67 results on '"J. Dyer"'
Search Results
2. Geometry of certain finite Coxeter group actions
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Gustav I. Lehrer and M. J. Dyer
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Group (mathematics) ,General Mathematics ,010102 general mathematics ,Coxeter group ,Diagonal ,Geometry ,010103 numerical & computational mathematics ,01 natural sciences ,Stratification (mathematics) ,Character (mathematics) ,Conjugacy class ,Reflection (mathematics) ,Fundamental domain ,0101 mathematics ,Mathematics - Abstract
We determine a fundamental domain for the diagonal action of a finite Coxeter group $W$ on $V^{\oplus n}$, where $V$ is the reflection representation. This is used to give a stratification of $V^{\oplus n}$, which is respected by the group action, and we study the geometry, topology and combinatorics of this stratification. These ideas are used to obtain results on the classification of root subsystems up to conjugacy, as well as a character formula for $W$.
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- 2018
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3. Structure and resilience of bald eagle roost networks
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Bryan D. Watts and Rodney J. Dyer
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0106 biological sciences ,military ,Computer science ,business.industry ,Environmental resource management ,military.commander ,Bald eagle ,Resilience (network) ,business ,010603 evolutionary biology ,01 natural sciences ,010605 ornithology ,Nature and Landscape Conservation - Published
- 2018
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4. Sex-specific graphs: Relating group-specific topology to demographic and landscape data
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Philip Bertrand, Rodney J. Dyer, Jeff Bowman, Paul J. Wilson, and Micheline Manseau
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Male ,0106 biological sciences ,0301 basic medicine ,Population Dynamics ,Metapopulation ,Environment ,Biology ,Network topology ,010603 evolutionary biology ,01 natural sciences ,Life history theory ,03 medical and health sciences ,biology.animal ,Genetic variation ,Mustelidae ,Genetics ,Animals ,Ecology, Evolution, Behavior and Systematics ,Ontario ,Ecology ,Vertebrate ,15. Life on land ,Graph ,Genetics, Population ,030104 developmental biology ,Genetic structure ,Biological dispersal ,Female ,Animal Distribution - Abstract
Sex-specific genetic structure is a commonly observed pattern among vertebrate species. Facing differential selective pressures, individuals may adopt sex-specific life history traits that ultimately shape genetic variation among populations. Although differential dispersal dynamics are commonly detected in the literature, few studies have used genetic structure to investigate sex-specific functional connectivity. The recent use of graph theoretic approaches in landscape genetics has demonstrated network capacities to describe complex system behaviours where network topology represents genetic interaction among subunits. Here, we partition the overall genetic structure into sex-specific graphs, revealing different male and female dispersal dynamics of a fisher (Pekania [Martes] pennanti) metapopulation in southern Ontario. Our analyses based on network topologies supported the hypothesis of male-biased dispersal. Furthermore, we demonstrated that the effect of the landscape, identified at the population level, could be partitioned among sex-specific strata. We found that female connectivity was negatively correlated with snow depth, whereas connectivity among males was not. Our findings underscore the potential of conducting sex-specific analysis by identifying landscape elements or configuration that differentially promotes or impedes functional connectivity between sexes, revealing processes that may otherwise remain cryptic. We propose that the sex-specific graph approach would be applicable to other vagile species where differential sex-specific processes are expected to occur.
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- 2017
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5. The emblematic minnows of the North American Great Plains: A synthesis of threats and conservation opportunities
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Shannon K. Brewer, Robert Mollenhauer, Thomas A. Worthington, Daniel R. Logue, Nicole Farless, Joseph J. Dyer, Joshuah S. Perkin, Anthony A. Echelle, Worthington, TA [0000-0002-8138-9075], Brewer, SK [0000-0002-1537-3921], and Apollo - University of Cambridge Repository
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0106 biological sciences ,Ecology (disciplines) ,Drainage basin ,Management, Monitoring, Policy and Law ,Aquatic Science ,Biology ,habitat complexity ,Oceanography ,010603 evolutionary biology ,01 natural sciences ,Invasive species ,Abundance (ecology) ,fragmentation ,Ecology, Evolution, Behavior and Systematics ,geography ,geography.geographical_feature_category ,Ecology ,010604 marine biology & hydrobiology ,flow alteration ,Fragmentation (computing) ,conservation ,non-native species ,Great Plains ,Habitat ,Guild ,Conservation status - Abstract
© 2017 John Wiley & Sons Ltd. Anthropogenic changes to the Great Plains rivers of North America have had a large, negative effect on a reproductive guild of pelagic-broadcast spawning (PBS) cyprinid fishes. The group is phylogenetically diverse, with multiple origins of the PBS mode. However, because of incomplete life-history information, PBS designation often relies only on habitat and egg characteristics. We identified 17 known or candidate PBS fishes and systematically synthesized the literature on their biology and ecology in relation to major threats to persistence. Research output on an individual species was unrelated to conservation status, but positively correlated with breadth of distribution. The PBS species have opportunistic life-history strategies and are typically short-lived (generally 1-3 years) fishes. Many PBS species have truncated ranges showing declines in both distribution and abundance, especially those endemic to the Rio Grande catchment. Fundamental habitat associations are unknown for many species, particularly regarding seasonal shifts and early life stages. Critical thermal tolerances have been quantified for five PBS species and are generally > 35°C. Turbidity and salinity changes are linked to responses at multiple life stages, but information is lacking on interactions between water quality and quantity. Hydrologic alteration appears to be a primary threat to PBS species, through complex interactions with landscape fragmentation, and habitat change. We highlight areas where scientific and management communities are lacking information and underline areas of potential conservation gain.
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- 2018
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6. Salivary cortisol and α-amylase responses to repeated bouts of downhill running
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Stuart Semple, Christopher W. Bach, Andrew J. McKune, and Barry J. Dyer
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Downhill running ,Saliva ,medicine.medical_specialty ,biology ,business.industry ,Significant group ,Repeated measures design ,Endocrinology ,Anthropology ,Internal medicine ,Genetics ,biology.protein ,Medicine ,Sympathoadrenal system ,Every Hour ,Amylase ,Anatomy ,business ,Ecology, Evolution, Behavior and Systematics ,Salivary cortisol - Abstract
Objectives To determine the hypothalamic-pituitary-adrenal (HPA) axis and sympathoadrenal (SA) system response to repeated bouts of downhill running. Methods Eleven active but untrained males (age: 19.7 ± 0.4 y; VO2peak 47.8 ± 3.6 ml/kg/min) performed two 60 min bouts of downhill running (−13.5% gradient), separated by 14 days, at a speed eliciting 75% of their VO2peak on a level grade. Saliva samples were collected before (baseline), after, and every hour for 12 h and every 24 h for 6 days after each run. Salivary cortisol and α-amylase levels were measured as markers of the HPA axis and SA response, respectively. Results were analyzed using repeated measures ANOVA (12 h period: 2 × 14; 24 h intervals 2 × 7, P ≤ 0.05) with Tukey post-hoc tests where appropriate. Paired samples t-tests were used to compare collapsed data vs. baseline measurements. Results There were no significant group × time interactions for cortisol or α-amylase for the hourly samples up to 12 h after each run, nor for the 24 h samples up to 6 days later. The 24 h samples for α-amylase showed a significant group effect between runs (Run 1: 69.77 ± 7.68 vs. Run 2: 92.19 ± 7.67 U/ml; P = 0.04). Significant time effects were measured for both cortisol (decreased 2 h to 12 h post-run) and α-amylase (elevated immediately after, 1 h and 2 h post-run) (P < 0.001). Conclusion The 24 h period group effect for salivary α-amylase suggested an adaptation in the sympathoadrenal system that may alter the systemic inflammatory response to exercise-induced muscle damage but may also reflect enhanced mucosal immunity. Am. J. Hum. Biol. 26:850–855, 2014. © 2014 Wiley Periodicals, Inc.
