306,141 research outputs found
Time domain reflectometry applied to MMIC passive component modeling
No full textThe time domain facilities of a network analyzer, combined with the tools of network synthesis, were recently used for experimental modeling of discontinuities in an S-parameter measurement set, so as to allow the instrument calibration directly to the ports of the device under test. The technique proved to be very useful in those cases where the discontinuities, that lie before the unknown device, cannot be isolated by the usual calibration methods, and therefore, since network synthesis deals only with frequency domain information, it is impossible to optimize the model's parameters, since they are affected by errors due to discontinuities. This paper describes a procedure which allows to isolate the response of the device under test, and to derive its complete model; when it to reach a reasonable accuracy it gives anyway a topology, which is a good starting point for other optimization routines that can be used for obtaining a better match, on a broad frequency band. This can be accomplished by optimzing the first approach topology to which other circuit elements have been added, so as to take into account second order effects especially at the higher frequencies. The technique was applied to model and characterize passive discrete components used in MMIC. The experimental results show the validity of the approac
Biometria, dormência e germinação de sementes de Butia eriospatha (Martius ex Drude) Beccari
No full textProjeto acadêmico (graduação) - Universidade Federal de Santa Catarina. Campus Curitibanos. Ciências Rurais.Butia eriospantha (Martius ex Drude) Beccari conhecido popularmente como butiá-da-serra é uma espécie nativa do bioma Mata Atlântica, encontrada no sul do Brasil, pertencente à família Arecaceae. Por ser uma palmeira que possui diferentes finalidades, esta passou a ser motivo de comércio ilegal nacional e internacional, e, por consequência da grande exploração e pouca regeneração natural, além da predação por bovinos e por apresentar uma germinação lenta, B. eriospatha encontra-se atualmente na lista das espécies brasileiras ameaçadas de extinção. Pouco se sabe sobre sua germinação e os mecanismos envolvidos nesse processo, assim como pouco se conhece sobre as características biométricas de seus frutos e sementes. Desse modo o principal objetivo deste trabalho é desenvolver metodologias para testes em laboratório que avaliam o processo de germinação e o vigor de sementes de B. eriospatha. Serão coletados frutos de sete matrizes (palmeiras), localizadas no município de Curitibanos/ SC, após as análises biométrica dos frutos, pirênios e sementes, serão realizados os testes de germinação, iniciando com o teste para a verificação da dormência, na sequência, teste para a verificação do substrato mais adequado, além disso, serão analisados também os efeitos das temperaturas de 25 e 30ºC sob a germinação, e a curva de embebição será determinada. Ainda, as matrizes serão avaliadas quanto ao vigor das sementes, através do desenvolvimento de metodologias para testes de condutividade elétrica e tetrazólio. Espera-se após as análises dos experimentos, recomendar metodologias adequadas para os testes em laboratório, que auxiliarão na diferenciação de lotes de sementes, bem como nos programas de multiplicação em viveiros, através do qual serão obtidas mudas de melhor qualidade, o que possibilita a retirada desta espécie da lista de espécies ameaçadas de extinção
Confronto sperimentale tra metodi termodinamici per la determinazione della posizione del punto morto superiore
No full textButia eriospatha (Arecaceae): comportamento meiótico, palinologia e biometria de frutos
No full textTCC (graduação)- Universidade Federal de Santa Catarina. Campus Curitibanos. Agronomia.A espécie Butia eriospatha (Mart. ex Drude) Becc (Arecaceae) é nativa da região sul do Brasil e Uruguai e se encontra na lista de espécies brasileiras ameaçadas de extinção. O conhecimento das características reprodutivas de espécies silvestres é muito importante uma vez que podem ser utilizadas como base para serviços de melhoramento e outros estudos que podem levar a uma melhor conservação da mesma. Desse modo, o presente trabalho teve como objetivo realizar análise e registro do comportamento meiótico, análises palinológicas por meio da determinação da viabilidade, citoquímica e morfologia dos grãos de pólen, assim como, realizar análises biométricas com os frutos e sementes de B. eriospatha. O comportamento meiótico se mostrou regular e sem anormalidades, e o número cromossômico da espécie foi de 2n 2x=32. A viabilidade polínica determinada por colorimetria revelou que os corantes testados foram eficientes, demonstrando altas médias de viabilidade de 82,50%. O teste citoquímico demonstrou que os grãos de pólen são amido e lipídeo-positivos, e os mesmos foram classificados como grandes, mônades, prolatos, monosulcados e com ornamentação micro-reticulada. Dentre as variáveis estudadas em relação à biometria de frutos e sementes, houve grande variação no número de sementes por frutos e altura das sementes, que apresentaram grau de umidade de 14,31%
Il fiore dei miei ricordi: Gilberto Beccari e la traduzione dei Recuerdos di Unamuno
No full textL’articolo prende in esame il lavoro di Gilberto Beccari come traduttore italiano delle opere di Unamuno. L’analisi si concentra in particolare sulla traduzione dei Recuerdos, pubblicati con il titolo Il fiore dei miei ricordi, ed è finalizzata non soltanto a mettere in luce le tecniche traduttorie utilizzate da Beccari, ma anche a valutare le implicazioni letterarie legate alle sue scelte. Nella conclusione si evidenzia l’importanza del traduttore come mediatore culturale tra Italia e Spagna
Detailed Combustion Analysis of a Supercharged Double-Fueled Spark Ignition Engine
No full textThe main goal of researches in the field of automotive engineering is to obtain a large-scale implementation
of low- or zero-emissions vehicles in order to substantially reduce air pollution in urban
areas. A fundamental step toward this green transition is represented by the improvement of current
internal combustion (IC) engines in terms of fuel economy and pollutant emissions. The spark ignition
(SI) engines of modern light-duty vehicles are supercharged, down-sized, and equipped with direct
injection. Gaseous fuels, such as liquefied petroleum gas (LPG) or natural gas (NG), proved to be a
valid alternative to gasoline in order to reduce pollutant emissions and increase fuel economy. In
previous works the authors investigated the simultaneous combustion, in an SI engine, of gasoline
and a gaseous fuel (referred to as Double-Fuel operation, DF) both in the naturally aspirated and
supercharged version; a significant increment of engine efficiency and a great reduction of pollutant
emissions were obtained with respect to pure gasoline operation, with almost unchanged performance.
