bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Covariance with Incomplete Data Via Semiparametric Model Transformations
Authors: Grigoletto Matteo , Akritas Michael G.
Published: May 2004

Summary. We propose a method for fitting semiparametric models such as the proportional hazards (PH), additive risks (AR), and proportional odds (PO) models. Each of these semiparametric models implies that some transformation of the conditional cumulative hazard function (at each t) depends linearly on the covariates. The proposed method is based on nonparametric estimation of the conditional cumulative hazard function, forming a weighted average over a range of t‐values, and subsequent use of least squares to estimate the parameters suggested by each model. An approximation to the optimal weight function is given. This allows semiparametric models to be fitted even in incomplete data cases where the partial likelihood fails (e.g., left censoring, right truncation). However, the main advantage of this method rests in the fact that neither the interpretation of the parameters nor the validity of the analysis depend on the appropriateness of the PH or any of the other semiparametric models. In fact, we propose an integrated method for data analysis where the role of the various semiparametric models is to suggest the best fitting transformation. A single continuous covariate and several categorical covariates (factors) are allowed. Simulation studies indicate that the test statistics and confidence intervals have good small‐sample performance. A real data set is analyzed.
Allometric Extension
Authors: Bartoletti Stefania , Flury Bernard D. , Nel Daan G.
Published: May 2004

Summary. Constants of allometric growth are commonly estimated by the first eigenvector of the covariance matrix of log measurements. Hills (1982, in Encyclopedia of Statistical Sciences, 48–54) defines a model of allometric extension for two related species by the conditions that (a) the constants of allometric growth are identical for both species and (b) the vector of mean differences is proportional to the common first eigenvector of both covariance matrices. We give a test for allometric extension and discuss estimation of the parameters of the allometric extension model, including standard errors.
On the Equivalence of Meta‐Analysis Using Literature and Using Individual Patient Data
Authors: Mathew Thomas , Nordstrom Kenneth
Published: May 2004

Summary. When data come from several independent studies for the purpose of estimating treatment‐control differences, meta‐analysis can be carried out either on the best linear unbiased estimators computed from each study or on the pooled individual patient data modelled as a two‐way model without interaction, where the two factors represent the different studies and the different treatments. Assuming that observations within and between studies are independent having a common variance, Olkin and Sampson (1998) have obtained the surprising result that the two meta‐analytic procedures are equivalent, i.e., they both produce the same estimator. In this article, the same equivalence is established for the two‐way fixed‐effects model without interaction with the only assumption that the observations across studies be independent. A consequence of the equivalence result is that, regardless of the covariance structure, it is possible to get an explicit representation for the best linear unbiased estimator of any vector of treatment contrasts in a two‐way fixed‐effects model without interaction as long as the studies are independent. Another interesting consequence is that, for the purpose of best linear unbiased estimation, an unbalanced two‐way fixed‐effects model without interaction can be treated as several independent unbalanced one‐way models, regardless of the covariance structure, when the studies are independent.
Estimating the Extent of Tracking in Interval‐Censored Chain‐Of‐Events Data
Authors: Satten Glen A.
Published: May 2004

Summary. This paper describes a method for determining whether the times between a chain of successive events (which all individuals experience in the same order) are correlated, for data in which the exact event times are not observed. Such data arise when individuals are only observed occasionally to determine which events have occurred. In such data, the (unknown) event times are interval censored. In addition, some individuals may have experienced some of the events before their first observation and may be lost to follow‐up before experiencing the last event. Using a frailty model proposed by Aalen (1988, Mathematical Scientist13, 90–103) but which has never been used to analyze real data, we examine whether individuals who develop early markers of HIV infection can also be expected to develop antibody and other indicators of HIV infection more rapidly.
Binary Regression for Risks in Excess of Subject‐Specific Thresholds
Authors: Zhang Heping , Zelterman Daniel
Published: May 2004

Summary. We describe models for binary valued data to be used to explain the incidence of disease given the level of a known risk factor. Every individual has an unobservable tolerance of the risk. Risk levels below the individual tolerance do not increase the disease incidence above the background, unexposed rate. We estimate parameters from both the tolerance distribution and the risk function for a large group of mice exposed to very low levels of a known carcinogen.
Rank‐Based Tests for Dose Finding in Nonmonotonic Dose–Response Settings
Authors: Chen Yuh‐Ing
Published: May 2004

Summary. Lim and Wolfe (1997, Biometrics53, 410–418) proposed rank‐based multiple test procedures for identifying the dose levels that are more effective than the zero‐dose control in randomized complete block designs when it can be assumed that the efficacy of the increasing dose levels is monotonically increasing up to a point, followed by a monotonic decrease. Modifications of the Lim–Wolfe tests are suggested that provide more practical and powerful alternatives. Two numerical examples are illustrated and the results of a Monte Carlo power study are presented.
A Comment on Optimal Allocations for Bioequivalence Studies
Authors: Senn Stephen , Grieve Andrew P.
Published: May 2004

Summary. A method purporting to provide optimal allocations in bioequivalence studies fails to do so on both statistical and practical grounds. Reasons as to why this is so are given.
Localization of a Quantitative Trait Locus via a Bayesian Approach
Authors: George A. W. , Mengersen K. L. , Davis G. P.
Published: May 2004

