Optimizing Antenna Arrays for Spatial Multiplexing: Towards 6G Systems

In this paper we discuss the design of antenna arrays to be used for multiplexing applications. In particular, we introduce a suitable performance index to analyze the effect of the antenna geometry and the distribution of users for the overall performance of Multi-User Multiple Input Multiple Output systems. By means of such performance index, antenna arrays can be designed so as to increase the number of multiplexed parallel sub-channels. Numerical results show that a proper design could allow to double the contemporary served users and the overall system throughput

Spectral and polarimetric characterization of the Gas Pixel Detector filled with dimethyl ether

The Gas Pixel Detector belongs to the very limited class of gas detectors optimized for the measurement of X-ray polarization in the emission of astrophysical sources. The choice of the mixture in which X-ray photons are absorbed and photoelectrons propagate, deeply affects both the energy range of the instrument and its performance in terms of gain, track dimension and ultimately, polarimetric sensitivity. Here we present the characterization of the Gas Pixel Detector with a 1 cm thick cell filled with dimethyl ether (DME) at 0.79 atm, selected among other mixtures for the very low diffusion coefficient. Almost completely polarized and monochromatic photons were produced at the calibration facility built at INAF/IASF-Rome exploiting Bragg diffraction at nearly 45 degrees. For the first time ever, we measured the modulation factor and the spectral capabilities of the instrument at energies as low as 2.0 keV, but also at 2.6 keV, 3.7 keV, 4.0 keV, 5.2 keV and 7.8 keV. These measurements cover almost completely the energy range of the instrument and allows to compare the sensitivity achieved with that of the standard mixture, composed of helium and DME.Comment: 20 pages, 11 figures, 5 tables. Accepted for publication by NIM

Awake fiberoptic intubation in patients with stenosis of the upper airways. Utility of the laryngeal nerve block

Awake fiberoptic intubation (AFOI) is mandatory to manage difficult airways. Superior laryngeal nerve block (SLNB) could reduce risks and improve patient comfort. The aim of this study is to assess the procedural comfort of SLNB during AFOI in a population of patients undergoing upper airway oncological surgery. Forty patients were randomized into two groups and were treated with continuous infusion of remifentanil, topic anesthesia and intercricoid block. In the study group (=20), SLNB was performed with lidocaine (L-SLNB); in the control group (n=20) SLNB was performed using saline (S-SLNB). AFOI was more comfortable in the L-SLNB group compared to S-SLNB patients [FOICS ≤ 1 in 18 patients (90%) L-SLNB; 2 (10%) S-SLNB (P<0.001)]. Intubation was faster in L-SLNB (47.45 ±15.38 sec) than S-SLNB (80.15 ±37.91 sec) (p<0.001). The SLNB procedure during AFOI is a safe and comfortable procedure in a population of patients undergoing upper airways surgery. Time to intubation was shorter in L-SLNB than in S-SLNB

Low energy polarization sensitivity of the Gas Pixel Detector

An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been proposed to be included in many upcoming space missions to fill the gap of about 30 years from the first (and to date only) positive measurement of polarized X-ray emission from an astrophysical source. The estimated sensitivity of the current prototype peaks at an energy of about 3 keV, but the lack of readily available polarized sources in this energy range has prevented the measurement of detector polarimetric performances. In this paper we present the measurement of the Gas Pixel Detector polarimetric sensitivity at energies of a few keV and the new, light, compact and transportable polarized source that was devised and built to this aim. Polarized photons are produced, from unpolarized radiation generated with an X-ray tube, by means of Bragg diffraction at nearly 45 degrees. The employment of mosaic graphite and flat aluminum crystals allow the production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from the diffraction of unpolarized continuum or line emission. The measured modulation factor of the Gas Pixel Detector at these energies is in good agreement with the estimates derived from a Monte Carlo software, which was up to now employed for driving the development of the instrument and for estimating its low energy sensitivity. In this paper we present the excellent polarimetric performance of the Gas Pixel Detector at energies where the peak sensitivity is expected. These measurements not only support our previous claims of high sensitivity but confirm the feasibility of astrophysical X-ray photoelectric polarimetry.Comment: 15 pages, 12 figures. Accepted for publication in NIM