The Raman spectrum of CaCO3 polymorphs calcite and aragonite: A combined experimental and computational study

Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a “hybrid” functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm−1 for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to 18O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra

The vibrational spectrum of CaCO3 aragonite: A combined experimental and quantum-mechanical investigation

The vibrational properties of CaCO3 aragonite have been investigated both theoretically, by using a quantum mechanical approach (all electron Gaussian type basis set and B3LYP HF-DFT hybrid functional, as implemented in the CRYSTAL code) and experimentally, by collecting polarized infrared (IR) reflectance and Raman spectra. The combined use of theory and experiment permits on the one hand to analyze the many subtle features of the measured spectra, on the other hand to evidentiate limits and deficiencies of both approaches. The full set of TO and LO IR active modes, their intensities, the dielectric tensor (in its static and high frequency components), and the optical indices have been determined, as well as the Raman frequencies. Tools such as isotopic substitution and graphical animation of the modes are available, that complement the analysis of the spectrum

Quantum walks: a comprehensive review

Quantum walks, the quantum mechanical counterpart of classical random walks, is an advanced tool for building quantum algorithms that has been recently shown to constitute a universal model of quantum computation. Quantum walks is now a solid field of research of quantum computation full of exciting open problems for physicists, computer scientists, mathematicians and engineers. In this paper we review theoretical advances on the foundations of both discrete- and continuous-time quantum walks, together with the role that randomness plays in quantum walks, the connections between the mathematical models of coined discrete quantum walks and continuous quantum walks, the quantumness of quantum walks, a summary of papers published on discrete quantum walks and entanglement as well as a succinct review of experimental proposals and realizations of discrete-time quantum walks. Furthermore, we have reviewed several algorithms based on both discrete- and continuous-time quantum walks as well as a most important result: the computational universality of both continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing Journa

An experimental study of salt movement and accumulation within unsaturated granular road pavements

Concentration of salts within road pavements has been shown to cause damage to road surfacings and affect road pavement performance. The present study explores the mechanisms of road pavement salinisation with a focus on roads within areas at risk of environmental salinity. Soil columns of unsaturated compacted clay subgrade and road pavement material were established under laboratory conditions. A number of combinations of surfacing, pavement structure and saline bath solution were constructed. Volumetric water content and electrical conductivity was measured over a period of several months using on-sample instrumentation and destructive means. The experimental design and preliminary results from instrumented columns and destructive testing of one set of columns harvested after 6 weeks are discussed

Design parameters for rockfall protection barriers in the rocks of the Narrabeen Group

The design of effective rockfall protection barriers from first principles can involve detailed site characterisation, extensive trajectory modelling and complex structural design. Alternatively, if the nature of the rockfall hazard can be characterised on the basis of the geological environment, then it is possible select a protection strategy with appropriately specified design considerations. In this paper, a parametric study of rockfall phenomena in areas of the Narrabeen Group is undertaken to determine the likely characteristics of the rockfall hazard that must be managed. Starting with statistical data on the size and shape of the rock debris, and measurements of the coefficients of restitution that are representative of the ground slopes in Narrabeen sandstone environments, a series of rockfall simulations are undertaken for potentially hazardous slopes extracted from the RTA's slope management database. The results present the distribution of energies and trajectories of blocks that are likely to enter road reserves in Narrabeen environments, and they suggest that fences with energy capacities up to 3200kJ, up to 4m high may be required to effectively manage the most severe rockfall risk in these areas. The parameters determined are especially useful in the context of producing a protection fence design that is specifically targeted to being both efficient and effective

Statistical evaluation of rockfall energy ranges for different geological settings of New South Wales, Australia

Structures used in rockfall protection are designed on the basis of the expected impact energy. This quantity is usually assessed using commercial lumped mass models that stochastically predict possible block trajectories on a given slope. In New South Wales, Australia, it is estimated that rockfall hazard involves values of energy which are much lower than those in Europe, Canada or the USA. However, this view has not been supported by any systematic study across the whole state. Such a study is presented in this paper. It applies to the five geological situations that are the most prone to rockfall in eastern Australia. Previous experimental findings, relating to block size distribution or restitution coefficients (reviewed herein), have been used to perform this statistical analysis. A newly formulated lumped mass program, which incorporates a relationship between the normal restitution coefficient and the impact angle, allows the adoption of normal restitution coefficients in excess of unity for impact angles lower than 30°. The results confirm that in three out of the five geological situations, the 95th percentile of impact energy is lower than 200 kJ, and less than 2000 kJ for the other two situations