bluuebunny/crossref_metadata_2025 huggingface dataset:
Untangling Herdan's law and Heaps' law: Mathematical and informetric arguments
Authors: Egghe Leo
Published: February 2007

Herdan's law in linguistics and Heaps' law in information retrieval are different formulations of the same phenomenon. Stated briefly and in linguistic terms they state that vocabularies' sizes are concave increasing power laws of texts' sizes. This study investigates these laws from a purely mathematical and informetric point of view. A general informetric argument shows that the problem of proving these laws is, in fact, ill‐posed. Using the more general terminology of sources and items, the author shows by presenting exact formulas from Lotkaian informetrics that the total number T of sources is not only a function of the total number A of items, but is also a function of several parameters (e.g., the parameters occurring in Lotka's law). Consequently, it is shown that a fixed T (or A) value can lead to different possible A (respectively, T) values. Limiting the T(A)‐variability to increasing samples (e.g., in a text as done in linguistics) the author then shows, in a purely mathematical way, that for large sample sizes T≈LAθ, where θ is a constant, θ6<1 but close to 1, hence roughly, Heaps' or Herdan's law can be proved without using any linguistic or informetric argument. The author also shows that for smaller samples, u is not a constant but essentially decreases as confirmed by practical examples. Finally, an exact informetric argument on random sampling in the items shows that, in most cases, T = T(A) is a concavely increasing function, in accordance with practical examples.
A comparative evaluation of search techniques for query‐by‐humming using the MUSART testbed
Authors: Dannenberg Roger B. , Birmingham William P. , Pardo Bryan , Hu Ning , Meek Colin , Tzanetakis George
Published: February 2007

Query‐by‐humming systems offer content‐based searching for melodies and require no special musical training or knowledge. Many such systems have been built, but there has not been much useful evaluation and comparison in the literature due to the lack of shared databases and queries. The MUSART project testbed allows various search algorithms to be compared using a shared framework that automatically runs experiments and summarizes results. Using this testbed, the authors compared algorithms based on string alignment, melodic contour matching, a hidden Markov model, n‐grams, and CubyHum. Retrieval performance is very sensitive to distance functions and the representation of pitch and rhythm, which raises questions about some previously published conclusions. Some algorithms are particularly sensitive to the quality of queries. Our queries, which are taken from human subjects in a realistic setting, are quite difficult, especially for n‐gram models. Finally, simulations on query‐by‐humming performance as a function of database size indicate that retrieval performance falls only slowly as the database size increases.
Web searcher interaction with the Dogpile.com metasearch engine
Authors: Jansen Bernard J. , Spink Amanda , Koshman Sherry
Published: February 2007

Metasearch engines are an intuitive method for improving the performance of Web search by increasing coverage, returning large numbers of results with a focus on relevance, and presenting alternative views of information needs. However, the use of metasearch engines in an operational environment is not well understood. In this study, we investigate the usage of Dogpile.com, a major Web metasearch engine, with the aim of discovering how Web searchers interact with metasearch engines. We report results examining 2,465,145 interactions from 534,507 users of Dogpile.com on May 6, 2005 and compare these results with findings from other Web searching studies. We collect data on geographical location of searchers, use of system feedback, content selection, sessions, queries, and term usage. Findings show that Dogpile.com searchers are mainly from the USA (84% of searchers), use about 3 terms per query (mean 5 2.85), implement system feedback moderately (8.4% of users), and generally (56% of users) spend less than one minute interacting with the Web search engine. Overall, metasearchers seem to have higher degrees of interaction than searchers on non‐metasearch engines, but their sessions are for a shorter period of time. These aspects of metasearching may be what define the differences from other forms of Web searching. We discuss the implications of our findings in relation to metasearch for Web searchers, search engines, and content providers.
Localization of TrkC to Schwann cells and effects of neurotrophin‐3 signaling at neuromuscular synapses
Authors: Hess Darren M. , Scott Marion O. , Potluri Srilatha , Pitts Elizabeth Vernon , Cisterni Claire , Balice‐Gordon Rita J.
Published: February 2007

