Review of Scientific Instruments最新文献

Measuring quantitative and accurate friction force at the nanoscale by means of atomic force microscopy is not straightforward. Numerous lateral force calibration methods have been proposed in the last decades. The most popular one is the wedge method that requires a specific calibration sample having areas that present constant slope and friction coefficient. In this paper, we propose to revisit the wedge method by using an original, cheap, and easy-to-make standard, which consists of a V-shaped scratch made by a Berkovich nanoindenter tip on a fused silica substrate. We show that the scratch has two large opposite facets characterized by the same moderate and constant friction coefficient and slope. This allows simplification of the data processing and a much more reliable and accurate lateral force microscopy calibration.

This paper presents the implementation of a picosecond resolution timing generator (TG) insensitive to process, voltage, and temperature (PVT) variations for automatic test equipment. The TG is implemented in field-programmable gate arrays (FPGAs) using two-stage time interpolation, which utilizes a multi-phase generator, IDELAY3, and carry-chain resources. To enhance the test rate, each channel of the proposed TG consists of four parallel operating edge generators. The TG performance will deteriorate severely without offset correction due to its sensitivity to PVT variations. To improve the adaptability of the TG, we design a robust offset canceler to ensure stable performance of the TG, resilient to PVT variations. With the proposed architecture and offset canceler, the PVT-insensitive TG achieves a time resolution of 5 ps and offers a maximum dynamic range of 10 s. It also shows improved worst case integral non-linearity ranging from -4.7 to +4.6 ps with the operating temperature continuously varying from 15 to 65 °C and voltage ranging from 0.95 to 1.01 V in FPGAs. The proposed TG can be implemented in the Ultrascale or Ultrascale+ FPGA platform.

The characterization of the spatial distribution of particle trajectories, or the respective current distribution, in powerful electron beams is an important scientific and practical task necessary to improve the quality of electron beam technologies. For various applications, a small divergence is required to transport the electron beam over long distances and focus it onto a small spot. Even if one has simultaneous knowledge of accelerating voltage, beam current, focus coil current (or magnetic field), and vacuum level overall, they provide little insight into the properties of the beam itself. In this work, visible cameras are used to study the shape of the electron beam when these parameters are varied. A series of pictures are collected at different camera orientations around the beam. The light emission comes from the argon background gas interacting with the energetic electrons composing the beam. The information is used to reconstruct the two-dimensional shape of the beam using tomographic inversion.

To accurately identify compound faults of bearings, a new noise reduction method is presented. With the new method, input signals and the order of Wiener filtering are adaptively determined according to feature mode decomposition (FMD), signal evaluation index, and Euclidean distance. First, to effectively separate frequency components from vibration signals, vibration signals are decomposed into modal components based on the FMD algorithm; second, kurtosis, root mean square, and variance, which are sensitive to fault information, are selected to build evaluation vectors. Third, the Euclidean distance between the evaluation vectors of the component signal and the original signal are calculated to represent the correlation among signals. By acquiring the two component signals that have the greatest and least correlation to original signals, an actual signal and a mixed signal required by Wiener filtering can be adaptively determined. Furthermore, the order of Wiener filtering is adaptively determined with maximum kurtosis as the criterion. Finally, fault features are extracted through the spectral analysis of signals after Wiener filtering and the type of compound faults is judged based on that. To demonstrate the accuracy and effectiveness of the proposed method, the proposed method is compared with the classical method. The result of comparison shows that the presented method can restrict the noise more effectively and determine the type of complex faults of bearings more accurately.

In this paper, an analytical expression for the overall bias of the complex-valued noisy sine wave frequency estimator returned by the interpolated discrete Fourier transform algorithm is derived. That bias is due to the effect of both the algorithm intrinsic approximation when rectangular windowing is adopted and wideband noise. The effect of the number of analyzed samples and the signal-to-noise ratio on the ratio between the overall estimation bias and the estimator standard deviation is also investigated. In addition, leveraging on the derived expression, a frequency estimator that compensates for the contribution due to the algorithm intrinsic approximation is proposed and its accuracy is compared with that of the classical frequency estimator.

