Página 1 dos resultados de 44 itens digitais encontrados em 0.026 segundos

Modelo de acessibilidade para o planejamento espacial de ações em saúde pública: o caso dos programas de vacinação contra a raiva e de esterilização para cães e gatos de Bogotá, Colômbia; Accessibility model for the spatial planning of public health actions: The case of rabies vaccination and sterilization programs for dogs and cats in Bogota, Colombia

Infante, Gina Paola Polo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 01/07/2013 Português
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Este estudo integrou sistemas de informação geográfica e métodos analíticos geoespaciais baseados em modelos de acessibilidade espacial e de locação-alocação com o objetivo de aprimorar o planejamento espacial de diferentes programas de saúde pública em áreas urbanas. Para estimar a acessibilidade espacial foi desenvolvido o modelo de três passos de área de influência flutuante (E3SFCA - Enhancement three-step floating catchment área) baseado em uma função Gaussiana, considerando um coeficiente de atrito e distâncias ao longo de uma rede de transporte, utilizando o algoritmo de Dijkstra. A metodologia foi aplicada e validada usando os programas de vacinação contra a raiva e de esterilização para cães e gatos da cidade de Bogotá, Colômbia. A escolha do método de cálculo da distância resolveu o problema de superestimação associado com a metodologia clássica que aplica zonas buffer em torno dos locais de serviço baseado em uma distância Euclideana. Em geral, não se encontrou uma adequada acessibilidade espacial aos dois programas. As zonas norte, central e periférica da cidade revelaram baixa ou nula acessibilidade aos serviços. Para determinar a alocação e realocação efetiva dos programas foram utilizados os problemas de máxima cobertura com demanda finita e de p-mediana ou de mínima impedância. A realocação proposta pelo modelo de máxima cobertura forneceu uma melhor distribuição dos serviços nas áreas mais povoadas com cães e gatos e garantiu uma acessibilidade espacial potencial a estes programas. O desenvolvimento deste trabalho pode trazer benefícios diretos para a sociedade em geral auxiliando no planejamento estratégico e melhorando a efetividade das ações públicas em áreas urbanas da América Latina.; This study integrated geographic information systems and geospatial analytical methods based on spatial accessibility and location-allocation models in order to improve the spatial planning of different public health programs in urban areas. To estimate the spatial accessibility...

Large discreet resource allocation: a hybrid approach based on dea efficiency measurement

Gomes,Eliane Gonçalves; Mello,João Carlos Correia Baptista Soares de; Meza,Lidia Angulo
Fonte: Sociedade Brasileira de Pesquisa Operacional Publicador: Sociedade Brasileira de Pesquisa Operacional
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 Português
Relevância na Pesquisa
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Resource allocation is one of the traditional Operations Research problems. In this paper we propose a hybrid model for resource allocation that uses Data Envelopment Analysis efficiency measures. We use Zero Sum Gains DEA models as the starting point to decrease the computational work for the step-bystep algorithm to allocate integer resources in a DEA context. Our approach is illustrated by a numerical example.

Large discreet resource allocation: a hybrid approach based on DEA efficiency measurement.

GOMES, E. G.; MELLO, J. C. C. B. S. de; MEZA, L. A.
Fonte: Pesquisa Operacional, v.28, n.3, p. 597-608, set./dez. 2008. Publicador: Pesquisa Operacional, v.28, n.3, p. 597-608, set./dez. 2008.
Tipo: Artigo em periódico indexado (ALICE)
Português
Relevância na Pesquisa
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Resource allocation is one of the traditional Operations Research problems. In this paper we propose a hybrid model for resource allocation that uses Data Envelopment Analysis efficiency measures. We use Zero Sum Gains DEA models as the starting point to decrease the computational work for the step-bystep algorithm to allocate integer resources in a DEA context. Our approach is illustrated by a numerical example.; 2008