Neurotrophins and their receptors, the Trks, are differentially expressed among the cell types that make up neuromuscular and other synapses, but the function and directionality of neurotrophin signaling at synapses are poorly understood. Here we demonstrate, via immunostaining, Western blotting, and RT‐PCR analyses, that TrkC, the receptor for neurotrophin‐3 (NT3), is expressed by mouse perisynaptic and myelinating Schwann cells from birth through adulthood and is unaltered after denervation. Analyses of transgenic mice in which the NT3 coding sequence is replaced by lacZ showed that NT3 is expressed in motor neurons and Schwann cells during perinatal development, but not in adult mice. In muscle, NT3 is expressed by intrafusal muscle fibers within spindles, as has been previously reported. Surprisingly, NT3 is also expressed in extrafusal muscle fibers during perinatal life and in adults. Genetic approaches were used to explore the roles of NT3 and TrkC signaling at neuromuscular synapses. Overexpression of NT3 in muscle fibers during development resulted in an increased number of perisynaptic Schwann cells at neuromuscular synapses, without altering synaptic size, suggesting that muscle‐derived NT3 might act as a mitogen or trophic factor for Schwann cells. Conditional deletion of NT3 from motor neurons did not alter the number of Schwann cells or other aspects of neuromuscular synaptic structure, suggesting that motor‐neuron‐derived NT3 is not required for normal development of perisynaptic Schwann cells or synapses. Together, these results demonstrate that NT3 expression is developmentally regulated in skeletal muscle and may modulate the number of Schwann cells at neuromuscular synapses. J. Comp. Neurol. 501:465–482, 2007. © 2007 Wiley‐Liss, Inc.
Fiber connections of the corpus glomerulosum pars rotunda, with special reference to efferent projection pattern to the inferior lobe in a percomorph teleost, tilapia (Oreochromis niloticus)
Authors: Yang Chun‐Ying , Xue Hao‐Gang , Yoshimoto Masami , Ito Hironobu , Yamamoto Naoyuki , Ozawa Hitoshi
Published: February 2007

Fiber connections of the corpus glomerulosum pars rotunda (GR) in a teleost, tilapia Oreochromis niloticus, were studied by biotinylated dextran amine injections into the GR and inferior lobe. After tracer injections into the GR, major groups of labeled somata were found bilaterally in the cortical nucleus and ipsilaterally in the nucleus intermedius. Numerous labeled terminals were found ipsilaterally in the central nucleus, nucleus of lateral recess, and diffuse nucleus (NDLI) of the inferior lobe. Some other connections were also elucidated in the present study, although these were less abundant. Notably, efferent projections to the inferior lobe were not evenly distributed within each lobar nucleus. Labeled terminals were confined to the cell body zone of central nucleus and the outer cell‐sparse layer of the nucleus of lateral recess. The rostrolateral portion of NDLI and ventrolateral portion of middle to caudal NDLI received few GR fibers, the rostromedial portion of NDLI a moderate density of fibers, and the rest of the nucleus numerous fibers. These different portions of the NDLI, to some extent, also differed in other afferent and efferent connections, suggesting regional specialization of the nucleus. Furthermore, restricted injections to the lobar nuclei suggest different efferent projections of the component cells of the GR: large and small cells. The large cells project only to the central nucleus, whereas the small cells project to the NDLI and nucleus of lateral recess. Therefore, the two types of GR cells appear to constitute parallel pathways from the pretectum to the inferior lobe. J. Comp. Neurol. 501:582–607, 2007. © 2007 Wiley‐Liss, Inc.
Differential hypertrophy and atrophy among all types of cutaneous innervation in the glabrous skin of the monkey hand during aging and naturally occurring type 2 diabetes
Authors: Paré Michel , Albrecht Phillip J. , Noto Christopher J. , Bodkin Noni L. , Pittenger Gary L. , Schreyer David J. , Tigno Xenia T. , Hansen Barbara C. , Rice Frank L.
Published: February 2007

Diabetic neuropathy (DN) is a common severe complication of type 2 diabetes. The symptoms of chronic pain, tingling, and numbness are generally attributed to small fiber dysfunction. However, little is known about the pathology among innervation to distal extremities, where symptoms start earliest and are most severe, and where the innervation density is the highest and includes a wide variety of large fiber sensory endings. Our study assessed the immunochemistry, morphology, and density of the nonvascular innervation in glabrous skin from the hands of aged nondiabetic rhesus monkeys and from age‐matched monkeys that had different durations of spontaneously occurring type 2 diabetes. Age‐related reductions occurred among all types of innervation, with epidermal C‐fiber endings preferentially diminishing earlier than presumptive Aδ‐fiber endings. In diabetic monkeys epidermal innervation density diminished faster, became more unevenly distributed, and lost immunodetectable expression of calcitonin gene‐related peptide and capsaicin receptors, TrpV1. Pacinian corpuscles also deteriorated. However, during the first few years of hyperglycemia, a surprising hypertrophy occurred among terminal arbors of remaining epidermal endings. Hypertrophy also occurred among Meissner corpuscles and Merkel endings supplied by Aβ fibers. After longer‐term hyperglycemia, Meissner corpuscle hypertrophy declined but the number of corpuscles remained higher than in age‐matched nondiabetics. However, the diabetic Meissner corpuscles had an abnormal structure and immunochemistry. In contrast, the expanded Merkel innervation was reduced to age‐matched nondiabetic levels. These results indicate that transient phases of substantial innervation remodeling occur during the progression of diabetes, with differential increases and decreases occurring among the varieties of innervation. J. Comp. Neurol. 501:543–567, 2007. © 2007 Wiley‐Liss, Inc.
Noradrenergic axon terminals contact gastric preautonomic neurons in the paraventricular nucleus of the hypothalamus in rats
Authors: Balcita‐Pedicino J.J. , Rinaman L.
Published: February 2007

