对我国高校“稳定率”的几点思考

高校“稳定率”是一个创新的概念,其确切涵义需要一个科学的表述。本文从“不稳定事件”发生的主体、涉及的人数、深层次背景、具体形态四个方面来理解高校“稳定率”的内涵,分析其特点。并就提高我国高校“稳定率”的方针原则、具体措施以及防范重点等问题进行了探讨。

High-resolution reconstruction of the ablative RT instability flowfield via convolutional neural networks

High-resolution flow field data has important applications in meteorology,aerospace engineering,high-energy physics and other fields.Experiments and numerical simulations are two main ways to obtain high-resolution flow field data,while the high experiment cost and computing resources for simulation hinder the specificanalysis of flow field evolution.With the development of deep learning technology,convolutional neural networks areused to achieve high-resolution reconstruction of the flow field.In this paper,an ordinary convolutional neuralnetwork and a multi-time-path convolutional neural network are established for the ablative Rayleigh-Taylorinstability.These two methods can reconstruct the high-resolution flow field in just a few seconds,and further greatlyenrich the application of high-resolution reconstruction technology in fluid instability.Compared with the ordinaryconvolutional neural network,the multi-time-path convolutional neural network model has smaller error and canrestore more details of the flow field.The influence of low-resolution flow field data obtained by the two poolingmethods on the convolutional neural networks model is also discussed.

GaAs HBT Microwave Power Transistor with On-Chip Stabilization Network

An lnGaP/GaAs HBT microwave power transistor with on-chip parallel RC stabilization network is developed with a standard GaAs MMIC process. From the stability factor K, the device shows unconditional stability in a wide frequency range due to the RC network. The power characteristics of the device as measured by a loadpull system show that the large-signal performance of the power transistor is affected slightly by the RC network. Psat is 30dBm at 5.4GHz,and PldB is larger than 21.6dBm at llGHz. The stability of the device due to RC network is proved by a power combination circuit. This makes the power transistor very suitable for applications in microwavc high power ttBT amplifiers.

Influence of heat treatment on electrochemical properties of Ti_(1.4)V_(0.6)Ni alloy electrode containing icosahedral quasicrystalline phase

The structures and electrochemical properties of the Ti1.4V0.6Ni ribbon before and after heat treatment are investigated systematically. The structure of the sample is characterized by X-ray powder diffraction analysis. Electrochemical properties including the discharge capacity, the cyclic stability and the high-rate discharge ability are tested. X-ray powder diffraction analysis shows that after heat treatment at 590 °C for 30 min, all samples mainly consist of the icosahedral quasicrystal phase (I-phase), Ti2Ni phase (FCC), V-based solid solution phase (BCC) and C14 Laves phase (hexagonal). Electrochemical measurements show that the maximum discharge capacity of the alloy electrode after heat treatment is 330.9 mA?h/g under the conditions that the discharge current density is 30 mA/g and the temperature is 30 °C. The result indicates that the cyclic stability and the high-rate discharge ability are all improved. In addition, the electrochemical kinetics of the alloy electrode is also studied by electrochemical impedance spectroscopy (EIS) and hydrogen diffusion coefficient (D).

Nano-Level Electron Beam Lithography

The JEOL JBX-5000LS is a vector type machine.The system hardware features an ion-pumped column,a LaB 6 electron emitter,25kV and 50kV accelerating voltage,and a turbo-pumped sample chamber.The resolution,stability,stitching and overlay of this system are evaluated.The system can write complex patterns at dimensions down to 30nm.The demonstrated overlay accuracy of this system is better than 40nm.

