Review of Scientific Instruments最新文献

In this paper, based on the sand cat swarm optimization (SCSO) algorithm, a dual-path differential perturbation sand cat swarm optimization algorithm integrated with escape mechanism (EDSCSO) is proposed. EDSCSO aims to solve the problems of the original SCSO, such as the limited diversity of the population, low efficiency of solving complex functions, and ease of falling into a local optimal solution. First, an escape mechanism was proposed to balance the exploration and exploitation of the algorithm. Second, a random elite cooperative guidance strategy was used to utilize the elite population to guide the general population to improve the convergence speed of the algorithm. Finally, the dual-path differential perturbation strategy is used to continuously perturb the population using two differential variational operators to enrich population diversity. EDSCSO obtained the best average fitness for 27 of 39 test functions in the IEEE CEC2017 and IEEE CEC2019 test suites, indicating that the algorithm is an efficient and feasible solution for complex optimization problems. In addition, EDSCSO is applied to optimize the three-dimensional wireless sensor network coverage as well as the unmanned aerial vehicle path planning problem, and it provides optimal solutions for both problems. The applicability of EDSCSO in real-world optimization scenarios was verified.

To address the challenge of low accuracy in traditional transformer fault diagnosis algorithms, this paper introduces a novel approach that utilizes the Artificial Hummingbird Algorithm (AHA) to optimize both Kernel Principal Component Analysis (KPCA) and Extreme Learning Machine (ELM). We propose the use of various gas concentration ratio features and apply the AHA algorithm to fine-tune the kernel function parameters of KPCA, thus establishing an AHA-KPCA feature extraction model. This model takes the expanded gas concentration ratio features as input and selects the top N principal components with a cumulative contribution rate above 95% to form the feature vectors for fault classification. Following this, the AHA algorithm is employed to optimize the input weights and hidden layer biases of the ELM, leading to the development of the AHA-ELM fault classification model. Ultimately, the principal components identified by AHA-KPCA serve as inputs for the simulation verification of the AHA-ELM model. Experimental results indicate that the proposed AHA-KPCA-ELM method attains an accuracy rate of 95.73%, surpassing traditional intelligent diagnostic methods and existing advanced algorithms, thereby confirming the effectiveness of our proposed method.

This article introduces an enhanced non-approximated control technique for the pitch and altitude control systems of unmanned helicopters. It takes into account unpredictable external disturbances and system dynamics. The integration of prescribed performance control into unmanned helicopter systems significantly improves the transient and steady-state response capabilities. This approach avoids the computational complexities often associated with neural networks and fuzzy control methods. By avoiding the need for function approximation, which can introduce inaccuracies and computational overhead, the controller design process is streamlined. This method's simplicity and ability to handle unknown disturbances make it highly suitable for real-world implementation, where robustness and efficiency are paramount. Finally, simulations are conducted to showcase the improved transient and steady-state response capabilities achieved by the proposed approach.

A ceramic-based pulse-forming line (PFL) is a solid-state device with a wide range of applications in compact pulsed power systems. In this paper, the characteristic impedance of a ceramic-based PFL is theoretically analyzed, and an improved PFL based on an impedance matching electrode is proposed. The improved PFL effectively increases the flat-top ratio and reduces the rise and fall times, enhancing its potential applicability. Experiments using the improved PFL show that, under a charging voltage of 33 kV and with an impedance matching load, the output pulse width can reach 86 ns with a matching impedance of 3.9 Ω. The improved PFL output waveform has a flat-top ratio that reaches 72%, compared with 49.5% in a typical PFL, and exhibits shorter rise and fall times.

The Roberts linkage is recognized for enabling long-period pendulum motion in a compact format. Utilizing this characteristic, we are developing a three-point Roberts linkage for vibration isolation systems, with an eye toward its potential contribution to the development of next-generation interferometric gravitational wave antennas. In this article, we derived the equations to determine the essential parameters when using this linkage as a vibration isolation system, namely, the equivalent pendulum length and the relationship between translational motion of the center of mass and rigid body rotation, from size parameters. In addition, we analyzed the behavior in response to various errors.

In the "method of four coefficients," electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (RH), and Nernst coefficient (Q) of a material are measured and typically fit or modeled with theoretical expressions based on Boltzmann transport theory to glean experimental insights into features of electronic structure and/or charge carrier scattering mechanisms in materials. Although well-defined and readily available reference materials exist for validating measurements of ρ and S, none currently exists for RH or Q. We show that measurements of all four transport coefficients-ρ, S, RH, and Q-can be validated using a single reference sample, namely, the low-temperature Seebeck coefficient Standard Reference Material® (SRM) 3451 (composition Bi2Te3+x) available from the National Institute for Standards and Technology (NIST) without the need for inter-laboratory sample exchange. RH and Q data for NIST SRM 3451 reported here for the temperature range 80-400 K complement the data already available for ρ and S and will therefore be of interest to researchers desiring to validate new or existing galvanomagnetic and thermomagnetic transport properties measurement systems.

