1,075 research outputs found
Evolutionary game theory in growing populations
Existing theoretical models of evolution focus on the relative fitness
advantages of different mutants in a population while the dynamic behavior of
the population size is mostly left unconsidered. We here present a generic
stochastic model which combines the growth dynamics of the population and its
internal evolution. Our model thereby accounts for the fact that both
evolutionary and growth dynamics are based on individual reproduction events
and hence are highly coupled and stochastic in nature. We exemplify our
approach by studying the dilemma of cooperation in growing populations and show
that genuinely stochastic events can ease the dilemma by leading to a transient
but robust increase in cooperationComment: 4 pages, 2 figures and 2 pages supplementary informatio
Radial distribution function of semiflexible polymers
We calculate the distribution function of the end--to--end distance of a
semiflexible polymer with large bending rigidity. This quantity is directly
observable in experiments on single semiflexible polymers (e.g., DNA, actin)
and relevant to their interpretation. It is also an important starting point
for analyzing the behavior of more complex systems such as networks and
solutions of semiflexible polymers. To estimate the validity of the obtained
analytical expressions, we also determine the distribution function numerically
using Monte Carlo simulation and find good quantitative agreement.Comment: RevTeX, 4 pages, 1 figure. Also available at
http://www.cip.physik.tu-muenchen.de/tumphy/d/T34/Mitarbeiter/frey.htm
Evolution of Galactic Discs: Multiple Patterns, Radial Migration and Disc Outskirts
We investigate the evolution of galactic disks in N-body Tree-SPH
simulations. We find that disks, initially truncated at three scale-lengths,
can triple their radial extent, solely driven by secular evolution. Both Type I
(single exponential) and Type II (down-turning) observed disk
surface-brightness profiles can be explained by our findings. We relate these
results to the strong angular momentum outward transfer, resulting from torques
and radial migration associated with multiple patterns, such as central bars
and spiral waves of different multiplicity. We show that even for stars ending
up on cold orbits, the changes in angular momentum exhibit complex structure as
a function of radius, unlike the expected effect of transient spirals alone.
Focussing on one of our models, we find evidence for non-linear coupling among
m=1, 2, 3 and 4 density waves, where m is the pattern multiplicity. We suggest
that the naturally occurring larger resonance widths at galactic radii beyond
four scale-lengths may have profound consequences on the formation and location
of breaks in disk density profiles, provided spirals are present at such large
distances. We also consider the effect of gas inflow and show that when
in-plane smooth gas accretion of ~5 M_sun/yr is included, the outer disks
become more unstable, leading to a strong increase in the stellar velocity
dispersion. This, in turn, causes the formation of a Type III (up-turning)
profile in the old stellar population. We propose that observations of Type III
surface brightness profiles, combined with an up-turn in the stellar velocity
dispersions beyond the disk break, could be a signature of ongoing
gas-accretion. The results of this study suggest that disk outskirts comprised
of stars migrated from the inner disk would have relatively large radial
velocity dispersions, and significant thickness when seen edge-on. [Abridged]Comment: Replaced with accepted version. New Fig. 5 added, Section 10
decreased in size, old Fig. 17 removed. Conclusions remain the same.
High-resolution version can be found at http://www.ivanminchev.co
The laurentian record of neoproterozoic glaciation, tectonism, and eukaryotic evolution in Death Vally, California
Neoproterozoic strata in Death Valley, California contain eukaryotic microfossils and glacial deposits that have been used to assess the severity of putative Snowball Earth events and the biological response to extreme environmental change. These successions also contain evidence for syn-sedimentary faulting that has been related to the rifting of Rodinia, and in turn the tectonic context of the onset of Snowball Earth. These interpretations hinge on local geological relationships and both regional and global stratigraphic correlations. Here we present new geological mapping, measured stratigraphic sections, carbon and strontium isotope chemostratigraphy, and micropaleontology from the Neoproterozoic glacial deposits and bounding strata in Death Valley. These new data enable us to refine regional correlations both across Death Valley and throughout Laurentia, and construct a new age model for glaciogenic strata and microfossil assemblages. Particularly, our remapping of the Kingston Peak Formation in the Saddle Peak Hills and near the type locality shows for the first time that glacial deposits of both the Marinoan and Sturtian glaciations can be distinguished in southeastern Death Valley, and that beds containing vase-shaped microfossils are slump blocks derived from the underlying strata. These slump blocks are associated with multiple overlapping unconformities that developed during syn-sedimentary faulting, which is a common feature of Cyrogenian strata along the margin of Laurentia from California to Alaska. With these data, we conclude that all of the microfossils that have been described to date in Neoproterozoic strata of Death Valley predate the glaciations and do not bear on the severity, extent or duration of Neoproterozoic Snowball Earth events
Giant HII Regions in NGC 7479 & NGC 6070
We present new results from our search for Giant H\,{\sc ii} Regions in
galaxies visible from the southern hemisphere. In this work we study two
galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with
different instruments at Las Campanas Observatory, we are able to resolve the
emission-line profile widths and determine the intrinsic velocity dispersion of
the ionised gas. We detect profile widths corresponding to supersonic velocity
dispersions in the six observed H\,{\sc ii} regions. We find that all of them
show at least two distinct kinematical components: a relatively narrow feature
(between ~11 and ~22\kms) and a broader (between ~31 and ~77\kms) component.
