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TUNNELING SPECTROSCOPY STUDY OF CALCIUM RUTHENATEBautista, Anthony 01 January 2010 (has links)
The ruthenates are perhaps one of the most diverse group of materials known up to date. These compounds exhibit a wide array of behaviors ranging from the exotic pwave superconductivity in Sr2RuO4, to the itinerant ferromagnetism in SrRuO3, and the Mott-insulating behavior in Ca2RuO4. One of the most intriguing compounds belonging to this group is Ca3Ru2O7 which is known to undergo an antiferromagnetic ordering at 56K and an insulating transition at 48K. Most intriguing, however, is the behavior displayed by this compound in the presence of an external magnetic field. For fields parallel to the a-axis, the compound undergoes a metamagnetic transition into the ferromagnetic region at 6 T. If the external field direction is changed to the b-axis then the result will be different. colossal magnetoresistance occurs and a fall in reistivity of up to three orders of magnitude is recorded at fields of 15T.
Most interesting, however, is the energy gap observed for this material. A number of groups have measured such gap with different methods and found conflicting results. For this reason it was of vital importance to perform measurements on this compound and try to resolve this issue. Tunneling spectroscopy is one of the most powerful techniques which can be used to probe the electronic properties of a material. The method is best suited to measure the density of states of a material and hence the nature of the strong correlations which dictate the properties of the compound. We performed a series of tunneling spectroscopy measurements by means of planar tunnel junctions. These types of junctions were chosen because of their stability over a large temperature range and their stability in the presence of an external field.
The anisotropies which showed up in the resistivity and magnetization measurements manifested also in our data. For tunneling parallel to the a-axis, we observed a gap opening at 48K with a width a peak to peak width of 2Δa ~258±15meV. As the temperature was lowered, the gap size increased reaching a maximum width of 2Δa ~ 845±38meVat 4.2K. Tunneling parallel to the b-axis, the gap has a much smaller size than the a-axis gap. At 48K the gap width is about 2Δb ~ 201±13 meV and reaches a maximum width of 2Δb ~ 366±33 meV at 4.2K. For the c-axis, the situation is different since the gap opens at 56K instead of 48K. The gap width at 56K is about 2Δc ~ 102±6meV and reaches a maximum width of 2Δc ~ 179±14 meV at 4.2K.
In the presence of an external field, we noticed that the overall behavior was always the same in the ab-plane but differed in c-axis direction. In our experiment, an external field was applied along the a-axis and measurements were made at 4.2K. For aaxis tunneling, the gap width decreased to a value of 2Δa ~ 587±27 meV at 4.2 K at 7T. On the other hand, the gap width in the b-axis direction decreased to a value of 2Δb ~ 308±25 meV for the same field. For the c-axis direction, the gap decreased to a value of 2Δc ~ 112±8 meV at 7T. The DOS of the c-axis differs for fields of 6T and above. A third peak emerges inside the gap on the valence side of the DOS. This third peak seems to be a direct consequence of the metamagnetic transition at 6T observed by other groups and may be attributable to a spin-filtering effect.
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The Baltics after "Dark": way to European UnionVachadze, Ana January 2011 (has links)
Focusing on the post-communist developments in Estonia, Latvia and Lithuania, the research prevails why the transition was successful in the Baltic States? Analyzing "the Baltic way" to the European Union, the paper discusses the certain aspects of economic, political and social transition. Cultural trauma of social change will also be concerned. Conceptual part of the work focuses on the theory of modernization which is discussed in the civilizational context. It is assumed that modernization is rather multi-dimensional than universal, homogeneous process. The Baltic modernization shows the patterns of original western European type of modernization with clearly defined end-up goal: political and cultural "return to the West". Empirical part of the research focuses on the economic, political and social transformation processes in the Baltic States. The main discussions on Economic transition heated around the question: how to build capitalism? What was possible and desirable? What policy should have been chosen? Baltic States went through the radical economic reform called "shock therapy". The essence of "this program is discussed in contradiction with "gradualism'" - an alternative strategy of economic transition. Political transition encompasses the state-building, nation-building and society...
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Nuclear Structure Study of Cd-110 through Internal Conversion ElectronsJigmeddorj, Badamsambuu 24 August 2012 (has links)
For many years, Cd-110 has been considered the classic example of a vibrational nucleus within both the Collective Model and the Interacting Boson Model (IBM).
As a vibrational nucleus, Cd-110 exhibits multi-phonon states. Recent studies on other cadmium isotopes have shown a breakdown of vibrational motion at the three-phonon level.
The latest study on Cd-112 suggests that some of these excitations may instead result from intruder bands. The study through internal conversion electrons is important to investigate intruder structures in Cd-110, using the enhanced E0 transitions between intruder states and spherical phonon states as a signature.
