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
A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration character...A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.展开更多
The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section ...The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.展开更多
In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are dis...In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are discussed ; a formula of maximum depth of scouring trough considering sediment size is given; and influence of mound foundation on bottom scours is investigated.展开更多
Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which ca...Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which can be used to calculate the wave particle velocity and wave pressure, is suitable to the complicated topography whose relative depth (d/lambda(0), ratio of the characteristic water depth to the characteristic wavelength in deep-water) is equal to or smaller than one. The governing equations are discretized with the improved 2-D Crank-Nicolson method in which the first-order derivatives are corrected by Taylor series expansion, And the general boundary conditions with an arbitrary reflection coefficient and phase shift are adopted in the model. The surface elevation, horizontal and vertical velocity components and wave pressure of standing waves are numerically calculated. The results show that the numerical model can effectively simulate the complicated standing waves, and the general boundary conditions possess good adaptability.展开更多
For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. ...For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. In this paper, a coupling calculation is carried out based on a practical model for the loop antenna. The ion cyclotron wave coupling performance depends greatly on the antenna current propagation constant and the phase of standing wave. For a small antenna-current-propagation constant, the antenna coupling performance is more sensitive to a π/2 change in the phase of standing wave.展开更多
The standing stock of phytoplankton (phy. ) and primary productivity (pp) in the Xiangshan Bay were observed in 1992. The results showed higher biological parameters in the bay. The average chlorophyll a (chl a) con...The standing stock of phytoplankton (phy. ) and primary productivity (pp) in the Xiangshan Bay were observed in 1992. The results showed higher biological parameters in the bay. The average chlorophyll a (chl a) concentration was (3. 50 5. 93 ) mg/m3 and the primary productivity (444. 5 871. 0) mg/(m2 d). The distribution of chl a and productivity showed distinct spatial and temporal patterns in the bay. The continent influence was Obvious at the top of the bay, lower seawater exchange and higher stability led to higher standing stock of phytoplankton and productivity. At the bay mouth, seawater exchanged continuously with adjacent waters by rapid currents, resulting in fast and unstable exchange and lower standing stock of phytoplankton and primary productivity. The seasonal characters of those parameters were pronounced, in the sequence of spring, summer, autumn and winter. The results of size--fractionated showed that the average contribution of the nano--and picoplankton (< 20pm) to total chl a and productivity were 75 % and 87%, respectively, indicating their importance in phytoplankton community biomass and productivity of the Xiangshan Bay.展开更多
Background: Although the standing long jump (SLJ) is a popular physical fitness assessment, it lacks an updated criterion-reference standard. This study generated the first normative SLJ test data for Chinese aged 8 -...Background: Although the standing long jump (SLJ) is a popular physical fitness assessment, it lacks an updated criterion-reference standard. This study generated the first normative SLJ test data for Chinese aged 8 - 18. Methods: From September 2005 to December 2011, comprehensive physical fitness assessments were conducted on 12,712 school students. The SLJ performances were significantly different between boys and girls (all age groups, p < 0.01). Results: The boys performed better than the girls in each age group. The mean difference increased as the age increased, depicting a prominent variance in muscular strength between boys and girls at age 12, and the variances became larger at age 18. Girls in the 70th percenttile performed similarly to boys performing in the 10th percentile. The onset of muscle strength for boys found in this study corresponded to the onset age of testosterone maturation of Chinese boys investigated in previous studies. Linear regression found age and BMI predicting SLJ significantly for boys and girls, explaining better SLJ results in older boy and the effect of their heavy body size. Conclusions: This study indicated a muscular strength difference between genders during growth and added supporting evidence to the hormonal influence of muscle growth during puberty.展开更多
Considerable irreversible capacity loss was observed after the electrode standing at small state-of-charge （SOC） for only a short term. Influence of SOC, standing time and the replacement elements of LaNis-type hydr...Considerable irreversible capacity loss was observed after the electrode standing at small state-of-charge （SOC） for only a short term. Influence of SOC, standing time and the replacement elements of LaNis-type hydrogen storage alloys to standing was discussed. Charge-transfer resistance, exchange current density （I0）, and hydrogen diffusion coefficient were determined based on the study of electrochemical impedance spectrum （EIS）, linear polarization （LP） and constant potential step （CPS）, respectively. The oxi- dation of metal Ni on the alloy surface after standing was responsible for the rapid deterioration of capacity, charge-transfer resistance and I0. Galvanostatic, LP, EIS and CPS measurements suggested the presence of an oxide and/or corrosion layer on the alloy surface of raw material and electrode after standing at 0% SOC for 2 d. It was proved that the first small semicircle in high-frequency region of EIS was related to this layer. Novel EIS model in metal hydride electrode was proposed accordingly.展开更多
