With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threat...With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threats to ecosystem stability.Understanding the current status of forest degradation and assessing potential carbon stocks in China are of strategic importance for making forest restoration efforts and enhancing carbon sequestration capacity.In this study,we used the national forest inventory data from 2009 to 2018 to develop a set of standard measures for assessing degraded forests across China,based on five key indicators:forest accumulation growth rate(FAGR),forest recruitment rate(FRR),tree species reduction rate(TSRR),forest canopy cover reduction rate(FCCRR),and forest disaster level(FDL).Additionally,we estimated standing carbon stock,potential carbon stock,and theoretical space to grow by developing a stand growth model,which accounts for stand density across different site classes,to evaluate the restoration potential of degraded forests.The results indicate that degraded forest area in China is 36.15 million hectares,accounting for 20.10% of a total forest area.Standing carbon stock and potential carbon stock of degraded forests in China are 23.93 million tons and 61.90 million tons,respectively.Overall,degraded forest varies significantly across different regions.The results highlight the important trade-offs among environmental factors,policy decisions,and forest conditions,providing a robust foundation for developing measures to enhance forest quality.展开更多
In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,...In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,turning motion,and turning motion with different radi by the voltage differential driving method.A prototype with a weight of 38 g and dimensions of 150×80×31 mm^(3) was fabricated.Firstly,the dynamics and kinematics of the piezoelectric robot were analyzed to obtain the trajectory of a point at the end of the piezoelectric robot leg.The motion principle of the piezo-electric robot was analyzed,and then the piezoelectric robot's modal analysis and harmonic response analysis were carried out using finite element analysis software.Finally,an experimental setup was built to verify the effectiveness and high efficiency of the robot's motion,and the effects of frequency,voltage,load,and height of the driving leg on the robot's motion performance were discussed.The performance test results show that the piezoelectric robot has a maximum veloc-ity of 66.79 mm/s at an excitation voltage of 320 V and a load capacity of 55 g.In addition,the H-BPR with unequal drive legs has better climbing performance,and the obtained conclusions are informative for selecting leg heights for piezoelectric robots.展开更多
The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limit...The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limitation,abundant nutrients,and rapid salinity shifts play a crucial role in shaping phytoplankton dynamics.The Qiantang River estuary-Hangzhou Bay(QRE-HZB)is a macrotidal estuary system known for its exceptionally high suspended solids concentration.To investigate the impact of TMZ on the standing crop and size structure of phytoplankton in the QRE-HZB,we conducted three cruises in dry,wet,and dry-to-wet transition seasons during 2022-2023,by assessing parameters including size fractionated chlorophyll a(chl a),turbidity,Secchi depth,temperature,salinity,nutrients,and mesozooplankton.Results reveal significant variations in the TMZ and associated environmental factors in different periods,which markedly influenced the phytoplankton chl-a concentration,size structure,and cell activity(pheophytin/chl a).The chl-a concentration was high with micro-phytoplankton predominance in wet season,while nano-phytoplankton dominated in dry season.Within the TMZ,lower chl-a concentrations and pico-chl-a contributions,alongside higher pheophytin/chl-a and micro-chl-a contributions,were observed.The Spearman’s rank correlation and generalized additive model analyses indicated strong correlations of chl-a concentrations with turbidity,nutrients,and mesozooplankton.Redundancy analysis further revealed that salinity,nutrients,and turbidity significantly regulated variations in size structure.Phytoplankton mortality within the TMZ was primarily driven by high turbidity and salinity fluctuations,reflecting the vigorous resuspension and mixing of freshwater and seawater in the QRE-HZB.These findings highlight that the standing crop and size structure of phytoplankton were strongly regulated by the TMZ and associated physicochemical factors in the macrotidal QRE-HZB.展开更多
In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our anal...In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our analysis provides an understanding of the precise spatial localization of atomic positions at the atomic level,utilizing advanced theoretical approaches and principles of quantum mechanics.The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics.A theoretical approach is constructed to describe the interaction between the system and external fields,specifically a control field and a probe field.The absorption spectrum of the probe field is thoroughly examined to clarify the spatial localization of the atom within the proposed configuration.A theoretical investigation found that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain.Specifically,the emergence of one and two sharp localized peaks was observed within a one-wavelength domain.We observed notable influences of the intensity of the control field,probe field detuning and decay rates on atomic localization.Ultimately,we have achieved an unprecedented level of ultrahigh resolution and precision in localizing an atom within an area smaller thanλ/35×λ/35.These findings hold promise for potential applications in fields such as Bose-Einstein condensation,nanolithography,laser cooling,trapping of neutral atoms and the measurement of center-of-mass wave functions.展开更多
When the free standing riser(FSR)is in service in the ocean,its mechanical properties are affected by various factors,including complex ocean current forces,buoyancy of the buoyancy can,and torque caused by the deflec...When the free standing riser(FSR)is in service in the ocean,its mechanical properties are affected by various factors,including complex ocean current forces,buoyancy of the buoyancy can,and torque caused by the deflection of the upper floating body.These loads have a great influence on the deformation and internal force of the FSR.The static performance of FSR is investigated in this research under various working conditions.The finite element model of FSR is established based on the co-rotational method.The arc length approach is used to solve the model.The load is exerted in increments.The current load on the riser changes with the configuration of the riser.The accuracy of the numerical method is verified by Abaqus software.The calculation time is also compared.Then,the effects of uniform current,actual current and floating body yaw motion on FSR are studied by parameter analysis.Additionally,the influence of the FSR on the ocean current after the failure of part of the buoyancy can chamber is analyzed.The results show that the numerical model based on the co-rotational method can effectively simulate the large rotation and torsion behavior of FSR.This method has high computational efficiency and precision,and this method can quickly improve the efficiency of numerical calculation of static analysis of deep-water riser.The proposed technology may serve as an alternative to the existing proprietary commercial software,which uses a complex graphical user interface.展开更多
Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a...Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a great influence on the concentration of nitrite tested by spectrophotometric method. In this context, three kinds of food samples are prepared, including canned mustard, canned fish and home-made pickled water. A series of standing times are placed during the sample pretreatments and the corresponding nitrite contents in these samples are detected by spectrophotometric method based on N-ethylenediamine dihydrochloride. This study aims to find out a reasonable standing time during the pretreatment of food sample, providing influence factor for precise detection of nitrite.展开更多
In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercriti...In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercritical case, we obtain the existence and stability of standing waves. Our results are complements to the results of Carles and Il’yasov’s artical, where orbital stability of standing waves have been studied for the 2D Schrödinger equation with combined nonlinearities and harmonic potential.展开更多
The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standi...The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.展开更多
Spraying nanocellulose onto films provides a quick and scalable way to create free-standing films with exceptional consistency and customizable thickness. This method increases the application of nanocellulose films i...Spraying nanocellulose onto films provides a quick and scalable way to create free-standing films with exceptional consistency and customizable thickness. This method increases the application of nanocellulose films in various industries and satisfies the requirements of large-scale production. In the field of biomedicine, spray-coated free-standing nanocellulose films hold great promise for applications such as drug delivery, tissue engineering, wound healing, device coatings, and biosensing. They are excellent nanomaterials for a variety of biomedical applications due to their special qualities, including biocompatibility, high mechanical strength, porous structure, large surface area, and adaptability. This paper reviewed the detailed exposure of the spray coating process of nanocellulose suspension onto free- standing films and its biomedical applications.展开更多
Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon...Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon stocks in the sacred forests of Bandrefam and Batoufam (western Cameroon). The floristic inventory and the stand structures were carried out in 25 m × 25 m plots for individuals with diameters greater than 10 cm;5 m × 5 m for individuals with diameters less than 10 cm. Carbon stocks were estimated using the non-destructive method and allometric equations. The floristic inventory identified 65 species divided into 57 genera and 30 families in the Bandrefam sacred forest and 45 species divided into 42 genera and 27 families in the Batoufam sacred forest. In the Bandrefam, the most important families are Phyllanthaceae (53.98%), Moraceae (21.69%), Lamiaceae (20.15%). At Batoufam, the most important families are Phyllanthaceae (39.73%), Fabaceae (28.47%), Araliaceae (23.77%). Malacantha alnifolia (55.14%), Vitex grandifolia (18.43%), Bosqueia angolensis (15.06%) were the most important species in Bandrefam. Otherwise, Malacantha alnifolia (28%), Polyscias fulva (22.73%), Psychotria sp. (21.28%) were the most important in Batoufam. The Bandrefam sacred forest has the highest tree density (2669 stems/ha). Total carbon stock is 484.88 ± 2.28 tC/ha at Batoufam and 313.95 ± 0.93 tC/ha at Bandrefam. The economic value varies between 5858.04 ± 27.62 USD/ha in Batoufam sacred forest and 3788.51 ± 11.26 USD/ha in Bandrefam sacred forest. The number of individuals and small-diameter trees has little influence on the carbon stocks in the trees. Medium-diameter trees store the most carbon, and very large-diameter trees, which are very poorly represented, store less carbon. In another way, wood density and the basal areas influence the carbon storage of the trees.展开更多
A growing recognition that uneven-aged silviculture can offer multiple benefits to forested ecosystems has encouraged some landowners in the southern region of the United States to convert even-aged pine stands into m...A growing recognition that uneven-aged silviculture can offer multiple benefits to forested ecosystems has encouraged some landowners in the southern region of the United States to convert even-aged pine stands into multi-aged stands.For shade-intolerant pines of the southern United States,however,few studies have examined residual tree growth following silvicultural treatments that convert even-aged stands to multi-aged stands.Understanding the growth response of residual trees to different kinds of stand conversion treatments is critical to stand development and sustainability,as trees must be recruited into larger size classes during the conversion process to develop the desired stand structure and maintain productivity.In this study,we utilized a replicated,long-term silvicultural experimental trial in the southeastern United States to assess the effects of two cutting treatments(dispersed"single tree cutting"that created small canopy gaps and the"patch cutting"that created 0.1-0.8ha patch openings)and an uncut control on the 14-year growth(~cutting cycle length)of residual longleaf pine(Pinus palustris Mill.)trees.We found that tree growth,measured as mean basal area increment(BAI),was significantly higher following patch cutting(mean BAI of 16.97cm^(2))compared to both the single tree cutting(13.33cm^(2))and the uncut control(12.68cm^(2))(p<0.001).In patch cutting,the size of the patch opening,the location of trees surrounding the patch opening,and the position of the tree canopy all had a significant effect on BAI.Trees surrounding patch openings of 0.4ha exhibited greater growth,with a mean BAI of 19.24cm^(2),compared to those surrounding 0.1 and 0.8ha patch openings,which had mean BAI values of 15.89 and 15.71cm^(2),respectively(p<0.001).The position of a tree around the patch opening also influenced tree growth,as residual trees more to the North,South,and East sides exhibited significantly higher mean BAI than trees on the West side of the patch openings(p<0.001).However,distance from the patch opening border did not significantly affect the mean BAI(p=0.522).In all treatments,dominant and co-dominant trees exhibited higher BAI than intermediate and overtopped trees,indicating that tree canopy position significantly influenced tree growth(p<0.001).Understanding how residual trees grow after these silvicultural treatments is crucial for thoroughly assessing their efficacy with longleaf pine.This study's findings will enhance our understanding of stand dynamics during stand conversion and help land managers anticipate the growth of longleaf pine into larger size categories after single tree and patch cuttings.展开更多
