Adaptive Paths Research Articles

Monkey see, monkey do

A new study shows that the independent adaptation to a ruminant lifestyle in two leaf-eating monkeys relied on parallel amino acid substitutions in ribonuclease gene duplicates. This discovery suggests that, given similar initial conditions, proteins may repeatedly follow similar adaptive evolutionary paths.

Landscape – What’s in it? Trends in European Landscape Science and Priority Themes for Concerted Research

Reflecting on the other papers in this special issue, this synopsis characterises some essential trends in European Landscape Ecology, including the challenges it is facing in society. It describes the various perspectives on the ‘contents’ of landscape that are currently being practiced, and especially considers the notion of ‘environment’ as something intrinsic to human activity. Landscape classification and typology are discussed in their potential but limited use for landscape science. The specificity of the European approach appears to be related to the large diversity of cultural landscapes, currently losing their functional ties with the land-use systems that had formed them. European landscape research reports show a large commitment to this decreasing diversity, a dedication characterised by a strong sense of ‘loss and grief’. On the other hand, it is concluded that European landscape research has a specific niche with a clear focus on applied landscape studies explicitly including people’s perceptions and images, as well as the participation of the public and stakeholders. Since globalisation tends to reinforce the detachment of people from their environment; an increased effort is needed to compensate for this effect, and therefore the consideration of the various dimensions of the landscape is today more pertinent than ever. Meeting the challenges of present landscapes, in the face of new multifunctional demands in old diverse landscapes, requires more than before the combination of various perspectives and methods, and of various scales of application, in order to design innovative and adaptive paths for the future.

Navigation protocols in sensor networks

We develop distributed algorithms for adaptive sensor networks that respond to directing a target through a region of space. We model this problem as an online distributed motion planning problem. Each sensor node senses values in its perception space and has the ability to trigger exceptions events we call “danger” and model as “obstacles”. The danger/obstacle landscape changes over time. We present algorithms for computing distributed maps in perception space and for using these maps to compute adaptive paths for a mobile node that can interact with the sensor network. We give the analysis to the protocol and report on hardware experiments using a physical sensor network consisting of Mote sensors. We also show how to reduce searching space and communication cost using Voronoi diagram.

Adaptive tool path generation from measured data

Conventional algorithms for tool path generation from measured points did not use the region-by-region idea to generate adaptive tool paths since it is difficult to obtain geometric information of scattered points directly, which is necessary for adaptive tool path generation. This paper presents a new strategy for determining geometric information of physical parts measured and then three-axis numerically controlled (NC) adaptive (region-based) tool paths that overcome the inherent drawback (redundant tool paths) can be directly generated from measured points. A new algorithm for computing offsets of B-spline surfaces constructed using chosen point data as control points is also proposed in the paper.

Adaptive Strategies of Firms in High-Velocity Environments

The adaptation-evolution strategies of firms have been a major area of interest. Internet based businesses operate in highly unstable environments witnessing shakeouts and changes in the industry structure. In this paper, we focus on the adaptive strategies and paths of adaptation of independent B2B marketplaces. The independent B2B marketplaces have undergone tremendous change with regard to their business models and products/services. Since their inception as pure market makers, these marketplaces have morphed into integration service providers with market making being one of the functions. What makes the adaptive strategies of B2B marketplaces interesting is the extremely short time period within which these changes happened. The research uses the case study methodology to identify the adaptive strategies of B2B marketplaces in terms of their product/service class evolution. The results based on the case studies suggest a three-stage adaptation model wherein the marketplaces progress through stages such as aggregation, transactions and integration.

System development of adaptive spraying paths for rapid prototyping

Traditional rapid prototyping (RP) uses one nozzle, with a single‐diameter, to conduct spraying of a RP part. The process is usually time‐consuming and inefficient. To improve the traditional method, this research aims to develop a new approach by planning an adaptive path and applying it to the spraying process of every slice. Each accurately sprayed slice then adds one upon another to form a RP part. The processing includes four steps, which will help to produce the adaptive path file, which can be input into the RP machine to make a prototype.

Artificial selection for high activity favors mighty mini-muscles in house mice.