Summary. A Bayesian approach to the direct mapping of a quantitative trait locus (QTL), fully utilizing information from multiple linked gene markers, is presented in this paper. The joint posterior distribution (a mixture distribution modeling the linkage between a biallelic QTL and N gene markers) is computationally challenging and invites exploration via Markov chain Monte Carlo methods. The parameter's complete marginal posterior densities are obtained, allowing a diverse range of inferences. Parameters estimated include the QTL genotype probabilities for the sires and the offspring, the allele frequencies for the QTL, and the position and additive and dominance effects of the QTL. The methodology is applied through simulation to a half‐sib design to form an outbred pedigree structure where there is an entire class of missing information. The capacity of the technique to accurately estimate parameters is examined for a range of scenarios.
Estimation of Age‐Specific Breeding Probabilities from Capture–Recapture Data
Authors: Schwarz Carl J. , Arnason A. Neil
Published: May 2004

Summary. We provide a new method for estimating the age‐specific breeding probabilities from recaptures or resightings of animals marked as young. Our method is more direct than previous methods and allows the modeler to fit and compare models where the age‐specific breeding proportions are equal over different cohorts or are a function of external covariates.
Generalized Nonlinear Models for Pharmacokinetic Data
Authors: Lindsey J. K. , Byrom W. D. , Wang J. , Jarvis P. , Jones B.
Published: May 2004

Summary.Phase I trials to study the pharmacokinetic properties of a new drug generally involve a restricted number of healthy volunteers. Because of the nature of the group involved in such studies, the appropriate distributional assumptions are not always obvious. These model assumptions include the actual distribution but also the ways in which the dispersion of responses is allowed to vary over time and the fact that small concentrations of a substance are not easily detectable and hence are left censored. We propose that a reasonably wide class of generalized nonlinear models allowing for left censoring be considered now that this is feasible with current computer power and sophisticated statistical packages. These modelling strategies are applied to a Phase I study of the drug flosequinan and its metabolite. This drug was developed for the treatment of heart failure. Because the metabolite also exhibits an active pharmacologic effect, study of both the parent drug and the metabolite is of interest.
Self‐Modeling for Two‐Dimensional Response Curves
Authors: Ladd William M. , Lindstrom Mary J.
Published: May 2004

Summary. Two‐dimensional response curves are an important experimental outcome in speech kinematics and other areas of research. These parameterized curves are usually obtained by recording the two‐dimensional location of an object over time. In this setting, time is the independent variable and the x and y locations on specified coordinate axes define the multivariate response. Collections of such parameterized curves can be obtained either from one subject or from a number of different subjects, each producing one or several realizations of the response curve. When only one dependent variable is observed over time and no parametric model is specified, self‐modeling regression (SEMOR) is an attractive modeling approach. SEMOR assumes that each of a collection of curves differs from a smooth, average shape function by some simple parametric transformation of the coordinate axes (usually linear). We will describe the extension of SEMOR to two‐dimensional parameterized curves using affine transformations of a two‐dimensional, time‐parameterized shape function.
Use of Binomial Group Testing in Tests of Hypotheses for Classification or Quantitative Covariables
Authors: Hung Ming‐Chin , Swallow William H.
Published: May 2004

Summary. In group testing, the test unit consists of a group of individuals. If the group test is positive, then one or more individuals in the group are assumed to be positive. A group observation in binomial group testing can be, say, the test result (positive or negative) for a pool of blood samples that come from several different individuals. It has been shown that, when the proportion (p) of infected individuals is low, group testing is often preferable to individual testing for identifying infected individuals and for estimating proportions of those infected. We extend the potential applications of group testing to hypothesis‐testing problems wherein one wants to test for a relationship between p and a classification or quantitative covariable. Asymptotic relative efficiencies (AREs) of tests based on group testing versus the usual individual testing are obtained. The Pitman ARE strongly favors group testing in many cases. Small‐sample results from simulation studies are given and are consistent with the large‐sample (asymptotic) findings. We illustrate the potential advantages of group testing in hypothesis testing using HIV‐1 seroprevalence data.
Active Life Expectancy from Annual Follow–Up Data with Missing Responses
Authors: Izmirlian Grant , Brock Dwight , Ferrucci Luigi , Phillips Caroline
Published: May 2004

Summary. Active life expectancy (ALE) at a given age is denned as the expected remaining years free of disability. In this study, three categories of health status are defined according to the ability to perform activities of daily living independently. Several studies have used increment‐decrement life tables to estimate ALE, without error analysis, from only a baseline and one follow‐up interview. The present work conducts an individual‐level covariate analysis using a three‐state Markov chain model for multiple follow‐up data. Using a logistic link, the model estimates single‐year transition probabilities among states of health, accounting for missing interviews. This approach has the advantages of smoothing subsequent estimates and increased power by using all follow‐ups. We compute ALE and total life expectancy from these estimated single‐year transition probabilities. Variance estimates are computed using the delta method. Data from the Iowa Established Population for the Epidemiologic Study of the Elderly are used to test the effects of smoking on ALE on all 5‐year age groups past 65 years, controlling for sex and education.
Modeling Human Fertility in the Presence of Measurement Error
Authors: Dunson David B. , Weinberg Clarice R.
Published: May 2004

