Search

Characterized by a complex contour profile involving arc, cycloid and involute, etc., the screw rotor is usually manufactured by a forming tool. The finished surface quality and efficiency of the screw rotor are determined by the cutting performance of the forming tool. However, the machining performance of the forming tool is closely related to the structure shape of cutting edge, which is then determined by the installation parameters of the forming tool. Therefore, to make the cutting performance of forming tool controllable, it is essential investigate the relationship between the cutting performance of the forming tool and its installation parameters at the design stage. In this paper, a novel installation parameter optimization design method of forming tool for screw rotor is presented. A parametric optimization program is designed to finalize the range of installation parameters satisfying the spatial meshing relation and machining equipment parameters. The profile characteristics of forming tool under different center distances and mounting angles have been investigated. For validation, several screw rotors were ground in experiments and the resulted profile errors were analyzed. The results show that the cost of precision grinding of screw rotor can be significantly reduced, without compromise of machining quality. As such, the proposed design method could serve as a promising platform to faciliate screw rotor manufacture.

Evidence linking

This paper considers solving the zero-sum games (ZSGs) of nonlinear stochastic systems under the architecture of dynamic event-triggered mechanism (DETM). The adaptive dynamic programming (ADP) approach with great approximate computing power is proposed to seek the saddle-point equilibrium solution of ZSGs. First, the Hamilton–Jacobi–Isaacs equation of stochastic version is constructed which is the key to solving the two-player ZSGs. Then, the ADP method is employed to search the approximated solution under the dynamic triggering mechanism. On the foundation of static event-triggered mechanism (SETM), the DETM is derived through introducing an internal dynamic invariable to further lower the update frequency for the strategies. Additionally, the stability of the closed system is demonstrated in detail via the Lyapunov theory. Finally, two representative examples are provided to present the availability and reliability of this approach from different perspectives.

Bifidobacterium bifidum strains, an important component of probiotic foods, can form biofilms on abiotic surfaces, leading to increased self-resistance. However, little is known about the molecular mechanism of B. bifidum biofilm formation. A time series transcriptome sequencing and untargeted metabolomics analysis of both B. bifidum biofilm and planktonic cells was performed to identify key genes and metabolites involved in biofilm formation. Two hundred thirty-five nonredundant differentially expressed genes (DEGs) (including vanY, pstS, degP, groS, infC, groL, yajC, tadB and sigA) and 219 nonredundant differentially expressed metabolites (including L-threonine, L-cystine, L-tyrosine, ascorbic acid, niacinamide, butyric acid and sphinganine) were identified. Thirteen pathways were identified during the integration of both transcriptomics and metabolomics data, including ABC transporters, quorum sensing, two-component system, oxidative phosphorylation, cysteine and methionine metabolism, glutathione metabolism, glycine, serine and threonine metabolism, and valine, leucine and isoleucine biosynthesis. The DEGs that relate to the integration pathways included asd, atpB, degP, folC, ilvE, metC, pheA, pstS, pyrE, serB, ulaE, yajC and zwf. The differentially accumulated metabolites included L-cystine, L-serine, L-threonine, L-tyrosine, methylmalonate, monodehydroascorbate, nicotinamide, orthophosphate, spermine and tocopherol. These results indicate that quorum sensing, two-component system and amino acid metabolism are essential during B. bifidum biofilm formation.

In the process of grinding, rubbing, plowing, and cutting occur successively between abrasive grains and workpiece material as the grinding depth increases. In precision grinding of the screw rotor, small grinding depth is generally introduced, which usually results in plowing. Therefore, it is essential to predict the surface roughness caused by plowing in order to make the process controllable. In this paper, an analytical method for predicting tooth surface roughness of the screw rotor in precision grinding has been proposed. This method takes the following factors into consideration, i.e., distribution law of the grain protrusion heights, variation of grinding depth, velocities and diameters of the screw rotor and grinding wheel at different contact points, and the dressing parameters of grinding wheel. A trajectory projection method has been employed to determine the groove depth and distribution left by the abrasive grains. With the proposed model, the distribution of roughness over the screw rotor tooth surface can be calculated. Verification experiments were conducted with several screw motors produced and surface roughness measured. The comparison results reveal a good agreement between predicted results and experimental results, showing the effectiveness of the proposed method. This study could shed light on the plowing phenomena in precision grinding and could provide great potential in achieving an effective control of the surface roughness.

