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排序方式: 共有1059条查询结果,搜索用时 31 毫秒
21.
Nathan S. Jacobson rew J. Eckel Ajay K. Misra Donald L. Humphrey 《Journal of the American Ceramic Society》1990,73(8):2330-2332
The reactions of a sintered α-SiC with 5% H2 /H2 O/Ar at 1300°C were studied. Thermomchemical modeling indicates that three reaction regions are expected, depending on the initial water vapor or equivalently oxygen content of the gas stream. A high oxygen content ( P (O2 ) > 10−22 atm) leads to a SiO2 formation. This generally forms as a protective film and limits consumption of the SiC (passive oxidation). An intermediate oxygen content (10−22 atm > P (O2 ) > 10−26 atm) leads to SiO and CO formation. These gaseous products can lead to rapid consumption of the SiC (active oxidation). Thermogravimetric studies in this intermediate region gave reaction rates which appear to be controlled by H2 O gas-phase transport to the sample and reacted microstructures showed extensive grain-boundary attack in this region. Finally, a very low oxygen content ( P (O2 ) < 10−26 atm) is thermochemically predicted to lead to selective removal of carbon and formation of free silicon. Experimentally low weight losses and iron silicides are observed in this region. The iron silicides are attributed to reaction of free silicon and iron impurities in the system. 相似文献
22.
Adam Jacobson Fan Zeng David Smith Nigel Boswell Thierry Peynot Michael Milford 《野外机器人技术杂志》2021,38(1):5-27
Robustly and accurately localizing vehicles in underground mines is particularly challenging due to the unavailability of GPS, variable and often poor lighting conditions, visual aliasing in long tunnels, and airborne dust and water. In this paper, we present a novel, infrastructure‐less, multisensor localization method for robust autonomous operation within underground mines. The proposed method integrates with existing mine site commissioning and operation procedures and includes both an offline map‐building process and an online localization algorithm. The approach combines the strengths of visual‐based place recognition, LIDAR‐based localization, and odometry in a particle filter fusion process. We provide an extensive experimental validation using new large data sets acquired in two operational Australian underground hard‐rock mines (including a 600m‐deep multilevel mine with approximately 33 km of mapping data and 7 km of vehicle localization) by actual mining vehicles during production operations. We demonstrate a significant increase in localization accuracy over prior state‐of‐the‐art SLAM research systems and real‐time operation, with processing times in the order of 10 Hz. We present results showing a mean error of 0.68 m from the Queensland Mine data set and 1.32 m from the New South Wales Mine data set and at least 86% reduction in error compared with prior state of the art. We also analyze the impact of the particle filter parameters with respect to localization accuracy. Together this study represents a new approach to positioning systems for currently deployed autonomous vehicles within underground mine environments. 相似文献
23.
A. Luo D. L. Jacobson R. Ponnappan 《Journal of Materials Engineering and Performance》1992,1(6):755-761
Thermal energy storage capsules made of Inconel 617 alloy were filled with high- purity LiF- MgF2- KF salts and thermally
cycled at 983 ± 100 K in vacuum for up to 5 years. The containment life performance characteristics with fluoride salts and
in vacuum were examined. Metallographic study indicated that the inside surfaces of the post- test containers had a corrosion
damage of 100 um in depth after 5 years of thermal cycling. The outer surface showed a vaporization damage of 120 μm after
the same period. After 5 years of thermal cycling, the aluminum concentration at the capsule interior surface was reduced
to 0.424 wt% from a nominal concentration of 1.34 wt% and chromium was reduced to 18.7 wt% from a nominal concentration of
21.8 wt%. A more significant depletion of aluminum and chromium was observed at the outer surfaces. Atomic absorption spectroscopy
(AAS) and differential thermal analysis (DTA) were used to reveal the alloying element dissolution and the changes in melting
temperature and heat of fusion of fluoride salts during thermal cycling. A modified diffusion equation for a one-dimensional
semi-infinite bar was applied to the depletion of aluminum on the interior surfaces of the containers. Good agreement was
obtained between the analysis and the measured concentration profiles.
Inconel 617 is a registered trademark of the Inco Alloys International, Inc. 相似文献
24.
