微塑料  生菜  聚苯乙烯微球  吸收  积累  健康风险  microplastics  lettuce  polystyrene microbeads  uptake  accumulation  human health risk  Microplastic (MP, 100 nm-5 mm) may present an attributable risk to ecosystem and human health, and its pollution has become a global environmental concern. Despite a wealth of information on the accumulation of MPs in aquatic species, there is no information on the uptake and accumulation of MPs by higher plants. Terrestrial edible plants are directly exposed to MPs when agricultural soil was applied with organic manure, sewage sludge as fertilizer or plastic mulching. In this paper, the uptake of two sizes of polystyrene (PS) microbeads (0.2 and 1.0 mum) and then their distribution and migration in an edible plant lettuce were firstly investigated based on laboratory experiments. We used fluorescent markers to track PS microbeads in plant tissues and found fluorescence to be a sensitive and reliable detection method. Sections from untreated control lettuce showed no autofluorescence. When roots were treated with fluorescently labeled PS microbeads, the microbeads could be identified by its fluorescence. Our main study investigated the uptake of 0.2 mum beads, as few luminescence signals were observed in lettuce roots for 1.0 mum beads in our experiment. We observed that 0.2 mum fluorescent microbeads were extracellularly trapped in the root cap mucilage (which is a highly hydrated polysaccharide) and a dark green tip (which was typical of lettuce roots exposed to label PS beads) was usually visible to the naked eye. Confocal images revealed that the PS luminescence signals were mainly located in the vascular system and on the cell walls of the cortex tissue of the roots, indicated that the beads passed through the intercellular space via the apoplastic transport system. Once inside the central cylinder, the 0.2 mum PS beads were transferred from the roots to the stems and leaves via the vascular system following the transpiration stream. We also observed that the PS beads adhered to one another and self-assembled systematically into grape-like and (chain) string-like clusters in the intercellular space of the root and stem vascular tissue of lettuce plant. In contrast to the root and stem, PS beads were dispersed in the leaf tissue. Here, for the first time we provide evidence of the adherence, uptake, accumulation, and translocation of submicrometer MPs within an edible plant. Our findings highlight the previously underappreciated human exposure pathway to MPs through the consumption of contaminated crops and emphasize the need for new management strategies to control the release of MPs waste products into the terrestrial environment. Ultimately, the potential impacts of low range sized MPs on food safety of crop plants and human health need to be urgently considered.  

ThIs Paper ExamIned VIsiTors To Bukhansan NatiOnal Park In Korea Based On First-time And Repeat vIsitatiOn. Bukhansan NatiOnal Park Is Korea's Most Heavily vIsited NatiOnal Park With Annual vIsitatiOn Of Six milliOn VIsiTors In 2015. Data Used In ThIs Article Were Collected On-site In The Park In 2007 And 2013 By The Korea NatiOnal Park Service (Knps). The Study Variables Included Socio-demographics  Travel Behavior  Motivation  And Satisfaction With Park Attributes  Services And Facilities. Data Were Analyzed By Each Study Year For First-time And Repeat Visitors. Results Showed Significant Differences For Both First-time And Repeat Visitors.On Several Socio-demographic  Travel Behavior  And Motivation Variables Within Each Study Year. For Satisfaction With Park Attributes  Facilities And Services  First-time VisiTors Were Significantly Different From Repeat VisiTors On Seven Variables For Both Years. implicatiOns Are Given Regarding Programs And Services To Improve visiTor satisfactiOn And Sustain The Natural  Cultural And HisTorical Resources At Bukhansan nAtional Park And Other nAtional Parks In Korea. Future Research Suggestions Are Provided To Learn More About visiTor Characteristics  StAndards Of Quality And Preferences In The National Parks.  

住房需求  住房供给  联立方程  Abstract  This  paper  addresses  the  issue  of  demand  and  supply  for  residential  housing  in  urban  China  since  the  late  1980s  when  the  urban  housing  market  became  commercialized.  We  start  with  the  basic  premise  that  the  standard  theory  of  demand  for  and  supply  of  consumer  durable  goods  is  applicable  to  urban  housing  in  China  after  the  market  for  housing  was  established.  In  a  simultaneous  equations  framework  we  provide  estimates  of  income  and  price  elasticities  of  demand  and  price  elasticity  of  supply.  Analysis  of  aggregated  annual  data  from  1987  to  2006  shows  that  the  rapid  increase  of  urban  residential  housing  can  be  well  explained  by  the  forces  of  demand  and  supply  i.e.  growth  in  income  and  change  in  construction  cost  determines  the  aggregated  movement  in  housing  price  to  a  large  extent.  We  have  found  the  (long-run)  income  elasticity  of  demand  for  urban  housing  to  be  about  1  and  the  price  elasticity  of  demand  to  be  between  -0.5  and  -0.6.   The  price  elasticity  of  supply  of  the  total  stock  of  housing  is  about  0.83.  Keywords:  housing  demand  housing  supply  simultaneous  equations  

In order to reduce ring-liner interface friction power loss  this paper focuses on the structure parameters of the top ring  and investigates how the value of those parameters will influence top ring-liner friction power loss and the minimum thickness of oil film at top ring-liner interface. A mixed lubrication model is developed to simulate the effect of varying design parameters on ring-liner friction. Case study shows that ring-liner friction power loss will be reduced with decreased axial ring height and barrel height. This study provides a theoretical basis for design the top ring with reduced friction power loss at ring-liner interface. (2013) Trans Tech Publications  Switzerland.  

This paper presents the digital PI control method for design and simulation of a high precision limited angle brushless torque motor control system in Field Programmable Gate Array device (FPGA). The direct drive structures which are widely applied in many servo control fields. Matlab Xilinx System GeneratorR toolbox based on Fixed-Point Arithmetic is used to design the digital PI controller using DSP architecture  plot the responses of the control system and generate the VHDL source code. The control system model consists of a digital PI  a real LABTM  and a real absolute Inductosyn  encoder to rpm and position blocks. Through loading generated codes in process of the simulation that built by the digital discrete model  it is verified that the rising time of current loop is only 1.2ms  and rate loop is 8ms  overshoot is rarely 4.2%. Finally  the comprehensive positioning accuracy of system can reach up to 5 arc sec  and the rate jitter achieves 5% with the 4 arc sec accuracy absolute Inductosyn. (2013) Trans Tech Publications  Switzerland.