Coastal areas face challenges in updating and enhancing the quality of coastal shelterbelt forests due to limited soil resource utilization,the biological characteristics of tree species,and the impact of coastal stor...Coastal areas face challenges in updating and enhancing the quality of coastal shelterbelt forests due to limited soil resource utilization,the biological characteristics of tree species,and the impact of coastal storm surges.This study,based on clarifying the connotation of stand quality(SQ)for Casuarina equisetifolia(C.equisetifolia),a typical coastal shelterbelt species,integrates stand growth conditions and structure,applying the AHP-EWM method to construct an SQ evaluation model.The model identifies key factors influencing the quality of C.equisetifolia stands and explores the mechanisms driving their growth processes.The results indicate that mean tree height,mean diameter at breast height,and stand density are key indicators for assessing the SQ of C.equisetifolia stands.The SQ of C.equisetifolia coastal shelterbelt stands varies across different land-sea positions,mainly influenced by stand age and soil nutrient levels.As stand age increases,the SQ initially improves and then declines.Additionally,C.equisetifolia trees growing in nutrient-rich soils exhibit better growth and higher SQ than those in poor soils.The findings of this study provide a theoretical foundation for the management and quality enhancement of coastal shelterbelt forests.展开更多
It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities follow...It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities following stand development in natural forests remains unclear,despite the critical roles Collembola plays in litter decomposition and nutrient cycling.We investigated the effects of tree species mixtures on Collembola abundance,diversity,and community structure by sampling pure and mixed jack pine(Pinus banksiana Lamb.)and trembling aspen(Populus tremuloides Michx.)of 15-year-old and 41-year-old stands in natural boreal forest.In total,6,620 individuals of Collembola were identified as belonging to 39 species/morphospecies.Our results showed significant effects of stand types on Collembola with higher abundance and richness in conifer and mixed stands than in broadleaf stands.Additionally,with stand development,we observed increased Collembola abundance and richness.In 15-year-old stands,Collembola abundance,richness,and evenness in mixed-species stands were comparable to those in single-species stands.However,as stands developed,tree mixture effects became more pronounced,resulting in higher Collembola abundance and richness in mixed-species stands compared to the average of single-species stands in 41-year-old stands.Further,we observed positive associations between the mixture effects on Collembola abundance and richness with soil nutrient contents.We conclude that tree species mixtures can significantly enhance Collembola abundance and diversity,particularly in older stands and those with elevated soil nutrient levels.展开更多
In this paper,different stands in Xianzhong Nursery of Pingjiang were selected as the research object to study the runoff generation and soil loss characteristics of different stands.The results showed that the annual...In this paper,different stands in Xianzhong Nursery of Pingjiang were selected as the research object to study the runoff generation and soil loss characteristics of different stands.The results showed that the annual surface runoff of each model in Pingjiang was between 50.50 and 70.38 mm,and the annual surface runoff of each stand decreased with years.There was no significant difference in the annual runoff between each stand,nor between each stand and its control.There were significant differences in soil erosion modulus among the models,and the number ranged from 139.20 to 197.79 t/(km^(2)·y).展开更多
The distance from the river is a crucial factor that affects the structure and function of desert riparian forests,impeding their regeneration and biodiversity due to water conditions.However,few studies have confirme...The distance from the river is a crucial factor that affects the structure and function of desert riparian forests,impeding their regeneration and biodiversity due to water conditions.However,few studies have confirmed the long-term variation in structure and function of this azonal riparian forest type caused by water stress.We hypothesize that a complex and diverse stand structure is associated with the distance from the river,and tree size plays a crucial role in establishing random frameworks for stability in forest stands.Our investigation was conducted in the lower Trim River.Based on long-term observation from 2005 to 2023,both stand structure parameters and diversity index were used.The variation in stand structure was analyzed using the least significant difference,and stand stability was assessed using Gaussian distribution and bivariate regression methods.Our study indicated that there were no significant differences in the response of size differentiation and crowding to distance from the river.However,a significant divergence in spatial pattern was observed at greater distances from the river,which became more pronounced over time.Regardless of the distance from the river or time-scale,there were significant differences in DBH,crown diameter and length.Furthermore,structural diversity exhibited varying trends with distance from the river and time-scale,indicating a diverse and complex pattern in stand structure due to water stress.The proportion of random frameworks for stability is influenced by the distance from the river,and tree size,especially crown diameter and length,plays an important role.Our research examines the multiple relationships among water conditions,forest structure,and function in an arid region,highlighting the significance of water conditions in the natural restoration of desert riparian forest ecosystems.The findings provide new insights for further exploration of the relationship between stand structure and stability,enhancing our understanding of the theory of random frameworks-stability.Overall,the study provides scientific guidance for sustainable forest management and conservation in the context of a changing climate,particularly regarding water stress.展开更多
