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The internal gelation process without cooling at room temperature is a significant challenge for the preparation of yttria-stabilized zirconia (YSZ) ceramic microspheres. In this work, a high-throughput and instant-mixing droplet microfluidic system that can prepare monodisperse YSZ ceramic microspheres was constructed. It mixed two stable solutions at room temperature in an active micromixer at a flow rate of mL/min, and then the mixed unstable precursor solution was quickly dispersed into sol droplets through a coaxial microfluidic device, and the droplets solidified into gel microspheres. The washed and dried gel microspheres could be sintered to obtain ceramic microspheres. Compared with no-micromixing and T-junction micromixers, the system had the best mixing performance and Y and Zr elements in the prepared ceramic microspheres were evenly distributed. Therefore, the system overcame the problem of precursor solution solidification and clogging of the device, and provided a new approach for the internal gelation process without cooling at room temperature.

There is the diverse range of disciplines studying various topics using x-ray techniques. Now, with the development of third-generation synchrotron sources, we can conduct experiments which require special properties of x-ray beam, such as coherence and polarization for studying materials characterization, structural changes, molecular or spin dynamics and so on. In this thesis, we would present the results of structural and dynamic studies by synchrotron-produced x-ray sources. First, the lipid phase-separated bilayers are studied by resonant soft x-ray scattering. In the novel finding, we find the domains of the so-called liquid ordered phase in the phase-separated mixed lipid-cholesterol multilayers constitute sub-domains which are three-dimensionally ordered. This is one of the few examples of ordered liquid phase within another liquid phase. This offers the possibility for the development of novel materials. We also discuss the utilization of coherent x-ray beams to study the dynamics of nanoparticles in polymer melts and magnetic spins in spin glass systems. The nanoparticles show different diffusive and often novel behaviors depending on the entanglement and the heat treatment. Studying the spin structures of spin glass is always interesting and challenging. Up to now, the detailed observation of spin glass phase transition associated critical behaviors have elucidated experimental studies, such as neutron scattering. Using coherent x-rays, we have been able to couple directly to the critical fluctuations of the so-called Edwards-Anderson (EA) order parameter and have observed the dynamical critical behaviors for the first time.

Due to low reservoir permeability and interlayer contradictions, high water injection pressure and low water injectivity index have become a big challenge in the waterflooding development of low-permeability reservoirs. Therefore, new pressure-lowering and injection-increasing technologies have been desired. Nanotechnology offers various creative ways to solve the problems of oil and gas production that also provided a potential oilfield chemical in pressure-decreasing application. However, successful pressure decreasing nanotechnology have rarely been reported. This manuscript reports nano-polysilicon as a new depressurization and injection-increasing agent. The stability of nano-polysilicon was studied in the present of various ions, including Na+, Ca2+, and Mg2+. This study finds that the addition of nanomaterials can improve porosity and permeability of porous media. Injection / draw down test method is taken to evaluate injection effects of nano-polysilicon into water wells, and flow resistance changes are investigated by infectivity index curve. Through injection performance evaluation experiment, it is found that the nano polysilicon technology has the ability to improve the permeability and weaken flow resistance of fluids. Field test results prove that biological nano-polysilicon technology has obvious effect on pressure reduction and injection-increasing. After the operation of test wells, injection-increasing nano-polysilicon technology has excellent performances with increasing injection rate by 40% and pressure drop by 10%. This work presents the first successful oilfield test of nanoagents in pressure-decreasing application that offers a novel, simple and pollution-free oilfield chemical. The importance of this work is not in stability and salt tolerance of nanoparticle but rather in their first real field application of depressurization, which takes an exciting example for nanotechnology to effectively solve another real difficulty in petroleum engineering.

