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This study presents a fabrication method for preparing Ni using material extrusion-based 3D printing. First, the corresponding printing process window was optimized by exploring the relationship between the layer thickness and printing parameters (printing air pressure, printing speed, and printing height) of different solid content slurries, slurries rheology, and platform heating temperature. Then, the experiments on Ni slurries with different solid contents under different post-treatment methods were investigated to obtain the effect of solid content and temperature on the material properties. The results show that when the solid content of Ni slurry increases from 70 to 84 wt. %, the relative density of Ni increases, the shrinkage decreases, and the mechanical properties increase; when the sintering temperature increases from 1250 to 1400 °C, the relative density of Ni increases, the shrinkage increases, the mechanical properties decrease, and the particle size increases. The relative density range is 82%–96.6%, the shrinkage range is 53.5%–59.6%, the tensile strength range is 237.7–294 MPa, and the hardness range is 51.6–104.8 HV. Finally, the relationship between slurry, manufacturing process, structure, and properties was established through process optimization and experimental results, and 3D models of different structures were prepared to complete the preparation of Ni with high structural integrity, good interlayer bonding, and excellent properties.

In the atomic cell of the spin exchange optical pumping system, the optical pumping inevitably introduces a magnetic field gradient, which affects the measurement result of the nuclear spin relaxation time a lot. To address this issue, our method achieves the measurement while excluding the influence of this magnetic field gradient. In this method, the pump laser is turned off after the spins of 87Rb and 129Xe have been effectively polarized, which results in the spin polarization of the 87Rb atoms being provided only by the spin exchange with 129Xe. Ultimately, the transverse and longitudinal components of the polarization of 129Xe are detected by the in situ 87Rb atom magnetometer to obtain the T1 and T2 of 129Xe under different conditions. Using our method, since the influence of inhomogeneity caused by the pump laser is eliminated, the relaxation characteristic of atomic cells can be measured more quickly, essentially, and conveniently, which helps compare the performance of different atomic cells and find the best cell fabrication process further.

In the atomic cell of a nuclear magnetic resonance gyroscope, a transverse bias field is applied to enable the in situ alkali magnetometer to sense the variations in the longitudinal magnetic field. During a single relaxation process of the noble gas, the longitudinal relaxation time is obtained by monitoring and fitting the signal of the magnetometer in real-time. The relaxation times measured using our method are nearly identical to those obtained using the conventional delayed pulse method, but in contrast, our method saves ∼90% of the time. By using the new method, fast and accurate batch testing for a large number of atomic cells can be achieved to optimize the manufacturing of the cells, which is helpful in speeding up the development of gyroscopes.

To examine mechanisms of the high speed and efficiency of propulsion of aquatic animals and to apply the findings to the design of underwater vehicles, this study uses dolphins as an example. The motion of aquatic animals is divided into three stages for the convenience of analysis of bio-propulsion: the oscillation of one-third of the rear body, the oscillation of the caudal fin, and the deformation of the caudal fin. We call the case multi-stage propulsion when all the stages are contained in a bio-propulsion. We investigate the effects of the phase difference between oscillations of the first and second stages φ on hydrodynamic performance and the chordwise deformation factor δc0 on hydrodynamic performance. The results show that when the phase difference was 90°, the propulsion efficiency was the highest and an appropriate caudal chordwise deformation could increase the propulsion efficiency, which was consistent with the result of previous studies. The key part of this paper is the comparative study between different propulsion modes in terms of fluid mechanism from multiple perspectives, such as the force generated by the oscillating motion, the shedding frequency of the wake vortex, and the spacings of vortices induced by different propulsion modes. The aim of this paper is to understand the mechanism supporting a larger thrust and higher efficiency of multi-stage propulsion and provide reference for the improvement and optimization of bionic propulsion in the future.

