431 research outputs found
Solitary Dust--Acoustic Waves in a Plasma with Two-Temperature Ions and Distributed Grain Size
The propagation of weakly nonlinear dust--acoustic waves in a dusty plasma
containing two ion species with different temperatures is explored. The
nonlinear equations describing both the quadratic and cubic plasma
nonlinearities are derived. It is shown that the properties of dust--acoustic
waves depend substantially on the grain size distribution. In particular, for
solitary dust--acoustic waves with a positive potential to exist in a plasma
with distributed grain size, it is necessary that the difference between the
temperatures of two ion species be large that that in the case of unusized
grains.Comment: 16 pages, 6 figure
Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)
KAGRA, the kilometer-scale underground gravitational-wave detector, is located at Kamioka. Japan. In April 2020, an astrophysics observation was performed at the KAGRA detector in combination with the GEO 600 detector; this observation operation is called O3GK. The optical configuration in O3GK is based on a power-recycled Fabry Perot-Michelson interferometer; all the mirrors were set at room temperature. The duty factor of the operation was approximately 53%, and the displacement sensitivity was approximately 1 x 10(-18) m/root Hz at 250 Hz. The binary-neutron-star (BNS) inspiral range was about 0.6 Mpc. The contributions of various noise sources to the sensitivity of O3GK were investigated to understand how the observation range could be improved; this study is called a "noise budget". According to our noise budget, the measured sensitivity could be approximated by adding up the effect of each noise. The sensitivity was dominated by noise from the sensors used for local controls of the vibration isolation systems, acoustic noise, shot noise, and laser frequency noise. Further, other noise sources that did not limit the sensitivity were investigated. This paper provides a detailed account of the KAGRA detector in O3GK, including interferometer configuration, status, and noise budget. In addition, strategies for future sensitivity improvements, such as hardware upgrades, are discussed
A New Type of Plasma Wakefield Accelerator Driven by Magnetowaves
We present a new concept for a plasma wakefield accelerator driven by
magnetowaves (MPWA). This concept was originally proposed as a viable mechanism
for the "cosmic accelerator" that would accelerate cosmic particles to ultra
high energies in the astrophysical setting. Unlike the more familiar Plasma
Wakefield Accelerator (PWFA) and the Laser Wakefield Accelerator (LWFA) where
the drivers, the charged-particle beam and the laser, are independently
existing entities, MPWA invokes the high-frequency and high-speed whistler mode
as the driver, which is a medium wave that cannot exist outside of the plasma.
Aside from the difference in drivers, the underlying mechanism that excites the
plasma wakefield via the ponderomotive potential is common. Our computer
simulations show that under appropriate conditions, the plasma wakefield
maintains very high coherence and can sustain high-gradient acceleration over
many plasma wavelengths. We suggest that in addition to its celestial
application, the MPWA concept can also be of terrestrial utility. A
proof-of-principle experiment on MPWA would benefit both terrestrial and
celestial accelerator concepts.Comment: revtex4, 4 pages, 6 figure
Development of Advanced Photon Calibrator for KAGRA
The KAGRA cryogenic gravitational-wave observatory has begun joint
observation with the worldwide gravitational waves detector network. Precise
calibration of the detector response is essential for the parameter estimation
of gravitational wave sources. The photon calibrator is the main calibrator in
LIGO, Virgo and KAGRA, and we used this calibrator in joint observation 3 on
2020 April with GEO600 in Germany. KAGRA improved the system for joint
observation 3 with three unique points: high laser power, power stabilization
system, and remote beam position control. KAGRA employs the 20 W laser and
divides it into two beams injected on the mirror surface. By using a high-power
laser, we can calibrate the response at the kHz region. To control the power of
each laser independently, we also installed an optical follower servo for each
beam power stabilization. By controlling the optical path of the photon
calibrater beam positions with pico-motors, we were able to characterize the
rotation response of the detector. We also installed a telephoto camera and QPD
to monitor beam position and controlled beam position to optimize mirror
response. In this paper, we discussed the statistical error with the result of
the relative power noise measurement. We also discussed systematic errors about
the power calibration model of photon calibrator and simulation of elastic
deformation effect with the finite element analysis.Comment: 16 pages, 10 figure
Advanced CT bone imaging in osteoporosis
Non-invasive and/or non-destructive techniques can provide structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, many studies indicate that BMD only partly explains bone strength. Quantitative assessment of macro- and microstructural features may improve our ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) DXA and CT, particularly volumetric quantitative CT (vQCT). Methods for assessing microstructure of trabecular bone non-invasively and/or non-destructively include high-resolution CT (hrCT), microCT (μCT), high-resolution magnetic resonance (hrMR) and microMR (μMR). vQCT, hrCT and hrMR are generally applicable in vivo; μCT and μMR are principally applicable in vitro. Despite recent progress made with these advanced imaging techniques, certain issues remain. The important balances between spatial resolution and sampling size, or between signal-to-noise and radiation dose or acquisition time, need further consideration, as do the complexity and expense of the methods vs their availability and accessibility. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry vs the more complex architectural features of bone or the deeper research requirements vs the broader clinical needs. The biological differences between the peripheral appendicular skeleton and the central axial skeleton must be further addressed. Finally, the relative merits of these sophisticated imaging techniques must be weighed with respect to their applications as diagnostic procedures, requiring high accuracy or reliability, compared with their monitoring applications, requiring high precision or reproducibility
Stellar Coronal and Wind Models: Impact on Exoplanets
Surface magnetism is believed to be the main driver of coronal heating and
stellar wind acceleration. Coronae are believed to be formed by plasma confined
in closed magnetic coronal loops of the stars, with winds mainly originating in
open magnetic field line regions. In this Chapter, we review some basic
properties of stellar coronae and winds and present some existing models. In
the last part of this Chapter, we discuss the effects of coronal winds on
exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief:
Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer
Reference Work
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