in some mobile systems, intelligent antennas are used to increase efficiency in a wide frequency band and different environmental and electromagnetic conditions. environmental factors, such as position of nearby objects, antenna mobility and even user type, can vary the antenna input impedance appreciably. therefore, it is necessary to incorporate an adaptive impedance matching circuit between ...

A quadrifilar helix antenna (QHA) operating at 0.94GHz is designed and realized in this paper. The designed QHA consists of four helical conductors which are excited in phase quadrature by employing a Wilkinson divider which shows good performance in return loss and transmission characteristic. According to the designed parameters of the helices and Wilkinson divider, a QHA is fabricated and me...

This paper describes an antenna system combining Global Navigation Satellite System (GNSS) with Iridium satellite communications and UHF 225-512 MHz communications on a handset to provide an integrated Communications Navigation (Comm/Nav) antenna. The GPS/GNSS/Iridium antenna is a folded Quadrifilar Helix Antenna (QHA) with novel features which improve frequency coverage compared to existing QH...

Analysis of the mutual coupling and its effect on the CQHA performance in LMS MIMO system are investigated and presented in this paper. Due to the complexity of the CQHA structure, the mutual coupling effects were mainly studied using electromagnetic simulation. The effect of the separation spacing between inner and outer QHA on the mutual coupling was investigated by comparing the element isol...

Acute reduction of portal vein blood flow (Qpv) increases hepatic arterial perfusion (Qha) [the hepatic arterial buffer response (HABR)]. Angiotensin II (AT-II) reduces Qpv, but its effect on HABR is not known. We explored interactions of AT-II and enalapril with hepatic blood flow regulation. Twenty healthy anesthetized pigs were randomized to receive AT-II (n = 8) from 5 to 61 ng/kg per min, ...

First-principles and classical molecular dynamics simulations have been performed to study the structural and thermodynamic properties of Pd under pressure. By comparing the Gibbs free energy, in the quasiharmonic approximation (QHA), of the face-centered cubic (fcc) phase with those of the hexagonal-close-packed (hcp) and body-centered-cubic (bcc) phases we found that the fcc phase is stable u...

We show here how first-principles quasiharmonic approximation QHA calculations in its simplest statically constrained form can be used to predict crystal structures at high temperatures. This approximation has been extensively used to investigate thermodynamic properties of Earth forming minerals and has offered excellent results for the major mantle phases at relevant conditions. We carefully ...

[1] The vibrational properties of Mg2SiO4 wadsleyite have been calculated over a wide pressure range using density functional perturbation theory (DFPT). Both the normal mode frequencies and their volume dependences are consistent with the available Raman and infrared data. We provide detailed information about vibrational properties that are still not experimentally available. The vibrational ...

We present inelastic neutron scattering measurements of Y3Al5O12. The measured neutron-weighted phonon density-of-states and optical frequencies are compared with the results from atomistic calculations within Quasi-Harmonic Approximation (QHA) over a wide temperature range, using both first principles density functional theory also an extended empirical interatomic-potential shell model scheme...

filtering of web pages with inappropriate contents is one of the major issues in the field of intelligent network's security. having a good intelligent filtering method with high accuracy and speed is needed for any country in order to control users' access to the web. so, it has been considered by many researchers. presenting web pages in an understandable way by machines is one of the most im...