bluuebunny/crossref_metadata_2025_split huggingface dataset:
The C : N : P stoichiometry of autotrophs – theory and observations
Authors: Ågren Göran I. 
Published: February 2004

AbstractEvolution has set biochemical constraints on the chemical composition of living organisms. These constraints seem to lead to increases in N : C and P : C ratios with increasing relative growth rate for all types of organisms. The N : P ratio also seems to decrease with relative growth rate for heterotrophs whereas autotrophs may show a more complex behaviour. Here I will show that, from biochemical considerations, N : C should increase linearly and P : C quadratically with relative growth rate in autotrophs with the consequence that N : P increases at low relative growth rates, passes a maximum and then decreases at high relative growth rates. These predictions are verified against observations for a freshwater alga (Selenastrum minutum) and a tree seedling (Betula pendula). Changes in temperature, light or other factors that affect the growth rate of autotrophs interact with nutrient supply in such a way that there are no simple rules for as to how N : P will change.
Uses and abuses of fractal methodology in ecology
Authors: Halley J. M. , Hartley S. , Kallimanis A. S. , Kunin W. E. , Lennon J. J. , Sgardelis S. P. 
Published: February 2004

AbstractFractals have found widespread application in a range of scientific fields, including ecology. This rapid growth has produced substantial new insights, but has also spawned confusion and a host of methodological problems. In this paper, we review the value of fractal methods, in particular for applications to spatial ecology, and outline potential pitfalls. Methods for measuring fractals in nature and generating fractal patterns for use in modelling are surveyed. We stress the limitations and the strengths of fractal models. Strictly speaking, no ecological pattern can be truly fractal, but fractal methods may nonetheless provide the most efficient tool available for describing and predicting ecological patterns at multiple scales.
Species overlap, speciation and the evolution of aggregation pheromones in bark beetles
Authors: Symonds Matthew R. E. , Elgar Mark A. 
Published: February 2004

AbstractTheoretical predictions suggest that species‐specific signals used in the attraction of mates should evolve to reduce the risk of mismating and hybridization. These predictions lead to the hypothesis that the signals of spatially overlapping (i.e. sympatric or syntopic) species should differ more substantially than those of non‐overlapping species. Earlier studies have tested this prediction for auditory and visual signals. Here we test the hypothesis using olfactory signals, specifically the aggregation pheromones of species from two genera of bark beetles, Dendroctonus and Ips. We found no direct evidence from within these genera regarding the fact that the chemical blends that make up these pheromones differ more substantially in species that overlap in their geographical ranges and/or host‐tree use than in allopatric taxa. However, when comparing between genera, the pheromones of overlapping species appear to be more similar than non‐overlapping species. We hypothesize that the species of host tree utilized by the beetles may have some influence on their pheromone blends. Additionally, within genera, species that overlap in host use tend to be more closely related than species that use different hosts. These results may provide indirect evidence for an effect of species overlap on the evolution of bark beetle pheromones.
Population genetics of transgene containment
Authors: Haygood Ralph , Ives Anthony R. , Andow David A. 
Published: February 2004

AbstractSeveral strategies have been proposed for creating transgenic cultivars from which transgene escape to wild relatives would seem unlikely; for example, to impede escape through pollen, a transgene could be inserted into chloroplast DNA (cpDNA), which in many crops is rarely transmitted through pollen. None of these strategies would be failsafe; for example, the rate of cpDNA transmission through pollen may be low but non‐zero in many crops. Here, we study how the probability distribution of escape time depends on the rates of pollen and seed flow from the crop to wild populations, the number and sizes of the wild populations, the selection coefficient for the transgene, and a leakage parameter characteristic of the strategy, for example, the rate of cpDNA transmission through pollen. We find that even with a leakage parameter as small as 10−3, the probability of escape within as few as 10 generations could be appreciable.
Australian and US interest rate swap markets: comparison and linkages
Authors: In Francis , Fang Victor , Brown Rob 
Published: February 2004