Biofilm formation by bacteria represents an adaptation strategy to the environment, and some special genes may lead to a strong biofilm phenotype. In this study, we attempted to find functional genes associated with bifidobacterial biofilm formation. Firstly, we evaluated the biofilm formation ability of bifidobacterial strains from six species, which showed that Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium animalis, Bifidobacterium adolescentis, and Bifidobacterium pseudocatenulatum had biofilm-forming and non-biofilm-forming strains, while all Bifidobacterium bifidum strains could form strong biofilms. Then 48 strains were selected for genome sequencing and comparative analysis. The gene-trait matching analysis revealed that B. bifidum biofilm formation phenotype may associate with their unique genes, involving in stress response, quorum sensing, two components, and peptide synthesis. B. pseudocatenulatum biofilm formation was positively correlated with the eps cluster (rfbX). While no genotype related to the biofilm phenotype was found in B. longum using this analysis, but all contain autoinducer-2 (AI-2) receptor genes. Moreover, luxS, rbsB, rfbX were selected for real-time qPCR analysis, suggesting that their expression are important to biofilm formation. These results indicated that strains carrying certain genes tend to form stronger biofilms than those formed by strains without these genes.

In the operation of positive displacement screw machine, the profile accuracy of the screw rotor has a significant effect on the meshing stability between male rotor and female rotor, which is the main factor for vibration, noise, sealing, and wear resistance. This sets extremely strict requirements of the profile accuracy of screw rotor. Therefore, in order to obtain precise screw rotor profile, form grinding is generally used as a finishing process in the manufacture of screw rotors. Unfortunately, the grinding wheel has to be frequently dressed due to inevitable grinding wheel wear. This will cause a substantial waste of time and thus lead to inefficiency. It is therefore desirable to be able to predict the profile error caused by grinding wheel wear in order to make it controllable. In this paper, the influence of installation angle, center distance, and grinding wheel wear on rotor profile error is investigated. A novel method has been proposed for prediction profile error of the screw rotor in precision form grinding. The proposed method has been employed to compensate profile error caused by grinding wheel wear and improve grinding efficiency. Verification experiments were conducted with several screw rotors produced and profile error measured. The comparison shows that the compensation results agree well with the numerical simulation results, showing the effectiveness of the proposed compensation method.

Biofilm formation has evolved as an adaptive strategy for bacteria to cope with harsh environmental conditions. Currently, little is known about the molecular mechanisms of biofilm formation in bifidobacteria. A time series transcriptome sequencing analysis of both biofilm and planktonic cells of Bifidobacterium longum FGSZY16M3 was performed to identify candidate genes involved in biofilm formation. Protein–protein interaction network analysis of 1296 differentially expressed genes during biofilm formation yielded 15 clusters of highly interconnected nodes, indicating that genes related to the SOS response (dnaK, groS, guaB, ruvA, recA, radA, recN, recF, pstA, and sufD) associated with the early stage of biofilm formation. Genes involved in extracellular polymeric substances were upregulated (epsH, epsK, efp, frr, pheT, rfbA, rfbJ, rfbP, rpmF, secY and yidC) in the stage of biofilm maturation. To further investigate the genes related to biofilm formation, weighted gene co-expression network analysis (WGCNA) was performed with 2032 transcript genes, leading to the identification of nine WGCNA modules and 133 genes associated with response to stress, regulation of gene expression, quorum sensing, and two-component system. These results indicate that biofilm formation in B. longum is a multifactorial process, involving stress response, structural development, and regulatory processes.

This study investigated the effects of Lactobacillus (L.) reuteri strains on airway inflammation, immune responses, and gut microbiota in a house dust mite (HDM)-induced allergic asthma murine model. The L. reuteri strains CCFM1072 and CCFM1040, which increased Treg populations in the spleen, lowered airway inflammation as compared to other strains, downregulated histamine, IL-17A, IL-5, and IL-13 levels in the lungs, and reduced Th2-related immunoglobulin concentrations in serum. Gut microbiota and metabolism analysis revealed that CCFM1072 maintained the diversity of the gut microbiota, promoted the growth of L. reuteri and Bacteroides thetaiotaomicron, and increased propionate levels, whereas CCFM1040 remodeled the structure of the gut microbiota, particularly promoting the growth of Bifidobacterium, and these promoted bacteria were linked to the improvement of airway inflammation. In summary, the two L. reuteri strains have effects on alleviating airway inflammation partly depending on modulating gut microbiota, albeit differently, and promoting Tregs proliferation.

