43,553 research outputs found
Applicability of Phase-Function Normalization Techniques for Radiation Transfer Computation
No full textThe applicability of recently-developed four phase-function (PF) normalization techniques for modeling radiation transfer in strongly anisotropic scattering media is intensively examined using the discrete-ordinate method. The three simple techniques via normalization of only the forward- and/or backward-scattering directions were shown to reduce normalization complexity whilst retaining diffuse radiation computation accuracy for Henyey-Greenstein (HG) PFs. For Legendre PFs, however, such simple techniques are found to result in unphysical negative PF value at one or few correction direction in some cases. Additionally, negative PF values can occur for these simple techniques for ballistic radiation transfer for both HG and Legendre PF types. If negative-intensity correction is applied, however, radiative heat transfer calculation can still converge regardless of the appearance of negative PF values. The relatively complex Hunter and Guo 2012 technique, in which normalization is realized through a correction matrix covering all discrete directions, is shown to be applicable for diffuse and ballistic radiation for both PF types.Peer reviewed
Solid-state stability of Z′ < 1 and Z′ = 2 polymorphs of N,N,N′,N′-tetrabenzylethylenediamine: a combined experimental and theoretical study
No full textThe synthesis and structural analysis by means of single crystal X-ray diffraction (SC-XRD) and DFT calculations, of two additional new polymorphs of the flexible organic molecule N,N,N′,N′-tetrabenzylethylenediamine (L) which is used as first sphere ligand in outer sphere adducts are reported. Slow crystallization of L in the solution-state yields two polymorphs (Lα-phase and Lβ-phase) with Z′ = 0.5, while fast crystallization by rapid cooling from solution and directly from melt, allows a third, less stable polymorph with Z′ = 2 (Lγ-phase). The latter structure can be seen as a low-density metastable phase obtained by trapping L molecules after they reached high mobility by thermal treatment (i.e., high energy state). The three L polymorphs have been also studied using quantum mechanical (QM) calculations specific for the solid state by comparing the sublimation energy for each polymorph, and by comparing the experimental X-ray structures against the optimized structures from DFT, showing that Lβ-phase is the most stable and Lγ-phase is the least stable phase. The high Z′ structure can be considered as a “crystal on the way” of a more stable form. These results provide insights about crystallization mechanisms and polymorphism in organic crystals. The potential use of conformational polymorphs of flexible ligands to prepare second sphere adducts with marked polymorphism is commented
Flow and heat transfer inside a new diversion-type gas heating device
No full textThe present paper characterizes ethylene glycol flow and heat transfer inside a new diversion-type gas heating device. A 2-D natural convection heat transfer model was built and solved by the finite volume method with unstructured body-fitted grids. The numerical model was first validated through temperature comparison with experimental measurements in a conventional device structure. Then analyses and comparisons of the flow fields and temperature distributions with use of different guide plate structures were carried out. The numerical results show that using the guide plate structures can form better organized flow patterns that augment heat transfer. The heat required for heating up the gas passing through the heating device can be reduced by 3% via installing two guide plates.Peer reviewed
Location of greenspace matters: a new approach to investigating the effect of the greenspace spatial pattern on urban heat environment
No full textContext: Although many prior efforts have found that both spatial composition and configuration of greenspaces significantly affect the urban heat environment globally, the spatially heterogeneous effects of greenspace spatial patterns on the urban heat environment remain poorly understood for urban spaces. Objectives: We proposed a spatially explicit approach to investigate the spatially heterogeneous cooling effects of greenspaces and map the relative contributions of the greenspace spatial patterns to the characterization of the urban heat environment. Methods: The proposed approach integrated the best subsets regression method, geographically weighted regression (GWR), and hierarchical partitioning analysis. Two cities in southeastern China were selected to test our model. Landsat 5 image obtained in the summer was used to estimate the land surface temperature (LST) and greenspace spatial patterns were extracted from 0.5-m aerial images. Results: The results revealed that LST of Guangzhou can be well predicted by the percent cover (PER), the number of patches (NP), the area-weighted mean of the patch area (AREA_AM), and the area-weighted mean of the perimeter-area fractal dimension (FRAC_MN), while that of Shenzhen can be predicted by PER, NP, AREA_AM and the mean of the related circumscribing circle (CIRCLE_MN). The inclusion of additional landscape metrics did not yield significantly higher accuracies. The dominant landscape metrics of greenspace that determine the LST varied spatially across the two cities, with the PER accounting for the greatest variation. Conclusion: The results of our work demonstrate that the location of greenspace is a significant factor affecting the urban heat environment. The proposed approach provides a new understanding of the interaction between the greenspace spatial patterns and urban heat environments, providing useful information for tailoring greenspace planning policies for specific local sites
Characteristics of land surface temperature clusters: Case study of the central urban area of Guangzhou
