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In this work, we study the stabilization behavior of micro-diffusion flame of n-heptane formed in a combustor with the inside diameter of 4 mm, in order to elucidate the unique stability mechanism due to miniaturization of diffusion flame downstream porous medium. Effects of incoming Reynolds number and fuel flow rate on overall flame shape, exhaust temperature, and wall temperature are examined experimentally. Furthermore, an energy balance model of the micro combustor is established and optimal working conditions are proposed. Liquid n-heptane is used as fuel and two types of outer tubes are employed in order to examine the role of the heat recirculation. It turns out that the outer tube increases the wall temperature and broadens the flame stability limits. The incoming Reynolds number changes flame position and energy balance in the micro combustors. At low Reynolds number, the outer tube allows the flame to stay close to the porous medium and, accordingly, the porous medium is substantially h...

Soil respiration is a key component of net CO 2 exchange in grassland ecosystems and directly influences the soil carbon pool dynamics. While numerous soil respiration studies in grazed grasslands exist, the accurate quantification of the net CO 2 exchange in grassland ecosystems throughout the entire year is required to determine whether grazed grasslands are carbon sinks or sources. In this study, we evaluated how stocking rate influenced soil respiration during the non-growing season in a typical grassland in the Hebei Province of North China. To examine the effects of stocking rate on soil respiration, soil respiration rates were measured using a soil greenhouse gas flux measurement system. Three stocking rates—ungrazed control (UG), moderate grazing (MG), and heavy grazing (HG)—were applied by grazing small tail sheep (ewes and lambs) at different densities from the end of June to early October in 2010 through 2013, and the relationships among soil respiration, stocking rate, and environmental factors were analyzed during the non-growing season (1 October 2013 to 30 April 2014). Variation in soil respiration followed a “V” pattern and was correlated with soil temperature and moisture for all stocking rates. Stocking rates did not significantly influence soil temperature or soil moisture; however, cumulative CO 2 emissions during the non-growing season decreased dramatically ( P − 2 ) > MG (0.38 ± 0.012 kg C m − 2 ) > HG (0.33 ± 0.009 kg C m − 2 ). The influences of air and soil temperature on soil respiration rate were best described by an exponential equation (R 2 = 0.43–0.55; P 2 = 0.46–0.67; P 2 = 0.56), with Q 10 values either increasing or decreasing relative to the UG treatment for the MG and HG treatment, respectively. Given the strong influence of grazing intensity on soil respiration in this grassland ecosystem, we suggest that the accurate estimates of annual soil respiration should routinely account for soil respiration during the non-growing season.

We took advantage of digital image correlation to measure the full-field deformation of sea ice in a uniaxial compression experiment in situ. The characteristics of failure mode, nonlinear behavior and crack propagation are all captured by the strain field of specimens. To our knowledge, this is the first attempt to experimentally capture sequential full-field deformations in the mechanical properties of sea ice. This achievement will extend the ability to further explore the complex mechanical behaviors of sea ice.

The liquid impact induced by slamming in the membrane-type tank is an important issue for the design of Floating Liquefied Natural Gas (FLNG) facilities. The free surface entrapping air may easily happen under shallow-water condition in the tank, which could result in structural local failure. Studying the effect of entrapped air on slamming load is essential to understand the air-free surface-elastic structure interaction. Thus, a series of experiments are designed and conducted in an elastic rectangular tank under shallow-water condition. The evolution of free surface and the development of entrapped air are analyzed quantitatively. Furthermore, both impact load and structural response are measured and studied in the spatial and temporal distribution under shallow-water condition. The results show that the air cavity plays a cushion role between free surface and elastic wall. Therefore, the impact mode is changed from liquid-direct impact to liquid-indirect impact. The existence of the air cavity leads to a significant reduction of the maximum slamming load and structural response but an increase in the pressure impulse in spatial distribution. It is suggested to consider the effect of the entrapped air on the determination of the slamming load for the design of super-large LNG tanks in the offshore engineering.

