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Abstract The lack of an MMC reliability evaluation approach that incorporates data on essential components' health monitoring in the already related research prevents reliability from being further improved. Therefore, this article proposes a real‐time reliability evaluation method of the multi‐state IGBT module in MMC through iterative calculation of the Markov chain model. The degradation process of the IGBT module is divided into multiple states based on the monitored bond wire failure, and the failure rate of the IGBT module is updated in real time using the accumulated monitoring data of junction temperature. The proposed method can more accurately reflect the real state of MMC compared with the binary state evaluation method. Besides, a multi‐channel high‐speed data acquisition board is designed to measuring the gate voltage and collector voltage of the IGBT for the health evaluation of IGBT modules in MMC; the typically measured results validate the effectiveness of the data acquisition board.

Abstract Meningeal lymphatic vessels (mLVs) play a pivotal role in regulating metabolic waste from cerebrospinal fluid (CSF). However, the current limitations in field of view and resolution of existing imaging techniques impede understanding the stereoscopic morphology and dynamic behavior of mLVs in vivo. Here, we utilized dual-contrast functional photoacoustic microscopy to achieve wide-field intravital imaging of the lymphatic system, including mLVs and glymphatic pathways. The stereoscopic photoacoustic microscopy based on opto-acoustic confocal features has a depth imaging capability of 3.75 mm, facilitating differentiation between mLVs on the meninges and glymphatic pathways within the brain parenchyma. Subsequently, using this imaging technique, we were able to visualize the dynamic drainage of mLVs and identify a peak drainage period occurring around 20–40 min after injection, along with determining the flow direction from CSF to lymph nodes. Inspiringly, in the Alzheimer’s disease (AD) mouse model, we observed that AD mice exhibit a ~ 70% reduction in drainage volume of mLVs compared to wild-type mice. With the development of AD, there is be continued decline in mLVs drainage volume. This finding clearly demonstrates that the AD mouse model has impaired CSF drainage. Our study opens up a horizon for understanding the brain’s drainage mechanism and dissecting mLVs-associated neurological disorders.

Abstract Capacitance and Insulated gate bipolar transistor (IGBT) junction temperature are two critical healthy parameters for modular multilevel converters (MMC) sub‐modules (SMs) condition monitoring. This paper proposes an integrated monitoring method for capacitance degradation and IGBT junction temperature variation. By measuring multiple characteristics of the same port voltage, the capacitance and the junction temperature can be obtained simultaneously, which greatly simplifies the measurement unit required for condition evaluation and realizes the submodule‐level condition monitoring at a lower cost. The capacitance is characterized by voltage changes during capacitor discharging and the junction temperature is monitored by capacitor voltage overshoot (peak value) during IGBT turn‐off. Theoretical analysis and experimental results verify the effectiveness of the proposed method and articulated the influence of load current, SM capacitor pre‐discharge voltage, and junction temperature. Moreover, an online data‐acquisition circuit for time‐specific capacitor voltage characterization is devised.

This study describes a method for real-time examination of the microvascular system based on the three-dimensional photoacoustic imaging system to prevent arterial complications, especially vascular embolism, during hyaluronic acid (HA) injections. Chicken embryos were used to simulate the superficial blood vessels of human skin, and then the target area was imaged by the photoacoustic imaging system for three-dimensional vascular imaging, and then the syringe and blood vessels were monitored, and the syringe angle and penetration depth were adjusted in time using an injection device to avoid puncturing the arterial vasculature and clogging the blood vessels. HA was then injected into smaller vessels on the dorsum of the tongue in mice and into thicker vessels on the dorsal portion of the tongue in rats to mimic embolization, and the post-operative recovery was reflected by the changes in the pixel dots of the extracted part of the blocked blood vessels, and it was observed that the blood flow in the area of the fine vessels was restored in about 3 days, whereas blood flow in the area of the large vessels was restored in only about 1 h. The method presented in this paper allows precise guidance of injectable filler HA, which has good application prospects in improving the safety of injection micro-plastic surgery and reducing the experience requirements for medical personnel.

Qinghai is located in a permafrost region, which belongs to the continental climate zone of the the Qinghai-Tibet Plateau. At the same time, freezing-thawing cycles are common destructive factors for roadbeds and foundations. In order to examine the effects of freezing-thawing cycles on actual projects in Qinghai and reveal the mechanisms of freezing-thawing cycles on damage of the projects, the freezing-thawing cycle test, unconfined compressive strength test and electron microscope scanning test of the undisturbed loess and remolded loess in the Xining area of Qinghai are conducted to analyze the influence of different freezing-thawing temperatures and different freezing-thawing cycles on the strength and microstructure of the undisturbed loess and remolded loess. The results show that when the loess undergoes 0-6 freezing-thawing cycles, the strength of the undisturbed loess and remolded loess gradually decreases. After 8-10 freezing-thawing cycles, the unconfined compressive strength of the loess first increases and then tends to be basically stable. The strength of the undisturbed loess decreases with the decrease of the freezing and thawing temperature. However, the strength of the remolded loess first increases and then decreases with the decrease of temperature. From a microscopic point of view, the decrease in freezing-thawing temperature and the increase in the number of freezing-thawing cycles both lead to the decomposition of large loess particles into small particles, and the arrangement of the particles has changed. The results are of reference value for actual project construction and construction in the Xining area of Qinghai.

