小电流接地选线装置中模数变换板的配置

本文主要介绍小电流接地选线装置中,高性能多路A/D模数变换板的配置、设计及性能技术指标。该A/D变换板是小电流接地微机选线装置中的重要部件,由于设计时着重考虑了其通用性和抗干扰性,所以它不仅适用于环境较恶劣的电力系统,也可用于各种性能较高、速度较快的微机多路采集系统。

DM-10全固态中波广播发射机模数转换板的原理分析与故障处理

模数转换板是全固态中波广播发射机的重要组成部分,对其进行研究有助于全面掌握中波发射机的工作原理,为故障分析与处理打下扎实的理论基础。本文以陕西循天公司生产的DM-10全固态中波广播发射机为例,阐述了为什么要进行模数转换,并对模数转换板进行了整体分析,还对常见故障进行了分析处理,旨在将模数转换板详细的呈现出来,为学习掌握中波发射机提供些许参考。

中波发射机模数转换板的故障分析与处理

全固态中波广播发射机是目前中波广播使用最多、普及度最高的发射机,内部功能齐全,整机效率高、质量好、稳定度高,有效提高了无线发射台站播出的稳定性和安全性,各功能板集成化,有利于技术人员的维护与故障处理。文章以循天公司生产的全固态中波广播发射机为例,分析了模数转换板的工作原理及故障处理方法,以期为学习掌握中波发射机提供参考。

一种实用的模数转换A／D板的研制

本文较详细地介绍了所设计的Ａ／Ｄ板的硬件组成及应用软件。实践证明：该板是最廉价的又是最实用的。

Mathe matical model and calculation for heat transfer during condensation on surfaces of corrugated plates

A mathematical model was established for condensation on surfaces of verticalcorrugated plates based on the mechanism of heat transfer enhancement to thin down the liquid filmdue to surface tension effect between corrugated plate surfaces and liquid films. The relative heattransfer coefficients of condensation on corrugation plates were calculated in contrast withequivalent vertical plane ones. The heat transfer enhancement effects for the main geometricparameters such as pitch, height, corrugation angle, tilt angle, and fillet radii of corrugationswere analyzed to guide the optimization of corrugation structure for application. A two-scalecorrugation is suggested, which can compromise both the enhanced heat transfer effect and adequatecross section area for flows, and it makes the heat transfer coefficient 1 to 2 times more than thatof an equivalent plane one.

Identification of material parameters from punch stretch test

To accurately describe the mechanical properties of aluminium alloy sheet during deformation, an inverse identification was presented to deal with material parameters from the popular punch stretch test. In the identification procedure, the optimization strategy combines finite element method （FEM）, Latin hypercube sampling （LHS）, Kriging model and multi-island genetic algorithm （MIGA）. The proposed approach is used on material parameter identification of aluminium alloy sheet 2D12. The anisotropic yield criterion Hill’90 is discussed. The results show that the Hill’90 anisotropic yield criterion with identified anisotropic material parameters has a good potential in describing the anisotropic behaviours. It provides a way to obtain the material parameters for FE simulations of sheet metal forming.

FINITE ELEMENT MODELING OF MODERATELY THICK COMPOSITE PLATE WITH PIEZOELECTRIC SENSORS AND ACTUATORS

A rectangular finite element for laminated plate with bonded and/or embedded piezoelectric sensors and actuators is developed based on the variational principle and the first order shear deformation theory. The element has four-node, 20-degrees-of-freedom with one potential degree of freedom for each piezoelectric layer to represent the piezoelectric behavior. The higher order derivation of deflection is obtained by using the normal rotation expressions to take the effects of transverse shear deformation into considerations. The finite element can accurately simulate the deformation of both thin and moderately thick plates. A Fortran program is written and a number of benchmark tests are exercised to verify its effectiveness. Results are compared well with the existing data. The unbalanced composite with piezoelectric layers is then analyzed by using the model. Results show that the changes of the ratio between the thickness of positive angle layers and the negative angle layers have an effect on the deformation of the structure under the same electric loading.

Influence of variables in deep drawing of AA 6061 sheet

Deep drawing is one of the most important processes for forming sheet metal parts.It is widely used for mass production of cup shapes in automobile,aerospace and packaging industries.Cup drawing,besides its importance as forming process,also serves as a basic test for the sheet metal formability.The effect of equipment and tooling parameters results in complex deformation mechanism.Existence of thickness variation in the formed part may cause stress concentration and may lead to acceleration of damage.Using TAGUCHI's signal-to-noise ratio,it is determined that the die shoulder radius has major influence followed by blank holder force and punch nose radius on the thickness distribution of the deep drawn cup of AA 6061 sheet.The optimum levels of the above three factors,for the most even wall thickness distribution,are found to be punch nose radius of 3 mm,die shoulder radius of 8 mm and blank holder force of 4 kN.