Wheat Grain Yield and Yield Stability in a Long-Term Fertilization Experiment on the Loess Plateau

To provide a scientific basis for sustainable land management, a 20-year fertility experiment was conducted in Changwu County, Shaanxi Province, China to investigate the effects of long-term application of chemical fertilizers on wheat grain yield and yield stability on the Loess Plateau using regression and stability analysis. The experiment consisted of 17 fertilizer treatments, containing the combinations of different N and P levels, with three replications arranged in a randomized complete block design. Nitrogen fertilizer was applied as urea, and P was applied as calcium superphosphate. Fertilizer rates had a large effect on the response of wheat yield to fertilization. Phosphorus, combined with N, increased yield significantly （P 〈 0.01）. In the unfertilized control and the N or P sole application treatments, wheat yield had a declining trend although it was not statistically significant. Stability analysis combined with the trend analysis indicated that integrated use of fertilizer N and P was better than their sole application in increasing and sustaining the productivity of rainfed winter wheat.

Effects of Tillage Management on Infiltration and Preferential Flow in a Black Soil, Northeast China

The impacts of no-tillage （NT） and moldboard plough （MP） managements on infiltration rate and preferential flow were characterized using a combined technique of double-ring device and dye tracer on a black soil （Mollisols） in Northeast China. The ob- jective of this study is to evaluate how tillage practices enhance soil water infiltration and preferential flow in favor of soil erosion con- trol in the study area. The steady infiltration rates under NT management are 1.6 and 2.1 times as high as those under MP management in the 6th and 8th years of the tillage management in place, while the infiltrated water amounts under NT management are 1.4 and 2.0 times as high as those under MP management, respectively. The depth of methylene blue penetrated into NT soil increases from 43 cm in the 6th year to 57 cm in the 8th year, which are 16 cm and 19 em deeper than those in MP soil, respectively. The results of morphol- ogic image show that more biological macro-pores occur in NT soil than in MP soil. These macro-pores play a key role in enhancing preferential flow in NT soil, which in turn promotes water infiltration through preferential pathways in NT soil. The results are helpful to policy-making in popularizing NT and have the implications for tillage management in regard to soil erosion control in black soil region of China.

System reliability analysis of seismic pseudo-static stability of rock wedge based on nonlinear Barton–Bandis criterion

Based on the nonlinear Barton–Bandis(B–B)failure criterion,this study considers the system reliability of rock wedge stability under the pseudo-static seismic load.The failure probability(Pf)of the system is calculated based on the Monte−Carlo method when considering parameter correlation and variability.Parameter analysis and sensitivity analysis are carried out to explore the influence of parameters on reliability.The relationships among the failure probability,safety factor(Fs),and variation coefficient are explored,and then stability probability curves of the rock wedge under the pseudo-static seismic load are drawn.The results show that the parameter correlation of the B–B failure criterion has a significant influence on the failure probability,but correlation increases system reliability or decreases system reliability affected by other parameters.Under the pseudo-static seismic action,sliding on both planes is the main failure mode of wedge system.In addition,the parameters with relatively high sensitivity are two angles related to the joint dip.When the coefficient of variation is consistent,the probability of system failure is a function of the safety factor.

Effect of strain rate on microstructural evolution and thermal stability of 1050 commercial pure aluminum

Effects of strain rate on the microstructure evolution and thermal stability of1050commercial pure aluminum processed by means of split Hopkinson pressure bar(SHPB)and Instron?3369mechanical testing machine were investigated.Samples in the deformed state and after various annealing treatments at423?523K(150?250°C)for1h were characterized by TEM and hardness test.The result reveals that the samples in the deformed state were mainly composed of elongated subgrains/cells with high density of dislocations.Microstructures of the quasi-static compressed aluminum were quite stable throughout the temperature range studied,and no significant grain growth was observed.However,for the dynamic impacted one,recrystallized grains with an average grain size of4.7μm were evolved after annealing at523K(250°C)for1h.It is suggested that the annealing behavior of this dynamic deformed aluminum is a continuous process of grain coarsening,rather than the traditional discontinuous recrystallization for the quasi-static compressed aluminum.