We explore the magnetic properties of a thin Co film deposited on Kapton® substrates using the magneto-optical Kerr effect in a longitudinal configuration. We developed a magnetometer integrated with a tensile testing machine to investigate magnetization reversal phenomena under applied strain. The tensile machine, custom-designed to fit the experimental constraints, applies uniaxial stress to the samples, facilitating the study of magnetoelastic effects. Calibration using digital image correlation ensures accurate strain measurements. Our findings demonstrate that the application of strain significantly influences the magnetization curves, highlighting the emergence of anisotropies and changes in coercive and saturation fields.

Short pulse laser (SPL) heated matter has opened an avenue to studying matter at conditions previously unattainable. While SPLs can generate matter at extreme densities and temperatures, characterization of the heated matter can be extremely challenging. The conditions are dynamic and require careful monitoring of the plasma evolution. Atomic processes under these conditions can provide a powerful tool to study fundamental plasma properties as they evolve. When utilizing the x-ray emission from these plasmas, it is often useful to resolve spectral details with high resolution. Sub-picosecond, time-resolved, high-resolution spectroscopy has previously been reported. We present a similar diagnostic (STreaked Orion High-Resolution X-ray spectrometer, or STOHREX) to measure the temporal evolution of spectral features with high spectral resolution. The diagnostic is the result of combining a high-resolution x-ray spectrometer with the LLNL sub-picosecond x-ray streak camera. The diagnostic was demonstrated in two campaigns: (1) To study spectral lineshapes using the 40 fs, 400 nm, Colorado State University ALEPH laser, and (2) to study buried layers using the 500 fs, 532 nm Atomic Weapons Establishment's Orion laser.

A simple method to self-start a Mamyshev oscillator (MO) using an optical beam shutter (OBS) in the cavity is presented. OBS is placed inside the cavity to introduce a strong optical fluctuation by switching its state (open/close). Stable mode-locking operation is achieved in fiber MO by using an OBS without requiring any external mode-locked seed source or pump modulation.

Geomagnetic vector measurement can obtain more geomagnetic information, which is one of the main development directions of geomagnetic measurement. To date, the magnetic flux gate magnetometer is the main tool for geomagnetic vector measurement; however, its drift issue cannot be ignored. To address this issue, we propose a geomagnetic vector measurement method based on bias and compensation fields and then develop a high-stability FHD (total-field F, horizontal component H, and declination D) vector magnetometer based on a proton sensor and a magnetic field generator. In addition, a dedicated experimental platform is constructed to verify the performance of the developed magnetometer in a geomagnetic station. Compared to the flux gate magnetometer, the experimental results indicate that the fourth-order differential noise of the declination D, horizontal component H, and vertical component Z are 1″, 0.27, and 0.15 nT, respectively, which are all lower than those of the flux gate magnetometer. In addition, the horizontal component H and vertical component Z of the flux gate magnetometer indicate more than 30 and 60 nT startup drift, respectively; in contrast, the proposed FHD magnetometer shows an excellent stability during a 16 h observation time.

Vacuum freeze-drying (VFD) technology has gained extensive application across various sectors, particularly in environmental applications, where it is primarily utilized for the fabrication of environmental functional materials and the conservation of environmental organisms. This technology is applicable to soil enhancement, the remediation of aquatic pollutants, energy storage in thermoelectric materials, and the preservation of bacterial cultures. This review synthesizes the most recent advancements in VFD technology within the environmental domain, elaborating on its technical fundamentals, operational procedures, practical applications, and distinctive benefits. Furthermore, the article explores the prospective development trajectory and potential challenges for this technology in the environmental sector, offering scientific guidance for its continued application and insights into its innovative progression.