Search

This study utilizes the improved fast and adaptive bidimensional empirical modal decomposition (IFABEMD) method to study the impact of relative vibration between the tool and the workpiece on surface topography. The sieving stop condition is determined based on the difference in standard deviation, effectively addressing the issue of modal mixing in the traditional bidimensional empirical modal (BEMD) method. Additionally, a novel boundary extension method is proposed using the Gerchberg algorithm. The decomposition example demonstrates that the IFABEMD method can effectively handle modal mixing and boundary effects. Finally, the relative vibration frequencies between the tool and the workpiece are identified by analyzing the spatial spectrum of the feature surface with vibration information. Simulation and experimental surface morphology decomposition results validate the effectiveness of the IFABEMD method in identifying relative vibration between the tool and the workpiece. [ABSTRACT FROM AUTHOR]

In the process of ultra-precision grinding, the dynamic characteristics of the aerostatic spindle system are important factors affecting the machined surface morphology. In order to study the influence of the dynamic characteristics of the spindle system on the medium frequency waviness error of the silicon wafer surface, this paper first establishes a dynamic model of the aerostatic spindle system considering the grinding force and the eccentricity of the spindle rotor based on Newton's law and the angular momentum law, analyzes the dynamic response and frequency characteristics of the spindle system, and conducts modal tests on the spindle system to verify the accuracy of the dynamic model. Then, the power spectral density analysis of the surface morphology of the silicon wafer after grinding is carried out, and the frequency components of the intermediate frequency band of the silicon wafer surface are obtained. Compared with the characteristic frequency of the spindle system and the vibration displacement curve of the end, it is found that the dynamic characteristics of the aerostatic spindle system are the main reason for the medium frequency waviness error on the surface of the silicon wafer. Finally, an optimization scheme for structural improvement of the aerostatic spindle system is given. Through the finite element analysis of the grinding machine, it is found that the vibration displacement of the spindle end after optimization is reduced by 52.8 % compared with that before optimization, which shows that the optimization scheme is effective and provides a reference for the structural design of the aerostatic spindle system. [ABSTRACT FROM AUTHOR]

Background: In this study, the complete mitogenome of Hemigrapsus sinensis was the first identified and analyzed. Objective: The complete mitochondrial genome of Hemigrapsus sinensis (Brachyura, Grapsoidea, Varunidae) and its phylogenetic position within Grapsoidea. Methods: The sample of Hemigrapsus sinensis was collected and DNA was extracted. After sequencing, NOVOPlasty was used for sequence assembly. Annotate sequences with MITOS WebServer, tRNAscan-SE2.0, and NCBI database. MEGA was used for sequence analysis and Phylosuite was used for phylogenetic tree construction. DnaSP was used to calculate Ka/Ks. Results: This mitochondrial genome shows that it was 15,900 bp and encoded 13 PCGs, 22 tRNA genes, two rRNA genes, and one control region. The genome composition tends to A + T (74.34%) and presents a negative GC-skew (− 0.22) and AT-skew (− 0.03). The PCGs initiation codon was the typical ATN and termination codon was the typical TAN, incomplete T or missing. The ML and BI trees showed that H. sinensis was most closely related to Hemigrapsus and clustered together with the Varunidae. And our phylogenetic trees provide proof that Ocypodoidea and Grapsoidea may be of common origin. Meanwhile, in the phylogenetic tree, parallel mixing of Chiromantes and Orisarma raised doubts over the traditional classification system. Besides, Incomplete Lineage sorting (ILS) was observed in Varunidae. In the subsequent analysis of evolution rate, we found that all of the PCGs (NAD4 was not calculated) had undergone negative selections, indicating the conservation of mitochondrial genes of H. sinensis during the evolution. Conclusion: Therefore, researching the complete mitogenome of H. sinensis would be contributing to molecular taxonomy, phylogenetic relationship, and breeding optimization within the Grapsoidea superfamily. [ABSTRACT FROM AUTHOR]

