VoIP协议栈的安全性研究

本文提出对VoIP协议栈的结构分析,包括VoIP信令（SIP协议）,会话描述协议（SDP）,密钥的建立（SDES,,MIKEY,ZRTP）,和SRTP协议,对VoIPx协议栈的相关协议作了简要说明,并分析了其相关的安全性。重点针对SIP、SRTP协议和ZRTP协议分析了其安全隐患并提出相关的改进方案。     

Design of the microlens arrays coupling with imaging fiber bundle

To ameliorate the disadvantages of imaging system coupled with imaging fiber bundle, a method by adding square aperture microlens arrays at both entrance and exit ends of the imaging fiber bundle is proposed to increase the system’s coupling efficiency. The expressions for solving the parameters of both ends’ microlens units are deducted particularly. The microlens arrays used for an infrared imaging fiber bundle with the single fiber diameter of 100 μm and core diameter of 70 μm are designed by this method. The simulation results show that compared with the system without microlens arrays, the fill factor of the imaging fiber bundle coupled microlens arrays system is increased from 44.4% to more than 90%, and the coupling efficiency is doubled too. So the design method is correct, and the introduction of microlens arrays into imaging fiber bundle coupled system is feasible and superior.     

Low loss Nb2O5 films deposited by novel remote plasma sputtering

We report the deposition of Nb2O5 films on unheated BK-7 glass substrates using remote plasma sputtering system. The remote plasma geometry allows pseudo separation of plasma and target bias parameters, which offers complete deposition rate control. Using appropriate oxygen flow rates, high-density and low-loss Nb2O5 films are deposited with rates up to 0.49 nm/s. Lower deposition rates (~0.026 nm/s) can also be obtained by working at low target current and voltage and at low pressure. Nb2O5 films deposited at different rates have the refractive index of about 2.3 and the extinction coefficient as low as 6.9×10-5.     

Gd3+‐Ion‐Doped Upconversion Nanoprobes: Relaxivity Mechanism Probing and Sensitivity Optimization

Paramagnetic gadolinium (Gd‐III)‐ion‐doped upconversion nanoparticles (UCNPs) are attractive optical‐magnetic molecule imaging probes and are a highly promising nanoplatform for future theranostic nanomedicine design. However, the related relaxivity mechanism of this contrast agent is still not well understood and no significant breakthrough in relaxivity enhancement has been achieved. Here, the origin and optimization of both the longitudinal (r₁) and transverse (r₂) relaxivities are investigated using models of water soluble core@shell structured Gd³⁺‐doped UCNPs. The longitudinal relaxivity enhancement of the nanoprobe is demonstrated to be co‐contributed by inner‐and outer‐sphere mechanisms for ligand‐free probes, and mainly by outer‐sphere mechanism for silica‐shielded probes. The origin of the transverse relaxivity is inferred to be mainly from an outer‐sphere mechanism regardless of surface‐coating, but with the r₂ values highly related to the surface‐state. Key factors that influence the observed relaxivities and r₂/r₁ ratios are investigated in detail and found to be dependent on the thickness of the NaGdF₄ interlayer and the related surface modifications. A two orders of magnitude (105‐fold) enhancement in r₁ relaxivity and 18‐fold smaller r₂/r₁ ratio compared to the first reported values are achieved, providing a new perspective for magnetic resonance (MR) sensitivity optimization and multimodality biological imaging using Gd³⁺‐doped UCNPs.     

浮式液化天然气装置上部模块加热系统的选择

浮式液化天然气(FLNG)装置是开采和加工深海天然气的一种新型海上装置,但其上部工艺模块受空间限制,须集约化布置,对其加热系统的选择显得尤为重要。通过对热媒油系统和蒸汽系统在海上装置的应用适应性分析,选择投资低、热效率高、操作简单、空间占用率低的热媒油加热系统,并以某海湾气田年产240×104t LNG热媒油废热系统的计算和设备选型为例,论证选择热媒油系统为佳。     

溶解性有机质化学结构表征的研究进展

溶解性有机质作为环境中重要的天然配位体和吸着载体,它的化学结构特性直接影响其在元素生物地球化学循环、重金属和有机污染物迁移过程中的作用。文章介绍了目前表征溶解性有机质化学结构的方法,包括离子交换色谱法、核磁共振、傅立叶红外光谱和荧光光谱分析,并提出了未来的研究展望。     

卡纸涂层对EB固化直接真空镀铝工艺的影响

通过改变卡纸涂布量和涂层中瓷土与碳酸钙的比例,研究了卡纸涂层对电子束固化直接真空镀铝工艺的影响。结果表明,随卡纸涂料量提高,表征涂层开放程度的油墨吸收性也随之提高,但卡纸的耐折性能则下降,电子束（EB）固化预涂料涂布量也随之增大;卡纸涂层材料中颜料的组成对卡纸性能及EB固化涂料预涂量有影响,随着颜料中瓷土含量降低,碳酸钙含量提高,涂层的开放程度提高,纸张光泽度下降。     

一种膨化硝铵炸药新配方的探讨

通过零氧平衡理论和线性规划手段计算出一系列的膨化硝铵炸药的配方,通过实验对不同配方产品性能进行比较,确定了一种新型膨化硝铵炸药炸药配方。     

广西某半氧化铜矿石预脱碳加温硫化浮选试验

广西某铜矿石铜氧化率在27%以上,且含1%左右的碳质,属难选半氧化铜矿石。矿山选矿厂采用直接常温浮选工艺处理该矿石,铜精矿品位只有18%左右且回收率不到60%。为了给现场工艺流程改造提供依据,以硫化钠为硫化剂、丁黄药+DY组合为捕收剂,在60 ℃下对该矿石进行了预脱碳加温硫化浮选试验,获得了Cu品位为20.57%、Cu回收率为62.75%的铜精矿,与现场生产相比,选别指标得到了显著提高。     

微磨料气射流切割深度建模

微磨料气射流切割技术具有无热影响区,工件受加工作用力小的优点,非常适合于切割硅和玻璃等硬脆材料薄板.切割深度是评价切割能力的重要参数之一.建立了微磨料气射流切割硬脆材料的切割深度半经验模型.通过全因素实验和回归分析确定了模型中的经验参数.该切割深度模型表明,切割深度随气压和射流角度的增加而增加,随喷嘴横移速度的增加而减小.通过比较实验值和预测曲线,分析了模型的预言能力.结果表明该模型能够有效地预言微磨料气射流切割深度.