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- 2014
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7. Ecological coassociations influence species' responses to past climatic change: an example from a Sonoran Desert bark beetle
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John D. Nason, Juan F. Fernández-Manjarrés, Ryan C. Garrick, and Rodney J. Dyer
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Bark beetle ,Genotype ,Range (biology) ,Climate Change ,Population ,Biology ,DNA, Mitochondrial ,Evolution, Molecular ,Euphorbia ,Genetics ,Vicariance ,Animals ,Herbivory ,education ,Mexico ,Ecosystem ,Phylogeny ,Ecology, Evolution, Behavior and Systematics ,Cell Nucleus ,Abiotic component ,education.field_of_study ,Herbivore ,Biotic component ,Models, Genetic ,Ecology ,fungi ,Bayes Theorem ,biology.organism_classification ,Coleoptera ,Phylogeography ,Genetics, Population ,Sympatric speciation ,Desert Climate - Abstract
Ecologically interacting species may have phylogeographical histories that are shaped both by features of their abiotic landscape and by biotic constraints imposed by their coassociation. The Baja California peninsula provides an excellent opportunity to examine the influence of abiotic vs. biotic factors on patterns of diversity in plant-insect species. This is because past climatic and geological changes impacted the genetic structure of plants quite differently to that of codistributed free-living animals (e.g. herpetofauna and small mammals). Thus, ‘plant-like’ patterns should be discernible in host-specific insect herbivores. Here, we investigate the population history of a monophagous bark beetle, Araptus attenuatus, and consider drivers of phylogeographical patterns in the light of previous work on its host plant, Euphorbia lomelii. Using a combination of phylogenetic, coalescent-simulation-based and exploratory analyses of mitochondrial DNA sequences and nuclear genotypic data, we found that the evolutionary history of A. attenuatus exhibits similarities to its host plant that are attributable to both biotic and abiotic processes. Southward range expansion and recent colonization of continental Sonora from the Baja peninsula appear to be unique to this taxon pair and probably reflect influences of the host plant. On the other hand, abiotic factors with landscape-level influences on a diverse suite of codistributed arid-adapted taxa, such as Plio- and Pleistocene-aged marine incursions in the region, also left genetic signatures in beetle and host plant populations. Superimposed on these similarities, bark beetle-specific patterns and processes were also evident: our data revealed two secondarily sympatric, reproductively isolated genetic lineages, as well as a previously unrecognized mid-peninsular warm desert refuge. Taken together, this work illustrates that the evolutionary history of species-specific insect herbivores may represent a mosaic of influences, including—but not limited to—those imposed by the host plant.
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- 2013
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8. Sodium valproate withdrawal correlates with reduced aggression
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Nicola Graham, Duncan Pritchard, Tim J. Dyer, F. Charles Mace, Marguerite Hoerger, and Heather Penney
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medicine.medical_specialty ,Aggression ,Challenging behaviour ,medicine.disease ,Pediatrics ,Epilepsy ,Conduct disorder ,Intervention (counseling) ,Learning disability ,medicine ,Autism ,Bipolar disorder ,Pshychiatric Mental Health ,medicine.symptom ,Psychiatry ,Psychology ,Clinical psychology - Abstract
Accessible Summary A 16-year-old boy diagnosed with a mild learning disability, atypical autism, attention-deficit hyperactivity disorder, bipolar disorder, conduct disorder and epilepsy was admitted to a residential special school for treatment of severe aggression. Prior to admission, he had been prescribed various psychotropic medications, including sodium valproate, to treat his aggressive behaviour, bipolar disorder and epilepsy. His behaviour improved when his medication was stopped. Summary People with learning disabilities are sometimes prescribed psychotropic medication to help manage their challenging behaviour. This case study describes how a multicomponent behavioural intervention in conjunction with the systematic withdrawal of sodium valproate was strongly correlated with reduced aggression. No symptoms of bipolar disorder or epilepsy were observed over the course of this 135-week case study. No aggression was observed during the last 20 weeks of the study. Aggressive behaviour as a possible side effect of sodium valproate should be considered in people with learning disabilities.
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- 2013
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9. Landscape modelling of gene flow: improved power using conditional genetic distance derived from the topology of population networks
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John D. Nason, Ryan C. Garrick, and Rodney J. Dyer
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education.field_of_study ,Ecology ,Population ,Population genetics ,Biology ,Field (geography) ,Gene flow ,Phylogeography ,Genetic distance ,Evolutionary biology ,Genetic variation ,Genetics ,Genetic variability ,education ,Ecology, Evolution, Behavior and Systematics - Abstract
Landscape genetics is a burgeoning field of interest that focuses on how site-specific factors influence the distribution of genetic variation and the genetic connectivity of individuals and populations. In this manuscript, we focus on two methodological extensions for landscape genetic analyses: the use of conditional genetic distance (cGD) derived from population networks and the utility of extracting potentially confounding effects caused by correlations between phylogeographic history and contemporary ecological factors. Individual-based simulations show that when describing the spatial distribution of genetic variation, cGD consistently outperforms the traditional genetic distance measure of linearized F(ST) under both 1- and 2-dimensional stepping stone models and Cavalli-Sforza and Edward's chord distance D(c) in 1-dimensional landscapes. To show how to identify and extract the effects of phylogeographic history prior to embarking on landscape genetic analyses, we use nuclear genotypic data from the Sonoran desert succulent Euphorbia lomelii (Euphrobiaceae), for which a detailed phylogeographic history has previously been determined. For E. lomelii, removing the effect of phylogeographic history significantly influences our ability to infer both the identity and the relative importance of spatial and bio-climatic variables in subsequent landscape genetic analyses. We close by discussing the utility of cGD in landscape genetic analyses.
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- 2010
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10. EFFECTS OF STIMULANT MEDICATION UNDER VARIED MOTIVATIONAL OPERATIONS
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Tim J. Dyer, Duncan Pritchard, Karen Thomas, F. Charles Mace, Lora Perry, Jane Kochy, and Kevin L. Prager
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Male ,medicine.medical_specialty ,Sociology and Political Science ,medicine.medical_treatment ,Psychological intervention ,Choice Behavior ,Young Adult ,Intellectual Disability ,Intervention (counseling) ,Intellectual disability ,medicine ,Humans ,Attention deficit hyperactivity disorder ,Attention ,Psychiatry ,Applied Psychology ,Motivation ,Methylphenidate ,Aggression ,Behavior change ,medicine.disease ,Stimulant ,Philosophy ,Treatment Outcome ,Attention Deficit Disorder with Hyperactivity ,Delayed-Action Preparations ,medicine.symptom ,Psychology ,Reports ,medicine.drug - Abstract
We evaluated the evocative effects of four conditions (high- and low-preference activities, low and divided attention) and stimulant medication on the behavior of a 16-year-old boy with attention deficit hyperactivity disorder and moderate mental retardation. All behavior (activity engagement, activity changes, inappropriate touching, rude behaviors, and physical aggression) improved with stimulant medication in most conditions, but undesirable behaviors were not reduced to acceptable levels in all conditions. This finding suggests that stimulant medication may be a valuable adjunct to function-based interventions.
