Cold sintering assisted CaF2 microwave dielectric ceramics for C-band antenna applications

A cold sintering process is adopted to pre-densify CaF₂ ceramics from 85.7% at 300 MPa to 91.7% at 750 MPa. Subsequent post-annealings at 1000–1150 °C lead to further improvements in densification, where great enhancements of grain size and crystallinity are also observed from the scanning and transmission electron micrographs. Significant advances in Qf values are achieved in the post-annealed CaF₂ ceramics. The optimum Qf value (80,522 GHz) is achieved after cold sintering at 750 MPa and post-annealing at 1000 °C, which is three times higher than the conventional sintered one at 1000 °C (26,448 GHz). Moreover, the obtained low-ε_r (5.9–6.5) of CaF₂ ceramics suggests broad application prospects in the high-band microwave communications. A microstrip patch antenna is fabricated using the CaF₂ ceramics as the substrate, which operates at 7.89 GHz in the C-band, with an S₁₁ of ?13.4 dB, simulated high gain and efficiency of 6.41 dBi and ?0.56 dB, respectively.     

基于有限元的全地形车车架刚性分析

通过建立全地形车车架的有限元模型,运用有限元分析的方法,采用合理的模型简化,对全地形车车架的弯曲刚度、侧向刚度和扭转刚度进行了力学分析,应力云图给出其薄弱部位;对车架提出了合理的改进意见,以保证全地形车车架具有足够的刚度。为全地形车车架结构的改进和优化提供了参考。     

Computer simulation of proteins adsorption on hydroxyapatite surfaces with calcium phosphate ions

Protein adsorption plays a key role in determining the biological properties of calcium phosphate biomaterials. Calcium (Ca) and phosphate (P) ions are involved in the protein adsorption process and influence the protein adsorption behaviors. In this study, the proteins adsorption on hydroxyapatite (HA) (001), (100), (110), (010) surfaces with Ca, P ions in solution were investigated by Molecular Dynamics (MD) simulation. The results reveal that basic proteins were more favorable to adsorb on HA surface than acidic proteins. HA (110) surface absorbed more acidic proteins than HA (001) and (100). HA (010) surface adsorbed more basic protein. Basic residues play a more important role than acidic residues in the adsorption process, as the basic residues have shown higher absorption energy than acidic residues, and they were more likely to adsorb on HA surfaces than to bind P ions in solution. Most of the active sites of protein, especially for acidic residues, are prefer to interact with HA surface through water molecules. Basic residues are more likely to adsorb onto HA surfaces directly. The presence of Ca, P ions in solution can influence the adsorption behaviors of protein. The formation of Ca, P ion cluster may lead to desorption of proteins. And they can compete with water molecules to bond to HA surfaces, acting as a bridge of protein interacting with HA surfaces instead of water-bridge. This Ca, P ions bridge connection make the adsorption energy of protein weakened. The results of this study provided new information at atomic/molecular level to further interpret the mechanism of protein adsorption on calcium phosphate surfaces with Ca, P ions. It is also helpful for designing new calcium phosphate biomaterials with specific surface properties to adsorb target protein for biomedical applications.     

钛合金结构件磁流变电解复合抛光试验研究

目的 针对钛合金结构件高质高效抛光需求，提出了磁流变电解复合抛光新方法，探究不同抛光参数对钛合金表面质量的影响，以实现钛合金构件的高质高效抛光。方法 深入探究了加工电压、加工间隙、电解质质量分数和抛光转速等参数对钛合金抛光表面粗糙度以及粗糙度变化率的影响，分析了不同抛光参数下的钛合金表面形貌变化，验证了磁流变电解复合抛光钛合金的可行性。结果 随着电解液中Na NO3质量分数的提高，钛合金表面粗糙度先减小后增大，质量分数为1.0%～2.5%时，得到了优于单磁流变抛光加工的抛光效果。不同加工电压下的表面粗糙度对比结果表明，在加工电压为0.1 V时，钛合金加工后表面粗糙度达到最小，而后随着加工电压的增大，加工区域表面粗糙度呈现增大趋势；随着加工间隙的增大，钛合金抛光表面粗糙度呈现先减小后增大的趋势；随着抛光工具转速增大，钛合金加工后表面粗糙度先减小后增大。相比于单一的磁流变抛光，磁流变电解复合抛光钛合金90 min，可使表面粗糙度从初始323 nm降低至15nm，加工效率提高了62.5%。结论 磁流变电解复合抛光工艺能够用于钛合金人工关节假体高效高质量的抛光。     

Removal of greases and lubricating oils from metal parts of machinery processes by subcritical water treatment

Toxic or persistent solvents have been widely used to remove greases and lubricants from various machine elements in the washing processes. In this study, an alternative degreasing method that employed subcritical state water was assessed. This environmentally benign solvent has significant potential for various degreasing applications. The operation time and temperature and flow rate of subcritical water had markedly positive impacts on the degreasing efficiency. However, the effect of pressure of subcritical water flow was minimal. The degreasing efficiency was also highly dependent on the physical characteristics and chemical composition of grease. The subcritical water treatment demonstrated a better degreasing efficiency than conventional degreasing methods. Only minor physical damage was observed on the metal parts after the subcritical water treatment. Conclusively, it was found that the subcritical water degreasing system can be used as an effective degreasing technology for machinery operations.     

