High levels of gene flow and genetic diversity in Irish populations of Salix caprea L. inferred from chloroplast and nuclear SSR markers

peer-reviewedBackground Salix caprea is a cold-tolerant pioneer species that is ecologically important in Europe and western and central Asia. However, little data is available on its population genetic structure and molecular ecology. We describe the levels of geographic population genetic structure in natural Irish populations of S. caprea and determine the extent of gene flow and sexual reproduction using both chloroplast and nuclear simple sequence repeats (SSRs). Results A total of 183 individuals from 21 semi-natural woodlands were collected and genotyped. Gene diversity across populations was high for the chloroplast SSRs (H T  = 0.21-0.58) and 79 different haplotypes were discovered, among them 48% were unique to a single individual. Genetic differentiation of populations was found to be between moderate and high (mean G ST  = 0.38). For the nuclear SSRs, G ST was low at 0.07 and observed heterozygosity across populations was high (H O  = 0.32-0.51); only 9.8% of the genotypes discovered were present in two or more individuals. For both types of markers, AMOVA showed that most of the variation was within populations. Minor geographic pattern was confirmed by a Bayesian clustering analysis. Gene flow via pollen was found to be approximately 7 times more important than via seeds. Conclusions The data are consistent with outbreeding and indicate that there are no significant barriers for gene flow within Ireland over large geographic distances. Both pollen-mediated and seed-mediated gene flow were found to be high, with some of the populations being more than 200 km apart from each other. These findings could simply be due to human intervention through seed trade or accidental transportation of both seeds and pollen. These results are of value to breeders wishing to exploit natural genetic variation and foresters having to choose planting material.Teagasc Walsh Fellowship Programm

Characterizing and reducing equifinality by constraining a distributed catchment model with regional signatures, local observations, and process understanding

Distributed catchment models are widely used tools for predicting hydrologic behavior. While distributed models require many parameters to describe a system, they are expected to simulate behavior that is more consistent with observed processes. However, obtaining a single set of acceptable parameters can be problematic, as parameter equifinality often results in several behavioral sets that fit observations (typically streamflow). In this study, we investigate the extent to which equifinality impacts a typical distributed modeling application. We outline a hierarchical approach to reduce the number of behavioral sets based on regional, observation-driven, and expert-knowledge-based constraints. For our application, we explore how each of these constraint classes reduced the number of behavioral parameter sets and altered distributions of spatiotemporal simulations, simulating a well-studied headwater catchment, Stringer Creek, Montana, using the distributed hydrology–soil–vegetation model (DHSVM). As a demonstrative exercise, we investigated model performance across 10 000 parameter sets. Constraints on regional signatures, the hydrograph, and two internal measurements of snow water equivalent time series reduced the number of behavioral parameter sets but still left a small number with similar goodness of fit. This subset was ultimately further reduced by incorporating pattern expectations of groundwater table depth across the catchment. Our results suggest that utilizing a hierarchical approach based on regional datasets, observations, and expert knowledge to identify behavioral parameter sets can reduce equifinality and bolster more careful application and simulation of spatiotemporal processes via distributed modeling at the catchment scale

Surfactant-aided exfoliation of molydenum disulphide for ultrafast pulse generation through edge-state saturable absorption

We use liquid phase exfoliation to produce dispersions of molybdenum disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (<6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q- switched fibre lasers, tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behaviour to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.Comment: 6 pages, 5 figure

Ultrafast Raman laser mode-locked by nanotubes

We demonstrate passive mode-locking of a Raman fiber laser using a nanotube-based saturable absorber coupled to a net normal dispersion cavity. This generates highly chirped 500 ps pulses. These are then compressed down to 2 ps , with 1.4 kW peak power, making it a simple wavelength-versatile source for various applications

Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS2_2 using multiphoton microscopy

We report second- and third-harmonic generation in monolayer MoS$_\mathrm{2}$ as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of $|\chi_s^{(2)}|=2.0\times10^{-20}$ m$^2$ V$^{-1}$ and for the first time for monolayer MoS$_\mathrm{2}$, $|\chi_s^{(3)}|=1.7\times10^{-28}$ m$^3$ V$^{-2}$. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of $|\chi_{b}^{(2)}|=2.9\times10^{-11}$ m V$^{-1}$ and $|\chi_{b}^{(3)}|=2.4\times10^{-19}$ m$^2$ V$^{-2}$, accounting for the sheet thickness. Experimental comparisons between MoS$_\mathrm{2}$ and graphene are also performed, demonstrating $\sim$3.4 times stronger third-order sheet nonlinearity in monolayer MoS$_\mathrm{2}$, highlighting the material's potential for nonlinear photonics in the telecommunications C band.Comment: Accepted by 2D Materials, 28th Oct 201

Exclusive neutral pion electroproduction in the deeply virtual regime

We present measurements of the ep -\u3e ep pi(0) cross section extracted at two values of four-momentum transfer Q(2) = 1.9 GeV(2) and Q(2) = 2.3 GeV(2) at Jefferson Lab Hall A. The kinematic range allows one to study the evolution of the extracted cross section as a function of Q(2) and W. Results are confronted with Regge-inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed

Beam-Target Double-Spin Asymmetry A(LT) in Charged Pion Production from Deep Inelastic Scattering on a Transversely Polarized He-3 Target at 1.4 \u3c Q(2) \u3c 2.7 GeV2

We report the first measurement of the double-spin asymmetry A(LT) for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized He-3 target. The kinematics focused on the valence quark region, 0.16 \u3c x \u3c 0.35 with 1.4 \u3c Q(2) \u3c 2.7 GeV2. The corresponding neutron A(LT) asymmetries were extracted from the measured He-3 asymmetries and proton over He-3 cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g(1T)(q) and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for pi(-) production on He-3 and the neutron, while our pi(+) asymmetries are consistent with zero