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排序方式: 共有838条查询结果,搜索用时 187 毫秒
81.
基于破片存速对某高空高速飞行器热防护结构的影响,提出一种用单一材料结构替代热防护系统(thermal protection system,TPS)复合结构毁伤的等效仿真方法.15 mmTPS热防护复合结构板经计算可等效为4.3 mm铝合金板,经试验验证误差仅为5.6%,吻合度较高,破片穿透板后,TPS复合材料层形成的破孔周围有明显扩孔现象.将试验与仿真结果对比发现:靶板正面与背面破孔直径误差分别为2.9%和2%,铝合金和TPS复合结构极限速度误差分别为2.3%和1.4%.结果表明,该方法对热防护复合结构的设计及优化具有一定参考价值. 相似文献
82.
Ha Tran Nguyen Le-Thu T. Nguyen Trung Thanh Nguyen Anh Tuan Luu Thang Van Le 《Journal of Polymer Research》2014,21(9):1-11
Novel 3-hexylthiophene-based hyperbranched conjugated polymers containing triphenylamine and benzo [c] [1, 2, 5] thiadiazole moieties were synthesized by Suzuki coupling polymerization of tris (4-bromophenyl) amine, 2,2′-(3-hexylthiophene-2,5-diyl) bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 4,7-dibromobenzo [c] [1, 2, 5] thiadiazole. Organic solvent-soluble polymers with number-average molecular weights of 24,000 and 42,000 g/mol were obtained in 54–57 % yields. Their structures, molecular weights and thermal properties were characterized via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopies, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide-angle powder X-ray diffraction (XRD) measurements. Optical investigation by UV–vis and fluorescence spectroscopies revealed that the incorporation of the benzo [c] [1, 2, 5] thiadiazole moiety in the hyperbranched polymer structure resulted in a red-shift of the maximum absorption wavelength and an increase in the solution-photoluminescence quantum yield, indicating an extension of the conjugation length. The UV–vis, DSC and XRD results demonstrated that the aggregation of conjugated polymer chains could effectively be reduced by the hyperbranched structures and that conjugation length extension via the introduction of benzo [c] [1, 2, 5] thiadiazole units led to the coexistence of both crystalline and amorphous phases in the solid state and in solution upon addition of a non-solvent. 相似文献
83.
Sheng-Wen Yu Shu-Ting Kuo Wei-Hsing Tuan Yu-Yu Tsai Ching-Hua Su 《Materials Letters》2011,65(23-24):3522-3524
The ions released from the polarized potassium sodium niobate (KNN), lithium-doped potassium sodium niobate (LKNN) and barium titanate (BT) specimens after soaking in a normal saline up to 28 days were monitored. The cytotoxicity of ion released products was evaluated. The cytotoxicity testing on these three lead-free piezoelectric ceramics exhibited low toxicity. However, the decrease of biaxial strength for KNN and the decrease of piezoelectric charge coefficient d33 for LKNN were noted after soaking in saline solution. Such decreases can be related to the release of ions from the surface of the KNN and LKNN specimens during soaking in saline solution. 相似文献
84.
Khac An Dao Anh Tuan Phan Hung Manh Do Tien Hung Luu Meiken Falke M. MacKenzie 《Journal of Materials Science: Materials in Electronics》2011,22(2):204-216
The synthesis of semiconductor nanowires is more and more interested to the applications for building blocks of the innovative
nano-sized devices and circuits, but the research and fabrication of these nanowires are also holding a number of difficulties
and challenges. Among many different kinds of semiconductor nanowires, Ga2O3 is increasingly grown for many promising applications in nano-device production, namely nanowire LED and Laser. So far there
are many synthesizing methods of semiconductor nanowires, among them the vapor–liquid–solid (VLS) method is simple, cheap
and popular. However, when we use the VLS method for nanowire growth, various technological problems exist. This paper aims
at investigating some influences of the growth technological conditions and Au metal catalyst on the morphology of Ga2O3 nanowire grown by VLS on GaAs substrate. The main considering factors include the different growing temperatures and times,
the effects of Au diffusion, Au droplets formation, Au cluster islands formation, and gas volume of the growing tube/ampoule
at the 10−1 torr low air pressure. The obtained experimental results regarding the structural properties of nanowires under these effects
investigated by scanning electron microscopy, field emission scanning electron microscopy, high angle annular dark field and
bright field, scanning transmission electron microscopy, energy-dispersive X-ray techniques, and focus ion beam are presented
and discussed. 相似文献
85.
