106 research outputs found
Noise characterization for LISA
We consider the general problem of estimating the inflight LISA noise power
spectra and cross-spectra, which are needed for detecting and estimating the
gravitational wave signals present in the LISA data. For the LISA baseline
design and in the long wavelength limit, we bound the error on all spectrum
estimators that rely on the use of the fully symmetric Sagnac combination
(). This procedure avoids biases in the estimation that would otherwise
be introduced by the presence of a strong galactic background in the LISA data.
We specialize our discussion to the detection and study of the galactic white
dwarf-white dwarf binary stochastic signal.Comment: 9 figure
Toxic effect of herbicides used for water hyacinth control on two insects released for its biological control in South Africa
The integrated control of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) has become necessary in South Africa, as biological control alone is perceived to be too slow in controlling the weed. In total, seven insect biological control agents have been released on water hyacinth in South Africa. At the same time, herbicides are applied by the water authorities in areas where the weed continues to be troublesome. This study investigated the assumption that the two control methods are compatible by testing the direct toxicity of a range of herbicide formulations and surfactants on two of the biological control agents released against water hyacinth, the weevil, Neochetina eichhorniae Warner (Coleoptera: Curculionidae) and the water hyacinth mirid,Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae). A number of the formulations used resulted in significant mortality of the mirid and the weevil. Products containing 2,4-D amine and diquat as active ingredients caused higher mortality of both agents (up to 80% for the mirid) than formulations containing glyphosate. Furthermore, when surfactants were added to enhance herbicide efficiency, it resulted in increased toxicity to the insects. We recommend that glyphosate formulations should be used in integrated control programmes, and that surfactants be avoided in order to reduce the toxic nature of spray formulations to the insect biological control agents released against water hyacinth
Raman analysis of bilayer graphene film prepared on commercial Cu(0.5 at% Ni) foil
This study reports the Raman analysis of bilayer graphene films prepared on commercial dilute Cu(0.5 at% Ni) foils using atmospheric pressure chemical vapor deposition. A bilayer graphene film obtained on Cu foil is known to have small areas of bilayer (islands) with a significant fraction of non-Bernal stacking, while that obtained on Cu/Ni is known to grow over a large area with Bernal stacking. In the Raman optical microscope images, a wafer-scale monolayer and large-area bilayer graphene films were distinguished and confirmed with Raman spectra intensities ratios of 2D to G peaks. The large-area part of bilayer graphene film obtained was assisted by Ni surface segregation because Ni has higher methane decomposition rate and carbon solubility compared with Cu. The Raman data suggest a Bernal stacking order in the prepared bilayer graphene film. A four-point probe sheet resistance of graphene films confirmed a bilayer graphene film sheet resistance distinguished from that of monolayer graphene. A relatively higher Ni surface concentration in Cu(0.5 at% Ni) foil was confirmed with time-of-flight secondary ion mass spectrometry. The inhomogeneous distribution of Ni in a foil and the diverse crystallographic surface of a foil (confirmed with proton-induced X-ray emission and electron backscatter diffraction, respectively) could be a reason for incomplete wafer-scale bilayer graphene film. The Ni surface segregation in dilute Cu(0.5 at% Ni) foil has a potential to impact on atmospheric pressure chemical vapor deposition growth of large-area bilayer graphene film.The South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation (NRF) of South Africa (grant no. 97994). M.J. Madito acknowledges the financial support from University of Pretoria and NRF for his PhD studies.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1097-45552017-05-31Physic
A dilute Cu(Ni) alloy for synthesis of large-area Bernal satcked bilayer graphene using atmospheric pressure chemical vapour deposition
A bilayer graphene film obtained on copper (Cu) foil is known to have a significant fraction of
non-Bernal (AB) stacking and on copper/nickel (Cu/Ni) thin films is known to grow over a
large-area with AB stacking. In this study, annealed Cu foils for graphene growth were doped with
small concentrations of Ni to obtain dilute Cu(Ni) alloys in which the hydrocarbon decomposition
