Metalinsulator transition induced by pressure in chemically bonded solids

Abstract

A review is given of metal-insulator transitions induced by pressure in chemically bonded solids.

After an introduction to energy band overlap mechanisms, which appear very useful to characterize the insulator-metal transitions in some solids (the rare gases He and Xe, the iso-electronic sequence of Xe, H₂ and I₂), some discussion is given of electron correlation in relation to molecular dissociation. However, it is to be emphasized that such dissociation is a sufficient, but not a necessary, condition for metallization in H. and I₂. For N₂, the above considerations, which focussed dominantly on ground-state properties as a function of pressure, need transcending because the observation of metallization in this system plainly involves thermal effects in an important way.

The final part of the review considers the way various low-dimensional solids (polyacetylene, TTF-TCNQ, and appropriate phases of H₂ and I₂) are altered by application of high pressures. Present understanding leads to the conclusion that there should be an interesting interplay between Hubbard on-site electron correlation, bond-charge repulsion and near-neighbour interaction, as a function of thermodynamic state.     

Kernel Theorems for Modulation Spaces

Journal of Fourier Analysis and Applications - We deal with kernel theorems for modulation spaces. We completely characterize the continuity of a linear operator on the modulation spaces $$M^p$$...     

Gadolinium(III)-Based Dual 1H/19F Magnetic Resonance Imaging Probes

We present two novel octadentate cyclen-based ligands bearing one (L¹) or two (L²) phenylacetamide pendants with two CF₃ groups either at positions 3 and 5 (L¹) or 4 (L²). The corresponding Gd³⁺ complexes possess one coordinated water molecule, as confirmed by luminescence lifetime measurements on the Eu^III and Tb^III analogues. A detailed ¹H and ¹⁷O relaxometric characterization has revealed the parameters that govern the relaxivities of these complexes. The water-exchange rate of the mono-amide derivative GdL¹ (k_ex²⁹⁸=1.52×10⁶ s⁻¹) is faster than that determined for the bis-amide complex GdL² (k_ex²⁹⁸=0.73×10⁶ s⁻¹). ¹H and ¹⁹F NMR studies have indicated that the complexes are present in solution almost exclusively as the square-antiprismatic (SAP) isomers. ¹⁹F NMR relaxation studies indicated Gd ⋅⋅⋅ F distances of 7.4±0.1 and 9.1±0.1 Å for GdL¹ and GdL², respectively. Phantom MRI studies revealed the favorable properties of GdL² as a dual ¹H/¹⁹F magnetic resonance imaging (MRI) probe, whereas the shorter Gd ⋅⋅⋅ F distance of GdL¹ reduces the signal-to-noise ratio due to the very short transverse relaxation time of the ¹⁹F NMR signal.     

On general infinite dimensional complementarity problems

The aim of this paper is to present a way to study directly generalized complementarity problems in normed spaces. By means of new results on infinite dimensional Lagrange theory we show some optimality conditions which reduce the study of the problems to the one of suitable systems of equalities and inequalities.     

Synthesis of highly regioregular poly[3‐(4‐alkoxyphenyl)‐thiophene]s by oxidative catalysis using copper complexes

A novel, easy, and cost‐effective synthetic procedure is reported for the production of very highly regioregular poly[3‐(4‐alkoxyphenyl)thiophene]s by means of oxidative coupling. Four copper complexes were synthesized and used as catalysts to obtain polymers with higher regioregularity compared to the previous oxidative coupling methodologies reported in the literature and similar to that obtained by McCullough and Rieke methods in the synthesis of poly‐3‐alkylthiophenes. The regioregularity of the synthesized polymers was investigated by UV–Visible characterization on polymer thin films and ¹H NMR analysis. The remarkable potentialities of these polymers have emerged from field‐effect transistor mobility measurements operated on devices with bottom‐contact configuration and hexamethyldisilazane‐treated SiO₂ gate dielectric, showing a well‐defined p‐type field‐effect response and maximum mobility values in air higher than 10^?4 cm² V^?1 s^?1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4351–4360     

1,4‐Phenylenebis(methylene) bis(9H‐carbazole‐9‐carbodithioate)

The molecules of the title compound, C₃₄H₂₄N₂S₄, lie across centres of inversion in the space group P2₁/n. The spacer unit linking the benzene rings and carbazole units is effectively planar, while the carbazole unit itself is slightly folded. Molecules are linked into sheets by a single C—H...π(arene) hydrogen bond and the hydrogen‐bonded sheets are themselves linked into a three‐dimensional framework structure by a single π–π stacking interaction.     

Neuromelanins Isolated from Different Regions of the Human Brain Exhibit a Common Surface Photoionization Threshold

Neuromelanin isolated from the premotor cortex, cerebellum, putamen, globus pallidus and corpus callosum of the human brain is studied by scanning probe and photoelectron emission microscopies and the results are compared with previously published work on neuromelanin from the substantia nigra. Scanning electron microscopy reveals common structure for all neuromelanins. All exhibit spherical entities of diameters between 200 and 400 nm, composed of smaller spherical substructures, ∼30 nm in diameter. These features are similar to that observed for many melanin systems including Sepia cuttlefish, bovine eye, and human eye and hair melanosomes. Photoelectron microscopy images were collected for all neuromelanins at specific wavelengths of ultraviolet light between 248 and 413 nm, using the spontaneous emission output from the Duke free electron laser. Analysis of the data establishes a common threshold photoionization potential for neuromelanins of 4.7 ± 0.2 eV, corresponding to an oxidation potential of −0.3 ± 0.2 V vs the normal hydrogen electrode (NHE). These results are consistent with previously reported potentials for neuromelanin from the substantia nigra of 4.5 ± 0.2 eV (−0.1 ± 0.2 V vs NHE). All neuromelanins exhibit a common low surface oxidation potential, reflecting their eumelanic component and their inability to trigger redox processes with neurotoxic effect.     

Multiphase Euler–Lagrange CFD simulation applied to Wet Flue Gas Desulphurisation technology

The gas and liquid hydrodynamics inside an Open Spray Tower has been simulated using a commercial CFD code, while a model that treats the absorption process of SO₂ has been developed and implemented in the software through dedicated modules. Besides SO₂ absorption also evaporation of slurry droplets and droplet-wall interaction are considered, the latter modeled with an empirical correlation and implemented in a sub-module.     

A simplified, flow-based calibration method for stereoscopic PIV

An improvement of the process of stereo-PIV calibration is presented. The central feature of the proposed technique is that the calibration of the stereoscopic system is based upon the measurement of a calibrated flow. This is achieved through an initial two-dimensional calibration of the measurement plane using a single target point, followed by a perspective and laser sheet thickness optimization that makes use of the measurement of a known reference flow, e.g., a uniform flow. This technique results in planar domain, three-component (2D–3C) measurements with a simpler calibration phase, which delivers uncompromised accuracy, compensates for the mechanical misalignment and eliminates the errors deriving from the classical target plate dot identification. The technique is particularly well suited for towing tanks and other large facilities, and is applied to the vortex system shed from an underwater bridge sail.