摘要：气候变化威胁人类的生存.化石燃料的过度使用导致CO_(2)持续排放是引起全球变暖和气候变化的主要因素,须尽快减少CO_(2)排放.捕获CO_(2)并将其转化为高附加值的燃料和化学品从而循环利用是减少CO_(2)净排放的有效措施.其中,CO_(2)催化加氢制甲酸(HCOOH)是碳捕获与利用(CCU)的有效途径之一,其产物HCOOH可用于防腐剂、牲畜饲料抗菌剂和食品添加剂,也可作为氢载体和直接甲酸燃料电池的燃料.目前,工业上生产HCOOH的工艺包括两个步骤:甲醇和CO在强碱条件下反应生成甲酸甲酯(HCO_(2)CH_(3)),随后水解为HCOOH.该工艺利用来自化石燃料的两种原料,排放出大量CO_(2),同时在水解步骤中使用了过量的酸性水,因此对生态环境产生一定的危害.近年来,以CO_(2)为可再生原料合成HCOOH被广泛研究,人们探索了电化学、光化学、生物和热化学反应等多种途径将CO_(2)还原为HCOOH,以期实现CO_(2)循环利用.上述方法距实际应用尚有一定距离,其中,CO_(2)催化加氢制HCOOH过程最先进,它与当前许多化学工业过程相似.由于CO_(2)分子的化学稳定性,CO_(2)加氢生成HCOOH在热力学上不利,可通过有机碱和无机碱形成甲酸-碱配合物,推动反应向生成HCOOH方向移动.然而,从甲酸基配合物中提取HCOOH需要额外的分离步骤,因此在无碱条件下直接将CO_(2)加氢生成HCOOH非常重要.本课题组致力于研究无碱条件下g-C_(3)N_(4)负载的Pd(记为Pd/CN)催化剂催化CO_(2)加氢合成HCOOH,前期研究(***.,2016,52,14302-14305和***.,2021,396,395-401)发现,通过控制Pd负载量可改变催化剂中Pd单原子/Pd纳米团簇的比例,且当两种状态Pd达到最佳比例时,催化剂催化活性最高.这表明在无碱CO_(2)加氢过程中,Pd单原子与纳米团簇间存在协同作用.此外,最近有关于单原子和纳米团簇在负载金属催化剂中不同作用的报道,如NixMg1-xO催化逆水气变换反应,Ir1/In_(2)O_(3)和Pd/Fe_(3)O_(4)催化CO_(2)加氢制乙醇反应等,这些工作得出相似的结论:单原子金属对CO_(2)活化有效,而纳米团簇对H_(2)活化有效.这对于设计以CO_(2)和H_(2)为反应物的金属催化剂很重要.本工作旨在考察类似的机理是否适用于Pd/CN催化剂在无碱条件下催化CO_(2)加氢制HCOOH过程.通过控制Pd负载量,合成了含有不同比例Pd单原子和Pd纳米团簇的Pd/CN催化剂,Pd与g-C_(3)N_(4)表面碱性位间的强静电相互作用使合成含有大量Pd单原子的Pd/CN催化剂成为可能.在Pd/CN催化剂催化无碱CO_(2)加氢制HCOOH过程中,当两种状态Pd达到最佳比例时,Pd单原子和Pd纳米簇之间存在协同作用,此时催化剂活性最高.实验表明,Pd纳米簇主要通过解离吸附参与H_(2)活化,Pd单原子对CO_(2)活化更有效.在最佳单原子比(单原子数/(单原子数+纳米簇)为41%)时,该催化剂表现出最高的活性,优于文献报道的相似反应条件下Pd催化剂活性.这些发现将为以CO_(2)和H_(2)分子为反应物的反应的催化剂设计提供一定的参考.

摘要：在高场磁体中,压缩磁径向应力比拉伸应力更受青睐,原因是它能降低磁体绕组内的整体峰值磁应力.这对于无绝缘高温超导(NI HTS)磁体尤为重要,因为压缩径向应力能够产生良好的匝间接触,这对于无绝缘高温超导线圈中的电流共享以及随之而来的自保护行为至关重要.根据关键磁体设计参数(如目标中心场、背景磁场、内外绕组直径和外部径向堆叠),我们给出了可以从解析上确定高场超导磁体具有压缩径向应力的电磁-力学条件.本文提出的方法可以识别干绕线圈中径向匝间接触行为的3种不同模式:(1)完全分离;(2)完全接触;以及(3)混合模式(即部分分离和接触).文章随后提出一种使用完全压缩径向应力电磁-力学条件来计算干绕线圈中应力分布的解析方法.并通过有限元分析示例验证了解析方法与数值方法的良好一致性.文章结果可以帮助磁体工程师在早期设计阶段更好地概览高场超导磁体的电磁-力学行为.

