WSN的极坐标最小能耗覆盖空洞修复算法

针对混合无线传感器网络中的覆盖空洞问题,提出了一种基于极坐标的空洞修复算法。首先,通过计算静态节点感知圆交叉点的位置确定空洞边界点,连接空洞边界点构造空洞多边形;其次,按照极坐标方法计算每个空洞多边形中的虚拟修复节点位置;最后,建立虚拟修复节点与移动节点之间的距离数据表,将表中移动节点移动到与之匹配的虚拟节点位置上,完成空洞修复。仿真结果表明,该算法能够有效判定并修复网络中的覆盖空洞,相比同类算法,所需移动修复节点数量较少,移动节点平均移动距离较短,在提高网络覆盖质量的同时延长了网络的生存周期。     

基于虚拟力的异构无线传感器网络覆盖优化策略

针对异构无线传感器网络覆盖优化过程中,固定Sink节点的虚拟作用力限制移动节点的位置移动,导致覆盖盲区得不到全局修复的问题,本文结合计算几何理论,提出基于Voronoi多边形形心引力的虚拟力覆盖优化算法（CAVFA）。虚拟力算法能有效指导移动节点的散布过程,形心引力能更好地实现全局的覆盖优化。通过合理设置虚拟力的距离阈值参数和优先级,调整固定节点对移动节点的约束。仿真表明,相比传统VFA算法和CBA算法,本文提出的CAVFA算法能够更有效地提高异构网络的覆盖率,且算法收敛速度更快。     

基于虚拟引力约束的光纤传感器网络节点空洞智能修复算法研究

针对传统光纤传感器网络节点空洞修复算法存在感知半径较低、距离阈值较短等问题,提出了基于虚拟引力约束的光纤传感器网络节点空洞修复算法.引入IVFA-B(Intensity-based Virtual Force AlgorithmWith Boundary Forces,IVFA-B)算法中的虚拟引力模型,分析异构网格中实现最大覆盖时两种异构节点感知半径的关系以及节点之间的最佳距离.将最佳距离和虚拟引力算法中的最佳距离阈值相结合,提供对异构网络的适应度,同时将节点移动概率引入节点移动距离公式中,实现光纤传感器网络节点空洞修复.仿真结果表明,所提出算法可以有效解决现有算法中存在的问题,在保证较为理想的覆盖效果基础上,延长感知半径和增大距离阈值.以此验证了所提算法具有较优应用性能.     

非并行二分法的覆盖空洞修复算法

针对无线传感器网络覆盖空洞影响网络服务质量问题，提出非并行二分法的分布式覆盖空洞修复算法CHRND，算法采用非并行方式选择具有劣弧的空洞边界节点作为覆盖空洞修复的驱动节点，采用基于弧二分法确定移动节点最佳目标位置。仿真实验结果表明，移动节点引入使得空洞不被分割基础上，CHRND算法能以较少数量移动节点实现覆盖空洞的完全修复。     

基于蜂窝结构的改进混合无线传感器网络覆盖优化算法

基于蜂窝结构的混合无线传感器网络（HWSN）覆盖优化算法HWSNBCS存在移动节点平均移动距离较大的问题,为此,提出一种改进的HWSN覆盖优化算法IHWSNBCS。寻找移动传感器节点初始位置与通过HWSNBCS算法得出的候选目标位置之间的最优匹配,将移动节点移动距离之和最小化问题转化为二分图最优匹配问题,利用带权二分图匹配算法KM寻找该匹配问题的最优解,从而得到移动节点最终的目标位置,并实现对HWSNBCS算法移动节点平均移动距离的进一步优化。实验结果表明,IHWSNBCS算法在取得与HWSNBCS算法相同网络覆盖率的前提下,移动节点的平均移动距离减少幅度达到38.87%～43.28%,单个移动节点的最大移动距离减少幅度达到22.65%～66.58%,降低了系统因重新部署移动传感器节点所产生的能耗以及单个传感器节点因能量耗尽而失效的概率,从而延长了网络生命周期,同时,IHWSNBCS的ΔCov-Dist性能指标为HWSNBCS算法的1.64～1.76倍,表明移动节点移动相同距离时IHWSNBCS算法的网络覆盖率提升更大。     

复杂环境下一种多移动节点的WSN三维覆盖算法

依据现实环境中对于复杂的山丘、沟壑等空间立体目标进行监测的需要,提出一种多移动节点的无线传感器网络三维覆盖算法。通过在三维空间中选取目标监测点,采用基于误警率的节点感知模型感知目标监测点,计算目标监测点的三维联合探测概率进行覆盖空洞分析,找出移动节点最优移动路径,调整移动节点移动位置实现对目标监测点的全覆盖,解决三维环境中恶劣复杂情况下的监测问题。仿真结果表明,该算法可有效探测覆盖空洞,并能够利用移动节点对其进行修复,在满足目标监测节点全覆盖的同时使移动节点的移动距离最优,降低网络能耗。     

