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81.
Value‐centric framework and pareto optimality for design and acquisition of communication satellites
Joy Brathwaite Joseph H. Saleh 《International Journal of Satellite Communications and Networking》2009,27(6):330-348
Investments in space systems are substantial, indivisible, and irreversible, characteristics of high‐risk investments. Traditional approaches to system design, acquisition, and risk mitigation are derived from a cost‐centric mindset, and as such they incorporate little information about the value of the spacecraft to its stakeholders. These traditional approaches are appropriate in stable environments. However, the current technical and economic conditions are distinctly uncertain and rapidly changing. Consequently, these traditional approaches have to be revisited and adapted to the current context. We propose that in uncertain environments, decision‐making with respect to design and acquisition choices should be value‐based. We develop a value‐centric framework, analytical tools, and an illustrative numerical example for communication satellites. Our two proposed metrics for decision‐making are the system's expected value and value uncertainty. Expected value is calculated as the expected NPV of the satellite. The cash inflow is calculated as a function of the satellite loading, its transponder pricing, and market demand. The cash outflows are the various costs for owning and operating the satellite. Value uncertainty emerges due to uncertainties in the various cash flow streams, in particular because of market conditions. We propagate market uncertainty through Monte Carlo simulation, and translate it into value uncertainty for the satellite. The end result is a portfolio of Pareto‐optimal satellite design alternatives. By using value and value uncertainty as decision metrics in the down‐selection process, decision‐makers draw on more information about the system in its environment, and in making value‐based design and acquisition choices, they ultimately make more informed and better choices. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
82.
PECVD silicon nitride passivation is quite frequently done at the end of AlGaN/GaN HEMT fabrication before substrate back-side lapping. However, the PECVD silicon nitride process is likely to produce pinholes in the passivation film. A very thick PECVD silicon nitride film may produce mechanical stress on the underlying device. Polyimide passivation has also been known to be effective for AlGaN/GaN HEMT and it can also serve as a stress buffer. However, polyimide can take up water while PECVD silicon nitride is a good diffusion barrier for water, etc. Thus it is expected that a dual PECVD silicon nitride/polyimide passivation will be a better choice than just a single layer of PECVD silicon nitride or polyimide. In this paper, we will demonstrate the application of a dual PECVD silicon nitride/polyimide passivation to AlGaN/GaN HEMT process. 相似文献
83.
David C. Joy 《Journal of microscopy》1987,147(1):51-64
Images in the scanning electron microscope (SEM) are formed from both low-energy secondary, and high-energy backscattered, electrons. The quantitative interpretation of SEM images therefore requires a model which can predict the magnitude of both of these signal components for a specimen whose geometry and chemistry is known. It is shown that the combination of a simple electron diffusion model with a Monte Carlo trajectory simulation allows both yields to be calculated, simultaneously, with good accuracy. Data, such as the magnitude and energy of the maximum secondary yield, the secondary variation with tilt, and the contribution of backscattered electrons to the secondary yield coefficient, computed from this model are in excellent agreement with experimental data. 相似文献
84.
David C. Joy 《Journal of microscopy》1984,136(2):241-258
Backscattered and secondary electrons are both used in the SEM for imaging purposes. The backscattered signal is the result of high angle elastic scattering events, while the secondary signal is the result of knock-on inelastic collisions. The characteristic differences between images in the two modes arise from the details of the relevant interactions in the two cases. In order to examine this in a quantitative manner Monte Carlo electron trajectory simulation techniques have been used. Calculations of the ultimate resolution and depth of information of the secondary and backscattered images are presented, together with simulations of the edge brightness effect in high resolution secondary images and an analysis of the microanalytical application of atom number contrast in the backscattered mode. 相似文献
85.
