To predict the segregation effect in metal injection moulding (MIM) injection, a bi-phasic model based on mixture theory is adopted in simulation. An explicit algorithm is developed and realized by the authors, which ...To predict the segregation effect in metal injection moulding (MIM) injection, a bi-phasic model based on mixture theory is adopted in simulation. An explicit algorithm is developed and realized by the authors, which conducts the simulation to be a cost-effective tool in MIM technology. In case of the bi-phasic simulation, the viscosity behaviours are necessary to be determined for the flows of each phase while only the viscosity of mixture is measurable by tests. It is a crucial problem for application of the bi-phasic simulation of MIM injection. A reasonable method is hence analysed and proposed to determine the viscosity behaviours of each phase. Even though this method may be furthermore modified in the future, it results in the practical simulation of segregation effects with reasonable parameters. The simulation results are compared with the measurements on injected specimens.展开更多
Metal injection moulding (MIM) is a new technology to manufacture small intricate parts in large quantity. Numerical simulation plays an important role in its development. To predict the specific segregation effect in...Metal injection moulding (MIM) is a new technology to manufacture small intricate parts in large quantity. Numerical simulation plays an important role in its development. To predict the specific segregation effect in MIM injection, mixture theory is adopted to model the injection flow by a bi-phasic model. This model conducts to the solution of two-coupled Stokes equations. It is an extremely computational consuming solution in the scope of the traditional algorithms, which induce a serious challenge to cost-effectivity of the MIM simulation. Referred to some methods proposed by Lewis in mono-phasic simulation and the implicit algorithms in MIM simulation, a new explicit algorithm is proposed and realized to perform efficiently this type of bi-phasic flow. Numerically this algorithm is devised to perform the simulation in a fully uncoupled manner except for a global solution of the pressure field in each time step. The physical coupling is taken into account in a sequential pattern by fractional steps.展开更多
A bi-phasic scaffold consisting of a columnar formaldehyde-acetalized polyvinyl alcohol (PVF) sponge and a cylindrical porous hydroxyapatite (HA) with a hollow center was devised. Rat bone marrow cells (rBMCs) were se...A bi-phasic scaffold consisting of a columnar formaldehyde-acetalized polyvinyl alcohol (PVF) sponge and a cylindrical porous hydroxyapatite (HA) with a hollow center was devised. Rat bone marrow cells (rBMCs) were seeded into the sponge placed in the hollow center of the cylindrical porous HA. The bi-phasic scaffold, a cylindrical porous HA and a PVF sponge separated from a bi-phasic scaffold after rBMC seeding, and a PVF sponge without rBMCs as a negative control, were implanted for 6 weeks into rat dorsal subcutaneous tissue. In each construct, bone formation was examined histologically and osteocalcin was measured immunochemically. Bone formation was observed in the bi-phasic scaffold and also in the cylindrical porous HA isolated from the bi-phasic scaffold. A significant difference in the quantity of osteocalcin was observed between the bi-phasic scaffold and the isolated cylindrical porous HA. No bone formation was found in the isolated PVF sponge. The bi-phasic scaffold as an outer layer of the scaffold seemed to inhibit the outflow of rBMCs from the PVF sponge. This type of bi-phasic scaffold may have two specific characteristics: Attachment of cells both in PVF sponge and cylindrical porous HA.展开更多
Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe ...Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.展开更多
The bit error rate （BER） performance of multi-user direct spreading bi-phase shift keying （DSBPSK） direct impulse ultra wideband （UWB） systems is analyzed and simulated based on a statistical indoor multi-path f...The bit error rate （BER） performance of multi-user direct spreading bi-phase shift keying （DSBPSK） direct impulse ultra wideband （UWB） systems is analyzed and simulated based on a statistical indoor multi-path fading channel model. The BER of the system is theoretically derived and given in closed form, which is expressed in terms of channel parameters and system parameters such as pulse width parameter, pulse repeat period, user number and pulse waveform. With this BER expression, the effect of these parameters on the system performance can be evaluated in a uniform way. Simulation results well match the theory numerical results, and prove that the multi-access interference （MAI） of DS-BPSK UWB is a normal distribution.展开更多
A variety of carbonyl compounds can be converted into oximes efficiently and conveniently in a novel ionic liquid/water bi-phasic system in the presence of sodium bicarbonate at ambient temperature. The ionic liquid 1...A variety of carbonyl compounds can be converted into oximes efficiently and conveniently in a novel ionic liquid/water bi-phasic system in the presence of sodium bicarbonate at ambient temperature. The ionic liquid 1-butyl-3-methyl imidazolium hexafluorophosphate [bmim]PF6 is immiscible with water or diethyl ether and can be easily recycled for reuse without noticeable droping in activity after separation of the products. The protocol is rapid, the yields are excellent, the method is simple and the ionic liquid can be reused.展开更多
