On symmetric semiparametric two-sample problem

We consider a two-sample problem where data come from symmetric distributions. Usual two-sample data with only magnitudes recorded, arising from case-control studies or logistic discriminant analyses, may constitute a symmetric two-sample problem. We propose a semiparametric model such that, in addition to symmetry, the log ratio of two unknown density functions is modeled in a known parametric form. The new semiparametric model, tailor-made for symmetric two-sample data, can also be viewed as a biased sampling model subject to symmetric constraint. A maximum empirical likelihood estimation approach is adopted to estimate the unknown model parameters, and the corresponding profile empirical likelihood ratio test is utilized to perform hypothesis testing regarding the two population distributions. Symmetry, however, comes with irregularity. It is shown that, under the null hypothesis of equal symmetric distributions, the maximum empirical likelihood estimator has degenerate Fisher information, and the test statistic has a mixture of χ²-type asymptotic distribution. Extensive simulation studies have been conducted to demonstrate promising statistical powers under correct and misspecified models. We apply the proposed methods to two real examples.     

Effects of nitrogen addition and mowing on nitrogen- and water-use efficiency of Artemisia frigida in a grassland restored from an abandoned cropland

氮添加和刈割对内蒙古弃耕草地冷蒿氮和水分利用效率的影响 在氮和水分限制的区域，植物氮利用效率(NUE)和水分利用效率(WUE)决定了它们在群落中的竞争优势。冷蒿(Artemisia frigida)是半干旱草地重度退化的先锋物种，在不同退化程度的草地中具有不 同的优势度，经常被认为是退化草地群落演替的指示物种。退化草地恢复过程中，氮添加和割草如何影响冷蒿的NUE和WUE尚不清晰。以内蒙古多伦县弃耕草地为研究对象，选取两个不同群落斑块(禾草和冷蒿为优势物种的斑块)，经过长期(2006–2013)氮添加和刈割(对照、氮添加、刈割、氮添加+刈割)处理后，研究冷蒿的NUE (叶片碳氮比)和WUE (叶片碳同位素，δ¹³C)对氮添加、刈割及其交互作用的响应； 结合植物和土壤的碳、氮同位素(δ¹³C和δ¹⁵N)及碳、氮库探究退化草地恢复过程中植物的资源利用策略及其机制。研究结果表明：(1)氮添加对冷蒿的WUE没有显著影响(P > 0.05)，但NUE 在禾草和冷蒿斑块 中分别显著降低了42.9%和26.6% (P < 0.05)；(2)植物对不同氮源(NH₄₊或NO_3-)的利用会引起植物和土壤δ¹⁵N的分馏，研究表明叶片和土壤的δ¹⁵N与NUE呈现相反的变化趋势，因此冷蒿的NUE对氮添加的响应与不同氮源的利用有关；(3)刈割不影响冷蒿的NUE (P > 0.05)，但在禾草斑块，冷蒿的WUE在刈割处理下显著提高了2.3% (P < 0.05)；(4)在禾草斑块，氮添加减缓了割草对冷蒿WUE的促进作用；(5)结构方程模型显示，土壤含水量直接或间接的调控着冷蒿的WUE和NUE。综上所述，在禾草斑块，氮添加+刈割处理维持较低的NUE和WUE，不利于冷蒿对资源的竞争，进一步降低其优势度，这也预示着氮添加+ 刈割处理会促进退化草地的恢复。     

Subnetwork identification and chemical modulation for neural regeneration: A study combining network guided forest and heat diffusion model

Background: The induction of neural regeneration is vital to the repair of spinal cord injury (SCI). While compared with peripheral nervous system (PNS), the regenerative capacity of the central nervous system (CNS) is extremely limited. This indicates that modulating the molecular pathways underlying PNS repair may lead to the discovery of potential treatment for CNS injury.Methods: Based on the gene expression profiles of dorsal root ganglion (DRG) after a sciatic nerve injury, we utilized network guided forest (NGF) to rank genes in terms of their capacity of distinguishing injured DRG from sham-operated controls. Gene importance scores deriving from NGF were used as initial heat in a heat diffusion model (HotNet2) to infer the subnetworks underlying neural regeneration in the DRG. After potential regulators of the subnetworks were found through Connectivity Map (cMap), candidate compounds were experimentally evaluated for their capacity to regenerate the damaged neurons.Results: Gene ontology analysis of the subnetworks revealed ubiquinone biosynthetic process is crucial for neural regeneration. Moreover, almost half of the genes in these subnetworks are found to be related to neural regeneration via text mining. After screening compounds that are likely to modulate gene expressions of the subnetworks, three compounds were selected for the experiment. Of them, trichostatin A, a histone deacetylase inhibitor, was validated to enhance neurite outgrowth in vivo via an optic nerve crush mouse model.Conclusions: Our study identified subnetworks underlying neural regeneration, and validated a compound can promote neurite outgrowth by modulating these subnetworks. This work also suggests an alternative approach for drug repositioning that can be easily extended to other disease phenotypes.