基于IXP425的防火墙硬件平台设计

针对中小企业对硬件防火墙的需要,文章设计了一种基于IntelIXP425的防火墙硬件平台,并介绍了IXP425的选取和芯片特性,系统硬件平台结构和电路设计中的难点及解决方法。测试结果表明,该硬件平台性能良好,稳定可靠。     

Crystal and molecular structure of a crown-bridgedp-t-butyl-calix[4]arene (1:1) pyridine complex. Host-guest interaction model based on molecular mechanics analysis [1]

The crystal and molecular structure of a crownedp-t-butyl-calix[4]arene (1:1) pyridine complex is reported. Colourless transparent prismatic crystals (obtained from pyridine) C₅₄H₇₄O₈·C₅H₅N,a=13.486(4),b=15.193(4),c=16.432(5) Å, =116.44(4)°, space groupP2₁,Z=2,D _calc=1.02g cm^–3, CuK radiation =1.5418 Å (CuK )=4.99 cm^–1. Refinement was carried out using 1702 reflections withI>3(I) toR 0.12. The macrocycle shows a distorted cone conformation which defines an intramolecular apolar cavity whose elliptical aperture is 11.5×8.6 Å calculated as distances between the two opposite central C atoms of the Bu ^t groups. A molecule of pyridine is included in this cavity, whereas the intermolecular cavities of the host lattice remain empty. The influence of the guest molecule on the conformation of the calixarene-crown is discussed. Potential energy calculations are performed in order to understand the nature of the host-guest interactions responsible for the stabilisation of the complex. Evidence for stabilizing CH₃- interactions are obtained from the calculations. Supplementary Data relevant to this article have been deposited with the British Library as supplementary Publication No. SUP 82068 (9 pages).     

基于DPA-Switch的小功率四路输出开关电源设计

DPA-Switch系列器件具有TOP和Tiny系列的技术特点,采用脉宽调制(PWM)和跳周期调制(PSM)目结合的新型调制方式来调节输出电压,并具有低功耗和高效率等优点.利用该系列器件设计一种小功率四路输出的单端正激式开关电源,给出了简化设计步骤和参数计算.     

双极晶体管LNA的分析与设计

低噪声放大器（LNA）在射频系统中是作为接收端的前端，其增益、噪声、非线性、匹配等性能对整个接收机至关重要。随着现代通信电子技术的发展，迫切需要低噪声、高增益、低偏置、小体积的射频放大器。我们利用Ansoft的设计软件designer，设计了用于1．5GHz的低噪声放大器，器件选用Philip公司的BFG425W双极晶体管，文章主要从共发LNA电路的噪声分析入手，通过对电路的分析与仿真，对其参数进行了优化，最后提出了几点改进的措施。     

Comparative analysis of real and \mathcal{P}\mathcal{T}-symmetric Scarf potentials

The Scarf I and Scarf II potentials are discussed within a common mathematical framework, which is then specified to handle the two potentials separately both in the conventional Hermitian and in the -symmetric setting. The physically admissible solutions are identified in each case together with the corresponding energy eigenvalues. Several main differences between the -symmetric Scarf I and II potentials are pointed out. These include the presence and absence of the quasi-parity quantum number, the sign of the pseudo-norm, the mechanism of the spontaneous breakdown of symmetry and the non- orthogonality of otherwise admissible solutions in the Scarf I potential. Similarities and differences with respect to the corresponding Hermitian systems are also pointed out.