scholarly journals Strength Deterioration Mechanism of Bentonite Modified Loess After Wetting- Drying Cycles

2021 ◽  
Author(s):  
Ze-Lin Niu ◽  
Jian Xu ◽  
Yan-Feng Li ◽  
Ze-Feng Wang ◽  
Bao Wang
Keyword(s):  
Fractal Dimension ◽  
Friction Angle ◽  
Damage Mechanism ◽  
Area Ratio ◽  
Regression Equations ◽  
Strength Deterioration ◽  
Damage Degree ◽  
Pore Area ◽  
Before And After ◽  
Loess Region

Abstract The employment of bentonite modified loess (BML) is a common method of constructing the anti-seepage lining of landfills in the loess region of China, and its long-term secure performance is threatened by wetting-drying (W-D) cycles. Taking the remolded loess (RL) and BML with 15% in mass of bentonite as research objects, the W-D cycles test, scanning electron microscope (SEM) test and direct shear test were carried out to analyze the effects of W-D cycles on the microstructure and shear strength of samples. The regression equations between strength and micro-pore structure parameters were established by the multivariate linear stepwise regression method. The damage mechanism of BML after W-D cycles was studied by establishing damage degree models based on pore area ratio and cohesion. Results indicate that the water absorption and expansion of bentonite effectively block the intergranular pores, resulting in more medium and small pores and more pronounced surface contact of particles. After W-D cycles, the particle arrangement of samples before and after bentonite modification tends to be loose. Both the pore area ratio and fractal dimension increase and tend to stabilize after five cycles. The BML exhibits lower pore area ratio and greater fractal dimension while its cohesion and internal friction angle show more significant decrease after W-D cycles than those of RL. The damage variables based on pore area ratio and cohesion well describe the W-D induced damage of loess before and after modification from macro- and micro-scale perspectives. The damage degree of samples increases with W-D cycles, but the increment decreases.

scholarly journals Strength Deterioration Mechanism of Bentonite Modified Loess After Wetting-Drying Cycles

2021 ◽  
Author(s):  
Zelin Niu ◽  
Jian Xu ◽  
Yanfeng Li ◽  
Zefeng Wang ◽  
Bao Wang
Keyword(s):  
Fractal Dimension ◽  
Friction Angle ◽  
Damage Mechanism ◽  
Regression Equations ◽  
Strength Deterioration ◽  
Damage Degree ◽  
Before And After ◽  
Lower Porosity ◽  
Deterioration Mechanism ◽  
Loess Region

Abstract The employment of bentonite modified loess (BML) is a common method of constructing the anti-seepage lining of landfills in the loess region of China, and its long-term secure performance is threatened by wetting-drying (W-D) cycles. Taking the remolded loess (RL) and BML with 15% in mass of bentonite as research objects, the W-D cycles test, scanning electron microscope (SEM) test and direct shear test were carried out to analyze the effects of W-D cycles on the microstructure and shear strength of samples. The regression equations between strength and micro-pore structure parameters were established by multivariate linear stepwise regression method. The damage mechanism of BML after W-D cycles was studied by establishing damage degree models based on porosity and cohesion. Results indicate that clay minerals such as montmorillonite in BML absorb water and expand to fill the macropores, resulting in more medium and small pores and more pronounced surface contact of particles. After W-D cycles, the particle arrangement of samples before and after bentonite modification tends to be loose. Both the porosity and fractal dimension increase and tend to stabilize after five cycles. The BML exhibits lower porosity and greater fractal dimension while its cohesion and internal friction angle show more significant decrease after W-D cycles than those of RL. The damage variables based on porosity and cohesion well describe the W-D induced damage of loess before and after modification from macro- and micro-scale perspectives. The damage degree of samples increases with W-D cycles, but the increment decreases.