The nuclear structure of Cd-110 has been studied with In-110 beta decay through internal conversion electrons performed at TRIUMF using the 8pi spectrometer.
The level scheme of Cd-110 through internal conversion electron transitions was constructed using the electron-gamma coincidence matrix.
The sub-shell ratios and multipolarities are determined and compared with the evaluated data set.
The absolute internal conversion coefficients for some mixed transitions were determined using an internal calibration efficiency for Si(Li) detector and relative efficiency for HPGe detector.
The 396 keV and 708 keV E0 transitions have been observed between intruder and spherical phonon states.
The E0 transition strength of 0.115(71) was determined for 708.21 keV line.
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Measuring Trust in Post-Communist States: Making the Case for Particularized Trust.Ford, Nicole M. 01 November 2017 (has links)
While the literature on democracy and its relationship to trust provides little consensus regarding the role of trust, researchers have emphasized the importance of generalized trust over particularized in relation to democracy. This research marks a departure from this consensus, and exposes the neglected role of personal relationships in fostering successful democracy.
One of the key measurements of democracy in a country is social trust. There are three forms of trust: generalized, particularized and institutional. Previously, the measurement of social trust focused on the importance of generalized trust, that is, trust in those we do not know (Putnam, 1993; Fukuyama, 1995, et. al). Generalized trust is marked as having the greatest benefits for democracy. Those who are generalized trusters have the will to bridge across ethnicities and join civic groups in larger numbers. Institutional trust is society's trust in its institutions. Countries ranking high on institutional trust are also believed to have positive democratic outcomes. By contrast, particularized trust is often dismissed because it is seen as highly atomizing and, therefore, incapable of making bridges to ethnic others resulting in a bankruptcy of democratic values. Thus, the combination of institutional and generalized trust has been the main crux of measurement and understanding in relation to a country's ability to democratize.
The problem with this approach is two fold: first, it assumes the unidimensionality of trust and ultimately resigns a country of trusters to one category or the other with often negative impacts. The reality is, we are not solely one truster or the other: we are a combination of each form of trust. Secondly, this approach is Western in focus and does not account for the differentiation within cultures and is therefore unable to truly account for trust in a society. Nor does it account for new forms of trust and civil society in the new digital age. Recently, some questions about the legitimacy of this approach have surfaced and new methods have been employed to ascertain the true nature of social trust, however these methods have also fallen short (Gibson 2001; Bhary, et. al. 2005). Because trust is one measure used to determine the amount of democracy in a nation or the ability for it, accurate description is vital.
Here, the author will take a new approach and focus on the importance of the often overlooked particularized trust, as well as control for the importance of institutionalized trust. Using Khodyakov's (2007) research on trust and the Soviet case as the launching pad, the author will empirically examine trust in the former Soviet Union today. Using the most recent World Values Survey data, a new trust variable will be constructed that will be better able to capture the true, dynamic nature of trust. Placing this new trust variable in a Bayesian hierarchical linear model which will control for country level variables, it will be revealed that particularized trust can and does have positive impacts on support for democracy, debunking current notions to the contrary.
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The Topology and Dynamics of Surface Diffeomorphisms and Solenoid EmbeddingsHui, Xueming 07 April 2023 (has links)
We study two topics on surface diffeomorphisms, their mapping classes and dynamics. For the mapping classes of a punctured disc, we study the $\ZxZ$ subgroups of the fundamental groups of the corresponding mapping tori. An application is the proof of the fact that a satellite knot with braid pattern is prime. For the mapping classes of the disc minus a Cantor set, we study a special type of reducible mapping class. This has direct application on the embeddings of solenoids in $\mathbb{S}^3$. We also give some examples of other types of mapping classes of the disc minus a Cantor set. For the dynamics of surface diffeomorphisms, we prove three formulas for computing the topological pressure of a $C^1$-generic conservative diffeomorphism with no dominated splitting and show the continuity of topological pressure with respect to these diffeomorphisms. We prove for these generic diffeomorphisms that there is no equilibrium states with positive measure theoretic entropy. In particular, for hyperbolic potentials, there are no equilibrium states. For $C^1$ generic conservative diffeomorphisms on compact surfaces with no dominated splitting and $\phi_m(x):=-\frac{1}{m}\log \Vert D_x f^m\Vert, m \in \mathbb{N}$, we show that there exist equilibrium states with zero entropy and there exists a transition point $t_0$ for the one parameter family $\lbrace t \phi_m\rbrace_{t\geq 0}$, such that there is no equilibrium states for $ t \in [0, t_0)$ and there is an equilibrium state for $t \in [t_0,+\infty)$.
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