Hypothalamic neural activity is modulated by viscerosensory signals that are carried in large part by noradrenergic (NA) inputs to the paraventricular nucleus of the hypothalamus (PVN). The present study examined the ultrastructural relationship of NA axon varicosities with the somata and dendrites of identified gastric preautonomic PVN neurons in adult male rats. NA varicosities were visualized by immunoperoxidase labeling of dopamine beta hydroxylase (DbH), and gastric preautonomic PVN neurons were identified by immunogold labeling of pseudorabies virus (PRV) transported retrogradely and transneuronally from injection sites in the stomach wall. Among 1,136 DbH‐positive varicosities identified within the parvocellular PVN in four rats, approximately 36% formed either a close apposition or a synaptic contact with a somatic or dendritic profile. The majority of identified contacts between DbH‐ and PRV‐positive profiles were classified as close appositions that lacked clear synaptic specializations. Approximately 65% of identified synaptic contacts between DbH‐ and PRV‐positive profiles were classified as symmetric (Gray's type II) synapses. DbH‐positive terminals formed close appositions and synaptic contacts with dendritic and somatic compartments of PRV‐positive neurons, although dendrites were contacted nearly five times more often than somata. These findings invite continued work to delineate the functional role of NA signaling pathways in conveying interoceptive signals to preautonomic PVN neurons under normal and pathophysiological conditions. J. Comp. Neurol. 501:608–618, 2007. © 2007 Wiley‐Liss, Inc.
Decreased neurogenesis in aged rats results from loss of granule cell precursors without lengthening of the cell cycle
Authors: Olariu Ana , Cleaver Kathryn M. , Cameron Heather A.
Published: February 2007

It is well established that neurogenesis in the dentate gyrus slows with aging, but it is unclear whether this change is due to slowing of the cell cycle, as occurs during development, or to loss of precursor cells. In the current study, we find that the cell cycle time of granule cell precursors in middle‐aged male rats is not significantly different from that in young adults. The size of the precursor pool, however, was 3–4 times smaller in the middle‐aged rats, as determined using both cumulative bromodeoxyuridine (BrdU) labeling as well as labeling with the endogenous marker of cell proliferation, proliferating cell nuclear antigen (PCNA). Loss of precursor cells was much greater in the granule cell layer than in the hilus, suggesting that dividing cells in the hilus belong to a distinct population, most likely glial progenitors, that are less affected by aging than neuronal precursors. BrdU‐labeled precursor cells and young neurons, labeled with doublecortin, appeared to be lost equally from rostral and caudal, as well as suprapyramidal and infrapyramidal, subregions of the granule cell layer. However, doublecortin staining did show large parts of the caudal granule cell layer with few if any young neurons at both ages. Taken together, these findings indicate that precursor cells are not distributed evenly within the dentate gyrus in adulthood but that precursors are lost from throughout the dentate gyrus in old age with no concomitant change in the cell cycle time. J. Comp. Neurol. 501:659–667, 2007. Published 2007 Wiley‐Liss, Inc.
Retinotectal ganglion cells in the zebrafish, Danio rerio
Authors: Ott Matthias , Walz Bastian C. , Paulsen Uta J. , Mack Andreas F. , Wagner Hans‐Joachim
Published: February 2007

The morphology of retinotectal ganglion cells was investigated by retrograde transport of dextran amines applied into the optic tectum in vitro. Based on criteria such as stratification pattern and size of the dendritic processes, as well as the shape and position of the soma within the dendritic field, three main groups of ganglion cell types with a total of nine different types were identified. The first group included monostratified cells, of which two types (Ma2 and Mb5) may be ON‐ and OFF‐variants, and the third (Mb6) had its dendritic field as a narrow band at the inner border of the inner plexiform layer. These three cells had the largest dendritic fields, with areas exceeding 40,000 μm2. In two additional monostratified cells the dendrites were spread over the entire width of either sublamina a or sublamina b of the inner plexiform layer (Ma, Mb). They were of intermediate size with mean dendritic field areas between 10,000 and 20,000 μm2. The second group contained two types of bistratified cells (Bb4/5 and Bb4,5/5,6) with two distinct bands of dendritic stratifications in sublamina b. One of them had the smallest dendritic field (below 5,000,mm2) of all cell types in the sample. The diffuse cells of the third group had their dendrites across the entire width of the inner plexiform layer. The sample of retinotectal cells investigated in this study included types described previously (Mangrum et al. [2002] Vis Neurosci 19:767–779) but also new types not described previously. J. Comp. Neurol. 501:647–658, 2007. © 2007 Wiley‐Liss, Inc.
The temporal and spatial variability of rainfall power
Authors: Smith James A. , De Veaux Richard D.
Published: February 2007