No full textLand surface temperature (LST) clusters within cities are typical regions reflecting the spatial heterogeneity of the urban thermal environment. To explore the spatial heterogeneity of the urban thermal environment in the central urban area of Guangzhou, we used the localized contour tree method to identify high- and low-LST clusters. In addition, to understand the characteristics of LST clusters (characteristics of the thermal environment and landscape distribution within the LST cluster), we obtained thermal field value (TFV) data based on the rules of equal-area division and determined the urban functional grid (UFG) based on multi-source data. We found that the characteristics of the high- and low-LST clusters significantly differed. Compared with that of the low-LST clusters, the spatial distribution of the high-LST clusters is denser. The number and total area of low-LST clusters are smaller than that of high-LST clusters, although the average area of low-LST clusters is larger. The spatial heterogeneity of the 10 types of UFGs within the high- and low-LST clusters is significant. The developed and ecological UFGs classified from 10 types of UFGs affect the formation of LST clusters. In addition, there are main UFGs that affect the mean TFV of the LST clusters. This study provides a new approach for the identification of LST clusters and a new perspective for exploring the spatial heterogeneity of urban thermal environments
Using nighttime light data to identify the structure of polycentric cities and evaluate urban centers
No full textStudying the structure of polycentric cities promotes a better understanding of the process of urban development and contributes to urban planning and management. However, existing studies cannot compare the level differences between urban centers and quantify the overall urban center development level within polycentric cities. Therefore, we combined nighttime light (NTL) data and the natural city (NC) to conduct this study from multiple perspectives. First, NCs were determined from Luojia-1A NTL data with high spatial resolution. Second, urban centers were selected from NCs. Third, urban center level (UCL) was proposed to compare the level differences of urban centers. Fourth, urban center development index (UCDI) was proposed to quantify the overall urban center development level within a polycentric city. A quantitative verification method was used to confirm that the detection accuracy of urban center identification is high. Furthermore, the applicability of the proposed method in different NTL datasets was verified by the identification of urban centers and the calculation of UCDIs. Unlike traditional methods, the shape and scope of the urban center identified using the proposed method are not restricted by administrative boundaries. Moreover, the level differences of urban centers and the overall urban center development level within a polycentric city, can be expressed by quantitative indicators, which helps in comparing the differences between urban centers
Reborn Translated: Xiaolu Guo as a World Author
No full textThis paper introduces the concept of “world author,” taking as its exemplar the Chinese British writer and filmmaker Xiaolu Guo. It investigates how Guo utilizes her bilingualism to construct and negotiate her creative agency, especially when dealing with the political and commercial forces imposed on diasporic authors. Through engaging with Rebecca Walkowitz’s idea of world literature as being “born translated,” I point out that the translational should not be limited to the thematic and representational arrangements internal to a given text. Instead, translation as movements between linguistic systems and media forms can generate multipleversions of a text, to the point that such translational multiplicity fundamentally challenges its supposed singularity. This argument is demonstrated with Guo’s self-translation of the stories of Fenfang and her filmic adaptation of the novel UFO in Her Eyes. Through these examples of what I call “translational rebirths,” I demonstrate the importance of paratextual details and intertextual connections between clusters of an author’s creative output for the interpretation and appreciation of l’oeuvre d’un auteur instead of une oeuvre d’art. This case study also shows the need for the academic debates on world literature to go beyond the singularity of texts and evaluative criteria of worldliness based on this assumption, so that the discipline can realize its full potential in accommodating multilingual transnational authors like Guo
Estimates of Power Shortages and Affected Populations during the Initial Period of the Ukrainian-Russian Conflict
No full textSince the outbreak of the Ukrainian-Russian conflict on 24 February 2022, Ukraine’s economy, society, and cities have been devastated and struck on multiple fronts, with large numbers of refugees fleeing to neighboring countries. The lighting systems in Ukrainian cities have been severely restricted due to Russian missile bombing and curfew policies. The power shortages adversely affected the livelihoods of the Ukrainian residents dramatically. For a timely assessment of the power shortages’ extent and the affected population in Ukraine, this study tracked the dynamics of nighttime light emissions in Ukraine based on the newly developed daily Black Marble product (VNP46A2) from NASA. The results show that the average light radiance in Ukrainian urban areas has decreased by about 37% since the eruption of the war, with Kiev city being the most dramatic region, having a post-conflict decrease of about 51%. In addition, by introducing near-real-time population data, we have implemented a survey of the affected population in Ukraine suffering from war-induced power shortages. Estimates show that about 17.3 million Ukrainian residents were affected by power shortages. In more detail, the number of children under 10 years old was about 2.35 million (about 5.24% of the total population), while the number of elderly people over 60 years old was about 3.53 million (about 7.86% of the total population). Generally, the results of this study could contribute positively to the timely assessment of the impact of the conflict and the implementation of humanitarian relief
- …
