一种新型的基于自组网车载通信系统MAC协议

提出了一种新型的基于自组网车载通信系统的MAC协议。该协议采用竞争与预约相结合的方法,有效地解决了隐藏、暴露终端等问题。仿真结果表明该协议能够保证节点快速可靠地接入信道,而且对网络规模不敏感。     

Mechanically Induced Cation Redistribution and Spin Canting in Nickel Ferrite

The structural and magnetic evolution in nickel ferrite (NiFe₂O₄) caused by high-energy milling are investigated by Mössbauer spectroscopy. It is found that the nanostructural state of the milled NiFe₂O₄ is characterized by a reduced concentration of iron ions on tetrahedral sites. The degree of inversion in NiFe₂O₄ is calculated from the subspectral area ratio of both high- and zero-field Mössbauer spectra. Several interesting features are involved in the work, e.g., superparamagnetic relaxation, mechanically induced cation redistribution, and spin-canting effect.     

New modifications of poly(vinyl alcohol)s and their applications

Poly(vinyl alcohol) (PV-OH), prepared from poly(viny) acetate), is used widely in many industries. Various grades have been produced, with different degree of polymerization and degree of hydrolysis. Recently, novel modified (PV-OH)s with anion, cation, silanol or hydrophobic groups have been studied and developed. They have new properties in addition to those of ordinary PV-OH and have new applications. The methods of modification and the characteristics and some applications of the modified polymers are described.     

A/B-Ratio and Transport Properties of (La0.85Sr0.15)sCoO3−δ Perovskites

The perovskites (La_0.85Sr_0.15)_0.98CoO_{3 –} and (La_0.85Sr_0.15)_1.00CoO_{3 –} have been investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical conductivity relaxation (ECR). This system was chosen in order to investigate the influence of cation vacancies on the transport properties in the materials. From ECR-measurements it is concluded that no difference in the chemical diffusion coefficient for oxide ions between the two samples can be found. The activation energy for the chemical diffusion coefficient has been found to be 107 ± 5 kJ mol^{– 1}. However, the surface exchange coefficient differs between the two samples. The Co-rich sample has a significantly higher surface exchange coefficient than the A/B-stoichiometric sample. For both samples the surface exchange coefficient was almost independent of the temperature. At all temperatures the Co-rich sample had a significantly higher electrical conductivity. The difference in electrical conductivity between the two samples diminished when going to higher temperatures. Both materials can be assigned to a single phase hexagonal perovskite. An annealed sample of (La_0.85Sr_0.15)_0.98CoO_{3 –} did however contain an unidentified secondary phase on the surface.     

Hydration Characteristics of Sodium Sulfate Slag Cement System

The hydration characteristics by thermal analysis ( DTA ) were determined, and an isothermal calorimeter (IC) was used to study the pastes . The experimental results indicate: (1) The main hydration products of SSC are C-S-H( I ) gel with a low Ca/Si ratio, crystalline Thomsonite-type and AFt-type phases containing certain alkali cations; (2) No phases of the AFm-type and high alkaline Ca( OH)2 in SSC system could benefit the hydrated cements to improve its strength and durability; (3) Crystalline Thomsonite-type and AFt-type phases containing Na will greatly reduce free alkali and alleviate the harmness of alkali aggregate reaction ( AAR) in SSC system; (4) Similar to ordinary Portland cement( OPC), the hydration process of SSC could be classified into five stages : initial, induction, acceleration, deceleration and decay; (5) Regardless of the activator used, the apparent activation energy is higher with the increased slag in cement system, and the rising temperature could promote the hydration of SSC.     

Effect of Nb Doping on (Sr,Ba)TiO3 (BST) Ceramic Samples

The effect of doping the Sr_0.3Ba_0.7Ti_(1–5y/4)Nb _y O₃ ceramic with different concentration of Nb is studied by scanning electron microscopy (SEM), X-ray diffraction and thermoelectric analysis. It is observed that the grain size decreases as the Nb concentration increases. The critical temperature T _c has a linear decrease at a rate of 19°C/mol% of Nb. The temperature dependence of the dielectric permittivity presents strongly broadened curves, which suggest a non Curie-Weiss behavior near the transition temperature. The diffuse phase transition coefficient () was also determined and its value leads to the conclusion that the degree of disorder in the system increases with the presence of the Nb cation.     

Attempts to Synthesize Zeolitic Composites from Stellerite

A feasible method to synthesize NaA and NaY zeolite from stellerite, the very cheap raw material found in China, was reported in this article to reduce the cost of zeolite synthesis for the first time. After stellerite is calcined above 973 K with sodium carbonate, this natural zeolite can be slowly dissolved in alkali solution and partly forms the gels, then transforms to zeolite NaA or NaY by structural rearrangement. The effect of synthetic conditions such as the ratio of different cation used in the reactive mixture on the resulting zeolite is examined. Furthermore, a new NaA/MCM-41 composite possessing both micropore and mesopore is synthesized by adding the NaA zeolite into the synthetic system, and the impact of zeolite additive on the pore structure of final porous composite is also explored.     

Synthesis and characterization of Ce-doped mesoporous anatase with long-range ordered mesostructure

The effect of cerium cation on the formation of titania crystallites using H⁺ as catalyst under mild condition has been investigated. The results indicated that the presence of cerium cation can improve the selectivity of producing anatase crystallites and inhibit the growth of crystallites. The Ce-doped mesoporous titania with highly crystallized pore walls consisting of anatase nanoparticles was synthesized by anatase crystallites assembly. The long-range ordered mesostructure was characterized by low angle and wide angle X-ray diffraction (XRD), N₂ adsorption-desorption, transmission electron microscopy (TEM) and selected area electron diffraction (SAED).     

非跟踪体制炮位侦察雷达目标自动识别技术的实现

非跟踪体制炮位侦察雷达要实现目标的自动识别，其关键技术是背景杂波的处理和对目标信号的识别。文中提出了采用脉冲积累技术，对非相参脉冲串信号处理进行视频积累，由门限判决器判断有无目标回波、抑制噪声和杂乱脉冲干扰，降低系统的虚警率；采用杂波存储技术存储全画面杂波，建立静态杂波图，有效地抑制地物杂波的影响；采用单片机主-从系统双机速度识别技术，对回波信号进行速度识别和相关处理，实现非跟踪体制炮位侦察雷达目标自动识别。