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- 2009
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11. Apparent absence of the quasi-biennial oscillation in sea level pressure in the south indian and south atlantic oceans
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T. G. J. Dyer
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Quasi-biennial oscillation ,Atmospheric Science ,Sea surface temperature ,Oceanography ,Atmospheric pressure ,North Atlantic oscillation ,Oscillation ,Climatology ,Zonal and meridional ,Southern Hemisphere ,Sea level ,Geology - Abstract
Monthly mean sea level pressure over the Indian and South Atlantic oceans can be represented adequately by a few uncorrelated pressure fields derived using principal component analysis. Apart from a major, and general, field both zonal and meridional compensatory pressure systems appear to occur over this region of the Southern Hemisphere (approximately 10°W to 60°E and 20.5°S to 40.5°S). the time series of these fields were submitted to spectral analyses, and apart from an oscillation centred at 20 months in the third component there was no evidence suggesting the existence of the quasi-biennial oscillation in the pressure data. This result conflicts with those for rainfall over southern Africa, and sea level pressure and sea surface temperature around Australia.
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- 2007
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12. A two-generation analysis of pollen pool genetic structure in flowering dogwood, Cornus florida (Cornaceae), in the Missouri Ozarks
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Peter E. Smouse, Victoria L. Sork, Rodney J. Dyer, Robert D. Westfall, and Victoria J. Apsit
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Genetic diversity ,biology ,media_common.quotation_subject ,Cornaceae ,Plant Science ,biology.organism_classification ,medicine.disease_cause ,Gene flow ,Horticulture ,Population bottleneck ,Pollen ,Botany ,Forest ecology ,Genetic structure ,Genetics ,medicine ,Reproduction ,Ecology, Evolution, Behavior and Systematics ,media_common - Abstract
Anthropogenic landscape change can disrupt gene flow. As part of the Missouri Ozark Forest Ecosystem Project, this study examined whether silvicultural practices influence pollen-mediated gene movement in the insect-pollinated species, Cornus florida L., by comparing pollen pool structure (Φ s t ) among clear-cutting, selective cutting, and uncut regimes with the expectation that pollen movement should be least in the uncut regime. Using a sample of 1500 seedlings-10 each from 150 seed parents (43 in clear-cut, 74 in selective, and 33 in control sites) from six sites (each ranging from 266 to 527 ha), eight allozyme loci were analyzed with a pollen pool structure approach known as TWOGENER (Smouse et al., 2001; Evolution 55: 260-271). This analysis revealed that pollen pool structure was less in clear-cut (Φ C = 0.090, P < 0.001) than in uncut areas (Φ U = 0.174, P < 0.001), with selective-cut intermediate (Φ S = 0.125, P < 0.001). These estimates translate into more effective pollen donors (N c p ) in clear-cut (N c p = 5.56) and selective-cut (N e p = 4.00) areas than in uncut areas (N e p = 2.87). We demonstrate that Φ C ≤ Φ S ≤ Φ U , with Φ C significantly smaller than Φ U (P < 0.034). The findings imply that, as long as a sufficiently large number of seed parents remain to provide adequate reproduction and to avoid a genetic bottleneck in the effective number of mothers, silvicultural management may not negatively affect the effective number of pollen parents, and hence subsequent genetic diversity in Cornus florida.
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- 2005
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13. Population Graphs: the graph theoretic shape of genetic structure
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John D. Nason and Rodney J. Dyer
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education.field_of_study ,Population ,Graph theory ,Biology ,Coalescent theory ,Phylogeography ,Evolutionary biology ,Genetic variation ,Genetic structure ,Genetics ,Genetic representation ,education ,Ecology, Evolution, Behavior and Systematics ,Isolation by distance - Abstract
Patterns of intraspecific genetic variation result from interactions among both historical and contemporary evolutionary processes. Traditionally, population geneticists have used methods such as F-statistics, pairwise isolation by distance models, spatial autocorrelation and coalescent models to analyse this variation and to gain insight about causal evolutionary processes. Here we introduce a novel approach (Population Graphs) that focuses on the analysis of marker-based population genetic data within a graph theoretic framework. This method can be used to estimate traditional population genetic summary statistics, but its primary focus is on characterizing the complex topology resulting from historical and contemporary genetic interactions among populations. We introduce the application of Population Graphs by examining the range-wide population genetic structure of a Sonoran Desert cactus (Lophocereus schottii). With this data set, we evaluate hypotheses regarding historical vicariance, isolation by distance, population-level assignment and the importance of specific populations to species-wide genetic connectivity. We close by discussing the applicability of Population Graphs for addressing a wide range of population genetic and phylogeographical problems.
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- 2004
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14. The effect of weather factors on the performance of herbicides to control Alopecurus myosuroides in winter wheat
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L V Collings, A M Blair, A P Gay, C J Dyer, and N Mackay
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biology ,business.industry ,Clodinafop-propargyl ,Alopecurus myosuroides ,Winter wheat ,Plant Science ,biology.organism_classification ,Agronomy ,Agriculture ,Christian ministry ,business ,Weather factors ,Weed ,Agronomy and Crop Science ,Ecology, Evolution, Behavior and Systematics - Abstract
Collings, L. V., Blair, A. M., Gay, A. P., Dyer, C. J., MacKay, W. (2003). The effect of weather factors on the performance of herbicides to control Alopecurus myosuroides in winter wheat. Weed Research, 43 (2), 146-153. Sponsorship: Ministry of Agriculture Fisheries and Food (now DEFRA)
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- 2003
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15. Defining the landscape of adaptive genetic diversity
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Rodney J. Dyer and Andrew J. Eckert
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Pinus contorta ,Genetic diversity ,Natural selection ,Fitness landscape ,Ecology ,Biology ,biology.organism_classification ,Genetic architecture ,Molecular ecology ,Evolutionary biology ,Genetics ,Architecture ,Construct (philosophy) ,Ecology, Evolution, Behavior and Systematics - Abstract
Whether they are used to describe fitness, genome architecture or the spatial distribution of environmental variables, the concept of a landscape has figured prominently in our collective reasoning. The tradition of landscapes in evolutionary biology is one of fitness mapped onto axes defined by phenotypes or molecular sequence states. The characteristics of these landscapes depend on natural selection, which is structured across both genomic and environmental landscapes, and thus, the bridge among differing uses of the landscape concept (i.e. metaphorically or literally) is that of an adaptive phenotype and its distribution across geographical landscapes in relation to selective pressures. One of the ultimate goals of evolutionary biology should thus be to construct fitness landscapes in geographical space. Natural plant populations are ideal systems with which to explore the feasibility of attaining this goal, because much is known about the quantitative genetic architecture of complex traits for many different plant species. What is less known are the molecular components of this architecture. In this issue of Molecular Ecology, Parchman et al. (2012) pioneer one of the first truly genome-wide association studies in a tree that moves us closer to this form of mechanistic understanding for an adaptive phenotype in natural populations of lodgepole pine (Pinus contorta Dougl. ex Loud.).