Height-independent topographic parameters of worn surfaces

2011 ◽  
Vol 2 (1) ◽  
pp. 35-40
Author(s):  
I. Barányi ◽  
Á. Czifra ◽  
Gabor Kalácska
Keyword(s):  
Fractal Dimension ◽  
Surface Area ◽  
Friction And Wear ◽  
Area Ratio ◽  
Mean Square ◽  
Surface Area Ratio ◽  
Surface Microtopography ◽  
Steel Material ◽  
Before And After ◽  
Topographic Parameters

Surface microtopography plays a dual role in the course of friction and wear processes. It affectsthe contact and temperature conditions, and it undergoes significant changes in accordance with the wearmechanism. Fractal dimension (Df), root mean square gradient (Sdq), surface area ratio (Sdr) and surfacekurtosis (Sku) parameters of microtopographies provides opportunities for understanding more deeply thewear processes independently from the amplitude of the roughness. Wear experiments and surfaceroughness measurements before and after wear were performed. Investigations extended to wear in thecourse of the non-lubricated ferrodo-steel material pairs, and lubricated camshaft-bushing pairs.

scholarly journals Effect of Freeze-Thaw Cycles on Triaxial Strength Property Damage to Cement Improved Aeolian Sand (CIAS)

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2801
Author(s):  
Jun Li ◽  
Fengchi Wang ◽  
Fu Yi ◽  
Fengyuan Wu ◽  
Jiashun Liu ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Weibull Distribution ◽  
Crack Length ◽  
Phase Distribution ◽  
Ct Scanning ◽  
Friction Angle ◽  
Image Process ◽  
Aeolian Sand ◽  
Freeze Thaw ◽  
Pore Area

Natural aeolian sand has the characteristics of low cohesion and poor water stability. In order to improve its crack resistance properties in the process of freeze-thaw cycles, P.O 42.5 ordinary Portland cement was added to form a mixture called cement improved aeolian sand (CIAS). SEM was used to analyze the microscopic micro-structure of CIAS at different times (7 days and 28 days). The mechanical properties of CIAS samples affected by freeze-thaw cycles were tested in a triaxial instrument, and gray-scale images of the three-phase distribution in the CIAS after freeze-thaw cycling were obtained by computed tomography (CT) scanning technology. The pore characteristic parameters (pore area, fractal dimension, and crack length) were studied by digital image process technique. Based on classical Griffith fracture theory, the development of the crack length and crack width with increasing freeze-thaw cycles is determined. Assuming that the pore area subordinates to the Weibull distribution, the parameters of the Weibull distribution, the damage evolution defined by the elastic modulus attenuation, and the pore area development of CIAS were determined. Research shows the cohesion decreases and internal friction angle increases with increasing cycle numbers. Three development patterns are observed: crack growth, crack closure, and crack merging, and the three patterns interact during freeze-thaw cycling. Furthermore, the fractal dimension of the pore edge fluctuates with the increasing number of freeze-thaw cycles. This work provides a theoretical basis for the application of aeolian sand and develops a method for disaster prevention in applications of freeze-thaw cycling.

Heat Power Determination of Dv-290 Refrigerator’s Evaporator on the Basis of Thermodynamic Parameters of Inlet Air / Określenie Mocy Cieplnej Parownika Chłodziarki Dv-290 Na Podstawie Parametrów Termodynamicznych Powietrza Wlotowego

2012 ◽  
Vol 57 (4) ◽  
pp. 911-920
Author(s):  
Bernard Nowak ◽  
Zbigniew Kuczera
Keyword(s):  
Thermodynamic Parameters ◽  
Thermal Power ◽  
Correlation Coefficients ◽  
Specific Humidity ◽  
Physical Parameters ◽  
Air Cooling ◽  
Regression Equations ◽  
Evaporation And Condensation ◽  
Before And After ◽  
The Given

Abstract The present paper introduces a method for calculating the thermal power of DV-290 mining air cooler’s evaporator. The power usually differs from the nominal power given by the manufacturer. The thermodynamic parameters of cooled air are not obtained as a result of in situ measurements, but in indirect manner that is by determining the evaporation and condensation’s pressure values of R407C refrigerant. The pressure dependencies formulated as a function of air enthalpy at the evaporator’s inlet were obtained using calculations of a computer program which solves the system of equations describing heat and mass transfer in the refrigerator’s compressor on the basis of previous measurements of air performed before and after its cooling. The obtained dependencies are demonstrated in a graphical (fig. 2 and fig. 3) and analytical (the regression equations (19) and (20)) manner, the values of correlation coefficients are also presented. For the known evaporation and condensation pressure values of the refrigerant, and thus for its basic physical parameters the complete thermal power of the evaporator was determined, that is its: air cooling overt power, dehumidification occult power, temperature, relative humidity and specific humidity of air after its cooling. In addition, using the mentioned method, the capacity of DV-290 refrigerator’s evaporator is provided for the given thermodynamic parameters of air before cooling, along with air thermodynamic parameters after cooling.