Heavy grazing and unsuitable farming practices have led to grassland degradation in northern China. This study examined soil CO2 efflux (Fc) from five land-use types during the non-growing season on the southeastern edge of the Mongolian Plateau in China. The land-use types included three native vegetation steppes subjected to differing stocking rates [ungrazed (UG), moderately grazed (MG) and heavily grazed (HG)], a fertilized annual cropland (CL) and a perennial pasture (PP) used for haying and winter grazing. Values of Fc were measured at 3-day to 2-week intervals during the non-growing season in two contrasting hydrological years (2012-13 and 2013-14) using closed chambers. The Fc during 1 Oct. 2013 to 30 April 2014 averaged 475 mg C m−2 for all sites compared to a significantly (P

Three micro combustors with different thermal insulations were tested. The baseline was a narrow quartz tube with inner diameter of 4 mm, named CS. A one-layer recuperator and a vacuum insulation recuperator were employed to recover exhaust heat of CS. These two combustors were named CA and CB, respectively. N-heptane was used as fuel and injected into the combustors at normal conditions. Results show that heat recirculation can effectively extend fuel-lean limits of CA and CB. The vacuumed recuperator can greatly reduce heat loss, and increase wall temperature and porous medium temperature. Heat loss in CA is 25% higher than that in CB at fuel flow rates of 0.45 mg/s and 0.9 mg/s. Additionally, concentrations of CO and O 2 in CS are higher than that in CA and CB, indicating that heat recirculation can increase combustion efficiency. Finally, three combustors are numerically simulated. Ratio of axial gas temperature to wall temperature is obtained. This ratio is used to calculate recirculated heat. Results show that in CS, only 7.7% of combustion heat is recovered. While for combustors with heat recirculation, the minimum recovered heat is up to 12.1% of combustion heat.

In this study, the effects of accelerated ageing under pre-strain on the maximum elongation of composite solid propellants were investigated. The maximum elongation of aged composite solid propellants at different ageing times, temperatures and pre-strains were determined. An ageing model was developed to analyse the effects of pre-strain and temperature on model parameters. Results show that pre-strain can increase the maximum elongation significantly during accelerated ageing, and the increasing amplitude exhibits a linear relationship with ageing temperature and pre-strain. The physical tension effect caused by pre-strain is a cumulative effect of the stress on samples and shows obvious characteristics of stress relaxation. The relaxation time is independent of pre-strain and exhibits an exponential relationship with ageing temperature. The effect of pre-strain on chemical ageing is related to a critical temperature T C . For the HTPB propellant investigated in this study, the T C is between 65 °C and 70 °C. When the ageing temperature is below T C , pre-strains have almost no effect on the ageing rate constant for maximum elongation k e ; however, at temperatures above T C , they may promote chain scission reactions and decrease k e .

Thrust control enables solid rocket motors to be more manoeuverable and controllable. To improve the thrust control and anti-ablative performance of solid rocket motors, a new type of motor controlled by secondary flow and a pintle is proposed: numerical simulation of two typical pintle thrusters is presented. The influence of different pintle positions, injection angle, and flow ratios on the effective throat area ratio, outlet pressure, and wall temperature of the pintle were studied. The results showed that the new type of motor can reduce the wall temperature of the pintle. Increasing the secondary flow ratio and injecting the secondary flow in reverse can increase control performance. When the total flow rate is constant, the injection of a secondary flow can reduce the outlet pressure.

The original version of this article unfortunately contained mistakes in the “Affiliation” and “Acknowledgements” sections.