Simulation of Airblast Load and Its Effect on RC Structures

In the analysis of a structure subjected to an explosion event, the determination of the blast load constitutes a crucial step. The effect of the blast load on the structure depends not only on the peak shock overpressure, but also the impulse (hence the duration). For structures with a regular geometry, the blast load may be fairly well estimated using appropriate empirical formulae; however, for more complex situations, a direct simulation using appropriate computational techniques is necessary. This paper presents a numerical simulation study on the prediction of the blast load in free air using a hydrocode, with focus on the sensitivity of the simulated blast load to the mesh grid size. The simulation results are compared with empirical predictions. It is found that the simulated blast load is sensitive to the mesh size, especially in the close-in range, and with a practically affordable mesh grid density, the blast load tends to be systematically underestimated. The study is extended to internal blast cases. An example concrete slab under internal explosion is analyzed using a coupled analysis scheme. The internal blast load from the simulation is examined and the response of the RC slab is commented.

Design for CNN Templates with Performance of Global Connectivity Detection

The cellular neural/nonlinear network (CNN) is a powerful tool for image and video signal processing,robotic and biological visions. This paper discusses a general method for designing template of the global connectivitydetection (GCD) CNN, which provides parameter inequalities for determining parameter intervals for implementing thecorresponding functions. The GCD CNN has stronger ability and faster rate for determining global connectivity in binarypatterns than the GCD CNN proposed by Zarandy. An example for detecting the connectivity in complex patterns isgiven.

Spallation Mechanism of RC Slabs Under Contact Detonation

The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely. Correctly predicting the damage caused by any potential contact detonation can lead to better fortification design to withstand the blast Ioadings. It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls. Existing studies on this topic often employ simplified material models and 1D wave analysis, which cannot reproduce the realistic response in the spallation process. Numerical simulations are therefore carried out under different contact blast Ioadings in the free air using LS-DYNA. Sophisticated concrete and reinforcing bar material models are adopted, taking into account the strain rate effect on both tension and compression. The erosion technique is used to model the fracture and failure of materials under tensile stress. Full processes of the deformation and dynamic damage of reinforced concrete （RC） slabs and plain concrete slabs are thus observed realistically. It is noted that with the increase of quantity of explosive, the dimensions of damage crater increase and the slabs experience four different damage patterns, namely explosive crater, spalling, perforation, and punching. Comparison between the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent, and meanwhile attenuate the ejection velocity and decrease the size of the concrete fragments. Therefore, optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.

Globulin-platelet model predicts minimal fibrosis and cirrhosis in chronic hepatitis B virus infected patients

AIM： To establish a simple model consisting of the rou- tine laboratory variables to predict both minimal fibrosis and cirrhosis in chronic hepatitis B virus （HBV）-infected patients. METHODS： We retrospectively investigated 114 chron- ic HBV-infected patients who underwent liver biopsy in two different hospitals. Thirteen parameters were analyzed by step-wise regression analysis and correla- tion analysis. A new fibrosis index [globulin/platelet （GP） model] was developed, including globulin （GLOB） and platelet count （PLT）. GP model = GLOB （g/mL） x 100/PLT （x 109/L）. We evaluated the receiver operating characteristics analysis used to predict minimal fibrosis and compared six other available models. RESULTS： Thirteen clinical biochemical and hemato- logical variables [sex, age, PLT, alanine aminotransfer- ase, aspartate aminotransferase （AST）, albumin, GLOB, total bilirubin （T.bil）, direct bilirubin （D.bil）, glutamyl-transferase, alkaline phosphatase, HBV DNA and pro- thrombin time （PT）] were analyzed according to three stages of liver fibrosis （F0-F1, F2-F3 and F4）. Bivariate Spearman＇s rank correlation analysis showed that six variables, including age, PLT, T.bil, D.bil, GLOB and PT, were correlated with the three fibrosis stages （FS）. Cor- relation coefficients were 0.23, -0.412, 0.208, 0.220, 0.314 and 0.212; and P value was 0.014, 〈 0.001, 0.026, 0.018, 0.001 and 0.024, respectively. Univariate analysis revealed that only PLT and GLOB were signifi- cantly different in the three FS （PLT： F = 11.772, P 〈 0.001; GLOB： F = 6.612, P = 0.002）. Step-wise multiple regression analysis showed that PLT and GLOB were also independently correlated with FS （R2 = 0.237）. By Spearman＇s rank correlation analysis, GP model was significantly correlated with the three FS （r = 0.466, P 〈 0.001）. The median values in F0-F1, F2-F3 and F4 were 1.461, 1.720 and 2.634. Compared with the six available models （fibrosis index, AST-platelet ratio, FIB-4, fibrosis-cirrhosis index and age-AST model and age-PLT ratio）, GP model showed a highest correlation coefficient. The sensitivity and positive predictive value at a cutoff value 〈 1.68 for predicting minimal fibrosis F0-F1 were 72.4% and 71.2%, respectively. The speci- ficity and negative predictive value at a cutoff value 〈 2.53 for the prediction of cirrhosis were 84.5% and 96.7%. The area under the curve （AUC） of GP model for predicting minimal fibrosis and cirrhosis was 0.762 [95% confidence interval （CI）： 0.676-0.848] and 0.781 （95% CI： 0.638-0.924）. Although the differences were not statistically significant between GP model and the other models （P all 〉 0.05）, the AUC of GP model was the largest among the seven models. CONCLUSION： By establishing a simple model using available laboratory variables, chronic HBV-infected patients with minimal fibrosis and cirrhosis can be di- agnosed accurately, and the clinical application of this model may reduce the need for liver biopsy in HBV- infected patients.

