Design and realization of ad-hoc VoIP with embedded p-SIP server

In this paper we design and implement the pseudo session initiation protocol (p-SIP) server embedded in each mobile node to provide the ad-hoc voice over Internet protocol (VoIP) services. The implemented p-SIP server, being compatible with common VoIP user agents, integrates the standard SIP protocol with SIP presence to handle SIP signaling and discovery mechanism in the ad-hoc VoIP networks. The ad-hoc VoIP signaling and voice traffic performances are analyzed using E-model R rating value for up to six hops in the implemented test-bed. We also conduct the interference experiments to imitate the practical ad-hoc VoIP environment. The analyzed results demonstrate the realization of ad-hoc VoIP services by using p-SIP server.     

A parallel direct solver for the self-adaptive hp Finite Element Method

In this paper we present a new parallel multi-frontal direct solver, dedicated for the hp Finite Element Method (hp-FEM). The self-adaptive hp-FEM generates in a fully automatic mode, a sequence of hp-meshes delivering exponential convergence of the error with respect to the number of degrees of freedom (d.o.f.) as well as the CPU time, by performing a sequence of hp refinements starting from an arbitrary initial mesh. The solver constructs an initial elimination tree for an arbitrary initial mesh, and expands the elimination tree each time the mesh is refined. This allows us to keep track of the order of elimination for the solver. The solver also minimizes the memory usage, by de-allocating partial LU factorizations computed during the elimination stage of the solver, and recomputes them for the backward substitution stage, by utilizing only about 10% of the computational time necessary for the original computations. The solver has been tested on 3D Direct Current (DC) borehole resistivity measurement simulations problems. We measure the execution time and memory usage of the solver over a large regular mesh with 1.5 million degrees of freedom as well as on the highly non-regular mesh, generated by the self-adaptive hp$hp$-FEM, with finite elements of various sizes and polynomial orders of approximation varying from p=1$p=1$ to p=9$p=9$. From the presented experiments it follows that the parallel solver scales well up to the maximum number of utilized processors. The limit for the solver scalability is the maximum sequential part of the algorithm: the computations of the partial LU factorizations over the longest path, coming from the root of the elimination tree down to the deepest leaf.     

In2O3 + xBaO (x = 0.5-5 at.%) - A novel material for trace level detection of NOx in the ambient

Indium oxide (In₂O₃) doped with 0.5-5 at.% of Ba was examined for their response towards trace levels of NO_x in the ambient. Crystallographic phase studies, electrical conductivity and sensor studies for NO_x with cross interference for hydrogen, petroleum gas (PG) and ammonia were carried out. Bulk compositions with x ≤ 1 at.% of Ba exhibited high response towards NO_x with extremely low cross interference for hydrogen, PG and ammonia, offering high selectivity. Thin films of 0.5 at.% Ba doped In₂O₃ were deposited using pulsed laser deposition technique using an excimer laser (KrF) operating at a wavelength of (λ) 248 nm with a fluence of ∼3 J/cm² and pulsed at 10 Hz. Thin film sensors exhibited better response towards 3 ppm NO_x quite reliably and reproducibly and offer the potential to develop NO_x sensors (Threshold limit value of NO₂ and NO is 3 and 25 ppm, respectively).     

电阻抗扫描成像计算机辅助诊断方法研究

为了提高电阻抗扫描成像EISI(Electrical Impedance Scanning Imaging)在乳腺疾病检查方面的准确性,将独立分量方法(ICA)应用于EISI数据的特征提取,并结合支持向量机(SVM)进行乳腺疾病计算机辅助诊断(CAD)。实验结果表明:ICA方法所提取的特征对于乳腺疾病分类是有效的。对于良性肿瘤和恶性肿瘤的鉴别,提出的CAD方法灵敏度为74.2%,特异度为82.8%,准确度为80%。结合所提出的CAD方法和传统的EISI检查方法,可以提高EISI在乳腺疾病检查方面的可靠性,降低假阳性率,避免对良性肿瘤患者进行活检。     

Structural and electrical properties of mixed oxides of manganese and vanadium: A new semiconductor oxide thermistor material

