Packing potential index for binary mixtures of granular soil

Packing procedure is the mechanical process of forming a packing of soil particles, such as funnel pouring, tamping, rodding, pluviation, compaction, vibration, compression, etc. For a sand-silt mixture, packing procedure and particle shape have significant effects on the density of the binary mixture. However, these two factors have not been considered in most of the existing particle packing density models. Thus, the existing particle packing density models are not applicable to sand-silt mixtures. In this paper, we aim to study the packing procedure and particle shape effects on density of binary mixtures. We firstly define a packing potential index, which is a measure of volume reduction potential due to mixing of two components of a binary mixture system under a packing procedure. To understand the nature of packing potential index, we compare the packing potential indices of 24 different types of mixtures collected from the literature; the 24 types of mixtures were formed by two different types of packing procedure (i.e., for achieving minimum and maximum void ratios). It is found that the packing potential index is nearly independent of packing procedure but significantly dependent on the compound particle shapes of a mixture. Then, we mathematically link the packing potential index to the particle interaction parameters used in the particle packing density models. And we analyze the data to discuss the effect of packing procedure on the void ratios of sand-silt mixtures. We then propose an approach within the framework of particle packing density model to predict the void ratios of sand-silt mixtures under different packing procedures with the consideration of particle shape effect

A multi-variable equation for relationship between limiting void ratios of uniform sands and morphological characteristics of their particles

The limiting void ratios (i.e., the minimum and the maximum void ratios) are two important index properties, which are related to the compressibility, shear strength, and permeability of granular soils. Experimental studies have shown that the limiting void ratios are correlated to morphological properties of soil particles (i.e. particle size and particle shape). However, empirical equations available in literature for the limiting void ratios are generally single-variable functions of either particle size, or particle shape. In this study, we propose multi-variable equations, in which the limiting void ratios are functions of both particle size and particle shape. The coupled effects of particle size and particle shape on the limiting void ratios are illustrated. Advantages of the proposed multi-variable equations over the existing single-variable equations are shown by comparing the calculated void ratios with the experimental data on a large number of uniform sand samples. The proposed multi-variable equations can be applied to predict the limiting void ratios of uniform sands encountered in geotechnical engineering projects in order to properly support heavy loads

Strength–dilatancy and critical state behaviours of binary mixtures of graded sands influenced by particle size ratio and fines content

Binary granular soil mixtures, as common heterogeneous soils, are ubiquitous in nature and man-made deposits. Fines content and particle size ratio are two important gradation parameters for a binary mixture, which have potential influences on mechanical behaviours. However, experimental studies on drained shear behaviour considering the whole range of fines content and different particle size ratios are scarce in the literature. For this purpose, a series of drained triaxial compression tests was performed on dense binary silica sand mixtures with four different particle size ratios to investigate systematically the effects of fines content and particle size ratio on the drained shear behaviours. Based on these tests, the strength-dilation behaviour and critical state behaviour were examined. It was observed that both fines content and particle size ratio have significant influence on the stress–strain response, the critical state void ratio, the critical state friction angle, the maximum dilation angle, the peak friction angle and the stress–dilatancy relation. The underlying mechanism for the effects of fines content and particle size ratio was discussed from the perspective of the kinematic movements at particle level

Association of Hypertension With Both Occurrence and Outcome of Symptomatic Patients With Mild Intracranial Atherosclerotic Stenosis: A Prospective Higher Resolution Magnetic Resonance Imaging Study.

BACKGROUND: Intracranial atherosclerotic plaque causing mild luminal stenosis might lead to acute ischemic events. However, the difference between culprit and nonculprit lesions is unclear, as are the factors associated with favorable treatment outcomes. PURPOSE: To quantify characteristics of intracranial atherosclerosis with mild luminal stenosis and to identify factors associated with lesion type (culprit or nonculprit) and with clinical outcomes. STUDY TYPE: Prospective POPULATION: 293 patients who had acute stroke with mild luminal stenosis (<50%) in the middle cerebral or basilar artery. FIELD STRENGTH/SEQUENCE: 3.0 T higher resolution magnetic resonance imaging (hrMRI) of intracranial arteries and whole brain MR images. ASSESSMENT: Morphological and compositional analysis of plaques was performed. This included assessment of plaque volume, plaque burden, remodeling ratio, eccentricity, intraplaque hemorrhage, and enhancement ratio. Clinical outcomes were assessed according to the modified Rankin Scale (mRS) at day 90, with a favorable outcome being defined as a 90-day mRS ≤2. STATISTICAL TESTS: The odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by a logistic regression model. RESULTS: Hypertension (OR 5.2; 95% CI 2.6-10.3; P < 0.05) and hrMRI enhancement ratio (OR 2.7; 95% CI 1.4-5.1; P < 0.05) were independently associated with lesion type. Patients without hypertension had significantly more (P < 0.05) favorable outcomes (124/144) than patients with hypertension (97/149). Most hypertensive patients without any previous blood pressure control (54/63) had a favorable outcome. However, these patients were significantly younger (P < 0.05) than those with adequate blood pressure control. After adjusting for all significant characteristics, hypertension duration (OR 1.19; 95% CI 1.09-1.29; P < 0.05), hypertension management (OR 2.49; 95% CI 1.18-5.26; P < 0.05), and enhancement ratio (OR 0.01; 95% CI 0.001-0.157; P < 0.05) were found to be independent high-risk factors for outcome prediction. DATA CONCLUSION: hrMRI provided incremental value over traditional risk factors in identifying higher risk intracranial atherosclerosis with mild luminal stenosis. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 2

