Use of narrow-pore filters in He II transfer devices - new results

With the aim of finding simple methods for the fabrication of He II refilling devices, He II flow has been studied through filters made from various fine powders (oxides and metals, grain sizes in the range 0.05–2 μm) by compacting them under pressure. The results obtained for the different states of He II flow, especially in the “breakthrough” and “easy flow” range, are explained by the fountain effect, He II hydrodynamics and the choking effect. According to the results, pressedpowder filters can be classified into three groups with different flow characteristics, of which the “good transfer filters” with a behaviour neatly described by simple theory are suitable for use in He II refilling devices.

Formation Mechanism of Cracks in Saturated Sand

The formation mechanism of “water film” (or crack) in saturated sand is analyzed theoretically and numerically. The theoretical analysis shows that there will be no stable “water film” in the saturated sand if the strength of the skeleton is zero and no positions are choked. It is shown by numerical simulation that stable water films initiate and grow if the choking state keeps unchanged once the fluid velocities decrease to zero in the liquefied sand column. The developments of “water film” based on the model presented in this paper are compared with experimental results.

Influence of Obstacle-Produced Turbulence on Development of Premixed Flames

An investigation into influence of obstructions on premixed flame propagation has been carried out in a semi-open tube. It is found that there exists flame acceleration and rising overpressure along the path of flame due to obstacles. According to the magnitude of flame speeds, the propagation of flame in the tube can be classified into three regimes: the quenching, the choking and the detonation regimes. In premixed flames near the flammability limits, the flame is observed first to accelerate and then to quench itself after propagating past a certain number of obstacles. In the choking regime, the maximum flame speeds are somewhat below the combustion product sound speeds, and insensitive to the blockage ratio. In the more sensitive mixtures, the transition to detonation (DDT) occurs when the equivalence ratio increases. The transition is not observed for the less sensitive mixtures. The dependence of overpressure on blockage ratio is not monotonous. Furthermore, a numerical study of flame acceleration and overpressure with the unsteady compressible flow model is performed, and the agreement between the simulation and measurements is good.

Cracks in saturated sand

The formation mechanism of water film (or crack) in saturated sand is analyzed numerically It is shown that there will be no stable "water film" in the saturated sand even if the strength of the skeleton is zero and no positions are choked. The stable water films initiate and grow if the choking state keeps unchangeable once the fluid velocities of one position decreases to zero in a liquefied sand column. A simplified method for evaluating the thickness of water film is presented according to a solidification wave theory. The theoretical results obtained by the simplified method are compared with the numerical results and the experimental results of Kokusho.

Study on the Mechanism of Detonation to Quasi-detonation Transition

In this paper, the mechanism of detonation to quasi-detonation transition was discussed, a new physical model to simulate quasi-detonation was proposed, and one-dimensional theoretical and numerical simulation was conducted. This study firstly demonstrates that the quasi-detonation is of thermal choking. If the conditions of thermal choking are created by some disturbances, the supersonic flow is then unable to accept additional thermal energy, and the CJ detonation becomes the unstable quasi-detonation precipitately. The kinetic energy loss caused by this transition process is firstly considered in this new physical model. The numerical results are in good agreement with previous experimental observations qualitatively, which demonstrates that the quasi-detonation model is physically correct and the study are fundamentally important for detonation and supersonic combustion research.

A study on water film in saturated sand

Water film can serve as a sliding surface and cause landslides on gentle slopes. The development of "water film" in saturated sand is analyzed numerically and theoretically based on a quasi-three-phase model. It is shown that stable water films initiate and grow if the choking state (where the fluid velocity decreases to near zero) remains steady in a liquefied sand column. Discontinuity can occur in pore water velocity, grain velocity and pore pressure after the initiation of a water film. However, the discontinuity and water film can disappear once the choking state is changed. The key to the formation of water film is the choking in the sand column caused by eroded fine grains.

Gas-liquid two phase flow through a vertical 90deg elbow bend

Pressure drop data are reported for two phase air-water flow through a vertical to horizontal 90° elbow bend set in 0.026 m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2 m s -1. The elbow bend pressure drop was best correlated in terms of le/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart-Martinelli model gave prediction of the data.