Source-channel coding and modulation for wireless image transmissions

Lu, Jin
Fonte: Universidade Rice Publicador: Universidade Rice
Português
Relevância na Pesquisa
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This thesis proposes new algorithms for image transmissions over wireless communication channels. The wireless image transmission is the first step in offering multimedia services over current wireless cellular networks. It is also a challenging problem because a wireless channel usually has a very high bit error rate and sometimes severe fading. The objective of this work is to achieve minimum end-to-end average distortion of the transmitted images. This work subsumes a number of results obtained by other researchers to date. In contrast to the other systems and algorithms, this work obtains a closed form bit allocation algorithm to minimize the average distortion for binary feedforward memoryless channels. This not only greatly reduces the computational expense of bit allocation, but also proves in theory that the optimal bit allocation is none increasing. The results are then extended to binary feedback channels, binary fading channels and power constrained channels. Two approaches from different directions achieve the efficient wireless image transmission. One approach applies joint source and channel coding to protect transmitted image information in given noisy channels. The other reduces the channel raw bit error rate directly by designing good spreading sequences in spreading spectrum systems. The first part of the thesis proposes bit allocation schemes for a variety of binary wireless channels. The so-called progressive transmission system is the main concern since it is very powerful and efficient for highly loaded communication channels. The second part of the thesis investigates the design and implementation of a new class of real-valued spreading sequences for Code Division Multiple Access (CDMA) systems. These new spreading sequences reduce the multiple access interference in multiuser spreading spectrum systems...

Research on Multirobot Pursuit Task Allocation Algorithm Based on Emotional Cooperation Factor

Fang, Baofu; Chen, Lu; Wang, Hao; Dai, Shuanglu; Zhong, Qiubo
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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Multirobot task allocation is a hot issue in the field of robot research. A new emotional model is used with the self-interested robot, which gives a new way to measure self-interested robots' individual cooperative willingness in the problem of multirobot task allocation. Emotional cooperation factor is introduced into self-interested robot; it is updated based on emotional attenuation and external stimuli. Then a multirobot pursuit task allocation algorithm is proposed, which is based on emotional cooperation factor. Combined with the two-step auction algorithm recruiting team leaders and team collaborators, set up pursuit teams, and finally use certain strategies to complete the pursuit task. In order to verify the effectiveness of this algorithm, some comparing experiments have been done with the instantaneous greedy optimal auction algorithm; the results of experiments show that the total pursuit time and total team revenue can be optimized by using this algorithm.

Asset Allocation under the Basel Accord Risk Measures

Wen, Zaiwen; Peng, Xianhua; Liu, Xin; Sun, Xiaoling; Bai, Xiaodi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/08/2013 Português
Relevância na Pesquisa
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Financial institutions are currently required to meet more stringent capital requirements than they were before the recent financial crisis; in particular, the capital requirement for a large bank's trading book under the Basel 2.5 Accord more than doubles that under the Basel II Accord. The significant increase in capital requirements renders it necessary for banks to take into account the constraint of capital requirement when they make asset allocation decisions. In this paper, we propose a new asset allocation model that incorporates the regulatory capital requirements under both the Basel 2.5 Accord, which is currently in effect, and the Basel III Accord, which was recently proposed and is currently under discussion. We propose an unified algorithm based on the alternating direction augmented Lagrangian method to solve the model; we also establish the first-order optimality of the limit points of the sequence generated by the algorithm under some mild conditions. The algorithm is simple and easy to implement; each step of the algorithm consists of solving convex quadratic programming or one-dimensional subproblems. Numerical experiments on simulated and real market data show that the algorithm compares favorably with other existing methods...