An understanding of population adaptation and maintenance mechanisms under interference from large herbivores is lacking and is a major focus of ecological research. In the Eurasian steppe, which has been subjected to continuous interference from domesticated ungulates throughout history and shows increased grazing, it is particularly urgent to analyze the ecological adaptation strategies of widely distributed Stipa plants. In this study, Stipa breviflora in a group of desert steppes in the Mongolian Plateau was selected to study the potential mechanism underlying the maintenance of dominant populations under the continuous interference of heavy grazing from the new perspective of seed germination rate. Laboratory experimental results showed that the values of the phenotypic traits of S. breviflora seeds were lower under a heavy grazing treatment than under a non-grazing treatment, but the seed germination rate did not decrease. The awns of non-grazed seeds significantly affected the seed germination rate, while those of heavily grazed seeds did not. Field observations showed that grazing does not significantly affect the population density of S. breviflora at different growth stages except in extremely wet and dry years. Our study suggests that under heavy grazing, S. breviflora uses an “opportunistic” ecological strategy to ensure population maintenance by increasing the seed germination rate and reducing dispersal via changes in associated seed phenotypic traits.

Current estimates of global indirect N

Seed germination plays an important role in determining the composition and regeneration of plant populations (Stipa breviflora). However, the influencing factors and strategies employed for seed germination in desert grasslands under grazing remain unknown. Therefore, in this study, the reproductive allocation, seed density, seed properties, and corresponding seed germination rates of S. breviflora were examined. Possible situations encountered during dispersal were also simulated to determine their effects on seed germination. The results showed that reproductive individual density not subjected to grazing were significantly higher than those subjected to moderate and heavy grazing. For seed density and seed bank in soil, the highest values were observed for the no grazing treatment, followed by the moderate and heavy grazing treatments. The seed density for germination of soil seed banks was nearly one-fourth of seed density during the growing season. In addition, grazing treatments affected the phenotypic characteristics of seeds and reduced the lower limit of the weight of germinable seeds. Awn removal significantly increased germination. The longest germination time was observed for seeds that entered the soil at an angle of 0°. Our research demonstrated that grazing negatively affected the desert grassland edificator. Individual plants adopted different adaptation strategies under different grazing intensities; for example, a fixed proportion of the seed number and seed germination number of S. breviflora in the soil seed bank was maintained by exceeding the minimum weight of a seed for seed germination. During seed dispersion, the awn effectively prevented germination under unfavourable conditions and helped seeds enter the soil at an optimal angle for promoting germination.

Summary This note presents the design of a scalable software package named ImagePy for analysing biological images. Our contribution is concentrated on facilitating extensibility and interoperability of the software through decoupling the data model from the user interface. Especially with assistance from the Python ecosystem, this software framework makes modern computer algorithms easier to be applied in bioimage analysis. Availability and implementation ImagePy is free and open source software, with documentation and code available at https://github.com/Image-Py/imagepy under the BSD license. It has been tested on the Windows, Mac and Linux operating systems.

The self-ignition characteristics of a solid fuel under supersonic flow have been investigated theoretically and numerically. Time-dependent two-dimensional axisymmetric compressible Navier–Stokes equations and species transport equations are solved numerically. Turbulence closure is achieved using the shear stress transport k-ω model. Polymethylmethacrylate fuel and a global one-step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence–chemistry interaction modeled by an eddy-dissipation model. The numerical results generally agree with the experimental data in the published literature. The flame spread and pressurization during the self-ignition of polymethylmethacrylate in the combustor have been studied. The effect of inlet flow conditions and the geometry of the combustor on self-ignition behavior have been analyzed. Three stages of flame spread (namely, heat accumulation, secondary recirculation zone self-ignition, and orderl...

Silver-graphene composite materials with enhanced electrical and mechanical properties are reported in this work. Ag nanoparticles are in-situ synthesized on the graphene oxide (GO) by chemical reduction of Ag salt mixed with GO in aqueous solution. After hydrogen reduction of GO, powder metallurgy technique and hot-extruding are employed to prepare Ag-rGO composite bulk material. The composite shows improved mechanical properties. The tensile strength of Ag-rGO composite is up to 190 MPa, 5.5% higher than that of pure Ag. The hardness of Ag-rGO is as high as 75 (HV), which is much higher than most carbon-reinforced Ag materials. Moreover, the ductility and conductivity of the Ag-rGO composite material still keep 43% and 1.6 μΩ cm, respectively. The electrical endurance test demonstrates the Ag-rGO composites owns excellent electrical properties. The material has an electrical endurance of 400,000 under current of 20 A and voltage of 220 V. This promising material has great potential application in electric apparatus.

