catena-Poly[bis­(4-amino­pyridinium) [[tetra­aqua­nickel(II)]-μ-benzene-1,2,4,5-tetra­carboxyl­ato] dihydrate]

The asymmetric unit of the title compound, {(C5H7N2)2[Ni(C10H2O8)(H2O)4]·2H2O}n, contains an NiII atom, two water mol­ecules of coordination, one half of a benzene-1,2,4,5-tetra­carboxyl­ate (btec) anionic ligand, one 4-amino­pyridinium cation (papy) and an uncoordinated water mol­ecule. The metal center lies on an inversion center and adopts an octa­hedral geometry with the carboxyl­ate groups tilted out of the mean plane formed by the btec. In the crystal, mol­ecules are linked into one-dimensional coordination polymers running along the ac diagonal. The crystal structure is consolidated by N—H⋯O and O—H⋯O hydrogen bonds

Nonlinear Dynamic Analysis of Seismically Base-Isolated Structures by a Novel OpenSees Hysteretic Material Model

The complex response characterizing elastomeric isolation bearings is reproduced by employing a novel uniaxial hysteretic model that has been recently formulated and successfully implemented in OpenSees. Such a novel OpenSees material model offers several advantages with respect to differential models typically available in commercial software products for structural analysis, such as 3D-BASIS and CSi programs. Firstly, it is based on a set of only five model parameters that have a clear mechanical significance; such a property not only allows one to drastically simplify the parameters identification process, but it also allows the model to be used in practice. In addition, the model does not require numerical methods for the evaluation of the restoring force since the latter is computed by solving an algebraic equation. To encourage researchers and designers to adopt the proposed model for research and practical purposes, we demonstrate its accuracy by performing some numerical tests in OpenSees. In particular, we first employ the recently implemented model to compute the nonlinear dynamic response of a seismically base-isolated structure with elastomeric bearings and, subsequently, we compare the results with those obtained by modeling the seismic isolators with the OpenSees BoucWen uniaxial material model, that is one of the most popular and accurate hysteretic models currently available in OpenSees

Network-based indicators of Bitcoin bubbles

The functioning of the cryptocurrency Bitcoin relies on the open availability of the entire history of its transactions. This makes it a particularly interesting socio-economic system to analyse from the point of view of network science. Here we analyse the evolution of the network of Bitcoin transactions between users. We achieve this by using the complete transaction history from December 5th 2011 to December 23rd 2013. This period includes three bubbles experienced by the Bitcoin price. In particular, we focus on the global and local structural properties of the user network and their variation in relation to the different period of price surge and decline. By analysing the temporal variation of the heterogeneity of the connectivity patterns we gain insights on the different mechanisms that take place during bubbles, and find that hubs (i.e., the most connected nodes) had a fundamental role in triggering the burst of the second bubble. Finally, we examine the local topological structures of interactions between users, we discover that the relative frequency of triadic interactions experiences a strong change before, during and after a bubble, and suggest that the importance of the hubs grows during the bubble. These results provide further evidence that the behaviour of the hubs during bubbles significantly increases the systemic risk of the Bitcoin network, and discuss the implications on public policy interventions

An interface capturing method for liquid-gas flows at low-Mach number

Multiphase, compressible and viscous flows are of crucial importance in a wide range of scientific and engineering problems. Despite the large effort paid in the last decades to develop accurate and efficient numerical techniques to address this kind of problems, current models need to be further improved to address realistic applications. In this context, we propose a numerical approach to the simulation of multiphase, viscous flows where a compressible and an incompressible phase interact in the low-Mach number regime. In this frame, acoustics is neglected but large density variations of the compressible phase can be accounted for as well as heat transfer, convection and diffusion processes. The problem is addressed in a fully Eulerian framework exploiting a low-Mach number asymptotic expansion of the Navier-Stokes equations. A Volume of Fluid approach (VOF) is used to capture the liquid-gas interface, built on top of a massive parallel solver, second order accurate both in time and space. The second-order-pressure term is treated implicitly and the resulting pressure equation is solved with the eigenexpansion method employing a robust and novel formulation. We provide a detailed and complete description of the theoretical approach together with information about the numerical technique and implementation details. Results of benchmarking tests are provided for five different test cases

