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991.
The aim of this study is to describe the ultrastructure of the hepatopancreas of P. argentinus in intermoult. P. argentinus hepatopancreas was studied using standard TEM techniques. Each tubule consists of four cellular types: E (embryonic), F (fibrillar), R (resorptive) and B (blister like). E-cells have embryonic features and some of them were found in mitosis. F, R and B cells possess an apical brush border. F-cells have a central or basal nucleus, a conspicuous RER, and dilated Golgi cisternae. R cells show a polar organization of organelles in three areas: apical, with numerous mitochondria and sER tubules, a central area with the nucleus and RER, and a basal area containing a sER-like tubule system and mitochondria. B-cells were observed at different stages of their life cycle. In an early differentiation stage they comprise an apical endocytotic complex and Golgi vesicles. The fusion of endocytotic and Golgi vesicles originates subapical vacuoles. During maturation, a big central vacuole is formed by coalescence of subapical vacuoles. The central vacuole is eliminated by holocrine secretion. The ultrastructure suggests that F-cells synthesize proteins, R-cells storage nutrients and B-cells have a secretory or excretory function, and confirms the independent origin of F, B and R cells from the embryonic cells. 相似文献
992.
Verd J. Uranga A. Abadal G. Teva J.L. Torres F. Lopez J.L. Perez-Murano E. Esteve J. Barniol N. 《Electron Device Letters, IEEE》2008,29(2):146-148
This letter presents the design, fabrication, and demonstration of a CMOS/microelectromechanical system (MEMS) electrostatically self-excited resonator based on a submicrometer-scale cantilever with ~1 ag/Hz mass sensitivity. The mechanical resonator is the frequency-determining element of an oscillator circuit monolithically integrated and implemented in a commercial 0.35 mum CMOS process. The oscillator is based on a Pierce topology adapted for the MEMS resonator that presents a mechanical resonance frequency of ~6 MHz, a relative low quality factor of 100, and a large motional resistance of ~25 M. The MEMS oscillator has a frequency stability of ~1.6 Hz resulting in a mass resolution of ~1 ag (1 ag = 10-18 g in air conditions. 相似文献
993.
The present technical note describes a computer tool for determining the horizon brightness diffuse irradiance on a tilted plane in the model of Perez. The applied procedure considers the configuration factor concept, which is calculated using the unit-sphere method. The results obtained with this procedure, which is more exact than the one followed by Perez, are compared with the ones obtained with Perez's proposal. It may be observed that for small angles of inclination differences are up to 36%, and that said differences decrease when the angle of inclination increases. For angles higher than 77.15°, differences become lower than 1%. It may be concluded that the described procedure, together with the computer tool for implementing it, is adequate for determining the horizon brightness irradiance on a tilted plane, once the radiance of this area of the sky dome is known. 相似文献
994.
Claude Lucat Patrick Ginet Christophe Castille Hlne Debda Francis Mnil 《Microelectronics Reliability》2008,48(6):872-875
A new process derived from screen-printing technology and based on thick sacrificial layers has been developed in our laboratory for the fabrication of films partially released from the substrate. The sacrificial layer acts as a stable mechanical support during the firing of the active layer and is totally removed after the final thermal treatment of the sample. Fabrication of a copper electrothermal actuator was undertaken to demonstrate the efficiency of this simple, collective and low cost process. Passive components based on this new process include the fabrication of heating resistors, strain gauges and microchannels. Moreover, the process can also be used to facilitate the implementation of piezoelectric devices. 相似文献
995.
996.
Ana Isabel Nájera Yolanda Barcina Mercedes de Renobales L. J. R. Barron 《European Food Research and Technology》1998,207(3):197-201
The influence of traditional smoking on the triglyceride (TG) composition of Idiazabal cheese during ripening was studied
using HPLC. The partition numbers (PNs) of the TGs ranged between 22 and 53, the groupings of TG peaks with PN values of 36,
34, and 38 being the main contributors. Statistically significant differences between the smoked and the unsmoked cheeses
were recorded during the ripening period. Smoking had a significant effect on certain groups of TGs at different ripening
times and no effect on others. The differences in the TG profiles of the cheeses were the result of differing levels of lipolytic
activity, which was heightened by smoking.
