Connection Probability Research Articles

Quantifying spatial morphology and connectivity of urban heat islands in a megacity: A radius approach

Urban heat island (UHI) effect is an important ecological consequence of rapid urbanization. Although the spatio-temporal evolution of urban heat islands (UHIs) and their driving forces have been discussed in previous studies, the accurate identification of the spatial morphology and connectivity of UHIs is currently lacking. Taking Beijing City as an example, the radius approach (RA) was applied to identify the thresholds of UHIs, and multiple indexes were calculated to analyze the changing connectivity of UHIs from 2000 to 2015. The results showed that the UHIs in Beijing City formed archipelagos, which composed of single main heat island that occupied >79.85% of the total area, and small heat islands scattered in the centers of surrounding districts. In 15 years, the total area occupied by UHIs increased by 30.04%, indicating that the UHI effect became worse. As for landscape patterns of UHIs, aggregation index (AI) increased by 1.6%, landscape shape index (LSI) decreased by 4.1%, and probability of connectivity (PC) increased by 69.1%, all indicating that the distribution of UHIs became more compact, and the connectivity between islands increased. Different expansion types had different influences on the landscape patterns of UHIs: the edge-expansion reduced the fragmentation of UHIs and increased connectivity between islands, the infilling expansion made the boundaries of UHIs regular, and the leapfrog expansion made the AI slight decrease. Based on the radius approach, identifying the range of multi-center UHIs and their spatial expansion type can provide an effective planning guideline for mitigating the negative UHI effect.

Isolated trees and small woody patches greatly contribute to connectivity in highly fragmented tropical landscapes

Decreasing landscape connectivity, due to habitat loss and agricultural expansion, is a threat for species movement and other flux-dependent ecological processes. Tree cover within the agricultural matrix provides perching sites, dispersal routes, and extra habitat for animals. Isolated trees and living fences in tropical pastures add structural complexity to actual matrices, but their role in landscape connectivity is undervalued. Our main objective was to assess the potential value of small (≤1ha) woody patches for maintaining landscape connectivity in highly fragmented landscapes using birds as focal species. We used high-resolution images and LIDAR data to classify different tree cover types. We assess the probability of connectivity for different hypothetical dispersal distances between woody patches, using a graph-theoretic approach and simulating scenarios that differed in tree cover composition. We estimated the impacts and contribution of tree cover class removals on landscape connectivity. The connectivity index increased widely among scenarios with increasing tree cover composition. The highest connectivity value was obtained in the scenario that included all arboreal elements currently present in the matrix. Small wooded patches and isolated trees contributed from 26% to 59% to overall connectivity. The presence of small (≤1ha) patches of tree cover greatly enhance landscape connectivity for animals with low vagility and behavioral limitations on crossing gaps. Isolated trees and living fences play a crucial role in increasing habitat reachability within rural landscapes and ensuring and enhancing connectivity for animals that perform daily-movements at short-distances. The spatial distribution of arboreal elements within landscapes could be optimized to increase connectivity and must be considered in conservation planning.

