A theoretical model for impact protection of flexible polymer material

The relationship between the protective performance of flexible polymer material and material parameters(elasticmodulus,viscosity coefficient)is explored,an impact collision motion equation between two bodies is establishedfrom the viscoelastic material constitutive,and the relationship between the kinematic response and the materialparameters is obtained.Based on the Kelvin constitutive model,a theoretical model for impact between the pro-tective body and the protected body is established,then the dynamic response is obtained.The feasibility of themodel was verified by drop hammer experiment,and the material parameters(elastic modulus,viscosity coeffi-cient)were obtained by formula.The model is discretized and the relationship between local impact response andmaterial parameters is analyzed.The discussion results on the relationship between the impact response and theprotective material performance indicate that adjusting the elastic modulus,viscosity coefficient,and thicknessof the protective material can effectively improve protective effect.

Elastic Properties of Potassium Halides under Pressure

The moderate-pressure elastic properties of potassium halides KX （X=F, Cl, Br） was studied theoretically using the density functional theory （DFT） with normconserving pseudopotentials method. The phase transformation from the B1 phase （NaCl-type structure） to the denser B2 phase （CsCl-type structure） occurred at 7.7, 3.46 and 2.96 GPa for KF, KCI and KBr, respectively. The elastic stiffness coefficients and bulk modulus of these materials were calculated as function of hydrostatic pressure and compared with both the experimental and theoretical values.

Elastically restrained Bernoulli-Euler beams applied to rotary machinery modelling

Facing the lateral vibration problem of a machine rotor as a beam on elastic supports in bending,the authors deal with the free vibration of elastically restrained Bernoulli-Euler beams carrying a finite number of concentrated elements along their length.Based on Rayleigh’s quotient,an iterative strategy is developed to find the approximated torsional stiffness coefficients,which allows the reconciliation between the theoretical model results and the experimental ones,obtained through impact tests.The mentioned algorithm treats the vibration of continuous beams under a determined set of boundary and continuity conditions, including different torsional stiffness coefficients and the effect of attached concentrated masses and rotational inertias, not only in the energetic terms of the Rayleigh’s quotient but also on the mode shapes,considering the shape functions defined in branches.Several loading cases are examined and examples are given to illustrate the validity of the model and accuracy of the obtained natural frequencies.

Analysis on the Economical and Intensive Utilization of Regional Construction Land in Zunyi City of Guizhou Province

Taking Zunyi City of Guizhou Province as research area, the research performed spatial dynamic analysis and elastic coefficient method to evaluate the e- conomical and intensive utilization of the regional construction land, and to discuss the decision direction for economical and intensive utilization of the regional con- struction land. The results showed that, the population based land utilization both in Zunyi and the city districts and counties indicated extensive trend. The economy- based land utilization in Zunyi City, as well as in Huichun, Zunyi and Tongzi County presented intensive trend, however the other districts and counties were in extensive tendency. It concluded that the economical and intensive utilization of construction land should be focused on the rural collective construction land, and the potential tapping of rural collective construction land in rocky desertification area should be the first priority, otherwise, the regional economic development was unbalanced be- tween different district and county in Zunyi.

Dynamic Analysis of Supply and Demand Coupling of Ecosystem Services in Loess Hilly Region:A Case Study of Lanzhou,China

The relationship between the supply and demand for ecosystem services(ESs)is a key issue for the rational allocation of natural resources and optimisation of sustainable development capacity.This paper investigateed the dynamic evolution features of supply and demand of four ESs in Lanzhou of China,namely,water supply,food supply,carbon fixation and soil retention services.The crosssectional data of 2005 and 2017 were used for calculating ESs value and its supply and demand through ArcGIS software,InVEST model,elastic coefficient model and coupling coordination model.Results showed that:1)from 2005 to 2017,the supply of water supply services increased,the demand of soil retention services decreased,and the supply and demand of food supply and carbon fixation services increased.The high-value areas of service supply were mainly distributed in the rocky mountain areas in the southeast and northwest with high vegetation coverage,while the high-value areas of demand were mainly distributed in the urban areas and surrounding areas with high population density.2)There were five different types of coupling relations.Water supply service was dominated by a negative coupling type D,which means that the decrease in demand for ESs has had a positive response on the supply of ESs.Negative coupling type C was the main type of food supply and carbon fixation services,which means that the increase in demand for ESs has had a negative response on the supply of ESs.All three services were supplemented by a positive coupling type A,which means that the increase in demand for ESs has had a positive response on the supply of ESs.Soil retention service generally exhibits a positive coupling type B,which means that the decrease in demand for ESs has had a negative response on the supply of ESs.3)Over the past 12 yr,the coordination degree of supply and demand of water supply,food supply and soil retention services decreased,and the coordination degree of carbon fixation service increased.Various types of ES had a low degree of coupling and coordination,showing different characteristics of temporal and spatial evolution.The areas with imbalanced ESs supply and demand were mainly distributed in urban areas dominated by construction land.The research results are valuable to the optimisation of urban and rural ecological environments and the sustainable development of territory space under the framework of ecological civilisation,including similar ecologically vulnerable areas in other developing countries.