Summary.The probability of conception in a given menstrual cycle is closely related to the timing of intercourse relative to ovulation. Although commonly used markers of time of ovulation are known to be error prone, most fertility models assume the day of ovulation is measured without error. We develop a mixture model that allows the day to be misspecified. We assume that the measurement errors are i.i.d. across menstrual cycles. Heterogeneity among couples in the per cycle likelihood of conception is accounted for using a beta mixture model. Bayesian estimation is straightforward using Markov chain Monte Carlo techniques. The methods are applied to a prospective study of couples at risk of pregnancy. In the absence of validation data or multiple independent markers of ovulation, the identifiability of the measurement error distribution depends on the assumed model. Thus, the results of studies relating the timing of intercourse to the probability of conception should be interpreted cautiously.
A Revisit on Tests for Homogeneity of the Risk Difference
Authors: Lui Kung‐Jong , Kelly Colleen
Published: May 2004

Summary. Lipsitz et al. (1998, Biometrics54, 148–160) discussed testing the homogeneity of the risk difference for a series of 2 × 2 tables. They proposed and evaluated several weighted test statistics, including the commonly used weighted least squares test statistic. Here we suggest various important improvements on these test statistics. First, we propose using the one‐sided analogues of the test procedures proposed by Lipsitz et al. because we should only reject the null hypothesis of homogeneity when the variation of the estimated risk differences between centers is large. Second, we generalize their study by redesigning the simulations to include the situations considered by Lipsitz et al. (1998) as special cases. Third, we consider a logarithmic transformation of the weighted least squares test statistic to improve the normal approximation of its sampling distribution. On the basis of Monte Carlo simulations, we note that, as long as the mean treatment group size per table is moderate or large (≥16), this simple test statistic, in conjunction with the commonly used adjustment procedure for sparse data, can be useful when the number of 2 × 2 tables is small or moderate (≤32). In these situations, in fact, we find that our proposed method generally outperforms all the statistics considered by Lipsitz et al. Finally, we include a general guideline about which test statistic should be used in a variety of situations.
Kir4.1 expression by astrocytes and oligodendrocytes in CNS white matter: a developmental study in the rat optic nerve
Authors: Kalsi Amanpreet S. , Greenwood Kirsty , Wilkin Graham , Butt Arthur M.
Published: May 2004

Deletion studies in transgenic mice indicate that the potassium inward rectifying channel Kir4.1 is crucial for oligodendrocyte differentiation and has a special role in regulation of extracellular potassium (K+), a major function of astrocytes. However, there are conflicting reports on whether Kir4.1 is expressed by white matter astrocytes and oligodendrocytes, raising doubts over its functions. Here, we have examined Kir4.1 expression in astrocytes and oligodendrocytes of the rat optic nerve, a typical central nervous system white matter tract. Single and double immunofluorescence labelling was performed on frozen sections from optic nerves aged postnatal day (P)5, 10, 15, 20 and adult, using anti‐Kir4.1 antibodies and the glia‐specific antibodies glial fibrillary acidic protein (GFAP, astrocytes), carbonic anhydrase II (CAII, oligodendrocyte somata and processes) and myelin basic protein (MBP, oligodendrocyte myelin sheaths). The results demonstrate Kir4.1 expression in rows of glial cells as early as P5, and this pattern persisted throughout development and into adulthood, consistent with early expression of Kir4.1 on developing oligodendrocytes. Clear co‐expression of Kir4.1 and GFAP is first evident at P10 and increases to adult levels by P15 and P20, which correlates with the development of K+ regulation between P15 and P20. Astrocyte expression of Kir4.1 is localized to perivascular end‐feet and fine processes within the fascicles of myelinated axons, consistent with a role in K+ spatial buffering between nodes of Ranvier and blood vessels. By contrast, Kir4.1 is concentrated in the cell bodies of oligodendrocytes, and there is no apparent co‐expression with MBP+ myelin sheaths, suggesting oligodendroglial Kir4.1 channels are not involved in K+ regulation. The results support roles for Kir4.1 in both oligodendrocyte differentiation and K+ regulation by astrocytes.
Cerebral cortex three‐dimensional profiling in human fetuses by magnetic resonance imaging
Authors: Sbarbati Andrea , Pizzini Francesca , Fabene Paolo F. , Nicolato Elena , Marzola Pasquina , Calderan Laura , Simonati Alessandro , Longo Laura , Osculati Antonio , Beltramello Alberto
Published: May 2004

