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排序方式: 共有7192条查询结果,搜索用时 62 毫秒
91.
在功率受限的机会频谱接入(OSA)研究中,大多使用完全可观测马尔可夫决策过程(MDP)对环境建模,以提高物理层或介质访问控制(MAC)层指标,但由于感知设备的限制,无法保证用户对环境完全感知。为解决该问题,提出一种基于部分可观测马尔可夫决策过程(POMDP)与Sarsa(λ)的跨层OSA优化设计方案。结合MAC层和物理层,采用POMDP对功率受限且有感知误差的次用户频谱感知和接入过程进行建模,并将其转换为信念状态MDP(BMDP),使用Sarsa(λ)算法对其进行求解。仿真结果表明,在功率受限条件下,该Sarsa(λ)-BMDP方案的有效传输容量、吞吐量和频谱利用率分别比完全可观测Q-MDP方案低9%、7%和3%左右,其误比特率比基于点的值迭代PBVI-POMDP方案低20%左右,比Q-MDP方案高16%左右。 相似文献
92.
High purity multi-walled carbon nanotubes were synthesized from aromatic hydrocarbons (benzene, toluene, xylene and trimethyl benzene) using ferrocene as the source of Fe catalyst. Screening studies of aromatic feeds at 675 °C, residence time of 14 s and Fe/C atom ratio of 1.07%, resulted in feedstock carbon conversion of 20-31%, CNT yield of 19.8-30.5%, and catalyst yield of 5.3-8.3 (g CNT/g catalyst). While the quality of the CNTs as determined by TGA, SEM, TEM and Raman spectroscopy, were high and comparable for different feedstocks; their carbon conversion, CNT yield and catalyst yield differed noticeably. A process optimization study for toluene feed showed that carbon conversion of more than 39%, CNT yield of 38.7% and catalyst yield of 18.3 can be achieved at temperature of 800 °C, Fe/C atom ratio of 0.47%, and residence time of 10-20 s. 相似文献
93.
Raman spectra of virgin and damaged graphite edge planes 总被引:1,自引:0,他引:1
First-order Raman spectra of virgin and ion irradiated highly oriented pyrolytic graphite were performed along the basal and edge planes. Ion irradiation was performed in the low fluence regime (≈ 1012–1013 ions cm−2) using a 400 keV Ar+ beam in order to a introduce controlled amount of defects in the structure. Virgin edge Raman spectra reveal the presence of a 1351 cm−1 structure (D*) shifted 10 cm−1 away from the disorder induced D-line found upon irradiating or grinding the graphite surface.The 1351 cm−1 D* structure is then considered as the feature coming from the rupture of the D6h4 space group symmetry. A comparison between D* and the classical 1360 cm−1 D-line is discussed in terms of induced disorder. 相似文献
94.
Hiroya Nakata Takayoshi Kiguchi Osamu Hino 《Journal of the American Ceramic Society》2022,105(4):2791-2803
To understand the role of phosphate ester dispersant, we investigated the rheology of a BaTiO slurry. For the model case, a coarse-grain molecular dynamics (CGMD) simulation was performed with the butyral polymer didodecyl hydrogen phosphate (DHP) in the toluene/ethanol solvent. By systematically analyzing the effect of DHP from an atomic-scale first principle and from all-atom MD to microscale CGMD simulation, we investigated how the adsorption of a DHP dispersant on a BaTiO surface affects the microstructure rheology of a BaTiO slurry. The first-principle and all-atom MD simulation suggests that DHP molecules prefer to locate near the BaTiO surface. CGMD simulation shows a reduction in viscosity with an increase in dispersants, suggesting that the dispersant population near the BaTiO surface plays a key role in controlling the rheology of the BaTiO slurry. In this study, we propose an approach for understanding the BaTiO slurry with molecular-level simulations, which would be a useful tool for efficient optimization of slurry preparation. 相似文献
95.
Both confocal Raman microspectroscopy and atomic force microscopy (AFM) have been undertaken to study the crystalline and the morphological aspects of cast PA 6 films at a sub-microscopic scale. The percentages of the different crystalline structures present within PA 6 cast films, i.e. the monoclinic α, the pseudo-hexagonal β, and the monoclinic γ, have been measured by confocal Raman microspectroscopy. In cast films, the prevailing structure is the β one. AFM has been used to characterize the morphology of the PA 6 films. Simultaneously, the deformed state has been considered as well. Our main interest has been to follow the evolution of the percentage of each crystalline structure as a function of the plastic deformation mechanisms which are responsible of the yielding of PA 6 films: shear banding for temperatures T lower than 160 °C and formation of fibrils for 相似文献
96.
Xiaozhen Yang 《Polymer》2004,45(12):4241-4248
The conformational distribution change of amorphous poly(lactic acid) (PLA) induced by deformation has been studied using Raman spectroscopy. Spectroscopic features associated with the rotational isomeric states (ttt, ttg′, tg′t, tg′g′) have been established experimentally and supported by normal coordinate analysis. Deformation induced a significant increase in the most favorable tg′t conformation. Based on the relative intensities of Raman-active skeletal modes, a quantitative method has been developed that can be used to elucidate structural changes in a variety of deformed polymer samples. For biaxially oriented PLA films, the overall tg′t conformation increased from the 76% in undeformed sample to a value as high as 92%. The change in conformational distribution in the amorphous phase follows a different trend (76-88%) as compared to the increase in sample crystallinity (0-43%). A large change in amorphous chain conformation occurred at relatively low draw ratios. In contrast, the large change in the degree of crystallinity occurred at higher draw ratios. 相似文献
97.
本文通过多种分析测试手段,详细研究了环型聚苯乙烯(RPS)分子链结构、聚集态结构、热性能及稀溶液性质,并与线型聚苯乙烯(LPS)作了对照。结果表明:RPS链结构确为环状结构,由于链结构不同于LPS,因此链刚性及其随分子量的变化关系也不同于LPS,这是导致其性质与LPS存在很大差异的根本原因。RPS链堆积较LPS松散,由于线团密度RPS大于LPS,所以宏观上二者比容并无多大差异,但RPS比容受分子量影响较LPS大。RPS的Tg随分子量变化关系受自由体积和构象熵即链刚性两种因素的影响。动态光散射及小角X光散射实验结果说明,RPS的扩散行为、流体力学半径和无扰分子尺寸与LPS相比有很大不同。 相似文献
98.
High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed. 相似文献
99.
A. Barrera J.A. Montoya M. Viniegra J. Navarrete G. Espinosa A. Vargas P. del Angel G. Prez 《Applied Catalysis A: General》2005,290(1-2):97-109
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO2 (70, 85 wt.%)–Al2O3 (15, 0 wt.%)–WOx (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WOx and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al2O3 addition. Various oxidation states of WOx species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WOx species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W6+ and reduced-state WOx species (either W4+ or W0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers. 相似文献
100.
Carbon-encapsulated Fe nanoparticles with size between 5 and 20 nm were synthesized via a picric acid-detonation-induced pyrolysis of ferrocene, which is characterized by a self-heating and extremely fast process. The nanoparticles exhibit well-constructed core-shell structures, with bcc-Fe cores and graphitic shells. The graphitic shells can protect effectively the cores against the attack of HNO3 solution. The formation of the core-shell nanoparticles can be selectively controlled by adjusting the composition of the picric acid-ferrocene mixture, which determines C/Fe atomic ratio of the reaction system. The core-shell nanoparticles are preferably formed at low C/Fe atomic ratios, while tubular structures are formed at high C/Fe ratio. The possible pathway for the carbon-encapsulated Fe nanoparticles formation is discussed briefly. 相似文献