In this paper,different stands in Dongjiang Lake Reservoir area of Zixing were selected as the research objects,and the runoff generation and soil loss characteristics of different stands were studied.The results show...In this paper,different stands in Dongjiang Lake Reservoir area of Zixing were selected as the research objects,and the runoff generation and soil loss characteristics of different stands were studied.The results showed that the annual surface runoff of each model in Zixing was between 43.24 and 50.99 mm,and there was no significant difference in the annual runoff between each stand and its control.There were significant differences in soil erosion modulus among the models,and the number ranged from 127.37 to 165.58 t/(km 2·y).展开更多
Warm-wet climatic conditions are widely regarded as conducive to remarkable tree growth,alleviating climatic pressures.However,the notable decline in tree growth observed in the southern edge of boreal forests has hei...Warm-wet climatic conditions are widely regarded as conducive to remarkable tree growth,alleviating climatic pressures.However,the notable decline in tree growth observed in the southern edge of boreal forests has heightened concerns over the spatial-temporal dynamics of forest decline.Currently,attaining a comprehensive grasp of the underlying patterns and their propelling factors remains a formidable challenge.We collected tree ring samples from a network of 50 sites across the Greater Xing'an Mountains.These samples were subsequently grouped into two distinct clusters,designated as Groups A and B.The percentage change of growth(GC,%)and the proportion of declining sites were utilized to assess forest decline.The decline in tree growth within Larix gmelinii forests exhibits significant regional variation,accompanied by temporal fluctuations even within a given region.Group A exhibited a pronounced increase in frequency(59.26%)of occurrences and encountered more severe declines(21.65%)in tree growth subsequent to the 1990s,contrasting sharply with Group B,which observed lower frequencies(20.00%)and relatively less severe declines(21.02%)prior to the 1980s.The primary impetus underlying the opposite radial growth increments observed in Larix gmelinii trees from the interplay between their differential response to temperatures and wetter climatic conditions,which is significantly influenced by varying stand densities.In cold-dry conditions,low-density forests may experience soil water freezing,exacerbating drought conditions and thereby inhibiting tree growth,in Group B.Trees growth in high-density stands is restrained by warm-wet conditions,in Group A.These results provide new insights into the variability at the southern edge of the boreal forest biome with different responses to density and climate.展开更多
Neighborhood competition is a critical driver of individual tree growth,and aboveground biomass(AGB)accumulation,which together play key roles in forest dynamics and carbon storage.Therefore,accurate biomass estimatio...Neighborhood competition is a critical driver of individual tree growth,and aboveground biomass(AGB)accumulation,which together play key roles in forest dynamics and carbon storage.Therefore,accurate biomass estimation is essential for understanding ecosystem functioning and informing forest management strategies to mitigate climate change.However,integrating neighborhood competition into biomass estimation models,particularly for young mixed forest stands,remains unexplored.In this study,we examined how incorporating neighborhood competition improves biomass prediction accuracy and how the influence of neighborhood competition differs between Scots pine(Pinus sylvestris L.)and Pyrenean oak(Quercus pyrenaica Willd.),as well as the relative contributions of intra-and interspecific competition to AGB.Our findings revealed that including neighborhood competition alongside tree size variables(DBH and total tree height)significantly improved the predictive accuracy of AGB models for Scots pine.This addition reduced the root mean square error(RMSE)by 14% and improved the model efficiency factor(MEF)by 15%.Furthermore,intraspecific competition in Scots pine slightly reduced AGB,whereas interspecific competition had a significant negative effect on AGB.In contrast,DBH alone was the best predictor of AGB for Pyrenean oak,as neighborhood competition did not improve model performance.Also,intra-and interspecific competition in Pyrenean oak had positive but nonsignificant effects on AGB.These findings highlight the important role of competition in biomass models and suggest species-specific approaches in competition dynamics to inform sustainable forest management and climate change adaptation strategies.展开更多
基金supported by National Key Research and Development Program of China(No.2021YFD2200405(S.R.L.))Natural Science Foundation of China(Grant No.31971653).
文摘With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threats to ecosystem stability.Understanding the current status of forest degradation and assessing potential carbon stocks in China are of strategic importance for making forest restoration efforts and enhancing carbon sequestration capacity.In this study,we used the national forest inventory data from 2009 to 2018 to develop a set of standard measures for assessing degraded forests across China,based on five key indicators:forest accumulation growth rate(FAGR),forest recruitment rate(FRR),tree species reduction rate(TSRR),forest canopy cover reduction rate(FCCRR),and forest disaster level(FDL).Additionally,we estimated standing carbon stock,potential carbon stock,and theoretical space to grow by developing a stand growth model,which accounts for stand density across different site classes,to evaluate the restoration potential of degraded forests.The results indicate that degraded forest area in China is 36.15 million hectares,accounting for 20.10% of a total forest area.Standing carbon stock and potential carbon stock of degraded forests in China are 23.93 million tons and 61.90 million tons,respectively.Overall,degraded forest varies significantly across different regions.The results highlight the important trade-offs among environmental factors,policy decisions,and forest conditions,providing a robust foundation for developing measures to enhance forest quality.
