Research on Multiscale Modeling and Experiment of CFRP Milling.

High-quality milling of carbon fiber reinforced polymer (CFRP) composites is of great importance for the high-performance manufacturing of structures made of this hard-to-machine material. In this paper, a multiscale finite element (FE) model, considering the thermal-mechanical coupling effect, was developed to simulate the milling process and reveal its material removal mechanism. The corresponding milling experiments were conducted to validate the simulated cutting forces and temperature, which were in good agreement with the experiment results. In the macroscale model, the Hashin failure criteria were used to estimate the failure of the composites. In the microscale model, the fibers, matrix, and the fiber-matrix interface were modeled separately, to investigate the mechanisms of material removal behavior during milling, among fiber breakage, matrix cracking, and fiber-matrix debonding. Based on the macroscale numerical and experimental results, the higher cutting speed was demonstrated to improve the surface quality of CFRP milling. According to the results from the microscale model, the material removal mechanism varies depending on the orientation of the fibers and can be divided into four stages. The outcome of this work provides guidelines to further investigate optimal manufacturing parameters for the milling of CFRP composites and their cutting mechanisms.

Modeling and Analysis of Wave Energy Harvester with Symmetrically Distributed Galfenol Cantilever Beams.

In response to the challenges of difficult energy supply and high costs in ocean wireless sensor networks, as well as the limited working cycle of chemical batteries, a cylindrical wave energy harvester with symmetrically distributed multi-cantilever beams was designed with Galfenol sheet as the core component. The dynamic equation of the device was established, and ANSYS transient dynamic simulations and Jiles-Atherton hysteresis model analysis were conducted to develop a mathematical model of the induced electromotive force of the Galfenol cantilever beam as a function of deformation. Experimental validation demonstrated that the simulated results of the cantilever beam deformation had an average error of less than 7% compared to the experimental results, while the average error between the theoretical and experimental values of the induced electromotive force of the device was around 15%, which preliminarily verifies the validity of the mathematical model of the device, and should be subject to further research and improvement.

The influence of pressure on the acoustic cavitation in saturated CO2-expanded N, N-dimethylformamide.

CO2-expanded organic solvent is a kind of important fluid medium and has broad applications in chemical industry, environmental protection and other fields. Ultrasonic cavitation in gas expanded liquids (GXLs) is conducive to enhancing mass transfer and producing many exciting phenomena. In this paper, the ultrasonic cavitations and streaming in the saturated CO2-expanded liquid N, N-dimethylformamide (DMF) at 4.2 MPa and 5.2 MPa are observed by a high-speed camera. The cavitation intensity and time trace of pressure pulses are recorded using a PZT hydrophone. The influences of gas-liquid equilibrium pressure and ultrasonic power on the cluster dynamics of transient and stable cavitation are examined. The excess molar enthalpies required for CO2 dissociation from DMF are calculated by Peng-Robinson equations of state and the change of surface free energy of CO2-expanded DMF is predicted. The results show that the excess enthalpy of the mixture is one of the key factors to control ultrasonic cavitation at high pressurized conditions, while the surface tension is the key factor for low pressure. As the increase of applied ultrasonic power, the formation and collapsing frequency of bubble clusters increases, and the amplitude and cyclic frequency of pressure pulse are enhanced. The transient cavitation intensity increases as it reaches a maximum value at a certain ultrasonic power and then decreases. The change trends of stable cavitation intensity under different pressures are basically same. It can be concluded from the evidence that ultrasonic cavitation in CO2-expanded DMF is affected by the combined effect of compression and substitution: compression depresses the nucleation and growth of bubbles, while the high solubility of CO2 in DMF is conducive to the generation of bubbles in cavitation.

Ultrasonic cavitation in CO2-expanded N, N-dimethylformamide (DMF).

