Bond rolling resistance and its effect on yielding of bonded granulates by DEM analyses

A discrete element modelling of bonded granulates and investigation on the bond effect on their behaviour are very important to geomechanics. This paper presents a two‐dimensional (2‐D) discrete element theory for bonded granulates with bond rolling resistance and provides a numerical investigation into the effect of bond rolling resistance on the yielding of bonded granulates. The model consists of mechanical contact models and equations governing the motion of bonded particles. The key point of the theory is that the assumption in the original bond contact model previously proposed by the authors (55th CSCE‐ASCE Conference, Hamilton, Ont., Canada, 2002; 313–320; J. Eng. Mech. (ASCE) 2005; 131 (11):1209–1213) that bonded particles are in contact at discrete points, is here replaced by a more reliable assumption that bonded particles are in contact over a width. By making the idealization that the bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring, dashpot, bond, slider or divider), we establish a bond rolling contact model together with bond normal/tangential contact models, and also relate the governing equations to local equilibrium. Only one physical parameter β needs to be introduced in the theory in comparison to the original bond discrete element model. The model has been implemented into a 2‐D distinct element method code, NS2D. Using the NS2D, a total of 86 1‐D, constant stress ratio, and biaxial compressions tests have been carried out on the bonded granular samples of different densities, bonding strengths and rolling resistances. The numerical results show that: (i) the new theory predicts a larger internal friction angle, a larger yielding stress, more brittle behaviour and larger final broken contact ratio than the original bond model; (ii) the yielding stress increases nonlinearly with the increasing value of β, and (iii) the first‐yield curve (initiation of bond breakage), which define a zone of none bond breakage and which shape and size are affected by the material density, is amplified by the bond rolling resistance in analogous to that predicted by the original bond model. Copyright © 2006 John Wiley & Sons, Ltd.     

Low-cost volcano surveillance from space: case studies from Etna, Krafla, Cerro Negro, Fogo, Lascar and Erebus

 Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large (3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement to conventional monitoring methods. Received: 21 January 1997 / Accepted: 3 April 1997     

Application of precise 142Nd/144Nd analysis of small samples to inclusions in diamonds (Finsch,South Africa) and Hadean Zircons (Jack Hills,Western Australia)

¹⁴⁶Sm–¹⁴²Nd and ¹⁴⁷Sm–¹⁴³Nd systematics were investigated in garnet inclusions in diamonds from Finsch (S. Africa) and Hadean zircons from Jack Hills (W. Australia) to assess the potential of these systems as recorders of early Earth evolution. The study of Finsch inclusions was conducted on a composite sample of 50 peridotitic pyropes with a Nd model age of 3.3 Ga. Analysis of the Jack Hills zircons was performed on 790 grains with ion microprobe ²⁰⁷Pb/²⁰⁶Pb spot ages from 3.95 to 4.19 Ga. Finsch pyropes yield 100 × ?¹⁴²Nd = ? 6 ± 12 ppm, ?¹⁴³Nd = ? 32.5, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.1150. These results do not confirm previous claims for a 30 ppm ¹⁴²Nd excess in South African cratonic mantle. The lack of a ¹⁴²Nd anomaly in these inclusions suggests that isotopic heterogeneities created by early mantle differentiation were remixed at a very fine scale prior to isolation of the South African lithosphere. Alternatively, this result may indicate that only a fraction of the mantle experienced depletion during the first 400 Myr of its history. Analysis of the Jack Hills zircon composite yielded 100 × ?¹⁴²Nd = 8 ± 10 ppm, ?¹⁴³Nd = 45 ± 1, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.5891. Back-calculation of this present-day ?¹⁴³Nd yields an unrealistic estimate for the initial ?¹⁴³Nd of ? 160 ?-units, clearly indicating post-crystallization disturbance of the ¹⁴⁷Sm–¹⁴³Nd system. Examination of ^146,147Sm–^142,143Nd data reveals that the Nd budget of the Jack Hills sample is dominated by non-radiogenic Nd, possibly contained in recrystallized zircon rims or secondary subsurface minerals. This secondary material is characterized by highly discordant U–Pb ages. Although the mass fraction of altered zircon is unlikely to exceed 5–10% of total sample, its high LREE content precludes a reliable evaluation of ¹⁴⁶Sm–¹⁴²Nd systematics in Jack Hills zircons.     

Photoelectric lightcurves of asteroids 42 Isis, 45 Eugenia, 56 Melete, 103 Hera, 532 Herculina,and 558 Carmen

Photoelectric observations of six asteroids are presented. The following synodic periods of rotation and amplitudes of variation are reported: 42 Isis, P = 13^h.59, Δm = 0.32; 45 Eugenia, P = 5^h.70, Δm = 0.30; 56 Melete, P = 13^h.7 or 19^h.0, Δm = 0.06; 532 Herculina, P = 9^h.408, Δm = 0.15; 558 Carmen, P ≈ 10^h, Δm ≈ 0.25. The asteroid 103 Hera exhibited no periodic variation in excess of about 0.03 magnitude. The period found for 532 Herculina is one half that previously reported by other observers.     

