David A. Dickey

• PhD
• Professor (Full) at North Carolina State University

We examined Hg(II) bioaccumulation and compartmentalization patterns in conjunction with antioxidant responses in four aquatic insect species: two caddisflies (Chimarra sp. and Hydropsyche betteni) and two mayflies (Maccaffertium modestum and Isonychia sp). Total antioxidant capabilities differed among unexposed larvae, with both caddisfly species...

A recent large-scale welfare study in North America involving 106 Asian (Elephas maximus) and 131 African (Loxodonta africana) elephants at 64 accredited facilities identified links (i.e., risk factors) between zoo environmental factors and a number of welfare outcomes (stereotypic behavior, ovarian acyclicity, hyperprolactinemia, walking and recum...

Identifying links between environmental, social, management, and health factors as they relate to physiological stress in captive elephants is crucial for the improvement of welfare and husbandry practices in North American zoos. Studies have examined the effects of short-term and chronic elevations in glucocorticoids in small groups of elephants,...

Background and aimsSoil nitrogen (N) immobilization from cover crop residues may help suppress weeds. We established a gradient of cereal rye shoot biomass to determine the extent that soil N can be immobilized and its effect on redroot pigweed (Amaranthus retroflexus L.). MethodsA microplot study was conducted in no-till cereal rye (Secale cereale...

Cointegration tests are studied for seasonal time series with large periods. The study is performed asymptotically as the period tends to infinity, which is shown to allow a simple limit distribution to be established. These results offer a simple diagnostic tool for cointegration when the seasonal period is expected to be large, and its critical v...

The effect of CO2concentration (330 and 675 μL·L⁻¹) and photosynthetic photon flux (PPF) (mean daily peaks of 550–1400 μmol·m⁻²·s⁻¹) on total mineral contents in shoots was studied in chrysanthemum [Dendranthema ×grandiflorum (Ramat) Kitam ‘Fiesta’] during three times of the year. Growth (as measured by shoot dry weight) and shoot mineral contents...

There is little information addressing the impact of quantity of pre-plant phosphate charge in soilless substrate and leaching during production on soluble phosphate longevity when post-plant phosphate is omitted. Two experiments were conducted growing Petunia ×hybrida ‘Primetime White' seedling crops over a 42-d period in a sphagnum peat moss-perl...

Background Ozone is an air pollutant widely known to cause a decrease in productivity in many plant species, including soybean (Glycine max (L.) Merr). While the response of cultivated soybean to ozone has been studied, very little information is available regarding the ozone response of its wild relatives. Results Ozone-resistant wild soybean acc...

The objective of this study was to determine how plant species, fertilizer potential acidity/basicity rating (PABR), and fertilizer concentration affect root substrate pH. Three experiments were conducted. In the first experiment, 13 herbaceous species were grown in a root substrate of three sphagnum peatmoss: one perlite (v/v) with deionized water...

Tulips were grown under field conditions from mid-November through early-June. Plants were harvested and dissected into eight organs on twenty-one dates. These parts were dried, weighed, and analyzed for N, P, K, Ca, and Mg. A transition (as determined by curve join points) from a linear to a steep negative cubic response occurred prior to shoot em...

Although many factors that influence substrate pH have been quantified, the effect from fertilizers continues to be elusive. A multifactorial experiment was conducted to test macronutrient effects using a rarely used statistical method known as the central composite design. Five nutrient factors, including nitrogen (N) carrier ratio (NH4+ vs. NO3-)...

To guarantee future global food security and sustainable crop production, there is strong need for broadening the relatively narrow genetic base of the soybean (Glycine max [L. Merr.]) germplasm and looking for new resources to develop soybean cultivars. Wild soybean (Glycine soja [Sieb. and Zucc.]) may be an excellent source of new agronomic allel...

