The monoamine hypothesis has been accepted as the most common hypothesis of major depressive disorder (MDD) for a long period because of its simplicity and understandability. Actually, most currently ...used antidepressants have been considered to act based on the monoamine hypothesis. However, an important problem of the monoamine hypothesis has been pointed out as follows: it fails to explain the latency of response to antidepressants. In addition, many patients with MDD have remained refractory to currently used antidepressants. Therefore, monoamine‐alternate hypotheses are required to explain the latency of response to antidepressants. Such hypotheses have been expected to contribute to identifying hopeful new therapeutic targets for MDD. Past studies have revealed that the volume of the hippocampus is decreased in patients with MDD, which is likely caused by the failure of the hypothalamic–pituitary–adrenal axis and following elevation of glucocorticoids. Two hypotheses have been proposed to explain the volume of the hippocampus: (i) the neuroplasticity hypothesis; and (ii) the neurogenesis hypothesis. The neuroplasticity hypothesis explains how the hippocampal volume is decreased by the morphological changes of hippocampal neurons, such as the shortening length of dendrites and the decreased number and density of spines. The neurogenesis hypothesis explains how the hippocampal volume is decreased by the decrease of neurogenesis in the hippocampal dentate gyrus. These hypotheses are able to explain the latency of response to antidepressants. In this review, we first overview how the neuroplasticity and neurogenesis hypotheses have been developed. We then describe the details of these hypotheses.
Aluminium alloys are re-evaluated as most feasible way to satisfy the industrial needs of light-weight structural materials. However, unlike conventional structural metals such as iron and titanium, ...aluminium does not have easily accessible secondary phases, which means that aluminium-based alloys cannot be strengthened by harnessing multiple phases. This leaves age hardening as the only feasible strengthening approach. Highly concentrated precipitates generated by age hardening generally play a dominant role in shaping the mechanical properties of aluminium alloys. In such precipitates, it is commonly believed that the coherent interface between the matrix and precipitate does not contribute to crack initiation and embrittlement. Here, we show that this is not the case. We report an unexpected spontaneous fracture process associated with hydrogen embrittlement. The origin of this quasi-cleavage fracture involves hydrogen partitioning, which we comprehensively investigate through experiment, theory and first-principles calculations. Despite completely coherent interface, we show that the aluminium-precipitate interface is a more preferable trap site than void, dislocation and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy, while hydrogen atoms are stably trapped up to an extremely high occupancy over the possible trap site. Our insights indicate that controlling the hydrogen distribution plays a key role to design further high-strength and high-toughness aluminium alloys.
Abstract Excellent strength–ductility balance in metastable Fe–Cr–Ni austenitic alloys stems from phase transformation from austenite (fcc structure) to α ʹ martensite (bcc structure) during ...deformation, namely deformation-induced α ʹ martensitic transformation (DIMT). Here, DIMT in a metastable Fe–17Cr–7Ni austenitic alloy was detected in situ and characterized in three dimensions (3D) by employing synchrotron radiation X-ray microtomography. This technique utilizes refraction contrast, which is attributable to the presence of phase boundaries between the parent austenite and the newly formed α ʹ martensite phase. By combining microtomography and position-sensitive X-ray diffraction, we succeeded in crystallographically identifying multiple α ʹ martensite phases continuously transformed in four groups from a single parent austenitic phase.
X-ray tomography is employed to observe the effects of intermetallic compound particles on the nucleation and growth of hydrogen micropores at high temperatures in Al-Zn-Mg-Cu aluminum alloys. ...Hydrogen micropores are heterogeneously nucleated on particles during exposure at 748K. Growth and coalescence of the hydrogen micropores are observed with increasing exposure time. Interactions between hydrogen micropores and particles have a significant influence on the growth and coalescence of hydrogen micro pores. The growth speed of hydrogen micropores, nucleated on spherical, small particles is faster than those on other nucleation sites.
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The nucleation, growth, and coalescence of microvoids are examined in high Zn and Mn content 7XXX aluminum alloys using high-resolution synchrotron X-ray microtomography. The results have clearly ...shown that the addition of Mn content (0.6% mass) increases the ultimate tensile strength with limited ductility. The loading step in which each microvoid was nucleated together with its nucleation site is determined by tracking the microvoids in reverse chronological order from the final loading step towards the initial stress-free loading step. It was observed that microvoids were initiated due to particle cracking, and void nucleation occurs continuously with the applied strain. Furthermore, it was also observed that the particle underwent multiple fractures. It was concluded the ductile fracture was dominated by the nucleation and growth of microvoids due to particle fracture.
•The damage micromechanisms of high Mn and Zn content 7XXX Al alloys is evaluated using Synchrotron X-ray microtomography.•Addition of Mn content (0.6% mass) increases the ultimate tensile strength with limited ductility.•The presence of Al7Cu2Fe particles clusters reduced the applied strain for void nucleation due to particle cracking.
Front video and sensor data captured by vehicle-mounted event recorders are used for not only traffic accident evidence but also safe-driving education as near-miss traffic incident data. However, ...most event recorder (ER) data shows only regular driving events. To utilize near-miss data for safe-driving education, we need to be able to easily and rapidly locate the appropriate data from large amounts of ER data through labels attached to the scenes/events of interest. This paper proposes a method that can automatically identify near-misses with objects such as pedestrians and bicycles by processing the ER data. The proposed method extracts two deep feature representations that consider car status and the environment surrounding the car. The first feature representation is generated by considering the temporal transitions of car status. The second one can extract the positional relationship between the car and surrounding objects by processing object detection results. Experiments on actual ER data demonstrate that the proposed method can accurately identify and tag near-miss events.
This paper proposes a methodology for surrogate-based microstructural optimization of structural metals that integrates a limited number of 3D image-based numerical simulations with microstructural ...quantification, coarsening and optimisation processes. The support vector machine that was used had an infill sampling criterion to reduce the number of numerical trials, and the proposed methodology was found to be effective for wrought 2024 aluminium alloy with irregularly shaped particles. Appropriate objective functions were defined to assess particle damage. The number of design parameters, which quantitatively express the size, shape, and spatial distribution of particles, was initially 41, but they were reduced to four during a two-step coarsening process. The surrogate model provided highly accurate predictions, and the size, shape, and spatial distribution values of the optimal and weakest particles were successfully identified. It was shown that the optimal particle was small, spherical, sparsely dispersed, and perpendicular to the loading direction. However, it was also found that the smallest and most independent particle with a spherical shape was not necessarily strong, which implies the effects of particle clustering. It was also concluded that the dependency of in-situ particle strength on size was of crucial importance for weaker particles. The shape and spatial distribution of stronger particles were, however, more crucial for suppressing their internal stress than was their size. The results show that the proposed methodology offers a cost-efficient solution for microstructural designs involving 3D high-fidelity simulations that cannot be obtained with the existing approaches for developing materials.
3D contour maps of the objective function I1 (the maximum value of the maximum principal stress in particles) predicted by the surrogate model Display omitted
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