Dynamic Bit Allocation for Object Tracking in Bandwidth Limited Sensor Networks

Masazade, Engin; Niu, Ruixin; Varshney, Pramod K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/10/2011 Português
Relevância na Pesquisa
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In this paper, we study the target tracking problem in wireless sensor networks (WSNs) using quantized sensor measurements under limited bandwidth availability. At each time step of tracking, the available bandwidth $R$ needs to be distributed among the $N$ sensors in the WSN for the next time step. The optimal solution for the bandwidth allocation problem can be obtained by using a combinatorial search which may become computationally prohibitive for large $N$ and $R$. Therefore, we develop two new computationally efficient suboptimal bandwidth distribution algorithms which are based on convex relaxation and approximate dynamic programming (A-DP). We compare the mean squared error (MSE) and computational complexity performances of convex relaxation and A-DP with other existing suboptimal bandwidth distribution schemes based on generalized Breiman, Friedman, Olshen, and Stone (GBFOS) algorithm and greedy search. Simulation results show that, A-DP, convex optimization and GBFOS yield similar MSE performance, which is very close to that based on the optimal exhaustive search approach and they outperform greedy search and nearest neighbor based bandwidth allocation approaches significantly. Computationally, A-DP is more efficient than the bandwidth allocation schemes based on convex relaxation and GBFOS...

Scheduling and allocation algorithm for an elliptic filter

Marikkannan, Sangeetha
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/02/2012 Português
Relevância na Pesquisa
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A new evolutionary algorithm for scheduling and allocation algorithm is developed for an elliptic filter. The elliptic filter is scheduled and allocated in the proposed work which is then compared with the different scheduling algorithms like As Soon As Possible algorithm, As Late As Possible algorithm, Mobility Based Shift algorithm, FDLS, FDS and MOGS. In this paper execution time and resource utilization is calculated using different scheduling algorithm for an Elliptic Filter and reported that proposed Scheduling and Allocation increases the speed of operation by reducing the control step. The proposed work to analyse the magnitude, phase and noise responses for different scheduling algorithm in an elliptic filter.; Comment: 12 pages

Joint User-Association and Resource-Allocation in Virtualized Wireless Networks

Parsaeefard, Saeedeh; Dawadi, Rajesh; Derakhshani, Mahsa; Le-Ngoc, Tho
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/08/2015 Português
Relevância na Pesquisa
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In this paper, we consider a down-link transmission of multicell virtualized wireless networks (VWNs) where users of different service providers (slices) within a specific region are served by a set of base stations (BSs) through orthogonal frequency division multiple access (OFDMA). In particular, we develop a joint BS assignment, sub-carrier and power allocation algorithm to maximize the network throughput, while satisfying the minimum required rate of each slice. Under the assumption that each user at each transmission instance can connect to no more than one BS, we introduce the user-association factor (UAF) to represent the joint sub-carrier and BS assignment as the optimization variable vector in the mathematical problem formulation. Sub-carrier reuse is allowed in different cells, but not within one cell. As the proposed optimization problem is inherently non-convex and NP-hard, by applying the successive convex approximation (SCA) and complementary geometric programming (CGP), we develop an efficient two-step iterative approach with low computational complexity to solve the proposed problem. For a given power-allocation, Step 1 derives the optimum userassociation and subsequently, for an obtained user-association, Step 2 find the optimum power-allocation. Simulation results demonstrate that the proposed iterative algorithm outperforms the traditional approach in which each user is assigned to the BS with the largest average value of signal strength...

An NBDMMM Algorithm Based Framework for Allocation of Resources in Cloud

Alam, Mansaf; Shakil, Kashish Ara
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/12/2014 Português
Relevância na Pesquisa
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Cloud computing is a technological advancement in the arena of computing and has taken the utility vision of computing a step further by providing computing resources such as network, storage, compute capacity and servers, as a service via an internet connection. These services are provided to the users in a pay per use manner subjected to the amount of usage of these resources by the cloud users. Since the usage of these resources is done in an elastic manner thus an on demand provisioning of these resources is the driving force behind the entire cloud computing infrastructure therefore the maintenance of these resources is a decisive task that must be taken into account. Eventually, infrastructure level performance monitoring and enhancement is also important. This paper proposes a framework for allocation of resources in a cloud based environment thereby leading to an infrastructure level enhancement of performance in a cloud environment. The framework is divided into four stages Stage 1: Cloud service provider monitors the infrastructure level pattern of usage of resources and behavior of the cloud users. Stage 2: Report the monitoring activities about the usage to cloud service providers. Stage 3: Apply proposed Network Bandwidth Dependent DMMM algorithm .Stage 4: Allocate resources or provide services to cloud users...

