不确定性、学习与新技术序列投资决策

以不同性质不确定性与其解决方式(学习)和效率对投资价值的影响为切入点,研究新技术序列投资行为背后的决策机制与路径.在现有研究基础上,引入企业内部学习的异质性特征,把技术不确定性的解决效率分解为学习能力、累积学习效应与边际学习效应3个层次进行讨论.运用实物期权方法构建包含学习效应的新技术序列投资决策模型,并得到最优决策规则,通过数值方法对不同参数进行比较静态分析,并阐述结果的经济与管理涵义.     

非对称情况下的多物品拍卖

本文讨论当投标人之间存在不同的预算约束时两物品的序贯增价拍卖,对于物品之间不同的关系(互补、替代或者不相干的关系),物品价值大小的不同及与预算大小之间的关系,在一个简单的完全信息模型下,我们分不同情况讨论投标人的均衡出价策略,并发现对卖方来说,先拍卖价值高的物品是弱占优的策略。     

Sequential tuning of complex computer models

We propose a method that uses a sequential design instead of a space filling design for estimating tuning parameters of a complex computer model. The goal is to bring the computer model output closer to the real system output. The method fits separate Gaussian process (GP) models to the available data from the physical experiment and the computer experiment and minimizes the discrepancy between the predictions from the GP models to obtain estimates of the tuning parameters. A criterion based on the discrepancy between the predictions from the two GP models and the standard error of prediction for the computer experiment output is then used to obtain a design point for the next run of the computer experiment. The tuning parameters are re-estimated using the augmented data set. The steps are repeated until the budget for the computer experiment data is exhausted. Simulation studies show that the proposed method performs better in bringing a computer model closer to the real system than methods that use a space filling design.     

A general inverse sampling scheme and its application to adaptive cluster sampling

Not having a variance estimator is a seriously weak point of a sampling design from a practical perspective. This paper provides unbiased variance estimators for several sampling designs based on inverse sampling, both with and without an adaptive component. It proposes a new design, which is called the general inverse sampling design, that avoids sampling an infeasibly large number of units. The paper provide estimators for this design as well as its adaptive modification. A simple artificial example is used to demonstrate the computations. The adaptive and non‐adaptive designs are compared using simulations based on real data sets. The results indicate that, for appropriate populations, the adaptive version can have a substantial variance reduction compared with the non‐adaptive version. Also, adaptive general inverse sampling with a limitation on the initial sample size has a greater variance reduction than without the limitation.     

Multistage methodologies for comparing several treatments with a control

We consider the problem of constructing a set of fixed-width simultaneous confidence intervals for the treatment-control differences of means for several independent normal populations with a common unknown variance. Taking c observations from the control population instead of the usual vector-at-a-time approach, purely sequential estimation methodology is developed and asymptotic second-order characteristics are provided. Brief remarks on the accelerated sequential and three-stage methodologies have been added. Next, with the help of simulations, performances of the purely sequential, accelerated sequential and three-stage estimation techniques are compared. Overall, the second-order asymptotics are found to provide useful approximations even for moderate sample sizes.     

Sequential experimental design and response optimisation

We consider the situation where one wants to maximise a functionf(θ,x) with respect tox, with θ unknown and estimated from observationsy _k . This may correspond to the case of a regression model, where one observesy _k =f(θ,x _k )+ε _k , with ε _k some random error, or to the Bernoulli case wherey _k ∈{0, 1}, with Pr[y _k =1|θ,x _k |=f(θ,x _k ). Special attention is given to sequences given by , with an estimated value of θ obtained from (x₁, y₁),...,(x _k ,y _k ) andd _k (x) a penalty for poor estimation. Approximately optimal rules are suggested in the linear regression case with a finite horizon, where one wants to maximize ∑ _i=1 ^N w _i f(θ, x _i ) with {w _i } a weighting sequence. Various examples are presented, with a comparison with a Polya urn design and an up-and-down method for a binary response problem.     

浅析语境化暗示配置方式对图像意义的影响

语境/语境化虽是许多学科的常用概念,但迄今鲜有著作能确切地界定它。最近,国外在话语分析方面的研究取得了不少进步和共识,其中最重要的一点就是将语境/语境化视作对客观世界在人们心理层面的选择性呈现。这一理论构想引出不少新研究话题,比如对语境化过程中选择性心理呈现具体细节的研究。作为对上述问题的初步探讨,通过分析一幅漫画中的意义语境化过程来说明语境化暗示配置方式对图像意义解读的影响,并在此基础上讨论了这种影响对话语分析实践的启示。     

An adaptive sampling scheme guided by BART—with an application to predict processor performance

The evaluation of new processor designs is an important issue in electrical and computer engineering. Architects use simulations to evaluate designs and to understand trade‐offs and interactions among design parameters. However, due to the lengthy simulation time and limited resources, it is often practically impossible to simulate a full factorial design space. Effective sampling methods and predictive models are required. In this paper, the authors propose an automated performance predictive approach which employs an adaptive sampling scheme that interactively works with the predictive model to select samples for simulation. These samples are then used to build Bayesian additive regression trees, which in turn are used to predict the whole design space. Both real data analysis and simulation studies show that the method is effective in that, though sampling at very few design points, it generates highly accurate predictions on the unsampled points. Furthermore, the proposed model provides quantitative interpretation tools with which investigators can efficiently tune design parameters in order to improve processor performance. The Canadian Journal of Statistics 38: 136–152; 2010 © 2010 Statistical Society of Canada     

A computationally simple bivariate survival estimator for efficacy and safety

Both treatment efficacy and safety are typically the primary endpoints in Phase II, and even in some Phase III, clinical trials. Efficacy is frequently measured by time to response, death, or some other milestone event and thus is a continuous, possibly censored, outcome. Safety, however, is frequently measured on a discrete scale; in Eastern Cooperative Oncology Group clinical trial E2290, it was measured as the number of weekly rounds of chemotherapy that were tolerable to colorectal cancer patients. For the joint analysis of efficacy and safety, we propose a non-parametric, computationally simple estimator for the bivariate survival function when one time-to-event is continuous, one is discrete, and both are subject to right-censoring. The bivariate censoring times may depend on each other, but they are assumed to be independent of both event times. We derive a closed-form covariance estimator for the survivor function which allows for inference to be based on any of several possible statistics of interest. In addition, we derive its covariance with respect to calendar time of analysis, allowing for its use in sequential studies.     

从认知语言学角度看影响句子结构的因素

日常生活中人们主要靠语言来传递思想,没有语言这个媒介,人们之间的交流会困难得多。要想达到成功交际的目的,交际者产出的必须是交际双方所在文化认可的、有一定结构的句子。认知语言学研究语言背后的认知理据,揭示语言的本质。通过从认知语言学角度分析交际者使用特定句子结构的原因,认为动词、动词所在构式、识解方式、象似性、语篇连贯的需求等是影响交际者选择某种特定句子结构的因素,从而为交际者使用的句子结构提供深层次上的认知理据。