Imaging plays a vital role in the diagnosis and treatment of skin diseases. However, pure optical imaging technique is limited to the visualization of superficial skin tissues. Ultrasonic imaging technique can detect deep tissues, but it lacks detailed information on microscopic pathological structures. Photoacoustic imaging is an advanced technology that bridges the spatial-resolution gap between optical and ultrasonic techniques, by the modes of optical excitation and acoustic detection. Photoacoustic dermoscopy (PAD), based on photoacoustic technology, can noninvasively obtain high-resolution anatomical structures by endogenous absorbers, such as melanin, hemoglobin, lipids, etc. In the past years, PAD has gradually been developed in clinical dermatology for the diagnosis of melanoma, psoriasis, port-wine stains, dermatitis, skin grafting, and testing the efficacy of cosmetics. This protocol provides detailed procedures for PAD construction, including component selection, equipment setup, and system calibration. A step-by-step guide for human skin imaging is provided as an example application. Image reconstruction and troubleshooting procedures are also elaborated. PAD offers the 3D volumetric images of human skin, and quantitatively analyzes the vascular morphology in the dermis. The protocol will provide clinicians with standardized and reasonable guidance in dermatological imaging.

Abstract A micro-electromechanical system (MEMS) scanning mirror accelerates the raster scanning of optical-resolution photoacoustic microscopy (OR-PAM). However, the nonlinear tilt angular-voltage characteristic of a MEMS mirror introduces distortion into the maximum back-projection image. Moreover, the size of the airy disk, ultrasonic sensor properties, and thermal effects decrease the resolution. Thus, in this study, we proposed a spatial weight matrix (SWM) with a dimensionality reduction for image reconstruction. The three-layer SWM contains the invariable information of the system, which includes a spatial dependent distortion correction and 3D deconvolution. We employed an ordinal-valued Markov random field and the Harris Stephen algorithm, as well as a modified delay-and-sum method during a time reversal. The results from the experiments and a quantitative analysis demonstrate that images can be effectively reconstructed using an SWM; this is also true for severely distorted images. The index of the mutual information between the reference images and registered images was 70.33 times higher than the initial index, on average. Moreover, the peak signal-to-noise ratio was increased by 17.08% after 3D deconvolution. This accomplishment offers a practical approach to image reconstruction and a promising method to achieve a real-time distortion correction for MEMS-based OR-PAM.

Loess, a collapsible soil, is widely distributed in the Qinghai–Tibet Plateau in China. In the meantime, loess is a sustainable and green building material that is widely used in traditional residential buildings. However, previous studies have focused on the properties of loess itself, ignoring the influence of climatic conditions on loess buildings, as well as a series of engineering problems such as soil spalling caused by freezing and thawing, cold cracks in walls, and settlement deformation of foundation. This research presents a series of laboratory tests on both undisturbed and remolded loess. The tests investigated changes in the unconfined compressive strength (UCS) of both types of loess after different freeze–thaw cycles. The freeze–thaw-induced changes to the internal structures of the loess were also investigated using a scanning electron microscope (SEM) and X-ray diffraction test (XRD). The test results showed that: (1) with increasing freeze–thaw cycles, the UCS of both the undisturbed and remolded loess appeared to first increase and then decrease, and the stress–strain curves showed a stronger strain-softening tendency. (2) The compressive strength of undisturbed loess is higher than remolded loess. (3) SEM analysis showed that the large particles inside the loess sample were gradually broken down into small particles, which led to an accumulative increase in fine particles and a decrease in the porosity. With the increase in the number of freeze–thaw cycles, the particles inside the soil become denser, and the strength increases. (4) Freezing and thawing have less effect on loess minerals. (5) The conclusion can provide a reference value for the protection of loess buildings in Qinghai and the management of freeze–thaw disasters.

In damage mechanics, the deep excavation of soil is a process of damage development, and soil failure can be considered a process of continuously transforming undisturbed soil to damaged soil. Therefore, this study considered the occurrence of soil damage during the pit excavation, established a soil damage model, damage evolution equation, and soil damage constitutive relationship, and then deduced a calculate model of the pile displacement under the consideration of soil damage. Based on the principle of the stratum loss method, the surface settlement around a deep excavated pit was assumed as a skewed distribution curve, and the surface settlement of the pile-anchor supporting pit was solved. Based on this established method, finite element analysis software was used to calculate the surface subsidence for a field case, and the numerical results were compared with monitoring data in the field. The results revealed that, to a certain extent, soil damage affected the distribution of surface settlement in excavated pits. With the development of soil damage, the mechanical properties of soil gradually decreased, which led to increased surface settlement and changes in the direction of the excavation pit. Because soil damage is an important factor causing surface settlement, it is meaningful to consider soil damage when calculating the surface settlement in the deep excavation of pits.