Asymmetric Effects on Escape Rates of Bistable System

The asymmetric effects on the escape rates from the stable states x±in the bistable system are analyzed. The results indicate that the multiplicative noise and the additive noise always enhance the particle escape from stable states x±of bistable.However,the asymmetric parameter r enhances the particle escape from stable state x_+,and holds back the particle escape from stable state x_-.

Electrogastrography associated with symptomatic changes after prokinetic drug treatment for functional dyspepsia

AIM:To evaluate the effect of prokinetic drugs on electrogastrography(EGG) parameters according to symptomatic changes in patients with functional dyspepsia(FD).METHODS:Seventy-four patients with FD were prospectively enrolled in this study between December 2006 and December 2010.We surveyed the patients using a questionnaire on dyspeptic symptoms before and after an 8-wk course of prokinetic drug treatment.We also measured cutaneous pre-prandial and postprandial EGG recordings including percentage of gastric waves(normogastria,bradygastria,tachygastria),dominant frequency(DF),dominant power(DP),dominant frequency instability coefficient(DFIC),dominant power instability coefficient(DPIC),and the ratio of post-prandial to fasting in DP before and after the 8-wk course of prokinetic drug treatment.RESULTS:Fifty-two patients(70%) achieved symptomatic improvement after prokinetic drug treatment.Patients who had normal gastric slow waves showed symptom improvement group after treatment.Postprandial DF showed a downward trend in the symptom improvement group,especially in the itopride group.Post-prandial DP was increased regardless of symptom improvement,especially in the itopride group and mosapride group.Post-prandial DFIC and DPIC in the symptom improvement group were significantly increased after the treatment.The EGG power ratio was increased after treatment in the symptom improvement group(0.50 ± 0.70 vs 0.93 ± 1.77,P = 0.002),especially in the itopride and levosulpiride groups.CONCLUSION:Prokinetics could improve the symptoms of FD by regulating gastric myoelectrical activity,and EGG could be a useful tool in evaluating the effects of various prokinetics.

Achieving remarkable piezoelectric activity in Sb-Mn co-modified CaBi_(4)Ti_(4)O_(15) piezoelectric ceramics

CaBi_(4)Ti_(4)O_(15)(CBT)-based Aurivillius high-temperature piezoceramics with different Sb-Mn co-doping amounts were synthesized via the conventional sintering technique.The influences of doping amount on the product were studied via their crystal structure,microstructure,and piezoelectric performance.It is found that an appropriate Sb-Mn co-doping amount can effectively optimize the crystal structure and decrease the oxygen vacancy concentration in CBT ceramics,leading to enhanced electrical properties.Optimized electrical performance with a high Curie temperature(TC)of 792℃and a remarkable piezoelectric coefficient(d33)of 25 p C/N were achieved at a doping amount(x)of 0.05.Furthermore,this ceramic is found to exhibit an excellent thermal stability,with d33 retaining 88%of its original value after annealing at 600℃for 2 h.Moreover,this ceramic shows a high electrical resistivity(ρ)of 1.35×10^(8)Ω·cm with a small dielectric loss(tanδ)of 1.7%at 400℃.Because of such outstanding piezoelectric performance,it is believed that these Sb-Mn co-doped CBT ceramics could be potential candidates for high-temperature piezoelectric applications.

Efficient Mass Transport and Electrochemistry Coupling Scheme for Reliable Multiphysics Modeling of Planar Solid Oxide Fuel Cell Stack

A multiphysics model for a production scale planar solid oxide fuel cell （SOFC） stack is important for the SOFC technology, but usually requires an unpractical amount of computing resource. The major cause for the huge computing resource requirement is identified as the need to solve the cathode O2 transport and the associated electrochemistry. To overcome the technical obstacle, an analytical model for solving the O2 transport and its coupling with the electrochemistry is derived. The analytical model is used to greatly reduce the numerical mesh complexity of a multiphysics model. Numerical test shows that the analytical approximation is highly accurate and stable. A multiphysics numerical modeling tool taking advantage of the analytical solution is then developed through Fluent@. The numerical efficiency and stability of this modeling tool are further demonstrated by simulating a 30- cell stack with a production scale cell size. Detailed information about the stack performance is revealed and briefly discussed. The multiphysics modeling tool can be used to guide the stack design and select the operating parameters.

