1,065 research outputs found
On Convergence of Tracking Differentiator with Multiple Stochastic Disturbances
In this paper, the convergence and noise-tolerant performance of a tracking
differentiator in the presence of multiple stochastic disturbances are
investigated for the first time. We consider a quite general case where the
input signal is corrupted by additive colored noise, and the tracking
differentiator itself is disturbed by additive colored noise and white noise.
It is shown that the tracking differentiator tracks the input signal and its
generalized derivatives in mean square and even in almost sure sense when the
stochastic noise affecting the input signal is vanishing. Some numerical
simulations are performed to validate the theoretical results
A Realistic 3D Non-Stationary Channel Model for UAV-to-Vehicle Communications Incorporating Fuselage Posture
Considering the unmanned aerial vehicle (UAV) three-dimensional (3D) posture,
a novel 3D non-stationary geometry-based stochastic model (GBSM) is proposed
for multiple-input multiple-output (MIMO) UAV-to-vehicle (U2V) channels. It
consists of a line-of-sight (LoS) and non-line-of-sight (NLoS) components. The
factor of fuselage posture is considered by introducing a time-variant 3D
posture matrix. Some important statistical properties, i.e. the temporal
autocorrelation function (ACF) and spatial cross correlation function (CCF),
are derived and investigated. Simulation results show that the fuselage posture
has significant impact on the U2V channel characteristic and aggravate the
non-stationarity. The agreements between analytical, simulated, and measured
results verify the correctness of proposed model and derivations. Moreover, it
is demonstrated that the proposed model is also compatible to the existing GBSM
without considering fuselage posture.Comment: 12 pages, 8 figures, CNCO
Effects of sunlight on tundra nitrous oxide and methane fluxes in maritime Antarctica
The relationships of nitrous oxide (N2O) and methane (CH4) emissions to other environmental parameters have been studied extensively in Antarctic terrestrial ecosystems. However, the effects of sunlight on soil N2O and CH4 fluxes are neglected across the Antarctic tundra. Here, fluxes of N2O and CH4 from maritime Antarctic tundra soils were measured in the absence and presence of sunlight during three summers. The N2O fluxes averaged −4.6±1.2 μg·m−2·h−1 in the absence of sunlight and 5.7±1.5 μg·m−2·h−1 in its presence; CH4 fluxes averaged 119.8±24.5 μg·m−2·h−1 (absence) and −40.5±28.3 μg·m−2·h−1 (presence). The correlations between N2O and CH4 fluxes and other environmental variables (e.g., soil moisture, temperature, organic and inorganic material) were not statistically significant (P>0.05) at all sites. On average, sunlight significantly increased N2O emissions and CH4 uptake by 10.3 μg·m−2·h−1 and 160.3 μg·m−2·h−1, respectively. This study indicates that sunlight is critical for accurately estimating N2O and CH4 budgets from maritime Antarctica and necessary for constraining the role of their emissions from tundra soil
Potential methane production rates and its carbon isotopic composition from ornithogenic tundra soils in coastal Antarctic
Methane (CH4) is one of important greenhouse gases with chemical activity. The determination of isotopic compositions for CH4 emitted from the soils helps us to understand its production mechanisms. CH4 isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of CH4 have been reported from Antarctic tundra soils. In this paper, ornithogenic soil profiles were collected from four penguin colonies, and potential CH4 production rates and its 13C ratio (δ13C) were investigated based upon laboratory incubation experiments. The mean CH4 production rates are highly variable in these soil profiles, ranging from 0.7 to 20.3 μg CH4−C kg−1∙h−1. These ornithogenic soils had high potential production rates of CH4 under ambient air incubation or under N2 incubation, indicating the importance of potential CH4 emissions from penguin colonies. Most of the soil samples had higher δ13C-CH4 under N2 incubation (−39.28%~−43.53%) than under the ambient air incubation (−42.81%~−57.19%). Highly anaerobic conditions were conducive to the production of CH4 enriched in 13C, and acetic acid reduction under N2 incubation might be a predominant source for soil CH4 production. Overall the δ13C-CH4 showed a significant negative correlation with CH4 production rates in ornithogenic tundra soils under N2 incubation (R2=0.41, p<0.01) or under the ambient air incubation (R2=0.50, p<0.01). Potential CH4 production from ornithogenic soils showed a significant positive correlation with total phosphorus (TP) and NH4+−N contents, pH and soil moisture (Mc), but the δ13C-CH4 showed a significant negative correlation with TP and NH4+−N contents, pH and Mc, indicating that the deposition amount of penguin guano increased potential CH4 production rates from tundra soils, but decreased the δ13C-CH4. The CH4 emissions from the ornithogenic soils affect carbon isotopic compositions of atmospheric CH4 in coastal Antarctica
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