39,000 research outputs found
The evolution of the Mira variable R Hydrae
The Mira variable R Hydrae is well known for its declining period, which Wood
& Zarro (1981) attributed to a possible recent thermal pulse. Here we
investigate the long-term period evolution, covering 340 years, going back to
its discovery in AD 1662. Wavelets are used to determine both the period and
semi-amplitude. We show that the period decreased linearly between 1770 and
1950; since 1950 the period has stabilized at 385 days. The semi-amplitude
closely follows the period evolution. Detailed analysis of the oldest data
shows that before 1770 the period was about 495 days. We find no evidence for
an increasing period during this time as found by Wood & Zarro. IRAS data shows
that the mass loss dropped dramatically around AD 1750. The decline agrees with
the mass-loss formalism from Vassiliadis & Wood, but is much larger than
predicted by the Bloecker mass-loss law. An outer detached IRAS shell suggests
that R Hya has experienced such mass-loss interruptions before. The period
evolution can be explained by a thermal pulse occuring around AD 1600, or by an
non-linear instability leading to an internal relaxation of the stellar
structure. The elapsed time between the mass-loss decline giving rise to the
outer detached shell, and the recent event, of approximately 5000 yr suggests
that only one of these events could be due to a thermal pulse. Further
monitoring of R Hya is recommended, as both models make strong predictions for
the future period evolution. R Hya-type events, on time scales of 10^2-10^3 yr,
could provide part of the explanation for the rings seen around some AGB and
post-AGB stars.Comment: 13 pages. MNRAS, accepted for publicatio
Bose-Einstein condensation in complex networks
The evolution of many complex systems, including the world wide web, business
and citation networks is encoded in the dynamic web describing the interactions
between the system's constituents. Despite their irreversible and
non-equilibrium nature these networks follow Bose statistics and can undergo
Bose-Einstein condensation. Addressing the dynamical properties of these
non-equilibrium systems within the framework of equilibrium quantum gases
predicts that the 'first-mover-advantage', 'fit-get-rich' and
'winner-takes-all' phenomena observed in competitive systems are
thermodynamically distinct phases of the underlying evolving networks
Development of a Cohesion Questionnaire for Youth: The Youth Sport Environment Questionnaire
The purpose of the current study was to initiate the development of a psychometrically sound measure of cohesion for youth sport groups. A series of projects were undertaken in a four-phase research program. The initial phase was designed to garner an understanding of how youth sport group members perceived the concept of cohesion through focus groups (n = 56), open-ended questionnaires (n = 280), and a literature review. In Phase 2, information from the initial projects was used in the development of 142 potential items and content validity was assessed. In Phase 3, 227 participants completed a revised 87-item questionnaire. Principal components analyses further reduced the number of items to 17 and suggested a two-factor structure (i.e., task and social cohesion dimensions). Finally, support for the factorial validity of the resultant questionnaire was provided through confirmatory factor analyses with an independent sample (n = 352) in Phase 4. The final version of the questionnaire contains 16 items that assess task and social cohesion in addition to 2 negatively worded spurious items. Specific issues related to assessing youth perceptions of cohesion are discussed and future research directions are suggested
Some asymptotic properties of duplication graphs
Duplication graphs are graphs that grow by duplication of existing vertices,
and are important models of biological networks, including protein-protein
interaction networks and gene regulatory networks. Three models of graph growth
are studied: pure duplication growth, and two two-parameter models in which
duplication forms one element of the growth dynamics. A power-law degree
distribution is found to emerge in all three models. However, the parameter
space of the latter two models is characterized by a range of parameter values
for which duplication is the predominant mechanism of graph growth. For
parameter values that lie in this ``duplication-dominated'' regime, it is shown
that the degree distribution either approaches zero asymptotically, or
approaches a non-zero power-law degree distribution very slowly. In either
case, the approach to the true asymptotic degree distribution is characterized
by a dependence of the scaling exponent on properties of the initial degree
distribution. It is therefore conjectured that duplication-dominated,
scale-free networks may contain identifiable remnants of their early structure.
