Pressure-Induced Amorphization of Small Pore Zeolites-the Role of Cation-H2O Topology and Anti-glass Formation

Systematic studies of pressure-induced amorphization of natrolites (PIA) containing monovalent extra-framework cations (EFC) Li+, Na+, K+, Rb+, Cs+ allow us to assess the role of two different EFC-H2O configurations within the pores of a zeolite: one arrangement has H2O molecules (NATI) and the other the EFC (NAT(II)) in closer proximity to the aluminosilicate framework. We show that NAT(I) materials have a lower onset pressure of PIA than the NAT(II) materials containing Rb and Cs as EFC. The onset pressure of amorphization (P-A) of NAT(II) materials increases linearly with the size of the EFC, whereas their initial bulk moduli (P-1 phase) decrease linearly. Only Cs- and Rb-NAT reveal a phase separation into a dense form (P-2 phase) under pressure. High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) imaging shows that after recovery from pressures near 25 and 20 GPa long-range ordered Rb-Rb and Cs-Cs correlations continue to be present over length scales up to 100 nm while short-range ordering of the aluminosilicate framework is significantly reduced-this opens a new way to form anti-glass structuresopen

Titanium dioxide engineered for near-dispersionless high terahertz permittivity and ultra-low-loss

Realising engineering ceramics to serve as substrate materials in high-performance terahertz(THz) that are low-cost, have low dielectric loss and near-dispersionless broadband, high permittivity, is exceedingly demanding. Such substrates are deployed in, for example, integrated circuits for synthesizing and converting nonplanar and 3D structures into planar forms. The Rutile form of titanium dioxide (TiO2) has been widely accepted as commercially economical candidate substrate that meets demands for both low-loss and high permittivities at sub-THz bands. However, the relationship between its mechanisms of dielectric response to the microstructure have never been systematically investigated in order to engineer ultra-low dielectric-loss and high value, dispersionless permittivities. Here we show TiO2 THz dielectrics with high permittivity (ca. 102.30) and ultra-low loss (ca. 0.0042). These were prepared by insight gleaned from a broad use of materials characterisation methods to successfully engineer porosities, second phase, crystallography shear-planes and oxygen vacancies during sintering. The dielectric loss achieved here is not only with negligible dispersion over 0.2-0.8 THz, but also has the lowest value measured for known high-permittivity dielectrics. We expect the insight afforded by this study will underpin the development of subwavelength-scale, planar integrated circuits, compact high Q-resonators and broadband, slow-light devices in the THz band

Insights into the Molecular Mechanisms of the Anti-Atherogenic Actions of Flavonoids in Normal and Obese Mice

Obesity is a major and independent risk factor for cardiovascular disease and it is strongly associated with the development of dyslipidemia, insulin resistance and type 2 diabetes. Flavonoids, a diverse group of polyphenol compounds of plant origin widely distributed in human diet, have been reported to have numerous health benefits, although the mechanisms underlying these effects have remained obscure. We analyzed the effects of chronic dietary supplementation with flavonoids extracted from cranberry (FLS) in normal and obese C57/BL6 mice compared to mice maintained on the same diets lacking FLS. Obese mice supplemented with flavonoids showed an amelioration of insulin resistance and plasma lipid profile, and a reduction of visceral fat mass. We provide evidence that the adiponectin-AMPK pathway is the main mediator of the improvement of these metabolic disorders. In contrast, the reduced plasma atherogenic cholesterol observed in normal mice under FLS seems to be due to a downregulation of the hepatic cholesterol synthesis pathway. Overall, we demonstrate for the first time that the molecular mechanisms underlying the beneficial effects of flavonoids are determined by the metabolic state

Educational Policies Committee Minutes, March 3, 2011

Subcommittee Reports Curriculum Subcommittee Academic Standards Subcommittee General Education Subcommitte

Density matrix renormalisation group calculations of molecular exciton energies in poly(p-phenylene vinylene)

Starting from the Pariser-Parr-Pople theory of π-conjugated systems, we construct a model of the low lying excitations of poly(p-phenylene vinylene). The model is based on the bonding HOMO and LUMO states of the molecular repeat units. The model is numerically tractable in that it is solved for oligomers of up to 15 units using the density matrix renormalisation group method. The energy of the 1 1Bu- exciton is in good agreement with experimental results for oligomers, and approaches ca. 2.7 eV for oligomers of 15 units. Likewise, we predict a 21Ag+ exciton at ca. 2.8 eV, a 13Bu+ exciton at 1.6 eV and the singlet exciton binding energy as being 1.4 eV for single chains. We extend this approach to target other absorption bands. For example, we find a localised Frenkel exciton at 5.8 eV, in excellent agreement with the 6 eV absorption peak in PPV. © 1997 Elsevier Science S.A

The electronic structure of conjugated polymers

The density matrix renormalisation group (DMRG) method is a powerful computational technique for calculating the electronic and geometrical structures of one-dimensional conjugated polymers. First, we solve the Pariser-Parr-Pople-Peierls model for trans-polyene oligomers. We investigate the energies and solitonic structures. Next, we solve the Pariser-Parr-Pople model for the light emitting phenyl polymers, and ascertain the nature of the excited states. Finally, we discuss how the DMRG method can be extended to ZINDO and ab initio Hamiltonians, and to electron-phonon problems

Theory of molecular excitons in the phenyl-based organic semiconductors

Starting from the Pariser-Parr-Pople model of π conjugated systems, a model of the low-lying excitations of poly(para-phenylene) (PPP) and poly(para-phenylenevinylene) (PPV) is introduced, based on the bonding HOMO and LUMO states of the repeat units. The inter-phenyl hybridisation is treated as a phenomenological parameter. The model is solved using exact diagonalisation and the density matrix renormalisation group method. The predicted exciton energies for PPV agree well with absorption experiments on short oligomers and thin films. For a 15 phenylene-unit oligomer, an exciton gap of 2.7 eV is predicted, with a binding energy of ca. 1.4 eV. For PPP the exciton gap is 3.0 eV and the binding energy is ca. 1.7 eV. © 1997 Elsevier Science B.V

Symmetry-adapted density matrix renormalization group calculations of the primary excited states of poly(para-phenylene vinylene).

The Pariser-Parr-Pople model of pi-conjugated electrons is solved by a three-block, symmetry-adapted density matrix renormalization group (DMRG) method for the light emitting polymer, poly(para-phenylene vinylene). The energies of the primary excited states are calculated. There is excellent agreement between theory and experiment when solid state screening is incorporated into the model parameters, enabling us to make an identification of the origin of the key spectroscopic features. Appendices describe important technical aspects of the three-block DMRG approach: Local Hilbert space efficiency and its relation to the matrix product formulation of the DMRG; an efficient computational procedure for constructing symmetry-adapted states for DMRG calculations; and correct superblock state targeting to ensure good convergence of the method

The low energy electronic structure of poly(p-phenylene vinylene)

A two state molecular orbital model of poly(p-phenylene vinylene) (PPV) is solved using the density matrix renormalisation group method. The energies and spatial correlation functions of the low lying states are calculated. A band of tightly bound 1Bu- excitons and a band of charge-transfer 1Ag+ excitons exist below the band gap. In the limit of infinite chains, the lowest lying 1Bu- exciton is at ca. 2.6 eV, while the lowest lying 1Ag+ exciton is at ca. 2.9 eV. The band threshold is at 3.2 eV. © 1999 El1sevier Science S.A. All rights reserved