Nutrient limitation of woody debris decomposition in a tropical forest:contrasting effects of N and P addition

1.Tropical forests represent a major terrestrial store of carbon (C), a large proportion of which is contained in the soil and decaying organic matter. Woody debris plays a key role in forest C dynamics because it contains a sizeable proportion of total forest C. Understanding the factors controlling the decomposition of organic matter in general, and woody debris in particular, is hence critical to assessing changes in tropical C storage. 2.We conducted a factorial fertilization experiment in a tropical forest in South China to investigate the influence of nitrogen (N) and phosphorus (P) availability onwoody debris decomposition using branch segments (5-cm diameter) of four species (Acacia auriculaeformis, Aphanamixis polystachya, Schefflera octophylla, Carallia brachiata) in plots fertilized with +N, +P, or +NP, and controls. 3.Fertilization with +P and +NP increased decomposition rates by 5-53% and the magnitude was species-specific. Contrary to expectations, we observed no negative effect of +N addition on decay rates or mass loss of woody debris in any of the four study species. Decomposition rates of woody debris were higher in species with lower C:P ratios regardless of treatment. 4.We observed significant accumulation of P in the woody debris of all species in plots fertilized with +P and +NP during the early stages of decomposition. N-release from woody debris of Acacia (N-fixing) was greater in the +P plots towards the end of the study, whereas fertilization with +N had no impact on the patterns of nutrient release during decomposition. 5.Synthesis: Our results indicate that decomposition of woody debris is primarily constrained by P availability in this tropical forest. However, contrary to expectations, +N addition did not exacerbate P-limitation. It is conceivable that decay rates of woody debris in tropical forests can be predicted by C:P or lignin:P ratios but additional work with more tree species is needed to determine whether the patterns we observed are more generally applicable

Nonlinear Free Vibration Analysis of Axisymmetric Polar Orthotropic Circular Membranes under the Fixed Boundary Condition

This paper presents the nonlinear free vibration analysis of axisymmetric polar orthotropic circular membrane, based on the large deflection theory of membrane and the principle of virtual displacement. We have derived the governing equations of nonlinear free vibration of circular membrane and solved them by the Galerkin method and the Bessel function to obtain the generally exact formula of nonlinear vibration frequency of circular membrane with outer edges fixed. The formula could be degraded into the solution from small deflection vibration; thus, its correctness has been verified. Finally, the paper gives the computational examples and comparative analysis with the other solution. The frequency is enlarged with the increase of the initial displacement, and the larger the initial displacement is, the larger the effect on the frequency is, and vice versa. When the initial displacement approaches zero, the result is consistent with that obtained on the basis of the small deflection theory. Results obtained from this paper provide the accurate theory for the measurement of the pretension of polar orthotropic composite materials by frequency method and some theoretical basis for the research of the dynamic response of membrane structure

Case-control study on fragility fractures in coal miners: A comparison between surface and underground workers

BackgroundThe prevalence of osteoporosis and osteopenia is higher among underground coal miners than surface workers. The special underground work environment and unhealthy habits such as smoking, drinking, and a high-salt diet may lead to changes in bone metabolism, increasing the risk of fragility fractures and placing a heavy economic burden on individuals and society. ObjectiveTo identify potential factors influencing fragility fractures among coal miners in different working environments and to provide a basis for targeted preventive measures to reduce the occurrence of fragility fractures.MethodsMale participants who attended at least one of the physical examinations in Kailuan Group between June 2006 and December 2020 were included in the study. The participants were divided into two groups based on their working environment: surface or underground. A case-control study was conducted, where patients with new fragility fractures served as the case group and participants without fragility fractures served as the control group. The two groups were matched with a case:control ratio of 1:4 by age (±1 year) and the same year of physical examination. The matching process was repeated twice, once for the surface working population and once for the underground working population. The analysis of risk factors was conducted using conditional logistic regression models.ResultsAmong a total of 113138 employees in Kailuan Group, 82631 surface workers and 30507 underground workers were included, respectively. The number of individuals who suffered fragility fractures was 1375, accounting for 1.22% of the total population. The incidence of fragility fractures in underground workers was significantly higher than that in surface workers (1.63%>1.07%, P<0.001). The results of conditional logistic regression model showed that current smoking (OR=1.26, 95%CI: 1.05, 1.51), manual labor (OR=1.37, 95%CI: 1.06, 1.78), diabetes (OR=1.26, 95%CI: 1.04, 1.54), sinus tachycardia (OR=1.81, 95%CI: 1.23, 2.66), history of stroke (OR=1.51, 95%CI: 1.09, 2.09), education at college and above (OR=0.65, 95%CI: 0.45, 0.95), high income level (OR=0.69, 95%CI: 0.54, 0.90), elevated hemoglobin (OR=0.91, 95%CI: 0.85, 0.98), and elevated total cholesterol (OR=0.90, 95%CI: 0.82, 0.99) were associated with fragility fractures in the surface working population of coal mines; current smoking (OR=1.48, 95%CI: 1.17, 1.87), current drinking (OR=1.26, 95%CI: 1.01, 1.56), manual labor (OR=2.64, 95%CI: 1.41, 4.94), history of dust exposure (OR=1.28, 95%CI: 1.03, 1.58), and obesity (OR=0.72, 95%CI: 0.52, 0.96) were associated with fragility fractures in the underground working population of coal mines.ConclusionIn preventing fragility fractures, special attention should be paid to the bone health of underground workers engaged in manual labor or having a history of dust exposure. It is important to correct their unhealthy behaviors in a timely manner, such as smoking and drinking, and to appropriately increase body weight to prevent fragility fractures. For surface workers, particular attention should be given to the high-risk group for fragility fractures, such as low family income per capita, manual labor, and having a history of stroke or diabetes; in addition, close monitoring of their resting heart rate, hemoglobin levels, and total cholesterol levels may help prevent fragility fractures

