增值税减税能否提高制造业企业全要素生产率？——基于增值税税率下调事件的经验研究

深化税制改革是激发市场主体活力、加快制造业转型、实现经济高质量发展的重要路径。基于2016—2020年中国沪深A股上市公司数据,研究了2018年和2019年增值税税率下调对制造业企业全要素生产率的影响。研究发现,增值税减税提高了制造业企业的全要素生产率。异质性分析结果显示,对于市场竞争地位高、国有产权、处于成熟期以及高市场化地区的企业而言,增值税减税对全要素生产率的提升效应显著。渠道分析表明,研发投入、人力资本投入以及资本配置效率是增值税减税影响企业全要素生产率的主要渠道。因此,政府部门应继续深化增值税改革,缩小制造业与其他行业的税率差异,切实减轻制造业企业税收负担,同时应加大对民营、初创等弱势企业的财政扶持力度,全面提高各类企业的全要素生产率。     

Evaluating the Effectiveness of Risk-Reduction Strategies for Consumer Chemical Products

Communication about risks offers a voluntary approach to reducing exposure to pollutants. Its adequacy depends on its impact on behavior. Estimating those impacts first requires characterizing current activities and their associated risk levels, and then predicting the effectiveness of risk-reduction strategies. Characterizing the risks from chemical consumer products requires knowledge of both the physical and the behavioral processes that influence exposures. This article presents an integrated approach that combines consumer interviews, users' beliefs and behaviors, and quantitative exposure modeling. This model was demonstrated in the context of consumer exposure to a methylene chloride-based paint stripper, showing how it could be used to evaluate current levels of risk and predict the effectiveness of proposed voluntary risk-reduction strategies.     

On a statistic useful in dimensionality reduction in multivariable linear stochastic system

In this paper we study the sampling properties of a test statistic which has important applications in the area of linear stochastic control systems with multi-inputs and multi-outputs. The statistic is the ratio of a partial sum of the eigenvalues of a sample covariance matrix and its trace. It turns out that using a method due to Sugiura we may derive a useful approximation for its distribution up to and including terms of order l/n, where n denotes the appropriate size. Numerical illustrations using real data are given.     

沟槽面在湍流减阻中的技术研究及应用进展

针对长输管道中存在的能源消耗问题，分别从湍流边界层流动特性、拟序结构、条带结构、转捩等方面归纳了沟槽面湍流减阻的国内外研究现状，讨论了沟槽的几何形状和尺度、流场压力梯度、沟槽面放置方式对沟槽减阻效能的影响。对沟槽面的减阻机理进行了综述，分析了存在的问题。指出需要利用先进的实验技术如PIV等图像处理手段,并结合计算流体力学软件对湍流边界层的瞬时流场进行研究，以找出沟槽面湍流减阻的机理。数值模拟了在平板中部横向布置的下凹沟槽的流场情况，得到了一种小涡流动结构，同时验证了这种结构在减阻中的作用，阐述了对减阻的另一种认识,并对沟槽面湍流减阻技术及其工业利用进行了展望。     

关于国有股减持的若干探讨

本文主要探讨了减持国有股的核心目的,国有股减持的比例问题,减持公司的选择原则和国有股减持与保证股市稳定的关系。     

Error reduction in density estimation under shape restrictions

For the problems of nonparametric estimation of nonincreasing and symmetric unimodal density functions with bounded supports we determine the projections of estimates onto the convex families of possible parent densities with respect to the weighted integrated squared error. We also describe the method of approximating the analogous projections onto the respective density classes satisfying some general moment conditions. The method of projections reduces the estimation errors for all possible values of observations of a given finite sample size in a uniformly optimal way and provides estimates sharing the properties of the parent densities.     

Partial least squares estimator for single-index models

The partial least squares (PLS) approach first constructs new explanatory variables, known as factors (or components), which are linear combinations of available predictor variables. A small subset of these factors is then chosen and retained for prediction. We study the performance of PLS in estimating single-index models, especially when the predictor variables exhibit high collinearity. We show that PLS estimates are consistent up to a constant of proportionality. We present three simulation studies that compare the performance of PLS in estimating single-index models with that of sliced inverse regression (SIR). In the first two studies, we find that PLS performs better than SIR when collinearity exists. In the third study, we learn that PLS performs well even when there are multiple dependent variables, the link function is non-linear and the shape of the functional form is not known.     

A technique for uncertainty reduction based on order commonality

The use of commonality is widely diffused as a criterion to reduce uncertainty in demand forecasts for the master production schedule (MPS). Nevertheless, studies have mostly focused on exploiting component commonality in make to stock and assemble to order manufacturing. This paper refers to planning environments with two specific characteristics. First, the degree of certainty of the demand is extremely low, due to product complexity, with poor modularization and standardization, and to the presence of few customers of large dimensions. Second, the delivery lead time is less than the total lead time. In this situation, demand for MPS planning units is extremely uncertain and sporadic. It is therefore necessary to formulate in advance forecasts of customer orders with a redundant configuration. In this paper a technique for the reduction of demand uncertainty is introduced, based on the exploitation of order commonalities. In particular, relations between order commonality and uncertainty reduction in a planning environment with such complex features are illustrated. Then, guidelines for the implementation of the technique in order to reduce over-planning in the master production schedule are provided. Finally, the performances of the technique are empirically analysed by means of both a simulation model and experimental application in a telecommunication systems manufacturer     

磨料射流及高分子减阻改善射流性能的实验研究

本文设计了磨料射流系统及喷嘴结构,实验研究了磨料射流切割与破碎物料的性能,确定了磨料喷嘴出口的最佳长度,对清水和磨料溶液进行了射流冲击性能比较试验;并进一步在磨料射流中加入高分子聚合物添加剂,实验证明,高分子减阻剂同样对磨料射流性能有改善.     

能量摄取、膳食构成及体育锻炼在减肥中的作用

本文论述了能量摄取、膳食构成、体育锻炼与体脂的关系以及在减肥中的作用，并通过对湖北省某高校男、女大学生超重率的调查，发现普通系无论是男生还是女生其超重率一般并不比体育系男女生高（Ｐ＞０．０５）．提出不宜以超重作为评定个体肥胖的标准。