Two of the regions show a complex narrow profile in all ion lines, which can be
further split into two components with different radial velocities. Whereas the
wing broadening of the overall profile can be fitted with a low-intensity broad
component for almost all profiles, in one region it was better reproduced by
two separate shell-like wings. We have analysed the impact that the presence of
multiple components has on the location of the H{\sc ii} regions in the
plane. Although the overall distribution confirms the
presence of a regression, the precise location of the regions in the plane is
strongly dependent on the components derived from the profile fitting.Comment: This manuscript has been accepted for publication in Monthly Notices
of the Royal Astronomical Society Main Journal. 16 pages, 11 figure
Fabrication of Microstripline Wiring for Large Format Transition Edge Sensor Arrays
We have developed a process to integrate microstripline wiring with transition edge sensors (TES). The process includes additional layers for metal-etch stop and dielectric adhesion to enable recovery of parameters achieved in non-microstrip pixel designs. We report on device parameters in close-packed TES arrays achieved with the microstrip process including R(sub n), G, and T(sub c) uniformity. Further, we investigate limits of this method of producing high-density, microstrip wiring including critical current to determine the ultimate scalability of TES arrays with two layers of wiring
Mobility promotes and jeopardizes biodiversity in rock-paper-scissors games
Biodiversity is essential to the viability of ecological systems. Species
diversity in ecosystems is promoted by cyclic, non-hierarchical interactions
among competing populations. Such non-transitive relations lead to an evolution
with central features represented by the `rock-paper-scissors' game, where rock
crushes scissors, scissors cut paper, and paper wraps rock. In combination with
spatial dispersal of static populations, this type of competition results in
the stable coexistence of all species and the long-term maintenance of
biodiversity. However, population mobility is a central feature of real
ecosystems: animals migrate, bacteria run and tumble. Here, we observe a
critical influence of mobility on species diversity. When mobility exceeds a
certain value, biodiversity is jeopardized and lost. In contrast, below this
critical threshold all subpopulations coexist and an entanglement of travelling
spiral waves forms in the course of temporal evolution. We establish that this
phenomenon is robust, it does not depend on the details of cyclic competition
or spatial environment. These findings have important implications for
maintenance and evolution of ecological systems and are relevant for the
formation and propagation of patterns in excitable media, such as chemical
kinetics or epidemic outbreaks.Comment: Final submitted version; the printed version can be found at
http://dx.doi.org/10.1038/nature06095 Supplementary movies are available at
http://www.theorie.physik.uni-muenchen.de/lsfrey/images_content/movie1.AVI
and
http://www.theorie.physik.uni-muenchen.de/lsfrey/images_content/movie2.AV
Establishing Foundation Archives: A Reader and Guide to First Steps
This publication is an anthology of papers presented at a conference held at the Rockefeller Archive Center in January 1990, and sponsored by the Council on Foundations. This collaboration of the Archive Center and the Council provided a rare opponunity for foundations to learn both why preserving documents is imponant and how several foundations have approached finding a repository or setting up and managing an archives. Participants in the conference had the added privilege of conferring with experts and seeing an operating archive as they toured the Rockefeller Archive Center.Foundations are institutions that are shaping private initiatives for the public good, so documenting this aspect of American society falls uniquely under the stewardship of the organizations themselves. Foundation documents often provide the only surviving records of the important contributions of nonprofits and foundations to civic life. These records will help to inform future judgments and ensure that the history of the field is not lost. The publication of this volume was intended to make the information shared at the conference more widely available and to provide an entry point and a primer for foundations as they begin their records and archives journey
The compositional and evolutionary logic of metabolism
Metabolism displays striking and robust regularities in the forms of
modularity and hierarchy, whose composition may be compactly described. This
renders metabolic architecture comprehensible as a system, and suggests the
order in which layers of that system emerged. Metabolism also serves as the
foundation in other hierarchies, at least up to cellular integration including
bioenergetics and molecular replication, and trophic ecology. The
recapitulation of patterns first seen in metabolism, in these higher levels,
suggests metabolism as a source of causation or constraint on many forms of
organization in the biosphere.
We identify as modules widely reused subsets of chemicals, reactions, or
functions, each with a conserved internal structure. At the small molecule
substrate level, module boundaries are generally associated with the most
complex reaction mechanisms and the most conserved enzymes. Cofactors form a
structurally and functionally distinctive control layer over the small-molecule
substrate. Complex cofactors are often used at module boundaries of the
substrate level, while simpler ones participate in widely used reactions.
Cofactor functions thus act as "keys" that incorporate classes of organic
reactions within biochemistry.
The same modules that organize the compositional diversity of metabolism are
argued to have governed long-term evolution. Early evolution of core
metabolism, especially carbon-fixation, appears to have required few
innovations among a small number of conserved modules, to produce adaptations
to simple biogeochemical changes of environment. We demonstrate these features
of metabolism at several levels of hierarchy, beginning with the small-molecule
substrate and network architecture, continuing with cofactors and key conserved
reactions, and culminating in the aggregation of multiple diverse physical and
biochemical processes in cells.Comment: 56 pages, 28 figure
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