The effects of ocean acidification on marine organisms and ecosystem

海洋酸化是CO2排放引起的另一重大环境问题.工业革命以来,海洋吸收了人类排放CO2总量的三分之一.目前,海洋每年吸收的量约为人类排放量的四分之一(即约每小时吸收100万吨以上的CO2),对缓解全球变暖起着重要的作用.然而,随着海洋吸收CO2量的增加,表层海水的碱性下降,引起海洋酸化.海洋酸化会引起海洋系统内一系列化学变化,从而影响到大多数海洋生物的生理、生长、繁殖、代谢与生存,可能最终导致海洋生态系统发生不可逆转的变化,影响海洋生态系统的平衡及对人类的服务功能.地球历史上曾多次发生过海洋酸化事件,伴随着生物种类的灭绝,其内在联系虽然不甚明确,却也可能暗示未来海洋酸化可能对海洋生态系统产生重大的影响.Ocean acidification is known as another global change problem caused by increasing atmospheric CO2.Since the industrial revolution, the oceans have absorbed more than one third of the anthropogenic CO2 released to the atmosphere, currently, at a rate of over 1 million tons per hour, totaling to about one quarter of all anthropogenic CO2 emissions annually.Uptake of CO2 by the ocean has played an important role in stabilizing climate by mitigating global warming.However, rising ocean carbon levels caused by the uptake of anthropogenic CO2 (acidic gas) leads to increased ocean acidity (reduced pH) and related changes in ocean carbonate chemistry, or "ocean acidification".Recent research has shown that ocean acidification affects the physiology, growth, survival, and reproduction of many, if not most marine organisms.Ultimately, future ocean acidification may lead to significant changes in many marine ecosystems, with consequential impact on ecosystem services to societies.Several ocean acidification events are known to have occurred during Earth’s history, each coinciding with high rates of species’ extinctions.Although the mechanisms involved in past massive species extinction associated with ocean acidification events, they certainly hint potential disastrous impacts on ecosystem functions in short future.中国科学院“百人计划”(2006-067); 国家自然科学基金(40872168)资

黄土丘陵区混交林中油松和沙棘树干液流 对降雨脉冲的响应

以黄土丘陵区油松-沙棘混交林为研究对象，运用热扩散式探针( TDP) 于2015 年 6&mdash;10 月对油松和沙棘的树干液流密度( Fd ) 进行连续观测，同步测定了光合有效辐射 ( PAＲ) 、水汽压亏缺( VPD) 和土壤水分( SWC) 等环境因子，分析两树种对降雨利用的差异．采 用Threshold-delay 模型、多元回归分析和偏相关分析方法，研究两树种Fd 对降雨的响应过程， 并确定环境因子对Fd 的影响．结果表明: 随着降雨量递增，两树种Fd 的最大变化量都先上升 后降低; 其中0～1 mm 降雨范围内，油松Fd ( －16．3%) 和沙棘Fd ( －6．3%) 都明显降低; 1～5 mm 降雨范围内，油松Fd ( －0．4%) 降低而沙棘Fd ( 9．0%) 明显升高．油松和沙棘Fd 对降雨响应的最 小降雨阈值( ＲL ) 分别为6．4 和1．9 mm，滞后时间( &tau;) 为1．96 和1．67 d．降雨前油松Fd 峰值集 中在12: 00&mdash;12: 30( 70%) ，沙棘Fd 峰值分别集中在10: 30&mdash;12: 00( 48%) 和16: 00&mdash;16: 30 ( 30%) ; 降雨后油松Fd 峰值集中在11: 00&mdash;13: 00( 40%) ，沙棘Fd 峰值分别集中在12: 00&mdash; 13: 00( 52%) 和16: 30&mdash;17: 00( 24%) ．降雨前影响油松和沙棘Fd 的环境因子大小顺序为PAＲ＞ VPD; 降雨后影响油松Fd 的环境因子大小顺序为PAＲ＞VPD＞0 ～ 20 cm SWC( SWC0～ 20 ) ，影响沙 棘Fd 的环境因子大小顺序为SWC0～ 20＞PAＲ＞VPD．油松-沙棘混交林对水分利用的稳定性较高．</p

Numerical simulation of ti-based metallic glasses as whipple shield bumper by smoothed particle hydrodynamics methods

The debris clouds produced by hypervelocity impacts on Ti-based metallic glasses (Ti-MGs) and Al-6061-T6 bumper were studied by smoothed particle hydrodynamics (SPH) methods. The change of the vanguard shape, dispersion and ejection angle were also obtained with the same bumper thickness to the projectile-diameter ratio (h/d). For the same h/d valve, the debris cloud of Ti-MGs bumper had a more widely dispersion and ejection angle than with Al-6061-T6 bumper; the vanguard velocity of Ti-MGs bumper was also lower than Al-6061-T6 bumper. Moreover, for the same bumper areal density, the vanguard of the debris cloud in MGs bumper was plane-shaped. This study demonstrates that Ti-MGs exhibit an excellent bumper protection performance, which asset can pave new paths for their further applications. © 2020 Trans Tech Publications Ltd, Switzerland

