Field sweep rate dependence of the coercive field of single-molecule magnets: a classical approach with applications to the quantum regime

A method, based on the Neel-Brown model of thermally activated magnetization reversal of a magnetic single-domain particle, is proposed to study the field sweep rate dependence of the coercive field of single-molecule magnets (SMMs). The application to Mn12 and Mn84 SMMs allows the determination of the important parameters that characterize the magnetic properties: the energy barrier, the magnetic anisotropy constant, the spin, tau_0, and the crossover temperature from the classical to the quantum regime. The method may be particularly valuable for large SMMs that do not show quantum tunneling steps in the hysteresis loops.Comment: 6 pages, 6 figure

Proof-of-Prestige: A Useful Work Reward System for Unverifiable Tasks

As cryptographic tokens and altcoins are increasingly being built to serve as utility tokens, the notion of useful work consensus protocols, as opposed to number-crunching PoW consensus, is becoming ever more important. In such contexts, users get rewards from the network after they have carried out some specific task useful for the network. While in some cases the proof of some utility or service can be proved, the majority of tasks are impossible to verify. In order to deal with such cases, we design Proof-of-Prestige (PoP) - a reward system that can run on top of Proof-of-Stake blockchains. PoP introduces prestige which is a volatile resource and, in contrast to coins, regenerates over time. Prestige can be gained by performing useful work, spent when benefiting from services and directly translates to users minting power. PoP is resistant against Sybil and Collude attacks and can be used to reward workers for completing unverifiable tasks, while keeping the system free for the end-users. We use two exemplar use-cases to showcase the usefulness of PoP and we build a simulator to assess the cryptoeconomic behaviour of the system in terms of prestige transfer between nodes.Comment: 2019 IEEE International Conference on Blockchain and Cryptocurrency (ICBC 2019

Mind the gap: modelling video delivery under expected periods of disconnection.

In this work we model video delivery under expected periods of disconnection, such as the ones experienced in public transportation systems. Our main goal is to quantify the gains of users' collaboration in terms of Quality of Experience (QoE) in the context of intermittently available and bandwidth-limited WiFi connectivity. Under the assumption that Wi-Fi connectivity is available within underground stations, but absent between them, at first, we define a mathematical model which describes the content distribution under these conditions and we present the users' QoE function in terms of undisrupted video playback. Next, we expand this model to include the case of collaboration between users for content sharing in a peer-to-peer (P2P) way. Lastly, we evaluate our model based on real data from the London Underground network, where we investigate the feasibility of content distribution, only to find that collaboration between users increases significantly their QoE

Magnetic "Molecular Oligomers" based on decametallic supertetrahedra: A giant Mn49 cuboctahedron and its Mn25Na4 fragment

et al.Two nanosized Mn and MnNa clusters based on analogues of the high-spin (S=22) [Mn Mn (μ-O)] supertetrahedral core are reported. Mn and MnNa complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground-state values (Mn: S=61/2; MnNa: S=51/2) with the Mn cluster displaying single-molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.This work was supported by the Cyprus Research Promotion Foundation grant ANABAVMISH/PAGIO/0308/12 which is co-funded by the Republic of Cyprus and the European Regional Development Fund, the US National Science Foundation (Grant DMR-1213030 to G.C.), and the Spanish MINECO (Project FEDER-MAT2012-38318-C03-01).Peer Reviewe

Tube streaming: Modelling collaborative media streaming in urban railway networks

We propose a quality assessment framework for crowdsourced media streaming in urban railway networks. We assume that commuters either tune in to some TV/radio channel, or submit requests for content they desire to watch or listen to, which eventually forms a playlist of videos/podcasts/tunes. Given that connectivity is challenged by the movement of trains and the disconnection that this movement causes, users collabo-ratively download (through cellular and WiFi connections) and share content, in order to maintain undisrupted playback. We model collaborative media streaming for the case of the London Underground train network. The proposed quality assessment framework comprises a utility function which characterises the Quality of Experience (QoE) that users (subjectively) perceive and takes into account all the necessary parameters that affect smooth playback. The framework can be used to assess the media streaming quality in any railway network, after adjusting the related parameters. To the best of our knowledge, this is the first study to quantify the perceptual quality of collaborative media streaming in (underground) railway networks from a modelling perspective, as opposed to a systems perspective. Based on real commuter traces from the London Underground network, we evaluate whether audio and video can be streamed to commuters with acceptable QoE. Our results show that even with very high-speed Internet connection, users still experience disruptions, but a carefully designed collaborative mechanism can result in high levels of perceived QoE even in such disruptive scenarios

Synthesis and Structural Characterization of a Metal Cluster and a Coordination Polymer Based on the [Mn6(μ4-O)2]10+ Unit

A new 1-D coordination polymer {[Mn6O2(O2CMe)10(H2O)4]·2.5H2O}∞ (1·2.5H2O)∞ and the cluster [Mn6O2(O2(O2CPh)10 (py)2(MeCN)(H2O)]·2MeCN (2·2MeCN) are reported. Both compounds were synthesized by room temperature reactions of [Mn3(μ3-O)(O2CR)6(L)2(L′)] (R = Me, L = L′ = py, (1·2.5H2O)∞; R = Ph, L = py, L′ = H2O, 2·2MeCN) in the presence of 3-hydroxymethylpyridine (3hmpH) in acetonitrile. The structures of these complexes are based on hexanuclear mixed-valent manganese carboxylate clusters containing the [Mn4IIMn2III(μ4-O)2]10+ structural core. (1·2.5H2O)∞ consists of zigzag chain polymers constructed from [Mn6O2(O2CMe)10(H2O)4] repeating units linked through acetate ligands, whereas 2·2MeCN comprises a discrete Mn6-benzoate cluster

Overcoming the crystallization bottleneck: a family of gigantic inorganic {Pdx}L(x=84, 72) palladium macrocycles discovered using solution techniques

The {Pd84}Ac wheel, initially discovered serendipitously, is the only reported giant palladium macrocycle—a unique structure that spontaneously assembles from small building blocks. Analogues of this structure are elusive. A new modular route to {Pd84}Ac is described, allowing incorporation of other ligands, and a new screening approach to cluster discovery. Structural assignments were made of new species from solution experiments, overcoming the need for crystallographic analysis. As a result, two new palladium macrocycles were discovered: a structural analogue of the existing {Pd84}Ac wheel with glycolate ligands, {Pd84}Gly, and the next in a magic number series for this cluster family—a new {Pd72}Prop wheel decorated with propionate ligands. These findings confirm predictions of a magic number rule for the family of {Pdx} macrocycles. Furthermore, structures with variable fractions of functional ligands were obtained. Together these discoveries establish palladium clusters as a new class of tunable nanostructures. In facilitating the discovery of species that would not have been discovered by orthodox crystallization approaches, this work also demonstrates the value of solution-based screening and characterization in cluster chemistry, as a means to decouple cluster formation, discovery, and isolation