14,195 research outputs found
Universal temperature dependence of optical excitation life-time and band-gap in chirality assigned semiconducting single-wall carbon nanotubes
The temperature dependence of optical excitation life-time, Gamma, and
transition energies, E_ii, were measured for bucky-papers of single-wall carbon
nanotubes (SWCNTs) and inner tubes in double-wall carbon nanotubes (DWCNTs)
using resonant Raman scattering. The temperature dependence of Gamma and E_ii
is the same for both types of samples and is independent of tube chirality. The
data proves that electron-phonon interaction is responsible for temperature
dependence of E_ii(T). The temperature independent inhomogeneous contribution
to Gamma is much larger in the SWCNT samples, which is explained by the
different SWCNT environment in the two types of samples. Gamma of the inner
tubes for the bucky-paper DWCNT sample is as low as \sim 30 meV, which is
comparable to that found for individual SWCNTs
Signatures of Introgression across the Allele Frequency Spectrum.
The detection of introgression from genomic data is transforming our view of species and the origins of adaptive variation. Among the most widely used approaches to detect introgression is the so-called ABBA-BABA test or D-statistic, which identifies excess allele sharing between nonsister taxa. Part of the appeal of D is its simplicity, but this also limits its informativeness, particularly about the timing and direction of introgression. Here we present a simple extension, D frequency spectrum or DFS, in which D is partitioned according to the frequencies of derived alleles. We use simulations over a large parameter space to show how DFS carries information about various factors. In particular, recent introgression reliably leads to a peak in DFS among low-frequency derived alleles, whereas violation of model assumptions can lead to a lack of signal at low frequencies. We also reanalyze published empirical data from six different animal and plant taxa, and interpret the results in the light of our simulations, showing how DFS provides novel insights. We currently see DFS as a descriptive tool that will augment both simple and sophisticated tests for introgression, but in the future it may be usefully incorporated into probabilistic inference frameworks
Oncogenic K-Ras suppresses IP<sub>3</sub>-dependent Ca<sup>2+</sup> release through remodeling of IP<sub>3</sub>Rs isoform composition and ER luminal Ca<sup>2+</sup> levels in colorectal cancer cell lines
The GTPase Ras is a molecular switch engaged downstream of G-protein coupled receptors and receptor tyrosine inases that controls multiple cell fate-determining signalling athways. Ras signalling is frequently deregulated in cancer underlying associated changes in cell phenotype. Although Ca2+ signalling pathways control some overlapping functions with Ras, and altered Ca2+ signalling pathways are emerging as important players in oncogenic transformation, how Ca2+ signalling is remodelled during transformation and whether it has a causal role remains unclear. We have investigated Ca2+ signalling in two human colorectal cancer cell lines and their isogenic derivatives in which the mutated K-Ras allele (G13D) has been deleted by homologous recombination. We show that agonist-induced Ca2+ release from intracellular stores is enhanced by loss of K-RasG13D through an increase in the ER store content and a modification of IP3R subtype abundance. Consistently, uptake of Ca2+ into mitochondria and sensitivity to apoptosis was enhanced as a result of KRasG13D loss. These results suggest that suppression of Ca2+ signalling is a common response to naturally occurring levels of K-RasG13D that contributes to a survival
advantage during oncogenic transformation
Interpreting the genomic landscape of introgression.
Introgression, the transfer of genetic material between species through hybridisation, occurs in many taxa and has important consequences. Genomic studies allow us to characterise the landscape of introgression across the genome, shedding light on both its adaptive benefits and the incompatibilities that help to maintain species barriers. Studies taking a genome-wide view suggest that adaptive introgression may be common, but that introgressed variation between many species is selected against throughout much of the genome. Confounding factors can complicate interpretations from these data, and computational simulations have proved vital to illustrate expected patterns under different scenarios. Future developments will move beyond correlative evidence to explicit models that account for how selection and genetic drift influence introgressed variation
Sensing as a Service: An Exploration into the Practical Implementations of DSA
The cognitive radio literature generally assumes that the functions required for non-cooperative secondary DSA are integrated into a single radio system. It need not be so. In this paper, we model cognitive radio functions as a value chain and explore the implications of different forms of organization of this value chain. We initially explore the consequences of separating the sensing function from other cognitive radio functions
Rigorous conditions for the existence of bound states at the threshold in the two-particle case
In the framework of non-relativistic quantum mechanics and with the help of
the Greens functions formalism we study the behavior of weakly bound states as
they approach the continuum threshold. Through estimating the Green's function
for positive potentials we derive rigorously the upper bound on the wave
function, which helps to control its falloff. In particular, we prove that for
potentials whose repulsive part decays slower than the bound states
approaching the threshold do not spread and eventually become bound states at
the threshold. This means that such systems never reach supersizes, which would
extend far beyond the effective range of attraction. The method presented here
is applicable in the many--body case
Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance
Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society B. Biological Sciences 285 (2018): 20181178, doi:10.1098/rspb.2018.1178.The costs of predation may exert significant pressure on the mode of communication used by an
animal, and many species balance the benefits of communication (e.g. mate attraction) against
the potential risk of predation. Four groups of toothed whales have independently evolved
narrowband high-frequency (NBHF) echolocation signals. These signals help NBHF species
avoid predation through acoustic crypsis by echolocating and communicating at frequencies
inaudible to predators such as mammal-eating killer whales. Heaviside’s dolphins
(Cephalorhynchus heavisidii) are thought to exclusively produce NBHF echolocation clicks with
a centroid frequency around 125 kHz and little to no energy below 100 kHz. To test this, we
recorded wild Heaviside’s dolphins in a sheltered bay in Namibia. We demonstrate that
Heaviside’s dolphins produce a second type of click with lower frequency and broader
bandwidth in a frequency range that is audible to killer whales. These clicks are used in burst-pulses and occasional click series but not foraging buzzes. We evaluate three different
hypotheses and conclude that the most likely benefit of these clicks is to decrease transmission
directivity and increase conspecific communication range. The expected increase in active space
depends on background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz Sea State
1) the active space of NBHF signals. This dual click strategy therefore allows these social
dolphins to maintain acoustic crypsis during navigation and foraging, and to selectively relax
their crypsis to facilitate communication with conspecifics.This research was supported by a Fulbright U.S. Research Fellowship, the National Geographic
Society’s Emerging Explorers Grant in conjunction with the Waitt Foundation (38115) and the
University of Pretoria’s Zoology Department. TG was funded by the Claude Leon Foundation,
and SE was funded by the South African National Research Foundation. FHJ acknowledges
funding from the Office of Naval Research (N00014-1410410) and an AIAS-COFUND
fellowship from Aarhus Institute of Advanced Studies
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