In this paper a statistical model of raindrop size distributions is used to examine the temporal variability of rainfall power and to develop techniques for estimating rainfall power from observations of rainfall rate and radar reflectivity factor. The model of raindrop size distributions is based on the assumptions that: 1) raindrop arrival rate at the ground can be represented by a Poisson process with randomly varying rate of occurrence and 2) diameters of raindrops have a lognormal distribution with parameters that are time‐varying random processes. The lognormal distribution plays a central role in both characterization of the temporal variability of rainfall power and in state estimation of rainfall power from rainfall rate and radar reflectivity observations. Empirical results are presented using drop‐size data from a number of sites in the United States. Spatial variability of rainfall power is examined empirically using the rainfall power‐reflectivity relationships developed from drop‐size data and radar data from the southern plains region of the United States.
An empirical bayes approach to the Behrens‐Fisher problem
Authors: Duong Q. P. , Shorrock R. W.
Published: February 2007

This paper is inspired by recent work of G.A. Barnard, who treats the Behrens‐Fisher problem from a Bayesian point of view, and provides calculator programs to implement the solutions (including the classical fiducial solution). We review Barnard's work, and generalize his family of priors in a manner that makes it convenient to estimate the form of the prior from the observed variance ratio. A calculator program is provided to give an empirical estimate (based on marginal maximum likelihood), in an interesting special case, of a parameter of the prior distribution. In addition, programs similar to Barnard's are provided to calculate Bayes or Empirical Bayes p‐values and confidence intervals.
Multistate survival models for partially censored data
Authors: Ataharul Islam M. , Singh Karan P.
Published: February 2007

Multistate survival models for partially censored data are of great interest for investigating factors attributing to transitions from one state of survival to other states of survival or death. Kay (1982) extended the proportional hazards model for a multistate framework with several transient states. However, in his framework, Kay did not incorporate reverse transitions. This paper discusses an extension of the proportional hazards model for several transient states under a competing risk framework for transitions and reverse transitions. The relationship with the multistate product‐limit method is also shown in this paper.
Estimating the effect of emissions strategies on wet deposition of sulfates
Authors: Stein Michael L.
Published: February 2007

The computer model RADM (Regional Acid Deposition Model) has been developed to study the effect of emissions reduction strategies on acid deposition. By running RADM on past meteorology under both present and proposed emissions, it is possible to assess the impact of a change in emissions on acid deposition. Combining these computer simulations with daily monitoring data available at select locations allows for much more precise and possibly much less biased estimation of the effect of the change of emissions on wet deposition than just using the computer simulations. This paper investigates changes in wet sulfate deposition, although the same procedures can be applied to any other component of precipitation computed by RADM and measured at least daily at a monitoring site.
Chronic disease surveillance and testing of clustering of disease and exposure: Application to leukemia incidence and TCE‐contaminated dumpsites in upstate New York
Authors: Waller Lance A. , Turnbull Bruce W. , Clark Larry C. , Nasca Philip
Published: February 2007

Surveillance of large geographic areas for “clusters” of adverse health events, particularly cancers, has interested statisticians and epidemiologists. Recent statistical research involves so‐called “focused” clustering of disease, i.e. aggregation of incident cases of disease in the vicinity of prespecified, putative foci of increased risk. We introduce a statistical test of focused clustering with optimal, or near‐optimal power properties. This test, and two other recent tests of focused clustering are illustrated and compared using leukemia incidence data for 1978–1982 in a region of upstate New York, with inactive hazardous waste sites containing trichloroethylene acting as the suspected foci. Once potential problem areas are identified, more localized methods may be applied.
Assessing attainment of ground water cleanup standards using modified sequential t‐tests
Authors: Roger John
Published: February 2007

Assessing the attainment of Superfund cleanup standards in ground water can be complex due to measurements with skewed distributions, seasonal or periodic patterns, high variability, serial correlations, and censoring of observations below the laboratory detection limit. The attainment decision is further complicated by trends and transient changes in the concentrations as a result of the cleanup effort. EPA contracted Westat to prepare a guidance document recommending statistical procedures for assessing the attainment of ground water cleanup standards. The recommended statistical procedures were to require a minimum of statistical training. The recommended procedures included a sequential t‐test based on yearly average concentrations.

Further research and simulations by Westat indicate that modifications of the sequential t‐test have better performance and are easier to use than the originally proposed sequential t‐test, particularly with highly skewed data. This paper presents three modified sequential t‐tests with simulation results showing how the sequential t‐test and the modifications perform under a variety of situations similar to those found in the field. The modified tests use an easy‐to‐calculate approximation for the log likelihood ratio and an adjustment to improve the power of the test for small sample sizes. Using the log transformed yearly averages improves the test performance with skewed data. Expected sample sizes and practical considerations for application of these tests are also discussed.
Statistical methods for assessing environmental effects on human genetic disorders
Authors: Piegorsch Walter W. , Taylor Jack A.
Published: February 2007