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- 2012
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16. Photoinitiated polymerization of styrene from self-assembled monolayers on gold. II. Grafting rates and extraction
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Rolf Schmidt, Daniel J. Dyer, Rituparna Paul, and Jianxin Feng
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Materials science ,Polymers and Plastics ,Soxhlet extractor ,Organic Chemistry ,Radical polymerization ,Extraction (chemistry) ,Dithiol ,Infrared spectroscopy ,Styrene ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Polymerization ,Polymer chemistry ,Materials Chemistry ,Polystyrene - Abstract
Ultrathin films of polystyrene (PS) were grown from self-assembled monolayers by the “grafting-from” technique. The initiating system consisted of a dithiol azobisisobutyronitrile-type free-radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform-reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water-jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284–3291, 2002
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- 2002
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17. Executive development: outer goals and inner coaching
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Thomas J. Dyer
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Power (social and political) ,Knowledge management ,Restructuring ,Process (engineering) ,business.industry ,Order (exchange) ,Phenomenon ,Terrorism ,General Medicine ,Public relations ,business ,Productivity ,Coaching - Abstract
© 2002 Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ert.10027 If the Enron debacle has shown us anything, it is the apparent arrogance that exists at the executive levels of some companies. A “power dominates” belief system is responsible for the arrogance that drove the destructive behavior of the executives. An equally ineffective belief system of those witnessing the process prevented them from taking appropriate challenging actions. Reconstructing belief systems is a powerful tool in shifting behavior in a productive direction. Many HR managers feel powerless to address dysfunctional behavior in the executive ranks. This is why it is critical to provide both executives and HR managers with a new pathway for executive development that addresses the inner resources that are related to the achievement of outer goals. The Enron phenomenon isn’t the only thing that has brought attention to how business leadership functions. The events of last September 11 have accelerated the need for today’s executives to be more than managers. They must be compassionate leaders who are able to facilitate employees through some of their personal issues in order to maintain productivity. This requirement goes beyond the executive’s ability to process his or her own emotions, not only through tragedy but also at the executive table where so many unproductive behaviors block the executive team’s potential. The issues that influence these newly demanded behaviors become apparent with higher levels of awareness. This article describes an executive-development process that gives executives and those interacting with them a framework in which to address important business goals and explore and restructure beliefs related to those goals. This process can virtually eliminate the business environment in which an Enron-type disaster can occur. It can also provide the skills and mind-set that executives need to address employee concerns, even in a crisis situation like the terrorist attacks on September 11. This is good not only for executives, managers, and workers, but also for the overall health of the company. The executive-development process includes these elements
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- 2002
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18. Estimation of the nitrogen requirement of winter wheat in the UK: a multiple regression approach
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Roger Sylvester-Bradley, G. Goodlass, and Chris J Dyer
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Nutrition and Dietetics ,Winter wheat ,chemistry.chemical_element ,Soil classification ,Soil type ,Nitrogen ,Crop ,Agronomy ,chemistry ,Soil water ,Linear regression ,Agronomy and Crop Science ,Nitrogen requirement ,Food Science ,Biotechnology ,Mathematics - Abstract
In this study, multi-site crop response data were examined so as to improve guidelines for crop nitrogen requirement and efficient fertiliser use on winter wheat over a range of soil types. The parameters which had most individual effect on nitrogen requirement (the economic optimum amount of fertiliser N (Nopt)) were soil type and previous cropping. Interactions between soil type and soil N supply as measured by soil mineral nitrogen analysis were also important. Yield had no effect. Descriptive models were developed for Nopt. The simplest, based on N index, rainfall and soil type, accounted for 40% of the variation in Nopt. This was improved to 51% by adding spring analysis of soil mineral nitrogen. The model could be improved by inclusion of measured yield or a seasonal term, but the precision of predicted Nopt was not improved significantly, 41% of cases being within ±25 kg ha -1 of the optimum without yield and 42% with yield. The study showed that some of the inputs currently used to determine N requirement need to be revised and additional terms added. However, even the best estimates have poor predictive precision. Le lien entre le rendement et les besoins en azote d'une culture peut conduire a des applications excessives de fertilisants. Cette etude examine les besoins en azote et les fertilisants efficaces utilises sur le ble d'hiver pour differents types de sols. Les parametres ayant l'effet le plus important sur le besoin en azote sont le type de sol et la culture precedente. Cependant, les meilleures estimations restent tout de meme imprecises.
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- 2002
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19. Pollen pool heterogeneity in shortleaf pine,Pinus echinataMill
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Victoria L. Sork and Rodney J. Dyer
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Ecology ,food and beverages ,Biology ,medicine.disease_cause ,biology.organism_classification ,medicine.anatomical_structure ,Pollen ,Genetic structure ,Botany ,otorhinolaryngologic diseases ,Genetics ,medicine ,Temperate climate ,Microsatellite ,Gamete ,Tree species ,Ecology, Evolution, Behavior and Systematics ,Pinus echinata ,Isolation by distance - Abstract
Pollen is the dominant vector of gamete exchange for most temperate tree species. Because pollen movement influences the creation, maintenance and erosion of genetic structure in adult populations, it is important to understand what factors influence the process of pollen movement. Isolation by distance in pollen donor populations can create highly structured pollen polls by increased sampling of local fathers. Extrinsic factors, such as the intervening vegetative structure and local pollen donor densities, can also influence the genetic composition of local pollen pools. Using paternally inherited chloroplast microsatellite markers, we examined the structure and diversity of pollen pools in Pinus echinata Mill. in southern Missouri, USA. Our analysis is based on a multivariate AMOVA analysis of stands ( ∪ 1 ha; six per region) nested within regions ( ∪ 800 ha; four each). Significant multilocus structure of the pollen pool within regions ( φ SR = 0.095), but not among regions ( φ RT = 0.010), indicates that pollen movement is relatively restricted. Furthermore, the significant correlation between pairwise genetic and physical distances (Mantel correlation; ρ = 0.32) provided support for the isolation by distance hypothesis. Our results indicated that availability of pollen donors did not affect diversity of the pollen pool, measured by the number of unique multilocus genotypes at each stand. However, pollen pool diversity was negatively associated with vegetative structure, measured as total forest tree density. Our findings indicated that on-going pollen movement within continuous forest is relatively restricted as a result of both isolation by distance and vegetative structure.