The complete mitogenome of Parachiloglanis hodgarti was sequenced and characterized, which is the first mitogenome of the genus Parachiloglanis within Sisoridae. The mitogenome is 16 511-bp long and included 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, and one control region. The genome composition was A+T biased (58.64%) and exhibited a positive AT-skew (0.095) and a negative GC-skew (−0.283). Compared with other Sisoridae fishes, the characteristics of nucleotide skews, codon usage, and amino acid usage of the P. hodgarti mitogenome are more similar to those of non-Glyptosternoid fishes. Furthermore, the phylogenetic trees show that Sisoridae fishes fall into four major clades and P. hodgarti (Clade I) is basal to the Sisoridae family, forming a sister clade to the Glyptosternoids (Clade IV). The topological structures constructed in this study raised doubts over the traditional classification system. These results will help better understand the features of the P. hodgarti mitogenome and provide a reference for further phylogenetic research on Sisoridae species. [ABSTRACT FROM AUTHOR]

Daphniopsis tibetana is widely distributed in Xinjiang, Qinghai, Tibet of China, as well as in Russia and India, which is the dominant zooplankton in many high-altitude (4000 m) salt lakes. D. tibetana can adapt to saline waters, whereas the other species of the superorder Cladocera can only inhabit in freshwater. However, the phylogenetic status of D. tibetana in Branchiopoda remains unclear primarily because of limited mitogenome. In this study, complete mitochondrial genome sequences of D. tibetana were sequenced and annotated for the first time to obtain a comprehensive understanding of its phylogenetic status. The complete mitogenome of D. tibetana is 16196 bp in length. It contains 37 genes, including two ribosomal RNAs (12S and 16S rRNAs) genes, 22 transfer RNA (tRNA) genes, 13 protein-coding genes, and one non-coding region. The overall base composition is 29.6% A, 33.2% T, 19.0% G, and 18.2% C with a high AT bias (62.8%). Except for trnS1 (GCT), most tRNAs have a typical cloverleaf secondary structure. Phylogenetic analysis based on maximum likelihood and Bayesian inference generates identical phylogenetic topology and shows the phylogenetic status of D. tibetana, which reconfirm the distinction between the genera Daphniopsis and Daphnia. Meanwhile, the class Branchiopoda is clustered into three clades (Anostraca, Notostraca, and Diplostraca) with high support values. These results provide not only a comprehensive understanding of the characteristics of D. tibetana mitogenome and its phylogenetic position in Diplostraca, but also information for future research on the phylogeny of Branchiopoda. [ABSTRACT FROM AUTHOR]

The knowledge of the added mass and damping characteristics induced by the vibration of the propeller in water is important to predict the hydroelastic behavior of the propulsion system. A three-dimensional panel method combined with the finite element method is conducted to analyze the properties of wet modes and added dampings of marine propellers by imposing three different non-penetration boundary conditions. One is imposed on the blade surface of the equilibrium position. The other is named a partly non-penetration boundary condition, which is imposed on the blade surface of real-time vibration position. Only the corrections of the flow velocities that are exerted on the blade surface by the real-time vibration and the equilibrium positions are considered. The third one takes both the correction of the normal vectors and the flow velocities enforced on the blade surface of the real-time vibration and the equilibrium positions into account, and is termed as a completely non-penetration boundary condition. It is observed that the third boundary condition must be applied for analyzing the wet mode frequencies of lightweight propellers, especially for those which have a small blade number. In addition, the added damping is overestimated by applying the first and second boundary conditions. [ABSTRACT FROM AUTHOR]

