Ni_2P/TiO_2-Al_2O_3催化剂的制备及其加氢脱硫、脱氮性能

采用溶胶-凝胶法制备了TiO2-Al2O3复合载体,采用浸渍法制备了Ni2P/TiO2-Al2O3催化剂,并用X射线衍射(XRD)、N2吸附比表面积(BET)测定、热重-差热分析(TG-DTA)、X射线光电子能谱(XPS)等技术对催化剂的结构和性质进行了表征.催化剂加氢脱硫(HDS)和脱氮(HDN)活性评价在实验室固定床连续反应装置上,以噻吩和吡啶为模型反应物进行.考察了不同载体、Ni2P负载量、标称Ni/P摩尔比、催化剂焙烧温度对Ni2P/TiO2-Al2O3催化剂上同时进行的噻吩加氢脱硫和吡啶加氢脱氮性能的影响.结果表明,TiO2含量为80%(w)的TiO2-Al2O3复合氧化物为载体,Ni2P负载量为30.0%(w),标称Ni/P摩尔比为1/2,催化剂焙烧温度为500℃时,Ni2P/TiO2-Al2O3催化剂加氢脱硫脱氮活性最高.在360℃,3.0MPa,氢油比800(V/V),液时体积空速1.5h-1的条件下,噻吩HDS和吡啶HDN转化率分别为61.32%和64.43%.     

Current in Periodic Lorentz Gases with Twists

We study electrical current in two-dimensional periodic Lorentz gas in the presence of a twist force on the scatterers. In this deterministic system, billiard orbits are still geodesics between collisions, but do not reflect elastically when reaching the boundary. When the horizon is finite, i.e. the free flights between collisions are bounded, the resulting current J is proportional to the strength of the twist force measured by ε. We also prove the existence of a unique SRB measure, for which the Pesin entropy formula and Young’s expression for the fractal dimension are valid.     

The Spectrum of the Billiard Laplacian of a Family of Random Billiards

Random billiards are billiard dynamical systems for which the reflection law giving the post-collision direction of a billiard particle as a function of the pre-collision direction is specified by a Markov (scattering) operator P. Billiards with microstructure are random billiards whose Markov operator is derived from a “microscopic surface structure” on the boundary of the billiard table. The microstructure in turn is defined in terms of what we call a billiard cellQ, the shape of which completely determines the operator P. This operator, defined on an appropriate Hilbert space, is bounded self-adjoint and, for the examples considered here, a Hilbert-Schmidt operator. A central problem in the statistical theory of such random billiards is to relate the geometric characteristics of Q and the spectrum of P. We show, for a particular family of billiard cell shapes parametrized by a scale invariant curvature K (Fig. 2), that the billiard Laplacian P−I is closely related to the ordinary spherical Laplacian, and indicate, by partly analytical and partly numerical means, how this provides asymptotic information about the spectrum of P for small values of K. It is shown, in particular, that the second moment of scattering about the incidence angle closely approximates the spectral gap of P.     

中国城市航空网络的实证研究与分析

以城市为节点，城市间直航线路为边，实证地研究了中国城市航空网络的拓扑性质.研究表明，中国城市航空网络是一个小世界网络，具有短的平均路径长度和大的簇系数，且其度分布服从双段幂律分布.它的度度相关性质与世界航空网络和北美航空网络都不相同.当度较小时，世界航空网络和北美航空网络都是正相关的，但中国城市航空网络未表现出度度相关性；而对于度较大的节点，世界航空网络中其邻点平均度几乎是一个常值，但中国城市航空网络却呈现出负相关性.以往的实证研究暗示，节点具有明确几何位置的网络，如计算机互联网、电力网络等，不表现层次性.但是中国城市航空网络展现出明显的层次性，表明地理因素对其结构演化的影响并不强烈.进一步地，以城市间直航计划每周提供的座位数为边权，研究了网络的含权性质，发现该网络节点度权之间是幂律相关的，相关指数为1.37.     

