Trend Of Gradual Decrease Research Articles

Current status and trend analysis of chronic heart failure research based on CNKI database and CiteSpace

Abstract. Purpose: Chronic heart failure (CHF) is a serious cardiac disease and has become a common and high-incidence disease worldwide. This study aims to investigate the current status and trends of research on CHF over the past decade (2013-2023), in order to understand the latest developments in this field and future research directions. Methods: Using the China National Knowledge Infrastructure (CNKI) as the data source, visual analysis software CiteSpace 5.5 R1 was employed to visualize and analyze CHF-related research, exploring authors, institutions, keywords, and development trends of relevant studies. Results: A total of 1907 articles were included. Visual analysis revealed that research authors were relatively dispersed, with few collaborative publications. The collaboration among main research teams was insufficient, and the main research institutions were also relatively dispersed. Hot keywords included chronic heart failure, heart failure, chronic congestive heart failure, cardiac function, quality of life, prognosis, ventricular remodeling, brain natriuretic peptide, etc., forming nine clusters. Conclusion: The publication volume of CHF over the past decade showed a trend of gradual decrease followed by an increase. The impact of cardiac function on patients prognosis and quality of life has received relatively high attention in the field of chronic heart failure.

Influence of the friction and wear performance of TiB2/7075 aluminum-based composite materials prepared by friction stir processing

Aluminum-based composite layers with different TiB2 contents were prepared by implanting TiB2 reinforcement powders with mass fractions of 1%, 3%, 5%, and 7% into 7075 aluminum alloy sheets using Friction Stir Processing (FSP) technique. The influence of TiB2 content on the friction and wear performance of the modified aluminum-based composite layers was investigated. The results showed that the incorporation of TiB2 reinforcement powders can reduce the friction coefficient and wear volume of the materials, thereby improving the friction and wear performance. Moreover, as the mass fraction of TiB2 reinforcement powder increases, the overall friction coefficient and wear volume of the composite materials exhibit a gradual decrease trend, with adhesive wear being the predominant wear mechanism.

Exploration of Vegetation Change Trend in the Greater Khingan Mountains Area of China Based on EEMD Method

Vegetation, especially forest ecosystems, plays an important role in the global energy flow and material cycle. The vegetation index (VI) is an important index reflecting the dynamic change in vegetation and directly reflects the response of ecosystem to global climate change. The Greater Khingan Mountains Forest region is located in the northeast of China. It is the largest primeval forest region in China, which is well preserved and less affected by human activities. It is of great significance to study the driving mechanism of forest vegetation change for future ecological prediction and management. In this study, GIMMS NDVI data were used to explore the characteristics of nonlinear temporal and spatial variation of NDVI in the Greater Khingan Mountains and its relationship with climatic factors. Firstly, the EEMD method was used to analyze the characteristics of vegetation change in the study area from 1982 to 2015. Secondly, the relationship between vegetation change and climate was discussed by using precipitation and temperature data. The results showed that the following: (1) from 1982 to 2015, the interannual change in vegetation in the Greater Khingan Mountains presented a trend of slow fluctuation and gradual decrease (SLOPE = −0.1645/10,000, p < 0.01). (2) The spatial distribution of vegetation change had obvious geographical differences, and in the central region, the overall distribution characteristics had an obvious browning trend, and in the northwest and southeast, the distribution characteristics had a green trend. (3) The correlation analysis results of vegetation change and climate factors showed that NDVI change was significantly positively correlated with temperature and precipitation; additionally, NDVI change was more correlated with temperature with a range of 0.8–1 than precipitation. (4) The results of vegetation attribution analysis in four typical areas of the study area showed that the following: the coniferous forest area has good cold tolerance and drought tolerance, the correlation between vegetation change and climate factors (temperature, precipitation) was not the strongest, which was 0.537 and 0.828, respectively. The ecological transition area and the broad-leaved forest area, which was located at the edge of the study area, have relatively fragile ecosystems, showed a strong correlation with precipitation, and the correlation coefficients reached 0.670 and 0.632, respectively. The surface water resources provide favorable conditions for the growth of vegetation, it showed a weak correlation with precipitation, and the correlation coefficient was 0.5349.

