mlsa-iai-msu-lab/ru_sci_bench_zho_cite_reranking huggingface dataset:
Improving the hydrodynamic performance of the SUBOFF bare hull model: a CFD approach

The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle (AUV), calculate its hydrodynamic coefficients, and consider the flow characteristics of underwater bodies. In addition, three important parts of the SUBOFF bare hull, namely the main body, nose, and tail, are modified and redesigned to improve its hydro-dynamic performance. A three-dimensional (3D) simulation is carried out using the computational fluid dynamics (CFD) method. To simulate turbulence, the k-ω shear stress transport (SST) model is employed, due to its good prediction capability at reasonable computational cost. Considering the effects of the length-to-diameter ratio (LTDR) and the nose and tail shapes on the hydrodynamic coefficients, it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model. The final proposed model shows lower drag by about 14.9% at u = 1.5 m·s~(-1). Moreover, it produces 8 times more lift than the SUBOFF model at u = 6.1 m·s~(-1). These effects are due to the attachment of the fluid flow at the tail area of the hull, which weakens the wake region.
Development of land use transitions research in China

With the introduction of the concept of land use transition into China, related researches have been carried out extensively in the past two decades, which enrich the knowledge of land system science. This paper describes the development of research on land use transitions in China from the perspectives of conceptual connotations, theoretical model, research methods, and research progress and prospects. With the in-depth investigation of land use transitions, the concept and connotations of land use morphology are developed and encapsulated as two kinds, i.e., dominant morphology and recessive morphology. The dominant morphology refers to the land use structure of a certain region over a certain period of time, with features such as the quantity and spatial pattern of land use types. While the recessive morphology includes the land use features in the aspects of quality, property rights, management mode, input, output and function. Accordingly, the concept of land use transition is further developed, and the theoretical model of regional land use transitions is established. Thereafter, three innovative integrated approaches to study land use transitions are put forward, i.e., multidisciplinary research framework for recessive land use transition, transect and horizontal comparison. To date, there have been 62 Ph.D. and 166 M.S. dissertations on the topic of “land use transition” in China. During 2002-2019, the National Natural Science Foundation of China has funded 48 research programs on the theme of “land use transition”. As such, the Chinese scholars have adapted the concept derived from western literature to the situations and experiences in China.
Accumulation phenomena in fluvial processes and the corresponding stochastic model

Accumulation occurs widely in fluvial processes. Accurately accounting for the effects of previous water and sediment conditions on accumulation is essential for studying riverbed evolution. In this study, to reveal the physical mechanisms of accumulation, various geometric observations of both the upstream and downstream reaches of dams on several typical fluvial channels were analyzed. The changes in water and sediment conditions were defined as external disturbances. Assuming that the probability of an external disturbance conforms to a Poisson distribution, and that the response intensity induced by an individual disturbance decays exponentially over time, a mathematical description of the accumulation of internal responses to external disturbances is given. Furthermore, a corresponding theoretical model for simulating the spatiotemporal readjustments of characteristic river variables is proposed based on stochastic theory. The proposed models are then applied to investigate spatiotemporal readjustment in the upper and lower reaches of dams following their construction. The results indicate that temporally, the vertical, lateral, and overall readjustment rates of the reaches are relatively fast in the early period following dam construction but then decrease rapidly over time. Accumulated riverbed degradation, channel width, and sedimentation continuously increase until a new dynamic equilibrium is reached. These phenomena reflect the representative accumulation characteristics of fluvial processes. Spatially, the erosion intensities in downstream reaches decrease nonlinearly along the channel until eventually diminishing. The unbalanced spatial distribution of erosion intensity arises from the system response characterized by propagation in space but decay over time, which is characteristic of accumulation phenomena after disturbances. The results of the developed model show that the spatiotemporal readjustments of the studied cross-sections and channel reaches can be accurately described by the unified theoretical formula derived herein. The model predictions show good agreement with observed field data with determination coefficients of 0.92, 0.93, 0.76, and 0.95 for vertical, lateral, longitudinal, and overall readjustments, respectively. The proposed theoretical models account for both the accumulation characteristics of fluvial processes and their spatial distributions. In demonstrating the proposed approach, this study provides a theoretical basis and new calculation method for quantitatively describing the spatiotemporal readjustments of non-equilibrium fluvial channels following external disturbances.
Colonization of Bacillus cereus NJSZ-13, a species with nematicidal activity in Masson pine (Pinus massoniana Lamb.)