Sodium sulfate: Deposition and dissolution of silica 总被引:1,自引:0,他引:1
Nathan S. Jacobson 《Oxidation of Metals》1989,31(1-2):91-103
The hot-corrosion process for SiO2-protected materials involves deposition of Na2SO4 and dissolution of the protective SiO2
scale. Dew points for Na
2SO4 deposition are calculated as a function of pressure, sodium content, and sulfur content. Expected dissolution regimes for SiO2 are calculated as a function of Na2SO4 basicity, hence
generated by fuels with 0.5% and 0.05% S. Controlled-condition burner-rig tests on quartz verify some of these predicted dissolution regimes. However, the basicity of Na2SO4 is not always a simple function of
(Na2O) show that carbon creates basic conditions in Na2SO4, which explains the extensive corrosion of SiO2-protected materials containing carbon, such as SiC. 相似文献
25.
The formation of SiO(g) from SiC by either active oxidation or an oxidation-reduction process is discussed. The Wagner criterion for the transition from active to passive oxidation is generalized for any oxidant. Kinetic modeling of both active oxidation and oxidation-reduction is described.Symbols
-
-
MW
SiC/MW
Si
- CO
CO(g) boundary layer thickness
- ox
gaseous-oxidant, boundary layer thickness
-
stoichiometric factor from Eqs. (2)–(4), # of CO produced/# of oxidant (on oxygen atom basis)
-
gas viscosity
-
concentration of diffusing gas species in boundary layer
-
concentration of major gas species in boundary layer
- oxide
density of SiO2
-
D
diffusion coefficient of diffusing species in gas-boundary layer
-
D
CO
diffusion coefficient of CO(g)
-
D
ox
gas diffusion coefficient of oxidant
-
J
flux, rate of weight loss limited by diffusion in gas-boundary layer
-
J
CO
flux of CO(g)
-
J
ox
flux of gaseous oxidant
-
K
g
linear oxide growth constant, weight/(length2 time)
-
k
g
linear oxide growth constant, length/time
-
k
l
linear volatilization constant for SiO2,k
lo+k
ls, weight/(length2 time)
-
k
lo
linear volatilization constant for oxygen from SiO2, weight/(length2 time)
-
k
ls
linear volatilization constant for silicon from SiO2, weight/(length2 time)
-
k
l
linear volatilization constant for SiO2, length/time
-
k
p
parabolic oxide growth constant, weight2/(length4 time)
-
k
p
parabolic oxide growth constant, length2/time
-
L
sample length parallel to gas flow direction
- (M/A)1
specific weight change due to oxygen gain and associated carbon loss in paralinear oxidation
- (M/A)1L
limiting value of weight change due to oxygen gain and associated carbon loss in paralinear oxidation
- (M/A)2
specific weight change due to silicon loss and associated carbon loss in paralinear oxidation
-
MW
C
molecular weight of carbon
-
molecular weight of O2
-
MW
Si
molecular weight of silicon
-
MW
SiC
molecular weight of silicon carbide
-
molecular weight of silica
-
n
number of oxygen atoms per oxidant molecule
-
P
CO
eq
eqiilibrium CO(g) pressure
-
P
CO
g
CO(g) pressure outside of boundary layer
-
P
CO
i
CO(g) pressure at SiC-gas interface
-
P
ox
g
oxidant gas pressure outside of boundary layer
-
P
ox
i
oxidant gas pressure at SiC-gas interface
-
R
gas constant
-
t
time
-
T
absolute temperature
-
v
linear gas velocity
-
x
oxide thickness
-
x
L
limiting oxide thickness achieved in paralinear oxidation
-
x
t
oxide thickness at which transition from linear to parabolic growth occurs 相似文献
26.
The effects of the selective adenosine (ADO) A3 receptor agonist IB-MECA (N6-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide) on cultured newborn rat cardiomyocytes were examined in comparison with ADO, the ADO A1 receptor-selective agonist R-PIA (N6-R-phenylisopropyladenosine), or the ADO A3 selective antagonist MRS 1191 (3-ethyl-5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1, 4-(+/-)-dihydropyridine-3,5 dicarboxylate), using digital image analysis of Feulgen-stained nuclei. At high concentration, IB-MECA (>/=10 microM ) and ADO (200 microM) induced apoptosis; however, R-PIA or MRS 1191 did not have any detectable effects on cardiac cells. In addition, DNA breaks in cardiomyocytes undergoing apoptosis following treatment by IB-MECA were identified in situ using the nick end labeling of DNA ("TUNEL"-like) assay. In the presence of >/=10 microM IB-MECA, disorder in the contraction waves appeared, and a decrease in the frequency of beats was observed. Analysis with light microscopy revealed that the number of contracting cells decreased in a concentration-dependent manner. The A3 receptor agonist IB-MECA caused an increase in intracellular free calcium concentration ([Ca2+]i). The drug produced a rapid rise followed by a sustained increase in [Ca2+]i, which lasted for 40-60 s. Finally, cessation of beating and Ca2+ transients were observed. Full recovery of contractile activity and rhythmical Ca2+ transients were observed 15-20 min after IB-MECA treatment. The induction of apoptosis in the cardiocytes by IB-MECA led to the appearance of features of apoptotic nuclei: the onset of condensation, compacting, and margination of nuclear chromatin. These effects were accompanied by the disintegration of the structural framework of the nucleus and nuclear breakdown. The results suggest that activation of the A3 adenosine receptor may participate in the process of apoptosis in cardiomyocytes. 相似文献
27.