基金supported by the National Natural Science Foundation of China(No.12372005)the Aeronautical Science Foundation of China(No.ASFC-2024Z070050001)the Natural Science Foundation of Liaoning Province(2024-MSBA-32).
文摘In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,turning motion,and turning motion with different radi by the voltage differential driving method.A prototype with a weight of 38 g and dimensions of 150×80×31 mm^(3) was fabricated.Firstly,the dynamics and kinematics of the piezoelectric robot were analyzed to obtain the trajectory of a point at the end of the piezoelectric robot leg.The motion principle of the piezo-electric robot was analyzed,and then the piezoelectric robot's modal analysis and harmonic response analysis were carried out using finite element analysis software.Finally,an experimental setup was built to verify the effectiveness and high efficiency of the robot's motion,and the effects of frequency,voltage,load,and height of the driving leg on the robot's motion performance were discussed.The performance test results show that the piezoelectric robot has a maximum veloc-ity of 66.79 mm/s at an excitation voltage of 320 V and a load capacity of 55 g.In addition,the H-BPR with unequal drive legs has better climbing performance,and the obtained conclusions are informative for selecting leg heights for piezoelectric robots.
基金Supported by the National Key Research and Development Program of China(No.2021 YFC 3101702)the Key R&D Program of Zhejiang(No.2022 C 03044)+2 种基金the Scientific Research Fund of the Second Institute of Oceanography,MNR(No.JG 1521)the Project of State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography(No.SOEDZZ 2202)the National Program on Global Change and Air-Sea Interaction(Phase Ⅱ)-Hypoxia and Acidification Monitoring and Warning Project in the Changjiang River estuary,and Long-term Observation and Research Plan in the Changjiang River estuary and Adjacent East China Sea(LORCE)Project(No.SZ 2001)。
文摘The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limitation,abundant nutrients,and rapid salinity shifts play a crucial role in shaping phytoplankton dynamics.The Qiantang River estuary-Hangzhou Bay(QRE-HZB)is a macrotidal estuary system known for its exceptionally high suspended solids concentration.To investigate the impact of TMZ on the standing crop and size structure of phytoplankton in the QRE-HZB,we conducted three cruises in dry,wet,and dry-to-wet transition seasons during 2022-2023,by assessing parameters including size fractionated chlorophyll a(chl a),turbidity,Secchi depth,temperature,salinity,nutrients,and mesozooplankton.Results reveal significant variations in the TMZ and associated environmental factors in different periods,which markedly influenced the phytoplankton chl-a concentration,size structure,and cell activity(pheophytin/chl a).The chl-a concentration was high with micro-phytoplankton predominance in wet season,while nano-phytoplankton dominated in dry season.Within the TMZ,lower chl-a concentrations and pico-chl-a contributions,alongside higher pheophytin/chl-a and micro-chl-a contributions,were observed.The Spearman’s rank correlation and generalized additive model analyses indicated strong correlations of chl-a concentrations with turbidity,nutrients,and mesozooplankton.Redundancy analysis further revealed that salinity,nutrients,and turbidity significantly regulated variations in size structure.Phytoplankton mortality within the TMZ was primarily driven by high turbidity and salinity fluctuations,reflecting the vigorous resuspension and mixing of freshwater and seawater in the QRE-HZB.These findings highlight that the standing crop and size structure of phytoplankton were strongly regulated by the TMZ and associated physicochemical factors in the macrotidal QRE-HZB.
文摘In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our analysis provides an understanding of the precise spatial localization of atomic positions at the atomic level,utilizing advanced theoretical approaches and principles of quantum mechanics.The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics.A theoretical approach is constructed to describe the interaction between the system and external fields,specifically a control field and a probe field.The absorption spectrum of the probe field is thoroughly examined to clarify the spatial localization of the atom within the proposed configuration.A theoretical investigation found that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain.Specifically,the emergence of one and two sharp localized peaks was observed within a one-wavelength domain.We observed notable influences of the intensity of the control field,probe field detuning and decay rates on atomic localization.Ultimately,we have achieved an unprecedented level of ultrahigh resolution and precision in localizing an atom within an area smaller thanλ/35×λ/35.These findings hold promise for potential applications in fields such as Bose-Einstein condensation,nanolithography,laser cooling,trapping of neutral atoms and the measurement of center-of-mass wave functions.
基金supported by the National Natural Science Foundation of China(Grant No.52271299).
文摘When the free standing riser(FSR)is in service in the ocean,its mechanical properties are affected by various factors,including complex ocean current forces,buoyancy of the buoyancy can,and torque caused by the deflection of the upper floating body.These loads have a great influence on the deformation and internal force of the FSR.The static performance of FSR is investigated in this research under various working conditions.The finite element model of FSR is established based on the co-rotational method.The arc length approach is used to solve the model.The load is exerted in increments.The current load on the riser changes with the configuration of the riser.The accuracy of the numerical method is verified by Abaqus software.The calculation time is also compared.Then,the effects of uniform current,actual current and floating body yaw motion on FSR are studied by parameter analysis.Additionally,the influence of the FSR on the ocean current after the failure of part of the buoyancy can chamber is analyzed.The results show that the numerical model based on the co-rotational method can effectively simulate the large rotation and torsion behavior of FSR.This method has high computational efficiency and precision,and this method can quickly improve the efficiency of numerical calculation of static analysis of deep-water riser.The proposed technology may serve as an alternative to the existing proprietary commercial software,which uses a complex graphical user interface.
