Re effects in model Ni-based superalloys investigated with first-principles calculations and atom probe tomography

The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.     

915 nm单频Nd∶YAG晶体衍生光纤激光器

报道了一种基于Nd∶YAG晶体衍生光纤(NYDF)的915 nm单频光纤激光器.使用掺杂原子数分数为2.5％的Nd∶ YAG晶体作为纤芯材料,高纯度石英管作为包层材料,利用熔芯法制备Nd∶ YAG晶体衍生光纤,其传输损耗为8 dB/m,在915 nm处其增益系数为1.16 dB/cm.基于Nd∶YAG晶体衍生光纤,实现了一个稳定的915 nm单频光纤激光器,信噪比大于50 dB.实验结果表明Nd∶ YAG晶体衍生光纤有潜力应用于890～920 nm单频激光器.     

Tl系1223相超导体的不可逆线

研究了(Tl_(0.5)Pb_(0.5))(Sr_(0.8)Ba_(0.2))_2Ca_2Cu_3O_y超导体的不可逆场H~*(T),并与Y系、Bi系和Tl1212相超导体作了比较。实验表明,在77K下Tl 1223相的不可逆场高达5T。证明了该材料在高温下的磁通钉扎比Bi系超导体和Tl 1212相超导体强得多,并对此作了讨论,由磁滞回线估计的磁化电流密度J_c在77K和2T磁场下大于10~4A/cm~2。     

S+C band optical amplification in Er~(3+)-Tm~(3+) co-doped fiber

A new type of optical amplifier based on co-doping erbium in thulium doped fiber is proposed to realize S C band gain by dual-wavelength (800 1410 nm) pumping scheme which is obtainable from laser diode. A novel model is established for the co-doped fiber considering the Er3 to Tm3 energy transfer process. Using appropriate fiber parameters and energy transfer parameters, the coupled rate equations are analyzed and solved; the concentrations of Er3 and Tm3 and fiber length were optimized to get more uniform gain. The results predicted that the S C band gain can be achieved at the same time by co-doping erbium in thulium doped fluoride fiber.     

Ultrafast Photoelectric Effects in Heterojunctions of La0.7Sr0.3MnO3 and Si

Ultrafast photoelectric effects have been observed in p-n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3_/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of -25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV//mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser.     

对于2002年高考数学第21题的一点思考

原题　 ( )给出两块面积相同的正三角形纸片 ,要求用其中一块剪拼成一个正三棱锥模型 ,另一块拼成一个正三棱柱模型 ,使它们的全面积都与原三角形的面积相等 ,请设计一种剪拼方法 ,分别用虚线标示在图中并作简要说明 .( )试比较你剪拼的正三棱锥与正三棱柱的体积的大小 .( ) (略 )标准答案是一种解法 ,摘要如下 :解　 ( )剪法如图 1、图 2所示图 1　　　　　　图 2( )设给出正三角形的边长为 2 ,则V锥 - V柱 =( 13h锥 - h柱 ) . 34=( 69- 36 ) . 34<0 .所以 V柱 >V锥 .这道题另一种迥然不同的剪法 (如图 3) ,先把正三角形拼成一个长…     

基于最大熵模型的微博传播网络中的链路预测

微博是基于用户关注关系建立的具有媒体特性的实时信息分享社交平台.微博上的信息扩散具有快速性、爆发性和时效性.理解信息的传播机理,预测信息转发行为,对研究微博上舆论的形成、产品的推广等具有重要意义.本文通过解析微博转发记录来研究影响信息转发的因素或特征,把微博信息转发预测问题抽象为链路预测问题,并提出基于最大熵模型的链路预测算法.实例验证的结果表明:1)基于最大熵模型的算法在运行时间上具有明显的优势;2)在预测结果方面,最大熵模型比同类其他算法表现优异;3)当训练集大小和特征数量变化时,基于最大熵模型的预测结果表现稳定.该方法在预测链路时避免了特征之间相互独立的约束,准确率优于其他同类方法,对解决复杂网络中其他类型的预测问题具有借鉴意义.     

A compact electro-absorption modulator based on graphene photonic crystal fiber

A compact electro-absorption modulator based on graphene photonic crystal fiber is proposed. To enhance the graphene–light interaction efficiency, the innermost six air-holes of photonic crystal fiber are replaced by two large semicircular holes, and monolayer graphene is deposited on the two large semicircular holes. By optimizing the structure parameters, a strong graphene–light interaction is obtained. Moreover, the switch on–off point of the modulator is unchangeable,which is only related to the frequency of the incident light. The influence factors of this composite structure have been analyzed. The proposed modulator is compared with other graphene-based modulators, and the results show that it is filled without dielectric spacer. There are some excellent performances, such as an extinction ratio 7 dB of y-polarization mode,3-dB modulation bandwidth of 70 GHz with small footprint of 205 μm, and a consumption of energy per bit 59 pJ/bit.