Fourfold benzocyclobutene-functionalized perylene bisimide (PBI 4) has been synthesized and its structure was characterized by FTIR, MS and NMR. PBI 4 can react either with itself, or the appropriate dienophiles to form the corresponding products under appropriate temperature. The polymer film obtained from the reaction of PBI 4 with methyl vinyl silicone rubber possessed excellent film forming properties including flatness. The optical properties of PBI 4 and polymer film obtained from the reaction of PBI 4 and methyl vinyl silicone rubber have been determined by UV/vis and fluorescence spectroscopy.

Hybrid porous materials based on AIBN initiated radical polymerization of octavinylsilsesquioxane in THF were reported in detail. The choice of reactant concentration has a major influence on their porous properties. The resulting hybrid porous materials exhibit high BET specific surface areas (up to 1080 m2 g−1) and exceptional hydrogen uptake (2.00 wt.% at 1.0 bar and 77 K).

Grazing can dramatically affect arid grassland communities that are very vulnerable to environmental changes due to its relatively short and sparse ground coverage, low biomass, sandy soil and inter-annual precipitation found in the desert steppe. The study investigates the effects of different grazing durations on vegetation and soil properties of a desert steppe community. The experiment was conducted in Xisu Banner in Inner Mongolia with five treatments: CG (continuous grazing), 40UG (40 d ungrazed), 50UG (50 d ungrazed), 60UG (60 d ungrazed) and UG (ungrazed). The biomass of both shrub and annual-biennial plant communities were significantly decreased by CG. Continuous grazing and 40UG significantly reduced the ANPP (aboveground net primary productivity) by the end of the three year study. 60UG treatment increased soil organic carbon (OC), total nitrogen concentration (TN) and total phosphorus concentration (TP) concentrations and 50UG increased the TN and total phosphorus concentration (TK) concentrations, whereas CG, 40UG and 50UG decreased soil OC, TP and available phosphorus concentration (AP) concentrations. The perennial plant species of the desert steppe were generally tolerant for grazing. The annual-biennial plant species had large variability in ANPP because of the inter-annual precipitation. Our results highlight that inter-annual precipitation variations could strongly modify the community responses to grazing in arid ecosystems.

The liquid fuel combustion in a meso-scale burner with porous media was experimentally investigated for n-heptane/air mixtures of varying equivalence ratios and flow speeds. Infrared thermography and appropriately placed thermocouples were to measure the surface temperature of the burner. A video camera recorded changes in the flame. Liquid heptane combustion in a meso-scale burner was demonstrated to be affected by many factors. First, heptanes droplets were formed at the capillary tip, and oscillating combustion occurred in the absence of a porous medium, resulting in an unstable flame, which could be easily blown out. Second, the addition of a porous medium stabilized the flame, but its position was affected by the airflow velocity and the position of the porous medium. Finally, the outer tube affected the flammable limits of the burner. The flame could easily be blown out in the absence of an outer tube. Furthermore, a double-layer vacuum tube insulated the burner more effectively and significantly reduced its heat loss.

