The electronic structure of liquid water within density functional theory

In the last decade, computational studies of liquid water have mostly concentrated on ground state properties. However recent spectroscopic measurements have been used to infer the structure of water, and the interpretation of optical and x-ray spectra requires accurate theoretical models of excited electronic states, not only of the ground state. To this end, we investigate the electronic properties of water at ambient conditions using ab initio density functional theory within the generalized gradient approximation (DFT/GGA), focussing on the unoccupied subspace of Kohn-Sham eigenstates. We generate long (250 ps) classical trajectories for large supercells, up to 256 molecules, from which uncorrelated configurations of water molecules are extracted for use in DFT/GGA calculations of the electronic structure. We find that the density of occupied states of this molecular liquid is well described with 32 molecule supercells using a single k-point (k = 0) to approximate integration over the first Brillouin zone. However, the description of the density of unoccupied states (u-EDOS) is sensitive to finite size effects. Small, 32 molecule supercell calculations, using Gamma-the point approximation, yield a spuriously isolated state above the Fermi level. Nevertheless, the more accurate u-EDOS of large, 256 molecule supercells may be reproduced using smaller supercells and increased k-point sampling. This indicates that the electronic structure of molecular liquids like water is relatively insensitive to the long-range disorder in the molecular structure. These results have important implications for efficiently increasing the accuracy of spectral calculations for water and other molecular liquids.Comment: 12 pages, 11 figures (low quality) Submitted to JChemPhy

Sensitivity analysis in a market with memory

A general market model with memory is considered in terms of stochastic functional differential equations. We aim at representation formulae for the sensitivity analysis of the dependence of option prices on the memory. This implies a generalization of the concept of delta.Comment: Withdrawn by the authors due to an error in equation (2.6). A new work is in preparatio

Key factors and barriers to the adoption of cold ironing in europe

The first cases of successful implementation of cold ironing can be found in Alaska about twenty years ago. In that case, the energy cost was lower than in Europe where cold ironing has been developed only in the latest years at few ports. The present paper investigates the innovative process of cold ironing at European level. Firstly, its recent development in Europe is documented as well as the main concern of its corresponding legislation. Then, the adoption of this initiative by the “green ports” concept is discussed. Secondly, the technical barriers, such as lack of standardization of electricity parameters are mentioned. And given that port electrical infrastructure needed onshore represents a huge investment that not all ports are financially able to do, the financial problematic is treated explicitly taking into account the cost of energy at ports (directly provided by electric centrals or converted) against the energy cost onboard. Finally, conclusions are drawn covering the main barriers confronted by this technology and the future premises of cold ironing at European ports considering the social and environmental benefits in terms of air and noise pollution.cold ironing, energy cost, technology barrier, European ports, environmenta

Deconstructing the Blockchain to Approach Physical Limits

Transaction throughput, confirmation latency and confirmation reliability are fundamental performance measures of any blockchain system in addition to its security. In a decentralized setting, these measures are limited by two underlying physical network attributes: communication capacity and speed-of-light propagation delay. Existing systems operate far away from these physical limits. In this work we introduce Prism, a new proof-of-work blockchain protocol, which can achieve 1) security against up to 50% adversarial hashing power; 2) optimal throughput up to the capacity C of the network; 3) confirmation latency for honest transactions proportional to the propagation delay D, with confirmation error probability exponentially small in CD ; 4) eventual total ordering of all transactions. Our approach to the design of this protocol is based on deconstructing the blockchain into its basic functionalities and systematically scaling up these functionalities to approach their physical limits.Comment: Computer and Communications Security, 201

The Swift Gamma-Ray Burst redshift distribution: selection biases and optical brightness evolution at high-z?

We employ realistic constraints on astrophysical and instrumental selection effects to model the Gamma-Ray Burst (GRB) redshift distribution using {\it Swift} triggered redshift samples acquired from optical afterglows (OA) and the TOUGH survey. Models for the Malmquist bias, redshift desert, and the fraction of afterglows missing because of host galaxy dust extinction, are used to show how the "true" GRB redshift distribution is distorted to its presently observed biased distribution. We also investigate another selection effect arising from a correlation between $E_{{\rm iso}}$ and $L_{{\rm opt}}$. The analysis, which accounts for the missing fraction of redshifts in the two data subsets, shows that a combination of selection effects (both instrumental and astrophysical) can describe the observed GRB redshift distribution. Furthermore, the observed distribution is compatible with a GRB rate evolution that tracks the global SFR, although the rate at high-$z$ cannot be constrained with confidence. Taking selection effects into account, it is not necessary to invoke high-energy GRB luminosity evolution with redshift to explain the observed GRB rate at high-$z$.Comment: Version 2. Includes new data, figures and refined analysi