Three myths from the language acquisition literature

THREE POPULAR ASSERTIONS HAVE HINDERED THE PROMOTION OF AN EMPIRICIST APPROACH TO LANGUAGE ACQUISITION: (a) that Brown and Hanlon (1970) claimed to offer data that parents do not reinforce their children's grammaticality; (b) that Brown and Hanlon also claimed to offer data that parents do not provide negative evidence (i.e., corrective feedback) for ungrammaticality; and (c) that Gold (1967) claimed to offer a formal proof showing that, without negative evidence, a child cannot acquire a language solely from environmental input. In this paper I offer introductory comments on the nature-nurture distinction (including interactionism, and the nativists' claim to have found a gene for language). Next I debunk the three aforementioned assertions by arguing that the authors (Brown & Hanlon; Gold) never made the claims attributed to them; review evidence on the role of reinforcement and corrective feedback in language acquisition; and offer some concluding comments.     

Squeezed算符和Schwinger算符的几种显示表达式

通过角动量算符的拆解定理 ,把 Squeezed算符和 Schwinger算符的普通指数形式转换成正规排列和反正规排列的形式     

利用MM理论分析保险公司的资本结构

本文利用公司财务理论中的ＭＭ资本结构理论,建立一个两阶段模型,从一个理想的经营环境出发,分析了公司所得税、破产风险和代理成本等因素对保险公司资本结构的影响。     

Consistency of semiparametric maximum likelihood estimators for two‐phase sampling

Semiparametric maximum likelihood estimators have recently been proposed for a class of two‐phase, outcome‐dependent sampling models. All of them were “restricted” maximum likelihood estimators, in the sense that the maximization is carried out only over distributions concentrated on the observed values of the covariate vectors. In this paper, the authors give conditions for consistency of these restricted maximum likelihood estimators. They also consider the corresponding unrestricted maximization problems, in which the “absolute” maximum likelihood estimators may then have support on additional points in the covariate space. Their main consistency result also covers these unrestricted maximum likelihood estimators, when they exist for all sample sizes.     

The Comparative Statics of Constrained Optimization Problems

This paper develops and applies some new results in the theory of monotone comparative statics. Let f be a real‐valued function defined on R^l and consider the problem of maximizing f(x) when x is constrained to lie in some subset C of R^l. We develop a natural way to order the constraint sets C and find the corresponding restrictions on the objective function f that guarantee that optimal solutions increase with the constraint set. We apply our techniques to problems in consumer, producer, and portfolio theory. We also use them to generalize Rybcsynski's theorem and the LeChatelier principle.     

Efficiency with Endogenous Population Growth

In this paper, we generalize the notion of Pareto efficiency to make it applicable to environments with endogenous populations. Two efficiency concepts are proposed: ℘‐efficiency and 𝒜‐efficiency. The two concepts differ in how they treat potential agents that are not born. We show that these concepts are closely related to the notion of Pareto efficiency when fertility is exogenous. We prove a version of the first welfare theorem for Barro–Becker type fertility choice models and discuss how this result can be generalized. Finally, we study examples of equilibrium settings in which fertility decisions are not efficient, and we classify them into settings where inefficiencies arise inside the family and settings where they arise across families.     

车辆行驶运动稳定性的简化分析

:本文通过简化车轮受力模型 ,利用线性近似稳定性定理 ,分析车辆行驶的稳定性问题 ,找出车辆出现不稳定性时与临界速度有关的参数 ,提出计算临界速度的简化公式     

A note on a strong renewal theorem

Let {S_n, n ≥ 1} be a sequence of partial sums of independent and identically distributed non-negative random variables with a common distribution function F. Let F belong to the domain of attraction of a stable law with exponent α, 0 < α < 1. Suppose H(t) = ? N(t), t ? 0, where N(t) = max(n : S_n ≥ t). Under some additional assumptions on F, the difference between H(t) and its asymptotic value as t → ∞ is estimated.     

关于Post-Gamma算子的点态近估计

综合利用概率论中的中心极限定理的一种渐近展开形式和Bojanic-Cheng方法,研究了Post-Gamma算子 对局部有界函数的点态逼近估计,得到精确的逼近阶,并进一步证明了此估计在连续点处是渐进最优的.     

Testing for Unit Roots in Dynamic Panels in the Presence of a Deterministic Trend: Re-examining the Unit Root Hypothesis for Real Stock Prices and Dividends

In this paper, we suggest a similar unit root test statistic for dynamic panel data with fixed effects. The test is based on the LM, or score, principle and is derived under the assumption that the time dimension of the panel is fixed, which is typical in many panel data studies. It is shown that the limiting distribution of the test statistic is standard normal. The similarity of the test with respect to both the initial conditions of the panel and the fixed effects is achieved by allowing for a trend in the model using a parameterisation that has the same interpretation under both the null and alternative hypotheses. This parameterisation can be expected to increase the power of the test statistic. Simulation evidence suggests that the proposed test has empirical size that is very close to the nominal level and considerably more power than other panel unit root tests that assume that the time dimension of the panel is large. As an application of the test, we re-examine the stationarity of real stock prices and dividends using disaggregated panel data over a relatively short period of time. Our results suggest that while real stock prices contain a unit root, real dividends are trend stationary.