一种改进菱形网格覆盖空洞修复算法

覆盖空洞的产生会严重影响目标监测区域的网络性能。本文提出一种基于混合传感器网络的改进菱形网格覆盖空洞修复算法。该算法通过改进的菱形贴片方式,指导移动节点到指定位置消除空洞区域。仿真结果表明,与TNR算法相比较,本文算法可以有效减少移动节点的使用数目,提高移动节点的利用率。     

一种无线传感器网络的概率覆盖增强算法

覆盖与连通问题是无线传感器网络的基本问题.研究考虑连通性的概率覆盖增强算法,构建覆盖空洞的修补半径,提出了移动距离和修补半径的关系模型.通过这个关系模型,移动节点在修补圆上选择保持连通的修补位置;根据这个移动距离和空洞面积,移动节点进一步创建空洞的优先级,选择优先级最高的空洞进行修补,节能而高效地实现覆盖增强.仿真结果表明,所提出的算法既能得到较高的覆盖率,又能保证整个网络的连通性.     

无线传感器网络覆盖空洞修复策略

无线传感器网络中节点因能量耗尽或环境破坏而失效导致覆盖空洞现象。提出了一种最佳匹配节点策略(BFNP)修复覆盖空洞。最佳匹配节点策略主要思想是当基站发现网络中节点失败时,首先检测覆盖空洞,然后通过选取距离由空洞边界围所成多边形的最小覆盖圆圆心最近的非活跃节点来替换失败节点,并激活该节点修复覆盖空洞。仿真结果表明最佳匹配节点策略能保证较好的网络覆盖质量,充分利用了网络中的能量资源,延长了网络的生存时间,且性能优于覆盖空洞修补算法(CHPA)。     

一种鲁棒的无线传感器网络覆盖空洞修补方法

在静态节点和少量移动节点构成的无线传感器混合网络中,针对部分静态节点失效会导致形成若干覆盖空洞的问题,提出了一种鲁棒的空洞修复算法。受鱼群运动模式的启发,该算法以网络覆盖率为目标函数,将移动节点的位置迁移过程抽象为人工鱼的生物行为,在传统鱼群觅食、追尾、聚群运动模式的基础上又定义鱼跃、优胜劣汰重生两个新的运动行为以提高寻优的收敛性;在人工鱼状态更新的过程中,采用自适应的视野和步长;最后以实际随机部署的移动节点距离目标点最近为原则,通过鱼群寻优完成空洞目标位置的修补。模拟实验结果表明,该算法无需修补前的地理位置信息和空洞探测,鲁棒性强,能够在使用较少移动节点的情况下快速完成空洞修复,显著地提高了网络覆盖率。     

A technique for monitoring SO2 in combustion exhausts: Use of a non-Nernstian sensing element in combination with an upstream catalytic filter

Detection of sulfur dioxide (SO₂) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO₂, NO, CO₂, CO, and hydrocarbon (C₃H₆)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)_xCr_yO_z) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO₂, NO, CO, and C₃H₆, but the presence of NO₂ or NO (“NO_x”, at 100 ppm by volume) still interfered with the SO₂ response of the Pt–(Ba,Cu)_xCr_yO_z sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO₂ and a response equivalent to about 20 ppm SO₂ in the absence of SO₂. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NO_x interference but at the cost of a reduced SO₂ response magnitude (120 ppm SO₂ yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)_xCr_yO_z sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO₂ drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation.     

Influence of doping BiYO3 and Nb2O5 on PTCR characteristics of BaTiO3 thermistor ceramics

Nb₂O₅-doped (1 − x)Ba_0.96Ca_0.04TiO₃-xBiYO₃ (where x = 0.01, 0.02, 0.03 and 0.04) lead-free PTC thermistor ceramics were prepared by a conventional solid state reaction method. X-ray diffraction, scanning electron microscope, Agilent E4980A and resistivity-temperature measurement instrument, were used to characteristic the lattice distortion, microstructure, temperature dependence of permittivity and resitivity-temperature dependence. It was revealed that the tetragonality c/a of the perovskite lattice, the microstructure and the Curie temperature changed with the BiYO₃ content. In order to decrease the room temperature resistivity, the effect of Nb₂O₅ on the room temperature resistivity was also studied, and its optimal doping content was finally chosen as 0.2 mol%. The 0.97Ba_0.96Ca_0.04TiO₃-0.03BiYO₃-0.002Nb₂O₅ thermistor ceramic exhibited a low ρ_RT of 3.98 × 10³ Ω cm, a typical PTCR effect of ρ_max/ρ_min > 10³ and a T_c of 153 °C.     

