Exciplex Fluorescence Thermometry of Falling Hexadecane Droplets

1992 ◽  
Vol 114 (2) ◽  
pp. 450-457 ◽  
Author(s):  
T. R. Hanlon ◽  
L. A. Melton

Exciplex fluorescence thermometry has been used to measure the temperature of 283 micron hexadecane droplets falling through a quiescent, oxygen-free, approximately 500°C ambient. After a period of negligible change, the derived droplet temperatures exhibit a sharp rise of about 100°C followed by a gentle increase to approximately 200°C. The derived temperatures, although averaged over most of the volume of the droplet, still provide some evidence of internal processes in the droplet due to the partially selective optical sampling of the droplet volume, in which fluorescence from the region between 0.50 and 0.75 of the droplet radius contributes disproportionately. At longer times, the droplet is presumed to be approximately homogeneous, and the exciplex fluorescence thermometry measurements provide accurate, interpretable temperatures for the freely falling droplets.

1990 ◽  
Vol 112 (4) ◽  
pp. 1008-1013 ◽  
Author(s):  
M. R. Wells ◽  
L. A. Melton

The temperature of 225-μm-dia decane droplets, which have fallen 100 mm through a hot quiescent, oxygen-free environment, has been measured using exciplex fluorescence thermometry. The droplets were doped with pyrene, and the relative intensities of pyrene monomer and excimer emissions were used to determine the droplet temperatures. The droplet temperature increases approximately 0.4°C per °C increase in the ambient temperature up to an ambient temperature of 200°C. Less than 10 percent evaporation was observed for the droplets at the highest ambient temperatures.


1989 ◽  
Vol 43 (2) ◽  
pp. 274-278 ◽  
Author(s):  
John H. Stufflebeam

An experimental program is described that investigates the application of exciplex fluorescence to the internal thermometry of flowing liquid decane in the temperature range 24–91°C. Decane is doped with pyrene and excited by laser radiation at 354.7 nm. A library of temperature-dependent, exciplex fluorescence spectra is obtained from a static, isothermal solution, and the spectral features are analyzed to produce a temperature-prediction algorithm. The solution then flows through a temperature gradient region, and the laser-induced fluorescence spectra that are recorded are used to determine the local temperature in the solution by application of the algorithm. Excellent agreement between the predicted temperatures and those measured by thermocouples in contact with the solution is realized. The experiment demonstrates the high accuracy and spatial resolution obtainable with this laser-based thermometry technique.


2020 ◽  
Author(s):  
Anne-Sophie Hacquin ◽  
Sacha Altay ◽  
Emma de Araujo ◽  
Coralie Chevallier ◽  
Hugo Mercier

A safe and effective COVID-19 vaccine is our only hope to decisively stop the spread of the SARS-CoV-2. But a vaccine will only be fully effective if a significant share of the population agrees to get it. Five consecutive surveys of a large, nationally representative sample (N = 1000 for each wave) surveyed attitudes towards a future COVID-19 vaccine in France from May 2020 to October 2020. We found that COVID-19 vaccine refusal has steadily increased, reaching an all-time high with only 23% of participants willing to probably or certainly take a future COVID-19 vaccine in September 2020. Vaccine hesitant individuals are more likely to be women, young, less educated, to vote at the political extremes, to be dissatisfied with the government’s response to the COVID-19 crisis, and to feel less at risk of COVID-19. The reasons why French people would refuse to take the COVID-19 vaccine are similar to those offered for other vaccines, and these reasons are strikingly stable across gender, age and educational level. Finally, most French people declare they would not take the vaccine as soon as possible but would instead rather wait or not take it at all.


Author(s):  
KSENIA A. Batishcheva ◽  
ATLANT E. Nurpeiis

With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.