文摘Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a great influence on the concentration of nitrite tested by spectrophotometric method. In this context, three kinds of food samples are prepared, including canned mustard, canned fish and home-made pickled water. A series of standing times are placed during the sample pretreatments and the corresponding nitrite contents in these samples are detected by spectrophotometric method based on N-ethylenediamine dihydrochloride. This study aims to find out a reasonable standing time during the pretreatment of food sample, providing influence factor for precise detection of nitrite.
文摘In this paper, we study the existence of standing waves for the nonlinear Schrödinger equation with combined power-type nonlinearities and a partial harmonic potential. In the L<sup>2</sup>-supercritical case, we obtain the existence and stability of standing waves. Our results are complements to the results of Carles and Il’yasov’s artical, where orbital stability of standing waves have been studied for the 2D Schrödinger equation with combined nonlinearities and harmonic potential.
基金supported by the National Natural Science Foundation of China(Grant Nos.52278407 and 52378407)the China Postdoctoral Science Foundation(Grant No.2023M732670)the support by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation.
文摘The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.
文摘Spraying nanocellulose onto films provides a quick and scalable way to create free-standing films with exceptional consistency and customizable thickness. This method increases the application of nanocellulose films in various industries and satisfies the requirements of large-scale production. In the field of biomedicine, spray-coated free-standing nanocellulose films hold great promise for applications such as drug delivery, tissue engineering, wound healing, device coatings, and biosensing. They are excellent nanomaterials for a variety of biomedical applications due to their special qualities, including biocompatibility, high mechanical strength, porous structure, large surface area, and adaptability. This paper reviewed the detailed exposure of the spray coating process of nanocellulose suspension onto free- standing films and its biomedical applications.
文摘Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon stocks in the sacred forests of Bandrefam and Batoufam (western Cameroon). The floristic inventory and the stand structures were carried out in 25 m × 25 m plots for individuals with diameters greater than 10 cm;5 m × 5 m for individuals with diameters less than 10 cm. Carbon stocks were estimated using the non-destructive method and allometric equations. The floristic inventory identified 65 species divided into 57 genera and 30 families in the Bandrefam sacred forest and 45 species divided into 42 genera and 27 families in the Batoufam sacred forest. In the Bandrefam, the most important families are Phyllanthaceae (53.98%), Moraceae (21.69%), Lamiaceae (20.15%). At Batoufam, the most important families are Phyllanthaceae (39.73%), Fabaceae (28.47%), Araliaceae (23.77%). Malacantha alnifolia (55.14%), Vitex grandifolia (18.43%), Bosqueia angolensis (15.06%) were the most important species in Bandrefam. Otherwise, Malacantha alnifolia (28%), Polyscias fulva (22.73%), Psychotria sp. (21.28%) were the most important in Batoufam. The Bandrefam sacred forest has the highest tree density (2669 stems/ha). Total carbon stock is 484.88 ± 2.28 tC/ha at Batoufam and 313.95 ± 0.93 tC/ha at Bandrefam. The economic value varies between 5858.04 ± 27.62 USD/ha in Batoufam sacred forest and 3788.51 ± 11.26 USD/ha in Bandrefam sacred forest. The number of individuals and small-diameter trees has little influence on the carbon stocks in the trees. Medium-diameter trees store the most carbon, and very large-diameter trees, which are very poorly represented, store less carbon. In another way, wood density and the basal areas influence the carbon storage of the trees.
基金The USDA NIFA McIntire Stennis project#1014653 and the University of Florida Institute of Food and Agricultural Sciences funded the research presented in this publication.
文摘A growing recognition that uneven-aged silviculture can offer multiple benefits to forested ecosystems has encouraged some landowners in the southern region of the United States to convert even-aged pine stands into multi-aged stands.For shade-intolerant pines of the southern United States,however,few studies have examined residual tree growth following silvicultural treatments that convert even-aged stands to multi-aged stands.Understanding the growth response of residual trees to different kinds of stand conversion treatments is critical to stand development and sustainability,as trees must be recruited into larger size classes during the conversion process to develop the desired stand structure and maintain productivity.In this study,we utilized a replicated,long-term silvicultural experimental trial in the southeastern United States to assess the effects of two cutting treatments(dispersed"single tree cutting"that created small canopy gaps and the"patch cutting"that created 0.1-0.8ha patch openings)and an uncut control on the 14-year growth(~cutting cycle length)of residual longleaf pine(Pinus palustris Mill.)trees.We found that tree growth,measured as mean basal area increment(BAI),was significantly higher following patch cutting(mean BAI of 16.97cm^(2))compared to both the single tree cutting(13.33cm^(2))and the uncut control(12.68cm^(2))(p<0.001).In patch cutting,the size of the patch opening,the location of trees surrounding the patch opening,and the position of the tree canopy all had a significant effect on BAI.Trees surrounding patch openings of 0.4ha exhibited greater growth,with a mean BAI of 19.24cm^(2),compared to those surrounding 0.1 and 0.8ha patch openings,which had mean BAI values of 15.89 and 15.71cm^(2),respectively(p<0.001).The position of a tree around the patch opening also influenced tree growth,as residual trees more to the North,South,and East sides exhibited significantly higher mean BAI than trees on the West side of the patch openings(p<0.001).However,distance from the patch opening border did not significantly affect the mean BAI(p=0.522).In all treatments,dominant and co-dominant trees exhibited higher BAI than intermediate and overtopped trees,indicating that tree canopy position significantly influenced tree growth(p<0.001).Understanding how residual trees grow after these silvicultural treatments is crucial for thoroughly assessing their efficacy with longleaf pine.This study's findings will enhance our understanding of stand dynamics during stand conversion and help land managers anticipate the growth of longleaf pine into larger size categories after single tree and patch cuttings.
