Suitable Weir Heights to Improve the Provision of Environmental Flows in Urban Rivers

Many studies have been conducted on environmental flow(e-flow)assessment and supply,but e-flow shortages remain common in many urban rivers.In addition to known reasons such as ever-increasing competition among water users and inadequate execution of designed e-flow supply plans,we propose that designing weir heights without explicitly considering e-flows is another major cause of this problem.In this paper,we suggest that the measures for satisfying e-flows be extended from the water supply stage to the river channel design stage.We establish a new weir height determination framework that would more effectively satisfy the required e-flows.The new framework differs from previous frameworks,in which flood control and water retention are the major concerns and the flow during floods is set as the inflow.In the new framework,e-flow provision and flow velocity maintenance are added concerns and the actual flows for e-flow supply are set as the inflow.As a case study of the new framework’s effectiveness,we applied it to the Shiwuli River,a typical channelized urban river in Hefei,China.The old framework specified too-high weir height to meet the e-flow requirements,whereas the new framework offered more reasonable heights that improved e-flow provision.

A New Method of Assessing Environmental Flows in Channelized Urban Rivers

Assessing environmental flows （e-flows） for urban rivers is important for water resources planning and river protection, Many e-flow assessment methods have been established based on species＇ habitat pro- vision requirements and pollutant dilution requirements, To avoid flood risk, however, many urban rivers have been transformed into straight, trapezoidal-profiled concrete channels, leading to the disappearance of valuable species, With the construction of water pollution-control projects, pollutant inputs into rivers have been effectively controlled in some urban rivers, For these rivers, the e-flows determined by tradi- tional methods will be very small, and will consequently lead to a low priority being given to river pro- tection in future water resources allocation and management, To more effectively assess the e-flows of channelized urban rivers, we propose three e-flow degrees, according to longitudinal hydrological con- nectivity （high, medium, and low）, in addition to the pollutant dilution water requirement determined by the mass-balance equation, In the high connectivity scenario, the intent is for the e-flows to maintain flow velocity, which can ensure the self-purification of rivers and reduce algal blooms; in the medium connectivity scenario, the intent is for the e-flows to permanently maintain the longitudinal hydrological connectivity of rivers that are isolated into several ponds by means of weirs, in order to ensure the exchange of material, energy, and information in rivers; and in the low connectivity scenario, the intent is for the e-flows to intermittently connect isolated ponds every few days （which is designed to further reduce e-flows）, The proposed methods have been used in Shiwuli River, China, to demonstrate their effectiveness, The new methods can offer more precise and realistic e-flow results and can effectively direct the construction and management of e-flow supply projects,

Switching plasticity in compensated ferrimagnetic multilayers for neuromorphic computing

Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing.In this work,we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin–orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier.Therefore,the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field.Moreover,we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior.This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing.

Microscopic mechanisms analysis of various dielectric response processes in oil-paper insulation with different insulating states

Various dielectric response processes in the oil-paper insulation are sensitively affected by the insulating states(ageing degrees and moisture contents).However,the existing research is still incomplete in revealing the microscopic mechanisms of various dielectric response processes in oil-paper insulation with different insulating states.Given this issue,the genetic algorithm is first adopted to extract the Dissado–Hill(D–H)model parameters by simulating the frequency domain spectroscopy(FDS)of oil-paper insu-lation.Then,the change laws of the extracted D–H model parameters are adopted to reveal the microscopic mechanisms of various dielectric response processes.Microscopic mechanisms of four dielectric response processes are studied,which are quasi-dc relax-ation,loss peak relaxation,optical frequency relaxation,and DC conductance.Meanwhile,due to the dielectric response processes being dominated by various polar particles(methanol,ethanol,furfural,and water molecule),the contents of various ageing by-products dissolved in the insulating oil are measured to support the above analysis.In this respect,a dielectric theoretical reference for the FDS technique to research the insulating states of oil-paper insulation is provided.

An improved second-order kinetic model for degradation analysis of transformer paper insulation under non-uniform thermal field

The ageing kinetic model is regarded as an effective tool to describe the degradation of transformer paper insulation.However,the temperature of the transformer winding is unevenly distributed,and the existing ageing kinetic models only depend on experimental data of accelerated thermal ageing at a constant temperature.Given this issue,this work proposes an improved second-order kinetic model accounting for the non-uniform thermal field.First,oil-paper insulation samples with different ageing stages are prepared under the non-uniform thermal field.Then,the sample's experimental data of moisture dispersion and distribution of degree of polymerisation are collected.On this basis,the improved second-order kinetic model is derived to simulate insulating paper's ageing process subjected to an axial temperature gradient.Further,the relationship of the parameters in the improved second-order kinetic model with the temperature and moisture content at different winding heights is obtained.Finally,the proposed model is validated,and the results show that the proposed model is more scientific than the traditional models to describe the degradation of paper insulation.In that respect,this work illustrates an improved second-order kinetic model to provide a reference for the ageing assessment/life prediction of transformer paper insulation under the non-uniform thermal field.

Observation of thickness-tuned universality class in superconducting β-W thin films

The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in b - W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of tc⊥1~ 8 nm and then from multiple quantum criticality to single criticality at tc⊥2~ 16 nm. Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at tc‖~ 8 nm. The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality.

Molecular Scaffold Growth of Two-Dimensional, Strong Interlayer-Bonding-Layered Materials

Currently,most two-dimensional(2D)materials that are of interest to emergent applications have focused on van der Waals–layered materials(VLMs)because of the ease with which the layers can be separated(e.g.,graphene).Strong interlayer-bonding-layered materials(SLMs)in general have not been thoroughly explored,and one of the most critical present issues is the huge challenge of their preparation,although their physicochemical proper-ty transformation should be richer than VLMs and deserves greater attention.MAX phases are a classi-cal kind of SLM.