A functionalized enol lactone containing a protected α-amino acid

The crystal structure of N-(3,9-dimethyl-4-phenyl-2,5-dioxo-3,4-dihydro-2H,5H-pyrano[3,2-c]chromen-3-yl)-N-methylbenzamide methanol monosolvate, C28H23NO5·CH3OH, has been determined at room temperature by X-ray diffraction. Structural parameters are discussed with reference to ab initio calculations

3-[2-(1H-1,3-Benzodiazol-2-yl)eth­yl]-1,3-oxazolidin-2-one

In the title compound, C12H13N3O2, the dihedral angle between the oxazolone ring and the benzimidazole unit is 45.0 (5)°, exhibiting a staggered conformation at the Cα—Cβ bond. In the crystal, a strong N—H⋯N hydrogen bond links the mol­ecules into a C(4) chain along the c axis while a C—H⋯O hydrogen-bonding inter­action generates a C(5) chain along the a axis, i.e. perpendicular to the other chain

Polarization preserving ultra fast optical shutter for quantum information processing

We present the realization of a ultra fast shutter for optical fields, which allows to preserve a generic polarization state, based on a self-stabilized interferometer. It exhibits high (or low) transmittivity when turned on (or inactive), while the fidelity of the polarization state is high. The shutter is realized through two beam displacing prisms and a longitudinal Pockels cell. This can represent a useful tool for controlling light-atom interfaces in quantum information processing.Comment: 4 pages, 6 figure

(S)-2-[(2-Hy­droxy­benz­yl)aza­nium­yl]-4-(methyl­sulfan­yl)butano­ate

The zwitterionic title compound, C12H17NO3S, is a reduced Schiff base derived from (S)-N-(2-hy­droxy­benzyl­idene)methio­nine. An intra­molecular inter­action between the N—H and carboxyl­ate groups forms a roughly planar (r.m.s. deviation = 0.1405 Å) five-membered ring containing the H(N), N, Cα, C(carboxyl­ate) and O atoms in a penta­gonal conformation. In the crystal, a supra­molecular triangle-shaped motif is generated by mol­ecules held together by O—H⋯O and N—H⋯O hydrogen bonds

catena-Poly[[[μ-aqua-penta­aqua­dizinc(II)]-μ4-benzene-1,2,4,5-tetra­carboxyl­ato] dihydrate]

The asymmetric unit of the title compound, {[Zn2(C10H2O8)(H2O)6]·2H2O}n, contains two distinct Zn atoms joined by a bridging water molecule and two bridging carboxyl­ate groups belonging to distinct halves of benzene-1,2,4,5-tetra­carboxyl­ate (tbec) tetra­anionic ligands, both lying on crystallographic inversion centres. The structure of this new isopolymorphic one-dimensional coordination polymer features asymmetric bimetallic octa­hedral knots. O—H⋯O hydrogen bonds between water molecules and carboxylate O atoms help to consolidate the crystal packing

A real-time KLT implementation for radio-SETI applications

SETI, the Search for ExtraTerrestrial Intelligence, is the search for radio signals emitted by alien civilizations living in the Galaxy. Narrow-band FFT-based approaches have been preferred in SETI, since their computation time only grows like N*lnN, where N is the number of time samples. On the contrary, a wide-band approach based on the Kahrunen-Lo`eve Transform (KLT) algorithm would be preferable, but it would scale like N*N. In this paper, we describe a hardware-software infrastructure based on FPGA boards and GPU-based PCs that circumvents this computation-time problem allowing for a real-time KLT