UNIQUENESS CONDITIONS OF CL-STRUCTURES IN GL-STRUCTURE EQUIVALENCE CLASSES OF SYSTEM RECONSTRUCTABILITY ANALYSIS

This paper first introduces the basic notions of overall systems with logical relations, their subsystems, structure representation graphs, sets of H-structures and G-structures with logical relations S _H ^L and S _G ^L, immediate refinement and aggregate with logical relations, structure-graph mappings r_V ^L, r_G ^L, etc., and the notions of inclusiveness with logical relations, upper bounding and lower bounding with logical relations. Then it proves the sufficient conditions under which representation graphs R ^L form a lattice. By defining the least upper bound and largest lower bound of (R^L, ) and recommending a lemma on distributivity, this paper proves the sufficient conditions under which G-structures with logical relations form Boolean lattices. Finally after defining the M-structures and C-structures with logical relations, i.e. M-structures and C-structures, this paper proposes the sufficient conditions for the uniqueness of C-structures in G-structure equivalence classes, and proves that the C ^L-structure is the least refined GL-structure in equivalence class S _G ^L/r _G ^L.     

Fast modular exponentiation of large numbers with large exponents

In many problems, modular exponentiation |x^b|_m is a basic computation, often responsible for the overall time performance, as in some cryptosystems, since its implementation requires a large number of multiplications.It is known that |x^b|_m=|x^|b|_(m)|_m for any x in [1,m−1] if m is prime; in this case the number of multiplications depends on (m) instead of depending on b. It was also stated that previous relation holds in the case m=pq, with p and q prime; this case occurs in the RSA method.In this paper it is proved that such a relation holds in general for any x in [1,m−1] when m is a product of any number n of distinct primes and that it does not hold in the other cases for the whole range [1,m−1].Moreover, a general method is given to compute |x^b|_m without any hypothesis on m, for any x in [1,m−1], with a number of modular multiplications not exceeding those required when m is a product of primes.Next, it is shown that representing x in a residue number system (RNS) with proper moduli m_i allows to compute |x^b|_m by n modular exponentiations |x_i^b|_mi in parallel and, in turn, to replace b by |b|_(mi) in the worst case, thus executing a very low number of multiplications, namely log₂m_i for each residue digit.A general architecture is also proposed and evaluated, as a possible implementation of the proposed method for the modular exponentiation.     

Forest carbon densities and uncertainties from Lidar, QuickBird, and field measurements in California

Greenhouse gas inventories and emissions reduction programs require robust methods to quantify carbon sequestration in forests. We compare forest carbon estimates from Light Detection and Ranging (Lidar) data and QuickBird high-resolution satellite images, calibrated and validated by field measurements of individual trees. We conducted the tests at two sites in California: (1) 59 km² of secondary and old-growth coast redwood (Sequoia sempervirens) forest (Garcia-Mailliard area) and (2) 58 km² of old-growth Sierra Nevada forest (North Yuba area). Regression of aboveground live tree carbon density, calculated from field measurements, against Lidar height metrics and against QuickBird-derived tree crown diameter generated equations of carbon density as a function of the remote sensing parameters. Employing Monte Carlo methods, we quantified uncertainties of forest carbon estimates from uncertainties in field measurements, remote sensing accuracy, biomass regression equations, and spatial autocorrelation. Validation of QuickBird crown diameters against field measurements of the same trees showed significant correlation (r = 0.82, P < 0.05). Comparison of stand-level Lidar height metrics with field-derived Lorey's mean height showed significant correlation (Garcia-Mailliard r = 0.94, P < 0.0001; North Yuba R = 0.89, P < 0.0001). Field measurements of five aboveground carbon pools (live trees, dead trees, shrubs, coarse woody debris, and litter) yielded aboveground carbon densities (mean ± standard error without Monte Carlo) as high as 320 ± 35 Mg ha^− 1 (old-growth coast redwood) and 510 ± 120 Mg ha^− 1 (red fir [Abies magnifica] forest), as great or greater than tropical rainforest. Lidar and QuickBird detected aboveground carbon in live trees, 70-97% of the total. Large sample sizes in the Monte Carlo analyses of remote sensing data generated low estimates of uncertainty. Lidar showed lower uncertainty and higher accuracy than QuickBird, due to high correlation of biomass to height and undercounting of trees by the crown detection algorithm. Lidar achieved uncertainties of < 1%, providing estimates of aboveground live tree carbon density (mean ± 95% confidence interval with Monte Carlo) of 82 ± 0.7 Mg ha^− 1 in Garcia-Mailliard and 140 ± 0.9 Mg ha^− 1 in North Yuba. The method that we tested, combining field measurements, Lidar, and Monte Carlo, can produce robust wall-to-wall spatial data on forest carbon.     