As an essential coastal structure, a breakwater is generally designed to be stable and reliable during its lifetime. With respect to stability, failure modes usually are statistically indep...

The profile accuracy of screw rotors plays a vital role in stabilizing the meshing operation between mated rotors. Such stability can minimize the vibration and noise, as well as improve the sealing performance and wear resistance. This is the main reason why form grinding is extensively applied as a finishing process to maintain high screw rotor profile accuracy. Since the installation parameters for form grinding wheels affect both the grinding wheel profile accuracy and grinding performance, it is essential to obtain reasonable installation parameters to guarantee the high precision and good grinding performance of form grinding wheels. In this paper, a novel optimization design method for form grinding wheels for screw rotors has been proposed. For the first time, the relationship between the grinding wheel installation parameters and profile accuracy is established to evaluate the grinding performance. A parameterized program has been designed based on space engagement theory. The characteristics of the contact line and profile features of form grinding wheels under different installation parameters have been investigated. Then, the proposed method was employed to select the correct range of installation parameters. To validate the proposed method, a set of experiments, including the manufacture and measurement of several screw rotors, was carried out. The results reveal that the precision of the screw profile is significantly improved compared with the empirical method, thus showing the effectiveness of the proposed method.

Biofilms are aggregates of microorganisms that adhere to the surface of certain substances and produce extracellular polymers to improve their resistance to stress. However, only some Bifidobacterium strains can form biofilms on abiotic surfaces. The study evaluated the biofilm-forming abilities of six Bifidobacterium strains on grape seed flour (GSF) with a particle size of 80–120 μm. Bifidobacterium animalis, Bifidobacterium bifidum, and Bifidobacterium adolescentis formed weak biofilms, whereas Bifidobacterium pseudo, Bifibacterium breve, and Bifidobacterium longum formed strong biofilms on GSF. B. pseudo cells formed biofilm particles with a diameter of 2 mm, and their cell numbers reached 2.04 × 109 CFU/g at 32 h. There were almost no viable cells in the culture without GSF after 60 h; however, the number of biofilm cells on GSF was still over 106 CFU/g, indicating that biofilms improve cell survival. Field-emission scanning electron microscopy revealed the following stages in the bifidobacterial biofilm formation process: adsorption to GSF, secretion of extracellular substance, biofilm maturation and dispersal, and cell death. Collectively, these results strongly suggest that GSF is beneficial for Bifidobacterial biofilm growth, providing a theoretical basis for the production of highly resistant probiotics in the food industry.

This paper presents a new mesoscopic transport model for describing the diffusion of chloride in cement-based materials simultaneously subjected to freeze-thaw (FT) conditions and incorporated with chloride ions (Ch-I). The model uses the concept of freeze-thaw stress (FT-S) to reflect the effect of freezing and thawing cycles on the transport of ionic concentrations in porous materials and the concentration gradient of chloride for calculating the effect of different concentrations of chloride ions. In addition to determining the effect of FT-S, the model also considers the interactional effects between environmental exchanges, namely the effects of different temperatures, Cl− concentrations (10.5 g/L, 21.0 g/L and 42.0 g/L), and pore size distributions. The mesoscopic model is validated using experimental data obtained from coupling tests of chloride corrosion and freeze-thaw cycles. Compared with the typical Fick’s results, advantageous agreement between the calculated and measured chloride concentration profiles is demonstrated. The new mesoscopic diffusion model can help compensate for the lack of research on the effect of freeze-thaw cycles on chloride diffusion.

Determining the rheological properties of cement-based materials and selecting the types and amounts of superplasticisers (SPs) that are appropriate for actual projects are important and topical issues. In this study, the rheological properties of cement pastes with different types of SP were investigated using an AR2000ex rheometer. A colour function method (CFM), in combination with the experimental data, was used to calculate and determine the rheological properties. This paper presents a new selection method (rapid determination system (RDS)) for determining the most suitable SPs. The results show that shear stress, plastic viscosity, normal stress and other mechanical properties are influenced by different volumes and types of SPs. Based on the CFM and RDS, 0·38% HW (a polycarboxylate-type SP) was determined to be the most appropriate.

