Organometallic Neptunium Chemistry

Fifty years have passed since the foundation of organometallic neptunium chemistry, and yet only a handful of complexes have been reported, and even fewer fully characterised. Yet increasingly, combined synthetic/spectroscopic/computational studies are demonstrating how covalently binding, soft, carbocyclic organometallic ligands provide an excellent platform for advancing the fundamental understanding of the differences in orbital contributions and covalency in f-block metal – ligand bonding. Understanding the subtleties are key to the safe handling and separations of the highly radioactive nuclei. This review describes the complexes that have been synthesised to date, presents a critical assessment on the successes and difficulties in their analysis, and the bonding information they have provided. Because of the recent work to start new Np air-sensitive inorganic chemistry labs, the importance of radioactivity, the basics of Np decay and its ramifications (including the radiochemical synthesis of one organometallic) and the available anhydrous starting materials are also surveyed. The review also highlights a range of instances in which important differences in the chemical behaviour between Np and its closest neighbours, uranium and plutonium, are found.JRC.G.I.5-Advanced Nuclear Knowledg

Solving hidden terminal problem in MU-MIMO WLANs with fairness and throughput-aware precoding and a degrees-of-freedom-based MAC design

© 2016, Shrestha et al. We generally emphasize that the zeroforcing (ZF) technique backed by an appropriate medium access control (MAC) protocol can be used to address the inevitable hidden terminal (HT) problem in multi-user multiple input multiple output (MU-MIMO) wireless local area network (WLAN) settings. However, to address the implementation-specific requirements of MU-MIMO WLANs, such as fairness in client access and throughput of the network, we propose a fairness and a throughput-aware ZF precoding in our design at the physical layer (PHY). This precoding scheme not only solves the HT problem but also meets the fairness and the throughput requirements of MU-MIMO WLANs. Besides, we design a MAC layer protocol, supportive to PHY, which decides transmission opportunities (TXOPs) among access points (APs) based on the available degrees of freedom (DoF). We make a mandatory provision in our design that APs should have a sufficient DoF. This can ensure collision-free transmission whenever APs/transmitters transmit in the HT scenario. Additionally, we design an improved channel sounding process for MU-MIMO WLANs with a less signaling overhead than IEEE802.11ac. We demonstrate the feasibility of our PHY in a USRP2/GNU Radio testbed prototype in the lab settings. It is found that our PHY improves the SNR and effective SNR of the received signal from about 5 to 11 dB in the HT scenario. The performance of our MAC design is checked with simulation studies in a typical six-antenna AP and clients scenario. We observe that our MAC protocol has a slightly higher signaling overhead than traditional ready to send/clear to send (RTS/CTS) due to design constraints; however, the signaling time overheads are reduced by 98.67 μs compared to IEEE802.11ac. Another interesting aspect to highlight is the constant Throughput gain of four to five times that of the traditional RTS/CTS. Our MAC protocol obtains this gain as early as 98.67 μs compared to IEEE802.11ac

Zeroforcing precoding based MAC design to address hidden terminals in MU-MIMO WLANs

© 2015 IEEE. This paper focuses on the Medium Access Control (MAC) layer design for an inevitable Hidden Terminal problem in Multi User Multiple Input Multiple Output (MU-MIMO) Wireless Local Area Networks (WLANs). Specifically, our MAC design is supported by the precoding vectors obtained by Zeroforcing technique which are used to address the Hidden Terminals. An efficient channel sounding process is used by our MAC protocol to obtain the Channel State Information (CSI) from the desired and undesired clients which are used to calculate the precoding vectors at the transmitters (Access Points). Our MAC design then uses these precoding vectors in order to null interferences among the undesired clients to avoid collision of signals and to maintain the concurrent transmissions among the desired clients. The the parameters such as network capacity, signaling overheads and fairness are considered in the design. Our MAC layer design shows a slightly higher signaling overhead compared to RTS/CTS scheme. However, due to the concurrent transmissions after the handshaking process, the cost of singling overheads are compensated. The simulation study of our MAC layer design shows a remarkable constant network capacity gain of 4-5 times in comparison to traditional RTS/CTS. Moreover, the gain is irrespective to the available air-time

How important is diversity for capturing environmental-change responses in ecosystem models?