Identification of modal parameters of ultra-precision machine tools is an important method to study the dynamic characteristics of structures. Compared with theoretical modeling method, modal testing is a more concise and efficient way. Traditional experimental methods such as an impact hammer testing are unsuitable for use under operational conditions. This paper demonstrates the principle of a complex frequency-domain method for modal identification of ultra-precision fly-cutting machine tools. Modal testing is performed while cutting a circular copper workpiece, which means that all structural modes are excited by cutting force, rather than external vibration sources. Before extracting modal parameters, the raw data is preprocessed with a Kalman filter to reduce the impact of spindle frequency and its harmonics. The time-domain data is then transformed into power spectral density data, and the least-squares method is used to fit modal parameters in the frequency domain. Then, both the single-reference and poly-reference modal experiments are implemented. The steady-state criterion is established to evaluate the quality of calculating results. Finally, contrastive experiments between the proposed and experimental methods validate the effectiveness of the least-squares complex frequency-domain method, and the dominant natural frequencies are thoroughly investigated. [ABSTRACT FROM AUTHOR]

The vertical density gradients of salinity and suspended sediment concentration (SSC) cause stratification in estuaries, which play a vital role in the turbulence structure, water mixing, and sediment transport. To investigate the effect of stratification, especially SSC-induced stratification, on maintaining the estuarine turbidity maximum (ETM), we conducted in situ measurements on sediment dynamics at the upper and central ETM sites in the South Passage of Changjiang Estuary in July 2018. The gradient Richardson number was estimated as a proxy for the stratification that is attributable to salinity or/and SSC. We found that salinity-induced stratification was observed mainly on the surface and in the middle layers, whereas SSC-induced stratification occurred mainly in the near-bottom layers. Furthermore, at the central ETM, the baroclinic effect was enhanced during the neap tide when the salinity-induced stratification was stronger than that during the spring tide. In the early phase of floods with minimum velocity during the neap tide, salinity-induced stratification suppressed the turbulence and vertical diffusion of sediments. Moreover, the flocculation enhanced the settling process within the water column. Consequently, high concentrations of fine-grained sediments formed near the bottom and promoted SSC-induced stratification, thereby leading to the continuous accumulation and trapping of sediments. In conclusion, the interactions among the "salinity- and SSC-induced stratification" processes served as crucial constraints of the temporal and spatial variations of the ETM in the Changjiang Estuary. [ABSTRACT FROM AUTHOR]

In order to study the influence mechanism of dynamic characteristics on medium-frequency waviness error, the dynamic model of tool tip position of ultraprecision fly-cutting machine tool is firstly established, and the response test of tool tip position of machine tool is also carried out to identify relevant dynamic parameters. Then the dynamic vibration response of the machine tool is obtained by using intermittent cutting forces as input signal. The simulation results of the surface shape characteristics caused by the dynamic characteristics of the fly-cutting machine tool are obtained through the surface simulation. Finally, the simulation surface shape and the experimental surface shape are compared to verify the correctness and effectiveness of the tool tip dynamic model of the fly-cutting machine tool and the arc shape feature in the medium-frequency waviness error. [ABSTRACT FROM AUTHOR]

In the process of cutting, the relative vibration between the cutter and the workpiece has an important effect on the surface topography. In this study, the bidimensional empirical mode decomposition (BEMD) method is used to identify such effect. According to Riesz transform theory, a type of isotropic monogenic signal is proposed. The boundary data is extended on the basis of a similarity principle that deals with serious boundary effect problem. The decomposition examples show that the improved BEMD can effectively solve the problem of boundary effect and decompose the original machined surface topography at multiple scales. The characteristic surface topography representing the relative vibration between the cutter and the workpiece through feature identification is selected. In addition, the spatial spectrum analysis of the extracted profile is carried out. The decimal part of the frequency ratio that has an important effect on the shape of the contour can be accurately identified through contour extraction and spatial spectrum analysis. The decomposition results of simulation and experimental surface morphology demonstrate the validity of the improved BEMD algorithm in realizing the relative vibration identification between the cutter and the workpiece. [ABSTRACT FROM AUTHOR]

