6,354 research outputs found
Investigation of infrared phonon modes in multiferroic single-crystal FeTeOBr
Reflection and transmission as a function of temperature (5--300 K) have been
measured on single crystals of the multiferroic compound FeTeOBr
utilizing light spanning the far infrared to the visible portions of the
electromagnetic spectrum. The complex dielectric function and optical
properties were obtained via Kramers-Kronig analysis and by fits to a
Drude-Lortentz model. Analysis of the anisotropic excitation spectra via
Drude-Lorentz fitting and lattice dynamical calculations have lead to the
observation of all 52 IR-active modes predicted in the plane and 43 or the
53 modes predicted along the b axis of the monoclinic cell. Assignments to
groups (clusters) of phonons have been made and trends within them are
discussed in light of our calculated displacement patterns.Comment: 9 pages, 7 figure
Hole Doping Dependence of the Coherence Length in Thin Films
By measuring the field and temperature dependence of magnetization on
systematically doped thin films, the critical current
density and the collective pinning energy are determined in
single vortex creep regime. Together with the published data of superfluid
density, condensation energy and anisotropy, for the first time we derive the
doping dependence of the coherence length or vortex core size in wide doping
regime directly from the low temperature data. It is found that the coherence
length drops in the underdoped region and increases in the overdoped side with
the increase of hole concentration. The result in underdoped region clearly
deviates from what expected by the pre-formed pairing model if one simply
associates the pseudogap with the upper-critical field.Comment: 4 pages, 4 figure
Critical Current Density and Resistivity of MgB2 Films
The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2.Comment: 11 pages, 3 figure
Role of interband scattering in neutron irradiated MgB thin films by Scanning Tunneling Spectroscopy measurements
A series of MgB thin films systematically disordered by neutron
irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis
orientation of the films allowed a reliable determination of local density of
state of the band. With increasing disorder, the conductance peak moves
towards higher voltages and becomes lower and broader, indicating a monotonic
increase of the gap and of the broadening parameter. These results are
discussed in the frame of two-band superconductivity.Comment: The text will be submitted in Latex format, and the corresponding pdf
file should take 6 pages. There are 5 figures (eps files submitted) and 1
tabl
Improving the security of secure direct communication based on secret transmitting order of particles
We analyzed the security of the secure direct communication protocol based on
secret transmitting order of particles recently proposed by Zhu, Xia, Fan, and
Zhang [Phys. Rev. A 73, 022338 (2006)], and found that this scheme is insecure
if an eavesdropper, say Eve, wants to steal the secret message with Trojan
horse attack strategies. The vital loophole in this scheme is that the two
authorized users check the security of their quantum channel only once. Eve can
insert another spy photon, an invisible photon or a delay one in each photon
which the sender Alice sends to the receiver Bob, and capture the spy photon
when it returns from Bob to Alice. After the authorized users check the
security, Eve can obtain the secret message according to the information about
the transmitting order published by Bob. Finally, we present a possible
improvement of this protocol.Comment: 4 pages, no figur
Superconducting properties of nanocrystalline MgB thin films made by an in situ annealing process
We have studied the structural and superconducting properties of MgB thin
films made by pulsed laser deposition followed by in situ annealing. The
cross-sectional transmission electron microscopy reveals a nanocrystalline
mixture of textured MgO and MgB with very small grain sizes. A
zero-resistance transition temperature () of 34 K and a zero-field
critical current density () of A/cm were obtained.
The irreversibility field was 8 T at low temperatures, although severe
pinning instability was observed. These bulk-like superconducting properties
show that the in situ deposition process can be a viable candidate for MgB
Josephson junction technologies
Beyond Context: Exploring Semantic Similarity for Tiny Face Detection
© 2018 IEEE. Tiny face detection aims to find faces with high degrees of variability in scale, resolution and occlusion in cluttered scenes. Due to the very little information available on tiny faces, it is not sufficient to detect them merely based on the information presented inside the tiny bounding boxes or their context. In this paper, we propose to exploit the semantic similarity among all predicted targets in each image to boost current face detectors. To this end, we present a novel framework to model semantic similarity as pairwise constraints within the metric learning scheme, and then refine our predictions with the semantic similarity by utilizing the graph cut techniques. Experiments conducted on three widely-used benchmark datasets have demonstrated the improvement over the-state-of-the-arts gained by applying this idea
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