基金supported by the Fujian Forestry Science and Technology Research Project(2023FKJ15)Fuzhou Forestry Science and Technology Research Project(2130206)+1 种基金Special Fund Project for Scientific and Technological Innovation of Fujian Agriculture and Forestry University(KFB23173)University Key Lab for Geomatics Technology&Optimize Resources Utilization in Fujian Province(KJG20104A).
文摘Coastal areas face challenges in updating and enhancing the quality of coastal shelterbelt forests due to limited soil resource utilization,the biological characteristics of tree species,and the impact of coastal storm surges.This study,based on clarifying the connotation of stand quality(SQ)for Casuarina equisetifolia(C.equisetifolia),a typical coastal shelterbelt species,integrates stand growth conditions and structure,applying the AHP-EWM method to construct an SQ evaluation model.The model identifies key factors influencing the quality of C.equisetifolia stands and explores the mechanisms driving their growth processes.The results indicate that mean tree height,mean diameter at breast height,and stand density are key indicators for assessing the SQ of C.equisetifolia stands.The SQ of C.equisetifolia coastal shelterbelt stands varies across different land-sea positions,mainly influenced by stand age and soil nutrient levels.As stand age increases,the SQ initially improves and then declines.Additionally,C.equisetifolia trees growing in nutrient-rich soils exhibit better growth and higher SQ than those in poor soils.The findings of this study provide a theoretical foundation for the management and quality enhancement of coastal shelterbelt forests.
基金support from the National Natural Science Foundation of China(NSFC)for the Excellent Young Scientists Fund(overseas)and NSFC Grant(No.32401546)the Scientific Research Startup Fund Project of Zhejiang A&F University(Grant No.2024LFR019)the Natural Sciences and Engineering Research Council of Canada(RGPIN-2014-04181,STPGP428641,RTI-2017-00358,and STPGP506284).
文摘It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities following stand development in natural forests remains unclear,despite the critical roles Collembola plays in litter decomposition and nutrient cycling.We investigated the effects of tree species mixtures on Collembola abundance,diversity,and community structure by sampling pure and mixed jack pine(Pinus banksiana Lamb.)and trembling aspen(Populus tremuloides Michx.)of 15-year-old and 41-year-old stands in natural boreal forest.In total,6,620 individuals of Collembola were identified as belonging to 39 species/morphospecies.Our results showed significant effects of stand types on Collembola with higher abundance and richness in conifer and mixed stands than in broadleaf stands.Additionally,with stand development,we observed increased Collembola abundance and richness.In 15-year-old stands,Collembola abundance,richness,and evenness in mixed-species stands were comparable to those in single-species stands.However,as stands developed,tree mixture effects became more pronounced,resulting in higher Collembola abundance and richness in mixed-species stands compared to the average of single-species stands in 41-year-old stands.Further,we observed positive associations between the mixture effects on Collembola abundance and richness with soil nutrient contents.We conclude that tree species mixtures can significantly enhance Collembola abundance and diversity,particularly in older stands and those with elevated soil nutrient levels.
基金Supported by Hunan Forestry Science and Technology Plan(OT-S-KTA5,2024YBC15)Science and Technology Plan of Hunan Province(2021SFQ19).
文摘In this paper,different stands in Xianzhong Nursery of Pingjiang were selected as the research object to study the runoff generation and soil loss characteristics of different stands.The results showed that the annual surface runoff of each model in Pingjiang was between 50.50 and 70.38 mm,and the annual surface runoff of each stand decreased with years.There was no significant difference in the annual runoff between each stand,nor between each stand and its control.There were significant differences in soil erosion modulus among the models,and the number ranged from 139.20 to 197.79 t/(km^(2)·y).
基金supported by the Third Xinjiang Scientific Expedition and Research Program of the Ministry of Science&Technology of China(Grant No:2022xjkk0300)National Science Foundation of China(Grant No:32260285)+1 种基金Graduate Research Innovation Project of the Xinjiang Uygur Autonomous Region(Grant No:XJ2024G049)Excellent Doctoral Innovation Program of Xinjiang University(Grant No:XJU2024BS121).
