Ge_x Si_(1-x)/Si超晶格中纵声学声子的喇曼散射强度研究

本文用光弹理论,在全面考虑了超晶格中两种材料的声速,质量密度和光弹常数存在差别的基础上,计算了Ge_xSi_(1-x)/Si超晶格中折迭纵声学声子的喇曼散射强度,在高达50cm~(-1)的频率范围内,理论值和实验符合得很好。     

Insight into the chemomechanical coupling mechanism of kinesin molecular motors

Kinesin is a two-headed biological molecular motor that can walk processively on microtubule via consumption of ATP molecules. The central issue for the molecular motor is how the chemical energy released from ATP hydrolysis is converted to the kinetic energy of the mechanical motion, namely the mechanism of chemomechanical coupling. To address the issue, diverse experimental methods have been employed and a lot of models have been proposed. This review focuses on the proposed models as well as the qualitative and quantitative comparisons between the results derived from the models and those from the structural, biochemical and single-molecule experimental studies.     

Contract Theory-Based Incentive Mechanism for Full Duplex Cooperative NOMA with SWIPT Communication Networks

Cooperative Non-Orthogonal Multiple Access (NOMA) with Simultaneous Wireless Information and Power Transfer (SWIPT) communication can not only effectively improve the spectrum efficiency and energy efficiency of wireless networks but also extend their coverage. An important design issue is to incentivize a full duplex (FD) relaying center user to participate in the cooperative process and achieve a win–win situation for both the base station (BS) and the center user. Some private information of the center users are hidden from the BS in the network. A contract theory-based incentive mechanism under this asymmetric information scenario is applied to incentivize the center user to join the cooperative communication to maximize the BS’s benefit utility and to guarantee the center user’s expected payoff. In this work, we propose a matching theory-based Gale–Shapley algorithm to obtain the optimal strategy with low computation complexity in the multi-user pairing scenario. Simulation results indicate that the network performance of the proposed FD cooperative NOMA and SWIPT communication is much better than the conventional NOMA communication, and the benefit utility of the BS with the stable match strategy is nearly close to the multi-user pairing scenario with complete channel state information (CSI), while the center users get the satisfied expected payoffs.     

新体制引信干扰机理分析

为应对新体制无线电引信带来的威胁,从引信对抗角度以超宽带无线电引信为研究对象,研究干扰作用下其失效机理。揭示了超宽带无线电引信敏感干扰波形响应机理,理论推导了周期调制干扰信号作用下引信响应特性,仿真计算了在射频噪声、正弦波调幅、正弦波调频以及扫频正弦波调幅干扰信号作用下超宽带引信接收机相关器输出响应特性。以干信比增益为表征参量,通过理论计算、仿真及试验验证得出结论：周期类调制干扰中调幅类干扰对超宽带引信干扰效果最好。     

Synthesis of flower-like WS2 by chemical vapor deposition

Flower-like tungsten disulfide (WS₂) with a diameter of 5-10 μm is prepared by chemical vapor deposition (CVD). Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy are used to characterize its morphological and optical properties, and its growth mechanism is discussed. The key factors for the formation of flower-like WS₂ are determined. Firstly, the cooling process causes the generation of nucleation dislocations, and then the "leaf" growth of flower-like WS₂ is achieved by increasing the temperature.     

Evolution of helium bubbles in nickel-based alloy by post-implantation annealing

Nickel-based alloys have been considered as candidate structural materials used in generation IV nuclear reactors serving at high temperatures. In the present study, alloy 617 was irradiated with 180-keV helium ions to a fluence of 3.6×10¹⁷ ions/cm² at room temperature. Throughout the cross-section transmission electron microscopy (TEM) image, numerous over-pressurized helium bubbles in spherical shape are observed with the actual concentration profile a little deeper than the SRIM predicted result. Post-implantation annealing was conducted at 700 ℃ for 2 h to investigate the bubble evolution. The long-range migration of helium bubbles occurred during the annealing process, which makes the bubbles of the peak region transform into a faceted shape as well. Then the coarsening mechanism of helium bubbles at different depths is discussed and related to the migration and coalescence (MC) mechanism. With the diffusion of nickel atoms slowed down by the alloy elements, the migration and coalescence of bubbles are suppressed in alloy 617, leading to a better helium irradiation resistance.     

