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In special launch scenarios such as armament and aerospace, the scale of the launch system is severely restricted, which causes unstable combustion of propellant. An embedded structure for the small propulsion system driven by solid propellant is proposed to overcome this problem. This study aims to demonstrate the two-phase flow behaviors and launch safety of the combustion chamber with an embedded structure. A two-dimensional two-phase flow model based on the modified two-fluid theory is developed to describe the detailed two-phase flow behaviors in the combustion chamber during launching. Different from most of the existing studies, the constitutive equations determined from actual physical conditions are used to close the system of continuity equations. The numerical results are compared with that of the experiment to verify the accuracy of the numerical model. On this basis, the launch performance of the embedded structure is investigated. The numerical results indicate that the embedded structure facilitates the ignition process and reduces the risk of excessive pressure, but decreases the muzzle velocity at the same time. In addition, the effect of design parameters on launch safety is further investigated. Design parameters directly affect the launch safety, and the selection of reasonable parameters is a useful method for enhancing the launch performance. [ABSTRACT FROM AUTHOR]

In order to solve the problem of magnetic targets magnetic field modeling, a magnetic dipole array model was established, a modeling inversion equation system was constructed, and the degree of sickness of the solved equation system under different numbers of magnetic dipoles was quantitatively analyzed based on the coefficient matrix condition number. In order to solve the problem of the pathological system of magnetic field modeling equations, a regularization method based on the conjugate gradient least squares method was designed to invert the magnetic moment parameters of the magnetic dipole. In order to analyze the applicability of the regularization method in magnetic field modeling inversion, the magnetic moment solving accuracy, the magnetic moment solving robustness, calculation time, and other metrics are defined. A detailed test of the ship model was designed, and the magnetic field passing characteristics of the two types of ship models at different positive and horizontal conditions at two depths were measured. Under the condition of no interference and interference, the conjugate gradient least squares method is used to invert the magnetic field model, and the numerical test analysis shows that the conjugate gradient least squares method has higher applicability than the generalized inverse solution method and the stepwise regression method. Under the condition of interference, the relative error of magnetic field fitting of the array model with 15 magnetic dipoles is 0.1537, and the relative error of magnetic field extrapolation is 0.0868. The method proposed has the advantages of high accuracy and strong robustness in solving the magnetic moment of the magnetic dipole array model. [ABSTRACT FROM AUTHOR]

In order to study the simulation ability of a solenoid on a ship magnetic field, a new composite model based on a double row magnetic dipole array model with an ellipsoid was designed. The time-domain characteristics, such as magnetic field characteristics, magnetic inclination cosine, magnetic field scalar gradient, and magnetic field spatial distribution characteristics, were extracted. It was verified that the model can accurately simulate the magnetic field characteristics of ships through ship model experiments and simulation analysis. To further quantitatively and accurately analyze the simulation ability of the composite model for ship magnetic fields, a dynamic time wrapping measurement method based on one-dimensional time series was adopted to calculate the similarity of four characteristic quantities: magnetic field vector, magnetic field modulus, magnetic inclination cosine, and magnetic field scalar gradient. The results showed that the composite model has high simulation ability for ship magnetic fields. [ABSTRACT FROM AUTHOR]

Electron kinetics plays an essential role in CO2 splitting in non-equilibrium plasmas. Indigenous resources, particularly CO2 rich in the Martian atmosphere, are utilized as the feedstock for the technology of in situ propellant production (ISPP) in Mars missions. To obtain electron kinetics including electron energy distribution function (EEDF) and transport coefficients, a Boltzmann analysis is adopted. In view of ISPP in the upper Martian atmosphere, the complicated variation of the gas composition with the altitude in both dayside and nightside is considered. The composition of gas mixture is derived from the previous measurement data through site survey and numerical models. According to the results of calculation, altitude affects the behavior of EEDFs and transport coefficients in both dayside and nightside. The rapid drop in CO2 content and the rise in O content with altitude lead to a broader EEDF. The reduction of the critical breakdown electric field strength with the increasing altitude is ascribed to the combined effects of the decline of the attachment coefficient and enhancement of the ionization coefficient. The electron energy loss mechanism is presented for the analysis of energy efficiency. At low mean electron energy, electron energy is mostly transferred to vibrational levels of CO2. With the increasing electron energy, more energy-demanding processes, like ionization and electronic excitation, become essential pathways of energy loss. [ABSTRACT FROM AUTHOR]

Due to its atomically ultrathin morphology and superior optoelectronic properties, graphene has been broadly studied and utilized in phototransistors, photoconductors, or heterojunction nanostructures. However, in practical devices, the disadvantages of graphene should be concerned for its high dark current, very low on/off ratio, and high-priced fabrication cost. We report the photodetecting of the graphene/insulator/silicon heterojunction. The insulator layer is optimized to achieve balanced optoelectronic properties in terms of an Iph/Idark ratio of 4.17 × 103, a responsivity of 35 mA W−1, and a detectivity of 6.39 × 1010 Jones at a wavelength of 658 nm, with low operating voltage and static power dissipation (0.84 nW). Besides, response speed and degradation in the environment are tested. The mechanisms are revealed and analyzed by I-V measurements. [ABSTRACT FROM AUTHOR]

