Study of the variation of the optical properties of calcite with applied stress, useful for specific rock and material mechanics

Calcite (CaCO3, trigonal crystal system, space group R3 ¯ c) is a ubiquitous carbonate phase commonly found on the Earth’s crust that finds many useful applications in both scientific (mineralogy, petrology, geology) and technological fields (optics, sensors, materials technology) because of its peculiar anisotropic physical properties. Among them, photoelasticity, i.e., the variation of the optical properties of the mineral (including birefringence) with the applied stress, could find usefulness in determining the stress state of a rock sample containing calcite by employing simple optical measurements. However, the photoelastic tensor is not easily available from experiments, and affected by high uncertainties. Here we present a theoretical Density Functional Theory approach to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm). The results were compared with those available in literature, further extending the knowledge of the photoelasticity of calcite, and clarifying an experimental discrepancy in the sign of the p41 photoelastic tensor component measured in past investigations. The methods here described and applied to a well-known crystalline material can be used to obtain the photoelastic properties of other minerals and/or materials at desired pressure and temperature conditions

Structural, thermal and surface force chracterisation of modified layer silicates: : Results on talc, kaolinite and montmorillonite

none3noneF. Dellisanti; V.Minguzzi; G.ValdrèF. Dellisanti; V.Minguzzi; G.Valdr

Electrochemical data on redox properties of human Cofilin-2 and its Mutant S3D

The reported data are related to a research paper entitled "Phosphorylated cofilin-2 is more prone to oxidative modifications on Cys39 and favors amyloid fibril formation" [1]. Info about the formation and redox properties of the disulfide bridge of a protein is quite difficult to obtain and only in a few cases was it possible to observe a cyclic voltammetry (CV) signal [2,3]. Human cofilin-2 contains two cysteines (Cys39 and Cys80) which can be oxidized in suitable conditions and form a disulfide bridge [1]. For this purpose, CV measurements were carried out on human cofilin-2 WT and its mutant S3D immobilized on a gold electrode coated by an anionic self-assembled monolayer (SAM), after a pre-oxidation time which was fundamental for observing a CV signal relating to the oxidation/reduction process of the disulfide bridge of the proteins. The data include CV curves obtained with and without electrochemical pre-oxidation and after oxidation with H2O2. In addition, the plot of the cathodic peak current vs. electrochemical pre-oxidation time and the pH dependence of the formal potential (E°’) are reported. The data obtained by CV measurements were used to determine the time required to form the disulfide bridge for the immobilized proteins and, consequently, to observe the CV signal, to calculate the E°’ values and analyse the pH dependence of E°’. The electrochemical data were provided which will be useful for further electrochemical investigations regarding proteins bearing disulfide bridge(s) or cysteines prone to oxidation

N and Z odd-even staggering in Kr + Sn collisions at Fermi energies

The odd-even staggering of the yield of final reaction products has been studied as a function of proton (Z) and neutron (N) numbers for the collisions 84 Kr+112 Sn and 84 Kr+124 Sn at 35 MeV/nucleon, in a wide range of elements (up to Z ~ 20). The experimental data show that staggering effects rapidly decrease with increasing size of the fragments. Moreover the staggering in N is definitely larger than the one in Z. Similar general features are qualitatively reproduced by the GEMINI code. Concerning the comparison of the two systems, the staggering in N is in general rather similar, being slightly larger only for the lightest fragments produced in the n-rich system. In contrast the staggering in Z, although smaller than that in N, is sizably larger for the n-poor system with respect to the n-rich one.Comment: 6 pages, 5 figures, Revtex forma

From light to heavy nuclear systems, production and decay of fragments studied with powerful arrays

Reactions between heavy-ions at various energy regimes produce many nuclear fragments which can be populated in highly excited states. The study of these fragments, detected at the end of their particle decay, is important to investigate nuclear forces and structure effects. In recent years there have been many efforts to extend these studies towards the drip-lines, i.e. to systems far from the β-stability valley, by using accelerated radioactive beams. The development of such infrastructures is accompanied by the development of more powerful detectors and associated electronics, capable to identify ions with very different sizes and kinetic energies. Here we give two examples which show how advanced arrays can contribute to the studies on nuclear phenomena. The examples come from the European FAZIA collaboration and from recent campaigns with the GARFIELD apparatus, the latter in operation at the INFN Legnaro Laboratory (Italy) where the SPES RIB facility is under construction

Benchmarking dispersion-corrected DFT methods for the evaluation of materials with anisotropic properties: Structural, electronic, dielectric, optical and vibrational analysis of calcite (CaCO3, space group: R 3 c)

Calcite (CaCO3, space group R3c) is a solid phase whose well-known highly anisotropic physical properties can be exploited to compare and calibrate various theoretical simulation methods. In this work, to benchmark different ab initio Density Functional Theory approaches that include for the first time corrections for dispersive forces, a systematic analysis of structural, electronic, dielectric, optical and vibrational properties of calcite is performed. The simulations considered the generalized-gradient approximation functional PBE and the hybrid B3LYP and PBE0, whereas the DFT-D2 and DFT-D3 schemes were adopted to account for the long-range interactions. This study suggests an overall better agreement between the theoretical results obtained with the DFT functionals corrected for the dispersive forces, with a better performance of hybrid functionals over PBE

Thermodynamic, elastic, and vibrational (IR/Raman) behavior of mixed type-AB carbonated hydroxylapatite by density functional theory

The present investigation reports the equation of state, thermodynamic, and thermoelastic properties of type AB carbonated apatite [CAp-AB, Ca10(CO3)B(PO4)5(CO3)A, space group P1], as obtained from density functional theory simulations and the quasi-harmonic approximation. The static (0 K) third-order Birch-Murnaghan equation of state resulted in the parameters K0 = 104.3(8) GPa, K′ = 4.3(1), and V0 = 517.9(2) Å3, whereas at room temperature (300 K) they were KT = 101.98 GPa, K′ = 4.12, and V0 = 524.486 GPa. Thermodynamics and thermoelasticity were calculated in the temperature range 0-800 K and between 0 and 30 GPa. Furthermore, the dependence of the infrared/Raman spectra of type-AB carbonated apatite with pressure is also reported, which could be useful for researchers interested in vibrational spectroscopy. The theoretical results corroborate the few experimental ones on a similar type-AB carbonated hydroxylapatite and provide further details over wide pressure and temperature ranges on the elastic, thermodynamic, and infrared/Raman properties of this important mineral found in both geological and biological environments

Kaolinite and dickite behaviour after deformation by compaction and shear

The structural changes produced on commercial powdered kaolin deformed by compaction and shear was investigated by X-ray diffraction (XRD), low temperature FTIR, differential thermal analysis and thermogravimetry (DTA/TG). Kaolin is composed by 40% of well orderered kaolinite, 18% of dickite and 42% of quartz. The deformation was induced through a specifically built planetary ball milling working in a controlled thermodynamic environment at room temperature and at a vacuum of 0.13 Pa (10-3 Torr). In this controlled environment the mechanical apparatus induces simultaneous compaction and shear stress to the material. Kaolin samples were milled for 1, 5, 10 and 20 hours. The deformation treatment produces a kaolinite structural order decrease, from a low-defect kaolinite to a high-defect kaolinite according to the AGFI index determined by XRD. An index to evaluate the changes produced on dickite was determined following a fitting procedure. The results indicated that dickite is apparently less affected by the deformation than kaolinite. A structural order was defined by FTIR and the results were correlated with AGFI results