The growth of Ag-nanofilaments in the solid electrolyte films of memristors based on Ag30S2P14O42 is investigated. After the formation of the Ag-nanofilaments in the solid electrolyte, the memory cells are switched to the high conductive state. With a positive voltage applied on the Ag electrode of the cells, the Ag-nanofilaments gradually become thicker due to the reduction and diffusion of Ag+ cations in the solid electrolyte. The relationship between the thickening rate of the Ag-nanofilaments and the concentration of the Ag+ cations surrounding them is analyzed, and the results show that the thickening of the Ag-nanofilaments is determined by the reduction and diffusion of Ag+ cations in the solid electrolyte.

The transverse relaxation time τ2 of the built-in alkali metal magnetometer is an important parameter to characterize its performance and the working state of the nuclear magnetic resonance (NMR) oscillator system. The method we propose to measure τ2 is to apply the frequency-scanning magnetic fields along the x-axis and obtain τ2 from the 3 dB bandwidth of the measured x-axis amplitude–frequency response curve of the magnetometer. We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method to demonstrate the rationality of this measuring method. Then, both the actual experiment and the simulation experiment results are presented to verify the validity and good accuracy of the method. All the sampled frequencies in the scanning range should be far away from both the 129Xe and 131Xe NMR frequencies, to avoid introducing any influence on the nuclear spins; therefore, this method can provide a non-interference way for measurement of τ2, helping us monitor the NMR oscillator system’s state under normal operating conditions.

Magnetic field gradients reduce the transverse relaxation time of nuclear spins, which usually degrades the sensitivity of atomic sensors based on nuclear spins. We demonstrate improved magnetic field gradient compensation by applying first-order and second-order magnetic gradients simultaneously in a cubic vapor cell containing 87Rb vapor and 129Xe gas. Compared with applying only first-order magnetic gradient compensation, the transverse relaxation time of 129Xe is up to 4.3 times longer when applying both first-order and second-order compensating magnetic gradients, which indicates that the total magnetic gradient is greatly suppressed by the joint compensation in our experiment. The magnetic gradients induced by the polarized 87Rb spins, the static magnetic field, and the residual magnetic field are also explored. As the main sources of internal magnetic inhomogeneities, these gradients are experimentally validated to have a sizable value. Furthermore, the total internal magnetic gradient in the system could be self-compensated when the directions of these internal gradient components are appropriately set. The experimental results in this paper are important for suppressing the magnetic gradients and optimizing the gradient compensation in nuclear magnetic resonance systems.

We analyze the scale factor linearity, steady-state, transient, and noise characteristics of a nuclear magnetic resonance oscillator coupled with the phase-locked loop, which makes its performance improvement possible by a balanced strategy in optimizing parameters based on the proposed model. The numerical simulation indicates that the simple oscillator system gives a better scale factor linearity and transient response than the coupled system, while the steady-state solution is similar between the two with experimental validation. The phase and magnetic noise suppression is necessary to ensure the dynamic response of the coupled system. The characteristic analysis not only facilitates the rapid-response optimization of the coupled oscillator system under a dynamic environment but also enlightens corresponding steady-state tracking precision.

In the atomic cell of the spin exchange optical pumping system, the optical pumping inevitably introduces a magnetic field gradient, which affects the measurement result of the nuclear spin relaxation time a lot. To address this issue, our method achieves the measurement while excluding the influence of this magnetic field gradient. In this method, the pump laser is turned off after the spins of 87Rb and 129Xe have been effectively polarized, which results in the spin polarization of the 87Rb atoms being provided only by the spin exchange with 129Xe. Ultimately, the transverse and longitudinal components of the polarization of 129Xe are detected by the in situ87Rb atom magnetometer to obtain the T1 and T2 of 129Xe under different conditions. Using our method, since the influence of inhomogeneity caused by the pump laser is eliminated, the relaxation characteristic of atomic cells can be measured more quickly, essentially, and conveniently, which helps compare the performance of different atomic cells and find the best cell fabrication process further. [ABSTRACT FROM AUTHOR]

We analyze the amplitude-frequency, phase-frequency, signal amplification, linear range, and vector characteristics of the built-in vector atomic magnetometer operating at extreme off-resonance condition in a nuclear magnetic resonance oscillator, which makes possible its performance improvement by a balanced strategy in optimizing the parameters based on the proposed model. The experiment validates our prediction of the amplitude-frequency characteristic, and the numerical simulation indicates that the applied carrier field with following demodulation procedure holds the potential to give one order of magnitude, which is experimentally-validated to have at least twice, signal enhancement and enable the vector characteristic, where a large longitudinal static field and an appropriate transverse relaxation time are preferred to have optimized characteristics depending on different applications.

