Influência dos parâmetros operacionais no comportamento dinâmico de chumaceiras axiais de esmagamento de película compressível

No presente trabalho são estudadas chumaceiras axiais de esmagamento de película compressível. A lubrificação deste componente mecânico, é conseguida por meio de um fluido gasoso justificando a obtenção de soluções por via de experimentação numérica, uma vez que atualmente ainda não é possível recorrer-se a métodos analíticos. Através da simulação numérica, analisa-se a influência de alguns parâmetros operacionais na resposta deste tipo de chumaceira. Na análise dos resultados verifica-se que a posição média final do elemento suportado é independente da espessura de película inicial utilizada, desde que esta não ultrapasse o valor limite em que a pressão gerada não consiga fazer face à aceleração da massa durante a fase descendente, resultando no contacto entre as superfícies dos elementos da chumaceira. A utilização de frequências elevadas é recomendável uma vez que promove uma maior separação de superfícies, menor dissipação de energia por parte da película lubrificante e menor amplitude de oscilação do elemento suportado, embora com as desvantagens do período transiente ser superior e do ganho do afastamento do elemento suportado se reduzir significativamente, seguindo um modelo assimptótico. Em condições de pressão constante e frequência elevada, o sistema, com o aumento da massa, reage de forma a permitir uma melhor lubrificação da chumaceira e a reduzir a oscilação do elemento suportado. Por outro lado, a rigidez do sistema aumenta fazendo face a uma possível sobrecarga.

Cerebral Microembolization During Aortic Valve Replacement Using Minimally Invasive or Conventional Extracorporeal Circulation: A Randomized Trial.

To compare intraoperative cerebral microembolic load between minimally invasive extracorporeal circulation (MiECC) and conventional extracorporeal circulation (CECC) during isolated surgical aortic valve replacement (SAVR), we conducted a randomized trial in patients undergoing primary elective SAVR at a tertiary referral hospital. The primary outcome was the procedural phase-related rate of high-intensity transient signals (HITS) on transcranial Doppler ultrasound. HITS rate was used as a surrogate of cerebral microembolism in pre-defined procedural phases in SAVR using MiECC or CECC with (+F) or without (-F) an oxygenator with integrated arterial filter. Forty-eight patients were randomized in a 1:1 ratio to MiECC or CECC. Due to intraprocedural Doppler signal loss (n = 3), 45 patients were included in final analysis. MiECC perfusion regimen showed a significantly increased HITS rate compared to CECC (by a factor of 1.75; 95% confidence interval, 1.19-2.56). This was due to different HITS rates in procedural phases from aortic cross-clamping until declamping [phase 4] (P = 0.01), and from aortic declamping until stop of extracorporeal perfusion [phase 5] (P = 0.05). Post hoc analysis revealed that MiECC-F generated a higher HITS rate than CECC+F (P = 0.005), CECC-F (P = 0.05) in phase 4, and CECC-F (P = 0.03) in phase 5, respectively. In open-heart surgery, MiECC is not superior to CECC with regard to gaseous cerebral microembolism. When using MiECC for SAVR, the use of oxygenators with integrated arterial line filter appears highly advisable. Only with this precaution, MiECC confers a cerebral microembolic load comparable to CECC during this type of open heart surgery.

Degradation of [14C]GlcDGD in the marine sediment by monitoring radioactivity in the aqueous and gas phase using liquid scintillation counting (LSC) techniques

