330 research outputs found
Dynamics of Limit Cycle Oscillator Subject to General Noise
The phase description is a powerful tool for analyzing noisy limit cycle
oscillators. The method, however, has found only limited applications so far,
because the present theory is applicable only to the Gaussian noise while noise
in the real world often has non-Gaussian statistics. Here, we provide the phase
reduction for limit cycle oscillators subject to general, colored and
non-Gaussian, noise including heavy-tailed noise. We derive quantifiers like
mean frequency, diffusion constant, and the Lyapunov exponent to confirm
consistency of the result. Applying our results, we additionally study a
resonance between the phase and noise.Comment: main paper: 4 pages, 2 figure; auxiliary material: 5-7 pages of the
document, 1 figur
Development of Seebeck-Coefficient Measurement Systems Using Kelvin-Probe Force Microscopy
Thermoelectric device is investigated by a number of researchers in order to enhance the thermoelectric efficiency. It is known that the efficiency can be improved by quantum effect. However, it is difficult to measure the thermoelectric characteristics of nanometer-scale structures. Thus a new measurement method is expected to be developed. We propose to apply Kelvin-probe force microscopy (KFM) to characterization of thermoelectric materials. KFM can locally observe surface potential of Fermi energy of a sample without touching the sample surface. In the present paper, we estimate the Seebeck coefficient of thin Si-on-insulator layers using KFM
New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant
Although collisionless shocks are ubiquitous in astrophysics, certain key
aspects of them are not well understood. In particular, the process known as
collisionless electron heating, whereby electrons are rapidly energized at the
shock front, is one of the main open issues in shock physics. Here we present
the first clear evidence for efficient collisionless electron heating at the
reverse shock of Tycho's supernova remnant (SNR), revealed by Fe-K diagnostics
using high-quality X-ray data obtained by the Suzaku satellite. We detect
K-beta (3p->1s) fluorescence emission from low-ionization Fe ejecta excited by
energetic thermal electrons at the reverse shock front, which peaks at a
smaller radius than Fe K-alpha (2p->1s) emission dominated by a relatively
highly-ionized component. Comparison with our hydrodynamical simulations
implies instantaneous electron heating to a temperature 1000 times higher than
expected from Coulomb collisions alone. The unique environment of the reverse
shock, which is propagating with a high Mach number into rarefied ejecta with a
low magnetic field strength, puts strong constraints on the physical mechanism
responsible for this heating, and favors a cross-shock potential created by
charge deflection at the shock front. Our sensitive observation also reveals
that the reverse shock radius of this SNR is about 10% smaller than the
previous measurement using the Fe K-alpha morphology from the Chandra
observations. Since strong Fe K-beta fluorescence is expected only from
low-ionization plasma where Fe ions still have many 3p electrons, this feature
is key to diagnosing the plasma state and distribution of the immediate
postshock ejecta in a young SNR.Comment: 7 pages, 9 figures, resubmitted to ApJ with minor changes following
the referee repor
Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission
Supernova remnants (SNRs) retain crucial information about both their parent
explosion and circumstellar material left behind by their progenitor. However,
the complexity of the interaction between supernova ejecta and ambient medium
often blurs this information, and it is not uncommon for the basic progenitor
type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here
we present a powerful new observational diagnostic to discriminate between
progenitor types and constrain the ambient medium density of SNRs solely using
Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs
and detect Fe K alpha emission from 23 young or middle-aged remnants, including
five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K
alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in
Type Ia remnants being significantly less ionized than in core-collapse SNRs.
Within each progenitor group, the Fe K alpha luminosity and centroid are well
correlated, with more luminous objects having more highly ionized Fe. Our
results indicate that there is a strong connection between explosion type and
ambient medium density, and suggest that Type Ia supernova progenitors do not
substantially modify their surroundings at radii of up to several parsecs. We
also detect a K-shell radiative recombination continuum of Fe in W49B and IC
443, implying a strong circumstellar interaction in the early evolutionary
phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur
Synchronization of uncoupled oscillators by common gamma impulses: from phase locking to noise-induced synchronization
Nonlinear oscillators can mutually synchronize when they are driven by common
external impulses. Two important scenarios are (i) synchronization resulting
from phase locking of each oscillator to regular periodic impulses and (ii)
noise-induced synchronization caused by Poisson random impulses, but their
difference has not been fully quantified. Here we analyze a pair of uncoupled
oscillators subject to common random impulses with gamma-distributed intervals,
which can be smoothly interpolated between regular periodic and random Poisson
impulses. Their dynamics are charac- terized by phase distributions, frequency
detuning, Lyapunov exponents, and information-theoretic measures, which clearly
reveal the differences between the two synchronization scenarios.Comment: 18 page
Environmental DNA preserved in marine sediment for detecting jellyfish blooms after a tsunami
堆積物の環境DNAで探る過去の出来事 --津波直後のクラゲ大発生を検知--. 京都大学プレスリリース. 2021-08-23.Environmental DNA (eDNA) can be a powerful tool for detecting the distribution and abundance of target species. This study aimed to test the longevity of eDNA in marine sediment through a tank experiment and to use this information to reconstruct past faunal occurrence. In the tank experiment, juvenile jack mackerel (Trachurus japonicus) were kept in flow-through tanks with marine sediment for two weeks. Water and sediment samples from the tanks were collected after the removal of fish. In the field trial, sediment cores were collected in Moune Bay, northeast Japan, where unusual blooms of jellyfish (Aurelia sp.) occurred after a tsunami. The samples were analyzed by layers to detect the eDNA of jellyfish. The tank experiment revealed that after fish were removed, eDNA was not present in the water the next day, or subsequently, whereas eDNA was detectable in the sediment for 12 months. In the sediment core samples, jellyfish eDNA was detected at high concentrations above the layer with the highest content of polycyclic aromatic hydrocarbons, reflecting tsunami-induced oil spills. Thus, marine sediment eDNA preserves a record of target species for at least one year and can be used to reconstruct past faunal occurrence
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