This paper analyzed the hydroelastic behaviors of hydrofoils and marine propellers immersed in incompressible, inviscid and irrotational fluids. Strongly coupled fluid–structure interaction analyses were performed using a three-dimensional (3-D) potential-based panel method in conjunction with a 3-D finite element method. The present method is developed for hydroelastic analyses of geometrically complex-shaped propeller blades, and the application of the method to the hydroelastic problems of hydrofoils is straightforward. The parameters dominating the added-mass and -damping matrices of the hydrofoils and propellers are examined. The effects of the translational motion of the hydrofoil and the rotational motion of the propeller on the added-mass and -damping matrices are compared based on different non-penetration boundary conditions and distributions of the inflow velocity. It is found that for hydroelastic analyses of propellers, the reduced frequency, i.e., the ratio of excitation frequency to rotational frequency, is a key parameter for determining the added-mass and -damping matrices of the propellers. The effect of the advance ratio on the added-mass and -damping matrices of the propeller blade depends upon the ratio of excitation frequency to rotational frequency. For hydrofoils, the added-damping matrix is significantly affected by the ratio of the excitation frequency multiplied by chord length and divided by axial inflow velocity. [ABSTRACT FROM AUTHOR]

The sheet current model considering the end effects is applied to design a six-degree-of-freedom (6-DOF) active vibration isolation system (AVIS) driving by the voice coil motors (VCMs). Compared with the charge model, the sheet current method represents higher calculation efficiency. Then, the hybrid functions (HFs) are employed to identify the multi-input and multi-output (MIMO) AVIS, and the identification parameters are used to design the controller. To promote the control performance, the composite nonlinear feedback (CNF) controller is designed based on the identification parameters. Consequently, the simulations and experiments are carried out, compared with PID controller, the CNF controller shows quicker response and smaller overshoot, i.e., the CNF controller achieves the dynamic damping ratio during the control. Thus, the experimental results demonstrate the better performance of the CNF controller. [ABSTRACT FROM AUTHOR]

Aerostatic bearings are of great importance for improving machining accuracy of a workpiece surface. The dynamics of air bearings and aerostatic spindle system in ultra-precision machine, which mainly causes mid-spatial waviness errors, has a great effect on surface topography. The dynamic coefficients of the thrust bearings were determined by adopting the perturbation method and finite difference method with MATLAB® software. In addition, the influences of the spindle speed and tilt angle conducted upon the dynamics of the thrust bearings were investigated in detail. The dynamic response of the spindle system, which is closely related to the performance of the thrust bearing and does not work only by the effect of the journal bearing, supported by pressured air film was obtained. The simulation analysis of spindle responses under cutting force and experiment results is well matched, and the analysis method proposed in this paper can be also applicable to other air bearing spindle systems. [ABSTRACT FROM AUTHOR]

The dynamics of a radial bearing and aerostatic spindle system in an ultraprecision fly-cutting machine cause mid-spatial waviness errors, which have a significant effect on surface topographies. Air bearings, which are externally pressurized, comprise two journal bearings and two thrust bearings with orifice restrictors. The dynamic coefficients of the radial bearings are obtained by adopting the perturbation and finite difference methods with the MATLAB® software. In addition, the influences of the spindle speed and tilt angle on the dynamics of the radial bearings are investigated in detail. The simulation results show that the rotating speed has a little impact on stiffness but having a great impact on damping, and the theoretical values of static stiffness are almost the same as the experimental values. The dynamic responses of the spindle system supported by pressurized air film are obtained, and the simulation analysis of spindle responses under cutting forces is also well matched to the experiment results. [ABSTRACT FROM AUTHOR]

