Liquid-propellant droplet vaporization and combustion in high pressure environments

In order to correct the deficiencies of existing models for high-pressure droplet vaporization and combustion, a fundamental investigation into this matter is essential. The objective of this research are: (1) to acquire basic understanding of physical and chemical mechanisms involved in the vaporization and combustion of isolated liquid-propellant droplets in both stagnant and forced-convective environments; (2) to establish droplet vaporization and combustion correlations for the study of liquid-propellant spray combustion and two-phase flowfields in rocket motors; and (3) to investigate the dynamic responses of multicomponent droplet vaporization and combustion to ambient flow oscillations

Overview of Combustion Instabilities in Liquid-Propellant Rocket Engines

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Metal-organic frameworks as chemical sensors

Metaloorganske mreže su posebna klasa spojeva u kemiji materijala koja predstavlja najbolju simbiozu kemije organskih i anorganskih spojeva u jednom. Građeni su od više metalnih centara ili metalnih klastera povezanih međusobno organskim ligandima koji se u terminologiji metaloorganskih mreža nazivaju linkerima tvoreći pritom mrežu koja ovisno o veličini svojih pora može selektivno propuštati samo one molekule koje su svojim proporcijama manje od spomenutih pora. Zbog već navedenih specifičnosti u strukturi, metaloorganske mreže su pronašle primjenu u raznim područjima znanosti i tehnologije od kojih se zasigurno najviše izdvaja primjena kao kemijskih senzora. Metaloorganske mreže mogu se nadograđivati čime se postiže pojačavanje signala. Takvi spregnuti kemijski senzori svojom specifičnom građom omogućavaju selektivnost i smanjenje koncentracije analita potrebne za detekciju. S obzirom da su metaloorganske mreže dio kemije materijala čiji razvoj je novijeg datuma, do sada su uspješno razvijeni mnogi kemijski senzori bazirani na sustavima u kojima glavnu ulogu prepoznavanja signala imaju metaloorganske mreže. Najbolje istraženi kemijski senzori su MOF-ovi čije se djelovanje bazira na interferometriji, površinski lokaliziranoj plazmatskoj rezonanciji, luminescenciji i koloidnim kristalima. Očekuje se kako će daljnjim razvojem znanosti zasada samo velik potencijal metaloorganskih mreža u budućnosti imati veću primjenu koja se neće bazirati samo na specifičnoj selektivnosti i poboljšanjima starijih tehnika detekcije, već i u primjeni koja će biti korisnija za cijelokupno područje prirodnih i tehničkih znanosti

Nonlinear analysis of pressure oscillations in ramjet engines

Pressure oscillations in ramjet engines have been studied using an approximate method which treats the flow fields in the inlet and the combustor separately. The acoustic fields in the combustor are expressed as syntheses of coupled nonlinear oscillators corresponding to the acoustic modes of the chamber. The influences of the inlet flow appear in the admittance function at the inlet /combustor interface, providing the necessary boundary condition for calculation of the combustor flow. A general framework dealing with nonlinear multi-degree-of-freedom system has also been constructed to study the time evolution of each mode. Both linear and nonlinear stabilities are treated. The results obtained serve as a basis for investigating the existence and stabilities of limit cycles for acoustic modes. As a specific example, the analysis is applied to a problem of nonlinear transverse oscillations in ramjet engines

Relationship between seed harvesting method and seed physiological quality for a number of Pioneer maize hybrids

The seed germination and seed vigor of eight Pioneer Hi-Bred maize hybrids were evaluated immediately after harvesting and a year later. The aim was to determine whether the seed showed loss of germination and vigor when shelled mechanically. The seed was cleaned but not dressed, and then germinated according to the ISTA standard procedure in four seed analysis laboratories. In addition, the seed of two randomly chosen hybrids was divided into four fractions based on size and shape, and the germination of each fraction was examined separately. All the germination results were acceptable according to the ISTA (2010) standard (over 90%), but a higher germination percentage was observed after manual shelling than after mechanical shelling. The number of abnormal seedlings, however, was higher for mechanically shelled seeds than for those harvested as whole ears. When the seed of separate seed fractions was tested, the germination percentage was lowest for the medium-sized round fraction and highest for the large flat fraction. The seed vigor of three of the hybrids was highest when maize seeds were harvested shelled rather than on the ear. For all the hybrids the germination percentage was lower for both groups when analyzed a year after harvesting. Better germination results were obtained for all the hybrids after whole ear harvesting than in the shelled group, but the difference was not significant. In the vigor tests the results obtained for mechanically shelled seed were superior to those for whole ear harvesting for the same three hybrids, but again the difference was not significant. The experiments should be repeated over several years to determine whether mechanically shelling maize seed negatively affects seed germination and vigor

