粤港澳大湾区水安全协同调控理论框架研究

针对粤港澳大湾区水问题多维交织特性,基于流域系统整体观梳理总结了技术上可控、逻辑上关联的5个水安全调控子系统结构,包括：河势调控子系统、内河水环境水生态调控子系统、外江咸潮调控子系统、城市暴雨洪涝调控子系统、外江洪潮调控子系统。探讨了各子系统关键机理、系统间的协同作用原理、协同调控的关键技术需求及协同调控模型算法架构,构建了大湾区水安全协同调控理论框架,以珠江河口为例开展了粤港澳大湾区水安全协同调控理论的应用,为大湾区水问题系统治理提出了新的解决方案。     

A generalized series approach to MR spectroscopic imaging

The problem of precise spatial localization of spectral information in magnetic resonance (MR) spectroscopic imaging is addressed. A novel method, called GSLIM (generalized spectral location by imaging), is proposed to make possible the marriage of high-resolution proton imaging with spectroscopic imaging and localization. This method improves on the conventional Fourier series inversion method used in chemical shift imaging (CSI) and the compartmental modeling method used in SLIM by using a generalized series framework for optimal representation of the spectral function. In this way, a priori information extracted from proton imaging can be used, as in SLIM, and the robustness and data consistency of CSI are also retained. Simulation results show that GSLIM can significantly reduce spectral leakage in CSI and inhomogeneity errors in SLIM. It can also reveal compartmental inhomogeneities, and can easily be extended to handle other a priori constraints when necessary. This approach, with some further development, may achieve an optimal combination of sensitivity, quantitative accuracy, speed, and flexibility for in vivo spectroscopy.     

Selective activation of small motor axons by quasitrapezoidalcurrent pulses

We have found a method to activate electrically smaller nerve fibers without activating larger fibers in the same nerve trunk. The method takes advantage of the fact that action potentials are blocked with less membrane hyperpolarization in larger fibers than in smaller fibers. In our nerve stimulation system, quasitrapezoidal-shaped current pulses were delivered through a tripolar cuff electrode to effect differential block by membrane hyperpolarization. The quasitrapezoidal-shaped pulses with a square leading edge, a 350 microsecond(s) plateau, and an exponential trailing phase ensured the block of propagating action potentials and prevented the occurrence of anodal break excitation. The tripolar cuff electrode design restricted current flow inside the cuff and thus eliminated the undesired nerve stimulation due to a "virtual cathode." Experiments were performed on 13 cats. The cuff electrode was placed on the medial gastrocnemius nerve. Both compound and single fiber action potentials were recorded from L7 ventral root filaments. The results demonstrated that larger alpha motor axons could be blocked at lower current levels than smaller alpha motor axons, and that all alpha fibers could be blocked at lower current levels than gamma fibers. A statistical analysis indicated that the blocking threshold was correlated with the axonal conduction velocity or fiber diameter. This method could be used in physiological experiments and neural prostheses to achieve a small-to-large recruitment order in motor or sensory systems.     

Effect of geometric parameters of fibers on water absorption of blocks

Conclusion A comparison was made of the water absorption of two fiber-reinforced concrete blocks with different geometric parameters of the fibers. It was found that in the case of using thin fibers d=0.5 mm (block No. 2), the water absorption by weight was less and it was distributed more uniformly over the entire length than in the case of using fibers with d=1.5 mm (block No. 1). A dependence of the coefficient of variation on W_w was established (a decrease of W_w causes a decrease of C_v and vice versa). This was displayed especially clearly in block No. 1 (thick fibers) and less so in block No. 2. Furthermore, it was found that the addition of thin fibers directly into the concrete mixer (into the mixed concrete) leads to their clumping and ultimately to the occurrence of hedgehogs in the concrete and to worsening of W_w. Clumping of fibers occurs little, if at all, when thick fibers are added to the concrete mixer. Precisely the addition of fibers to the concrete mix is one of the most complex problems in the given area of construction.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 11, pp. 23–24, November, 1991.     

Thermal Conductivity of Gelatinized Starches

The thermal conductivity (k) of gelatinized high-amylose and high-amylopectin starches was determined, using the heated probe method. The granular starches, mixed with distilled water at 1 to 4 kg water/ kg dry solids, were gelatinized at 120°C. Similar k values which varied from 0.434 to 0.548 W/mK in the temperature range 30 to 70°C were obtained for both starch gels. Experimental data were fitted to six structural models, representing various geometries for mixtures of water and dry starch. The perpendicular model, based on heat conduction in series through layers of dry starch and water, yielded best correlations. The predicted thermal conductivity of dry gelatinized starch (k_s) increased linearly with temperature T (K) according to the equation:      

Effect of certain factors on the strength of ready-mixed concrete

Conclusion The strength of concrete was investigated. It was found that in the case of charging individual concrete components into TMs mounted on the chassis of KrAZ and KamAZ trucks, high-grade concrete cannot always be prepared with such a technological scheme.It was established that with a yield of various volumes of ready-mixed concrete from TMs, the strength of the concrete from the smaller volume (3.5 m³) was higher an age 1 day than of concrete from a volume of 4 m³.However, at age 28 days the strengths equalize. Furthermore, the concrete taken from 3.5 m³ was more uniform. In addition to this, an attempt was made to predict how the concrete strength would increase directly in structures during operation of tunnels constructed by the open method during the year.It was established that the maximum gain of strength of concrete will occur in the summer, in June and July. At the same time, in August there are great differences between the ambient temperature and humidity. This means that there will not be enough moisture for active hydration of cement, the concrete will have shrinkage and an increase of concrete strength may not only be markedly retarded but may stop entirely. In the winter, spring, and fall, the strength of concrete will increase, but apparently less intensely than in the summer.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 11, pp. 21–22, November, 1991.     

Influence of strain rate on the nature of failure under prolonged static and cyclical loads. 2. Examples of calculation

Based on a physicomechanical model of intercrystallite failure in materials, such as presented in the previous communication, we have proposed a computational algorithm for the endurance of polycrystalline material under cyclical load. We have provided examples for the calculation of the cyclical strength in austenitic steel under various strain rates. Comparison of the theoretical results against the experimental data demonstrated the possibility of using the model developed here to describe the quantitative relationships governing intercrystallite failure of the material over a broad range of load regimes.Translated from Problemy Prochnosti, No. 8, pp. 42–47, August, 1991.     

A robust kinematic hardening rule for cyclic plasticity with ratchetting effects

Summary A robust kinematic hardening rule is proposed which appropriately blends the deviatoric stress rate rule and the Tseng-Lee rule in order to satisfy both the experimental observations made by Phillips et al. [1]–[5] and the nesting of the yield surface to the limit surface. The work presented in Part I is confined to the theoretical formulation of kinematic hardening rule with limited correlation to experimental results. A more general expression for the plastic modulus is proposed. The expressions proposed by McDowell and by Dafalias can be obtained as a special case of the proposed expression. An additional parameter is introduced that reflects the dependence of the plastic modulus on the angle between the deviatoric stress rate tensor and the direction of the limit backstress relative to the yield backstress.