An amendment to this paper has been published and can be accessed via the original article.

Multiscale visualization of human anatomical structures is revolutionizing clinical diagnosis and treatment. As one of the most promising clinical diagnostic techniques, photoacoustic imaging (PAI), or optoacoustic imaging, bridges the spatial-resolution gap between pure optical and ultrasonic imaging techniques, by the modes of optical illumination and acoustic detection. PAI can non-invasively capture multiple optical contrasts from the endogenous agents such as oxygenated/deoxygenated hemoglobin, lipid and melanin or a variety of exogenous specific biomarkers to reveal anatomy, function, and molecular for biological tissues in vivo, showing significant potential in clinical diagnostics. In 2001, the worldwide first clinical prototype of the photoacoustic system was used to screen breast cancer in vivo, which opened the prelude to photoacoustic clinical diagnostics. Over the past two decades, PAI has achieved monumental discoveries and applications in human imaging. Progress towards preclinical/clinical applications includes breast, skin, lymphatics, bowel, thyroid, ovarian, prostate, and brain imaging, etc., and there is no doubt that PAI is opening new avenues to realize early diagnosis and precise treatment of human diseases. In this review, the breakthrough researches and key applications of photoacoustic human imaging in vivo are emphatically summarized, which demonstrates the technical superiorities and emerging applications of photoacoustic human imaging in clinical diagnostics, providing clinical translational orientations for the photoacoustic community and clinicians. The perspectives on potential improvements of photoacoustic human imaging are finally highlighted. [ABSTRACT FROM AUTHOR]

Significance: The classification of melasma is critical for correct clinical diagnosis, treatment selection, and postoperative measures. However, preoperative quantitative determination of melasma type remains challenging using conventional Wood's lamp and optical dermoscopy techniques. Aim: Using photoacoustic microscopy (PAM) to simultaneously obtain the two diagnostic indicators of melanin and blood vessels for melasma classification and perform quantitative analysis to finally achieve accurate classification, rather than relying solely on physicians' experience. Approach: First, the patients were classified by experienced dermatologists with Wood's lamp and optical dermoscopy. Next, the patients were examined in vivo using the PAM imaging system. Further, the horizontal section images (X-Y plane) of epidermal melanin and dermal vascular involvement were extracted from the 3D photoacoustic imaging results, which are important basis for PAM to quantitatively classify melasma. Results: PAM can quantitatively reveal epidermal thickness and dermal vascular morphology in each case and obtain the quantitative diagnostic indicators of melanin and blood vessels. The mean vascular diameter in lesional skin (223.2 µm) of epidermal M+V-type was much larger than that in non-lesional skin (131.6 µm), and the mean vascular density in lesional skin was more than three times that in non-lesional skin. Importantly, vascular diameter and density are important parameters for distinguishing M type from M+V type. Conclusions: PAM can obtain the data of epidermal thickness, pigment depth, subcutaneous vascular diameter, and vascular density, and realize the dual standard quantitative melasma classification by combining the parameters of melanin and blood vessels. In addition, PAM can provide new diagnostic information for uncertain melasma types and further refine the typing. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) modules are widely used as power switching devices. In actual working conditions, the failure of bonding wires is one of the most important failure modes. At present, the influence of bonding wire failure is not considered in the reliability evaluation of the device, resulting in a large error in the life prediction result. Therefore, this paper proposes a life evaluation method for IGBT modules that takes into account the failure of the bonding wire. The transient thermal impedance of 1200 V/50 A IGBT module under the failure conditions of different numbers of bonding wires is calculated by constructing a finite element simulation model of device electro‐thermal coupling. Both simulation and experimental results show that with the increase of the number of bonding wire failures, the transient thermal impedance curve of the device rises and the steady‐state thermal impedance increases. The Foster thermal network models of the devices are updated, and the number of power cycles of the device with bonding wire failure under DC and sinusoidal pulse width modulation (SPWM) conditions is calculated. When the number of bonding wire failures and fatigue accumulation have a linear relationship, the life will be reduced by 48.29% compared to the healthy state. [ABSTRACT FROM AUTHOR]

The influence of pH of the gelatin solution on the cycle performance of the sulfur cathode for lithium-sulfur batteries was studied. Scanning electron microscopy measurements revealed that the cathode prepared with pH 10.0 gelatin solution as a binder showed a uniform distribution. The charge/discharge experiments of the lithium-sulfur batteries showed that an initial capacity of 1137 mAh g-1 and a reversible capacity of 642 mAh g-1 after 30 cycles were achieved, which were higher than those of the cathodes prepared at pH 5.0 and 8.0. To understand the effect of the pH value of the gelatin solution on the cycle performance of sulfur cathodes, electrochemical impedance spectroscopy and X-ray diffractometry were carried out. [ABSTRACT FROM AUTHOR]