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81.
Planning collision-free trajectories in time-varying environments: a two-level hierarchy 总被引:1,自引:0,他引:1
We propose a two-level hierarchy for planning collision-free trajectories in time varying environments. Global geometric algorithms for trajectory planning are used in conjunction with a local avoidance strategy. Simulations have been developed for a mobile robot in the plane among stationary and moving obstacles. Essentially, the robot has a global geometric planner that provides a coarse global trajectory (the path and velocity along it), which may be locally modified by the low-level local avoidance module if local sensors detect any obstacles in the vicinity of the robot. This hierarchy makes effective use of the complementary aspects of the global trajectory planning approaches and the local obstacle avoidance approaches. 相似文献
82.
We report the fluorescence properties of Sm3+-doped lead telluroborate glasses of composition PbF2.TeO2.H3BO3.Sm2O3 as a function of Sm3+ concentration. A Judd-Ofelt scheme was used to determine the intensity parameters and radiative properties of Sm3+ ion. The emission and decay measurements were carried out at 402 nm excitation. Beyond 1.0 mol% Sm3+ concentration, the luminescence quenching is observed. The decay curves of 4G5/2 level are well fitted to a single exponential function. The evaluated radiative properties suggest that the 4G5/2 → 6H7/2 transition is responsible for reddish-orange luminescence which might be used in the development of visible lasers. 相似文献
83.
Mahesha B. Herath Stephen E. Creager Rama V. Rajagopal Olt E. Geiculescu Darryl D. DesMarteau 《Electrochimica acta》2009,54(24):5877-5883
We report synthesis, characterization and ion transport in polyether-based ionic melt electrolytes consisting of Li salts of low-basicity anions covalently attached to polyether oligomers. Purity of the materials was investigated by HPLC analysis and electrospray ionization mass spectrometry. The highest ionic conductivity of 7.1 × 10−6 S/cm at 30 °C was obtained for the sample consisting of a lithium salt of an arylfluorosulfonimide anion attached to a polyether oligomer with an ethyleneoxide (EO) to lithium ratio of 12. The conductivity order of various ionic melts having different polyether chain lengths suggests that at higher EO:Li ratios the conductivity of the electrolytes at room temperature is determined in part by the amount of crystallization of the polyether portion of the ionic melt. 相似文献
84.
85.
Low-stress creep behaviour of a two-phase Zr–2.5%Nb alloy, differently heat treated, has been investigated using helical test
specimens. The phase diagram of the α (hcp) + β (bcc) alloy is characterized by the monotectoid reaction at 893 ± 10 K: β
1 → (α + β
2) where β
1 (Zr–20Nb) and β
2 (Zr–80Nb) have widely differing compositions. At the creep testing temperature, 818 K, which is close to but below the monotectoid
temperature, the creep rate for samples with the equilibrium α + β
2 structure has been found to be considerably higher, over an order of magnitude, than that in samples with the metastable
α + β
1 structure. Microstructural changes accompanying the markedly enhanced creep rate for the α + β
2 structure at stresses as low as 1–4 MPa have been explained in terms of the relative stability of the β
1 and the β
2 phases during the creep process. An attempt has been made to elicit the likely mechanism underlying the observed enhancement
of creep rate and the changes in morphology, composition and volume fraction of the β phase. 相似文献
86.
The effect of alkali and alkaline earth oxides on the crystallization of lithia-alumina-silica glasses has been studied. Crystallization
behaviour of glasses has been investigated using DTA and XRD techniques. The principal crystallization phases are identified
asβ-spodumene solid solution and lithium metasilicate. The crystallization temperature of glasses decreases with increase in
the values of the ionic field strength of the alkali and alkaline earth cations. Addition of these oxides at lower concentrations
has no significant effect on the crystalline phases. 相似文献
87.
In this study, anhydrous sodium metaborate (NaBO2), an industrial and technologically important boron compound, synthesis from concentrated tincal (CT) was carried out. Experiments with different temperature and time were performed in the parametric investigation to map out the reaction mechanism. Crystalline phase characterization of metaborates products indicates that anhydrous NaBO2 synthesis from CT occurred at 400 °C with 5 h of reaction conditions. At the end of synthesis, the obtained anhydrous NaBO2 product can be used in many fields without having the calcination step due to the advantages of this method. 相似文献
88.
89.
90.
This short note reports the results concerning electron paramagnetic resonance (EPR) and optical absorption spectra of Cu2+ ions doped in sodium potassium sulphate both at 300K and 77K. 相似文献