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1.
提出一种新的流行病传播模型,基于平均场理论,研究传染媒介和传播延迟同时存在对网络中流行病传播行为的影响.理论分析和仿真结果表明,传染媒介和传播延迟同时存在显著增强了网络中流行病爆发的危险性,并加速了流行病的传播.研究还发现,对于给定的有效传播率,均匀网络中流行病的感染程度分别与传染媒介的传染概率和传播延迟呈对数关系,无标度网络中流行病的感染程度与传染媒介的传染概率呈幂率关系,而与传播延迟之间则存在线性关系. 相似文献
2.
1 .IntroductionWiththedevelopmentofoceantechnology ,moreandmoreextremelylargeandlongflexibleoff shoreplatformsusedforoilexplorationanddrillingoperationarebuiltinhostileoceanenvironments .Ingeneral,thiskindofplatformsisanonlineardistributedparametersystemanditsnaturalfrequencyfallsclosertothedominantwavefrequencieswiththeincreaseofwaterdepth .Besides ,itsstructureisverycomplexandtheexternalwaveforceontheplatformisuncertain .Thus ,theseplatformsarepronetoexcessivewave inducedoscillationsunderbot… 相似文献
3.
运用复杂网络理论的分析方法,在世界海运船期数据的基础上,构建海洋货运网络。通过拓扑结构分析,描述了网络的空间格局,并采用k-core算法对网络进行分层,提出使用最大连通规模的相对大小及网络效率的相对大小衡量该类网络抗毁性,并提出以整体网络及分层后的多层网络进行随机攻击的方式,分析该网络的抗毁性,结果表明:海洋货运网络具有小世界效应,网络密集且度分布近似幂律分布,符合复杂网络的基本特征。网络对于随机出现的各类海洋灾害所造成的网络损毁具有很强的抗毁性,网络中节点损毁数量为影响网络规模及效率的主要因素,一般性攻击对于网络造成的影响集中于网络效率的下降,关键性节点损毁对于网络整体的运输情况影响不明显。 相似文献
4.
For microearthquake surveys conducted with small networks in regions where the seismic velocity structure has large vertical gradients, the formal errors accompanying hypocentral solutions obtained by a generalized inverse method may be misleading since they do not incorporate the effects of nonlinearity in travel times. An alternative method for estimating uncertainties involves calculating travel time residuals over a regular grid and using the F statistic to contour confidence volumes. We present a statistical expression for the latter confidence limits that is applicable when an independent estimate of arrival time errors is available from observations accumulated for a number of earthquakes. Synthetic experiments comparing the results of the grid search and generalized inverse methods show that in cases where solutions are obtained either without S wave information or for epicenters which lie well outside the network, the effects of nonlinearity on the shape of the confidence regions may be significant. However, for the well-observed events both methods yield comparable confidence volumes in good agreement with the distribution of hypocenters obtained from repeated locations incorporating random errors. The generalized inverse method has the advantage that it requires fewer calculations, so the examination of systematic errors in hypocentral parameters produced by uncertainties in the seismic velocity structure can be studied in a more computationally efficient manner. Except in the cases of poorly resolved earthquakes, the effects of nonlinearity on uncertainties in hypocentral parameters can be observed by the application of the F statistic to the variation of the generalized inverse travel time residuals with focal depth. 相似文献
5.
ARP协议设计使之易受到ARP缓存污染的攻击。ARP缓存污染又衍生出中间人攻击等各种网络安全问题。现有的解决方案多种多样但各有优缺点。本文基于ARP缓存污染攻击规律,利用动态IP-MAC绑定算法配合交换机ARP检查功能,设计了1种适用于大型网络的、灵活易部署的ARP缓存污染解决方案。实验证明了解决方案的有效性。 相似文献
6.
The height of a wave at the time of its breaking, as well as the depth of water in which it breaks, are the two basic parameters that are required as input in design exercises involving wave breaking. Currently the designers obtain these values with the help of graphical procedures and empirical equations. An alternative to this in the form of a neural network is presented in this paper. The networks were trained by combining the existing deterministic relations with a random component. The trained network was validated with the help of fresh laboratory observations. The validation results confirmed usefulness of the neural network approach for this application. The predicted breaking height and water depth were more accurate than those obtained traditionally through empirical schemes. Introduction of a random component in network training was found to yield better forecasts in some validation cases. 相似文献
7.