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- 2001
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20. Avoiding Type II error in assessing lead toxicity plaintiffs
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Frank J. Dyer
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Analysis of covariance ,medicine.medical_specialty ,media_common.quotation_subject ,Variance (accounting) ,Ambiguity ,Conservatism ,Tort ,medicine.disease ,Lead poisoning ,Psychiatry and Mental health ,Clinical Psychology ,medicine ,Causation ,Psychology ,Psychiatry ,Law ,media_common ,Type I and type II errors - Abstract
This article discusses statistical parallels between excessive conservatism and insufficient conservatism in rendering forensic opinions. The elements of a tort are reviewed and their relation to psychological and psychiatric opinions is also discussed, as are psychometric and clinical approaches to assessment of impairment and causation in individual lead poisoned children. It is argued that assessments in lead poisoning cases consisting solely of cranial nerve examinations result in considerable Type II Error. Sources of Type II Error in research using analysis of covariance techniques to study the toxic effects of lead include variance stealing, use of excessive numbers of covariates, lack of attention to interactions, and use of covariates that are actually substitute measures of lead ingestion. When experts cite nonsignificant findings of studies of low-level lead exposure, it inappropriately negates lead effects in more severely lead poisoned plaintiffs. In true experimental studies where there is no ambiguity regarding causation, the destructive effects of lead are quite clear. © 1998 John Wiley & Sons, Ltd.
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- 1998
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21. gener: a server-based analysis of pollen pool structure
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Rodney J. Dyer
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Ecology ,Population size ,Biology ,medicine.disease_cause ,Biochemistry ,General Biochemistry, Genetics and Molecular Biology ,Data set ,Permutation ,Genetic marker ,Pollen ,Genetic variation ,Statistics ,medicine ,Test statistic ,Statistic - Abstract
The server-based program gener performs the two-generation analysis of pollen flow for data consisting of mother/offspring arrays using genetic markers. The gener program decomposes the genetic variance sampled by maternal individuals within and among pollen pool components of genetic variance and is accessible from http://dyerlab.bio.vcu.edu. These estimates are used to construct the test statistic, Φft, whose significance is tested via permutation. The Φft statistic can subsequently be used to quantify genetic effective pollen donor population size (Nep), effective mating area and dispersal distance. Furthermore, the gener program can calculate Φft values for all pairs of substrata within the data set.
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- 2005
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22. Clinical presentation of the lead-poisoned child on mental ability tests
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Frank J. Dyer
- Subjects
medicine.diagnostic_test ,Cognitive disorder ,medicine.disease ,Verbal reasoning ,Lead poisoning ,Test (assessment) ,Developmental psychology ,Clinical Psychology ,Arts and Humanities (miscellaneous) ,El Niño ,medicine ,Psychological testing ,Blood lead level ,Lead (electronics) ,Psychology ,Clinical psychology - Abstract
Current literature on effects of childhood lead poisoning and high blood lead level on psychological test performance was reviewed. A pathognomic configuration of mental ability test scores is described. A sample of 18 moderately to severely lead poisoned children was found to have a significantly higher frequency of this score configuration than either a comparison sample or the Black subsample of the original WISC-R standardization group. Implications for clinical practice and research are discussed.
- Published
- 1993
- Full Text
- View/download PDF
23. ChemInform Abstract: Crystalline Boron Nanowires
- Author
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Min-Feng Yu, Carolyn Jones Otten, Mark J. Dyer, John M. Cowley, William E. Buhro, Oleg R. Lourie, and Rodney S. Ruoff
- Subjects
Chemistry ,Doping ,Nanowire ,chemistry.chemical_element ,General Medicine ,Carbon nanotube ,Conductivity ,law.invention ,Chemical engineering ,Nanoelectronics ,Covalent bond ,law ,Boron ,Electrical conductor - Abstract
Ideal nanowire interconnects for nanoelectronics will be refractory, covalently bonded, and highly conductive, irrespective of crystallographic orientation. Theoretical studies suggest that boron nanotubes should be stable and exhibit higher electrical conductivities than those of carbon nanotubes. We describe CVD growth of elemental boron nanowires, which are found to be dense nanowhiskers rather than nanotubes. Conductivity measurements establish that they are semiconducting, with electrical properties consistent with those of elemental boron. High conductivities should be achievable through doping.
- Published
- 2010
- Full Text
- View/download PDF
24. Optimum plant densities for three semi-leafless combining pea (Pisum sativum) cultivars under contrasting field conditions
- Author
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D. Rogers-Lewis, C. J. Dyer, M. C. Heath, and C. M. Knott
- Subjects
Agriculture, Multidisciplinary ,Sativum ,Agronomy ,Soil organic matter ,Soil water ,Sowing ,Habit (biology) ,Soil classification ,Cultivar ,Biology ,Soil type ,Agronomy and Crop Science - Abstract
SUMMARY Yield and yield components of three semi-leafless pea (Pisum sativum) cultivars, of contrasting seed type/growth habit, were assessed at target planting densities of 40–140 plants/m2 on nine sites over three years. Flat-topped parabolic/asymptotic yield/density relationships were obtained. The plant density required to maximise (p max) and optimise (p opt) yield differed between cultivars: Helka, small blue, p max 126 plants/m2, p opt 101 plants/m2; Solara, large blue, p max 124 plants/m2, p opt 94 plants/m2; and Countess, white-seeded, p max 104 plants/m2, p opt 71 plants/m2. Near-maximum yields were maintained between 70 and 140 plants/m2 due to the ability of the pea crop to make compensatory increases in the number of pods per plant as density declined. Yield/density responses were influenced by site (e.g. soil type) more than by seasonal factors. The risk of yield reductions occurring at densities below 70 plants/m2 was greater on a mineral soil than on a fertile organic soil. On the basis of agronomic and economic considerations, there was no evidence that target plant densities required to optimise yield should necessarily be higher for semi-leafless cultivars studied than for conventional leafed peas.
- Published
- 1991
- Full Text
- View/download PDF
25. Direkte Beobachtung von aus Enantiomeren aufgebauten enantiomorphen Monoschicht-Kristallen mit der Rastertunnelmikroskopie
- Author
-
David M. Walba, Forrest Stevens, and Daniel J. Dyer
- Subjects
Materials science ,General Medicine - Published
- 1996
- Full Text
- View/download PDF
26. O592 Psychosocial aspects of Turner Syndrome
- Author
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Z.M. van der Spuy, N. Matebese, and Silks J. Dyer
- Subjects
medicine.medical_specialty ,business.industry ,Turner syndrome ,medicine ,Obstetrics and Gynecology ,General Medicine ,Psychiatry ,medicine.disease ,business ,Psychosocial - Published
- 2009
- Full Text
- View/download PDF
27. Powers of discerning: challenges to understanding dispersal processes in natural populations
- Author
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Rodney J. Dyer
- Subjects
Ecology ,Seed dispersal ,Genetics ,Biological dispersal ,Biology ,Pollen dispersal ,Ecology, Evolution, Behavior and Systematics ,Natural (archaeology) ,Molecular ecology - Abstract
In this issue of Molecular Ecology, authors Robledo-Arnuncio & Garcia present a compelling approach for quantifying seed dispersal in plant populations. Building upon methods previously used for quantification of pollen dispersal, the authors not only examine the behaviour of the model with respect to sample sizes, dispersal distance, and the kurtosis of the dispersal function but also provide an empirical example using Prunus mahaleb.