城市化背景下景观破碎化及连接度动态变化研究——以昆明市为例

城市化不仅改变景观类型和组成，也导致空间形态变化与自然生境连接度的降低，刻画不同城市化过程中人工表面、耕地与自然生境的空间关系对于研究其景观生态效应，尤其是对不同景观之间的相互作用以及结构和功能的变化具有重要意义。以云南省昆明市为研究区，分析了1990-2015年城市扩张导致的破碎化与形态变化对景观连接度的影响。利用城市破碎指数（UFI）刻画景观破碎水平，进一步基于形态学空间格局分析（MSPA）得到耕地和自然生境的七类景观形态要素（核心、岛状斑块、桥接、环岛、孔隙、边缘和支线），选取了3种边缘宽度比较边缘宽度对景观形态的影响差异，然后通过概率连接度指数（PC）和斑块重要值（dPC）评估景观连接度的变化。在4 km×4 km的网格基础上计算平均UFI和dPC，利用三维曲面分析不同变量之间的相关性。结果表明：过去25年间，昆明市人工表面不断扩大，占用大量耕地并导致景观破碎度的增加，速率呈逐年增加的趋势；MSPA结果显示，耕地表现出持续稳定的消减，自然生境景观形态类型前期变化不大，2010年后有较大幅度改变，表现出从稳定、波动到破碎的过程，不同边缘宽度下存在显著差别，边缘宽度越大则连接度变化越为明显，表明城市化对小型绿色斑块影响较大；斑块重要值与UFI的变化表现出一致性，变化集中于东部地区，随着UFI的增加景观连接度逐年降低；相关性分析显示，随着破碎度的增加，景观连接度经历了从波动到稳定下降的过程。总体上，昆明市城市化造成耕地的持续减少，虽未造成大面积自然生境丧失，但在一定程度上降低了连接度，需要从空间格局上加以管控，避免对整体景观连接度产生负面影响。;Urbanization can not only change the landscape types and composition, but also change the spatial morphology and decrease the natural habitat connectivity. Depicting the spatial relationship between artificial surface, arable land and natural habitat is of great significance to examine the landscape ecological effects, especially for the interaction between different landscapes and changes of structure and function. The effects of fragmentation and morphological changes on landscape connectivity with urban expansion of Kunming City, Yunnan Province in 1990-2015 were analyzed in this study by using the urban fragmentation index (UFI) to depict the level of landscape fragmentation. Based on morphological spatial pattern analysis (MSPA), seven landscape morphological elements (core, islet, bridge, loop, perforation, edge, and branch) of arable land and natural habitat were obtained. Three edge widths were selected to compare the influence of edge widths on the landscape morphology. The landscape connectivity changes were evaluated by probability of connectivity (PC) and importance value of patches (dPC). The average UFI and dPC were calculated on the grid of 4 km×4 km, and the correlation among different variables were analyzed by the three-dimensional curved surface graph. The results showed that the artificial surface in Kunming has been expanding, occupying a large amount of arable land. The annual increase rate of landscape fragmentation has been increasing in the past 25 years. The results of MSPA indicated that the arable land showed a continuous and stable declining trend, and the landscape morphology of natural habitat showed little change from 1990 to 2010. After 2010, there has been a dynamic process from stability to fluctuation and then to fragmentation. There were significant differences between different edge widths. The wider the edge width was, the more obvious the change of connectivity was. This fact indicated that urbanization had a more serious impact on small green patches. The change of dPC was consistent with that of the UFI, and the change was concentrated in the eastern region of Kunming. With the increase of the UFI, the landscape connectivity decreased year by year. The correlation analysis showed that the landscape connectivity experienced a process from fluctuation to steady decline with the increase of fragmentation. In general, the urbanization of Kunming has caused continuous reduction of arable land. Although the loss of large-scale natural habitat has not been caused by the urbanization, the connectivity has been reduced to a certain extent. It is necessary to control the spatial pattern to avoid the negative impact of the urbanization on the overall landscape connectivity.

A lower bound for point-to-point connection probabilities in critical percolation

Consider critical site percolation on $\mathbb{Z}^d$ with $d \geq 2$. We prove a lower bound of order $n^{- d^2}$ for point-to-point connection probabilities, where $n$ is the distance between the points. Most of the work in our proof concerns a `construction' which finally reduces the problem to a topological one. This is then solved by applying a topological fact, which follows from Brouwer's fixed point theorem. Our bound improves the lower bound with exponent $2 d (d-1)$, used by Cerf in 2015 to obtain an upper bound for the so-called two-arm probabilities. Apart from being of interest in itself, our result gives a small improvement of the bound on the two-arm exponent found by Cerf.

