Effects of particle size of mono-disperse granular flows impacting a rigid barrier   总被引：4，自引：0，他引：4  

Yifei Cui  Clarence E. Choi  Luis H. D. Liu  Charles W. W. Ng 《Natural Hazards》2018,91(3):1179-1201

Understanding the interaction between complex geophysical flows and barriers remains a critical challenge for protecting infrastructure in mountainous regions. The scientific challenge lies in understanding how grain stresses in complex geophysical flows become manifested in the dynamic response of a rigid barrier. A series of physical flume tests were conducted to investigate the influence of varying the particle diameter of mono-dispersed flows on the impact kinematics of a model rigid barrier. Particle sizes of 3, 10, 23 and 38 mm were investigated. Physical tests results were then used to calibrate a discrete element model for carrying out numerical back-analyses. Results reveal that aside from considering bulk characteristics of the flow, such as the average velocity and bulk density, the impact load strongly depends on the particle size. The particle size influences the degree of grain inertial stresses which become manifested as sharp impulses in the dynamic response of a rigid barrier. Impact models that only consider a single impulse using the equation of elastic collision warrant caution as a cluster of coarse grains induce numerous impulses that can exceed current design recommendations by several orders of magnitude. Although these impulses are transient, they may induce local strucutral damage. Furthermore, the equation of elastic collision should be adopted when the normalized particle size with the flow depth, δ/h, is larger than 0.9 for Froude numbers less than 3.5.  相似文献   

Rb‐Sr and Sm‐Nd isotopic and REE studies of igneous components in the bulk matrix domain of Martian breccia Northwest Africa 7034          下载免费PDF全文

Laurence E. Nyquist  Chi‐Yu Shih  Francis M. McCubbin  Alison R. Santos  Charles K. Shearer  Zhan X. Peng  Paul V. Burger  Carl B. Agee 《Meteoritics & planetary science》2016,51(3):483-498

The bulk matrix domain of the Martian breccia NWA 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia. Both ¹⁴⁷Sm‐¹⁴³Nd and ¹⁴⁶Sm‐¹⁴²Nd age results for mineral separates from the bulk matrix portion of breccia NWA 7034 suggest that various lithological components in the breccia probably formed contemporaneously ~4.44 Ga ago. This old age is in excellent agreement with the upper intersection ages (4.35–4.45 Ga) for U‐Pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous‐textured clasts. Consequently, we confirm an ancient age for the igneous components that make up the NWA 7034 breccia. Substantial disturbance in the Rb‐Sr system was detected, and no age significance could be gleaned from our Rb‐Sr data. The disturbance to the Rb‐Sr system may be due to a thermal event recorded by bulk‐rock K‐Ar ages of 1.56 Ga and U‐Pb ages of phosphates at about 1.35–1.5 Ga, which suggest partial resetting from an unknown thermal event(s), possibly accompanying breccia formation. The NWA 7034 bulk rock is LREE enriched and similar to KREEP‐rich lunar rocks, which indicates that the earliest Martian crust was geochemically enriched. This enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on Mars that have been detected in studies of other Martian meteorites.  相似文献   

Cellular diagnostics and coral health: declining coral health in the Florida Keys     

Downs CA  Fauth JE  Robinson CE  Curry R  Lanzendorf B  Halas JC  Halas J  Woodley CM 《Marine pollution bulletin》2005,51(5-7):558-569

Coral reefs within the Florida Keys are disappearing at an alarming rate. Coral cover in the Florida Keys National Marine Sanctuary declined by 38% from 1996 to 2000. In 2000, populations of Montastraea annularis at four sites near Molasses Reef within the Florida Keys National Marine Sanctuary and one reef within Biscayne National Park were sampled on a quarterly basis. Anecdotal observations showed corals at Alina's Reef in Biscayne National Park appeared healthy in March, but experienced an acute loss of coral cover by August. Cellular Diagnostic analysis indicated that Alina's Reef corals were in distress: they had been afflicted with a severe oxidative damaging and protein-denaturing stress that affected both the corals and their symbiotic zooxanthellae. This condition was associated with a significant xenobiotic detoxification response in both species, reflecting probable chemical contaminant exposure. These results demonstrate that applying a Cellular Diagnostic approach can be effective in helping to identify stress and its underlying causes, providing diagnostic and prognostic biomarkers of coral health.  相似文献   

