Influence of Geometrical Factors on the Physico-Chemical Properties of Perovskite and Layered Perovskite Oxides

A brief qualitative comparison is made of perovskite ABO sub 3 and layered perovskite ABO sub 3 and layered perovskite A sub 2 BO sub 4 oxides with special emphasis on the influence of geometrical factors on certain physico-chemical properties. The layered perovskite oxides are distinguished from three-dimensional oxides by a looser packing, frustration in three-dimensional interactions, more internal pressure on B--O bonds for small tolerance factors, and by different values of site-percolation thresholds. Their influence on electronic configurations of metal ions, stabilities and syntheses of compounds is discussed. The influence of increased anisotropy in layered oxides on localisation of charge carriers and in suppressing the onset of long-range ferromagnetic ordering is also discussed.

Onnellisten kylät : Vertaileva tapaustutkimus Kumpulan ja Sundsbergin asukkaiden subjektiivisesta hyvinvoinnista sekä onnellisuuden rakentumisesta

The aim of this masters thesis was to examine subjective wellbeing and personal happiness. Empirical study of happiness is part of broader wellbeing reseach and is based on an idea that the best experts of personal wellbeing are the individuals themselves. In addition to perceptions of personal happiness, the aim was also to acquire knowledge about personal values and components personal happiness is based on. In this study, moving into certain community and the charesteristics of neigbourhood contributing happiness, were defined to represent these values. The object was, through comparative casestudy, to obtain knowledge about subjective wellbeing of the inviduals in two different residental areas inside metropolitan area of Helsinki. In comparative case study the intention usually is that the examined units represent spesific "cases" from something broader and therefore the results can be somehow generalized. Consequently the chosen cases in this study were selected due to their image of "urban village" and thus the juxtapositioning was constructed between secluded post-suburban village and more heterogeneous urban village better attached to excisting urban structure. The researh questins were formed as follows: Are there any differencies between the areas regarding the components personal happines is based on? Are there any differencies between the areas regarding the level of residents subjective wellbeing? Based on the residents assesments, what are the most important charesteristics of neigbourhood contributing personal happiness? The data used in order to gain aswers to these questions was obtained from internet-based survey questionnaire. Based on the data residents of post-suburban village Sundsberg seem to share highly family oriented set of values and actualizing these values is ensured with high income, wealth and secure work situation. Insteadt in Kumpula the components of happiness seem place more towards learning and personal developement, interesting leisure and hobbies and specially having an influence regarding communal decisions. Conserning subjective wellbeing of residents there can be seen some differencies as well. Personal life is experienced a bit more happier in Sundsberg than in Kumpula. People are more satified with their personal health and job satisfaction in Sundsberg and additionally feelings of loneliness, inadequancy and frustration are bit more common in Kumpula. Regarding the charesteristics of neigbourhood contributing happiness data suggests that key charesteristics of area are peacefulness and safely, good location and connections and proximity of parks and recreational areas. These charesteristics were concidered highly significant in both areas but they were experienced to actualize better in Kumpula. In addition to these components the residents in Kumpula were overall more satisfied with various charecteristics contiburing happiness in their residental area. Besides these attributes mentioned above residents in Kumpula emphasize also some "softer" elements connecting into social, functional and communal side of area. From Sundsberg point of view residental area best contributing happiness is child friendly and safe community based on likeminded people who share the same sosioeconomical situation. The results of this study can be linked back into the society and metropolitan area, which they were chosen from as a cases to be studied. The results can thereby be seen as an example of differentation of conditions of personal happiness between certain population segments. It is possible to detect an spatial dimetion to this process as well and thereby the results suggests that regional segmentation affects between high-ranking residental areas as well. Thereby the results of this reseach contributes to the debate on innovative, diverse and dynamic urban area and as well cohesion of metropolitan area and the society in whole.

Magnetic studies of a mixed antiferromagnetic system Fe1?xNixPS3

The magnetic properties of the layered compounds FePS3, NiPS3 and the mixed system Fe1-xNixPS3 have been investigated. All the compounds show a maximum in chi at a temperature T(max) followed by the onset of antiferromagnetic order at low temperatures at T(N). As the composition is changed there is a continuous change in T(N) and in the ratio T(N)/T(max). Our results , show that in the mixed antiferromagnetic system Fe1-xNixPS3, the strongly antiisotropic Fe component imposes its anisotropy on the weakly anisotropic Ni component. We find also no frustration or spin-glass-like ordering at any composition.