Are there clinical features of a sensitized cough reflex?

Cough reflex hypersensitization is a key feature in patients with troublesome cough. The clinical consequence of this hypersensitive state is typified by bouts of coughing often triggered by low threshold stimuli encountered by the patient during normal daily activities including exposure to aerosols, scents and odours, a change in air temperature and when talking or laughing. These features are often perceived by cough patients to be the most disruptive aspect of their condition and undoubtedly contribute to impaired quality of life. Patients with troublesome cough may describe a range of additional symptoms and sensations including an 'urge to cough' or the feeling of an 'itch' at the back of the throat, or a choking sensation and occasionally chest pain or breathlessness. It is uncertain if these features arise due to the processes responsible for cough reflex sensitization or as a direct consequence of the underlying cough aetiology. In an attempt to understand the clinical features of a sensitized cough reflex, the spectrum of symptoms typically described by cough patients will be reviewed and possible underlying mechanisms considered. Since an intact cough reflex is crucial to airway protection, anti-tussive treatment that attenuates the hypersensitive cough state rather than abolishing the cough reflex completely would be preferable. Identifying such agents remains a clinical, scientific and pharmacological challenge. (c) 2008 Elsevier Ltd. All rights reserved.

L’asphyxie en médecine légale : une étude rétrospective de six ans sur les suffocations non-chimiques au Québec

La suffocation est une forme d’asphyxie dans laquelle l’oxygène ne peut atteindre le sang. Il existe divers types de suffocation dont la suffocation par confinement/ environnementale, les étouffements externe et interne, et les asphyxies traumatique/ positionnelle. La littérature scientifique sur la suffocation est relativement pauvre, étant principalement constituée de revues de cas et de quelques séries de cas limités à un contexte particulier de suffocation. Dans le contexte actuel d’une médecine basée sur les preuves, les ouvrages de médecine légale n’ont guère d’études pour appuyer leurs enseignements, tirés essentiellement de l’expérience personnelle de générations de médecins légistes. Le présent projet vise à palier ce manque de données sur la suffocation, un type de décès pourtant important en pratique médico-légale. Il s’agit d’une étude rétrospective de six ans portant sur tous les cas de suffocation non-chimique ayant été autopsiés au Laboratoire de sciences judiciaires et de médecine légale. À notre connaissance, cette étude est la première à établir le portrait systématique des morts par suffocation non-chimique en milieu médico-légal. Elle permet, entre autres, de confirmer les modes de décès usuels par catégorie de suffocation, le type de victime et les contextes courants. Généralement, les résultats concordent avec la littérature, appuyant ainsi le savoir commun des pathologistes sur la suffocation non-chimique. Toutefois, certaines dissimilitudes ont été notées quant aux modes de décès lors de l’étouffement externe. Par ailleurs, les questions reliées à la classification des asphyxies et aux définitions souvent contradictoires sont discutées. En un effort de normalisation, ce projet souligne les divergences retrouvées dans les classifications usuelles et tente d’en dégager les définitions courantes afin de proposer un modèle de classification unifié.

Toxicity of Effluent from a Titanium Dioxide Factory on some Marine Animals

Toxicity of effluent from a titanium dioxide factory containing sulphuric acid residue with soluble iron metallic salts and insoluble material such as silica, etc. on fishes, decapods and molluscs was studied. The effluent caused changes in pH and oxygen depletion of the sea water. Sublethal effects of the precipitate of ferrous salts were also studied. Dilutions of effluent up to 1:150 were LC100 for all organisms used while 1:200 dilution was LC50 for fishes at 36 hr and for other organisms at 48 hr. But death of organisms at this concentration was caused by pH changes and oxygen depletion and did not account for the effects of the precipitate. Below this level precipitation started soon after mixing with sea water causing death of organisms by choking their gills and siphons. Dilutions,< 1:1000 were 96 hr LCO.

