Using Si and Ge nanostructures as substrates for surface-enhanced Raman scattering based on photoinduced charge transfer mechanism

The possibility of utilizing the Si and Ge nanostructures to promote surface-enhanced Raman scattering (SERS) is discussed. The vibronic coupling of the conduction band and valence band states of Si or Ge with the excited and ground states of the target molecule during the charge transfer (CT) process could enhance the molecular polarizability tensor. Using H-terminated silicon nanowire (H-SiNW) and germanium nanotube (H-GeNT) arrays as substrates, significant Raman enhancement of the standard probes, Rodamine 6G (R6G), dye (Bu(4)N)(2)[Ru(dcbpyH)(2)-(NCS)(2)] (N719), and 4-aminothiophenol (PATP), are demonstrated. The abundant hydrogen atoms terminated on the surface of SiNW and GeNT arrays play a critical role in promoting efficient CT and enable the SERS effect.     

Suitability of Different 13C Solid-state NMR Techniques in the Characterization of Humic Acids

Qualitative and quantitative analyses of humic acids (HAs) with five different ¹³C solid-state NMR techniques were assessed using HAs of various origins and locations. The NMR techniques compared are: (1) direct polarization/magic angle spinning (DP/MAS) at 13 kHz, (2) conventional cross polarization (CP)/MAS at 5 kHz, (3) ramp-CP/MAS at 8 kHz, (4) CP/total sideband suppression (TOSS) at 4.5 kHz, and (5) DP/MAS corrected by CP/spin-lattice relaxation with TOSS. The spectra from the five techniques were first compared qualitatively. Then, each spectrum was divided into eight regions for quantitative evaluation. DP/MAS spectra were used as quantitative references. Ramp-CP/MAS and CP/TOSS spectra gave consistently better results than those of the conventional CP/MAS spectra at a ¹³C frequency of 75 MHz, which were incorrect due to spinning sidebands. CP/MAS at low magnetic fields (22.6 and 50.6 MHz ¹³C frequency) indicated improved integration results but lower resolution. Correction factors calculated by comparison with DP/MAS will be useful to convert the non-quantitative peak areas in the CP/TOSS and ramp-CP/MAS spectra into more quantitative results.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

Simulation of particle flow in a bell-less type charging system of a blast furnace using the discrete element method

A three-dimensional model was established by the discrete element method （DEM） to analyze the flow and segregation of particles in a charging process in detail. The simulation results of the burden falling trajectory obtained by the model were compared with the industrial charging measurements to validate the applicability of the model. The flow behavior of particles from the weighing hopper to the top layer of a blast furnace and the heaping behavior were analyzed using this model. A radial segregation index （RSI） was used to evaluate the extent of the size segregation in the charging process. In addition, the influence of the chute inclination angle on the size segregation and burden profile during the charging process was investigated.     

Discrete Maximum Principle Based on Repair Technique for Finite Element Scheme of Anisotropic Diffusion Problems

In this paper, we construct a global repair technique for the finite element scheme of anisotropic diffusion equations to enforce the repaired solutions satisfying the discrete maximum principle. It is an extension of the existing local repair technique. Both of the repair techniques preserve the total energy and are easy to be implemented. The numerical experiments show that these repair techniques do not destroy the accuracy of the finite element scheme, and the computational cost of the global repair technique is lower than the local repair technique when the diffusion tensors are highly anisotropic.     

基于节点重构的扩散方程有限体积格式

研究扭曲网格上扩散方程的九点格式.以经典的九点格式为基础,在通量连续条件下,构造出节点未知量一种新的计算方法,进而得到所希望的格式.分析及数值实验表明,在扭曲网格上,该格式对具有连续或间断扩散系数的问题能够保持较高的精度.     

Thermal and kinetic behaviors of pyrolytic carbon black and gas coal in co-combustion

Journal of Thermal Analysis and Calorimetry - In this study, a combustion study of tire pyrolytic carbon black (CBp), gas coal (GC), and their blends was carried out by thermogravimetric analysis...     

稀土掺杂固态量子存储研究进展

量子存储对量子信息网络的实现至关重要,是当前量子信息领域的研究前沿和热点.在实现量子存储的多种媒质中,稀土掺杂固体材料由于具有较长的光学相干时间和较宽的光学吸收带宽而备受研究人员的关注.本文将系统地介绍稀土掺杂固态量子存储在材料体系、存储协议、应用范围等方面的重要进展,着重从物理机理、实验方法和新近成果等方面,阐述基于原子频梳协议的稀土掺杂固态量子存储方案,并对该方案的未来发展做简要展望.     

基于Kerckhoffs原则的图像隐密算法

针对图像隐密算法中加密秘密信息的问题,将Kerckhoffs原则应用到图像隐密算法中.在对比密码技术和隐密技术的异同点的基础上,分析了在图像隐密算法中使用Kerckhoffs原则的重要性,通过使用掩护图像集,将秘密信息分散隐藏在掩护图像集合的某个子集中,从而减少含密图像被攻击者发现的几率,并且在算法中使用加密手段抵抗密码分析者的攻击.分析表明,本文提出的基于Kerckhoffs原则的图像隐密算法可以提高隐密的安全性,保证秘密信息不被攻击者获得.     

一种改进的动态载荷时域识别方法

根据在离散时间间隔内未知外载荷按线性交化的这一更为合理的假定，给出了比例阻尼系统的一种改进的载荷时域识别方法。即若已知结构的任一种响应：位移、速度或加速度，根据本文推导出的递推连锁计算公武便可确定未知作用力的时程。算例表明，本方法简便、有效，且具有较强的抗噪能力。