Adaptive Lag Research Articles

Adaptive Lag Synchronization for Competitive Neural Networks With Mixed Delays and Uncertain Hybrid Perturbations

This paper investigates the problem of adaptive lag synchronization for a kind of competitive neural network with discrete and distributed delays (mixed delays), as well as uncertain nonlinear external and stochastic perturbations (hybrid perturbations). A simple but robust adaptive controller is designed such that the response system can lag-synchronize with a drive system. Based on the Lyapunov stability theory and some suitable Lyapunov-Krasovskii functionals, several sufficient conditions ensuring the lag synchronization are developed. Our synchronization criteria are easily verified and do not need to solve any linear matrix inequality. Some existing results are improved and extended. Moreover, the designed adaptive controller has better anti-interference capacity and is more practical than the usual adaptive controller. Numerical simulations are exploited to show the effectiveness of the theoretical results.

Adaptive lag synchronization and parameters adaptive lag identification of chaotic systems

This Letter investigates the problem of adaptive lag synchronization and parameters adaptive lag identification of chaotic systems. In comparison with those of existing parameters identification schemes, the unknown parameters are identified by adaptive lag laws, and the delay time is also identified in this Letter. Numerical simulations are also given to show the effectiveness of the proposed method.

Adaptive lag synchronization in coupled chaotic systems with unidirectional delay feedback

Lag synchronization in unidirectionally coupled chaotic systems is investigated in this paper. Based on the invariance principle of differential equations, a new adaptive delay feedback scheme is proposed to realize the lag synchronization effectively in the coupled chaotic systems. As an example, numerical simulations for the coupled Hindmarsh–Rose (HR) neuron models are conducted, which is in good agreement with the theoretical analysis. More interestingly, it is found that there is a fine U-shaped structure in the lag synchronization curve for the HR neuron model. Furthermore, lag synchronization and the corresponding U-shaped structure are robust against the small mismatch of parameters and noisy disturbances.

LAG PROJECTIVE STOCHASTIC PERTURBED SYNCHRONIZATION FOR CHAOTIC SYSTEMS AND ITS APPLICATION IN SECURE COMMUNICATION

In this paper, a simple and systematic adaptive feedback method for achieving lag projective stochastic perturbed synchronization of a new four-wing chaotic system with unknown parameters is presented. Moreover, a secure communication scheme based on the adaptive feedback lag projective synchronization of the new chaotic systems with stochastic perturbation and unknown parameters is presented. The simulation results show the feasibility of the proposed method.

Adaptive lag synchronization in unknown stochastic chaotic neural networks with discrete and distributed time-varying delays

In this Letter, we have dealt with the problem of lag synchronization and parameter identification for a class of chaotic neural networks with stochastic perturbation, which involve both the discrete and distributed time-varying delays. By the adaptive feedback technique, several sufficient conditions have been derived to ensure the synchronization of stochastic chaotic neural networks. Moreover, all the connection weight matrices can be estimated while the lag synchronization is achieved in mean square at the same time. The corresponding simulation results are given to show the effectiveness of the proposed method.

Adaptive lag synchronization of unknown chaotic delayed neural networks with noise perturbation

In this Letter, the adaptive lag synchronization issue of unknown chaotic delayed neural networks with noise perturbation is considered in detail. Via adaptive feedback control techniques, the suitable parameters update laws are proposed, then several sufficient conditions are derived to ensure lag synchronization of unknown delayed neural networks with or without noise perturbation. Moreover, some appropriate comparisons are made to contrast to some of existing results about complete synchronization of chaotic systems with or without noise perturbation. Then, a numerical example with its computer simulations is provided to illustrate and verify the effectiveness of the proposed adaptive scheme. Finally, the proposed adaptive feedback scheme is applied to the secure communication.

Niche construction, human behavior, and the adaptive-lag hypothesis

Niche construction is the process whereby organisms modify selective environments, thereby affecting evolution. The niche-construction perspective is particularly relevant to researchers using evolutionary methods to interpret human behavior and society. On the basis of niche-construction theory, we argue against the hypothesis that modern humans experience an atypically large adaptive lag. We stress that humans construct their world largely to suit themselves and frequently buffer adaptive lag through cultural niche construction. Where they are unable to do that, natural selection of genes rapidly ensues. Our argument has implications for evolutionary psychology and human behavioral ecology, and suggests that the methods of the latter are potentially applicable to all human societies, even postindustrial ones.