- Published
- 2007
- Full Text
- View/download PDF
28. COMPUTED TOMOGRAPHY FINDING OF PORTAL VENOUS GAS IN A PATIENT WHO SURVIVED MESENTERIC INFARCTION
- Author
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Evan J. Dyer and Ian Faragher
- Subjects
Male ,medicine.medical_specialty ,Abdominal pain ,Mesenteric infarction ,medicine.medical_treatment ,Portal venous pressure ,Ischemia ,Computed tomography ,Diagnosis, Differential ,Laparotomy ,Mesenteric Vascular Occlusion ,medicine ,Embolism, Air ,Humans ,Aged ,Aged, 80 and over ,medicine.diagnostic_test ,Portal Vein ,business.industry ,General Medicine ,medicine.disease ,Surgery ,Embolism ,Radiology ,Presentation (obstetrics) ,medicine.symptom ,Tomography, X-Ray Computed ,business - Abstract
Hepatic portal venous gas can be a marker of serious intra-abdominal pathology with mortality between 29% and 79%. We report a case of portal venous gas discovered on computerized tomography in a patient presenting with abdominal pain. The finding was unusual in that the patient was not critically unwell at presentation and made a good recovery after laparotomy with small bowel resection.
- Published
- 2005
- Full Text
- View/download PDF
29. Direct Observation of Enantiomorphous Monolayer Crystals from Enantiomers by Scanning Tunneling Microscopy
- Author
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David M. Walba, Forrest Stevens, and Daniel J. Dyer
- Subjects
Materials science ,Direct observation ,General Medicine ,General Chemistry ,Catalysis ,Electrochemical scanning tunneling microscope ,law.invention ,Crystallography ,Liquid crystal ,law ,Monolayer ,Enantiomer ,Scanning tunneling microscope ,Chirality (chemistry) - Published
- 1996
- Full Text
- View/download PDF
30. Comment on the paper ‘On the application of some stochastic models to precipitation forecasting’ by T. G. J. Dyer
- Author
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T. G. J. Dyer and N. Nicholls
- Subjects
Atmospheric Science ,Stochastic modelling ,Econometrics ,Environmental science ,Precipitation - Published
- 1978
- Full Text
- View/download PDF
31. Rainfall along the east coast of southern Africa, the southern oscillation, and the latitude of the subtropical high pressure belt
- Author
-
T. G. J. Dyer
- Subjects
Atmospheric Science ,East coast ,El Niño Southern Oscillation ,Variables ,Climatology ,media_common.quotation_subject ,Principal component analysis ,Southern oscillation ,Subtropical ridge ,Regression analysis ,Geology ,Latitude ,media_common - Abstract
Eighteen rainfall series within a latitude belt 28°08′S to 30°25′S are inspected for relationships with Pittock's L index for the latitude of the subtropical high pressure belt (eastern Australia), and the southern oscillation index. Principal components analysis is used to reduce the dimensions of each of the three data sets, and the components for the pressure systems are used as independent variables in a step-wise regression analysis; rainfall components are taken as the dependent variables. Useful relationships exist between rainfall and Pittock's L, but there is no evidence to suggest that the same situation applies for the southern oscillation index. The results agree with those recently obtained for Mauritius by M. D. Dennett.
- Published
- 1979
- Full Text
- View/download PDF
32. On the intra-annual variation in rainfall over the sub-continent of southern Africa
- Author
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T. G. J. Dyer
- Subjects
Series (stratigraphy) ,Geography ,Climatology ,Principal component analysis ,Period (geology) ,General Earth and Planetary Sciences ,Climate change ,Annual variation ,Variation (astronomy) ,General Environmental Science - Abstract
The variation in intra-annual variance in rainfall over Southern Africa is examined for evidence to support the contention that it has undergone a systematic upward change over the period 1921-1974. A principal components analysis on the data shows that the time series of intra-annual variances may be represented by four components. Although each of the four principal component time series possesses an oscillation in the region of the biennial wave, there is little evidence to suggest that the within-year variation in rainfall is undergoing any type of upward trend.
- Published
- 1982
- Full Text
- View/download PDF
33. On the components of time series; the removal of spatial dependence
- Author
-
T. G. J. Dyer
- Subjects
Atmospheric Science ,Variable (computer science) ,Series (mathematics) ,Meteorology ,Climatology ,Principal component analysis ,Linear model ,Environmental science ,Precipitation ,Spatial dependence ,Residual ,Microscale chemistry - Abstract
A linear model is fitted to the precipitation series of each group of stations formed by principal component analysis on 157 precipitation records (Dyer 1975). Precipitation can thus be decomposed into independent components one each for regional temporal effect, regional spatial effect, and a residual or micro-effect. Each region has a temporal effect which is analysed for trend, enabling the conclusion to be made that Southern Africa's precipitation budget is stationary. On the other hand, trend on a microscale is present over randomly distributed parts of the country. Spectral analysis shows the oscillatory behaviour of the regional temporal effects, and provides information useful to the fitting of stochastic forecasting models to the data. The technique solves the problem of dependence between meteorological time series, and can be applied to any variable.
- Published
- 1976
- Full Text
- View/download PDF
34. An analysis of Manley's central England temperature data: I
- Author
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T. G. J. Dyer
- Subjects
Atmospheric Science ,Series (stratigraphy) ,Climatology ,Equator ,Spectral analysis ,Declination ,Geology ,Secular variation - Abstract
Manley's (1974) temperature data for central England are subjected to analyses which suggest that they should be treated as a set of monthly time series. Secular variation is found for the months October to April inclusive. Extended methods dealing with spectral analysis are used to focus attention on the mainly longer-period oscillations. Oscillations of lengths 10–12 and 22–25 years are suggested for some months. Burg's maximum entropy spectral method has been used to resolve signals in the very low frequencies. The combined variance associated with these oscillations is shown to increase for months near mid-year when the sun has its maximum north declination and to decrease for months on either side of June and July to a minimum when the sun has greatest south declination. Furthermore, the variance associated with months when the sun changes direction in declination and crosses the equator appears to receive boosts.
- Published
- 1976
- Full Text
- View/download PDF
35. PERSISTENCE AND MONTHLY MEAN TEMPERATURES OVER CENTRAL ENGLAND
- Author
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T. G. J. Dyer
- Subjects
Persistence (psychology) ,Atmospheric Science ,Environmental science ,Demography - Published
- 1978
- Full Text
- View/download PDF
36. Secular changes in South African rainfall: 1880 to 1972
- Author
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T. G. J. Dyer, M. N. Mametse, and P. D. Tyson
- Subjects
Atmospheric Science ,Series (stratigraphy) ,Geography ,Climatology ,Period (geology) - Abstract
Analysis of time series for 157 stations with records covering the period 1910–1972 and for fewer stations with records extending back to 1880 suggests that the commonly held view that South Africa, as a whole, is undergoing progressive desiccation must be questioned. Instead the data suggest the specific regional occurrence of weak (but nonetheless readily discernible) oscillations of 16–20 and 10–12 years, the ubiquity of 3–4 year fluctuations and the spatially distinctive occurrence of a quasi-biennial oscillation.
