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Stress and Microstructure Study of W/Si X-ray Multilayers with Different Structural Parameters
摘要： X-ray Timing and Polarimetry (XTP) telescope is proposed by using nested focusing optics with a large effective area for studies in the field of high energy physics (energy region of 1–30 keV). High-reflectance and low-stress W/Si multilayers are required for this telescope to improve the spectral response and maintain the figure quality of the mirrors simultaneously. In this paper, we focused on the study of stress and layer structure of W/Si periodic multilayers at different d-spacings (thickness of period), thickness ratios, and bilayer numbers. The results show that the stress of the multilayer increased from ?73.3 to ?465.5 MPa with increase in the d-spacing from 2.7 to 5.5 nm, while the change in the average interface width was negligible, from 0.31 to 0.36 nm. For the multilayers prepared with different thickness ratios of W, from 0.3 to 0.67 (d = 3.7 nm), the lowest stress appeared at the ratio of ～0.46, and the average interface width was unchanged. The number of bilayers (N = 80–160) had negligible effects on both the layer structure and the stress, and the multilayers exhibited a very smooth surface morphology with a root-mean-square roughness of 0.19 nm. To further study the microstructural changes of the multilayer, X-ray diffraction measurements of the samples with different d-spacings and thickness ratios were performed. An increased crystallization along with phase changes were observed in the samples prepared with thicker W layers, which can increase the compressive stress of the multilayer.
关键词： W/Si Multilayer,Stress,X-ray,Crystallization,Interface Width
更新于2025-09-23 15:22:29
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Joining of AlN and Al with Compositional Graded Layer by Centrifugal Mixed-Powder Method
摘要： In this study, joining of AlN and Al with compositional graded layer is made by centrifugal mixed-powder method (CMPM). The mixed-powder of AlN particles and Al particles is inserted into a spinning mold with bulk-shaped AlN, and then molten Al is poured into the spinning mold with the mixed-powder and bulk-shaped AlN. As a result, the molten Al penetrates into the space between the mixed-powder by the centrifugal force, and at the same time, the Al particles can be melted by heat from the molten Al. Then AlN and Al can be joined with compositional graded layer after solidification. Micromechanics-based analysis is also employed to understand the thermal stress relaxation by the compositional graded layer.
关键词： Joining,Ceramics/metal joining,Thermal stress relaxation,Functionally graded materials (FGMs),Micro-mechanics,Centrifugal mixed-powder method (CMPM)
更新于2025-09-23 15:22:29
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Novel SPECT Technologies and Approaches in Cardiac Imaging
摘要： Recent novel approaches in myocardial perfusion single photon emission CT (SPECT) have been facilitated by new dedicated high-efficiency hardware with solid-state detectors and optimized collimators. New protocols include very low-dose (1 mSv) stress-only, two-position imaging to mitigate attenuation artifacts, and simultaneous dual-isotope imaging. Attenuation correction can be performed by specialized low-dose systems or by previously obtained CT coronary calcium scans. Hybrid protocols using CT angiography have been proposed. Image quality improvements have been demonstrated by novel reconstructions and motion correction. Fast SPECT acquisition facilitates dynamic flow and early function measurements. Image processing algorithms have become automated with virtually unsupervised extraction of quantitative imaging variables. This automation facilitates integration with clinical variables derived by machine learning to predict patient outcome or diagnosis. In this review, we describe new imaging protocols made possible by the new hardware developments. We also discuss several novel software approaches for the quantification and interpretation of myocardial perfusion SPECT scans.
