ABSTRACT
Understanding the transport processes of soil moisture and heat is critical for vegetation restoration in karst rocky desertification areas where serious soil erosion and extensive exposure of carbonate rocks occur. Numerical simulation can provide an important approach to explore the transport processes of soil moisture and heat, but few studies employing this technique have been carried out in karst rocky desertification areas of southwest China. In this study, a model of coupled soil moisture and heat transport was established using HYDRUS-1D based on the high-resolution data of soil moisture, soil temperature, and meteorological parameters obtained throughout a year in a typical karst rocky desertification area in Yunnan province, southwest China. The modeling results reflect the rainfall-infiltration-evaporation processes in rocky desertification areas well. The frequently rainfall events in small intensity in the study site often induced great variations of soil moisture in the near-surface soil layer (< 1-cm depth). However, soil moisture in deep soil layer (> 10-cm depth) kept stable during light rainfall events, implying that the deep soil was only influenced by heavy rainfall events. The variations of soil temperature showed a high sinusoidal fitting trend. At the annual scale, variations of soil temperature were distinct apparent evident below the depth of 40 cm, but no evident daily variations were observed. The simulated fluxes of soil water showed that the vapor fluxes were lower than the liquid water fluxes by 3-6 orders of magnitude, suggesting the control of soil thermal gradients. Our results also indicate that the vapor flux has great significance for plant water utilization in the drought periods. The simulation errors are small for soil temperature but slightly more significant for the soil moisture in deep soil layer. This primary failure may result from the occurrence of preferential flows at the rock-soil interface, which needed to be further investigated in the future.
Subject(s)
Conservation of Natural Resources , Soil , China , Ecosystem , Hot TemperatureABSTRACT
A high accuracy variable beam entrance Faraday cup (VBEFC) system is designed in this work. The presented VBEFC system is designed for the beam current profile measurement of the transient hollow cathode discharge (THCD) generated pulsed electron beam, which is a new source of high energy flux for metallic material processing. By proper designs of the beam entrance array, fast response electron collector, grounding, and shielding, this VBEFC system is capable of determining the radial profile and its temporal evolution of the THCD generated electron beam. The results of the electron beam current and current density distributions collected at varying radial locations and times under multiple voltages are presented in this paper. The experimental results show that both the amplitude and the current density of the THCD electron beam at a given radius always increased with the increase in the accelerating voltage, which is coincident with the self-focused propagation of the electron beam promoted by the voltage.
ABSTRACT
Pentachlorophenol (PCP) is frequently detected in the aquatic environment and has been implicated as an endocrine disruptor in fish. In the present study, 4-month-old zebrafish (Danio rerio) were exposed to 1 of 4 concentrations of PCP (0.1, 1, 9, and 27 µg/L) for 70 d. The effects of PCP exposure on plasma thyroid hormone levels, and the expression levels of selected genes, were measured in the brain and liver. The PCP exposure at 27 µg/L resulted in elevated plasma thyroxine concentrations in male and female zebrafish and depressed 3, 5, 3'-triiodothyronine concentrations in males only. In both sexes, PCP exposure resulted in decreased messenger RNA (mRNA) expression levels of thyroid-stimulating hormone ß-subunit (tshß) and thyroid hormone receptor ß (trß) in the brain, as well as increased liver levels of uridine diphosphoglucuronosyl transferase (ugt1ab) and decreased deiodinase 1 (dio1). The authors also identified several sex-specific effects of PCP exposure, including changes in mRNA levels for deiodinase 2 (dio2), cytosolic sulfotransferase (sult1 st5), and transthyretin (ttr) genes in the liver. Environmental PCP exposure also caused an increased malformation rate in offspring that received maternal exposure to PCP. The present study demonstrates that chronic exposure to environmental levels of PCP alters plasma thyroid hormone levels, as well as the expression of genes associated with thyroid hormone signaling and metabolism in the hypothalamic-pituitary-thyroid (HPT) axis and liver, resulting in abnormal zebrafish development.
