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1. Evolutionary accessibility of mutational pathways

Author

Franke, Jasper, Klözer, Alexander, de Visser, J. Arjan G. M., and Krug, Joachim

Subjects
Quantitative Biology - Populations and Evolution
Abstract

Functional effects of different mutations are known to combine to the total effect in highly nontrivial ways. For the trait under evolutionary selection (`fitness'), measured values over all possible combinations of a set of mutations yield a fitness landscape that determines which mutational states can be reached from a given initial genotype. Understanding the accessibility properties of fitness landscapes is conceptually important in answering questions about the predictability and repeatability of evolutionary adaptation. Here we theoretically investigate accessibility of the globally optimal state on a wide variety of model landscapes, including landscapes with tunable ruggedness as well as neutral `holey' landscapes. We define a mutational pathway to be accessible if it contains the minimal number of mutations required to reach the target genotype, and if fitness increases in each mutational step. Under this definition accessibility is high, in the sense that at least one accessible pathwayexists with a substantial probability that approaches unity as the dimensionality of the fitness landscape (set by the number of mutational loci) becomes large. At the same time the number of alternative accessible pathways grows without bound. We test the model predictions against an empirical 8-locus fitness landscape obtained for the filamentous fungus \textit{Aspergillus niger}. By analyzing subgraphs of the full landscape containing different subsets of mutations, we are able to probe the mutational distance scale in the empirical data. The predicted effect of high accessibility is supported by the empirical data and very robust, which we argue to reflect the generic topology of sequence spaces., Comment: 16 pages, 4 figures; supplementary material available on request

Published
2011
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2. Octupole and hexadecapole bands in152Sm

Author

J. N. Orce, A. Fitzler, D. Bandyopadhyay, A. Dewald, A. Linnemann, D. Tonev, J. L. Wood, S. W. Yates, W. D. Kulp, P. Pejovic, P. Kudejova, M. Mynk, J. Jolie, T. Pissulla, J.-M. Régis, S. Christen, P. E. Garrett, O. Möller, A. Schiller, M. Masur, K. Jessen, Ashok Kumar, Alexander Lisetskiy, M. T. McEllistrem, S. R. Lesher, D. Martin, S. N. Choudry, C. Fransen, and A. Kloezer

Subjects
Physics, Nuclear and High Energy Physics, Excited state, Gamma spectroscopy, Coulomb excitation, Atomic physics, Spectroscopy, Critical point (mathematics), Radioactive decay
Abstract

The nucleus {sup 152}Sm is characterized by a variety of low-energy collective modes, conventionally described as rotations, {beta} vibrations, and {gamma} vibrations. Recently, it has been suggested that {sup 152}Sm is at a critical point between spherical and deformed collective phases. Consequently, {sup 152}Sm is being studied by a variety of techniques, including radioactive decay, multi-step Coulomb excitation, in-beam ({alpha},2n{gamma}) {gamma}-ray spectroscopy, and (n,n'{gamma}) spectroscopy. The present work focuses on the latter two reactions; these have been used to investigate the low-lying bands associated with the octupole degree of freedom, including one built on the first excited 0{sup +} band. In addition, the K{sup {pi}} = 4{sup +} hexadecapole vibrational band has been identified.

Published
2005
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3. Investigation of [sup 152]Sm by Complementary Reactions

Author

P. E. Garrett, W. D. Kulp, J. L. Wood, J. M. Allmond, D. Bandyopadhyay, S. Christen, S. N. Choudry, D. Cline, D. Dashdorj, A. Dewald, A. Fitzler, C. Fransen, A. B. Hayes, H. Hua, K. Jessen, J. Jolie, A. Kloezer, P. Kudejova, A. Kumar, S. R. Lesher, A. Linnemann, A. Lisetskiy, D. Martin, M. Masur, M. T. McEllistrem, O. Möller, M. G. Mynk, C. J. McKay, J. N. Orce, P. Pejovic, T. Pissulla, J.-M. Regis, A. Schiller, R. Teng, D. Tonev, C. Y. Wu, S. W. Yates, Jan Jolie, Andreas Zilges, Nigel Warr, and Andrey Blazhev

Subjects
Phase transition, Complementary experiments, Phonon, Critical point (thermodynamics), Chemistry, Excited state, Nuclear structure, Coulomb excitation, Atomic physics, Ground state
Abstract

Understanding the nuclear structure of 152Sm, along with other N = 90 isotones, has long posed a challenge. A rapid transition in shape between the spherical N = 88 150Sm and well‐deformed N = 92 154Sm is observed, along with strong evidence for shape coexistence. Competing ideas have been put forward over the decades, with the most recent being that N = 90 is at the critical point of a shape phase transition. Until recently, the lack of high‐precision data has not allowed the competing models to be extensively tested. In a coordinated program of investigation, a series of complementary experiments, which include high‐statistics β decay, multi‐step Coulomb excitation, the 150Nd(α,2n) reaction, and the (n,n′γ) reaction, have been performed for 152Sm. These experiments have revealed the existence of a pairing‐isomer band, a hexadecapole band, the lack of multi‐phonon β vibrational bands, and the repetition of structures built on the first excited Kπ = 0+ as built on the ground state. The status of these coo...