The objective of the study was to analyze the treatment outcomes for staghorn stones in patients with solitary kidney using either the single-tract or the multi-tract minimally invasive percutaneous nephrolithotomy (MPCNL). We retrospectively reviewed 105 patients who underwent MPCNL for staghorn calculi in solitary kidney from 2012 to 2014. The patients who underwent the single-tract approach (71 patients) were assigned to Group 1. The 34 patients who underwent the multi-tract approach (34 patients) were assigned to Group 2. We recorded and compared the patient's demographics, intraoperative parameters, and post-operative outcomes. We also analyzed any complications as a result of the particular procedure, as well as any resulting stone-free rates (SFRs). The mean number of access tracts was 2.38 ± 0.70 (range 2-4) for Group 2. The mean operative time was longer for Group 2, p = 0.01. The initial SFR was 52.1 % for Group 1 and 47.1 % for Group 2 after the one-session procedure, p = 0.63.The final SFR improved to 83.1 and 79.4 % for both groups following auxiliary treatment, p = 0.65. The mean hemoglobin drop was higher in Group 2 as compared to Group 1, p < 0.01. There was no significant difference in the change of mean serum creatinine in either group. There were fewer overall complications in Group 1 than in Group 2 (23.9 vs. 44.1 %). Almost half of the patients who underwent multi-tract MPCNL required an additional procedure to achieve satisfactory stone clearance. The results showed that single-tract MPCNL might be a better treatment option for staghorn stones in a solitary kidney with the same therapeutic outcome, but with less complications. [ABSTRACT FROM AUTHOR]

Purpose: To compare the treatment outcomes between retrograde intrarenal surgery (RIRS) and minimally invasive percutaneous nephrolithotomy (MPCNL) for the management of stones larger than 2 cm in patients with solitary kidney. Methods: Between December 2012 and March 2014, 53 patients with a solitary kidney suffering from urinary stones larger than 2 cm were treated with RIRS. The outcomes of these patients were compared to a cohort of similar solitary kidney stone patients who underwent MPCNL using a matched-pair analysis (1:1 scenario). Cases were matched sequentially using the following criteria: size, number and location of stones, age, BMI, gender and previous ipsilateral open surgery. Results: A stone-free rate (SFR) of 43.4 % was achieved after a single procedure in patients treated with RIRS and a SFR of 71.70 % in patients treated with MPCNL ( p = 0.003). The operative time for RIRS was longer ( p = 0.002), but the median hospital stay was shorter ( p < 0.001). Average drop in hemoglobin level was comparable in both groups (9.30 vs. 10.85 g/L, p = 0.35). The transfusion rate as well as the incidence of postoperative complications such as fever and urosepsis was not statistically different between these two groups. Major complications (Clavien score 3a-4a) occurred in 3.77 and 1.89 %, RIRS and MPCNL, respectively ( p = 1.000). Conclusions: Patients with a solitary kidney suffering from stones larger than 2 cm in size who undergo MPCNL had a higher SFR than RIRS. The complications were comparable in both groups. Even though RIRS patients spent less time in hospital, this procedure might not be an effective treatment as MPCNL in solitary kidneys with larger and multiple stones. [ABSTRACT FROM AUTHOR]

Multi-pellet formulations are advantageous for the controlled release of drugs over single-unit dosage forms. To understand the diffusion controlled drug release mechanism, the pellet structure and drug release from a single pellet (not at dose level) were studied using synchrotron radiation X-ray computed microtomography (SR-μCT) and a sensitive LC/MS/MS method. The purpose of this article is to introduce a powerful, non-invasive and quantitative technique for studying individual pellet microstructures and to investigate the relationship between the microstructure and drug release from single pellets. The data from the single pellet dissolution measurements demonstrated that the release profile of capsules containing approximately 1,000 pellets per unit dose was the summation of the release profiles of the individual pellets. The release profiles of single tamsulosin hydrochloride (TSH) pellets formed three groups when a cluster analysis was performed, and the dissolution rate of the individual pellets correlated well with the combined effects of the drug loading, volume and surface area of the pellets ( R = 0.9429). In addition, the void microstructures within the pellet were critical during drug release. Therefore, SR-μCT is a powerful tool for quantitatively elucidating the three-dimensional microstructure of the individual pellets; because the microstructure controls drug release, it is an important parameter in the quality control of multi-pellet formulations. [ABSTRACT FROM AUTHOR]

new type of magnesia modification alkali-activated cement was prepared, the strength, setting time, shrinkage ratio and cracking behavior, as well as the composition and structure of the hydration product were investigated. The results indicate that the setting time of this cement is similar to that of the ordinary commercial cements; its strength reaches the standard of 42.5 degree cement, its cracking resistance has been remarkably improved because of the micro-aggregate effect of fly ash and shrinkage compensating of magnesia. [ABSTRACT FROM AUTHOR]