Boundary element method (BEM) coupled with the isogeometric boundary based on Non-Uniform Rational B-Splines (NURBS), which is termed IGABEM, is a new numerical method and has attracted wide attention in recent years. In this paper, IGABEM is first applied to the liquid sloshing problem in the horizontal rectangular, circular or elliptical annular tanks with multiple porous baffles, assuming incompressible, irrotational and inviscid flows. As a key improvement compared with the conventional polynomial shape function in BEM, the IGABEM for the analysis of liquid sloshing can exactly represent the geometry no matter how coarse discretize the studied boundary, which then produces no geometrical errors. A zoning method is carried out to study arrangement of the multiple porous baffles in the tanks. Neighboring zones is joined together by the boundary conditions of the porous baffles and virtual interface which correlate the flux and velocity potential. By discretizing boundaries of each zone using the isogeometric function, the governing integral equation on the boundary by using BEM can be formulated into the dynamic equation in frequency domain. Three configurations of baffles are taken into account such as the top-mounted baffles, bottom-mounted baffles and annular baffles. The results obtained by the proposed method are verified by comparing with the reported solutions and very good agreement is obtained. The effects of tank's geometry, liquid filling level and the baffle's parameters with various lengths, submergence depths, number of baffles, and porosities on the natural sloshing frequency, wave surface elevation, sloshing force and velocity field are investigated and several conclusions are achieved.

The variation of steady burning rate for heterogeneous propellants over a wide range of pressure is studied by experimental methods and theoretical analysis. Two kinds of heterogeneous propellants, GATo-1 CMDB propellant and 86 series composite propellant, are selected. An explanation for two inflection points observed in burning rate–pressure curve is presented. It is concluded that condensed-phase reaction dominates the burning process in the low-pressure region, which presents a low-pressure exponent, whereas heat feedback from the gas phase predominates in the high-pressure region with a high-pressure exponent. In the medium-pressure region, these two factors influence the burning process cooperatively and pressure exponent reduces first and then rises. Results calculated from the model show good agreement with experimental data. Thermal parameters analysis indicate burning rate is more sensitive to thermal conductivity of condensed phase, activation energy of condensed phase, specific heat capacity, ...

The purpose of this paper is to investigate the combustion process and its change with time due to solid-fuel regression in a solid-fuel scramjet combustor. The combustion process is simplified in the sequence changing of three regression shapes. The solid fuel uses hydroxyl-terminated polybutadiene with a global one-step reaction mechanism. Numerical simulations based on the shear stress transport k-ω model are confirmed by experiments. The simulation data generally agree with the experimental data published in the literature. For simplification, three typical instants during the combustion process, implying three different internal shapes due to fuel regression, are considered. With the sequence of three regression shapes, the fuel diffusion from a solid-fuel surface becomes more extensive and, furthermore, enhances the global combustion efficiency, which is nearly up to 45% at the outlet of the combustor. The simulation results also reveal that the cavity in the combustor provides a fuel enrichment zon...

The novel polyhedral oligomeric silsesquioxane (POSS)–titania aerogels which contain different contents of titania were successfully prepared by the sol–gel process and subsequently supercritical drying with carbon dioxide. All the aerogels are monolithic and the densities of those aerogels are low. The FTIR spectra of the aerogels showed the resulting POSS–TiO2 composite aerogels had homogeneous Si–O–Ti bonds. The microstructure, surface composition and thermal stability were measured by FESEM, XPS and TGA. With the increasing of titania contents, the aggregated particles of the aerogels in the microstructure got larger and larger. The texture of the aerogels was measured by XRD and nitrogen adsorption/desorption and showed that they were amorphous and had high surface area (>500 m2/g).

The synthesis and characterization of Zr-POSS and Hf-POSS coordination polymers were reported. The IR data and the solid-state 29Si MAS NMR indicated the existence of SiOM linkage. The polarized optical microscopy images and the XRD data suggested their crystalline nature.

