Model and phase-diagram analysis of photothermal instabilities in an optomechanical resonator

A study of the phototermal instabilities in a Fabry-Perot cavity is reported, where one mirror consists of a silicon-nitride membrane coated by the molecular organic semiconductor tris(8-hydroxyquinoline) aluminum and silver layers. We propose a theoretical model to describe the back-action associated with the delayed response of the cavity field to the radiation pressure force and the photothermal force. For the case under investigation, the photothermal force response occurs on a timescale that is comparable to that of mirror oscillations and dominates over the radiation pressure force. A phase diagram analysis has been performed to map the stability of the static solution as a function of the control parameters. The model equations are integrated numerically and the time history is compared to experimental measurements of the transmitted field and displacement of the membrane. In both experimental and theoretical data we observe large amplitude oscillations when the cavity length is scanned at a low speed compared to the growth rate of the instability. The perturbation is found to evolve through three regimes: sinusoidal oscillations, double peaks and single peaks followed by a lethargic regime. When the cavity length is scanned in opposite directions, dynamical hysteresis is observed, whose extension has a power law dependence on the scanning rate

Alq3 coated silicon nanomembranes for cavity optomechanics

The optomechanical properties of a silicon-nitride membrane mirror covered by Alq3 and Silver layers are investigated. Excitation at two laser wavelengths, 780 and 405 nm, corresponding to different absorptions of the multilayer, is examined. Such dual driving will lead to a more flexible optomechanical operation. Topographic reconstruction of the whole static membrane deformation and cooling of the membrane oscillations are reported. The cooling, observed for blue laser detuning and produced by bolometric forces, is deduced from the optomechanical damping of the membrane eigenfrequency. We determine the presence of different contributions to the photothermal response of the membrane

Cognitive Impairment in People Living with HIV and the Impact of Mood: Results from a Cross-Sectional Study

Background: Human Immunodeficiency Virus (HIV) infection represents a significant public health concern and, consequently, the incidence of HIV-Associated Neurocognitive Disorder (HAND) has grown over the years. The present study aims to assess HAND with the Montreal Cognitive Assessment (MoCA) in People Living With HIV/AIDS (PLWHA) to find significant associations with cognitive impairment. Methods: The study included 210 PLWHA, aged from 30 to 81 years, of whom, 137 (65.2%) were males. They were assessed at the Immunology Service of the University Hospital of Monserrato, Cagliari, Italy, between November 2022 and April 2023. Results: The sample showed an overall optimal response to antiretroviral therapy, as shown by the excellent levels of CD4+ lymphocytes and HIV RNA copies. A sum of 115 subjects (54.8%) were considered cognitively impaired and the multivariate analysis demonstrated that it was independently associated with duration of infection (OR: 0.96), age (OR: 1.12), alanine aminotransferase (ALT) (OR: 1.02), and depression (OR: 1.33). By dichotomizing the variables, the significance of the association was confirmed for age (65-year threshold) (chi 2: 5.142, p = 0.0233) and depression (chi 2: 7.834, p = 0.0051). Conclusions: Our study demonstrates that it is hard to find both statistically and clinically significantly associated variables with cognitive impairment in PLWHA, and that the strongest independent association is with depressed mood

Studio preliminare per la progettazione di un sistema RADAR per la rilevazione degli APR nell’ambito del progetto cluster top-down RADARDRONE

Lo scopo di questo rapporto interno è di illustrare lo studio preliminare effettuato nel biennio 2019-2020 per la progettazione di un sistema RADAR per la rilevazione degli APR (Aeromobili a Pilotaggio Remoto) nell’ambito del progetto RADARDRONE. RADARDRONE è la denominazione di un progetto cluster top down che intende mettere a sistema le competenze, conoscenze ed esperienze nel campo della Ricerca Tecnologica possedute dall’OAC (Osservatorio Astronomico di Cagliari), dal DIEE (Dipartimento di Ingegneria Elettrica ed Elettronica) dell’Università degli Studi di Cagliari e dalla compagine di aziende ed organizzazioni altamente innovative facenti parte del cluster

GAIA,Progettazione, realizzazione e caratterizzazione della GAIA Board

GAIA,Progettazione, realizzazione e caratterizzazione della GAIA Board. In questo report viene illustrata la GAIA board implementata per fornire e monitorare il BIAS degli LNA (Low Noise Amplifier) installati nei ricevitore radioastronomici

