401 research outputs found
Why torus-unstable solar filaments experience failed eruption?
To investigate the factors that control the success and/or failure of solar
eruptions, we study the magnetic field and 3-Dimensional (3D) configuration of
16 filament eruptions during 2010 July - 2013 February. All these events, i.e.,
erupted but failed to be ejected to become a coronal mass ejection (CME), are
failed eruptions with the filament maximum height exceeding . The
magnetic field of filament source regions is approximated by a potential field
extrapolation method. The filament 3D configuration is reconstructed from three
vantage points by the observations of STEREO Ahead/Behind and SDO spacecraft.
We calculate the decay index at the apex of these failed filaments and find
that in 7 cases, their apex decay indexes exceed the theoretical threshold
() of the torus instability. We further determine the
orientation change or rotation angle of each filament top during the eruption.
Finally, the distribution of these events in the parameter space of rotation
angle versus decay index is established. Four distinct regimes in the parameter
space are empirically identified. We find that, all the torus-unstable cases
(decay index ), have a large rotation angles ranging from . The possible mechanisms leading to the rotation and failed eruption
are discussed. These results imply that, besides the torus instability, the
rotation motion during the eruption may also play a significant role in solar
eruptions
Disordered hyperuniformity signals functioning and resilience of self-organized vegetation patterns
In harsh environments, organisms may self-organize into spatially patterned
systems in various ways. So far, studies of ecosystem spatial self-organization
have primarily focused on apparent orders reflected by regular patterns.
However, self-organized ecosystems may also have cryptic orders that can be
unveiled only through certain quantitative analyses. Here we show that
disordered hyperuniformity as a striking class of hidden orders can exist in
spatially self-organized vegetation landscapes. By analyzing the
high-resolution remotely sensed images across the American drylands, we
demonstrate that it is not uncommon to find disordered hyperuniform vegetation
states characterized by suppressed density fluctuations at long range. Such
long-range hyperuniformity has been documented in a wide range of microscopic
systems. Our finding contributes to expanding this domain to accommodate
natural landscape ecological systems. We use theoretical modeling to propose
that disordered hyperuniform vegetation patterning can arise from three
generalized mechanisms prevalent in dryland ecosystems, including (1) critical
absorbing states driven by an ecological legacy effect, (2) scale-dependent
feedbacks driven by plant-plant facilitation and competition, and (3)
density-dependent aggregation driven by plant-sediment feedbacks. Our modeling
results also show that disordered hyperuniform patterns can help ecosystems
cope with arid conditions with enhanced functioning of soil moisture
acquisition. However, this advantage may come at the cost of slower recovery of
ecosystem structure upon perturbations. Our work highlights that disordered
hyperuniformity as a distinguishable but underexplored ecosystem
self-organization state merits systematic studies to better understand its
underlying mechanisms, functioning, and resilience.Comment: 34 pages, 6 figures; Supplementary Materials, 19 pages, 10 figures, 2
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Dynamics of a Viral Infection Model with General Contact Rate between Susceptible Cells and Virus Particles
This paper investigates the dynamic behavior of a viral infection model with
general contact rate between susceptible host cells and free virus particles. If the basic reproduction number of the virus is less than unity, by LaSalle’s invariance principle, the disease-free equilibrium is globally asymptotically stable. If the basic reproduction number of the virus is greater than unity, then the virus persists in the host and the endemic equilibrium is locally asymptotically stable
Nitrogen Removal in a Horizontal Subsurface Flow Constructed Wetland Estimated Using the First-Order Kinetic Model
We monitored the water quality and hydrological conditions of a horizontal subsurface constructed wetland (HSSF-CW) in Beijing, China, for two years. We simulated the area-based constant and the temperature coefficient with the first-order kinetic model. We examined the relationships between the nitrogen (N) removal rate, N load, seasonal variations in the N removal rate, and environmental factors—such as the area-based constant, temperature, and dissolved oxygen (DO). The effluent ammonia (NH4 + -N) and nitrate (NO3 −-N) concentrations were significantly lower than the influent concentrations (p \u3c 0.01, n = 38). The NO3 −-N load was significantly correlated with the removal rate (R 2 = 0.96, p \u3c 0.01), but the NH4 + -N load was not correlated with the removal rate (R 2 = 0.02, p \u3e 0.01). The area-based constants of NO3 −-N and NH4 + -N at 20 ◦C were 27 ± 26 (mean ± SD) and 14 ± 10 m·year−1 , respectively. The temperature coefficients for NO3 −-N and NH4 + -N were estimated at 1.004 and 0.960, respectively. The area-based constants for NO3 −-N and NH4 + -N were not correlated with temperature (p \u3e 0.01). The NO3 −-N area-based constant was correlated with the corresponding load (R 2 = 0.96, p \u3c 0.01). The NH4 + -N area rate was correlated with DO (R 2 = 0.69, p \u3c 0.01), suggesting that the factors that influenced the N removal rate in this wetland met Liebig’s law of the minimum
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