Instability development of a viscous liquid drop impacting a smooth substrate

We study the instability development during a viscous liquid drop impacting a smooth substrate, using high speed photography. The onset time of the instability highly depends on the surrounding air pressure and the liquid viscosity: it decreases with air pressure with the power of minus two, and increases linearly with the liquid viscosity. From the real-time dynamics measurements, we construct a model which compares the destabilizing stress from air with the stabilizing stress from liquid viscosity. Under this model, our experimental results indicate that at the instability onset time, the two stresses balance each other. This model also illustrates the different mechanisms for the inviscid and viscous regimes previously observed: the inviscid regime is stabilized by the surface tension and the viscous regime is stabilized by the liquid viscosity.Comment: 4 pages, 5 figure

Epidemiología de la patología de la mucosa oral más frecuente en niños

El odontólogo responsable de tratar al niño debe tener en cuenta la posibilidad de encontrar cualquier condición patológica a nivel de la mucosa oral sobre todo a edades tempranas. Por ello, hemos tratado de aunar en nuestro estudio tanto la información más actualizada como nuestra propia experiencia para intentar ofrecer los datos de mayor interés, desde el punto de vista epidemiológico, que nos permita diagnosticar la patología de la mucosa oral más frecuente en la población infantil. Los estudios epidemiológicos realizados estos últimos años han mostrado la dispar apreciación de los diferentes investigadores y una gran variabilidad en las prevalencias de las lesiones mucosas orales en las diferentes zonas del mundo. Tanto lo expuesto con anterioridad como la falta de uniformidad en los criterios de elaboración de los estudios epidemiológicos explica que el porcentaje de las lesiones orales observadas en los diferentes grupos de niños estudiados nos ofrezcan una gran variabilidad con porcentajes comprendidos entre el 4,1% y 52,6%. Las lesiones que más frecuentemente han sido tenidas en cuenta por los diferentes autores y que más aparecen en los diferentes estudios son: la estomatitis aftosa recurrente, el herpes labial, la lengua fisurada, la lengua geográfica, la candidosis oral y las lesiones traumáticas, con prevalencias que respectivamente muestran rangos de 0,9% al 10,8%, del 0,78% al 5,2%, del 1,49% al 23%, del 0,60% al 9,8% y del 0,01% al 3,7%. Frente a la gran cantidad de alteraciones que podemos encontrarnos, debemos ser capaces de detectar dichas lesiones y llevar a cabo un correcto diagnóstico diferencial, eslabón esencial del plan de tratamiento. La siguiente exposición tiene como fin, basándonos en una revisión de los diferentes estudios nacionales e internacionales, aportar datos sobre la patología de la mucosa oral más significativa de la población infantil en cuanto a prevalencia y diagnóstico diferencial.Dentists who treat children must be alert to the possibility of finding diseases of the oral mucosa, especially in younger children. The present study aimed to review the most updated information and the experience of our group in order to yield epidemiological data that assist diagnosis of the most common diseases of the oral mucosa in children. Recent epidemiologic studies have shown a wide variability in the prevalence of oral mucosal lesions in different regions of the world and have led researchers to draw disparate conclusions. Moreover, studies have not been designed using standard criteria, further explaining the wide variability in the percentage of different groups of children with oral lesions, which ranges from 4.1 to 52.6%. The lesions most frequently considered by authors and that most often appear in the different studies are: recurrent aphthous stomatitis (0.9-10.8%), labial herpes (0.78-5.2%), fissured tongue (1.49-23%), geographic tongue (0.60-9.8%), oral candidiasis (0.01-37%) and traumatic injury (0.09%-22.15%). Dentists must be able to detect any of the numerous possible disorders and perform the correct differential diagnosis, key to the treatment plan. The aim of this paper, based on a review of the different national and international studies, is to contribute data on the most important oral mucosal diseases in the paediatric population in terms of prevalence and differential diagnosis

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Towards faster real algebraic numbers

AbstractThis paper presents a new encoding scheme for real algebraic number manipulations which enhances current Axiom’s real closure. Algebraic manipulations are performed using different instantiations of sub-resultant-like algorithms instead of Euclidean-like algorithms. We use these algorithms to compute polynomial gcds and Bezout relations, to compute the roots and the signs of algebraic numbers. This allows us to work in the ring of real algebraic integers instead of the field of real algebraic numbers avoiding many denominators

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Splashing of liquids: interplay of surface roughness with surrounding gas

