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Results for “stability boundary”

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At least 127 records · Page 7Linked to original sources
PubMed1998

Simian Y chromosomes: species-specific rearrangements of DAZ, RBM, and TSPY versus contiguity of PAR and SRY.

The three human male specific expressed gene families DAZ, RBM, and TSPY are known to be repetitively clustered in the Y-specific region of the human Y Chromosome (Chr). RBM and TSPY are Y-specifically conserved in simians, whereas DAZ cannot be detected on the Y chromosomes of New World monkeys. The proximity of SRY to the pseudoautosomal region (PAR) is highly conserved and thus most effectively stabilizes the pseudoautosomal boundary on the Y (PABY) in simians. In contrast, the non-recombining part of the Y Chrs, including DAZ, RBM, and TSPY, was exposed to species-specific amplifications, diversifications, and rearrangements. Evolutionary fast fixation of any of these variations was possible as long as they did not interfere with male fertility.

Animals↗
PubMed2004

Simple mathematical models for interacting wild and transgenic mosquito populations.

Two discrete-time models for interacting populations of wild and genetically altered mosquito are presented, where the genetically altered mosquitoes are grouped into a single population without distinguishing their zygosity. The birth and death rates for both populations are density-dependent, and the mating rates between the mosquitoes are assumed to be either constant or proportional to the total populations for the two models, respectively. The existence and stability of the boundary and positive equilibria are investigated. In particular, it is shown that bifurcations from both boundary and positive equilibria can appear for the model with proportional mating rates. Stable equilibria, periodic-doubling bifurcations, aperiodic oscillations, and chaotic behavior are all illustrated by numerical simulations.

Algorithms↗
PubMed2005

The impact of environmental fluctuations on structured discrete time population models: resonance, synchrony and threshold behaviour.

External forcing of a discrete time ecological system does not just add variation to existing dynamics but can change the dynamics. We study the mechanisms that can bring this about, focusing on the key concepts of excitation and suppression which emerge when analysing the power spectra of the system in linear approximation. Excitation, through resonance between the system dynamics and the external forcing, is the greater the closer the system is to the boundary of the stability region. This amplification means that the extinction of populations becomes possible sooner than expected and, conversely, invasion can be significantly delayed. Suppression and the consequent redistribution of power within the spectrum proves to be a function both of the connectivity of the network graph of the system and the way that external forcing is applied to the system. It is also established that colour in stochastic forcing can have a major impact, by enhancing resonance and by greater redistribution of power. This can mean a higher risk of extinction through larger fluctuations in population numbers and a higher degree of synchrony between populations. The implications of external forcing for stage-structured species, for populations in competition and for trophic web systems are studied using the tools and concepts developed in the paper.

Ecosystem↗
PubMed1999

Resistance of a food chain to invasion by a top predator.

We study the invasion of a top predator into a food chain in a chemostat. For each trophic level, a bioenergetic model is used in which maintenance and energy reserves are taken into account. Bifurcation analysis is performed on the set of nonlinear ordinary differential equations which describe the dynamic behaviour of the food chain. In this paper, we analyse how the ability of a top predator to invade the food chain depends on the values of two control parameters: the dilution rate and the concentration of the substrate in the input. We investigate invasion by studying the long-term behaviour after introduction of a small amount of top predator. To that end we look at the stability of the boundary attractors; equilibria, limit cycles as well as chaotic attractors using bifurcation analysis. It will be shown that the invasibility criterion is the positiveness of the Lyapunov exponent associated with the change of the biomass of the top predator. It appears that the region in the control parameter space where a predator can invade increases with its growth rate. The resulting system becomes more resistant to further invasion when the top predator grows faster. This implies that short food chains with moderate growth rate of the top predator are liable to be invaded by fast growing invaders which consume the top predator. There may be, however, biological constraints on the top predator's growth rate. Predators are generally larger than prey while larger organisms commonly grow slower. As a result, the growth rate generally decreases with the trophic level. This may enable short food chains to be resistant to invaders. We will relate these results to ecological community assembly and the debate on the length of food chains in nature.