Author(s):  
Tatiani De Azevedo Lobo ◽  
Marli M. Moraes Da Costa

Resumo: O presente ensaio busca apresentar e fomentar algumas questões pertinentes ao debate contemporâneo sobre a pobreza, demonstrando a importância do tema no cenário mundial. Para tanto, inicialmente discorre-se sobre a construção histórico-social da pobreza e suas características contemporâneas. Com efeito, aponta-se a limitação dos fatores tradicionalmente apresentados como causadores da pobreza, como cultura, genética, geografia etc. Além disso, apresentam-se as formas atuais de monitorar o fenômeno, como o coeficiente de Gini e o IDH. Posteriormente, aborda-se a distribuição mundial da pobreza. Nesse ponto, colaciona-se que a pobreza é um problema mundial. No entanto, é perceptível que o Sul ainda concentra maior número de indivíduos pobres do que o Norte. Na esteira dos últimos dados da pesquisa realizada pelas Nações Unidas, houve uma nítida ascensão do Sul, especialmente nos indicadores sociais ligados à educação. A seguir, trata-se do capital social e da Teoria das Capacidades, apresentando-se novas abordagens da pobreza. Assim, o capital social trata de uma ideia utilizada para verificar a rede de relacionamento dos indivíduos. Já a Teoria das Capacidades está ligada com a ideia de oportunidade da liberdade. Por fim, estuda-se as políticas públicas, bem como seu aspecto fragmentário. Conclui-se, assim, sobre a necessidade de implementação de políticas públicas elaboradas sob a égide de novos paradigmas, a fim de possibilitar o tratamento específico do fenômeno da pobreza, conforme as peculiaridades de cada local. Para tanto foi utilizado neste trabalho o método de abordagem hipotético-dedutivo, o método de procedimento monográfico e a técnica de pesquisa, operacionalizados por meio do emprego de vasta pesquisa bibliográfica. Abstract: This essay seeks to provide and foster some relevant to the contemporary debate on poverty issues, demonstrating the importance of the issue on the world stage. For this purpose, initially spoke about the historical and social construction of poverty and its contemporary features. Indeed, he pointed out the limitation of the factors traditionally presented as the cause of poverty, as a culture, genetics, geography, etc. Furthermore, we presented the current ways of monitoring the phenomenon, such as the Gini coefficient and the HDI. Subsequently addressed the global distribution of poverty. At this point, if collated that poverty is a worldwide problem. However, it is apparent that the South still more concentrated than the poor North individuals. In the wake of recent data from research conducted by the United Nations, there was a sharp rise in the South, especially in social indicators related to education. Next, we treated the capital and the Theory of Capabilities, presenting new approaches to poverty. Thus, social capital is an idea used to verify the relationship network of individuals. Already Capabilities Theory is linked with the idea of freedom of opportunity. Finally, we studied public policy, as well as its fragmentary appearance. Thus, it is concluded on the need to implement public policies prepared under the aegis of new paradigms to enable specific treatment of the phenomenon of poverty, according to the peculiarities of each site. For that was used in this work the method of hypothetical-deductive approach, the method of procedure and the monographic research technique, operationalized through the use of extensive academic research.


2013 ◽  
Vol 13 (16) ◽  
pp. 8489-8503 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.


1983 ◽  
Vol 38 (9-10) ◽  
pp. 711-718 ◽  
Author(s):  
U. Margna ◽  
T. Vainjärv

A short treatment of excised buckwheat cotyledons with a solution of kinetin lead to an up to 9-fold stimulation of anthocyanin biosynthesis, to an about 50 percent increase in the accumula­tion of rutin, and to an about 30 percent increase, on the average, in the accumulation of C-glycosylflavones in the treated material during its posttreatment incubation in the dark. When the treated cotyledons were incubated in a solution of ʟ--phenylalanine anthocyanin accumulation in the dark practically attained the same high level as it was observed in the illuminated cotyledons fed with exogenous ʟ--phenylalanine. In experiments with l4C-labelled L-phenylalanine kinetin induced a sharp rise in the labelling (resp. in the utilization of exogenous substrate for biosynthesis) of anthocyanins and rutin in the dark and a slight increase in the radioactivity of C-glycosylflavones. Similar labelling changes occurred in the illuminated cotyledons. However, both kinetin and light still more effectively promoted biosynthetic use of the endogenous sub­strate. As a result the relative portion of flavonoids formed from exogenous L-phenylalanine under these conditions showed a decrease as compared with the ratio of precursor use in the un­treated cotyledons. The results show that low accumulation rates of anthocyanins and other flavo­noids in the dark are conditioned by the limited access of substrate (ʟ--phenylalanine) molecules to the flavonoid enzymes lending further support to the idea that flavonoid biosynthesis is normally controlled at the substrate rather than at the enzymic level.


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