Understanding workaholics' motivations: a self-determination perspective

In order to explain the diverging well-being outcomes of workaholism, this study aimed to examine the motivational orientations that may fuel the two main components of workaholism (i.e. working excessively and working compulsively). Drawing on Self-Determination Theory, both autonomous and controlled motivation were suggested to drive excessive work, which therefore was expected to relate positively to both well-being (i.e. vigor) and ill-health (i.e. exhaustion). Compulsive work, in contrast, was hypothesized to originate exclusively out of controlled motivation and therefore to only associate positively with ill-being. Structural equation modeling in a heterogeneous sample of Belgian white-collar workers (N=370) confirmed that autonomous motivation associated positively with excessive work, which then related positively to vigor. Controlled motivation correlated positively with compulsive work, which therefore related positively with exhaustion. The hypothesized path from controlled motivation to exhaustion through excessive work was not corroborated. In general, the findings suggest that primarily compulsive work yields associations with ill-being, since it may stem from a qualitatively inferior type of motivation

Plantas de soja oriundas de sementes de alto e baixo vigor dentro de um mesmo lote

The using of high quality seeds is extremely important to farmers, considering that vigor is one of the physiological attributes of quality and being the seeds of low vigor one of the possible factors responsible for the decline in productivity. The aim of this work was to evaluate the influence of seed vigor on vegetative and component yield aspects. The experiment consisted of a completely randomized experimental design, where each bucket containing soybean plants was considered one experimental unit, having 100 buckets for each vigor level. The vigor levels were high and low, being considered of high vigor the seeds that provided faster seedling emergence until the fifth day after sowing, and low vigor the seeds that provided later emergency, being included in this zone the ones that emerged after the sixth day. The yield components evaluated were: plant height, stem diameter, number of pods per plant, number of green pods per plant, number of seeds per plant and seed weight per plant. The results show that plants descendant from seeds of high vigor are more productive than plants from seeds of low vigor, within the same seed lot. The high vigor seeds originate plants population with less variation in vegetative and yield attributes, within the same lot of seeds and the number of pods per plant is the yield component responsible for the biggest production of high vigor seeds.Sem bolsaA utilização de sementes de alta qualidade constitui-se em uma ferramenta de extrema importância para o agricultor, considerando que o vigor é um dos atributos da qualidade fisiológica e sendo as sementes de baixo vigor um dos possíveis fatores responsáveis pela queda de produtividade. O objetivo do presente trabalho foi avaliar a influência do vigor de sementes, sobre aspectos vegetativos e os componentes de rendimento. O experimento consistiu em um delineamento experimental inteiramente casualizado, onde cada balde contendo as plantas de soja foi considerado uma unidade experimental, tendo 100 baldes para cada nível de vigor. Os níveis de vigor foram alto e baixo, sendo consideradas de alto vigor as sementes que proporcionaram emergência das plântulas até o quinto dia após a semeadura e de baixo vigor as sementes que proporcionaram emergência mais tardiamente, sendo incluídas nesta faixa também as que emergiram após o sexto dia. Os componentes do rendimento avaliados foram: altura de plantas, diâmetro do colmo, número de vagens por planta, número de vagens verdes por planta, número de sementes por planta e peso de sementes por planta. Os resultados mostram que as plantas provenientes de sementes de alto vigor são mais produtivas que as plantas provenientes de sementes de baixo vigor, dentro do mesmo lote de sementes. As sementes de alto vigor originam populações de plantas com menor variação em atributos vegetativos e de rendimento, dentro de um mesmo lote de sementes e o número de vagens por planta é o componente de rendimento responsável pela maior produção das sementes de alto vigor