Seven human fetuses of crown/rump length corresponding to gestational ages ranging from the 12th to the 16th week were studied using a paradigm based on three‐dimensional reconstruction of the brain obtained by magnetic resonance imaging (MRI). The aim of the study was to evaluate brain morphology in situ and to describe developmental dynamics during an important period of fetal morphogenesis. Three‐dimensional MRI showed the increasing degree of maturation of the brains; fronto‐occipital distance, bitemporal distance and occipital angle were examined in all the fetuses. The data were interpreted by correlation with the internal structure as visualized using high‐spatial‐resolution MRI, acquired using a 4.7‐T field intensity magnet with a gradient power of 20 G cm−1. The spatial resolution was sufficient for a detailed detection of five layers, and the contrast was optimized using sequences with different degrees of T1 and T2 weighting. Using the latter, it was possible to visualize the subplate and marginal zones. The cortical thickness was mapped on to the hemispheric surface, describing the thickness gradient from the insular cortex to the periphery of the hemispheres. The study demonstrates the utility of MRI for studying brain development. The method provides a quantitative profiling of the brain, which allows the calculation of important morphological parameters, and it provides informative regarding transient features of the developing brain.
A test of the hypothesis that a pathway of intraguild predation limits densities of a wolf spider
Authors: Lensing Janet R. , Wise David H.
Published: May 2004

Abstract.  1. The high number of potential predatory interactions among the many arthropod generalist predators in terrestrial food webs makes exhaustive testing of interaction strengths by field experiments unfeasible. Thus, correlative patterns and laboratory observations of behaviour often form the basis of inferences about the strength of interaction pathways involving generalist predators (intraguild predation).

2. Previous research has revealed a negative correlation between survival of juvenile wolf spiders of the genus Schizocosa (Lycosidae) and densities of another abundant spider family, the Gnaphosidae.

3. Feeding trials in laboratory microcosms with a leaf‐litter substrate revealed that gnaphosids prey on juvenile Schizocosa in a structurally complex habitat.

4. Gnaphosid densities were manipulated in two different field experiments, each conducted in a different year, in order to test directly the hypothesis that intraguild predation by gnaphosids limits densities of juvenile Schizocosa.

5. Reducing numbers of gnaphosids, and doubling their numbers to two times the mean natural density, had no impact on the survival of juvenile Schizocosa in either field experiment. This finding suggests that correlative patterns in nature and feeding trials in the laboratory may at times provide deceptively simple and potentially misleading generalisations about the strengths of interaction pathways in complex networks of generalist predators.
Guards and thieves: antagonistic interactions between two ant species coexisting on the same ant‐plant
Authors: Raine Nigel E. , Gammans Nicola , Macfadyen Iain J. , Scrivner Gareth K. , Stone Graham N.
Published: May 2004

Abstract.  1. The simultaneous occupation of a rare understorey ant‐acacia Acacia mayana by its guarding ant Pseudomyrmex ferrugineus, and an apparent opportunist parasite of the mutualism, the generalist ant Camponotus planatus is described. The two ant species occur together in 30.7% of the 26 mature A. mayana plants [23.5% of all trees (n = 34)] surveyed, but C. planatus is absent from saplings below 1 m in height (n = 8).

2. While P. ferrugineus shows behaviour compatible with effective host‐tree defence, C. planatus does not attack phytophagous insects and appears ineffective as an ant‐guard. Camponotus planatus does, however, occupy swollen thorns (pseudogalls) on the host tree, and harvests nectar from extrafloral leaf nectaries. It is proposed that C. planatus is a parasite of the Acacia–Pseudomyrmex mutualism.

3. Camponotus planatus does not harvest the second trophic reward produced by the tree for its Pseudomyrmex ant‐guards, protein‐rich food (Beltian) bodies. Camponotus planatus lack the specialised larval adaptations needed to use Beltian bodies as brood food, suggesting that this resource is potentially more resistant to exploitation by generalists than extrafloral nectar.

4. In competition for access to nectaries, C. planatus effectively displaced P. ferrugineus in 99.8% of encounters. These results suggest not only that C. planatus is a parasite of this mutualism, but also that it is able to effectively counteract the aggression shown to other insects by the resident ant‐guards.
Bottom‐up and top‐down effects in a tritrophic system: the population dynamics of Plutella xylostella (L.)–Cotesia plutellae (Kurdjumov) on different host plants
Authors: Karimzadeh Javad , Bonsall Michael B. , Wright Denis J.
Published: May 2004

Abstract.  1. The effects of host‐plant resistance on the population dynamics of the Diamondback moth, Plutella xylostella L., and its solitary parasitoid, Cotesia plutellae (Kurdjumov), were studied in replicated time‐series experiments.

2. Host‐plant resistance did not affect the equilibrial abundance of the Diamondback moth, but it affected the dynamics of Diamondback moth populations.

3. The mean population size of Diamondback moth showed no significant difference between Brassica rapa (a susceptible host plant) and Brassica napus (a partially resistant host plant) either in the presence or absence of the parasitoid.

4. Time‐series analysis suggests that the dynamics of Diamondback moth on B. rapa were underpinned by delayed density‐dependent processes. In contrast, the dynamics of the moth on B. napus were influenced by a direct density‐dependent process.

