Showing papers by "York University published in 2006"

The fourth data release of the Sloan Digital Sky Survey

Abstract: This paper describes the Fourth Data Release of the Sloan Digital Sky Survey (SDSS), including all survey-quality data taken through 2004 June. The data release includes five-band photometric data for 180 million objects selected over 6670 deg2 and 673,280 spectra of galaxies, quasars, and stars selected from 4783 deg2 of those imaging data using the standard SDSS target selection algorithms. These numbers represent a roughly 27% increment over those of the Third Data Release; all the data from previous data releases are included in the present release. The Fourth Data Release also includes an additional 131,840 spectra of objects selected using a variety of alternative algorithms, to address scientific issues ranging from the kinematics of stars in the Milky Way thick disk to populations of faint galaxies and quasars.

The sloan digital sky survey quasar survey: Quasar luminosity function from data release 3

Abstract: We determine the number counts and z = 0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg2 of imaging data from SDSS Data Release 3. The sample extends from i = 15 to 19.1 at z 3 and to i = 20.2 for z 3. The number counts and luminosity function agree well with the results of the Two Degree Field QSO Redshift Survey (2QZ) at redshifts and luminosities at which the SDSS and 2QZ quasar samples overlap, but the SDSS data probe to much higher redshifts than does the 2QZ sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best-fit model has a flatter bright-end slope at high redshift than at low redshift. For z < 2.4 the data are best fit by a redshift-independent slope of ? = -3.1 [?(L) ? L?]. Above z = 2.4 the slope flattens with redshift to ? -2.37 at z = 5. This slope change, which is significant at the 5 ? level, must be accounted for in models of the evolution of accretion onto supermassive black holes.

Do biotic interactions shape both sides of the humped-back model of species richness in plant communities?

Abstract: A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity-diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity.

Dominant Shareholders, Corporate Boards and Corporate Value: A Cross-Country Analysis

Abstract: We investigate the relation between corporate value and the proportion of the board made up of independent directors in 799 firms with a dominant shareholder across 22 countries. We find a positive relation, especially in countries with weak legal protection for shareholders. The findings suggest that a dominant shareholder, were he so inclined, could offset, at least in part, the documented value discount associated with weak country-level shareholder protection by appointing an 'independent' board. The cost to the dominant shareholder of doing so is the loss in perquisites associated with being a dominant shareholder. Thus, not all dominant shareholders will choose independent boards.

Uncertainty, Opportunism, and Governance: The Effects of Volatility and Ambiguity on Formal and Relational Contracting

Abstract: Comparing the effectiveness of contractual and relational governance in constraining opportunism under conditions of volatility and ambiguity, we hypothesize that relational contracts will be robus...

A comparison of propensity score methods: a case-study estimating the effectiveness of post-AMI statin use.

Abstract: There is an increasing interest in the use of propensity score methods to estimate causal effects in observational studies. However, recent systematic reviews have demonstrated that propensity score methods are inconsistently used and frequently poorly applied in the medical literature. In this study, we compared the following propensity score methods for estimating the reduction in all-cause mortality due to statin therapy for patients hospitalized with acute myocardial infarction: propensity-score matching, stratification using the propensity score, covariate adjustment using the propensity score, and weighting using the propensity score. We used propensity score methods to estimate both adjusted treated effects and the absolute and relative risk reduction in all-cause mortality. We also examined the use of statistical hypothesis testing, standardized differences, box plots, non-parametric density estimates, and quantile-quantile plots to assess residual confounding that remained after stratification or matching on the propensity score. Estimates of the absolute reduction in 3-year mortality ranged from 2.1 to 4.5 per cent, while estimates of the relative risk reduction ranged from 13.3 to 17.0 per cent. Adjusted estimates of the reduction in the odds of 3-year death varied from 15 to 24 per cent across the different propensity score methods.

A Catalog of broad absorption line quasars from the sloan digital sky survey third data release

Abstract: We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release. An automated algorithm was used to match a continuum to each quasar and to identify regions of flux at least 10% below the continuum over a velocity range of at least 1000 km s-1 in the C and Mg absorption regions. The model continuum was selected as the best-fit match from a set of template quasar spectra binned in luminosity, emission line width, and redshift, with the power-law spectral index and amount of dust reddening as additional free parameters. We characterize our sample through the traditional "balnicity" index and a revised absorption index, as well as through parameters such as the width, outflow velocity, fractional depth, and number of troughs. From a sample of 16,883 quasars at 1.7 ≤ z ≤ 4.38, we identify 4386 (26.0%) quasars with broad C absorption, of which 1756 (10.4%) satisfy traditional selection criteria. From a sample of 34,973 quasars at 0.5 ≤ z ≤ 2.15, we identify 457 (1.31%) quasars with broad Mg absorption, 191 (0.55%) of which satisfy traditional selection criteria. We also provide a supplementary list of 39 visually identified z > 4.38 quasars with broad C absorption. We find that broad absorption line quasars may have broader emission lines on average than other quasars.

