A new method of kinematic analysis and singularity analysis is proposed for a 7-DOF redundant manipulator with three consecutive parallel axes. First, the redundancy angle is described according to ...the self-motion characteristics of the manipulator, the position and orientation of the end-effector are separated, and the inverse kinematics of this manipulator is analyzed by geometric methods with the redundancy angle as a constraint. Then, the Jacobian matrix is established to derive the conditions for the kinematic singularities of the robotic arm by using the primitive matrix method and the block matrix method. Then, the kinematic singularities conditions in the joint space are mapped to the Cartesian space, and the singular configuration is described using the end poses and redundancy angles of the robotic arm, and a singularity avoidance method based on the redundancy angles and end pose is proposed. Finally, the correctness and feasibility of the inverse kinematics algorithm and the singularity avoidance method are verified by simulation examples.
Density functional theory (DFT) calculations have been performed to study the mechanism of the recently reported Co‐catalyzed ligand‐controlled hydroarylation of styrenes as a means of preparing 1,1‐ ...or 1,2‐diarylalkanes. The present study corroborates the previously proposed three‐step mechanism, comprising CH activation (CH oxidative addition), styrene insertion, and reductive elimination. In the CH activation and reductive elimination steps, our calculations suggest that styrene does not coordinate to the Co center. In the insertion step, styrene is inserted into the CoH bond rather than the CoC bond. Furthermore, the rate‐ and regiodetermining step is found to be CC reductive elimination. It is significant that the regioselectivity observed experimentally has been successfully reproduced by our calculations. More importantly, in analyzing the origin of the ligand‐controlled regioselectivity, we have found that the steric effects of different ligands mainly determine the observed regioselectivity. Both the shape (i.e., “umbrella‐up” or “umbrella‐down”) and bulkiness of the ligand contribute to the steric effect.
Theoretical rationale for regioselectivity: Density functional theory calculations have been performed on a recently reported Co‐catalyzed ligand‐controlled hydroarylation of styrenes. This reaction yields either linear (see scheme) or branched products, depending on the ligand employed. Calculations indicate that this regioselectivity can mainly be attributed to the steric effect of the ligands.
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•Temperature affects the diurnal pattern of soil respiration by altering the response of heterotrophic components to environmental factors.•The diurnal peak time of soil respiration ...lags behind the diurnal peak time of soil temperature.•Warming advanced the diurnal peak time of net ecosystem carbon exchange compared to the diurnal peak time of soil respiration.
Analyzing the diurnal pattern of soil respiration is essential for understanding the potential mechanisms of carbon cycle. Additionally, long-term and high temporal frequency soil respiration observations are crucial and valuable at different time scales, particularly in alpine regions. Therefore, it is critical to conduct research on the diurnal pattern of soil respiration in areas sensitive to global warming. Here, four group (including soil respiration, heterotrophic respiration, net ecosystem carbon exchange, and net ecosystem carbon exchange under warming condition) of experiments were designed with a total 12 chambers, and data collected during growing season in 2023 (April to September) obtained by automatic observation system at hour-scale and four-parameter Gaussian equation were used to investigate the diurnal pattern of soil respiration and net ecosystem carbon exchange in alpine meadow ecosystem on the northeastern Qinghai-Tibet Plateau. The results indicated that: 1) the soil temperature was crucial factor for the variations in diurnal pattern of soil respiration and net ecosystem carbon exchange in four experiments. The response of the heterotrophic components to the diurnal variation in soil temperature induced diurnal lag between soil respiration and soil temperature, with mean lag time of 1.7 h. 2) The diurnal peak time of net ecosystem carbon exchange was 1–3 h earlier than respiration, and the diurnal variation of soil tempiration was one of the main driving forces. 3) Additionally, warming advanced the diurnal peak time of net ecosystem carbon exchange by 1.2–2 h through explaining the parameters of the Gaussian function. It also promoted microbial resistance, thereby limiting the increase in soil respiration during nighttime. The study suggested that temperature varied soil microenvironment and biochemical processes in alpine meadow ecosystem, thus affecting the diurnal pattern. Indeed, this study focused solely on traditional factors, and further investigations were needed, particularly from a biotic perspective, to validate these conclusions.
Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, SARS-CoV-2 variants capable of breakthrough infections have attracted global attention. These variants have significant mutations ...in the receptor-binding domain (RBD) of the spike protein and the membrane (M) protein, which may imply an enhanced ability to evade immune responses. In this study, an examination of co-mutations within the spike RBD and their potential correlation with mutations in the M protein was conducted. The EVmutation method was utilized to analyze the distribution of the mutations to elucidate the relationship between the mutations in the spike RBD and the alterations in the M protein. Additionally, the Sequence-to-Sequence Transformer Model (S2STM) was employed to establish mapping between the amino acid sequences of the spike RBD and M proteins, offering a novel and efficient approach for streamlined sequence analysis and the exploration of their interrelationship. Certain mutations in the spike RBD, G339D-S373P-S375F and Q493R-Q498R-Y505, are associated with a heightened propensity for inducing mutations at specific sites within the M protein, especially sites 3 and 19/63. These results shed light on the concept of mutational synergy between the spike RBD and M proteins, illuminating a potential mechanism that could be driving the evolution of SARS-CoV-2.
Polymorphism has been the subject of investigation across different research disciplines. In biology, polymorphism could be interpreted in such a way that discrete biomacromolecules can adopt ...diversiform specific conformations/packing arrangement, and this polymorph-dependent property is essential for many biochemical processes. For example, bacterial flagellar filament, composed of flagellin, switches between different supercoiled state allowing the bacteria to swim and tumble. However, in artificial supramolecular systems, it is often challenging to achieve polymorph control and prediction, and in most cases, two or more concomitant polymorphs of similar formation energies coexist. Here, we show that a tetrameric protein with properly oriented binding sites on its surface can arrange into diverse protein tubes with distinct helical parameters by adding specifically designed inducing ligands. We examined several parameters of the ligand that would influence the protein tube formation and found that the flexibility of the ligand linker and the dimerization pose of the ligand complex is critical for the successful production of the tubes and eventually influence the specific helical polymorphs of the formed tubes. A surface lattice accommodation model was further developed to rationalize the geometrical relationship between each helical tube type. Molecular simulation was used to elucidate the interactions between ligands and SBA and molecular basis for polymorphic switching of the protein tubes. Moreover, the kinetics of structural formation was studied and the ligand design was found that can affect the kinetics of the protein polymerization pathway. In short, our designed protein tubes serves as an enlightening system for understanding how a protein polymer composed of a single protein switches among different helical states.
GNSS spoofing interference utilizes falsified navigation signals to launch attacks on GNSS systems, posing a significant threat to applications that rely on GNSS signals for positioning, navigation, ...and time services. Therefore, achieving effective localization of the sources causing spoofing interference is crucial in ensuring the secure operation of GNSS. This article proposes a method for locating GNSS spoofing interference sources using a moving array antenna. Firstly, the proposed method utilizes the inherent characteristics of the double-differenced carrier phase from the deception signals received by the array antenna to effectively extract the spoofing signals. Subsequently, by moving the antenna array, the original carrier phase single-difference data of multiple observation points for deception signals are fused to provide a cost function for direct localization of spoofing interference, and a solution method for the cost function is designed. The proposed method addresses the challenge of extracting and localizing GNSS spoofing interference weak signals, effectively avoiding the data correlation of traditional two-step methods for DOA estimation parameters and ensuring the location accuracy of spoofing interference and the robustness of the method. The effectiveness of the proposed method has been validated through simulation experiments, and its adaptability to factors such as errors in carrier phase measurements has been examined. The method exhibits strong applicability and is well-suited for the hardware platform of the GNSS nulling antenna, thereby enabling it to possess simultaneous capabilities in both anti-interference and spoofing interference localization.
