@article{4265, abstract = {The reasons that sex and recombination are so widespread remain elusive. One popular hypothesis is that sex and recombination promote adaptation to a changing environment. The strongest evidence that increased recombination may evolve because recombination promotes adaptation comes from artificially selected populations. Recombination rates have been found to increase as a correlated response to selection on traits unrelated to recombination in several artificial selection experiments and in a comparison of domesticated and nondomesticated mammals. There are, however, several alternative explanations for the increase in recombination in such populations, including two different evolutionary explanations. The first is that the form of selection is epistatic, generating linkage disequilibria among selected loci, which can indirectly favor modifier alleles that increase recombination. The second is that random genetic drift in selected populations tends to generate disequilibria such that beneficial alleles are often found in different individuals; modifier alleles that increase recombination can bring together such favorable alleles and thus may be found in individuals with greater fitness. In this paper, we compare the evolutionary forces acting on recombination in finite populations subject to strong selection, To our surprise, we found that drift accounted for the majority of selection for increased recombination observed in simulations of small to moderately large populations, suggesting that, unless selected populations are large, epistasis plays a secondary role in the evolution of recombination.}, author = {Otto, Sarah and Barton, Nicholas H}, issn = {0014-3820}, journal = {Evolution; International Journal of Organic Evolution}, number = {10}, pages = {1921 -- 1931}, publisher = {Wiley-Blackwell}, title = {{Selection for recombination in small populations}}, doi = {10.1111/j.0014-3820.2001.tb01310.x}, volume = {55}, year = {2001}, } @article{4266, abstract = {Hybridization may influence evolution in a variety of ways. If hybrids are less fit, the geographical range of ecologically divergent populations may be limited, and prezygotic reproductive isolation may be reinforced. If some hybrid genotypes are fitter than one or both parents, at least in some environments, then hybridization could make a positive contribution. Single alleles that are at an advantage in the alternative environment and genetic background will introgress readily, although such introgression may be hard to detect. 'Hybrid speciation', in which fit combinations of alleles are established, is more problematic; its likelihood depends on how divergent populations meet, and on the structure of epistasis. These issues are illustrated using Fisher's model of stabilizing selection on multiple traits, under which reproductive isolation evolves as a side-effect of adaptation in allopatry. This confirms a priori arguments that while recombinant hybrids are less fit on average, some gene combinations may be fitter than the parents, even in the parental environment. Fisher's model does predict heterosis in diploid F1s, asymmetric incompatibility in reciprocal backcrosses, and (when dominance is included) Haldane's Rule. However, heterosis arises only when traits are additive, whereas the latter two patterns require dominance. Moreover, because adaptation is via substitutions of small effect, Fisher's model does not generate the strong effects of single chromosome regions often observed in species crosses.}, author = {Barton, Nicholas H}, issn = {962-1083}, journal = {Molecular Ecology}, number = {3}, pages = {551 -- 568}, publisher = {Wiley-Blackwell}, title = {{The role of hybridization in evolution}}, doi = {10.1046/j.1365-294X.2001.01216.x}, volume = {10}, year = {2001}, } @inbook{4267, abstract = {The flow of genes from the dense and well-adapted centre of a species' distribution interferes with adaptation to marginal environments, and may sharply limit a species' range. Deterministic models of a linear habitat suggest that populations could in principle adapt to very steep environmental gradients, by increasing their genetic variability. However, random fluctuations in sparse populations reduce this variance, and may be crucial in limiting the species' range.}, author = {Barton, Nicholas H}, booktitle = {Integrating ecology and evolution in a spatial context}, isbn = {9780521840002}, pages = {365 -- 392}, publisher = {Cambridge University Press}, title = {{Adaptation at the edge of a species' range}}, year = {2001}, } @inbook{4278, abstract = {The ability of species to migrate that has interested ecologists for many years. Now that so many species and ecosystems face major environmental change, the ability of species to adapt to these changes by dispersing, migrating, or moving between different patches of habitat can be crucial to ensuring their survivial. This book provides a timely and wide-ranging overview of the study of dispersal and incorporates much of the latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species and community levels are considered. The potential of new techniques and models for studying dispersal, drawn from molecular biology and demography, is also explored. Perspectives and insights are offered from the fields of evolution, conservation biology and genetics. Throughout the book, theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible. }, author = {Barton, Nicholas H}, booktitle = {Dispersal}, isbn = {9780198506591}, publisher = {Oxford University Press}, title = {{The evolutionary consequences of gene flow and local adaptation: Future approaches}}, year = {2001}, } @proceedings{4449, abstract = {Embedded software is software that interacts with physical processes. As em- bedded systems increasingly permeate our daily lives on all levels, from micros- copic devices to international networks, the cost-efficient development of reliable embedded software is one of the grand challenges in computer science today. The purpose of the workshop is to bring together researchers in all areas of computer science that are traditionally distinct but relevant to embedded software develop- ment, and to incubate a research community in this way. The workshop aims to cover all aspects of the design and implementation of embedded software, inclu- ding operating systems and middleware, programming languages and compilers, modeling and validation, software engineering and programming methodologies, scheduling and execution time analysis, networking and fault tolerance, as well as application areas, such as embedded control, real-time signal processing, and telecommunications.