720 research outputs found
How topography induces reproductive asynchrony and alters gypsy moth invasion dynamics
No full text1. Reproductive asynchrony, a temporal mismatch in reproductive maturation between an individual and potential mates, may contribute to mate-finding failure and Allee effects that influence the establishment and spread of invasive species. Variation in elevation is likely to promote variability in maturation times for species with temperature-dependent development, but it is not known how strongly this influences reproductive asynchrony or the population growth of invasive species.
2. We examined whether spatial variation in reproductive asynchrony, due to differences in elevation and local heterogeneity in elevation (hilliness), can explain spatial heterogeneity in the population growth rate of the gypsy moth, Lymantria dispar (L.), along its invasion front in Virginia and West Virginia, USA.
3. We used a spatially explicit model of the effects of reproductive asynchrony on mating success to develop predictions of the influences of elevation and elevational heterogeneity on local population growth rates. Population growth rates declined with increased elevation and more modestly with increased elevational heterogeneity. As in earlier work, we found a positive relationship between the population growth rate and the number of introduced egg masses, indicating a demographic Allee effect. At high elevations and high heterogeneity in elevation, the population growth rate was lowest and the density at which the population tended to replace itself (i.e., the Allee threshold) was highest.
4. An analysis of 22 years of field data also showed decreases in population growth rates with elevation and heterogeneity in elevation that were largely consistent with the model predictions.
5. These results highlight how topographic characteristics can affect reproductive asynchrony and influence mate-finding Allee effects in an invading non-native insect population. Given the dependence of developmental rates on temperature in poikilotherms, topographic effects on reproductive success could potentially be important to the population dynamics of many organisms.Peer reviewe
Individual and Aggregate Money Demands
No full textI construct a model in which money and bond holdings are consistent with individual decisions and aggregate variables such as production and interest rates. The agents are infinitely-lived, have constant-elasticity preferences, and receive a fraction of their income in money. Each agent solves a Baumol-Tobin money management problem. Markets are segmented because financial frictions make agents trade bonds for money at different times. Trading frequency, consumption, government decisions and prices are mutually consistent. An increase in inflation, for example, implies higher trading frequency, more bonds sold to account for seigniorage, and lower real balances. JEL codes:E3, E4, E5money demand, cash management, inventory problem, market segmentation
Rotación de presidentes ejecutivos y directores en Venezuela
No full text(Disponible en idioma inglés únicamente) El propósito de este estudio es propiciar una mejor comprensión de las estructuras y los mecanismos de conducción empresarial fuera de Estados Unidos, observando una economía emergente específica: Venezuela. Primero formulamos un índice de prácticas de conducción empresarial de las compañías inscritas en bolsa, cuyos resultados generales indican que Venezuela exhibe puntajes de gestión empresarial relativamente bajos. Descubrimos, empleando esta muestra limitada, que existe una relación positiva entre este índice de conducción empresarial y sus subcomponentes y mediciones alternativas de valor (coeficiente de Tobin, relación precio/valor contable y pago de dividendos). En este entorno, caracterizado por un mercado financiero subdesarrollado, un sistema jurídico débil, una aplicación precaria de la normativa legal y una elevada concentración de la propiedad, abordamos la cuestión de si el sistema de conducción empresarial funciona en lo absoluto en Venezuela. Nos interesa especialmente estudiar las siguientes dos cuestiones, las cuales constituyen condiciones necesarias para el buen funcionamiento de cualquier sistema de conducción empresarial. En primer lugar, ¿es más probable que presidentes ejecutivos de desempeño deslucido pierdan su cargo que sus colegas de mejor desempeño? En segundo lugar, ¿le corresponde a la junta directiva la tarea de vigilar al presidente ejecutivo o simplemente cumplir una labor de asesoría? A tal fin, recabamos información detallada de 51 compañías venezolanas durante el período de 1984 a 2002. Una vez controladas características relacionadas con el presidente ejecutivo, la junta directiva, la propiedad, las empresas y los períodos abarcados, hallamos que el desempeño financiero precario hace aumentar considerablemente la probabilidad de la rotación de presidentes ejecutivos y directores. Los elementos de juicio empíricos también se corresponden con la idea de que, en Venezuela, los directores desempeñan principalmente una función de asesoría y no de vigilancia de la labor del presidente ejecutivo.