5. Although measures of short‐term parasitism showed a significantly higher rate of parasitism by C. plutellae on Diamondback moth feeding on B. napus compared with B. rapa, this individual performance does not translate into differences in the population dynamics. Analysis shows no significant difference in the persistence time of the population‐level interaction between the host and parasitoid on the two different host plants.
Liquidity Dynamics Across Small and Large Firms
Authors: Chordia Tarun , Shivakumar Lakshmanan , Subrahmanyam Avanidhar
Published: May 2004

In this paper, we analyse cross‐sectional heterogeneity in the time‐series variation of liquidity in equity markets. Our analysis uses a broad time‐series and cross‐section of liquidity data. We find that average daily changes in liquidity exhibit significant heterogeneity in the cross‐section; the liquidity of small firms varies more on a daily basis than that of large firms. A steady increase in aggregate market liquidity over the past decade is more strongly manifest in large firms than in small firms. Absolute stock returns are an important determinant of liquidity. We investigate cross‐sectional differences in the resilience of a firm's liquidity to information shocks. We use the sensitivity of stock liquidity to absolute stock returns as an inverse measure of this resilience, and find that the measure exhibits considerable cross‐sectional variation. Firm size, return volatility, institutional holdings, and volume are all significant cross‐sectional determinants of this measure.

(J.E.L.: D82, G10, G14).
Breaking up the collective farms
Authors: Ravallion Martin , Van De Walle Dominique
Published: May 2004

The de‐collectivization of Vietnamese agriculture was a crucial step in the country's transition to a market economy. The assignment of land‐use rights had to be decentralized and local cadres ostensibly had the power to capture this process. We assess the realized land allocation against explicit counter‐factuals. Depending on the region, we find that 95–99 percent of maximum aggregate consumption was realized by a land allocation that generated lower inequality overall, with the poorest absolutely better off. We attribute this outcome to initial conditions at the time of reform and actions by the centre to curtail the power of local elites.
Host‐marking behaviour as a quantitative signal of competition in the walnut fly Rhagoletis juglandis
Authors: Nufio César R. , Papaj Daniel R.
Published: May 2004

Abstract.  1. Walnut‐infesting flies in the Rhagoletis suavis species group actively re‐use hosts for oviposition despite engaging in a genus‐typical host‐marking behaviour which, in other Rhagoletis groups, deters oviposition. In a study of the walnut fly, R. juglandis (Cresson), alternative hypotheses for the putative marking behaviour were evaluated.

2. The oviposition site attraction hypothesis proposes that the host mark guides females to oviposition sites on occupied fruit. The competition intensity signal hypothesis proposes that the host mark is an indicator of the level of competition to be incurred if fruit are re‐used.

3. In a field cage, females were presented simultaneously with fruit previously exposed to 25 females that were also allowed to oviposit and engage in the putative marking behaviour, and control fruit on which females were allowed only to oviposit. The occurrence of host marking reduced a female's propensity to oviposit from 46% to just over 10%, consistent with the competition intensity signal hypothesis only.

4. In a laboratory assay, the duration of host marking was correlated positively with the size of a female's clutch. This result, also consistent with the competition intensity signal hypothesis, suggests that the amount of marking pheromone on a fruit is a reliable indicator of the number of eggs already deposited within.

5. In a second field‐cage experiment, females were allowed to mark on fruit for 0, 10, 20, or 30 min and fruit were presented to test females. Whether or not females alighted on a particular host was not affected by the duration of marking; however, the frequency of both ovipositor probing and egg deposition decreased with increasing duration of marking. Consistent with the competition intensity signal hypothesis, this result suggests that the host mark permits females to assess the level of competition that a clutch will incur within re‐used fruit.
Male indifference to female traits in an arctiid moth (Utetheisa ornatrix)
Authors: Iyengar Vikram K. , Eisner Thomas
Published: May 2004

Abstract.  1. Female Utetheisa ornatrix (Lepidoptera: Arctiidae) mate selectively with large males able to transmit sizeable quantities of nutrient and defensive pyrrolizidine alkaloid with the spermatophore. The female gauges male size indirectly by assessment of the male's courtship pheromone.

2. Male Utetheisa invest upward of 10% of body mass in spermatophore production, and could therefore have been expected to be choosy; however, when offered females differing in alkaloid content, body mass, or mating status, males showed disregard of these parameters, both in their choice of partner and in their allocation of resources to the spermatophore.

3. It is concluded that Utetheisa males do not have the option to select females by comparison shopping. Females broadcast their attractant pheromone for less than an hour per day. Given this time constraint and the potentially high cost of mate localisation, males may have no choice but to mate on an opportunistic basis.
Morphometric analysis of shank‐to‐flute ratio in rotary nickel–titanium files
Authors: Biz M. T. , Figueiredo J. A. P.
Published: May 2004

Aim  To evaluate the shank‐to‐flute ratio in rotary nickel–titanium (Ni‐Ti) instruments.

Methodology  The cutting portion of 15 size 30 Ni‐Ti rotary instruments, ProFile .04, ProFile .06, Pow R .02, Pow R .04 and Quantec series 2000, were examined. The handles of the instruments were fixed to a bench and supported by a removable resin base. The cutting portion was then manually abraded with abrasive strips along one aspect of their length. All instruments were fixed in a stub that permitted the adaptation and inspection of six instruments at the same time. A scanning electron microscope (SEM; Phillips model XL 20; Eindhmoven, the Netherlands) at ×60 magnification was used to collect cross‐sectional measurements of the shank and the flutes at the first, third and fifth flutes from the tip. The software autocad 2000 was used to measure these areas.