Ascending arousal network connectivity during recovery from traumatic coma

BackgroundIt is not currently possible to predict which patients will develop chronic disorders of consciousness (DoC) after severe traumatic brain injury (TBI). Although the ascending arousal network (AAN) supports human consciousness, it is unknown which AAN pathways must be preserved for patients to recover consciousness. MethodsSixteen patients with acute traumatic coma and 16 matched healthy controls were scanned with high angular resolution diffusion imaging (HARDI). All patients recovered consciousness (Recovery Cohort). Nine were scanned longitudinally: first in the ICU (Acute), then at ≥5 months post-injury (Follow-up). Six separate patients with post-traumatic DoC were scanned ≥5 months post-injury (Chronic DoC Cohort). For each AAN pathway, we computed the median relative change in Acute-to-Follow-up Connectivity Probability (CP) in the Recovery Cohort. We then used Wilcoxon tests with Bonferroni correction to compare CP in each AAN pathway in the Recovery Cohort at Follow-up versus the Chronic DoC Cohort. In an exploratory analysis, we used principal component analysis (PCA) to determine whether linear combinations of AAN CP values could separate the Chronic DoC Cohort from the Recovery Cohort and the healthy controls. ResultsIn the Recovery Cohort, the largest relative AAN CP changes were in the brainstem-to-thalamus (median [IQR] = 0.7 [0.09, 0.9]) and forebrain-to-occipital lobe (−0.8 [−0.9, −0.8]) pathways. The AAN connections that differed in the cross-sectional analysis between the Recovery Cohort at Follow-up and the Chronic DoC Cohort included brainstem-to-hypothalamus (W = 53, PBonf = 0.02), brainstem-to-temporal lobe (W = 52, PBonf = 0.04), and thalamus-to-temporal lobe (W = 54, PBonf = 0.009). Plotting the first two principal components of AAN connectivity resulted in a linear separation of Chronic DoC patients from other study groups. ConclusionsWe provide evidence for a longitudinal increase in brainstem-thalamic connectivity during recovery of consciousness after traumatic coma. Cross-sectional analyses revealed that brainstem-hypothalamus, brainstem-temporal lobe, and thalamus-temporal lobe connectivity differed between patients who recovered consciousness and those with a chronic DoC. These observations provide the basis for further investigation into AAN connectivity as a biomarker for recovery of consciousness after traumatic coma.

An Optimal Security Management Framework for Backhaul-aware 5G-Vehicle to Everything (V2X)

Cellular (C) setups facilitate the connectivity amongst the devices with better provisioning of services to its users. Vehicular networks are one of the representative setups that aim at expanding their functionalities by using the available cellular systems like Long Term Evolution (LTE)-based Evolved Universal Terrestrial Radio Access Network (E-UTRAN) as well as the upcoming Fifth Generation (5G)-based functional architecture. The vehicular networks include Vehicle to Vehicle (V2V), Vehicle to Infrastructure (V2I), Vehicle to Pedestrian (V2P) and Vehicle to Network (V2N), all of which are referred to as Vehicle to Everything (V2X). 5G has dominated the vehicular network and most of the upcoming research is motivated towards the fully functional utilization of 5G-V2X. Despite that, credential management and edge-initiated security are yet to be resolved under 5G-V2X. To further understand the issue, this paper presents security management as a principle of sustainability and key-management. The performance tradeoff is evaluated with the key-updates required to maintain a secure connection between the vehicles and the 5G-terminals. The proposed approach aims at the utilization of high-speed mmWave-based backhaul for enhancing the security operations between the core and the sub-divided functions at the edge of the network through a dual security management framework. The evaluations are conducted using numerical simulations, which help to understand the impact on the sustainability of connections as well as identification of the fail-safe points for secure and fast operations. Furthermore, the evaluations help to follow the multiple tradeoffs of security and performance based on the metrics like mandatory key updates, the range of operations and the probability of connectivity.

Study on Connectivity Probability of Vanets Under Adverse Weather Conditions at 5.9 Ghz

Vehicular ad hoc networks (VANETs) are an important part of the next generation of intelligent transportation. For multimedia information transmissions, VANETs require high speed and a low-delay link between the vehicles. This paper focuses on a connectivity analysis of VANET high-speed and low-delay connections under different traffic densities and adverse weather conditions. In this paper, a channel measurement at 5.9 GHz under two kinds of traffic densities is first carried out. Then, the measured data for the path loss are used in the VANET model for the connectivity probability. Finally, we consider the influence of adverse weather conditions on the wireless signal and simulate the influence on the high-speed and low-delay data connectivity of VANETs. The results show that adverse weather will have a certain impact on vehicle-to-vehicle (V2V) communication.