- Published
- 1975
- Full Text
- View/download PDF
37. Automorphism Groups of Two Generator Metabelian Groups
- Author
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S. Bachmuth, H. Y. Mochizuki, J. Dyer, and G. Baumslag
- Subjects
p-group ,Pure mathematics ,Group isomorphism ,Group of Lie type ,Quasisimple group ,Inner automorphism ,Symmetric group ,Metabelian group ,General Mathematics ,Outer automorphism group ,Mathematics - Published
- 1987
- Full Text
- View/download PDF
38. On the application of some stochastic models to precipitation forecasting
- Author
-
T. G. J. Dyer
- Subjects
Atmospheric Science ,Autoregressive model ,Meteorology ,Stochastic modelling ,Statistics ,Exponential smoothing ,Statistical model ,Precipitation ,Trigonometry ,Regression ,Mathematics - Abstract
The equivalent of 157 rainfall records for South Africa have been subjected to various statistical modelling techniques. These include: autoregression; multiple linear and trigonometric regression; and exponential smoothing. Between them the models cover short- and long-term forecasting. the trigonometric model provides a useful forecasting aid. Estimation of the parameters in this model stem from the spectra of the raw rainfall data. the models described are limited neither to rainfall nor the area of the globe from which the present data were obtained.
- Published
- 1977
- Full Text
- View/download PDF
39. The effect of volcanic eruptions on global turbidity, and an attempt to detect long-term trends due to man
- Author
-
A. J. Dyer
- Subjects
Atmospheric Science ,geography ,geography.geographical_feature_category ,Volcano ,Climatology ,Environmental science ,Context (language use) ,Turbidity ,Stratosphere ,Term (time) - Abstract
Following a brief discussion of early radiation measurements and the interpretation of the effects of volcanic eruptions in the light of current knowledge of the stratosphere, recent radiation data from USSR, Japan, USA and Australia are examined. Whilst the effects of the Agung eruption are clearly seen on a global scale, the analysis yields no convincing evidence for a recent world-wide increase in atmospheric turbidity. The need for extreme measurement accuracy is emphasized in the context of long-term atmospheric monitoring.
- Published
- 1974
- Full Text
- View/download PDF
40. Measurements of evaporation and heat transfer in the lower atmosphere by an automatic eddy-correlation technique
- Author
-
A. J. Dyer
- Subjects
Atmosphere ,Atmospheric Science ,Meteorology ,Heat transfer ,Evaporation ,Eddy covariance ,Energy balance ,Environmental science ,Humidity ,Precipitation ,Atmospheric sciences ,Standard deviation - Abstract
Following the development of an automatic instrument for the determination of evaporation and sensible-heat transfer by the eddy-correlation technique, a large number of measurements of these eddy fluxes have been made over level pasture-land. The observations, taken at a height of 4 m, are in excellent agreement with the energy balance. Individual measurements, of 5-min duration, are distributed about a strict energy balance with a standard deviation of 31 per cent, due mainly to horizontal gradients of wind, temperature, and humidity below 4 m height. Over a period of several hours these gradients average out to negligible values. The short response time of the sensing equipment (∽ 0·3 sec) ensures that, for conditions of moderate and high instability, significant deficiencies in eddy-flux measurements occur only with winds exceeding 10 m sec−1. A quantity ϵ, the ‘evaporation fraction,’ i.e., the ratio of evaporation to evaporation plus sensible-heat transfer, is found to increase markedly after rain, and to gradually decrease during the succeeding dry period. This increase can be quantitatively related to the amount of rain. The average value of ϵ during February-March 1960 was 0·56, whilst a value of 0·54 can be computed from annual totals of precipitation and net day-time radiation income.
- Published
- 1961
- Full Text
- View/download PDF
41. An experimental study in micro-meteorology
- Author
-
A. J. Dyer and W. C. Swinbank
- Subjects
Atmospheric Science ,Momentum (technical analysis) ,Meteorology ,Turbulence ,Instrumentation ,Environmental science ,Humidity ,Sensible heat ,Instability ,Wind speed ,Water vapor - Abstract
A description is presented of the experimental techniques used on four micrometeorological expeditions. The instrumentation was designed to provide half-hourly mean values of wind speed, temperature and humidity at a number of levels up to 16 metres, and of the vertical fluxes of heat, water vapour, net radiation and sensible heat into the ground. The observational material is to be published separately. Analysis of the observations, all for the unstable case, shows close similarity between the turbulent transfer processes for heat and water vapour over the whole range of stability represented by the measurements. Both are more strongly influenced by instability than the exchange of momentum, the difference in behaviour becoming more marked with increasing instability. It is suggested that the similarity between heat and water vapour transfer is due to a correlation between the temperature and specific humidity of the air which originates at the evaporating surface.
- Published
- 1967
- Full Text
- View/download PDF
42. The spatial variability of eddy fluxes in the constant flux layer
- Author
-
A. J. Dyer and B. B. Hicks
- Subjects
Physics ,Atmospheric Science ,Momentum (technical analysis) ,Tilt (optics) ,Flux (metallurgy) ,Meteorology ,Heat flux ,Turbulence ,Eddy covariance ,Spatial variability ,Atmospheric sciences ,Constant (mathematics) - Abstract
At the 1970 International Comparison of Turbulence Instruments held at Tsimlyansk, U.S.S.R., a large number of momentum and heat flux measurements were obtained simultaneously with two Fluxatrons. The data are analysed from the point of view of spatial variation of eddy fluxes, bearing in mind the limitations of the sensors, the variability of the eddy fluxes themselves, and the possibility of errors due to tilt. It is concluded that, at the Tsimlyansk site, the variation of heat and momentum fluxes both in the vertical (4 – 14 m) and the horizontal (1 – 150 m) is of the order 10 per cent or less. This result is in accord with traditional opinion, and provides a satisfactory experimental basis for the concept of a ‘constant flux layer’.
- Published
- 1972
- Full Text
- View/download PDF
43. PROTEIN DENATURATION IN FROZEN AND STORED FISH
- Author
-
W. J. Dyer
- Subjects
Biochemistry ,Chemistry ,Food Science - Published
- 1951
- Full Text
- View/download PDF
44. Flux-gradient relationships in the constant flux layer
- Author
-
A. J. Dyer and B. B. Hicks
- Subjects
Physics ,Atmospheric Science ,Wind profile power law ,Meteorology ,Monin–Obukhov similarity theory ,Eddy covariance ,Range (statistics) ,Flux ,Thermodynamics ,Shear velocity ,Constant (mathematics) ,Water vapor - Abstract
An analysis is made of the Monin-Obukhov function ΦM in the familiar wind profile equation, using data from two recent expeditions to Gurley (New South Wales) and Hay (New South Wales). In one, the friction velocity u* is determined directly by the eddy correlation method, and in the other, conducted during mid-winter when small heat-fluxes were experienced, by the use of a friction coefficient applied to a low-level wind. By collating with a similar earlier analysis for heat and water vapour transfer, the variations of ΦM, ΦH and ΦW with stability are presented in tabular form in the z/L range − 0.01 to − 1.0. Within this range the empirical relationships ΦM = (1 − 16 z/L)−1/4 and ΦH, W = (1 − 16 z/L)−1/2, and the implied equality between Ri and z/L, are found to approximate the data to within a few per cent.
