First record of the non-pollinating fig wasp Odontofroggatia galili Wiebes, 1980 from Malta (Hymenoptera, Chalcidoidea, Agaonidae)

The fig wasp Odontofroggatia galili is reported for the first time from Malta. Odontofroggatia is a non-pollinating fig wasp genus associated with a narrow range of host plant species, among them Ficus microcarpa, a widespread ornamental tree native to Asia.peer-reviewe

Convolutive superposition for multicarrier cognitive radio systems

Recently, we proposed a spectrum-sharing paradigm for single-carrier cognitive radio (CR) networks, where a secondary user (SU) is able to maintain or even improve the performance of a primary user (PU) transmission, while also obtaining a low-data rate channel for its own communication. According to such a scheme, a simple multiplication is used to superimpose one SU symbol on a block of multiple PU symbols.The scope of this paper is to extend such a paradigm to a multicarrier CR network, where the PU employs an orthogonal frequency-division multiplexing (OFDM) modulation scheme. To improve its achievable data rate, besides transmitting over the subcarriers unused by the PU, the SU is also allowed to transmit multiple block-precoded symbols in parallel over the OFDM subcarriers used by the primary system. Specifically, the SU convolves its block-precoded symbols with the received PU data in the time-domain, which gives rise to the term convolutive superposition. An information-theoretic analysis of the proposed scheme is developed, which considers different amounts of network state information at the secondary transmitter, as well as different precoding strategies for the SU. Extensive simulations illustrate the merits of our analysis and designs, in comparison with conventional CR schemes, by considering as performance indicators the ergodic capacity of the considered systems.Comment: 29 pages, 8 figure

Rapidly time-varying reconfigurable intelligent surfaces for downlink multiuser transmissions

Until now, researchers in wireless communications have mainly focused their attention on slowly time-varying designs of reconfigurable intelligent surfaces (RISs), where the spatial-phase gradient across the RIS is varied at the rate equal to the inverse of the channel coherence time. Additional degrees of freedom for controlling EM waves can be gained by applying a time modulation to the reflection response of RISs during the channel coherence time interval, thereby attaining rapidly time-varying RISs. In this paper, we develop a general framework where a downlink multiuser transmission over single-input single-output slow fading channels is assisted by a digitally controlled rapidly time-varying RIS. We show that reconfiguring the RIS at a rate greater than the inverse of the channel coherence time might be beneficial from a communication perspective depending on the considered network utility function and the available channel state information at the transmitter (CSIT). The conclusions of our analysis in terms of system design guidelines are as follows: (i) if the network utility function is the sum-rate time-averaged network capacity, without any constraint on fair resource allocation, and full CSIT is available, it is unnecessary to change the electronic properties of the RIS within the channel coherence time interval; (ii) if partial CSIT is assumed only, a rapidly time-varying randomized RIS allows to achieve a suitable balance between sum-rate time-averaged capacity and user fairness, especially for a sufficiently large number of users; (iii) regardless of the available amount of CSIT, the design of rapid temporal variations across the RIS is instrumental for developing scheduling algorithms aimed at maximizing the network capacity subject to some fairness constraints.Comment: Accepted for publication in IEEE Transactions on Communications. Cite as: F. Verde, D. Darsena, and V. Galdi, "Rapidly time-varying reconfigurable intelligent surfaces for downlink multiuser transmissions," in IEEE Transactions on Communications, 2024, doi: https://doi.org/10.1109/TCOMM.2024.335895

LUCRETIUS AND HIS DE RERUM NATURA SIX CENTURIES AFTER A CONVERSATION WITH DAVID SEDLEY

In this interview David Sedley reflects on some important points of hisseminal interpretation of Lucretius’ De rerum natura six centuries after its discovery in1417 by Poggio Bracciolini (Terranuova, now Terranuova Bracciolini, 1380 – Florence,1459)

ANCORA SULLO STATUTO VERITATIVO DELLA SENSAZIONE IN EPICURO

The main goals of this article are, on the one hand, to show the peculiar features of the Epicurean view of sense-perception (aisthesis), the first criterion of truth of Epicurus’ canonic; and, on the other hand, to critically discuss a recent contribution by Alexander Bown (“Epicurus on Truth and Falsehood”, Phronesis, 61 (4), 2016, p. 463-503), which deals with Epicurus’ double notion of truth (i.e. the truth of sense-perceptions/aistheseis and the truth of opinions/hypolepseis). Besides Book 10 of Diogenes Laertius’ Lives of Eminent Philosophers and Epicurus’ Letter to Herodotus, columns LXXII-LXXIII of PHerc. 1012 (including a work by the Epicurean philosopher Demetrius Lacon) and a passage from Sextus Empiricus’ Against the Logicians (M, VIII, 9) will be examined in order to explain the meaning of truth linked by Epicurus to perceptible objects (aistheta)

Boethus the Epicurean

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STiCMAC: A MAC Protocol for Robust Space-Time Coding in Cooperative Wireless LANs

Relay-assisted cooperative wireless communication has been shown to have significant performance gains over the legacy direct transmission scheme. Compared with single relay based cooperation schemes, utilizing multiple relays further improves the reliability and rate of transmissions. Distributed space-time coding (DSTC), as one of the schemes to utilize multiple relays, requires tight coordination between relays and does not perform well in a distributed environment with mobility. In this paper, a cooperative medium access control (MAC) layer protocol, called \emph{STiCMAC}, is designed to allow multiple relays to transmit at the same time in an IEEE 802.11 network. The transmission is based on a novel DSTC scheme called \emph{randomized distributed space-time coding} (\emph{R-DSTC}), which requires minimum coordination. Unlike conventional cooperation schemes that pick nodes with good links, \emph{STiCMAC} picks a \emph{transmission mode} that could most improve the end-to-end data rate. Any station that correctly receives from the source can act as a relay and participate in forwarding. The MAC protocol is implemented in a fully decentralized manner and is able to opportunistically recruit relays on the fly, thus making it \emph{robust} to channel variations and user mobility. Simulation results show that the network capacity and delay performance are greatly improved, especially in a mobile environment.Comment: This paper is a revised version of a paper with the same name submitted to IEEE Transaction on Wireless Communications. STiCMAC protocol with RTS/CTS turned off is presented in the appendix of this draf