Photoelectric lightcurve and period of rotation of the asteroid 182 Elsa

Photoelectric observations on five consecutive nights yield a period of rotation of 80 ± 2 hr with an amplitude of 0.7 magnitude for 182 Elsa, making it the longest period of rotation known to date. 182 Elsa is classed as an S object with a diameter of 48 km.     

Geochemistry and petrogenesis of a peralkaline granite complex from the Midian Mountains, Saudi Arabia

A zoned intrusion with a biotite granodiorite core and arfvedsonite granite rim represents the source magma for an albitised granite plug near its eastern margin and radioactive siliceous veins along its western margin. A study of selected REE and trace elements of samples from this complex reveals that the albitised granite plug has at least a tenfold enrichment in Zr, Hf, Nb, Ta, Y, Th, U and Sr, and a greatly enhanced heavy/light REE ratio compared with the peralkaline granite. The siliceous veins have even stronger enrichment of these trace elements, but a heavy/light REE ratio and negative eu anomaly similar to the peralkaline granite. It is suggested that the veins were formed from acidic volatile activity and the plug from a combination of highly fractionated magma and co-existing alkaline volatile phase. The granodiorite core intrudes the peralkaline granite and has similar trace element geochemistry. The peralkaline granite is probably derived from the partial melting of the lower crust in the presence of halide-rich volatiles, and the granodiorite from further partial melting under volatile-free conditions.     

Initial volatilization temperatures and average volatilization rates of coal — Their relationship to coal rank and other characteristics

Two thermal parameters, initial volatilization temperature (IVT) and average volatilization rate (AVR), have been determined by thermogravimetric analysis in argon for 38 coal samples ranging in rank from lignite to low-volatile bituminous. Both IVT and AVR are correlated with percent volatile matter and vitrinite reflectance.The IVT values increase gradually from about 250 to 445°C with increasing rank; however, a change in slope is observed in the region of high-volatile bituminous coals (from about 340°C to about 380°C) when IVT's are plotted against percent volatile matter or percent fixed carbon. The changes in slope near 340°C and near 380°C occur at “coalification jumps” recognized on the basis of changes in the optical and chemical character of the macerals. In general, AVR values decrease gradually with increasing rank for the lignite and sub-bituminous coals and for the medium- and low-volatile bituminous coals; however, a sharp increase in AVR occurs in high-volatile bituminous coals. The change in slope of the IVT curves and sharp increase in the AVR values for high-volatile bituminous coals reflect the development of new, higher vapor pressure organic compounds produced during this stage of the coalification process.A plot of AVR vs IVT reveals three regions which correspond to: (1) lignite and sub-bituminous coals; (2) high-volatile bituminous coals; and (3) medium- to low-volatile bituminous coals.     

The Use of Geographically Weighted Regression for Spatial Prediction: An Evaluation of Models Using Simulated Data Sets

Increasingly, the geographically weighted regression (GWR) model is being used for spatial prediction rather than for inference. Our study compares GWR as a predictor to (a) its global counterpart of multiple linear regression (MLR); (b) traditional geostatistical models such as ordinary kriging (OK) and universal kriging (UK), with MLR as a mean component; and (c) hybrids, where kriging models are specified with GWR as a mean component. For this purpose, we test the performance of each model on data simulated with differing levels of spatial heterogeneity (with respect to data relationships in the mean process) and spatial autocorrelation (in the residual process). Our results demonstrate that kriging (in a UK form) should be the preferred predictor, reflecting its optimal statistical properties. However the GWR-kriging hybrids perform with merit and, as such, a predictor of this form may provide a worthy alternative to UK for particular (non-stationary relationship) situations when UK models cannot be reliably calibrated. GWR predictors tend to perform more poorly than their more complex GWR-kriging counterparts, but both GWR-based models are useful in that they provide extra information on the spatial processes generating the data that are being predicted.     

Asteroid rotation: III. 1978 Observations

Photoelectric observations of 32 asteroids observed from Table Mountain Observatory during the second half of 1978 are reported. Rotation periods were obtained for most objects. Absolute magnitudes and phase functions were not determined for any of these asteroids. The geometric mean rotation period of the 32 asteroids observed is 14.2 ± 1.6 hr, as compared to 9.38 ± 0.35 hr for 182 asteroids analyzed in Paper I (A. W. Harris and J. A. Burns, 1979, Icarus 40, 115–144). We attribute this difference to an observational selection effect which favors detection of fast rotation, as discussed in Paper I. If this is true, then the present sample contains the reverse bias, since it is complete in that a period (in some cases very approximate) was obtained for each object observed, but fast rotators are underrepresented due to prior discovery of their rotation properties.