Abnormal softening of Ti-metallic glasses during nanosecond laser shock peening

Nanosecond laser shock peening (NLSP) has been proved to be an effective way to enhance the mechanical properties of metallic components through modifying the surface microstructures. However, the micromechanism of structure and property fluctuations induced by shock wave propagation is still limited due to the intrinsic defects in crystalline materials. Here, NLSP treatment has been performed into the Ti-metallic glasses. Owing to the absence of dislocations, grain boundary and phase segregation, the structural signals caused by the shock wave could come into sight. According to grid nanoindentation results, the shock-affected region can be divided into three sections: (I) the rapid softening region, (II) the recovery region and (III) the matrix region. The fronted first pop-in event and the reduced hardness found in the subsurface region provide clear evidence of the release wave-induced structural rearrangement. The abnormal change of the average volume of the shear transformation zone (STZ) could be explained by a two-step transformation mechanism, due to the fluctuations of the "weak spot" induced by the release stress wave. By means of these results, this work provides an opportunity to shed light on the common laser-solid interaction

Rejuvenation, embryonic shear bands and improved tensile plasticity of metallic glasses by nanosecond laser shock wave

The structural and mechanical responses of Ti-based and Zr-based metallic glasses (MGs) treated by the nanosecond laser shock wave were investigated. A rejuvenation transition was observed, due to the structural rearrangement of neighboring atoms in the instantaneous shock process. Plenty of embryonic shear bands occurred along the shock-affected zone. A damped model of the shock pressure was established to describe the characteristic of the embryonic shear bands. The results showed that the shear band initiation in the nanosecond scale along the length direction was divided into two stages: the initial low propagation stage and the following fast propagation stage, because of the reduction of the shock pressure. The hardness of the shock-affected zone displayed a maximal decrease of 25% in the critical zone between the two propagation stages, due to the combined effect of the structural rejuvenation and the compressive residual stress. A schematic of the energy landscape was proposed to explain the relationship between the rejuvenation and the formation of the embryonic shear bands. The maximum tensile plasticity increased by 0.46%. The results demonstrated that the MGs possessed different shear band propagation modes in the initiation stages, which deepened the understanding of the deformation mechanism in the MGs.</p

Excellent irradiation tolerance and mechanical behaviors in high-entropy metallic glasses

This study investigated ion-irradiation performance and mechanical behavior of high-entropy metallic glasses (HE-MGs) irradiated at room temperature. The critical fluence for blister formation in ZrTiHfCuBeNi HE-MGs was higher than ZrTiHfCuBe HE-MGs because of the larger mixing entropy and negative mixing enthalpy. The ZrTiHfCuBeNi HE-MGs maintained a more moderate hardness value than ZrTiHfCuBe HE-MGs at a fluence of 1.0 x 10(18) ions/cm(2), implying a better irradiation tolerance and capacity of helium atoms. There was not a serrated flow or pop-in event that occurred in the HE-MGs after ion irradiation, which indicated that the formation of serrations was restricted. The total displacement and peak intensity in the creep relaxation spectrum increased as the ion fluence increased. The ZrTiHfCuBeNi HE-MGs exhibited a lesser change in peak intensity and relaxation time. This study demonstrated that HE-MGs may exhibit a favorable response to high levels of helium implantation, which exhibits potential uses under extreme irradiation conditions. (C) 2019 Elsevier B.V. All rights reserved.</p

Mechanism of local hardening in metallic glass during He ion irradiation

When exposed to He radiation, metallic glasses (MGs) often undergo a unique transformation and mechanical evolution, unlike their crystalline counterparts. However, the relationship between He bubble evolution and the mechanical response is largely unknown. Here, a localized hardness change along ion irradiation direction was discovered under the condition that He ion irradiation does not induced nanocrystallizaiton. The location of the localized hardening peak shifted to the right, and this was accompanied by nucleation and growth of the He bubbles as the fluence increased. Besides, coalescence and overlap of the He bubbles were observed in the central of the bubble layer at the highest fluence. The localized hardness change was quantified by a model based on the He bubbles size and density. The results of this study provide insights into the effect of He bubbles on mechanical evolution and pave the way for designing MGs suitable for the nuclear industry.</p

JUNO Sensitivity on Proton Decay p→νˉK+p\to \bar\nu K^+ Searches

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this paper, the potential on searching for proton decay in $p\to \bar\nu K^+$ mode with JUNO is investigated.The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits to suppress the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar\nu K^+$ is 36.9% with a background level of 0.2 events after 10 years of data taking. The estimated sensitivity based on 200 kton-years exposure is $9.6 \times 10^{33}$ years, competitive with the current best limits on the proton lifetime in this channel