Ming Tian Taylor Ticer Qikun Wang Sierra Walker Anthony Pham Annie Suh Sara Busatto Irina Davidovich Rawan Al‐Kharboosh Laura Lewis‐Tuffin Baoan Ji Alfredo Quinones‐Hinojosa Yeshayahu Talmon Shane Shapiro Felix Rückert Joy Wolfram 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(10)
Extracellular vesicles secreted from adipose‐derived mesenchymal stem cells (ADSCs) have therapeutic effects in inflammatory diseases. However, production of extracellular vesicles (EVs) from ADSCs is costly, inefficient, and time consuming. The anti‐inflammatory properties of adipose tissue‐derived EVs and other biogenic nanoparticles have not been explored. In this study, biogenic nanoparticles are obtained directly from lipoaspirate, an easily accessible and abundant source of biological material. Compared to ADSC‐EVs, lipoaspirate nanoparticles (Lipo‐NPs) take less time to process (hours compared to months) and cost less to produce (clinical‐grade cell culture facilities are not required). The physicochemical characteristics and anti‐inflammatory properties of Lipo‐NPs are evaluated and compared to those of patient‐matched ADSC‐EVs. Moreover, guanabenz loading in Lipo‐NPs is evaluated for enhanced anti‐inflammatory effects. Apolipoprotein E and glycerolipids are enriched in Lipo‐NPs compared to ADSC‐EVs. Additionally, the uptake of Lipo‐NPs in hepatocytes and macrophages is higher. Lipo‐NPs and ADSC‐EVs have comparable protective and anti‐inflammatory effects. Specifically, Lipo‐NPs reduce toll‐like receptor 4‐induced secretion of inflammatory cytokines in macrophages. Guanabenz‐loaded Lipo‐NPs further suppress inflammatory pathways, suggesting that this combination therapy can have promising applications for inflammatory diseases. 相似文献
86.
Madjid Mohseni Joy Lan Zhao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(2):146-151
Coupling UV photolysis and biofiltration was evaluated as an effective treatment strategy for the enhanced degradation of hardly biodegradable aromatic volatile organic compounds (VOCs). o‐Xylene, a recalcitrant and poorly water‐soluble VOC, was used as a model compound and treated in two parallel treatment systems with and without UV pretreatment. Contaminated streams with flow rates of 0.186–0.384 m3 h?1 and inlet o‐xylene concentrations of up to 0.22 g m?3 were passed through the treatment system. About 20% (between 10 and 35%) of o‐xylene was converted into water‐soluble intermediates during the UV photolysis stage, which partially oxidized o‐xylene to more water‐soluble and biodegradable byproducts. The untreated contaminant along with the byproducts of UV photolysis was then removed effectively in the biofiltration stage, with improvements of up to 100% compared with the control biofiltration process. The results suggested that combined UV photolysis–biofiltration is promising as an effective technique to eliminate hydrophobic and recalcitrant organic compounds from contaminated air steams. Copyright © 2005 Society of Chemical Industry 相似文献
87.
David C. Joy 《Journal of microscopy》1986,143(3):233-248
Charge collection microscopy, usually known by the acronym EBIC (Electron Beam Induced Current) imaging, is a powerful technique for the observation and characterization of semiconductor materials and devices in the scanning electron microscope. Quantitative interpretation of EBIC images is often difficult because of the problem of accurately representing the electron-beam interaction with the semiconductor. This paper uses a Monte Carlo technique to simulate the electron-beam interaction, and it is shown that this permits simple analytical point-source solutions to be generalized to fully represent the experimental situation of an extended, non-uniform, carrier source. The model is demonstrated by application to EBIC imaging in the Schottky barrier geometry. 相似文献
88.
Although electron beams with energies of a few keV can excite fluorescent X-ray production from solids, ion beams of comparable energy cannot do so. The reason for this situation is that it is the velocity of the incident particle, rather than its energy, which determines whether an ionization event can be generated. 相似文献
89.
Electron beam-induced deposition (EBID) provides a simple way to fabricate submicron- or nanometer-scale structures from various elements in a scanning electron microscope (SEM). The growth rate and shape of the deposits are influenced by many factors. We have studied the growth rate and morphology of EBID-deposited nanostructures as a function of the tungsten hexafluoride (WF6) and tetraethylorthosilicate (TEOS) precursor gas pressure and growth time, and we have used Monte Carlo simulations to model the growth of tungsten and silicon oxide to elucidate the mechanisms involved in the EBID growth. The lateral radius of the deposit decreases with increasing pressure because of the enhanced vertical growth rate which limits competing lateral broadening produced by secondary and forward-scattered electrons. The morphology difference between the conical SiO(x) and the cylindrical W nanopillars is related to the difference in interaction volume between the two materials. A key parameter is the residence time of the precursor gas molecules. This is an exponential function of the surface temperature; it changes during nanopillar growth and is a function of the nanopillar material and the beam conditions. 相似文献
90.
In the variable pressure scanning electron microscope (VP-SEM) the incident electrons pass through a gaseous environment and the beam is scattered by these interactions. We show here that the experimental intensity profile of the scattered beam can be described as Gaussian in form to a high level of accuracy. This provides a rapid means of accounting for the effects of beam scatter in imaging and microanalysis because the standard deviation of the Gaussian is a simple function of parameters such as working distance, beam energy, gas type and pressure. 相似文献