Control of magnetic states and spin interactions in bilayer CrCl3 with strain and electric fields: an ab initio study.

Using ab initio density functional theory, we demonstrated the possibility of controlling the magnetic ground-state properties of bilayer CrCl[Formula: see text] by means of mechanical strains and electric fields. In principle, we investigated the influence of these two fields on parameters describing the spin Hamiltonian of the system. The obtained results show that biaxial strains change the magnetic ground state between ferromagnetic and antiferromagnetic phases. The mechanical strain also affects the direction and amplitude of the magnetic anisotropy energy (MAE). Importantly, the direction and amplitude of the Dzyaloshinskii-Moriya vectors are also highly tunable under external strain and electric fields. The competition between nearest-neighbor exchange interactions, MAE, and Dzyaloshinskii-Moriya interactions can lead to the stabilization of various exotic spin textures and novel magnetic excitations. The high tunability of magnetic properties by external fields makes bilayer CrCl[Formula: see text] a promising candidate for application in the emerging field of two-dimensional quantum spintronics and magnonics.

Variability of urban drainage area delineation and runoff calculation with topographic resolution and rainfall volume.

Designing green stormwater infrastructure (GSI) requires an accurate estimate of the contributing drainage area and a model for runoff generation. We examined some factors that add to the uncertainty associated with these two design steps in the urban environment. Delineated drainage areas at five GSI sites in southeastern Pennsylvania (PA) were compared for digital elevation model (DEM) resolutions (grid cell sizes) ranging from 8 to 300 cm. The findings point to an optimal DEM resolution range of 30-60 cm, with up to 100 cm resolution providing acceptable results for some sites. The delineated areas were validated with the observed flow and rainfall records at three sites by examining curve number (CN) values calculated for individual storms. The calculated CNs decreased with increasing rainfall volume, which supports a recommendation to consider a range of CNs in the GSI design process. The variation in calculated CNs was higher for the overestimated drainage areas derived from coarser DEM resolutions. We hypothesize that the observed continued decrease of CNs at high rainfall is the result of inlet bypass, a potentially significant factor in urban hydrology. The findings from this study provide insight into the variability in expected delineated drainage areas using standard methods in GSI design.

Spin Hall effect of transmitted light through α-Li3N-type topological semimetals.

The spin Hall effect of light occurring in topological semimetals provides unprecedented opportunities to exploit novel photonic properties and applications. In particular, pristine α-Li3N-type crystal has recently been predicted to be a type-I nodal-line semimetal based on density functional theory. Herein, the spin Hall effect of transmitted light through thin films of α-Li3N-type topological semimetals is investigated. We show that the prominent intense peak and dip emerging in the spectra of spin Hall shifts occur at the high-energy side of interband absorption of α-Li3N-type semimetals and show redshifts with increasing the incident angle or permittivity of the exit medium. In addition, type-I nodal-line semimetal under a compressive lattice strain is transformed into a type-II one such that the main intense peak and dip show blueshifts. Inversely, the tensile strain induces the formation of a triply degenerate nodal point in α-Li3N-type semimetals, causing the main intense peak and dip to show redshifts. Moreover, the influences of alloying and hole-doping in α-Li3N-type semimetals on the spin Hall effect of light are also discussed. Our findings may provide clear strategies to accurately engineer and detect the structural or phase change in topological materials.

Evapotranspiration in green stormwater infrastructure systems.

Evapotranspiration (ET) is a viable runoff reduction mechanism and an important player in the hydrologic cycle of vegetated green stormwater infrastructure (GSI). As a dynamic process, ET is dependent on both meteorological factors (e.g., rainfall characteristics, relative humidity, and air temperature) and GSI properties (e.g., soil media type). This paper investigates the role of ET in runoff volume reduction of green roofs and rain gardens through a comprehensive literature review. Evapotranspiration is mostly unaccounted in the design and crediting of GSI systems because of the complex interaction of soil, plants, and climate that makes its quantification difficult. To improve vegetated GSI design for runoff volume reduction, design methods should consider ET and infiltration processes concurrently. Two methods, complex and simple, are reviewed and discussed herein. The simple method requires minimal input information compared to the more complex continuous simulation method; however continuous simulation yields volume reduction values more similar to field observations. It is demonstrated that modifying the drainage structure and using fine-grained in-situ soils can potentially increase ET in vegetated GSI systems. None of the available ET predictive equations, mostly derived from agricultural sciences, are found to precisely match observed GSI ET data. Until further research is conducted on GSI ET estimation methods, the 1985 Hargreaves method is recommended when performing continuous simulations. The 1985 Hargreaves method is simple, requires limited input data that are readily available, and generates reasonable results. Technical recommendations and directions for future research are provided.

Risk analysis of urban stormwater infrastructure systems using fuzzy spatial multi-criteria decision making.

Design and performance of stormwater infrastructure systems in urban areas have direct implications in social, environmental and public health problems and are of utmost importance to urban authorities and managers. Risk analysis in urban stormwater systems has become a must because of the extensive consequences of flooding in urban areas and limited funding for the rehabilitation and renovation of stormwater systems. Complexity, multidimensionality, and inherent uncertainties of the urban stormwater systems require the risk analysis approach to be comprehensive and able to address different uncertainties and spatial aspects of the problem. The objective of this study is to provide a comprehensive framework for risk analysis in urban stormwater systems. Multi Criteria Decision Making (MCDM), geographic information systems (GIS), and fuzzy sets theory are used to consider the diverse risk-affecting criteria, facilitate the analysis of spatial data and information and formulate the ambiguity and uncertainty of problem, respectively. The presented framework uses a Fuzzy Analytic Hierarchy Process (FAHP) for determining the weights of risk-affecting criteria (i.e. Hydrological and Hydraulic, Traffic, Social, Economic, Environmental, Structural, and Green space) in the presence of multiple decision makers. The Autodesk Storm and Sanitary Analysis model is used for the Hydrological and Hydraulic simulations. FSAW and FTOPSIS methods are used to provide the final product of the framework, i.e., a risk map that presents a risk level for each channel in the network. The framework is applied to District 11 of the capital city of Iran, Tehran as a real case study. The resulted risk maps indicate a high or very high flooding risk for 17.07 to 41.95 km of the stormwater channels in the study area, covering about 10.5 to 26% of the total length of the channels. The presented framework was found to be a suitable risk analysis tool in urban stormwater systems.

Dependence of topological and optical properties on surface-terminated groups in two-dimensional molybdenum dinitride and tungsten dinitride nanosheets.

Using ab initio methods, the topological and optical properties of surface-functionalized XN2 sheets (X = Mo, W) were investigated. Based on first principles calculations and the K·p effective model, the existence of topological nodal-line states in potassium-functionalized XN2 sheets (K2MoN2 and K2WN2) is reported. This study shows that a nodal line ring exists near the Fermi level in the absence of spin-orbit coupling (SOC). When SOC is included, the band-crossing points are gapped, giving rise to a new nodal ring along Γ-K. This band-crossing is protected due to the existence of mirror reflection and time-reversal symmetry. These calculations demonstrate the inclusion of electron-hole (e-h) interactions, which were further confirmed through the optical absorption of functionalized MoN2, revealing the presence of strongly bound excitons below the absorption onset where they depend strongly on the terminated surface groups. Moreover, the surface terminated groups change the energy distribution range of the exciton, which can be used to tune the absorption of infrared (IR) and visible light. Interestingly, F2MoN2 has several strongly bound excitons, with the first exciton having a binding energy of 1.35 eV, larger than the corresponding one in the transition metal dichalcogenide MoS2.