在2—D不变性矩快速计算的基础上，利用人工神经网络，使用不变性矩完成2—D形状的识别。实验结果与现有文献的结果比较，本文采用的方法具有特征数目少、意义统一、识别快速、准确的特点。 相似文献
8.
In this paper, we study the synchronization between different motifs. First, the synchronization between two networks with different topology structures and different dynamical behaviours is studied. With the open-plus-closed-loop(OPCL) method, conditions for two different networks to realize synchronization are given. Then based on the theoretical results achieved, the synchronization between different motifs is studied, which verifies the effectiveness and feasibility of the synchronization scheme. 相似文献
9.
Accessible high-quality observation datasets and proper modeling process are critically required to accurately predict sea level rise in coastal areas. This study focuses on developing and validating a combined least squares-neural network approach applicable to the short-term prediction of sea level variations in the Yellow Sea, where the periodic terms and linear trend of sea level change are fitted and extrapolated using the least squares model, while the prediction of the residual terms is performed by several different types of artificial neural networks. The input and output data used are the sea level anomalies (SLA) time series in the Yellow Sea from 1993 to 2016 derived from ERS-1/2, Topex/Poseidon, Jason-1/2, and Envisat satellite altimetry missions. Tests of different neural network architectures and learning algorithms are performed to assess their applicability for predicting the residuals of SLA time series. Different neural networks satisfactorily provide reliable results and the root mean square errors of the predictions from the proposed combined approach are less than 2?cm and correlation coefficients between the observed and predicted SLA are up to 0.87. Results prove the reliability of the combined least squares-neural network approach on the short-term prediction of sea level variability close to the coast. 相似文献
10.
This paper considers the global stability of controlling an uncertain complex network to a homogeneous trajectory of the uncoupled system by a local pinning control strategy. Several sufficient conditions are derived to guarantee the network synchronisation by investigating the relationship among pinning synchronisation, network topology, and coupling strength. Also, some fundamental and yet challenging problems in the pinning control of complex networks are discussed: (1) what nodes should be selected as pinned candidates? (2) How many nodes are needed to be pinned for a fixed coupling strength? Furthermore, an adaptive pinning control scheme is developed. In order to achieve synchronisation of an uncertain complex network, the adaptive tuning strategy of either the coupling strength or the control gain is utilised. As an illustrative example, a network with the Lorenz system as node self-dynamics is simulated to verify the efficacy of theoretical results. 相似文献
11.
The paper considers the random phase errors in the phase shifters which are used in an antenna array to steer the beam in the look direction, and analyzes the effect of these errors on the performance of the optimal processor which maximizes the output SNR by deriving the expressions for the output signal power, residual interference power, output SNR, and the array gain as a function of the variance of these errors. The paper also considers the phase quantization error which arises in the digital phase shifters and shows how the performance of the optimal processor depends on the number of bits of the digital phase shifters. 相似文献
12.
The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field. 相似文献
13.
An approach based on artificial neural network (ANN) is used to develop predictive relations between hydrodynamic inline force on a vertical cylinder and some effective parameters. The data used to calibrate and validate the ANN models are obtained from an experiment. Multilayer feed-forward neural networks that are trained with the back-propagation algorithm are constructed by use of three design parameters (i.e. wave surface height, horizontal and vertical velocities) as network inputs and the ultimate inline force as the only output. A sensitivity analysis is conducted on the ANN models to investigate the generalization ability (robustness) of the developed models, and predictions from the ANN models are compared to those obtained from Morison equation which is usually used to determine inline force as a computational method. With the existing data, it is found that least square method (LSM) gives less error in determining drag and inertia coefficients of Morison equation. With regard to the predicted results agreeing with calculations achieved from Morison equation that used LSM method, neural network has high efficiency considering its convenience, simplicity and promptitude. The outcome of this study can contribute to reducing the errors in predicting hydrodynamic inline force by use of ANN and to improve the reliability of that in comparison with the more practical state of Morison equation. Therefore, this method can be applied to relevant engineering projects with satisfactory results. 相似文献
14.