Damage Assessment of the Attacked Airports Based on Image Analysis

2013 ◽  
Vol 321-324 ◽  
pp. 1168-1171
Author(s):  
Xiao Nan Zhang ◽  
Jun Feng Yang ◽  
Si Liang Du ◽  
Jun Zhi
Keyword(s):  
Damage Assessment ◽  
Automatic Method ◽  
Analysis Method ◽  
Image Information ◽  
Damage Degree ◽  
Before And After ◽  
Battle Damage Assessment ◽  
Damage Extent ◽  
Modern War ◽  
Assessment Result

Battle Damage Assessment (BDA) is to assess the damage degree of enemy’s target after being attacked. In modern war, combat commanders always make decision on the basis of BDA. In this paper, an automatic method for assessing the damage extent of an attacked airport based on the image taken before and after a strike is described. Firstly, the airport blockade condition is analyzed and damage assessment criteria of airport are proposed. Secondly, three steps of the image information pretreatment are carried out and a reliability analysis method of image information is proposed. Lastly, damage assessment result is calculated to verify the validity and availability of the proposed method.

Effect of Carbon Pre-Treatment on Pd Dispersion in Synthesis of Pd/C Catalyst

2014 ◽  
Vol 804 ◽  
pp. 149-152 ◽  
Author(s):  
Ji Sun Kim ◽  
Jae Ho Baek ◽  
Myung Hwan Kim ◽  
Seong Soo Hong ◽  
Man Sig Lee
Keyword(s):  
Surface Area ◽  
Nitrogen Adsorption ◽  
Area Ratio ◽  
High Dispersion ◽  
Co Chemisorption ◽  
Pd Dispersion ◽  
Before And After ◽  
Pre Treatment ◽  
Treated Carbon ◽  
Adsorption Desorption

In this study, we confirmed effect of carbon pre-treatment on Pd dispersion in synthesis of Pd/C catalyst. Physical characteristics on the surface of before and after pre-treated carbon were analyzed by nitrogen adsorption-desorption analysis. The dispersion and size of Pd particles were analyzed by XRD, FE-TEM and CO-chemisorption. After pre-treatment, surface area of carbon were decreased. And mesopore area ratio were increased with decreasing micropore area ratio. In the case of pre-treated carbon, we confirmed high dispersion of Pd particles.

scholarly journals Shear Strength Deterioration Effect and Slope Reliability Analysis Under Extreme Ice-snow Melting Conditions 

2021 ◽  
Author(s):  
Tongqiang Xiong ◽  
Jianlin Li ◽  
Lehua Wang ◽  
Huafeng Deng ◽  
Xiaoliang Xu
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Soil Samples ◽  
Creep Model ◽  
Shear Strength Parameters ◽  
Snow Melting ◽  
Strength Deterioration ◽  
Melting Cycle ◽  
Deformation Stability ◽  
Deterioration Effect