Bacillus cereus NJSZ-13, an endophytic bacterium with nematicidal activity, was isolated from stems of healthy Pinus elliottii Engelm. Colonization of P. massoniana Lamb. by endophytic B. cereus was studied using scanning electron microscopy and confocal laser scanning microscopy. After the plasmid pGFP78 containing the green fluorescent protein (GFP) gene was transformed into the NJSZ-13 strain, the NJSZ-13:gfp showed the same nematicidal activity and growth curve as the wild-type strain, and the plasmid pGFP78 was stably maintained in strain NJSZ-13 for at least 96 h of bacterial cultivation on medium without antibiotics. After inoculation into Masson pine roots, colonization of the NJSZ-13:gfp strain in plant roots and stems was visualized using confocal laser scanning and the strain was enumerated in inoculated roots and stems. These results suggest that NJSZ-13:gfp is an efficient colonizer of Masson pine and can transfer vertically from roots to stems.
Simple phenols in tropical woods determined by UHPLC-PDA and their antioxidant capacities: an experimental design for Randall extraction using environmentally friendly solvents

A comprehensive experimental design was developed to determine suitable conditions (volume, percentage of solvent, extraction temperature) for the ethanol extraction of phenolic compounds from ten tropical woody plants. Wenge, angelim vermelho, zebrano, merbau, tigerwood, angelim pedra, jatoba, angelim amargoso, massaranduba, and doussie woods were used in experiments. The effects of three independent variables and their interactions on the yields of cinnamic and benzoic acid derivates were analyzed using UHPLC-PDA. The most significant parameters were found to be solvent percentage, extraction volume, and extraction temperature. Optimal conditions for the extraction of phenolic compound contents were an 80 ℃ extraction temperature, a 30 mL extraction volume, and the use of pure water as the extraction solvent. The tested species of woods contained mainly cinnamic acid derivates. Water extracts after hydrolysis contained greater amounts of cinnamic acid derivates than those extracts from non-hydrolyzed material. The total phenolics content was highest in water extracts of tigerwood, wenge and merbau; however, the extract of merbau wood was a stronger radical scavenger in ABTS+ assays: 34.11 ± 0.02 mM Trolox equivalents per g of dry extract. The main compounds possessing antioxidant activity in the extracts of vermelho wood assessed by UHPLC analysis were hydroxycinnamic acids.
Comparison of seed morphology of two ginkgo cultivars

Ginkgo biloba L. is a precious relic tree species with important economic value. Seeds, as a vital reproductive organ of plants, can be used to distinguish cultivars of the species. We chose 400 seeds from two cultivars of ginkgo (‘‘Fozhi’’ and ‘‘Maling’’; 200 seeds for each cultivar) as the study material and used the Gielis equation to fit the projected shape of these seeds. The coefficients of variation (CV) in root mean squared errors (RMSE) obtained from the fitted data were used to compare the level of inter-cultivar variations in seed shape. We also used the covariance analysis to compare the allometric relationships between seed weights and projected areas of these two cultivars. The Gielis equation fitted well the seed shapes of two ginkgo cultivars. The lower CV in RMSE of cultivar ‘‘Fozhi’’ than ‘‘Maling’’ indicated a less symmetrical seed shape in the latter than the former. The bootstrap percentile method showed that the seed shape differences between the two cultivars were significant. However, there was no significant difference in the exponents between the seed weights and the projected areas of these two cultivars. Overall, the significant differences in shapes between the seeds of two ginkgo cultivars were well explained by the Gielis equation; this model can be further extended to compare morphological differences in other ginkgo cultivars, and even for plant seeds or animal eggs that have similar oval shapes.
Blooms of Prorocentrum donghaiense reduced the species diversity of dinoflagellate community

Most of reported harmful algal blooms(HABs)of microalgae(75%)have been caused by dinoflagellates. Studies on the negative effects of HABs have generally focused on animals,valuable organisms in particular,and environmental factors such as dissolved oxygen and nutrients,but relatively fewer on community level,particularly that using metagenomic approach. In this study,we reported an investigation on the effects of a HAB caused by the dinoflagellate Prorocentrum donghaiense on the species diversity and community structure of the dinoflagellate sub-community via a pyrosequencing approach for the samples taken before,during,and after the bloom season of P. donghaiense in the East China Sea. We sequenced partial 28S rRNA gene of dinoflagellates for the field samples and evaluated the species richness and diversity indices of the dinoflagellate community,as a sub-community of the total phytoplankton. We obtained 800 185 valid sequences(categorized into 560 operational taxonomic units,OTUs)of dinoflagellates from 50 samples and found that the biodiversity of dinoflagellate community was significantly reduced during the blooming period in comparison to that in pre-and after-blooming periods,as reflected in the four diversity indices:the species richness expressed as the number of OTUs,Chao1 index,Shannon index(evenness),and Gini-Simpson index. These four indices were all found to be negatively correlated to the cell density of the bloom species P. donghaiense. Correlation analyses also revealed that the P. donghaiense cell abundance was correlated negatively with NO_3~--N,and NO_2~--N,but positively with total nitrogen(TN)and total phosphorus(TP). Principal coordinates analysis(PCoA)showed that the community structure of dinoflagellates was markedly different among the different sampling periods,while the redundancy analysis(RDA)revealed P. donghaiense abundance,salinity,NO_3~--N,and SiO_3~(2-)were the most four significant factors shaping the dinoflagellate community structure. Our results together demonstrated that HABs caused by the dinoflagellate P. donghaiense could strongly impact the aquatic ecosystem on the sub-community level which the blooming species belongs to.
Carbon isotopes and lignin phenols for tracing the floods during the past 70 years in the middle reach of the Changjiang River