SMRT sequencing and ddPCR reveal the complexity of developmental trajectories and temporal dynamics of gut bifidobacterial communities in infants

Infant intestinal microbiome is closely linked with health and risk of disease. Bifidobacterium are important components of the infant gut and are known to confer various health effects on the host. However, few studies have described the precise composition and dynamics of early infant gut bifidobacterial communities. Thus, this was a pilot study aiming to describe the developmental trajectories and temporal dynamics of bifidobacterial communities in infants before 6 months of age. A total of 28 fecal samples from 4 infants (GF, ZZ, QM, TN, respectively) were collected and analyzed after 5, 15, 30, 60, 90, 120, 150, and 180 days of birth by a bifidobacteria-target method (based on single-molecule real-time sequencing of partial bifidobacterial rpsK genes) in conjunction with droplet digital polymerase chain reaction (ddPCR). The infant fecal microbiota comprised a total of 11 bifidobacterial species, including 4 major species, i.e., B. dentium (37.35 %), B. catenulatum (32.04 %), B. breve (22.24 %), and B. animalis (8.02 %). The infant microbiota showed highly individualized developmental trajectories. The leading species for GF was B. catenulatum, with a relatively stable developmental trajectory. In ZZ, B. breve was enriched, and the developmental trajectory was rather fluctuating. The most abundant species for QM and TN was B. dentium. The developmental trajectory of B. dentium in QM showed a trend of gradual decrease, whereas an opposite trend was seen in samples of TN. The results of ddPCR confirmed large variations in quantities of bifidobacteria between infants and suggested discordances in temporal dynamics of bifidobacterial communities during the first half year of infancy. In conclusion, our results suggested that the early infant gut bifidobacterial microbiota was highly complex and temporal dynamics, with individualized developmental trajectories, which should be considered in future research of infant gut microbiota.

Physiological Responses of Chionanthus retusus Seedlings to Drought and Waterlogging Stresses

Understanding the adaptability of Chionanthus retusus Lindl. et Paxt. to extreme water conditions will help in exploring the potential application of this species in barren mountains. Three-year-old Chionanthus retusus seedlings were used in a greenhouse pot experiment that analyzed the effect of different moisture gradients on growth, photosynthetic and fluorescence characteristics, protective enzyme system, osmotic substance regulation and cell membrane damage. The results indicated that C. retusus can effectively grow at a relative soil water content of 44.6% and above and can maintain growth for 20 days under flooded conditions. Under drought stress, net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and intercellular carbon dioxide concentration (Ci) all showed a trend of gradual decrease. The trend of change was similar under waterlogging conditions. The maximal quantum yield of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ΦPSII), photochemical quenching coefficient (qP), and electron transport rate (ETR) all decreased as drought deepened. Malondialdehyde (MDA) content decreased first and then increased. However, superoxide dismutase (SOD) activity content, peroxidase (POD) activity content, and proline (Pro) activity content showed a trend of increasing and then decreasing. C. retusus had good adaptability in the slight drought treatment group and flooded treatment group but showed intolerance in the high drought group, which could still last for approximately 21 days. C. retusus was found to have a strong adaptability to water stress and can be used as an afforestation tree in barren mountains.

CuO/HAp composites: Excellent dielectric materials

The present study deals with the dielectric properties of hydroxyapatite based nanocomposites. Hydroxyapatite (HAp) ceramic has been prepared by facile wet chemical precipitation technique. The synthesized HAp is used as a matrix material and copper oxide (CuO) is used as a reinforcing material for the preparation of composites. The CuO/HAp particle reinforced composites have been developed just by mixing them mechanically with variable concentrations. These composites are characterised by X-ray diffraction, and FTIR techniques. The dielectric properties like dielectric constant, dissipation factor and AC conductivity were investigated in the frequency range 10 Hz–2 MHz. All CuO blended composites show higher dielectric constant than pure HAp. Composite with 60% HAp–40% CuO has exhibited highest dielectric constant. The composites show a trend of gradual decrease in dielectric constant and dielectric loss with increase in frequency. The AC conductivity remains constant in low frequency region and increases linearly at high frequencies. The dielectric properties are found to be the function of concentration of metal oxide particles. The composites may be used for high k-material applications.

Current Epidemiology of the General Anesthesia Practice for Cesarean Delivery Using a Nationwide Claims Database in Japan: A Descriptive Study.

