87 research outputs found
Strings with Extrinsic Curvature: An Analysis of the Crossover Regime
We present the results of a set of Monte Carlo simulations of Dynamically
Triangulated Random Surfaces embedded in three dimensions with an extrinsic
curvature dependent action. We analyze several observables in the crossover
regime and discuss whether or not our observations are indicative of the
presence of a phase transition.Comment: (Contribution to Lattice 92 Proceedings.) Latex file (5 pages),
requires espcrc2.sty. 2 figures not included. Syracuse preprint
SU-HEP-4241-52
The Erpenbeck high frequency instability theorem for ZND detonations
The rigorous study of spectral stability for strong detonations was begun by
J.J. Erpenbeck in [Er1]. Working with the Zeldovitch-von Neumann-D\"oring (ZND)
model, which assumes a finite reaction rate but ignores effects like viscosity
corresponding to second order derivatives, he used a normal mode analysis to
define a stability function V(\tau,\eps) whose zeros in
correspond to multidimensional perturbations of a steady detonation profile
that grow exponentially in time. Later in a remarkable paper [Er3] he provided
strong evidence, by a combination of formal and rigorous arguments, that for
certain classes of steady ZND profiles, unstable zeros of exist for
perturbations of sufficiently large transverse wavenumber \eps, even when the
von Neumann shock, regarded as a gas dynamical shock, is uniformly stable in
the sense defined (nearly twenty years later) by Majda. In spite of a great
deal of later numerical work devoted to computing the zeros of V(\tau,\eps),
the paper \cite{Er3} remains the only work we know of that presents a detailed
and convincing theoretical argument for detecting them.
The analysis in [Er3] points the way toward, but does not constitute, a
mathematical proof that such unstable zeros exist. In this paper we identify
the mathematical issues left unresolved in [Er3] and provide proofs, together
with certain simplifications and extensions, of the main conclusions about
stability and instability of detonations contained in that paper.
The main mathematical problem, and our principal focus here, is to determine
the precise asymptotic behavior as \eps\to \infty of solutions to a linear
system of ODEs in , depending on \eps and a complex frequency as
parameters, with turning points on the half-line
The Phase Diagram of Fluid Random Surfaces with Extrinsic Curvature
We present the results of a large-scale simulation of a Dynamically
Triangulated Random Surface with extrinsic curvature embedded in
three-dimensional flat space. We measure a variety of local observables and use
a finite size scaling analysis to characterize as much as possible the regime
of crossover from crumpled to smooth surfaces.Comment: 29 pages. There are also 19 figures available from the authors but
not included here - sorr
Why sequence all eukaryotes?
Life on Earth has evolved from initial simplicity to the astounding complexity we experience today. Bacteria and archaea have largely excelled in metabolic diversification, but eukaryotes additionally display abundant morphological innovation. How have these innovations come about and what constraints are there on the origins of novelty and the continuing maintenance of biodiversity on Earth? The history of life and the code for the working parts of cells and systems are written in the genome. The Earth BioGenome Project has proposed that the genomes of all extant, named eukaryotes-about 2 million species-should be sequenced to high quality to produce a digital library of life on Earth, beginning with strategic phylogenetic, ecological, and high-impact priorities. Here we discuss why we should sequence all eukaryotic species, not just a representative few scattered across the many branches of the tree of life. We suggest that many questions of evolutionary and ecological significance will only be addressable when whole-genome data representing divergences at all of the branchings in the tree of life or all species in natural ecosystems are available. We envisage that a genomic tree of life will foster understanding of the ongoing processes of speciation, adaptation, and organismal dependencies within entire ecosystems. These explorations will resolve long-standing problems in phylogenetics, evolution, ecology, conservation, agriculture, bioindustry, and medicine
Standards Recommendations for the Earth BioGenome Project
Funder: Howard Hughes Medical InstituteFunder: National Science Foundation; Grant(s): DBI:IIBR:CAREER #1943371A global international initiative such as the Earth BioGenome Project (EBP) requires both agreement and coordination on standards to ensure that the collective effort generates rapid progress towards its goals. To this end, the EBP initiated five technical standards committees comprising volunteer members from the global genomics scientific community: Sample Collection and Processing, Sequencing and Assembly, Annotation, Analysis, and, IT and Informatics. The current versions of the resulting standards documents are available on the EBP website, with the recognition that opportunities, technologies and challenges may improve or change in the future requiring flexibility for the EBP to meet its goals. Here, we describe some highlights from the proposed standards, and areas where additional challenges will need to be met.NIH, EMBL, NSF, Smithsonian, NMNH, USDA, HHM
Standards recommendations for the Earth BioGenome Project
A global international initiative, such as the Earth BioGenome Project (EBP), requires both agreement and coordination on standards to ensure that the collective effort generates rapid progress toward its goals. To this end, the EBP initiated five technical standards committees comprising volunteer members from the global genomics scientific community: Sample Collection and Processing, Sequencing and Assembly, Annotation, Analysis, and IT and Informatics. The current versions of the resulting standards documents are available on the EBP website, with the recognition that opportunities, technologies, and challenges may improve or change in the future, requiring flexibility for the EBP to meet its goals. Here, we describe some highlights from the proposed standards, and areas where additional challenges will need to be met
Global Patterns of Bacterial Beta-Diversity in Seafloor and Seawater Ecosystems
Background
Marine microbial communities have been essential contributors to global biomass, nutrient cycling, and biodiversity since the early history of Earth, but so far their community distribution patterns remain unknown in most marine ecosystems.
Methodology/Principal Findings
The synthesis of 9.6 million bacterial V6-rRNA amplicons for 509 samples that span the global ocean's surface to the deep-sea floor shows that pelagic and benthic communities greatly differ, at all taxonomic levels, and share <10% bacterial types defined at 3% sequence similarity level. Surface and deep water, coastal and open ocean, and anoxic and oxic ecosystems host distinct communities that reflect productivity, land influences and other environmental constraints such as oxygen availability. The high variability of bacterial community composition specific to vent and coastal ecosystems reflects the heterogeneity and dynamic nature of these habitats. Both pelagic and benthic bacterial community distributions correlate with surface water productivity, reflecting the coupling between both realms by particle export. Also, differences in physical mixing may play a fundamental role in the distribution patterns of marine bacteria, as benthic communities showed a higher dissimilarity with increasing distance than pelagic communities.
Conclusions/Significance
This first synthesis of global bacterial distribution across different ecosystems of the World's oceans shows remarkable horizontal and vertical large-scale patterns in bacterial communities. This opens interesting perspectives for the definition of biogeographical biomes for bacteria of ocean waters and the seabed
The Earth BioGenome Project 2020: Starting the clock
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