文摘The distance from the river is a crucial factor that affects the structure and function of desert riparian forests,impeding their regeneration and biodiversity due to water conditions.However,few studies have confirmed the long-term variation in structure and function of this azonal riparian forest type caused by water stress.We hypothesize that a complex and diverse stand structure is associated with the distance from the river,and tree size plays a crucial role in establishing random frameworks for stability in forest stands.Our investigation was conducted in the lower Trim River.Based on long-term observation from 2005 to 2023,both stand structure parameters and diversity index were used.The variation in stand structure was analyzed using the least significant difference,and stand stability was assessed using Gaussian distribution and bivariate regression methods.Our study indicated that there were no significant differences in the response of size differentiation and crowding to distance from the river.However,a significant divergence in spatial pattern was observed at greater distances from the river,which became more pronounced over time.Regardless of the distance from the river or time-scale,there were significant differences in DBH,crown diameter and length.Furthermore,structural diversity exhibited varying trends with distance from the river and time-scale,indicating a diverse and complex pattern in stand structure due to water stress.The proportion of random frameworks for stability is influenced by the distance from the river,and tree size,especially crown diameter and length,plays an important role.Our research examines the multiple relationships among water conditions,forest structure,and function in an arid region,highlighting the significance of water conditions in the natural restoration of desert riparian forest ecosystems.The findings provide new insights for further exploration of the relationship between stand structure and stability,enhancing our understanding of the theory of random frameworks-stability.Overall,the study provides scientific guidance for sustainable forest management and conservation in the context of a changing climate,particularly regarding water stress.
基金Supported by Science and Technology Plan of Hunan Province(2021SFQ19)Hunan Forestry Science and Technology Plan(OT-S-KTA5,2024YBC15).
文摘In this paper,different stands in Dongjiang Lake Reservoir area of Zixing were selected as the research objects,and the runoff generation and soil loss characteristics of different stands were studied.The results showed that the annual surface runoff of each model in Zixing was between 43.24 and 50.99 mm,and there was no significant difference in the annual runoff between each stand and its control.There were significant differences in soil erosion modulus among the models,and the number ranged from 127.37 to 165.58 t/(km 2·y).
基金National Nature Science Foundation of China(No.32371871)。
文摘Warm-wet climatic conditions are widely regarded as conducive to remarkable tree growth,alleviating climatic pressures.However,the notable decline in tree growth observed in the southern edge of boreal forests has heightened concerns over the spatial-temporal dynamics of forest decline.Currently,attaining a comprehensive grasp of the underlying patterns and their propelling factors remains a formidable challenge.We collected tree ring samples from a network of 50 sites across the Greater Xing'an Mountains.These samples were subsequently grouped into two distinct clusters,designated as Groups A and B.The percentage change of growth(GC,%)and the proportion of declining sites were utilized to assess forest decline.The decline in tree growth within Larix gmelinii forests exhibits significant regional variation,accompanied by temporal fluctuations even within a given region.Group A exhibited a pronounced increase in frequency(59.26%)of occurrences and encountered more severe declines(21.65%)in tree growth subsequent to the 1990s,contrasting sharply with Group B,which observed lower frequencies(20.00%)and relatively less severe declines(21.02%)prior to the 1980s.The primary impetus underlying the opposite radial growth increments observed in Larix gmelinii trees from the interplay between their differential response to temperatures and wetter climatic conditions,which is significantly influenced by varying stand densities.In cold-dry conditions,low-density forests may experience soil water freezing,exacerbating drought conditions and thereby inhibiting tree growth,in Group B.Trees growth in high-density stands is restrained by warm-wet conditions,in Group A.These results provide new insights into the variability at the southern edge of the boreal forest biome with different responses to density and climate.
基金the 2019 call for the predoctoral contract at the University of Valladolid cofinanced by Banco de Santander and projects‘CLU-2019-01-Unidad de Excelencia Instituto iuFOR’,‘PID2021-126275OB-C21’and‘PID2021-126275OB-C22’-Integrated Forest Management along complexity gradients(IMFLEX)‘MCIN/AEI/10.13039/501100011033/FEDER,UE’,which received financial support from the Regional Government of Castilla and León,Spainthe European Regional Development Fund(ERDF).
文摘Neighborhood competition is a critical driver of individual tree growth,and aboveground biomass(AGB)accumulation,which together play key roles in forest dynamics and carbon storage.Therefore,accurate biomass estimation is essential for understanding ecosystem functioning and informing forest management strategies to mitigate climate change.However,integrating neighborhood competition into biomass estimation models,particularly for young mixed forest stands,remains unexplored.In this study,we examined how incorporating neighborhood competition improves biomass prediction accuracy and how the influence of neighborhood competition differs between Scots pine(Pinus sylvestris L.)and Pyrenean oak(Quercus pyrenaica Willd.),as well as the relative contributions of intra-and interspecific competition to AGB.Our findings revealed that including neighborhood competition alongside tree size variables(DBH and total tree height)significantly improved the predictive accuracy of AGB models for Scots pine.This addition reduced the root mean square error(RMSE)by 14% and improved the model efficiency factor(MEF)by 15%.Furthermore,intraspecific competition in Scots pine slightly reduced AGB,whereas interspecific competition had a significant negative effect on AGB.In contrast,DBH alone was the best predictor of AGB for Pyrenean oak,as neighborhood competition did not improve model performance.Also,intra-and interspecific competition in Pyrenean oak had positive but nonsignificant effects on AGB.These findings highlight the important role of competition in biomass models and suggest species-specific approaches in competition dynamics to inform sustainable forest management and climate change adaptation strategies.
