Exact solutions to chaotic and stochastic systems

We investigate functions that are exact solutions to chaotic dynamical systems. A generalization of these functions can produce truly random numbers. For the first time, we present solutions to random maps. This allows us to check, analytically, some recent results about the complexity of random dynamical systems. We confirm the result that a negative Lyapunov exponent does not imply predictability in random systems. We test the effectiveness of forecasting methods in distinguishing between chaotic and random time-series. Using the explicit random functions, we can give explicit analytical formulas for the output signal in some systems with stochastic resonance. We study the influence of chaos on the stochastic resonance. We show, theoretically, the existence of a new type of solitonic stochastic resonance, where the shape of the kink is crucial. Using our models we can predict specific patterns in the output signal of stochastic resonance systems.Comment: 31 pages, 18 figures (.eps). To appear in Chaos, March 200

Susceptibilidad de Anopheles albimanus a los insecticidas en cuatro localidades de Tumbes

El control de los vectores de importancia médica ha sido parte vital en la estrategia global para el control de los mosquitos involucrados en la transmisión de enfermedades, y la aplicación de insecticidas representa la medida de intervención práctica más importante y utilizada para reducir las enfermedades transmitidas por estos insectos vectores (Casabé et al.,1988). Sin embargo, en la actualidad, el incremento considerable de las enfermedades transmitidas por mosquitos ha originado un grave problema de salud pública, debido en parte al desarrollo de resistencia a los insecticidas en las poblaciones de mosquitos (Hemingway et al., 2004; Liu et al., 2004) y de resistencia de los parásitos a los medicamentos antipalúdicos (Phillips, 2001; Hemingway et al., 2002). La Organización Mundial de la Salud (OMS) define la resistencia como una característica heredada que otorga una mayor tolerancia a un plaguicida o grupo de plaguicida, de tal modo que los individuos resistentes sobreviven a una concentración del compuesto (o compuestos) que normalmente sería mortal para la especie (OMS,1992)

Poverty and Microfinance in Bolivia

A major accomplishment of development finance in recent years has been the expansion of the supply of financial services for the poor. Little information exists, however, about the extent to which microfinance actually reaches the poor. This study analyzed a sample of clients served by five microfinance organizations in Bolivia. The data revealed that these organizations reach many rural and urban poor, but not the poorest of the poor. Group-based lenders reach a somewhat poorer clientele than those organizations making individual loans. The individual lenders, however, seem to be able to better adjust loan sizes to fit the creditworthiness of the client. Therefore, individual lenders appear to face fewer constraints in increasing loan sizes in response to client demand. The ability of these organizations to adjust to loan demand may be important in influencing their ability to retain clients as competition among organizations increases

Victimization, Urbanicity, and the Relevance of Context: School Routines, Race and Ethnicity, and Adolescent Violence

The United States is undergoing a historical racial and ethnic demographic shift. There is limited criminological research exploring if and how these changes influence variation in the relationship between routine activity theory and adolescent violence. Although the link between routine activities and victimization has been tested and well established, criminologists have questioned if routine activities can explain adolescent violence across different social contexts. Prior research demonstrates that there are potential nuances in the theoretical connections between routine activities and victimization, particularly when considering race and ethnicity. This study builds on previous research by questioning if the elements of routine activities predict victimization across predominately urban, rural, and suburban schools. The implications of the relevance of school context in the relationships between routine activities and adolescent victimization will also be discussed more generally

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. The interpretation seeks to establish connections between key characteristics of the clients and features of the lending technologies that lead to the matching of classes of borrowers with particular organizations and that influence the choice of market niches. Data on loan sizes suggest the existence of different but broadly overlapping market niches associated with three tiers of clients. The sharpest distinction is between urban and rural clients. The matching between clients and organizations also reflects a weak but positive correlation between levels of poverty and loan sizes. According to an index of basic needs fulfillment of their clients, these organizations can be ranked as: FIE and Caja Los Andes (first tier), BancoSol (second tier), and PRODEM and Sartawi (third tier). The same ranking is obtained when clients are ordered according to loan size, the ratio of loan size to the value of sales, and the value of monthly sales. The three tiers of clients are associated with different socio-economic features of their household-enterprises: sex, education, household size, access to electricity, water supplies, and sewage facilities, employment-generating capacity of the enterprise, informality and separation of household and enterprise, occupations and the like. The development of lending technologies that do not rely on standard financial statements and collateralizable assets is a formidable innovation that explains the outreach and sustainability of these organizations. Differences in the guarantees required for loans dominate distinctions in lending technology. Trade-offs between loan size, interest rates, and guarantee requirements attract different subsets of the clientele. Joint liability seems to be appropriate for very poor people, but group borrowers eventually outgrow this relationship. Caja Los Andes and FIE have shown that it is possible to supply individual loans to poor people and be profitable. Most clients are satisfied with the services received. The lowest satisfaction concerns loan sizes and loan-size rationing may be widespread. At least in urban areas, increasing competition will force these organizations to improve their services and adjust loan sizes. All of these organizations are expanding the frontier of microfinance by developing lending technologies for a much poorer clientele than is reached by collateral-based lenders. This is a formidable achievement