1000 resultados para Endoderm Formation
Resumo:
Bubble formation from single horizontal orifices submerged in Newtonian liquids has been investigated for such chamber volumes that both the pressure inside the chamber and flow rate into the bubble are time dependent. The data collected show that under these conditions the bubble volume decreases exponentially with increase in orifice submergence. The equations for the generalized two stage model of bubble formation, taking the variation of gas flow rate with time into account, have been derived. These equations reduce to the cases of constant gas flow rate and constant pressure when adequate constraints are imposed. The results obtained under intermediate conditions have been quantitatively explained on the basis of these equations.
Resumo:
Bubble formation under constant pressure conditions has been investigated for wide range of variation of liquid properties.Air bubbles were formed from single horizontal orifices submerged in liquids whose viscosity varied from 1·0 to 600 cPs and surface tension from 37 to 72 dyn/cm. Air flow rate was varied from 2 to 250 cm3/sec and the orifice diameter from 0·0515 to 0·4050 cm.
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A model based on two step mechanism of bubble formation is proposed. The resulting equations are used to explain the discrepancies existing in the literature. Data have been collected over a wide range of variables to test the model.
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Benzene drops were formed in continuous media of water and glycerine of varying physical properties. The effect on drop volumes of variables like volumetric flow-rate, interfacial tension, continuous phase viscosity and capillary diameter was studied. An equation has been developed, based on a two stage drop formation mechanism, which predicts drop volumes within an average error of 7 per cent for the range of physical properties employed in this investigation.
Biosynthesis of valine and isoleucine in plants I. Formation of α-acetolactate in Phaseolus radiatus
Resumo:
1. 1. The presence of an enzyme system in plants catalyzing the formation of α-acetolactate from pyruvate has been demonstrated; the system in green gram (Phaseolus radiatus) has been partially purified and its characteristics have been studied.2. Free acetaldehyde is formed as a product of the reaction and so the reaction is mainly diverted towards the formation of acetoin. 3. The system requires thiamine pyrophosphate and a divalent metal ion (Mn2+ or Mg2+) for maximum activity. The optimum pH is around 6.0 and the optimum temperature is 60°. 4. The system is very labile in absence of pyruvate, Mn2+ and DPT. 5. The Km values for pyruvate, Mn2+, Mg2+ and DPT are 3·10−2 M. 5·10−5 M, 2·10−5 M, and e·10−6 M respectively. The activation energy is 3540 cal/mole. 6. The enzyme is strongly inhibited by p-chloromercuribenzoate and the inhibition can be reversed partially by 2-mercaptoethanol, BAL or cysteine. Heavy metals, such as Hg2+ and Ag+, are inhibitory but l-valine does not inhibit the reaction.
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Single-step low-temperature solution combustion (LCS) synthesis was adopted for the preparation of LaMnO3+ (LM) nanopowders. The powders were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),surface area and Fourier transform infrared spectroscopy (FTIR). The PXRD of as-formed LM showed a cubic phase but, upon calcination (900degrees C, 6 h), it transformed into a rhombohedral phase. The effect of fuel on the formation of LM was examined, and its structure and magnetoresistance properties were investigated. Magnetoresistance (MR) measurements on LM were carried out at 0, 1, 4 and 7 T between 300 and 10 K. LM (fuel-to-oxidizer ratio; = 1) showed an MR of 17% at 1 T, whereas, for 4 and 7 T, it exhibited an MR of 45 and 55%, respectively, near the TM-I. Metallic resistivity data below TM-I showed that the double exchange interaction played a major role in this compound. It was interesting to observe that the sample calcined at 1200 degrees C for 3 h exhibited insulator behavior.
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It was found that ceric oxalate is an intermediate product in the oxidation of oxalic acid by ammonium hexanitrato cerate in solvents such as acetonitrile, and a mixture of acetonitrile and glacial acetic acid. Conditions for the formation of ceric oxalate and its decomposition into carbon dioxide and cerous oxalate have been studied. An analytical method for the estimation of oxalic acid in non-aqueous media has been evolved based on this reaction.
Resumo:
Bubble formation from porous discs submerged in liquids of different physical properties has been investigated. It is found the number of sites effective for bubble formation is much smaller than the total potentially available sites. The number of effective sites is found to be a function of the surface tension, viscosity, and density of the liquid and the gas flow rate through the disc. A model proposed on the basis of bubble formation from an isolated nozzle and the close packed arrangement of the formed bubbles, explains the phenomenon adequately. © 1970.
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An approach, starting with the bubble formation model of Khurana and Khumar, has been presented, which is found to be reasonably applicable to the formation of both bubbles and drops from single submerged nozzles. The model treats both the phenomena jointly as the formation of a dispersed phase entity resulting from injection, whose size depends upon operating parameters and physical properties.
