Colossal dielectric constants in transition-metal oxides

Many transition-metal oxides show very large ("colossal") magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation. In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today's most investigated material with colossal dielectric constant. Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2-xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

State estimator synthesis for position dependent flexible systems with position independent error convergence

In this paper a state estimator for high tech flexible systems with an inherent nonlinearity in the output dynamics is proposed. We consider an application in which sensor measurements of the flexible system become parameter (position) dependent. An LPV setting is proposed for the design of estimators that estimate flexible modes of the system. The possibility of pole placement for the error dynamics is investigated and characterized. In particular, necessary and sufficient conditions are derived for the estimator convergence to be parameter independent. In addition, an eigenvalue-shifting technique that improves the convergence of the estimated flexible modes is presented. Simulation results on a basic example and a full flexible system model are used to demonstrate the merits of the proposed estimation algorithms

Modal observer design for a flexible motion system with state dependent sensor positions

This paper focuses on observer design for a flexible motion system with a state dependent output map. After rewriting the modal system to parameter varying form sufficient conditions are derived to obtain a parameter varying modal observer with bounded L2 gain. These conditions translate to linear matrix inequalities (LMIs) when the time derivative of the Lyapunov function is multiconvex. The derived theory is applied to a model of the Herringbone Pattern Planar Actuator (HPPA) where noise and input disturbance affect the system. Using the theory it is possible to estimate independent rigid body motion in six degrees of freedom (DoF) and two flexible modes

Modal observer design for a flexible motion system with state dependent sensor positions

This paper focuses on observer design for a flexible motion system with a state dependent output map. After rewriting the modal system to parameter varying form sufficient conditions are derived to obtain a parameter varying modal observer with bounded L2 gain. These conditions translate to linear matrix inequalities (LMIs) when the time derivative of the Lyapunov function is multiconvex. The derived theory is applied to a model of the Herringbone Pattern Planar Actuator (HPPA) where noise and input disturbance affect the system. Using the theory it is possible to estimate independent rigid body motion in six degrees of freedom (DoF) and two flexible modes

Infrared Multiple-Photon Dissociation Spectroscopy of Tripositive Ions: Lanthanum-Tryptophan Complexes

Collision-induced charge disproportionation limits the stability of triply charged metal ion complexes and has thus far prevented successful acquisition of their gas-phase IR spectra. This has curtailed our understanding of the structures of triply charged metal complexes in the gas phase and in biological environments. Herein we report the first gas-phase IR spectra of triply charged La-III complexes with a derivative of tryptophan (N-acetyl tryptophan methyl ester), and an unusual dissociation product, a lanthanum amidate. These spectra are compared with those predicted using density functional theory. The best structures are those of the lowest energies that differ by details in the a-interaction between La3+ and the indole rings. Other binding sites on the tryptophan derivative are the carbonyl oxygens. In the lanthanum amidate, La3+ replaces an H+ in the amide bond of the tryptophan derivative

Structure and Reactivity of the Distonic and Aromatic Radical Cations of Tryptophan

In this work, we regiospecifically generate and compare the gas-phase properties of two isomeric forms of tryptophan radical cations-a distonic indolyl N-radical (H3N+ - TrpN(center dot)) and a canonical aromatic pi (Trp(center dot+)) radical cation. The distonic radical cation was generated by nitrosylating the indole nitrogen of tryptophan in solution followed by collision-induced dissociation (CID) of the resulting protonated N-nitroso tryptophan. The p-radical cation was produced via CID of the ternary [Cu-II(terpy)(Trp)](center dot 2+) complex. CID spectra of the two isomeric species were found to be very different, suggesting no interconversion between the isomers. In gas-phase ion-molecule reactions, the distonic radical cation was unreactive towards n-propylsulfide, whereas the pi radical cation reacted by hydrogen atom abstraction. DFT calculations revealed that the distonic indolyl radical cation is about 82 kJ/mol higher in energy than the pi radical cation of tryptophan. The low reactivity of the distonic nitrogen radical cation was explained by spin delocalization of the radical over the aromatic ring and the remote, localized charge (at the amino nitrogen). The lack of interconversion between the isomers under both trapping and CID conditions was explained by the high rearrangement barrier of ca. 137 kJ/mol. Finally, the two isomers were characterized by infrared multiple-photon dissociation (IRMPD) spectroscopy in the similar to 1000-1800 cm(-1) region. It was found that some of the main experimental IR features overlap between the two species, making their distinction by IRMPD spectroscopy in this region problematic. In addition, DFT theoretical calculations showed that the IR spectra are strongly conformation-dependent

Infrared Multiple-Photon Dissociation Spectroscopy of Tripositive Ions: Lanthanum–Tryptophan Complexes

Collision-induced charge disproportionation limits the stability of triply charged metal ion complexes and has thus far prevented successful acquisition of their gas-phase IR spectra. This has curtailed our understanding of the structures of triply charged metal complexes in the gas phase and in biological environments. Herein we report the first gas-phase IR spectra of triply charged La^III complexes with a derivative of tryptophan (<i>N</i>-acetyl tryptophan methyl ester), and an unusual dissociation product, a lanthanum amidate. These spectra are compared with those predicted using density functional theory. The best structures are those of the lowest energies that differ by details in the π-interaction between La³⁺ and the indole rings. Other binding sites on the tryptophan derivative are the carbonyl oxygens. In the lanthanum amidate, La³⁺ replaces an H⁺ in the amide bond of the tryptophan derivative