Quantile regression in partially linear varying coefficient models

Semiparametric models are often considered for analyzing longitudinal data for a good balance between flexibility and parsimony. In this paper, we study a class of marginal partially linear quantile models with possibly varying coefficients. The functional coefficients are estimated by basis function approximations. The estimation procedure is easy to implement, and it requires no specification of the error distributions. The asymptotic properties of the proposed estimators are established for the varying coefficients as well as for the constant coefficients. We develop rank score tests for hypotheses on the coefficients, including the hypotheses on the constancy of a subset of the varying coefficients. Hypothesis testing of this type is theoretically challenging, as the dimensions of the parameter spaces under both the null and the alternative hypotheses are growing with the sample size. We assess the finite sample performance of the proposed method by Monte Carlo simulation studies, and demonstrate its value by the analysis of an AIDS data set, where the modeling of quantiles provides more comprehensive information than the usual least squares approach.Comment: Published in at http://dx.doi.org/10.1214/09-AOS695 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

The Wetting of Leaf Surfaces and Its Ecological Significances

Leaf wettability, indicating the affinity for water on leaf surfaces, is a common phenomenon for plants in a wide variety of habitats. The contact angle (θ) of water on leaves measured at the gas, solid and liquid interface is an index of surface wettability. Leaves are termed as “super-hydrophilic” if θ 110°, the leaves are classified as being non-wettable, while θ > 130° for highly non-wettable and θ > 150° for super-hydrophobic. Both internal and external factors can influence leaf wettability. The chemical composition and structure of leaf surfaces are internal causes, but the external environment can also influence wettability by affecting the structure and composition of the surface. The main internal factors that affecting leaf wettability include the content and microstructure of the epidermal wax, the number, size and pattern of trichomes, stomatal density, the shape of epidermal cells, and leaf water status. The leaf contact angles increased with the increasing of leaf wax content. However, studies have shown that the contact angles were more dependent on the complexity of wax structure than on the absolute amount. For trichomes, there are three types of interaction between trichomes and water droplets, including (1) low trichomes density: no apparent influence of trichomes on the location of surface moisture, droplet formation and retention ; (2) medium trichomes density: trichomes appear to circle surface moisture into patches; (3) high trichomes density: trichomes appear to hold water droplets above the trichomes. In some cases, a higher stomatal density was accompanied with a higher contact angles. While, it was also observed that there was no significant correlation between contact angle and stomatal density for some species. For the effects of epidermal cells on leaf wettability, it was generally considered that the combination of a dense layer of surface wax and the convex epidermal cells was what created a hydrophobic leaf surface. However, the influence of leaf water content on contact angle of water droplets on different leaf surfaces was complex, e.g., contact angles increased with decreasing of leaf water content, contact angle remained to be constant with different leaf water content

The Development of Mobile Short Video Communication in the Context of the Mobile Internet

In the context of the mobile Internet, continuously upgraded media and increasing numbers of terminal devices has enabled information communication to become instant and abundant. The lifestyle of the public has also changed with the evolution of the Internet. The public’s growing enthusiasm for watching short videos on smart phones are one example. This paper discusses changes in the communication environment, namely the concept and development of mobile short videos. Application of Lasswell’s “5W” model to mobile short video communication, is used to analyze this form of communication, using Meipai, a Chinese mobile short video application, as a case study. Suggestions for potential development in this area are also considered

Posterior Inference in Bayesian Quantile Regression with Asymmetric Laplace Likelihood

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135059/1/insr12114.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135059/2/insr12114_am.pd

Rejoinder

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134939/1/insr12181.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134939/2/insr12181_am.pd

A Fuzzy Bayesian Network Model for Quality Control in O2O e-Commerce

With the popularization of the online to offline (O2O) e-commerce on fresh food products, how to control the quality is becoming increasingly important. To adequately address this problem, this paper presents a fuzzy Bayesian network model for effectively controlling the quality in O2O ecommerce. Reasoning about uncertain events and incomplete data through an intelligent simulation with Bayesian networks provides a convenient and fast method of evaluation and analysis for e-commerce platforms to quickly select fresh food suppliers. Such a model is capable of appropriately modelling the uncertainty inherent in the fresh food product distribution process. It focuses on the identification of the critical factors that affect the food product quality along the supply chain. This leads to the development of a complete selection and evaluation system for the quality in O2O e-commerce. A simulation study is conducted that shows the proposed model is applicable for effectively controlling the quality in O2O e-commerce. Ultimately, the unloading level, warehouse inspection and warehouse monitoring are determined as the entry points for quality control, with corresponding degrees of influence of 44%, 37%, and 34%. The main points to protect the quality of food are introduced, which provides a theoretical basis for solving fresh food safety problems for business platforms

Efficient Removal of Ultrafine Particles from Diesel Exhaust by Selected Tree Species : Implications for Roadside Planting for Improving the Quality of Urban Air

Human exposure to airborne ultrafine (?1 μm) particulate pollution may pose substantial hazards to human health, particularly in urban roadside environments where very large numbers of people are frequently exposed to vehicle-derived ultrafine particles (UFPs). For mitigation purposes, it is timely and important to quantify the deposition of traffic-derived UFPs onto leaves of selected plant species, with particularly efficient particle capture (high deposition velocity), which can be installed curbside, proximal to the emitting vehicular sources. Here, we quantify the size-resolved capture efficiency of UFPs from diesel vehicle exhaust by nine temperate-zone plant species, in wind tunnel experiments. The results show that silver birch (79% UFP removal), yew (71%), and elder (70.5%) have very high capabilities for capture of airborne UFPs. Metal concentrations and metal enrichment ratios in leaf leachates were also highest for the postexposure silver birch leaves; scanning electron microscopy showed that UFPs were concentrated along the hairs of these leaves. For all but two species, magnetic measurements demonstrated substantial increases in the concentration of magnetic particles deposited on the leaves after exposure to the exhaust particulates. Together, these new data show that leaf-deposition of UFPs is chiefly responsible for the substantial reductions in particle numbers measured downwind of the vegetation. It is critical to recognize that the deposition velocity of airborne particulate matter (PM) to leaves is species-specific and often substantially higher (?10 to 50 times higher) than the "standard" V d values (e.g., 0.1-0.64 cm s -1 for PM 2.5) used in most modeling studies. The use of such low V d values in models results in a major under-estimation of PM removal by roadside vegetation and thus misrepresents the efficacy of selected vegetation species in the substantial (≫20%) removal of PM. Given the potential hazard to health posed by UFPs and the removal efficiencies shown here (and by previous roadside measurements), roadside planting (maintained at or below head height) of selected species at PM "hotspots" can contribute substantially and quickly to improve in urban air quality and reductions in human exposure. These findings can contribute to the development and implementation of mitigation policies of traffic-derived PM on an international scale