关键词： fast myocardial perfusion single photon emission computed tomography,quantification,single photon emission computed tomography,low dose,myocardial perfusion imaging,stress only
更新于2025-09-23 15:22:29
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Differences between Motile and Nonmotile Cells of Haematococcus pluvialis in the Production of Astaxanthin at Different Light Intensities
摘要： Haematococcus pluvialis, as the best natural resource of astaxanthin, is widely used in nutraceuticals, aquaculture, and cosmetic industries. The purpose of this work was to compare the differences in astaxanthin accumulation between motile and nonmotile cells of H. pluvialis and to determine the relationship between the two cells and astaxanthin production. The experiment design was achieved by two different types of H. pluvialis cell and three different light intensities for an eight day induction period. The astaxanthin concentrations in nonmotile cell cultures were significantly increased compared to motile cell cultures. The increase of astaxanthin was closely associated with the enlargement of cell size, and the nonmotile cells were more conducive to the formation of large astaxanthin-rich cysts than motile cells. The cyst enlargement and astaxanthin accumulation of H. pluvialis were both affected by light intensity, and a general trend was that the higher the light intensity, the larger the cysts formed, and the larger the quantity of astaxanthin accumulated. In addition, the relatively low cell mortality rate in the nonmotile cell cultures indicated that the nonmotile cells have a stronger tolerance to photooxidative stress. We suggest that applying nonmotile cells as the major cell type of H. pluvialis to the induction period may help to enhance the content of astaxanthin and the stability of astaxanthin production.
关键词： photooxidative stress,light intensity,astaxanthin,Haematococcus pluvialis
更新于2025-09-23 15:22:29
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On the Test Method for Determining Residual Stress on the Surface of Tempered Glass
摘要： The residual stress on the surface of tempered glass is very important for its safe service and the quality control. In this study, the sphere indentation and grazing angle surface polarimetry are compared to evaluate the surface residual stress of tempered glass. The test results showed that the measured results are similar, but the data dispersion of the sphere indentation method is little larger. The main reason is stemmed from the different tested area, of which residual stress is a mean value measured by the grazing angle polarization method. Yet for the indentation method, the residual stress in the micro region of glass is more susceptible to the inhomogeneity of material itself. However, it is difficult to select the right multiple optical path difference for the grazing angle polarization method, and it is only applicable when inspecting the tin surface of tempered glass, as well as the tin surface examination instrument. Thus, as a nondestructive testing method, indentation method can be widely used to measure the surface residual stress of glass without being influenced by other factors.
关键词： Indentation method,Surface residual stress,Grazing angle surface polarimetry,Tempered glass
更新于2025-09-23 15:22:29
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Taurine protects against NMDA-induced retinal damage by reducing retinal oxidative stress
摘要： This study aimed to evaluate effect of TAU on NMDA-induced changes in retinal redox status, retinal cell apoptosis and retinal morphology in Sprague–Dawley rats. Taurine was injected intravitreally as pre-, co- or post-treatment with NMDA and 7 days post-treatment retinae were processed for estimation of oxidative stress, retinal morphology using H&E staining and retinal cell apoptosis using TUNEL staining. Treatment with TAU, particularly pre-treatment, significantly increased retinal glutathione, superoxide dismutase and catalase levels compared to NMDA-treated rats; whereas, the levels of malondialdehyde reduced significantly. Reduction in retinal oxidative stress in TAU pre-treated group was associated with significantly greater fractional thickness of ganglion cell layer within inner retina and retinal cell density in inner retina. TUNEL staining showed significantly reduced apoptotic cell count in TAU pre-treated group compared to NMDA group. It could be concluded that TAU protects against NMDA-induced retinal injury in rats by reducing retinal oxidative stress.
关键词： Retina,Oxidative stress,Taurine,NMDA
更新于2025-09-23 15:22:29
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Effect of Hot Electron Stress on AlGaN/GaN HEMTs of Hydrogen Poisoning
摘要： We have investigated the effect of hot electron stress on the electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) of hydrogen poisoning. The AlGaN/GaN HEMTs were biased at the semi-on state, and they suffered from the hot electron stress. The devices of hydrogen poisoning were degraded, while there is almost no degradation for the fresh ones. The hot electron stress leads to the significantly positive shift of threshold voltage and the notable decrease of drain-to-source current for the AlGaN/GaN HEMTs of hydrogen poisoning. For the AlGaN/GaN HEMTs of hydrogen poisoning, the trap density increases by about one order of magnitude after the hot electron stress experiment. The physical mechanism can be attributed to electrically active traps due to the dehydrogenation of passivated point defects at AlGaN surface, AlGaN barrier layer, and heterostructure interface. The results of this study may be useful in the design and application of AlGaN/GaN HEMTs.
