The Dry Cracking of Cementitious Materials in the Eccentric Ring Test and the Concentric Ring Test

In order to reduce the randomness of the occurrence of cracks and shorten the long cracking time in the traditional concentric ring tests,the elliptical ring test,the square-eccentric ring test,and the eccentric ring test have been gradually developed.In this paper,we reported experiments on the eccentric ring test and concentric ring test that were carried out to compare the differences between the two methods.It is found that an increase in the water-cement ratio and the amount of aggregate will increase the cracking time.However,a more obvious cracking tendency of cement-based materials can be seen in the eccentric ring test.The correlation between humidity and strain was established by the use of the Kelvin equation and the Laplace equation so that the coupling analysis of humidity and strain during the drying process of cement-based materials could be determined.The experimental results show that the external surface humidity will decrease rapidly in the early stage of drying,while the interior areas of the cement-based materials decrease more slowly.The closer to the inner circle will decrease the humidity slowly.

Modelling of Wideband Concentric Ring Frequency Selective Surface for 5G Devices

Frequency selective surfaces(FSSs)play an important role in wireless systems as these can be used as filters,in isolating the unwanted radiation,in microstrip patch antennas for improving the performance of these antennas and in other 5G applications.The analysis and design of the double concentric ring frequency selective surface(DCRFSS)is presented in this research.In the sub-6 GHz 5G FR1 spectrum,a computational synthesis technique for creating DCRFSS based spatial filters is proposed.The analytical tools presented in this study can be used to gain a better understanding of filtering processes and for constructing the spatial filters.Variation of the loop sizes,angles of incidence,and polarization of the concentric rings are the factors which influence the transmission coefficient as per the thorough investigation performed in this paper.A novel synthesis approach based on mathematical equations that may be used to determine the physical parameters ofDCRFSSbased spatial filters is presented.The proposed synthesis technique is validated by comparing results from high frequency structure simulator(HFSS),Ansys electronic desktop circuit editor,and an experimental setup.Furthermore,the findings acquired from a unit cell are expanded to a 2×2 array,which shows identical performance and therefore proves its stability.

Spatiotemporal analysis of urban growth on forest and agricultural land using geospatial techniques and Shannon entropy method in the satellite town of Ethiopia,the western fringe of Addis Ababa city

Rapid conversion of conserved land and cropland to non-agricultural purposes is threatening the ecological areas and dominant agricultural activities that are the main sources of livelihood in urban fringe areas of Addis Ababa City.The combinations of government policy,socioeconomic,demographic dynamics,and biophysical triggers have driven such transformation.However,the recent fast urban expansion and infrastructural development could have accelerated the severity and rate at which urban growth impacts the ecosystem and fertile agricultural land.Yet,little attention is given about their impacts on forest and farming communities in the western fringe areas of Addis Ababa during the recent past.This study,therefore,aimed at quantifying and analyzing the trends of the urban growth and its impacts on flora and agricultural land in Sebeta-Awas town using an integrated GIS tool,remote sensing technique,and Shannon entropy method.Landsat TM of 1986,ETM+of 2002,and OLI of 2019 were used to produce land use/land cover(LULC)classes.Object-based classification technique was carried out to generate the LULC and to measure the changes in the urban land-use class within the satellite town in the year 1986,2002,and 2019.Shannon entropy method was applied to model study area’s urban sprawl,growth trend,and spatial change.Over the past three decades(1986-2019),Sebeta-Awas town has experienced severe urban sprawl following lack of proper development control and management.The annual urban growth rates of 1.2,5.5,and~15%for the periods of 1986,2002,and 2019,respectively were obtained mainly at the expenses of agricultural land(25.48%)and forest land(16.6%),catalyzed urban sprawl which finally led to serious deforestation and reduction in rural farmland.The findings indicate that the average of entropy index increased from 0.02 in the year 1986 to 0.996 in the year 2019,indicating more dispersed urban growth to the outskirts,and spatially indicating anticlockwise shifting.In this regard,more than 90.2%of forest loss due to agricultural encroachment,built-up area expansion,and construction was widely observed in Sebeta and Alem Gena areas,of course,Northeast zone in this study.It is concluded that deforestation and continual evacuation of farming communities in the urban fringe areas due to rapid urban expansion in the name of investment and infrastructural development is expected to be worsened in the near future unless strong policy revision and management actions are undertaken.

A comparative study on four major cities in Northeastern Thailand using urban land density function

Urban land density is an important factor to understand how cities expand.An“Inverse S-shape Rule”was implemented for the first time to analyze urban land density in Northeastern Thailand using the four cities Khon Kaen,Udon Thani,Nakhon Phanom,and Nong Khai as study sites.Land density function was tested using different data classification techniques from previous studies.Each city was investigated over two different time periods between 2002 and 2015.Declining pattern characteristics of metropolitan area density outward from city centers can be quantified by fitting the parameters to urban land density functions.An inverse S-shape function was identified as the best data fit.The four selected cities showed conventional density variation for decline in urban land area from city centers to outlying areas.Overall trend indicated that cities became more compact over time since the density differences between the urban core and urban fringe were greater with increasing infilling growth within the urban boundary.All four cities increased in size over time;however,the increasing amount of built-up land in the surrounding rural areas did not follow the same trend in each case.Some functional parameters required careful interpretation because of the linear shape of the city as in the case of Nakhon Phanom.Using highly detailed urban data resulted in lower densities of urban areas compared to the conventional pixel-based classification,and this affected the overall shape of the inverse S-shape function.The fitted parameters and their changing trends indicated that the urban land density function was useful for understanding urban form and urban sprawl in Thailand.Results can be used to develop a specific framework for other cities with similar attributes in the future.

Widely Tunable Fiber Ring Laser with High Concentration Erbium-Doped Fiber

We report a high power and widely tunable erbium-doped fiber (EDF) ring laser using 1480nm pump and high concentration EDF. Large tuning range up to 105nm (1513-1618 nm) has been obtained by optimizing of the EDF length.