DEA models for supply chain efficiency evaluation

Abstract: An appropriate performance measurement system is an important requirement for the effective management of a supply chain. Two hurdles are present in measuring the performance of a supply chain and its members. One is the existence of multiple measures that characterize the performance of chain members, and for which data must be acquired; the other is the existence of conflicts between the members of the chain with respect to specific measures. Conventional data envelopment analysis (DEA) cannot be employed directly to measure the performance of supply chain and its members, because of the existence of the intermediate measures connecting the supply chain members. In this paper it is shown that a supply chain can be deemed as efficient while its members may be inefficient in DEA-terms. The current study develops several DEA-based approaches for characterizing and measuring supply chain efficiency when intermediate measures are incorporated into the performance evaluation. The models are illustrated in a seller-buyer supply chain context, when the relationship between the seller and buyer is treated first as one of leader-follower, and second as one that is cooperative. In the leader-follower structure, the leader is first evaluated, and then the follower is evaluated using information related to the leader's efficiency. In the cooperative structure, the joint efficiency which is modelled as the average of the seller's and buyer's efficiency scores is maximized, and both supply chain members are evaluated simultaneously. Non-linear programming problems are developed to solve these new supply chain efficiency models. It is shown that these DEA-based non-linear programs can be treated as parametric linear programming problems, and best solutions can be obtained via a heuristic technique. The approaches are demonstrated with a numerical example.

Selective preference in visual fixation away from negative images in old age? An eye-tracking study.

Abstract: Recent studies have suggested that older individuals selectively forget negative information. However, findings on a positivity effect in the attention of older adults have been more mixed. In the current study, eye tracking was used to record visual fixation in nearly real-time to investigate whether older individuals show a positivity effect in their visual attention to emotional information. Young and old individuals (N = 64) viewed pairs of synthetic faces that included the same face in a nonemotional expression and in 1 of 4 emotional expressions (happiness, sadness, anger, or fear). Gaze patterns were recorded as individuals viewed the face pairs. Older adults showed an attentional preference toward happy faces and away from angry ones; the only preference shown by young adults was toward afraid faces. The age groups were not different in overall cognitive functioning, suggesting that these attentional differences are specific and motivated rather than due to general cognitive change with age.

Executive control in a modified antisaccade task : Effects of aging and bilingualism

Abstract: Two studies are reported that assess differences associated with aging and bilingualism in an executive control task. Previous work has suggested that bilinguals have an advantage over monolinguals in nonlinguistic tasks involving executive control; the major purpose of the present article is to ascertain which aspects of control are sensitive to the bilingual experience. Study 1 used an antisaccade task and found no effects of aging or bilingualism. Study 2 used the identical visual display but coupled to keypress responses. The results showed that bilinguals resolved various types of response conflict faster than monolinguals and that this bilingual advantage generally increased with age. A speculative interpretation of this pattern of results is offered in conclusion.

A developmental perspective on bullying

Abstract: ::::::::::::: :::::::::::::::: :::::::::::: In this paper, we examined the forms and relationship contexts of bullying in adolescence. Using cross-sectional data, we assessed grade and sex differences in self-reports of bullying and sexually harassing peers, as well as reports of dating aggression from1896 students from early to late adolescence. Reports of bullying others were highest around the school transition, with lowest levels at the end of high school. Boys reported more bullying and sexual harassment than girls. Sexual harassment of same- and opposite-sex peers increased over the early adolescent years and leveled off in later high-school years. There were no sex differences in the prevalence of indirect or physical aggression with a dating partner. Adolescents who bullied were at increased risk for the other forms of relationship aggression. These data highlight bullying as a relationship problem and point to the need for prevention programs to curtail the use of power and aggression in adolescent relationships. Aggr. Behav. 32:376–384, 2006. r 2006 Wiley-Liss, Inc.

Coordination of metabolic plasticity in skeletal muscle.