Todiscover thrust-oscillation characteristics in solid rocketmotors, analyticalmodeling andnumerical simulation are carried out by an experimentalmotor in the vonKarman Institute for FluidDynamics. The numericalmethod by means of amesh sensitivity analysis is proposed for validation. Velocity profiles, oscillation frequencies, and pressure amplitudes were obtained by numerical simulations and then compared with the experimental data. Various cases with different inlet temperatures are proposed to investigate the influences of parameters on the oscillation characteristics. The results indicate that it is not a necessary condition for vortex-shedding frequency to approach a certain acoustic frequency when periodic oscillations are generated. Oscillations are more severe if the vortexsheddingphenomenon coupleswithhigh-order acousticmodes.Velocitymagnitude in the combustion chamber is the main factor that influences the vortex-shedding frequency; meanwhile, the pressure amplitude is mostly determined by themeanMach number. Theoretical modeling in conjunction with numerical calculations proves that the ratio of dimensionless thrust amplitude to pressure amplitude is predominantly determined by the throat-to-port-area ratio J, and it varies inversely as J. An integrated formula is presented to describe the relationship between thrust amplitude and pressure amplitude.

The new cyclometalated racemic-chelated N-heterocyclic carbene palladium (II) complexes Fa-b derived from G have been prepared. The structure of cyclometalated race-chelated bidentate NHC-palladium (II) complexes Fa-b was characterized by 1H NMR, 13C NMR X-ray, MS, and crystal diffraction.

The synthesis of novel POSS-based organic–inorganic hybrid mesoporous materials networks functionalized with amine groups through Schiff base chemistry is reported. The material shows uniform mesoporous size. Nitrogen sorption analyses give high specific surface areas of 641–1103 m 2 g −1 with pore volumes of 0.47–0.53 mL g −1 . The combined results of FTIR, solid 13 C NMR and 29 Si NMR show that the POSS building blocks are successfully weaved in the porous structure without obvious alteration of the POSS structural characteristics. The hybrid materials show excellent thermal stability.

The effects of NaOH addition on hydrogen absorption/desorption properties of the Mg(NH 2 ) 2 –2LiH system were investigated systematically by means of dehydrogenation/hydrogenation measurements and structural analyses. It is found that the NaOH-added Mg(NH 2 ) 2 –2LiH samples exhibit an enhanced dehydrogenation/hydrogenation kinetics. In particular, a ∼36 °C reduction in the peak temperature for dehydrogenation is achieved for the Mg(NH 2 ) 2 –2LiH–0.5NaOH sample with respect to the pristine sample. Structural examinations reveal that NaOH reacts with Mg(NH 2 ) 2 and LiH to convert to NaH, LiNH 2 and MgO during ball milling. Then, their co-catalytic effects result in a significant improvement in the dehydrogenation/hydrogenation kinetics of the Mg(NH 2 ) 2 –2LiH system. This finding will help in designing and optimizing the novel high-performance catalysts to further improve hydrogen storage in the amide-hydride combined systems.

The boron trifluoride induced Suzuki-Miyaura cross-coupling of aryltriazenes with arylboronic acids catalyzed by Pd(OAc)2 without added ligands has been achieved for the first time. The reactions performed at room temperature under an argon atmosphere give biaryls in good to excellent yields. It is noteworthy that the reactions were conducted under mild and ligand-free conditions.

To understand effects of an air groove on working characteristics of micro Swiss-roll combustors, combustion of premixed CH4/air is conducted in 2 micro Swiss-roll combustors, one with an air groove and the other without. Experimental results show that stable combustion of premixed CH4/air in 2 combustors can be achieved and the flame is kept in combustor's center. An air groove can extend flammable limit of the combustor and make it work at a larger excess air coefficient and a lower methane flow rate. Furthermore, it increases the radial surface temperature gradient on outer wall of the combustor. Additionally, the combustor with an air groove is numerically simulated. Numerical results indicate that hot combustion products play a strong role in heating incoming mixtures. On one hand, it makes premixed flame surface inclined across inlet channel; on the other hand, it makes flame position vary with flow velocity, excess air coefficient and heat loss to the environment.

