2,440 research outputs found
Preferential accumulation of bubbles in Couette-Taylor flow patterns
We investigate the migration of bubbles in several flow patterns occurring within the gap between a rotating inner cylinder and a concentric fixed outer cylinder. The time-dependent evolution of the two-phase flow is predicted through three-dimensional Euler-Lagrange simulations. Lagrangian tracking of spherical bubbles is coupled with direct numerical simulation of the Navier-Stokes equations. We assume that bubbles do not influence the background flow (one-way coupling simulations). The force balance on each bubble takes into account buoyancy, added-mass, viscous drag and shear-induced lift forces. For increasing velocities of the rotating inner cylinder, the flow in the fluid gap evolves from the purely azimuthal steady Couette flow to Taylor toroidal vortices and eventually a wavy vortex flow. The migration of bubbles is highly dependent on the balance between buoyancy and centripetal forces (mostly due to the centripetal pressure gradient) directed toward the inner cylinder and the vortex cores. Depending on the rotation rate of the inner cylinder, bubbles tend to accumulate alternatively along the inner wall, inside the core of Taylor vortices or at particular locations within the wavy vortices. A stability analysis of the fixed points associated with bubble trajectories provides a clear understanding of their migration and preferential accumulation. The location of the accumulation points is parameterized by two dimensionless parameters expressing the balance of buoyancy, centripetal attraction toward the inner rotating cylinder, and entrapment in Taylor vortices. A complete phase diagram summarizing the various regimes of bubble migration is built. Several experimental conditions considered by Djéridi et al.1 are reproduced; the numerical results reveal a very good agreement with the experiments. When the rotation rate is further increased, the numerical results indicate the formation of oscillating bubble strings, as observed experimentally by Djéridi et al.2. After a transient state, bubbles collect at the crests or troughs of the wavy vortices. An analysis of the flow characteristics clearly indicates that bubbles accumulate in the low-pressure regions of the flow field
Monolingual and bilingual spanish-catalan speech recognizers developed from SpeechDat databases
Under the SpeechDat specifications, the Spanish member of SpeechDat consortium has recorded a Catalan database that includes one
thousand speakers. This communication describes some experimental work that has been carried out using both the Spanish and the
Catalan speech material.
A speech recognition system has been trained for the Spanish language using a selection of the phonetically balanced utterances from
the 4500 SpeechDat training sessions. Utterances with mispronounced or incomplete words and with intermittent noise were discarded.
A set of 26 allophones was selected to account for the Spanish sounds and clustered demiphones have been used as context dependent
sub-lexical units. Following the same methodology, a recognition system was trained from the Catalan SpeechDat database. Catalan
sounds were described with 32 allophones. Additionally, a bilingual recognition system was built for both the Spanish and Catalan
languages. By means of clustering techniques, the suitable set of allophones to cover simultaneously both languages was determined.
Thus, 33 allophones were selected. The training material was built by the whole Catalan training material and the Spanish material
coming from the Eastern region of Spain (the region where Catalan is spoken).
The performance of the Spanish, Catalan and bilingual systems were assessed under the same framework. The Spanish system exhibits
a significantly better performance than the rest of systems due to its better training. The bilingual system provides an equivalent
performance to that afforded by both language specific systems trained with the Eastern Spanish material or the Catalan SpeechDat
corpus.Peer ReviewedPostprint (published version
Los vínculos entre tecnología y práctica especializada en rehabilitación : el modelo de la tecnología gimnástica en la España del siglo XIX
La tecnología gimnástica ha mostrado un papel determinante en la configura¬ción la especialidad médica de rehabilitación y medicina física. Su estudio constituye un eje fundamental para comprender la fuerte división del trabajo existente en este campo, con una especialidad médica y diversas profesiones ligadas a la rehabilita¬ción y la fisioterapia. Este proceso se produjo en dos fases bien diferenciadas en su estructura: la absorción de los saberes y los desarrollos tecnológicos formulados por los gimnastas de principios del siglo XIX, y la delegación en el uso de estos mismo dispositivos, de utilidad diagnóstica escasa y de gran consumo de tiempo de trabajo. Ambos factores favorecieron la aparición de las nuevas profesiones
Fully coupled simulations of non-colloidal monodisperse sheared suspensions
In this work we investigate numerically the dynamics of sheared suspensions in the limit of vanishingly small fluid and particle inertia. The numerical model we used is able to handle the multi-body hydrodynamic interactions between thousands of particles embedded in a linear shear flow. The presence of the particles is modeled by momentum source terms spread out on a spherical envelop forcing the Stokes equations of the creeping flow. Therefore all the velocity perturbations induced by the moving particles are simultaneously accounted for.
The statistical properties of the sheared suspensions are related to the velocity fluctuation of the particles. We formed averages for the resulting velocity fluctuation and rotation rate tensors. We found that the latter are highly anisotropic and that all the velocity fluctuation terms grow linearly with particle volume fraction. Only one off-diagonal term is found to be non zero (clearly related to trajectory symmetry breaking induced by the non-hydrodynamic repulsion force). We also found a strong correlation of positive/negative velocities in the shear plane, on a time scale controlled by the shear rate (direct interaction of two particles). The time scale required to restore uncorrelated velocity fluctuations decreases continuously as the concentration increases. We calculated the shear induced self-diffusion coefficients using two different methods and the resulting diffusion tensor appears to be anisotropic too.