Resistive switching behavior and mechanism of room-temperature-fabricated flexible Al/TiS2-PVP/ITO/PET memory devices

The mixture of two-dimensional (2D) TiS₂ nanoflakes and polyvinylpyrrolidone (PVP) exhibits a nonvolatile, bipolar resistive switching behavior with a low resistance state (LRS)/high resistance state (HRS) current ratio of ～10² in the devices with a flexible Al/TiS₂-PVP/indium tin oxide (ITO)/polyethylene terephthalate (PET) structure. The polymer-assistant liquid-phase exfoliation of 2D nanoflakes from TiS₂ bulk material is processed in low-boiling solvent. And the fabrication process of these devices is performed entirely at room temperature. Such an energy-saving and scalable production process indicates a huge potential of large-scale industrial application. The AFM and TEM characterizations showed that the exfoliated 2D TiS₂ are flakes at micrometer scale with a layer-number of mostly 7 or 8. Both the HRS and the LRS can be kept for more than 10⁴ s. The endurance of devices was obtained over 100 direct current (DC) sweeping cycles with remarkable separations between different resistive states. The distributions of writing (set) and erasing (reset) voltages show that set and reset voltages are small (<2 V). Also, the resistive switching characteristics of the devices are stable during 1000 bending cycles. The switching behavior is explained by the thinning and recovery of Schottky barriers within devices.     

Periodically poled lithium niobate whispering gallery mode microcavities on a chip

In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques.The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×10~5. Second harmonic generation(SHG) with an efficiency of 2.2×10~(-6) mW(-1) is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.     

石墨烯射频器件研究进展

石墨烯因具有优良的电学特性,在半导体行业中受到广泛关注,特别因其具有超薄的结构和极高的载流子迁移率,为解决短沟道效应提供了可能,并且在高速电子领域具有应用前景.近年来,使用石墨烯作为沟道材料制备射频晶体管及射频电路是发挥石墨烯材料优势的一个重要研究方向.制造高性能的射频器件,首先要制备出高性能的石墨烯材料.在金属衬底上沉积均匀的单层石墨烯材料或者在绝缘衬底上外延生长单层、双层石墨烯材料都是获得高质量石墨烯材料的常用方法.器件结构及工艺流程的设计也是提升晶体管射频性能的重要因素,多指栅结构、T型栅结构、埋栅结构以及自对准工艺的发展能够有效改善石墨烯射频晶体管的截止频率及最大振荡频率.石墨烯晶体管独特的电学特性使得其除了可以构造与其他半导体材料电路相似的射频电路结构,还可以构造出功能完整并且结构更加简单的新型射频电路结构.     

A Novel Quantum Group Proxy Blind Signature Scheme Based on Five-Qubit Entangled State

A novel quantum group proxy blind signature scheme based on five-qubit entangled state is proposed. The quantum key distribution, quantum encryption algorithm and some laws of quantum mechanics (such as quantum no-cloning theorem and Heisenberg uncertainty principle) are used to guarantee the unconditional security of this scheme. Analysis result shows that the signature can neither be forged nor disavowed by any malicious attackers and our scheme satisfies all the characteristics of group signature and proxy signature. This protocol can be applied in real life such as E-commerce transaction.

     

Prediction improvements of ignition characteristics of isolated coal particles with a one-dimensional transient model

A modified 1-D transient model considering intra-particle thermal conduction is adopted to improve the predictions of the ignition characteristics of isolated coal particles. The study aims at resolving the incorrect prediction on the variation trend of ignition temperature T_i with the change of oxygen concentration X_O2, interpreting the contradictory dependencies on coal particle size and furnace temperature and clarifying the conditions when the intra-particle thermal conduction should be considered. The predictions are compared with microgravity data in which the buoyancy effect is minimized. The results reveal that the previous ignition model with transient adiabatic criterion fails to predict the T_i variation with X_O2, since it cannot accurately predict T_i and delay time in the low X_O2 region. Instead, the ignition model with flammability limit ignition criterion can well predict T_i in a wide range of X_O2. Intra-particle thermal conduction causes remarkable temperature differences for large coal particles, and moreover, the variation trends of surface and center temperatures with particle size are very different. The center temperature at ignition drops remarkably with increasing particle size, while the surface temperature barely changes or slightly increases with particle size. At the same particle size, the variation trends of surface and center temperatures with furnace temperature are also opposite. The ignition mode and variation trend of ignition surface temperature with particle size depends on the heating rate and particle size itself. The contradictory experimental results reported by different researchers are attributed to the particle size and temperature measurement location. The conditions necessary to consider the intra-particle thermal conduction are discussed. Lastly, the effect of the intraparticle thermal conduction is shown on an ignition mode diagram.