The impact of climate change on growth of local white spruce populations in Québec, Canada

In the near future, forest tree species growing in eastern Canada are expected to be affected by climate change due to an increase of human-induced greenhouse gas emissions. In this study, models were developed to estimate the impact of climate change on growth in white spruce ( Picea glauca (Moench) Voss). Data were collected in a genecological test, replicated in three locations, and involving 45 distinct geographical seed sources, most of them represented by five open-pollinated families. Transfer models predicting the performance of seed sources were developed, based on temperature and precipitation differentials between the geographical origin of seed sources and the experimental site locations. These models were validated using data collected in a second genecological test series. We found that white spruce populations located within the sampled area were optimally adapted to their local environment for thermal conditions but not for moisture conditions; populations that originated from sites receiving more precipitation generally showed higher tree growth than the local sources. We predict that the adaptive lag currently related to precipitation will increase under global warming conditions. Simulations of growth under various scenarios of climate change indicated that it would be diminished tangibly under more intense warming. However, for a given temperature increase, the relative loss in growth will be less if precipitation is reduced than if it increases. Consequently, predictions based solely on temperature change appear inaccurate, and more effort should be directed toward better anticipating the magnitude and the direction of changes in precipitation patterns at the regional scale. The necessity of human intervention to assist tree migration under climate change is examined.

The Fungus Penicillium citrinum Thom 1910 VKM FW-800 Isolated from Ancient Permafrost Sediments As a Producer of the Ergot Alkaloids Agroclavine-1 and Epoxyagroclavine-1

The study of the secondary metabolites of the relict strain Penicillium citrinum VKM FW-800 isolated from ancient Arctic permafrost sediments showed that this fungus produces agroclavine-1 and epoxyagroclavine-1, which are rare ergot alkaloids with the 5R,10S configuration of the tetracyclic ergoline ring system. The production of the alkaloids by the fungus showed a biphasic behavior, being intense in the phase of active growth and slowing down in the adaptive lag phase and in the stationary growth phase. The addition of zinc ions to the incubation medium led to a fivefold increase in the yield of the alkaloids. The alkaloids-producing Penicillium fungi isolated from different regions exhibited the same tendencies of growth and alkaloid production.

Alternative expectations models and exchange rate dynamics

This paper reconsiders the issue of exchange rate dynamics in light of recent empirical evidence on the possible failure of rational exchange rate expectations. The Dornbusch model is respecified using three popular models of exchange rate expectations tested by Frankel and Froot. A key result of the paper is that with adaptive or distributed lag expectations the exchange rate may either overshoot or undershoot in response to monetary expansion. In addition, if expectations are regressive, and asset holders base their perceptions of the long-run equilibrium exchange rate on a simple purchasing power parity calculation, either overshooting or undershooting may occur. © 1998 John Wiley & Sons, Ltd.

The degradation of L-histidine, imidazolyl-L-lactate and imidazolylpropionate by Pseudomonas testosteroni.

1. Imidazol-5-ylpropionate and imidazol-5-yl-lactate are degraded by Pseudomonas testosteroni via inducible pathways. 2. Growth on either compound as the sole source of carbon results in the induction of the enzymes for histidine catabolism. 3. The pathway of histidine degradation in this organism, a non-fluorescent Pseudomonad, is shown to be the same as that operating in Pseudomonas fluorescens and Pseudomonas putida. It consists of the successive formation of urocanate, imidazol-4-on-5-ylpropionate, N-formimino-l-glutamate, N-formyl-l-glutamate and glutamate. 4. Whole cells of P. testosteroni accumulate urocanate in the reaction mixture when incubated with imidazolylpropionate, but only after an adaptive lag period which is removed by previous growth on imidazolylpropionate as the source of carbon. 5. Imidazolyl-lactate is oxidized to imidazolylpyruvate, which then gives rise to histidine by specific transamination with l-glutamate. 6. Cells grown on histidine, urocanate or imidazolylpropionate are also able to degrade imidazolyllactate. 7. Mutants lacking urocanase are unable to grow on imidazolylpropionate, imidazolyl-lactate, histidine or urocanate. One with impaired histidase activity cannot utilize histidine or imidazolyl-lactate, but grows normally on imidazolylpropionate or urocanate. A mutant unable to grow on imidazolylpropionate is indistinguishable from the wild-type with respect to growth on histidine, imidazolyl-lactate or urocanate. 8. Thus it is established that imidazolyl-lactate is metabolized via histidine whereas imidazolylpropionate enters the histidine degradation pathway after conversion into urocanate.