Variance Based Algorithm for Grouped-Subcarrier Allocation in OFDMA Wireless Systems

Hamdi, Noureddine
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/07/2012 Português
Relevância na Pesquisa
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In this paper, a reduced complexity algorithm is proposed for grouped-subcarriers and power allocation in the downlink of OFDMA packet access wireless systems. The available subcarriers for data communication are grouped into partitions (groups) where each group is defined as a subchannel. The scheduler located at the base station allocates subchannels to users based on the variance of subchannel gains. The proposed algorithm for group allocation is a two-step algorithm that allocates groups to users based on the descending order of their variances to resolve the conflicting selection problem, followed by a step of fairness proportionality enhancement. To reduce the feedback burden and the complexity of the power allocation algorithm, each user feeds back the CSI on each group if the variance of gains of subcarriers inside it is less than a predefined threshold. To Show the performance of the proposed scheme, a selection of simulation results is presented.; Comment: 5 pages, 6 Figures

A Regularized Saddle-Point Algorithm for Networked Optimization with Resource Allocation Constraints

Simonetto, Andrea; Keviczky, Tamas; Johansson, Mikael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/08/2012 Português
Relevância na Pesquisa
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We propose a regularized saddle-point algorithm for convex networked optimization problems with resource allocation constraints. Standard distributed gradient methods suffer from slow convergence and require excessive communication when applied to problems of this type. Our approach offers an alternative way to address these problems, and ensures that each iterative update step satisfies the resource allocation constraints. We derive step-size conditions under which the distributed algorithm converges geometrically to the regularized optimal value, and show how these conditions are affected by the underlying network topology. We illustrate our method on a robotic network application example where a group of mobile agents strive to maintain a moving target in the barycenter of their positions.; Comment: This is an extended version of a paper accepted for CDC 2012 with identical title

Correlation-aware Resource Allocation in Multi-Cell Networks

Bandari, Dorna; Pottie, Gregory; Frossard, Pascal
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/12/2011 Português
Relevância na Pesquisa
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We propose a cross-layer strategy for resource allocation between spatially correlated sources in the uplink of multi-cell FDMA networks. Our objective is to find the optimum power and channel to sources, in order to minimize the maximum distortion achieved by any source in the network. Given that the network is multi-cell, the inter-cell interference must also be taken into consideration. This resource allocation problem is NP-hard and the optimal solution can only be found by exhaustive search over the entire solution space, which is not computationally feasible. We propose a three step method to be performed separately by the scheduler in each cell, which finds cross-layer resource allocation in simple steps. The three- step algorithm separates the problem into inter-cell resource management, grouping of sources for joint decoding, and intra- cell channel assignment. For each of the steps we propose allocation methods that satisfy different design constraints. In the simulations we compare methods for each step of the algorithm. We also demonstrate the overall gain of using correlation-aware resource allocation for a typical multi-cell network of Gaussian sources. We show that, while using correlation in compression and joint decoding can achieve 25% loss in distortion over independent decoding...

