814 research outputs found
Spatial damping of propagating sausage waves in coronal cylinders
Sausage modes are important in coronal seismology. Spatially damped
propagating sausage waves were recently observed in the solar atmosphere. We
examine how wave leakage influences the spatial damping of sausage waves
propagating along coronal structures modeled by a cylindrical density
enhancement embedded in a uniform magnetic field. Working in the framework of
cold magnetohydrodynamics, we solve the dispersion relation (DR) governing
sausage waves for complex-valued longitudinal wavenumber at given real
angular frequencies . For validation purposes, we also provide
analytical approximations to the DR in the low-frequency limit and in the
vicinity of , the critical angular frequency separating trapped
from leaky waves. In contrast to the standing case, propagating sausage waves
are allowed for much lower than . However, while able
to direct their energy upwards, these low-frequency waves are subject to
substantial spatial attenuation. The spatial damping length shows little
dependence on the density contrast between the cylinder and its surroundings,
and depends only weakly on frequency. This spatial damping length is of the
order of the cylinder radius for , where
and are the cylinder radius and the Alfv\'en speed in the
cylinder, respectively. We conclude that if a coronal cylinder is perturbed by
symmetric boundary drivers (e.g., granular motions) with a broadband spectrum,
wave leakage efficiently filters out the low-frequency components.Comment: 6 pages, 2 figures, to appear in Astronomy & Astrophysic
Recommended from our members
Review of fan-use rates in field studies and their effects on thermal comfort, energy conservation, and human productivity
This paper is a literature review of field studies on fan-use rates and their effects on thermal comfort, energy conservation, and human productivity. In the assessed literature, fans are more popular in Asia, and more used in mixed-mode (MM) and naturally ventilated (NV) buildings than in air-conditioned (AC) buildings. On the basis of collected fan-use models, probit regression models of fan-use rates and ambient environments were obtained and indicate that the essential trigger of fan-use is a warm environment rather than building types. This result helps us to understand the control behaviors and comfort requirements of occupants. Also, fans could provide benefits in three aspects: widening neutral temperatures, saving energy, and improving occupants’ productivity. First, using fans in buildings elevates the neutral temperature and the upper limit of neutral zone (0.5 thermal sensation scale) averages by about 3 K in ranges from 25.7℃ to 28.7℃ and 27.5℃ to 30.7℃, respectively. Second, fan-use reduces AC-use rates in MM buildings in summer. The regression models based on the collected AC-use rate models illustrate that, on average, AC-use is expected to be reduced by about 15% in summer when fans are used. Third, providing occupants access to fans could improve occupants’ productivity. Based on the limited data available, a 3-K temperature extension is achieved by fans ensuring productivity not decreasing. This review could shed some light on the extension of the neutral temperature range, predictions of MM buildings’ energy consumptions, and methods to enhance productivity. Additionally, this review suggests some valuable directions for future research on fans
Comparison of Transient Behaviors of Wind Turbines with DFIG Considering the Shaft Flexible Models
A robust control strategy to improve transient stability for AC-DC interconnected power system with wind farms
MSG-BART: Multi-granularity Scene Graph-Enhanced Encoder-Decoder Language Model for Video-grounded Dialogue Generation
Generating dialogue grounded in videos requires a high level of understanding
and reasoning about the visual scenes in the videos. However, existing large
visual-language models are not effective due to their latent features and
decoder-only structure, especially with respect to spatio-temporal relationship
reasoning. In this paper, we propose a novel approach named MSG-BART, which
enhances the integration of video information by incorporating a
multi-granularity spatio-temporal scene graph into an encoder-decoder
pre-trained language model. Specifically, we integrate the global and local
scene graph into the encoder and decoder, respectively, to improve both overall
perception and target reasoning capability. To further improve the information
selection capability, we propose a multi-pointer network to facilitate
selection between text and video. Extensive experiments are conducted on three
video-grounded dialogue benchmarks, which show the significant superiority of
the proposed MSG-BART compared to a range of state-of-the-art approaches.Comment: 5 pages,3 figure
- …