Implications of ground water chemistry and flow patterns for earthquake studies   总被引：2，自引：0，他引：2  

Guangcai W  Zuochen Z  Min W  Cravotta CA  Chenglong L 《Ground water》2005,43(4):478-484

Ground water can facilitate earthquake development and respond physically and chemically to tectonism. Thus, an understanding of ground water circulation in seismically active regions is important for earthquake prediction. To investigate the roles of ground water in the development and prediction of earthquakes, geological and hydrogeological monitoring was conducted in a seismogenic area in the Yanhuai Basin, China. This study used isotopic and hydrogeochemical methods to characterize ground water samples from six hot springs and two cold springs. The hydrochemical data and associated geological and geophysical data were used to identify possible relations between ground water circulation and seismically active structural features. The data for delta18O, deltaD, tritium, and 14C indicate ground water from hot springs is of meteoric origin with subsurface residence times of 50 to 30,320 years. The reservoir temperature and circulation depths of the hot ground water are 57 degrees C to 160 degrees C and 1600 to 5000 m, respectively, as estimated by quartz and chalcedony geothermometers and the geothermal gradient. Various possible origins of noble gases dissolved in the ground water also were evaluated, indicating mantle and deep crust sources consistent with tectonically active segments. A hard intercalated stratum, where small to moderate earthquakes frequently originate, is present between a deep (10 to 20 km), high-electrical conductivity layer and the zone of active ground water circulation. The ground water anomalies are closely related to the structural peculiarity of each monitoring point. These results could have implications for ground water and seismic studies in other seismogenic areas.  相似文献   

On the paper of F. F. Evison, C. E. Ingham, R. H. Orr, and J. H. Le Fort, "Thickness of the Earth's Crust in Antarctica and the Surrounding Oceans."     

Charles R. Bentley  Ned A. Ostenso 《Geophysical Journal International》1962,6(3):292-298

  相似文献   

The groove and spur structures of Chagos atolls and their coral zonation     

Charles R.C. Sheppard 《Estuarine, Coastal and Shelf Science》1981,12(5):549-IN2

  相似文献   

Brightness variations of the white light corona during the years 1964–67     

Richard T. Hansen  Charles J. Garcia  Shirley F. Hansen  Harold G. Loomis 《Solar physics》1969,7(3):417-433

Observations of the white light corona were made on over 900 days during the years 1964–67 at heights between 1.125 and 2.0 R with the K-coronameter at Mount Haleakala and Mauna Loa, Hawaii. The brightness distribution of the minimum corona was elliptical with average equatorial intensities three times the polar. Coronal features of the new cycle at 1.125 R occurred predominantly in the sunspot zones at 25–30° latitude and in a high latitude zone which migrated toward the North pole before solar maximum. The brightness of the inner corona doubled over this period and a close association is found between the average corona and 10.7-cm solar radio flux. Electron densities in the equatorial regions were nearly twice those of Van de Hulst's model corona, in agreement with the results of recent eclipse observations.At Hawaii Institute of Geophysics.  相似文献   

Quantitative measurements of pollutant binding to dissolved humic materials compared with bulk properties of humic materials     

Charles W. Carter  Irwin H. Suffet 《Organic Geochemistry》1985,8(1):145-146

  相似文献   

Auroral Infrasonic Waves and Poleward Expansions of Auroral Substorms at Inuvik, N.W.T., Canada     

Charles R. Wilson 《Geophysical Journal International》1971,26(1-4):179-181

Summary Observations at Inuvik (70.4° dipole latitude) have shown that supersonic motions of auroral arcs that sweep across the zenith from south to north during poleward expansions of auroral substorms do not generate observable auroral infrasonic waves. This is in contrast to the fact that equator-ward supersonic motions of similar auroral arcs do produce large amplitude infrasonic bow waves. These results imply an asymmetry in the basic generation mechanism of infrasound within the auroral electrojet arcs.  相似文献   

An analytic model for upper atmosphere densities based upon Jacchia's 1970 models     

Charles E. Roberts Jr. 《Celestial Mechanics and Dynamical Astronomy》1971,4(3-4):368-377

An analytic model is presented which gives upper atmospheric densities as a function of the exospheric temperature and the altitude. The densities produced are identical to those produced by Jacchia's 1970 models (1970) for altitudes between 90 and 125 km and closely approximate Jacchia's values for altitudes greater than 125 km.  相似文献