Introduction. Rapid urbanization causes critical changes in global, as well as changes in earth surface temperature. The transformation of land use purposes significantly affects the surface temperature and exacerbates the effect of the negative heat island. Therefore, it is important to conduct a study to optimize urban cooling. Gives town-planning recommendations for limiting the negative impact of urban heat islands (UHI) on human. Analyzing urban and suburban planning in the city of Hanoi, the author proposes the use of certain town-planning principles that contribute to reducing the effect UHI. Materials and methods. This study is focused on green space using as a means of combating environmental problems due to the effect of urban heat island and creating a favorable urban ecological environment. The definition of the relationship between the ratio of green spaces and a decrease in temperature is given. The analysis was taken from 21 green spaces of the city of Hanoi. Results. The study showed a relationship between the intensity of heat reduction and the shape indicator of green space - a linear inverted system and the positive effect of the green zone on reducing the effects of heat island. Conclusions. One of the most important tasks of a city planner is the placement and adjustment of industrial zones of the city, the main transport arteries of the city, meaning that the placement and planning of industrial, residential and public territories, and also the system of roads depends on the formation of “heat islands”, which in the tropical climate of Vietnam, adversely affects human health.

Introduction. The simulation of urban microclimates, including the urban heat island (UHI) phenomenon, has turned all the more important for urban planning. Presently, the analysis of this phenomenon is feasible thanks to high computational power of computers and links between computer modeling instruments and databases that contain information on urban environments. Advanced hardware helps to study characteristics of urban microclimates by analyzing and assessing their exposure to various climatic and anthropogenic urban factors (urban morphology, land use, construction sites, albedo, etc.) Materials and methods. ENVI-met is a software model used to simulate microclimates in urban environments. This software can optimize proportions of buildings and streets, outdoor shading, outdoor space planning, air movement, and use of construction materials in respect of thermal comfort and measures taken to mitigate consequences of urban heat islands within the framework of environmental planning of new districts. The co-authors analyze Ha Dong, a Hanoi district characterized by the high density of high-rise buildings. The co-authors consider the example of this district to study the process of detailed simulation, analysis and assessment of UHI effects. Results. ENVI-met and its simulation capacity is employed to prove that the air temperature in Wang Fu, an urban area, gradually rises from 8 am to 5 pm, when the air temperature reaches its maximal value of 32.28 °C during the period of sixteen hours. UHI intensity was maximal between midnight and 1 am on May 29, 2017, when it reached 2.41 °C. Conclusions. Cities are complex systems exposed to a wide array of interactive factors that influence the urban climate change. The value of R2 equal to 0.94 has proven the reliability of ENVI-met applied to simulate and imitate the climate of Hanoi, which is a hot and damp tropical city.

We present a theoretical study of roughness-related scattering mechanisms for electrons in single heterostructures, especilaly in Gaussian-doped ZnO surface quantum wells. We show that besides the conventional scatterings there must exist roughness-related mechanisms of charge origin, which stem from fluctuations the electron density and the donor density in the bulk ZnO. The strength of the two charge-origin scattering sources is found to be comparable with the one of the standard one from fluctuations in the barrier position. The effect of the dielectric discontinuity on the scattering mechanisms is discussed.

Introduction. The paper presents a method to simulate the maximum intensity of urban heat island (UHI) based on urban geometry using H/W parameters, where H — building height and W — width of neighboring street. Urban heat island is determined by the increase in the temperature in the city centers compared to the surrounding rural areas. Materials and methods. The research is based on remote sensing technology to analyze the thermal surface of Hanoi city. It was run in different seasons thereby determining the expansion of the heat island effect over the years. The research method is based on Oke’s model number theory. An area is selected in the city center with high construction density to simulate the intensity of UHI. Results. The study shows that population growth affects the urbanization process. Over the years the urban land area is affected by the expansion of the heat island effect. Based on Oke’s model, calculations of UHI maximum intensity in Nhan Chinh block (Thanh Xuan district of Hanoi) were made. The estimation showed that the higher the building and the greater the distance from the road, the greater the intensity of the heat island. Accordingly, the lower the building and the smaller the distance from the road, the lower the intensity of the heat island. Conclusions. Using the Oke’s model to estimate heat island intensity based on the height-to-distance ratio of a building to a road makes process modeling possible. As a result, the planner can offer solutions to eliminate the negative impact of the urban heat island effect.

Abstract. We present a theoretical study of the effect due to spontaneous polarization of ZnO on the low-temperature mobility of the two-dimensional electron gas (2DEG) in a ZnO surface quantum well (SFQW). We proved that for the O-polar face this causes an attraction of electrons by the positive charges bound on the surface, while for the Zn-polar face a repulsion of them far away therefrom by the negative bound charges of the same magnitude. Accordingly, surface roughness scattering is drastically enhanced in the former case, but reduced in the latter one. Therefore, the low-temperature 2DEG mobility in ZnO SFQWs with O-polar face is found to be dominated by surface roughness. Our theory was illustrated for the sample prepared by bombardment of the O-polar face by 100-eV hydrogen ions. The surface roughness scattering enables an explanation of the 2DEG mobility, especially, the reason of low values for the mobility in the dependence from the carrier density which has not been understood when starting from impurity scattering.