The current status of general anesthesia practice for cesarean delivery in Japan remains unknown. Therefore, using a nationwide claims database, we aimed to investigate general anesthesia use for cesarean delivery over a period of 15 years, and to analyze the general anesthesia practice in Japan. Patients who claimed the Japanese general anesthesia claim code (L008) for cesarean delivery between 1 January 2005, and 31 March 2020, were analyzed. Primary endpoint was the prevalence of general anesthesia use. We used two definitions of general anesthesia: L008 code only (insurance definition) and combination of the L008 code with muscle relaxant use (clinical definition). The general anesthesia claim cohort (L008) included 10,972 cesarean deliveries at 1111 institutions from 2005 to 2020. Muscle relaxants were used in 27.3% of L008 claims cases. The rate of general anesthesia use for cesarean delivery ranged from 3.9% in clinical definition to 14.4% in insurance definition of all cesarean deliveries. We observed a temporal trend of gradual decrease in general anesthesia use, regardless of its definition (p for trend < 0.001). We recommend the clinical definition of general anesthesia as the combination of L008 code and muscle relaxant use in a claims-based approach.

Structure Prediction and Potential Inhibitors Docking of Enterovirus 2C Proteins

Human enterovirus infections are mostly asymptomatic and occasionally could be severe and life-threatening. The conserved non-structural 2C from enteroviruses protein is a promising target in antiviral therapies against human enteroviruses. Understanding of 2C-drug interactions is crucial for developing the potential antiviral agents. While functions of enterovirus 2C proteins have been widely studied, three-dimensional structure information of 2C is limited. In this study, the structures of 2C proteins from 20 enteroviruses were simulated and reconstructed using I-TASSER programs. Subsequent docking studies of the known 22 antiviral inhibitors for 2C proteins were performed to uncover the inhibitor-binding characteristics of 2C. Among the potential inhibitors, the compound hydantoin exhibited the highest broad-spectrum antiviral activities with binding to 2C protein. The anti-enteroviral activity of GuaHCL, compound 19b, R523062, compound 12a, compound 12b, quinoline analogs 12a, compound 19d, N6-benzyladenosine, dibucaine derivatives 6i, TBZE-029, fluoxetine analogs 2b, dibucaine, 2-(α-hydroxybenzyl)-benzimidazole (HBB), metrifudil, pirlindole, MRL-1237, quinoline analogs 10a, zuclopenthixol, fluoxetine, fluoxetine HCl, and quinoline analogs 12c showed a trend of gradual decrease. In addition, the free energy with 22 compounds binding to EV 2C ranged from −0.35 to −88.18 kcal/mol. Our in silico studies will provide important information for the development of pan-enterovirus antiviral agents based on 2C.

Effect of S2O32−-S addition on Anammox coupling sulfur autotrophic denitrification and mechanism analysis using N and O dual isotope effects

Anaerobic ammonia oxidation (Anammox) coupling sulfur autotrophic denitrification is an effective method for the advanced nitrogen removal from the wastewater with limited carbon source. The influence of S2O32−-S addition on Anammox coupling sulfur autotrophic denitrification was investigated by adding different concentrations of S2O32−-S (0, 39, 78, 156 and 312 mg/L) to the Anammox system. The contribution of sulfur autotrophic denitrification and Anammox to nitrogen removal at S2O32−-S concentrations of 156 mg/L was 75% ∼83% and 17%∼25%, respectively, and the mixed system achieved completely nitrogen removal. However, Anammox bioactivity was completely inhibited at S2O32−-S concentrations up to 312 mg/L, and only sulfur autotrophic denitrification occurred. The isotopic effects of NO2−-N (δ15NNO2 and δ18ONO2) and NO3−-N (δ15NNO3 and δ18ONO3) during Anammox coupling sulfur autotrophic denitrification showed a gradual decrease trend with the increase of S2O32−-S addition. The ratios of δ15NNO2:δ18ONO2 and δ15NNO3:δ18ONO3 was maintained at 1.30–2.41 and 1.36–2.52, respectively, which revealed that Anammox was dominant nitrogen removal pathway at S2O32−-S concentrations less than 156 mg/L. Microbial diversity gradually decreased with the increase of S2O32−-S. The S2O32−-S addition enhanced the S2O32−-driven autotrophic denitrification and weakened the Anammox, leading to a gradually decreasing trend of the proportion of Candidatus Brocadia as Anammox bacteria from the initial 27% to 4% (S2O32−-S of 156 mg/L). Yet Norank-f-Hydrogenophilaceae (more than 50%) and Thiobacillus (54%) as functional bacteria of autotrophic denitrification obviously increased. The appropriate amount of S2O32−-S addition promoted the performance of Anammox coupling sulfur autotrophic denitrification achieved completely nitrogen removal.

