Efficient Semiparametric Prediction Intervals

The construction of prediction intervals and regions and their probability content for nonlinear systems with nonparametric disturbances is considered. The semiparametric efficiency bound for estimating the probability content of a known interval (region) and estimators that attain the bound are developed. Semiparametric efficient estimation of optimal prediction intervals (regions) which either (i) maximize probability content given interval length (region area) or (ii) maximize interval length (region area) given probability content is studied. The estimated probability content of (i) is found to have the same limiting behavior as if the interval (region) were known with certainty and hence attains the semiparametric efficiency bound. Further, the estimated probability of the estimated interval (region) approximates the true coverage probability to order root-n for (i) but order smaller than root-n for (ii). A Monte Carlo experiment is conducted to compare the new predictors to competitors.

Models of foreign exchange intervention: Estimation and testing

We propose a general non-linear simultaneous equations framework for the econometric analysis of models of intervention in foreign exchange markets by central banks in response to deviations of exchange rates from possibly time-varying target levels. We consider efficient estimation of possibly non-linear response functions and tests of functional form, the latter making use of the econometric literature on testing in the presence of nuisance parameters unidentified under a null hypothesis. The methodology is applied in an analysis of recent activity of the Bank of Canada with respect to the Canada-U.S. exchange ratCentral bank intervention, nonlinear simultaneous equations, time series, semiparametric methods

The density of mid-sized Kuiper belt objects from ALMA thermal observations

The densities of mid-sized Kuiper belt objects are a key constraint into understanding the assembly of objects in the outer solar system. These objects are critical for understanding the currently unexplained transition from the smallest Kuiper belt objects with densities lower than that of water to the largest objects with significant rock content. Mapping this transition is made difficult by the uncertainties in the diameters of these objects, which maps into an even larger uncertainty in volume and thus density. The substantial collecting area of the Atacama Large Millimeter Array allows significantly more precise measurements of thermal emission from outer solar system objects and could potentially greatly improve the density measurements. Here we use new thermal observations of four objects with satellites to explore the improvements possible with millimeter data. We find that effects due to effective emissivity at millimeter wavelengths make it difficult to use the millimeter data directly to find diameters and thus volumes for these bodies. In addition, we find that when including the effects of model uncertainty, the true uncertainties on the sizes of outer solar system objects measured with radiometry are likely larger than those previously published. Substantial improvement in object sizes will likely require precise occultation measurements.Comment: AJ, in pres

A Comparison of Seed- and Seedling-Focused Ecologically Based Weed Management Strategies

Many farmers target weeds at the seedling stage, aiming to control weeds with the minimum amount of labor necessary to avoid crop yield loss. Other farmers with a more long-term, seed-focused approach aim to prevent weeds from setting seed so that emergence will be decreased in subsequent crops. These strategies likely vary in short- and long-term effects on farm ecological and economic health. In 2014–2016, I compared these strategies in a test crop of onion. Unexpectedly, due to high yields, the more labor intensive, seed-focused strategy was the most profitable. Case-study interviews of farmers who have adopted each approach indicated seed-focused management improves over time, whereas seedling-focused management becomes more challenging. A key obstacle for both seed- and seedling-focused management was the control of weeds directly in the crop row, where mechanical cultivation tools are only marginally effective due to the need to avoid crop damage. In 2015–2016, I tested the hypothesis that rather than using just one tool, “stacking” on a second or third type of tool would increase efficacy. Indeed, for most tool combinations tested, efficacy increased in an additive manner when more tools were used. One particular combination of three tools exhibited a synergistic increase in efficacy, even over a range of conditions, suggesting that farmers could improve intra-row weed control by adopting this technology. Weed seedling control could be further improved by decreasing the burden on cultivation through a more diverse set of ecologically based weed management practices. Such tactics could be benefited by improved knowledge of the timing of weed seed germination and emergence. In 2014, I recorded the timing of emergence of weed species at Rogers Farm in Old Town, ME and found that many weed species had peak emergence periods that could be targeted by ecologically based management tactics. Overall, my research results provide farmers several ways to enhance effectiveness of ecologically based weed management by encouraging more thoughtful selection of preventative, suppressive, and reactive tactics, increased efficacy of weed seedling control, and improved timing of management activities

Food habits of Steller sea lions (Eumetopias jubatus) off Oregon and northern California, 1986–2007

We described the diet of the eastern stock of Steller sea lions (Eumetopias jubatus) from 1416 scat samples collected from five sites in Oregon and northern California from 1986 through 2007. A total of 47 prey types from 30 families were identified. The most common prey was Pacific hake (Merluccius productus), followed by salmonids (Oncorhynchus spp.), skates (Rajidae), Pacific lamprey (Lampetra tridentata), herrings (Clupeidae), rockfish (Sebastes spp.), and northern anchovy (Engraulis mordax). Steller sea lion diet composition varied seasonally, annually, and spatially. Hake and salmonids were the most commonly identified prey in scats collected during the summer (breeding season), whereas hake and skate were most common in the nonbreeding season. Continued research on Steller sea lion diet and foraging behavior in the southern extent of their range is necessary to address issues such as climate change, interaction with competing California sea lions, and predation impacts on valuable or sensitive fish stocks

ALMA Thermal Observations of Europa

We present four daytime thermal images of Europa taken with the Atacama Large Millimeter Array. Together, these images comprise the first spatially resolved thermal dataset with complete coverage of Europa's surface. The resulting brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a typical linear resolution of roughly 200 km. At this resolution, the images capture spatially localized thermal variations on the scale of geologic and compositional units. We use a global thermal model of Europa to simulate the ALMA observations in order to investigate the thermal structure visible in the data. Comparisons between the data and model images suggest that the large-scale daytime thermal structure on Europa largely results from bolometric albedo variations across the surface. Using bolometric albedos extrapolated from Voyager measurements, a homogenous model reproduces these patterns well, but localized discrepancies exist. These discrepancies can be largely explained by spatial inhomogeneity of the surface thermal properties. Thus, we use the four ALMA images to create maps of the surface thermal inertia and emissivity at our ALMA wavelength. From these maps, we identify a region of either particularly high thermal inertia or low emissivity near 90 degrees West and 23 degrees North, which appears anomalously cold in two of our images.Comment: 9 pages, 3 figures, accepted for publication in the Astronomical Journa