteínas. Los niveles de glucosa sanguínea se determinaron por el método de GOD-POD. La administración de los extractos de cloroformo y metanol no presentaron ningún efecto sobre la SD, en cambio el tratamiento con el extracto de hexano (PM) a dosis de 200 y 400 mg/kg, inhibió la diabetes y sus complicaciones. Ambas dosis redujeron significativamente los niveles de glucosa sanguínea (35.75 y 47.78% en las ratas diabéticas, 50.64 y 57.10% en las ratas diabéticas), el aumento de la glucogénesis y la disminución de la gluconeogénesis conduce el metabolismo de la glucosa hacia la normalidad. Estas dosis disminuyeron la hiperlipidemia reduciendo el colesterol (41.56%, 46.08%) y los triglicéridos (37.5%, 46.27%) así como también mejoran las actividades antioxidantes de las enzimas hepáticas. Su efecto se comparó con la glibenclamida y tolbutamida, fármacos usados como antidiabeticos. El extracto de hexano disminuyo la hiperinsulinemia en un 24% en SD. PM mostró un cambio significativo in vitro sobre la formación de los AGEs con valores de IC50 de 48.3 mg/ml comparable al efecto inhibidor de la aminoguanidina con valores de IC50 de 27.2 mg/ml. Se redujo en las ratas con diabetes crónica los niveles de HbA1C en un 6.4%. Por lo que se concluye que el extracto hexánico de los bulbos de Prosthechea michuacana posee actividad anti-hiperglucémica, antihiperlipemica, mejora la hiperinsulinemia mostrando un cambio significativo en la formación de AGEs, lo que puede llegar a ser de importancia en el tratamiento de la diabetes y sus complicaciones

Development and assessment of fire-related risk unavailability matrices to support the application of the maintenance rule in a PWR nuclear power plant

Two methods are presented which serve to incorporate the fire-related risk into the current practices in nuclear power plants with respect to the assessment of configurations. The development of these methods is restricted to the compulsory use of fire probabilistic safety assessment (PSA) models. The first method is a fire protection systems and key safety functions unavailability matrix which is developed to identify structures, systems, and components significant for fire-related risk. The second method is a fire zones and key safety functions (KSFs) fire risk matrix which is useful to identify fire zones which are candidates for risk management actions. Specific selection and quantification methodologies have been developed to obtain the matrices. The Monte Carlo method has been used to assess the uncertainty of the unavailability matrix. The analysis shows that the uncertainty is sufficiently bounded. The significant fire-related risk is localized in six KSF representative components and one fire protection system which should be included in the maintenance rule. The unavailability of fire protection systems does not significantly affect the risk. The fire risk matrix identifies the fire zones that contribute the most to the fire-related risk. These zones belong to the control building and electric penetrations building.Peer ReviewedPostprint (published version