Endoscopic ultrasound elastography for evaluation of lymph nodes and pancreatic masses:A multicenter study

AIM:To evaluate the ability of endoscopic ultrasound(EUS) elastography to distinguish benign from malignant pancreatic masses and lymph nodes.METHODS:A multicenter study was conducted and included 222 patients who underwent EUS examination with assessment of a pancreatic mass(n=121) or lymph node(n=101).The classification as benign or malignant,based on the real time elastography pattern,was compared with the classif ication based on the B-mode EUS images and with the fi nal diagnosis obtained by EUS-guided fi ne needle aspiration(EUS-FNA) and/or by surgical pathology.An interobserver study was performed.RESULTS:The sensitivity and specificity of EUS elastography to differentiate benign from malignant pancreatic lesions are 92.3% and 80.0%,respectively,compared to 92.3% and 68.9%,respectively,for the conventional B-mode images.The sensitivity and specificity of EUS elastography to differentiate benign from malignant lymph nodes was 91.8% and 82.5%,respectively,compared to 78.6% and 50.0%,respectively,for the B-mode images.The kappa coefficient was 0.785 for the pancreatic masses and 0.657 for the lymph nodes.CONCLUSION:EUS elastography is superior compared to conventional B-mode imaging and appears to be able to distinguish benign from malignant pancreatic masses and lymph nodes with a high sensitivity,specificity and accuracy.It might be reserved as a second line examination to help characterise pancreatic masses after negative EUS-FNA and might increase the yield of EUS-FNA for lymph nodes.

Quantitative Assessment of the Impact of China's Direct Grain Subsidies on Grain Yield--Based on the Empirical Analysis of Panel Data Pertaining to 29 Provinces in the Period 2004-2007

We build the influence function empirical model of China's grain production at the present stage in view of the factors influencing direct grain subsidies,using Cobb-Douglas production function model.And we estimate the elasticity coefficient of impact of China's direct grain subsidies on grain yield,using the panel data pertaining to 29 provinces in the period 2004-2007;comparatively analyze the validity and limitation of policy factors of direct grain subsidies on China's grain yield.The results show that at the present stage,the elasticity coefficient of impact of China's direct grain subsidies on grain yield is 0.002 3,and under the existing subsidy system and level,direct grain subsidies play a positive role in increasing grain yield,but the role is limited;the elasticity coefficient of impact of the food price on grain yield is much larger than that of impact of direct grain subsidies on grain yield.Therefore,the government should strengthen and improve direct grain subsidy policies;in the mean time,pay full attention to the use of market mechanism to consolidate the basic role of the food price in promoting food security to a great extent.

Techno-Economic Assessment of Non-Revenue Water: A Case Study at AER, GWCL

This study utilizes multiple regression analysis and the technique for computing economies of scale to evaluate the dynamics of NRW in the AER of GWCL. Data on monthly total production, billed consumption, total revenue, total production cost and the volume of NRW spanning the period January 2015 to June 2019, was obtained from the headquarters of AER and used for the analysis. The study showed that NRW averaged 59.3% for the period under consideration, which far exceeds the 25% threshold set by the World Bank for developing economies. It was also established that a fairly inelastic relationship exists between NRW and total revenue. Results further show that resources are not optimally used in the AER as proof of diseconomies of scale was observed.