Wireless Sensor Network Deployment of 3D Surface Based on Enhanced Grey Wolf Optimizer

Aiming at the difficulty of deploying wireless sensor networks (WSNs) on three-dimensional (3D) surfaces, based on the grey wolf optimizer (GWO), an enhanced version of the grey wolf optimizer is proposed for deploying WSNs on 3D surfaces, namely the enhanced grey wolf optimizer (EGWO), which is characterized by enhanced exploitation and exploration ability of the algorithm. The novelty of EGWO is that the grey wolf population is divided into two parts, one part is responsible for the outer-layer encircle and the other is responsible for the inner-layer encircle, and the introduction of Tent mapping. The purpose of this is to enhance the exploitation and exploration ability of the algorithm respectively, so as to improve the convergence and optimization precision of the algorithm. In addition, in terms of WSN deployment in 3D surfaces, this paper improves the means of determining the perceived blind zone. Meanwhile, a novel method to calculate the WSNs coverage area of simple and complex 3D surfaces is presented by combining the grid and integral of the 3D surfaces. The EGWO is favorably compared with the GWO and three existing variants of the grey wolf optimizer when testing on 12 well-known benchmark functions. The simulation experiment results show that compared with the existing algorithms, EGWO can provide a very competitive search result in terms of optimization precision and convergence performance. Finally, this paper applies EGWO to the 3D surface deployment of WSN. Simulations show that compared with the other three deployment algorithms, EGWO can improve the network coverage of WSN, which can save network deployment costs. In addition, the probability of network connectivity deployed by EGWO is higher, that is, EGWO can provide a better deployment solution.

IMPROVING RELIABILITY IN MAS BY RULE BASED LOGIC AND CRYPTOGRAPHIC TECHNIQUES

Mobile agent (MA) is a composition of software paradigm, having the capability to move from one host to another across dynamic network environment and execute task assigned by its user. Reliability is one of the most important issues in mobile agent-based system (MAS) which was addressed by many researchers. In this paper, we enhance the reliability in MAS with the support of intrusion detection system (IDS) and effective routing. Routing is an important process to find optimal path which improves network throughput and reliability. Collision-free (CF) – network graph exploration method is designed for identifying optimal path for MAs. Security is a crucial aspect due to various malicious node activities and must be considered while estimating reliability. In our process, HMAC-SHA1 algorithm is performed for detecting malicious agent and rule-based logic (RBL) is designed to identify malicious host. Further, we calculate reliability of MAS with respect to status of network and its condition which includes link connectivity and malicious node probability. Finally, we are simulating our performance by using various factors such as size of MAS, malicious ratio and number of mobile agents in MAS, etc. These factors are significant to show improved reliability of our proposed system.

Impulsivity Relates to Relative Preservation of Mesolimbic Connectivity in Patients with Parkinson Disease.

The relationship between Parkinson Disease (PD) pathology, dopamine replacement therapy (DRT), and impulse control disorder (ICD) development is still incompletely understood. Given the sensorimotor-lateral substantia nigra (SN) selective degeneration associated with PD, we posit that a relative sparing of the limbic-medial SN in the context of DRT drives impulsive, reward-seeking behavior in PD patients with recent history of severe impulsivity. Impulsive and control participants were selected from a consecutive list of PD patients receiving pre-operative deep brain stimulation (DBS) planning scans including 3T structural MRI and 64 direction diffusion tensor imaging (DTI). Using previously identified substantia nigra (SN) subsegment network connectivity profiles to develop classification targets, split-hemisphere target-based SN segmentation with probabilistic tractography was performed. The relative subsegment volumes and strength of connectivity between the SN and the limbic, associative, and motor network targets were compared. Our results show that there is greater probability of connectivity between the SN and limbic network targets relative to motor and associative network targets in PD patients with recent history of severe impulsivity as compared to PD patients without impulsivity (P=0.0075). We did not observe relative volumetric subsegment differences across groups. Firstly, our results suggest that fine-grained, atlas-derived classification targets may be used in PD to parcellate and classify functionally distinct subsegments of the SN, with the apparent preservation of previously reported topographical limbic-medial SN, associative-ventral SN, and sensorimotor-lateral SN orientation. We suggest that relative, as opposed to absolute, degeneration amongst SN-associated dopaminergic networks relates to the impulsivity phenotype in PD.

