59,170 research outputs found
Gyrotropic magnetic effect and the magnetic moment on the Fermi surface
The current density induced in a clean metal by a
slowly-varying magnetic field is formulated as the low-frequency
limit of natural optical activity, or natural gyrotropy. Working with a
multiband Pauli Hamiltonian, we obtain from the Kubo formula a simple
expression for in terms of the
intrinsic magnetic moment (orbital plus spin) of the Bloch electrons on the
Fermi surface. An alternate semiclassical derivation provides an intuitive
picture of the effect, and takes into account the influence of scattering
processes in dirty metals. This "gyrotropic magnetic effect" is fundamentally
different from the chiral magnetic effect driven by the chiral anomaly and
governed by the Berry curvature on the Fermi surface, and the two effects are
compared for a minimal model of a Weyl semimetal. Like the Berry curvature, the
intrinsic magnetic moment should be regarded as a basic ingredient in the
Fermi-liquid description of transport in broken-symmetry metals.Comment: The Supplemental Material can be found at
http://cmt.berkeley.edu/suppl/zhong-arxiv15-suppl.pd
Diversity across Seasons of Culturable Pseudomonas from a Desiccation Lagoon in Cuatro Cienegas, Mexico.
Cuatro Cienegas basin (CCB) is a biodiversity reservoir within the Chihuahuan desert that includes several water systems subject to marked seasonality. While several studies have focused on biodiversity inventories, this is the first study that describes seasonal changes in diversity within the basin. We sampled Pseudomonas populations from a seasonally variable water system at four different sampling dates (August 2003, January 2004, January 2005, and August 2005). A total of 70 Pseudomonas isolates across seasons were obtained, genotyped by fingerprinting (BOX-PCR), and taxonomically characterized by 16S rDNA sequencing. We found 35 unique genotypes, and two numerically dominant lineages (16S rDNA sequences) that made up 64% of the sample: P. cuatrocienegasensis and P. otitidis. We did not recover genotypes across seasons, but lineages reoccurred across seasons; P. cuatrocienegasensis was isolated exclusively in winter, while P. otitidis was only recovered in summer. We statistically show that taxonomic identity of isolates is not independent of the sampling season, and that winter and summer populations are different. In addition to the genetic description of populations, we show exploratory measures of growth rates at different temperatures, suggesting physiological differences between populations. Altogether, the results indicate seasonal changes in diversity of free-living aquatic Pseudomonas populations from CCB
The first analytical expression to estimate photometric redshifts suggested by a machine
We report the first analytical expression purely constructed by a machine to
determine photometric redshifts () of galaxies. A simple and
reliable functional form is derived using galaxies from the Sloan
Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method
automatically dropped the and bands, relying only on , and
for the final solution. Applying this expression to other SDSS-DR10
galaxies, with measured spectroscopic redshifts (), we achieved a
mean and a scatter when averaged up to . The method was
also applied to the PHAT0 dataset, confirming the competitiveness of our
results when faced with other methods from the literature. This is the first
use of symbolic regression in cosmology, representing a leap forward in
astronomy-data-mining connection.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS Letter
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