}, editor = {Henzinger, Thomas A}, isbn = {9783540426738}, location = {Tahoe City, CA, USA}, publisher = {ACM}, title = {{EMSOFT: Embedded Software}}, doi = {10.1007/3-540-45449-7}, volume = {2211}, year = {2001}, } @inproceedings{4475, abstract = {We provide an overview of the current status of HYTECH, and reflect on some of the lessons learned from our experiences with the tool. HYTECH is a symbolic model checker for mixed discrete-continuous systems that are modeled as automata with piecewise-constant polyhedral differential inclusions. The use of a formal input language and automated procedures for state-space traversal lay the foundation for formally verifying properties of hybrid dynamical systems. We describe some recent experiences analyzing three hybrid systems. We point out the successes and limitations of the tool. The analysis procedure has been extended in a number of ways to address some of the tool's shortcomings. We evaluate these extensions, and conclude with some desiderata for verification tools for hybrid systems.}, author = {Henzinger, Thomas A and Preussig, Joerg and Wong Toi, Howard}, booktitle = {Proceedings of the 40th IEEE Conference on Decision and Control}, isbn = {0780370619}, location = {Orlando, FL, USA}, pages = {2887 -- 2892}, publisher = {IEEE}, title = {{Some lessons from the HYTECH experience}}, doi = {10.1109/.2001.980714}, volume = {3}, year = {2001}, } @inproceedings{4477, abstract = {The assume-guarantee paradigm is a powerful divide-and-conquer mechanism for decomposing a verification task about a system into subtasks about the individual components of the system. The key to assume-guarantee reasoning is to consider each component not in isolation, but in conjunction with assumptions about the context of the component. Assume-guarantee principles are known for purely concurrent contexts, which constrain the input data of a component, as well as for purely sequential contexts, which constrain the entry configurations of a component. We present a model for hierarchical system design which permits the arbitrary nesting of parallel as well as serial composition, and which supports an assume-guarantee principle for mixed parallel-serial contexts. Our model also supports both discrete and continuous processes, and is therefore well-suited for the modeling and analysis of embedded software systems which interact with real-world environments. Using an example of two cooperating robots, we show refinement between a high-level model which specifies continuous timing constraints and an implementation which relies on discrete sampling.}, author = {Henzinger, Thomas A and Minea, Marius and Prabhu, Vinayak}, booktitle = {Proceedings of the 4th International Workshop on Hybrid Systems}, isbn = {9783540418665}, location = {Rome, Italy}, pages = {275 -- 290}, publisher = {Springer}, title = {{Assume-guarantee reasoning for hierarchical hybrid systems}}, doi = {10.1007/3-540-45351-2_24}, volume = {2034}, year = {2001}, } @inproceedings{4478, abstract = {Giotto is a principled, tool-supported design methodology for implementing embedded control systems on platforms of possibly distributed sensors, actuators, CPUs, and networks. Giotto is based on the principle that time-triggered task invocations plus time-triggered mode switches can form the abstract essence of programming real-time control systems. Giotto consists of a programming language with a formal semantics, and a retargetable compiler and runtime library. Giotto supports the automation of control system design by strictly separating platform-independent functionality and timing concerns from platform-dependent scheduling and communication issues. The time-triggered predictability of Giotto makes it particularly suitable for safety-critical applications with hard real-time constraints. We illustrate the platform-independence and time-triggered execution of Giotto by coordinating a heterogeneous flock of Intel x86 robots and Lego Mindstorms robots.}, author = {Henzinger, Thomas A and Horowitz, Benjamin and Kirsch, Christoph}, booktitle = {Proceedings of the 2nd ACM SIGPLAN workshop on Languages, compilers and tools for embedded systems}, isbn = {9781581134254}, location = {New York, NY, United States}, pages = {64 -- 72}, publisher = {ACM}, title = {{Embedded control systems development with Giotto}}, doi = {10.1145/384197.384208}, year = {2001}, } @inproceedings{4479, abstract = {Giotto provides an abstract programmer’s model for the implementation of embedded control systems with hard real-time constraints. A typical control application consists of periodic software tasks together with a mode switching logic for enabling and disabling tasks. Giotto specifies time-triggered sensor readings, task invocations, and mode switches independent of any implementation platform. Giotto can be annotated with platform constraints such as task-to-host mappings, and task and communication schedules. The annotations are directives for the Giotto compiler, but they do not alter the functionality and timing of a Giotto program. By separating the platform-independent from the platform-dependent concerns, Giotto enables a great deal of flexibility in choosing control platforms as well as a great deal of automation in the validation and synthesis of control software. The time-triggered nature of Giotto achieves timing predictability, which makes Giotto particularly suitable for safety-critical applications.}, author = {Henzinger, Thomas A and Horowitz, Benjamin and Kirsch, Christoph}, booktitle = {Proceedings of the 1st International Workshop on Embedded Software}, isbn = {9783540426738}, location = {Tahoe City, CA, USA}, pages = {166 -- 184}, publisher = {ACM}, title = {{Giotto: A time-triggered language for embedded programming}}, doi = {10.1007/3-540-45449-7_12}, volume = {2211}, year = {2001}, }