An experiment was conceived in which we monitored degradation of GlcDGD. Independent of the fate of the [14C]glucosyl headgroup after hydrolysis from the glycerol backbone, the 14C enters the aqueous or gas phase whereas the intact lipid is insoluble and remains in the sediment phase. Total degradation of GlcDGD then is obtained by combining the increase of radioactivity in the aqueous and gaseous phases. We chose two different sediment to perform this experiment. One is from microbially actie surface sediment sampled in February 2010 from the upper tidal flat of the German Wadden Sea near Wremen (53° 38' 0N, 8° 29' 30E). The other one is deep subsurface sediments recovered from northern Cascadia Margin during Integrated Ocean Drilling Program Expedition 311 [site U1326, 138.2 meters below seafloor (mbsf), in situ temperature 20 °C, water depth 1,828 m. We performed both alive and killed control experiments for comparison. Surface and subsurface sediment slurry were incubated in the dark at in situ temperature, 4 °C and 20 °C for 300 d, respectively. The sterilized slurry was stored at 20 °C. All incubations were carried out under N2 headspace to ensure anaerobic conditions. The sampling frequency was high during the first half-month, i.e., after 1, 2, 7, and 14 d; thereafter, the sediment slurry was sampled every 2 months. At each time point, samples were taken in triplicate for radioactivity measurements. After 300 d of incubation, no significant changes of radioactivity in the aqueous phase were detected. This may be the result of either the rapid turnover of released [14C] glucose or the relatively high limit of detection caused by the slight solubility (equivalent to 2% of initial radioactivity) of GlcDGD in water. Therefore, total degradation of GlcDGD in the dataset was calculated by combining radioactivity of DIC, CH4, and CO2, leading to a minimum estimate.

Alkenone stable carbon isotopes, planktic foraminfera stable carbon isotopes, alkenone unsaturation indices and calculated sea surface temperatures and atmospheric pCO2 for ODP Site 165-999

Temperature reconstructions indicate that the Pliocene was ~3 °C warmer globally than today, and several recent reconstructions of Pliocene atmospheric CO2 indicate that it was above pre-industrial levels and similar to those likely to be seen this century. However, many of these reconstructions have been of relatively low temporal resolution, meaning that these records may have failed to capture variations associated with the 41 Kyr glacial-interglacial cycles thought to operate in the Pliocene. Here we present a new, high temporal resolution alkenone carbon isotope based record of pCO2 spanning 2.8 to 3.3 million years ago from ODP Site 999. Our record is of high enough resolution (~19 Kyrs) to resolve glacial-interglacial changes beyond the intrinsic uncertainty of the proxy method. The record suggests that Pliocene CO2 levels were relatively stable, exhibiting variation less than 55 ppm. We perform sensitivity studies to investigate the possible effect of changing sea surface temperature, which highlights the importance of accurate and precise SST reconstructions for alkenone palaeobarometry, but demonstrate that these uncertainties do not affect our conclusions of relatively stable pCO2 levels during this interval.

(Table 1) Concentrations and carbon isotopic compositions of CH4 and CO2 at DSDP Site 76-533

The principal gaseous carbon-containing components identified in the first 400 m of sediment at Deep Sea Drilling Project Site 533, Leg 76, are methane (CH4) and carbon dioxide (CO2). Below a sub-bottom depth of about 25 m, sediment cores commonly contained pockets caused by the expansion of gas upon core recovery. The carbon isotopic composition (d13C per mil relative to PDB standard) of CH4 and CO2 in these gas pockets has been measured, resulting in the following observations: (1) d13C-CH4 values increase with depth from approximately -94 per mil in the uppermost sediment to about -66 per mil in the deepest sediment, reflecting a systematic but nonlinear depletion of 12C with depth. (2) d13C-CO2 values also increase with depth of sediment from about -25 per mil to about -4 per mil, snowing a depletion of 12C that closely parallels the trend of the isotopic composition of CH4. The magnitude and parallel distribution of d13C values for both CH4 and CO2 are consistent with the concept that the formation of the CH4 resulted from the microbiological reduction of CO2 from organic substances. These results imply that CH4 and CO2 incorporated in gas hydrates at this site are biogenic.

Feed materials : a bibliography of classified report literature /

"'Feed materials' refers to U metal, fabricated into fuel elements but not clad, and UF₆, both normal isotopic content, suitable for introduction into Pu-production reactors or gaseous diffusion cascades."

The tidal and other problems,

At head of title: Contributions to cosmogony and the fundamental problems of geology.

Study of an inorganic system for the recovery of oxygen (30-day evaluation program)

Cover title.