Ionisation energy,electron affinity,and mass spectral decomposition mechanisms of RDX isomers upon electron attachment and electron ionisation

ABSTRACT

The structures, ionisation energies (IE), and electron affinities (EA) of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) isomers upon loss and gain of an electron were calculated using density functional theory (DFT) methods. The adiabatic electron affinities (EA_ad) range from 1 to 2 eV. The vertical detachment energies are between 1.3 and 4.0 eV. The adiabatic ionisation energies (IE_ad) are in the 9.9–10.2 eV range. The vertical ionisation energies are in the 10.4–10.9 eV range. It is shown that NO₂^?/NO₂ loss would be common in anions and cations, respectively. Isomerisation and N—N bond dissociation accompany cation and anion formation, respectively. The suggested mass spectral fragmentation products for the cations along the S₀ surface are 84, 130, and 176 amu, in agreement with earlier mass spectrometry studies.     

GaN基蓝绿光LED电应力老化分析

对InGaN/GaN多量子阱蓝光和绿光LED进行了室温20,40,60 mA加速电流下的电应力老化研究,发现蓝光与绿光样品经过60 mA电流老化424 h后,其电学性能表现出一定的共性与差异性:在小测量电流下,绿光样品的光衰减幅度较蓝光样品大~9%;而在较大测量电流 (20 mA)下,两者的光衰减幅度基本相同 (18%)。同时,蓝绿光样品的正向电学性能随老化时间的变化幅度基本一致,反映出它们具有相似的退化机制,绿光样品老化后增多的缺陷大部分体现为简单的漏电行为,而并非贡献于非辐射复合中心。在此基础上对GaN基外延结构进行了优化,优化后的LED长期老化的光衰减幅度较参考样品降低了3%。     

15N-Traceruntersuchungen zum Mechanismus der N2O-Bildung in Böden

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N₂O and N₂, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N₂O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate.

This study was conducted to measure the path of N₂O formation in Haplic Phaeozen: using [¹⁵N] ammonium and [¹⁵N] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are:

- Under anaerobic conditions (～ 90% of the water holding capacity = WHC) N₂O originates mainly from the nitrate pool by denitrification.

- As expected, the N₂O formation is low under aerobic conditions (～ 80% WHC) but the gas originates directly from the ammonium and not from the nitrate pool, probably as a byproduct of the nitrification process.     

Thermal and Thermo-Oxidative Degradation of Biodegradable Poly(Ester Urethane) Containing Poly(L-Lactic Acid) and Poly(Butylene Succinate) Blocks

A novel biodegradable poly(ester urethane; PEU) was synthesized by chain extension reaction of dihydroxylated poly(L-lactic acid; PLLA) and poly(butylene succinate; PBS) using diisocyanate as a chain extender. The kinetics of thermal and thermo-oxidative degradation of PEU containing PLLA and PBS blocks were studied by thermogravimetric analysis (TGA). TGA results indicated that PEU was more stable in air than in nitrogen and went through a two-stage degradation process irrespective of the experimental atmosphere. Activation energy of each stage was calculated by means of Kissinger, Kim-Park, Friedman, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose methods. For the first stage, the activation energy value obtained in air was slightly higher than the corresponding value obtained in nitrogen; and for the second stage, the activation energy showed a much higher value in air than in nitrogen. The Coats-Redfern method was employed to study the degradation mechanism of each stage. The results indicated that the degradation of the first stage follows the P3/4 mechanism irrespective of the experimental atmosphere; the degradation of the second stage of PEU obeys the P1 mechanism in nitrogen while P3/2 in air.