Phytoplankton Species Diversity Patterns and Associated Driving Factors in China’s Jiulong River Estuary: Roles That Nutrients and Nutrient Ratios Play

Understanding diversity patterns and associated driving factors are the critical topics in macroecology and conservation biology. Phytoplankton are highly susceptible to environmental changes in estuaries, particularly eutrophication. This study examined phytoplankton alpha and beta diversity using investigation data in May (springtime), August (summer) and November (autumn) 2009 in China’s Jiulong River estuary, where it was easily polluted because of considerable discharge from a highly dense human population and low self-purification capacity with its limited river basin area, potentially resulting in eutrophication and then influencing phytoplankton diversity. Potential influencing factors were also explored, including dissolved oxygen, salinity, nutrients, nutrient ratios, geographic and hydrologic distance, and so on. The results indicated that Shannon’s index (H’) and Pielou’s index (J) decreased from the estuary’s upper to middle and then increased from middle to lower reaches, Simpson’s (D) observed the opposite trend and species number (S) gradually increased from the estuary’s upper to lower reaches. For beta diversity, all the indices showed a gradual decrease trend from the estuary’s upper to lower reaches, where also, turnover dominated beta diversity for all seasons. It is noteworthy that the significant roles that nutrients and nutrient ratios played in shaping phytoplankton diversity patterns and the nutrient balance were characterized by excess nitrogen (N) and silicon (Si) and limited phosphorus (P), which could potentially cause diatom blooms. Findings also showed that decreasing Si concentrations can help to reduce overall pollution levels as well as the restoration of the estuary’s ecosystem better than just reducing N alone. Accordingly, this study advocates for the protection of the entire estuary system with particular emphasis on its upper reaches. Moreover, greater attention should also be paid to impacts associated with N input and nutrient ratio trade-offs to the prospective watershed management of this estuary. This study provides a practical approach to explore estuarine diversity in a comprehensive way, which can inform effective biodiversity conservation and also be applied to other marine ecosystems to better guide sustainable management and conservation practices.

Revealing the Genetic Structure and Differentiation in Endangered Pinus bungeana by Genome-Wide SNP Markers

Understanding the genetic variation and differentiation of natural populations is essential for their protection, specifically if the species status is endangered as with Pinus bungeana. Here, we used 346,840 high density and strong specificity SNP loci to carry out genetic analyses (i.e., genetic diversity, genetic structure, phylogeny, and geographical differentiation) on 52 P. bungeana individuals from 5 populations (4 natural and one artificial) representing the main regions of the species distribution in China. Genetic diversity assessment indicated a trend of genetic diversity gradual decrease from west to east across the species distribution areas. Population genetic structure, PCA and phylogenetic analyses consistently indicated that populations in the central and eastern regions were clustered together, while those from the western regions were separated. Mantel test values indicated the presence of geographic isolation among populations, an important factor contributing to the observed genetic differentiation. The maximum likelihood tree and potential migration events inferred from TreeMix analysis indicated the presence of historical genetic exchanges between the west of Qinling Mountains and the Lvliang Mountains populations. Based on the generated genetic information, in situ and ex situ conservation strategies for P.bungeana germplasm resources are proposed, these strategies could be valuable for the conservation, protection and genetic improvement of this endangered species.

Simulation of Carbon Exchange from a Permafrost Peatland in the Great Hing’an Mountains Based on CoupModel

Climate change is accelerating its impact on northern ecosystems. Northern peatlands store a considerable amount of C, but their response to climate change remains highly uncertain. In order to explore the feedback of a peatland in the Great Hing’an Mountains to future climate change, we simulated the response of the overall net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary production (GPP) during 2020–2100 under three representative concentration pathways (RCP2.6, RCP6.0, and RCP8.5). Under the RCP2.6 and RCP6.0 scenarios, the carbon sink will increase slightly until 2100. Under the RCP8.5 scenario, the carbon sink will follow a trend of gradual decrease after 2053. These results show that when meteorological factors, especially temperature, reach a certain degree, the carbon source/sink of the peatland ecosystem will be converted. In general, although the peatland will remain a carbon sink until the end of the 21st century, carbon sinks will decrease under the influence of climate change. Our results indicate that in the case of future climate warming, with the growing seasons experiencing overall dryer and warmer environments and changes in vegetation communities, peatland NEE, ER, and GPP will increase and lead to the increase in ecosystem carbon accumulation.