Infrared reflection absorption spectroscopy (IRRAS) is a powerful surface-sensitive analytical technique to characterize the adsorbed molecules on metal surfaces down to (sub)monolayer coverage. In this paper, a new (inert) gas cell is presented that expands the scope of the commercially available Bruker PMA50 module. The cell is designed as a sample holder to measure thin films of molecules adsorbed on a metal substrate under a specific gaseous atmosphere. The dimensions of the cell are chosen in such a way that it can be transferred into a glovebox via the standard entrance port (Ø150 mm), allowing the investigation of air-sensitive molecules under an inert-gas atmosphere. The cell has two hose connections through which the gas atmosphere can be varied as desired. This also allows for studying the reactivity of the adsorbed structures toward the surrounding gas in situ and in a (potentially) time-dependent fashion. Furthermore, the metal substrate can be irradiated via an exposure window to investigate the influence of light on the adsorbed molecules and/or their reactivity. Using the polarization-modulation (PM-) IRRAS technique along with the described gas cell, an air-sensitive molybdenum(0) tricarbonyl complex adsorbed on an Au(111) surface is investigated. This complex reacts with molecular oxygen to the molybdenum(VI) trioxo analog, and this conversion is accelerated by irradiation with light of 365 and 440 nm.

Passive shimming is widely used in magnetic resonance imaging (MRI) systems due to its excellent efficacy and cost-effectiveness. However, conventional shim tray structures have difficulty in effectively adjusting magnetic field distributions under specific conditions. This limitation can lead to insufficient cancellation of harmonics and result in significant residual forces on the trays, impeding accurate placement of the trays. In this study, instead of using the conventional design of the shim tray slot, we propose a dedicated passive shimming tray tailored for 3T cryogen-free animal MRI superconducting magnets. Passive shimming experiments were conducted to evaluate the performance of this novel design, in which we were able to improve the peak-to-peak magnetic field homogeneity within the 180 mm diameter imaging region, reducing peak-to-peak (p-p) variation from 349.35 ppm to 19.08 ppm. Furthermore, the p-p homogeneity of the magnetic field measured at the imaging area with a diameter of spherical volume (DSV) of 160 mm reached 8.67 ppm. In addition, we strictly controlled the residual magnetic force of the shim tray to ensure its accurate placement. The experimental results indicate that the proposed structural optimization method and the residual magnetic force control strategy show potential in high-field MRI instruments requiring high homogeneity and handling of high residual magnetic force.

Donepezil hydrochloride is a widely used medication for treating Alzheimer's disease. This study utilized terahertz time-domain spectroscopy to analyze the fingerprint spectra of donepezil hydrochloride, identifying five characteristic absorption peaks at 1.65, 2.44, 2.56, 3.31, and 3.75 THz. The vibrational spectrum of the donepezil hydrochloride crystal was further examined using solid-state density functional theory. Based on simulation calculations, the characteristic peaks were identified and analyzed in detail, focusing on long-range ordering and weak interaction networks. The results demonstrate that terahertz spectroscopy is an effective tool for studying intermolecular interactions in drug crystals.

Magnetic force microscopy (MFM) is a well-established technique in scanning probe microscopy that allows for the imaging of magnetic samples with a spatial resolution of tens of nm and stray fields down to the mT range. The spatial resolution and field sensitivity can be significantly improved by measuring in vacuum conditions. This improvement originates from the higher quality-factor (Q-factor) of the cantilever's oscillation in vacuum compared to ambient conditions. However, while high Q-factors are desirable as they directly enhance the magnetic measurement signal, they pose a challenge when performing standard MFM two-pass (lift) mode measurements. At high Q-factors, amplitude-based topography measurements become impossible, and the MFM phase response behaves non-linearly. Here, we present a modified two-pass mode implementation in a vacuum atomic force microscope that addresses these issues. By controlling the Q-factor in the first pass and using a phase-locked loop technique in the second pass, high Q-factor measurements in vacuum are enabled. Measuring the cantilever's frequency shift instead of the phase shift eliminates the issue of emerging nonlinearities. The improvements in MFM signal-to-noise ratio are demonstrated using a nano-patterned magnetic sample. The elimination of non-linear responses is highlighted through measurements performed on a well-characterized multilayer reference sample. Finally, we discuss a technique that avoids topography-induced artifacts by following the average sample slope. The newly developed, sensitive, and distortion-free high quality-factor two-pass mode has the potential to be widely implemented in commercial setups, facilitating high-resolution MFM measurements and advancing studies of modern magnetic materials.