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Understanding the behavior of matter at extreme pressures of the order of a megabar (Mbar) is essential to gain insight into various physical phenomena at macroscales—the formation of planets, young stars, and the cores of super-Earths, and at microscales—damage to ceramic materials and high-pressure plastic transformation and phase transitions in solids. Under dynamic compression of solids up to Mbar pressures, even a solid with high strength exhibits plastic properties, causing the induced shock wave to split in two: an elastic precursor and a plastic shock wave. This phenomenon is described by theoretical models based on indirect measurements of material response. The advent of x-ray free-electron lasers (XFELs) has made it possible to use their ultrashort pulses for direct observations of the propagation of shock waves in solid materials by the method of phase-contrast radiography. However, there is still a lack of comprehensive data for verification of theoretical models of different solids. Here, we present the results of an experiment in which the evolution of the coupled elastic–plastic wave structure in diamond was directly observed and studied with submicrometer spatial resolution, using the unique capabilities of the x-ray free-electron laser (XFEL). The direct measurements allowed, for the first time, the fitting and validation of the 2D failure model for diamond in the range of several Mbar. Our experimental approach opens new possibilities for the direct verification and construction of equations of state of matter in the ultra-high-stress range, which are relevant to solving a variety of problems in high-energy-density physics.

Abstract Laser-induced periodic surface structure (LIPSS), which has a period smaller than the laser wavelength, is expected to become a potential technique for fine surface processing. We report the microscopic and macroscopic observations of the crystallinity of LIPSSs, where the characteristics such as defects generation and residual strain were analyzed, respectively. The LIPSSs were formed on a Si substrate using two different femtosecond pulses from Ti:Sapphire laser with near-infrared wavelength (0.8 μm) and free-electron laser (FEL) with mid-infrared wavelength (11.4 μm). The photon energies of the former and latter lasers used here are higher and lower than the Si bandgap energies, respectively. These LIPSSs exhibit different crystalline states, where LIPSS induced by Ti:Sapphire laser show residual strain while having a stable crystallinity; in contrast, FEL-LIPSS generates defects without residual strain. This multiple analysis (microscopic and macroscopic observations) provides such previously-unknown structural characteristics with high spatial resolution. To obtain LIPSS with suitable properties and characteristics based on each application it is paramount to identify the laser sources that can achieve such properties. Therefore, identifying the structural information of the LIPSS generated by each specific laser is of great importance.

Brain computer interfaces based on steady-state visually evoked potential (SSVEP-BCI) have been developed substantially in recent years, but these are not available to patients with severe paralysis or eye-impairment who lost the control ability of eye-movement. This paper proposes an eye-movement-independent SSVEP-BCI available in the eyes-closed state based on the modulation of SSVEP elicited by performing a mental task. Although performance of the proposed BCI depended on subjects, electrode locations, mental tasks employed, and flickering frequencies, the mean precision and recall, which were obtained from the confusion matrix, reached 72% to 95% using the support vector machine classifier across 18 normal subjects under the stimulus frequency of 10Hz or 14Hz. Results from simulated information transfer rate and its inter-individual difference suggest that it is adequate to set an inter-trial interval at 2s to 3s for better performance of the proposed BCI. It is consequently feasible to develop a practical eye-movement-control-independent BCI by optimizing the parameters such as the stimulation frequency and electrode sites each user.

Background/purpose: The onset and progression of periodontitis involve bacterial infection and the immune response. T cells function in the immune response and reportedly induce bone resorption in inflammatory bone loss. However, the exact role of T cells in periodontal destruction remains unclear. Using our experimental model of periodontitis, we aimed to investigate the influence of T cells on periodontal destruction. Materials and methods: Male athymic nude (Nu) and euthymic wild-type (WT) rats were divided into the immunized (I-Nu and I-WT), non-immunized (nI-Nu and nI-WT). The immunized groups were immunized intraperitoneally with lipopolysaccharide (LPS). The non-immunized groups received phosphate-buffered saline (PBS). Nothing was administered to the non-treated groups. LPS was applied to the right palatal gingival sulcus in the immunized and non-immunized groups daily for 20 days. Loss of attachment, numbers of inflammatory cells and osteoclasts, and levels of alveolar bone were investigated histopathologically and histometrically. Osteoclasts were stained with tartrate-resistant acid phosphatase. The numbers of IL-4-positive cells were evaluated immunohistologically. Results: Loss of attachment, numbers of inflammatory cells, levels of alveolar bone, and the number of osteoclasts were significantly increased in the nI-WT group compared with the nI-Nu group. However, the parameters were significantly increased in the I-Nu group compared with the I-WT group. The number of IL-4-positive cells was greater in the I-WT group than in the I-Nu group. Conclusion: T cells promote inflammation in non-immunized animals; however, they regulate these processes in immunized animals.