Appropriate sample size and effects of microscopic parameters on the shear strength and strain localisation of 2D cohesive-frictional granular assemblies

Granular materials are made up of smaller particles, manifestation of microstructure results in a macroscopic response of granular material. Understanding the overall mechanical behaviour from microscopic parameters is one of the main challenges in many engineering fields including civil engineering. When modelling this kind of material by Discrete Element Model (DEM) using idealized circular grains, the effects of appropriate sample size and microscopic parameter changes have been a crucial subject. Previous research has primarily relied on the case of purely frictional granular materials. In this paper, we use DEM to investigate the appropriate sample size and the relationship between microscopic parameters and the macroscopic responses of cohesive-frictional granular assemblies by performing a series of biaxial tests. Our findings indicate that a minimum number of particles is required to balance between mechanical behaviour and computing time. In addition, through extensive parametric studies, the paper explores the impact of factors such as interparticle bonds, intergranular friction coefficients, and initial void index on the overall shear behaviour of granular assemblies. Also, the result reveals a strong correlation between shear band formation and the break field of cohesive contact (static variable) and the translations and rotations of grains (kinematic variable)

DEM investigation on strain localization in a dense periodic granular assembly with high coordination number

Strain localization is one of key phenomena which have been studied extensively in geomaterials and for different kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Theoretical, experimental, and numerical research have been dedicated to this subject for a long while. In the numerical aspects, strain localization inside the periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular disks and subjected to biaxial loading with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions. This formation has the origins of the irreversible losing of cohesive contacts, viewed as micro-crackings which strongly concentrated in the periodic shear zones. This micromechanical feature is therefore strongly related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the sample’s displacement fluctuation fields

On the Interference Alignment Designs for Secure Multiuser MIMO Systems

In this paper, we propose two secure multiuser multiple-input multiple-output transmission approaches based on interference alignment (IA) in the presence of an eavesdropper. To deal with the information leakage to the eavesdropper as well as the interference signals from undesired transmitters (Txs) at desired receivers (Rxs), our approaches aim to design the transmit precoding and receive subspace matrices to minimize both the total inter-main-link interference and the wiretapped signals (WSs). The first proposed IA scheme focuses on aligning the WSs into proper subspaces while the second one imposes a new structure on the precoding matrices to force the WSs to zero. When the channel state information is perfectly known at all Txs, in each proposed IA scheme, the precoding matrices at Txs and the receive subspaces at Rxs or the eavesdropper are alternatively selected to minimize the cost function of an convex optimization problem for every iteration. We provide the feasible conditions and the proofs of convergence for both IA approaches. The simulation results indicate that our two IA approaches outperform the conventional IA algorithm in terms of average secrecy sum rate.Comment: Updated version, updated author list, accepted to be appear in IEICE Transaction

Researching migration methods, entropy and energy diagram to process ground penetrating radar data

Electromagnetic wave velocity is the most important parameter in processing ground penetrating radar data. Migration algorithm which heavily depends on wave velocity is used to concentrate scattered signals back to their correct locations. Depending wave velocity in urban area is not easy task by using traditional methods (i.e., common midpoint). We suggest using entropy and energy diagram as standard for achieving suitable velocity estimation. The results of one numerical model and areal data indicate that migrated section using accurate velocity has minimum entropy or maximum energy. From the interpretation, size and depth of anomalies are reliably identified

The Impact of Viral Marketing on Emotion and Impulse Buying Behavior: A Case Study of Online Fashion

Impulsive online shopping is becoming a habit for many young consumers, especially for fashion products. This study aims to analyze the influence of viral marketing on emotions and impulsive online shopping behavior of young people for fashion products in Vietnam. The results showed that viral marketing with characteristics such as entertainment, source credibility, visual appeal, informativeness, and irritation all had a significant impact on emotions and impulsive online shopping behavior. Therefore,some suggestions are proposed for applying viral marketing to promote impulsive online shopping behavior for fashion products. Keywords: Viral marketing, Impulse buying behavior, Online shopping, Emotions, Fashion. DOI: 10.7176/EJBM/15-7-03 Publication date: April 30th 202