After 14 generations of selection for voluntary wheel running, mice from the four replicate selected lines ran, on average, twice as many revolutions per day as those from the four unselected control lines. To examine whether the selected lines followed distinct strategies in the correlated responses of the size and metabolic capacities of the hindlimb muscles, we examined mice from selected lines, housed for 8 wk in cages with access to running wheels that were either free to rotate ("wheel access" group) or locked ("sedentary"). Thirteen of twenty individuals in one selected line (line 6) and two of twenty in another (line 3) showed a marked reduction ( approximately 50%) in total hindlimb muscle mass, consistent with the previously described expression of a small-muscle phenotype. Individuals with these "mini-muscles" were not significantly smaller in total body mass compared with line-mates with normal-sized muscles. Access to free wheels did not affect the relative mass of the mini-muscles, but did result in typical mammalian training effects for mitochondrial enzyme activities. Individuals with mini-muscles showed a higher mass-specific muscle aerobic capacity as revealed by the maximal in vitro rates of citrate synthase and cytochrome c oxidase. Moreover, these mice showed the highest activities of hexokinase and carnitine palmitoyl transferase. Females with mini-muscles showed the highest levels of phosphofructokinase, and males with mini-muscles the highest levels of pyruvate dehydrogenase. As shown by total muscle enzyme contents, the increase in mass-specific aerobic capacity almost completely compensated for the reduction caused by the "loss" of muscle mass. Moreover, the mini-muscle mice exhibited the lowest contents of lactate dehydrogenase and glycogen phosphorylase. Interestingly, metabolic capacities of mini-muscled mice resemble those of muscles after endurance training. Overall, our results demonstrate that during selection for voluntary wheel running, distinct adaptive paths that differentially exploit the genetic variation in morphological and physiological traits have been followed.

Wave packet dynamics on adaptive moving grids

A new hybrid moving grid approach to wave packet dynamics is described. Exterior points within a nonrigid frame follow Lagrangian trajectories obtained by solving the hydrodynamic equations of motion. Internal grid points within one or more open windows follow non-Lagrangian adaptive paths. Within these windows, problems encountered with quantum trajectories near wave function nodes are circumvented by directly solving the moving path transform of the Schrödinger equation. Excellent results are obtained for evolution of the density in a double well potential even though multiple ripples develop in the density.

Ethanol impairs behavioral strategy use in naive rats but does not prevent spatial learning in the water maze in pretrained rats.

Ethanol impairs performance in the water maze in rats. A detailed behavioral analysis is required to fully evaluate the nature of the impairment. A detailed behavioral analysis was carried out to evaluate the effect of ethanol on performance in the water maze task in male hooded rats given 2.0 or 6.0 g/kg ethanol by gavage. Multiple measures of water maze strategies learning and spatial learning were studied. Water maze trials were recorded on videotape and digitized for offline analysis. Some rats were naive at the start of spatial training, whereas other rats received water maze strategies pretraining prior to spatial training to familiarize them with the general behavioral strategies required in the task. Naive ethanol-treated rats exhibited both spatial learning and water maze behavioral strategies impairments. There was no evidence of a spatial learning impairment that was independent of an associated behavioral strategies impairment. Further, ethanol impaired the ability of naive rats to swim to a stable visible platform. Pretrained ethanol-treated rats performed significantly better than naive ethanol-treated rats on almost all measures, and were indistinguishable from controls on most measures. These results suggest that ethanol may impair water maze performance in naive rats by interfering with their ability to acquire and use required water maze behavioral strategies and generate adaptive swim paths. Ethanol does not prevent robust spatial learning in rats that are familiar with required water maze behavioral strategies.

Adaptive least-expected time paths in stochastic, time-varying transportation and data networks

In congested transportation and data networks, travel (or transmission) times are time-varying quantities that are at best known a priori with uncertainty. In such stochastic, time-varying (or STV) networks, one can choose to use the a priori least-expected time (LET) path or one can make improved routing decisions en route as traversal times on traveled arcs are experienced and arrival times at intermediate locations are revealed. In this context, for a given origin-destination pair at a specific departure time, a single path may not provide an adequate solution, because the optimal path depends on intermediate information concerning experienced traversal times on traveled arcs. Thus, a set of strategies, referred to as hyperpaths, are generated to provide directions to the destination node conditioned upon arrival times at intermediate locations. In this paper, an efficient label-setting-based algorithm is presented for determining the adaptive LET hyperpaths in STV networks. Such a procedure is useful in making critical routing decisions in Intelligent Transportation Systems (ITS) and data communication networks. A side-by-side comparison of this procedure with a label-correcting-based algorithm for solving the same problem is made. Results of extensive computational tests to assess and compare the performance of both algorithms, as well as to investigate the characteristics of the resulting hyperpaths, are presented. An illustrative example of both procedures is provided. © 2001 John Wiley & Sons, Inc.

