Origin and evolution of recent Leonid meteor showers

The four most prominent returns of the Leonid shower in the past decade fall into two broad classes. The 1966 and 1969 showers were of short duration, had a high proportion of small particles, and occured with the longest apparent delay after the perihelion passage of the parent comet Temple-Tuttle. By contrast, the 1961 and 1965 returns were of long duration, and had more large particles. The 1961 return preceded the comet. There are three major influences on particle orbits: ejection velocity, radiation pressure, and close encounters with planets. The observations are explainable in a qualitative way on the basis of the first two. But some speculation concerning the results of planetary perturbations are invoked

Duality Theory And the Consistent Estimation Of Technological Parameters: Why Cost Function Estimation Can Be Wrong

In this article we show that technological parameter estimates obtained by estimating a cost function that is derivable as the dual of a production function can be biased and inconsistent if the stochastic structure of the model arises from certain types of behavioural assumptions made about rational agents. We consider a specific example in which firms are uncertain about prices. We show that when actual prices differ from expected prices and firms have to make decisions on the basis of their expectations, the inherited stochastic specification of the dual system is highly non-linear in the disturbance terms making consistent parameter estimation impossible by conventional methods. This is demonstrated by a Monte Carlo simulation study of two text-book examples using synthetic data. It is also shown that this type of result can arise when the researcher derives the error structure from the assumption that agents make optimization errors.cost functions; duality; estimation

On the nature of spectral line broadening in solar coronal dimmings

We analyze the profiles of iron emission lines observed in solar coronal dimmings associated with coronal mass ejections, using the EUV Imaging Spectrometer on board Hinode. We quantify line profile distortions with empirical coefficients (asymmetry and peakedness) that compare the fitted Gaussian to the data. We find that the apparent line broadenings reported in previous studies are likely to be caused by inhomogeneities of flow velocities along the line of sight, or at scales smaller than the resolution scale, or by velocity fluctuations during the exposure time. The increase in the amplitude of Alfv\'en waves cannot, alone, explain the observed features. A double-Gaussian fit of the line profiles shows that, both for dimmings and active region loops, one component is nearly at rest while the second component presents a larger Doppler shift than that derived from a single-Gaussian fit.Comment: 16 pages, 11 figures - Accepted for publication in Ap

MULTIPRODUCT PRODUCTION CHOICES AND PESTICIDE REGULATION IN GEORGIA

An increasing emphasis on surface and groundwater quality and food safety may result in some form of pesticide regulations. A restricted profit function model of Georgia agriculture is used to examine the short-run effects of 2 and 5 percent reductions in all pesticides. Point estimates of short-run impacts, along with their 90 percent confidence intervals are presented.Agricultural and Food Policy,

FORECASTING AGRICULTURAL PRICES USING A BAYESIAN COMPOSITE APPROACH

Forecast users and market analysts need quality forecast information to improve their decision-making abilities. When more than one forecast is available, the analyst can improve forecast accuracy by using a composite forecast. One of several approaches to forming composite forecasts is a Bayesian approach using matrix beta priors. This paper explains the matrix beta approach and applies it to three individual forecasts of U.S. hog prices. The Bayesian composite forecast is evaluated relative to composites made from simple averages, restricted least squares, and an adaptive weighting technique.Demand and Price Analysis,

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

This article investigates the ignition of low-exothermicity reactive porous solids exposed to a maintained source of heat (hotspot), without oxygen limitation. The gas flow within the solid, particularly in response to pressure gradients (Darcy’s law), is accounted for. Numerical experiments related to the ignition of low-exothermicity porous materials are presented. Gas and solid products of reaction are included. The first stage of the paper examines the (pseudo-homogeneous) assumption of a single temperature for both phases, amounting to an infinite rate of heat exchange between the two. Isolating the effect of gas production and flow in this manner, the effect of each on the ignition time is studied. In such cases, ignition is conveniently defined by the birth of a self-sustained combustion wave. It is found that gas production decreases the ignition time, compared to equivalent systems in which the gas-dynamic problem is effectively neglected. The reason for this is quite simple; the smaller heat capacity of the gas allows the overall temperature to attain a higher value in a similar time, and so speeds up the ignition process. Next, numerical results using a two-temperature (heterogeneous) model, allowing for local heat exchange between the phases, are presented. The pseudo-homogeneous results are recovered in the limit of infinite heat exchange. For a finite value of heat exchange, the ignition time is lower when compared to the single-temperature limit, decreasing as the rate of heat exchange decreases. However, the decrease is only mild, of the order of a few percent, indicating that the pseudo-homogeneous model is in fact a rather good approximation, at least for a constant heat-exchange rate. The relationships between the ignition time and a number of physico-chemical parameters of the system are also investigated