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Estudo prospectivo de sonda capacitiva não intrusiva duplo-sensor para medir fração volumétrica in situ em escoamentos contendo água, óleo e ar; Prospective study of a non-intrusive double-sensor capacitive probe for in-situ volumetric fraction measurements in oil-water-air flows

Almeida, Israel Frank dos Santos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/12/2006 Português
Relevância na Pesquisa
65.77%
Sensores capacitivos são amplamente utilizados em vários sistemas de medida, tanto na indústria como em laboratórios de pesquisa. Estes dispositivos medem variadas grandezas físicas, como deslocamento, força, pressão, densidade e concentração de substâncias em escoamentos bifásicos, entre outros. Sua aplicação vêm sendo utilizada há algum tempo de forma relativamente elementar, necessitando ainda de estudos específicos para entender a fundo o fenômeno de transferência de carga. A sonda proposta neste trabalho visa melhorar a aquisição do sinal capacitivo e obter uma medida precisa de fração volumétrica em condições bifásicas e trifásicas. Portanto, é necessário um circuito transdutor que transmita de forma precisa a capacitância registrada entre os eletrodos dos sensores até uma central de aquisição. Neste trabalho buscamos desenvolver um modelo de sonda para medir frações volumétricas in situ. Para tanto, apresentamos as etapas de calibração dos sensores, através de válvulas de fechamento rápido, e validamos a técnica sob determinadas condições e variados padrões de escoamento. Dois sensores de geometrias distintas (anéis e hélices) foram utilizados na composição da sonda capacitiva não intrusiva. Propõe-se a solução do sistema linear para medição direta de fração volumétrica em escoamento trifásico.; Capacitive sensors are widely employed in many measurement systems in both industry and laboratory activities. These devices measure several physical quantities such as displacement...

Ultramicroeletrodo de irídio com filme de mercúrio eletrodepositado para medidas in situ de íons metálicos e pesticidas em solos e águas naturais; Iridium based ultramicroelectrodes with an electro-platted mercury film for in situ determination of metallic ions and pesticides in soil and natural waters

Silva Júnior, Paulo Roberto Vieira da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/06/2009 Português
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65.66%
Neste trabalho foram desenvolvidas metodologias para a determinação de substâncias de interesse, como metais pesados (micronutrientes e contaminantes), macronutrientes e pesticidas em solo e águas naturais com ultramicroeletrodo de irídio recoberto com filme de Hg eletrodepositado (UME Ir-Hg) e técnicas voltamétricas, utilizando uma cápsula porosa de cerâmica como cela eletroquímica. As metodologias de medidas com os ultramicroeletrodos foram desenvolvidas inicialmente em condições controladas e posteriormente aplicadas a medidas in-situ, com experimentos com águas naturais e solos, conduzidos em laboratório e também com posteriores medidas em amostras reais. Segundo os resultados obtidos foi possível explorar as metodologias voltamétricas, principalmente as de pulso e redissolução anódica, como ferramentas para estudos in-situ dos metais Cd(II), Pb(II) e Cu(II) e do inseticida organofosforado paration metílico, substâncias de grande interesse, obtendo-se um bom nível de repetibilidade e sensibilidade, com limites de detecção em amostras reais de centenas de ppb's.; In this work a methodology for determination of metallic ions (micronutrients and contaminants), macronutrients and pesticides in soil and natural waters was developed using an Hg plated iridium based ultramicroelectrode and voltammetric techniques...

Medição de tensões residuais em filmes finos durante o processo de deposição.; Thin films residual stress measurement during deposition process.

Lagatta, Cristiano Fernandes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/07/2011 Português
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75.78%
Neste trabalho foram realizadas algumas deposições de filmes de Nitreto de Titânio sobre substrato de aço inoxidável. Foi utilizado o processo conhecido como triodo magnetron sputtering. Os parâmetros de deposição foram mantidos entre as deposições, exceto pela voltagem de bias no substrato, que foi variada de uma deposição para outra. Medições in-situ das tensões residuais no filme depositado foram realizadas. As medições foram feitas através do método da curvatura do substrato, utilizando-se um sensor capacitivo posicionado dentro da câmara de deposição. Embora o dispositivo não tenha sido capaz de quantificar os valores de tensão, foi possível identificar a natureza das mesmas, indicando se elas são de caráter trativo ou compressivo. Comprovou-se a possibilidade do uso de sistemas capacitivos para medições em sputtering. Observou-se que os filmes depositados apresentaram tensões de caráter trativo durante as deposições.; In this work, a series of depositions of titanium nitride thin films was conducted in a triode unbalanced magnetron sputtering chamber. Similar parameters were selected during each deposition, except for the substrate bias voltage, which was different for every deposition. An in-situ measurement of film residual stresses was carried out as the depositions proceeded. This measurement was based on substrate curvature...

