746 research outputs found
On-Site Calibration-Based Estimation Method of Forward Seabed Elevation Using Forward Scan Sonar
This paper addresses a novel calibration-based estimation method to measure the forward seabed elevation (FSE) where an area illuminated by forward scan sonar (FSS) for unmanned underwater vehicles (UUVs). The conventional method measures the FSE using one or two down-facing single-beam sonars; this method can, however, cause errors. In order to accurately measure the FSE, a sensor capable of measuring the 2D space of the seabed is needed, such as FSS. The method proposed in this work consists in estimating the FSE, by analyzing the acoustic beam distribution characteristics of FSS. A novel FSS beam distribution model is proposed, which simplifies beam distribution characteristics. Then, on-site calibration is conducted to estimate the parameters of this model. Based on the estimated model, templates can he generated and compared with FSS data acquired at the experiment in order to estimate geometrical information at the FSE. The FSE of the best matched template is the estimated FSE of the FSS data acquired in the experiment. In order to verify the performance of the proposed method, experiments using an UUV were carried out in an indoor water tank. We also verified that the proposed method performed well even when there were objects on the seabed.11Nsciescopu
Electron Beam Supercollimation in Graphene Superlattices
Although electrons and photons are intrinsically different, importing useful
concepts in optics to electronics performing similar functions has been
actively pursued over the last two decades. In particular, collimation of an
electron beam is a long-standing goal. We show that ballistic propagation of an
electron beam with virtual no spatial spreading or diffraction, without a
waveguide or external magnetic field, can be achieved in graphene under an
appropriate class of experimentally feasible one-dimensional external periodic
potentials. The novel chiral quasi-one-dimensional metallic state that the
charge carriers are in originates from a collapse of the intrinsic helical
nature of the charge carriers in graphene owing to the superlattice potential.
Beyond providing a new way to constructing chiral one-dimensional states in two
dimensions, our findings should be useful in graphene-based electronic devices
(e.g., for information processing) utilizing some of the highly developed
concepts in optics.Comment: 7 pages, 4 figures (including supporting online material), published
online in Nano Letter
New Generation of Massless Dirac Fermions in Graphene under External Periodic Potentials
We show that new massless Dirac fermions are generated when a slowly varying
periodic potential is applied to graphene. These quasiparticles, generated near
the supercell Brillouin zone boundaries with anisotropic group velocity, are
different from the original massless Dirac fermions. The quasiparticle
wavevector (measured from the new Dirac point), the generalized pseudospin
vector, and the group velocity are not collinear. We further show that with an
appropriate periodic potential of triangular symmetry, there exists an energy
window over which the only available states are these quasiparticles, thus,
providing a good system to probe experimentally the new massless Dirac
fermions. The required parameters of external potentials are within the realm
of laboratory conditions.Comment: 4 pages, 4 figure
Cultural Foundations of Contentious Democracy in South Korea
This study takes a cultural approach to examine the unstable and contentious nature of Korean democracy. Analyzing an original nationwide survey conducted in 2015, we find that the democratic and participatory culture of the Korean people underlies Korean democracy. This finding suggests substantial tension between the participatory orientation of the public and Korean representative democracy
Charge-spin correlation in van der Waals antiferromagenet NiPS3
Strong charge-spin coupling is found in a layered transition-metal
trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the
electronic structure using several experimental and theoretical tools:
spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy,
and density-functional calculations. NiPS3 displays an anomalous shift in the
optical spectral weight at the magnetic ordering temperature, reflecting a
strong coupling between the electronic and magnetic structures. X-ray
absorption, photoemission and optical spectra support a self-doped ground state
in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide
magnets are a useful candidate for the study of correlated-electron physics in
two-dimensional magnetic material.Comment: 6 pages, 3 figur
Analysis of speech and tongue motion in normal and post-glossectomy speaker using cine MRI
Objective Since the tongue is the oral structure responsible for mastication, pronunciation, and swallowing functions, patients who undergo glossectomy can be affected in various aspects of these functions. The vowel /i/ uses the tongue shape, whereas /u/ uses tongue and lip shapes. The purpose of this study is to investigate the morphological changes of the tongue and the adaptation of pronunciation using cine MRI for speech of patients who undergo glossectomy. Material and Methods Twenty-three controls (11 males and 12 females) and 13 patients (eight males and five females) volunteered to participate in the experiment. The patients underwent glossectomy surgery for T1 or T2 lateral lingual tumors. The speech tasks āa soukā and āa geeseā were spoken by all subjects providing data for the vowels /u/ and /i/. Cine MRI and speech acoustics were recorded and measured to compare the changes in the tongue with vowel acoustics after surgery. 2D measurements were made of the interlip distance, tongue-palate distance, tongue position (anterior-posterior and superior-inferior), tongue height on the left and right sides, and pharynx size. Vowel formants Fl, F2, and F3 were measured. Results The patients had significantly lower F2/Fl ratios (F=5.911, p=0.018), and lower F3/F1 ratios that approached significance. This was seen primarily in the /u/ data. Patients had flatter tongue shapes than controls with a greater effect seen in /u/ than /i/. Conclusion The patients showed complex adaptation motion in order to preserve the acoustic integrity of the vowels, and the tongue modified cavity size relationships to maintain the value of the formant frequencies
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