Study of the Influence of Nanoparticles on the Molecular Model of an Ideal Fluid

In the article a molecular model of oil with nanoparticles on the basis of the model of ideal fluid is considered. It is assumed that the molecular model of the oil can be represented as a homogenous distribution of identical molecules in space. It is assumed that the central interaction between the oil molecules and nanoparticles, results in a change of the model parameters. It is shown that for an ideal fluid the effect of nanoparticles is reduced to a change of the coefficient at the pressure.

Modeling the Process of Transportation of Seed Cotton through the Parameters of the Food Zone

In the process of separating the fiber from the seed, the density of the seed roll in the roll box of the saw gin is constantly changing. With an increase in the density of the seed roll, the quality indicators of fiber and seed deteriorate, energy consumption increases, machine breakdowns increase, and with a decrease in density, the productivity of the machine decreases. For this reason, the regulation of the density of the seed roll is one of the important problems in the ginning process. For this, the speed of rotation of the feed rollers changes, which, with an increase in speed, the mass of cotton increases, and with a decrease, it decreases. Thus, the density of the seed roll is controlled. The article describes the problem of regulating the density of a seed roll in a saw gin of the DP series, an overview of the work on regulating the operation of the machine is given. In this work, the force of cotton pressure between two feed rollers is also theoretically investigated. Graphs of changes in the force of cotton pressure between two rollers are plotted depending on various initial pressure forces. The results of the study will be used in the further improvement of the cotton feeding regulation in order to maintain the optimum density of the seed roll, which will preserve the quality of the fiber and seeds while increasing the productivity of the machine.

Microstructure, domain structure, ferroelectric and piezoelectric properties of textured bismuth-containing ceramics

In this report,the processes of texture formation in grain-oriented ferroelectric ceramics based on layer-structured ferroelectric Bi_(4)Ti_(3)O_(12)(LSBT)prepared by hot forging method are considered.The microstructural and X-ray methods revealed the axial textured formation in ferroelectric ceramic that are used to estimate the orientation factor of ceramics.For the first time,the domain structure changes when poling the anisotropic ferroelectric ceramics are investigated.The anisotropy of electromechanical,piezoelectric and ferroelectric properties of ferroelectric ceramics due to the crystal texture existence in it is studied.The aim of this study is to study the processes of crystalline texture formation in polycrystalline BLSF and to establish the dependence of the electrophysical properties of ceramics on the degree of texturing.Ceramics were textured using the hot stamping(HS)method developed at the Research Institute of Physics.The mechanism of the method is that the workpiece is subjected to uniaxial pressure and free radial deformation occurs due to the plastic flow of the material until the workpiece fills the free volume of the mold,which is created by placing the workpiece in the mold with a gap.The study of the microstructure of ceramics showed that an increase in the firing temperature in the range 950-1050℃ causes a sharp decrease in porosity and increases the density to 7.95 g/cm^(3),which is 98%of theoretical.An X-ray analysis was performed and microstructural studies were carried out,which revealed the formation of an axial texture in ceramics.The features of the switching processes of textured ceramics are revealed.The characteristics of the polarization switching of ceramics in the directions parallel and perpendicular(⊥)of the pressure axis during hot processing were obtained from the dielectric hysteresis P(E)loops,i.e.,axis axial texture.The⊥-cut ceramics are characterized by a more complete polarization switching,which is associated with the additional orientation of the(001)crystallographic planes in the textured material,as well as the presence of a threshold switching field.In the temperature range from-196 to+600℃,the anisotropy of the electro physical properties of ceramics due to the presence of a crystalline texture in it was studied.The dielectric constant,electrical conductivity,piezoelectric and elastic coefficients were measured for sections of ceramics of different orientations relative to the axis of the texture.The anisotropy of the dielectric constant and electrical conductivity manifests itself weakly at room temperature and increases sharply when approaching the Curie temperature.In the temperature range+20-400℃,the high thermal stability of the piezoelectric module d_(33),measured by the quasistatic method,was established.

