Linear Response Theory and Optical Conductivity of Floquet Topological Insulators

Motivated by the quest for experimentally accessible dynamical probes of Floquet topological insulators, we formulate the linear response theory of a periodically driven system. We illustrate the applications of this formalism by giving general expressions for optical conductivity of Floquet systems, including its homodyne and heterodyne components and beyond. We obtain the Floquet optical conductivity of specific driven models, including two-dimensional Dirac material such as the surface of a topological insulator, graphene, and the Haldane model irradiated with circularly or linearly polarized laser, as well as semiconductor quantum well driven by an ac potential. We obtain approximate analytical expressions and perform numerically exact calculations of the Floquet optical conductivity in different scenarios of the occupation of the Floquet bands, in particular, the diagonal Floquet distribution and the distribution obtained after a quench. We comment on experimental signatures and detection of Floquet topological phases using optical probes.Comment: 16 pages, 10 figure

Higher-order Floquet topological phases with corner and bulk bound states

We report the theoretical discovery and characterization of higher-order Floquet topological phases dynamically generated in a periodically driven system with mirror symmetries. We demonstrate numerically and analytically that these phases support lower-dimensional Floquet bound states, such as corner Floquet bound states at the intersection of edges of a two-dimensional system, protected by the nonequilibrium higher-order topology induced by the periodic drive. We characterize higher-order Floquet topologies of the bulk Floquet Hamiltonian using mirror-graded Floquet topological invariants. This allows for the characterization of a new class of higher-order "anomalous" Floquet topological phase, where the corners of the open system host Floquet bound states with the same as well as with double the period of the drive. Moreover, we show that bulk vortex structures can be dynamically generated by a drive that is spatially inhomogeneous. We show these bulk vortices can host multiple Floquet bound states. This "stirring drive protocol" leverages a connection between higher-order topologies and previously studied fractionally charged, bulk topological defects. Our work establishes Floquet engineering of higher-order topological phases and bulk defects beyond equilibrium classification and offers a versatile tool for dynamical generation and control of topologically protected Floquet corner and bulk bound states.Comment: v2: 13 pages, 8 figures, 3 appendices; new references, and new analytical and numerical work showing the robustness of Z invariant without diagonal mirror symmetrie

BANCOSOL: THE CHALLENGE OF GROWTH FOR MICROFINANCE ORGANIZATIONS

This paper focuses on the difficulties inherent in the prudent management of growth of microfinance organizations and on potential limits to the increased efficiency, profitability, and sustainability expected from growth and large size. The paper addresses both positive and negative implications of rapid growth for microfinance organizations. The experience of BancoSol in Bolivia is used to illustrate these questions. Building upon the successful experience of PRODEM, BancoSol was chartered as a private commercial bank in 1992. The paper discusses the intangible assets inherited from PRODEM that gave BancoSol a head start and the additional advantages that resulted from formalization as a bank, in particular from the authorization to mobilize deposits. BancoSol shows outstanding success in terms of breadth, depth, and quality of outreach and in terms of sustainability. It is the microfinance organization with the largest number of clients in Latin America and it reaches poor clients who could never expect to gain access to conventional financial institutions. The paper discusses the incentive structure associated with a lending technology that has resulted in low loan arrears and the cost- effective supply of small loans. Success is explained by a strong concern with financial viability, development of a lending technology appropriate for the market niche, a long learning period, and upgrading into a formal intermediary. As it grew, BancoSol had to face a reduction of revenues as a proportion of productive assets and an increase in the average cost of funds, which combined reduced its operating margin by 13 percentage points. This challenge was fully met by reducing operating expenses as a proportion of productive assets. While growth of PRODEM had been mostly constrained by too rigid access to donor funds, growth of BancoSol has been constrained by threats on asset quality and by diminishing marginal economies of size. Portfolio efficiency has grown steadily. This growth has been the net outcome, however, of reductions in transactions efficiency and of increases in average loan size after transformation into BancoSol. The paper explores the sources of increases in average loan size and it concludes that mission drift has not occurred at BancoSol, which continues to focus on small loans to microentrepreneurs. The evolution in transactions efficiency is related, in turn, to sources of extensive (installed capacity) and intensive (productivity) growth. Extensive growth has been rapid at BancoSol and it tends to dampen productivity increases. Finally, the paper reviews the pressures from growth on the original informal culture of the organization and the gradual establishment of more formal structures.Agricultural Finance,