Binary oxides of manganese and vanadium have been synthesized by solid state sintering, in which the mass ratio of the individual components Mn₂O₃ and VO₂ have been varied from 90:10 to 5:95. The bulk ceramic samples were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray analysis. The initial compositions either rich in Mn₂O₃ or in equi-proportion by mass with VO₂ yield β-Mn₂V₂O₇ or a new crystalline form of Mn₂V₂O₇, with unit cell parameters: a = 7.73091 Å, b = 6.640788 Å, c = 6.70779 Å α = γ = 90° and β = 98.7086° which is designated as γ-Mn₂V₂O₇. The compositions, richer in VO₂ produce MnV₂O₆ co-existing with V₂O₅ the proportion of which increases with increase in VO₂. The surface microanalysis shows a spherical-granular morphology in Mn₂V₂O₇ structure and plate/rod-like structures co-existing with granular morphology in case of MnV₂O₆ together with V₂O₅. The electrical parameters of the negative temperature coefficient thermistors were determined. Depending on the constituent oxide composition, the NTC thermistors showed room temperature resistivity in the range of 6.52 × 10² to 6.1 × 10⁶ Ω-cm. The thermistor constant and activation energy are in the range of 0.12–0.458 eV and 1393–4801 K, respectively.     

瞬变电磁法在变电站地质物探中的应用

在电力系统地质探测方面,为了查明引发滑坡的地质形态特征,简要介绍了瞬变电磁法(TEM)的工作原理及其探测方法,并以滇东北区某变电站周边边坡进行探测为例,通过对视电阻率成像图进行分析,得到了视深断面图的地形特征,总结了地质形态的分布情况.与传统的电阻率法相比,瞬变电磁法能够高效、简便地运用在山地环境的地质物探中.     

温控烧结法制备高温PTCR陶瓷

本实验以固相合成的(Ba_(0.6)Pb_(0.4))TiO_3为主要原料,在较宽的温度范围内(1280—1360℃)制得了Tc>320℃、室温电阻率低达几十Ω·cm、升阻差在五个数量级以上的PTCR材料。实验结果得出:采用高温快速升温、从烧结温度快速降温至某一温度并保温一段时间的温控烧结方法(TCS),有利于提高材料的性能。     

基于大尺寸地层模型的砂岩储层油基钻井液侵入模拟

选用扇形砂岩地层模块作为大尺寸地层模型,以钻井液侵入多功能物理模拟系统为平台,实施了长时间油基钻井液侵入实验,总结了侵入过程中地层模块径向电阻率、油基钻井液滤液滤失流量和侵入深度的变化规律,获得了不同物性条件下的油基钻井液侵入特征;实现了地层条件下的砂岩储层油基钻井液侵入数值模拟。研究结果表明：油基钻井液侵入过程中,地层模块径向电阻率向远离井壁方向依次开始增大,且增大速度随径向深度增大而降低。侵入初期,滤液滤失流量迅速减小,累计滤失量增幅变缓,侵入深度较浅;侵入达到动态平衡后,滤液滤失流量趋于稳定,累计滤失量随侵入时间线性增加,侵入深度增大速度极慢。与高孔渗砂岩储层相比,低孔渗砂岩储层中的滤液滤失流量和累计滤失量更大,侵入更快、更深,径向电阻率率先增大且增大速度更快。     

船舶电缆密封技术

为了正确掌握船舶内置电缆密封技术，文中根据电缆密封装置的特点和具体设计要求，对常用的多种密封材料性能的优劣进行了分析，并展望密封材料及密封工艺的发展前景。     

土石复合介质电阻率结构模型及影响因素分析

多相土石复合介质电阻率特性由于影响因素较多,目前对于其理论模型研究较少。在前人提出的非饱和土电阻率结构模型的基础上,基于土石介质串联和土石介质并联两种结构形式,建立了多相土石复合介质电阻率结构模型,并分析了含水率、孔隙率、土石比和饱和度对土石复合介质电阻率特性的影响规律,结果表明:当土石颗粒本身的成分不变时,影响土石复合介质电阻率特性的主要因素有含水率、孔隙率、土石比三个因素,其敏感程度从大到小依次为含水率、孔隙率和土石比。