The methods of moment and genetic algorithm (GA) are combined to optimize the Yagi Uda antenna array and Log periodic dipole antenna (LPDA) array. The element lengths and spacing are optimized for the Yagi Uda arra...The methods of moment and genetic algorithm (GA) are combined to optimize the Yagi Uda antenna array and Log periodic dipole antenna (LPDA) array. The element lengths and spacing are optimized for the Yagi Uda array; while the ratio factor of spacing to length as well as the ratio of length to diameter of the elements are optimized for LPDA array. The results show that the main parameters, such as gain and pattern, have been improved apparently; and the high back lobe level of LPDA can be reduced greatly, therefore, GA is a very competent method for optimizing the linear array as well as in other fields.展开更多
Cosmic rays(CR)play an important role in space weather-related studies.Their temporal variability,both of a quasi-periodic character as well as an irregular one,has been studied from ground-based direct measurements,a...Cosmic rays(CR)play an important role in space weather-related studies.Their temporal variability,both of a quasi-periodic character as well as an irregular one,has been studied from ground-based direct measurements,as well as from cosmogenic nuclides,over a long time.We attempt to describe the current knowledge of selected quasi-periodicities in CR flux in the energy range above the atmospheric threshold,from direct measurements.The power spectrum density(PSD)of the CR time series as measured by neutron monitors(NMs)and by muon detectors has a rather complicated character.Along with the shape(slope)of the PSD,knowledge of the contribution of quasi-periodic variations(q-per)to the CR signal is of importance for the modulation,as well as for checking the links of CR to space weather,and/or to space climate effects.The rotation of the Earth and solar rotation cause two types of mechanisms behind the certain q-per observed in secondary CR on the Earth’s surface.Solar activity and solar magnetic field cyclicities contribute to the q-per signals in CR if studied over a longer time.The complexity of the spatial structure of the interplanetary magnetic field(IMF)and its evolution within the heliosphere,in addition to the changes in the geomagnetic field,cause variability in contributions of the q-per in CR.Wavelet spectra are useful tools for checking the fine structure of q-per and their temporal behaviour.Over a long time NMs and muon telescopes provide information about q-per in CR.展开更多
文摘The methods of moment and genetic algorithm (GA) are combined to optimize the Yagi Uda antenna array and Log periodic dipole antenna (LPDA) array. The element lengths and spacing are optimized for the Yagi Uda array; while the ratio factor of spacing to length as well as the ratio of length to diameter of the elements are optimized for LPDA array. The results show that the main parameters, such as gain and pattern, have been improved apparently; and the high back lobe level of LPDA can be reduced greatly, therefore, GA is a very competent method for optimizing the linear array as well as in other fields.
基金Project VEGA 2/0040/13 for supportKuwait for supporting project HS-13-01
文摘Cosmic rays(CR)play an important role in space weather-related studies.Their temporal variability,both of a quasi-periodic character as well as an irregular one,has been studied from ground-based direct measurements,as well as from cosmogenic nuclides,over a long time.We attempt to describe the current knowledge of selected quasi-periodicities in CR flux in the energy range above the atmospheric threshold,from direct measurements.The power spectrum density(PSD)of the CR time series as measured by neutron monitors(NMs)and by muon detectors has a rather complicated character.Along with the shape(slope)of the PSD,knowledge of the contribution of quasi-periodic variations(q-per)to the CR signal is of importance for the modulation,as well as for checking the links of CR to space weather,and/or to space climate effects.The rotation of the Earth and solar rotation cause two types of mechanisms behind the certain q-per observed in secondary CR on the Earth’s surface.Solar activity and solar magnetic field cyclicities contribute to the q-per signals in CR if studied over a longer time.The complexity of the spatial structure of the interplanetary magnetic field(IMF)and its evolution within the heliosphere,in addition to the changes in the geomagnetic field,cause variability in contributions of the q-per in CR.Wavelet spectra are useful tools for checking the fine structure of q-per and their temporal behaviour.Over a long time NMs and muon telescopes provide information about q-per in CR.
