EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposedPublisher PDFPeer reviewe

An ultra-light cylindrical GEM detector as inner tracker at KLOE-2

Abstract We are developing a low-mass, fully cylindrical and dead-zone-free GEM detector as inner tracker for the KLOE experiment upgrade at the DA Φ NE Φ factory. The inner tracker will be composed of five concentric layers of cylindrical triple-GEM detectors (C-GEM), completely realized with very thin polyimide foils. The final result is a very light detector: only 0.2% of X 0 per layer inside the active area. We successfully built and tested with an X-ray gun a small-size prototype operated in current mode with an Ar/CO 2 = 70 / 30 gas mixture. The very positive results obtained with the prototype open the way for a completely new and competitive category of ultra-light fully sensitive vertex detectors for high-energy physics experiments

Synthesis of circular isophoric sparse arrays by using compressive-sensing

A design approach for large-scale sparse arrays based on Compressive Sensing has been recently introduced in the literature and extended to include complex EM effects and scan performance. However, that approach cannot directly control the number of excitation amplitudes. Here, we apply a two-step procedure that first synthesizes continuous rings with unconstrained amplitudes using an iterative ℓ1-norm minimization approach, and then replaces them with a circular isophoric ring array with a number of elements proportional to the original amplitude of each ring. The procedure is demonstrated for an isotropic array of a 10λ radius, for which a reference solution based on the analytical density-taper approach is available in the literature. Results show the capability of the proposed method to achieve a significant reduction of the array aperture (20%) with 25% less elements or 4dB lower peak side lobe level

Reconfigurable aperiodic array synthesis by Compressive Sensing

Aperiodic arrays represent an attractive technology for applications requiring multiple pencil beams or contour beams, such as in radars, satellite communication and mw-sensor systems. These antennas are typically designed to either produce high-directivity beams over a given scan range or a single beam with a specified complex shape. In this manuscript we present a CS approach for the synthesis of a single aperiodic array layout capable of radiating multiple beams with different shapes The approach aims at designing reconfigurable arrays with least number of elements as well as the optimal excitation set for each of the desired beams. Preliminary results for an array providing both pencil and a flattop coverage are presented

Multi-Element Aperiodic Array Synthesis by Compressive Sensing

In recent years, Compressive Sensing has attracted considerable attention in various areas of antennas and electromagnetics, including the synthesis of sparse array antennas. The CS synthesis of arrays achieves higher accuracy than analytical methods and allows for the fast and deterministic design of large complex arrays, without resorting to computationally expensive Global Optimization methods. The CS approach presented here has been previously studied by the authors for the design of maximally sparse arrays in the presence of mutual coupling effects, beam scanning degradation, as well as the imposition of symmetries for design modularity. In this manuscript the authors demonstrate another (yet unexplored) capability of such an approach, i.e., to incorporate different element types and determine their optimum combination in the course of the array synthesis procedure. Numerical examples are illustrated for large arrays comprising uniform circular aperture elements and operating in a SATCOM multi-beam scenario. It is shown that by exploiting this capability it is possible to simultaneously reduce the number of elements and gain scan loss

Application of the Compressive-Sensing Approach to the Design of Sparse Arrays for SATCOM Applications

Current SATCOM systems employ multiple reflectors with a one-feed-per-beam configuration to synthesize narrow spot-beams. However, these systems are very complex and offer very limited reconfigurability. Active antenna arrays are attractive solutions [1], although are often expensive due to the large number of elements and electronic components involved. Aperiodic array antennas can substantially reduce the number of elements and costs with respect to regular arrays but their design is challenging [2]. Several synthesis methods have been proposed, yet aperiodic array design techniques are not as mature as those in use for their regular array counterparts. These methods are often either: (i) accurate but computationally expensive (e.g. Genetic Algorithms [3]), or; (ii) efficient but simplified (e.g. Density Tapered method [4]). Compressive Sensing (CS) has been recently applied to the synthesis of sparse antenna arrays. The method can optimize large maximally sparse antenna array problems in a fast, deterministic and flexible way [5]. In previous research publications, the authors have (i) extended the original formulation to the multi-beam scenario; (ii) exploited array layout symmetry and modular design; and (iii) hybridized the original iterative optimization procedure with a full-wave EM analysis, so as to include the effects of mutual coupling into the design process and studied for arrays of strongly coupled antennas elements, such as dipoles, as well as large planar arrays of pipe horns [6, 7]. Additionally the authors have addressed multi element type design [8] and, more recently, are investigating reconfigurable arrays (i.e. arrays designed to provide a set of arbitrary-shaped beams) and isophoric arrays (i.e. arrays with a single excitation amplitude). The main directions are summarized in Fig. 1

Characteristic Basis Function Analysis of Large Aperture-Fed Antenna Arrays

The Characteristic Basis Function Method (CBFM) is applied to rapidly compute the impedance and radiation characteristics of electrically large aperture-fed antenna arrays. A stationary formula for the antenna input admittance matrix is expressed in terms of a product of matrix blocks that are readily available from a method of moment formulation. Numerical results are shown for large arrays of waveguide antennas requiring more than 2 million basis functions, which is reduced by a factor of 9000, so that the solution for the currents are still obtainable in-core on a single desktop computer, while being orders faster than commercial software codes or a standard MoM approach, provided that sufficient memory is available for the Gaussian elimination

A Simple Method for Optimal Antenna Array Thinning Using a Broadside MaxGain Beamformer

A simple and effective method for optimal antenna array thinning employing a broadside-scanned maximum gain beamformer is presented. Starting from a fully populated λ/2-spaced regular lattice, the array is thinned by progressively 'turning off' the element(s) with the lowest weight(s) of the weight vector realizing maximum gain. The accuracy and effectiveness of the method is validated against a rigorous combinatorial search method that can be used to find the optimal irregular array configuration solution in small to moderate-sized arrays. Furthermore, to evaluate the robustness of the proposed approach, the effects of beam steering have been investigated for linear arrays consisting of 10-40 antenna elements as well. Good results can be obtained for close to broadside scanned arrays, which is of importance for the directly radiating arrays that are currently being considered as modern satellite systems

Performances of linseed oil-free bakelite RPC prototypes with cosmic ray muons

A comparative study has been performed on Resistive Plate Chambers (RPC) made of two different grades of bakelite paper laminates, produced and commercially available in India. The chambers, operated in the streamer mode using argon, tetrafluroethane and isobutane in 34:59:7 mixing ratio, are tested for the efficiency and the stability with cosmic rays. A particular grade of bakelite (P-120, NEMA LI-1989 Grade XXX), used for high voltage insulation in humid conditions, was found to give satisfactory performance with stable efficiency of > 96% continuously for more than 130 days. A thin coating of silicone fluid on the inner surfaces of the bakelite RPC is found to be necessary for operation of the detector.Comment: 6 figures, Presented in IX International Workshop on Resistive Plate Chamber and related Detectors-2007, TIFR, Mumbai, India, February 13-16, 200

COVID-19 dentistry-related aspects: a literature overview

A new coronavirus (Sars-CoV-2) was detected in China at the end of 2019 and has since caused a worldwide pandemic. This virus is responsible for an acute respiratory syndrome (COVID-19), distinguished by a potentially lethal interstitial bilateral pneumonia. Because Sars-CoV-2 is highly infective through airborne contamination, the high infection risk in the dental environment is a serious problem for both professional practitioners and patients. This literature overview provides a description of the clinical aspects of COVID-19 and its transmission, while supplying valuable information regarding protection and prevention measures