The microstructure of the suspension is found to be drastically modified by particle interactions. First the probability density function of velocity fluctuations showed a transition from exponential to Gaussian behavior as particle concentration varies. Second the probability of finding close pairs while the particles move under shear flow is strongly enhanced by hydrodynamic interactions when the concentration increases
Turbulent fluid acceleration generates clusters of gyrotactic microorganisms
The motility of microorganisms is often biased by gradients in physical and
chemical properties of their environment, with myriad implications on their
ecology. Here we show that fluid acceleration reorients gyrotactic plankton,
triggering small-scale clustering. We experimentally demonstrate this
phenomenon by studying the distribution of the phytoplankton Chlamydomonas
augustae within a rotating tank and find it to be in good agreement with a new,
generalized model of gyrotaxis. When this model is implemented in a direct
numerical simulation of turbulent flow, we find that fluid acceleration
generates multi-fractal plankton clustering, with faster and more stable cells
producing stronger clustering. By producing accumulations in high-vorticity
regions, this process is fundamen- tally different from clustering by
gravitational acceleration, expanding the range of mechanisms by which
turbulent flows can impact the spatial distribution of active suspensions.Comment: 5 pages, 4 figure
Determinants of profitability in Spanish financial institutions. Comparing aided and non-aided entities
The last financial crisis has led to the greatest contribution of public funds ever made to Spanish banks. This paper studies why the need for support has been asymmetric, with not all of the institutions requiring aid. Based on profitability of assets (ROA), we determine using panel data econometric and logit response models the components of profit and loss accounts that generated profitability as well as the factors leading to some entities to ask for aid. The analyses show that before the beginning of the crisis there were significant differences between entities that needed aid and those that did not. The most profitable banks grounded their success in the traditional revenue components of financial institutions (such as margin on interest rates and commissions), as well as in revenues obtained from participated companies and extraordinary results. The model offers a tool to detect entities in difficulties in advance, reducing the financial and social costs of public interventions. The factors more impacting on profitability of Spanish institutions are also identifie
Evaluación genética de la planta forestal : concepto y resultados disponibles para rodales de pinos españoles
Presentamos una revisión de conceptos y resultados
relacionados con la evaluación genética de los pinos
españoles, centrada en los patrones de variación
geográfica entre poblaciones. Tras describir
someramente los principales mecanismos genéticos
que explican esta variación, se comentan los
distintos tipos de ensayos, a la luz de la legislación
vigente sobre materiales de reproducción. Hemos
elegido los principales resultados obtenidos hasta la
fecha, con un grado de divulgación muy diverso:
desde tesis doctorales y trabajos fin de carrera hasta
comunicaciones en congresos y artículos científicos
en revistas indexadas. Nuestro principal objetivo es
dar a conocer la gran potencialidad de la variación
intraespecífica de nuestras principales especies
forestales de forma que se pueda sacar el máximo
partido de ella dentro de una gestión forestal
sostenible.________________________________We are presenting a revision of concepts and results
related to the genetic evaluation of Spanish pines,
focused on geographical variation patterns among
populations. After describing briefly the main
genetic mechanisms underlying this variation, we
comment the different types of genetic trials, at the
light of the current legislation on FRM. We chose
the main results obtained up till now, yet with a
diverse divulgation level: from doctoral Thesis and
Master reports up to congress proceedings and
papers on the scientific citation index. Our main goal
is highlighting the wide potential of intraspecific
variation of our main forest species such that it can
be optimally used in the framework of a sustainable
forest management
Thickness of the buccal bone wall and root angulation in the maxilla and mandible: an approach to cone beam computed tomography
Background: The objective of this paper is to anatomically describe the bone morphology in the maxillary and mandibular tooth areas, which might help in planning post-extraction implants. Methods: CBCT images (Planmeca ProMax 3D) of 403 teeth (208 upper teeth and 195 lower teeth) were obtained from 49 patients referred to the Dental School of Seville from January to December 2014. The thickness of the facial wall was measured at the crest, point A, 4mm below, point B, and at the apex, point C. The second parameter was the angle formed between the dental axis and the axis of the basal bone. Results: A total of 403 teeth were measured. In the maxilla, 89.4% of incisors, 93.94% of canines, 78% of premolars and 70.5% of molars had a buccal bone wall thickness less than the ideal 2mm. In the mandible, 73.5% of incisors, 49% of canines, 64% of premolars and 53% of molars had <1mm buccal bone thickness as measured at point B. The mean angulation in the maxilla was 11.67±6.37° for incisors, 16.88±7.93° for canines, 13.93±8.6° for premolars, and 9.89±4.8° for molars. In the mandible, the mean values were 10.63±8.76° for incisors, 10.98±7.36° for canines, 10.54±5.82° for premolars and 16.19±11.22° for molars. Conclusions: The high incidence of a buccal wall thickness of less than 2mm in over 80% of the assessed sites indicates the need for additional regeneration procedures, and several locations may also require custom abutments to solve the angulation problems for screw-retained crowns
Com difondre una innovació pedagògica? El cas de l'aprenentatge servei a Catalunya.
quest text té per objectiu analitzar la difusió de l'aprenentatge servei (APS), una pràctica educativa innovadora que s'ha estès al llarg dels darrers anys a Catalunya. L'article comença presentant els principis que ha seguit la seva implantació; continua analitzant l'acció dels agents, entitats i persones que s'han dedicat expressament a difondre i ajudar a arrelar projectes educatius d'APS; també estudia les relacions de partenariat i la creació de xarxes que s'han produït al llarg d'aquests anys, i acaba apuntant algunes línies de futur per avançar en la implantació de l'APS. Entre d'altres, es destaquen consideracions com ara que l'APS s'ha difós sabent que és més un descobriment que no pas un invent, i reconeixent les bones experiències que ja es duien a terme seguint aquesta pràctica educativa al nostre país, vinculant-lo a una determinada concepció de l'educació i cooperant entre tots els agents implicats en els diferents àmbits i territoris educatius
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