New fluorescent materials with a low cost, hypotoxicity, and concealment are desired for the application of anti-counterfeiting. Herein, we report a CsCu2I3@Cs3Cu2I5 composite with a triple-mode photoluminescence (PL) feature by simply adjusting the excitation wavelengths, which are ascribed to the multiple excited states of different phases in the CsCu2I3@Cs3Cu2I5 composite. The broadband emission and high quantum yield (∼51%) of the composite originate from the structure-oriented self-trapped excitons effect of Cs3Cu2I5 and CsCu2I3 phases. Moreover, the incorporation of polyethylene oxide (PEO) into this composite improves the stability of CsCu2I3@Cs3Cu2I5@PEO against harsh environments. The CsCu2I3@Cs3Cu2I5@PEO composite has a slight decay of ∼5% of its initial PL intensity and only a 3.5% shift of the corresponding color coordinate after 30 days of storage. More importantly, its initial PL intensity shows only 10.3% decay under ultraviolet exposure for 200 h. Our work provides a promising approach to design materials for advanced anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Narrowband photodetectors have broad application prospects in many fields where only a range of specific wavelengths of light needs to be detected. However, the current narrowband detectors have some disadvantages, such as the integration is difficult, the full width at half-maximum is not narrow enough, and the spectral rejection ratio is not ideal (≤20). Here, we present a self-filtering photodetector based on MAPbX3 single crystals with a very narrow spectral response and a full width of 15 nm at half maximum. It also shows a high responsivity (∼100 mA/W) and a high spectral rejection ratio (∼300). What is more, the response spectrum can be tuned within a certain range (from 440 to 560 nm) by varying the halide composition and thus its bandgap. This provides a new design paradigm for self-filtering narrowband photodetectors. [ABSTRACT FROM AUTHOR]

Acoustic signals generated by underwater spark discharge (UWSD) can be used in a wide range of applications. The characteristics with different electrode configurations need further study for more practical application. The generation mechanism and the main characteristic indices of UWSD acoustic signals were analyzed. The acoustic signal time-frequency characteristics with different electrode gap distances and materials were calculated and compared. The results show that there is an electrode gap distance that maximizes the energy of the acoustic signal, and this gap distance is related to the impedance matching between the discharge channel and the external circuit. The proportion of low-frequency components in the acoustic signal decreases with the increase in the electrode gap distance. [ABSTRACT FROM AUTHOR]

The control of discharge mode and the optimization of energy efficiency are of particular concern as the significant impact on the application of the underwater plasma discharge system. In this paper, the RLC parameters of each part of the underwater discharge system are investigated, and the equivalent circuit is obtained. Typical waveforms of current and voltage for different underwater discharge modes are displayed. The correlation between the equivalent RLC parameters of the discharge system and the discharge modes and energy is illustrated. The equivalent circuit of the underwater plasma discharge system is utilized to analyze the effects of the power source, electrode, and liquid dielectric parameters. The influences of these parameters can be identical to the impacts on the RLC parameters of the underwater discharge system equivalent circuit simultaneously, and then, the effects on the discharge modes and energy can be better understood. It can be concluded that the relative relationship of system equivalent RLC parameters determines the discharge mode, and the impedance matching between the discharge channel and the external circuit determines the discharge energy. [ABSTRACT FROM AUTHOR]

Underwater discharge sound sources are widely utilized. The acoustic signals generated by underwater discharge consist of shock waves and bubble pulsations. The shock wave is a major component of underwater discharge sound sources and is worthy of further study. The minimum-phase cepstrum method is selected to separate the shock wave, and a customized experiment is designed to determine the optimal parameters of this method. The mixed shock wave bubble signal and single shock wave signal are simulated and fitted and are transmitted and received in the anechoic pool, respectively. Different parameters are used to process the signals, and the optimal parameters are selected by comparing the separation results. To verify the validity of the method, the shock waves generated with the same electrode and circuit parameters in the anechoic pool and non-anechoic pool are separated and compared. Experimental results show that this shock wave separation method exhibits significant performance. This method of shock wave separation is of service to the research of underwater discharge acoustic sources. [ABSTRACT FROM AUTHOR]

The influences of ion bombardment on the field emission performance of tetrapod ZnO nanostructures are reported. As the scanning electron microscopy images and photoluminescence spectrum show, the tips of the field emitters are destroyed and the surface state of the field emitters is also changed after the ion bombardment. The ion bombardment has a considerable effect on the field emission properties of the tetrapod ZnO field emitters. After Ar+ ion bombardment with the energy of 3 keV and the ion current of 0.05 μA for 30 min, the turn-on field increases about 63% and the threshold field increases about 77%, respectively. There are two main reasons for the variation in field-emission property: (1) the decrement of the field enhancement factor β, which is caused by the variation in morphology of field emitter; (2) the increment of work function φ, which is caused by the changed concentration of the surface oxygen vacancy. [ABSTRACT FROM AUTHOR]