Animals↗
PubMed2000

One-dimensional dynamics for traveling fronts in coupled map lattices

Multistable coupled map lattices typically support traveling fronts, separating two adjacent stable phases. We show how the existence of an invariant function describing the front profile allows a reduction of the infinitely dimensional dynamics to a one-dimensional circle homeomorphism, whose rotation number gives the propagation velocity. The mode locking of the velocity with respect to the system parameters then typically follows. We study the behavior of fronts near the boundary of parametric stability, and we explain how the mode locking tends to disappear as we approach the continuum limit of an infinite density of sites.

Journal Article↗
PubMed2001

Pattern formation near onset of a convecting fluid in an annulus.

Numerical simulations of the time-dependent Swift-Hohenberg equation are used to test the predictions of Cross [Phys. Rev. A 25, 1065 (1982)] that Rayleigh-Bénard convection in the form of straight rolls or of an array of dislocations may be observed in an annular domain, depending on the values of inner radius r(1), outer radius r(2), reduced Rayleigh number epsilon, and initial states. As r(1) is decreased for a fixed r(2) and for different choices of epsilon and of symmetric and random initial state, we find that there are indeed ranges of these parameters for which the predictions of Cross are qualitatively correct. However, when the radius difference r(2)-r(1) becomes larger than a few roll diameters, a new pattern is observed consisting of stripe domains separated by radially oriented grain boundaries. The relative stabilities of the various patterns are compared by evaluating their Lypunov functional densities.

Journal Article↗
PubMed2000

Levels of control and closure in complex semiotic systems

It is natural to advance closures as atomic processes of universal evolution, and to analyze this concept specifically. Real complex systems like organisms and complex mechanisms cannot exist at either extreme of complete closure or lack of closure, nevertheless we should consider the properties of closures in general, the introduction of boundaries, a corresponding stability, the establishment of system autonomy and identity, and thereby the introduction of emergent new system of potentially new types. Our focus should move from simple physical closure of common objects and classical self-organizing systems to semiotically closed systems that maintain cyclic relations of perception, interpretation, decision, and action with their environments. Thus, issues arise concerning the use and interpretation of symbols, representations, and/or internal models (whether explicit or implicit) by the system; and the syntactic, semantic, and pragmatic relations among the sign tokens, their interpretations, and their use or function for the systems in question. Primitive semiotic closures are hypothesized as equivalent to simple control systems, and in turn equivalent to simple organisms. This leads us directly to the grand hierarchical control theories of Turchin, Powers, and Albus, which provide an explicit mechanism for the formation of new levels within complex semiotically closed systems.

Journal Article↗
PubMed1982

Identification of synthesized [r-w] continua for adult and child speakers.

A continuing problem in speech research is the comparison of phonetically similar but acoustically distinct sounds such as the comparison between adult speech and child speech. This problem is especially important in the remediation of speech disorders. In this study, we focus on this problem as manifested in the disordered production of [r] sounds. Stimuli which varied in F2 and F3 onset frequencies were synthesized to span continua from [r] to [w] for adult, child, and scaled adult (formants 1.5 times adult values) speakers. These stimuli were presented to 18 naive adults for identification as "R"or "W" at three listening sessions to test for stability of category boundaries. Significant shifts in category boundaries were found for all three continua between sessions one and two but not between sessions two and three. Category boundaries in terms of formant frequencies showed significant differences between the adult and childlike continua. Rescaling these values on a psychophysical dimension and adjusting for formant spread brought the category boundaries into close alignment. In free choice testing, synthesized [r] and [w] stimuli were identified by most subjects at least as well as natural [r] and [w] stimuli but synthesized child [r] stimuli were identified by most subject considerably better than natural child [r] stimuli.

Child Language↗
PubMed1981

[The role of speech sound expectation in categorical perception (author's transl)].