Thermodynamic description of the Al–Fe–Zr system

The Fe–Zr and Al–Fe–Zr systems were critically assessed by means of the CALPHAD technique. The solution phases, liquid, face-centered cubic, body-centered cubic and hexagonal close-packed, were described by the substitutional solution model. The compounds with homogeneity ranges, hex.- Fe₂Zr, Fe₂Zr, FeZr₂ and FeZr₃ in the Fe–Zr system, were described by the two-sublattice model in formulas such as hex.- Fe₂(Fe,Zr), (Fe,Zr)₂(Fe,Zr), (Fe,Zr)Zr₂ and (Fe,Zr)(Fe,Zr)₃ respectively. The compounds Al_mZr_n except Al₂Zr in the Al–Zr system were treated as line compounds (Al,Fe)_mZr_n in the Al–Fe–Zr system. The compounds FeZr₂ and FeZr₃ in the Fe–Zr system were treated as (Al,Fe,Zr)Zr₂ and (Al,Fe,Zr)(Fe,Zr)₃ in the Al–Fe–Zr system, respectively. All compounds in the Al–Fe system and hex.- Fe₂Zr in the Fe–Zr system have no solubilities of the third components Zr or Al, respectively, in the Al–Fe–Zr system. The ternary compounds _λ1${\lambda }_1$ with C14 structure and _λ2${\lambda }_2$ with C15 structure in the Al–Fe–Zr system were treated as _λ1${\lambda }_1$- (Al,Fe,Zr)₂(Fe,Zr) with Al₂Zr in the Al–Zr system and _λ2${\lambda }_2$- (Al,Fe,Zr)₂(Fe,Zr) with Fe₂Zr in the Fe–Zr system, respectively. And the ternary compounds _τ1${\tau }_1$, _τ2${\tau }_2$ and _τ3${\tau }_3$ in the Al–Fe–Zr system were treated as (Al,Fe)₁₂Zr, Fe(Al,Zr)₂Zr₆ and Fe₇Al₆₇Zr₂₆, respectively. A set of self-consistent thermodynamic parameters of the Al–Fe–Zr system was obtained.     

Restricted arc-connectivity of digraphs

Since interconnection networks are often modeled by graphs or digraphs, the edge-connectivity of a graph or arc-connectivity of a digraph are important measurements for fault tolerance of networks.The restricted edge-connectivity λ^′(G) of a graph G is the minimum cardinality over all edge-cuts S in a graph G such that there are no isolated vertices in G−S. A connected graph G is called λ^′-connected, if λ^′(G) exists.In 1988, Esfahanian and Hakimi [A.H. Esfahanian, S.L. Hakimi, On computing a conditional edge-connectivity of a graph, Inform. Process. Lett. 27 (1988), 195-199] have shown that each connected graph G of order n?4, except a star, is λ^′-connected and satisfies λ^′(G)?ξ(G), where ξ(G) is the minimum edge-degree of G.If D is a strongly connected digraph, then we call in this paper an arc set S a restricted arc-cut of D if D−S has a non-trivial strong component D₁ such that D−V(D₁) contains an arc. The restricted arc-connectivity λ^′(D) is the minimum cardinality over all restricted arc-cuts S.We observe that the recognition problem, whether λ^′(D) exists for a strongly connected digraph D is solvable in polynomial time. Furthermore, we present some analogous results to the above mentioned theorem of Esfahanian and Hakimi for digraphs, and we show that this theorem follows easily from one of our results.     

d-Dimensional Range Search on Multicomputers

The range tree is a fundamental data structure for multidimensional point sets, and, as such, is central in a wide range of geometric and database applications. In this paper we describe the first nontrivial adaptation of range trees to the parallel distributed memory setting (BSP-like models). Given a set of n points in d -dimensional Cartesian space, we show how to construct on a coarse-grained multicomputer a distributed range tree T in time O( s / p + T _c (s,p)) , where s = n log ^d-1 n is the size of the sequential data structure and T _c (s,p) is the time to perform an h -relation with h=Θ (s/p) . We then show how T can be used to answer a given set Q of m=O(n) range queries in time O((s log m)/p + T _c (s,p)) and O((s log m)/p + T _c (s,p) + k/p) , where k is the number of results to be reported. These parallel construction and search algorithms are both highly efficient, in that their running times are the sequential time divided by the number of processors, plus a constant number of parallel communication rounds. Received June 1, 1997; revised March 10, 1998.