Prótons foram observados ‘pegando uma onda’ na superfície de um núcleo atômico

Physics Letters B

Volume 760, 10 September 2016, Pages 273–278

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus 133Sb

G. Bocchia, b, S. Leonia, b, , , B. Fornalc, G. Colòa, b, P.F. Bortignona, b, S. Bottonia, b, A. Braccoa, b, C. Michelagnolid, D. Bazzaccoe, A. Blancf, G. de Franced, M. Jentschelf, U. Kösterf, P. Muttif, J.-M. Régisg, G. Simpsonh, T. Soldnerf, C.A. Ure, i, W. Urbanj, L.M. Frailek, R. Lozeval, B. Belvitoa, b, G. Benzonib, A. Brucem, R. Carrolln, N. Cieplicka-Oryǹczakb, c, F.C.L. Crespia, b, F. Didierjeanl, J. Jolieg, W. Korteno, T. Kröllp, S. Lalkovskin, q, H. Machk, N. Mărgineanr, B. Melons, D. Mengonie, t, B. Millionb, A. Nanninis,

http://dx.doi.org/10.1016/j.physletb.2016.06.065

Get rights and content

Open Access funded by SCOAP³ - Sponsoring Consortium for Open Access Publishing in Particle Physics

Under a Creative Commons license

Source/Fonte

Abstract

The γ-ray decay of excited states of the one-valence-proton nucleus ¹³³Sb has been studied using cold-neutron induced fission of ²³⁵U and ²⁴¹Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between γ-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr₃(Ce) scintillators, revealed a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus ¹³²Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.

Keywords

• Neutron induced fission; 
• Gamma spectroscopy; 
• Nuclear state lifetime; 
• Large Ge array;
• Particle-core couplings

FREE PDF GRATIS: Physics Letters B

Nova pesquisa dobra o número estimado de espécies de aves no mundo

How Many Kinds of Birds Are There and Why Does It Matter?

George F. Barrowclough , Joel Cracraft, John Klicka, Robert M. Zink

Published: November 23, 2016 http://dx.doi.org/10.1371/journal.pone.0166307

Source/Fonte: Wendy Paulson

Abstract

Estimates of global species diversity have varied widely, primarily based on variation in the numbers derived from different inventory methods of arthropods and other small invertebrates. Within vertebrates, current diversity metrics for fishes, amphibians, and reptiles are known to be poor estimators, whereas those for birds and mammals are often assumed to be relatively well established. We show that avian evolutionary diversity is significantly underestimated due to a taxonomic tradition not found in most other taxonomic groups. Using a sample of 200 species taken from a list of 9159 biological species determined primarily by morphological criteria, we applied a diagnostic, evolutionary species concept to a morphological and distributional data set that resulted in an estimate of 18,043 species of birds worldwide, with a 95% confidence interval of 15,845 to 20,470. In a second, independent analysis, we examined intraspecific genetic data from 437 traditional avian species, finding an average of 2.4 evolutionary units per species, which can be considered proxies for phylogenetic species. Comparing recent lists of species to that used in this study (based primarily on morphology) revealed that taxonomic changes in the past 25 years have led to an increase of only 9%, well below what our results predict. Therefore, our molecular and morphological results suggest that the current taxonomy of birds understimates avian species diversity by at least a factor of two. We suggest that a revised taxonomy that better captures avian species diversity will enhance the quantification and analysis of global patterns of diversity and distribution, as well as provide a more appropriate framework for understanding the evolutionary history of birds.

Citation: Barrowclough GF, Cracraft J, Klicka J, Zink RM (2016) How Many Kinds of Birds Are There and Why Does It Matter? PLoS ONE 11(11): e0166307. 

doi: 10.1371/journal.pone.0166307

Editor: Andy J. Green, Consejo Superior de Investigaciones Cientificas, SPAIN

Received: May 11, 2016; Accepted: October 23, 2016; Published: November 23, 2016

Copyright: © 2016 Barrowclough et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: This paper received support from the U.S. National Science Foundation awards 1241066 and 1146423 (J.C.) and DEB 0815057 (J.K.).

Competing interests: The authors have declared that no competing interests exist.

FREE PDF GRATIS: PLoS One

Novas pegadas de Laetoli (Tanzânia) fornecem evidências de variação de tamanho corporal acentuada nos primeiros hominídeos

New footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominins

Fidelis T Masao Elgidius B Ichumbaki Marco Cherin Angelo Barili Giovanni Boschian Dawid A Iurino Sofia Menconero Jacopo Moggi-Cecchi Giorgio Manzi

University of Dar es Salaam, Tanzania; Università di Perugia, Italy; Sapienza Università di Roma, Italy; Università di Pisa, Italy; Studio Associato Grassi, Italy; Università di Firenze, Italy

DOI: http://dx.doi.org/10.7554/eLife.19568

Published December 14, 2016

Cite as eLife 2016;5:e19568

Abstract

Laetoli is a well-known palaeontological locality in northern Tanzania whose outstanding record includes the earliest hominin footprints in the world (3.66 million years old), discovered in 1978 at Site G and attributed to Australopithecus afarensis. Here, we report hominin tracks unearthed in the new Site S at Laetoli and referred to two bipedal individuals (S1 and S2) moving on the same palaeosurface and in the same direction as the three hominins documented at Site G. The stature estimates for S1 greatly exceed those previously reconstructed for Au. afarensis from both skeletal material and footprint data. In combination with a comparative reappraisal of the Site G footprints, the evidence collected here embodies very important additions to the Pliocene record of hominin behaviour and morphology. Our results are consistent with considerable body size variation and, probably, degree of sexual dimorphism within a single species of bipedal hominins as early as 3.66 million years ago.