Renormalization of Crossing Probabilities in the Planar Random-Cluster Model

The study of crossing probabilities - i.e. probabilities of existence of paths crossing rectangles - has been at the heart of the theory of two-dimensional percolation since its beginning. They may be used to prove a number of results on the model, including speed of mixing, tails of decay of the connectivity probabilities, scaling relations, etc. In this article, we develop a renormalization scheme for crossing probabilities in the two-dimensional random-cluster model. The outcome of the process is a precise description of an alternative between four behaviors: - Subcritical: Crossing probabilities, even with favorable boundary conditions, converge exponentially fast to 0. - Supercritical: Crossing probabilities, even with unfavorable boundary conditions, converge exponentially fast to 1. - Critical discontinuous: Crossing probabilities converge to 0 exponentially fast with unfavorable boundary conditions and to 1 with favorable boundary conditions. - Critical continuous: Crossing probabilities remain bounded away from 0 and 1 uniformly in the boundary conditions. The approach does not rely on self-duality, enabling it to apply in a much larger generality, including the random-cluster model on arbitrary graphs with sufficient symmetry, but also other models like certain random height models.

Joint Energy-Saving Scheduling and Secure Routing for Critical Event Reporting in Wireless Sensor Networks

With the growing concerns about energy saving and security problems in wireless sensor networks (WSNs), we investigated a joint energy saving scheduling and secure routing algorithm for critical event reporting in WSN. When a critical event has been detected, the notification must be safely sent to the sink node through the uplink transmission, and the sink node needs to broadcast the alarm messages to the whole network through the downlink transmission. In the uplink, a joint power allocation and secure routing strategy (JPASR) has been proposed to maximize the routing secure connection probability (RSCP) under the constraint of power. Meanwhile, combined with the level-by-level sleeping scheduling method, the energy-saving and secure uplink transmission can be guaranteed. In the downlink, an energy-first multi-point relays set selection mechanism (EFMSS) is designed to choose the backbone nodes to broadcast messages, and the backbone nodes are waken up by the same level-by-level sleeping scheduling method as the uplink transmission. With the two-step procedure, the critical events are appropriately dealt with and the responses are broadcast to the whole network. Extensive simulations results demonstrate that the energy saving and security performances of the proposed method are superior to the existing ones.

BS-UE Association and Power Allocation in Heterogeneous Massive MIMO Systems

We consider a downlink Heterogeneous Massive Multiple-Input Multiple-Output (HM-MIMO) system with the macro-base station (BS) having hundreds of antennas and each of the micro-BSs having tens of antennas. Two lower bounds and one approximation of the achievable per-user equipment (UE) rate in closed forms under this system are derived and compared in terms of network utility. Using the derived approximation, three BS-UE association approaches are proposed. Firstly, a simple, sub-optimal, and heuristic multiple BS-UE association approach is designed, which achieves around 25% utility performance improvement compared with the conventional maximum received signal strength (Max-RSS) approach. Secondly, based on the results given by this heuristic approach, a learning approach for BS-UE association using convolutional neural network (CNN) is introduced. After being fully trained, the CNN can take any new BS-UE configuration as input and provide a sub-optimal BS-UE association for that configuration directly. It has only a small performance degradation compared with the proposed heuristic approach. Thirdly, realizing that the BS-UE connection probability in the proposed CNN architecture can be considered as a power allocation ratio, a combined power allocation and association approach is proposed. Its performance achieves as high as 60% utility improvement compared with the Max-RSS association and is also comparable to that achieved by the max-min power allocation approach which requires more than $10000\times $ running time. It is remarkable that by using the gradients of the derived achievable per-UE rate approximation with respect to the power control coefficients, accurate target data is in fact not required for training in this approach.

Homophily as a Process Generating Social Networks: Insights from Social Distance Attachment Model

Real-world social networks often exhibit high levels of clustering, positive degree assortativity, short average path lengths (small-world property) and right-skewed but rarely power law degree distributions. On the other hand homophily, defined as the propensity of similar agents to connect to each other, is one of the most fundamental social processes observed in many human and animal societies. In this paper we examine the extent to which homophily is sufficient to produce the typical structural properties of social networks. To do so, we conduct a simulation study based on the Social Distance Attachment (SDA) model, a particular kind of Random Geometric Graph (RGG), in which nodes are embedded in a social space and connection probabilities depend functionally on distances between nodes. We derive the form of the model from first principles based on existing analytical results and argue that the mathematical construction of RGGs corresponds directly to the homophily principle, so they provide a good model for it. We find that homophily, especially when combined with a random edge rewiring, is sufficient to reproduce many of the characteristic features of social networks. Additionally, we devise a hybrid model combining SDA with the configuration model that allows generating homophilic networks with arbitrary degree sequences and we use it to study interactions of homophily with processes imposing constraints on degree distributions. We show that the effects of homophily on clustering are robust with respect to distribution constraints, while degree assortativity can be highly dependent on the particular kind of enforced degree sequence.