Methods are presented for assessing interactions and other effects between genetic and environmental factors for human disease or cancer susceptibility. Statistical estimation and testing approaches are based on a simple multinomial sampling model for the case‐control sampling scenario. It is noted that logistic regression methods can facilitate computation of likelihood‐based statistics in this setting. Additional models for collapsibility over genotypes within the genetic factor are considered. Monte Carlo comparisons show that the method appears to retain nominal significance levels at total sample sizes above 100. At smaller sample sizes, a goodness‐of‐fit statistic is suggested for testing the interactive effect between the genetic and environmental factors.
On kendall's tau as a test of trend in time series data
Authors: El‐Shaarawi A. H. , Niculescu Stefan P.
Published: February 2007

Kendall's tau is often used to detect the presence of trend in environmental time series data. Assuming stationarity, a general expression for the variance of the associated S score is derived. The results are specialized to the cases of MA(1) and MA(2). Asymptotic normality of tau is established. It is shown that the variance of tau is strongly affected by the assumption of statistical dependence. A seasonal model with non‐zero correlations between successive seasons and years is considered. Simulation results indicate that the effects of departures from distributional assumptions are less important when compared to the effects of departures from the independence assumption.
Global trend of acid wet deposition — a parametric modelling of sulfate concentrations
Authors: Liu Jian
Published: February 2007

In this report, we examine acid wet deposition data collected sequentially in time at multiple monitoring stations. The key objective here is to give a reasonable description of the overall trend pattern of the wet deposition of sulfate. We proceed by first modelling the data collected at each individual station to obtain individual trend estimates at that particular station and then pooling together these trend components by means of a multiple random effects model. Our conclusion is that the overall trend in the United States exhibits a U‐shape.
Simulation of coral reefs and crown‐of‐thorns starfish
Authors: Crimp O. N. , Braddock R. D.
Published: February 2007

Coral reefs are subject to attack and predation by the starfish Acanthaster planci or crown‐of‐thorns. This paper describes a simulation model of the natural processes of a coral reef and its reaction to, and recovery from starfish attacks. The modelling of a reef section is based on a pixel representation of the area. On this are imposed the normal reef processes of coral recruitment, growth, competition and mortality. These were represented in computer form and a suitable computer package was produced and tuned to represent a typical hard coral mid‐shelf reef of the Great Barrier Reef. Fine tuning required the inclusion of a background mortality to ensure that the output extended over centuries, and exhibited the essential properties of real coral communities.

The second phase of the simulation was to model the effects of a starfish attack, its likelihood of occurrence, strength and dietary preferences. Again, these may be tuned to represent the before and after effects of attacks as observed on the reef.

The results of the simulations lead to the conclusion that the modelled coral community exhibited considerable stability (persistence and resilience) in the face of frequent and severe Acanthaster outbreaks. Regardless of the outbreak intensity, the coral community rapidly regained its pre‐outbreak cover of the area in about eight years. Some changes in the community composition were found in the periods immediately after outbreaks. However, the pre‐outbreak composition of the community was always restored within 20–30 years.
Nutrient trends in the Baltic Sea
Authors: Sandén Per , Rahm Lars
Published: February 2007

The Baltic Sea has been subject to an increased load of nutrients during the last century. The effect of this load is obscured sometimes by a lack of data but always by large seasonal variations. A non‐parametric method was used for trend tests at nine different sampling stations from the whole Baltic Sea. Time series from 1968–1990, based on data from HELCOM and ICES databases, were analyzed for trend in concentrations of NO3, NH4, PO4, total phosphorous and total nitrogen.

About 60% of the test statistics gave significant trends at 5% confidence levels. Total nitrogen, total phosphorous, NO3, and PO4 have generally increased in the Baltic Sea. The increase is in the range of 1–4% yr−1. Ammonium shows decreasing trend in the Baltic Sea, with a slope of 3–8% yr−1. Regional differences are, however, found for most of the constituents.
Score tests for the single‐hit poisson model in limiting dilution assays
Authors: Cyr Louis , Singh Karan P.
Published: February 2007

While estimators of the relative frequency of responding cells in limiting dilution assays (LDAs) have been critically evaluated, other statistical issues concerning this quantal assay have not received similar attention. This study investigates LDA validity tests designed to detect deviations from the single‐hit Poisson model. The method employed by Armitage (1959) to detect host variability, or a variable number of false negatives, is extended to other violations of the single‐hit Poisson model. In general, this methodology, based on the general theory of Neyman (1955), is shown to produce asymptotically most powerful and locally most efficient tests for many alternative hypotheses. In addition to composite hypotheses, this method can be extended to produce tests for separate families of hypotheses. These methods are compared with existing LDA validity tests including the weighted regression method of Gart and Weiss (1967), the double‐hit model of Cox (1962), and the general chi‐square goodness‐of‐fit statistic. Monte Carlo simulations show that these score tests have good power and acceptable rejection levels at 0.05 and 0.01. In particular, the score test designed to detect deviations from the Weibull model is shown to produce good power for many alternative models. The chi‐square goodness‐of‐fit statistic, the most widely used LDA validity test, is shown to lack power in detecting many alternative hypotheses.
Design‐based versus model‐based estimates of spatial means: Theory and application in environmental soil science
Authors: Brus Dick J. , DeGruijter Jaap J.
Published: February 2007

