Selection of Maize Genotypes Resistant to Pink Stem Borer and Sugarcane Borer

Maize is an important economic crop grown in Nigeria. Its production is dramatically affect by the pink stem borer--Sesamia caIamistis （Hampson, Noctuidae） and sugarcane borer--Eldana saccharina （Walker, Pyralidae） that are endemic in Southeastern Nigeria. In areas of stress, existing genotypes may marginally do well due to their inherent capabilities. Therefore, it is possible to find useful genes in such areas of stress, since such genes have been responsible for the survival of host crops over the years. Evaluation study was conducted for a range of agronomic characteristics and resistance attributes for 209 local maize collections from Southeastern Nigeria along with three improved check varieties. Field trials were conducted at three locations in a total of four environments in 2001. Highly significant genotypic variances as were noted in all the traits, are indicative of the magnitude of variation that exists among the genotypes, thus providing the opportunity of selection for desirable traits. Furthermore, four traits, namely, leaf feeding, ear damage, stalk lodging and yield were used from across the environments to construct a rank summation index （RSI）, which was used to rank the entries for resistance to stem borers. This RSI led to the identification of 11 genotypes which represents the best 5% of the 212 genotypes in resistance ability. Genotype AMA TZBR-WC1 （from International Institute of Tropical Agriculture （IITA）, Ibadan） had the best overall resistance levels, followed by genotypes SE NG-77 and SE NG-67 （from Umuahia North）, SE NG-62 （from Ikwuano）, SE NG-148 （from Ukwa West）, SE NG-106 （from Bende）, SE NG-119 （from Isiala Ngwa）, SE NG-33 （from Ikwuano） and SE NG-65 （from Umuahia North）.

Review on ranking and selection: A new perspective

In this paper,we briefly review the development of ranking and selection(R&S)in the past 70 years,especially the theoretical achievements and practical applications in the past 20 years.Different from the frequentist and Bayesian classifications adopted by Kim and Nelson(2006b)and Chick(2006)in their review articles,we categorize existing R&S procedures into fixed-precision and fixed-budget procedures,as in Hunter and Nelson(2017).We show that these two categories of procedures essentially differ in the underlying methodological formulations,i.e.,they are built on hypothesis testing and dynamic programming,respectively.In light of this variation,we review in detail some well-known procedures in the literature and show how they fit into these two formulations.In addition,we discuss the use of R&S procedures in solving various practical problems and propose what we think are the important research questions in the field.

DESIGN SAMPLING AND REPLICATION ASSIGNMENT UNDER FIXED COMPUTING BUDGET

For many real world problems, when the design space is huge and unstructured, and time consuming simulation is needed to estimate the performance measure, it is important to decide how many designs to sample and how long to run for each design alternative given that we have only a fixed amount of computing time. In this paper, we present a simulation study on how the distribution of the performance measures and distribution of the estimation errors/noises will affect the decision. From the analysis, it is observed that when the underlying distribution of the noise is bounded and if there is a high chance that we can get the smallest noise, then the decision will be to sample as many as possible, but if the noise is unbounded, then it will be important to reduce the noise level first by assigning more replications for each design. On the other hand, if the distribution of the performance measure indicates that we will have a high chance of getting good designs, the suggestion is also to reduce the noise level, otherwise, we need to sample more designs so as to increase the chances of getting good designs. For the special case when the distributions of both the performance measures and noise are normal, we are able to estimate the number of designs to sample, and the number of replications to run in order to obtain the best performance.

Efficient learning for decomposing and optimizing random networks

In this study,we consider the problem of node ranking in a random network.A Markov chain is defined for the network,and its transition probability matrix is unknown but can be learned by sampling random interactions among nodes.Our objective is to decompose the Markov chain into several ergodic classes and select the best node in each ergodic class.We propose a dynamic sampling procedure,which gives a probability guarantee on correct decomposition and maximizes a weighted probability of correct selection of the best node in each ergodic class.Numerical experiment results demonstrate the efficiency of the proposed sampling procedure.

Degrees of freedom in low rank matrix estimation

The objective of this paper is to quantify the complexity of rank and nuclear norm constrained methods for low rank matrix estimation problems. Specifically, we derive analytic forms of the degrees of freedom for these types of estimators in several common settings. These results provide efficient ways of comparing different estimators and eliciting tuning parameters. Moreover, our analyses reveal new insights on the behavior of these low rank matrix estimators. These observations are of great theoretical and practical importance. In particular, they suggest that, contrary to conventional wisdom, for rank constrained estimators the total number of free parameters underestimates the degrees of freedom, whereas for nuclear norm penalization, it overestimates the degrees of freedom. In addition, when using most model selection criteria to choose the tuning parameter for nuclear norm penalization, it oftentimes suffices to entertain a finite number of candidates as opposed to a continuum of choices. Numerical examples are also presented to illustrate the practical implications of our results.

Stochastic systems simulation optimization

With the advance of new computational technology,stochastic systems simulation and optimization has become increasingly a popular subject in both academic research and industrial applications.This paper presents some of recent developments about the problem of optimizing a performance function from a simulation model.We begin by classifying different types of problems and then provide an overview of the major approaches,followed by a more in-depth presentation of two specific areas:optimal computing budget allocation and the nested partitions method.