Lattice model for rapidly folding protein-like heteropolymers

Protein folding is a relatively fast process considering the astronomical number of conformations in which a protein could find itself. Within the framework of a lattice model, we show that one can design rapidly folding sequences by assigning the strongest attractive couplings to the contacts present in a target native state, Our protein design can be extended to situations with both attractive and repulsive contacts. Frustration is minimized by ensuring that all the native contacts are again strongly attractive. Strikingly, this ensures the inevitability of folding and accelerates the folding process by an order of magnitude, The evolutionary implications of our findings are discussed.

Dynamic and thermodynamic anomalies of water at low temperatures: from bulk water to reverse micelles and DNA hydration layer

Liquid water is known to exhibit remarkable thermodynamic and dynamic anomalies, ranging from solvation properties in supercritical state to an apparent divergence of the linear response functions at a low temperature. Anomalies in various dynamic properties of water have also been observed in the hydration layer of proteins, DNA grooves and inside the nanocavity, such as reverse micelles and nanotubes. Here we report studies on the molecular origin of these anomalies in supercooled water, in the grooves of DNA double helix and reverse micelles. The anomalies have been discussed in terms of growing correlation length and intermittent population fluctuation of 4- and 5-coordinated species. We establish correlation between thermodynamic response functions and mean squared species number fluctuation. Lifetime analysis of 4- and 5-coordinated species reveals interesting differences between the role of the two species in supercooled and constrained water. The nature and manifestations of the apparent and much discussed liquid-liquid transition under confinement are found to be markedly different from that in the bulk. We find an interesting `faster than bulk' relaxation in reverse micelles which we attribute to frustration effects created by competition between the correlations imposed by surface interactions and that imposed by hydrogen bond network of water.

Transport and magnetic properties of Nd1-xPbxMnO3 single crystals

Transport and magnetic properties of flux-grown Nd1−xPbxMnO3 single crystals (x=0.15–0.5) are studied in the temperature range 300–77 K and 280–2 K, respectively. Magnetization measurements with a superconducting quantum interference device confirm a paramagnetic to ferromagnetic transition around 110, 121, 150, 160, and 178 K for x=0.15, 0.2, 0.3, 0.4, and 0.5, respectively. Four probe resistivity measurements at low temperatures show a monotonic increase for x=0.15 which represents a ferromagnetic insulating (FMI) phase. For Nd0.8Pb0.2MnO3 there is a slope change present in the resistivity profile at 127 K where metal to insulator transition (MI) sets in. For x=0.3 this MI transition is more prominent. However, both these samples have FMI phase at low temperature. When the concentration of lead increases (x>0.3) the sample displays a clear insulator to metal transition with a low temperature ferromagnetic metallic phase. On the basis of these measurements we have predicted the phase diagram of Nd1−xPbxMnO3. Magnetization measurements by a vibration sample magnetometer point out the appreciable differences between zero field cooled and field cooled profiles below the ferromagnetic to paramagnetic transition temperature for all x. These are indicative of magnetic frustration.

Crystal-field interaction in the pyrochlore magnet Ho2Ti2O7

Neutron time-of-flight spectroscopy has been employed to study the crystal-field interaction in the pyrochlore titanate Ho2Ti2O7. The crystal-field parameters and corresponding energy-level scheme have been determined from a profile fit to the observed neutron spectra. The ground state is a well separated Eg doublet with a strong Ising-like anisotropy, which can give rise to frustration in the pyrochlore lattice. Using the crystal-field parameters determined for the Ho compound as an estimate of the crystal-field potential in other pyrochlore magnets, we also find the Ising type behavior for Dy. In contrast, the almost planar anisotropy found for Er and Yb prevents frustration, because of the continuous range of possible spin orientations in this case.

Quantum phases of dimerized and frustrated Heisenberg spin chains with s=1/2, 1 and 3/2: an entanglement entropy and fidelity study

We study here different regions in phase diagrams of the spin-1/2, spin-1 and spin-3/2 one-dimensional antiferromagnetic Heisenberg systems with frustration (next-nearest-neighbor interaction J(2)) and dimerization (delta). In particular, we analyze the behaviors of the bipartite entanglement entropy and fidelity at the gapless to gapped phase transitions and across the lines separating different phases in the J(2)-delta plane. All the calculations in this work are based on numerical exact diagonalizations of finite systems.

Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges

We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(1)(F)) and antiferromagnetic (J(1)(A)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(2)(F)). In this model frustration is present due to the non-zero J(2)(F). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(2)(F) and large J(1)(F)/J(1)(A). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(1)(F), the phase diagram in the space of J(1)(A)-J(2)(F) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.

