Elastic electron scattering from water vapor and ice at high momentum transfer

We compare the area, peak separation, and width of the H and O elastic peak for light and heavy water, as observed in spectra of keV electrons scattered over large angles. Peak separation is well reproduced by the theory, but the O:H area ratio is somewhat larger than expected and is equal to the O:D area ratio. Thus no anomalous scattering from H was observed. Only minor differences are observed for scattering from a gaseous or a solid target. The extracted mean kinetic energy of H and D agreed within 5% with the calculated ones for ice. For the more difficult vapor measurements agreement was on a 12% level. A preliminary attempt to extract the O kinetic energy in ice agreed within 10% with the calculated values.This work was made possible by financial support of the Australian Research Council

Electron spectroscopy using two-dimensional electron detection and a camera in a single electron counting mode

A brief description is given of an economical implementation of the read out of a two-dimensional detector in an electron spectrometer by a charge coupled device camera, using a pulse counting mode. Count rates up to 10 kHz can be handled in this way. A comparison with results obtained using a resistive anode detector is given for the case of electron scattering from Xe atoms. Good agreement was obtained between both detection techniques, establishing the validity of the method described here.This research was made possible by a grant of the Australian Research Council

The orbits of subdwarf-B + main-sequence binaries. II. Three eccentric systems; BD+29 3070, BD +34 1543 and Feige 87

The predicted orbital-period distribution of the subdwarf-B (sdB) population is bi-modal with a peak at short ( 250 days) periods. Observationally, many short-period sdB systems are known, but the predicted long period peak is missing as orbits have only been determined for a few long-period systems. As these predictions are based on poorly understood binary-interaction processes, it is of prime importance to confront the predictions with reliable observational data. We therefore initiated a monitoring program to find and characterize long-period sdB stars. In this paper we aim to determine the orbital parameters of the three long-period sdB+MS binaries BD+29 3070, BD+34 1543 and Feige 87, to constrain their absolute dimensions and the physical parameters of the components. High-resolution spectroscopic time series were obtained with HERMES at the Mercator telescope on La Palma, and analyzed to determine the radial velocities of both the sdB and MS components. Photometry from the literature was used to construct the spectral-energy distribution (SED) of the binaries. Atmosphere models were used to fit these SEDs and to determine the surface gravities and temperatures of both components of all systems. Spectral analysis was used to check the results of the SEDs. An orbital period of 1283 +- 63 d, a mass ratio of q = 0.39 +- 0.04 and a significant non-zero eccentricity of e = 0.15 +- 0.01 were found for BD+29 3070. For BD+34 1543 we determined P = 972 +- 2 d, q = 0.57 +- 0.01 and again a clear non-zero eccentricity of e = 0.16 +- 0.01. Last, for Feige 87 we found P = 936 +- 2 d, q = 0.55 +- 0.01 and e = 0.11 +- 0.01. BD+29 3070, BD+34 1543 and Feige 87 are long period sdB + MS binaries on clearly eccentric orbits. These results are in conflict with the predictions of stable Roche-lobe overflow models.Comment: 15 pages, 6 figures, Accepted by A&

Increased physical protection of soil carbon in the mineral soil of a poplar plantation after five years of free atmospheric CO₂ enrichment (FACE)

International audienceFree air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the existence of protection offered by the soil matrix and minerals. Fresh litter entering the soil enhances microbial activity which induces the binding of organic matter and soil particles into macro-aggregates. As the enclosed organic matter is decomposed, microbial and decomposition products become associated with mineral particles. This association results in the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the micro- and small macro-aggregates weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions. This study reveals that: 1) Species has an effect on the formation of macro-aggregates. The choice of species in a plantation or the effect of global change on species diversity, may therefore affect the stabilization and protection of soil C in aggregates. And 2) Increased atmospheric CO2 concentration increases the stabilization and protection of soil C in micro-aggregates formed within macro-aggregates. This mechanism increases the C sink of forest soils under increasing atmospheric CO2 concentration

Effects of free atmospheric CO₂ enrichment (FACE), N fertilization and poplar genotype on the physical protection of carbon in the mineral soil of a polar plantation after five years

International audienceFree air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the small macro-aggregate and free micro-aggregate weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions, although not significantly. This study reveals that FACE did not affect the formation of aggregates. We did, however, observe a trend of increased stabilization and protection of soil C in micro-aggregates formed within macro-aggregates under FACE. Moreover, the largest effect on aggregate formation was due to differences in species, i.e. poplar genotype. P. euramericana increased the formation of free micro-aggregates which means that more newly incorporated soil C was stabilized and protected. The choice of species in a plantation, or the effect of global change on species diversity, may therefore affect the stabilization and protection of C in soils

Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap

We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission frequency. The decay rates averaged over all dipole orientations are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2? outside the gap, in agreement with theory. We discuss the effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap.Comment: 5 figures, update author lis

A precise characterisation of the top quark electro-weak vertices at the ILC

Top quark production in the process $e^+e^- \to t\bar{t}$ at a future linear electron positron collider with polarised beams is a powerful tool to determine indirectly the scale of new physics. The presented study, based on a detailed simulation of the ILD detector concept, assumes a centre-of-mass energy of $\sqrt{s}=500\,$GeV and a luminosity of $\mathcal{L}=500\,{\rm fb}^{-1}$ equally shared between the incoming beam polarisations of $\mathcal{P}_{e^-}, \mathcal{P}_{e^+} =\pm0.8,\mp0.3$. Events are selected in which the top pair decays semi-leptonically and the cross sections and the forward-backward asymmetries are determined. Based on these results, the vector, axial vector and tensorial $CP$ conserving couplings are extracted separately for the photon and the $Z^0$ component. With the expected precision, a large number of models in which the top quark acts as a messenger to new physics can be distinguished with many standard deviations. This will dramatically improve expectations from e.g. the LHC for electro-weak couplings of the top quark.Comment: This work is an update of arXiv:1307.8102, minor changes w.r.t. v1 (typos, wrong grammar, incomplete sentences etc.