DOI: http://dx.doi.org/10.7554/eLife.19568.001

eLife digest

Fossil footprints are extremely useful tools in the palaeontological record. Their physical features can help to identify their makers, but can also be used to infer biological information. How did the track-maker move? How large was it? How fast was it going?

Footprints of hominins (namely the group to which humans and our ancestors belong) are pretty rare. Nearly all of the hominin footprints discovered so far are attributed to species of the genus Homo, to which modern humans belong. The only exceptions are the footprints that were discovered in the 1970s at Laetoli (in Tanzania) on a cemented ash layer produced by a volcanic eruption. These are thought to have been made by three members of the hominin species Australopithecus afarensis – the same species as the famous “Lucy” from Ethiopia – around 3.66 million years ago.

The extent to which body shape and size varied between different members of Au. afarensis – for example, between males and females – has been the subject of a long debate among researchers. Based on the skeletal remains found so far in East Africa, some scholars believe that individuals only varied moderately, as in modern humans, while others state that it was pronounced, as in some modern apes like gorillas.

Masao et al. have now unearthed new bipedal footprints from two individuals who were moving on the same surface and in the same direction as the three individuals who made the footprints documented in the 1970s. The estimated height of one of the new individuals (about 1.65 metres) greatly exceeds those previously published for Au. afarensis. This evidence supports the theory that body size varied considerably amongst individuals within the species.

Masao et al. tentatively suggest that the new footprints can be considered as a whole with the 1970s ones. The tall individual may have been the dominant male of a larger group, the others smaller females and juveniles. Thus, considerable differences may have existed between males and females in these remote human ancestors, similar to modern gorillas.

The newly discovered tracks are only 150 metres away from the previously discovered sets of footprints. This leaves open the possibility that additional tracks may be unearthed nearby that will further our knowledge about the variability and behaviour of our extinct ancestors.

DOI: http://dx.doi.org/10.7554/eLife.19568.002

Acknowledgements

This research is supported by the Italian School of Palaeoanthropology (University of Perugia; www.paleoantropologia.it), under the auspices of the Italian Ministry of Foreign Affairs and International Cooperation (Italian archaeological, anthropological and ethnological missions abroad) and the Italian Embassy in Dar es Salaam, Tanzania. The authors are grateful to the University of Dar es Salaam; the museum project consultant P Rich and the Ngorongoro Conservation Area Authority, without whom this discovery would have never been made; DM Kamamba, Director of Antiquities, Ministry of Natural Resources and Tourism; the University of Dar es Salaam for financial support; E Kazimoto for preliminary geological analysis; R Rettori for the organisation of the field season; S Grassi and A Grassi for 3D data processing and logistical support, R Pellizzon for photographs; P Blasi, M Lombardi, G Peter, L Quattrini, B Zamagni, A Songita and his assistants for the field work. R Blumenschine, M Haeusler, O Kullmer, J Njau, Y Rak, B Wood and R Wunderlich provided useful comments on an earlier version of the paper.

FREE PDF GRATIS: eLIFE

Como as células podem se "lembrar" quem elas são? Mero acaso, fortuita necessidade ou design inteligente?

Polymer model with Epigenetic Recoloring Reveals a Pathway for the de novo Establishment and 3D Organization of Chromatin Domains

D. Michieletto, E. Orlandini, and D. Marenduzzo

Phys. Rev. X 6, 041047 – Published 9 December 2016

ABSTRACT

One of the most important problems in development is how epigenetic domains can first be established, and then maintained, within cells. To address this question, we propose a framework that couples three-dimensional chromatin folding dynamics to a “recoloring” process modeling the writing of epigenetic marks. Because many intrachromatin interactions are mediated by bridging proteins, we consider a “two-state” model with self-attractive interactions between two epigenetic marks that are alike (either active or inactive). This model displays a first-order-like transition between a swollen, epigenetically disordered phase and a compact, epigenetically coherent chromatin globule. If the self-attraction strength exceeds a threshold, the chromatin dynamics becomes glassy, and the corresponding interaction network freezes. By modifying the epigenetic read-write process according to more biologically inspired assumptions, our polymer model with recoloring recapitulates the ultrasensitive response of epigenetic switches to perturbations and accounts for long-lived multidomain conformations, strikingly similar to the topologically associating domains observed in eukaryotic chromosomes.