To research the performance of a solid fuel scramjet combustor, a solid fuel regression rate model was coupled into a quasi-one-dimensional flow equation, and so the flow parameters and fuel regression rate could be calculated together. According to the regression rate and the combustor diameter in the previous moment, the combustor diameter of the next moment could be obtained. The unsteady combustion and flow matter in the combustor was simplified into a steady calculation of every moment by solving the boundary condition at different moments independently. The numerical results were compared to actual experimental data from the literature, and they agreed well with the experiment. Taking the fuel/air ratio and Mach number as the optimization conditions, the initial size of the combustor could be obtained. On the basis of an optimized combustor, the relevant parameters’ variation rules were calculated and analyzed. It was found that during the working process, the combustor flow field could be k...

An effective and easy-to-handle process for the desulfitative Suzuki cross-couplings of arylsulfonyl chlorides and boronic acids in the presence of a recyclable polymer-supported NHC-Pd complex was developed. The supported catalyst could be reused several times with little loss of catalytic activity.

The influence on the regression rate of the inlet parameters of a solid fuel (PMMA) under supersonic cross flow has been investigated theoretically and numerically. Based on two-dimensional compressible N-S equations and species transport equations, the regression rate values were obtained by adding to the source term in the quality、momentum and energy of the fuel. With different inlet parameters , i.e., stagnation temperature and pressure , the combustion conditions were analyzed at the flame-holding zone and the constant diameter cylindrical section. Comparison between numerical results with test data showed fair agreement, indicating the correctness of the calculation model. The results show that increasing the amount of oxygen or the mixture of the fuel and oxidant can improve the combustion efficiency; the inlet mass flow of air、stagnation temperature and depth of cavity has a great impact on the regression rate, then the impact of the length of cavity was slightly smaller, the impact of the stagnation pressure was minimum.

The characteristics of self-ignition and self-sustained combustion of a solid fuel under supersonic cross flow have been investigated theoretically and numerically. A time dependent two-dimensional, axisymmetric compressible Navier-Stokes equations and species transport equations are solved numerically. Turbulence model is using the Shear Stress Transport k  model. The PMMA fuel and a global one step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence-chemistry interaction modeled using eddy-dissipation model. The numerical model is validated by comparing the numerical results with experimental data. The flame spread and pressurization during self-ignition of PMMA in combustor have been studied. The behaviors of both sustained and un-sustained combustion in SFSCRJ combustor have been analyzed. The simulation results reveal that three stages of flame spread are identified during the self-ignition transient, which consists of heat accumulation, self-ignition in the secondary recirculation zone, and whole combustor self-ignition orderly. The pressure suddenly rises in combustor during the third stage. The difference of combustor shape affects the self-ignition. There have always been high temperature zone and high mass fraction of reaction products in combustor during sustained combustion. Once the recirculation zone area and residual time provided by cavity are unable to meet the time needed for chemical reaction of reactants and the ignition of fresh mixture, flame is blew out by supersonic cross flow.

Numerical simulations were performed to analyze the performance of solid fuel scramjet (SFSCRJ) operating at Mach 4 to 6, with the primary goal being to investigate the feasibility of low takeover speed for SFSCRJ. The numerical model was created based on previous experiments with a constant area isolator added before combustor. Airflow is changed to subsonic in isolator and return to supersonic in the diverging section at the Mach 4 condition. The flow was not thermally choked at higher Mach condition, with a series of compression and expansion waves generating in the flameholding zone. The effect of flight Mach number is discussed from a viewpoint of total pressure recovery and combustion efficiency. The results show the feasibility of SFSCRJ operating at low flight Mach. To investigate the effect of inflow condition on combustor performance, different contraction ratios in the inlet are assumed at flight Mach 5 condition, resulting in different pressures at the entrance of isolator for numerical simulations. It is found that the performance of combustor is enhanced with the increase of inflow static pressure. There exists a tradeoff between the improved performance of combustor and the increased total pressure loss in the inlet.

