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1.
保费随机的复合二项风险模型的破产概率 总被引：2，自引：0，他引：2
在离散时间的情况下,对保险费的收取过程和索赔过程都是复合二项过程的风险模型进行研究,证明最终破产概率的积分方程,并就指数分布的情形给出破产概率的具体计算方法,而且利用离散鞅得到Lundberg不等式。 相似文献
2.
J Fedorowicz 《Journal of the American Society for Information Science》1982,33(4):223-232
A Zipfian model of an automatic bibliographic system is developed using parameters describing the contents of it database and its inverted file. The underlying structure of the Zipf distribution is derived, with particular emphasis on its application to work frequencies, especially with regard to the inverted flies of an automatic bibliographic system. Andrew Booth developed a form of Zipf's law which estimates the number of words of a particular frequency for a given author and text. His formulation has been adopted as the basis of a model of term dispersion in an inverted file system. The model is also distinctive in its consideration of the proliferation of spelling errors in free text, and the inclusion of all searchable elements from the system's inverted file. This model is applied to the National Library of Medicine's MEDLINE. The model carries implications for the determination of database storage requirements, search response time, and search exhaustiveness. 相似文献
3.
From a number of ML estimators (typically unbiased) of practical interest which include the variance for a Gaussian distribution, the standard deviation for a Laplace distribution, the variance for a Rayleigh distribution and a “spread parameter” for a Cauchy distribution, we design robust estimators according to an emphasis balance between normalized performance and normalized robustness. We measure performance with inverted MSE and robustness with a differential geometric approach. 相似文献
4.
本文是文献[1]的基础，我们将在给定非参数回归统计性质的基础上，讨论一个较详细的非参数回归统计模型的置信区间估计，并给出对收入分布区间估计的实际应用结果。 相似文献
5.
Pere Arqué-Castells 《Research Policy》2012,41(5):897-912
Venture capitalists (VCs) fund the development of promising inventions to turn them into marketable innovations. During this development stage portfolio firms are likely to garner even more inventions at least until the product is fully developed. Once the product is fully developed the focus shifts from development to sales so the number of generated inventions should decrease. This behavior implies that VCs are likely to spur invention according to an inverted U-shape over time. We empirically examine whether patent trajectories are consistent with this hypothesized inverted U-shape using a self-collected dataset containing 233 VC-backed firms and a large set of controls operating in Spain. We find that firms’ patenting activity increases after VC investments. This increase is substantially more pronounced the first two years following VC investments, i.e., patent trajectories follow an inverted U-shape over time. Our more demanding specifications suggest that the sharp increase in patenting right after VCs’ investments is caused by a positive treatment effect over and beyond any likely selection effect. Moreover, we defend that the increase in patenting is not just due to the fact that VCs give money so that firms can patent pre-VC inventions, but also to the fact that VCs fund the development of inventions. 相似文献
6.
资源拼凑曾经是新创企业实现价值创造的重要策略,如今却面临弱化企业家精神的质疑。本研究以非新创民营中小企业为研究对象,聚焦不确定环境下的政企互动情景,对非新创民营中小企业的资源拼凑行为与企业家精神的内在关联予以揭示。研究发现,资源拼凑与企业创新导向呈倒U型关系,并对企业前瞻性和风险偏好均存在消极影响。政商关系对资源拼凑与企业家精神的关系存在“双刃剑”效应,环境不确定性对资源拼凑与企业家精神的关系存在倒U型的调节作用。因此,重振优秀企业家精神的关键在于把握“亲清有度”的政企互动准则和价值逻辑。非新创民营中小企业需要重新审视资源拼凑的战略意义并赋予其更为深刻的行动内涵,实现高质量、跨越式发展。 相似文献
7.
随着微课程的兴起,翻转课堂也应运而生,成为教育界的一颗新星。本文归纳了微课程的概念,对翻转课堂进行了简要介绍,在此基础上总结出实施翻转课堂的原因以及翻转课堂的实践模式。 相似文献
8.
一级倒立摆仿真模型的建立 总被引：1，自引：0，他引：1
针对一级倒立摆系统,首先利用牛顿力学的知识建立了数学模型,然后利用Simulink及其封装功能建立了倒立摆系统的仿真模型,使模型更具灵活性,给仿真带来很大方便。 相似文献
9.
