70 research outputs found
Interacting Crumpled Manifolds: Exact Results to all Orders of Perturbation Theory
In this letter, we report progress on the field theory of polymerized
tethered membranes. For the toy-model of a manifold repelled by a single point,
we are able to sum the perturbation expansion in the strength g of the
interaction exactly in the limit of internal dimension D -> 2. This exact
solution is the starting point for an expansion in 2-D, which aims at
connecting to the well studied case of polymers (D=1). We here give results to
order (2-D)^4, where again all orders in g are resummed. This is a first step
towards a more complete solution of the self-avoiding manifold problem, which
might also prove valuable for polymers.Comment: 8 page
Heterozygous, Polyploid, Giant Bacterium, Achromatium, Possesses an Identical Functional Inventory Worldwide across Drastically Different Ecosystems
Achromatium is large, hyperpolyploid and the only known heterozygous bacterium. Single cells contain approximately 300 different chromosomes with allelic diversity far exceeding that typically harbored by single bacteria genera. Surveying all publicly available sediment sequence archives, we show that Achromatium is common worldwide, spanning temperature, salinity, pH, and depth ranges normally resulting in bacterial speciation. Although saline and freshwater Achromatium spp. appear phylogenetically separated, the genus Achromatium contains a globally identical, complete functional inventory regardless of habitat. Achromatium spp. cells from differing ecosystems (e.g., from freshwater to saline) are, unexpectedly, equally functionally equipped but differ in gene expression patterns by transcribing only relevant genes. We suggest that environmental adaptation occurs by increasing the copy number of relevant genes across the cell’s hundreds of chromosomes, without losing irrelevant ones, thus maintaining the ability to survive in any ecosystem type. The functional versatility of Achromatium and its genomic features reveal alternative genetic and evolutionary mechanisms, expanding our understanding of the role and evolution of polyploidy in bacteria while challenging the bacterial species concept and drivers of bacterial speciation
The one-loop elastic coefficients for the Helfrich membrane in higher dimensions
Using a covariant geometric approach we obtain the effective bending
couplings for a 2-dimensional rigid membrane embedded into a
-dimensional Euclidean space. The Hamiltonian for the membrane has three
terms: The first one is quadratic in its mean extrinsic curvature. The second
one is proportional to its Gaussian curvature, and the last one is proportional
to its area. The results we obtain are in agreement with those finding that
thermal fluctuations soften the 2-dimensional membrane embedded into a
3-dimensional Euclidean space.Comment: 9 page
Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics
Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044
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