Dynamics of gravity dam-reservoir systems

The response of a long concrete gravity dam-reservoir system for a harmonic rigid base acceleration normal to the dam axis is investigated.The hydrodynamic pressure acting on the vertical wet surface of the dam is first evaluated in closed form as a function of the unknown deflections of the dam-reservoir interface and the ground acceleration. Employing finite element techniques, the motion of the dam is investigated. The hydrodynamic pressures enter the equation of motion of the dam as loadings in excess of the inertia load.In this approach, the general flexibility of the dam cross-section and the compressibility of water are taken into account. The viscosity of water and the effect of the surface waves are neglected.The coupling between the dam and the reservoir results in changes in the mass and stiffness properties of the dam which depend on the excitation frequency. For an excitation frequency greater than the fundamental frequency of the reservoir, the damping properties of the dam are also modified.     

Computation of stresses and strains in dams made of local materials,earth slopes,and their foundations,by the finite element method

Conclusion The experinece of the application of the finite element method shows that this is the most efficient and convenient of the methods used at the present time for the computation of stresses in slopes and earth dams. The computer program based on this method can take into account any arbitrary geometry of the cross section, a large diversity in the loading conditions and in the porperties of the construction material and of the foundation. The results obtained so far in the practical applications indicate that the finite element method can be used with confidence for the computation of earth and rockfill dams and their foundations, both under static and dynamic loads, including seismic forces. This paper was written during Professor W. D. Liam Finn's stay in the USSR, in accordance with the scientific exchange program concluded between the Academy of Sciences of the USSR and the Canadian Research Council. Part of the investigations described in this paper were supported by this Council at the University of British Columbia through Grant No. 1498. Canada: All-Union Scientific Institute of Irrigation and Hydraulics of the USSR. Translated from Gidrotekhnicheskoe Stoitel'stvo, No. 6, pp. 22–27, June, 1968.     

负荷加固情况下钢梁性能和强度的试验研究

对4点加载的W型梁进行试验,分析抗弯构件在加载作用下进行加固时的性能和承载力。试验结果显示:对于侧向扭转屈曲主导的破坏模式下的大跨构件,未加固梁的预加载力增加53%会导致加固梁的侧向屈曲荷载最多减少14.2%,但是预加载对构件极限荷载没有影响。对相同加固方式下跨度较短的构件进行试验发现:未加固梁的预加载增加50%会导致加固梁的极限承载力减少13%。然后,当构件在加载或者不加载情况下进行加固时,其挠曲变形变化并不大。对于由弯曲屈服主导的破坏模式下的构件,预加载对于加固构件的极限承载力并没有影响。     

CMOS DAC充当数控分压器

数字电位器在可接受8位分辨率的应用中,可作为极佳的数控分压器,例如Analog Devices的AD5160。本篇设计实例介绍在需要更高分辨率的应用中如何使用CMOS DAC作为分压器。     

Crystal Facet Engineering of Single-Crystalline TiC Nanocubes for Improved Hydrogen Evolution Reaction

Single-crystalline {100} faceted TiC is of great significance in theory to a large number of engineering applications owing to its extraordinary catalytic properties. However, the {111} planes are prevalent in conventional TiC powders given their favorable thermodynamic stability during the initial low stoichiometric growth stage. Herein, a disproportionation–decomposition strategy is developed to directly produce Ti and C atoms to synthesize single-crystalline {100} faceted TiC powders. Outstanding electrochemical performance of TiC {100} crystal planes in terms of the hydrogen evolution reaction is evidenced by an overpotential of 392 mV at 10 mA cm⁻², which is 52% lower than that of randomly faceted TiC counterparts (815 mV).     

Enhancing Ion Migration in Grain Boundaries of Hybrid Organic–Inorganic Perovskites by Chlorine

Ionicity plays an important role in determining material properties, as well as optoelectronic performance of organometallic trihalide perovskites (OTPs). Ion migration in OTP films has recently been under intensive investigation by various scanning probe microscopy (SPM) techniques. However, controversial findings regarding the role of grain boundaries (GBs) associated with ion migration are often encountered, likely as a result of feedback errors and topographic effects common in to SPM. In this work, electron microscopy and spectroscopy (scanning transmission electron microscopy/electron energy loss spectroscopy) are combined with a novel, open‐loop, band‐excitation, (contact) Kelvin probe force microscopy (BE‐KPFM and BE‐cKPFM), in conjunction with ab initio molecular dynamics simulations to examine the ion behavior in the GBs of CH₃NH₃PbI₃ perovskite films. This combination of diverse techniques provides a deeper understanding of the differences between ion migration within GBs and interior grains in OTP films. This work demonstrates that ion migration can be significantly enhanced by introducing additional mobile Cl^? ions into GBs. The enhancement of ion migration may serve as the first step toward the development of high‐performance electrically and optically tunable memristors and synaptic devices.     

Activation,Deactivation and Reversibility in a Series of Homogeneous Iridium Dehydrogenation Catalysts

Dehydrogenation is a sustainable form of oxidation catalysis, as it avoids any primary oxidant and the waste that would accompany it. Homogeneous catalyst design for this reaction is delicate: the catalyst must have a sufficient H₂ affinity to abstract two hydrogen atoms from the substrate but not so much affinity as to fail to release them as free H₂. N-Heterocyclic carbene (NHC) ligands achieve this balancing act in a series of iridium catalysts based on the Ir(IMe)₂ motif (IMe=N,N′-dimethylimidazol-2-ylidene). Catalyst design also needs to account for mechanistic points outside of the catalytic cycle itself. To enter the cycle, there is often an initial precatalyst activation process, and elucidating this can lead to optimization of both precatalyst and reaction conditions. To leave the cycle, we can have reversible formation of off-cycle species as well as an irreversible catalyst deactivation step. In our Cp*Ir(IMe)₂Cl precatalyst for dehydrogenative oxidation, Cp* is lost in the activation step. This suggested moving to a catalyst precursor lacking the Cp*, [Ir(IMe)₂(CO)₂]⁺. Catalyst deactivation produces a series of unusual cluster cations such as [Ir₆(IMe)₈(CO)₂H₁₄]²⁺. Among applications, dehydrogenative oxidation can be useful in upgrading of biomass glycerol by conversion to lactate, as a part of hydrogen borrowing chemistry and in reversible hydrogenation/dehydrogenation for H₂ storage.