Relevance of Ebola virus VP35 homo-dimerization on the type I interferon cascade inhibition

Ebola virus high lethality relies on its ability to efficiently bypass the host innate antiviral response, which senses the viral dsRNA through the RIG-I receptor and induces type I interferon a/b production. In the bypassing action, the Ebola virus protein VP35 plays a pivotal role at multiple levels of the RIG-I cascade, masking the viral 50 -triphosphorylated dsRNA from RIG-I, and interacting with other cascade components. The VP35 type I interferon inhibition is exerted by the C-terminal domain, while the N-terminal domain, containing a coiled-coil region, is primarily required for oligomerization. However, mutations at key VP35 residues L90/93/107A (VP35-3m) in the coiled-coil region were reported to affect oligomerization and reduce type I interferon antagonism, indicating a possible but unclear role of homo-oligomerization on VP35 interaction with the RIG-I pathway components. In this work, we investigated the VP35 dimerization thermodynamics and its contribution to type I interferon antagonism by computational and biological methods. Focusing on the coiled-coil region, we combined coarse-grained and all-atom simulations on wild type VP35 and VP35-3m homo-dimerization. According to our results, wild type VP35 coiled-coil is able to self-assemble into dimers, while VP35-3m coiled-coil shows poor propensity to even dimerize. Free-energy calculations confirmed the key role of L90, L93 and L107 in stabilizing the coiled-coil homo-dimeric structure. In vitro type I interferon antagonism studies, using full-length wild type VP35 and VP35-3m, revealed that VP35 homo-dimerization is an essential preliminary step for dsRNA binding, which appears to be the main factor of the VP35 RIG-I cascade inhibition, while it is not essential to block the other steps

Upgrading of the L-P band cryogenic receiver of the Sardinia Radio Telescope: A feasibility study

The Sardinia Radio Telescope is a quasi-Gregorian system with a shaped 64 m diameter primary reflector and a 7.9 m diameter secondary reflector. It was designed to operate with high efficiency across the 0.3–116 GHz frequency range. The telescope is equipped with a cryogenic coaxial dual-frequency L-P band receiver, which covers a portion of the P-band (305–410 MHz) and the L-band (1300–1800 MHz). Although this receiver has been used for years in its original design, with satisfactory results, it presents some parts that could be upgraded in order to improve the performances of the system. With the passing of time and with technology advances, the presence of unwanted human-made signals in the area around the telescope, known as radio frequency interferences, has grown exponentially. In addition, the technology of the receiver electronic control system became obsolete and it could be replaced with next-generation electronic boards, which offer better performances both service reliability and low generation of unwanted radio frequency signals. In this paper, a feasibility study for improving the L-P band receiver is discussed, taking into account the mitigation of the main radio frequency interferences. With this study, it is possible to have a sensitive instrument that can be used for scientific research at low frequencies (P- and L-bands), which are usually populated by signals from civil and military mobile communications, TV broadcasting and remote sensing applications

Progettazione, realizzazione e caratterizzazione della catena ricevente per il sistema SADino precursore del Sardinia Aperture Array Demonstrator (SAAD)

Il presente rapporto tecnico riassume la progettazione, realizzazione e caratterizzazione della catena di componenti a microonde e a radio frequenza per l’acquisizione del segnale del sistema SADino, precursore del Sardinia Aperture Array Demonstrator (SAAD). Il progetto SAAD prevede la realizzazione di un aperture array composto da 128 antenne Vivaldi a doppia polarizzazione lineare [1-7], installate al sito del Sardinia Radio Telescope (SRT), ciascuna delle quali verrà collegata alla sua catena dedicata di componenti a microonde per l’acquisizione del segnale, che permette di trasportare il segnale analogico rilevato in radio frequenza dall’antenna fino al back-end digitale. Con l’obiettivo di eseguire velocemente i primi test, inizialmente si è deciso di implementare parzialmente l’array SAAD. L’implementazione parziale del sistema SAAD prende appunto il nome di SADino, che prevede la realizzazione di un mini-array di 16 elementi a doppia polarizzazione, con il quale è possibile effettuare le prime osservazioni e i primi test di beam-forming con il back-end digitale dedicato basato sulle schede Italian Tile Processing Module (iTPM) [8]. Con SADino sono state scelte solo 16 antenne (a doppia polarizzazione) dell’intero array SAAD da 128 elementi, disposte in maniera casuale, poiché il back-end digitale iTPM è dotato di soli 32 ingressi. La catena ricevente (una per ogni canale di polarizzazione di ciascuna antenna Vivaldi) è stata progettata basandosi sui risultati di una campagna di misure, effettuata nell’estate del 2020, utile a valutare la presenza in banda di segnali interferenti generati dall’uomo e indesiderati per le attività di ricerca radioastronomica, noti come radio frequency interference (RFI) [6]. Per l’esecuzione di tale campagna di misure, si è utilizzata una delle antenne Vivaldi del SAAD, equipaggiandola con una catena di acquisizione del segnale che ha fatto da precursore (almeno per quanto riguarda la valutazione degli stadi di amplificazione) alla versione finale di catena ricevente da utilizzare sul sistema SADino, precursore dell’intero SAAD. L’obiettivo di questa campagna di misure RFI è stato quello di selezionare una banda di frequenze il più possibile libera da segnali indesiderati e contenuta ovviamente all’interno della banda di lavoro delle antenne che costituiscono l’array. Le antenne Vivaldi del SAAD sono state progettate per lavorare con buona efficienza in un range di frequenze che va da 50 MHz a 500 MHz [4], mentre i componenti a microonde che costituiscono la catena di acquisizione del segnale sono ottimizzati per lavorare nel range di frequenze selezionato in base ai risultati delle misure RFI e all’interno del quale poi opererà il telescopio. In questo rapporto interno vengono presentati i risultati della campagna di misure RFI preliminare, illustrando la catena ricevente utilizzata per queste misure (vedi Sezione 2). Nella Sezione 3 viene descritta la progettazione, realizzazione e caratterizzazione della catena di componenti a microonde per ciascuna antenna del sistema SADino. Nella Sezione 4 viene descritto il sistema di alimentazione che permette di alimentare i componenti attivi inseriti all’interno della catena ricevente e, infine, nella Sezione 5 si riportano le considerazioni conclusive sul lavoro svolto