Bacterial degradation of nitrilotriacetic acid (NTA).

Pseudomonas sp. was isolated from sewage effluent by elective culture with nitrilotriacetic acid (NTA) as its sole nitrogen and carbon source for growth. NTA-nitrogen was converted to biomass and ammonium by growing cultures with small quantities of nitrite (< 1 ppm) being produced. Washed cell suspensions degraded all of the NTA-nitrogen to ammonium before total conversion of the NTA-carbon to carbon dioxide and water. Resting cell suspensions grown from NTA oxidized NTA, aminodiacetic acid, and glycine immediately, whereas methylaminodiacetic acid was oxidized only after an adaptive lag period, and sarcosine was not oxidized at all. Oxidation of aminodiacetic acid was always more rapid than NTA. Nitrosamines or other nitroso compounds were not found in culture or resting cell supernatants incubated with NTA.

Effects of nitrogen supplements on nitrogen fixation by Aerobacter aerogenes

1. 1. The effects of limiting concentrations of NH 4 + and amino acids on nitrogen fixation by Aerobacter aerogenes have been compared. 2. 2. The organism exhibited typical diphasic growth during the fixation of nitrogen in the presence of NH 4 +, whereas in the presence of amino acids growth was continuous and uninterrupted by a prefixation lag period. 3. 3. The effect of added aspartic acid on nitrogen fixation was similar to that of amino acids. However, pyruvate added together with NH 4 + did not prevent the prefixation lag period. 4. 4. The duration of the adaptive lag period varied in direct proportion to the amount of NH 4 + present when mixed supplements of NH 4 + and amino acids were used. 5. 5. The intracellular ninhydrin-positive material that was present at the onset of the lag period decreased considerably by the termination of this period. 6. 6. It was suggested that NH 4 + exerted an antagonistic influence on the nitrogen-fixing system (‘nitrogenase’). Exhaustion of NH 4 + from the medium caused a release of this inhibition and nitrogenase synthesis took place during the adaptive lag period at the expense of the amino acid pool which was derived through nitrogen (inducer)-stimulated protein turnover.

THE NATURE OF THE "ADAPTIVE LAG" IN URIC ACID ACCUMULATION BY THE YEAST, CANDIDA UTILIS.

THE NATURE OF THE "ADAPTIVE LAG" IN URIC ACID ACCUMULATION BY THE YEAST, CANDIDA UTILIS.

The Assimilation of Nitrogen from Ammonium Salts and Nitrate by Fungi

SUMMARY 1. The assimilation of inorganic nitrogen by Scopulariopsis brevicaulis and some physiologically similar species has been studied. Their failure to assimilate completely from ammonium sulphate has been shown to be due to the fall in pH of the medium induced by the initial uptake of ammonia. 2. Complete assimilation of ammonia takes place in the presence of the neutral salts of each of thirteen organic acids investigated. The organic acids act prima rily through their buffering effect which prevents or slows down the fall in pH. They are not specifically required for ammonia assimilation by these fungi and can be effectively replaced by certain inorganic buffers. 3. The influence of several external factors on the rate of assimilation of ammo nia, nitrate, and nitrite has been studied in S. brevicaulis. In corresponding condi tions the mycelium assimilates ammonia more rapidly than .nitrate over a wide range of conditions. 4. Ammonia, even in very low concentration, completely suppresses nitrate assimilation when both sources of nitrogen are present together. Nitrite, how ever, is assimilated simultaneously with ammonia. It is therefore concluded that ammonia blocks the reduction of nitrate to nitrite by the fungus. 5. The suppression of nitrate assimilation in the presence of ammonia is com mon to many mould fungi besides S. brevicaulis, and is believed to have adaptive significance in natural habitats. 6. The nitrate-reducing and assimilating system is formed, even when S. brevi caulis is grown in complete absence of nitrate (ammonia medium with organic acid). It comes into action rapidly when the inhibiting effect of ammonia is removed. Similarly, nitrate-grown mycelium is capable of assimilating ammonia at maximal rate without any adaptive lag.