谈谈DAM中波广播发射机的调试维护工作

DAM中波发射机的电路结构和工作原理比较复杂,本文根据实际维护情况对该类发射机的主要电路板的维护工作进行了分类分析,并对需要调整的部分电路板的调试工作进行了细致的阐述。

Bankruptcy Probability and Stock Prices： The Effect of Altman Z-Score Information on Stock Prices Through Panel Data

There is an extensive branch of literature that examines the success of Altman＇s Z-score in predicting bankruptcy or financial distress. The goal of this research paper is to investigate the stock price performance of firms that exhibit a large probability of bankruptcy according to the model of Airman. Regardless of the validity of Airman＇s Z-score, we utilize a new empirical design that relates stock price movements to Altman＇s Z-score. We focus and examine, through the methodology of panel data, whether stocks that have a high probability of bankruptcy underperform stocks with a low probability of bankruptcy or if there are differences in the way the markets react to the financial health of the sample firms.

DAM 10 kW循环调制数字调幅广播发射机调试方法分析

DAM 10 kW循环调制数字调幅广播发射机投入使用之后表现出了整机效率高的特点,在整个运行的过程中有着十分稳定的功能性,本文分析DAM 10 kW循环调制数字调幅广播发射机的性能特征,并进一步探究DAM 10 kW循环调制数字调幅广播发射机调试方法,希望本文的观点能为关注此话题的研究者提供参考意见。

Numerical simulation of grooving method for floor heave control in soft rock roadway

Grooving method can restrain the deformation and destruction of surrounding rock by transferring the maximum stress to deep rock,bringing about the effective control for floor heave in soft rock roadway. Based on this important effect,and to discuss the relationship between cutting parameters and pressurerelief effect,this paper carried out a numerical simulation of grooving along bottom slab and two sides of gateway with finite difference software FLAC^（2D）.The results show that the control effect on floor heave in soft rock tunnel can be improved by selecting appropriate cutting parameters.Appropriately increasing the crevice depth in the middle of the floor can improve the stress state of bottom slab by stress transfer. So the floor heave can be more effectively controlled.To lengthen the crevice in the corners of roadway can simultaneously transfer the maximum stresses of bottom slab and two sides to deep rock,and promote the pressure-relief effect.Extending the crevice length and crevice width on both sides within a certain range can decrease the stress concentration in the corners of roadway,and reduce the deformation of two sides.The cutting position beneficial to restrain the floor heave is close to the bottom slab.

Numerical simulation on the risk of roof water inrush in Wuyang Coal Mine

Water-inrush in mine is one of the mine disasters caused by mining.In order to assess the risk of roof water-inrush in Wuyang Coal Mine based on the geological material of the coal mine,we built numerical models for the roof fracture and seepage development rule by using RFPA2D and COMSOL respectively,to analyze the changes in fracture zone,stress,water pressure and seepage vector with the advancement of working face,and compared the results with the field investigated data.The numerical simulation results indicate that:(1) with the advancement of the working faces,the stress relief range and fracture zone in the overlying strata increased rapidly up to about 90 m,and then tended to remain constant,reaching a final height of about 95 m which agrees with the field investigation;(2) the seepage flow constantly increased with a larger flow volume both in the front and rear area,where the stress concentration are the most serious.