Abstract Extreme ice-snow melting in winter affects the infiltration process of snow water on the slope surface significantly, and plays an important role in the deformation stability of landslide. The fluctuation trend of slope stability under ice-snow melting is the same as that of soil volume water content. The deterioration effect of mechanical parameters will directly affect the deformation stability of bank slope. Based on this, the ice-snow melting cycle model test of slope soil was designed and carried out. The results are showed.(1) We were established an ice-snow melting model based on physical process. In the process of ice-snow melting, the soil cohesion and internal friction Angle have obvious deterioration effect .The deterioration of cohesion is obviously larger than that of internal friction Angle. In the early part of the ice-snow melting cycle, the deterioration of shear strength parameters is very obvious. Among them, the deterioration of shear strength parameters caused by the first four ice-snow melting cycles accounted for about 70% of the total deterioration. After the G2/T2 ice-snow melting cycle, the degree of phase deterioration gradually decreases. The deterioration trend of shear parameters of soil samples gradually tends to be gentle. (2) In the ice-snow melting cycle, the inside of the soil samples have micro-cracks, fissures repeatedly opened and closed, gradually developed and converged. The result is that the soil samples change from dense state to loose state where internal cracks develop. The internal damage of soil samples is the fundamental reason for the gradual deterioration of shear strength.（3）We are keep to the relative independence principle of creep model and unsaturated seepage equation. We are studied and improved the parameter solving method of creep model. The modified model is reasonable and effective. The creep trend and main characteristics of the unsaturated soil can be described well. Shear strength deterioration effect and slope reliability analysis under extreme ice-snow melting conditions .It has important reference significance to the protection of extreme snow and ice disaster on the bank slope.

Megan’s Law 20 Years Later: An Empirical Analysis and Policy Review

2018 ◽  
Vol 45 (7) ◽  
pp. 1028-1046 ◽  
Author(s):  
Kristen M. Zgoba ◽  
Wesley G. Jennings ◽  
Laura M. Salerno
Keyword(s):  
Sex Offenders ◽  
Sex Offender ◽  
Risk Group ◽  
High Risk Group ◽  
Regression Equations ◽  
Megan's Law ◽  
Multivariate Logistic Regression ◽  
Recidivism Rates ◽  
Before And After ◽  
General Recidivism

This present study examines the sexual and general recidivism rates of 547 convicted sex offenders released before and after the enactment of Megan’s Law in New Jersey. Presenting the longest Megan’s Law evaluation, participants were followed for an average of 15 years after release (range = 10-29 years). Bivariate and multivariate logistic regression equations were estimated to identify covariates significantly associated with both sexual and general recidivism. Group-based trajectories of general recidivism within the 10 years post–prison release were also estimated and compared according to pre–Megan’s Law and post–Megan’s Law release status. No differences in recidivism rates were noted between the cohorts, but differences emerged in the offending trajectories of the high-risk group of offenders within 10 years of release. These results highlight the lack of impact that sex offender registration and notification (SORN) laws have on sexual and general reoffending rates postrelease.

scholarly journals Evolution Rules of Fractures for Mudstone under Compression Shear Load and the Fractal Characteristics of Broken Blocks

2019 ◽  
Vol 2019 ◽  
pp. 1-7 ◽  
Author(s):  
Zhaoyun Chai ◽  
Jinbo Bai ◽  
Haiyang Zhang ◽  
Pan Yang
Keyword(s):  
Fractal Dimension ◽  
Compression Test ◽  
Shear Fracture ◽  
Fractal Theory ◽  
Friction Angle ◽  
Shear Loading ◽  
Shear Load ◽  
Deformation And Failure ◽  
Fractal Characteristics ◽  
Logarithmic Relationship

Failure of rocks is commonly induced by compressive and shear coupling loading. Knowledge of the mechanism and process of deformation and failure of rocks under compressive shear loading condition is an important basis for the study of stability in rock engineering. Based on the nonlinear fractal theory, it is possible to examine the evolution rules of fractures in mudstone under compression shear load and the fractal characteristics of broken blocks using the shear compression test with variable angles of mudstone specimens in natural conditions. This research shows that the cohesion and friction angle parameters of rock samples are achieved by draw Mohr’s strength envelope according to the test date of variable-angle shear compression test. It also shows that the shape of load-displacement curves of rocks can be divided into four stages: compaction, elastic, plastic, and fracture, and the curve can accurately represent the transformation and breakage characteristics of rock during shear fracture. And the distribution of broken blocks shows a strong statistical resemblance to the fractal distribution, and the fractal dimension is able to reflect the distribution characteristics of broken blocks. With increasing the shear angle, the fractal dimension of broken blocks decreases in a logarithmic relationship.

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