180 research outputs found
Bidirectional Decoding for Statistical Machine Translation
This paper describes the right-to-left decoding method, which translates an input string by generating in right-to-left direction. In addition, presented is the bidirectional decoding method, that can take both of the advantages of left-to-right and right-to-left decoding method by generating output in both ways and by merging hypothesized partial outputs of two directions. The experimental results on Japanese and English translation showed that the right-to-left was better for Englith-to-Japanese translation, while the left-to-right was suitable for Japanese-to-English translation. It was also observed that the bidirectional method was better for English-to-Japanese translation
Gravitational inflaton decay and the hierarchy problem
We study implications of the large-N species solution to the hierarchy
problem, proposed by G. Dvali, for reheating of the universe after inflation.
Dvali's proposal contains additional N~10^{32} Z_2-conserved quantum fields
beyond the Standard Model particles with mass ~1 TeV, which weaken gravity by a
factor of 1/N, and thus explain the hierarchy between the Plank scale and the
electroweak scale. We show that, in this scenario, the decay rates of inflaton
fields through gravitational decay channels are enhanced by a factor of N, and
thus they decay into N species of the quantum fields very efficiently, in the
limit that quantum gravity effects are unimportant for the gravitational decay
rate. In order not to over-reheat the universe, inflaton mass, vacuum
expectation value of inflaton, or non-minimal gravitational coupling should be
tightly fine-tuned. Our conclusion holds even when the gravitational decay is
prohibited by some symmetry of the theory; the universe may still be
over-reheated via annihilation of inflatons, if the number density of inflaton
quanta is greater than the critical value.Comment: 6 pages, submitted to PRD, (v2) references added, (v3) revised to
have inflaton quanta canonically normalize
Effects of Gravitational Chern-Simons during Axion-SU(2) Inflation
In this paper, we examine the viability of inflation models with a spectator
axion field coupled to both gravitational and SU(2) gauge fields via
Chern-Simons couplings. Requiring phenomenological success of the axion-SU(2)
sector constrains the coupling strength of the gravitational Chern-Simons term.
We find that the impact of this term on the production and propagation of
gravitational waves can be as large as fifty percent enhancement for the
helicity that is not sourced by the gauge field, if the cut-off scale is as low
as = 20H. The effect becomes smaller for a larger value of ,
while the impact on the helicity sourced by the gauge field is negligible
regardless of .Comment: 15 pages, 4 figures (v2) References added and typos corrected.
Submitted to JCA
Introducing Nonuniform Strain to Graphene Using Dielectric Nanopillars
A method for inducing nonuniform strain in graphene films is developed.
Pillars made of a dielectric material (electron beam resist) are placed between
graphene and the substrate, and graphene sections between pillars are attached
to the substrate. The strength and spatial pattern of the strain can be
controlled by the size and separation of the pillars. Application of strain is
confirmed by Raman spectroscopy as well as from scanning electron microscopy
(SEM) images. From SEM images, the maximum stretch of the graphene film reaches
about 20%. This technique can be applied to the formation of band gaps in
graphene.Comment: Appl. Phys. Express, in pres
Reheating of the universe after inflation with f(phi)R gravity
We show that reheating of the universe occurs spontaneously in a broad class
of inflation models with f(phi)R gravity (phi is inflaton). The model does not
require explicit couplings between phi and bosonic or fermionic matter fields.
The couplings arise spontaneously when phi settles in the vacuum expectation
value (vev) and oscillates, with coupling constants given by derivatives of
f(phi) at the vev and the mass of resulting bosonic or fermionic fields. This
mechanism allows inflaton quanta to decay into any fields which are not
conformally invariant in f(phi)R gravity theories.Comment: 4 pages, (v2) references added, (v3) revised to have inflaton quanta
canonically normalize
OCT with a Visible Broadband Light Source Applied to High-Resolution Nondestructive Inspection for Semiconductor Optical Devices
Optical coherence tomography with a visible broadband light source (vis-OCT) was developed for high-resolution and nondestructive measurements of semiconductor optical devices. Although a near-infrared (NIR) light source should be used for medical OCT to obtain deep penetration of biological samples, a visible broadband light source is available as a low-coherence light source for industrial products. Vis-OCT provides higher axial resolution than NIR-OCT, because the axial resolution of an OCT image is proportional to the square of the center wavelength of the light source. We developed vis-OCT with an axial resolution of less than 1 μm in air and obtained cross-sectional profiles and images of ridge-type waveguides having heights and widths of several μm. Additionally, we performed cross-sectional measurements and imaging of a stacked semiconductor thin layer. The measured values were similar to those measured by scanning electron microscopy, and the effectiveness of vis-OCT for nondestructive inspection of semiconductor optical devices was demonstrated
Development of a broadband superluminescent diode based on self-assembled InAs quantum dots and demonstration of high-axial-resolution optical coherence tomography imaging
We developed a near-infrared (NIR) superluminescent diode (SLD) based on self-assembled InAs quantum dots (QDs) and demonstrated high-axial-resolution optical coherence tomography (OCT) imaging using this QD-based SLD (QD-SLD). The QD-SLD utilized InAs QDs with controlled emission wavelengths as a NIR broadband light emitter, and a tilted waveguide with segmented electrodes was prepared for edge-emitting broadband electroluminescence (EL) spanning approximately 1–1.3 μm. The bandwidth of the EL spectrum was increased up to 144 nm at a temperature of 25 °C controlled using a thermoelectric cooler. The inverse Fourier transform of the EL spectrum predicted a minimum resolution of 3.6 μm in air. The QD-SLD was subsequently introduced into a spectral-domain (SD)-OCT setup, and SD-OCT imaging was performed for industrial and biological test samples. The OCT images obtained using the QD-SLD showed an axial resolution of ~4 μm, which was almost the same as that predicted from the spectrum. This axial resolution is less than the typical size of a single biological cell (~5 μm), and the practical demonstration of high-axial-resolution OCT imaging shows the application of QD-SLDs as a compact OCT light source, which enables the development of a portable OCT system
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