随机振动响应峰值因子的预计理论研究

简要介绍了超越概率理论、超越频次理论、损伤等效理论和功率谱密度(PSD)的时域拟合理论等4种常见的峰值因子预计理论,并基于三角级数提出了一种新的预计理论。结合试飞加速度数据样本,对比分析超越频次理论、PSD时域拟合理论和三角级数理论的预估精度。研究表明,上述4种常见的预计理论本质上属于统计学理论;PSD时域拟合理论预计的峰值因子波动较大,峰值因子与归一化次数满足高斯分布;三角级数理论的预估精度较高,但缺乏离散峰个数的合理判据。

煤矿开采沉陷预计理论与方法研究

煤矿的开采要建立在安全的基础上,开采沉陷对矿区开采安全的影响非常大,本文针对矿区开采沉陷的主要影响因素、预计参数确定以及误差进行分析与讨论,研究开采沉陷预计方法中的优点与不足。

开采速度对地表建筑物损害影响分析

以Knothe动态预计理论为基础 ,引入岩石流变变形力学模型 ,分析回采工作面的开采速度变化、停采对地面建筑物保护的影响。分析结果表明 :在保护建筑物下应保持匀速的开采速度 ;回采工作面停采及开采速度的变化都会引起建筑物的破坏应力增加 ,对地面建筑物保护非常不利 ;在特定的地质采矿条件下 ,存在一个对建筑物不利的开采速度危险区域 ,避开这一开采速度区域开采 。

APPLICATION OF MECHANICAL RELIABILITY PREDICATION BASED ON FUZZY THEORY

Mechanical reliability prediction (MRP) is an important task of mechanical reliability design. In the initial design stage (IDS), the lack of reliability data and some fuzzy characteristics of MRP make this work hardness. Because fuzzy synthetical assessment (FSA) can well utilize expert′s experience and fuzzy data, it is used to assess the influence factors of reliability. On the basis of the assessed results, the predicted value of reliability is inferred by the fuzzy inference system (FIS). This approach particularly suits to predict the reliability of complex machinery (including other products) in IDS, so that it can remedy some defects of the existing methods. An example is discussed to interpret how to utilize it.

Effects of a theory of planned behavior-based intervention on breastfeeding behaviors after cesarean section:A randomized controlled trial

Objectives:To examine the efficacy of an intervention based on the theory of planned behavior(TPB)in improving breastfeeding behavior among women with cesarean sections(C-sections).Methods:This research was a randomized controlled trial.Women with planned elective C-sections were recruited to participate in a randomized controlled trial between June and September 2020.One hundred thirty-two women were divided randomly into the intervention(n=66)and control group(n=66)by systematic random sampling.In the intervention group,an intervention project was implemented after Keywords:Breastfeeding Cesarean section Intervention studies Theory of planned behavior the C-section to establish positive breastfeeding attitudes,cultivate supportive subjective norms,enhance perceived behavioral control,and strengthen breastfeeding intention to change behaviors.Those in the control group received routine pre-and post-delivery care.Exclusive breastfeeding rate and breast problem were collected at 5 days,2 weeks,and 1 month after C-section.The modified Breastfeeding Attrition Prediction Tool(BAPT)on the first day in the hospital,two weeks,and one month after C-section and Numerical Rating Scale(NRS)24 h postoperatively were used to compare the intervention effect between the two groups.Results:After the intervention,the intervention group had significantly higher exclusive breastfeeding rates than the control group at five days(86.4%vs.60.6%),two weeks(77.3%vs.57.6%),and one month(74.2%vs.50.0%)after the C-section.Besides,the intervention group was less likely to have sore nipples at five days(6.1%vs.18.2%in the control group,P<0.05)and two weeks(9.1%vs.12.1%in the control group,P<0.05).After two weeks of intervention,attitude scores(90.64±8.31 vs.87.20±8.15,P<0.05),subjective norm scores(88.07±24.65 vs.79.42±19.47,P<0.05)and behavior control scores in the intervention group were significantly higher than those in the control group.After one month of intervention,attitude scores(90.34±10.35 vs.84.22±10.51,P<0.05)and behavior control scores(43.13±5.02 vs.39.15±4.69,P<0.05)in the intervention group were significantly higher than those in the control group,which resulted in the higher breastfeeding intention in the intervention group.Conclusion:This study indicated that the TPB-based interventions effectively improved women's breastfeeding behaviors after C-sections.

Electromagnetic radiation early warning criterion of rock burst based on statistical theory

Rock bursts are serious natural disasters encountered worldwide in coal mining and rock engineering.In order to forecast rock bursts more effectively,a new rock burst forecasting index E,consisting of intensity and the number of pulses,is proposed,on the basis of abnormal characteristic symptoms of electromagnetic radiation(EMR) generated before rock bursts,combined with statistical theory.The index is distributed as a χ2 distribution with 2 degrees of freedom,i.e.,E～χ 2(2).Via this index,a quantitative comprehensive forecasting criterion of EMR was initially established.E values were calculated when the occurrence probability of the occurrence of a rock burst was 50%,70% and 90%.Appropriate measures should be taken when using these values on the scene.Using EMR data collected in the Nanshan Mine of the Hegang mining area,we verified that the analytical result were consistent with actual situations.This index is of theoretical importance and as a reference for forecasting rock bursts in coal mines.

Mine water discharge prediction based on least squares support vector machines

In order to realize the prediction of a chaotic time series of mine water discharge,an approach incorporating phase space reconstruction theory and statistical learning theory was studied.A differential entropy ratio method was used to determine embedding parameters to reconstruct the phase space.We used a multi-layer adaptive best-fitting parameter search algorithm to estimate the LS-SVM optimal parameters which were adopted to construct a LS-SVM prediction model for the mine water chaotic time series.The results show that the simulation performance of a single-step prediction based on this LS-SVM model is markedly superior to that based on a RBF model.The multi-step prediction results based on LS-SVM model can reflect the development of mine water discharge and can be used for short-term forecasting of mine water discharge.

