2,505 research outputs found
The rise and fall of the social science curriculum project in Iceland, 1974-84: Reflections on reason and power in educational progress
Far-ultraviolet Emission-line Morphologies of the Supernova Remnant G65.3+5.7
We present the first far-ultraviolet (FUV) emission-line morphologies of the
whole region of the supernova remnant (SNR) G65.3+5.7 using the FIMS/SPEAR
data. The morphologies of the C IV {\lambda}{\lambda}1548, 1551, He II
{\lambda}1640, and O III] {\lambda}{\lambda}1661, 1666 lines appear to be
closely related to the optical and/or soft X-ray images obtained in previous
studies. Dramatic differences between the C IV morphology and the optical [O
III] {\lambda}5007 image provide clues to a large resonant-scattering region
and a foreground dust cloud. The FUV morphologies also reveal the overall
distribution of various shocks in different evolutionary phases and an
evolutionary asymmetry between the east and the southwest sides in terms of
Galactic coordinates, possibly due to a Galactic density gradient in the global
scale. The relative X-ray luminosity of G65.3+5.7 to C IV luminosity is
considerably lower than those of the Cygnus Loop and the Vela SNRs. This
implies that G65.3+5.7 has almost evolved into the radiative stage in the
global sense and supports the previous proposal that G65.3+5.7 has lost its
bright X-ray shell and become a member of mixed-morphology SNRs as it has
evolved beyond the adiabatic stage.Comment: 6 pages, 3 figures, accepted for publication in The Ap
Analysis of Spatial Structure of the SPica H II Region
Far ultraviolet (FUV) spectral images of the Spica H II region are first
presented here for the Si II* 1533.4A and Al II 1670.8A lines and then compared
with the optical Halpha image. The H alpha and Si II* images show enhanced
emissions in the southern part of the H II region where H I density increases
outwards. This high density region, which we identify as part of the
"interaction ring" of the Loop I superbubble and the Local Bubble, seems to
bound the southern H II region. On the other hand, the observed profile of Al
II shows a broad central peak, without much difference between the northern and
southern parts, which we suspect results from multiple resonant scattering. The
extended tails seen in the radial profiles of the FUV intensities suggest that
the nebula may be embedded in a warm ionized gas. Simulation with a spectral
synthesis code yields the values of the Lyman continuum luminosity and the
effective temperature of the central star similar to previous estimates with
10^46.2 photons s^-1 and 26,000 K, respectively, but the density of the
northern H II region, 0.22 cm^-3, is much smaller than previous estimates for
the H alpha brightest region.Comment: 15 pages, 5 figures, accepted for Ap
Using Josephson junctions to determine the pairing state of superconductors without crystal inversion symmetry
Theoretical studies of a planar tunnel junction between two superconductors
with antisymmetric spin-orbit coupling are presented. The half-space Green's
function for such a superconductor is determined. This is then used to derive
expressions for the dissipative current and the Josephson current of the
junction. Numerical results are presented in the case of the Rashba spin-orbit
coupling, relevant to the much studied compound CePtSi. Current-voltage
diagrams, differential conductance and the critical Josephson current are
presented for different crystallographic orientations and different weights of
singlet and triplet components of the pairing state. The main conclusion is
that Josephson junctions with different crystallographic orientations may
provide a direct connection between unconventional pairing in superconductors
of this kind and the absence of inversion symmetry in the crystal.Comment: 16 pages, 10 figure
Andreev reflection from non-centrosymmetric superconductors and Majorana bound state generation in half-metallic ferromagnets
We study Andreev reflection at an interface between a half metal and a
superconductor with spin-orbit interaction. While the absence of minority
carriers in the half metal makes singlet Andreev reflection impossible, the
spin-orbit interaction gives rise to triplet Andreev reflection, i.e., the
reflection of a majority electron into a majority hole or vice versa. As an
application of our calculation, we consider a thin half metal film or wire
laterally attached to a superconducting contact. If the half metal is disorder
free, an excitation gap is opened that is proportional to the spin-orbit
interaction strength in the superconductor. For electrons with energy below
this gap a lateral half-metal--superconductor contact becomes a perfect triplet
Andreev reflector. We show that the system supports localized Majorana end
states in this limit.Comment: 14 pages, 3 figure
Externally Dispersed Interferometry for Precision Radial Velocimetry
Externally Dispersed Interferometry (EDI) is the series combination of a
fixed-delay field-widened Michelson interferometer with a dispersive
spectrograph. This combination boosts the spectrograph performance for both
Doppler velocimetry and high resolution spectroscopy. The interferometer
creates a periodic spectral comb that multiplies against the input spectrum to
create moire fringes, which are recorded in combination with the regular
spectrum. The moire pattern shifts in phase in response to a Doppler shift.
Moire patterns are broader than the underlying spectral features and more
easily survive spectrograph blurring and common distortions. Thus, the EDI
technique allows lower resolution spectrographs having relaxed optical
tolerances (and therefore higher throughput) to return high precision velocity
measurements, which otherwise would be imprecise for the spectrograph alone.Comment: 7 Pages, White paper submitted to the AAAC Exoplanet Task Forc
Supersymmetric Electroweak Cosmic Strings
We study the connection between supersymmetry and a topological bound
in a two-Higgs-doublet system with an gauge group. We derive the Bogomol'nyi equations from
supersymmetry considerations showing that they hold provided certain conditions
on the coupling constants, which are a consequence of the huge symmetry of the
theory, are satisfied. Their solutions, which can be interpreted as electroweak
cosmic strings breaking one half of the supersymmetries of the theory, are
studied. Certain interesting limiting cases of our model which have recently
been considered in the literature are finally analyzed.Comment: 20 pages, RevTe
- …