Abstract: Skeletal muscle is a highly malleable tissue, capable of pronounced metabolic and morphological adaptations in response to contractile activity (i.e. exercise). Each bout of contractile activity results in a coordinated alteration in the expression of a variety of nuclear DNA and mitochondrial DNA (mtDNA) gene products, leading to phenotypic adaptations. This results in an increase in muscle mitochondrial volume and changes in organelle composition, referred to as mitochondrial biogenesis. The functional consequence of this biogenesis is an improved resistance to fatigue. Signals initiated by the exercise bout involve changes in intracellular Ca2+ as well as alterations in energy status (i.e. ATP/ADP ratio) and the consequent activation of downstream kinases such as AMP kinase and Ca2+-calmodulin-activated kinases. These kinases activate transcription factors that bind DNA to affect the transcription of genes, the most evident manifestation of which occurs during the post-exercise recovery period when energy metabolism is directed toward anabolism, rather than contractile activity. An important protein that is affected by exercise is the transcriptional coactivator PGC-1alpha, which cooperates with multiple transcription factors to induce the expression of nuclear genes encoding mitochondrial proteins. Once translated in the cytosol, these mitochondrially destined proteins are imported into the mitochondrial outer membrane, inner membrane or matrix space via specific import machinery transport components. Contractile activity affects the expression of the import machinery, as well as the kinetics of import, thus facilitating the entry of newly synthesized proteins into the expanding organelle. An important set of proteins that are imported are the mtDNA transcription factors, which influence the expression and replication of mtDNA. While mtDNA contributes only 13 proteins to the synthesis of the organelle, these proteins are vital for the proper assembly of multi-subunit complexes of the respiratory chain, when combined with nuclear-encoded protein subunits. The expansion of skeletal muscle mitochondria during organelle biogenesis involves the assembly of an interconnected network system (i.e. a mitochondrial reticulum). This expansion of membrane size is influenced by the balance between mitochondrial fusion and fission. Thus, mitochondrial biogenesis is an adaptive process that requires the coordination of multiple cellular events, including the transcription of two genomes, the synthesis of lipids and proteins and the stoichiometric assembly of multisubunit protein complexes into a functional respiratory chain. Impairments at any step can lead to defective electron transport, a subsequent failure of ATP production and an inability to maintain energy homeostasis.

Effect of bilingualism and computer video game experience on the Simon task.

Abstract: A group of 97 participants who were monolingual or bilingual and who had extensive practice playing computer video games or not completed two Simon tasks. The tasks were presented in two conditions that manipulated the number of response switches required in each block of trials. Bilingualism and video-game experience each influenced a different aspect of performance: Video-game players were faster in most conditions, including control conditions that did not include conflict from irrelevant position; bilinguals were faster only in a condition that required the most controlled attention to resolve conflict from the position and the stimulus. The results show the potential of experience to modify performance and point to subtle processing differences in various versions of the Simon task. Resume Un groupe compose de 97 participants unilingues ou bilingues, adeptes ou non de jeux video a l'ordinateur, ont effectue deux tâches de Simon. Les tâches etaient presentees en fonction de deux conditions experimentales, qui modifiaient le nombre de permutations necessaires aux reponses donnees a chaque bloc d'essais experimentaux. Le bilinguisme et la pratique des jeux video a l'ordinateur ont eu, tous deux, un effet sur un aspect distinct de la performance : les joueurs de jeux video etaient plus rapides dans la plupart des conditions, y compris les conditions de controle qui n'entrainaient aucun conflit lorsque le participant choisissait une position non pertinente; les participants bilingues etaient plus rapides uniquement lorsqu'ils etaient soumis a la condition qui demandait le niveau le plus eleve d'attention pour resoudre un conflit provoque par la position et le stimulus. Les resultats de l'etude montrent que l'experience peut modifier le rendement et met en evidence des differences de traitement subtiles pendant l'execution de differentes versions de la tâche de Simon. The Simon task, developed as a means of studying the relationship between gender and handedness (Simon & Rudell, 1967), has become a powerful tool for demonstrating the effect of stimulus-response compatibility on performance and is the basis for a wide range of research investigating attentional processes and executive functions (review in Lu & Proctor, 1995). In the task, stimuli containing both position and response information are presented with a rule that requires participants to ignore the position and respond only to the relevant target feature. When the stimulus appears on the same display side as the correct response key, both position and response information converge on the correct response and the trial is called congruent. When the position conflicts with the correct response, the trials are called incongruent. The reliable increment in response time for the incongruent trials compared to the congruent ones, usually between 20 and 30 milliseconds, is the Simon effect. The task is deceptively simple, yet the requirement to attend only to the target information in the face of conflicting position information engages a variety of processes. The most prevalent explanation for the Simon effect is that it reflects stimulus-response (S-R) incompatibility because of response-selection processes: The location is coded even though it is irrelevant, creating longer reaction times when the stimulus location and the response key are incongruent (Lu & Proctor, 1995). In the dual-route interpretation, the conflict is attributed to response-response (R-R) incompatibility: The position engages automatic processes that activate the same side response and the target information is processed by an intentional system that associates the feature with a response (Hommel, 1993). Conflicting outcomes from these two systems take time to resolve and create the Simon effect. Finally, in a formulation offered by Hommel, Proctor, and Vu (2004), the features from the position and the response are integrated into an "event file" and the sequence of these combinatory representations determines the response time for a particular trial. …

Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales

Abstract: We present a sample of 221 new quasar pairs with proper transverse separations Rprop < 1 h-1 Mpc over the redshift range 0.5 < z < 3.0, discovered from an extensive follow-up campaign to find companions around the Sloan Digital Sky Survey and 2dF QSO Redshift Survey quasars. This sample includes 26 new binary quasars with separations Rprop < 50 h-1 kpc (? < 10''), more than doubling the number of such systems known. We define a statistical sample of binaries selected with homogeneous criteria and compute its selection function, taking into account sources of incompleteness. The first measurement of the quasar correlation function on scales 10 h-1 kpc < Rprop < 400 h-1 kpc is presented. For Rprop 40 h-1 kpc, we detect an order of magnitude excess clustering over the expectation from the large-scale (Rprop 3 h-1 Mpc) quasar correlation function, extrapolated down as a power law (? = 1.53) to the separations probed by our binaries. The excess grows to ~30 at Rprop ~ 10 h-1 kpc and provides compelling evidence that the quasar autocorrelation function gets progressively steeper on submegaparsec scales. This small-scale excess can likely be attributed to dissipative interaction events that trigger quasar activity in rich environments. Recent small-scale measurements of galaxy clustering and quasar-galaxy clustering are reviewed and discussed in relation to our measurement of small-scale quasar clustering.

Single-Column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer

Abstract: The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.

The Effectiveness of Cognitive Behavior Therapy for Borderline Personality Disorder: Results from the Borderline Personality Disorder Study of Cognitive Therapy (BOSCOT) Trial

Abstract: The outcome of a randomized controlled trial of cognitive behavior therapy in addition to treatment as usual (CBT plus TAU) compared with TAU alone (TAU) in one hundred and six participants meeting diagnostic criteria for borderline personality disorder is described. We anticipated that CBT plus TAU would decrease the number of participants with in-patient psychiatric hospitalizations or accident and emergency room contact or suicidal acts over twelve months treatment and twelve months follow-up, compared with TAU. We also anticipated that CBT plus TAU would lead to improvement in a range of secondary outcomes of mental health and social functioning compared to TAU. Of the 106 participants randomized, follow-up data on 102 (96%) was obtained at two years. Those randomized to CBT were offered an average of 27 sessions over 12 months and attended on average 16 (range 0 to 35). We found that the global odds ratio of a participant in the CBT plus TAU group compared with the TAU alone group having any of the outcomes of a suicidal act, in-patient hospitalization, or accident and emergency contact in the 24 months following randomization was 0.86 (95% confidence interval [CI] 0.45 to 1.66, p = 0.66). The corresponding global odds ratio, excluding accident and emergency room contact, was 0.75 (95% CI 0.37 to 1.54, p = 0.44). In terms of the number of suicidal acts, there was a significant reduction over the two years in favor of CBT plus TAU over TAU, with a mean difference of -0.91 (95% CI -1.67 to -0.15, p = 0.020). Across both treatment arms there was gradual and sustained improvement in both primary and secondary outcomes, with evidence of benefit for the addition of CBT on the positive symptom distress index at one year, and on state anxiety, dysfunctional beliefs and the quantity of suicidal acts at two year follow-up. CBT can deliver clinically important changes in relatively few clinical sessions in real clinical settings.

Processing Limitations in Children With Specific Language Impairment: The Role of Executive Function

Abstract: Research suggests that children with specific language impairment (SLI) have processing limitations; however, the mechanisms involved have not been well defined or investigated in a theory-guided manner. The theory of constructive operators was used as a framework to explore processes underlying limited processing capacity in children with SLI. Mental attentional capacity, mental attentional interruption, and 2 specific executive functions (shifting and updating) were examined in 45 children with SLI and 45 children with normally developing language, aged 7 to 12 years. The results revealed overall group differences in performance on measures of mental attention, interruption, and updating, but not shifting. The findings supported the premise that mental attention predicted language competence, but that this relationship was mediated partially by updating.