Received 15 June 2016

DOI: https://doi.org/10.1103/PhysRevX.6.041047

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

AUTHORS & AFFILIATIONS

D. Michieletto1, E. Orlandini2, and D. Marenduzzo1

1SUPA, School of Physics and Astronomy, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom

2Dipartimento di Fisica e Astronomia and Sezione INFN, Università di Padova, Via Marzolo 8, Padova 35131, Italy

POPULAR SUMMARY

Epigenetic modifications are biochemical marks that form patterns along chromosomes and regulate gene expression. The epigenetic patterning of chromosomes enables cellular differentiation, while leaving the underlying DNA sequence unchanged. How these patterns are established and then maintained across cell division is far from understood, however. Here, we show that a polymer model with “recolorable” segments can explain epigenetic memory and the self-organization of long-lived epigenetic domains.

We theoretically consider a model of epigenetic switches that consists of a chromatin fiber modeled as a semiflexible chain made of beads (roughly 30 nm) connected by a harmonic potential. In our model, we assume that two similar epigenetic marks experience self-attractive interactions. We investigate how the folding dynamics of the chromatin in three dimensions is coupled to the creation of epigenetic modifications and how the model transitions between an epigenetically disordered phase and an epigenetically ordered phase. We are able to explain the physically observed phenomenon of “epigenetic memory,” in which genes that are switched off are only infrequently reactivated. In addition, we show that by breaking detailed balance, our model is able to display epigenetic domains with long-lived boundaries that last throughout the simulation runtime of a few hours and that are reminiscent of so-called “topologically associated domains,” recently observed in vivo. In conclusion, we argue that epigenetic modifications are likely modulated by a positive feedback mechanism and that their ATP-mediated regulation is key to control topologically associated domains and, ultimately, gene expression.

We expect that our findings will motivate future studies of how epigenetic domains and, consequently, gene expression are coupled with chromatin folding dynamics.

FREE PDF GRATIS: Physical Reviews X Sup. Info.

Edição especial da Evolutionary Biology sobre padrões evolucionários, grátis até 30/12/2016

Evolutionary Biology

Volume 43, Issue 4, December 2016

Special issue on Evolutionary Patterns

Issue Editors:

 

• Nathalie Gontier

ISSN: 0071-3260 (Print) 1934-2845 (Online)

In this issue (14 articles)

1. Synthesis Paper

   Guest-Editorial Introduction: Converging Evolutionary Patterns in Life and Culture

   Nathalie GontierPages 427-445

   Download PDF (567KB) View Article
2. Synthesis Paper

   How to Rethink Evolutionary Theory: A Plurality of Evolutionary Patterns

   Telmo PievaniPages 446-455

   Download PDF (419KB) View Article
3. Synthesis Paper

   Genealogies: Pedigrees and Phylogenies are Reticulating Networks Not Just Divergent Trees

   David A. MorrisonPages 456-473

   Download PDF (1870KB) View Article
4. Synthesis Paper

   Lateral and Vertical Transfer in Biology, Linguistics and Anthropology: An Account of Widely Neglected Ideas in the Formation of Evolutionary Theories

   Frank KressingPages 474-480

   Download PDF (422KB) View Article
5. Synthesis Paper

   Cultural Evolution: A Review of Theory, Findings and Controversies

   Alex MesoudiPages 481-497

   Download PDF (571KB) View Article
6. Synthesis Paper

   Navigating Disciplinary Boundaries: Script, Games and the Role of Language

   Alex de VoogtPages 498-505

   Download PDF (1159KB) View Article
7. Synthesis Paper

   Origins of Life: Chemical and Philosophical Approaches

   Vera M. KolbPages 506-515

   Download PDF (549KB) View Article
8. Synthesis Paper

   Patterns and Processes in Cultural Evolution

   Michael Bradie, Juan L. BouzatPages 516-530

   Download PDF (716KB) View Article
9. Synthesis Paper

   Three Trends in the History of Life: An Evolutionary Syndrome

   Daniel W. McSheaPages 531-542

   Download PDF (494KB) View Article
10. Synthesis Paper

    From the Cell to the Ecosystem: The Physiological Evolution of Symbiosis

    Ricardo Guerrero, Mercedes BerlangaPages 543-552

    Download PDF (1612KB) View Article
11. Synthesis Paper

    Evolutionary Connectionism: Algorithmic Principles Underlying the Evolution of Biological Organisation in Evo-Devo, Evo-Eco and Evolutionary Transitions

    Richard A. Watson, Rob Mills, C. L. Buckley, Kostas Kouvaris…Pages 553-581

    Download PDF (952KB) View Article
12. Synthesis Paper

    Life With or Without Names

    M. Casiraghi, A. Galimberti, A. Sandionigi, A. Bruno, M. LabraPages 582-595

    Download PDF (471KB) View Article
13. Synthesis Paper

    The Symbiotic Self

    Jan SappPages 596-603

    Download PDF (381KB) View Article
14. Synthesis Paper

    Time: The Biggest Pattern in Natural History Research

    Nathalie GontierPages 604-637

    Download PDF (2156KB) View Article