The method of this paper is based on change in the geometrical shape of the reflectarray plane which is similar to a concave shape and with this changing, it is tried to make the incident waves orthogonal as much as p...The method of this paper is based on change in the geometrical shape of the reflectarray plane which is similar to a concave shape and with this changing, it is tried to make the incident waves orthogonal as much as possible in order to remove the phase error caused by incident wave variation. The other benefit of this work is omitting frequency change error caused by path difference between reflectarray antenna bandwidth. Two types of reflectarray antennas operating at X-band frequency with a linear polarization are considered in this design: concave and flat reflectarray antennas with the diameter of 135 mm. elements which are used in this paper are variable-size patches. The proposed reflectarray antenna (concave) approximately has 25% 3-dB bandwidth which shows an increment in bandwidth about 18% compared to flat reflectarray antenna.展开更多
The negative effects of greenhouse gas(GHG)emissions,such as climate change and global warming,have become major environmental concerns,especially for the construction industry,which is the third-highest source of GHG...The negative effects of greenhouse gas(GHG)emissions,such as climate change and global warming,have become major environmental concerns,especially for the construction industry,which is the third-highest source of GHG emissions among industrialized countries.Presently,underground utility projects are considered one of the most common types of construction,primarily due to aging infrastructure across North America and the subsequent rehabilitation of old pipelines and installation of new pipelines and facilities.Given the increasing demand being placed on the industry,the need to study airborne emissions associated with different underground construction technologies has risen,which will be helpful in selecting the most sus-tainable underground construction methods.This study investigates pollutant emis-sion from two common trenchless methods used in underground construction,hand tunneling and pilot-tube method(PTM),through their varying GHG footprint sources and emissions measured by the United States Environmental Protection Agency(EPA).This paper analyzes a case from Edmonton,Canada,in which both PTM and hand tunneling were used by comparing the suggested indexes,including HC,CO,NO_(3) PM,CO_(2),and SO_(2).In this case study,both methods were used in the installation of a new 68-cm diameter(27 in.)clay sewer line with an overbur-den depth of 12.9 m(42 ft)and length of 60 m(197 ft).Results indicated that the amount of airborne emissions was reduced between 17%and 36%through the use of PTM compared to the traditional hand tunnelling method.展开更多
文摘The method of this paper is based on change in the geometrical shape of the reflectarray plane which is similar to a concave shape and with this changing, it is tried to make the incident waves orthogonal as much as possible in order to remove the phase error caused by incident wave variation. The other benefit of this work is omitting frequency change error caused by path difference between reflectarray antenna bandwidth. Two types of reflectarray antennas operating at X-band frequency with a linear polarization are considered in this design: concave and flat reflectarray antennas with the diameter of 135 mm. elements which are used in this paper are variable-size patches. The proposed reflectarray antenna (concave) approximately has 25% 3-dB bandwidth which shows an increment in bandwidth about 18% compared to flat reflectarray antenna.
文摘The negative effects of greenhouse gas(GHG)emissions,such as climate change and global warming,have become major environmental concerns,especially for the construction industry,which is the third-highest source of GHG emissions among industrialized countries.Presently,underground utility projects are considered one of the most common types of construction,primarily due to aging infrastructure across North America and the subsequent rehabilitation of old pipelines and installation of new pipelines and facilities.Given the increasing demand being placed on the industry,the need to study airborne emissions associated with different underground construction technologies has risen,which will be helpful in selecting the most sus-tainable underground construction methods.This study investigates pollutant emis-sion from two common trenchless methods used in underground construction,hand tunneling and pilot-tube method(PTM),through their varying GHG footprint sources and emissions measured by the United States Environmental Protection Agency(EPA).This paper analyzes a case from Edmonton,Canada,in which both PTM and hand tunneling were used by comparing the suggested indexes,including HC,CO,NO_(3) PM,CO_(2),and SO_(2).In this case study,both methods were used in the installation of a new 68-cm diameter(27 in.)clay sewer line with an overbur-den depth of 12.9 m(42 ft)and length of 60 m(197 ft).Results indicated that the amount of airborne emissions was reduced between 17%and 36%through the use of PTM compared to the traditional hand tunnelling method.