Prevalencia de TSH neonatal elevada y factores perinatales relacionados con asfixia Bogotá 2012

Introducción: la asfixia perinatal es la tercera causa de muerte en menores de 5 años. Las secuelas neurológicas suponen una carga importante para las familias y los sistemas de salud (1). Los estudios que relacionan el efecto de la asfixia perinatal sobre las hormonas tiroideas son escasos. El estudio sobre predictores de asfixia es un tema de investigación permanente. El objetivo principal fue determinar la prevalencia de TSH de cordón elevada y su relación con factores perinatales asociados a asfixia. Métodos: estudio descriptivo retrospectivo. La muestra estuvo conformada por todos los recién nacidos con TSH de cordón elevada y un segundo grupo seleccionado de forma aleatoria con TSH de cordón normal. Tomada de una población de neonatos atendidos en una clínica de Bogotá durante el 2012. Resultados: la prevalencia de TSH de cordón elevada fue de 14,7%. Los resultados sugieren una posible asociación entre alteraciones en las pruebas de bienestar fetal, presencia de infección materna, parto distócico, dificultad respiratoria y APGAR bajo y la presencia de TSH elevada p<0,05. Discusión: La alta prevalencia de TSH de cordón elevada podría relacionarse con las características de alto riesgo que presenta esta población. La elevación transitoria de la TSH neonatal de cordón en neonatos con alteraciones del bienestar fetal asociada a eventos hipóxicos agudos, sugiere que esta hormona podría ser un marcador de asfixia perinatal.

Management of tracheobronchial foreign body in children

To study cases of foreign bodies (FB) in the tracheobronchial tree investigating the clinical and radiological FB characteristics, complications and endoscopic and surgical intervention. Medical and radiological records review of all FB aspiration cases treated at S (a) over tilde uo Paulo State University Hospital over the last 30 years. One hundred and sixty-four FB cases were analyzed; 57% were male, 84% of these were under 16 years old. The most common clinical manifestations were coughing (68.3%) and choking (54.9%). The most common FBs were seeds (peanut, bean, maize) and also small metal or plastic objects. Radiography was normal in 21.3%, atelectasis was present in 40.9%, hyperinsufflation in 17.1% and the FB was radio-opaque in 20.7%. FB time in the bronchial tree varied from hours to years. The most serious complications, as fibroatelectasis and difficult resolution pneumonia, were caused by the long time that the FB remained in the bronchial tree. FB extraction was by endoscopy in 89% of cases, while 6% required surgical extraction or resection of destroyed part of lung, and 5% spontaneously eliminated the FB. There was no mortality in this series. Coughing and choking were the commonest clinical findings. Most FBs were dried seeds. Complications were due to delays in diagnosis, and most would not have existed if the doctor had given credence to the history. Radiography can be normal as most FBs are radiotransparent. FB extraction was by endoscopy, but a few cases required surgery and others were spontaneously eliminated.

Foreign body in the tracheobronchial tree

A 20-year experience with the treatment of 74 patients (83.8% children) for foreign body aspiration is reviewed. The object of this review is to show the clinical manifestations, the radiological findings, the nature and distribution in the bronchial tree, and complications due to longstanding (months or years) foreign bodies in the bronchial tree. The most common foreign bodies found were peanuts (13.5%), corn (13.5%), and beans (13.5%). The most frequent clinical manifestation was choking (67.5%), and the most frequent radiological finding was atelectasis (41.8%). The most serious complication was bronchiectasis needing resection in six patients who had the foreign body retained for years in the bronchial tree. In conclusion, in spite of an obvious foreign body in the tracheobronchial tree many cases are not diagnosed, and a longstanding foreign body in the airway may be responsible for irreversible complications.

Critical parameter determination of sonic flow controller diamond microtubes and micronozzles

In this article, the authors measure throughput of sonic diamond microtubes and micronozzles that can work as passive gas flow controllers and flow meters under choking conditions. The behavior of the outlet pressure through the microdevices using an experimental setup with constant volume and constant temperature was determined in order to obtain the critical throughput, the critical mass flow rate, and the discharge coefficients of the diamond sonic microdevices. © 2007 American Vacuum Society.