We proposed a new bias-approach method for measuring longitudinal relaxation time of 129Xe. Compared with the delayed pulse method, the measuring time of the proposed single-scan bias-approach is significantly decreased by more than 20 times, and the differences are 2% and 0.7% of two sample cell A and B respectively. By giving a small static magnetic field in the transverse domain, a π-pulse-induced 87Rb magnetometer signal bias with respect to the longitudinal magnetization of xenon was obtained. We then use a π/2 pulse to find the half-life time of longitudinal relaxation. Since the bias-approach has a low requirement of the systematic robust, it naturally becomes a more efficient method to measure the longitudinal relaxation time with respect to the noble gas in the vapor cell.

This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, demonstrating the great potential of the bistable buckled beam for wideband rotation motion energy harvesting.

A fast and accurate determination of longitudinal relaxation time is put forward for hyperpolarized 129Xe. The theoretical framework for the method is developed. Measurement of the longitudinal relaxation time is by the determination of a close-loop response of 129Xe magnetization to the external magnetic fields and is implemented with a highly sensitive Rb magnetometer. The indirect measurement dramatically reduces the time consuming than the conventional inversion-recovery method and is more suitable for the samples with long longitudinal relaxation time.

Cyanoketene (OCCHCN) has been reported as a potential alternative insulation gas for SF6 in Patent US0135817. Stationary point equilibrium geometries on the ground state have been optimized at the B3LYP/6-311+G(d,p) level, and the harmonic vibration frequencies are calculated at the same level. The HOMO-LUMO energy gaps (Eg), ionization potentials (IP), and electron affinities (EA) of the studied molecules are obtained. The minimum energy path (MEP) is obtained by the intrinsic reaction coordinate (IRC) theory, and the energetic information is further refined by QCISD(T) (single-point) method. The results show that OCCHCN can be used as SF6 alternative insulation gas in high voltage equipment according to potential energy surface analysis. As the isomerization and the cleavage reactions potential barriers are lower than the Eg and IP values, resulting in OCCHCN is not easy to be ionized and excited.

Monolayer WTe2, which is predicted to be large-gap quantum spin Hall (QSH) insulators with distorted 1T (1T’) structure, attracts rapidly growing interests. However, the intrinsic semimetallic nature of the monolayer 1T’-WTe2 limits their direct applications based on QSH effect. By first-principles density functional theoretical calculations, we demonstrate a phase transition from semimetal to QSH insulator under the uniaxial strains along a and b axis in monolayer 1T’-WTe2. The electronic phase transition results from the geometric structure deformation upon the uniaxial strains. This suggests monolayer 1T’-WTe2 as a promising material for application in strain-tunable topological quantum electronics.

The memory structures Pt/Al2O3/(TiO2)x(Al2O3)1−x/Al2O3/p-Si(nominal composition x = 0.05, 0.50 and 0.70) were fabricated by using rf-magnetron sputtering and atomic layer deposition techniques, in which the dielectric constant and the bottom of the conduction band of the high-k composite (TiO2)x(Al2O3)1−x were adjusted by controlling the partial composition of Al2O3. With the largest dielectric constant and the lowest deviation from the bottom of the conduction band of Si, (TiO2)0.7(Al2O3)0.3 memory devices show the largest memory window of 7.54 V, the fast programming/erasing speed and excellent endurance and retention characteristics, which were ascribed to the special structural design, proper combination of dielectric constant and band alignment in the high-k composite (TiO2)0.7(Al2O3)0.3.

Polymer based memristive devices can offer simplicity in fabrication and at the same time promise functionalities for artificial neural applications. In this work, inherent learning and memory functions have been achieved in polymer memristive devices employing Polyvinyl Alcohol. The change in conduction in such polymer devices strongly depends on the pulse amplitude, duration and time interval. Through repetitive stimuli training, temporary short-term memory can transfer into consolidated long-term memory. These behaviors bear remarkable similarities to certain learning and memory functions of biological systems.