Results  The shank percentage value was, on average, equal to or greater than the flute percentage value at the sites analyzed. A regular and proportional pattern of increase of shank and flute measurements, as well as the ratio between them, was preserved. There was no significant difference between instruments and between flute sites on the same instrument (P > 0.05). However, the Quantec instruments had a flute area twice the flute area of the other instruments.

Conclusions The instruments had a shank percentage measurement value equal to or greater than the flute percentage value; the cross‐sectional shank‐to‐flute ratio was preserved. The instruments had similar shank areas, but the flute area of the Quantec instruments was twice their shank area; i.e. the design of the Quantec files provides longitudinal reinforcement by means of a gain in flute area.
Accuracy of the DTC torque control motor for nickel‐titanium rotary instruments
Authors: Yared G. , Kulkarni G. K.
Published: May 2004

Aim  To determine the torque output and examine the accuracy of five identical DTC torque control (DTC) motors.

Methodology  Torque settings on the DTC motors for the .04 ISO ProFile nickel‐titanium (NiTi) rotary instruments were evaluated at 350 r.p.m. A modification of the ANSI/ADA Specification No. 28 setup for the evaluation of torsional properties of endodontic instruments was used. A handpiece was attached to the motor and gripped with a vice. An .07 Orifice Shaper, size 50, was inserted in the handpiece. The instrument tip was clamped in a chuck connected to a torque sensor. The motor was then activated to rotate the instrument in a clockwise direction until reversal of the rotation occurred. The actual torque generated at the reversal of the rotation was recorded. Ten tests were carried out at each torque setting. A new Orifice Shaper was used for each test. The means of the actual torque values generated by the motors at the different torque settings were compared with the torque values claimed by the manufacturer and analysed using analysis of variance and the Student's t‐test (α = 0.05).

Results  The actual torque values were significantly higher than the torque preset on the motors (P < 0.0001) and did not differ significantly among the motors (P > 0.05).

Conclusions  The actual torque deviated from the preset torque and was higher than the reported torque at fracture of several NiTi rotary instruments. The usefulness of these motors is questionable.
A complex of the Escherichia coli cell division proteins FtsL, FtsB and FtsQ forms independently of its localization to the septal region
Authors: Buddelmeijer Nienke , Beckwith Jon
Published: May 2004

Summary Three membrane proteins required for cell division in Escherichia coli, FtsQ, FtsL and FtsB, localize to the cell septum. FtsL and FtsB, which each contain a leucine zipper‐like sequence, are dependent on each other for this localization, and each of them is dependent on FtsQ. However, FtsQ is found at the cell division site in the absence of FtsL and FtsB. FtsQ, in turn, requires FtsK for its localization. Here, we show that FtsL, FtsB and FtsQ form a complex in vivo. Strikingly, this complex forms in the absence of FtsK, which is required for the localization of all three proteins to the mid‐cell. These findings indicate that the FtsL, FtsB, FtsQ interactions can take place in cells before movement to the mid‐cell and that migration to this position might occur only after the formation of the complex. Evidence indicating the regions of the three proteins involved in complex formation is presented. These findings provide the first example of preassembly of a subcomplex of cell division proteins before their localization to the septal region.
Regulated site‐specific recombination of the she pathogenicity island of Shigella flexneri
Authors: Sakellaris Harry , Luck Shelley N. , Al‐Hasani Keith , Rajakumar Kumar , Turner Sally A. , Adler Ben
Published: May 2004

Summary The she pathogenicity island (PAI) is a chromosomal, laterally acquired, integrative element of Shigella flexneri that carries genes with established or putative roles in virulence. We demonstrate that spontaneous, precise excision of the element from its integration site in the 3′ terminus of the pheV tRNA gene is mediated by an integrase gene (int) and a gene designated rox (regulator of excision), both of which are carried on the she PAI. Integrase‐mediated excision occurs via recombination between a 22 bp sequence at the 3′ terminus of pheV and an imperfect direct repeat at the pheV‐distal boundary of the PAI. Excision leads to the formation of a circular episomal form of the PAI, reminiscent of circular excision intermediates of other mobile elements that are substrates for lateral transfer processes such as conjugation, packaging into phage particles and recombinase‐mediated integration into the chromosome. The circle junction consists of the pheV‐proximal and pheV‐distal boundaries of the PAI converging on a sequence identical to 22 bp at the 3′ terminus of pheV. The isolated circle was transferred to Escherichia coli where it integrated specifically into phe tRNA genes, as it does in S. flexneri, independently of recA. We also demonstrate that Rox stimulates, but is not essential for, excision of the she PAI in an integrase‐dependent manner. However, Rox does not stimulate excision by activating the transcription of the she PAI integrase gene, suggesting that it has an excisionase function similar to that of a related protein from the P4 satellite element of phage P2.
Screening for synthetic lethal mutants in Escherichia coli and identification of EnvC (YibP) as a periplasmic septal ring factor with murein hydrolase activity
Authors: Bernhardt Thomas G. , De Boer Piet A. J.
Published: May 2004