Wet deposition and transport analysis has been performed for ammonium (NH4+) in North Carolina, USA. Multiple regression analysis is employed to model the temporal trend and seasonality in monthly volume-weighted mean NH4+ concentrations in precipitation from 1983 to 1996 at six National Atmospheric Deposition Program/National Trends Network (NADP/...

Retrospective analyses of a 23 year data set on abundance of Age 0 southern flounder in 105 estuarine nursery areas in the coastal region of North Carolina showed that discernible temporal and spatial patterns exist among clusters of stations. Furthermore, these patterns could be quantitatively related to certain meteorological and hydrological var...

The objective of this paper is to investigate the relationships between Spanish electricity spot prices and the US dollar/Euro (USD/Euro) exchange rate during the period 2005-2007, taking into account the study of the association between dollar and oil prices, in order to better understand the evolution of the former over time. The first finding in...

We examined Hg(II) bioaccumulation and compartmentalization patterns in conjunction with antioxidant responses in four aquatic insect species: two caddisflies (Chimarra sp. and Hydropsyche betteni) and two mayflies (Maccaffertium modestum and Isonychia sp). Total antioxidant capabilities differed among unexposed larvae, with both caddisfly species...

Differencing is often used to render a time series stationary. The decision of how much differencing to do is usually based on plots of data, the autocorrelation function or a statistical test. Hence, it may happen that an analyst mistakenly differences a stationary series. When that happens, the inverse autocorrelation function takes on a specific...

Water level time series records from the Neuse and Pamlico River Estuaries were statistically compared to local and distant wind field data, water level records within the Pamlico Sound and also coastal ocean sites to determine the relative contribution of each time series to water levels in the Neuse and Pamlico Estuaries. The objectives of this s...

Some previous research links stroke incidence to weather, some links strokes to air pollution, and some report seasonal effects. Alveolar inflammation was proposed as the mechanistic link. We present a unified model of time, weather, pollution, and upper respiratory infection (URI) incidence. We combined existing databases: US Environmental Protect...

We used a decadal data set, with weekly to biweekly sampling in April-October and monthly sampling in November- March, to characterize climatic (hurricane-level storms, a sustained 3-yr drought) and anthropogenic influences on N and P concentrations and loadings to a large eutrophic, poorly flushed estuary, the Neuse Estuary of the Albemarle-Pamlic...

Students were introduced to the concept of statistical process control (SPC)through a simple inline mixing experiment. An aqueous stream with a high concentration of green food coloring was diluted with a stream of tap water and dye concentration was monitored in situ spectroscopically before and after an inline mixer. SPC charts were created to ev...

Dimensional stability of tufted carpets has been a continuing problem in the carpet industry for years. When a tufted carpet is installed by the stretch-in method, it experiences stress relaxation over time which can cause the carpet to buckle, wrinkle and become loose with the only option being a costly re-stretching of the carpet. Analysis of the...

We explore a periodogram-based unit root test that is invariant to nonzero means and invariant to nuisance parameters in the error series. We present modifications to account for trends and deterministic seasonal components.

The North Carolina State University Coastal and Estuary Model & Environmental Prediction System (CEMEPS) is a coupled system of mathematical models. CEMEPS contains a suite of interactively linked atmospheric, oceanic, estuary and river model components. The model architecture couples mesoscale atmospheric models or event models such as hurricanes...

One way of handling nonstationarity in time series is to compute first differences and fit a model to the differenced series unless the differenced series also looks nonstationary. In that case, second- or higher-order differencing is done. To decide if the current degree of differencing is sufficient, one can look at the autocorrelation function f...

A collection of data taken over time is called a time series. Often the goal of time series analysis is to model the correlation structure of the data for the purposes of making correct inferences or forecasting future values of the time series. When a series has constant mean and variance, and the covariance between two observations is a function...

Parameters describing trunk dynamics have been shown to be related to low back injury risk. The objective of this paper was to develop a relationship between static workplace variables and trunk kinematic variables. The independent variables considered in this study consisted of the inputs to the Revised NIOSH Lifting Equation. These include the be...