Due to the tunability in mass transfer, solvation and solubility, gas-expanded liquids show advantages over traditional organic solvents in many characteristics. Ultrasonication is a commonly used method to promote heat and mass transfer. The introduction of ultrasonic technology into the gas-expanded liquid system can promote the polymerization of polymer monomers, enhance extraction efficiency, and control the growth size of nanocrystals, etc. Although acoustic cavitation has been extensively explored in aqueous solutions, there are still few studies on cavitation in organic liquids, especially in gas-expanded liquid systems. In this article, the development of cavitation bubble cloud structure in CO2-expanded N, N-dimethylformamide (DMF) was observed by a high-speed camera, and the cavitation intensity was recorded using a spherical hydrophone. It was found that the magnitude of the transient cavitation energy was not only related to input power, but also closely related to CO2 content. The combination of ultrasound (causing a rapid alternation of gas solubility) and gas-expanded liquid system (causing a decrease in viscosity and surface tension of liquids) is expected to provide a perfect platform for high-speed mass transfer.

Design and Analysis of a Magnetically Coupled Multi-Frequency Hybrid Energy Harvester.

The approach to improve the output power of piezoelectric energy harvester is one of the current research hotspots. In the case where some sources have two or more discrete vibration frequencies, this paper proposed three types of magnetically coupled multi-frequency hybrid energy harvesters (MHEHs) to capture vibration energy composed of two discrete frequencies. Electromechanical coupling models were established to analyze the magnetic forces, and to evaluate the power generation characteristics, which were verified by the experimental test. The optimal structure was selected through the comparison. With 2 m/s2 excitation acceleration, the optimal peak output power was 2.96 mW at 23.6 Hz and 4.76 mW at 32.8 Hz, respectively. The superiority of hybrid energy harvesting mechanism was demonstrated. The influences of initial center-to-center distances between two magnets and length of cantilever beam on output power were also studied. At last, the frequency sweep test was conducted. Both theoretical and experimental analyses indicated that the proposed MHEH produced more electric power over a larger operating bandwidth.

Isolation and molecular identification of endophytic diazotrophs from seeds and stems of three cereal crops.

Ten strains of endophytic diazotroph were isolated and identified from the plants collected from three different agricultural crop species, wheat, rice and maize, using the nitrogen-free selective isolation conditions. The nitrogen-fixing ability of endophytic diazotroph was verified by the nifH-PCR assay that showed positive nitrogen fixation ability. These identified strains were classified by 879F-RAPD and 16S rRNA sequence analysis. RAPD analyses revealed that the 10 strains were clustered into seven 879F-RAPD groups, suggesting a clonal origin. 16S rRNA sequencing analyses allowed the assignment of the 10 strains to known groups of nitrogen-fixing bacteria, including organisms from the genera Paenibacillus, Enterobacter, Klebsiella and Pantoea. These representative genus are not endophytic diazotrophs in the conventional sense. They may have obtained nitrogen fixation ability through lateral gene transfer, however, the evolutionary forces of lateral gene transfer are not well known. Molecular identification results from 16S rRNA analyses were also confirmed by morphological and biochemical data. The test strains SH6A and MZB showed positive effect on the growth of plants.

[Clinical study on continuous plasma filtration absorption treatment for burn sepsis].