While undergoing structural deformation, DNA experiences changes in the interactions between its internal base pairs, presenting challenges to conventional elastic methods. To address this, we ...propose the Discrete Critical State (DCS) model in this paper. This model combines surface discrete frame theory with gauge theory and Landau phase transition theory to investigate DNA's structural deformation, phase transitions, and chirality. Notably, the DCS model considers both the internal interactions within DNA and formulates an overall equation using unified physical and geometric parameters. By employing the discrete frame, we derive the evolution of physical quantities along the helical axis of DNA, including geodesic curvature, geodesic torsion, and others. Our findings indicate that B-DNA has a significantly lower free energy density compared to Z-DNA, which is in agreement with experimental observations. This research reveals that the direction of base pairs is primarily governed by the geodesic curve within the helical plane, aligning closely with the orientation of the base pairs. Moreover, the geodesic curve has a profound influence on the arrangement of base pairs at the microscopic level and effectively regulates the configuration and geometry of DNA through macroscopic-level free energy considerations.
Currently, the new operational tactic of the swarming unmanned aerial vehicles (UAVs) combat is becoming a hotspot in military research, and evaluating the combat efficiency and the roles of UAVs is ...of vital importance for the future development of UAVs. However, most of the recent studies on the swarming UAVs combat are merely qualitative analyses. This paper proposes an operational effectiveness evaluation method of the swarming UAVs combat system based on a system dynamics (SD) model. The weapons in the combat process are divided into nine subsystems and we build corresponding nine in-trees models using the rate-variable in-trees modeling method. The final SD model is established based on the nine in-trees and the characteristics of swarming UAVs are considered. Taking the surviving rate of UAVs and task completion degree as the evaluation indicators, the model simulation shows that over 50% of the enemy ground targets can be destroyed in 15-time units, although some UAVs may be damaged. It is also confirmed through comparison experiments with other combat patterns that the swarming UAVs play a crucial role in improving the system combat efficiency and can decompose the function of traditional high-value weapon platforms.
In the conventional space-time signal model, the statistical amplitude of the clutter is assumed to be a specific distribution. For sea clutter, a pulse-to-pulse correlation matrix is added to the ...temporal covariance matrix to describe the motion of the sea surface. However, such sea clutter model cannot reflect the property of the sea clutter. In this paper, a space-time model for the sea clutter is presented based on the physical sea surface model, in which the clutter amplitude is deterministic instead of statistic. The reflectivity and the radial velocity of the sea clutter for any specific position and time are computed based on the physical sea surface. Both the aforementioned two factors vary with time, which corresponds to the time variation of the sea surface. Moreover, the spatial channel decorrelation is modeled, which has an effect on the spatial covariance matrix of the sea clutter. The simulated angle-Doppler spectra and the signal-to-clutter-plus-noise-ratio loss show that the reflectivity of the sea clutter makes the space-time-adaptive-processing performance degrade, and the radial velocity of the sea clutter results in a more significant spread of the clutter power spectrum in sea state 4 than sea state 2. The Doppler spectrum can be acquired by the space-time model proposed in this paper instead of the experimental Doppler model for sea clutter. For a given sea state, the low range resolution has a more prominent effect on the power spectrum because of severer spatial channel decorrelation.
Current structural and functional investigations of cholesteryl ester transfer protein (CETP) inhibitor design are nearly entirely based on a fully active mutation (CETP
) constructed for protein ...crystallization, limiting the study of the dynamic structural features of authentic CETP involved in lipid transport under physiological conditions. In this study, we conducted comprehensive molecular dynamics (MD) simulations of both authentic CETP (CETP
) and CETP
. Considering the structural differences between the N- and C-terminal domains of CETP
and CETP
, and their crucial roles in lipid transfer, we identified the two domains as binding pockets of the ligands for virtual screening to discover potential lead compounds targeting CETP. Our results revealed that CETP
displays greater flexibility and pronounced curvature compared to CETP
. Employing virtual screening and MD simulation strategies, we found that ZINC000006242926 has a higher binding affinity for the N- and C-termini, leading to reduced N- and C-opening sizes, disruption of the continuous tunnel, and increased curvature of CETP. In conclusion, CETP
facilitates the formation of a continuous tunnel in the "neck" region, while CETP
does not exhibit such characteristics. The ligand ZINC000006242926 screened for binding to the N- and C-termini induces structural changes in the CETP unfavorable to lipid transport. This study sheds new light on the relationship between the structural and functional mechanisms of CETP. Furthermore, it provides novel ideas for the precise regulation of CETP functions.
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