Solid particles in the tropical lowest stratosphere

Nielsen, J. K.; Larsen, N.; Cairo, F.; Di Donfrancesco, G.; Rosen, J. M.; Durry, G.; Held, G.; Pommereau, J. P.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 685-695
Português
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65.53%
We report in situ and remote observations proving occasional occurrence of solid particles in the tropical lowest stratosphere, 200km from deep convective events. The particles were found during field campaigns in Southeast Brazil (49.03 W 22.36 S). They occur in the altitude range from 17.5 to 20.8 km, at temperatures up to at least 10 K above the expected frost point temperature. While stability of ice particles at these altitudes is unexpected from a theoretical point of view, it is argued that these observations are indications of tropospheric air masses penetrating into the stratosphere during convective overshoots. It is argued that the intrusion of tropospheric air must have carried a large amount of water with it, which effectively hydrated the lowest stratosphere, and consequently suppressed sublimation. This conclusion is further supported by a separate water vapor mixing ratio profile obtained at the same observation site.

ANALYSIS OF THE EARTH CONSTRUCTION’S THERMAL BEHAVIOR – IN SITU MEASUREMENT AND EVALUATION OF THERMAL PERFORMANCE OF THREE RAMMED EARTH CASE STUDIES

Sampaio, Sofia; Gomes, Maria da Glória; Borges Abel, António
Fonte: Grupo Tierra, Universidad de Valladolid Publicador: Grupo Tierra, Universidad de Valladolid
Tipo: Aula
Português
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65.6%
The emergence of the new paradigm of sustainable construction related to the concern of excessive energy consumption of our society, led to the investigation of techniques, materials and construction solutions that could causes less environmental impact. Consequently, the interest given to ancient techniques that dealt with earth constructive solutions aroused, which has captivated the interest of architects, builders and people in general. Although this type of material is associated to a less dignified and poor construction, the search for modern expression in new buildings’ design has shown the physical and plastic potential of the usage of earth in modern architecture. However, the regulation of the constructions’ minimum requirements related to materials’ mechanical strength and thermal performance (such as the Portuguese Thermal Building Regulation- RCCTE), has been one of the biggest obstacles in spreading and growing the application of this technique. This study intends to increase the knowledge of the thermal behavior of this type of construction. In this article, the results of in situ measurement campaigns, carried out during the summer and winter periods, are presented. They were performed on three different single-family dwellings located in Abrantes...

Feasibility of an in situ measurement device for bubble size and distribution

Junker, Beth; Maciejak, Walter; Darnell, Branson; Lester, Michael; Pollack, Michael
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Português
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65.75%
The feasibility of in situ measurement device for bubble size and distribution was explored. A novel in situ probe measurement system, the EnviroCam™, was developed. Where possible, this probe incorporated strengths, and minimized weaknesses of historical and currently available real-time measurement methods for bubbles. The system was based on a digital, high-speed, high resolution, modular camera system, attached to a stainless steel shroud, compatible with standard Ingold ports on fermenters. Still frames and/or video were produced, capturing bubbles passing through the notch of the shroud. An LED light source was integral with the shroud. Bubbles were analyzed using customized commercially available image analysis software and standard statistical methods. Using this system, bubble sizes were measured as a function of various operating parameters (e.g., agitation rate, aeration rate) and as a function of media properties (e.g., viscosity, antifoam, cottonseed flour, and microbial/animal cell broths) to demonstrate system performance and its limitations. For selected conditions, mean bubble size changes qualitatively compared favorably with published relationships. Current instrument measurement capabilities were limited primarily to clear solutions that did not contain large numbers of overlapping bubbles.

A High Temperature Capacitive Pressure Sensor Based on Alumina Ceramic for in Situ Measurement at 600 °C

Tan, Qiulin; Li, Chen; Xiong, Jijun; Jia, Pinggang; Zhang, Wendong; Liu, Jun; Xue, Chenyang; Hong, Yingping; Ren, Zhong; Luo, Tao
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 30/01/2014 Português
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65.61%
In response to the growing demand for in situ measurement of pressure in high-temperature environments, a high temperature capacitive pressure sensor is presented in this paper. A high-temperature ceramic material-alumina is used for the fabrication of the sensor, and the prototype sensor consists of an inductance, a variable capacitance, and a sealed cavity integrated in the alumina ceramic substrate using a thick-film integrated technology. The experimental results show that the proposed sensor has stability at 850 °C for more than 20 min. The characterization in high-temperature and pressure environments successfully demonstrated sensing capabilities for pressure from 1 to 5 bar up to 600 °C, limited by the sensor test setup. At 600 °C, the sensor achieves a linear characteristic response, and the repeatability error, hysteresis error and zero-point drift of the sensor are 8.3%, 5.05% and 1%, respectively.

