1,058 research outputs found
Geometry shapes evolution of early multicellularity
Organisms have increased in complexity through a series of major evolutionary
transitions, in which formerly autonomous entities become parts of a novel
higher-level entity. One intriguing feature of the higher-level entity after
some major transitions is a division of reproductive labor among its
lower-level units. Although it can have clear benefits once established, it is
unknown how such reproductive division of labor originates. We consider a
recent evolution experiment on the yeast Saccharomyces cerevisiae as a unique
platform to address the issue of reproductive differentiation during an
evolutionary transition in individuality. In the experiment, independent yeast
lineages evolved a multicellular "snowflake-like'' cluster form in response to
gravity selection. Shortly after the evolution of clusters, the yeast evolved
higher rates of cell death. While cell death enables clusters to split apart
and form new groups, it also reduces their performance in the face of gravity
selection. To understand the selective value of increased cell death, we create
a mathematical model of the cellular arrangement within snowflake yeast
clusters. The model reveals that the mechanism of cell death and the geometry
of the snowflake interact in complex, evolutionarily important ways. We find
that the organization of snowflake yeast imposes powerful limitations on the
available space for new cell growth. By dying more frequently, cells in
clusters avoid encountering space limitations, and, paradoxically, reach higher
numbers. In addition, selection for particular group sizes can explain the
increased rate of apoptosis both in terms of total cell number and total
numbers of collectives. Thus, by considering the geometry of a primitive
multicellular organism we can gain insight into the initial emergence of
reproductive division of labor during an evolutionary transition in
individuality.Comment: 7 figure
The Binary Nature of PSR J2032+4127
PSR J2032+4127 is a gamma-ray and radio-emitting pulsar which has been
regarded as a young luminous isolated neutron star. However, its recent
spin-down rate has extraordinarily increased by a factor of two. We present
evidence that this is due to its motion as a member of a highly-eccentric
binary system with a 15-solar-mass Be star, MT91~213. Timing observations show
that, not only are the positions of the two stars coincident within 0.4 arcsec,
but timing models of binary motion of the pulsar fit the data much better than
a model of a young isolated pulsar. MT91~213, and hence the pulsar, lie in the
Cyg~OB2 stellar association, which is at a distance of only 1.4-1.7 kpc. The
pulsar is currently on the near side of, and accelerating towards, the Be star,
with an orbital period of 20-30 years. The next periastron is well-constrained
to occur in early 2018, providing an opportunity to observe enhanced
high-energy emission as seen in other Be-star binary systems.Comment: 8 pages, 5 figures. Accepted for publication in MNRA
An l^{p}-Version of von-Neumann Dimension For Banach Space Representations of Sofic Groups
A. Gournay defined a notion of -dimension for subspaces of the
l^{q}-left-regular representation of an amenable discrete group. We give an
alternative definition that works for sofic groups and a different notion for
groups satisfying the Connes embedding conjecture, and for more general
representations on Banach spaces. We extend certain results due to Gournay, as
well as discuss l^{p}-Betti numbers of Free groups.Comment: 65 pages, 7 figures. This is the final version. To appear in Journal
of Functional Analysis. Much of the old article has been added to
arXiv:1302.2286 so as to make the two papers roughly the same lengt
Bridging the biodiversity data gaps: Recommendations to meet users’ data needs
A strong case has been made for freely available, high quality data on species occurrence, in order to track changes in biodiversity. However, one of the main issues surrounding the provision of such data is that sources vary in quality, scope, and accuracy. Therefore publishers of such data must face the challenge of maximizing quality, utility and breadth of data coverage, in order to make such data useful to users. Here, we report a number of recommendations that stem from a content need assessment survey conducted by the Global Biodiversity Information Facility (GBIF). Through this survey, we aimed to distil the main user needs regarding biodiversity data. We find a broad range of recommendations from the survey respondents, principally concerning issues such as data quality, bias, and coverage, and extending ease of access. We recommend a candidate set of actions for the GBIF that fall into three classes: 1) addressing data gaps, data volume, and data quality, 2) aggregating new kinds of data for new applications, and 3) promoting ease-of-use and providing incentives for wider use. Addressing the challenge of providing high quality primary biodiversity data can potentially serve the needs of many international biodiversity initiatives, including the new 2020 biodiversity targets of the Convention on Biological Diversity, the emerging global biodiversity observation network (GEO BON), and the new Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)
Remarks on eigenspectra of isolated singularities
We introduce a simple calculus, extending a variant of the Steenbrink
spectrum, for describing Hodge-theoretic invariants of (smoothings of) isolated
singularities with (relative) automorphisms. After computing these
"eigenspectra" in the quasi-homogeneous case, we give three applications to
singularity bounding and monodromy of VHS.Comment: 23 page
G92-1097 Root and Crown Rot: Winterkill Complex of Winter Wheat
Root and crown rot--winterkill complex is discussed, including nature of the complex, symptoms, control, and management rationale. Root and crown rot of winter wheat is an interrelated disease complex caused by the interaction of infection of roots and crowns by Bipolaris sorokiniana and/or Fusarium graminearum and harsh winter conditions. It is an insidious, persistent and inconspicuous disease complex that reduces wheat yields each year. In extreme cases, entire fields or large areas within fields are killed. The ultimate effect is loss of stands, poor plant vigor, reduced yield and lower grain quality
Tidal streams in a MOND potential: constraints from Sagittarius
We compare orbits in a thin axisymmetric disc potential in MOND to those in a
thin disc plus near-spherical dark matter halo predicted by a CDM
cosmology. Remarkably, the amount of orbital precession in MOND is nearly
identical to that which occurs in a mildly oblate CDM Galactic halo (potential
flattening q=0.9), consistent with recent constraints from the Sagittarius
stream. Since very flattened mass distributions in MOND produce rounder
potentials than in standard Newtonian mechanics, we show that it will be very
difficult to use the tidal debris from streams to distinguish between a MOND
galaxy and a standard CDM galaxy with a mildly oblate halo.
If a galaxy can be found with either a prolate halo, or one which is more
oblate than this would rule out MOND as a viable theory. Improved
data from the leading arm of the Sagittarius dwarf - which samples the Galactic
potential at large radii - could rule out MOND if the orbital pole precession
can be determined to an accuracy of the order of .Comment: 7 pages, 3 figures. Final version accepted for publication in MNRAS.
The modelling of the Sagittarius stream has been improved, but otherwise the
conclusions remain the sam
Are megaquakes clustered?
We study statistical properties of the number of large earthquakes over the
past century. We analyze the cumulative distribution of the number of
earthquakes with magnitude larger than threshold M in time interval T, and
quantify the statistical significance of these results by simulating a large
number of synthetic random catalogs. We find that in general, the earthquake
record cannot be distinguished from a process that is random in time. This
conclusion holds whether aftershocks are removed or not, except at magnitudes
below M = 7.3. At long time intervals (T = 2-5 years), we find that
statistically significant clustering is present in the catalog for lower
magnitude thresholds (M = 7-7.2). However, this clustering is due to a large
number of earthquakes on record in the early part of the 20th century, when
magnitudes are less certain.Comment: 5 pages, 5 figure
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