APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers

Eleven candidate damped Lya absorption systems were identified in 27 spectra of the quasars from the APM z>4 survey covering the redshift range 2.83.5). High resolution echelle spectra (0.8A FWHM) have been obtained for three quasars, including 2 of the highest redshift objects in the survey. Two damped systems have confirmed HI column densities of N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold. We have discovered the highest redshift damped Lya absorber known at z=4.383 in QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift path available for damped surveys for z>3. We combine this high redshift sample with other quasar samples covering the redshift range 0.008 < z < 4.7 to study the redshift evolution and the column density distribution function for absorbers with log N(HI)>=17.2. In the HI column density distribution f(N)=kN^-beta we find evidence for breaks in the power law, flattening for 17.221.2. The column density distribution function for the data with log N(HI)>=20.3 is better fit with the form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the number density per unit redshift is evident in the higher column density systems with an apparent decline in N(z) for z>3.5.Comment: To appear in MNRAS. Latex file (10 pages of text) plus 14 separate postscript figure files. Requires mn.sty. Postscript version with figures embedded is available at http://www.ociw.edu/~lisa/publications.htm

Evolution of Neutral Gas at High Redshift -- Implications for the Epoch of Galaxy Formation

Though observationally rare, damped Lya absorption systems dominate the mass density of neutral gas in the Universe. Eleven high redshift damped Lya systems covering 2.84 QSO Survey, extending these absorption system surveys to the highest redshifts currently possible. Combining our new data set with previous surveys we find that the cosmological mass density in neutral gas, omega_g, does not rise as steeply prior to z~2 as indicated by previous studies. There is evidence in the observed omega_g for a flattening at z~2 and a possible turnover at z~3. When combined with the decline at z>3.5 in number density per unit redshift of damped systems with column densities log N(HI)>21 atoms cm^-2, these results point to an epoch at z>3 prior to which the highest column density damped systems are still forming. We find that over the redshift range 2<z<4 the total mass in neutral gas is marginally comparable with the total visible mass in stars in present day galaxies. However, if one considers the total mass visible in stellar disks alone, ie excluding galactic bulges, the two values are comparable. We are observing a mass of neutral gas comparable to the mass of visible disk stars. Lanzetta, Wolfe & Turnshek (1995) found that omega_g(z~3.5) was twice omega_g(z~2), implying a much larger amount of star formation must have taken place between z=3.5 and z=2 than is indicated by metallicity studies. This created a `cosmic G-dwarf problem'. The more gradual evolution of omega_g we find alleviates this. These results have profound implications for theories of galaxy formation.Comment: To appear in MNRAS. Latex file (4 pages of text) plus 3 separate postscript figure files. Requires mn.sty. Postscript version with figures embedded is available at http://www.ociw.edu/~lisa/publications.htm

Style and Performance of Agricultural Market Advisory Services

This paper describes the degree of marketing activeness of market advisory programs for corn and soybeans, and analyzes the relationship between activeness degree and pricing performance. The data set employed consists of advisory programs tracked by the AgMAS Project at the University of Illinois between 1995 and 2001. Cluster analysis was conducted to group the programs according to their degree of activeness. Panel data regression models were estimated to evaluate the relationship between activeness degree and pricing performance. In the corn market, point estimates indicate a positive effect of the degree of activeness on pricing performance, but this effect is of small magnitude and statistically insignificant. For soybeans,there is a stronger positive relationship between activeness degree and performance, with an estimated effect of activeness on performance larger in magnitude and statistically significant. This positive relationship suggests that active marketing programs are based on superior information and/or analytical skills.Agribusiness, Marketing,

Improved Searches for HI in Three Dwarf Spheroidal Galaxies

Previous searches for HI in our Galaxy's dwarf spheroidal companions have not been complete enough to settle the question of whether or not these galaxies have HI, especially in their outer parts. We present VLA observations of three dwarf spheroidals: Fornax, Leo II, and Draco, all of which have known stellar velocities. The new data show no HI emission or absorption. Column density limits in emission are 4--7 x 10^18 atoms/cm^2 in the centers of the galaxies. The importance of the new observations is that they cover larger areas than previous searches and they are less plagued by confusion with foreground (Galactic) HI. The apparent absence of neutral gas in the Fornax dwarf spheroidal is especially puzzling because recent photometry shows evidence of stars only 10^8 years old. We discuss whether the VLA observations could have missed significant amounts of HI.Comment: 20 pages, 7 figures; to appear in the Astronomical Journa

AN EVALUATION OF CROP FORECAST ACCURACY FOR CORN AND SOYBEANS: USDA AND PRIVATE INFORMATION SERVICES

Using 1971-2000 data, we examine the accuracy of corn and soybean production forecasts provided by the USDA and two private services. All agencies improved their forecasts as the harvest progressed, and forecast errors across the agencies were highly correlated. Relative accuracy varied by crop and month. In corn, USDA 's forecasts ranked as most accurate in all periods except in August during recent times, and improved more markedly as harvest progressed. In soybeans, forecast errors were very similar with the private agencies ranking as most accurate in August and September and making largest relative improvements in August during recent times. The USDA provided the most accurate October and November forecasts.Crop Production/Industries,

The Lense-Thirring effect in the Jovian system of the Galilean satellites and its measurability