It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of...It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of standing waves for ultrasonic purification of magnesium alloy melt,numerical simulation and relevant experiment were carried out.The numerical simulation was broken into two main aspects.On one hand,the ultrasonic field propagations within the cells with various shapes were characterized by numerical solutions of the wave equation and with a careful choice of geometry a nearly idealized standing wave field was finally obtained.On the other hand,within such a standing wave field the agglomeration behavior of oxidation inclusions in magnesium alloy melt was analyzed and discussed.The agglomeration time and agglomeration position of oxidation inclusions were predicted with numerical simulation method.The results show that the oxidation inclusions whose apparent densities are close to the density of the melt can agglomerate at wave nodes in a short time which to a great extent enhances and accelerates the separation of oxidation inclusions from magnesium alloy melt.展开更多
Asymptotic solutions up to third-order which describe irrotational finite amplitude standing waves are derived in Lagrangian coordinates. The analytical Lagrangian solution that is uniformly valid for large times sati...Asymptotic solutions up to third-order which describe irrotational finite amplitude standing waves are derived in Lagrangian coordinates. The analytical Lagrangian solution that is uniformly valid for large times satisfies the irrotational condition and the pressure p = 0 at the free surface, which is in contrast with the Eulerian solution existing under a residual pressure at the free surface due to Taylor＇s series expansion. In the third-order Lagrangian approximation, the explicit parametric equation and the Lagrangian wave frequency of water particles could be obtained. In particular, the Lagrangian mean level of a particle motion that is a function of vertical label is found as a part of the solution which is different from that in an Eulerian description. The dynamic properties of nonlinear standing waves in water of a finite depth, including particle trajectory, surface profile and wave pressure are investigated. It is also shown that the Lagrangian solution is superior to an Eulerian solution of the same order for describing the wave shape and the kinematics above the mean water level.展开更多
We study the existence and stability of the standing waves of two coupled SchrSdinger equations with potentials ｜x｜bi（bi ∈ R,i = 1, 2）. Under suitable conditions on the growth of the nonlinear terms, we first est...We study the existence and stability of the standing waves of two coupled SchrSdinger equations with potentials ｜x｜bi（bi ∈ R,i = 1, 2）. Under suitable conditions on the growth of the nonlinear terms, we first establish the existence of standing waves of the SchrSdinger system by solving a L2-normalized minimization problem, then prove that the set of all minimizers of this minimization problem is stable. Finally, we obtain the least energy solutions by the Nehari method and prove that the orbit sets of these least energy solutions are unstable, which generalizes the results of [11] where b1 = b2 = 2.展开更多
Vertically standing graphene（VSG） sheets have been fabricated by using plasma enhanced chemical vapor deposition（PECVD） method.The lateral size of VSG nanosheets could be well controlled by varying the substrate t...Vertically standing graphene（VSG） sheets have been fabricated by using plasma enhanced chemical vapor deposition（PECVD） method.The lateral size of VSG nanosheets could be well controlled by varying the substrate temperature.The higher temperature usually gives rise to a smaller sheet size.The wettability of VSG films was tuned between hydrophobicity and hydrophilicity by means of oxygen and hydrogen plasma treatment.The supercapacitor electrode made of VSG sheets exhibited an ideal double-layer-capacitor feature and the specific capacitance reached a value up to 9.62 F·m^（-2）.展开更多
Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach ...Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number.Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge(upper limit)to the angle that a Chapman-Jouguet(CJ)detonation occurs(lower limit).For pathological detonation cases,however,the CJ detonation cannot be achieved,and thus the lower limit of the standing window of ODW should be revisited.In present study,two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation,that is,the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process,have been used for studying standing behavior of ODW.The steady detonation polar analysis of ODW is carried out for both reaction systems.The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW.Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics,Mach number of incoming flow and heat effect of reactions.It is found that the standing window of ODW is determined by the specific heat ratio,the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow,regardless of whether the detonation is pathological or not.展开更多
This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large ruptur...This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.展开更多
Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstan...Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.展开更多
In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a ...In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra-low-frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward-moving auroral arcs near the spacecraft footprints. Here we present the first observational evidence from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all-sky imager to support the scenario that standing hydromagnetic waves can generate the quasi-periodic appearance of poleward-moving auroral arcs. In this specific event, the observed waves were toroidal branches of the standing hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground-based optical data.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Funded by the National Basic Research Program (973 program) (No. 2011CB707602)the Digital Manufacturing Equipment and Technology National Key Laboratory,Huazhong University of Science and Technology (No. DMETKF2009002)National Sciences Foundation-Guangdong Natural Science Foundation,China (No.U0934004)
文摘A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.