The Lake Tian E Zhou(TEZ,an oxbow lake)was formed during the rerouting of the Changjiang River in 1972,with strong influences from the main river channel and flood events. Herein,a sediment core was collected from the Lake TEZ for the measurements of carbon isotopes and biomarkers,including stable carbon isotopes(δ~(13)C),radiocarbon composition(Δ~(14)C),and lignin phenols,as well as lead-210 to reconstruct recent heavy flood events over the past 70 years. At the 24-26 cm interval,the sediment contained the highest OC%,TN%,and lignin phenols content,as well as significantly depleted ~(13)C but enriched ~(14)C,corresponding to the extreme flood event in 1998. In addition,statistics from t-test showed that lignin phenols normalized to OC(Λ8),the concentration of 3,5-dihydroxy benzoic acid(3,5-BD),and the ratio of p-hydroxy benzophenone to total hydroxyl phenols(PHB/HP)were all significantly different between the layers containing flood deposits and the layers deposited under normal non-flood conditions(p<0.05). These results indicate that the later three parameters are highly related to flood events and can be used as compelling proxies,along with sediment chronology,for hydrological changes and storm/flood events in the river basin and coastal marine environments.
Heterojunction Incorporating Perovskite and Microporous Metal–Organic Framework Nanocrystals for Efficient and Stable Solar Cells

In this paper, we present a facile approach to enhance the efficiency and stability of perovskite solar cells (PSCs) by incorporating perovskite with microporous indium-based metal–organic framework [ In_(12)O(OH)_(16)(H_2O)_5(btc)_6]_n (In-BTC) nanocrystals and forming heterojunction light-harvesting layer. The interconnected micropores and terminal oxygen sites of In-BTC allow the preferential crystallization of perovskite inside the regular cavities, endowing the derived films with improved morphology/crystallinity and reduced grain boundaries/defects. Consequently, the In-BTC-modified PSC yields enhanced fill factor of 0.79 and power conversion efficiency (PCE) of 20.87%, surpassing the pristine device (0.76 and 19.52%, respectively). More importantly, over 80% of the original PCE is retained after 12 days of exposure to ambient environment (25 °C and relative humidity of ~ 65%) without encapsulation, while only about 35% is left to the pristine device.
Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power. Moreover, the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades. Among these compounds, layered two-dimensional (2D) materials, such as graphene, black phosphorus, transition metal dichalcogenides, IVA-VIA compounds, and MXenes, have generated a large research attention as a group of potentially high-performance thermoelectric materials. Due to their unique electronic, mechanical, thermal, and optoelectronic properties, thermoelectric devices based on such materials can be applied in a variety of applications. Herein, a comprehensive review on the development of 2D materials for thermoelectric applications, as well as theoretical simulations and experimental preparation, is presented. In addition, nanodevice and new applications of 2D thermoelectric materials are also introduced. At last, current challenges are discussed and several prospects in this field are proposed.
Control Parameter Optimization of Thermostatically Controlled Loads Using a Modified State-queuing Model

Thermostatically controlled loads (TCLs) are one of the best candidates to participate in direct load control (DLC). However, little attention is given to the parameter optimization of the TCLs control system due to the complexity of the TCLs'dynamics. In this paper, the parameters of the feedback control system based on the direct compressor control mechanism (DCCM) are optimized using the modified state-queuing (SQ) model, which can provide good characterizaton and greatly simplifies the dynamics of the TCLs. The simulation results verify the effectiveness of the proposed method.
On the State-dependent Switched Energy Functions of DFIG-based Wind Power Generation Systems