顶板导水裂缝带高度数值模拟研究

针对工作面回采后,顶板导水裂缝带发育高度规律,为掌握地下开采引起的岩层移动规律和确定导水裂缝带高度参数,以某矿为实际工程背景,采用数值模拟、理论预计两种方法,分别对该矿工作面回采后顶板导高进行探究,并将两者结果进行对比分析。结果表明数值模拟导水裂缝带发育高度为24.32m;而理论预计的结果为27.34m;两者结果大致相当,综合确定该矿最大导水裂缝带发育高度为24.32m,为煤层安全开采提供了科学决策依据。

Spectrum sensing sequence prediction in cognitive radio networks

Spectrum sensing is one of the key issues in cognitive radio networks. Most of previous work concenates on sensing the spectrum in a single spectrum band. In this paper, we propose a spectrum sensing sequence prediction scheme for cognitive radio networks with multiple spectrum bands to decrease the spectrum sensing time and increase the throughput of secondary users. The scheme is based on recent advances in computational learning theory, which has shown that prediction is synonymous with data compression. A Ziv-Lempel data compression algorithm is used to design our spectrum sensing sequence prediction scheme. The spectrum band usage history is used for the prediction in our proposed scheme. Simulation results show that the proposed scheme can reduce the average sensing time and improve the system throughput significantly.

Mechanism and practice of rock control in deep large span cut holes

Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pre- stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control prin- ciples and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.

A TREND DISPLACEMENT ANALYSIS FOR SPACE AND TIME ON XINTAN LANDSLIDE

This paper, having made systematic trend analysis on the front and rear segments of Xintan landslide for space and time respectively by using matbematical statistical principles,discovered that there is obvious trend displacement Of the monitoring points in the rear margin area of the slope and the rates of trend displacement gradually increase with time whereas there is no trend displacement of the monitoring points in the front margin area. This result suggests that the rear margin area of segment is an area of overall sliding and is transforming towards destabilization whereas the front margin area is an area of relative stability. This analytical result well coincides with the conclusion of evaluation on dynamic stability. The analytical result mentioned above shows that the medium to short term forecast and prediction of slope stability can be made by using trend displacement analysis technique in order to achieve the goal of timely evaluation and prevention.

Theoretical Study on N=126 Shell Evolution

The nuclei around magic number N=126 are investigated in the deformed relativistic mean field (RMF)model with effective interactions TMA.We focus investigations on the N=126 isotonic chain.The N=126 shellevolution is studied by analyzing the variations of two-neutron (proton) separation energies,quadruple deformations,single particle levels etc.The good agreement of two-neutron separation energies between experimental data and calculatedvalues is reached.The RMF theory predicts that the sizes of N=126 shell become smaller and smaller withthe increasing of proton number Z.However,the N=126 shell exists in our calculated region all along.According tothe calculated two-proton separation energies,the RMF theory suggests ^(220)Pu is a two-proton drip-line nucleus in theN=126 isotonic chain.

From electronic excited state theory to the property predictions of organic optoelectronic materials

We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.

Investigations on Several Mechanical Problems in Windblown Sand Movement

It is very necessary for investigation on mechanism of windblown sand movement to understand and find out effective measures of preventing and reducing windblown sand, This also deals with some general features and hot spots in the scientific forelands. such as multi-scale problems. interactions among. multi-physical-fields, randomness and nonlinearity as well as complex systems. In recent years, a series of experiments in wind tunnels and theoretical modeling as well as computer simulation have been taken by our research group （the Laboratory of Environmental Mechanics on Windblown Sand Movement in Lanzhou University ）in a cross-disciplinary （mechanics and geography） viewpoint. Several original and essential studies were explored such as the main regularities of charges on sand particles, the mechanisms of electric field in windblown sand flux, the effects induced by the electric field on the flux, the microwave propagations, the evolution process of windblown and flux under mutual couple interations among several physical fields, and the simulation of the main features of Aeolian sand ripples.

Preliminary Lattice Study of I=0 KK Scattering

We deliver the realistic ab initio lattice investigations of KK^- scattering. In the Asqtad-improved staggered dynamical fermion formulation, we carefully measure KK^- four-point function in the I=0 channel by moving wall sources without gauge fixing, and clearly find an attractive interaction in this channel, which is in agreement with the theoretical predictions. An essential ingredient in our lattice calculation is to properly treat the disconnected diagram. Moreover, we explain the difficulties of these lattice calculations, and discuss the way to improve the statistics. Our lattice investigations are carried out with the MILC 2 ＋ 1 gauge configuration at lattice spacing a ≈ 0.15 fro.

Charmed-Hadron Production in Υ(1S) Semi-inclusive Decay

In the framework of the NRQCD factorization formalism,we calculate the decay rate for the process Υ(1 S) → ccgg to the next-to-leading order(NLO) in the relative velocity v of the b quark in the bottomonium rest frame.We also study the momentum distributions of the charm quark and the charmed-hadron in the decay.The momentum distribution of the charmed-hadron is obtained by convolving the charm quark momentum distribution with a fragmentation function of the charm quark into the hadron.In addition,we fit the nonperturbative NRQCD matrix element v 2 Υ through comparing the theoretical prediction with the measurement from the BaBar collaboration for the decay rate of Υ(1 S) → D + X.In return,taking this matrix element as an input parameter,we predict the decay rates as well as the momentum distributions for a collection of charmed-hadrons in the process Υ(1S) → ccgg → hX.