This feature is inherited from the idealized model of pure duplication growth,
for which the exact finite-size degree distribution is found and its asymptotic
properties studied.Comment: 19 pages, including 3 figure
Role Ambiguity in Sport Teams
The general purpose of the present study was to examine the nature of role ambiguity in sport teams and to explore the construct validity of the operational definition of role ambiguity developed by Beauchamp, Bray, Eys, and Carron (2002). Role ambiguity was operationalized as a multidimensional construct (Scope of Responsibilities, Behavioral Responsibilities, Evaluation of Performance, and Consequences of Not Fulfilling Responsibilities) that occurs in two contexts, offense and defense. Consistent with the a priori hypothesis, perceptions of role ambiguity exhibited some degree of within-group consistency and group-level variability, but most of the variance in role ambiguity was seen at the individual level. Also, perceptions of role ambiguity decreased from early to late season. Finally, veteran athletes experienced less role ambiguity than first-year athletes at the beginning of the season, but not at the end. Implications of the findings and suggestions for future research are discussed
Item Wording and Internal Consistency of a Measure of Cohesion: The Group Environment Questionnaire
A common practice for counteracting response acquiescence in psychological measures has been to employ both negatively and positively worded items. However, previous research has highlighted that the reliability of measures can be affected by this practice (Spector, 1992). The purpose of the present study was to examine the effect that the presence of negatively worded items has on the internal reliability of the Group Environment Questionnaire (GEQ). Two samples (N = 276) were utilized, and participants were asked to complete the GEQ (original and revised) on separate occasions. Results demonstrated that the revised questionnaire (containing all positively worded items) had significantly higher Cronbach α values for three of the four dimensions of the GEQ. Implications, alternatives, and future directions are discussed
The Effect of Role Ambiguity on Competitive State Anxiety
The purpose of this study was to examine the relationship between role ambiguity and precompetition state anxiety (A-state). Consistent with multidimensional anxiety theory (Martens, Vealey, & Burton, 1990), it was hypothesized that role ambiguity would be positively related to cognitive but not to somatic A-state. Based on the conceptual model presented by Beauchamp, Bray, Eys, and Carron (2002), role ambiguity in sport was operationalized as a multidimensional construct (i.e., scope of responsibilities, role behaviors, role evaluation, and role consequences) potentially manifested in each of two contexts, offense and defense. Consistent with hypotheses, ambiguity in terms of the scope of offensive role responsibilities predicted cognitive A-state (R2 = .19). However, contrary to hypotheses, offensive role-consequences ambiguity also predicted somatic A-state (R2 = .09). Results highlight the importance of using a multidimensional approach to investigate role ambiguity in sport and are discussed in terms of both theory advancement and possible interventions
Percolation in Directed Scale-Free Networks
Many complex networks in nature have directed links, a property that affects
the network's navigability and large-scale topology. Here we study the
percolation properties of such directed scale-free networks with correlated in-
and out-degree distributions. We derive a phase diagram that indicates the
existence of three regimes, determined by the values of the degree exponents.
In the first regime we regain the known directed percolation mean field
exponents. In contrast, the second and third regimes are characterized by
anomalous exponents, which we calculate analytically. In the third regime the
network is resilient to random dilution, i.e., the percolation threshold is
p_c->1.Comment: Latex, 5 pages, 2 fig
Statistical Dynamics of Religions and Adherents
Religiosity is one of the most important sociological aspects of populations.
All religions may evolve in their beliefs and adapt to the society
developments. A religion is a social variable, like a language or wealth, to be
studied like any other organizational parameter.
Several questions can be raised, as considered in this study: e.g. (i) from a
``macroscopic'' point of view : How many religions exist at a given time? (ii)
from a ``microscopic'' view point: How many adherents belong to one religion?
Does the number of adherents increase or not, and how? No need to say that if
quantitative answers and mathematical laws are found, agent based models can be
imagined to describe such non-equilibrium processes.
It is found that empirical laws can be deduced and related to preferential
attachment processes, like on evolving network; we propose two different
algorithmic models reproducing as well the data. Moreover, a population
growth-death equation is shown to be a plausible modeling of evolution dynamics
in a continuous time framework. Differences with language dynamic competition
is emphasized.Comment: submitted to EP
Penalized Orthogonal-Components Regression for Large p Small n Data
We propose a penalized orthogonal-components regression (POCRE) for large p
small n data. Orthogonal components are sequentially constructed to maximize,
upon standardization, their correlation to the response residuals. A new
penalization framework, implemented via empirical Bayes thresholding, is
presented to effectively identify sparse predictors of each component. POCRE is
computationally efficient owing to its sequential construction of leading
sparse principal components. In addition, such construction offers other
properties such as grouping highly correlated predictors and allowing for
collinear or nearly collinear predictors. With multivariate responses, POCRE
can construct common components and thus build up latent-variable models for
large p small n data.Comment: 12 page
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