A comprehensive theoretical study of the half-metallicity in the zigzag graphene nanoribbons (ZGNRs) by adsorption of the zigzag hydrogen fluoride chains was presented. The ZGNR by adsorption of the hydrogen fluoride chains could be half-metallic when a critical length of the hydrogen fluoride chain is achieved on the ZGNR at low temperature. It was found that the strong dipole moments of the hydrogen fluoride chains act as the constant electric field. Our results suggest a huge possibility in spintronics device applications for achieving half-metallicity in the ZGNRs without the excessively high external electric fields.

In this work, we fabricate BaTiO3/La0.67Sr0.33MnO3 (BTO/LSMO) ferroelectric tunnel junction on (001) SrTiO3 substrate by pulsed laser deposition method. Combining piezoresponse force and conductive-tip atomic force microscopy, we demonstrate robust and reproducible polarization-controlled tunneling behaviors with the resulting tunneling electroresistance value reaching about 102 in ultrathin BTO films (∼1.2 nm) at room temperature. Moreover, local poling areas with different conductivity are finally achieved by controlling the relative proportion of upward and downward domains, and different poling areas exhibit stable transport properties.

Upward self-poling phenomenon was observed in PbZr0.2Ti0.8O3 ferroelectric films which were grown on (001) SrTiO3 substrate with either p-type La0.7Sr0.3MnO3 or n-type SrRuO3 buffered layer, or on n-type (001) Nb-SrTiO3 substrate. Both upward self-poling and epitaxial strain are strong in the super-thin PbZr0.2Ti0.8O3 epitaxial films, while they become weak and finally disappear in thick epitaxial films or thin epitaxial films with high-density oxygen vacancies. Besides, both of them disappear in PbZr0.2Ti0.8O3 polycrystalline films on Pt/TiO2/SiO2/Si substrate. Therefore, the main origin of upward self-poling is epitaxial strain rather than p-n/Schottky junction or charged vacancies in PbZr0.2Ti0.8O3 epitaxial films here.

Au-assisted growth of InN nanowires (NWs) was accomplished by a simple chemical vapor deposition system. The as-prepared InN NWs exhibit two morphologies with different growth directions: periodic NWs (PNWs) and smooth NWs (SNWs) along and , respectively. The PNWs with crinoids morphology resulted when larger Au particles (∼40 nm in diameter) were used, while the SNWs with smooth sidewalls were obtained when smaller Au particles (∼10 nm in diameter) served as the collector. Furthermore, the mechanism of this growth behavior was discussed in terms of the effect of catalyst nanoparticle size.

We have proposed a kind of memristive device based on the junctions employing Ti as the reactive electrodes. The role of electrically-derived redox of Ti in such memristive switching is shown. The structural and chemical evidence of the electrically-derived oxidation is presented by TEM and XPS experiment, respectively. Due to the redox of the top electrode Ti and the consequent drift of oxygen vacancies, the device shows two distinct resistance states under a sweeping voltage loading. ON state is controlled by tunneling process, while OFF state is controlled by Schottky emission conductive mechanism. The failure behaviors of such memristive junctions are also discussed. In the light of the redox principle, we demonstrate that the devices could be recovered by loading a long electrical reduction treatment.

We proposed a new bias-approach method for measuring longitudinal relaxation time of 129Xe. Compared with the delayed pulse method, the measuring time of the proposed single-scan bias-approach is significantly decreased by more than 20 times, and the differences are 2% and 0.7% of two sample cell A and B respectively. By giving a small static magnetic field in the transverse domain, a π-pulse-induced 87Rb magnetometer signal bias with respect to the longitudinal magnetization of xenon was obtained. We then use a π/2 pulse to find the half-life time of longitudinal relaxation. Since the bias-approach has a low requirement of the systematic robust, it naturally becomes a more efficient method to measure the longitudinal relaxation time with respect to the noble gas in the vapor cell. [ABSTRACT FROM AUTHOR]