The $L^{2}$ boundedness condition in nonamenable percolation

Let $G=(V,E)$ be a connected, locally finite, transitive graph, and consider Bernoulli bond percolation on $G$. In recent work, we conjectured that if $G$ is nonamenable then the matrix of critical connection probabilities $T_{p_{c}}(u,v)=\mathbb {P}_{p_{c}}(u\leftrightarrow v)$ is bounded as an operator $T_{p_{c}}:L^{2}(V)\to L^{2}(V)$ and proved that this conjecture holds for several classes of graphs, including all transitive, nonamenable, Gromov hyperbolic graphs. In notation, the conjecture states that $p_{c}<p_{2\to 2}$, where for each $q\in [1,\infty ]$ we define $p_{q\to q}$ to be the supremal value of $p$ for which the operator norm $\|T_{p}\|_{q\to q}$ is finite. We also noted in that work that the conjecture implies two older conjectures, namely that percolation on transitive nonamenable graphs always has a nontrivial nonuniqueness phase, and that critical percolation on the same class of graphs has mean-field critical behaviour. In this paper we further investigate the consequences of the $L^{2}$ boundedness conjecture. In particular, we prove that the following hold for all transitive graphs: i) The two-point function decays exponentially in the distance for all $p<p_{2\to 2}$; ii) If $p_{c}<p_{2\to 2}$, then the critical exponent governing the extrinsic diameter of a critical cluster is $1$; iii) Below $p_{2\to 2}$, percolation is “ballistic" in the sense that the intrinsic (a.k.a. chemical) distance between two points is exponentially unlikely to be much larger than their extrinsic distance; iv) If $p_{c}<p_{2\to 2}$, then $\|T_{p_{c}}\|_{q\to q} \asymp (q-1)^{-1}$ and $p_{q\to q}-p_{c} \asymp q-1$ as $q\downarrow 1$; v) If $p_{c}<p_{2\to 2}$, then various ‘multiple-arm’ events have probabilities comparable to the upper bound given by the BK inequality. In particular, the probability that the origin is a trifurcation point is of order $(p-p_{c})^{3}$ as $p \downarrow p_{c}$. All of these results are new even in the Gromov hyperbolic case. Finally, we apply these results together with duality arguments to compute the critical exponents governing the geometry of intrinsic geodesics at the uniqueness threshold of percolation in the hyperbolic plane.

Recovery of Structural Controllability into Critical Infrastructures under Malicious Attacks

The problem of controllability of networks can be seen in critical infrastructure systems which are increasingly susceptible to random failures and/or malicious attacks. The ability to recover controllability quickly following an attack can be considered a major problem in control systems. If this is not ensured, it can enable the attacker to create more disrup-tions as well as, like the electric power networks case, violate real-time restrictions and result in the control of the network degrading and its observability reducing significantly. Thus, the present paper examines structural controllability problem that has been in focus through the equivalent problem of the Power Dominating Set (PDS) introduced in the context of electrical power network control. However, the controllability optimisation problem can be seen as computationally infeasible regarding large complex networks because such problems are considered NP-hard and as having low approximability. Hence, the ability of structural controllability recoverability will be explored as per the PDS formulation, especially following perturbations in which an attacker with sufficient knowledge of the network topology is only able to completely violate the current driver control nodes of the original control network leading to a degradation of controllability of dependent nodes. The results highlight that the use of directed Laplacian matrix can be a useful approach for analysing structural controllability of a network. The simulation results show also that an increase of a connectivity probability of the distribution of links in Directed ER networks can minimise the number of driver control nodes which is highly desirable while monitoring the entire network.

TCDS: A Time-Relevant Graph Based Topology Control in Triple-Layer Satellite Networks

In a triple-layer satellite (TLS) network with GEO, MEO and LEO, maintaining connectivity of topology confronts the challenge of intermittent visibility due to periodically orbital motions of nodes. To address this issue, in this letter, we develop a time-relevant graph called as space-time graph (STG) model for depicting the topological structure with fine granularity, by taking into account time-domain and spatial-domain properties. With STG, a Time-evolving Connected Dominating Set (TCDS) algorithm is proposed to construct a backbone network for efficient topology control with high spatial and temporal accessibility of the triple-layer network. The simulation results demonstrate better efficiency of the proposed algorithm with respects to the average hop and connectivity probability, compared with time-evolving multi-layered clustering (TEMC) algorithm and single time-slot clustering (STC) algorithm.