A Stretch/Bend Method for In Situ Measurement of the Delamination Toughness of Coatings and Films Attached to Substrates

He, M. Y.; Hutchinson, John W.; Evans, Anthony G.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
Português
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65.61%
A stretch/bend method for the in situ measurement of the delamination toughness of coatings attached to substrates is described. A beam theory analysis is presented that illustrates the main features of the test. The analysis is general and allows for the presence of residual stress. It reveals that the test produces stable extension of delaminations, rendering it suitable for multiple measurements in a single test. It also provides scaling relations and enables estimates of the loads needed to extend delaminations. Finite element calculations reveal that the beam theory solutions are accurate for slender beams, but overestimate the energy release rate for stubbier configurations and short delaminations. The substantial influence of residual stress on the energy release rate and phase angle is highly dependent on parameters such as the thickness and modulus ratio for the two layers. Its effect must be included to obtain viable measurements of toughness. In a companion paper, the method has been applied to a columnar thermal barrier coating deposited onto a Ni-based super-alloy.; Engineering and Applied Sciences

The Response of Stratospheric Water Vapor to a Changing Climate: Insights from In Situ Water Vapor Measurements

Sargent, Maryann Racine
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
Português
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65.7%
Stratospheric water vapor plays an important role in the Earth system, both through its role in stratospheric ozone destruction and as a greenhouse gas contributing to radiative forcing of the climate. Highly accurate water vapor measurements are critical to understanding how stratospheric water vapor concentrations will respond to a changing climate. However, the past disagreement among water vapor instruments on the order of 1 – 2 ppmv hinders understanding of the mechanisms which control stratospheric humidity, and the reliable detection of water vapor trends. In response to these issues, we present a new dual axis water vapor instrument that combines the heritage Harvard Lyman-(alpha) hygrometer with the newly developed Harvard Herriott Hygrometer (HHH). The Lyman-(alpha) instrument utilizes ultraviolet photo-fragment fluorescence detection, and its accuracy has been demonstrated though rigorous laboratory calibrations and in situ diagnostic procedures. HHH employs a tunable diode near-IR laser to measure water vapor via direct absorption in a Herriott cell; it demonstrated in-flight precision of 0.1 ppmv (1-sec) with accuracy of 5%±0.5 ppmv. We describe these two measurement techniques in detail along with our methodology for calibration and details of the measurement uncertainties. We also examine the recent flight comparison of the two instruments with several other in situ hygrometers during the 2011 MACPEX campaign...

A Space weather information service based upon remote and in-situ measurements of coronal mass ejections heading for Earth: A concept mission consisting of six spacecraft in a heliocentric orbit at 0.72 AU

Ritter, Birgit; Meskers, Arjan J. H.; Miles, Oscar; Ru??wurm, Michael; Scully, Stephen; Rold??n Aranda, Andr??s; Hartkorn, Oliver; J??stel, Peter; R??ville, Victor; Lupu, Sorina; Ruffenach, Alexis
Fonte: EDP Sciences Publicador: EDP Sciences
Tipo: Artigo de Revista Científica
Português
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75.6%
The Earth???s magnetosphere is formed as a consequence of interaction between the planet???s magnetic field and the solar wind, a continuous plasma stream from the Sun. A number of different solar wind phenomena have been studied over the past 40 years with the intention of understanding and forecasting solar behavior. One of these phenomena in particular, Earth-bound interplanetary coronal mass ejections (CMEs), can significantly disturb the Earth???s magnetosphere for a short time and cause geomagnetic storms. This publication presents a mission concept consisting of six spacecraft that are equally spaced in a heliocentric orbit at 0.72 AU. These spacecraft will monitor the plasma properties, the magnetic field???s orientation and magnitude, and the 3D-propagation trajectory of CMEs heading for Earth. The primary objective of this mission is to increase space weather forecasting time by means of a near real-time information service, that is based upon in-situ and remote measurements of the aforementioned CME properties. The obtained data can additionally be used for updating scientific models. This update is the mission???s secondary objective. In-situ measurements are performed using a Solar Wind Analyzer instrumentation package and fluxgate magnetometers...