Effect of Polyvinyl Acetate Stabilization on the Swelling-Shrinkage Properties of Expansive Soil

Polyvinyl acetate constitutes a class of polymers that can entirely dissolve in water to form a solution. In this study, polyvinyl acetate as a nontraditional chemical stabilizer was used in soil improvement. Laboratory tests were carried out to evaluate the effect of polyvinyl acetate on swelling-shrinkage properties of expansive soil. A series of shrink/swell tests were performed with adding polyvinyl acetate as amendment at a concentration 3 g/cm3 to four aggregate sizes in the range of 0–0.5 mm, 0.5–1 mm, 1-2 mm, and 2–5 mm and five concentrations 1.5 g/cm3, 3 g/cm3, 4.5 g/cm3, 6 g/cm3, and 9 g/cm3 to soils with aggregate size in the range of 0.5–1 mm for comparison of results with those of untreated soils. The results show that all the linear swelling ratio (LSWR) and linear shrinkage ratio (LSHR) values of the treated specimens decrease. SEM images and the test results indicate the achieved reduction in volume change of the soil tested using soil pore filling and particle encapsulation

Cumulative exposure to remnant cholesterol and the risk of fragility fractures: a longitudinal cohort study

ObjectiveTo investigate the association between cumulative remnant cholesterol (cumRC) and the risk of new-onset fragility fractures.MethodsThis study included individuals who participated in the 2006, 2008, and 2010 Kailuan health examinations. Baseline characteristics were compared between groups according to cumRC quartiles. The incidence density was calculated, and the log-rank test was used to compare the cumulative incidence. Cox proportional hazards models were used to estimate the hazard ratio (HR) and 95% confidence interval (CI), and restricted cubic spline was used to examine the possibly non-linear relation between cumRC and the risk of fragility fractures. Additional analyses were performed with stratification by age (≥ or &lt;65 years).ResultsA total of 43,839 individuals were included in this study. During the median follow-up period of 10.97 years, a total of 489 fragility fractures occurred. Multivariable Cox proportional hazards regression model 3 showed that the Q1 and Q4 groups versus the Q2 group were associated with a higher HR of fragility fracture (HR 1.61, 95% CI: 1.23–2.11; HR 1.38, 95% CI: 1.06–1.81), and restricted cubic spline regression analysis showed a non-linear relationship between cumRC level and the risk of fragility fractures (POverall association &lt; 0.001, PNon-linear association = 0.001). The association was significant in the age group &lt;65 years but not in the age group ≥65 years. The sensitivity analyses were consistent with the main results.ConclusionsBoth too high and too low cumRC levels were associated with a greater risk of fragility fractures, and this association was more significant in young and middle-aged people

Research on the Construction of Malware Variant Datasets and Their Detection Method

Malware detection is of great significance for maintaining the security of information systems. Malware obfuscation techniques and malware variants are increasingly emerging, but their samples and API (application programming interface) sequences are difficult to obtain. This poses difficulties for the development of malware variant detection models. To address this issue in this paper, we first generated a malware variant dataset using the obfuscation technique based on the disassembly and decompilation of malware. Then, an API call dataset of these malware variants was constructed through sandboxing. Compared to similar work, the malware variants and their obfuscated API call sequences generated in this paper were all runnable. After that, taking a public API call sequence dataset of obfuscation-free malware as input, a BERT (bidirectional encoder representation from transformers) pretrained model for malware detection was constructed. To enhance the ability of this pretrained model to handle obfuscation and variants, in this paper, we used adversarial training to improve the robustness and generalization of the detection model under obfuscation. As the experimental results show, the proposed scheme can improve the classification performance of malware variants under obfuscation. The accuracy of the malware variant classification was close to that of the unobfuscated case