This paper describes the numerical investigations concerning the characteristics of the flowfield in the solid fuel scramjet (SFSCRJ) and the rate of mixing or combustion enhancement when a cavity structure is used in the scramjet combustor. The goal of the paper is to study the influence of the cavity in the solid fuel scramjet, mainly about the length-to-depth ratio (L/D) of the cavity. The computational conditions of the numerical investigations are operated under the non-reactive conditions and reactive conditions respectively. The numerical investigations of the scramjet combustor concentrate on the appropriate structures for maximize mixing or combustion efficiency and minimum total pressure loss. The cavity effect is discussed from a viewpoint of mixing efficiency, total pressure loss and combustion efficiency. Compared with the combustor without cavity, the combustor with cavity is found to enhance the mixing efficiency apparently while decreasing the total pressure loss. It is noted that there exists an appropriate length-to-depth ratio (L/D) of the cavity regarding the mixing or combustion efficiency and the total pressure loss. Meanwhile, compared with the different length-to-depth ratio (L/D) of the cavity, the mixing and combustion efficiency is not monotonically increasing or decreasing with the variation of the length-to-depth ratio (L/D) of the cavity. So there exists a best length-to-depth ratio (L/D) to get the best performance of the combustor. The investigation of the cavity L/D ratio would provide some insight into the design considerations of cavity for solid fuel scramjet.

The boron trifluoride-induced Suzuki-Miyaura cross-coupling of aryltriazenes with arylboronic acids catalyzed by palladium(II) acetate without added ligands is achieved for the first time.

A mechanistic understanding on the enhanced kinetics of hydrogen storage in the NaBH(4)-added Mg(NH(2))(2)-2LiH system is provided by carrying out experimental investigations associated with first-principles calculations. It is found that the operating temperatures for hydrogen desorption of the Mg(NH(2))(2)-2LiH system are reduced by introducing NaBH(4), and the NaBH(4) species seems almost unchanged during dehydrogenation/hydrogenation process. First-principles calculations reveal that the presence of NaBH(4) in the Mg(NH(2))(2)-2LiH system facilitates the formation of Mg vacancies in Mg(NH(2))(2). The appearance of Mg vacancies not only weakens the N-H bonds but also promotes the diffusion of atoms and/or ions, consequently resulting in the improvement of the reaction kinetics of hydrogen desorption/absorption of the NaBH(4)-added Mg(NH(2))(2)-2LiH system. This finding provides us with a deep insight into the role played by NaBH(4) in the Li-Mg-N-H system, as well as ideas for designing high-performance catalysts for metal-N-H-based hydrogen storage media.

To study the infrared signature of afterburning exhaust plume of solid rocket motor, the coupling calculation model for infrared radiation transfer in the afterburning plume was built. The radiation source term was induced to energy equation, thus the plume flow field and radiation transfer was calculated in a coupling way. Finite rate chemistry reaction model was used to simulate the 10 species afterburning exhaust plume; finite volume method and discrete ordinates method was separately used to solve the plume flow field and the radiation transfer equation. The spectral radiation intensity from 1 m � to 15 m � and radiation intensity contour were obtained, and both of them accord well with the experimental data from reference. The results show that the radiation characteristics in the near plume field can be captured varying with the physical characteristics of flow field, which shows that the coupling solution can increase the calculation resolution of radiation transfer.

In this article, a three-axis Ultraviolet Optical Sensor (UVOS) is designed, which can solve the problem of attitude determination for large field observation in the near-earth orbit. By applying an irregular optical system, i.e. the reflecting arrays and combined optical system, a circular large field of view is divided into 8 sub-fields. UVOS will provide the three-axis attitude information and autonomous navigation data after image overlapping and image-processing. The maximum yaw angle of the three-axis ultraviolet optical sensor is less than 0.07°, and the maximum pitch angle is less than 0.15°. The UVOS can measure 5 magnitudes. It is can be treated as an important sensor for the space vehicles of deep space exploration.