Published
2009
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4. Investigation of [sup 152]Sm by Complementary Reactions

Author

Garrett, P. E., primary, Kulp, W. D., additional, Wood, J. L., additional, Allmond, J. M., additional, Bandyopadhyay, D., additional, Christen, S., additional, Choudry, S. N., additional, Cline, D., additional, Dashdorj, D., additional, Dewald, A., additional, Fitzler, A., additional, Fransen, C., additional, Hayes, A. B., additional, Hua, H., additional, Jessen, K., additional, Jolie, J., additional, Kloezer, A., additional, Kudejova, P., additional, Kumar, A., additional, Lesher, S. R., additional, Linnemann, A., additional, Lisetskiy, A., additional, Martin, D., additional, Masur, M., additional, McEllistrem, M. T., additional, Möller, O., additional, Mynk, M. G., additional, McKay, C. J., additional, Orce, J. N., additional, Pejovic, P., additional, Pissulla, T., additional, Regis, J.-M., additional, Schiller, A., additional, Teng, R., additional, Tonev, D., additional, Wu, C. Y., additional, Yates, S. W., additional, Jolie, Jan, additional, Zilges, Andreas, additional, Warr, Nigel, additional, and Blazhev, Andrey, additional

Published
2009
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5. Octupole and hexadecapole bands in152Sm

Author

Garrett, P E, primary, Kulp, W D, additional, Wood, J L, additional, Bandyopadhyay, D, additional, Christen, S, additional, Choudry, S, additional, Dewald, A, additional, Fitzler, A, additional, Fransen, C, additional, Jessen, K, additional, Jolie, J, additional, Kloezer, A, additional, Kudejova, P, additional, Kumar, A, additional, Lesher, S R, additional, Linnemann, A, additional, Lisetskiy, A, additional, Martin, D, additional, Masur, M, additional, McEllistrem, M T, additional, Möller, O, additional, Mynk, M, additional, Orce, J N, additional, Pejovic, P, additional, Pissulla, T, additional, Regis, J M, additional, Schiller, A, additional, Tonev, D, additional, and Yates, S W, additional

Published
2005
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6. Investigation of 152Sm by Complementary Reactions.

Author

Garrett, P. E., Kulp, W. D., Wood, J. L., Allmond, J. M., Bandyopadhyay, D., Christen, S., Choudry, S. N., Cline, D., Dashdorj, D., Dewald, A., Fitzler, A., Fransen, C., Hayes, A. B., Hua, H., Jessen, K., Jolie, J., Kloezer, A., Kudejova, P., Kumar, A., and Lesher, S. R.

Subjects
NUCLEAR structure, ISOTOPES, PHASE transitions, COULOMB excitation, PHONONS, NUCLEAR isomers
Abstract

Understanding the nuclear structure of 152Sm, along with other N = 90 isotones, has long posed a challenge. A rapid transition in shape between the spherical N = 88 150Sm and well-deformed N = 92 154Sm is observed, along with strong evidence for shape coexistence. Competing ideas have been put forward over the decades, with the most recent being that N = 90 is at the critical point of a shape phase transition. Until recently, the lack of high-precision data has not allowed the competing models to be extensively tested. In a coordinated program of investigation, a series of complementary experiments, which include high-statistics β decay, multi-step Coulomb excitation, the 150Nd(α,2n) reaction, and the (n,n′γ) reaction, have been performed for 152Sm. These experiments have revealed the existence of a pairing-isomer band, a hexadecapole band, the lack of multi-phonon β vibrational bands, and the repetition of structures built on the first excited Kπ = 0+ as built on the ground state. The status of these coordinated studies is examined. [ABSTRACT FROM AUTHOR]

Published
2009
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7. Octupole and hexadecapole bands in 152Sm.

Author

P PEG Garrett, W WDK Kulp, J JLW Wood, D DB Bandyopadhyay, S SC Christen, S SC Choudry, A AD Dewald, A AF Fitzler, C CF Fransen, K KJ Jessen, J JJ Jolie, A AK Kloezer, P PK Kudejova, A AK Kumar, S SRL Lesher, A AL Linnemann, A AL Lisetskiy, D DM Martin, M MM Masur, and M MTM McEllistrem

Published
2005

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