A Novel Method of Small Object Detection in UAV Remote Sensing Images Based on Feature Alignment of Candidate Regions

To solve the problem of low detection accuracy of small objects in UAV optical remote sensing images due to low contrast, dense distribution, and weak features, this paper proposes a small object detection method based on feature alignment of candidate regions is proposed for remote sensing images. Firstly, AFA-FPN (Attention-based Feature Alignment FPN) defines the corresponding relationship between feature mappings, solves the misregistration of features between adjacent levels, and improves the recognition ability of small objects by aligning and fusing shallow spatial features and deep semantic features. Secondly, the PHDA (Polarization Hybrid Domain Attention) module captures local areas containing small object features through parallel channel domain attention and spatial domain attention. It assigns a larger weight to these areas to alleviate the interference of background noise. Then, the rotation branch uses RROI to rotate the horizontal frame obtained by RPN, which avoids missing detection of small objects with dense distribution and arbitrary direction. Next, the rotation branch uses RROI to rotate the horizontal box obtained by RPN. It solves the problem of missing detection of small objects with dense distribution and arbitrary direction and prevents feature mismatch between the object and candidate regions. Finally, the loss function is improved to better reflect the difference between the predicted value and the ground truth. Experiments are conducted on a self-made dataset. The experimental results show that the mAP of the proposed method reaches 82.04% and the detection speed reaches 24.3 FPS, which is significantly higher than that of the state-of-the-art methods. Meanwhile, the ablation experiment verifies the rationality of each module

A Novel Method of Small Object Detection in UAV Remote Sensing Images Based on Feature Alignment of Candidate Regions

To solve the problem of low detection accuracy of small objects in UAV optical remote sensing images due to low contrast, dense distribution, and weak features, this paper proposes a small object detection method based on feature alignment of candidate regions is proposed for remote sensing images. Firstly, AFA-FPN (Attention-based Feature Alignment FPN) defines the corresponding relationship between feature mappings, solves the misregistration of features between adjacent levels, and improves the recognition ability of small objects by aligning and fusing shallow spatial features and deep semantic features. Secondly, the PHDA (Polarization Hybrid Domain Attention) module captures local areas containing small object features through parallel channel domain attention and spatial domain attention. It assigns a larger weight to these areas to alleviate the interference of background noise. Then, the rotation branch uses RROI to rotate the horizontal frame obtained by RPN, which avoids missing detection of small objects with dense distribution and arbitrary direction. Next, the rotation branch uses RROI to rotate the horizontal box obtained by RPN. It solves the problem of missing detection of small objects with dense distribution and arbitrary direction and prevents feature mismatch between the object and candidate regions. Finally, the loss function is improved to better reflect the difference between the predicted value and the ground truth. Experiments are conducted on a self-made dataset. The experimental results show that the mAP of the proposed method reaches 82.04% and the detection speed reaches 24.3 FPS, which is significantly higher than that of the state-of-the-art methods. Meanwhile, the ablation experiment verifies the rationality of each module

Tidal wetland resilience to sea level rise increases their carbon sequestration capacity in United States

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, F., Lu, X., Sanders, C. J., & Tang, J. Tidal wetland resilience to sea level rise increases their carbon sequestration capacity in United States. Nature Communications, 10(1), (2019): 5434, doi: 10.1038/s41467-019-13294-z.Coastal wetlands are large reservoirs of soil carbon (C). However, the annual C accumulation rates contributing to the C storage in these systems have yet to be spatially estimated on a large scale. We synthesized C accumulation rate (CAR) in tidal wetlands of the conterminous United States (US), upscaled the CAR to national scale, and predicted trends based on climate change scenarios. Here, we show that the mean CAR is 161.8 ± 6 g Cm−2 yr−1, and the conterminous US tidal wetlands sequestrate 4.2–5.0 Tg C yr−1. Relative sea level rise (RSLR) largely regulates the CAR. The tidal wetland CAR is projected to increase in this century and continue their C sequestration capacity in all climate change scenarios, suggesting a strong resilience to sea level rise. These results serve as a baseline assessment of C accumulation in tidal wetlands of US, and indicate a significant C sink throughout this century.This study was partially funded by Natural Science Foundation of China (31300419, 31670621, 31870463), the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0408), R&D Program of Guangdong Provincial Department of Science and Technology (2018B030324003) and Pearl River Nova Program of Guangzhou (201710010140) awarded to F.W. J.T. is supported by the NOAA National Estuarine Research Reserve Science Collaborative (NA09NOS4190153 and NA14NOS4190145). C.J.S. is supported by Australian Research Council (DE160100443)