We investigate a test for unit roots in autoregressive time series based on the maximization of the unconditional likelihood. Models including mean and time trend adjustments are considered. We give percentiles for the resulting tests which are more powerful than the currently popular least squares tests. We show that the limit distributions are un...

Periodograms are often used to characterize time series. They decompose the variation in the data into periodic components and their statistical properties for stationary series are well understood. The periodogram can be computed for any sequence of numbers and we are interested in studying its statistical properties when the underlying data have...

This article demonstrates the use of two datasets as an aid in teaching polynomial and nonlinear regression. The data were gathered by Galileo during his studies of falling bodies and projectiles. In analyzing and discussing these data, students are challenged to give thought to parsimony, independent and dependent variables, and the importance of...

Project No. 92-15. ICMR Tech Report 93-08. The research on which the report is based was supported in part by the United States Environmental Protection Agency and the North Carolina Department of Environment, Health, and Natural Resources (EHNR), through the Albemarle-Pamlico Estuarine Study. Contents of the publication do not necessarily reflect...

For some time now, macroeconomists have been aware that many macroeconomic time-series are not stationary in their levels and that many time-series are most adequately represented by first differences.1 In the parlance of time-series analysis, such variables are said to be integrated of order one and are denoted I(1). The level of such variables ca...

Reducing agricultural nonpoint source (NPS) pollution by implementing best management practices (BMPs) throughout entire watersheds' is being studied in 20 Rural Clean Water Program (RCWP) projects throughout the United States. The Taylor Creek – Nubbin Slough RCWP Project area is located directly north of Lake Okeechobee in southern Florida. The w...

Durante las �ltimas d�cadas se ha producido un creciente inter�s en nuestro pa�s en relaci�n a las econom�as regionales dada la necesidad de los gobiernos regionales de obtener informaci�n sobre sus econom�as para as� llevar a cabo actuaciones de pol�tica econ�mica m�s efectivas y eficientes. En este marco, los modelos econom�tricos constituyen una...

A test for the null hypothesis that a time series has characteristic equations with two unit roots is presented. The test, based on a standard regression computation, is shown to have good power properties when compared to previously existing tests.

The decision on whether or not to include a unit root in an autoregressive operator has profound implications. Formal tests for the presence of unit roots give analysts objective guidance in this decision. This article is a practical guide to the use of these tests.

Let the time series {Yt: t ∈ (1, 2, …)} satisfy Yt = ρYt-1 + Zt and Zt + Σ i=1 aiZt−1 = et + Σ j=1 βjet-j, where {et} is a sequence of normal, independently distributed (NID(0, σ)) random variables, and y0 = 0. Associated with the Zt process are the characteristic equations m + Σ i=1aim = 0 and m + Σ j=1βjm = 0, the roots of which are assumed to be...

Recently, methods for detecting unit roots in autoregressive and autoregressive-moving average time series have been proposed. The presence of a unit root indicates that the time series is not stationary but that differencing will reduce it to stationarity. The tests proposed to date require specification of the number of autoregressive and moving...

[eng] Transportation costs and monopoly location in presence of regional disparities. . This article aims at analysing the impact of the level of transportation costs on the location choice of a monopolist. We consider two asymmetric regions. The heterogeneity of space lies in both regional incomes and population sizes: the first region is endowed...

This article introduces the periodogram based unit root test at seasonal frequencies. We find that the normalized periodogram ordinate is not affected by the seasonality factor, implying that the test statistic has, asymptotically, the same mixture of chi-square distribution under the null of zero frequency unit root. Thus the periodogram based tes...

We discuss two applications of the logistic function in time series. In the first, we look at a transfer function model for some stream flow data. Using a logistic function of lagged flow, we allow the lag relationship between the upstream and downstream stations to vary over time. In the second application, we look at properties of the autoregress...