Glass, Gel, and Liquid Crystals: Arrested States of Graphene Oxide Aqueous Dispersions

Colloidal systems with competing interactions are known to exhibit a range of dynamically arrested states because of the systems' inability to reach its underlying equilibrium state due to intrinsic frustration. Graphene oxide (GO) aqueous dispersions constitute a class of 2D-anisotropic colloids with competing interactions long-range electrostatic repulsion, originating from ionized groups located on the rim of the sheets, and weak dispersive attractive interactions originating from the unoxidized graphitic domains. We show here that aqueous dispersions of GO exhibit a range of arrested states, encompassing fluid, glass, and gels that coexist with liquid-crystalline order with increasing volume fraction. These states can be accessed by varying the relative magnitudes of the repulsive and attractive forces. This can be realized by changing the ionic strength of the medium. We observe at low salt concentrations, where long-range electrostatic repulsion dominates, the formation of a repulsive Wigner glass, while at high salt concentrations, when attractive forces dominate, the formation of gels exhibits a nematic to columnar liquid-crystalline transition. The present work highlights how the chemical structure of GO hydrophilic ionizable groups and hydrophobic graphitic domains coexisting on a single sheet gives rise to a rich and complex array of arrested states.

Structural and magnetic properties of ultra-small scale eutectic CoFeZr alloys

Aiming to develop high mechanical strength and toughness by tuning ultrafine lamellar spacing of magnetic eutectic alloys, we report the mechanical and magnetic properties of the binary eutectic alloys Co90.5Zr9.5 and Fe90.2Zr9.8, as well as the pseudo-binary eutectic alloys Co82.4Fe8Zr9.6, Co78Fe12.4Zr9.6 and Co49.2Fe49.2Zr9.6 developed by suction-casting. The lower lamellar spacing around 100 nm of the eutectics Co49.2Fe49.2Zr9.6 yields a high hardness of 713(+/- 20) VHN. Magnetic measurements reveal high magnetic moment of 1.92 mu B (at 5 K) and 1.82 mu B (at 300 K) per formula unit for this composition. The magnetization vs. applied field data at 5 K show a directional preference to some extent and therefore smaller non-collinear magnetization behavior compared to Co11Zr2 reported in the literature due to exchange frustration and transverse spin freezing owing to the presence of smaller Zr content. The decay of magnetization as a function of temperature along the easy axis of magnetization of all the eutectic compositions can be described fairly well by the spin wave excitation equation Delta M/M(0) = BT3/2 + CT5/2. (C) 2014 Elsevier B.V. All rights reserved.

Mono layer to Interdigitated Partial Bilayer Smectic C Transition in Thiophene-Based Spacer Mesogens: X-ray Diffraction and C-13 Nuclear Magnetic Resonance Studies

Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state C-13 NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

Clima emocional, inseguridad y miedo al delito : percepciones diferenciales en función del autoposicionamiento ideológico

Resumen: El clima emocional no es la simple suma de las emociones individuales sino un afecto colectivo generado por cómo los individuos interactúan unos con otros como respuestas colectivas a sus condiciones económicas, políticas y sociales (de Rivera, 2014). Por su parte, en el contexto argentino la inseguridad es el principal problema social percibido en los últimos años. Sobre este marco, se realizó un estudio con el objetivo de analizar el clima emocional, la percepción de inseguridad y el miedo al delito junto a otros factores psicosociales asociados, y de explorar los perfiles perceptivos diferenciales según el auto-posicionamiento ideológico. La muestra, intencional, estuvo compuesta por 516 estudiantes universitarios. Los resultados dan cuenta de un clima emocional negativo (enfado y desesperanza), baja confianza institucional, frustración anómica y alta percepción de inseguridad. Se observan diferencias al comparar a los participantes en función de su autoposicionamiento ideológico. La percepción del clima emocional es más positivo cuánto más a la izquierda se ubican los participantes, manifestando mayor seguridad, menor desesperanza y enfado. Exhiben además menos miedo al delito, menor preocupación por la inseguridad y menor probabilidad de victimización. Sin embargo, quienes se posicionan ideológicamente hacia la derecha muestran mayores niveles de frustración anómica, y la confianza (o desconfianza) institucional varía por el posicionamiento ideológico en función de la institución. Finalmente, la heteropercepción de inseguridad es mayor que la autopercepción, surgiendo de este modo mecanismos defensivos como la ilusión de invulnerabilidad, que conllevan mayor riesgo.

What happened during the climate change negotiations in Copenhagen 2009?

4 p.