14,965 research outputs found
Zero-bias peaks in spin-orbit coupled superconducting wires with and without Majorana end-states
One of the simplest proposed experimental probes of a Majorana bound-state is
a quantized (2e^2/h) value of zero-bias tunneling conductance. When temperature
is somewhat larger than the intrinsic width of the Majorana peak, conductance
is no longer quantized, but a zero-bias peak can remain. Such a non-quantized
zero-bias peak has been recently reported for semiconducting nanowires with
proximity induced superconductivity. In this paper we analyze the relation of
the zero-bias peak to the presence of Majorana end-states, by simulating the
tunneling conductance for multi-band wires with realistic amounts of disorder.
We show that this system generically exhibits a (non-quantized) zero-bias peak
even when the wire is topologically trivial and does not possess Majorana
end-states. We make comparisons to recent experiments, and discuss the
necessary requirements for confirming the existence of a Majorana state.Comment: 5 pages, 4 Figure
Development and application of computer software techniques to human factors task data handling problems Final report, 21 Jun. 1965 - 21 Jun. 1966
Computer software techniques applied to human factors task data handling problem
Testing Theoretical Evolutionary Models with AB Dor C and the Initial Mass Function
We assess the constraints on the evolutionary models of young low-mass
objects that are provided by the measurements of the companion AB Dor C by
Close and coworkers and by a new comparison of model-derived IMFs of
star-forming regions to the well-calibrated IMF of the solar neighborhood.
After performing an independent analysis of Close's imaging and spectroscopic
data for AB Dor C, we find that AB Dor C is not detected at a significant level
(SN 1.2) in the SDI images when one narrow-band image is subtracted from
another, but that it does appear in the individual SDI frames as well as the
images at JHK. Using the age of 75-150 Myr for AB Dor from Luhman, Stauffer, &
Mamajek, the luminosity predicted by the models of Chabrier & Baraffe is
consistent with the value that we estimate. We measure a spectral type of
M6+/-1 from the K-band spectrum of AB Dor C, which is earlier than the value of
M8+/-1 from Close and is consistent with the model predictions when a dwarf
temperature scale is adopted. In a test of these models at much younger ages,
we show that the low-mass IMFs that they produce for star-forming regions are
similar to the IMF of the solar neighborhood. If the masses of the low-mass
stars and brown dwarfs in these IMFs of star-forming regions were
underestimated by a factor of two as suggested by Close, then the IMF
characterizing the current generation of Galactic star formation would have to
be radically different from the IMF of the solar neighborhood.Comment: 15 pages, accepted to the Astrophysical Journa
Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840
We present simultaneous optical polarimetry and X-ray data of the near
synchronous polar RX J2115-5840. We model the polarisation data using the
Stokes imaging technique of Potter et al. We find that the data are best
modelled using a relatively high binary inclination and a small angle between
the magnetic and spin axes. We find that for all spin-orbit beat phases, a
significant proportion of the accretion flow is directed onto the lower
hemisphere of the white dwarf, producing negative circular polarisation. Only
for a small fraction of the beat cycle is a proportion of the flow directed
onto the upper hemisphere. However, the accretion flow never occurs near the
upper magnetic pole, whatever the orientation of the magnetic poles. This
indicates the presence of a non-dipole field with the field strength at the
upper pole significantly higher. We find that the brightest parts of the hard
X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200
In democracies an effective media and opposition are both needed to sanction leaders’ foreign policy missteps
Common wisdom in international affairs is that when democratically elected leaders and governments make threats towards other states, these are credible; voters will punish leaders who do not follow through on their words. New research by Philip B. K. Potter and Matthew A. Baum argues however, that not all democracies are equal in the credibility of their threats of military action. By analyzing data on international military disputes over a 35-year period, they find that both an effective and widespread media, and a robust opposition are needed in order for voters to become aware of foreign policy blunders. Without either of these, leaders can avoid following through on their threats with little fear of being punished by voters