Buried corrugated steel culverts are universally regarded as a structure with strong deformation adaptability and dispersed the upper load by corrugated steel structures surrounding soil constraints to enhance the carrying capacity and the use of soil-structure interaction. A lot of factors influence the earth pressure of the buried corrugated steel culvert, such as culvert stiffness, physical characteristics of the backfill (bulk density, deformation modulus and internal friction angle), geometry of structure and backfilling height. The finite element program of ANSYS has been used to research the elastic modulus, Poisson’s ratio, internal friction angle of soil, inertia moment of corrugated steel plate and pipe diameter affect the rigidity and flexibility of buried corrugated steel culvert. By defining path lines in the finite element post-processing, extracting and comparing the horizontal and vertical directions soil displacements along the lines, and doing impact pa-rameter analysis. Classification for flexible and rigid pipes of the buried corrugated steel pipe culvert structure has been made according to the analysis results. A theoretical reference has been provided for the design and construction of the buried corrugated steel pipe culverts.

For recovering potato protein from potato processing wastewater, the effects of temperature, pH, volumetric airflow rate, liquid loading volume and sparging time on the foam separation performances were investigated using the column with the spiral internal component (SIC). A two-stage foam separation technology was designed to improve both the enrichment ratio and recovery percentage of potato protein. The results showed that the SIC and specially the increase of temperature were effective for improving the enrichment ratio of potato protein. A best enrichment ratio of potato protein of 4.69 was obtained under the optimal conditions of temperature 45 °C, pH 7, volumetric airflow rate 100 mL/min, liquid loading volume 300 mL and sparging time 90 min. The total recovery percentage of potato protein was as high as 73.4% by using the two-stage foam separation technology. So the two-stage technology was effective for the protein recovery from potato processing wastewater.

The theoretical analysis of flexible multi-body system is a long-term and complicated problem. So the single flexible body dynamics should be studied firstly. Quasi-variational principle of non-conservative single flexible body dynamics is established under the cross-link of particle rigid body dynamics and deformable body dynamics. Some important problems are studied in quasi-variational principle of non-conservative single flexible body dynamics. The vibration problem of unrestrained beam can be solved very well by using quasi-variational principle.Copyright © 2010 by ASME

With the development of hydromechanics and aeromechanics, the interest in non-conservative and non-selfadjoint problems has increased. However some traditional variational methods are not applicable to these problems, which have no energy functional in full variable form. And weighted residuals method is the general name of a series of approximate numerical methods for non-energy variational equations. Generalized Galerkin method is just one of weighted residual method, which is engineer’s experience summary in long practical applied process for the numerical analysis methods. Generalized Galerkin method is often used for dynamic response problems. In this paper, the general process for solving geometric nonlinear elasto-dynamics problem in non-conservative system is presented. The vibration problem of elastic thin plate with large deflection in non-conservative system is solved by generalized Galerkin method. Finally, some correlative problems are discussed.Copyright © 2010 by ASME

Based on coupled properties of electricity, magnetism, heat and force, it is hard to solve the material’s electric behavior, magnetic behavior, temperature field, stress distribution and deformation distribution under the action of all kinds of external fields in usual way. It is necessary that the problems are solved by numerical methods. However variational principle is the foundation of these numerical methods which were widely used. In this paper, the generalized variational principles of electro-magneto-thermo-elasto-dynamics are established by variational integral method. And these variational principles can be degenerated into variational principles of simple coupled properties materials, which offer theoretical support for numerical methods of coupled problems of electro-magneto-thermo-elasticity.Copyright © 2009 by ASME

Based on base forces theory framework, the basic equations of time boundary value problem of large elastic deformation in non-conservative systems are defined. According to the corresponding relations between generalized forces and generalized displacements, the basic equations of elasto-dynamics are multiplied by corresponding virtual quantities, integrated and then added algebraically. Considering that both body forces and surface forces are fellow forces, the generalized Hamilton-type quasi-variational principles with three kinds of variables of large elastic deformation based on base forces theory in non-conservative systems are established. Then they are degenerated. Applying the Hamilton-type quasi-potential energy principle, analytic solutions of large deformation cantilever beam problem in non-conservative systems is obtained. Finally, some correlative problems are discussed.Copyright © 2008 by ASME

Magnetism and magnetoelectric effect of armchair BC4N nanoribbons are explored from density functional theory. 100% spin polarization presents in the N-rich nanoribbons due to sigma-dangling bond states induced by the unpaired N atoms. In the nanoribbons with “paired” B and N atoms, however, striking magnetism is also found to survive, rationalized by a unique zigzag-like pairing pattern. The ribbons can present remarkable edge magnetoelectric effects, for which the edge magnetoelectric coefficient is defined and calculated. The obtained d0 magnetism and the large magnetoelectric effect are helpful to explore possible spintronic applications in BCN systems.