03-03 "Reconciling Growth and Environment"
No full textMacroeconomic theory and policy are strongly based on the assumption that economic growth is a fundamental goal. The environmental realities of the twenty- first century compel a reassessment of macro theory in terms of the impact of current growth patterns on planetary ecosystems.This paper examines the macroeconomic impacts of growth in terms of several major areas of conflict between economic demands and ecosystem capacities:
The Profitability of Speculators in Currency Futures Markets
No full textUsing weekly data on the positions of different types of participants in currency futures markets we present evidence that suggests speculators are profitable. Across six currencies, speculators’ gross profits are seemingly positive in 60 per cent of weeks. The profits are significant even after accounting for transactions costs. Our estimated speculator profits are consistent both with speculators being paid a risk premium and with speculators having superior forecasting ability.exchange rates; futures markets; speculators
Precautionary Saving Over the Lifecycle
No full textThis paper studies the quantitative importance of precautionary wealth accumulation relative to life—cycle saving for retirement. Section 1 examines panel data on earnings from the PSID. Using a bivariate normal model of random effects, we find that second— period—of—life earnings are strongly positively correlated with initial earnings but have a higher variance. Section 2 studies the consequences for life—cycle saving. Households know their youthful earning power as they enter the labor market, but only in midlife do they learn their actual second—period earning ability. For plausible calibrations, precautionary saving only adds 5—6% to aggregative life—cycle wealth accumulation. Nevertheless, we find that, given borrowing constraints on households’ behavior, the variety of earning profiles that our bivariate normal model generates itself stimulates more than twice as much extra wealth accumulation as precautionary saving.
Characterization of Water Vapor and Carbon Dioxide Spectral Line Parameters in the Two micron Region
No full text1. R. M. Sova, M. E. Thomas, D. Tobin, D. Byrum and L. L. Strow, ""Characterization of Candidate DLAL Lidar Water Vapor and Carbon Dioxide Absorption Lines in the Two Micron Region,'' SPIE Proccedings - Optical Instrumentation for Regional and Global Atmospheric Studies 2365, Nov., 1994.Author Institution: Applied Physics Laboratory, Laurel, Maryland 20723.; University of Maryland Baltimore County, Baltimore Marviand 21228.DIAL lidar for water vapor and temperature remote sensing in the eye safe atmospheric window regions has been receiving much interest. Such systems rely on accurate spectral line characterization. Typically the HITRAN data base on atmospheric spectral lines is used. However, the database is incomplete and not sufficiently accurate. A series of transmittance measurements are made on water vapor and carbon dioxide to verify and improve the HITRAN data base in spectral . A 3 meter base path White cell attached to a BOMEM DA3.02 is used for the transmittance measurements. The White cell is set to a path length of 216 meters for all experiments. Measurements on pure at various pressures, broadened and broadened are collected at room temperature. Also, measurements on pure at various pressures and broadened are collected at room temperature. Data analysis is performed on lines that are accessible by lasers. The measured spectrum is converted to the absorption coefficient and is fitted to a synthetic spectrum to determine the spectral line parameters. This includes the pressure shift, halfwidth and line strength. Water vapor exhibits a strong pressure shift effect. Oxygen broadening is observed to be significantly less than that due to nitrogen. Some lines show good agreement (within a few percent) with the HITRAN database, other lines disagree by more than . Thus care must be exercised in applying the HITRAN data based to DLAL lidar applications. The pressure shift, self-halfwidth and oxygen-broadened halfwidth are not available on the HITRAN database
Int J Behav Med