Enhanced cycling stability of Mg-F co-modified LiNi_(0.6)Co_(0.2)Mn_(0.2-y)Mg_yO_(2-z)F_z for lithium-ion batteries

The layered LiNi0.6Co0.2Mn0.2-yMgyO2-zFz（0≤y≤0.12, 0≤z≤0.08） cathode materials were synthesized by combining co-precipitation method and high temperature solid-state reaction, with the help of the ball milling, to investigate the effects of F-Mg doping on LiNi0.6Co0.2Mn0.2O）2. Compared with previous studies, this doping treatment provides substantially improved electrochemical performance in terms of initial coulombic efficiency and cycle performance. The LiNi0.6Co0.2Mn0.11Mg0.09O1.96F0.04 electrode delivers an high capacity retention of 98.6% during the first cycle and a discharge capacity of 189.7 m A·h/g（2.8-4.4 V at 0.2 C）, with the capacity retention of 96.3% after 100 cycles. And electrochemical impedance spectroscopy（EIS） results show that Mg-F co-doping decreases the charge-transfer resistance and enhances the reaction kinetics, which is considered to be the major factor for higher rate performance. It is demonstrated that LiNi0.6Co0.2Mn0.11Mg0.09O1.96F0.04 is a promising cathode material for lithium-ion batteries for excellent electrochemical properties.

Effects of time lag and stress loading rate on permeability in low permeability reservoirs

In order to study the effect of time lag and stress loading rates on rock deformation,the conventional stepped stress loading mode was changed into a continuous mode to investigate the effect of effective pressure on permeability and porosity.The time lag effect of rock deformation illustrating the relationship between changes in permeability and steady time was studied.Permeability reduction ratios were measured under different stress loading rates which were achieved by different pump rate settings.The results show that permeability and porosity gradually decrease with increases in effective pressure.Permeability at high effective pressure attains stability quickly.Steady times at low effective pressure are very long.Reduction in permeability at lower stress loading rates is small,while,in contrast,it is large at high stress loading rates.

Effects of porosity heterogeneity on chemical dissolution-front instability in fluid-saturated rocks

Homogeneity and heterogeneity are two totally different concepts in nature.At the particle length scale,rocks exhibit strong heterogeneity in their constituents and porosities.When the heterogeneity of porosity obeys the random uniform distribution,both the mean value and the variance of porosities in the heterogeneous porosity field can be used to reflect the overall heterogeneous characteristics of the porosity field.The main purpose of this work is to investigate the effects of porosity heterogeneity on chemical dissolution front instability in fluid-saturated rocks by the computational simulation method.The related computational simulation results have demonstrated that:1) since the propagation speed of a chemical dissolution front is inversely proportional to the difference between the final porosity and the mean value of porosities in the initial porosity field,an increase in the extent of the porosity heterogeneity can cause an increase in the mean value of porosities in the initial porosity field and an increase in the propagation speed of the chemical dissolution front.2) An increase in the variance of porosities in the initial porosity field can cause an increase in the instability probability of the chemical dissolution front in the fluid-saturated rock.3) The greater the mean value of porosities in the initial porosity field,the quicker the irregular morphology of the chemical dissolution front changes in the supercritical chemical dissolution systems.This means that the irregular morphology of a chemical dissolution front grows quicker in a porosity field of heterogeneity than it does in that of homogeneity when the chemical dissolution system is at a supercritical stage.