OBJECTIVE: To observe the therapeutic effects of continuous plasma filtration absorption (CPFA) treatment on burn sepsis. METHODS: Thirty burn patients with sepsis hospitalized in Beijing Fengtai You'anmen Hospital from July 2009 to October 2012 were treated by CPFA for twice besides routine treatment. The blood samples were collected at five sites (A, B, C, D, and E, respectively) of blood purification equipment before and after CPFA, before and after hemoabsorption, and before hemofiltration. The plasma levels of TNF-α, IL-1ß, IL-6, IL-10, interleukin-1 receptor antagonist (IL-1RA), soluble tumor necrosis factor receptor (sTNFR) I , and sTNFR-II from sites A, C, and E were determined with ELISA before CPFA was performed for the first time, and those from sites B and D were determined with ELISA after CPFA was performed for the first time. Plasma levels of the above-mentioned cytokines from sites A and B were determined with ELISA before CPFA and after CPFA was performed for the second time. The data of plasma levels of IL-1ßP3, IL-1RA, sTNFR-I, sTNFR-II, and TNF-α before CPFA and after CPFA was performed for the second time were collected for calculation of the ratios of IL-1RA to IL-1ß and sTNFR-I plus sTNFR-II to TNF-α. The expression rate of human leukocyte antigen DR (HLA-DR) on the CD14 positive monocytes, acute physiology and chronic health evaluation (APACHE) II score, body temperature, pulse, respiratory rate, and leukocyte count of patients were evaluated or recorded before CPFA and after CPFA was performed for the second time. Patients'condition was observed. Data were processed with paired t test. RESULTS: The plasma levels of TNF-α, IL-1ß, IL-6 and IL-10 from site B after CPFA was performed for the second time were significantly lower than those from site A before CPFA was performed for the first time (with t values respectively 7.05, 5.23, 4.73, 2.37, P values below 0.01). After CPFA was performed for the first time, the plasma levels of TNF-α, IL-1ß, and IL-6 from site D were significantly lower than those from site C before CPFA was performed for the first time (with t values respectively 5.48, 2. 17, 1.78, P < 0.05 or P <0.01). The plasma levels of all cytokines were close between site B after CPFA was performed for the first time and site E before CPFA was performed for the first time (with t values from 0.04 to 1.05, P values above 0.05). The plasma levels of TNF-α, IL-1ß, and IL-6 from site B after CPFA was performed for the second time were significantly lower than those from site A before CPFA was performed for the second time (with t values from 1.87 to 5.93, P <0.05 or P <0.01). The ratios of IL-1RA to IL-1ß and sTNFR-I plus sTNFR-II to TNF-α, and expression rate of HLA-DR were increased significantly after CPFA was performed for the second time as compared with those before CPFA (with t values from 3.99 to 7. 80, P values below 0.01). APACHE II score after CPFA was performed for the second time was 11 ± 6, which was lower than that before CPFA (22 ± 7, t =4.63, P <0.01). After CPFA was performed for the second time, body temperature, pulse, and respiratory rate of patients were improved (with t values from 1.95 to 3.55, P values below 0.05) , and the leukocyte count was significantly decreased (t =4.36, P <0.01) as compared with those before CPFA. All patients survived and were discharged with length of stay of (27 ± 31) d, and no adverse effects occurred during CPFA treatment. CONCLUSIONS: CPFA, which combines hemoabsorption and hemofiltration, can facilitate the treatment of burn sepsis by decreasing the level of pro-inflammatory cytokines efficiently, alleviating systemic inflammatory response, and improving the immune status.

[Preliminary study on outcome of xenogeneic (porcine) acellular dermal matrix in vivo].

OBJECTIVE: To investigate the outcome of xenogeneic (porcine) acellular dermal matrix in vivo. METHODS: Xenogeneic (porcine) acellular dermal matrix was prepared by removing cellular components with trypsin and triton X-100 and was embedded under the skin of SD rat. Gross and histological changes were observed periodically. RESULTS: There was no cellular components but with intact basal membrane, and collagen was found to have a regular arrangement in xenogeneic (porcine) acellular dermal matrix. Grossly, the xenogeneic (porcine) acellular dermal matrix was found to disintegrate gradually. Histological examination revealed that xenogeneic (porcine) acellular dermal matrix was mainly infiltrated by inflammatory cells in one week after implantation. After one week, fibroblasts and capillary vessel increased in number gradually, and collagen began to arrange densely in regular manner. CONCLUSION: Xenogeneic (porcine) acellular dermal matrix disintegrates gradually after transplantation, inducing growth of fibroblasts and capillaries.