AbstractWe investigate and compare the determinants of US and Australian interest rate swap spreads and the linkages between these markets. The slope of the risk‐free term structure is the most significant determinant and its importance is greater for longer terms to maturity. Interest rate levels and, in Australia, the default premium also have some impact. The influences of interest rate volatility, the liquidity premium and (in the USA) the default premium are small or negligible. We hypothesise, and our evidence confirms, that the US swap market significantly affects the Australian swap market but not vice‐versa.
Size and book to market effects and the Fama French three factor asset pricing model: evidence from the Australian stockmarket
Authors: Gaunt Clive 
Published: February 2004

AbstractThe present study adds to the sparse published Australian literature on the size effect, the book to market (BM) effect and the ability of the Fama French three factor model to account for these effects and to improve on the asset pricing ability of the Capital Asset Pricing Model (CAPM). The present study extends the 1981–1991 period examined by Halliwell, Heaney and Sawicki (1999) a further 10 years to 2000 and addresses several limitations and findings of that research. In contrast to Halliwell, Heaney and Sawicki the current study finds the three factor model provides significantly improved explanatory power over the CAPM, and evidence that the BM factor plays a role in asset pricing.
Examining the forward pricing function of the Australian equity index futures contract
Authors: Ivanovic Irena , Howley Peter 
Published: February 2004

AbstractThe relationship between the Australian equity index futures and spot prices is examined. Tests indicate that futures prices with one, two and three months to maturity are unbiased predictors of the spot and hence provide an efficient hedging mechanism for Australian equity index market participants, while six‐, nine‐ and twelve‐month futures prices are biased predictors of spot prices, indicating that speculative opportunities may exist in futures contracts for these time spreads. An analysis of the short‐run dynamic properties of the long‐run equilibrium relationship found that for all time spreads the futures prices respond to changes in the long‐run equilibrium, and for the twelve‐month contract, both futures and spot prices adjust to return to the long‐run equilibrium.
Reflexive orienting in response to eye gaze and an arrow in children with and without autism
Authors: Senju Atsushi , Tojo Yoshikuni , Dairoku Hitoshi , Hasegawa Toshikazu 
Published: February 2004

Background:  This study investigated whether another person's social attention, specifically the direction of their eye gaze, and a non‐social directional cue, an arrow, triggered reflexive orienting in children with and without autism in an experimental situation.Methods:  Children with autism and typically developed children participated in one of two experiments. Both experiments involved the localization of a target that appeared to the left or right of the fixation point. Before the target appeared, the participant's attention was cued to the left or right by either an arrow or the direction of eye gaze on a computerized face.Results:  Children with autism were slower to respond, which suggests a slight difference in the general cognitive ability of the groups. In Experiment 1, although the participants were instructed to disregard the cue and the target was correctly cued in only 50% of the trials, both groups of children responded significantly faster to cued targets than to uncued targets, regardless of the cue. In Experiment 2, children were instructed to attend to the direction opposite that of the cues and the target was correctly cued in only 20% of the trials. Typically developed children located targets cued by eye gaze more quickly, while the arrow cue did not trigger such reflexive orienting in these children. However, both social and non‐social cues shifted attention to the cued location in children with autism.Conclusion:  These results indicate that eye gaze attracted attention more effectively than the arrow in typically developed children, while children with autism shifted their attention equally in response to eye gaze and arrow direction, failing to show preferential sensitivity to the social cue. Difficulty in shifting controlled attention to the instructed side was also found in children with autism.
Maternal sensitivity and infant triadic communication
Authors: Peter Hobson R. , Patrick Matthew P.H. , Crandell Lisa E. , García Pérez Rosa M. , Lee Anthony 
Published: February 2004