Compared with the long use of carbon materials in human history, the debut of carbon materials in the Chicago Pile-1 nuclear reactor took place only 70 years ago. Since then, carbon materials have played important roles in nuclear reactors, especially in high temperature gas-cooled reactors (HTRs) because of their many excellent properties. As the most promising candidate for Generation IV reactors, a demonstration plant for HTRs, an HTR pebble-bed module (HTR-PM) is currently under construction in China. In the HTR-PM, carbon materials act as the core structural material, reflector, fuel matrix, moderator, and thermal and neutron shields. Because the dimensions and properties of the carbon are generally influenced by the high temperature and neutron irradiation in the HTR-PM, there are rigorous requirements for their performance. Since the precursor materials such as cokes and natural graphite, and the subsequent forming method play a critical role in determining the structure, properties and performance of the material under irradiation, a judicious selection of the raw materials and forming method is required to obtain the desired structure and properties. This paper introduces the detailed property requirements of different carbon materials in the HTR-PM and their fabrication processes. In addition, the current status and future commercialization of the HTR-PM in China and abroad are presented. In order to meet the requirement of full local production in a commercial HTR, long-term considerations such as the sustainable and stable supply of the raw materials, optimization of the manufacturing process in the local production of nuclear graphite for structural graphite and graphite pebbles, and the stable production and reduced cost of the precursor materials are discussed. Finally, current progress and future arrangements for the irradiation testing of Chinese nuclear graphite at the Oak Ridge National Laboratory (USA) are presented. This manuscript is intended to act as a reference for carbon material producers who intend to develop nuclear graphite and carbon materials for use in future commercial HTRs. Meanwhile, a great deal of information introduced in the manuscript is also useful for scientific researchers of carbon materials.

The failure modes of rock and soil under compression are complex phenomena that have not been explained in a mechanical perspective. However, large amounts of studies indicate that the failure modes of rock and soil samples can be categorized into eight types. In this work, the inner tensile stress and the dissipation and conversion of energy of rock and soil under compression are analyzed, then the effective conversion coefficient of energy is deduced, thus the tensile failure criterion of rock and soil under compression is established. Combined with the shear strength criterion of Mohr–Coulomb, a tensile joint shear strength criterion for rock and soil under compression is built. Therefore, a mechanical criterion model concerning the failure modes of rock and soil under compression is established and verified by tests. This model easily explains the test results in the existing literature and many natural phenomena, such as collapse.

This paper presents a measurement of the three-dimensional structures of a micellar solution flow in a curvilinear microchannel using confocal micro particle image velocimetry. An aqueous solution of cetyltrimethylammonium chloride/sodium salicylate was used as the working fluid, and fluorescent beads were added as tracer particles. With the aid of a fast-moving piezo stage, the three-dimensional flow structure was measured by scanning the flow layer by layer in the depth direction. It was found that the internal flow oscillates, and is typically twisted. In addition, the flow direction changes according to geometric curvature. Based on the statistics of velocity features, the viscoelastic flow field inside the curved microchannel shares the main features of elastic turbulence.

As the main components of the matrix graphite of pebble fuel elements for HTR-PM, the natural flake graphite powder (NFGP) and artificial graphite powder (AGP) must present suitable microstructural features such as specific surface area (SSA), particle size distribution (PSD), and ash contents. As a regular method, the graphite powders are purified at high temperature of ~2500 °C with the purge of halogens to obtain their high purity prior to the powder treatments such as pulverizing, shaping, and particle classification, which may introduce impurities into the graphite powders during the powder treatment process. Therefore, the purification of NFGP and AGP should be carried out after the powder treatment to prevent the graphite powders from being contaminated and reduce the cost. In this manuscript, the microstructural features of NFGP and AGP before and after purification were comparatively analyzed to figure out the effects of purification process on the microstructures of NFGP and AGP. Results showed that purification had great influences on the ash contents and the contents of impurity elements, SSA, and degree of graphitization of graphite powders. However, the purification had little influence on the PSD of graphite powders. The significant decrease of SSA of graphite powders through the purification was due to the reduction of BJH adsorption cumulative volume and porosity. Comparing with those of the NFGP, the properties and microstructure of the AGP changed more through the purification process, which was probably due to the original un-graphitized coke of AGP before purification.

At the beginning, a comparative analysis was made on the oxidation corrosion rate and ash content of A3-3 matrix graphite (MG) pebbles lathed before and after high temperature purification (HTP) treatment. Their oxidation corrosion rate and ash contents were almost identical, which indicated that the HTP process was to purify the entire MG pebbles and not limited on the surfaces. Furthermore, the multiple mechanical and thermal properties of MG treated without and with the treatment of HTP at ~1900°C were compared and their microstructure features were characterized as well. As the crush strength, oxidation corrosion rate, and erosion rate of MG without HTP treatment did not satisfy the specifications, the comprehensive properties and purity of MG with HTP were improved in various degrees through the HTP process so that all performances met the requirements of the A3-3 MG. The improvement of crush strength and erosion rate of MG in the HTP process could be mainly attributed to the upgradation of ordered microstructure and corresponding increase of density. However, the enhancement of oxidation corrosion rate was due to the synergistic effects of microstructural optimization and reduction of impurity elements, especially the transition metal elements of MG in the HTP process.