A Differential Pressure Instrument with Wireless Telemetry for In-Situ Measurement of Fluid Flow across Sediment-Water Boundaries

Gardner, Alan T.; Karam, Hanan N.; Mulligan, Ann E.; Harvey, Charles F.; Hammar, Terence R.; Hemond, Harold F.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 09/01/2009 Português
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65.6%
An instrument has been built to carry out continuous in-situ measurement of small differences in water pressure, conductivity and temperature, in natural surface water and groundwater systems. A low-cost data telemetry system provides data on shore in real time if desired. The immediate purpose of measurements by this device is to continuously infer fluxes of water across the sediment-water interface in a complex estuarine system; however, direct application to assessment of sediment-water fluxes in rivers, lakes, and other systems is also possible. Key objectives of the design include both low cost, and accuracy of the order of ±0.5 mm H2O in measured head difference between the instrument's two pressure ports. These objectives have been met, although a revision to the design of one component was found to be necessary. Deployments of up to nine months, and wireless range in excess of 300 m have been demonstrated.

Dating of chemical weathering processes by in situ measurement of U-series disequilibria in supergene Fe-oxy/hydroxides using LA-MC-ICPMS

Bernal, Juan; Eggins, Stephen; McCulloch, Malcolm; Grun, Rainer; Eggleton, Richard
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.61%
Constraints on the timing of weathering processes in the northern Australian regolith have been obtained by in situ measurement of U-series disequilibria in U-rich supergene Fe-oxy/hydroxides using a laser ablation-MC-ICPMS technique. This approach has pe

Optical vernier technique for in-situ measurement of the length of long Fabry-Perot cavities

Rakhmanov, M.; Evans, M.; Yamamoto, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/09/1998 Português
Relevância na Pesquisa
65.68%
We propose a method for in-situ measurement of the length of kilometer size Fabry-Perot cavities in laser gravitational wave detectors. The method is based on the vernier, which occurs naturally when the laser incident on the cavity has a sideband. By changing the length of the cavity over several wavelengths we obtain a set of carrier resonances alternating with sideband resonances. From the measurement of the separation between the carrier and a sideband resonance we determine the length of the cavity. We apply the technique to the measurement of the length of a Fabry-Perot cavity in the Caltech 40m Interferometer and discuss the accuracy of the technique.; Comment: LaTeX 2e, 12 pages, 4 figures

Re-observing the EUV emission from Abell 2199: in-situ measurement of background distribution by offset pointing

Lieu, R.; Bonamente, M.; Mittaz, J. P. D.; Durret, F.; Santos, S. Dos; Kaastra, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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65.66%
The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phenomenon. There has been many unsuccessful attempts to `trivialize' the findings. In this Letter we present direct evidence to prove that the most recent of such attempts, which attributes the detected signals to a background non-uniformity effect, is likewise excluded. We address the issue by a re-observation of A2199 which features a new filter orientation, usage of a more sensitive part of the detector and, crucially, includes a background pointing at $\sim$ 2$^o$ offset - the first {\it in situ} measurement of its kind. We demonstrate quantitatively two facts: (a) the offset pointing provides an accurate background template for the cluster observation, while (b) data from other blank fields do not. We then performed point-to-point subtraction of the {\it in situ} background from the cluster field, with appropriate propagation of errors. The resulting cluster radial profile is consistent with that obtained by our original method of subtracting a flat asymptotic background. The emission now extends to a radius of 20 arcmin; it confirms the rising prominence of EUV excess beyond $\sim$ 5 arcmin as previously reported.; Comment: 11 pages...

In situ Measurement of Biaxial Modulus of Si Anode for Li-ion Batteries

Sethuraman, Vijay A.; Chon, Michael J.; Shimshak, Maxwell; Van Winkle, Nathan; Guduru, Pradeep R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/08/2011 Português
Relevância na Pesquisa
65.61%
We report in situ measurement of biaxial moduli of a Si thin-film electrode as a function of its lithium concentration. During lithiation, biaxial compressive stress is induced in the Si film and it undergoes plastic flow. At any state-of-charge (SOC), a relatively small delithiation-relithiation sequence unloads and reloads the film elastically. From the stress and strain changes during a delithiation-relithiation cycle, the biaxial modulus of the film is calculated. Stress change is obtained by measuring the change in substrate curvature using a Multi-beam Optical Sensor; the elastic strain change is obtained from the change in SOC. By repeating these measurements at several different values of SOC, the biaxial modulus was seen to decrease from ca. 70 GPa for Li0.32Si to ca. 35 GPa for Li3.0Si. Such a significant reduction in elastic modulus has important implications for modeling stress evolution and mechanical degradation in Si-based anodes.; Comment: 8 pages, 3 figures