We investigate the interplay between substrate roughness and surrounding gas pressure in controlling the dynamics of splashing when a liquid drop hits a dry solid surface. We associate two distinct forms of splashing with each of these control parameters: prompt splashing is due to surface roughness and corona splashing is due to instabilities produced by the surrounding gas. The size distribution of ejected droplets reveals the length scales of the underlying droplet-creation process in both cases.Comment: 6 pages, 6 figure

Grao de estereotípia e variábeis afectivo-motivacionais da aprendizaxe escolar: autoconceito e autoestima

[Resumo] Este estudo ten por obxectivo a análise das posíbeis relacións entre estereotipos de xénero e autoconceito-autoestima. Para tal propósito a mostra inicial de 842 alllnas e alunos de 20 e 40 da ESO das catro províncias galegas foi dividida en grupos atendendo ao grao de estereotípia, dos cais seleccionamos os mais extremos do contínuo: alunado non estereotipado (N = 229) e moi estereotipado (N =209). Os resultados indicaron que as alunas non estereotipadas obtiñan pontuacións mais elevadas nas catro dimensións do autoconceito avaliadas (xeral, académico, verbal e matemático) en relación coas suas compañeiras estereotipadas, que pola contra apresentaron unha autoestima mais negativa. Sen embargo, entre os alunos estereotipados e non estereotipados praticamente non se amosaron diferéncias nestas variábeis analisada

Drop Impact on Liquid Surfaces: Formation of Lens and Spherical Drops at the Air-Liquid Interface

Droplets at the air-liquid interface of immiscible liquids usually form partially-submerged lens shapes (e.g. water on oil). In addition to this structure, we showed that droplets released from critical heights above the target liquid can sustain the impact and at the end maintain a spherical ball-shape configuration above the surface, despite undergoing large deformation. Spherical drops are unstable and will transform into the lens mode due to slight disturbances. Precision dispensing needles with various tip diameter sizes were used to release pendant drops of deionized water onto the surface of fluorocarbon liquid (FC-43, 3M). A cubic relationship was found between the nozzle tip diameter and the released droplet diameter. Drop impact was recorded by a high speed camera at a rate of 2000 frames per second. In order for the water drops to sustain the impact and retain a spherical configuration at the surface of the target liquid pool, it is required that they be of a critical size and be released from a certain height; otherwise the commonly observed lens shape droplets will form at the surface

Characterization of cell response in Chlamydomonas moewusiicultures exposed to the herbicide paraquat: Induction of chlorosis

[Abstract] The use of herbicides constitutes the principal method of weed control, but the introduction of these compounds into the aquatic environment can provoke severe consequences for non-target organisms such as microalgae. Effects of the widely used herbicide paraquat were assessed on the green freshwater microalga Chlamydomonas moewusii by means of the analysis of its photosynthetic pigment content, using a traditional spectrophotometric technique that provides population bulk measurements, and by means of flow cytometry, which allowed characterizing the microalgal response at a single-cell level. Results obtained reveal that paraquat concentrations above 50 nM induce chlorosis in a percentage of microalgal cells depending on herbicide concentration and exposure time, as reflected by a reduced cell chlorophyll autofluorescence and pigment content of the biomass. Cell viability in these cultures was also reduced in a concentration dependent way. The possibility of analysing chlorotic and non-chlorotic subpopulations separately allowed the study of morphological properties and physiological status of both cell types, leading to the conclusion that chlorotic cells are non-viable cells, based on their reduced size and complexity and their inability to be stained in the fluorescein diacetate assay. In the case of non-chlorotic cells, cell viability was reduced with the increase of paraquat concentration. Non-chlorotic cells in these cultures showed an increased size and complexity in comparison with control cells, probably due to a growth inhibition. Chlorophyll fluorescence was the most sensitive parameter since even cells exposed to the lowest concentration assayed, 50 nM, although not chlorotic, showed a significantly reduced chlorophyll fluorescence with respect to control cells, reflected also by a reduced chlorophyll content of the biomass.Galicia: Consellería de Innovación, Industria e Comercio; 08MDS020103PRMinisterio de Educación y Ciencia; CGL2004-02037

Creation of prompt and thin-sheet splashing by varying surface roughness or increasing air pressure

A liquid drop impacting a solid surface may splash by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that air pressure and surface roughness influence both splash mechanisms. Roughness increases prompt splashing at the advancing contact line but inhibits the formation of the thin sheet. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but for prompt splashing as well. The threshold pressure depends on impact velocity, liquid viscosity and surface roughness