The influence of a polymeric nucleating additive on the crystallisation in glass fibre reinforced polyamide 6 composites

Short glass fibre reinforced polyamide 6 composites compounded with a polymeric nucleating additive based on polyamide 2.2 of different content (0, 0.1 and 0.2 wt%) and processed by injection moulding have been studied to characterise the additive effect on the crystallisation kinetics and morphology. Differential scanning calorimetrical and optical hot stage experiments have shown a significant increase in the overall crystallisation rate as well as the spherulitic growth, respectively with nucleating additive content. Additionally, the presence of glass fibres is proven to enhance crystallisation. Atomic force microscopy confirms the existence of a transcrystalline layer in the vicinity of the glass fibres. The nucleating additives have significantly decreased the spherulitic size from about 15 to 20 μm towards less than 5 μm, which leads to an improved fibre-to-matrix contact. Those morphological changes are seen as the reason for a strong increase in the Martens heat deflection temperature from 145 to 164 °C characterising an improved thermal stability.     

Numerical characterization of compressive response and damage evolution in laminated plates containing a cutout

A micromechanical constitutive model [Liang Z, Lee HK, Suaris W. Micromechanics-based constitutive modeling for unidirectional laminated composites. Int J Solid Struct 2006;43:5674–89], based on the concept of the ensemble-volume average for laminated composites, is implemented into a finite element program to numerically characterize the compressive response and damage evolution in laminated plates containing a cutout. Prior to the implementation of the model into the finite element program, the predicted moduli of laminated composites are compared with analytical bounds and experimental data for the validation and verification of the constitutive model. A series of numerical simulations for a uniaxial test of laminated plate specimens containing a cutout are conducted using the implemented constitutive model. The predictions are compared with experimental data [Lessard LB, Chang FK. Damage tolerance of laminated composites containing an open hole and subjected to compressive loadings: Part II-Experiment. J Compos Mater 1991;25:44–64; Chang FK, Lessard LB. Damage tolerance of laminated composites containing an open hole and subjected to compressive loadings: Part I-Analysis. J Compos Mater 1991;25:2–43] to verify the accuracy of the implemented constitutive model. A parametric study is also carried out to illustrate the influence of the geometry of the specimens on the behavior of laminated plates. It is shown that the implemented constitutive model is suitable for the analysis of the constitutive behavior of laminated plates having a dilute or moderate fiber volume fraction.     

Analysis of the dynamic flexural behaviour of composite beams at low temperature

In this study, the dynamic flexural behaviour at low temperatures of beams of three carbon/epoxy laminates is evaluated, analysing the influence of temperature on the mechanical strength, stiffness and absorbed energy until failure. Three-point bending tests were performed under dynamic conditions at three different temperatures (20 °C, −60 °C and −150 °C), and the results were compared with those found under static conditions at the same temperatures. Both the mechanical strength and the absorbed energy decreased when the temperature diminished in all the laminates. No significant influence of temperature was noted on the effective flexural modulus. Two analytical models, using the classical laminated theory and the first-order shear deformation laminate theory, and a numerical model were used to analyse the experimental results of the tests. The models allowed to ensure the use of the equations, which do not consider inertia forces, to calculate the test parameters, and they provided the specimen support span to neglect shear effects. They served also to determine the origin of the noise present in the load measured in the dynamic tests.     

The influence of polyphony on the dynamical modelling of musical timbre

This letter addresses the problem of pattern recognition of polyphonic musical timbre. Frame-level dynamics of audio features are particularly difficult to model, although they have been identified as crucial perceptive dimensions of timbre perception. Recent studies seem to indicate that traditional means to model data dynamics, such as delta-coefficients, texture windows or Markov modelling, do not provide any improvement over the best static models for real-world, complex polyphonic textures of several seconds’ length. This contradicts experimental data on the perception of individual instrument notes. This letter describes an experiment to identify the cause of this contradiction. We propose that the difficulty of modelling the dynamics of full songs results either from the complex structure of the temporal succession of notes, or from the vertical polyphonic nature of individual notes. We discriminate between both hypothesis by comparing the performance of static and dynamical algorithms on several specially designed datasets, namely monophonic individual notes, polyphonic individual notes, and polyphonic multiple-note textures. We conclude that the main cause of the difficulty of modelling dynamics of real-world polyphonic musical textures is the polyphonic nature of the data.