Prediction of remaining life of power transformers based on left truncated and right censored lifetime data

Prediction of the remaining life of high-voltage power transformers is an important issue for energy companies because of the need for planning maintenance and capital expenditures. Lifetime data for such transformers are complicated because transformer lifetimes can extend over many decades and transformer designs and manufacturing practices have evolved. We were asked to develop statistically-based predictions for the lifetimes of an energy company's fleet of high-voltage transmission and distribution transformers. The company's data records begin in 1980, providing information on installation and failure dates of transformers. Although the dataset contains many units that were installed before 1980, there is no information about units that were installed and failed before 1980. Thus, the data are left truncated and right censored. We use a parametric lifetime model to describe the lifetime distribution of individual transformers. We develop a statistical procedure, based on age-adjusted life distributions, for computing a prediction interval for remaining life for individual transformers now in service. We then extend these ideas to provide predictions and prediction intervals for the cumulative number of failures, over a range of time, for the overall fleet of transformers.Comment: Published in at http://dx.doi.org/10.1214/00-AOAS231 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Pine Tip Moth (Lepidoptera: Tortricidae) Infestation Rates as Influenced by Site and Stand Characteristics in Loblolly Pine Plantations in East Texas

Three young loblolly pine plantations grown on contrasting soil types produced quantitatively and qualitatively different host material for pine tip moths during 1985 and 1986. Amounts, periodicity, and availability of soil moisture regulated internal moisture conditions within host trees. Host xylem moisture potential in conjunction with soil nutrient status governed tree growth and influenced pine tip moth infestation rates. Pines on a sandy site exhibited the poorest growth with lowest infestation rates, indicative of low-quality hosts with little if any tolerance to damage. A clayey site produced vigorous plant growth with moderate infestation rates. The less apparent hosts appeared capable of withstanding pine tip moth attack and overcoming damage. Pines on a loamy site grew at moderate rates and received the highest infestation rates. This moderate growth indicated susceptible stand conditions

Reviews

Reviews of Discovering the Future; The Business of Paradigms, by Joel Baker; Translate to Communicate: A Guide for Translators, by Mary M.F. Massoud; A Farmer\u27s Primer on Growing Soybeans on Riceland, by R. K. Pandey

Disturbance Effects on Aquatic Vegetation in Regulated and Unregulated Lakes in Northern Minnesota

The effects of water-level regulation on aquatic macrophyte communities were investigated by comparing two regulated lakes in northern Minnesota with a nearby unregQlated lake. Natural annual fluctuations of about 1.8 m were replaced with fluctuations of 1.1 m and 2. 7 m in the regulated lakes, and the timing of water-level changes was also altered. Quadrats were sampled along transects that followed depth contours representing different plant habitats in the unregulated lake. Ordinations showed that the macrophyte communities at all sampled depths of the regulated lakes differed from those in the unregulated lake. The unregulated lake supported structurally diverse plant communities at all depths. In the lake with reduced fluctuations, only four taxa were present along transects that were never dewatered; all were erect aquatics that extended through the entire water column. In the lake with increased fluctuations, rosette and mat-forming species dominated transects where drawdown occurred in early winter and disturbance resulted from ice formation in the sediments. The natural hydrologic regime at the unregulated lake resulted in intermediate disturbance and high diversity. There was either too little or too much disturbance from water-level fluctuations in the regulated lakes, both resulting in reduced structural diversity

Implications for Faunal Habitat Related to Altered Macrophyte Structure in Regulated Lakes in Northern Minnesota

Water-level regulation has altered the plant species composition and thus the structure of nearshore aquatic macrophyte communities in two regulated lakes in northern Minnesota as compared with a nearby unregulated lake. Results of previous faunal studies in the regulated lakes were used as a basis for assessing the effects of vegetation changes on faunal communities. The unregulated lake with mean annual water-level fluctuations of 1.6 m supported structurally diverse plant communities and varied faunal habitat at all depths studied. Mean annual fluctuations on one regulated lake were reduced to 1.1 m, and dense beds of four erect aquatic macrophytes dominated the 1. 75-m depth that was never dewatered. We suggest that this lack of plant diversity and structural complexity resulted in diminished habitat for invertebrates, reduced availability of invertebrates as food for waterbirds and fish, reduced winter food supplies for muskrats, and reduced feeding efficiency for adult northern pike, yellow perch, and muskellunge. Mean annual fluctuations in the other regulated lake were increased to 2.7 m, and rosette and mat-forming species dominated the 1.25-m depth that was affected by winter drawdowns. We suggest that the lack of larger canopy plants resulted in poor habitat for invertebrates, reduced availability of invertebrates as food for waterbirds and fish, and poor nursery and adult feeding habitat for many species of fish. In addition, the timing and extent of winter drawdowns reduced access to macrophytes as food for muskrats and as spawning habitat for northern pike and yellow perch. In regulated lakes throughout the world, indirect effects on aquatic fauna resulting from alteration of wetland and aquatic macrophyte communities should be considered when water-level management plans are developed