文摘The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.
文摘In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are discussed ; a formula of maximum depth of scouring trough considering sediment size is given; and influence of mound foundation on bottom scours is investigated.
基金This subject was partly supported by the National Excellent Youth Foundation of China (Grant No. 49825161)
文摘Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which can be used to calculate the wave particle velocity and wave pressure, is suitable to the complicated topography whose relative depth (d/lambda(0), ratio of the characteristic water depth to the characteristic wavelength in deep-water) is equal to or smaller than one. The governing equations are discretized with the improved 2-D Crank-Nicolson method in which the first-order derivatives are corrected by Taylor series expansion, And the general boundary conditions with an arbitrary reflection coefficient and phase shift are adopted in the model. The surface elevation, horizontal and vertical velocity components and wave pressure of standing waves are numerically calculated. The results show that the numerical model can effectively simulate the complicated standing waves, and the general boundary conditions possess good adaptability.
文摘For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. In this paper, a coupling calculation is carried out based on a practical model for the loop antenna. The ion cyclotron wave coupling performance depends greatly on the antenna current propagation constant and the phase of standing wave. For a small antenna-current-propagation constant, the antenna coupling performance is more sensitive to a π/2 change in the phase of standing wave.
基金Zhejiang Natural Scientific Foundation of China under contract! No. 394014.
文摘The standing stock of phytoplankton (phy. ) and primary productivity (pp) in the Xiangshan Bay were observed in 1992. The results showed higher biological parameters in the bay. The average chlorophyll a (chl a) concentration was (3. 50 5. 93 ) mg/m3 and the primary productivity (444. 5 871. 0) mg/(m2 d). The distribution of chl a and productivity showed distinct spatial and temporal patterns in the bay. The continent influence was Obvious at the top of the bay, lower seawater exchange and higher stability led to higher standing stock of phytoplankton and productivity. At the bay mouth, seawater exchanged continuously with adjacent waters by rapid currents, resulting in fast and unstable exchange and lower standing stock of phytoplankton and primary productivity. The seasonal characters of those parameters were pronounced, in the sequence of spring, summer, autumn and winter. The results of size--fractionated showed that the average contribution of the nano--and picoplankton (< 20pm) to total chl a and productivity were 75 % and 87%, respectively, indicating their importance in phytoplankton community biomass and productivity of the Xiangshan Bay.
文摘Background: Although the standing long jump (SLJ) is a popular physical fitness assessment, it lacks an updated criterion-reference standard. This study generated the first normative SLJ test data for Chinese aged 8 - 18. Methods: From September 2005 to December 2011, comprehensive physical fitness assessments were conducted on 12,712 school students. The SLJ performances were significantly different between boys and girls (all age groups, p < 0.01). Results: The boys performed better than the girls in each age group. The mean difference increased as the age increased, depicting a prominent variance in muscular strength between boys and girls at age 12, and the variances became larger at age 18. Girls in the 70th percenttile performed similarly to boys performing in the 10th percentile. The onset of muscle strength for boys found in this study corresponded to the onset age of testosterone maturation of Chinese boys investigated in previous studies. Linear regression found age and BMI predicting SLJ significantly for boys and girls, explaining better SLJ results in older boy and the effect of their heavy body size. Conclusions: This study indicated a muscular strength difference between genders during growth and added supporting evidence to the hormonal influence of muscle growth during puberty.
基金supported by the National High Technology Research and Development Program of China (863 Program, 2011AA03A408)
文摘Considerable irreversible capacity loss was observed after the electrode standing at small state-of-charge （SOC） for only a short term. Influence of SOC, standing time and the replacement elements of LaNis-type hydrogen storage alloys to standing was discussed. Charge-transfer resistance, exchange current density （I0）, and hydrogen diffusion coefficient were determined based on the study of electrochemical impedance spectrum （EIS）, linear polarization （LP） and constant potential step （CPS）, respectively. The oxi- dation of metal Ni on the alloy surface after standing was responsible for the rapid deterioration of capacity, charge-transfer resistance and I0. Galvanostatic, LP, EIS and CPS measurements suggested the presence of an oxide and/or corrosion layer on the alloy surface of raw material and electrode after standing at 0% SOC for 2 d. It was proved that the first small semicircle in high-frequency region of EIS was related to this layer. Novel EIS model in metal hydride electrode was proposed accordingly.