Solar radiation effects on the Sardinia Radio Telescope performances

The Sardinia Radio Telescope, a 64-metre diameter fully steerable radio telescope operated by INAF, will be upgraded in order to extend its current operating frequency range 0.3-26.5 GHz up to 116 GHz, thanks to a National Operational Program (PON) funding assigned to INAF by the Italian Ministry of University and Research. The PON project is organized in nine Work Packages, one of which is dedicated to the accomplishment of a sophisticated metrology system designed to monitor the cause of the pointing errors and the reflector surface deformations. The entire antenna structure will therefore be equipped with a network of sensors, like thermal sensors, inclinometers, accelerometers, collimators, anemometers, strain gauges and others, to study environmental stresses and how they affect the SRT performances. This work is devoted to the investigation of the thermal stress effects produced by solar radiation. In particular, two analyses are carried out to confirm the relevance of a thorough temperature monitoring system, both conducted using Finite Element Analysis. First, a possible approach for the simulation of realistic thermal scenarios due to insolation is proposed and the effects on the pointing accuracy are analysed. Second, a feasible method to study the impacts that a differential heating of the Back Up Structure (BUS) produces on the radio telescope main reflector surface is presented. Finally, these effects are analysed as optical aberrations and modelled in terms of Zernike polynomials

SRT performance measurements (2018-2021)

Tests of characterization are periodically performed at SRT in order to check the status of the antenna, ensure a good functioning of the different components (e.g. active surface, receivers, backends, etc), and improve the observing performances at the different frequencies. In particular, the tests include measurements of beam shape, pointing, gain curves and focus for the different receivers (L, C, X and K-bands). We report the results of the main tests carried out after a long stop of the antenna due to the reparation of the main servo motors chillers in 2020 and compare them with those carried out during the recommissioning in 2018 (after the change of the actuators of the active surface). These results will be useful in order to compare the new status of the antenna after the upgrade of the new receivers at higher frequency (PON)

Status of the High-Frequency Upgrade of the Sardinia Radio Telescope

The Sardinia Radio Telescope is going through a major upgrade aimed at observing the universe at up to 116 GHz. A budget of 18.700.000 E has been awarded to the Italian National Institute of Astrophysics to acquire new state-of-the-art receivers, back-end, and high-performance computing, to develop a sophisticated metrology system and to upgrade the infrastructure and laboratories. This contribution draws the status of the whole project at eight months from the end of the funding scheme planned for August 2022

The high-frequency upgrade of the Sardinia Radio Telescope

We present the status of the Sardinia Radio Telescope (SRT) and its forthcoming update planned in the next few years. The post-process scenario of the upgraded infrastructure will allow the national and international scientific community to use the SRT for the study of the Universe at high radio frequencies (up to 116 GHz), both in single dish and in interferometric mode. A telescope like SRT, operating at high frequencies, represents a unique resource for the scientific community. The telescope will be ideal for mapping quickly and with relatively high angular resolution extended radio emissions characterized by low surface brightness. It will also be essential for spectroscopic and polarimetric studies of both Galactic and extragalactic radio sources. With the use of the interferometric technique, SRT and the other Italian antennas (Medicina and Noto) will operate within the national and international radiotelescope network, allowing astronomers to obtain images of radio sources at very high angular resolution

Design, Implementation, and Characterization of a Signal Acquisition Chain for SADino: The Precursor of the Italian Low-Frequency Telescope Named the Sardinia Aperture Array Demonstrator (SAAD)

Low-frequency aperture arrays represent sensitive instruments to detect signals from radio astronomic sources situated in the universe. In Italy, the Sardinia Aperture Array Demonstrator (SAAD) consists of an ongoing project of the Italian National Institute for Astrophysics (INAF) aimed to install an aperture array constituted of 128 dual-polarized Vivaldi antennas at the Sardinia Radio Telescope (SRT) site. The originally envisaged 128 elements of SAAD were re-scoped to the 16 elements of its precursor named SADino, with the aim to quickly test the system with a digital beam-former based on the Italian Tile Processing Module (iTPM) digital back-end. A preliminary measurements campaign of radio frequency interference (RFI) was performed to survey the less contaminated spectral region. The results of these measurements permitted the establishment of the technical requirements for receiving a chain for the SADino telescope. In this paper, the design, implementation, and characterization of this signal acquisition chain are proposed. The operative frequency window of SAAD and its precursor, SADino, sweeps from 260 MHz to 420 MHz, which appears very attractive for radio astronomy applications and radar observation in space and surveillance awareness (SSA) activities