The perspectives and concepts of the classical sampling or design‐based approach and the geostatistical or model‐based approach are compared. We show that unbiasedness and minimum variance in the design‐based approach is quite different from that in the model‐based approach and that design‐based strategies are always valid, whether or not there is spatial autocorrelation. Model‐based predictions of spatial means will generally not have the desirable property of unbiasedness in the design‐based sense. Model‐based strategies contain a risk arising from biased selection and they do not allow the accuracy of predictions to be assessed objectively, i.e., based on the sample data alone. Model‐based strategies are useful for local estimation, i.e., for many small blocks and points, provided that there are enough data to estimate the variogram. In a case study on phosphate saturation, design‐based and model‐based estimates of the areal fractions saturated with phosphate were similar, but with smaller blocks the differences increased to magnitudes of practical importance.
Grey box modelling in two time domains of a wastewater pilot scale plant
Authors: Carstensen J. , Madsen Henrik , Poulsen Niels Kjølstad , Nielsen Marinus K.
Published: February 2007

Wastewater treatment processes are characterized by the existence of many different biochemical and physical processes, which partly can be controlled through operation of the wastewater treatment plant. Time series models of these processes are very useful for gaining insight into real time operation of wastewater treatment systems which deal with variable influent flows and pollution loads. In this paper nonlinear time series models based on knowledge of the processes are established. Rates of the biochemical and hydraulic processes are identified, and by statistical methods these constants for the biochemical processes are estimated assuming Monod kinetics. The models are solely based on on‐line measurements of ammonia and nitrate concentrations and corresponding controlling signals from a wastewater pilot scale plant. The models only include those hydraulic and kinetic parameters which have been shown to be significant in a statistical sense, and hence can be quantified.
Statistical extrapolation of nutrient concentrations in the Baltic Sea
Authors: Nordgaard Anders , Hjorth Urban
Published: February 2007

In this paper we present some methods for extrapolating nutrient concentrations in the water mass of the Baltic Sea. One purpose is to find the total amounts of nutrients in different basins. Data are modelled as observations from a stochastic process having room coordinates as its parameters. The extrapolation is treated as a statistical prediction procedure divided into two steps. The first step estimates the mean of the concentration at the point to which the extrapolation is made. The second step adds to the estimated mean a linear combination of residuals between estimated means and actual response values in surroundingdatapoints. The coefficients in the linear combination and the number of surrounding points included are decided according to an estimated correlation model. The two steps both include heavy computer calculations consisting of model selection procedures and non‐linear programming algorithms. Three reasonable methods may be deduced from the two steps depending on how we estimate the mean and how correlated the residuals from the estimated means seem to be. The choice of method is based on validation towards the current data set. The extrapolated concentrations have also been integrated over the water volumes to obtain estimates of total amounts of the nutrients. Estimates from the three methods above have been compared.
Displaying inter‐ and intra‐regional variability of large‐scale survey results
Authors: Posch Maximilian , Kämäri Juha , Johansson Matti , Forsius Martin
Published: February 2007

Currently many European nations are taking part in a coordinated exercise on mapping critical loads of air pollutants for aquatic and terrestrial ecosystems. A statistically based lake survey and soil analyses from sites uniformly covering the country are used to assess the critical loads of sulphur and nitrogen for lakes and forest soils in Finland. When presenting results based on such large and spatially extensive data sets one has to take into account the user of this information. For the scientific community it is desirable to retain as much information as possible in the display of the results, whereas clarity and simplicity of presentation are crucial for the understanding and acceptance by policy‐makers. In this paper we present different methods for displaying spatially varying information, discuss various statistical descriptors for characterizing distributions by a few numbers, and compare the influence of alternative ways of aggregating data on the final display of results.
Trend analysis methods for environmental data
Authors: Esterby S. R.
Published: February 2007

Recently, the heightened interest in the assessment of the current state of environmental conditions and the detection of change in environmental conditions has led to a corresponding interest in statistical trend assessment methods. In the present paper, the analysis for trend is considered as part of the larger task of characterizing the variability of an environmental quality indicator when data are available from a monitoring programme. The features of several parametric and non‐parametric methods are discussed with respect to methods of accounting for seasonality, inherent models for trend, the ability to handle changes of different forms, the inclusion of concomitant variables in the analysis and the assumptions of the method. Examples of the analysis of water quality data using these methods are given.
Biometrical methods for testing dose effects of environmental stimuli in laboratory studies
Authors: Piegorsch Walter W.
Published: February 2007