Informal caregiving to dependent old people in the northeast of Portugal

Como resultado de una longevidad mayor, el envejecimiento de la población es una realidad global, especialmente en los países industrializados. Asociado a ese envejecimiento, debido a una mayor prevalencia de las enfermedades crónicas y, de este modo, a un mayor número de discapacitados, está también el aumento del número de dependencias e incapacidades, lo que implica necesariamente la presencia de una persona en el cuidado de personas mayores dependientes. Esa función es asumida habitualmente por la familia, dentro de la cual se desempeña el papel del cuidador informal. Con el fin de obtener un conocimiento acerca de dicho cuidado no remunerado en el distrito de Bragança, se desarrolló un estudio descriptivo y analítico con una muestra de 232 cuidadores/as. El estudio permitió concluir que existe un predominio de personas del género femenino, casadas, hijas de las personas que reciben los cuidados y cuyo nivel de estudios es el de educación primaria. La media de edad es de 57,96 años, con mayor representación por parte de personas con más de 70 años. Se observó, sin embargo, una proporción del 11,6% de cuidadores del género masculino, de los cuales la mayoría pertenece al grupo de edad de 65 años o más

Microfinance Market Niches and Client Profiles in Bolivia

This paper presents and interprets descriptive statistics generated from data obtained in a survey of clients of five microfinance organizations believed to be among the best in Bolivia. These lenders represent different combinations of organizational design, lending technology, and market area of operations. Two are regulated financial intermediaries and three are NGOs. Two operate in rural areas (PRODEM and Sartawi) and three operate in urban areas (BancoSol, FIE, and Caja Los Andes). Two offer individual loans and three grant loans through joint liability groups. The paper discusses household-enterprise profiles of a sample of 622 clients and identifies terms and conditions of loan contracts with these organizations to evaluate the depth and quality of their outreach.Marketing,segmentation,Bolivia,competition,microfinance

Factores de riesgo asociados a hipoglucemia en personas con diabetes mellitus tipo 2, Hospital Dr. Humberto Alvarado Vasquez-Julio a Diciembre de 2014

La Hipoglicemia constituye una emergencia médica, siendo la complicación más frecuente de los pacientes con diabetes que reciben insulina y el principal factor limitante de la optimización del control de la diabetes mellitus. De no ser tratada oportunamente, puede ocasionar daño neurológico permanente e incluso la muerte. Esta problemática es una realidad frecuente en la vida de los diabéticos tipo 1 y de los tipo 2. La incidencia de hipoglucemias sintomáticas en diabéticos es de dos por semana y la de hipoglucemias graves y temporalmente invalidantes, de un episodio por año las cuales son responsables del 2-4% de las muertes en este grupo poblacional. Este promedio se triplica en pacientes mayores de 75 años, con ingresos hospitalarios recientes y que reciben múltiples fármacos. El estudio se llevó a cabo en el Hospital Humberto Alvarado Vásquez, es un estudio Analítico, observacional de casos y controles, de corte transversal; el universo constituido por 755 pacientes Diabéticos tipo 2 que estuvieron ingresados en el periodo en estudio, la muestra total de 120 pacientes diabéticos constituida por 40 Casos y 80 Controles. En el cual se obtuvieron resultados de gran importancia como la asociación en la aparición de los síntomas y la dosificación del fármaco, la adecuada administración del mismo y en cierto porcentaje su asociación con la situación socioeconómica de los pacientes en estudio. Por lo que recomendamos Informar a nuestros pacientes diabéticos tipo 2 sobre cuáles fueron los hallazgos encontrados y de esta manera mejorar su condición y calidad de vida, a través de la práctica correcta de cuidados generales en esta patologí