When “where” is more important than “when”: Birthplace and birthdate effects on the achievement of sporting expertise

Abstract: In this study, we assessed whether contextual factors related to where or when an athlete is born influence their likelihood of playing professional sport. The birthplace and birth month of all American players in the National Hockey League, National Basketball Association, Major League Baseball, and Professional Golfer's Association, and all Canadian players in the National Hockey League were collected from official websites. Monte Carlo simulations were used to verify if the birthplace of these professional athletes deviated in any systematic way from the official census population distribution, and chi-square analyses were conducted to determine whether the players' birth months were evenly distributed throughout the year. Results showed a birthplace bias towards smaller cities, with professional athletes being over-represented in cities of less than 500,000 and under-represented in cities of 500,000 and over. A birth month/relative age effect (in the form of a distinct bias towards elite athletes being relatively older than their peers) was found for hockey and baseball but not for basketball and golf. Comparative analyses suggested that contextual factors associated with place of birth contribute more influentially to the achievement of an elite level of sport performance than does relative age and that these factors are essentially independent in their influences on expertise development.

Social Determinants of Health: Present Status, Unanswered Questions, and Future Directions:

Abstract: This article reviews the current status of theory and research concerning the social determinants of health. It provides an overview of current conceptualizations and evidence on the impact of various social determinants of health. The contributions of different disciplines—epidemiology, sociology, political economy, and the human rights perspective—to the field are acknowledged, but profound gaps persist in our understanding of the forces that drive the quality of various social determinants of health and why research is too infrequently translated into action. Many of these gaps in knowledge concern the political, economic, and social forces that make implementation of public policy agendas focused on strengthening the social determinants of health problematic. The author identifies the areas of inquiry needed to help translate knowledge into action.

Positive Versus Negative Perfectionism in Psychopathology: A Comment on Slade and Owens's Dual Process Model.

Abstract: This article reviews the concepts of positive and negative perfectionism and the dual process model of perfectionism outlined by Slade and Owens (1998). The authors acknowledge that the dual process model represents a conceptual advance in the study of perfectionism and that Slade and Owens should be commended for identifying testable hypotheses and future research directions. However, the authors take issue with the notion that there are two types of perfectionism, with one type of perfectionism representing a "normal" or "healthy" form of perfectionism. They suggest that positive perfectionism is motivated, at least in part, by an avoidance orientation and fear of failure, and recent attempts to define and conceptualize positive perfectionism may have blurred the distinction between perfectionism and conscientiousness. Research findings that question the adaptiveness of positive forms of perfectionism are highlighted, and key issues for future research are identified.

Emotion in psychotherapy: a practice-friendly research review

Abstract: This article reviews the process and outcome research on emotion in psychotherapy. Four distinct types of emotion processes are identified in the literature as useful in therapy, depending on a client's presenting concerns: emotional awareness and arousal; emotional regulation, active reflection on emotion (meaning making), and emotional transformation. Research findings are summarized to highlight the practical implications of these different emotion processes to psychotherapy. A range of selected treatments from different therapeutic orientations are addressed collectively as different types of emotion-focused, experiential therapies and are compared on the basis of how they work with emotion in session.

Work engagement among women managers and professionals in a Turkish bank: Potential antecedents and consequences

Abstract: Purpose – The paper aims to examine potential antecedents and consequences of work engagement in a sample of women managers and professionals employed by a large Turkish bank.Design/methodology/approach – Data were collected from 286 women, a 72 per cent response rate, using anonymously completed questionnaires. Engagement was assessed by three scales developed by Schaufeli et al.: vigor, dedication and absorption. Antecedents included personal demographic and work situation characteristics as well as work life experiences; consequences included measures of work satisfaction and psychological well‐being.Findings – The following results were observed. First, worklife experiences, particularly, control, rewards and recognition and value fit, were found to predict all three engagement measures. Second, engagement, particularly dedication, predicted various work outcomes (e.g. job satisfaction, intent to quit). Third, engagement, particularly vigor, predicted various psychological well‐being outcomes.Research...

Chapter 5 Functional Differential Equations with State-Dependent Delays: Theory and Applications

Abstract: Publisher Summary This chapter illustrates the recent work on equations with state dependent delays, with emphasis on particular models and on the emerging theory from the dynamical systems point of view. Several new results are presented. The chapter describes examples of differential equations with state dependent delays which arise in physics, automatic control, neural networks, infectious diseases, population growth, and cell production. Some of these models differ considerably from others, and most of them do not look simple. Typically the delay is not given explicitly as a function of what seems to be the natural state variable; the delay may be defined implicitly by a functional, integral or differential equation and should often be considered as part of the state variables.