Advantages of using a C-band phased array feed as a receiver in the Sardinia radio telescope for space debris monitoring

The population of space debris is continuously growing and it represents a potential problem for satellites and spacecraft. In fact, new collisions could exponentially rise the number of debris and so the level of threat represented by these objects. To prevent new collisions, the monitoring of space environment is necessary. For this reason, radar measurements are relevant, in particular to observe Space Debris in Low Earth Orbit. In recent years, the Sardinia Radio Telescope, a fully steerable wheel-and-track 64-m antenna, located in Sardinia (Italy), has been used as a receiver in a Pband bi-static radar for space debris monitoring purposes. In this paper the authors investigate the advantages of using a Phased Array Feed in C-band for space debris monitoring (e.g. improved sensitivity and gain, detection of the object trajectory allowed by multiple beams, improvement of the orbit determination of known and unknown debris), as a receiver of the Sardinia Radio Telescope compared to the already used mono-beam P-band receiver

Progettazione e realizzazione di due unità RADAR modulari per il rilevamento di Aeromobili a Pilotaggio Remoto (APR) nell’ambito del progetto cluster Top-Down RADARDRONE.

Lo scopo di questo rapporto interno è quello di descrivere la progettazione e la realizzazione di due prototipi di unità radar volti al rilevamento degli APR (Aeromobili a Pilotaggio Remoto), realizzati nell’ambito del progetto cluster top-down RADARDRONE e la successiva attività sperimentale condotta. RADARDRONE è la denominazione di un progetto cluster top-down che mette a sistema le competenze ed esperienze nel campo della ricerca tecnologica possedute dall’OAC (Osservatorio Astronomico di Cagliari), dal DIEE (Dipartimento di Ingegneria Elettrica ed Elettronica) dell’Università degli Studi di Cagliari e dalla compagine di aziende ed organizzazioni altamente innovative facenti parte del cluster. L’obiettivo principale del progetto è lo sviluppo di piccoli RADAR modulari, facilmente installabili, per il monitoraggio e la sicurezza delle aree critiche (per esempio aeroporti, porti, stadi di calcio, zone dove si svolgono grandi assembramenti di persone) o obiettivi sensibili al fine di fronteggiare eventuali intrusioni non autorizzate

Adaptation of an IRAM W-Band SIS Receiver to the INAF Sardinia Radio Telescope: A Feasibility Study and Preliminary Tests

Radio telescopes are used by astronomers to observe the naturally occurring radio waves generated by planets, interstellar molecular clouds, galaxies, and other cosmic objects. These telescopes are equipped with radio receivers that cover a portion of the radio frequency (RF) and millimetre-wave spectra. The Sardinia Radio Telescope (SRT) is an Italian instrument designed to operate between 300 MHz and 116 GHz. Currently, the SRT maximum observational frequency is 26.5 GHz. A feasibility study and preliminary tests were performed with the goal of equipping the SRT with a W-band (84–116 GHz) mono-feed radio receiver, whose results are presented in this paper. In particular, we describe the adaptation to the SRT of an 84–116 GHz cryogenic receiver developed by the Institute de Radio Astronomie Millimétrique (IRAM) for the Plateau de Bure Interferometer (PdBI) antennas. The receiver was upgraded by INAF with a new electronic control system for the remote control from the SRT control room, with a new local oscillator (LO), and with a new refrigeration system. Our feasibility study includes the design of new receiver optics. The single side band (SSB) receiver noise temperature measured in the laboratory, Trec ≈ 66 K at 86 GHz, is considered sufficiently low to carry out the characterisation of the SRT active surface and metrology system in the 3 mm band

Upgrading the Sardinia Radio Telescope to a bistatic tracking radar for space debris

In order to prevent the harmful impacts for spacecrafts deriving from the presence of space debris, many surveillance and monitoring programs of the space environment have been started in recent years. The Sardinia Radio Telescope is a new comer in such a scenario, but it has already showed its potential. However, since the actual receiving chain is not optimized for the reception of the echoes scattered from the debris, some modifications has been planned to upgrade the telescope and made it suitable for these types of observations