145 research outputs found
A Statistical Study on Photospheric Magnetic Nonpotentiality of Active Regions and Its Relationship with Flares during Solar Cycles 22-23
A statistical study is carried out on the photospheric magnetic
nonpotentiality in solar active regions and its relationship with associated
flares. We select 2173 photospheric vector magnetograms from 1106 active
regions observed by the Solar Magnetic Field Telescope at Huairou Solar
Observing Station, National Astronomical Observatories of China, in the period
of 1988-2008, which covers most of the 22nd and 23rd solar cycles. We have
computed the mean planar magnetic shear angle (\bar{\Delta\phi}), mean shear
angle of the vector magnetic field (\bar{\Delta\psi}), mean absolute vertical
current density (\bar{|J_{z}|}), mean absolute current helicity density
(\bar{|h_{c}|}), absolute twist parameter (|\alpha_{av}|), mean free magnetic
energy density (\bar{\rho_{free}}), effective distance of the longitudinal
magnetic field (d_{E}), and modified effective distance (d_{Em}) of each
photospheric vector magnetogram. Parameters \bar{|h_{c}|}, \bar{\rho_{free}},
and d_{Em} show higher correlation with the evolution of the solar cycle. The
Pearson linear correlation coefficients between these three parameters and the
yearly mean sunspot number are all larger than 0.59. Parameters
\bar{\Delta\phi}, \bar{\Delta\psi}, \bar{|J_{z}|}, |\alpha_{av}|, and d_{E}
show only weak correlations with the solar cycle, though the nonpotentiality
and the complexity of active regions are greater in the activity maximum
periods than in the minimum periods. All of the eight parameters show positive
correlations with the flare productivity of active regions, and the combination
of different nonpotentiality parameters may be effective in predicting the
flaring probability of active regions.Comment: 20 pages, 5 figures, 4 tables, accepted for publication in Solar
Physic
Experimental investigation of mechanically laminated straight or curved-and-tapered bamboo-concrete T-beams
This study echoes the rising demand for bio-based material in concrete composite structures in the race to accelerate carbon neutrality in construction. Noticing that most previous studies are focused on straight timber or engineered bamboo-to-concrete composite beams, this study developed straight or curved-and-tapered mechanically laminated bamboo-concrete (LBC) T-beams. Six layers of 26mm thick laminated bamboo panels were glue laminated together to form the bamboo beams. The curved bamboo beams have three different rises of arch: 50mm, 100mm and 150mm. All specimen beams were tested by four-point bending tests to evaluate their structural performances of the curved and straight LBC T-beams. To monitor the flange-to-web interface shear transfer, a novel interface shear slip calibration method that captures the longitudinal after-slip strain redistribution was developed and validated by strain gauge measurements. This study also highlights the interlayer shear bonding strength of laminated bamboo as the thresholding parameter that determines the composite beams' overall flexural strength, evidenced by detailed failure mode analysis. The proposed interface shear slip calibration method can be extended to the other types of shear connectors such as screws, nails, shear plates and notched connections
Hydrologic risk analysis in the Yangtze River basin through coupling Gaussian mixtures into copulas
Natural Sciences Foundation, Natural Science and Engineering Research Council of Canad
Development of endosperm cells and starch granules in common wheat
The objective of the present study was to understand the developmental regularity of wheat endosperm cells at different Days After Pollination (DAP) using microscopic and histochemical methods. Resin semi-thin sections of the endosperm and the enzymatically dissociated Starchy Endosperm Cells (SECs) were observed under a light microscope. The results showed that: (1) SECs were irregular-shaped and had two types of starch granules: large oval-shaped A-type starch granules and small spherical B-type starch granules. (2) The growth shape of SECs was referred to as S-curve and the fastest cell growth period was at 16–24 DAP. (3) The largest increase and growth of A-type starch granules were mainly at 4–16 DAP. B-type starch granules increased rapidly after 16 DAP and made up over 90% of the total starch granules in SEC during the late stage of endosperm development. (4) The nuclei of SEC deformed and degenerated during the middle and late stages of endosperm development and eventually disappeared. However, starch granules still increased and grew after the cell nuclei had degenerated. The investigations showed the development regularity of starch endosperm cells and starch granules, thereby improving the understanding of wheat endosperm development
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