Static and vibration analysis of isotropic and functionally graded sandwich plates using an edge-based MITC3 finite elements

Static and vibration analysis of isotropic and functionally graded sandwich plates using a higher-order shear deformation theory is presented in this paper. Lagrangian functional is used to derive the equations of motion. The mixed interpolation of tensorial components (MITC) approach and edge-based-strain technique is used to solve problems. A MITC3 three-node triangle element with 7 degree-of-freedoms per nodes that only requires the C0-type continuity is developed. Numerical results for isotropic and functionally graded sandwich plates with different boundary conditions are proposed to validate the developed theory and to investigate effects of material distribution, side-to-thickness ratio, thickness ratio of layers and boundary conditions on the deflection, stresses and natural frequencies of the plates

A nutrient method for cutivation of macroalgae Ulva papenfussii

Macroalgae species of the genus Ulva are widely distributed in the wild. Many species of this genus has been used as food as an attractive material for the study of materials, fuels, food etc.. In this paper, we are focusing on nutrient method for cultivation of Ulva papenfussii and A nutrient source for cultivation of U. papenfussii was also investigated with the perspective of utilizing the produced biomass for feed. U. papenfussii is fragmented into 1 × 1 cm size, then it keep in Ulva extract of 0.1 g/l concentrate for 7 days. Then continue to keep fragments in the following conditions: 20 ml/l of PES medium, 700 μmol photon/m2/s of light, 25oC of temperature, 3% of salinity, 28 days of time. Under this condition the productivity U. papenfussii was 17.8 g/l of weight and its growth rate was 4.3–6.5% day. Nutritional cultivation is successful for U. papenfussii speceies, which is of great importance to study the potential of producing seaweed varieties like blades for commercial application of seaweed species.

Exploring knowledge and attitudes toward the hepatitis B virus: an internet-based study among Vietnamese healthcare students

Context: Hepatitis B is a serious global public health problem, especially in developing countries such as Vietnam. Many studies worldwide have focused on health care workers, a population at high risk of infection with the hepatitis B virus (HBV), but there is little research that explores the high levels of risk faced by health care students. Aims: To assess the knowledge and attitudes of Vietnamese undergraduate students toward hepatitis B vaccination. Methods: A cross-sectional study was conducted among 1291 Vietnamese healthcare students between November 2017 and March 2018 via social media. Results: The mean score for knowledge was 4.0 ± 0.4, and the mean score for attitude was lower (3.5 ± 0.6). Levels of knowledge were higher (p<0.001) among sixth-year students, students who had been vaccinated, and students attending public universities. Most participants were well-informed about the diseases caused by HBV, with 1128 (87.4%) agreeing that HBV infection can lead to liver cancer. Nevertheless, 259 students believed that HBV cannot be spread by sharing a toothbrush with an infected person, and 18.7% thought that asymptomatic carriers are incapable of transmitting HBV. Conclusions: Although students had adequate knowledge of HBV, their scores for attitude and their rates of vaccination were low. This study therefore recommends improving the knowledge and attitudes of health care students through orientation and sensitization programs and improvements in their educational environment

The application of split step fourier migration to interpreting GPR data in Vietnam

Migration methods play an essential role in processing ground penetrating radar data. For estimating electromagnetic propagation velocity distribution, the finite - difference migration is used because of its reliable performance with high noise conditions. To optimize this migration algorithm, we propose using energy diagram as a criterion of looking for the correct velocity. If the velocity varies laterally and vertically, split step Fourier migration is used for creating a true image of subsurface structures. We applied these steps to real data in Vietnam. The results verified on field data show that migrated images with calculated velocity from energy diagram have the best quality