OAM multiple transmission using uniform circular arrays: numerical modeling and experimental verification with two digital television signals

In this work we present the outcomes of a radio-frequency OAM transmission between two antenna arrays performed in a real-world context. The analysis is supplemented by deep simulative investigations able to provide both a preliminary overview of the experimental scenario and a posteriori validation of the achieved results. As a first step, the far-field OAM communication link is tested at various frequencies and the corresponding link budget is studied by means of an angular scan generated by the rotation of the receiving system. Then, on the same site, two digital television signals encoded as OAM modes ($\ell$=1 and $\ell$=-1) are simultaneously transmitted at a common frequency of 198.5 MHz with good mode insulation.Comment: 16 pages, 14 figure

A New Approach to the Link Budget Concept for an OAM Communication Link

Following on from the increasing interest for electromagnetic waves carrying Orbital Angular Momentum (OAM), different configurations of antenna systems able to generate such beams have been proposed. However, in our opinion, a traditional radiation pattern approach does not provide the right picture of an OAM-based communication link. For this reason we propose a new general concept, the "OAM-link pattern", which takes into account the peculiar phase structure characterizing these waves. Focusing on OAM transmissions between antenna arrays, we introduce a formula for the link budget evaluation which describes the whole communication link and directly leads to a "classically shaped" main lobe pattern for a proper rephased reception in the case of uniform circular arrays.Comment: 4 pages, 3 figure

The Effects of Thermally Induced Interparticle Forces on the Expansion and Bubbling Behaviour of a Fluidized Bed

The paper addresses the transition to the bubbling regime of solid beds belonging to Geldart’s group A, from ambient temperature to 500°C. The analysis of the influence exerted by operating temperature on the variables that characterize both the homogeneous expansion of the bed and the onset of a steady bubbling regime is conducted on the fluidization map of the fluidized bed, namely the voidage velocity diagram into which results of the fluidization and bed collapse experiments are merged. The results obtained show that at elevated temperatures the ability of the fluidized bed to preserve the homogeneous fluidization regime is extended to unusually high voidage levels. Even past the appearance of a steady bubble flow, the dense phase voidage exhibits a residual dependence on interparticle forces induced by high temperature

TOWARDS A THEORETICAL MODEL OF SEGREGATING FLUIDIZATION OF TWO-SOLID BEDS

Fluidization of beds of two dissimilar solids is modelled by reworking the fundamental equations of fluidization. The approach followed illustrates the relationship between bed suspension and component segregation, as determined by differences in solid density and size. The need for empirical parameters is drastically reduced so that a unique representation of all types of mixture behaviour seems possible

The Fluidization Pattern of Density-Segregating Two-Solid Beds

An experimental work is presented meant to clarify the specific role played by density differences between components in the segregating fluidization process of two-solid beds. The overall behaviour of such systems is characterized by substituting the traditional concept of “minimum fluidization velocity” of the binary mixture with the “velocity interval of fluidization” of the bed, which is limited by its “initial” and “final” fluidization velocity”. The dependence of these characteristic velocities on parameters such as component densities and mixture composition is illustrated by several series of experiments. The experimental results are analysed in the light of the fundamental theory, so as to establish quantitative relationships for their prediction. The evolution of the axial profile of component concentration at varying fluidization velocity is also discussed

Oscillation thresholds via the novel MBR method with application to oncolytic virotherapy

Oncolytic virotherapy is a therapy for the treatment of malignant tumours. In some undesirable cases, the injection of viral particles can lead to stationary oscillations, thus preventing the full destruction of the tumour mass. We investigate the oscillation thresholds in a model for the dynamics of a tumour under treatment with an oncolytic virus. To this aim, we employ the minimum bifurcation roots (MBR) method, which is a novel approach to determine the existence and location of Hopf bifurcations. The application to oncolytic virotherapy confirms how this approach may be more manageable than classical methods based on the Routh–Hurwitz criterion. In particular, the MBR method allows to explicitly identify a range of values in which the oscillation thresholds fall

Deepening inside the pictorial layers of Etruscan sarcophagus of Hasti Afunei: An innovative micro-sampling technique for Raman/SERS analyses

The Hasti Afunei sarcophagus is a large Etruscan urn, made up of two chalky alabaster monoliths. Dated from the last quarter of the third century BC, it was found in 1826 in the small town of Chiusi (Tuscany- Il Colle place) by a landowner, Pietro Bonci Casuccini, who made it part of his private collection. The noble owner’s collection was sold in 1865 to the Royal Museum of Palermo (today under the name of Antonino Salinas Regional Archaeological Museum), where it is still displayed. The sarcophagus is characterized by a complex iconography that is meticulously illustrated through an excellent sculptural technique, despite having subjected to anthropic degradation and numerous restorative actions during the last century. During the restoration campaign carried out between 2016 and 2017, a targeted diagnostic campaign was carried out to identify the constituent materials of the artefact, the pigments employed and the executive technique, in order to get an overall picture of conservation status and conservative criticalities. In particular, this last intervention has allowed the use of the innovative micro-sampling technique, patented by the Cultural Heritage research group of Sapienza, in order to identify the employee of lake pigments through SERS analyses. Together with this analysis, Raman and NMR technique have completed the information requested by restorers, for what concerns the wax employed as protective layers, and allowed to rebuild the conservation history of the sarcophagus. In fact, together with the identification of red ocher and yellow ocher, carbon black, Egyptian blue and madder lake, pigments compatible with the historical period of the work, modern pigments (probably green Paris, chrome orange, barium yellow, blue phtalocyanine) have been recognized, attributable with not documented intervention during the eighteenth and twentieth centuries. © 2019 by the authors

BUBBLE-FREE FLUIDIZATION OF PARTICLES IN THE VOIDS OF A PACKING OF COARSE SPHERES

Confining a bed of relatively fine particles in a packing of coarse spheres prevents the onset of bubbly flow past their point of incipient fluidization. To improve present representations of confined fluidization, experiments on several cuts of solids of various density are analysed and interpreted by adapting some fundamental relationships of the fluidization theory to the peculiar geometry provided by the confining environment

Characterization of an Open GTEM Cell with the COMSOL Multiphysics® Software

The Gigahertz Transverse Electromagnetic (GTEM) cell is a device used for generating known, homogeneous fields for calibration purposes and for studies on Electromagnetic Compatibility (EMC) on a wide frequency range. With the aid of the COMSOL Multiphysics® simulation software, we have analyzed the electromagnetic behavior of an existing open GTEM cell at different operating frequencies. This study allowed us to identify the region internal to the cell where the field is most purely TEM. Moreover, experimental values obtained using the real GTEM have been compared to the simulated results, providing a good agreement with them

Modeling Orbital Angular Momentum (OAM) Transmission in Waveguides with the COMSOL Multiphysics® Software

The recent years have witnessed a growing interest in the possibility of enhancing the information transfer per unit bandwidth by exploiting the Orbital Angular Momentum (OAM) of light in both free-space and guided scenarios. In the proposed paper, the propagation of suitable OAM superpositions of waveguide eigenmodes in guiding structures with a circular symmetry is analyzed both theoretically and with the aid of the software COMSOL Multiphysics®, leading to the estimation of the power attenuation constants due to the finite conductivity of the metallic guide walls