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111.
António Betamio de Almeida Dídia Isabel Cameira Covas 《Canadian Metallurgical Quarterly》2007,133(8):937-948
The fundamental background of the solution for the steady-state flow in pressurized water closed-loop pipe systems, without any reservoirs in-between, is presented in this paper. The use of the steady-state mass balance and energy equations to calculate discharges and heads in this type of hydraulic system leads to an undetermined problem. The way to solve this indeterminacy is to consider an additional continuity equation associated with the difference between initial and final conditions, taking into account fluid compressibility and pipe-wall deformability. A complete formulation is derived considering pressure and temperature changes in the hydraulic system. Simplified formulae are presented for isothermal flows in simple systems and multiple closed-loops with pipes in series and in parallel. This problem can also be solved by a pseudotransient analysis technique applied to steady-state conditions. Proposed solutions for this problem are applied to steady-state flows and tested for different system configurations. 相似文献
112.
Participation of Doubly Fed Induction Wind Generators in System Frequency Regulation 总被引:4,自引:0,他引:4
This paper proposes a control scheme that allows doubly fed induction wind generators (DFIWG) to participate effectively in system frequency regulation. In this control approach, wind generators operate according to a deloaded optimum power extraction curve such that the active power provided by each wind turbine increases or decreases during system frequency changes. The control strategy defined at the wind generator to supply primary frequency regulation capability exploits a combination of control of the static converters and pitch control, adjusting the rotor speed and the active power according to the deloaded optimum power extraction curve. Results obtained in a small isolated system are presented to demonstrate the effectiveness of the approach. 相似文献
113.
Microglia Response and In Vivo Therapeutic Potential of Methylprednisolone‐Loaded Dendrimer Nanoparticles in Spinal Cord Injury
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114.
This paper presents a simple but effective method to identify and map the distribution of vegetation using hyperspectral data, which involves band ratios and principal component analysis (PCA). Using spectral data from the literature, we devised spectral indices focused on specific vegetation constituents (band positions are in nm): chlorophyll-a (461/422 and 807/638); chlorophyll-b (520/470 and 807/648); @-carotene (520/442); carotenoids (539/490 and 807/490); anthocyanin (510/530); phytochrome P730 (845/730), phytochrome P660 (778/658); lignin (1028/2101); cellulose (2211/2400); nitrogen (1731/1691); and leaf water content (1066/1452). In a second step, these indices were submitted to PCA. PCA eigenvector loadings were examined to decide which of the principal component (PC) images concentrate information directly related to the spectral signatures of specific vegetation constituents. An important aspect of this approach was that it predicted whether the target surface type would be highlighted by dark or bright pixels in the relevant PC image. Finally, the optimal PCs are selected and combined in a colour composite. In this study, we applied this method to atmospherically corrected Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data collected in the Alto Paraíso de Goiás (APG) region of central Brazil. The results from identifying and mapping the distribution of vegetation in the APG region were very encouraging. Photosynthetic and non-photosynthetic vegetation or a mixture of both were mapped on the basis of feature-oriented PC loadings. Discriminations between vegetation types were made, including identifying riparian forests, burn grasslands and resurgence zones, crops and several types of savannah and pastures. 相似文献
115.
Cristian Epifânio de Toledo José Carlos de Araújo Cicero Lima de Almeida 《International journal of remote sensing》2013,34(10):3683-3699
Reservoirs are the main water source in the Brazilian semiarid region, especially in the crystalline-geology watersheds, forming high-density reservoir networks (HdRN). However, in most cases, the construction of these reservoirs has been done without technical supervision. The objective of this work was to map and evaluate the spatial distribution of the 25,000 km2 Orós Reservoir Basin (ORB) HdRN, in semiarid Brazil, with the help of remote-sensing tools associated with geographic information systems (GIS). Using LANDSAT 5 images of the end of the 2011 rainy season of the ORB, the remote-sensing technique allowed the identification of 6002 polygons, which corresponded to only 4717 reservoirs (implying a misidentification of 21%). Between 2002 and 2011, a 17.5% increase (and 1.81% annual increase) in the number of reservoirs in the basin was observed, still lower than the annual increment from 1970 to 2002, when an average increase of 2.64% per year was observed, in other studies. The perimeter of the reservoirs ranged from 0.250 to 560 km and the individual water surface area ranged from 0.004 to 195.0 km2, resulting in a total surface of 465.0 km2. Analysing the surface area of the strategic reservoirs, results showed that the estimation of the surface area (from remote sensing with manual polygon adjustment) yielded values very close to those of the on-site monitored areas, with R2 = 0.99 and normalized difference index ranging from ?0.02 to +0.09. The reservoir density in the ORB in 2011 was 0.19 reservoirs km–2, higher than the recommended optimum density of 0.15 reservoirs km–2 basin. Analysis of reservoir density by municipality recorded values ranging from 0.02 to 0.40 reservoirs km–2. The sedimentary-geology municipalities presented a reservoir density on average 80% lower than the that of the crystalline-geology municipalities, indicating a strong relationship between geology and reservoir density. Neither population density nor rainfall explained the spatial distribution of reservoirs within the basin, both yielding R2 lower than 0.1. This remote-sensing survey of reservoirs demonstrated two major flaws: the misidentification of shadows as reservoirs and the inability to identify the presence of macrophytes, which negatively affected the number and surface area of the target reservoirs. Despite these problems, remote sensing has been shown to be a technique of great potential in the planning and management of water resources in regions with dense reservoir networks. 相似文献
116.