Projectile Combustion Effects on Ram Accelerator Performance

Thesis (Master's)--University of Washington, 2016-06

A unique behavior of sub-critical hydrocarbon permeability in activated carbon at low pressures

In our study on sub-critical hydrocarbon permeation in activated carbon, a minimum in the total permeability (B-T) at low pressure has been observed for only long-chain hydrocarbons such as n-hexane and n-heptane. Such an observation suggests that the minimum appearance depends on the properties of permeating vapors as well as the porous medium. In this paper a permeation model is presented to explain the minimum behavior with the allowance of the collision-reflection factor in the Knudsen diffusivity to be a function of surface loading. Surface diffusion was found to be very significant compared to other transport mechanisms such as Knudsen diffusion and gaseous viscous flow at low pressures. Since the gaseous viscous flow contributes negligibly to the B, at low pressures, the minimum appearance in the B, is mainly attributed to the interplay between Knudsen diffusion and surface diffusion. Also, the molecular structure of adsorbates plays an important role in the minimum appearance.

Nitrogen ecophysiology of Heron Island, a subtropical coral cay of the Great Barrier Reef, Australia

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha(-1) y(-1). The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, N-15 labelling and N-15 natural abundance (delta(15)N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3-) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3- uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3-, although NO3- is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in N-15 suggesting that the isotopic enrichment of guano (delta(15)N 9.9parts per thousand) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower delta(15)N (average 6.5parts per thousand) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of N-15-enriched NO3- (delta(15)N 7.9parts per thousand). Macroalgae from reefs with and without seabirds had similar delta(15)N values of 2.0-3.9parts per thousand suggesting that reef macroalgae do not utilise N-15-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated delta(15)N of 5.2parts per thousand, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.

Nitrogen removal from sludge digester liquids by nitrification/denitrification or partial nitritation/anammox: environmental and economical considerations

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N-2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this achievement turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.

Passive air sampling theory for semivolatile organic compounds

The mathematical modelling underlying passive air sampling theory can be based on mass transfer coefficients or rate constants. Generally, these models have not been inter-related. Starting with basic models, the exchange of chemicals between the gaseous phase and the sampler is developed using mass transfer coefficients and rate constants. Importantly, the inter-relationships between the approaches are demonstrated by relating uptake rate constants and loss rate constants to mass transfer coefficients when either sampler-side or air-side resistance is dominating chemical exchange. The influence of sampler area and sampler volume on chemical exchange is discussed in general terms and as they relate to frequently used parameters such as sampling rates and time to equilibrium. Where air-side or sampler-side resistance dominates, an increase in the surface area of the sampler will increase sampling rates. Sampling rates are not related to the sampler/air partition coefficient (K-SV) when air-side resistance dominates and increase with K-SV when sampler-side resistance dominates.

Anesthesia of captive African wild dogs (Lycaon pictus) using a medetomidine-ketamine-atropine combination

Seven captive male African wild dogs (Lycaon pictus) weighing 25-32 kg each, were anesthetized by i.m. injection via hand syringe with a combination of 1.5 mg/kg ketamine, 40 mu g/kg medetomidine, and 0.05 mg/kg atropine. Following endotracheal intubation, each animal was connected to a bain closed-circuit system that delivered 1.5% isoflurane and 2 L/min oxygen. Atipamezole (0.1 mg/kg i.v.; 0.1 mg/kg i.m.) was given at the end of each procedure (60 min following injection of medetomidine/ketamine/atropine). Time to sternal recumbency was 5-8 min. Times to standing after atipamezole administration were 8-20 min. This anesthetic regimen was repeated on three separate occasions (September 2000, February 2002, and October 2002) on all males to perform electroejaculation procedures. Each procedure was < 80 min from injection to standing. Dogs showed excellent muscle relaxation during the procedures. Arterial blood samples were collected at 10-min intervals for blood gases in one procedure (September 2000). Separate venous samples were taken from each dog during each procedure for hematology and biochemistry. These values were within the normal range for this species. Arterial hemoglobin oxygen saturation (SpO2) and heart rate (HR) were monitored continuously in addition to other anesthesia monitoring procedures (body temperature, respiratory rate [RR], capillary refill time, blink response, pupil position, deep pain perception reflex). All dogs maintained relatively stable SpO2 profiles during monitoring, with a mean (+/- SD) SpO2 of 92% +/- 5.4%. All other physiological variables (HR, RR, body temperature, blood pressure) were within normal limits. Following each procedure, normal behavior was noted in all dogs. All the dogs were reunited into the pack at completion of their anesthetic procedures. An injectable medetomidine-ketamine-atropine combination with maintenance by gaseous isoflurane and oxygen provides an inexpensive, reliable anesthetic for captive African wild dogs.