59,005 research outputs found
Magnetoconductivity in Weyl semimetals: Effect of chemical potential and temperature
We present the detailed analyses of magneto-conductivities in a Weyl
semimetal within Born and self-consistent Born approximations. In the presence
of the charged impurities, the linear magnetoresistance can happen when the
charge carriers are mainly from the zeroth (n=0) Landau level. Interestingly,
the linear magnetoresistance is very robust against the change of temperature,
as long as the charge carriers mainly come from the zeroth Landau level. We
denote this parameter regime as the high-field regime. On the other hand, the
linear magnetoresistance disappears once the charge carriers from the higher
Landau levels can provide notable contributions. Our analysis indicates that
the deviation from the linear magnetoresistance is mainly due to the deviation
of the longitudinal conductivity from the behavior. We found two
important features of the self-energy approximation: 1. a dramatic jump of
, when the Landau level begins to contribute charge
carriers, which is the beginning point of the middle-field regime, when
decreasing the external magnetic field from high field; 2. In the low-field
regime shows a behavior and results the
magnetoresistance to show a behavior. The detailed and
careful numerical calculation indicates that the self-energy approximation
(including both the Born and the self-consistent Born approximations) does not
explain the recent experimental observation of linear magnetoresistance in Weyl
semimetals.Comment: The accepted version. Extending the previous version by including the
discussions of self-consistent Born approximatio
An empirical evaluation of four variants of a universal species-area relationship
The Maximum Entropy Theory of Ecology (METE) predicts a universal
species-area relationship (SAR) that can be fully characterized using only the
total abundance (N) and species richness (S) at a single spatial scale. This
theory has shown promise for characterizing scale dependence in the SAR.
However, there are currently four different approaches to applying METE to
predict the SAR and it is unclear which approach should be used due to a lack
of empirical evaluation. Specifically, METE can be applied recursively or a
non-recursively and can use either a theoretical or observed species-abundance
distribution (SAD). We compared the four different combinations of approaches
using empirical data from 16 datasets containing over 1000 species and 300,000
individual trees and herbs. In general, METE accurately downscaled the SAR
(R^2> 0.94), but the recursive approach consistently under-predicted richness,
and METEs accuracy did not depend strongly on using the observed or predicted
SAD. This suggests that best approach to scaling diversity using METE is to use
a combination of non-recursive scaling and the theoretical abundance
distribution, which allows predictions to be made across a broad range of
spatial scales with only knowledge of the species richness and total abundance
at a single scale.Comment: main text: 20 pages, 2 tables, 3 figure
Identification of the major cause of endemically poor mobilities in SiC/SiO2 structures
Materials with good carrier mobilities are desired for device applications,
but in real devices the mobilities are usually limited by the presence of
interfaces and contacts. Mobility degradation at semiconductor-dielectric
interfaces is generally attributed to defects at the interface or inside the
dielectric, as is the case in Si/SiO2 structures, where processing does not
introduce detrimental defects in the semiconductor. In the case of SiC/SiO2
structures, a decade of research focused on reducing or passivating interface
and oxide defects, but the low mobilities have persisted. By invoking
theoretical results and available experimental evidence, we show that thermal
oxidation generates carbon di-interstitial defects inside the semiconductor
substrate and that they are a major cause of the poor mobility in SiC/SiO2
structures
A geometric and structural approach to the analysis and design of biological circuit dynamics: a theory tailored for synthetic biology
Much of the progress in developing our ability to successfully design genetic circuits with predictable dynamics has followed the strategy of molding biological systems to fit into conceptual frameworks used in other disciplines, most notably the engineering sciences. Because biological systems have fundamental differences from systems in these other disciplines, this approach is challenging and the insights obtained from such analyses are often not framed in a biologically-intuitive way. Here, we present a new theoretical framework for analyzing the dynamics of genetic circuits that is tailored towards the unique properties associated with biological systems and experiments. Our framework approximates a complex circuit as a set of simpler circuits, which the system can transition between by saturating its various internal components. These approximations are connected to the intrinsic structure of the system, so this representation allows the analysis of dynamics which emerge solely from the system's structure. Using our framework, we analyze the presence of structural bistability in a leaky autoactivation motif and the presence of structural oscillations in the Repressilator
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