Three kinds of electron-blocking layer(EBL) AlGaN based LED were compared numerically.They are conventional AlGaN EBL,AlGaN-GaN-AlGaN(AGA) and gradual Al composition AlGaN-GaN-AlGaN(GAGA) EBL.Their porfermance were analyzed involved carrier concentration in the active region,energy band diagram,electrostatic field and internal quantum efficiency(IQE).The results indicate that the LED with an GAGA EBL exhibits a better hole injection efficiency,a more peaceable efficiency droop,a lower electron leakage,and a smaller electrostatic field than the LED with a conventional AlGaN EBL or with an AGA EBL.

Effect of vibratory stress relief on titanium alloy Ti-6Al-4V fatigue life was investigated by numerical simulation method in this paper. This paper aimed to determine whether vibratory stress relief can adversely affect fatigue life of titanium alloy Ti-6Al-4V or not. Firstly, the modal analysis for titanium alloy Ti-6Al-4V specimen was carried out by using finite element method, then, using transient dynamic analysis method simulated specimen dynamic stress in vibratory stress relief process. Secondly, the finite element model that contained initial stress for VSR simulation was established. Vibratory stress relief was simulated by using transient dynamic analysis method. Finally, we used FE-safe software for fatigue simulation. It is concluded that titanium alloy Ti-6Al-4V fatigue strength increased with amplitude, but the phenomenon “much vibration” appeared when amplitude continued to increase that led to decrease of fatigue life.

A simplified model of the nano-structured polymeric surface was proposed,characterized by a one-dimensional periodic stripe patterned surface with alternate planar and homeotropic anchoring.This paper investigated the effect of both the coupling of nematic liquid crystals with alignment layer polymers and the coupling of the polymers with the substrate surface,on the anchoring of nematic liquid crystals at such a surface,using the extended anisotropic surface energy form proposed by Alexe-Ionescu et al.In our theoretical treatment,the equal anchoring strength of the two anchoring regions was assumed.The results show that the coupling of the polymer with the surface will affect the director field of the nematic,and reduce the relaxation distance as well as the total free energy of the system.

Magnetic fluid (MF) shows an increased saturation magnetization when exposed to a magnetic field. In order to improve the quality of servo-valve products by depressing and overcoming the self-excited high-frequency pressure oscillations and noise appearing in pilot stage of a hydraulic servo-valve, application of magnetic fluid in a hydraulic servo-valve is developed in this paper. Large damping can be introduced by the magnetic fluids into the servo-valve if magnetic fluids are filled into the working gaps of the hydraulic servo-valve torque motor. After the construction and working principle of a hydraulic servo-valve with magnetic fluids are introduced, the high-frequency pressure oscillation signals are tested and recorded when magnetic fluids are applied or not in the servo-valve. Experimental results are compared and analyzed by using FFT analysis method. It is shown that pressure oscillations of the servo-valve are depressed when magnetic fluids are applied.

Green InGaN/GaN multiple quantum well(MQW) LEDs employing InGaN/GaN superlattice(SL) structure were studied.The distribution of indium within the MQWs is changed by inserting the InGaN/GaN SL.Meanwhile,the average indium content of MQW does not change.Two InGaN-related peaks that were clearly found in the electroluminescence(EL) and photoluminescence(PL) spectrum,which are assigned to In-rich quantum dots(QD) and the InGaN matrix,respectively.It is suggested that the carrier drifts from the InGaN matrix to the In-rich QD.It could be concluded that employing SL structures is an effective way to adjust the wavelength of InGaN/GaN MQW without introducing new defects in the MQWs.

The preparation method of triblock Liquid Crystal(LC) elastomer films with thermal induced contraction was researched and their polarized characteristics and thermal induced contrasction rates were analyzed.By using the holographic exposure technology,a liquid crystal elastomer with a grid-like structure was prepared.Based on a polarization microscope and a He-Ne laser,grid-like structure and polarization were detected,respectively.The relationship between the LC molecular alignment and the polarization of LC elastomer was analyzed.In addition,the thermal induced contraction rate for LC elastomer was tested.The experimental results indicate that LC molecules are arranged perpendicular to grid-like structure.The deformation rate of thermal induced contraction for the liquid crystal elastomer can be achieved 12% in the LC phase transition temperature(65-80℃).

