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Ghee is a traditional Tibetan dairy product with high-fat content, low yield, plasticity, caseation, and rich nutrition. In this study, we analyzed the diversity of microbial communities in yak milk and ghee samples at high and low altitudes, especially the Lactobacillus genus, and further used metabolomic techniques to compare the differences in metabolites in yak ghee at different altitudes. The results showed that the increase in altitude had a significant and generally inhibitory effect on the microbial community diversity in milk ghee, and yak milk at high altitude was abundant in nutrients, which could antagonize the negative impact of increased altitude. Using non-targeted metabolomics, we infer the composition of flavor compounds in ghee: nine kinds of carboxylic acids, 11 kinds of esters, six kinds of ketones, two kinds of alcohols, and four kinds of alkene compounds, among which the key flavor compounds are dl-2-(acetylamino)-3-phenylephrine acid, 1-(4-methoxyphenyl)-2-propanone, sebacic acid, Lysope 18:1, and uracil 1-beta-d-arabinofuranoside. These flavor substances are found in Lactococcus, Lactobacillus, and Streptococcus. With the participation of Lactobacillus, it is synthesized through biosynthesis of alkaloids derived from ornithine, lysine, and nicotine acid and glyoxylate and decarboxylate metabolism, among which Lactococcus plays a key role. In this study, a variety of lactic acid bacteria related to ghee fermentation were screened out, revealing the composition of volatile flavor compounds in Gannan yak milk ghee in the Qinghai–Tibet Plateau and providing a reference for further key volatile flavor compounds and the formation mechanism of flavor compounds.

When a high-energy laser acts on a film surface, plasma flashes of both the air and film can be generated simultaneously. However, when the conventional plasma flash method is used to identify thin film damage, there is a misjudgment problem caused by the inability to distinguish the air and film plasma flashes. In order to solve the problem of misjudgment, the ignition times of air and thin film plasma flashes can be obtained, respectively. If the ignition times of air and thin film plasma flashes are not equal, they can be distinguished from the time difference. In this paper, a nanosecond Nd:YAG pulse laser is used to break down the air at room temperature and pressure, and the theoretical and experimental values of the ignition time of air plasma flash are obtained. The curves of the ignition time of air plasma flash with the laser wavelength, incident energy, focusing spot, and pulse width are simulated. The reasons for the changes are analyzed from the perspectives of multiphoton absorption, cascade ionization theory, and electromagnetic theory of laser breakdown gas. The results show that when the laser pulse width is 10 ns, the energy is 160 mJ, and the spot radius is 0.015 cm. The theoretical and experimental values of the ignition time of air plasma flash are 2.146 and 2 ns, respectively, which are in good agreement. Larger values of laser focus spot size and pulse width relate to a longer ignition time of the air plasma flash, whereas larger values of laser wavelength and incident energy are related to a shorter ignition time. The research reflects the characteristics and electronic transition of air plasma, as well as the micromorphological evolution of the interaction between laser and air, presents the process of air plasma flash generation and growth, and reveals the ignition mechanism of air plasma. It not only provides a basis for improving the traditional plasma flash identification method to identify film damage but also has a certain scientific significance for studying the generation mechanism of laser-supported combustion waves and detonation waves.

We investigated the damage morphology of porous silicon oxide film with a periodic hexagonal hole array irradiated by nanosecond pulsed laser, both experimentally and numerically. To understand the damage morphology, the temperature field distribution and the thermal stress distribution during the laser radiation process were investigated by finite element method. The simulation results show that the thermal stress regulated by periodic structural surface is the reason for the circumferential and discrete distribution of the damage points. The results provide ideas for improving the laser damage resistance of the structural surfaces.

The pathological and physiological process of spinal cord injury is complex, and there is currently no effective treatment method. Magnetic stimulation is an emerging electromagnetic therapy method in recent years, and studies have shown its potential to reduce cell apoptosis. This study used an improved Allen's method to replicate an incomplete spinal cord injury rat model, and repetitive magnetic stimulation (rMS) intervention was performed on the rats for 21 days. The research plan consists of two parts. The first part aims to observe the effects of rMS on motor function and neuronal cell apoptosis in rats. The Basso-Beattie-Bresnahan (BBB) score results indicate that rMS promotes the recovery of motor function in rats; H&E staining showed that rMS improved spinal cord structural damage and inflammatory infiltration; TUNEL and NeuN staining suggest that rMS can reduce cell apoptosis and promote neuronal cell survival. The second part aims to explore the mechanism of action of rMS. Immunofluorescence staining showed that after rMS intervention, the positive counts of PI3K and Akt increased, whereas the positive counts of caspase-3 decreased. Western blot showed that after rMS intervention, the expression of phospho-phosphatidylinositol-3 kinase (p-PI3K)/PI3K, phospho (p)-Akt/Akt, and Bcl-2 increased, whereas the expression of Bcl-2-associated X protein (Bax) and caspase-3 decreased. In summary, rMS can significantly reduce cell apoptosis in the damaged spinal cord and promote neuronal cell survival. Its mechanism of action may be related to promoting the expression of PI3K/Akt pathway proteins, upregulating the antiapoptotic protein Bcl-2, downregulating the proapoptotic protein Bax, and thereby inhibiting the expression of apoptotic protein caspase-3. NEW & NOTEWORTHY: Spinal cord injury is a serious disabling central nervous system disease. Recently, research on magnetic stimulation therapy for spinal cord injury has been increasing, and its potential has gradually attracted the attention of experts. This study found that repetitive magnetic stimulation (rMS) can improve motor function and reduce neuronal apoptosis in spinal cord injury rats. The mechanism may be related to increasing the expression of phosphatidylinositol-3 kinase (PI3K)/Akt protein, thereby inhibiting cell apoptosis and promoting neuronal survival. [ABSTRACT FROM AUTHOR]

