The landing zone – Ground for model transfer in chemistry

This essay proposes a new notion - the landing zone - in order to identify conceptual features that allow modelers to transfer mathematical tools across disciplinary borders. This discussion refers to the transferable models as ‘templates’. Templates are functions, equations, or computational methods that are capable of being generalized from a particular subject matter. There are formal and conceptual prerequisites for the transfer of a template to a new domain. A landing zone is an ontology that contributes to the satisfaction of these conditions for successful transfer. This paper presents a case study on a model in chemistry - the Quantum Theory of Atoms in Molecules (QTAIM) - that makes use of transferred templates from physics - the virial theorem and the wave function. The landing zone in this case is a new ontological notion, that of the topological atom, which prepares ground for the use of the virial theorem and the wave function in chemistry. The virial theorem requires that there exists in-principle stability to the system that it represents, and the wave function requires transformation in its representation that is justified. The ontology of QTAIM - the landing zone for these templates - grounds the scientific use of these templates in the context of chemistry.     

Distribution and status of the yellow-faced pocket gopher in Kansas

Previous research suggests that the yellow-faced pocket gopher ( Cratogeomys castanops ) occupies a restricted range in western Kansas that is surrounded by the range of the plains pocket gopher ( Geomys bursarius ), which is regarded as a superior competitor. To determine whether the plains pocket gopher has encroached on the range of the yellow-faced pocket gopher in the past 35 years and to better understand the geographic relationships of these species, we trapped pocket gophers in western Kansas and collected soil texture and land cover data. We used ArcView 3.2 to map the distributions of these species in the study area, as well as the kinds of soil and land cover found in their potential home ranges. Although the distributions of the 2 species overlap, they are strictly parapatric. The apparent cause of this parapatric relationship is differential tolerance of soil textures. The distribution of the yellow-faced pocket gopher in Kansas is limited to just 7 counties divided into 2 populations, both surrounded by the distribution of the plains pocket gopher. We found no evidence that the range of the plains pocket gopher has expanded at the expense of the yellow-faced pocket gopher in the past 35 years. Thus, although the yellow-faced pocket gopher remains a “species of greatest conservation need” in Kansas because of agricultural threats, it evidently is not imperiled at this time.     

Extremely low-coverage sequencing and imputation increases power for genome-wide association studies

Genome-wide association studies (GWAS) have proven to be a powerful method to identify common genetic variants contributing to susceptibility to common diseases. Here, we show that extremely low-coverage sequencing (0.1-0.5×) captures almost as much of the common (>5%) and low-frequency (1-5%) variation across the genome as SNP arrays. As an empirical demonstration, we show that genome-wide SNP genotypes can be inferred at a mean r(2) of 0.71 using off-target data (0.24× average coverage) in a whole-exome study of 909 samples. Using both simulated and real exome-sequencing data sets, we show that association statistics obtained using extremely low-coverage sequencing data attain similar P values at known associated variants as data from genotyping arrays, without an excess of false positives. Within the context of reductions in sample preparation and sequencing costs, funds invested in extremely low-coverage sequencing can yield several times the effective sample size of GWAS based on SNP array data and a commensurate increase in statistical power.     

The elastic constants of MgSiO3 perovskite at pressures and temperatures of the Earth's mantle.

The temperature anomalies in the Earth's mantle associated with thermal convection can be inferred from seismic tomography, provided that the elastic properties of mantle minerals are known as a function of temperature at mantle pressures. At present, however, such information is difficult to obtain directly through laboratory experiments. We have therefore taken advantage of recent advances in computer technology, and have performed finite-temperature ab initio molecular dynamics simulations of the elastic properties of MgSiO3 perovskite, the major mineral of the lower mantle, at relevant thermodynamic conditions. When combined with the results from tomographic images of the mantle, our results indicate that the lower mantle is either significantly anelastic or compositionally heterogeneous on large scales. We found the temperature contrast between the coldest and hottest regions of the mantle, at a given depth, to be about 800 K at 1,000 km, 1,500 K at 2,000 km, and possibly over 2,000 K at the core-mantle boundary.     

基于Weibull函数和价格折扣的易腐品库存订货与定价策略

【目的】研究需求率为售价的指数函数，变质率服从三参数Weibull分布的订货与定价策略。【方法】系统以利润最大化为目标函数，考虑商品变质时带来的成本，引入价格折扣，构建了库存模型。【结果】采用直接法和泰勒展开式对模型进行近似求解，提供算例分析以得到问题的近似解，通过对折扣率、变质率灵敏度分析给出了相应的合理化管理建议。【结论】零售商在处理保鲜期后的商品时引入的价格折扣越高销量越大。商品的流动环境因子的增加会使得零售商成本增加，在销售过程中可采用更为先进的交通工具和储存手段。     

Overcompensation and population cycles in an ungulate.

Although theoretical studies show that overcompensatory density-dependent mechanisms can potentially generate regular or chaotic fluctuations in animal numbers, the majority of realistic single-species models of invertebrate populations are not overcompensatory enough to cause sustained population cycles. The possibility that overcompensation may generate cycles or chaos in vertebrate populations has seldom been considered. Here we show that highly overcompensatng density-dependent mortality can generate recurrent population crashes consistent with those observed in a naturally limited population of Soay sheep. The observed interval of three or more years between crashes points to sharp 'focusing' of mortality over a narrow range of population density.