Lucy : Dancing Around The Cabin Door

https://digitalcommons.library.umaine.edu/mmb-vp/5190/thumbnail.jp

Critical current of a Josephson junction containing a conical magnet

We calculate the critical current of a superconductor/ferromagnetic/superconductor (S/FM/S) Josephson junction in which the FM layer has a conical magnetic structure composed of an in-plane rotating antiferromagnetic phase and an out-of-plane ferromagnetic component. In view of the realistic electronic properties and magnetic structures that can be formed when conical magnets such as Ho are grown with a polycrystalline structure in thin-film form by methods such as direct current sputtering and evaporation, we have modeled this situation in the dirty limit with a large magnetic coherence length ($\xi_f$). This means that the electron mean free path is much smaller than the normalized spiral length $\lambda/2\pi$ which in turn is much smaller than $\xi_f$ (with $\lambda$ as the length a complete spiral makes along the growth direction of the FM). In this physically reasonable limit we have employed the linearized Usadel equations: we find that the triplet correlations are short ranged and manifested in the critical current as a rapid oscillation on the scale of $\lambda/2\pi$. These rapid oscillations in the critical current are superimposed on a slower oscillation which is related to the singlet correlations. Both oscillations decay on the scale of $\xi_f$. We derive an analytical solution and also describe a computational method for obtaining the critical current as a function of the conical magnetic layer thickness.Comment: Extended version of the published paper. Additional information about the computational method is included in the appendi

Are factor endowments fate?

In recent theories of comparative development, the role of institutional differences has been crucial. Yet, what explains comparative institutional evolution? We investigate this issue by studying the coffee exporting economies of Latin America. Although homogeneous in many ways, they experienced radically different paths of economic (and political) development, which is conventionally traced to the differential organization of the coffee industry. We show that the different forms that the coffee economy took in the 19th century was critically determined by the legal environment determining access to land, and that different laws resulted from differences in the nature of political competition and the backgrounds of political elites. Our analysis suggests that explanations of institutional differences that stress economic fundamentals can only be part of the story. At least in the economies that we study, while geography, factor endowments and technology are clearly important, their implications for the institutional structure and thus development are conditional on the form that political competition takes in society. For interesting variations in economic outcomes, endowments are not fate.El papel de las diferencias institucionales ha sido crucial en las teorías recientes del desarrollo comparativo. Pero ¿Qué explica las diferencias comparativas en la evolución institucional? En este trabajo investigamos este asunto estudiando las economías exportadoras de café en Latinoamérica. Aunque similares, estas economías experimentaron diferentes modelos de desarrollo económico (y político) convencionalmente explicados en relación con su diferente organización de la industria cafetera. Este artículo muestra que las diferentes formas adoptadas por la economía cafetera en el siglo XIX estuvieron especialmente determinadas por el entorno legal del acceso a la tierra y de las diferentes leyes resultantes de las diferencias en la naturaleza de la competición política y de la formación de las elites políticas. Nuestro análisis sugiere que las explicaciones de diferencia institucional que presionan los fundamentos de la economía pueden ser sólo una parte de la explicación. Al menos en las economías que hemos estudiado, mientras la geografía, la dotación de recursos y la tecnología son claramente importantes en la explicación, sus implicaciones sobre la estructura institucional y, en consecuencia, sobre el desarrollo, dependen de la forma de competición política adoptada por la sociedad. Para las interesantes variaciones de los resultados económicos los recursos no son el destino

Report of the Citizens\u27 Dickey-Lincoln Project Impact Review Committee to Governor James B. Longley

The construction of the Dickey-Lincoln Hydroelectric Project. To examine, in depth, the proposal and its impact as seen by various segments of our society. The report will identify the factors that must carry the main weight in making a final determination

Approximate variational coupled cluster theory

We show that it is possible to construct an accurate approximation to the variational coupled cluster method, limited to double substitutions, from the minimization of a functional that is rigorously extensive, exact for isolated two-electron subsystems and invariant to transformations of the underlying orbital basis. This approximate variational coupled cluster theory is a modification and enhancement of our earlier linked pair functional theory. It is first motivated by the constraint that the inverse square root of the matrix that transforms the cluster amplitudes must exist. Low-order corrections are then included to enhance the accuracy of the approximation of variational coupled cluster, while ensuring that the computational complexity of the method never exceeds that of the standard traditional coupled cluster method. The effects of single excitations are included by energy minimization with respect to the orbitals defining the reference wavefunction. The resulting quantum chemical method is demonstrated to be a robust approach to the calculation of molecular electronic structure and performs well when static correlation effects are strong

Toward a descriptive model of galactic cosmic rays in the heliosphere

Researchers review the elements that enter into phenomenological models of the composition, energy spectra, and the spatial and temporal variations of galactic cosmic rays, including the so-called anomalous cosmic ray component. Starting from an existing model, designed to describe the behavior of cosmic rays in the near-Earth environment, researchers suggest possible updates and improvements to this model, and then propose a quantitative approach for extending such a model into other regions of the heliosphere

Structure formation by cosmic strings with a cosmological constant

Final published version.Comment: 4 Page

A Review of Drive Cycles for Electrochemical Propulsion

Automotive drive cycles have existed since the 1960s. They started as requirements as being solely used for emissions testing. During the past decade, they became popular with scientists and researchers in the testing of electrochemical vehicles and power devices. They help simulate realistic driving scenarios anywhere from system to component-level design. This paper aims to discuss the complete history of these drive cycles and their validity when used in an electrochemical propulsion scenario, namely with the use of proton exchange membrane fuel cells (PEMFC) and lithium-ion batteries. The differences between two categories of drive cycles, modal and transient, were compared; and further discussion was provided on why electrochemical vehicles need to be designed and engineered with transient drive cycles instead of modal. Road-going passenger vehicles are the main focus of this piece. Similarities and differences between aviation and marine drive cycles are briefly mentioned and compared and contrasted with road cycles. The construction of drive cycles and how they can be transformed into a ‘power cycle’ for electrochemical device sizing purposes for electrochemical vehicles are outlined; in addition, how one can use power cycles to size electrochemical vehicles of various vehicle architectures are suggested, with detailed explanations and comparisons of these architectures. A concern with using conventional drive cycles for electrochemical vehicles is that these types of vehicles behave differently compared to combustion-powered vehicles, due to the use of electrical motors rather than internal combustion engines, causing different vehicle behaviours and dynamics. The challenges, concerns, and validity of utilising ‘general use’ drive cycles for electrochemical purposes are discussed and critiqued