Background and method:  The aim of this study was to examine whether a mother's sensitivity towards her one‐year‐old infant is related to the infant's propensity to engage in ‘triadic’ relations – that is, to orientate to an adult's engagement with objects and events in the world, for example in sharing experiences with an adult. In order to determine that any effects were specific to infants’ behaviour in the interpersonal domain, we also tested their performance on tests of understanding means–ends relations and object permanence.Results:  The results were that high maternal sensitivity and low intrusiveness correlated with high levels of infant triadic interpersonal engagement with a stranger vis‐à‐vis performance on the non‐social tasks. There was also suggestive evidence that maternal sensitivity might be related to infants’ propensity to share experiences with the mother. Exploratory analyses revealed that these findings held up when the effects of maternal socio‐economic status and ethnic group were taken into account; and there was some indication that the effects of maternal intrusiveness on infant profiles of performance were more marked for mothers who did not have a partner.Conclusion:  There is a specific relation between maternal sensitivity and one‐year‐old infants’ propensity to engage with someone else in relation to the world.
The construction and validation of a new scale for measuring emotional response style in adolescents
Authors: Clarbour Jane , Roger Derek 
Published: February 2004

Background:  Research on children's emotional behaviour has been hampered by the lack of psychometric assessment scales. The present study reports on the construction and validation of a new self‐report instrument to measure the emotional response styles of adolescents.Method:  Exploratory and confirmatory factor analyses were carried out on the responses of three samples of adolescents aged between 11 and 14 years (total = 609) to an item pool derived from a scenario study. In addition to assessing reliability, the final form of the questionnaire was concurrently validated using a variety of related psychometric instruments as well as teacher ratings of pupils’ behaviour.Results:  The factor analyses of the item pool yielded three independent factors labelled social anxiety, malevolent aggression, and social self‐esteem. These categories correspond closely to the three dimensions that have emerged consistently from studies of children's temperament, labelled inhibited, undercontrolled and well‐adjusted. The three factors comprising the final Emotional Behaviour Scale (EBS) all demonstrated satisfactory internal (coefficient alpha) and re‐test reliability. Concurrent validation showed that the three factors were related in predictable ways to other related constructs, and comparisons with teacher ratings of pupils confirmed the relationship between the EBS subscales and children's actual social and emotional behaviour.Conclusion:  The new scale offers a valid and reliable instrument for assessing adolescent emotional behaviour, and current work is aimed at extending the research to the assessment of young offenders.
Psychosocial functioning of young children with learning problems
Authors: Gadeyne Els , Ghesquière Pol , Onghena Patrick 
Published: February 2004

Background:  In this study, psychosocial functioning of different groups of young children with learning problems was investigated using a diverse set of psychosocial variables (including behaviour problems, academic motivation, social preference, and self‐concept).Methods:  For this purpose, children with low academic achievement, with a specific learning disability based on an IQ–achievement discrepancy, and with a specific learning disability based on an achievement discrepancy, were selected out of 276 children of the first grade of regular primary schools. By means of multivariate analyses, their psychosocial functioning was compared to the functioning of children without learning problems.Results:  The total set of psychosocial variables was able to discriminate between children with and without learning problems, with medium effect size. Attention problems as reported by the teachers turned out to be the most important single psychosocial predictor for group discrimination. However, results varied according to the type of learning problem and the type of psychosocial problem. Children with a specific reading/spelling disability and children with low general academic achievement differed most from their peers without learning problems with regard to their psychosocial functioning. Poor cognitive self‐concept was related primarily to low academic achievement, poor learning motivation might be specific for math problems, and a low social preference score seemed most characteristic of children with a specific learning disability.Conclusions:  Studying several psychosocial variables simultaneously in different groups of children with learning problems leads to a further refinement of the current knowledge.
Comorbidity of PTSD and depression among refugee children during war conflict
Authors: Thabet Abdel Aziz Mousa , Abed Yehia , Vostanis Panos 
Published: February 2004

