9,099 research outputs found
Additional Acceleration of Protons and Energetic Neutrino Production in a Filamentary Jet of the Blazar Markarian 501
Blazars have been regarded as one of the most powerful sources of the highest
energy cosmic rays and also their byproducts, neutrinos. Provided that a
magnetized filamentary system is established in a blazar jet as well, we could
apply the mechanism of multi-stage diffusive shock acceleration to a feasible
TeV emitter, Mrk 501 to evaluate the achievable maximum energy of protons.
Taking conceivable energy restriction into account systematically, it seems
adequate to say that EeV-protons are produced at this site by our present
model. We also estimate neutrino fluxes generated by these accelerated protons
and discuss the detectability based on an updated kilometre-scale telescope
such as IceCube.Comment: 17 pages, 3 Postscript figure
Effects of mirror reflection versus diffusion anisotropy on particle acceleration in oblique shocks
Cosmic ray particles are more rapidly accelerated in oblique shocks, with the
magnetic field inclined with respect to the shock normal direction, than in
parallel shocks, as a result of mirror reflection at the shock surface and
slower diffusion in the shock normal direction. We investigate quantitatively
how these effects contribute to reducing the acceleration time over the whole
range of magnetic field inclinations. It is shown that, for quasi-perpendicular
inclination, the mirror effect plays a remarkable role in reducing the
acceleration time; whereas, at relatively small inclination, the anisotropic
diffusion effect is dominant in reducing that time. These results are important
for a detailed understanding of the mechanism of particle acceleration by an
oblique shock in space and heliosphereic plasmas.Comment: 6 pages, 2 figure
Bending and springback prediction method based on multi-scale finite element analyses for high bendability and low springback sheet generation
In this study, a sheet bendability and springback property evaluation technology through bending test simulations is newly developed using our multi-scale finite element analysis code, which is based on the crystallographic homogenization method
Behavior of Li abundances in solar-analog stars II. Evidence of the connection with rotation and stellar activity
We previously attempted to ascertain why the Li I 6708 line-strengths of
Sun-like stars differ so significantly despite the superficial similarities of
stellar parameters. We carried out a comprehensive analysis of 118 solar
analogs and reported that a close connection exists between the Li abundance
A_Li and the line-broadening width (v_r+m; mainly contributed by rotational
effect), which led us to conclude that stellar rotation may be the primary
control of the surface Li content. To examine our claim in more detail, we
study whether the degree of stellar activity exhibits a similar correlation
with the Li abundance, which is expected because of the widely believed close
connection between rotation and activity. We measured the residual flux at the
line center of the strong Ca II 8542 line, r_0(8542), known to be a useful
index of stellar activity, for all sample stars using newly acquired spectra in
this near-IR region. The projected rotational velocity (v_e sin i) was
estimated by subtracting the macroturbulence contribution from v_r+m that we
had already established. A remarkable (positive) correlation was found in the
A_Li versus (vs.) r_0(8542) diagram as well as in both the r_0(8542) vs. v_e
sin i and A_Li vs. v_e sin i diagrams, as had been expected. With the
confirmation of rotation-dependent stellar activity, this clearly shows that
the surface Li abundances of these solar analogs progressively decrease as the
rotation rate decreases. Given this observational evidence, we conclude that
the depletion of surface Li in solar-type stars, probably caused by effective
envelope mixing, operates more efficiently as stellar rotation decelerates. It
may be promising to attribute the low-Li tendency of planet-host G dwarfs to
their different nature in the stellar angular momentum.Comment: 12 pages, 9 figures; accepted for publication in Astron. Astrophys
Spaceflight and ageing: reflecting on Caenorhabditis elegans in space
The prospect of space travel continues to capture the imagination. Several competing companies are now promising flights for the general population. Previously, it was recognized that many of the physiological changes that occur with spaceflight are similar to those seen with normal ageing. This led to the notion that spaceflight can be used as a model of accelerated ageing and raised concerns about the safety of individuals engaging in space travel. Paradoxically, however, space travel has been recently shown to be beneficial to some aspects of muscle health in the tiny worm Caenorhabditis elegans. C. elegans is a commonly used laboratory animal for studying ageing. C. elegans displays age-related decline of some biological processes observed in ageing humans, and about 35% of C. elegans' genes have human homologs. Space flown worms were found to have decreased expression of a number of genes that increase lifespan when expressed at lower levels. These changes were accompanied by decreased accumulation of toxic protein aggregates in ageing worms' muscles. Thus, in addition to spaceflight producing physiological changes that are similar to accelerated ageing, it also appears to produce some changes similar to delayed ageing. Here, we put forward the hypothesis that in addition to the previously well-appreciated mechanotransduction changes, neural and endocrine signals are altered in response to spaceflight and that these may have both negative (e.g. less muscle protein) and some positive consequences (e.g. healthier muscles), at least for invertebrates, with respect to health in space. Given that changes in circulating hormones are well documented with age and in astronauts, our view is that further research into the relationship between metabolic control, ageing, and adaptation to the environment should be productive in advancing our understanding of the physiology of both spaceflight and ageing
Feedback-free optical cavity with self-resonating mechanism
We demonstrated the operation of a high finesse optical cavity without
utilizing an active feedback system to stabilize the resonance. The effective
finesse, which is a finesse including the overall system performance, of the
cavity was measured to be , and the laser power stored in
the cavity was kW, which is approximately 187,000 times greater
than the incident power to the cavity. The stored power was stabilized with a
fluctuation of , and we confirmed continuous cavity operation for more
than two hours. This result has the potential to trigger an innovative
evolution for applications that use optical resonant cavities such as compact
photon sources with laser-Compton scattering or cavity enhanced absorption
spectroscopy.Comment: 5 pages, 7 figure
Spin-Reorientation Transition of Field-Induced Magnetic Ordering Phases in the Anisotropic Haldane System
A possible spin-reorientation transition in field-induced magnetic ordering
phases of the S=1 Haldane system with large easy-plane anisotropy is proposed,
using an effective Lagrangian formalism as well as the density matrix
renormalization group method. Such a spin-reorientation transition is predicted
in the case where the applied magnetic field is inclined from the easy axis of
the anisotropy. We point out that this transition has a close connection with a
variation of the order parameter even at zero temperature, although it is
different from a quantum analog of the so-called spin-flop transition proposed
for the system having a strong easy axis anisotropy. In connection with a novel
phase observed recently in the Haldane system at high fields, we discuss
possible implications for the field-induced magnetic ordering.Comment: 14 pages, 7 figure
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