Bacterial cytokinesis is driven by the septal ring apparatus, the assembly of which in Escherichia coli is directed to mid‐cell by the Min system. Despite suffering aberrant divisions at the poles, cells lacking the minCDE operon (Min–) have an almost normal growth rate. We developed a generally applicable screening method for synthetic lethality in E. coli, and used it to select for transposon mutations (slm) that are synthetically lethal (or sick) in combination with ΔminCDE. One of the slm insertions mapped to envC (yibP), proposed to encode a lysostaphin‐like, metallo‐endopeptidase that is exported to the periplasm by the general secretory (Sec) pathway. Min– EnvC– cells showed a severe division defect, supporting a role for EnvC in septal ring function. Accordingly, we show that an EnvC–green fluorescent protein fusion, when directed to the periplasm via the twin‐arginine export system, is both functional and part of the septal ring apparatus. Using an in‐gel assay, we also present evidence that EnvC possesses murein hydrolytic activity. Our results suggest that EnvC plays a direct role in septal murein cleavage to allow outer membrane constriction and daughter cell separation. By uncovering genetic interactions, the synthetic lethal screen described here provides an attractive new tool for studying gene function in E. coli.
Homozygosity at the MTL locus in clinical strains of Candida albicans: karyotypic rearrangements and tetraploid formation†
Authors: Legrand Melanie , Lephart Paul , Forche Anja , Mueller Frank‐Michael C. , Walsh T. , Magee P.T. , Magee Beatrice B.
Published: May 2004

One hundred and twenty Candida albicans clinical isolates from the late 1980s and early 1990s were examined for homozygosity at the MTL locus. Of these, 108 were heterozygous (MTLa/MTLα), whereas seven were MTLa and five were MTLα. Five of the homozygous isolates were able to switch to the opaque cell morphology, while opaque cells were not detectable among the remaining seven. Nevertheless, all but one of the isolates homozygous at the MTL locus were shown to mate and to yield cells containing markers from both parents; the non‐mater was found to have a frameshift in the MTLα1 gene. In contrast to Saccharomyces cerevisiae, C. albicans homozygotes with no active MTL allele failed to mate rather than mating as a cells. There was no correlation between homozygosity and fluconazole resistance, mating and fluconazole resistance or switching and fluconazole resistance, in part because most of the strains were isolated before the widespread use of this antifungal agent, and only three were in fact drug resistant. Ten of the 12 homozygotes had rearranged karyotypes involving one or more homologue of chromosomes 4, 5, 6 and 7. We suggest that karyotypic rearrangement, drug resistance and homozygosity come about as the result of induction of hyper‐recombination during the infection process; hence, they tend to occur together, but each is the independent result of the same event. Furthermore, as clinical strains can mate and form tetraploids, mating and marker exchange are likely to be a significant part of the life cycle of C. albicans in vivo.
Role of KatG catalase‐peroxidase in mycobacterial pathogenesis: countering the phagocyte oxidative burst
Authors: Ng Vincent H. , Cox Jeffery S. , Sousa Alexandra O. , MacMicking John D. , McKinney John D.
Published: May 2004

Reactive nitrogen species (RNS) play an essential role in host defence against Mycobacterium tuberculosis (MTB) in the mouse model of tuberculosis (TB), as evidenced by the increased susceptibility of mice deficient in the inducible isoform of nitric oxide synthase (NOS2). In contrast, the role of reactive oxygen species (ROS) in protection against MTB is less clear, and mice defective in the ROS‐generating phagocyte NADPH oxidase (Phox) are relatively resistant. This suggests that MTB might possess efficient mechanisms to evade or counter the phagocyte oxidative burst, effectively masking the impact of this host defence mechanism. In order to assess the role of ROS detoxification pathways in MTB virulence, we generated a katG null mutant of MTB, deficient in the KatG catalase‐peroxidase‐peroxynitritase, and evaluated the mutant's ability to replicate and persist in macrophages and mice. Although markedly attenuated in wild‐type C57Bl/6 mice and NOS2–/– mice, the ΔkatG MTB strain was indistinguishable from wild‐type MTB in its ability to replicate and persist in gp91Phox–/– mice lacking the gp91 subunit of NADPH oxidase. Similar observations were made with murine bone marrow macrophages infected ex vivo: growth of the ΔkatG MTB strain was impaired in macrophages from C57Bl/6 and NOS2–/– mice, but indistinguishable from wild‐type MTB in gp91Phox–/– macrophages. These results indicate that the major role of KatG in MTB pathogenesis is to catabolize the peroxides generated by the phagocyte NADPH oxidase; in the absence of this host antimicrobial mechanism, KatG is apparently dispensable.
Historical catchment changes and temporal impact on sediment of the receiving basin, Port Jackson, New South Wales
Authors: TAYLOR S. E. , BIRCH G. F. , LINKS F.
Published: May 2004

