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For complex systems, the inhibition of self-excited vibration has always been a difficulty in engineering field. Currently, ultrasonic field energy as a special field energy could suppress vibration significantly. Unfortunately, vibration suppression mechanism has not been elucidated and intrinsic association with vibration field is still ambiguous. Here, we clarify coupling mechanism of ultrasonic field energy and unsteady vibration field energy firstly from the perspective of energy transfer and distribution. We find that it realizes spatially controllable redistribution of vibration field by changing distribution law of excitation waves, which makes vibration frequency migrate across scales. On this basis, we establish a relationship model between ultrasonic field energy and vibration field energy innovatively to accomplish precise vibration suppression. These insights generate important significance for active vibration suppression, which have broad applicability in flexible precision manufacturing, vibration inhibition of aircraft or satellite solar array, high-precision medical equipment and rail traffic stability control.

The ratio of stable isotopes of the elements in explosives differs depending on the raw materials obtained from different geographical sources or the production processes adopted. Hence, this ratio can be used as an important index for the comparison and trace of explosives. Isotope ratio mass spectrometry (IRMS), a high-precision method for the analysis of stable isotope ratios, has evolved into a mature tool in this regard. In combination with elemental analysis, gas chromatography, liquid chromatography, etc., IRMS is widely used in food safety, environmental protection, forensic science, and other fields. IRMS also plays an important role in the comparison and trace of explosives. Since its application to distinguish trinitrotoluene (TNT) produced in different countries in 1975, IRMS has been successfully used in the analysis of various explosives. However, there is no systematic summary on the research progress on the stable isotope ratio analysis of common explosives. This paper provides a brief description of the related principle, instrumental composition, and characteristics of stable isotope ratio analysis. Methods for the stable isotope ratio analysis of common explosives such as ammonium nitrate, black powder, TNT, pentaerythritol tetranitrate (PETN), and cyclotrimethylene trinitroamine (RDX) are reviewed. The bulk stable isotopic ratio analysis method was used in most of the studies to determine the total isotope ratio of the sample. A compound-specific isotope analysis method was also employed to determine the isotope ratio of organic explosives in a complex matrix. The reported stable isotope ratios of explosives such as ammonium nitrate, black powder, and TNT produced in different countries are summarized. The discrimination ability of the stable isotope ratio for explosives is discussed. Based on the stable isotope ratio, explosives from different sources can be distinguished effectively. By combining the results of elemental analysis with the ICP-MS results, the discrimination efficiency of different samples could be further improved. The influence of relevant factors on the isotope ratio during the production and storage of explosives are collated. There is a strong correlation between the stable isotope ratios of explosives and raw materials. The stable isotope ratios of TNT, PETN, and other explosives are related to that of nitric acid used in the production. The stable isotope ratios of nitrogen and oxygen in the explosive are relatively stable and almost unchanged within one year of production. The complexity of the environmental matrix at the explosion site and the low concentration of explosive residues make the stable isotope analysis of explosive residues challenging. However, the changes in the stable isotope ratio before and after the explosion are discussed. Since there is no information on the application of stable isotope analysis to the traceability of explosives, the paper mentions that the standardized explosive sample pretreatment, stable isotope analysis method, collection and analysis of large amounts of explosive samples, and explosive stable isotope database are the basis of explosive traceability. This paper also outlines the existing challenges in the analysis of the stable isotope ratios of explosives, including the small number of explosive samples, lack of a stable isotope explosive analysis database, and difficulty in the stable isotope analysis of explosive residues. Possible solutions to these problems are proposed, followed by suggestions for the future development of the stable isotope ratio analysis of common explosives. The suggestions include establishing an effective extraction and enrichment method for explosive residues, combining IRMS with GC or LC for analyzing explosives, establishing a comprehensive process for the analysis of the stable isotope ratios of inorganic and organic explosives, and comparison and analysis of the stable isotope analysis data using statistical methods.

Triacetone triperoxide (TATP) and its byproduct diacetone diperoxide (DADP) are commonly used home-made high explosives in bombing cases and terrorist attacks. However, these two peroxide explosives are unstable and prone to thermal decomposition, leading to challenges in sample collection and preparation in bombing cases. Therefore, there is an urgent need to develop an in situ identification method for TATP and DADP. Compared to the solvent-based swabbing methods commonly used for trace explosive collection, the tape lifting method can collect explosive particles and other potential evidence without damaging fingerprints or DNA. This study aims to develop a tape lifting method to collect trace explosive particles in bombing cases and an in situ method to identify TATP and DADP particles on the sticky side of transparent tape directly using laser confocal Raman spectroscopy. One type of fingerprint tape and two types of office tape were used to collect peroxide explosive particles followed by particle fixation on glass slides. Laser confocal Raman spectroscopy was applied to directly identify target particles, without peeling the attached tape off the glass slide. A solid-state laser emitting at 473 nm was suitable for Raman and imaging analysis of TATP and DADP. To mimic the real situation, the synthetic TATP and DADP were passed through a 100-mesh sieve, respectively. Fifty μg of each explosive powder was weighed, mixed and spread on a wooden table with dust in an area of 10 × 10 cm2. Subsequently, the samples were collected with the fingerprint tape. A targeted area of the tape with suspicious particles was imaged for analysis. Based on the difference between the characteristic Raman bands of TATP and DADP, the band ranges of 530–550 cm−1 and 750–770 cm−1 were selected, respectively, for obtaining the distribution information. The combination of Raman technology and the tape lifting method shows great potential for in situ identification of forensic samples by providing chemical and spatial information.

Multilayer colloidal crystal has been prepared by the layer-by-layer deposition of silica microspheres on a glass slide. Each layer is a slab consisting of a fcc close-packed colloidal arrays. By properly choosing the sizes of spheres, the whole spectral feature of multilayer colloidal crystal can be tuned. Here, we engineered a multilayer superlattice structure with an effective passband (380 nm) between two stop bands (366 nm and 400 nm). This gives a strong narrowing effect on emission spectrum (378 nm). With the stop bands at the shortwave and longwave edges of emission spectrum, the passband in the central wavelength region can be regarded as a strong decrease of suppression effect and enhancement of a narrow wavelength region of emission. The FWHM values of stop band modified emission spectrum were narrowed from 59 nm to 22 nm. The spectral narrowing modification effect of suitably engineered colloidal crystals shows up their importance in potential application as optical filters and lasing devices.

Nitro compounds such as 2,4,6-trinitrotoluene, cyclotrimethylene trinitramine, and pentaerythritol tetranitrate are common ingredients of high explosives found in homeland security threats, minefields, and industrial materials. This study aims at developing a convenient surface analysis method for rapid identification of these compounds by direct analysis in real time coupled with time-of-flight mass spectrometry. The possible ionization mechanisms and fragmentation pathways using the direct analysis in real-time ionization source were developed for each compound based on the ions produced by in-source collision-induced dissociation and acquired by a time-of-flight mass spectrometer. These compounds release nitro groups and form nitroless characteristic fragments with other nitro adducts during in-source collision-induced dissociation processes. The characteristic ion [M + C2H4N3O2]− produced by cyclotrimethylene trinitramine was observed for the first time to our best knowledge. Direct analysis i...

This paper, through mass spectrometric (MS) analysis for nitro compound explosives on a direct analysis in a real-time time-of-flight MS, indicates that even on a high-resolution MS with accurate mass measurement capabilities, there is no guarantee to obtain the unique molecular formula of a compound. By calculating spectra accuracy, highly accurate isotope pattern matching can be conducted to significantly improve performance of compound confirmation or identification.