An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland

Avva, J.; Kovac, J. M.; Miki, C.; Saltzberg, D.; Vieregg, A. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.65%
We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. Assuming a reliable extrapolation to higher frequencies, the measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as a promising northern site for UHE neutrino detection.; Comment: 7 pages, 7 figures, published in Journal of Glaciology

In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors

Billard, J.; Mayet, F.; Bosson, G.; Bourrion, O.; Guillaudin, O.; Lamblin, J.; Richer, J. P.; Riffard, Q.; Santos, D.; Iguaz, F. J.; Lebreton, L.; Maire, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.65%
Three-dimensional track reconstruction is a key issue for directional Dark Matter detection and it requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence needed as it is a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures: CF4 and CF4 + CHF3. The latter has been chosen for the MIMAC detector as we expect that adding CHF3 to pure CF4 will lower the electron drift velocity. This is a key point for directional Dark Matter as the track sampling along the drift field will be improved while keeping almost the same Fluorine content of the gas mixture. We show that the drift velocity at 50 mbar is reduced by a factor of about 5 when adding 30% of CHF3.; Comment: 19 pages, 14 figures. Minor corrections, matches published version in JINST

An optical vernier technique for in situ measurement of the length of long Fabry-Pérot cavities

Rakhmanov, M.; Evans, M.; Yamamoto, H.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /03/1999 Português
Relevância na Pesquisa
65.68%
We propose a method for in situ measurement of the length of kilometre-sized Fabry-Pérot cavities in laser gravitational wave detectors. The method is based on the vernier, which occurs naturally when the laser beam incident on the cavity has a sideband. By changing the length of the cavity over several wavelengths we obtain a set of carrier resonances alternating with sideband resonances. From the measurement of the separation between the carrier and a sideband resonance we determine the length of the cavity. We apply the technique to the measurement of the length of a Fabry-Pérot cavity in the Caltech 40m interferometer and discuss the accuracy of the technique.

In situ measurement, characterization, and modeling of two-phase pressure drop incorporating local water saturation in PEMFC gas channels

See, Evan
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
65.6%
Proton Exchange Membrane Fuel Cells (PEMFCs) have been an area of focus as an alternative for internal combustion engines in the transportation sector. Water and thermal management techniques remain as one of the key roadblocks in PEMFC development. The ability to model two-phase flow and pressure drop in PEMFCs is of significant importance to the performance and optimization of PEMFCs. This work provides a perspective on the numerous factors that affect the two-phase flow in the gas channels and presents a comprehensive pressure drop model through an extensive in situ fuel cell investigation. The study focused on low current density and low temperature operation of the cell, as these conditions present the most challenging scenario for water transport in the PEMFC reactant channels. Tests were conducted using two PEMFCs that were representative of the actual full scale commercial automotive geometry. The design of the flow fields allowed visual access to both cathode and anode sides for correlating the visual observations to the two-phase flow patterns and pressure drop. A total of 198 tests were conducted varying gas diffusion layer (GDL), inlet humidity, current density, and stoichiometry; this generated over 1500 average pressure drop measurements to develop and validate two-phase models. A two-phase 1+1 D modeling scheme is proposed that incorporates an elemental approach and control volume analysis to provide a comprehensive methodology and correlation for predicting two-phase pressure drop in PEMFC conditions. Key considerations...

Interpretation of monazite ages obtained via in situ analysis

Catlos, Elizabeth; Gilley, Lisa; Harrison, Timothy
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.58%
Monazite grains from Nepal and Vietnam were compositionally analyzed with an electron microprobe and dated (Th-Pb) with an ion microprobe. Five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population: (1) Pb loss due to diffusion, (2) dissolution/reprecipitation reactions along a retrograde path, (3) analytical uncertainties, (4) analyses of overlapping age domains, and (5) episodic monazite growth. The influence of these factors is sample-dependent, but can be evaluated: (1) using peak metamorphic conditions and X-ray element maps to assess potential polymetamorphism or retrogression, (2) obtaining other geochronologic data including previous work or dating other minerals in the sample, (3) evaluating any method-related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses, and (4) ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element (REE) oxide or allanite. Chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms. Instead of relying on monazite chemical composition...