Evolution of the Radio Remnant of Supernova 1987A: Morphological Changes from Day 7000
We present radio imaging observations of supernova remnant 1987A at 9 GHz,
taken with the Australia Telescope Compact Array over 21 years from 1992 to
2013. By employing a Fourier modeling technique to fit the visibility data, we
show that the remnant structure has evolved significantly since day 7000
(mid-2006): the emission latitude has gradually decreased, such that the
overall geometry has become more similar to a ring structure. Around the same
time, we find a decreasing trend in the east-west asymmetry of the surface
emissivity. These results could reflect the increasing interaction of the
forward shock with material around the circumstellar ring, and the relative
weakening of the interaction with the lower-density material at higher
latitudes. The morphological evolution caused an apparent break in the remnant
expansion measured with a torus model, from a velocity of 4600+150-200 km/s
between day 4000 and 7000 to 2400+100-200 km/s after day 7000. However, we
emphasize that there is no conclusive evidence for a physical slowing of the
shock at any given latitude in the expanding remnant, and that a change of
radio morphology alone appears to dominate the evolution. This is supported by
our ring-only fits which show a constant expansion of 3890+/-50 km/s without
deceleration between days 4000 and 9000. We suggest that once the emission
latitude no longer decreases, the expansion velocity obtained from the torus
model should return to the same value as that measured with the ring model.Comment: 11 pages, 5 figures, accepted for publication in ApJ, Figure 1 has
been scaled dow
Thermal-radiation-induced nonequilibrium carriers in an intrinsic graphene
We examine an intrinsic graphene connected to the phonon thermostat at
temperature T under irradiation of thermal photons with temperature T_r, other
than T. The distribution of nonequilibrium electron-hole pairs was obtained for
the cases of low and high concentration of carriers. For the case when the
interparticle scattering is unessential, the distribution function is
determined by the interplay of intraband relaxation of energy due to acoustic
phonons and interband radiative transitions caused by the thermal radiation.
When the Coulomb scattering dominates, then the quasi-equilibrium distribution
with effective temperature and non-equilibrium concentration, determined
through balance equations, is realized. Due to the effect of thermal radiation
with temperature concentration and conductivity of carriers in
graphene modify essentially. It is demonstrated, that at the negative
interband absorption, caused by the inversion of carriers distribution, can
occur, i.e. graphene can be unstable under thermal irradiation.Comment: 5 pages, 4 figure
High-resolution radio observations of SNR 1987A at high frequencies
We present new imaging observations of the remnant of Supernova (SN) 1987A at
44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA).
The 0\farcs35\times0\farcs23 resolution of the diffraction-limited image is
the highest achieved to date in high-dynamic range. We also present a new ATCA
image at 18 GHz derived from 2011 observations, which is super-resolved to
0\farcs25. The flux density is 402 mJy at 44 GHz and 816 mJy at 18
GHz. At both frequencies, the remnant exhibits a ring-like emission with two
prominent lobes, and an east-west brightness asymmetry that peaks on the
eastern lobe. A central feature of fainter emission appears at 44 GHz. A
comparison with previous ATCA observations at 18 and 36 GHz highlights higher
expansion velocities of the remnant eastern side. The 18-44 GHz spectral index
is (). The spectral index map
suggests slightly steeper values at the brightest sites on the eastern lobe,
whereas flatter values are associated with the inner regions. The remnant
morphology at 44 GHz generally matches the structure seen with contemporaneous
X-ray and H observations. Unlike the H emission, both the radio
and X-ray emission peaks on the eastern lobe. The regions of flatter spectral
index align and partially overlap with the optically-visible ejecta. Simple
free-free absorption models suggest that emission from a pulsar wind nebula or
a compact source inside the remnant may now be detectable at high frequencies,
or at low frequencies if there are holes in the ionised component of the
ejecta.Comment: References updated. High resolution version may be found at
http://ict.icrar.org/store/staff/gio/Papers/Zanardo_2013.pd
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