发射装置电路盒在工作过程中产生的热量,会对电路盒以及发射装置的可靠性产生影响。如何在电路盒的设计制造过程中尽量减少热量的产生,同时又能将工作中所产生的热量尽快散发出去,将热量产生的影响控制在电路盒正常工作范围内,是一个重要的问题。文章针对上述问题展开论述,阐述了散热性对发射装置电路盒工作性能的影响,分析了电路盒中热量的... 相似文献
86.
In this paper we derive an explicit expression for the log likelihood function of a continuous-time autoregressive model. Then, using earlier results relating the autoregressive coefficients to the set of positive parameters called residual variances ratios, we develop an iterative algorithm for computing the maximum likelihood estimator of the model, similar to one in the discrete-time case. A simple noniterative estimation method, which can be used to produce an initial estimate for the algorithm, is also proposed. 相似文献
87.
Thiocyanate ion and weak ammonia liquor from a coking operation were ozonated in a semi-batch reactor. In a typical case, 500 mg/L thiocyanate ion disappeared in 8 minutes using an ozone dose of 82 mg/min at pH 7. The cyanide ion concentration was maximized immediately after the thiocyanate ion disappeared. The ozone-to-thiocyanate ion stoichiometric molar ratio was found to be 2.0 ± 0.2. The rate constants for the reaction of thiocyanate ion and cyanide ion with ozone under the typical conditions listed above were 5.4 × 104 L2/(mmole2-min) and 1.5 L/(mmole-min), respectively. 相似文献
88.
Wideband direction-of-arrival estimation using frequency-domain frequency-invariant beamformers: an analysis of performance 总被引:1,自引:0,他引:1
Tuan Do-Hong Demmel F. Russer P. 《Microwave and Wireless Components Letters, IEEE》2004,14(8):383-385
This paper presents an extension of the wideband direction-of-arrival estimation method using frequency-domain frequency-invariant beamformers (Do-Hong et al., 2003) with an analysis of performance. An asymptotic expression for the root-mean-square error and a resolution threshold of signal-to-noise-ratio for resolving directions of sources are shown. A comparison of analysis and simulation as well as numerical results are also presented. 相似文献
89.
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川东北部宣汉—开江地区目前为川东地区天然气勘探的主要区块,钻井中井漏普遍,给钻井生产带来重大损失,严重影响井下施工安全。因此,正确认识漏失的性质、原因以预防和采取有效措施治理井漏是宣汉—开江地区钻井中迫切需要解决的问题。文章对宣汉—开江地区恶性井漏的特点及地质因素进行了分析,该区恶性井漏的特点是漏失井段长,漏失层段多,漏速大,漏失量大;沙溪庙组—自流井组、嘉五1亚段及飞仙关组地层恶性井漏特征明显,发生的频率高。资料表明,发生恶性井漏的漏层的漏失通道及储液空间主要为大型溶洞或大型裂缝系统;纵向压力剖面上,近地表正常静水柱压力带常发生恶性井漏,压力过渡带恶性井漏发生的频率相对较高,异常高压带较少发生恶性井漏;不同的压力带及复杂压力系统共存条件下,容易产生新的漏失通道或储液空间,诱发恶性漏失。 相似文献
90.
The number of channels of a multichannel rejection filter (MRF) has been optimized by the energy and probabilistic criteria. The matrix of MRF coefficients is defined. The paper includes analysis of the gain in signal detection effectiveness, in the presence of interference, as compared to the single-channel rejection filter. 相似文献