Parallel machine scheduling with step deteriorating jobs and setup times by a hybrid discrete cuckoo search algorithm

Guo, Peng; Cheng, Wenming; Wang, Yi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/09/2013 Português
Relevância na Pesquisa
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This article considers the parallel machine scheduling problem with step-deteriorating jobs and sequence-dependent setup times. The objective is to minimize the total tardiness by determining the allocation and sequence of jobs on identical parallel machines. In this problem, the processing time of each job is a step function dependent upon its starting time. An individual extended time is penalized when the starting time of a job is later than a specific deterioration date. The possibility of deterioration of a job makes the parallel machine scheduling problem more challenging than ordinary ones. A mixed integer programming model for the optimal solution is derived. Due to its NP-hard nature, a hybrid discrete cuckoo search algorithm is proposed to solve this problem. In order to generate a good initial swarm, a modified heuristic named the MBHG is incorporated into the initialization of population. Several discrete operators are proposed in the random walk of L\'{e}vy Flights and the crossover search. Moreover, a local search procedure based on variable neighborhood descent is integrated into the algorithm as a hybrid strategy in order to improve the quality of elite solutions. Computational experiments are executed on two sets of randomly generated test instances. The results show that the proposed hybrid algorithm can yield better solutions in comparison with the commercial solver CPLEX with one hour time limit...

On Optimum Power Allocation for the V-BLAST

Kostina, Victoria; Loyka, Sergey
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/05/2007 Português
Relevância na Pesquisa
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A unified analytical framework for optimum power allocation in the unordered V-BLAST algorithm and its comparative performance analysis are presented. Compact closed-form approximations for the optimum power allocation are derived, based on average total and block error rates. The choice of the criterion has little impact on the power allocation and, overall, the optimum strategy is to allocate more power to lower step transmitters and less to higher ones. High-SNR approximations for optimized average block and total error rates are given. The SNR gain of optimization is rigorously defined and studied using analytical tools, including lower and upper bounds, high and low SNR approximations. The gain is upper bounded by the number of transmitters, for any modulation format and type of fading channel. While the average optimization is less complex than the instantaneous one, its performance is almost as good at high SNR. A measure of robustness of the optimized algorithm is introduced and evaluated. The optimized algorithm is shown to be robust to perturbations in individual and total transmit powers. Based on the algorithm robustness, a pre-set power allocation is suggested as a low-complexity alternative to the other optimization strategies...

Distributed Power Allocation for Coordinated Multipoint Transmissions in Distributed Antenna Systems

Zhang, Xiujun; Sun, Yin; Chen, Xiang; Zhou, Shidong; Wang, Jing; Shroff, Ness B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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This paper investigates the distributed power allocation problem for coordinated multipoint (CoMP) transmissions in distributed antenna systems (DAS). Traditional duality based optimization techniques cannot be directly applied to this problem, because the non-strict concavity of the CoMP transmission's achievable rate with respect to the transmission power induces that the local power allocation subproblems have non-unique optimum solutions. We propose a distributed power allocation algorithm to resolve this non-strict concavity difficulty. This algorithm only requires local information exchange among neighboring base stations serving the same user, and is thus scalable as the network size grows. The step-size parameters of this algorithm are determined by only local user access relationship (i.e., the number of users served by each antenna), but do not rely on channel coefficients. Therefore, the convergence speed of this algorithm is quite robust to different channel fading coefficients. We rigorously prove that this algorithm converges to an optimum solution of the power allocation problem. Simulation results are presented to demonstrate the effectiveness of the proposed power allocation algorithm.; Comment: 11 pages, accepted by IEEE Transactions on Wireless Communications

WSR Maximized Resource Allocation in Multiple DF Relays Aided OFDMA Downlink Transmission

Wang, Tao; Vandendorpe, Luc
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.605706%
This paper considers the weighted sum rate (WSR) maximized resource allocation (RA) constrained by a system sum power in an orthogonal frequency division multiple access (OFDMA) downlink transmission system assisted by multiple decode-and-forward (DF) relays. In particular, multiple relays may cooperate with the source for every relay-aided transmission. A two-step algorithm is proposed to find the globally optimum RA. In the first step, the optimum source/relay power and assisting relays that maximize the rate is found for every combination of subcarrier and destination, assuming a sum power is allocated to the transmission at that subcarrier to that destination in the relay-aided transmission mode and the direct mode, respectively. In the second step, a convex-optimization based algorithm is designed to find the globally optimum assignment of destination, transmission mode, and sum power for each subcarrier to maximize the WSR. Combining the RAs found in the two steps, the globally optimum RA can be found. In addition, we show that the optimum RA in the second step can readily be derived when the system sum power is very high. The effectiveness of the proposed algorithm is illustrated by numerical experiments.; Comment: 13 pages and 14 figures...

