2,175 research outputs found
Solar microwave millisecond spike at 2.84 GHz
Using the high time resolution of 1 ms, the data of solar microwave millisecond spike (MMS) event was recorded more than two hundred times at the frequency of 2.84 GHz at Beijing (Peking) Observatory since May 1981. A preliminary analysis was made. It can be seen from the data that the MMS-events have a variety of the fast activities such as the dispersed and isolated spikes, the clusters of the crowded spikes, the weak spikes superimposed on the noise background, and the phenomena of absorption. The marked differences from that observed with lower time resolution are presented. Using the data, a valuable statistical analysis was made. There are close correlations between MMS-events and hard X-ray bursts, and fast drifting bursts. The MMS events are highly dependent on the type of active regions and the magnetic field configuration. It seems to be crucial to find out the accurate positions on the active region where the MMS-events happen and to make co-operative observations at different bands during the special period when specific active regions appear on the solar disk
Mid-IR high-index dielectric Huygens metasurfaces
In this paper, we proposed highly efficient all-dielectric Huygens' metasurfaces working at mid-IR frequencies. The meta-Atom of the designed Huygens' metasurface is a cubic dielectric resonator or its variety, which is made from PbTe that possesses a high refractive index of around 5 at mid-IR frequencies. By overlapping spectrally both the magnetic and electric dipole modes of the high-index dielectric resonators, a full phase coverage of 2π and an equal-magnitude transmission could be achieved, which are essential conditions for realizing a metasurface. Two Huygens' metasurfaces for beam bending are designed with a phase change between two consecutive meta-Atoms of π/4 and π/3, respectively. The simulation results agree well with the design theory.National Science Foundation (U.S.) (Grant CMMI-1266251
Experimental Test of Tracking the King Problem
In quantum theory, the retrodiction problem is not as clear as its classical
counterpart because of the uncertainty principle of quantum mechanics. In
classical physics, the measurement outcomes of the present state can be used
directly for predicting the future events and inferring the past events which
is known as retrodiction. However, as a probabilistic theory,
quantum-mechanical retrodiction is a nontrivial problem that has been
investigated for a long time, of which the Mean King Problem is one of the most
extensively studied issues. Here, we present the first experimental test of a
variant of the Mean King Problem, which has a more stringent regulation and is
termed "Tracking the King". We demonstrate that Alice, by harnessing the shared
entanglement and controlled-not gate, can successfully retrodict the choice of
King's measurement without knowing any measurement outcome. Our results also
provide a counterintuitive quantum communication to deliver information hidden
in the choice of measurement.Comment: 16 pages, 5 figures, 2 table
Gap Anisotropy in Iron-Based Superconductors: A Point-Contact Andreev Reflection Study of BaFeNiAs Single Crystals
We report a systematic investigation on c-axis point-contact Andreev
reflection (PCAR) in BaFeNiAs superconducting single crystals
from underdoped to overdoped regions (0.075 ). At optimal
doping () the PCAR spectrum feature the structures of two
superconducting gap and electron-boson coupling mode. In the scenario,
quantitative analysis using a generalized Blonder-Tinkham-Klapwijk (BTK)
formalism with two gaps: one isotropic and another angle dependent, suggest a
nodeless state in strong-coupling limit with gap minima on the Fermi surfaces.
Upon crossing above the optimal doping (), the PCAR spectrum show an
in-gap sharp narrow peak at low bias, in contrast to the case of underdoped
samples (), signaling the onset of deepened gap minima or nodes in the
superconducting gap. This result provides evidence of the modulation of the gap
amplitude with doping concentration, consistent with the calculations for the
orbital dependent pair interaction mediated by the antiferromagnetic spin
fluctuations.Comment: 5 pages, 4 figure
The Photometric System of Tsinghua-NAOC 80-cm Telescope at NAOC Xinglong Observatory
Tsinghua-NAOC (National Astronomical Observatories of China) Telescope
(hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at
Xinglong bservatory of NAOC, with main scientific goals of monitoring various
transients in the universe such as supernovae, gamma-ray bursts, novae,
variable stars, and active galactic nuclei. We present in this paper a
systematic test and analysis of the photometric performance of this telescope.
Based on the calibration observations on twelve photometric nights, spanning
the period from year 2004 to year 2012, we derived an accurate transformation
relationship between the instrumental magnitudes and standard Johnson
and Cousins magnitudes. In particular, the color terms and the
extinction coefficients of different passbands are well determined. With these
data, we also obtained the limiting magnitudes and the photometric precision of
TNT. It is worthwhile to point out that the sky background at Xinglong
Observatory may become gradually worse over the period from year 2005 to year
2012 (e.g., 21.4 mag vs. 20.1 mag in the V band).Comment: 12 pages,9 figures, accepted by RA
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