Regular hexagonal flowerlike zinc oxide (ZnO) whiskers have been fabricated on the indium tin oxide electrodes with glass panel. A relatively simple hydrothermal growth process of low temperature is developed. The field emission properties of the flowerlike ZnO nanowhiskers have a low field emission threshold voltage (2.2 V/μm at a current density of 0.1 μA/cm2) and a high current density of 1 mA/cm2 at an applied field of 6.3 V/μm. The hydrothermal process method and good field emission properties indicate their potential application in field emission display device with glass panels. [ABSTRACT FROM AUTHOR]

In the normal gate carbon nanotube field emission display (CNT-FED), the gate electrode is used to modulate and address the electron beam. This article proposes a novel gate architecture made on a glass substrate with diabololike funnels. Chemical corrosion was utilized to produce diabolo funnels in the glass dielectric layer. A metal layer was screen printed on the lower surface of the glass-mesh plate as an electron extraction gate electrode. MgO film was vaporized on the wall of the diabolo funnels. The electrons from CNT are transported in a diabolo mode via secondary electron emission over the wall of the diabolo funnel placed above the subemitters. As a result, electrons including the secondary electrons and backscatters are generated and the brightness of the diabolo mode gate architecture CNT-FED could increase obviously. [ABSTRACT FROM AUTHOR]

A novel gun double hop gun of rf power amplifier based on an always-on ringed cold cathode is suggested. Double hopping electron funnels, including a metal funnel and a glass funnel, are fabricated in. MgO film is deposited around the walls of the funnels by electron beam evaporation. Secondary electrons or backscatters (elastic and inelastic) escape from the dielectric film (MgO) under the bombardment of accelerated electrons and are driven to the exit window of the glass funnel by a modulated voltage. Among the escaping electrons, the ratios of secondary emission electrons, elastic scatters, and inelastic scatters are 90%, 9%, and 1%, respectively. Most of the escaping electrons at the exit window have low energy (<50 eV) and can be easily controlled by the modulated voltage with low amplitude (∼100 V) applied on the electrode of the glass funnel. The average velocity in the Z direction of the escaping electrons increases as the amplitude of the modulated voltage (Vgate) increases. The distributions of the velocities in the X and Y directions are found to be symmetrical. [ABSTRACT FROM AUTHOR]

We report a surface-conducted field emission cathode using ZnO nanotetrapods as the surface conduction emitter. The dependences of electron emission efficiency on ZnO nanotetrapod film thickness and the spacing between adjacent electrodes of surface emitter were studied. A maximum electron emission efficiency of 60% was obtained for an optimal device with film thickness of 8 μm and electrode spacing of 0.1 mm. A low turn-on voltage of about 100 V (corresponding to a field of 1 V/μm) at an emission current density of 0.6 mA/cm2 was obtained which is good enough for field emission displays. Good stability and uniformity were also demonstrated. [ABSTRACT FROM AUTHOR]

Carbon nanotubes have been grown on silicon substrates coated with nickel-catalyst films by chemical-vapor deposition using mixtures of acetylene and nitrogen. An effective aging treatment was carried out before the field-emission measurement of carbon-nanotube samples. The results show that the turn-on field is 1.8 V/μm at 2 μA emission current and that the highest emission current of 13 mA at the electrical field of 23 V/μm. This corresponds to the field-emission current density of 414 mA/cm2. Some discussions about the long growing time of carbon nanotubes, the aging process, and high-current field emission are given. [ABSTRACT FROM AUTHOR]

From recent research work, it has been found that the ZnO nanostructures have good field-emission performance. This article compares the emission characteristics of ZnO nanopins (such as I-V curve, thermal stability, and aging process) with those of carbon nanotubes. From this comparison, it can be seen that the emission characteristic of ZnO nanopins is close to that of carbon nanotubes. However, the emission performance of ZnO nanopins is much better than that of carbon nanotubes after baking at high temperature. Apart from this, the emission uniformity of ZnO cathode is quite good without an activation process. Therefore, ZnO nanopins can be used as field emitters in a field-emission-display device. [ABSTRACT FROM AUTHOR]

The authors measured the residual gas spectrum of a field emission display (FED) with carbon nanotube (CNT) emitters and found that the main residual gases inside a sealed CNT FED, containing an evaporated Ba getter, are H2, CH4, CO, Ar, and CO2, all of which are typical residual gases of electronic vacuum tubes. Additionally they also measured the electron stimulated desorption of gases by operating their field emission devices. [ABSTRACT FROM AUTHOR]