Marine ecosystem models used to investigate how global change affects ocean ecosystems and their functioning typically omit pelagic plankton diversity. Diversity, however, may affect functions such as primary production and their sensitivity to environmental changes. Here we use a global ocean ecosystem model that explicitly resolves phytoplankton diversity by defining subtypes within four phytoplankton functional types (PFTs). We investigate the model's ability to capture diversity effects on primary production under environmental change. An idealized scenario with a sudden reduction in vertical mixing causes diversity and primary-production changes that turn out to be largely independent of the number of coexisting phytoplankton subtypes. The way diversity is represented in the model provides a small number of niches with respect to nutrient use in accordance with the PFTs defined in the model. Increasing the number of phytoplankton subtypes increases the resolution within the niches. Diversity effects such as niche complementarity operate between, but not within PFTs, and are constrained by the variety of traits and trade-offs resolved in the model. The number and nature of the niches formulated in the model, for example via trade-offs or different PFTs, thus determines the diversity effects on ecosystem functioning captured in ocean ecosystem models

(E)-3-(4-Chloro­phen­yl)-1-(1-naphth­yl)prop-2-en-1-one

In the title compound, C19H13ClO, the benzene ring and the naphthalene system, are twisted by 12.3 (3) and 36.1 (2)°, respectively, and in opposite directions with respect to the central propenone bridge. The bond-angle pattern within the benzene ring is influence by both substituents; these influences are almost additive. In the crystal, the molecules are linked by C—H⋯O and C—H⋯Cl inter­actions

1-Methyl­piperazine-1,4-diium dipicrate

In the crystal structure of the title compound [systematic name: 1-methyl­piperazine-1,4-diium bis­(2,4,6-trinitro­phen­ol­ate)], C5H14N2 2+·2C6H2N3O7 −, the ionic components are connected by relatively strong N—H⋯O hydrogen bonds into centrosymmetric six-membered conglomerates, which comprise two dications and four anions. Besides Coulombic inter­actions, only weak C—H⋯O inter­actions and some stacking between picrates (separation between the planes of ca. 3.4 Å but only a small overlapping) can be identified between these ‘building blocks’ of the crystal structure. The piperazine ring adopts a chair conformation with the methyl substituent in the equatorial position. In the picrate anions, the twist angles of the nitro groups depend on their positions relative to the phenolate O atom: it is much smaller for the NO2 groups para to the C—O− group [15.23 (9)and 3.92 (14)°] than for the groups in the ortho positions [28.76 (13)–39.84 (11)°]

Tramadolium picrate

In the title salt {systematic name: [2-hy­droxy-3-(3-meth­oxy­phen­yl)cyclo­hexyl­meth­yl]dimethyl­aza­nium 2,4,6-trinitro­phenol­ate}, C16H26NO2 +·C6H2N3O7 −, the cation is protonated at the N atom. The cyclo­hexane ring adopts a chair conformation with the hy­droxy substituent in an axial position. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds link the cations and anions into supra­molecular chains along [100]

Opportunistic Access to PAL Channel for Multi-RAT GAA Transmission in Spectrum Access System

© 2017 IEEE. Spectrum Access System (SAS) is a three tier spectrum sharing framework proposed by the FCC. In this framework the aggregate interference of tier-3 General Authorised Access (GAA) users should be below a predetermined threshold anywhere within the tier-2 Priority Access Licensee (PAL) exclusion zone. GAA are expected to use a diverse range of Radio Access Technologies (RATs) with different levels of loading. We propose an optimal transmit power and probability of spectrum utilisation allocation scheme for GAA users that meets the average aggregate interference constraint within the GAA network. Most of the capacity maximisation studies consider the instantaneous aggregated interference from secondary users. In this paper we present an average aggregated interference method to optimise the capacity of GAA users in a single channel. Simulation results suggest that we can significantly increase the capacity of the channel by considering the probability spectrum utilisation of GAA users

The Impact on Full Duplex D2D Communication of Different LTE Transmission Techniques

© 2017 IEEE. To augment capacity of spectrum limited cellular systems, 3GPP proposed Licensed Assisted Access (LAA-LTE) while efforts are underway to standardize the standalone MulteFire (a small cell standalone version of LTE). LAA is expected to boost capacity of LTE via unlicensed spectrum (5GHz). On the other hand, recent advances in Self Interference Suppression (SIS) techniques allow radios to transmit and receive simultaneously on the same channel (i.e., in-band Full-Duplex, FD). As part of future wireless networks, Device-to-device (D2D) communications would find its great potential through this FD capability. However, due to high induced aggregate interference from FD and its impact on medium access probability, the rigorous and critical analysis is needed to find an optimum trade-off between performance efficiency and overheads. Using stochastic geometry and the random graph theory, in this article, we analyze the impact of different LTE network paradigms with HD/FD D2D devices. Moreover, the impact of state- of-the-art coexistence techniques (discontinuous transmission and listen-before-talk) recommended for LTE in unlicensed spectrum over HD/FD D2D network is also discussed. The analysis is supported with extensive simulation results that reveal insights of the coexistence mechanism efficiency employed by LTE, the impact of SIS and the cost of FD operation in D2D