In a high-power laser system, when the surface pressure of the optical film caused by laser plasma shock wave is greater than the adhesion per unit area of the film layer, the film will produce mechanical damage, and in serious cases, the whole system may not work. Therefore, studying the formation mechanism of optical film surface pressure and impulse caused by laser plasma shock wave is the key to ensure the normal operation of the high-power laser system. In this article, by studying the relaxation process of laser plasma shock wave on the surface pressure of optical film, and using the time accumulation effect of various pressures on the surface of the optical film, the calculation model of impulse on the optical film’s surface formed by laser plasma shock waves was established, and the variation rules of the impulse Ist{I}_{\text{st}} and impulse coefficient jj on the unit area of single-layer Al2O3 and HfO2 optical films with different parameters were obtained. When the incident laser wavelength λ\lambda was 1,064 nm, the energy EE was 0.1J0.1\hspace{.1em}\text{J}, the pulse width tp{t}_{\text{p}} was 10ns10\hspace{.25em}\text{ns}, the focal length of the focusing lens ff was 350mm350\hspace{.25em}\text{mm}, the distance between the film surface and the focal plane of the focusing lens z0{z}_{0} was 5mm5\hspace{.5em}\text{mm}, and the film radius RR was 5mm5\hspace{.5em}\text{mm}, the calculation and simulation results show that the impulse Ist{I}_{\text{st}} of the two films was 10−4Ns1{0}^{-4}\hspace{.5em}\text{N}\hspace{.5em}\text{s} order of magnitude, the impulse coefficient j of the two films was 10−5Ns/J1{0}^{-5}\hspace{.5em}\text{N}\hspace{.5em}\text{s/J}, the Al2O3 film with small atomic number will obtain larger Ist{I}_{\text{st}} and jj, Ist{I}_{\text{st}} and jj of the two films increase with the increase of EE and ff, and Ist{I}_{\text{st}} and jj of the two films decrease with the increase of z0{z}_{0} and tp{t}_{\text{p}}. In the total impulse transfer time (t0{t}_{0}), Ist{I}_{\text{st}} and jj both increase with the increase of RR.

With the goal of reducing ignition voltage, a new type of carbon-based bridge coating (CBBC) was prepared, and its ignition performance was investigated. The size of the bridge area with the lowest ignition voltage was determined, and a secondary ignition phenomenon that occurred during the experiment was analyzed. Self-made conductive carbon paste was printed on the Al _2 O _3 substrate by a screen printing process, and the ignition bridge was shaped using laser etching technology. Both ends of the CBBC were coated with conductive silver paste and lead on their electrodes. A stabilized DC power supply was used for the ignition experiment. The ignition performance of the CBBCs under different bridge sizes was measured, and scanning electron microscopy (SEM) characterization and analysis were performed on the surface of the ignition bridge area before and after the experiment. The CBBCs with a bridge area size of 300 × 300 μ m could be ignited at or under 24 V, and only part of the CBBCs could be triggered when the bridge area size was 500 × 500 μ m. Further, the ignition voltage may have been influenced by the poor uniformity of the coating thickness. Overall, the results demonstrate the following: (1) The CBBCs prepared in this experiment could be fully ignited at a voltage of 24 V, (2) a bridge size of 300 × 300 μ m could ensure stable ignition with low voltage, and (3) the tip discharge caused by the first fuse of the CBBCs was the root cause of the secondary ignition.

The effect of different superimposed structures on the transparent electromagnetic interference (EMI) shielding performance of graphene is reported. The average optical transmittance of a graphene/quartz sample with different superimposed structures in the Vis-near-infrared spectrum (400–2400 nm) is almost the same (84%). The EMI shielding efficiency (EMI SE) of the two samples after superposition is 4.85–3.96 dB, which has been greatly improved compared to the single sample. The EMI SE of the backward superposition is 0.5–0.2 dB larger than the interval superposition. The EMI SE of the interval superposition is 0.8–0.2 dB larger than the forward superposition. The backward superposition of graphene can absorb 55% of the electromagnetic waves, reflect 10%, and only 35% of the electromagnetic waves pass. We envision that graphene can obtain high EMI SE through different superimposed structures in the theoretical research and applications. [ABSTRACT FROM AUTHOR]

The accuracy of judging whether the film is damaged directly affects the accuracy of the measurement of the film laser damage threshold. When judging the film damage by the traditional plasma flash method, there is a problem of misjudgment caused by the failure to distinguish the film and air plasma flash. In order to eliminate misjudgment, the two flashes are accurately distinguished by the difference in the duration of the air and film plasma flash. This paper aims to obtain the theoretical and experimental values of the duration of the film plasma flash ( t f ) and analyze the factors affecting it. Firstly, taking single-layer hafnium oxide and aluminum oxide thin films as examples, when the wavelength of the incident laser is 1064 nm, the diameter of the laser focusing spot is 0.08 cm, the energy of the incident laser is 100 mJ, and the pulse width of incident laser is 10 ns, the t f of hafnium oxide, and aluminum oxide thin films are 542.7 and 299.6 ns, respectively. Secondly, the experimental study of t f was carried out. Through six experiments, the following results were obtained: (1) With the increase in incident laser energy, the t f of both films increases; (2) The t f of the hafnium oxide film is longer than that of the aluminum oxide film. (3) The experimental parameters are put into the calculation model, and the theoretical results are in good agreement with the experimental t f values. Finally, it is found that t f increases with the increase in incident laser energy and incident laser pulse width, and decreases with the increase in focusing spot diameter. [ABSTRACT FROM AUTHOR]