Background:  We examined the prevalence and nature of comorbid post‐traumatic stress reactions and depressive symptoms, and the impact of exposure to traumatic events on both types of psychopathology, among Palestinian children during war conflict in the region.Methods:  The 403 children aged 9–15 years, who lived in four refugee camps, were assessed by completing the Gaza Traumatic Events Checklist, the Child Post Traumatic Stress Reaction Index (CPTSD‐RI), and the Short Mood and Feelings Questionnaire (MFQ).Results:  Children reported experiencing a wide range of traumatic events, both direct experience of violence and through the media. CPTSD‐RI and MFQ scores were significantly correlated. Both CPTSD‐RI and MFQ scores were independently predicted by the number of experienced traumatic events, and this association remained after adjusting for socioeconomic variables. Exposure to traumatic events strongly predicted MFQ scores while controlling for CPTSD‐RI scores. In contrast, the association between traumatic events and CPTSD‐RI scores, while controlling for MFQ scores, was weak. The CPTSD‐RI items whose frequency was significantly associated with total MFQ scores were: sleep disturbance, somatic complaints, constricted affect, impulse control, and difficulties in concentration. However, not all remaining CPTSD‐RI items were significantly associated with exposure to traumatic events, thus raising the possibility that the association between depression and PTSD was due in part to symptom overlap.Conclusions:  Children living in war zones are at high risk of suffering from PTSD and depressive disorders. Exposure to trauma was not found to have a unique association with PTSD. The relationship between PTSD and depressive symptomatology requires further investigation.
Children's perspectives on their relationships with their nonresident fathers: influences, outcomes and implications
Authors: Dunn Judy , Cheng Helen , O'Connor Thomas G. , Bridges Laura 
Published: February 2004

Background:  Children's relationships with their nonresident fathers, and associations between these relationships, children's relationships with mothers and stepfathers, and the children's adjustment were studied in 162 children from single‐parent and stepfamilies, selected from a representative community sample in the UK, studied at 2 time points two years apart.Method:  Children were interviewed about their relationships with their nonresident fathers, mothers and stepfathers; mothers reported on children's adjustment, and other family variables.Results:  Positive child–nonresident father relationships were correlated with (a) contact between child and father, (b) the quality of the mother–child relationship, and (c) the frequency of contact between the mother and her former partner. Conflict between child and father was correlated with conflict between child and mother, and child and stepfather. Child–nonresident father contact and relationships were stable over 2 years, and related to children's adjustment; these associations were stronger for children from single‐parent families than for those with stepfathers, and for those whose mothers had been first pregnant as teenagers.Conclusions:  Associations between the quality of children's relationships with nonresident fathers and their adjustment need to be considered within the framework of the larger family system; child–father relationships are particularly important for children from ‘high risk’ families.
Juvenile arrest: a cross‐cultural comparison
Authors: Vermeiren Robert , Jones Stephanie M. , Ruchkin Vladislav , Deboutte Dirk , Schwab‐Stone Mary 
Published: February 2004

Background:  Cross‐national studies describing the psychopathological characteristics of arrested adolescents are virtually non‐existent. Such studies are important because they have implications for national policy on arrest, case‐management, and future research.Method:  To address this issue, self‐report surveys administered to representative groups of 12‐ to 16‐year‐old adolescents in New Haven, USA (N = 1138) and Antwerp, Belgium (N = 627) were compared. A number of internalizing and deviant behavior variables were compared between controls (C), non‐arrested antisocial (NA), and arrested antisocial (AR) participants.Results:  Similar cross‐national arrest rates and levels of antisocial behavior were found. NA and AR youths in both countries reported more internalizing problems, except for anxiety, and more deviant characteristics. Contrary to expectations, the level of depression was not higher in AR compared to NA youth when differences in antisocial behavior between NA and AR were controlled. Also unexpected, arrest showed an independent association with a number of deviant behavior variables.Conclusions:  Further research should investigate the underlying mechanisms of these associations, as this insight would be useful for developing future intervention and prevention programs, as well as for developing future national policies regarding juvenile antisocial behavior.
Heritability of attention problems in children: longitudinal results from a study of twins, age 3 to 12
Authors: Rietveld M.J.H. , Hudziak J.J. , Bartels M. , van Beijsterveldt C.E.M. , Boomsma D.I. 
Published: February 2004

