Showing papers by "Andrew L. Johnson published in 2017"

Warehouse design and management

Abstract: Warehouse design and operations have undergone major changes over the past decades. In particular, with the onset of e-commerce, the complexity of warehouse operations has increased multi-fold with the storage of large SKU assortment in small quantities, volatile demand patterns and primarily single-line customer orders. They have grown in size due to consolidation, new and fast identification and communication technologies have found their way into the warehouse and process automation technologies have progressed improving speed and operational efficiencies. In line with these developments, this special issue pays attention to new technologies and methods and how they impact warehouse design and management.

Isotopic temperatures from the early and mid-pliocene of the us middle atlantic coastal plain, and their implications for the cause of regional marine climate change

Abstract: Mean seasonal extreme temperatures on the seafloor calculated from the shell δ18O of the scallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina (∼ 210 km to the south). The lowest and highest temperatures calculated from each shell (using δ18Oseawater = 0.7‰) give mean values for winter and summer of 8.4 ± 1.1 °C (± 1σ) and 18.2 ± 0.6 °C in Virginia, and 8.6 ± 0.4 °C and 16.5 ± 1.1 °C in North Carolina (respective median temperatures: 13.3 °C and 12.6 °C). Patterns of ontogenetic variation in δ18O, δ13C and microgrowth increment size indicate summer water-column stratification in both areas, with summer surface temperatures perhaps 6 °C higher than on the seafloor. The low winter paleotemperatures in both areas are most simply explained by the greater southward penetration of cool northern waters in the absence of a feature equivalent to Cape Hatteras. The same current configuration but a warmer general climate can account for the high benthic seasonal range (over 15.0 °C in some cases) but warmer median temperatures (15.7–21.3 °C) derived from existing δ18O data from scallops of the higher Yorktown Formation (using δ18Oseawater = 0.7‰ for the upper Sunken Meadow Member and δ18Oseawater = 1.1‰ for the mid-Pliocene Rushmere, Morgarts Beach, and Moore House members). Existing δ18O data from the infaunal bivalve Mercenaria of the Rushmere Member yields a similarly high median temperature (21.6 °C) but a low seasonal range (9.2 °C), pointing to the periodic influence of warm currents, possibly at times when the Gulf Stream was exceptionally vigorous.

A production economics analysis for quantifying the efficiency of wind turbines

Abstract: We quantify the productive efficiency of a wind turbine, using power output and environmental variable data, measured either at the turbine or at a meteorological mast near the turbine. The methods described can potentially help with decision makings in asset procurement, maintenance planning, or wind turbine control optimization. The current recommendation from the International Electrotechnical Commission regarding turbine performance evaluation is to use a power curve or power coefficient. What is commonly used in practice is the average performance power curve or power coefficient. When using the power curve to quantify productive efficiency, one crucial shortcoming is the lack of a common best performance benchmark, while the power coefficient approach uses an absolute efficiency measure that is not achievable. We introduce a new approach for efficiency quantification based upon production economics' concepts which provides estimates of a best performance benchmark. Our specific approach has two main components: (a) a best performance power curve is estimated and used together with the average performance curve to show how well a turbine has performed relative to its full potential; and (b) a covariate matching procedure is developed to control for environmental influences for the comparison of turbine performances over different periods. Through a simulation study, we demonstrate that the proposed efficiency is more sensitive to potential changes in the turbine. When analyzing multi-year wind turbine data, we observe that the turbine's efficiency is improving during the first 2 years of operation and then remains relatively constant during years 3 and 4. Copyright © 2017 John Wiley & Sons, Ltd.

Power Curve Estimation: Functional Estimation Imposing the Regular Ultra Passum Law

Abstract: Imposing economic relationships such as the Regular Ultra Passum (RUP) law improves the statistical efficiency of nonparametric estimators in finite samples. RUP law bears relevance in engineering applications such as power curve estimation in the wind energy industry. Unfortunately, the few estimators known to satisfy the RUP law are based on deterministic assumptions that do not allow noise in the modeling. In most engineering applications, however, data are inevitably noisy, due to equipment calibration, natural variations, or other issues. Thus, we propose an estimator that satisfies the RUP law while also capable of handling noisy data. We use Monte Carlo simulations to show that the proposed estimator outperforms existing deterministic estimators, particularly when the scale of noise is large. We use the proposed method to estimate a power curve considering approximately 13,000 observations of a wind turbine. The results demonstrate that the proposed estimator is well suited for engineering applications with a high degree of noise.

A survey of aflatoxin and aflasafe awareness and management among nigerian maize farmers

Abstract: Aflatoxin is a potent mycotoxin that can cause cancer, stunted growth, and (in extreme instances) rapid death. Aflatoxin can contaminate many staple crops, including maize and groundnuts. As many as 4.5 billion people in the developing world may be chronically exposed. Scientists at the United States Department of Agriculture – Agricultural Resource Service, International Institute of Tropical Agriculture (IITA), and African Agricultural Technology Foundation have developed a biological control product called Aflasafe. IITA is currently working with the AgResults initiative to promote widespread adoption of Aflasafe in Nigeria and with the Aflasafe Technology Transfer and Commercialization Program to promote Aflasafe adoption in 11 African countries. In the fall of 2016, 902 oral surveys were administered to smallholder maize farmers in Nigeria. The survey was developed to obtain data regarding farmer awareness of aflatoxin and Aflasafe. At least 88% of farmers who head heard of aflatoxin claimed to recognize the negative health impacts of aflatoxin consumption on human and animal health. Private sector players were critical sources of information about Aflasafe for farmers. First-time users of Aflasafe persisted more frequently in purchasing the product in future growing seasons in some states than others. Stronger relationships between farmers and input suppliers seemed to increase the likelihood a farmer would repurchase. Farmers who purchase Aflasafe bundled with other inputs appeared more likely to repurchase than farmers who purchase Aflasafe stand-alone.