Silvio Frosini De Barros Ferraz Luis Miguel Silva Almeida Canteiro Capão Carlos Alberto Vettorazzi 《International journal of remote sensing》2013,34(3):459-472
The Amazon has been under an intense deforestation process for the last 30 years, causing landscape fragmentation in many different regions and at distinct stages. The fragmentation process is commonly assessed by land‐use maps derived from satellite sensor data and analysed at a landscape context. The analysis of fragmentation depends on an adequate choice of spatial resolution of land‐use maps, and temporal scale in landscape dynamics studies. In this study, spatial–temporal resolution variation effects on fragmentation assessment were analysed in the Quatro Cachoeiras watershed, located at central Rondônia, Brazilian Amazon. Land‐use maps derived from 1984 to 2002 satellite sensor data at 2‐year intervals were used for landscape structure analysis on 12 samples randomly distributed along the watershed. In the spatial resolution variation analysis, landscape metrics obtained at 30 m resolution were compared with those obtained at coarser spatial resolutions. Effects of temporal scale variation were tested by comparison of landscape metrics calculated at 2‐, 4‐ and 6‐year intervals in the studied period. Results show that fragmentation stage influences sensitivity of landscape metrics for spatial resolution and at initial stages of fragmentation finer spatial resolution is required. Also, coarser resolutions up to 100 m could be used to assess landscape fragmentation at regions and the adequate time interval for landscape dynamics studies should be between 3 and 4 years. 相似文献
117.
R. Almeida‐Filho Y. E. Shimabukuro A. Rosenqvist G. A. Sánchez 《International journal of remote sensing》2013,34(14):3735-3743
This study shows the use of dual‐polarized L‐band Synthetic Aperture Radar (SAR) data acquired by the Advanced Land Observing Satellite (ALOS) Phased Array type L‐band Synthetic Aperture Radar sensor (PALSAR) system for differentiation between primary forest and new deforestation fronts. Results showed that the new deforested areas are not unequivocally detected in either of the single bands individually. Although most of the recent deforestation appears brighter than mature forests in the HH band, the identification of new deforestation using only this band depends on the stage of the clearing process. Then, the contribution of the HV band through a normalized difference index (NDI) is important for detection of the new deforested fronts. Results indicate that the method can be used as the basis for an operational programme to monitor deforestation in the Brazilian Amazônia. 相似文献
118.
Javier Cámara Rogério de Lemos Marco Vieira Raquel Almeida Rafael Ventura 《Computing》2013,95(8):689-722
One of the major challenges related to self-adaptive software systems is the provision of assurances that the system is resilient against changes that may occur either in the system or its environment. These assurances should be based on complementary sources of evidence that collectively justify that the system is able to attain the specified levels of resilience. The contribution of this paper is the definition and development of an architecture-based approach that evaluates by comparison the adaptation mechanisms of a self-adaptive software system. The proposed approach relies on the identification of representative environmental and system changeloads (i.e., sequences of changes) used in the run-time stimulation of the system. The system response obtained from this stimulation is collected and aggregated into a probabilistic model that is employed in the evaluation of system resilience. Our approach is intended to be used before deployment, since the process often involves putting the system through adverse conditions which are not adequate when the system is in production. The feasibility and effectiveness of the proposed approach is demonstrated in the context of Rainbow, an architecture-based platform for self- adaptation, and Znn.com, a case study that reproduces the typical infrastructure for a news website. 相似文献
119.
Janaina I. S. Aguiar Jéssica S. G. Neto Sarah M. Almeida Claudia R. E. Mansur 《应用聚合物科学杂志》2013,128(3):1390-1397
During extraction of crude oil, water is generally present in the oil. This water‐in‐oil (w/o) mixture undergoes turbulent flow that promotes sheer forces, resulting in the appearance of emulsions. These emulsions can be highly stable due to the presence of compounds with polar characteristics such as asphaltenes, which act as natural emulsifiers and form resistant films at the oil–water interface. Nonionic surfactants based on polyoxides are widely used to prevent the formation or to break down w/o emulsions. To shed more light on the destabilization mechanism of w/o emulsions promoted by these surfactants, in this study the techniques of tensiometry and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR‐ATR) were applied to study the interface formed by poly(ethylene oxide)‐poly(propylene oxide) (PEO‐PPO) block copolymers and asphaltenic petroleum fractions. Initially, the critical micelle concentration of the copolymers in aqueous solution was determined. The results agreed with those found by tensiometry. The bottle test was used to evaluate the break‐down of the w/o emulsions in the presence of the PEO‐PPO block copolymers, and the results presented good agreement with those obtained by tensiometry and FTIR‐ATR. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
120.
Erika P. L. Almeida Fabiano S. Chaves Robson D. Vieira Renato F. Iida 《Analog Integrated Circuits and Signal Processing》2014,78(3):717-728
The use of TV white spaces as an alternative to overcome spectrum scarcity is a huge opportunity for new telecommunication systems and services. While being attractive for its desirable propagation characteristics, this part of the spectrum imposes a major difficulty from design and regulatory perspectives: how to optimize the use of spectrum and to ensure the protection of primary users, TV systems for example, at the same time. This paper discusses strategies to be adopted by geo-location database operators to calculate adaptive maximum permitted power levels for secondary devices, according to permissible levels of interference into the digital terrestrial television primary system. 相似文献