GaN is considered as a promising material for high power,high temperature and high frequency microwave applications,due to the wide band gap,high thermal stability and high breakdown voltage.Due to lack of suited homosubstrates,GaN is currently grown on heterosubstrates where SiC is the most popular choice for commercial applications.However,it is difficult to obtain high quality GaN because of the 33.1% mismatch of thermal expansion coefficients and the large lattice mismatch(3.5%) between GaN and SiC.In this paper,GaN epitaxial layers were grown on 6H-SiC substrates by metalorganic chemical vapor deposition.Samples employing high temperature AlN as buffer layers produce high quality GaN epitaxial layers. Five samples with different AlN buffer layers were prepared.The effects of the growth parameters of AlN buffer layers on characterizations of GaN were studied.The highest quality GaN layer grown on SiC substrate with AlN buffer was obtained by optimizing the growth parameters of the AlN buffer.The full width at half maximum of High-resolution X-ray diffraction on-axis(0002) and off-axis(1012) diffraction are 130 arcsec and 252 arcsec,respectively.The values are the best result of GaN grown on homemade 6H-SiC.The quality of GaN layers will be deteriorated by increasing the thickness or the growth Ⅴ/Ⅲ ratio of AlN buffer layers,while the low growth temperature of AlN buffers also deteriorate the quality of GaN layers.The strain in GaN also has been studied.It is found that the GaN layer with narrow XRC FWHM has less stress intensity.

The Young’s modulus of cross-linked poly(dimethylsiloxane) (PDMS) surface was quantitatively investigated as a function of UV/ozone treatment time across different length scales. An AFM was used to probe PDMS surface mechanical properties at the nanometer length scale. The Young’s modulus of each sample was estimated with continuum contact mechanics theory (Sneddon method) using AFM data by employing the hyperboloid tip shape model. A custom-built ATD device (JKR method) was also used which allowed us to simultaneously monitor the load, the contact area, and the relative displacement between (a) a lens (made either of PDMS elastomer or of Si3N4) and (b) surface-treated PDMS films upon loading and unloading on the micrometer to submillimeter length scales. The modulus of PDMS increased with increasing treatment time as observed by AFM as well as by ATD, which we explained by the gradual formation of a silica-like layer. For all specimens tested, the modulus values obtained were highest from AFM, lower from ATD, and lowest from bulk tensile experiments for the same UV/ozone dose. These results demonstrate the effect of the probed length scale of the tests used to assess mechanical performance

A spool type high temperature control valve is developed to control the flow rate of high temperature fuel supply for scramjet engines in this paper. The clearance between the friction pairs of the spool and sleeve is crucial for the proper performance of the valve working at the temperature as high as 700 K. The high temperature environment may cause problems to the valve, for instance the thermal deformation of the valve materials, the failure of the friction pairs inside the valve and even the damage of the operating proportional electromagnet. Therefore the thermodynamic analyses of the valve are carried out using 2D finite element analysis method. The heat transfer and fluid dynamic models, as well as the boundary conditions are introduced. The heat flux through the fluid/solid interface is calculated to connect the heat transfer models inside the solid domain and the fluid domain. By solving both the heat transfer and turbulent flow models in the solid and fluid domains, the flow field distribution inside the flow channel and the thermal field distribution inside all the parts of the valve are shown. Suggestions on the design of the valve are given according to the thermodynamic analysis results.

Being as a functional material, piezoelectric ceramics is applied to drive a micropump when it is composed to be a thin membrane on a brass film to form a diaphragm. According to the properties of the piezoelectric material, the stiffness of the diaphragm influences the vibration displacement and therefore the supply flow rate of the micropump. This paper focuses on the dynamic characteristic study of the micropump and the stiffness influence of the diaphragm on the characteristics. The mathematical model of the valve-less micropump considering the diaphragm stiffness is developed in order to predict the dynamic characteristics of the piezoelectric valve-less micropump. Using the 3-D finite element analysis (FEA) method, the static and vibration mode of the diaphragm are analyzed to obtain the diaphragm stiffness and natural frequency. The method using Matlab is to predict the pressure and flow rate characteristics of the micropump when the diaphragm stiffness is considered or not. Comparison of the simulation results shows the stiffness of the diaphragm influences the dynamic characteristics of micropumps. It also shows that the method combining FEA software with Matlab provides a possible and effective tool to take the diaphragm stiffness into account when the pressure and flow rate characteristics of micropumps are studied.

