584 research outputs found
Primordial Black Holes for the LIGO Events in the Axion-like Curvaton Model
We revise primordial black hole (PBH) formation in the axion-like curvaton
model and investigate whether PBHs formed in this model can be the origin of
the gravtitational wave (GW) signals detected by the Advanced LIGO. In this
model, small-scale curvature perturbations with large amplitude are generated,
which is essential for PBH formation. On the other hand, large curvature
perturbations also become a source of primordial GWs by their second-order
effects. Severe constraints are imposed on such GWs by pulsar timing array
(PTA) experiments. We also check the consistency of the model with these
constraints. In this analysis, it is important to take into account the effect
of non-Gaussianity, which is generated easily in the curvaton model. We see
that, if there are non-Gaussianities, the fixed amount of PBHs can be produced
with a smaller amplitude of the primordial power spectrum.Comment: 25 pages, 8 figure
Slowed response to peripheral visual stimuli during strenuous exercise
Recently, we proposed that strenuous exercise impairs peripheral visual perception because visual responses to peripheral visual stimuli were slowed during strenuous exercise. However, this proposal was challenged because strenuous exercise is also likely to affect the brain network underlying motor responses. The purpose of the current study was to resolve this issue. Fourteen participants performed a visual reaction-time (RT) task at rest and while exercising at 50% (moderate) and 75% (strenuous) peak oxygen uptake. Visual stimuli were randomly presented at different distances from fixation in two task conditions: the Central condition (2° or 5° from fixation) and the Peripheral condition (30° or 50° from fixation). We defined premotor time as the time between stimulus onset and the motor response, as determined using electromyographic recordings. In the Central condition, premotor time did not change during moderate (167 ± 19 ms) and strenuous (168 ± 24 ms) exercise from that at rest (164 ± 17 ms). In the Peripheral condition, premotor time significantly increased during moderate (181 ± 18 ms, P < 0.05) and strenuous exercise (189 ± 23 ms, P < 0.001) from that at rest (173 ± 17 ms). These results suggest that increases in Premotor Time to the peripheral visual stimuli did not result from an impaired motor-response network, but rather from impaired peripheral visual perception. We conclude that slowed response to peripheral visual stimuli during strenuous exercise primarily results from impaired visual perception of the periphery
Preparation of Some α-Substituted Cyclopropanecarboxylic Acids via Dichlorocarbene
Some α, β-unsaturated esters (1), including trans-crotonate, trans-α-methoxycrotonate, irans-α-fluorocrotonate, trans-cinnamate, trans-α-chlorocinnamate, cis- and trans-α-fluorocinnamates, fumarate, and maleate, were allowed to react with dichlorocarbene, generated by the thermal decomposition of sodium trichloroacetate at 120-160°C, to give the corresponding β, β-dichlorocyclopropanecarboxylates (2) in fair to good yields (38-88%). The additions of dichlorocarbene to these esters were stereospecific. A similar reaction of n-butyl acrylate gave only a very low yield (6%) of the dichlorocarbene adduct, probably because of the accompanying polymerization of the starting ester. The reduction of 1-unsubstituted or 1-methoxysubstituted 2, 2-dichloro-3-methylcyclopropanecarboxylate with tri-n-butyltin hydride at 90°C yielded both the completely reduced (3) and the partially reduced esters (4 and 5). That of 1-fluoro-substituted ester gave only the completely reduced product. These cyclopropanecarboxylates (2 and 3) were hydrolyzed with potassium hydroxide to give the corresponding free acids (6 and 7) in good yields (72-92%). The properties (bp, mp, nᴅ, pmr spectral data, etc.) of the cyclopropanecarboxylic acids and esters thus prepared are described
Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impurities
We calculate the intersubband absorption linewidth in quantum wells (QWs) due
to scattering by interface roughness, LO phonons, LA phonons, alloy disorder,
and ionized impurities, and compare it with the transport energy broadening
that corresponds to the transport relaxation time related to electron mobility.
Numerical calculations for GaAs QWs clarify the different contributions of each
individual scattering mechanism to absorption linewidth and transport
broadening. Interface roughness scattering contributes about an order of
magnitude more to linewidth than to transport broadening, because the
contribution from the intrasubband scattering in the first excited subband is
much larger than that in the ground subband. On the other hand, LO phonon
scattering (at room temperature) and ionized impurity scattering contribute
much less to linewidth than to transport broadening. LA phonon scattering makes
comparable contributions to linewidth and transport broadening, and so does
alloy disorder scattering. The combination of these contributions with
significantly different characteristics makes the absolute values of linewidth
and transport broadening very different, and leads to the apparent lack of
correlation between them when a parameter, such as temperature or alloy
composition, is changed. Our numerical calculations can quantitatively explain
the previously reported experimental results.Comment: 17 pages, including 15 figure
Constraining dark matter annihilation with HSC Low Surface Brightness Galaxies
Searches for dark matter annihilation signals have been carried out in a
number of target regions such as the Galactic Center and Milky Way dwarf
spheroidal galaxies (dSphs), among a few others. Here we propose low surface
brightness galaxies (LSBGs) asnovel targets for the indirect detection of dark
matter emission. In particular, LSBGs are known to have very large dark matter
contents and be less contaminated by extragalactic gamma-ray sources (e.g.,
blazars) compared to star forming galaxies. We report on an analysis that uses
eight LSBGs (detected by Subaru Hyper Suprime-Cam survey data) with known
redshifts to conduct a search for gamma-ray emission at the positions of these
new objects in Fermi Large Area Telescope data. We found no excesses of
gamma-ray emission and set constraints on the dark matter annihilation
cross-section. We exclude (at the 95% C.L.) dark matter scenarios predicting a
cross-section higher than 10^-23[cm^3/s] for dark matter particles of mass 10
GeV self-annihilating in the b_b channel. Although this constraint is weaker
than the ones reported in recent studies using other targets, we note that in
the near future, the number of detections of new LSBGs will increase by a few
orders of magnitude. We forecast that with the use of the full catalog of
soon-to-be-detected LSBGs the constraint will reach cross-section sensitivities
of ~ 3*10^-25 [cm^3/s] for dark matter particles with masses less than 10 GeV.Comment: 19 pages, 6 figures, accepted to JCA
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