The Intrinsic Ellipticity of Spiral Disks

We have measured the distribution of intrinsic ellipticities for a sample of 28 relatively face-on spiral disks. We combine H-alpha velocity fields and R and I-band images to determine differences between kinematic and photometric inclination and position angles, from which we estimate intrinsic ellipticities of galaxy disks. Our findings suggest disks have a log-normal distribution of ellipticities (mean epsilon =0.06) and span a range from epsilon= 0 (circular) to epsilon=0.2. We are also able to construct a tight Tully-Fisher relation for our face-on sample. We use this to assess the contribution of disk ellipticity on the observed Tully-Fisher scatter.Comment: 4 pages, 2 figures, to appear in "Disks of Galaxies: Kinematics, Dynamics and Perturbations" (ASP Conference Series), eds E.Athanassoula and A. Bosm

Agricultural R&D Lags from a Dual Perspective

This study examines the role of public agricultural research and development (R&D) in the process of knowledge production and productivity growth in U.S. agriculture from a new perspective. The seminal work of Griliches (1967) established the relationship between investments in R&D, the process of knowledge production, and the productivity enhancing benefits they create. In the literature on estimating knowledge production functions measures of multi-factor productivity (MFP) are regressed against measures of knowledge stocks, thereby enabling the researcher to quantify the relationship between the stream of investment expenditures and the productivity enhancing benefits they produce. A critical aspect of this research involves how to handle inter-temporal research spillovers, or in other words how to sum current and previous R&D expenditures into a measure that best represents the current stock of knowledge. This research expands on recently published work by Alston et al (2010) related to estimating the ideal lag structure for summing R&D investments, using data from the International Science and Technology Practice and Policy (InSTePP) Center at the University of Minnesota. We reproduce some of the analysis in the Alston et al (2010) research related to estimating knowledge production functions, but substitute an alternative measure of MFP in the analysis. Specifically, we re-estimate the knowledge production functions using a dual as opposed to a primal measure of productivity. The authors of this study have not seen this approach utilized in the literature, and we believe this novel approach will provide additional valuable insight on the process of knowledge production and productivity growth. Griliches and Jorgenson (1967) formalized the relationship between a dual and a primal measure of MFP. Commonly, a primal measure of MFP is defined as a measure of aggregate output divided by aggregate input. A dual measure can be defined as the ratio aggregate input to output prices. We outline the theoretical reasons why there may differences between the primal and dual measures of MFP. Furthermore, we compare the empirical measures of primal and dual MFP from the InSTePP database and identify differences in these measures over time. Many different lag structures for estimating knowledge stocks have been considered in the literature, including geometric, gamma, and trapezoidal distributions to name a few, and both the shape as well as the length of the distribution are important. The gamma distribution embodies several favorable characteristics: 1) all lag weights determined by the function are non-negative; 2) the shape implied is relatively smooth; 3) the gamma distribution is unimodal; 4) the distribution can be skewed to give more weight to more recent or more distant lags; and 5) the distribution can be characterized by only two parameters. We construct two grids of 64 gamma distributions based on a research lags of 35 and 50 years. The distributions can be represented by altering two parameters. The goal is to examine the best lag structure to represent the relationship between R&D expenditures, knowledge production, and the resulting productivity enhancing benefits. We do this by estimating knowledge production functions under the different lag specifications, and choose the specification that produces the lowest Sum-of-Squared Errors (SSE) in the regressions. The primary objective is to compare and contrast the results of the regression analysis with regards to the preferred lag structure using the dual as opposed to primal measure of MFP. Do the results from a primal and dual approach support a similar lag structure for summing R&D expenditures or do they contradict one another? The methodology of this study is well established, the results have direct significance to an important field of agricultural economics, and the potential to generate discussion and debate is high.Multi-factor Productivity, dual estimates, public R&D, lag distribution, Agricultural and Food Policy, Productivity Analysis,

A COMPARISON OF CAPITAL MEASURES IN U.S. AGRICULTURE

This study compares two panel data sets that measure capital input at the state-level in U.S. agriculture. Despite a number of similarities between the data sets, such as the composition of assets, aggregation procedures, and time frame, an examination of the final estimates of capital service flows reveals that they are drastically different for all 48 contiguous states. We examine the methods used to construct the capital series for each data set, consider some important differences in data sources and the types of data used to construct the capital measures, and outline the main assumptions concerning depreciation, service lives, interest rates, aggregation, and the scope of goods included in each of the data sets. The analysis indicates that an important statistic in the index of capital services in U.S. agriculture is the stock of buildings on farms. We conclude that the primary difference between the measures of capital input in the data sets relates to differences in estimates of the stock of buildings on farms. Given the apparent importance of the measure of the stock of buildings in the aggregate index of capital services in U.S. agriculture, more research is needed to ensure that the measure of the stock of buildings is accurate and meaningful. Once this has been accomplished there should be more agreement on an accurate measure of capital services in U.S. agriculture.Agricultural and Food Policy,