摘要：A BLOG CURATED BY 01《A Magazine》每期均邀请一位顶尖的时装设计师作为主编,因此每一期也呈现出截然不同的风格。对时装迷来说,读《A Magazine》就像是体味设计师气度的延伸,让他们走下时装的延展台,转而进入设计师的思想领域。而对杂志癖而言。

摘要：A 1 kbit antifuse one time programmable(OTP) memory IP,which is one of the non-volatile memory IPs,was designed and used for power management integrated circuits(ICs).A conventional antifuse OTP cell using a single positive program voltage(VPP) has a problem when applying a higher voltage than the breakdown voltage of the thin gate oxides and at the same time,securing the reliability of medium voltage(VM) devices that are thick gate transistors.A new antifuse OTP cell using a dual program voltage was proposed to prevent the possibility for failures in a qualification test or the yield *** the newly proposed cell,a stable sensing is secured from the post-program resistances of several ten thousand ohms or below due to the voltage higher than the hard breakdown voltage applied to the terminals of the *** layout size of the designed 1 kbit antifuse OTP memory IP with Dongbu HiTek's 0.18 μm Bipolar-CMOS-DMOS(BCD) process is 567.9 μm×205.135 μm and the post-program resistance of an antifuse is predicted to be several ten thousand ohms.

摘要：The problem of designing a digital frontend (DFE) was considered which can dynamically access or sense dual bands in any radio frequency (RF) regions without requiring hardware changes. In particular, second-order bandpass sampling (BPS) as a technique that enables to realize the multiband reception function was discussed. In a second-order BPS system, digital reconstruction filters were utilized to eliminate the interferences generated while down converting arbitrarily positioned RF-band signals by using the direct digitization method. However, the inaccuracy in the phase shift or the amplitude mismatch between the two sample streams may cause insufficient rejection of interference. Practical problems were studied, such as performance degradation in signal-to-interference ratio (SIR) and compensation methods to overcome them. In order to demonstrate the second- order BPS as a flexible DFE suitable for software-defined radio (SDR) or cognitive radio (CR), a DFE testbed with a reconfigurable structure was implemented. Moreover, with a view to further demonstrate the proposed compensation algorithms, experimental results show that dual bands are received simultaneously.

摘要：CELINE新创意总监PHOEBE PHILO大家还记得2006年1月5日Chloé的创意总监Phoebe Philo辞职回家带孩子的事情吧,最近这位小孩已经可以打酱油的妈妈被Bernard Arnault重新带回公众视线,她被任命为Celine的创意总监,10月正式上任。

摘要：对热轧的Zr-1Nb板材进行了不同变形量的冷加工,利用背散射电子衍射(EBSD)以及透射电子显微镜(TEM)研究了冷加工及热处理对其组织的影响。结果表明,随着冷加工变形量从30%增加到70%,晶粒尺寸逐渐从双态分布变为均匀分布。各种变形下的织构主要为(0001),且随着变形道次的增加强度逐渐增大。

摘要：影响噪声烦恼的声学参量较多,然而在传统噪声控制工程中,往往仅根据A计权声压级所需降低量进行控制方案设计,未能从烦恼改善程度优选方案.为此,本研究提出一种基于烦恼改善程度优选噪声控制方案的方法,并将该方法应用于变电站声屏障噪声控制方案的比选.结果表明,同一声屏障方案对不同关心点噪声烦恼的改善程度差异较大,A计权声压级降低量最大的声屏障方案对噪声烦恼的改善效果未必最好.因此,噪声控制工程设计中,宜根据所关心的声环境保护目标与噪声源的相对位置,选取对保护目标处噪声烦恼改善程度较大的方案.

摘要：历史悠久的北京雕漆工艺在20世纪90年代北京雕漆厂停产之后陷入低迷,工艺师们分散作业,市场萎缩。虽然有国家级非遗传承人文乾刚大师在国内外广获声誉,但从业人员日益减少且老龄化的问题日趋严重。非遗中心组织的一系列传承人收徒活动、2012年成立的北京华方雕漆艺术设计有限公司进行的商业活动等,均是努力使雕漆传承下去的有益尝试。本文通过尽量全面的考察和探访,呈现北京雕漆如何能够既保持工艺传统,又不断探索前路。

摘要：High-efficiency design of a mixed-flow pump has been carried out based on numerical analysis of a three-dimensional viscous *** analysis,the Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model were discretized by finite-volume *** grid system was constructed in the computational domain,which has O-type grids near the blade surfaces and H/J-type grids in other *** numerical results were validated with experimental data for the heads and hydraulic efficiencies at different flow *** hydraulic efficiency at the design flow coefficient was evaluated with variation of the geometric variables,i.e.,the area of the discharge and length of the vane in the *** result has shown that the hydraulic efficiency of a mixed-flow pump at the design condition is improved by the modification of the geometry.