In the areas of toxicology and environmental biology, the damaging effects of environmental chemicals or other stimuli on biological systems are often studied in controlled laboratory experiments. These usually involve animal and microbial systems. Data from such experiments are analysed via various statistical approaches, depending on the nature of the endpoint and aspects of the particular assay under study. Major endpoints of interest include carcinogenicity, mutagenicity, and teratogenicity. When the environmental stimulus is administered over a range of doses, it is of interest to estimate and/or test features of the dose response. In some instances, variance heterogeneity and overdispersion are present, and adjustments to the statistical methods are required. Herein, such methods for assessing dose response for the major endpoints noted above are discussed, with emphasis directed at testing for an increasing dose response.
Compliance testing of two or more water quality determinands using quantiles
Authors: Cotter A. J. R.
Published: February 2007

The testing of k > 1 water quality determinands for compliance with environmental regulations leads to difficulties in finding the probabilities of wrongly concluding (a) that one or more determinands failed when in fact all passed (joint type I error), and (b) that one or more passed when all failed (joint type II error). Also, owing to dependence among the determinands, some may contribute little to the compliance assessment and, if they serve no other purpose, are a waste of analytical resources. A method based on sample quantiles is suggested for estimating the theoretical number f of completely independent, notional determinands whose information content is equivalent to the k actual determinands being regulated. Next, the alternative strategies of individual and collective testing of the k determinands against regulations set as quantiles are compared in terms of joint type I and II error probabilities. The extreme cases of negative and positive dependence among the determinands set ranges for these probabilities, but even with moderate k they tend to be impractically broad for reliable decision making with either test strategy. Assuming independence as a worst case instead of negative dependence helps somewhat. It is explained how, alternatively, point estimates for the error probabilities are possible using f, given certain assumptions. Two schemes for regulating multiple determinands thus emerge, one based on an agreed worst‐case situation which places minimal reliance on assumed conditions, the other based on an estimated error situation utilizing f. The choice between them would be influenced by the rigour required of the tests. The relative performance of individual and collective testing is shown to depend on the parameters chosen for the tests, and the degree and sign of dependence among the determinands. The design of compliance testing schemes is crucial in determining whether most risk lies with waste producers or the receiving environment, and what effect the prescribed regulations will actually have in practice.
The analysis of radon survey data
Authors: Schwenke James R. , Butine Michael D.
Published: February 2007

Observed radon gas levels typically demonstrate a skewed sampling distribution. Traditional analyses to compare mean or median radon levels among different demographic groups rely on transformations of these data. The logarithmic transformation is one that is traditionally employed. Unfortunately, transformations such as the logarithmic tend to de‐emphasize extreme values. In radon gas research, these extreme values are of primary interest. The proposed methodology is based on characterizing the sampling distribution of radon levels by a non‐normal distribution. The mean radon level is estimated based on the assumed sampling distribution. Comparisons among groups are considered through a weighted analysis of variance. Results of a survey conducted by the state of Kansas are used as an example.
A comment on selecting sample sizes and discrete observation times for longitudinal mortality studies: Effects of skewed distributions for mortality times
Authors: Hines R. J. O'Hara , Hines W. G. S.
Published: February 2007

This note extends previously published results on selecting sample sizes and discrete observation times for longitudinal mortality studies to consider the effect of skewness in the distribution of mortality times.
Positive matrix factorization: A non‐negative factor model with optimal utilization of error estimates of data values
Authors: Paatero Pentti , Tapper Unto
Published: February 2007

A new variant ‘PMF’ of factor analysis is described. It is assumed that X is a matrix of observed data and σ is the known matrix of standard deviations of elements of X. Both X and σ are of dimensions n × m. The method solves the bilinear matrix problem X = GF + E where G is the unknown left hand factor matrix (scores) of dimensions n × p, F is the unknown right hand factor matrix (loadings) of dimensions p × m, and E is the matrix of residuals. The problem is solved in the weighted least squares sense: G and F are determined so that the Frobenius norm of E divided (element‐by‐element) by σ is minimized. Furthermore, the solution is constrained so that all the elements of G and F are required to be non‐negative. It is shown that the solutions by PMF are usually different from any solutions produced by the customary factor analysis (FA, i.e. principal component analysis (PCA) followed by rotations). Usually PMF produces a better fit to the data than FA. Also, the result of PF is guaranteed to be non‐negative, while the result of FA often cannot be rotated so that all negative entries would be eliminated. Different possible application areas of the new method are briefly discussed. In environmental data, the error estimates of data can be widely varying and non‐negativity is often an essential feature of the underlying models. Thus it is concluded that PMF is better suited than FA or PCA in many environmental applications. Examples of successful applications of PMF are shown in companion papers.
A seasonal Markov model for extremely low temperatures
Authors: Coles Stuart G. , Tawn Jonathan A. , Smith Richard L.
Published: February 2007