The feasibility of adding an interferometric swath bathymetric system to GLORIA, a 6.6 kHz long-range sidescan sonar, is discussed. The size of GLORIA's low-frequency transducer arrays and towfish precludes significant modifications, but even without such changes bathymetric errors could be several tens of metres over a usable swath somewhat smaller than the normal GLORIA swath. A swath bathymetry based on GLORIA will have random errors depending strongly on wind speed, water depth, and swath width. Within the range of these parameters, root-mean-square bathymetry errors in the range of 1-100 m can be expected 相似文献
15.
The essentially random motion of the towfish in a side scan sonar system limits the fidelity of the resultant image. Although corrective techniques have been developed to deal with the gross departures from a set of regular amplitude versus range samples along a straight locus as well as the gross rotational errors, sub-wavelength displacement errors are mostly ignored. This paper suggests a technique to estimate the appropriate displacement errors from the statistics of the measured data when there are few or no strong scatterers on an otherwise featureless sea floor. As it happens, the proposed technique is somewhat similar to an existing optical technique but is new to underwater sonar. We show in a series of simulated trials that it is possible to estimate the resultant sub-wavelength horizontal departure from a straight locus under some (hopefully) realistic operating conditions 相似文献
16.
网络拓扑发现是现代网络管理中1项重要研究课题,作者在已有算法的基础上,进行改进,提出了1种更加完备,高效的网络拓扑算法,并对其进行详细的描述。将算法应用到实际的网络拓扑发现中,收到良好效果。 相似文献
17.
研究分析无线移动Ad-hoc网络中动态源路由协议(DSR,Dynamic Source Routing)面临的多种安全威胁,在分析比较经典DSR安全协议SRP与Ariadne的优势和缺陷的基础上,重点讨论SDSR、SRDP等协议对于DSR安全的优化与改善,分析基于身份和门限的密码体系构建完善安全DSR路由协议的研究方向。 相似文献
18.
Forecasting ocean wave energy: Tests of time-series models 总被引：1，自引：0，他引：1
Gordon Reikard 《Ocean Engineering》2009,36(5):348-356
This paper evaluates the ability of time-series models to predict the energy from ocean waves. Data sets from four Pacific Ocean sites are analyzed. The energy flux is found to exhibit nonlinear variability. The probability distribution has heavy tails, while the fractal dimension is non-integer. This argues for using nonlinear models. The primary technique used here is a time-varying parameter regression in logs. The time-varying regression is estimated using both a Kalman filter and a sliding window, with various window widths. The sliding window method is found to be preferable. A second approach is to combine neural networks with time-varying regressions, in a hybrid model. Both of these methods are tested on the flux itself. Time-varying regressions are also used to forecast the wave height and wave period separately, and combine the forecasts to predict the flux. Forecasting experiments are run at an hourly frequency over horizons of 1-4 h, and at a daily frequency over 1-3 days. All the models are found to improve relative to a random walk. In the hourly data sets, forecasting the components separately achieves the best results in three out of four cases. In daily data sets, the hybrid and regression models yield similar outcomes. Because of the intrinsic variability of the data, the forecast error is fairly high, comparable to the errors found in other forms of alternative energy, such as wind and solar. 相似文献
19.
一种改进海面风速反演的分类神经网络方法 总被引：1，自引：0，他引：1
为了提高使用SSM/I资料反演全球海面风速的精度,发展了一个新型的神经网络方法.在这个方法中,使用高风速、中、低风速状态和天气状态分类的方法分别训练神经网络,然后根据其类别的不同使用不同的神经网络计算风速.此方法较好地去除了由于高风速和云天天气状态下训练样本数据的缺少所产生的误差,改进了在高风速状态下反演风速值比实际风速偏低的情况,使得反演的高风速值被校正到了正常位置.本方法反演海面风速的值与浮标实测风速值之间的均方根误差达到1.60m/s. 相似文献