No full textBackgroundThe process of translating scientific findings into clinical and public health settings has only recently received priority attention within the scientific community.PurposeFueled by \u201cFunding Opportunity Announcements\u201d from the National Institutes of Health and Centers for Disease Control and Prevention, scientists have begun to explore the pathways to effectively \u201ctransfer\u201d promising research accomplishments into effective and sustainable service programs within the health care delivery system.MethodUsing Glasgow\u2019s RE-AIM (Reach, Effectiveness, A-doption, Implementation and Maintenance) model as a guide, this research team enrolled 428 socially disadvantaged, culturally diverse women living with HIV/AIDS to test the dissemination and implementation of an evidence-based behavioral intervention designed to improve and sustain the physical and emotional health of participants into the Community Health Center (CHC) setting when conducted by trained CHC staff.ResultsFindings demonstrate the ability of trained CHC staff group leaders to attain results equivalent or superior to those achieved when conducted by research staff on the three principal study outcomes: depression, medication adherence and HIV viral load. Four of five CHCs involved in the study also identified and successfully obtained funding to continue to run intervention groups, supporting the adoption and sustainability components of the translation model.ConclusionThis study confirmed (a) the \u201ctranslatability\u201d of the Stress Management And Relaxation Training/Emotional Supportive Therapy (SMART/EST) Women\u2019s Program, from academic to CHC settings in two geographic regions with high HIV prevalence among women, (b) the ability of local staff (using the \u201ctrain the trainer\u201d model) to successfully achieve program fidelity and clinical outcomes, and (c) the sustainability the program beyond the auspices of research support, through supportive CHC leadership securing continued program funding.M01 RR016587/RR/NCRR NIH HHS/United StatesP30 AI073961/AI/NIAID NIH HHS/United StatesR01MH55463/MH/NIMH NIH HHS/United StatesR01MH61208/MH/NIMH NIH HHS/United StatesR18 PS000829/PS/NCHHSTP CDC HHS/United StatesR18PS000829/PS/NCHHSTP CDC HHS/United State
Voucher privatization with investment funds : an institutional analysis
No full textCommon wisdom among post-socialist reformers has beento use voucher investment funds to provide the corporate governance needed to restructure newly privatized enterprises after mass privatization efforts. The idea has been that mass privatization would spread the ownership too wide and make corporate governance difficult. The author examines the likely institutional behavior of voucher funds and the possible effects of their development on a transition economy. Since most policy advice has been in favor of voucher privatization with investment funds, the author can be seen as playing the devil's advocate, but his argument is institutional, not statistical. Policymaking requires insight and foresight into how institutions will tend to function. He concludes that voucher funds will introduce a bias in the economy away from the real industrial sector toward an ersatz"financial sector"that will have little if any positive financial role but will be well-protected by friendly regulators. One long-term consequence of voucher privatization with investment funds, according to this view, is a de facto"industrial policy"of real sector decapitalization in favor of short-term rent-seeking by fund managers through board sinecures and lucrative side deals with portfolio companies and through financial market manipulation and paper entrepreneurship in the"financial sector."Without strong corporate governance from the funds and without stable ownership of their own, many enterprise managers will exploit the post-socialist version of the"separation of ownership and control"to grab what they can in the form of salaries, bonuses, perquisites, and side deals. The most likely results of the strategy of voucher privatization with investment funds may be a two-sided grab fest by fund managers and enterprise managers -- together with the accompanying drift, stagnation, and decapitalization of the privatized industrial sector.Economic Adjustment and Lending,Payment Systems&Infrastructure,International Terrorism&Counterterrorism,Economic Theory&Research,Banks&Banking Reform,International Terrorism&Counterterrorism,Banks&Banking Reform,Economic Adjustment and Lending,Environmental Economics&Policies,Economic Theory&Research
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Two-country stock-flow-consistent macroeconomics using a closed model within a dollar exchange regime
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