1,132 research outputs found
An investigation of PDMS structures for optimized ferroelectret performance
This paper reports the ANSYS simulation and fabrication processes for optimising PDMS ferroelectret performance. The proposed model extends the previously published analytical models and compares this with simulation of individual void geometry. The ferroelectret material is fabricated from PDMS using 3D-printed plastic moulds. The analytical model and Ansys simulation results predict the variation in performance of the PDMS ferroelectret with the different void geometry and surface charge density. The theoretical maximum piezoelectric coefficient d33 achieved was about 220 pC/N. The experimental maximum d33 obtained was 172 pC/N
Topological Weyl semimetals in the chiral antiferromagnetic materials Mn3Ge and Mn3Sn
Recent experiments revealed that Mn3Sn and Mn3Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect
Surface water numerical modelling for the Galilee subregion Product 2.6.1 for the Galilee subregion from the Lake Eyre Basin Bioregional Assessment
No abstract available
Solar Neutrinos: What We Have Learned
The four operating solar neutrino experiments confirm the hypothesis that the
energy source for solar luminosity is hydrogen fusion. However, the measured
rate for each of the four solar neutrino experiments differs significantly (by
factors of 2.0 to 3.5) from the corresponding theoretical prediction that is
based upon the standard solar model and the simplest version of the standard
electroweak theory. If standard electroweak theory is correct, the energy
spectrum for \b8 neutrinos created in the solar interior must be the same (to
one part in ) as the known laboratory \b8 neutrino energy spectrum.
Direct comparison of the chlorine and the Kamiokande experiments, both
sensitive to \b8 neutrinos, suggests that the discrepancy between theory and
observations depends upon neutrino energy, in conflict with standard
expectations. Monte Carlo studies with 1000 implementations of the standard
solar model confirm that the chlorine and the Kamiokande experiments cannot be
reconciled unless new weak interaction physics changes the shape of the \b8
neutrino energy spectrum. The results of the two gallium solar neutrino
experiments strengthen the conclusion that new physics is required and help
determine a relatively small allowed region for the MSW neutrino parameters.Comment: LaTeX file, 19 pages. For hardcopy with figures contact
[email protected]. Institute for Advanced Study number AST 93/6
Quasi-energy-independent solar neutrino transitions
Current solar, atmospheric, and reactor neutrino data still allow oscillation
scenarios where the squared mass differences are all close to 10^-3 eV^2,
rather than being hierarchically separated. For solar neutrinos, this situation
(realized in the upper part of the so-called large-mixing angle solution)
implies adiabatic transitions which depend weakly on the neutrino energy and on
the matter density, as well as on the ``atmospheric'' squared mass difference.
In such a regime of ``quasi-energy-independent'' (QEI) transitions,
intermediate between the more familiar ``Mikheyev-Smirnov-Wolfenstein'' (MSW)
and energy-independent (EI) regimes, we first perform analytical calculations
of the solar nu_e survival probability at first order in the matter density,
beyond the usual hierarchical approximations. We then provide accurate,
generalized expressions for the solar neutrino mixing angles in matter, which
reduce to those valid in the MSW, QEI and EI regimes in appropriate limits.
Finally, a representative QEI scenario is discussed in some detail.Comment: Title changed; text and acronyms revised; results unchanged. To
appear in PR
Surface water numerical modelling for the Gloucester subregion. Product 2.6.1 for the Gloucester subregion from the Northern Sydney Basin Bioregional Assessment
No abstract available
Surface water numerical modelling for the Gloucester subregion. Product 2.6.1 for the Gloucester subregion from the Northern Sydney Basin Bioregional Assessment
No abstract available
Three-Neutrino Mixing and Combined Vacuum Oscillations and MSW Transitions of Solar Neutrinos
Assuming three flavour neutrino mixing takes place in vacuum, we investigate
the possibility that the solar nu_e take part in MSW transitions in the Sun due
to Delta m^2_{31} from 10^{-7} eV^2 to 10^{-4} eV^2, followed by long wave
length vacuum oscillations on the way to the Earth, triggered by Delta m^2_{21}
(or Delta m^2_{32}) from 10^{-12} eV^2 to 10^{-10} eV^2, Delta m^2_{31} and
Delta m^2_{21} (Delta m^2_{32}) being the corresponding neutrino mass squared
differences. The solar nu_e survival probability is shown to be described in
this case by a simple analytic expression. Depending on whether the vacuum
oscillations are due to Delta m^2_{21} or Delta m^2_{32} there are two very
different types of interplay between the MSW transitions and the vacuum
oscillations of the solar nu_e. Performing an analysis of the most recently
published solar neutrino data we have found several qualitatively new solutions
of the solar neutrino problem of the hybrid MSW transitions + vacuum
oscillations type. The solutions differ in the way the pp, 7Be and 8B neutrino
fluxes are affected by the transitions in the Sun and the oscillations in
vacuum. The specific features of the new solutions are discussed.Comment: 37 pages Latex, 16 Postscript Figure
Leading Order Textures for Lepton Mass Matrices
In theories with three light neutrinos, certain simplicity assumptions allow
the construction of a complete list of leading order lepton mass matrices.
These matrices are consistent with m_{tau} \neq 0, Delta m^2_{12} \ll Delta
m^2_{23}, theta_{23} approx 1, and theta_{13} = 0, as suggested by measurements
of atmospheric and solar neutrino fluxes. The list contains twelve generic
cases: two have three degenerate neutrinos, eight have two neutrinos forming a
Dirac state, and in only two cases is one neutrino much heavier than the other
two. For each of these twelve generic cases the possible forms for the
perturbations which yield m_{mu} are given. Ten special textures are also
found.Comment: 17 pages, added reference
Ammonium cations with high pK a in perovskite solar cells for improved high-temperature photostability
Phenethylammonium (PEA+) and butylammonium (BA+) are widely used in three-dimensional (3D) perovskites to form two-dimensional perovskites at film surfaces and grain boundaries (GBs) for defect passivation and performance enhancement. Here we show that these cations are unstable with 3D formamidinium (FA+)-containing perovskites under high-temperature light soaking. PEA+ and BA+ are found to deprotonate to amines, which then react with FA+ to produce (phenethylamino)methaniminium (PEAMA+) and (butylamino)methaniminium (BAMA+), respectively, severely limiting device high-temperature photostability. Removing these cations greatly improves the photostability but compromises device efficiency by leaving non-fully passivated surfaces and GBs. Ammonium cations with a high acid dissociation constant (pK a), including PEAMA+ (pK a = 12.0) and BAMA+ (pK a = 12.0), can replace PEA+ or BA+ for passivation and are stable with FA-based perovskites due to their resistance to further deprotonation. P–i–n structure solar cells with PEAMA+ additive maintained over 90% of their initial efficiency after light soaking at open circuit and 90 °C for 1,500 hours
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