Analyses on Temporal and Spatial Variation Characteristics of Erosion and Deposition in the Front Edge of Salt Marsh Wetland

Taking Yancheng Nature Reserve Salt Marsh as the research object,the remote sensing images from 2005 to 2020 were interpreted by using remote sensing and geographic information system technology.In this paper,the temporal and spatial variation characteristics of erosion and deposition in the front edge of salt marsh wetland were analyzed.The influence of sea level rise on the annual change of salt marsh area was analyzed.The characteristics of flow and sediment movement in salt marsh and the causes of erosion and deposition in front of salt marsh were analyzed.The results showed that:(1)During 2005-2007,the sea level was relatively low,and Spartina alterniflora in salt marsh expanded to the sea.Since 2007,the front edge of salt marsh wetland has coexisted with erosion and deposition.From 2008 to 2010,the front edge of salt marsh wetland once again showed a trend of comprehensive deposition to the sea side.From 2010 to 2012,the erosion of salt marsh wetland was serious.From 2012 to 2020,the front edge of salt marsh wetland in the range of 9 km south of Xinyang estuary was eroded.(2)The correlation analysis was carried out between the area of salt marsh wetland and sea level rise.Spartina alterniflora is easily affected by sea level change,owing to it having a low ecological niche.With the rise of sea level,the area of salt marsh has been decreasing since 2013.(3)In the front sea area of salt marsh wetland,the maximum velocity of the ebb and flood can reach the threshold velocity during the spring tide.The sediment starts to move at water depth of 10 m under wave actions.Owing to wave stirs up sediment and current transports the sediment,resuspended sediment causes the erosion of marsh-edge scarps.

Allocating redundancy,maintenance and spare parts for minimizing system cost under decentralized repairs

Reliability-redundancy allocation,preventive maintenance,and spare parts logistics are crucial for achieving system reliability and availability goal.Existing methods often concentrate on specific scopes of the system’s lifetime.This paper proposes a joint redundancymaintenance-inventory allocation model that simultaneously optimizes redundant component,replacement time,spares stocking,and repair capacity.Under reliability and availability criteria,our objective is to minimize the system’s lifetime cost,including design,manufacturing,and operational phases.We develop a unified system availability model based on ten performance drivers,serving as the foundation for the establishment of the lifetimebased resource allocation model.Superimposed renewal theory is employed to estimate spare part demand from proactive and corrective replacements.A bisection algorithm,enhanced by neighborhood exploration,solves the complex mixed-integer,nonlinear optimization problem.The numerical experiments show that component redundancy is preferred and necessary if one of the following situations occurs:extremely high system availability is required,the fleet size is small,the system reliability is immature,the inventory holding is too costly,or the handson replacement time is prolonged.The joint allocation model also reveals that there exists no monotonic relation between spares stocking level and system availability.

Theory assisted design of N-doped tin oxides for enhanced electrochemical CO2 activation and reduction

Clearly understanding the structure-function relationship and rational design of efficient CO2 electrocatalysts are still the challenges.This article describes the molecular origin of high selectivity of formic acid on N-doped SnO2 nanoparticles,which obtained via thermal treatment of g-C3N4 and SnCl2·2H2O precursor.Combined with density functional theory(DFT)calculations,we discover that N-doping effectively introduces oxygen vacancies and increases the charge density of Sn sites,which plays a positive role in CO2 activation.In addition,N-doping further regulates the adsorption energy of^*OCHO,^*COOH,^*H and promotes HCOOH generation.Benefited from above modulation,the obtained N-doped SnO2 catalysts with oxygen vacancies(Ov-N-SnO2)exhibit faradaic efficiency of 93% for C1 formation,88% for HCOOH production and well-suppression of H2 evolution over a wide range of potentials.