This article is a development of the previous work and shows the results of a detailed heat
release analysis, performed on the DF supercharged engine fueled with mixtures of gasoline and
NG in order to highlight the effects of engine speed, charging pressure, and fuel mixture composition
(the proportion between gasoline and NG) on the combustion speed.
It was found that both gasoline content in the DF mixture and supercharging pressure contribute
to increase the combustion speed, which, in some cases, produced engine-indicated efficiency
increments up to 5%. The wide set of experimental data presented in this article allows us to better
understand the combustion behavior of gasoline-NG fuel mixtures and can be also used to calibrate
combustion submodels integrated into engine numerical simulations
Performance and combustion analysis of a supercharged double-fuel spark ignition engine
No full textIn order to increase fuel economy and reduce pollutant emissions in the last decades light duty spark ignition (SI) engines have become smaller, supercharged and equipped with direct injection. A suitable alternative to oil derived fuel is represented by gaseous fuels, such as Natural Gas (NG) and Liquefied Petroleum Gas (LPG), whose higher knock resistance and better mixing capabilities substantially improve vehicle fuel economy and pollutant emissions. The simultaneous combustion of gasoline and gaseous fuel (Double-Fuel operation, DF) in a naturally aspirated SI engine has already been investigated in the past also by the same authors, proving remarkable results in terms of engine efficiency increment and exhaust emissions reduction. In this paper the authors present the results of a new methodical experimental study aimed to investigate engine performance, efficiency and pollutant emissions obtained on a supercharged SI engine operated in double fuel mode, with comparison to the use of "reference" pure fuels (i.e. gasoline and NG). A detailed heat release analysis is also performed with the aim to highlight the effect of fuel mixture composition (i.e. the proportion between gasoline and NG) and of charging pressure on the combustion speed
Heat Transfer Modeling of Hydrogen-Fueled Spark Ignition Engine
No full textCurrently, green hydrogen, generated through renewable energy sources, stands out as one of the best substitutes for fossil fuels in mitigating pollutant emissions and consequent global warming. Particularly, the utilization of hydrogen in spark ignition engines has undergone extensive study in recent years. Many aspects have been analyzed: the conversion of gasoline engines to hydrogen operation, the combustion duration, the heat transfer, and, in general, the engine thermal efficiency. Hydrogen combustion is characterized by a smaller quenching distance compared to traditional hydrocarbon fuels such as gasoline or natural gas and this produces a smaller thermal boundary layer and consequently higher heat transfer. This paper presents findings from experimental trials and numerical simulations conducted on a hydrogen-powered CFR (cooperative fuel research) engine, focusing specifically on heat transfer with combustion chamber walls. The engine has also been fueled with methane and isooctane (two reference fuels); both the engine compression ratio and the air/fuel ratio have been changed in a wide range in order to compare the three fuels in terms of heat transfer, combustion duration, and engine thermal efficiency in different operating conditions. A numerical model has been calibrated with experimental data in order to predict the amount of heat transfer under the best thermal efficiency operating conditions. The results show that, when operated with hydrogen, the best engine efficiency is obtained with a compression ratio of 11.9 and an excess air ratio (lambda) of 2
In-fixture calibration of an S-parameter measuring system by means of time domain reflectometry
No full textWe present a technique which resorts to the time domain capabilities of a vector network analyzer and to the network synthesia tools, in order to perform an in-fixture calibration of the S-parameter measurement system directly to the ports of the device under test. The effects of the customer's non ideal fixtures can be removed without requiring the insertion of standard components or particular loads, which can affect the calibration efectiveness. The inaccuracies due to the precision of the actual loads and to the connection repeatability are also avoided. Some simulation reeults demonstrate the very good capability of the technique. Experimental tests were also carried out on an actual microstrip transistor fixture, showing a very satisfactoty launcher modeling and de-embeddin
Reliable TDC position determination: a comparison of different thermodynamic methods through experimental data and simulations
No full textIt is known to internal combustion researcher that the correct determination of the crank position when the piston is at Top Dead Centre (TDC) is very important, since an error of 1 crank angle degree (CAD) can cause up to a 10% evaluation error on indicated mean effective pressure (IMEP) and a 25% error on the heat released by the combustion: the TDC position should be then known within a precision of 0.1 CAD. This task can be accomplished by means of a dedicated capacitive sensor, which allows a measurement within the required 0.1 degrees precision. Such a sensor has a substantial cost and its use is not really fast; a different approach can be followed using a thermodynamic method, whose input is the pressure curve sampled during the compression and expansion strokes of a “motored” (i.e. without combustion) cylinder.In this work the authors compare an original thermodynamic method with other ones available in literature, by means of both experimental and simulated pressure curves. A zero dimensional thermodynamic model was employed to obtain an extensive collection of numeric pressure curves by changing engine geometry (e.g. compression ratios from 10 to 20 were adopted), operative conditions and wall heat transfer laws. The in-cylinder mass leakage has been taken into account in the model.Moreover, in order to assess the reliability and robustness of each method, the typical measurement errors and disturbances related to indicating analysis have been taken into account. The capability of the investigated methods to provide the correct TDC position in presence of the above mentioned errors has been evaluated
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