The effects of specific hearer expectations on the categorical perception of speech sound continua were investigated. Subjects were asked to perform identification tests on synthetically produced /ba-da-ga/ continua. Hearer expectations for the /da/ category were raised and lowered, respectively, within the experimental group. Only the condition of raised expectation produced a change in the identification of the /da/ category: while the category boundaries themselves did not shift, the perception of /da/ sounds within these boundaries was significantly stabilized. Speech sound expectation apparently adapts to the structure provided by perceptual categories and thus contributes to an optimization of the perceptual process.

Adult↗
PubMed2004

Is NHS dentistry in crisis? 'Traffic light' maps of dentists distribution in England and Wales.

BACKGROUND: 'Traffic light' (red-yellow-green) maps are potentially powerful tools for 'at a glance' problem detection, for optimising resource allocation/reallocation, setting priorities, and targeting interventions to areas most in need. The maps can be also used for administrative area comparisons and performance monitoring over time. Interactive Web versions of the maps can be generated with many handy features to further empower organisations and decision makers. Methodological issues to consider when creating 'traffic light' maps include hue thresholding, data timeliness and stability of administrative boundaries. RESULTS: We used 'traffic light' maps to study the distribution of dentists per 1,000 population in all 304 English Primary Care Trusts (PCTs) and 22 Welsh Local Health Boards (LHBs) using datasets of dentist numbers per PCT (as at 31 December 2002) and LHB (as at 26 February 2004) from the Dental Practice Board, and 2001 Census population figures for PCTs and LHBs from the Office for National Statistics. The overall NHS dentists per 1,000 population figures for England (0.374) and Wales (0.359) are low compared to many other countries, with less than 0.3 dentist per 1,000 people available to 24.1% of the total population of England (81 PCTs or 26.6% of all PCTs) and 26.1% of the total population of Wales (6 LHBs or 27.3% of all LHBs). A general shortage of NHS dentists can be observed at a glance across England and Wales on all the 'traffic light' maps in our study, even on those using a more "tolerant" classification and an additional orange-yellow class. The distribution of NHS dentists in England and Wales was also found to be not uniform, with some PCTs/LHBs, especially those located in some of the deprived or less populated urban and rural communities, suffering significantly more shortage of dentists than others (see http://healthcybermap.org/PCT/dentists/). These results confirm recent media reports of a shortage of NHS dentists in various parts of England and Wales. CONCLUSION: Suitable programmes are urgently needed to increase the numbers of NHS dentists across England and Wales. We have included a set of recommendations to dental health policymakers and planners, in addition to ideas for further work.

Journal Article↗
PubMed2004

Observation and investigation of off-axis modes in a high-power Nd:YAG laser.

Unusual transverse patterns were observed in a cw-lamp-pumped Nd:YAG laser near the boundaries of the stability zones of the laser resonator. An interpretation of these patterns is given in terms of off-axis modes, which can be excited owing to spherical aberrations and astigmatism of the thermal lens and thermally induced birefringence. Additional evidence of the off-axis character of the observed modes was obtained by analysis of the temporal behavior of the observed patterns.

Journal Article↗
PubMedDate not supplied

[Hysteresis and multiplicity of dynamic states in open 2-substrate enzyme reactions with substrate inhibition].

A mathematical model of an open two-substrate enzymic with substrate inhibition has been analyzed. The hysteretic form of the reaction input characteristics resulting in the appearance of three alternative stationary states, O1, O2 and O3, has been obtained. The region of existence of a stable limit cycle has been determined within the framework of linear approximation. Analysis of the model to a non-linear approximation shows that close to the boundary of the stability region the unstable or stable limit cycle can surround O1 or O3 as well as the only stationary state O.

Enzymes↗
PubMed1992

From acting out to words and meaning.

