Deployment of cellular networks involves substantial capital investment. Competition motivates service providers to minimize these costs while maintaining service quality. We develop a cost-minimizing planning model that simultaneously determines three important variables – base station location, power level and frequency group assignments for the antennas at each selected base station. It can represent different antenna configurations and frequency groups commonly used in practice. The integer-programming problem is solved using a Lagrangian relaxation based heuristic and computational tests indicate good solution quality for reasonably large problems. We also note the appropriate role of such optimization models in the overall planning process. 相似文献
Recognition of preconflict situations has a powerful potential for early warning of violent political conflicts. This paper
focuses on the design and application of artificial neural networks as classifiers of preconflict situations. Achieving a
desired level of performance of the neural network relies on the appropriate construction of recognition space (selection
of indicators) and the choice of network architecture. A fast and effective method for the design of reliable neural recognition
systems is described. It is based on genetic algorithm techniques and optimizes both the configuration of input space and
the network parameters. The implementation of the methodology provides for increased performance of the classifier in terms
of accuracy, generalization capacity, computational and data requirements.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
Modern communication networks evolve towards integration of guaranteed-performance and best-effort service types. The coexistence
of these two service types offers substantial benefits, such as resource sharing between service classes, and the ability
of the user to select an appropriate service class according to its individual requirements and preferences. Notwithstanding,
such interaction gives rise to more complicated system behavior and related performance issues, which need to be explored
and understood in order to allow efficient network operation. In this paper we examine potential congestion phenomena, which
arise due to the combined effect of bandwidth sharing and user migration between service classes. We propose a simplified
fluid model for session flow, consisting of two coupled queues with state-dependent flows, which captures the essential ingredients
of service-class interaction. Our analysis shows that the system might exhibit bistable behavior, in the sense that transient
congestion may stir the system from a stable and efficient operating point to an inefficient and congested one. We identify
conditions which give rise to bistability, and propose a call admission control scheme which prevents the system from getting
trapped in a congested-type equilibrium, while not interfering with normal system operation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
Summary: A facile and organic‐solvent‐free method for preparing thermoprocessable multiwalled carbon nanotube (MWCNT)‐filled thermoplastics is presented. MWCNTs are oxidized, neutralized, and then assembled with cationic soap‐free poly(methyl methacrylate) (PMMA) particles directly in water. The spontaneous electrostatic coupling between the negatively charged MWCNTs and positively charged PMMA particles, and the viscoelastic and thermomechanical behavior of the nanocomposites, are investigated. The electrostatic coupling interactions improve the dispersion of nanotubes and facilitate the formation of filler networks in the polymer matrix.
Preparation of nanocomposites of oxidized MWCNTs and positively charged PMMA particles through electrostatic assembly. 相似文献
Summary: Coexisting bicontinuous morphologies, one ordered and one disordered, are investigated in a macrophase‐separated poly(styrene‐block‐isoprene) diblock copolymer/homopolystyrene (SI/hS) blend. Two‐phase behavior is attributed to the relatively high hS/S mass ratio (0.92). According to its crystallographic signature and channel coordination as discerned from three‐dimensional (3D) images generated by transmission electron microtomography (TEMT), the ordered morphology is classified as gyroid. The 3D local and global topological characteristics of both bicontinuous morphologies as measured directly from TEMT images are reported. The disordered morphology is further compared with molecular‐field simulations to ascertain the spatial distribution of the constituent species within the blend, thereby demonstrating the utility of high‐resolution 3D imaging coupled with molecular‐level simulations.
This paper studies a simple asymmetrically evolved community
network with a combination of preferential attachment and random
properties. An important issue about community networks is to
discover the different utility increments of two nodes, where the
utility is introduced to investigate the asymmetrical effect of
connecting two nodes. On the other hand, the connection of two nodes
in community networks can be classified as two nodes belonging to the
same or to different communities. The simulation results show that the
model can reproduce a power-law utility distribution P(u)~u-σ, σ = 2 + 1/p, which can be obtained by
using mean-field approximation methods. Furthermore, the model
exhibits exponential behaviour with respect to small values of a
parameter denoting the random effect in our model at the low-utility
region and a power-law feature with respect to big values of this
parameter at the high-utility region, which is in good agreement with
theoretical analysis. This kind of community network can reproduce
a unique utility distribution by theoretical and numerical analysis. 相似文献
This paper is concerned with the problem of robust stability for a
class of Markovian jumping stochastic neural networks (MJSNNs)
subject to mode-dependent time-varying interval delay and
state-multiplicative noise. Based on the Lyapunov--Krasovskii functional
and a stochastic analysis approach, some new delay-dependent
sufficient conditions are obtained in the linear matrix inequality
(LMI) format such that delayed MJSNNs are globally asymptotically
stable in the mean-square sense for all admissible uncertainties. An
important feature of the results is that the stability criteria are
dependent on not only the lower bound and upper bound of delay for all
modes but also the covariance matrix consisting of the correlation
coefficient. Numerical examples are given to illustrate the
effectiveness. 相似文献
Summary: Nanocomposite gels (NC gels) consisting of poly(N-alkylacrylamides) and exfoliated inorganic clay were prepared by in-situ, free-radical polymerization at high yield under mild conditions (near ambient temperature, without stirring). Various shapes and different surface forms of NC gels were readily obtained using corresponding vessels and templates, since NC gels were always mechanically tough. The view that polymer/clay networks are formed in NC gels was supported by dynamic viscoelastic and swelling measurements. The entirely different mechanical properties of NC gels, compared with conventional, chemically-crosslinked hydrogels (OR gels), are discussed on the basis of their network structure. In addition to functions previously reported, NC gels exhibit further interesting characteristics, such as inherent incombustibility, good thermal conductivity, large heat capacity, they can be readily colored and fabricated as foams. NC gels can be utilized as environmentally-friendly, soft materials from the viewpoints of resources and waste, as their primary component is water. 相似文献