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

DENSITY STATE AND SHEAR BEHAVIOR OF GRANULAR SOILS WITH INFLUENCE OF PARTICLE SIZE DISTRIBUTION

Heterogeneous granular soils are ubiquitous in nature and man-made deposits. Heterogeneity of soil is characterized by its particle size distribution (or fines content for gap-graded soils). The particle size distribution of soil is the main factor that affects its mechanical properties. However, in soil mechanics, the influence of particle size distribution on mechanical properties is only considered in an empirical manner. There are few analytical methods that can explicitly account for the effect of particle size distribution. In this study, there are two purposes: 1) to develop a particle packing theory for modeling the effect of particle size distribution on density states of granular soils, including densest, loosest, and critical density states, which are the fundamental properties relating to mechanical behavior of soil, and 2) to study the shear behavior of granular soils with influence of particle size distribution. The developed particle packing theory is able to predict the density state of multi-sized soils based on their particle morphological characteristics and particle size distribution. The particle packing theory providing an ability to analyze the effect of particle size distribution is important in the understanding of mechanical behavior due to the heterogeneity of soil. Based on the developed particle packing theory, a framework of modeling the critical state line of granular soils was established by explicitly considering their particle size distribution. Incorporating the evolution of particle size distribution due to particle breakage into the model, this framework can be used for predicting the critical state line of granular material with particle breakage. A series of drained triaxial compression tests on dense binary silica sand mixtures with 4 different particle size ratios was performed to systematically investigate the effects of fines content and particle size ratio on the drained shear behaviors. It was observed that both fines content and particle size ratio have significant influence on the drained shear behaviors of binary granular soil mixtures. A mechanism was proposed to illustrate the influences of fines content and particle size ratio on the drained shear behavior from the perspective of particle column buckling. The findings from this research is potentially useful for analyzing geotechnical engineering problems, such as liquefaction of silty sand, landslides of weathered soil, levee failure due to erosion of fine particles, and dam instability due to grain crushing. This study also has potential to be applied in the continuum mechanics for materials of heterogeneous nature

Hidden dynamics, synchronization, and circuit implementation of a fractional-order memristor-based chaotic system

Fractional calculus has always been regarded as an ideal mathematical tool to describe the memory of complex systems and special materials. A fractional-order memristor-based chaotic system with hidden dynamics is studied in this paper. The system can exhibit excellent dynamic behavior by introducing a quadratic nonlinear memristor. Asymmetric coexistence occurs when both the order and parameter change. Considering the practical application of fractional-order system, the spectral entropy (SE) algorithm is used to investigate the complexity of the system. Besides, synchronous experiment between two fractional-order system is carried out and the synchronization circuit is also designed. To verify the numerical simulation results, the hardware circuit is constructed, and the hidden attractors are successfully captured on the oscilloscope by hardware electronic circuit

Three-dimensional DEM simulation of cone penetration test by using circumferential periodic boundary

In order to explore the micro-mechanism of CPT, a new circumferential periodic boundary was developed to consider the three-dimensional axisymmetric problem with 1/4 of the cylinder. To validate the method, a drained triaxial test was modeled with the proposed method and the traditional full model. The results are comparable and the proposed method is very effective. The method was further used to simulate a cone penetration test in dry Fontainebleau sand. It was found that, the variation of cone radial stress and tip resistance during penetration from the model are in good agreement with the reported test results. The micromechanical responses, such as the distributions of particle displacement, internal stress and local porosity to cone penetration are extensively studied. The evolutions of fabric anisotropy during penetration are also discussed. The relationship between stress and fabric is quantitatively described using fabric tensor, which reveals the mechanism of cone penetration capacity microscopically. The results of the work not only improve the efficiency of three-dimensional discrete element method(DEM) simulation, but also promote better understanding of CPT mechanism. © 2016, Science Press. All right reserved

Model Test Research on Bearing Mechanism of Underreamed Ground Anchor in Sand

To improve the capacity of ground anchors, scholars and engineers worldwide have developed various types of underreamed anchors with expanded anchor parts. Underreamed anchors have a completely different mechanism from traditional shaft anchors. The expanded section of an underreamed anchor induces an end bearing force to endure the uplift force similar to a reversed pile. Therefore, the total resistance of an underreamed anchor includes friction and end bearing force. To clarify the bearing mechanism of underreamed anchors, a series of model tests were performed using fiber Bragg grating (FBG) sensors and the photogrammetry measuring method. Based on the tests, the distribution and development of the friction and end bearing force of the underreamed anchor model were acquired by the FBG sensors when being pulled out. Moreover, the deformation state of the soil around the anchor model was observed by the digital photogrammetry measuring method. Finally, the interaction mechanism between an underreamed anchor and surrounding sand was obtained, which was identified as the inherent reason for the distribution and development law of the resistance of the underreamed anchor in sand