- Published
- 1970
- Full Text
- View/download PDF
45. The turbulent transport of heat and water vapour in an unstable atmosphere
- Author
-
A. J. Dyer
- Subjects
Data limited ,Atmosphere ,Atmospheric Science ,Materials science ,Meteorology ,Direct assessment ,Turbulence ,Universal function ,Heat transfer ,Atmospheric instability ,Thermodynamics ,Water vapor - Abstract
Micro-meteorological data acquired during five expeditions to carefully chosen sites are analysed to determine the flux-gradient relation for the transfer of heat and water vapour in the lower atmosphere. The analysis takes the form of a direct assessment of the Monin-Obukhov universal functions φH and φW. Data for φH were available from all five expeditions, and for φW from two of these. It was found that φH = φW over the whole of the z/L range available, indicating an identity in mechanism for the turbulent transport of heat and water vapour over a freely evaporating surface. Over the range 0.02 0.2, φH was found to vary as |z/L|−1/2. Insufficient data limited the value of the corresponding analysis for φW Excellent agreement was found between the φH and φW data, and φ-curves assessed from a previous shape-function analysis (Swinbank and Dyer 1967). The empirical relation φ = (1–15 z/L)−0·55 agrees with the experimental values of φH and φW over the whole of the |z/L| range to within a few per cent, thus permitting numerical evaluation of φ.
- Published
- 1967
- Full Text
- View/download PDF
46. Global spread of volcanic dust from the Bali eruption of 1963
- Author
-
A. J. Dyer and B. B. Hicks
- Subjects
Atmospheric Science ,geography ,geography.geographical_feature_category ,Northern Hemisphere ,Atmospheric sciences ,Latitude ,Out of phase ,Amplitude ,Volcano ,Climatology ,Outflow ,Southern Hemisphere ,Stratosphere ,Geology - Abstract
The global spread of volcanic dust from the Mt. Agung eruption of 17 March 1963 is assessed on the basis of the decrement of direct solar radiation. The initial injection at 8°S lodged an equatorial reservoir in the stratosphere at a height of 22–23 km. Most of the dust remained in the Southern Hemisphere, but a significant fraction entered the lower Northern Hemisphere stratosphere. Seasonal effects appeared in both hemispheres, the apparent dust amounts showing a ‘winter’ maximum of constant amplitude in any one season with a poleward progression of 40 cm sec−1 between 30° and 90° latitude. At 15°N, seasonal effects were also evident but significantly out of phase with the sequence at higher latitudes, suggesting a hand-over in the horizontal transport process at 20°–30° latitude. Whilst the ‘winter’ maxima in the Northern Hemisphere were almost identical in amplitude for 1963 and 1964, the Southern Hemisphere data showed a significant reduction in dust amount over these years. The latter effect can be shown to imply an updraught in the lowest 2 km of the equatorial stratosphere of about 0·02 cm sec−1. By continuity, the poleward outflow from this circulation would be consistent with the observed rate of poleward progression. It is speculated that the seasonal effects could arise from an annual oscillation of the axis of this meridional circulation. Attempts to relate the observations by a diffusion model are less convincing, but in the absence of more direct information, no firm conclusion can be drawn. The paucity of suitable radiation data for equatorial regions severely limits the extent to which inferences can be made.
- Published
- 1968
- Full Text
- View/download PDF
47. Boron Deficiency and Translocation Profiles in Sunflower
- Author
-
Hurert J. Dyer, Kung-Woo Lee, and Catherine M. Whittle
- Subjects
inorganic chemicals ,Physiology ,fungi ,Front (oceanography) ,food and beverages ,chemistry.chemical_element ,Chromosomal translocation ,Cell Biology ,Plant Science ,General Medicine ,Biology ,Photosynthesis ,Sunflower ,chemistry ,Botany ,Genetics ,Boron - Abstract
The distribution of carbon-14 down the stems of comparable boron-deficient and boron-sufficient sunflower plants after photosynthesis of 14CO2 by a single exposed leaf was investigated. In boron-deficient plants the advancing front of radioactivity was always found less far down the stem than in boron-sufficient plants. The general shape of the profile is the same in the two sets of plants. We conclude that the velocity of translocation is reduced in the boron-deficient plants.
- Published
- 1966
- Full Text
- View/download PDF
48. The adjustment of profiles and eddy fluxes
- Author
-
A. J. Dyer
- Subjects
Atmospheric Science ,Molecular diffusion ,Flux (metallurgy) ,Meteorology ,Range (statistics) ,Environmental science ,Function (mathematics) ,Diffusion (business) ,Atmospheric sciences ,Wind speed - Abstract
An assessment is made using simple diffusion theory of the rate of adjustment of profiles and eddy fluxes for (a), the leading-edge case as a function of distance and (b), the horizontally uniform case as a function of time. The solutions of the appropriate diffusion equations obtained by Philip (1959) are used as the basis of the calculations. For the leading-edge case the fetch-height ratio for 90 per cent of the adjustment to be completed varies from 140 at a height of 0·5 metres to 530 at a height of 50 metres. The solution has application over a wide range of wind speed. For the case of horizontal uniformity and following an abrupt change in surface flux, 90 per cent of the adjustment is completed in 0·45 min at a height of 0·5 m increasing to 86 min at a height of 50 m. It is suggested that these values indicate that the choice of site and conditions for micrometeorological research is critical, and that disparity between a number of experiments may be a consequence of failure to satisfy these basic requirements.
- Published
- 1963
- Full Text
- View/download PDF
49. The spectral density technique for the determination of eddy fluxes
- Author
-
B. B. Hicks and A. J. Dyer
- Subjects
Physics ,Atmospheric Science ,Designed equipment ,Flux (metallurgy) ,Meteorology ,Spectral density ,Humidity ,Turbulent flux ,Spectral line ,Computational physics - Abstract
The determination of turbulent fluxes from measurements of spectral densities of velocity, temperature and humidity is discussed as a technique applicable to the open ocean. A preliminary investigation over land using specially designed equipment measuring spectral densities of wind and temperature at a single frequency indicates that present understanding of the Kolmogorov and flux/gradient relationships is adequate for the purpose. Although humidity spectra are included in the treatment, no measurements of them were made. Values of the effective Kolmogorov constants for velocity and temperature are found to be 0.54 ± 0.03 and 0.71 ± 0.04 respectively, in good agreement with other recent determinations. The principles of application of the technique at sea are discussed. The method assumes that the divergences of the eddy energy fluxes can be neglected. Whilst the present results appear to support this assumption, there is a need for further examination of this aspect.
- Published
- 1972
- Full Text
- View/download PDF
50. Observations of the modification of the microclimate at a leading edge
- Author
-
A. J. Dyer and T. V. Crawford
- Subjects
Hydrology ,Atmospheric Science ,Leading edge ,Microclimate ,Environmental science ,Atmospheric sciences - Abstract
Temperature profiles observed over a heavily irrigated grass field in the midst of dry surroundings show continuous modification up to the maximum height of measurement (5 m) even at a distance of 200 m from the leading edge. Considerable variation of eddy fluxes in the vertical is demonstrated. The surface fluxes are found to undergo gradual adjustment. These observations illustrate that a site of considerable extent is required for micrometeorological and agricultural studies before horizontal uniformity can be assumed.
- Published
- 1965
- Full Text
- View/download PDF
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