Convex cocompactness and stability in mapping class groups

We introduce a strong notion of quasiconvexity in finitely generated groups, which we call stability. Stability agrees with quasiconvexity in hyperbolic groups and is preserved under quasi-isometry for finitely generated groups. We show that the stable subgroups of mapping class groups are precisely the convex cocompact subgroups. This generalizes a well-known result of Behrstock and is related to questions asked by Farb-Mosher and Farb.Comment: 15 pages, 1 figur

What Can We Learn About the Sensitivity of Investment to Stock Prices with a Better Measure of Tobin's q?

This paper examines the responsiveness of investment to q (i.e., the ratio of a firm's market value to the replacement cost of its assets) using data on a unique type of firm: Real Estate Investment Trusts (REITs). For REITs, we have high quality estimates of the net asset value of the firm that we use to create relatively accurate measures of Tobin's q. In addition, REITs have institutional features that mitigate some of the complications faced by previous studies. We have three main results. First, there is little evidence of a statistical link between REIT investment and a traditional accounting-based measure of q. Second, REIT investment is highly sensitive to estimates of q that are based on analysts' appraisals of asset value. A REIT whose NAV-based q ratio rises from 1.0 to 1.1 will increase its assets by 4.3 percent in the next year. Third, the difference between the appraisal-based measure of q and the traditional accounting based measure typically increases with the age of the firm's assets and varies across types of properties. These results suggest that measurement error in q can lead to appreciable downward biases in investment sensitivities, even in an industry that seems to meet many of the assumptions in Tobin's original paper, but that Tobin's investment model performs well with a better measure of q.Investment; Tobin's q; Real Estate Investment Trusts

What Can We Learn About the Sensitivity of Investment to Stock Prices with a Better Measure of Tobin's q?

This paper examines the responsiveness of investment to q (i.e., the ratio of a firm's market value to the replacement cost of its assets) using data on a unique type of firm: Real Estate Investment Trusts (REITs). For REITs, we have high quality estimates of the net asset value of the firm that we use to create relatively accurate measures of Tobin's q. In addition, REITs have institutional features that mitigate some of the complications faced by previous studies. We have three main results. First, there is little evidence of a statistical link between REIT investment and a traditional accounting-based measure of q. Second, REIT investment is highly sensitive to estimates of q that are based on analysts' appraisals of asset value. A REIT whose NAV-based q ratio rises from 1.0 to 1.1 will increase its assets by 4.3 percent in the next year. Third, the difference between the appraisal-based measure of q and the traditional accounting based measure typically increases with the age of the firm's assets and varies across types of properties. These results suggest that measurement error in q can lead to appreciable downward biases in investment sensitivities, even in an industry that seems to meet many of the assumptions in Tobin's original paper, but that Tobin's investment model performs well with a better measure of q.Investment; Tobin's q; Real Estate Investment Trusts

Evaluation of the Langley 4- by 7-meter tunnel for propeller noise measurements

An experimental and theoretical evaluation of the Langley 4- by 7- Meter Tunnel was conducted to determine its suitability for obtaining propeller noise data. The tunnel circuit and open test section are described. An experimental evaluation is performed using microphones placed in and on the tunnel floor. The reflection characteristics and background noise are determined. The predicted source (propeller) near-field/far-field boundary is given using a first-principles method. The effect of the tunnel-floor boundry layer on the noise from the propeller is also predicted. A propeller test stand used for part of his evaluation is also described. The measured propeller performance characteristics are compared with those obtained at a larger scale, and the effect of the test-section configuration on the propeller performance is examined. Finally, propeller noise measurements were obtained on an eight-bladed SR-2 propeller operating at angles of attack -8 deg, 0 deg, and 4.6 deg to give an indication of attainable signal-to-noise ratios

The role of the equivalent blackbody temperature in the study of Atlantic Ocean tropical cyclones

Satellite measured equivalent blackbody temperatures of Atlantic Ocean tropical cyclones are used to investigate their role in describing the convection and cloud patterns of the storms and in predicting wind intensity. The high temporal resolution of the equivalent blackbody temperature measurements afforded with the geosynchronous satellite provided sequential quantitative measurements of the tropical cyclone which reveal a diurnal pattern of convection at the inner core during the early developmental stage; a diurnal pattern of cloudiness in the storm's outer circulation throughout the life cycle; a semidiurnal pattern of cloudiness in the environmental atmosphere surrounding the storms during the weak storm stage; an outward modulating atmospheric wave originating at the inner core; and long term convective bursts at the inner core prior to wind intensification

The Dynamics of Store Hour Changes and Consumption Behavior: Results of a Longitudinal Study of Consumer Attitudes toward Saturday Shopping in Germany

Americans who travel internationally are often shocked to discover retail outlets closed during weekend and evening hours in cities such as Paris, Rome and Berlin. Fortunately, based on the implicit assumption that demand clearly exists, retailers at various locations throughout the globe have increased their hours of operation. While political debate regarding a variety of issues (costs, the rights of labor, religion, etc.) often rages, there has been an implicit assumption that latent demand for longer hours of operation exists. Our study investigates through a longitudinal examination consumer perceptions of Saturday shopping in a country where such an activity was previously restricted. Specifically, we study perceptions of Saturday shopping among a sample of German college students who were raised with limited Saturday shopping hours. Data were gathered in 1996 – the year German legislation allowed expanded hours for retailers – and again in 1999, and comparisons are made. Strong differences are found between consumer attitudes towards Saturday shopping at the time of expansion and three years later, indicating the need for differentiating retail strategies in Germany and in other parts of the world that may soon be providing similar expanded retail access.Agribusiness,

Maps of routes to destinations and their utility for direction giving

How does one indicate objects in a drawn map while they are traveling to a specific destination? How are these notations, which are frequently anecdotal in nature, understood by those who are not familiar with the environment? This two-phase study examines qualities of hand-drawn maps drawn by subjects while en-route towards a specific destination. Next, another participant (who is unfamiliar with the geographic area drawn on the map) tests the accuracy of the map and its notations as the participant navigates the route drawn on the map. Using categorical coding and content analysis of the items noted on the map, statistical analysis is used to find correlations of activities and landmarks along one\u27s path in a Midwestern university campus and community

Do Stock Prices Really Reflect Fundamental Values? The Case of REITs

Real estate investment trust (REIT) stock prices deviate substantially from net asset values (NAV). Using REIT data since 1990, we find large positive excess returns to a strategy of buying stocks that trade at a discount to NAV, and shorting stocks trading at a premium to NAV. Estimated alphas from this strategy are between 0.9% and 1.8% per month, with little risk. Trading costs and short-sale constraints are not prohibitive and the results strengthen when we control for differences in liquidity or the extent of institutional ownership. We find that some variation in P/NAV makes sense, as premiums are positively related to recent and future NAV growth. However, there appears to be too much volatility in P/NAV, giving rise to potential profits from short-term mean reversion. The closed-end fund literature has some similar findings on stock price deviations from fundamental value, but compared to closed-end funds REITs are much larger and have much higher insider and institutional ownership. These differences suggest that REIT premiums and discounts reflect more than just small investor sentiment, which is a common explanation of why closed-end fund prices deviate from their fundamental value.