Association Between Bedtime at Night and Systolic Blood Pressure in Adults in NHANES.

Objectives: This study aimed to explore the association between bedtime at night and systolic blood pressure (SBP) in adults.Methods: We conducted a cross-sectional study composed of 7,642 individuals from the National Health and Nutrition Examination Survey (NHANES). Bedtime was defined as the response to the question: “What time do you usually fall asleep on weekdays or workdays?” SBP was taken using the average of all measured values. Multiple linear regression analyses were done to explore the relationship between bedtime and SBP.Results: The bedtime was changed from categorical variable to continuous variable for data analysis, and a significantly negative association was identified between bedtime and SBP (β, −0.23 [95% CI, −0.43, −0.02]). With the delay of bedtime, the SBP showed a gradual decrease trend, and it was dropped to the lowest at 0:00. After 0:00, the SBP was gradually increased with the delay of sleep time. The stratified analyses showed that in the female group, with the delay of bedtime, the range of SBP was decreased more obviously at 0:00. In the 18–45 year group, bedtime had little effect on SBP. Among ≥45 years old group, this trend was still the same. In the black group, an obvious downward trend was found at 22:00.Conclusion: With the delay of bedtime, the SBP had shown a gradual decrease trend, and it was dropped to the lowest at 0:00. After 0:00, the SBP was gradually increased with the delay of sleep time. Bedtime and SBP showed a U-shaped relationship.

Genome-wide transcriptome profiling and characterization of mannuronan C5-epimerases in Saccharina japonica

Alginate is a linear polysaccharide comprised of 1,4-linked-β-D-mannuronic acid (M) and α-L-guluronic acid (G). As the major cell wall polysaccharide in brown algae, alginate is widely used in the food, pharmaceutical, and chemical industries. Mannuronan C5-epimerases (MC5Es) catalyze the specific conversion of M to its C-5 epimer G, playing a key role in the modification of alginate. In this study, 143 MC5E gene sequences from Saccharina japonica (SjMC5Es) were identified based on the genome and transcriptome data. Transcriptomics analysis was conducted, and the results showed that the SjMC5Es varied in their spatial and temporal expression patterns. Most SjMC5Es exhibited higher expression in the basal blades of the algae at earlier developmental stages than at later adult stages, and the transcription levels of the SjMC5Es showed a clear trend of gradual increase or decrease from the basal to the distal blades. In addition, the β-D-mannuronic acid/α-L-guluronic acid (M/G) ratio of alginate from all samples was measured, and the M/G ratios were associated with the transcription levels of the SjMC5E genes. Finally, the highly expressed SjMC5E2 was characterized, soluble SjMC5E2 was heterologously expressed, and its mannuronan C5-epimerase activity was confirmed by 1H-nuclear magnetic resonance analysis. Our results provide a global view of the SjMC5Es in S. japonica and lay a foundation for further applications of MC5Es in improving the physiochemical properties of alginate.

Effect of different steel fiber types on mechanical properties of ultra-high performance concrete

The influence of steel fiber on the mechanical properties of ultra-high performance concrete (UHPC) were studied through slump, compressive strength, flexural strength test. The experimental results showed that the incorporation of steel fiber had an influence on the working performance of UHPC, and the slump and expansion degree of UHPC were inversely proportional to the volume content and length-diameter ratio of steel fiber. The steel fiber significantly improved the compressive and flexural strength of UHPC. The mechanical property of UHPC was the best when the steel fiber content was 4%, with 28 day compressive strength up to 163.2MPa and flexural strength up to 45.9MPa. UHPC showed a trend of gradual decrease of compressive strength and gradual increase of flexural strength with the increase of aspect ratio of steel fiber on the condition of constant volume content of steel fiber. The addition of special-shaped steel fiber can improve the compressive and flexural strength of UHPC effectively.