Rationality and Sensitivity of Resource Inputs on Outputs in Chaohu City

Here, we estimate the rationality of specific agricultural inputs and discuss the sensitivity of integrated agricultural output to various resources input for Chaohu City, China. We used two parameters, marginal output and elastic coefficient, and the Technique for Order Preference by Similarity to Ideal Solution （TOPSIS） method, which has an unambiguous geometric meaning and is simple and convenient, to integrate various output and input. The results indicate that for most of 2001-2009, agricultural inputs rose except that the number of people engaged in agricultural production fell. Although integrated agriculture output increased, the proportion of resources with a negative utilization efficiency was 23.82% from 2001 to 2009. Integrated output was more sensitive to agricultural pesticide, the irrigation ratio and the use of plastic film. Integrated outputs may be increased by moderate decreases in input. This type of agricultural production meets the requirements of resource saving and is a sustainable mode of resource utilization.

Grain Production Driven by Variations in Farmland Use in China:An Analysis of Security Patterns

自从1978年改革开放以来,随着经济的迅速发展,中国的耕地利用格局发生了很大的变化。耕地数量和质量的变化直接导致粮食生产的变动。本文利用来自政府部门的农业统计数据,分析了1978-2004年间中国耕地利用水平的时空动态格局,并通过构建"粮耕弹性系数"来反映耕地利用变化与粮食生产的互动关系。研究结果表明:耕地投入的增加和质量的提升在一定程度上缓解了1978年以来我国耕地资源严重流失给粮食生产安全带来的压力;自改革开放以来,中国耕地利用水平呈现由经济快速发展带来的普遍性提升局面,并随着经济发展程度由东南沿海向内陆递减,耕地利用水平的提升速率也呈现由东南沿海向内陆梯级递减态势。然而,耕地集约利用程度的不断提升,并不一定会带来粮食产量的持续稳定增长。耕地集约利用增长的边际效用递减特性,使得中国粮食生产安全的保障已逐步由耕地集约利用水平的提升转向了耕地面积的保护,由此导致耕地资源的数量成为了左右粮食生产安全的关键,这也为当今中国制定严格的耕地保护目标和战略提供了现实的科学依据。

Urban land expansion and its driving factors of mountain cities in China during 1990–2015

Land expansion of mountain cities in China is not systematically studied yet. This study identified 55 major mountain cities at and above prefecture level, and analyzed the land expansion characteristics and driving forces, based on visually interpreted data from TM images in 1990, 2000, 2010 and 2015. From 1990 to 2015, total built-up land area of the mountain cities increased by 3.87 times, 5.56% per year. The urban land growth was apparently accelerated after 2000, from 4.35% per year during 1990-2000 increased to 6.47% during 2000-2010 and 6.2% during 2010-2015. Compared to the urban population growth, the urban land expansion rate was 44% higher. As a result, the urban land area per capita increased, but it was still within the government control target, and also was much lower than the average of all cities in China. Urban development policy, changes to administrative divisions, GDP and population growth, and road construction were identified as the major driving forces of land expansion. Terrain conditions were not found a relevance to the urban land expansion rate during 1990-2015, but had a significant impact on the layout and shape, and also probably on the urban land efficiency.

Response of runoff to change of atmospheric 0℃ level height in summer in arid region of Northwest China

Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China(ARNC),the change trends,abrupt change points,and their significance of runoff and 0℃ level height(FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall(MK) nonparametric test,and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods.The results are indicated as follows:(1) in recent 50 years,there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature.The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains(NSQM) compared to that of the northern slope of the Kunlun Mountains(NSKM).Likewise,the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains(NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains(SSTM).However,the FLH on NSKM has been decreasing with the speed of 2.33 m every year.(2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions,and even in same region.(3) There is a positive significant relation between the summer runoff and FLH in ARNC(NSQM P <0.05;other three regions P <0.01).Therefore,the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC.(4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM,NSTM,NSQM,and SSTM are 7.19,3.80,2.79,and 6.63,respectively,which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC.The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.

A study on wheeze models

In this paper, the finite differenee schemes for the linear and nonlinear models of wheezes are given. The waveform of wheczes is analysed. It is shown that the numerical results of the lincar model of wheezes and Grotberg's theorehcal results coincide well. The numerical results of the nonlincar model of wheczes are in qualita tive agreement with our expcrimental observations. It is suggested that the nonlinear elastance coefficient (β) causes damping, and is closely related to the flow limitation and the airway collapse. Wheezes result from the interachon between the fluid forces and the wall forces and the airway wall flutter is a forced-vibration, rather than a self vibration.