In this paper we investigate the possibility of measuring the post-Newtonian general relativistic gravitomagnetic Lense-Thirring effect in the Jovian system of its Galilean satellites Io, Europa, Ganymede and Callisto in view of recent developments in processing and modelling their optical observations spanning a large time interval (125 years). The present day best observations have an accuracy between several kilometers to few tens of kilometers, which is just the order of magnitude of the Lense-Thirring shifts of the orbits of the Galilean satellites over almost a century. From a comparison between analytical development and numerical integration it turns out that, unfortunately, most of the secular component of the gravitomagnetic signature is removed in the process of fitting the initial conditions. Indeed, an estimation of the magnitude of the Lense-Thirring effect in the ephemerides residuals is given; the resulting residuals have a maximum magnitude of 20 meters only (over 125 years).Comment: Latex, 10 pages, 4 tables, 3 figures, 27 references. Invited paper for a Special Issue of Int. J. Mod. Phys. D on the Lense-Thirring effect, D. Grumiller edito

The NIR structure of the barred galaxy NGC253 from VISTA

[abridged] We used J and Ks band images acquired with the VISTA telescope as part of the science verification to quantify the structures in the stellar disk of the barred Sc galaxy NGC253. Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius. From the Ks image we obtain a new measure of the deprojected length of the bar of 2.5 kpc. The bar's strength, as derived from the curvature of the dust lanes in the J-Ks image, is typical of weak bars. From the deprojected length of the bar, we establish the corotation radius (R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), which provides the connection between the high-frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the inner Lindblad resonance. The second ring does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC253 has a down-bending profile with a break at R~9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation of the steep gradient in the surface brightness profile at large radii. The NIR photometry unveils the dynamical response of the NGC253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk's outer edge.Comment: Accepted for publication in Astronomy & Astrphysics. High resolution pdf file is available at the following link: https://www.dropbox.com/s/4o4cofs1lyjrtpv/NGC253.pd

The Marketing Performance of Illinois and Kansas Wheat Farmers

The purpose of this paper is to analyze the marketing performance of wheat farmers in Illinois and Kansas over 1982–2004. The results show that farmer benchmark prices for wheat in Illinois and Kansas fall in the middle third of the price range about half to three-quarters of the time. Consistent with previous studies, this refutes the contention that Illinois and Kansas wheat farmers routinely market the bulk of their wheat crop in the bottom portion of the price range. Tests of the average difference between farmer and market benchmark prices are sensitive to the market benchmark considered. The marketing performance of wheat farmers in Illinois and Kansas is about equal to the market if a 24- or 20-month market benchmark is used, slightly above the market if a 12-month price benchmark is used, and significantly less than the market if the harvest benchmark is used. The sensitivity of marketing performance to the market benchmark considered is explained by the seasonal pattern of prices. While Illinois producers performed slightly better than their counterparts in Kansas, notable differences in performance across these two geographic areas is not observed.benchmarks, Illinois, Kansas, marketing, performance, price, wheat, Agribusiness, Crop Production/Industries, Marketing, Production Economics, Productivity Analysis, Q11, Q13,

The Pricing Performance of Market Advisory Services in Corn and Soybeans Over 1995-2004

The purpose of this research report is to evaluate the pricing performance of market advisory services for the 1995-2004 corn and soybean crops. Marketing assumptions applied to advisory program track records are intended to accurately depict “real-world” marketing conditions facing a representative central Illinois corn and soybean farmer. Several key assumptions are: i) with a few exceptions, the marketing window for a crop year runs from September before harvest through August after harvest, ii) on-farm or commercial physical storage costs, as well as interest opportunity costs, are charged to post-harvest sales, iii) brokerage costs are subtracted for all futures and options transactions and iv) Commodity Credit Corporation (CCC) marketing loan recommendations made by advisory programs are followed wherever feasible. Based on these and other assumptions, the net price received by a subscriber to market advisory programs is calculated for the 1995-2004 corn and soybean crops. Market and farmer benchmarks are developed for the performance evaluations. Two market benchmarks are specified in order to test the sensitivity of performance results to changing benchmark assumptions. The 24-month market benchmark averages market prices for the entire 24-month marketing window. The 20-month market benchmark is computed in a similar fashion, except the first four months of the marketing window are omitted. Given the uncertainties involved in measuring the average price received by farmers, two alternative farmer benchmarks for central Illinois are specified. The market and farmer benchmarks are computed using the same assumptions applied to advisory program track records. Five basic indicators of performance are applied to advisory program prices and revenues over 1995-2004. Results show that advisory program prices fall in the top-third of the price range relatively infrequently. There is limited evidence that advisory programs as a group outperform market benchmarks, particularly after considering risk. The evidence is somewhat more positive with respect to farmer benchmarks, even after taking risk into account. For example, the average advisory return relative to the farmer benchmarks is 8 to $12 per acre with only a marginal increase in risk. Even though this return is small and mainly from corn, it nonetheless represents a non-trivial increase in net farm income per acre for grain farms in central Illinois. Test results also suggest that it is difficult to predict the year-to-year pricing performance of advisory programs based on past pricing performance. However, there is some evidence that performance is more predictable over longer time horizons, particularly at the extremes of performance rankings. The results raise the interesting possibility that even though advisory services do not appear to “beat the market,” they nonetheless provide the opportunity for some farmers to improve performance relative to the market. Mirroring debates about stock investing, the relevant issue is whether farmers can most effectively improve marketing performance by pursuing “active” strategies, like those recommended by advisory services, or “passive” strategies, which involve routinely spreading sales across the marketing window.Agricultural Finance, Financial Economics,