A Relative Position Code for Saccades in Dorsal Premotor Cortex

Spatial computations underlying the coordination of the hand and eye present formidable geometric challenges. One way for the nervous system to simplify these computations is to directly encode the relative position of the hand and the center of gaze. Neurons in the dorsal premotor cortex (PMd), which is critical for the guidance of arm-reaching movements, encode the relative position of the hand, gaze, and goal of reaching movements. This suggests that PMd can coordinate reaching movements with eye movements. Here, we examine saccade-related signals in PMd to determine whether they also point to a role for PMd in coordinating visual–motor behavior. We first compared the activity of a population of PMd neurons with a population of parietal reach region (PRR) neurons. During center-out reaching and saccade tasks, PMd neurons responded more strongly before saccades than PRR neurons, and PMd contained a larger proportion of exclusively saccade-tuned cells than PRR. During a saccade relative position-coding task, PMd neurons encoded saccade targets in a relative position code that depended on the relative position of gaze, the hand, and the goal of a saccadic eye movement. This relative position code for saccades is similar to the way that PMd neurons encode reach targets. We propose that eye movement and eye position signals in PMd do not drive eye movements, but rather provide spatial information that links the control of eye and arm movements to support coordinated visual–motor behavior

Capital Use Intensity and Productivity Biases

This is a substantially revised version of “Capital Use Intensity and Productivity Biases.” Andersen, Matt A.; Alston, Julian M.; Pardey, Philip G., St. Paul, MN: University of Minnesota, Department of Applied Economics; University of Minnesota, International Science and Technology Practice and Policy (InSTePP), 2007. (Staff paper P07-06; InSTePP paper 07-02)U.S. agriculture, pro-cyclical productivity, capital utilization, primal productivity bias, Productivity Analysis, D24, C51, Q1, O4, O47,

Capital Service Flows: Concepts and Comparisons of Alternative Measures in U.S. Agriculture

Measures of capital services are used in studies of production and to inform policies related to growth and development. A variety of methods have been used to measure capital stocks and service flows. In this study we review methods commonly used to measure capital service flows, and outline important assumptions used in constructing such measures. We examine two recently constructed data sets that measure capital inputs in U.S. agriculture. Substantial differences in the measures appear to have been caused by the use of a fixed real interest rate versus a variable real market interest rate to calculate capital services.capital measures, U.S. agriculture, state-level panel data, Agricultural and Food Policy, Agricultural Finance, Productivity Analysis,

Capital Use Intensity and Productivity Biases

Measures of productivity growth are often pro-cyclical. This study focuses on measurement errors in capital inputs, associated with unobserved variations in capital utilization rates, as an explanation for the existence of pro-cyclical patterns in measures of agricultural productivity. Recently constructed national and state-specific indexes of inputs, outputs, and productivity in U.S. agriculture for 1949-2002 are used to estimate production functions in growth rate form that include proxy variables for changes in the utilization of durable inputs. The proxy variables include an index of farmers’ terms of trade and an index of local seasonal growing conditions. We find that utilization responses by farmers are significant and bias measures of productivity growth in a pro-cyclical pattern. We quantify the bias, adjust the measures of productivity for the estimated utilization responses, and compare the adjusted and conventional measures.Productivity Analysis,

Capital Services in U.S. Agriculture: Concepts, Comparisons, and the Treatment of Interest Rates

This is a substantially revised version of “Capital Service Flows: Concepts and Comparisons of Alternative Measures in U.S. Agriculture.” Andersen, Matt A.; Alston, Julian M.; Pardey, Philip G., St. Paul, MN: University of Minnesota, Department of Applied Economics; University of Minnesota, International Science and Technology Practice and Policy (InSTePP), 2009. (Staff paper P09-8; InSTePP paper 09-03)Agricultural Finance,

Asset Utilization and Bias in Measures of U.S. Agricultural Productivity

A common observation is that measures of productivity growth are pro-cyclical, meaning they are higher (or grow faster) on average during periods of economic expansion than during periods of economic contraction. This study focuses on measurement errors related to capital inputs as an explanation for the existence of pro-cyclical patterns in measures of agricultural productivity. Calculating a time series of capital inputs is difficult and prone to errors. Myriad assumptions are required to construct a typical measure of the capital stock, and further, sometimes related, assumptions must be made about the utilization of the stock to derive a measure of capital service flows. We test the hypothesis that unmeasured changes in the utilization of capital can affect productivity measures. This is accomplished using recently constructed indexes of inputs, outputs, and productivity in U.S. agriculture for 1949-2002. We find that utilization responses by farmers are significant and bias measures of productivity growth in a pro-cyclical pattern. The bias is quantified and the measures of productivity are adjusted for the estimated utilization responses and compared to the original measures.Financial Economics,