Port Jackson (Sydney Harbour) is a major deep‐water estuary on the central New South Wales coast and is surrounded by a highly urbanised and industrialised catchment. Concentrations of trace metals and organochlorine pesticide residues are high in sediment in the upper reaches of the estuary. Historical fluxes of contaminants into the estuary were determined by radio‐isotopic dating of 12 sediment profiles in nine highly contaminated embayments. The onset of contamination in estuarine sediment was correlated with catchment‐wide urbanisation and industrialisation of Sydney. Contamination of estuarine sediment in Port Jackson first occurred ca 1860, near the present central business district and spread westward and northward. Trace‐metal contamination was initiated ∼20 years after the commencement of industry in the subcatchments, and a rapid increase in trace‐metal concentrations corresponds closely with maximum industrial activity in these catchments. Organochlorine pesticide residues occur in estuarine sediments 40–50 years after the onset of contamination by trace metals and their appearance closely corresponds with the manufacturing and application history of these compounds. The transit time of contaminants from fluvial catchment to incorporation in estuarine sediment is short (probably <2 years). Trace metals in sediment reached maximum concentrations in 1970 and a subsequent decrease in concentrations in the upper estuary reflects relocation of industry away from the estuary foreshores and tighter controls on industrial discharges. In Middle Harbour and the lower estuary, trace‐metal concentrations continue to increase, due to the comparatively recent increases in commercial and industrial growth in these areas.
Variety, age and origin of zircons in the mid‐Cenozoic Westonia Formation, southwestern Yilgarn Craton, Western Australia
Authors: De BROEKERT P. P. , WILDE S. A. , KENNEDY A. K.
Published: May 2004

The Westonia Formation comprises clayey quartz sand commonly exposed in interfluve breakaways in the southwestern Yilgarn Craton, Western Australia. As is typical of Cenozoic sediments in the region, it is texturally immature, poorly stratified and unfossiliferous, making it difficult to distinguish from the underlying deeply weathered Archaean granite. In order to verify the difference in origin and elucidate provenance, the varietal properties and U–Pb ages of zircons from the Westonia Formation and underlying granitic saprolite were compared. Zircons from the Westonia Formation comprise 11 distinct morphological varieties, seven of which are not present within the granitic saprolite. SHRIMP U–Pb ages of zircons from the granitic saprolite range from 2657 ± 13 to 2554 ± 10 Ma, corresponding to published age determinations of zircons from the Darling Range Batholith. Angular zircons from the Westonia Formation range in age from 2898 ± 12 to 2631 ± 11 Ma, reflecting a mixed provenance including local granitic rocks, and possibly greenstones in adjacent parts of the Yilgarn Craton. Rounded zircons from the Westonia Formation range in age from 1144 ± 38 to 467 ± 16 Ma (Late Mesoproterozoic – Early Palaeozoic), similar to detrital zircons from the Jarrahdale bauxite deposit and various stratigraphic levels in the Perth Basin. The Late Mesoproterozoic – Early Palaeozoic zircons at East Yornaning and Jarrahdale most likely resulted from burial of the southwestern Yilgarn Craton by sediment sourced from the Proterozoic Albany–Fraser–Wilkes and Pinjarra Orogens during the Early Permian glaciation, or during an earlier episode of mountain building associated with the final stages of the Pinjarra Orogeny. Most of the sedimentary cover was then reworked into the evolving Perth Basin during the Late Permian – Early Cretaceous. Remaining pockets on the craton were repeatedly recycled, leaving only the most chemically and physically resistant components, such as rounded zircons, in the Westonia Formation.
THE RETURNS TO EDUCATION AND TRAINING: EVIDENCE FROM THE MALAYSIAN FAMILY LIFE SURVEYS
Authors: Chung Tsung‐Ping
Published: May 2004

Abstract.  The main purpose of this paper is to investigate the private returns to education and training in the 1980s for a random sample of women in Malaysia. I estimate a Mincer type earnings function, augmented by information on the women's training experience. The results indicate that there are positive and economically significant returns to education and training. I also investigate the determinants of training and find that training participation is positively related to educational attainment, while if women are credit‐constrained they are significantly less likely to undertake training.
TRADE AND WAGE INEQUALITY: THE HONG KONG CASE
Authors: Fan C. Simon , Cheung Kui‐yin
Published: May 2004

Abstract.  This paper examines the effects of Hong Kong–mainland China trade on the wage inequality in Hong Kong. Because of the large volume of trade and the large income disparity between these two regions, this empirical study provides a good test of the theories on North–South trade. The econometric analyses show that the relative wage between the skilled and unskilled workers in Hong Kong increased as the share of the volume of Hong Kong's trade with mainland China in Hong Kong's total trade volume rose.
Welfare Reform and the Labour Supply of Lone Parents in Australia: A Natural Experiment Approach
Authors: Doiron Denise J.
Published: May 2004

Large shifts in the labour supply of lone parents in Australia were observed between 1986 and 1990. Changes in the observed characteristics of lone parents explain only a small portion of these shifts. Propensity score matching and difference‐in‐differences are used to estimate the effects of the substantial policy shifts implemented in 1987. Control groups are constructed from the sample of married mothers. Results suggest that the policy reforms caused a substantial increase in the employment of lone parents while causing a reduction in the hours of work among the workers.
The Race that Stops a Nation: The Demand for the Melbourne Cup
Authors: Narayan Paresh Kumar , Smyth Russell
Published: May 2004

This article uses the bounds testing procedure to cointegration, within an autoregressive distributed lag framework to estimate the determinants of attendance at the Melbourne Cup from its inception from 1861 to 2002. Following the literature on the demand for professional team sports, attendance is specified as a function of economic, demographic and race‐specific factors. The main findings are that real income and population size are the major determinants of attendance in the long run, while in the short run the weather is the most important factor explaining attendance.