Time series of temperatures during periods of extreme cold display long‐term seasonal variability and short‐term temporal dependence. Classical approaches to extremes circumvent these issues, but in so doing cannot address questions relating to the temporal character of the process, though these issues are often the most important. In this paper a model is developed with the following features: periodic seasonal effects; consistency with asymptotic extreme value theory; Markov description of temporal dependence. Smithet al.studied the properties of such a model in the stationary case. Here, it is shown how such a model can be fitted to a non‐stationary series, and consequently used to estimate temporal aspects of the extremal process of low temperatures which have most practical and scientific relevance.
A space‐time analysis of ground‐level ozone data
Authors: Guttorp Peter , Meiring Wendy , Sampson Paul D.
Published: February 2007

We examine hourly ozone data collected in connection with a model evaluation study for ozone transport in the San Joaquin Valley of California. A space‐time analysis of a subset of the data, 17 sites concentrated around the Sacramento area, indicates a relatively simple spatial covariance structure at night‐time, while the afternoon readings show a more complex spatial covariance, which is partly explained by observations from a single station with suspicious data. Simple separable space‐time covariance models do not appear applicable to these data.
From data and theory to environmental model: The case of rainfall runoff
Authors: Jakeman Anthony J. , Post David A. , Beck M. Bruce
Published: February 2007

Models of environmental systems, constructed for the purpose of predicting or understanding the effects of input changes, fall predominantly into two classes: those based on idealized equations of mathematical physics, and those based on compartmentalized conceptual descriptions of processes. Overparameterization is often a common feature of both these approaches. System identification offers the opportunity to begin model construction with simple structures and assumptions, and to build up the level of model detail by testing refinements for their consistency with system observations. We use rainfall runoff modelling to demonstrate this approach. We also use it to argue that model regionalization is a powerful technique to help generate better understanding and prediction of environmental systems. The construction of identifiable models which are transferable within a ‘region’ of similarity makes the exercise more tenable, and facilitates the jump to more generic models applicable in a wider (e.g. global) context.
Prediction of surface water turnover time in coastal waters using digital bathymetric information
Authors: Persson Johan , Håkanson Lars , Pilesjö Petter
Published: February 2007

This paper presents a new type of geographical information system (GIS) for scientific planning of coastal waters. One hypothesis in the work is that the morphometry of the coast plays a significant role for how the water system functions as a receiving water system, for example, as a receiver of industrial and urban pollution and in response to various forms of aquaculture. A digital technique for transferring information from standard charts into morphometric parameters expressing various characteristics of the coast has been developed. Empirical data on surface water turnover times, which are costly and demanding to determine with traditional hydrodynamic methods, has been obtained from the literature for 20 defined Swedish coastal areas. Two models for simple predictions of the median surface water turnover time, based on morphometric parameters, have been developed to exemplify the use of “morphometrical models” in expressing a coast ecological key parameter. In these models, more than 90 per cent of the variation in empirical values of surface water turnover times can be statistically explained by the topographic openness. The topographic openness describes the exposure of the coastal area towards the open sea or adjacent coastal area. The models are valid for the temperature stratified period (May–October) in areas non‐affected by tides, strong coastal currents and river inflow. The areas should also be in the size range 0.15–150 km2.
Forecasting hurricane tracks using the Kalman filter
Authors: Bril Gordon
Published: February 2007

A case study applies state space models and the Kalman filter to forecasting the path of hurricanes. The track of a hurricane is forecast by using its previous motion together with the historical record of storms which follow a similar path. Criteria are described for selecting the predictor storms, which are then incorporated into the measurement equation of the state space model. Linear and quadratic trend structural time series models are used in the transition equation of the state space model and forecasts are produced using the Kalman filter. Forecasts are obtained for hurricanes Andrew (1992), Bob (1991), Hugo (1989) and Gilbert (1988). The Kalman filter approach compares very favourably with the HURRAN and CLIPER benchmark models used by the National Hurricane Center.
Statistical analysis on markov‐modulated poisson processes
Authors: Ramesh N. I.
Published: February 2007

A class of doubly stochastic Poisson processes, which is termed a Markov‐modulated Poisson process, is studied. The maximum likelihood method is used to make inferences about the Markov‐modulated Poisson process. Expressions are derived for the likelihood function and for second‐order properties of both counts and intervals. A simple two‐state model is applied to a set of exposure data and to simulated data. Bivariate generalization of this process is also studied.
A minimum cost estimator for the mean of positively skewed distributions with applications to estimation of exposure to contaminated soils
Authors: Chen Ling
Published: February 2007

In this paper, a new flexible cost function is introduced in order to reduce the probability of underestimating the mean of positively skewed distributions by using the sample mean. Under this cost function, a minimum cost estimator is derived and its theoretical properties are studied. Simulation studies are based on the lognormal distribution and on a data set of chromium concentration from one of the EPA's toxic waste sites. The results show that the estimator proposed in this article is superior to the upper confidence limit (UCL) estimator currently being used by EPA to alleviate the underestimation problem.