rate of Cu will be enhanced by Ni during synthesis of large-area AB-stacked bilayer graphene
using atmospheric pressure chemical vapour deposition. The Ni doped concentration and the Ni
homogeneous distribution in Cu foil were confirmed with inductively coupled plasma optical
emission spectrometry and proton-induced X-ray emission. An electron backscatter diffraction
map showed that Cu foils have a single (001) surface orientation which leads to a uniform growth
rate on Cu surface in early stages of graphene growth and also leads to a uniform Ni surface
concentration distribution through segregation kinetics. The increase in Ni surface concentration
in foils was investigated with time-of-flight secondary ion mass spectrometry. The quality of graphene,
the number of graphene layers, and the layers stacking order in synthesized bilayer graphene
films were confirmed by Raman and electron diffraction measurements. A four point probe station
was used to measure the sheet resistance of graphene films. As compared to Cu foil, the prepared
dilute Cu(Ni) alloy demonstrated the good capability of growing large-area AB-stacked bilayer
graphene film by increasing Ni content in Cu surface layer.The
South African Research Chairs Initiative of the Department
of Science and Technology and National Research
Foundation of South Africa (Grant No. 97994). M. J. Madito
acknowledges the financial support from university of
Pretoria and NRF for his Ph.D. studies.http://scitation.aip.org/content/aip/journal/japam2016Physic
The Dependence of the Superconducting Transition Temperature of Organic Molecular Crystals on Intrinsically Non-Magnetic Disorder: a Signature of either Unconventional Superconductivity or Novel Local Magnetic Moment Formation
We give a theoretical analysis of published experimental studies of the
effects of impurities and disorder on the superconducting transition
temperature, T_c, of the organic molecular crystals kappa-ET_2X and beta-ET_2X
(where ET is bis(ethylenedithio)tetrathiafulvalene and X is an anion eg I_3).
The Abrikosov-Gorkov (AG) formula describes the suppression of T_c both by
magnetic impurities in singlet superconductors, including s-wave
superconductors and by non-magnetic impurities in a non-s-wave superconductor.
We show that various sources of disorder lead to the suppression of T_c as
described by the AG formula. This is confirmed by the excellent fit to the
data, the fact that these materials are in the clean limit and the excellent
agreement between the value of the interlayer hopping integral, t_perp,
calculated from this fit and the value of t_perp found from angular-dependant
magnetoresistance and quantum oscillation experiments. If the disorder is, as
seems most likely, non-magnetic then the pairing state cannot be s-wave. We
show that the cooling rate dependence of the magnetisation is inconsistent with
paramagnetic impurities. Triplet pairing is ruled out by several experiments.
If the disorder is non-magnetic then this implies that l>=2, in which case
Occam's razor suggests that d-wave pairing is realised. Given the proximity of
these materials to an antiferromagnetic Mott transition, it is possible that
the disorder leads to the formation of local magnetic moments via some novel
mechanism. Thus we conclude that either kappa-ET_2X and beta-ET_2X are d-wave
superconductors or else they display a novel mechanism for the formation of
localised moments. We suggest systematic experiments to differentiate between
these scenarios.Comment: 18 pages, 5 figure
O grupo psicoterapêutico e a interpretação na abordagem lacaniana: reflexão e redefinição de possibilidades e modos de atendimento na Saúde Coletiva
Procediment d’Oferta General de places de prà ctiques
Previous calculations on model systems for the cooperative binding of two NO2 molecules to carbon nanotubes using density functional theory and second order Moller–Plesset perturbation theory gave results differing by 30 kcal/mol. Quantum Monte Carlo calculations are performed to study the role of electronic correlations in these systems and resolve the discrepancy between these previous calculations. Compared to QMC binding energies, MP2 and LDA are shown to overbind, while B3LYP and BPW91 underbind. PW91 gives the best agreement with QMC with a binding energy differing by only 3 kcal/mol. Basis set effects are also shown to be important
PotentialitĂ©s de la dĂ©tection par fluorescence native induite par laser UV pour les sciences sĂ©parativesÂ
International audienc
La détection par fluorescence native induite par laser en électrophorèse capillaire
International audienc
Etude des potentialités en électrophorèse capillaire et nano-LC d’un détecteur à fluorescence native induite par laser UV
International audienc
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