We demonstrate the ``reversed-mode'' polymer-stabilized liquid crystal device. The incidence light goes through the film without the applied voltage and is diffracted with it. Because of relatively high liquid crystal percentage of 94%, the operating voltage of the device is less than 20 V. We explain this phenomenon using the molecular orientation model and the refractive index profile. The device can be used as display, optical switch, optical modulator and especially optical cross-connect deflector.

We mix azobenzene polymer and liquid crystal in certain ratio. Then the mixture is injected into cells. Nonlinearly photoinduced birefringence takes place when linearly polarized ultraviolet is applied with the pattern photomask covering on the cells, which results in the formation of azobenzene polymer doped liquid crystal grating. The obtained grating is characterized by an optical microscope and a He–Ne laser. The results indicate that the samples have clear grating structure, and the diffraction efficiencies can be modulated by electric field. The sample driving voltage is 0.6 V/μm. It is lower than the driving voltage of holographic polymer dispersed liquid crystal transmission grating and could be matched with the driving integrated circuit.

This paper proposed a discrete operation mode for a punchthrough (PT) phototransistor, which is suitable for low power application, since the bias current is only necessary during the read-out phase. Moreover, simulation results show that with the new operation mode, the photocurrent is much larger than that of continuous operation mode. An ultra-high responsivity of 2 × 107A/W at 10−9 W/cm2 is obtained with a small detector size of 1 μm2. In CMOS image sensor applications, with an integration time of 10 ms, a normalized pixel responsivity of 220 Vm2/Wsμm2 is obtained without any auxiliary amplifier.

First-principles plan-wave pseudopotential method is used to calculate the energy bandgap properties, bowing parameters and structural properties of wurtzite BexZn1-xO alloys. The results show that the energy bandgaps and bowing parameters of BexZn1-xO alloys increase with Be content increasing. We find the energy bandgaps corrected of BexZn1-xO alloys to be in accordance with the experimental value. The reason about the energy bandgap broadening is also analyzed. The average bowing parameter of BexZn1-xO alloys is 6.02 eV, which is in good agreement with previous experimental result. The bowing parameter mostly arises from volume deformation of alloy and charge transfer effect. Futhermore, we analyze the changes of lattice parameter, average bond length and average second-neighboring distance with Be content in BexZn1-xO alloys.

The appearance of gas bubbles in a valve-less micropump is generally undesirable as they can lead to performance deterioration, life reduction and even complete failure of the micropump. In order to predict influence of gas bubbles in valve-less micropump chamber on periodic driving pressure, the mathematical models, including volume change of chamber, continuity equation, effective bulk modulus and resistance coefficients of the nozzle and diffuser, are given to describe dynamic characteristics of piezoelectric valve-less nozzle/diffuser micropump. The influence of different gas bubble volume in chamber on the valve-less micropump periodic driving pressure is analyzed. Pressure pulsations with two gas bubbles into the valve-less micropump chamber are simulated and tested. Simulation and experimental results are given. Comparison of the results shows that the mathematical model and simulation method can handle the prediction of pressure pulsations accompanying gas bubble in the valve-less micropump.

We analyze the responsivity and signal-to-noise ratio (SNR) of a punchthrough enhanced phototransistor (PEPT). Measurement results show that the PEPT exhibits a good response to light over a wide range of intensity. Because the responsivity is still as high as 106 A/W when the bias voltage is as low as 0.2 V, the device is suitable for ultra-low voltage applications. Meanwhile, with 1–10 μA bias current, the PEPT shows the best performance for the responsivity and SNR. When incident light is as low as 3.8 × 10−8 W/cm2, the responsivity reaches approximately 108 A/W. The super high responsivity of PEPTs makes it possible to fabricate small sized photodetector.

The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathematical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to obtain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency.

Holographic polymer-dispersed liquid crystal (HPDLC) is formed by the diffusion of monomers and liquid crystals as a kind of switchable volume holography. The kinetics investigation of HPDLC is very important to improve the diffraction efficiency and optimize the formation conditions of HPDLC. Fourier analysis is widely adopted as analytical method of kinetics. In this paper, we make use of the one-dimensional infinite-length analytical method to develop a kinetics simulation for the real-time formation of the grating. Simultaneously， corresponding diffused kinetics equations and polymeric kinetics equations are given. Then, we find the relationship between these equations and refractive index modulation Δn, and obtain a diffraction efficiency equation which is appropriate for transmission Bragg volume grating. Finally, the ways of increasing diffraction efficiency of HPDLC is discussed. Our theoretical study should provide some useful guidance to improve the properties of HPDLC.