关键词： Hydrogen Poisoning,Hot Electron Stress,GaN HEMT
更新于2025-09-23 15:21:21
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Generation and distribution of residual stress during nano-grinding of monocrystalline silicon
摘要： Residual stress generated in grinding process of monocrystalline silicon can cause the wafer warpage, and di?culties in subsequent processes such as holding and scribing. It can also lead to the formation of cracks and the occurrence of corrosion, which is harmful for electrical performance of silicon component. In this study, with the method of step-wire wet etching, the phase transformation and distribution of residual stress in ground silicon wafer were examined by confocal laser micro-Raman spectroscopy. As the etching depth going down, the residual stress exhibits in the trends of decreasing of compressive stress and following a scatter distribution of tensile stress. During the nano-grinding processes of monocrystalline silicon, the generation mechanism of residual stress is computed by a series of the molecular dynamic (MD) simulation. Subsurface damage (SSD) in the form of phase-transformed silicon is observed, and the depth of SSD varies by the depth of cut. The volume shrinkage of phase-transformed silicon is also studied to explain the grinding mechanism and the reason for inducing residual stress of ground silicon. By adopted the Stony theory and volume shrinkage rate of amorphous phase from MD results, a theoretical model is established to determine the trend of compressive stress in subsurface of ground silicon.
关键词： monocrystalline silicon,residual stress,nano-grinding,phase transformation,molecular dynamics
更新于2025-09-23 15:21:21
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Solitons in discrete linear chains of chiral smectic liquid crystals with competing interactions
摘要： Chiral liquid crystals exhibit in-plane spontaneous polarizations, however, in their smectic (Sm) phase the primary-order parameter is the tilt vector associated with molecular rotations around the long axis parallel to the molecular directors. These molecular rotations can lead to several distinct phases among which an incommensurate order with a domain-wall texture is referred to as soliton. In this study, the formation of domain walls in smectic chiral (SmC) liquid crystals is analyzed, with emphasis on the competition between an Ising-like symmetric intermolecular interaction, an anti-symmetric intermolecular interaction due to molecular chirality and an applied in-plane electric field. It is found that the anti-symmetric intermolecular interaction increases the width of kink structures in the domain wall at moderate intensity of the y-component of the applied in-plane electric field. Increasing the x-component of the electric field creates unstable condition for soliton formation irrespective of magnitudes of the symmetric and chiral intermolecular interactions. The stability condition for single-kink structures in the discrete molecular chain is discussed, by estimating the Peierls stress experienced by the single-kink soliton. Results suggest that chirality lowers the Peierls–Nabarro barrier, hence increasing the lifetime of single-kink structures in the discrete medium.
关键词： Peierls stress,soliton lattice,Smectic chiral liquid crystals,orientational order,electroclinic effect
更新于2025-09-23 15:21:21
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Influence of Passivation Layers on Positive Gate Bias-Stress Stability of Amorphous InGaZnO Thin-Film Transistors
摘要： Passivation (PV) layers could effectively improve the positive gate bias-stress (PGBS) stability of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), whereas the related physical mechanism remains unclear. In this study, SiO2 or Al2O3 films with different thicknesses were used to passivate the a-IGZO TFTs, making the devices more stable during PGBS tests. With the increase in PV layer thickness, the PGBS stability of a-IGZO TFTs improved due to the stronger barrier effect of the PV layers. When the PV layer thickness was larger than the characteristic length, nearly no threshold voltage shift occurred, indicating that the ambient atmosphere effect rather than the charge trapping dominated the PGBS instability of a-IGZO TFTs in this study. The SiO2 PV layers showed a better improvement effect than the Al2O3 because the former had a smaller characteristic length (~5 nm) than that of the Al2O3 PV layers (~10 nm).
关键词： thin-film transistor (TFT),positive gate bias stress (PGBS),passivation layer,characteristic length,amorphous InGaZnO (a-IGZO)
更新于2025-09-23 15:21:21