Employing the poroelastic theory of acoustic waves in gels, the ultrasound (US) propagation in a gel medium filled by poroelastic spherical cells is studied. The equation of fast compressional wave, the phase velocity...Employing the poroelastic theory of acoustic waves in gels, the ultrasound (US) propagation in a gel medium filled by poroelastic spherical cells is studied. The equation of fast compressional wave, the phase velocity and the attenuation as a function of the elasticity, porosity and concentration of the cells into the gel matrix are investigated. The outcomes of the theory agree with the preliminary measurements done on PVA gel scaffolds inseminated by porcine liver cells at various concentrations. The feasibility of a non-invasive technique for the health assessment of soft biological tissues steaming by the model is analyzed.展开更多
Signal modulation is an essential design factor for proximity detectors and directly affects the system's potential performance.In order to achieve the advantages of chaotic codes bi-phase modulation(CCBPM)and lin...Signal modulation is an essential design factor for proximity detectors and directly affects the system's potential performance.In order to achieve the advantages of chaotic codes bi-phase modulation(CCBPM)and linear frequency modulation(LFM) simultaneously,this paper designed a waveform which combined chaotic codes bi-phase modulation and linear frequency modulation(CCBPM-LFM) for proximity detectors.The CCBPM-LFM waveform was analyzed in the aspect of time delay resolution(TDR) and Doppler tolerance(DT) based on ambiguity function(AF).Then,a ranging method,which we called instant correlation harmonic demodulation(ICHD),was presented for the detector using the CCBPM-LFM waveform.By combining time domain instant correlation with harmonic demodulation,the ICHD solved the problem caused by combination modulation and made the most of the linear frequency modulation(LFM) harmonics and the correlation of chaotic codes.Finally,a prototype was implemented and ranging experiments were carried out.From the theoretical analysis and experimental results,the proximity detector used the CCBPM-LFM waveform has an outstanding detection performance.展开更多
The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite(HA)and beta tri-calcium phosphate(β-TCP).Prior to fo...The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite(HA)and beta tri-calcium phosphate(β-TCP).Prior to formulating the paste,HA andβ-TCP were calcined at 800℃and 975℃(11 h),milled,and blended into 15%/85%HA/β-TCP volume-mixed paste.Fabricated cylindrical rods were subsequently sintered to 900℃,1100℃or 1250℃.The sintered specimens were characterized by helium pycnometry,X-ray diffraction(XRD),Fourier transform-infrared(FT-IR),and inductively coupled plasma(ICP)spectroscopy for evaluation of porosity,crystalline phase,functional-groups,and Ca:P ratio,respectively.Mechanical properties were assessed via 3-point bending and diametral compression.Qualitative microstructural evaluation using scanning electron microscopy(SEM)showed larger pores and a broader pore size distribution(PSD)for materials sintered at 900℃and 1100℃,whereas the 1250℃samples showed more uniform PSD.Porosity quantification showed significantly higher porosity for materials sintered to 900℃and 1250℃(p<0.05).XRD indicated substantial deviations from the 15%/85%HA/β-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased.Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes(p<0.05).Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.展开更多
文摘To predict the segregation effect in metal injection moulding (MIM) injection, a bi-phasic model based on mixture theory is adopted in simulation. An explicit algorithm is developed and realized by the authors, which conducts the simulation to be a cost-effective tool in MIM technology. In case of the bi-phasic simulation, the viscosity behaviours are necessary to be determined for the flows of each phase while only the viscosity of mixture is measurable by tests. It is a crucial problem for application of the bi-phasic simulation of MIM injection. A reasonable method is hence analysed and proposed to determine the viscosity behaviours of each phase. Even though this method may be furthermore modified in the future, it results in the practical simulation of segregation effects with reasonable parameters. The simulation results are compared with the measurements on injected specimens.
基金Supported by the Invited Professor Program of French Ministry of Education (No. 9808588) , the French-Chinese Advanced Research Program (M98-04)the Foundation for University Key Teacher by the Chinese Ministry of Education (GG-460-10613-2770).
文摘Metal injection moulding (MIM) is a new technology to manufacture small intricate parts in large quantity. Numerical simulation plays an important role in its development. To predict the specific segregation effect in MIM injection, mixture theory is adopted to model the injection flow by a bi-phasic model. This model conducts to the solution of two-coupled Stokes equations. It is an extremely computational consuming solution in the scope of the traditional algorithms, which induce a serious challenge to cost-effectivity of the MIM simulation. Referred to some methods proposed by Lewis in mono-phasic simulation and the implicit algorithms in MIM simulation, a new explicit algorithm is proposed and realized to perform efficiently this type of bi-phasic flow. Numerically this algorithm is devised to perform the simulation in a fully uncoupled manner except for a global solution of the pressure field in each time step. The physical coupling is taken into account in a sequential pattern by fractional steps.