Spatial-temporal Variation of Precipitation Concentration Degree and Precipitation Concentration Period in Gansu Province in Recent 50 Years

Inhomogeneity is the inherent attribute of precipitation and is usually an important factor affecting the occurrence of hydrological disasters such as floods and debris flows. Based on the monthly precipitation data of 27 national meteorological stations in the past 50 years, the spatial and temporal distribution characteristics of precipitation concentration degree (PCD) and precipitation concentration period (PCP) in Gansu Province were assessed in this study. The results indicated that: (a) the annual precipitation had distinct regional differences (annual average values were between 43.3-605.4 mm) and strong inter-annual fluctuations (coefficient of variation was usually above 0.20, some up to 0.40-0.45); (b) the main range of PCD was from 0.52 to 0.67, with significantly reduced inter-annual fluctuation and a long-term trend of gradual decrease; (c) the spatial-temporal variation of PCP was generally small, mainly concentrated in 192.8°-205.0°(mid-late July), and showed a slightly advanced variation tendency. Under the overall background of warming and wetting, Gansu Province presents evolution characteristics of PCD weakening and PCP advancing, and the formation mechanism and potential effects of this phenomenon require further attention.

Genomic Profiling and Prognostic Value Analysis of Genetic Alterations in Chinese Resected Lung Cancer With Invasive Mucinous Adenocarcinoma.

BackgroundInvasive mucinous adenocarcinoma (IMA) of the lung is a distinct histological subtype with unique clinical and pathological features. Despite previous genomic studies on lung IMA, the genetic characteristics and the prognosis-related biomarkers in Chinese surgically resected lung IMA remain unclear.MethodsWe collected 76 surgically resected primary tumors of invasive lung adenocarcinoma, including 51 IMA and 25 non-mucinous adenocarcinomas (non-IMA). IMA was further divided into pure-IMA (mucinous features≥90%) and mixed-IMA subgroups. Comprehensive genomic profiling based on targeted next-generation sequencing (NGS) of 425 genes was explored and genomic characteristics were evaluated for the correlation with postoperative disease-free survival (DFS).ResultsIMA had a unique genetic profile, with more diverse driver mutations and more tumor drivers/suppressors co-occurrence than that of non-IMA. The frequency of EGFR (72.0% vs. 40.0% vs. 23.1%, p=0.002) and ALK (undetected vs. 20.0% vs. 26.9%, p=0.015) alterations showed a trend of gradual decrease and increase from non-IMA to mixed-IMA to pure-IMA, respectively. The frequency of KRAS mutations in pure-IMA was higher than that in mixed-IMA, albeit statistically insignificant (23.1% vs. 4.0%, p=0.10). TP53 mutation was significantly less in pure-IMA compared to mixed-IMA and non-IMA (23.1% vs. 52.0% vs. 56.0%, p=0.03). Besides, IMA exhibited less arm-level amplifications (p=0.04) and more arm-level deletions (p=0.004) than non-IMA, and the frequency of amplification and deletion also showed a trend of gradual decrease and increase from non-IMA to mixed-IMA to pure-IMA, respectively. Furthermore, prognosis analysis in stage III IMA patients showed that patients harboring alterations in EGFR (mDFS=30.3 vs. 16.0 months, HR=0.19, P=0.027) and PI3K pathway (mDFS=36.0 vs. 16.0 months, HR=0.12, P=0.023) achieved prolonged DFS, while patients with poorly differentiated tumors (mDFS=14.1 vs. 28.0 months, HR=3.75, p=0.037) or with KRAS mutations (mDFS=13.0 vs. 20.0 months, HR=6.95, p=0.027) had shorter DFS. Multivariate analysis showed that KRAS mutations, PI3K pathway alterations, and tumor differentiation status were independent factors that have statistically significant influences on clinical outcomes of IMA patients.ConclusionOur study provided genomic insights into Chinese surgically resected lung IMA. We also identified several genomic features that may serve as potential biomarkers on postoperative recurrence in IMA patients with stage III disease.