Ultraviolet cues affect the foraging behaviour of blue tits

The function of avian ultraviolet (UV) vision is only just beginning to be understood. One plausible hypothesis is that UV vision enhances the foraging ability of birds. To test this, we carried out behavioural experiments using wild–caught blue tits foraging for cabbage moth and winter moth caterpillars on natural and artificial backgrounds. The light environment in our experiments was manipulated using either UV–blocking or UV–transmitting filters. We found that the blue tits tended to find the first prey item (out of four) more quickly when UV cues were present. This suggests that UV vision offers benefits to birds when searching for cryptic prey, despite the prey and backgrounds reflecting relatively little UV. Although there was no direct effect of UV on the time taken to find all four prey items in a trial, search performance in the absence of UV wavelengths tended to increase over the course of an experiment. This may reflect changes in the search tactics of the birds. To our knowledge, these are the first data to suggest that birds use UV cues to detect cryptic insect prey, and have implications for our understanding of protective coloration.

Offline real-time channel establishment in packet-switched networks

In this paper, the problem of real-time channel establishment in point-to-point connected networks using packet-switched store-and-forward routing is considered. Each message is associated with a real-time channel, which is an abstraction used to represent a source to destination connection. An offline real-time channel establishment algorithm that produces a feasible ordering, where all channels meet their deadline guarantees is presented. When scheduling a new channel, we allow partial reordering of previously scheduled channels, thereby increasing the size of the feasible set of channels compared to other methods. Alternative minimal routing paths when a channel cannot be scheduled on a path are also analyzed. Simulations show that our algorithm results in reducing the number of unschedulable messages compared to other existing algorithms. For the 2D mesh, the percentage of failed messages using our algorithm drops by as much as 65.69% compared to a previous algorithm [1]. Allowing offline adaptive paths results in reducing the percentage of failed messages for all methods and topologies examined, compared to non-adaptive routing.

Development and analysis of distributed acoustic echo cancellation microphone system

Abstract Acoustic echo cancellation using an adaptive transversal filter and the least mean square algorithm is the most effective technique of reducing acoustic echoes in a hands-free telephone system. However, a very high-order adaptive filter and multiple echo paths for each microphone result in difficulties in algorithm convergence and hardware implementation. This paper presents a distributed system which performs acoustic echo cancellation in the microphone unit. Each acoustic echo cancellation microphone unit has two closely spaced directional microphones pointing in opposite directions and a much lower order adaptive filter than in the earlier systems. Computer simulations were conducted based on real speech data collected from a typical conference room. Finally, a robust double-talk detector, which identifies three modes of operation, was developed and tested in real-time

Prediction signal controlled scans for improved motion compensated video coding

Interdependencies between prediction signal and prediction error in predictive coding schemes are investigated. Without additional side information, adaptive scan paths for DCT and nontransform coding of prediction error blocks can be derived from the prediction signal gradient. Simulations indicate that these paths efficiently scan some blocks when used alternatively to zigzag scan. >

From social evolutionism to biocultural evolutionism

A brief review of the evolutionism of Comte, Marx, Spencer, and Durkheim, representatives of the Masters, reveals an excessive concern with the integration of differentiation. This represents their most common feature, but neither it nor anything else adds up to a definite evolutionary theory. An antithetical convergence, with Comte excluded, refers to a varying utilization of the Darwinian “mechanism,” natural selection. It is not clear, however, that the masters fully grasped the meaning of natural selection, or indeed that this could be understood unequivocally. As a result they failed to convey unambiguously a fundamental interest in evolution to subsequent generations of social scientists. A period of estrangement from evolutionary theory ensued in which the focus seemed to shift from social evolution to social change. By the 1950s, sociology and anthropology experienced a revival of evolutionary interest largely in the form of a reiteration of old conceptions and problems. A critical glance at evolutionary biology reveals, next, an ambiguity in the concept of natural selection when understood as ultimate cause and mechanism of evolution. The basic significance of the evolutionistic alliance known as sociobiology lies in the latter's partial redressing of the ambiguity by way of the “maximization principle.” Equally important, indeed complementary, is the sociobiological appeal to the social sciences for help to discover the environmental parameters that impinge on the principle — and thus for a contribution to the development of a biocultural model. A few examples of biocultural theorizing follow that show varying degrees of systemic dependence between the biological and the cultural. The basic nomothetic thrust of the emerging biocultural model is to emphasize the adaptive paths along which cultural phenomena are likely to evolve.