Probabilistic seismic stability of three-dimensional slopes by pseudo-dynamic approach

Probabilistic analysis is a rational approach for engineering design because it provides more insight than traditional deterministic analysis. Probabilistic evaluation on seismic stability of three dimensional (3D) slopes is studied in this paper. The slope safety factor is computed by combining the kinematic approach of limit analysis using a three-dimensional rotational failure mechanism with the pseudo-dynamic approach. The variability of input parameters, including six pseudo-dynamic parameters and two soil shear strength parameters, are taken into account by means of Monte-Carlo Simulations (MCS) method. The influences of pseudo-dynamic input variables on the computed failure probabilities are investigated and discussed. It is shown that the obtained failure probabilities increase with the pseudo-dynamic input variables and the pseudo-dynamic approach gives more conservative failure probability estimates compared with the pseudo-static approach.

Removal of Co(Ⅱ) from aqueous solution by complexation-ultrafiltration and shear stability of PAA-Co complex

Removal of Co(Ⅱ) from aqueous solutions by complexation-ultrafiltration was investigated using polyacrylic acid sodium(PAAS) as complexing agent with the help of rotating disk membrane,and the shear ability of PAA-Co complex was studied. The effects of the mass ratio of PAAS to Co(Ⅱ)(P/M) and pH on the rejection of Co(Ⅱ) were studied,and the optimum conditions were P/M=8 and pH=7. The rejection of Co(Ⅱ) was over 97% when the rotating speed of the disk(n)was less than 710 r/min at the optimum P/M and pH. The distribution of the forms of cobalt on the membrane surface was established by the membrane partition model, and the critical shear rate,the smallest shear rate at which the PAA-Co complex begins to dissociate,was calculated to be1.4×10^4 s^-1,and the corresponding rotating speed was 710 r/min.The PAA-Co complex dissociated when the shear rate was greater than the critical one. The regeneration of PAAS and recovery of Co(Ⅱ) were achieved by shear-induced dissociation and ultrafiltration.

Comparative study of effectiveness of different var compensation devices in large-scale power networks

A comparison of the effectiveness of installing reactive power compensators,such as shunt capacitors,static var compensators(SVCs),and static synchronous compensators(STATCOMs),was presented in large-scale power networks.A suitable bus was first identified using modal analysis method.The single shunt capacitor,single SVC,and single STATCOM were installed separately on the most critical bus.The effects of the installation of different devices on power loss reduction,voltage profile improvement,and voltage stability margin enhancement were examined and compared for 57-and 118-bus transmission systems.The comparative study results show that SVC,and STATCOM are expensive compared to shunt capacitor,yet the effect of installing STATCOM is better than SVC and the effect of installing SVC is better than that of shunt capacitor in achieving power loss reduction,voltage profile improvement and voltage stability margin enhancement.

Analysis of Dynamic Characteristics of the 21st Century Maritime Silk Road

The 21st century Maritime Silk Road(MSR) proposed by China strongly promotes the maritime industry. In this paper, we use wind and ocean wave datasets from 1979 to 2014 to analyze the spatial and temporal distributions of the wind speed, significant wave height(SWH), mean wave direction(MWD), and mean wave period(MWP) in the MSR. The analysis results indicate that the Luzon Strait and Gulf of Aden have the most obvious seasonal variations and that the central Indian Ocean is relatively stable. We analyzed the distributions of the maximum wind speed and SWH in the MSR over this 36-year period. The results show that the distribution of the monthly average frequency for SWH exceeds 4 m(huge waves) and that of the corresponding wind speed exceeds 13.9 ms^(-1)(high wind speed). The occurrence frequencies of huge waves and high winds in regions east of the Gulf of Aden are as high as 56% and 80%, respectively. We also assessed the wave and wind energies in different seasons. Based on our analyses, we propose a risk factor(RF) for determining navigation safety levels, based on the wind speed and SWH. We determine the spatial and temporal RF distributions for different seasons and analyze the corresponding impact on four major sea routes. Finally, we determine the spatial distribution of tropical cyclones from 2000 to 2015 and analyze the corresponding impact on the four sea routes. The analysis of the dynamic characteristics of the MSR provides references for ship navigation as well as ocean engineering.