This paper proposes a novel state-dependent switched energy function (SdSEF) for general nonlinear autonomous systems, and constructs an SdSEF for doubly-fed induction generator (DFIG)-based wind power generation systems (WPGSs). Different from the conventional energy function, SdSEF is a piece-wise continuous function,and it satisfies the conditions of conventional energy functions on each of its continuous segments. SdSEF is designed to bridge the gap between the well-developed energy function theory and the description of system energy of complex nonlinear systems, such as power electronics converter systems. The stability criterion of nonlinear autonomous systems is investigated with SdSEF, and mathematical proof is presented. The SdSEF of a typical DFIG-based WPGS is simulated in the whole processes of a grid fault and fault recovery. Simulation results verify the negativeness of the derivative of each continuous segment of the SdSEF.
Stability Analysis of PLL Influenced by Control Loops in Grid-connected Converters Under Fault Disturbance

When the power grid suffers from grid faults that cause phase disturbances, the grid-connected converter becomes destabilized by the interaction between the phase-locked loop (PLL) and the control loop. In this paper, the stability of the PLL affected by the control loop under transient grid faults is studied. First, the equivalent model of the PLL under the influence of the control loop is established. Then, different response processes of PLLs under the ground fault with various control parameters are qualitatively analyzed. Furthermore, a small-signal model is proposed to assess the stability of the PLL under different control loop parameters. The system poles can be calculated to show the physical origin of the instability. Finally, simulations of a three-phase 21-level modular multilevel converter (MMC) built in PSCAD and a down-scale experiment is performed to verify the parameter influence of the control loop on the PLL.
Impedance Modeling and Stability Analysis of PV Grid-connected Inverter Systems Considering Frequency Coupling

Impedance analysis is an effective method to analyze the oscillation issue associated with grid-connected photovoltaic systems. However, the existing impedance modeling of a grid-connected photovoltaic inverter usually only considers the effect of a single perturbation frequency, ignoring the coupling frequency response between the internal control loops of a grid-connected inverter, which severely affects the accuracy of the stability analysis. Hence, a method of impedance modeling and stability analysis for grid-connected photovoltaic inverters considering cross-coupling frequency is proposed in this paper. First, the generation mechanism of frequency coupling in grid-connected photovoltaic inverters, and the relationship between the coupling frequency and perturbation frequency are analyzed. Secondly, a sequence impedance model of grid-connected photovoltaic systems considering the coupling frequency is established by using the harmonic linearization method. The impact of DC bus voltage control strategy on frequency coupling characteristics of a grid-connected photovoltaic system is evaluated, and the impact of a coupling frequency term on system stability is quantitatively analyzed. Finally, the advantages of the proposed method are verified by several simulations. The results show that the proposed impedance model can accurately predict the potential resonance points of the system, and the coupling frequency characteristics will become much stronger with smaller DC bus capacitance or larger bandwidth of the DC bus controller.
Impedance Modeling and Stability Analysis of a Three-phase Three-level NPC Inverter Connected to the Grid

The interaction between grid-connected inverters and the grid may cause stability issues, and compromise the reliable operation of the inverters. This study investigates the stability of a three-level neutral point clamped (NPC) inverter connected to the grid using impedance-based methods. Because the impedance model of a three-phase three-level NPC inverter has not yet been reported, this study fills the literature gap by analyzing the influence of three-level DC-side neutral point control on the impedance characteristics. By fully considering the DC bus dynamics and DC voltage control loop, and the current loop and phase-locked loop (PLL),the admittance model of a three-phase three-level NPC inverter is established and verified by simulation. Additionally, in the stability analysis of a three-level NPC inverter grid-connected system, the frequency coupling introduced by the PLL and DC bus dynamics is included with the help of an established admittance model. The stability of the grid-connected system under different grid short circuit ratios (SCR) and operating power levels is analyzed according to the Nyquist stability criterion. The experimental results revealed that the established impedance model of the three-phase three-level NPC inverter can properly represent the stability of this system.
A Mixed-integer SDP Solution to Distributionally Robust Unit Commitment with Second Order Moment Constraints

A power system unit commitment (UC) problem considering uncertainties of renewable energy sources is investigated in this paper, through a distributionally robust optimization approach. We assume that the first and second order moments of stochastic parameters can be inferred from historical data, and then employed to model the set of probability distributions. The resulting problem is a two-stage distributionally robust unit commitment with second order moment constraints, and it can be recast as a mixed-integer semidefinite programming (MI-SDP) with finite constraints. The solution algorithm of the problem comprises solving a series of relaxed MI-SDPs and a subroutine of feasibility checking and vertex generation. Based on the verification of strong duality of the semidefinite programming (SDP) problems,we propose a cutting plane algorithm for solving the MI-SDPs; we also introduce an SDP relaxation for the feasibility checking problem, which is an intractable biconvex optimization. Experimental results on the IEEE 6-bus system are presented, showing that without any tuning of parameters, the real-time operation cost of distributionally robust UC method outperforms those of deterministic UC and two-stage robust UC methods in general, and our method also enjoys higher reliability of dispatch operation.