Damage Evolution of Sandstone under Constant‐Amplitude Cyclic Loading Based on Acoustic Emission Parameters and Resistivity

In the real environment, besides static load, rock is more affected by cyclic load. There is a large difference in the mechanical properties exhibited by rocks under cyclic and static loading. Therefore, it is particularly necessary to investigate the mechanical characteristics of rock subjected to cyclic loading. These parameters of rock, acoustic emission (AE) and resistivity, are both sensitive to the failure process of rock, and they are complementary to the different stages of rock damage. Therefore, in this paper, the AE characteristics and resistivity properties of sandstone subjected to constant‐amplitude cyclic loading and unloading were experimentally investigated using a typical sandstone in Chongqing. The same three‐stage pattern was found for the AE evolution of sandstones during constant‐amplitude cyclic loading. Initial evolution stage: the rock deformation is fast with strong changes in the AE signal. The rock deformation developed slowly while the changes of the AE signal were stable in the constant velocity evolution stage. The rock deformation developed dramatically while the AE signal became more intense in accelerated evolution stage. The change in resistivity is characterized by a rapid decrease during the loading stage and a rapid rebound during the unloading stage. Overall, from the beginning of the cycle to the end of the cycle, the resistivity of the sandstone showed a general trend of gradual decrease, until the sudden increase in resistivity at the time of damage. Finally, a damage model based on AE parameters and resistivity was constructed by combining damage mechanics.

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节，季节性冻融交替是影响凋落物分解的重要环境因素之一，但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响，以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料，从凋落物基质质量、冻融环境等影响凋落分解的因素着手，采用模拟冻融循环过程（-5-5℃），研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现，3中典型林型凋落物经过不同冻融处理后，其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势，而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下，3种林型的凋落物碳绝对含量呈波动下降的趋势，说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下，有机碳释放有显著差异（P<0.05）。其中，冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放，但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下，亚高山森林土壤冻融事件频发将加快凋落物的分解，但变化程度受到凋落物质量控制。;In this study, we address the effects of freeze-thaw cycles on the process of litter decomposition in subalpine forests. In a microcosm experiment, we measured the dynamics of litter moss loss rates and organic carbon by controlling the freeze-thaw environment (-5-5℃) in three typical forests in the sub-alpine region in western Sichuan. The three forest types including coniferous, coniferous-broadleaf, and broadleaf forest were selected for our experiment design based on the criteria of their abundance in the study area. Our results showed that clear and significant differences (P<0.05) in all measured litter types were all observed due to the freeze-thaw treatments. Specially, the mass loss rate of litter in both coniferous-broadleaf and coniferous forests showed a slow-fast-slow trend. In contrast, in the broadleaf forests, the mass loss rates exhibited a gradual decrease trend. This fluctuation phenomenon implies that there is a balance between microbial-fixed exogenous carbon and substrate-released carbon. In conclusion, the increase of globally average temperature would accelerate the freeze-thaw cycles and thus significantly change the process of mass loss and nutrient cycles in the subalpine forests, but both the magnitude and direction of the freeze-thaw effects varied with initial litter quality.

Comparative Analysis of Water-Energy Cycle Processes Based on High-Resolution Assimilation Dataset of the Water-Energy Cycle in China Data Over Different Underlying Surfaces in Qinghai-Tibet Plateau

We used a High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC) to study the land-atmosphere interactions and meteorological characteristics in inhomogeneous underlying surface of the Qinghai-Tibet Plateau (QTP). Three different underlying surfaces (i.e., grassland, open shrubland, and barren or sparsely vegetated) of the QTP are selected and the meteorological elements on each underlying surface grid are averaged. We compared and analyzed the Green Vegetation Fraction (GVF), precipitation, soil moisture and soil temperature, and energy fluxes for three different land-use types in QTP. The results showed that the vegetation coverage of HRADC showed a gradual decrease trend from southeast to northwest throughout the Qinghai-Tibet Plateau. The GVF of the grassland in the southeast can reach more than 60% in summer, and only about 20% in sparse vegetation areas. HRADC can well reproduce the seasonal change trend of soil temperature and soil moisture in different underlying surfaces. The annual variation trend of soil temperature shows that the time of the deep soil temperature reaching the peak value lags behind the shallow layer. The annual averaged soil moisture over grassland is higher than that of open shrubland and barren land, which is consistent with the plateau precipitation distribution. The peak value of sensible heat flux over grassland is only 80 W·m-2 in April, and the latent heat flux can reach 90 W·m-2, and the net radiation of the barren land can reach 210 W·m-2 in July. This study is important to discover the water-energy cycle characteristics of QTP.