Management and pest management considerations on droughty soils: four year results

Four year survival of pines on droughty (Typic Quartzips~mments) soils was best for longleaf pine and Terr-Sorb -treated loblolly pine. Pest considerations include town ants and Nantucket pine tip moths on loblolly pine. Untreated loblolly pine had reduced leader and total height growth anH increased tip moth infestations, compared to Terra-Sorb and clay-slurry treated loblolly pine. Soil texture averaged less than eight percent silt and clay combined in the treatment areas

Civic Engagement and Advocacy in Rural Wisconsin: Youth Development Through Legislative Forums

Youth Development programming that engages youth to work side by side with local leaders creates an environment where youth develop civic skills. These skills include a greater understanding of the legislative process, their role in our democracy, and increased engagement in the democratic process. Through their participation in the Superior Days Legislative Forum, youth increase their civic skills, are inspired to create change in their communities, ask questions and respond to challenges by bringing legislative issues of concern unique to their community to the entire representative body at the state capitol. Youth delegates also gain experience partnering with adults from their communities, establish healthy developmental relationships, and expand their social networks. This article draws from research related to civic engagement, youth in decision-making roles, and programming intended to raise youth voice to make community change. This paper uses focus group interviews as well as post-then-preprogram surveys to understand the impact of the Superior Days Legislative Forum on youth participants

Host Quality of Baldcypress and Its Influence on Fruittree Leafroller, Archips Argyrospila (Walker) (Lepidoptera: Tortricidae), Performance in Forested Wetlands of Louisiana.

Ecological relationships between the fruittree leafroller (FTLR), (Archips argyrospila (Walker)) and a new host, baldcypress (Taxodium distichum (L.)), were investigated in southern Louisiana where persistent annual defoliation over increasingly larger areas has occurred since 1983. Defoliation was observed to correspond with common types of baldcypress foliage morphology; designated as open and appressed. Pondcypress, Shumard oak and citrus foliage also were examined. The objectives were to: (1) determine the relative suitability/susceptibility of foliage types, and (2) quantify parameters of foliage quality possibly influencing FTLR performance. Levels of defoliation, egg mass counts, and laboratory bioassays of: initial survival, host preference, growth, feeding, and development, were used as measures of FTLR performance. Parameters of foliage quality included physical attributes, protein precipitating capacity, and concentrations of: nutrients, total nonstructural carbohydrates, and acid detergent fiber. Defoliation was linked conclusively to baldcypress foliage morphology. Open morphology trees consistently received higher levels of defoliation ($\u3e$75%) compared to appressed types ($\u3c$50%). No statistical differences were detected between the number of egg masses on these types, suggesting foliage quality influenced FTLR success. Results of laboratory bioassays indicated that open morphology baldcypress was clearly the most suitable/susceptible host. Shumard oak and sweet citrus were unacceptable hosts. Open morphology foliage was distinctly selected over appressed foliage and yielded the highest initial FTLR survival. In addition, female larvae consumed more foliage and yielded heavier pupae when reared on the open foliage. Host associated differences in pupal weights were attributed to observed differences in consumption and developmental periods because utilization of consumed foliage was not different among hosts. Host quality findings suggested that appressed foliage was a poorer host because of defensive characteristics deterring consumption. Pondcypress was of similarly lower suitability/susceptibility due to asynchronus phenological development and undetermined mechanism(s) causing early pupation of larvae. Favorable plant constituents for insects generally declined and negative constituents increased between early and late instar stages, indicating a decline in cypress foliage quality over time. Open morphology foliage was characteristic of smaller trees and persuant to this, young trees appear to be most likely to receive high levels of FTLR defoliation

Changes in Wetland Vegetation in Regulated Lakes in Northern Minnesota, USA Ten Years after a New Regulation Plan Was Implemented

Lake-level regulation alters wetland plant communities and their role in providing faunal habitat. Regulation plans have sometimes been changed to restore ecosystem function; however, few studies have shown the effects of such changes. In 2000, a new plan was implemented for regulation of Rainy Lake and Namakan Reservoir in northern Minnesota, USA. We had studied wetland plant communities under the previous 1970 regulation plan in 1987 and used those data to evaluate changes during 2002–2006 and 2010 resampling efforts using the same methods. Ordinations showed that plant communities changed little on Rainy Lake, where regulation changes were minor. However, on Namakan Reservoir, substantial changes had occurred in both vegetation and faunal habitat within two years, as plants favored by dewatering were replaced by submersed aquatic plants favored by year-round flooding under the new 2000 regulation plan. After ten years, Namakan showed greater similarity to unregulated Lac La Croix but still differed overall. Longer-term studies may be needed to determine if the regulation-plan change continues to alter Namakan plant communities. The speed at which changes began suggests that studies on other regulated lakes should begin in the first growing season following implementation of a new regulation plan and should continue periodically for a decade or longer