This paper presents an explanation and illustration of the behavioural phenomenon of concretization through acting out. The phenomenon refers to the realization of fantasies and psychic conflicts pertaining to the traumatic past of Holocaust survivor parents, which might have been transmitted to the next generation narratively or beyond words. I have illustrated this phenomenon by material taken from the first stages of the analysis of a young man who shot and wounded his father during the latter's attempt to save him from suicide. The analytic experience facilitated the stabilization of ego boundaries and the emergence of a more secure sense of self.

Acting Out↗
PubMed1992

[Some dimensions of the forgotten body in psychoanalysis and psychosomatic medicine].

Bodily Experience is well reflected in psychoanalysis and psychosomatic medicine, the body is not forgotten. The first part of the paper summarizes the general and clinical knowledge on bodily experience. The second part deals with some still neglected dimensions of bodily experience. The first two dimensions are clinical perspectives. 1. The (ill) body can be functionalized as a help to stabilize fragile body boundaries. 2. The body is determined not only by intrapsychic conflicts but also by social influences, so that bodily behavior might not necessarily reflect intrapsychic attitudes but social (hyper-)adaptation. The following two dimensions may be important for psychosomatic research. 3. Causal and unidirectional models of body-soul influences lack complexity and should be replaced by differentiated interactional models. 4. Empirical studies on body experience have to take into account its subjective and unconscious character. Qualitative methods might be very helpful here.

Body Image↗
PubMed2005

Environmental characteristics of sandstorm of Minqin Oasis in China for recent 50 years.

The purpose of this present study is to investigate the frequency and variation of sandstorm in Minqin Oasis. Using daily observational data of sandstorm and other meteorologic data from 1954 to 2000, we have illuminated the relationship between sandstorm, meteorological parameters and human activities. The results of the analysis show that the highest frequency of sandstorms occurrence and their duration mainly focus on March, April and May, especially in April. Most of sandstorms occur from midday to nightfall, but relative few appear from midnight to forenoon, which apparently correlates to the daily variations of atmospheric thermal stability within atmospheric boundary layer. Monthly mean and annual mean duration of sandstorms coincide well with the frequencies of sandstorm occurrence.

China↗
PubMed1989

The stability of ecosystems.

Stability criteria and phase boundaries for complex ecosystems are obtained and contrasted with previously studied scenarios. The stability of such systems is determined by the behaviour of the largest eigenvalue of matrices governing the response of the system to small perturbations. As a result we show that ecosystems with unstructured cooperative interactions between arbitary species can be less stable than had been previously determined. We also examine hierarchical ecologies, and demonstrate their increased stability under certain conditions.

Animals↗
PubMedDate not supplied

pH changes in Immobiline gels due to low-molecular mass ion adsorption and conditions for salt front formation during electrophoretic desorption.

A simple theoretical model of low molecular mass ion adsorption on a weak exchanger is proposed. For a system containing immobilized charges in uniform concentration the pH change values connected with neutral salt addition and followed by further washing and voltage application are evaluated. The question of stability of the moving boundary, arising in the area near the electrodes, is considered for the constant current stabilization at different values of Immobiline concentration, pK values of Immoboline and salt concentration. The threshold values of ion mobility capable of providing a sharp salt front formation are also evaluated for conditions of strong adsorption. We found that, with extremely acidic Immobilines, a sharp salt front does not arise under the latter condition, even in the case of very high Immobiline concentrations.

Gels↗
PubMed2006

Non-Gibbsian stochastic light-mode dynamics of passive mode locking.

We study a stochastic light-mode system with non-Gibbsian steady state statistics, unravelling global nonequilibrium phase transition properties. It relates to the onset of passive mode-locking in the general case of lasers with arbitrary dispersion and Kerr nonlinearity that includes the nonsolitonic regime. The solution is facilitated by a special stationarity criterion imposed by the system gain balance. We show that the mode-locking phase transition is generic, and give exact expressions for the pulse power and its stability map. We find that at the boundary of the mode-locking stability the pulse power is exactly one half of the total intracavity power, and that the parameter region for the most resistant pulses against noise destabilization is not at the soliton condition.

Journal Article↗