改革开放以来,我国经济持续快速发展。与此同时,我国居民收入分配差距也不断呈现扩大趋势．根据“库兹涅茨倒U型假说”对收入分配与经济增长之间关系的阐述．我国收入分配差距的出现主要是由于劳动力市场不健全．存在着制度性制约因素。缩小收入分配差距,让“库兹涅茨倒U型”拐点加速到来,需要深化城乡体制改革,促进城乡经济社会一体化：进一步规范市场经济运行秩序,健全调控机制,改革和完善各项体制机制． 相似文献
10.
在合作创新网络动态演进过程中,发明者面临着怎样的机会与约束？本文以华为公司和苹果公司在美申请专利数据为样本,运用负二项模型,实证研究了发明者自我网络动态对其知识深度搜索及广度搜索行为的影响,并实证了网络社群动态对自我网络动态与知识搜索深度及广度关系的调节效应。研究发现：发明者自我网络扩张和自我网络衰退对知识搜索深度及广度之间都存在倒U型的影响,而自我网络稳定负向影响知识搜索深度及广度。进一步实证发现：发明者所处的网络社群扩张对自我网络扩张与知识搜索深度及广度间的关系具有正向调节作用,网络社群稳定对自我网络稳定与知识搜索深度及广度间的关系具有正向调节作用,网络社群衰退对自我网络衰退与知识搜索深度及广度间的关系具有正向调节作用。本研究弥补当前静态视角及单一层面对创新网络功能机制的研究,对指导创新主体构建及管理自身创新网络具有重要的现实意义。 相似文献
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12.
从资源配置的视角出发,针对多属性项目并存的条件,开发由战略匹配性、项目贡献度和研发成功率等三个方面构成的新型评价方法,并给出计算方法和应用实例,为企业研发投资决策和项目管理提供实用解决方案。 相似文献
13.
通过研究包含两类重要的积分函数：伽玛函数和贝塔函数的欧拉积分的定义及性质,进一步深入探讨其在定积分、广义积分中的应用.通过灵活运用它们可以简化运算和证明。 相似文献
14.
The continuous version of the Lotka distribution, more generally referred to outside of informetrics as the Pareto distribution, has long enjoyed a central position in the theoretical development of informetrics despite several reported drawbacks in modelling empirical data distributions, most particularly that the inverse power form seems mainly to be evident only in the upper tails. We give a number of published examples graphically illustrating this shortcoming. In seeking to overcome this, we here draw attention to an intuitively reasonable generalization of the Pareto distribution, namely the Pareto type II distribution, of which we consider two versions. We describe its basic properties and some statistical features together with concentration aspects and argue that, at least in qualitative terms, it is better able to describe many observed informetric phenomena over the full range of the distribution. Suggestions for further investigations, including truncated and time-dependent versions, are also given. 相似文献
15.
对于在企业网络中占据中心位置是否有益于企业绩效提升,现有研究往往从线性视角看待两者关系,缺乏从曲线视角的分析。构建以创业导向为中介、环境不确定性为调节因素的受调节的中介模型,研究发现:(1)网络中心性与企业绩效呈倒U型关系;(2)网络中心性与创业导向呈倒U型关系,创业导向在网络中心性与企业绩效的关系中起中介作用;(3)环境不确定性能够调节网络中心性与创业导向的关系,并通过中介效应影响企业绩效。 相似文献
16.
Weiming Wang Xiaoyan Gao Yongli Cai Hongbo Shi Shengmao Fu 《Journal of The Franklin Institute》2018,355(15):7226-7245
In this paper, we investigate the complex dynamics of a reaction–diffusion epidemic model with a saturated infection force analytically and numerically. We give the stability of the constant positive steady–states and the nonexistence/existence of nonconstant positive steady–states of the model which shows that, if the diffusion coefficients are properly chosen, the model exhibits stationary Turing pattern as a result of diffusion. Via numerical simulations, we present the evolutionary processes that involve organism distribution and the interaction of spatially distributed infection with local diffusion, and find that the model dynamics exhibits a diffusion-controlled formation growth of holes, stripes and spots pattern replication. In the viewpoint of epidemiology, we must regulate and control the parameters in the special range to control the disease. 相似文献
17.