Determination of the optimal spacing of water curtain boreholes for underground oil storage from the perspective of percolation theory

The spacing of water curtain boreholes is important for underground oil storage. It was usually determined using empirical method, in this study, a method for determining the optimal spacing of water curtain boreholes for underground oil storage was developed from the percolation theory of fractured rock masses. The connectivity of fractured rock masses with different fracture densities and geometric parameters was investigated considering two typical flow configurations, i.e., unidirectional and radial flow configurations. The percolation threshold was defined as the critical value with increasing fracture trace length. It was found that the percolation threshold in the unidirectional flow configuration was higher than that in the radial flow configuration. From the perspective of percolation theory, a method was developed for evaluating fracture network connectivity. In this method, the probability of connection of water curtain boreholes was related to a percolation parameter, which depended on the fracture density and trace length. The spacing of water curtain boreholes for the Huangdao underground oil storage facility was determined using the proposed method. The optimal spacing of the water curtain boreholes was validated against the connectivity tests in the field, indicating that the determined spacing was reasonable and that this method can provide guidance for the design of water curtain boreholes for other underground oil storage facilities.

Using landscape connectivity tools to identify conservation priorities in forested areas and potential restoration priorities in rubber plantation in Xishuangbanna, Southwest China

Maintaining connectivity is critical for fragmented habitat networks to retain native species. The tropical forest in Xishuangbanna, Southwest China, is a biodiversity hotspot for China, but is also vulnerable to deforestation due to rapid expansion of rubber plantations, thus better understanding of connectivity may be crucial to species persistence. To quantify the functional connectivity changes in the forest in Xishuangbanna from 1976 to 2014, and identify the conservation and restoration priorities for effective forest conservation and management. Using the graph theory (in Conefor sensinode 2.6), forest connectivity from 1976 to 2014 was quantified using probability of connectivity and number of components indexes. The importance of each forest patch during each period and the potential contribution of low-profit rubber plantation patches in 2014 was quantified and ranked by delta values for PC (dPC) index. Connectivity of forest in Xishuangbanna has progressively decreased over the last 40 years. The ten forest patches which had the highest dPC value remained almost the same for all five periods between 1976 and 2014, though relative importance varied. The 50 most potentially important low-profit rubber plantation patches were identified and mapped, and provide a target for effective restoration efforts to facilitate efficient use of funding to best improve conservation outcomes. Targeted and effective interventions for landscape scale conservation and management can be made based on graph theory and connectivity analysis. Restoring low-profit rubber provides a mechanism for reconnecting the forest as an effective conservation tool. Here we show the application of this approach to restore forest and most effectively increase connectivity at minimum economic cost.

Searching for Networks: Ecological Connectivity for Amphibians Under Climate Change.

Ecological connectivity depends on key elements within the landscape, which can support ecological fluxes, species richness and long-term viability of a biological community. Landscape planning requires clear aims and quantitative approaches to identify which key elements can reinforce the spatial coherence of protected areas design. We aim to explore the probability of the ecological connectivity of forest remnants and amphibian species distributions for current and future climate scenarios across the Central Corridor of the Brazilian Atlantic Forest. Integrating amphibian conservation, climate change and ecological corridors, we design a landscape ranking based on graph and circuit theories. To identify the sensitivity of connected areas to climate-dependent changes, we use the Model for Interdisciplinary Research on Climate by means of simulations for 2080-2100, representing a moderated emission scenario within an optimistic context. Our findings indicate that more than 70% of forest connectivity loss by climate change may drastically reduce amphibian dispersal in this region. We show that high amphibian turnover rates tend to be greater in the north-eastern edges of the corridor across ensembles of forecasts. Our spatial analysis reveals a general pattern of low-conductance areas in landscape surface, yet with some well-connected patches suggesting potential ecological corridors. Atlantic Forest reserves are expected to be less effective in a near future. For improved conservation outcomes, we recommend some landscape paths with low resistance values across space and time. We highlight the importance of maintaining forest remnants in the southern Bahia region by drafting a blueprint for functional biodiversity corridors.