Received: 29 December 1997 / Revised version: 9 March 1998 相似文献
997.
This work describes the relationships observed between the porosity of fired ceramic test pieces and the raw materials contents
in the unfired mixture. The investigation was carried out using the mixture experiments design approach coupled with response
surface methodology, which enables the calculation of statistically significant models for the properties from a limited number
of experimental results. Ten formulations of a clay mixture, potash feldspar and quartz sand were processed in the laboratory
under fixed conditions, similar to those used on wall and floor tile industrial practice, and characterized. Closed porosity
(CP) was estimated from the analysis of back-scattered SEM photomicrographs, open porosity (OP) was calculated as the product
of bulk density and water absorption, and total porosity (TP) was calculated from OP and CP values. Characterization results
were used to calculate statistically significant and valid regression equations, relating those properties with the raw material
contents in the unfired mixture. For the particular raw materials and processing conditions used, the models clearly show
how quartz contributes to increasing OP and the crucial role played by feldspar when CP and TP are to be minimized (circa 3 vol.%), and how the clay content can counteract that effect and lead to maximum closed porosity (∼14 vol.%). 相似文献
998.
Ana Estela Barbosa Thorkild Hvitved-Jacobsen 《Canadian Metallurgical Quarterly》2001,127(11):1014-1022
Highway runoff disposal without concern for its specific characteristics may be associated with high material and environmental costs. An understanding of storm water management has enlightened the importance of the impacts that nonpoint pollution may cause to both surface waters and groundwater. Several systems for highway runoff treatment exist, often based on detention and infiltration processes. This paper suggests a method for design and evaluation of the design of infiltration ponds for use in semiarid climates. The design principle is based on capture and infiltration of the most polluted runoff. It takes into account the rainfall and soil hydraulic characteristics for the determination of the design volume. Seasonal variations in rainfall and evaporation were considered. The soil characteristics—hydraulic conductivity, texture, pH, and cation exchange capacity—the volume of runoff which is infiltrated, and the infiltration area are used to calculate the movement of the most mobile heavy metal, Zn, in the soil. The method presented was based and applied to highway runoff but can be used for treatment of stormwater runoff from other sources. 相似文献
999.
Torres R.P. Loredo S. Valle L. Domingo M. 《Selected Areas in Communications, IEEE Journal on》2001,19(2):170-178
Ray-tracing techniques have proven to be very useful for the analysis and design of wireless systems both in urban microcells and in indoor picocells. At present, the optimization of these techniques enables not only the signal mean level but also the local statistics to be estimated accurately, which is of great practical importance. A wide range of comparisons between measurements and simulations confirming this have been carried out by the authors, and some examples are presented. The most interesting contribution of this paper is that starting from the signal information at one single point, obtained using ray-tracing techniques, it is possible to estimate the signal statistics in a local area of that point. This possibility substantially reduces the local statistics calculation time, confirming the idea that an efficient site specific channel model might be feasible. Finally, it is also shown that ray-tracing techniques are able to accurately estimate the first- and second-order statistics in those environments where the Clarke (1968) or isotropic scattering model is not applicable 相似文献
1000.
In this paper we consider, for the univariate lognormal diffusion process with exogenous factors, the inference for some parametric
functions that include as particular cases the trend and the covariance function of the process. Concretely, we obtain the
UMVU estimators of these functions and the efficiency of them relative to the corresponding ML estimators. Finally, we conclude
with an application to a particular case of exogenous factor.
This research was partially supported by DGYCIT PB97-0855 and BFM2000-0602 Grants. 相似文献