To secure good flowability and workability of SCC, the volume fraction of coarse aggregate keep at an extremely low level. A new kind of SCC pouring method named scattering-filling coarse aggregate process was invented: it was method to scatter 20% (volume fraction to the finished concrete) of extra coarse aggregate into the fresh SCC mixture to replace the fresh concrete mixture while the concrete was pouring. A high strength (82 MPa) SCC just composing 360 kg/m cement and 120 kg/m class F fly ash was prepared with this process. With an increase of the extra coarse aggregate replacing ratio from 0 to 30%, the compressive strength of SCC increased steadily and reached a peak value when this ratio is 20%, then the strength dropped sharply. The drying shrinkage ratio and the chloride ion permeability decreased with the increase of that ratio. The scattering-filling coarse aggregate process can cast high strength SCC with lower cementitious materials content and produce concrete with better performance than the ordinary process. [ABSTRACT FROM AUTHOR]

Land use change not only directly influences carbon storage in terrestrial ecosystems but can also cause energy-related carbon emissions. This study examined spatiotemporal land use change across Jiangsu Province, China; calculated vegetation carbon storage loss caused by land use change and energy-related carbon emissions; analysed the relationship among land use change, carbon emissions and social-economic development; and optimized land use structure to maximize carbon storage. Our study found that 13.61% of the province's land area underwent a change in type of land use between 1995 and 2010, mainly presented as built-up land expansion and cropland shrinkage, especially in southern Jiangsu. Land use change caused a 353.99 × 104 t loss of vegetation carbon storage loss. Energy-related carbon emissions increased 2.5 times from 1995 to 2013; the energy consumption structure has been improved to some extent while still relying on coal. The selected social-economic driving forces have strong relationships with carbon emissions and land use changes, while there are also other determinants driving land use change, such as land use policy. The optimized land use structure will slow the rate of decline in vegetation carbon storage compared with the period between 1995 and 2010 and will also reduce energy-related carbon emissions by 12%. [ABSTRACT FROM AUTHOR]

The family Sisoridae is one of the largest and most diverse Asiatic catfish families, with most species occurring in the water systems of the Qinhai-Tibetan Plateau and East Himalayas. At present, the phylogenetic relationship of the Sisoridae is relatively chaotic. In this study, the mitochondrial genomes (mitogenomes) of three species Creteuchiloglanis kamengensis, Glaridoglanis andersonii, and Exostoma sp. were systematically investigated, the phylogenetic relationships of the family were reconstructed and to determine the phylogenetic position of Exostoma sp. within Sisoridae. The lengths of the mitogenomes’ sequences of C. kamengensis, G. andersonii, and Exostoma sp. were 16,589 bp, 16,531 bp, and 16,529 bp, respectively. They all contained one identical control region (D-loop), two ribosomal RNAs (rRNAs), 13 protein-coding genes (PCGs) and 22 transfer RNA (tRNA) genes. We applied two approaches, Bayesian Inference (BI) and Maximum Likelihood (ML), to construct phylogenetic trees. Our findings revealed that the topological structure of both ML and BI trees exhibited significant congruence. Specifically, the phylogenetic tree strongly supports the monophyly of Sisorinae and Glyptosternoids and provides new molecular biological data to support the reconstruction of phylogenetic relationships with Sisoridae. This study is of great scientific value for phylogenetic and genetic variation studies of the Sisoridae. [ABSTRACT FROM AUTHOR]