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Normal growth and development require the precise control of gene expression. Transcription factors are proteins that regulate gene expression by binding specific sequences of DNA. Abnormalities in transcription are implicated in a variety of human diseases, including cancer, endocrine disorders and birth defects. Transcription factor GATA4 has emerged as an important regulator of normal development and function in a variety of endoderm- and mesoderm- derived tissues, including gut, heart and several endocrine organs, such as gonads. Mice harboring a null mutation of Gata4 gene die during embryogenesis due to failure in heart formation, complicating the study of functional role of GATA4 in other organs. However, the expression pattern of GATA4 suggests it may play a role in the regulation of ovarian granulosa cell development, function and apoptosis. This premise is supported by in vitro studies showing that GATA4 regulates several steroidogenic enzymes as well as auto-, para- and endocrine signaling molecules important for granulosa cell function. This study assessed the in vivo role of GATA4 for granulosa cell function by utilizing two genetically modified mouse strains. The findings in the GATA4 deficient mice included delayed puberty, impaired fertility and signs of diminished estrogen production. At the molecular level, the GATA4 deficiency leads to attenuated expression of central steroidogenic genes, Steroidogenic acute regulatory protein (StAR), Side-chain cleavage (SCC), and aromatase as a response to stimulations with exogenous gonadotropins. Taken together, these suggest GATA4 is necessary for the normal ovarian function and female fertility. Programmed cell death, apoptosis, is a crucial part of normal ovarian development and function. In addition, disturbances in apoptosis have been implicated to pathogenesis of human granulosa cell tumors (GCTs). Apoptosis is controlled by extrinsic and intrinsic pathways. The intrinsic pathway is regulated by members of Bcl-2 family, and its founding member, the anti-apoptotic Bcl-2, is known to be important for granulosa cell survival. This study showed that the expression levels of GATA4 and Bcl-2 correlate in the human GCTs and that GATA4 regulates Bcl-2 expression, presumably by directly binding to its promoter. In addition, disturbing GATA4 function was sufficient to induce apoptosis in cultured GCT- derived cell line. Taken together, these results suggest GATA4 functions as an anti-apoptotic factor in GCTs. The extrinsic apoptotic pathway is controlled by the members of tumor necrosis factor (TNF) superfamily. An interesting ligand of this family is TNF-related apoptosis-inducing ligand (TRAIL), possessing a unique ability to selectively induce apoptosis in malignant cells. This study characterized the previously unknown expression of TRAIL and its receptors in both developing and adult human ovary, as well as in malignant granulosa cell tumors. TRAIL pathway was shown to be active in GCTs suggesting it may be a useful tool in treating these malignancies. However, more studies are required to assess the function of TRAIL pathway in normal ovaries. In addition to its ability to induce apoptosis in GCTs, this study revealed that GATA4 protects these malignancies from TRAIL-induced apoptosis. GATA4 presumably exerts this effect by regulating the expression of anti-apoptotic Bcl-2. This is of particular interest as high expression of GATA4 is known to correlate to aggressive GCT behavior. Thus, GATA4 seems to protect GCTs from endogenous TRAIL by upregulating anti-apoptotic factors such as Bcl-2.
Resumo:
The present study focused on the associations between the personal experiences of intergroup contact, perceived social norms and the outgroup attitudes of Finnish majority and Russian-speaking minority youth living in Finland. The theoretical background of the study was derived from Allport s (1954) theory of intergroup contact (i.e., the contact hypothesis), social psychological research on normative influences on outgroup attitudes (e.g., Rutland, 2004; Stangor and Leary, 2006) and developmental psychological research on the formation of explicit (deliberate) and implicit (automatically activated) outgroup attitudes in adolescence (e.g., Barrett, 2007; Killen, McGlothlin and Henning, 2008). The main objective of the study was to shed light on the role of perceived social norms in the formation of outgroup attitudes among adolescents. First, the study showed that perceived normative pressure to hold positive attitudes towards immigrants regulated the relationship between the explicit and implicit expression of outgroup attitudes among majority youth. Second, perceived social norms concerning outgroup attitudes (i.e., the perceived outgroup attitudes of parents and peers) affected the relationship between intergroup contact and explicit outgroup attitudes depending on gender and group status. Positive social norms seem to be especially important for majority boys, who need both pleasant contact experiences and normative support to develop outgroup attitudes that are as positive as girls attitudes. The role of social norms is accentuated also among minority youth, who, contrary to majority youth with their more powerful and independent status position, need to reflect upon their attitudes and experiences of negative intergroup encounters in relation to the experiences and attitudes of their ingroup members. Third, the results are indicative of the independent effects of social norms and intergroup anxiety on outgroup attitudes: the effect of perceived social norms on the outgroup attitudes of youth seems to be at least as strong as the effect of intergroup anxiety. Finally, it was shown that youth evaluate intergroup contact from the viewpoint of their ingroup and society as a whole, not just based on their own experiences. In conclusion, the outgroup attitudes of youth are formed in a close relationship with their social environment. On the basis of this study, the importance of perceived social norms for research on intergroup contact effects among youth cannot be overlooked. Positive normative influences have the potential to break the strong link between rare and/or negative personal contact experiences and negative outgroup attitudes, and norms also influence the relationship between implicit and explicit attitude expression.
Resumo:
Atmospheric particles affect the radiation balance of the Earth and thus the climate. New particle formation from nucleation has been observed in diverse atmospheric conditions but the actual formation path is still unknown. The prevailing conditions can be exploited to evaluate proposed formation mechanisms. This study aims to improve our understanding of new particle formation from the view of atmospheric conditions. The role of atmospheric conditions on particle formation was studied by atmospheric measurements, theoretical model simulations and simulations based on observations. Two separate column models were further developed for aerosol and chemical simulations. Model simulations allowed us to expand the study from local conditions to varying conditions in the atmospheric boundary layer, while the long-term measurements described especially characteristic mean conditions associated with new particle formation. The observations show statistically significant difference in meteorological and back-ground aerosol conditions between observed event and non-event days. New particle formation above boreal forest is associated with strong convective activity, low humidity and low condensation sink. The probability of a particle formation event is predicted by an equation formulated for upper boundary layer conditions. The model simulations call into question if kinetic sulphuric acid induced nucleation is the primary particle formation mechanism in the presence of organic vapours. Simultaneously the simulations show that ignoring spatial and temporal variation in new particle formation studies may lead to faulty conclusions. On the other hand, the theoretical simulations indicate that short-scale variations in temperature and humidity unlikely have a significant effect on mean binary water sulphuric acid nucleation rate. The study emphasizes the significance of mixing and fluxes in particle formation studies, especially in the atmospheric boundary layer. The further developed models allow extensive aerosol physical and chemical studies in the future.