Background:  Twin studies of childhood behavior problems support the conclusion that individual differences in impulsivity, hyperactivity, and inattention are largely due to genetic influences. Non‐genetic variation is due to environmental influences that are unique to the individual, and possibly to rater contrast effects. In the present longitudinal twin study, we report on the size of genetic and environmental effects on individual differences in attention problems at ages 3, 7, 10 and 12 years.Methods:  Mothers were asked to complete the CBCL for their twin offspring when the children were 3 (n = 11,938), 7 (n = 10,657), 10 (n = 6,192), and 12 years old (n = 3,124). We focus on the Overactivity (OA) scale in the Child Behavior Checklist (CBCL/2–3), and on the Attention Problem (AP) scale of the CBCL/4–18. The data were analyzed using longitudinal structural equation modeling.Results:  Broad heritability of OA and AP is estimated at nearly 75%, at each age. A contrast effect was observed at age 3 only. The results revealed less stability of OA at age 3 to AP at age 7 (r = .40), compared to the stability from AP at age 7 and beyond (r = .70). Genetic effects explained between 76% and 92% of the covariance between OA and AP.Conclusions:  OA and AP are highly heritable at all ages in both genders. The same set of genes appears to be expressed in boys and girls. The size of genetic and environmental contributions remains the same across the ages studied. Stability in OA and AP is accounted for by genetic influences. Children who do not display OA or AP at a given age are unlikely to develop these problems at a subsequent age.
Familial clustering of latent class and DSM‐IV defined attention‐deficit/hyperactivity disorder (ADHD) subtypes
Authors: Rasmussen Erik R. , Neuman Rosalind J. , Heath Andrew C. , Levy Florence , Hay David A. , Todd Richard D. 
Published: February 2004

Background:  Findings from family and twin‐based studies of Attention Deficit/Hyperactivity Disorder (ADHD) have indicated that inattentive and combined subtypes cluster together among sibling pairs who both express ADHD symptoms. The current report examines the familial clustering of ADHD subtypes, defined according to latent class and DSM‐IV criteria, in a general population sample of 2,848 Australian twins, 1,013 of their non‐twin siblings and 4,036 female twins from Missouri, USA. Significant clustering of DSM‐IV inattentive and combined subtypes, and significant clustering of the same latent classes among siblings was predicted.Method:  Logistic regression was used to assess 1) the clustering of same and different subtype combinations among twin and twin‐sibling pairs and 2) whether genetic influences contribute significantly to the observed patterns of subtype combinations among siblings.Results:  With the exception of the DSM‐IV hyperactive‐impulsive subtype and the severe hyperactive‐impulsive latent class, all other sibling DSM‐IV and latent class ADHD subtypes consistently exhibited significant same‐subtype clustering with MZ probands, DZ probands and their siblings in both samples. Furthermore, a significant genetic influence contributing to subtype concordance was detected for every DSM‐IV subtype excluding hyperactive‐impulsive, and for all eight latent classes. While some instances of significant different‐subtype clustering among siblings was observed across both classification systems and samples, the particular subtype combinations involved were largely inconsistent across samples and no significant genetic influences contributing towards these discordant subtype combinations were detected.Conclusions:  For both DSM‐IV and latent class subtypes, the overall pattern of findings in both samples indicated significant familial clustering of same‐subtype combinations and significant genetic influences contributing to these patterns of subtype concordance, despite important sample differences. These findings further extend previous work and are most consistent with the presence of multiple independent forms of ADHD.