Microscopic Evaluation of Strain Distribution in Granular Materials during Shear

The evolution of local strains during shear of particles of a granular material is presented in this paper. A cylindrical specimen composed of 6.5-mm spherical plastic particles was loaded under an axisymmetric triaxial loading condition. Computed tomography (CT) was used to acquire three-dimensional images of the specimen at three shearing stages. The high-resolution CT images were used to identify the 3D coordinates of 400 particles. Nine strain components (normal, shear, and rotation), rotation angles, and local dilatancy angles for particle groups were calculated, and their frequency distribution histograms are presented and discussed. It was found that there is no preferred shear direction, and the standard deviation values for shear strain components (εxy, εxz, and εyz) were almost equal for the specific test shearing stage. Shear strains as high as 25.6% were recorded for some particle groups. Furthermore, granular particle groups rotated in the 3D space with almost equal amounts of rotation strains when loaded under axisymmetric triaxial condition. Rotation strain values are very close to the corresponding shear strains. Compared to particle sliding, rotation plays a major role in the shearing resistance of granular materials. The cumulative vertical rotation angles can be as high as 38° and the horizontal rotation angles have values as high as 60°. The statistical distributions of the local dilatancy angle (ψ1) of particle groups were calculated and found to be increasing as shearing continues. The “global” dilatancy angle value is very close to the mean local ψ1 during the first stage of shearing (i.e, when global εz = ?7.3%)     

Using lithium nitrate and pozzolanic glass powder in concrete as ASR suppressors

This investigation studies the influence of two different mineral admixtures, lithium nitrate (Li) and pozzolanic glass powder (PGP) on the expansion induced by alkali-silica reaction (ASR). Four numbers of concrete prisms were produced for each concrete mix to measure the expansion resulted from the ASR according to the test method of the BS 812-123:1999. Chemical analysis was performed using X-ray spectra. Test results confirmed that Li and PGP have significantly reduced the ASR expansion. Lower calcium to silica ratio (Ca/Si) was found in concrete mix contains (PGP) because of the high amorphous reactive silica and low calcium content in PGP compared to ordinary Portland cement CEM1. Similar components and minerals phases were obtained in different concrete mixes by using XRD.     

Lightweight validation of natural language requirements

In this paper, we report on our experiences of using lightweight formal methods for the partial validation of natural language requirements documents. We describe our approach to checking properties of models obtained by shallow parsing of natural language requirements, and apply it to a case study based on part of a NASA specification of the Node Control Software on the International Space Station. The experience reported supports our position that it is feasible and useful to perform automated analysis of requirements expressed in natural language. Indeed, we identified a number of errors in our case study that were also independently discovered and corrected by NASA's Independent Validation and Verification Facility in a subsequent version of the same document, and others that were not discovered. The paper describes the techniques we used, the errors we found and reflects on the lessons learned. Copyright © 2001 John Wiley & Sons, Ltd.     

Successive noise enhancement reduction

The capacity of direct sequence code division multiple access (DS-CDMA) systems is limited by multiple access interference (MAI). Commercial CDMA systems regarded MAI as additive noise and employed the matched filter detectors. This technique limits the number of users that can be supported in a DS-CDMA system and causes an increase in the bit error rates for active users in the system as the number of users increases or as the spreading factor decreases. Thus, advanced signal processing solutions for interference suppression are necessary. In this paper, we propose a new multiuser detector (MUD) detector technique and compare between its performance to other popular MUD detectors for the universal mobile telecommunications system (UMTS) physical layer.     

A hybrid approach for identifying non-human traffic in online digital advertising

Multimedia Tools and Applications - Click fraud is a serious problem facing online advertising business. The malicious intent of clicking online ads either committed by humans or by non-humans,...     

Ytterbium (III) oxide reinforced novel TeO2–B2O3–V2O5 glass system: Synthesis and optical,structural, physical and thermal properties

Different samples of xTeO₂.(25-y)B₂O₃.zV₂O₅.yYb₂O₃ (or TBVY) new glass material were synthesized by the classical melt-quenching method. Structural, optical, physical, and thermal analyses of the synthesized glasses were performed in addition to Monte Carlo simulation to test radiation shielding properties. The results showed that increasing ratios of Yb₂O₃ (y = 0.0, 0.5, 1.0, and 1.5 mol%) produced monotonic density values of the synthesized glasses ranging from 4.70058 g cm^?3 to 5.01038 g cm^?3. XRD and FTIR analyses were used to confirm the glass structure of all samples. Optical transmittance and absorption parameters varied almost monotonically with increasing ratios of Yb₂O₃ indicating the ability to predict and control these properties using Yb₂O₃ additive. Furthermore, simulated radiation interaction parameters, such as attenuation coefficients and half-value layer, exhibited well-behaved dependence on the concentration ratio of the Yb₂O₃ additive. This approach to glass material synthesis demonstrate the useful synergetic effect of combining structural, optical, and radiation characteristics.