文摘A bi-phasic scaffold consisting of a columnar formaldehyde-acetalized polyvinyl alcohol (PVF) sponge and a cylindrical porous hydroxyapatite (HA) with a hollow center was devised. Rat bone marrow cells (rBMCs) were seeded into the sponge placed in the hollow center of the cylindrical porous HA. The bi-phasic scaffold, a cylindrical porous HA and a PVF sponge separated from a bi-phasic scaffold after rBMC seeding, and a PVF sponge without rBMCs as a negative control, were implanted for 6 weeks into rat dorsal subcutaneous tissue. In each construct, bone formation was examined histologically and osteocalcin was measured immunochemically. Bone formation was observed in the bi-phasic scaffold and also in the cylindrical porous HA isolated from the bi-phasic scaffold. A significant difference in the quantity of osteocalcin was observed between the bi-phasic scaffold and the isolated cylindrical porous HA. No bone formation was found in the isolated PVF sponge. The bi-phasic scaffold as an outer layer of the scaffold seemed to inhibit the outflow of rBMCs from the PVF sponge. This type of bi-phasic scaffold may have two specific characteristics: Attachment of cells both in PVF sponge and cylindrical porous HA.
基金Specialized Research Fund for the Doc-toral Program of Higher Education (No.20020613005)
文摘Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.
基金The National High Technology Research and Deve-lopment Program of China (863Program) (Nos.2001AA123042,2003AA123330,2005AA123320).
文摘The bit error rate （BER） performance of multi-user direct spreading bi-phase shift keying （DSBPSK） direct impulse ultra wideband （UWB） systems is analyzed and simulated based on a statistical indoor multi-path fading channel model. The BER of the system is theoretically derived and given in closed form, which is expressed in terms of channel parameters and system parameters such as pulse width parameter, pulse repeat period, user number and pulse waveform. With this BER expression, the effect of these parameters on the system performance can be evaluated in a uniform way. Simulation results well match the theory numerical results, and prove that the multi-access interference （MAI） of DS-BPSK UWB is a normal distribution.
基金The project was supported by the National Natural Science Foundation of China(No 20272018)the Guangdong Natural Science Foundation(No 021166,04010458)the Scientific Research Foundation for the Retumed Overseas Chinese Scholars,State Education Ministry of China.
文摘A variety of carbonyl compounds can be converted into oximes efficiently and conveniently in a novel ionic liquid/water bi-phasic system in the presence of sodium bicarbonate at ambient temperature. The ionic liquid 1-butyl-3-methyl imidazolium hexafluorophosphate [bmim]PF6 is immiscible with water or diethyl ether and can be easily recycled for reuse without noticeable droping in activity after separation of the products. The protocol is rapid, the yields are excellent, the method is simple and the ionic liquid can be reused.
文摘Employing the poroelastic theory of acoustic waves in gels, the ultrasound (US) propagation in a gel medium filled by poroelastic spherical cells is studied. The equation of fast compressional wave, the phase velocity and the attenuation as a function of the elasticity, porosity and concentration of the cells into the gel matrix are investigated. The outcomes of the theory agree with the preliminary measurements done on PVA gel scaffolds inseminated by porcine liver cells at various concentrations. The feasibility of a non-invasive technique for the health assessment of soft biological tissues steaming by the model is analyzed.
基金supported by the State Key Program of Basic Research of China under Grant No.613196the National Natural Science Foundation of China under Grant No.61673066。
文摘Signal modulation is an essential design factor for proximity detectors and directly affects the system's potential performance.In order to achieve the advantages of chaotic codes bi-phase modulation(CCBPM)and linear frequency modulation(LFM) simultaneously,this paper designed a waveform which combined chaotic codes bi-phase modulation and linear frequency modulation(CCBPM-LFM) for proximity detectors.The CCBPM-LFM waveform was analyzed in the aspect of time delay resolution(TDR) and Doppler tolerance(DT) based on ambiguity function(AF).Then,a ranging method,which we called instant correlation harmonic demodulation(ICHD),was presented for the detector using the CCBPM-LFM waveform.By combining time domain instant correlation with harmonic demodulation,the ICHD solved the problem caused by combination modulation and made the most of the linear frequency modulation(LFM) harmonics and the correlation of chaotic codes.Finally,a prototype was implemented and ranging experiments were carried out.From the theoretical analysis and experimental results,the proximity detector used the CCBPM-LFM waveform has an outstanding detection performance.
文摘The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite(HA)and beta tri-calcium phosphate(β-TCP).Prior to formulating the paste,HA andβ-TCP were calcined at 800℃and 975℃(11 h),milled,and blended into 15%/85%HA/β-TCP volume-mixed paste.Fabricated cylindrical rods were subsequently sintered to 900℃,1100℃or 1250℃.The sintered specimens were characterized by helium pycnometry,X-ray diffraction(XRD),Fourier transform-infrared(FT-IR),and inductively coupled plasma(ICP)spectroscopy for evaluation of porosity,crystalline phase,functional-groups,and Ca:P ratio,respectively.Mechanical properties were assessed via 3-point bending and diametral compression.Qualitative microstructural evaluation using scanning electron microscopy(SEM)showed larger pores and a broader pore size distribution(PSD)for materials sintered at 900℃and 1100℃,whereas the 1250℃samples showed more uniform PSD.Porosity quantification showed significantly higher porosity for materials sintered to 900℃and 1250℃(p<0.05).XRD indicated substantial deviations from the 15%/85%HA/β-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased.Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes(p<0.05).Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.