Energy Harvesting for Physical-Layer Security in OFDMA Networks

Zhang, Meng; Liu, Yuan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/09/2015 Português
Relevância na Pesquisa
28.673242%
In this paper, we study the simultaneous wireless information and power transfer (SWIPT) in downlink multiuser orthogonal frequency-division multiple access (OFDMA) systems, where each user applies power splitting scheme to coordinate the energy harvesting and secrecy information decoding processes. Assuming equal power allocation across subcarriers, we formulate the problem to maximize the aggregate harvested power of all users while satisfying secrecy rate requirement of individual user by joint subcarrier allocation and optimal power splitting ratio selection. Due to the NP-hardness of the problem, we propose two suboptimal algorithms to solve the problem in the dual domain. The first one is an iterative algorithm that optimizes subcarrier allocation and power splitting in an alternating way. The second algorithm is based on a two-step approach that solves the subcarrier allocation and power splitting sequentially. The numerical results show that the proposed methods outperform conventional methods. It is also shown that the iterative algorithm performs close to the upper bound and the step-wise algorithm provides good tradeoffs between performance and complexity.; Comment: to appear in IEEE Trans. Inf. Foren. Sec. arXiv admin note: text overlap with arXiv:1409.3635

On Optimum Power Allocation for the V-BLAST

Kostina, Victoria; Loyka, Sergey
Fonte: IEEE Publicador: IEEE
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /07/2008 Português
Relevância na Pesquisa
28.503474%
A unified analytical framework for optimum power allocation in the unordered V-BLAST algorithm and its comparative performance analysis are presented. Compact closed-form approximations for the optimum power allocation are derived, based on average total and block error rates. The choice of the criterion has little impact on the power allocation and, overall, the optimum strategy is to allocate more power to lower step transmitters and less to higher ones. High-SNR approximations for optimized average block and total error rates are given. The SNR gain of optimization is rigorously defined and studied using analytical tools, including lower and upper bounds, high and low SNR approximations. The gain is upper bounded by the number of transmit antennas, for any modulation format and type of fading channel. While the average optimization is less complex than the instantaneous one, its performance is almost as good at high SNR. A measure of robustness of the optimized algorithm is introduced and evaluated. The optimized algorithm is shown to be robust to perturbations in individual and total transmit powers. Based on the algorithm robustness, a pre-set power allocation is suggested as a low-complexity alternative to the other optimization strategies...

DESPOT, a process-based tree growth model that allocates carbon to maximize carbon gain

Buckley, Thomas; Roberts, David W
Fonte: Heron Publishing Publicador: Heron Publishing
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.112654%
We present a new model of tree growth, DESPOT (Deducing Emergent Structure and Physiology Of Trees), in which carbon (C) allocation is adjusted in each time step to maximize whole-tree net C gain in the next time step. Carbon gain, respiration and the acquisition and transport of substitutable photosynthetic resources (nitrogen, water and light) are modeled on a process basis. The current form of DESPOT simulates a uniform, monospecific, self-thinning stand. This paper describes DESPOT and its general behavior in comparison to published data, and presents an evaluation of the sensitivity of its qualitative predictions by Monte Carlo parameter sensitivity analysis. DESPOT predicts determinate height growth and steady stand-level net primary productivity (NPP), but slow declines in aboveground NPP and leaf area index. Monte Carlo analysis, wherein the model was run repeatedly with randomly different parameter sets, revealed that many parameter sets do not lead to sustainable NPP. Of those that do lead to sustainable growth, the ratios at maturity of net to gross primary productivity and of leaf area to sapwood area are highly conserved.