The aim of the study was TPS diagnostic value determination in the serum of women with breast cancer as compared with MCA and CA 15-3. The relationship between the serum concentration of these antigens and patient age, clinical stage, histological grade, presence of metastases to lymph nodes and histological type of neoplasm was evaluated. Studies were conducted on the sera of 139 women before surgical procedure aged 28-81, treated in the Clinic of Oncology, at Karol Marcinkowski University of Medical Sciences in Poznań. The TPS concentration was determined using the "BEKI Diagnostics" immunoenzymatic method, MCA - by the "Roche" test and CA 15-3 concentration was determined by the "Abbott" immunofluorescent test. The study showed significantly higher levels of TPS, CA 15-3 and MCA in women with cancer, compared with values in healthy women and women with mastopathy. The highest median of concentration and frequency of occurrence was obtained for TPS. A correlation between enhancement of TPS and CA 15-3 concentration with clinical stage was observed. A similar connection was noted in women with metastases to the lymph nodes. Serum MCA concentration results did not demonstrate the above effects. The study suggests, that in estimating the clinical condition of women with breast cancer, the simultaneous determination of TPS with CA 15-3 seems to be a more useful prognostic factor than TPS or CA 15-3 with MCA. 相似文献
28.
Secure routing protocols for mobile ad hoc networks provide the required functionality for proper network operation. If the underlying routing protocol cannot be trusted to follow the protocol operations, additional trust layers, such as authentication, cannot be obtained. Threat models drive analysis capabilities, affecting how we evaluate trust. Current attacker threat models limit the results obtained during protocol security analysis over ad hoc routing protocols. Developing a proper threat model to evaluate security properties in mobile ad hoc routing protocols presents a significant challenge. If the attacker strength is too weak, we miss vital security flaws. If the attacker strength is too strong, we cannot identify the minimum required attacker capabilities needed to break the routing protocol. In this paper we present an adaptive threat model to evaluate route discovery attacks against ad hoc routing protocols. Our approach enables us to evaluate trust in the ad hoc routing process and allows us to identify minimum requirements an attacker needs to break a given routing protocol. 相似文献
29.
Ivar Jacobson 《程序员》2008,(10):14-14
几周前,我在美国访问了一家州政府。他们将自己全新的企业软件外包给了一家基于美国的国际软件公司,我们姑且称这家公司为Smarty,合同总价达到数百万美金。合同中包括下面这些条款: 相似文献
30.
The activities of iron (Fe) and aluminum (Al) were measured in Fe-Al alloys at 1573 K using the ion-current-ratio technique in a high-temperature Knudsen cell mass spectrometer. The Fe-Al solutions exhibited negative deviations from ideality over the entire composition range. The activity coefficientsγ Fe, andγ A1 are given by the following equations as a function of mole fraction (x Fe,x Al): 1 $$\begin{gathered} 0< \chi _{A1}< 0.4 \hfill \\ ln \gamma _{Fe} = - 4.511 ( \pm 0.008)\chi _{A1}^2 \hfill \\ ln \gamma _{A1} = - 4.462 ( \pm 0.029)\chi _{Fe}^2 + 0.325( \pm 0.013) \hfill \\ 0.6< \chi _{A1}< 1.0 \hfill \\ ln \gamma _{Fe} = - 4.065 ( \pm 0.006)\chi _{A1}^2 + 0.099( \pm 0.003) \hfill \\ ln \gamma _{A1} = - 4.092 ( \pm 0.026)\chi _{Fe}^2 + 0.002( \pm 0.001) \hfill \\ \end{gathered} $$ The results showed good agreement with those obtained from previous investigations at other temperatures by extrapolation of the activity data to 1573 K. 相似文献