247 research outputs found
Noise suppression using optimum filtering of OCs generated by a multiport encoder/decoder
We propose a novel receiver configuration using an extreme narrow band-optical band pass filter (ENB-OBPF) to reduce the multiple access interference (MAI) and beat noises in an optical code division multiplexing (OCDM) transmission. We numerically and experimentally demonstrate an enhancement of the code detectability, that allows us to increase the number of users in a passive optical network (PON) from 4 to 8 without any forward error correction (FEC)
Quantum-mechanical generation of gravitational waves in braneworld
We study the quantum-mechanical generation of gravitational waves during
inflation on a brane embedded in a five-dimensional anti-de Sitter bulk. To
make the problem well-posed, we consider the setup in which both initial and
final phases are given by a de Sitter brane with different values of the Hubble
expansion rate. Assuming that the quantum state is in a de Sitter invariant
vacuum in the initial de Sitter phase, we numerically evaluate the amplitude of
quantum fluctuations of the growing solution of the zero mode in the final de
Sitter phase. We find that the vacuum fluctuations of the initial Kaluza-Klein
gravitons as well as of the zero mode gravitons contribute to the final
amplitude of the zero mode on small scales, and the power spectrum is quite
well approximated by what we call the rescaled spectrum, which is obtained by
rescaling the standard four-dimensional calculation following a simple mapping
rule. Our results confirm the speculation raised in Ref.
\cite{Kobayashi:2003cn} before.Comment: 11 pages, 11 figure
Observation of Current-induced Nonlinear Spin Polarization in Pt-Py Bilayers
We experimentally observe nonlinear spin polarization in metallic bilayers of
platinum and permalloy by means of spin-torque ferromagnetic resonance (ST-FMR)
with the spin-Hall effects. The ST-FMR results under massive dc current
injection contain striking features, which are not caused by extrinsic Joule
heating, but by intrinsic nonlinear spin polarization. The emergence of
nonlinear spin polarization is consistent with observation of unidirectional
spin-Hall magnetoresistance due to magnon generation/annihilation. Moreover,
the magnon generation (annihilation) leads to effective magnetization shrinkage
(expansion) revealed by the ST-FMR measurements. The present study paves a way
to spin-Hall effect based nonlinear spintronic devices as well as
6th-generation mobile communication light sources
A New delta N Formalism for Multi-Component Inflation
The delta N formula that relates the final curvature perturbation on comoving
slices to the inflaton perturbation on flat slices after horizon crossing is a
powerful and intuitive tool to compute the curvature perturbation spectrum from
inflation. However, it is customarily assumed further that the conventional
slow-roll condition is satisfied, and satisfied by all components, during
horizon crossing. In this paper, we develop a new delta N formalism for
multi-component inflation that can be applied in the most general situations.
This allows us to generalize the idea of general slow-roll inflation to the
multi-component case, in particular only applying the general slow-roll
condition to the relevant component. We compute the power spectrum of the
curvature perturbation in multi-component general slow-roll inflation, and find
that under quite general conditions it is invertible.Comment: 24 pages, no figur
Are black holes over-produced during preheating?
We provide a simple but robust argument that primordial black hole (PBH)
production generically does {\em not} exceed astrophysical bounds during the
resonant preheating phase after inflation. This conclusion is supported by
fully nonlinear lattice simulations of various models in two and three
dimensions which include rescattering but neglect metric perturbations. We
examine the degree to which preheating amplifies density perturbations at the
Hubble scale and show that at the end of the parametric resonance, power
spectra are universal, with no memory of the power spectrum at the end of
inflation. In addition we show how the probability distribution of density
perturbations changes from exponential on very small scales to Gaussian when
smoothed over the Hubble scale -- the crucial length for studies of primordial
black hole formation -- hence justifying the standard assumption of
Gaussianity.Comment: 12 pages, 8 figures, revtex, added references for section
How are peer support activities utilized in society?: A Survey of University A Peer Supporter Alumni
本稿は日本学生相談学会第37回大会で発表した内容を再構成したものである
Motor flexibility to stabilize the toe position during obstacle crossing in older adults: an investigation using an uncontrolled manifold analysis
IntroductionAn age-related decrease in the ability to exploit the abundant degrees of freedom of the body, referred to as motor flexibility, leads to a heightened fall risk. The present study investigated motor flexibility to stabilize the toe position during obstacle crossing in older adults and its correlation with the magnitude of foot elevation.MethodsTwenty-six older adults (70.9 ± 7.4 years old) and 21 younger adults (25.4 ± 5.0 years old) walked and crossed an obstacle, during which the dominant limb was always the leading limb. An uncontrolled manifold (UCM) analysis was used to quantify the flexibility during obstacle crossing as the synergy index, with the vertical toe position being regarded as the performance variable and the segment angles of the lower limbs as the elemental variables.Results and discussionThe results showed that older participants had a significantly lower synergy index for the trailing limb before the moment of obstacle crossing than younger participants, suggesting reduced flexibility in part. The results also showed that, regardless of age, foot elevation was negatively correlated with the synergy index, suggesting that a so-called “conservative strategy” (i.e., a tendency to show extraordinarily high foot elevation to ensure collision avoidance) may be related to their reduced motor flexibility
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