In this paper we obtain the Leimkuhler curve in the case of some important statistical distributions proposed in the informetrics and econometrics literature. In this way, we complete the previous work of Burrell [Burrell, Q. L. (2005). Symmetry and other transformation features of Lorenz/Leimkuhler representations of informetric data. Information Processing and Management, 41, 1317–1329], where several open problems were stated. To do this, we use a recent and general definition of the Leimkuhler curve proposed by Sarabia [Sarabia, J. M. (2008a). A general definition of the Leimkuhler curve. Journal of Informetrics, 2, 156-163], and a new representation of the Leimkuhler curve in terms of the first-moment distribution of the population. Specifically, we obtain the Leimkuhler curve of the following distributions: classical and exponentiated Pareto distributions; three-parameter lognormal distribution; generalized gamma distribution, which includes to the exponential and classical gamma distributions among others; generalized beta distribution of the first kind and generalized beta distribution of the second kind, which includes as particular or limiting cases next important families like beta distribution of the second kind, Singh–Maddala, Dagum, Fisk or Lomax distributions. All the obtained Leimkuhler curves can be computed easily. 相似文献
18.
The classical probabilistic models attempt to capture the ad hoc information retrieval problem within a rigorous probabilistic framework. It has long been recognized that the primary obstacle to the effective performance of the probabilistic models is the need to estimate a relevance model. The Dirichlet compound multinomial (DCM) distribution based on the Polya Urn scheme, which can also be considered as a hierarchical Bayesian model, is a more appropriate generative model than the traditional multinomial distribution for text documents. We explore a new probabilistic model based on the DCM distribution, which enables efficient retrieval and accurate ranking. Because the DCM distribution captures the dependency of repetitive word occurrences, the new probabilistic model based on this distribution is able to model the concavity of the score function more effectively. To avoid the empirical tuning of retrieval parameters, we design several parameter estimation algorithms to automatically set model parameters. Additionally, we propose a pseudo-relevance feedback algorithm based on the mixture modeling of the Dirichlet compound multinomial distribution to further improve retrieval accuracy. Finally, our experiments show that both the baseline probabilistic retrieval algorithm based on the DCM distribution and the corresponding pseudo-relevance feedback algorithm outperform the existing language modeling systems on several TREC retrieval tasks. The main objective of this research is to develop an effective probabilistic model based on the DCM distribution. A secondary objective is to provide a thorough understanding of the probabilistic retrieval model by a theoretical understanding of various text distribution assumptions. 相似文献
19.
《Research Policy》2023,52(1):104625
This study sheds light on the relationship between agglomeration, entrepreneurs' internal resources and capabilities, and new ventures' innovativeness using a multilevel framework. We argue that the urban agglomeration of economic agents within a country has an inverted U-shaped relationship with new ventures' innovativeness, suggesting that both insufficient and excessive agglomeration might be detrimental to entrepreneurial innovativeness. Additionally, we perform interactions between individual level factors and urban agglomeration to examine the differential effects of entrepreneurs' internal resources and capabilities. Results confirm our hypothesising that the geographical concentration of economic agents within a country exerts an inverted U-shaped influence on new ventures' innovativeness. Furthermore, we find that entrepreneurs with higher levels of education or prior entrepreneurial experience are better equipped to benefit from agglomeration and to mitigate its negative effects; in contrast, at low levels of agglomeration, entrepreneurs with lower resources exhibit increasing marginal returns. Entrepreneurs in contact with other entrepreneurs are better positioned to deal with agglomeration externalities although their benefits and drawbacks are intensified. Our research contributes to the understanding of agglomeration externalities and entrepreneurial innovativeness, its non-linear dynamics and differential effects. 相似文献
20.
《Information processing & management》2005,41(2):275-288
Many information retrieval systems use the inverted file as indexing structure. The inverted file, however, requires inefficient reorganization when new documents are to be added to an existing collection. Most studies suggest dealing with this problem by sparing free space in an inverted file for incremental updates. In this paper, we propose a run-time statistics-based approach to allocate the spare space. This approach estimates the space requirements in an inverted file using only a little most recent statistical data on space usage and document update request rate. For best indexing speed and space efficiency, the amount of the spare space to be allocated is determined by adaptively balancing the trade-offs between reorganization reduction and space utilization. Experiment results show that the proposed space-sparing approach significantly avoids reorganization in updating an inverted file, and in the meantime, unused free space can be well controlled such that the file access speed is not affected. 相似文献