基金Projects(2007CB613701,2007CB613702)supported by the National Basic Research Program of ChinaProjects(50974037,50904018)supported by the National Natural Science Foundation of ChinaProject(NCET-08-0098)supported by the Program for New Century Excellent Talents in University of China
文摘It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of standing waves for ultrasonic purification of magnesium alloy melt,numerical simulation and relevant experiment were carried out.The numerical simulation was broken into two main aspects.On one hand,the ultrasonic field propagations within the cells with various shapes were characterized by numerical solutions of the wave equation and with a careful choice of geometry a nearly idealized standing wave field was finally obtained.On the other hand,within such a standing wave field the agglomeration behavior of oxidation inclusions in magnesium alloy melt was analyzed and discussed.The agglomeration time and agglomeration position of oxidation inclusions were predicted with numerical simulation method.The results show that the oxidation inclusions whose apparent densities are close to the density of the melt can agglomerate at wave nodes in a short time which to a great extent enhances and accelerates the separation of oxidation inclusions from magnesium alloy melt.
文摘Asymptotic solutions up to third-order which describe irrotational finite amplitude standing waves are derived in Lagrangian coordinates. The analytical Lagrangian solution that is uniformly valid for large times satisfies the irrotational condition and the pressure p = 0 at the free surface, which is in contrast with the Eulerian solution existing under a residual pressure at the free surface due to Taylor＇s series expansion. In the third-order Lagrangian approximation, the explicit parametric equation and the Lagrangian wave frequency of water particles could be obtained. In particular, the Lagrangian mean level of a particle motion that is a function of vertical label is found as a part of the solution which is different from that in an Eulerian description. The dynamic properties of nonlinear standing waves in water of a finite depth, including particle trajectory, surface profile and wave pressure are investigated. It is also shown that the Lagrangian solution is superior to an Eulerian solution of the same order for describing the wave shape and the kinematics above the mean water level.
基金supported by NSFC(11471331,11101418 and 11271360)
文摘We study the existence and stability of the standing waves of two coupled SchrSdinger equations with potentials ｜x｜bi（bi ∈ R,i = 1, 2）. Under suitable conditions on the growth of the nonlinear terms, we first establish the existence of standing waves of the SchrSdinger system by solving a L2-normalized minimization problem, then prove that the set of all minimizers of this minimization problem is stable. Finally, we obtain the least energy solutions by the Nehari method and prove that the orbit sets of these least energy solutions are unstable, which generalizes the results of [11] where b1 = b2 = 2.
基金Project supported by the National Basic Research Program of China(Grant No.2013CBA01603)the National Natural Science Foundation of China(Grant No.61335006)the Chinese Academy of Sciences(Grant Nos.1731300500015 and XDB07030100)
文摘Vertically standing graphene（VSG） sheets have been fabricated by using plasma enhanced chemical vapor deposition（PECVD） method.The lateral size of VSG nanosheets could be well controlled by varying the substrate temperature.The higher temperature usually gives rise to a smaller sheet size.The wettability of VSG films was tuned between hydrophobicity and hydrophilicity by means of oxygen and hydrogen plasma treatment.The supercapacitor electrode made of VSG sheets exhibited an ideal double-layer-capacitor feature and the specific capacitance reached a value up to 9.62 F·m^（-2）.
基金co-supported by the National Natural Science Foundation of China(No.11872213)the Open Fund of Key Laboratory of Transient Physics,NJUST(No.6142604180205)the Opening Project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology)(No.KFJJ17-11M)。
文摘Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number.Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge(upper limit)to the angle that a Chapman-Jouguet(CJ)detonation occurs(lower limit).For pathological detonation cases,however,the CJ detonation cannot be achieved,and thus the lower limit of the standing window of ODW should be revisited.In present study,two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation,that is,the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process,have been used for studying standing behavior of ODW.The steady detonation polar analysis of ODW is carried out for both reaction systems.The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW.Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics,Mach number of incoming flow and heat effect of reactions.It is found that the standing window of ODW is determined by the specific heat ratio,the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow,regardless of whether the detonation is pathological or not.
基金supported by the Australia government through the Australian Research Council’s Industrial Transformation Research Hub for nanoscience based construction material manufacturing(IH150100006)the Australia Coal Industry’s Research Program(C28068)。
文摘This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.
基金supported by the National Key R&D Program of China(No.2017YFE0301201)National Natural Science Foundation of China(No.11975038)the funding support from the State Key Laboratory of Nuclear Physics and Technology,Peking University(No.NPT2021ZZ03)。
文摘Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.
基金supported by the National Natural Science Foundation of China (grant numbers 41774168 and 41421003)
文摘In Earth's high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi-periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra-low-frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward-moving auroral arcs near the spacecraft footprints. Here we present the first observational evidence from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all-sky imager to support the scenario that standing hydromagnetic waves can generate the quasi-periodic appearance of poleward-moving auroral arcs. In this specific event, the observed waves were toroidal branches of the standing hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground-based optical data.
