Stress transition around large spherical inclusions in granular media

2020 ◽  
pp. 227-229
Author(s):  
S.J. Antony ◽  
M. Ghadiri
Keyword(s):  
Granular Media ◽  
Spherical Inclusions ◽  
Large Spherical

An intraerythrocytic virus and rickettsia of frogs from Algonquin Park, Ontario

1984 ◽  
Vol 62 (8) ◽  
pp. 1521-1524 ◽  
Author(s):  
Sherwin S. Desser ◽  
John R. Barta
Keyword(s):  
Electron Microscope ◽  
Rana Catesbeiana ◽  
Blood Parasites ◽  
Rana Clamitans ◽  
Virus Particles ◽  
Spherical Inclusions ◽  
Sphagnum Bog ◽  
Prokaryotic Microorganisms ◽  
Large Spherical

Two prokaryotic microorganisms were observed in the erythrocytes of frogs in a survey of blood parasites of six species of amphibians from a sphagnum bog adjacent to Lake Sasajewun, Algonquin Park, Ontario. A cytoplasmic virus was observed in 12 of 75 Rana catesbeiana and 1 of 75 Rana septentrionalis. The virus particles were hexagonal in section, measured 300–370 nm in diameter, and occurred in groups that were often surrounded by lamellar arrays of stacked membranes. Large spherical inclusions were seen in the erythrocytes of 2 of 57 Rana clamitans. In the electron microscope these inclusions were found to contain numerous rod-shaped prokaryotes which measured 1–1.7 μm × 200–300 nm. These organisms were ultrastructurally indistinguishable from rickettsiae.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

The microstructure change of low-carbon electrical steels by residual aluminum

1989 ◽  
Vol 47 ◽  
pp. 286-287
Author(s):  
C.K. Hou ◽  
C.T. Hu ◽  
Sanboh Lee
Keyword(s):  
Annealing Treatment ◽  
Low Carbon ◽  
Electrical Steels ◽  
Vacuum Degassing ◽  
Spherical Inclusions ◽  
Residual Aluminum ◽  
Average Grain Size ◽  
The Matrix ◽  
Fine Size ◽  
To Come

The fully processed low-carbon electrical steels are generally fabricated through vacuum degassing to reduce the carbon level and to avoid the need for any further decarburization annealing treatment. This investigation was conducted on eighteen heats of such steels with aluminum content ranging from 0.001% to 0.011% which was believed to come from the addition of ferroalloys.The sizes of all the observed grains are less than 24 μm, and gradually decrease as the content of aluminum is increased from 0.001% to 0.007%. For steels with residual aluminum greater than 0. 007%, the average grain size becomes constant and is about 8.8 μm as shown in Fig. 1. When the aluminum is increased, the observed grains are changed from the uniformly coarse and equiaxial shape to the fine size in the region near surfaces and the elongated shape in the central region. SEM and EDAX analysis of large spherical inclusions in the matrix indicate that silicate is the majority compound when the aluminum propotion is less than 0.003%, then the content of aluminum in compound inclusion increases with that in steel.

Electron-diffraction studies of amorphous carbon thin films

1993 ◽  
Vol 51 ◽  
pp. 1100-1101
Author(s):  
David A. Muller
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Amorphous Carbon ◽  
Glassy Carbon ◽  
Spherical Structure ◽  
Local Ordering ◽  
Carbon Arc ◽  
Similar Appearance ◽  
Carbon Thin Films ◽  
Large Spherical

The sp2 rich amorphous carbons have a wide variety of microstructures ranging from flat sheetlike structures such as glassy carbon to highly curved materials having similar local ordering to the fullerenes. These differences are most apparent in the region of the graphite (0002) reflection of the energy filtered diffracted intensity obtained from these materials (Fig. 1). All these materials consist mainly of threefold coordinated atoms. This accounts for their similar appearance above 0.8 Å-1. The fullerene curves (b,c) show a string of peaks at distance scales corresponding to the packing of the large spherical and oblate molecules. The beam damaged C60 (c) shows an evolution to the sp2 amorphous carbons as the spherical structure is destroyed although the (220) reflection in fee fcc at 0.2 Å-1 does not disappear completely. This 0.2 Å-1 peak is present in the 1960 data of Kakinoki et. al. who grew films in a carbon arc under conditions similar to those needed to form fullerene rich soots.

Role of contact couples and couple stress in the behaviour of granular media

1998 ◽  
Vol 08 (PR8) ◽  
pp. Pr8-87-Pr8-94
Author(s):  
F. Dedecker ◽  
Ph. Dubujet ◽  
B. Cambou
Keyword(s):  
Couple Stress ◽  
Granular Media

Avalanche Stratification - Experimental Tests of the “Metastable Wedge” and “Continuous Flow” Models

2000 ◽  
Vol 627 ◽  
Author(s):  
M. E. Swanson ◽  
M. Landreman ◽  
J. Michel ◽  
J. Kakalios
Keyword(s):  
Continuous Flow ◽  
Granular Media ◽  
Experimental Tests ◽  
Coarse Sand ◽  
Angle Of Repose ◽  
Flow Models ◽  
Maximum Angle ◽  
Stratification Effect ◽  
Upward Moving ◽  
Moving Layer

ABSTRACTWhen an initially homogeneous binary mixture of granular media such as fine and coarse sand is poured near the closed edge of a “quasi-two-dimensional” Hele-Shaw cell consisting of two vertical transparent plates held a narrow distance apart, the mixture spontaneously forms alternating segregated layers. Experimental measurements of this stratification effect are reported in order to determine which model, one which suggests that segregation only occurs when the granular material contained within a metastable heap between the critical and maximum angle of repose avalanches down the free surface, or one for which the segregation results from smaller particles becoming trapped in the top surface and being removed from the moving layer during continuous flow. The result reported here indicate that the Metastable Wedge model provides a natural explanation for the initial mixed zone which precedes the formation of the layers, while the Continuous Flow model explains the observed upward moving kink of segregated material for higher granular flux rates, and that both mechansims are necessary in order to understand the observed pairing of segregated layersfor intermediate flow rates and cell separations.

Stress fields in granular material and implications for performance of robot locomotion over granular media

2015 ◽  
Vol 8 (1) ◽  
pp. 2005-2009
Author(s):  
Diandong Ren ◽  
Lance M. Leslie ◽  
Congbin Fu
Keyword(s):  
Mechanical Properties ◽  
Granular Material ◽  
Granular Media ◽  
Rotation Frequency ◽  
Legged Locomotion ◽  
Working Environment ◽  
Navier Stokes ◽  
Maximum Speed ◽  
Sigmoid Curve ◽  
Multi Body

 Legged locomotion of robots has advantages in reducing payload in contexts such as travel over deserts or in planet surfaces. A recent study (Li et al. 2013) partially addresses this issue by examining legged locomotion over granular media (GM). However, they miss one extremely significant fact. When the robot’s wheels (legs) run over GM, the granules are set into motion. Hence, unlike the study of Li et al. (2013), the viscosity of the GM must be included to simulate the kinematic energy loss in striking and passing through the GM. Here the locomotion in their experiments is re-examined using an advanced Navier-Stokes framework with a parameterized granular viscosity. It is found that the performance efficiency of a robot, measured by the maximum speed attainable, follows a six-parameter sigmoid curve when plotted against rotating frequency. A correct scaling for the turning point of the sigmoid curve involves the footprint size, rotation frequency and weight of the robot. Our proposed granular response to a load, or the ‘influencing domain’ concept points out that there is no hydrostatic balance within granular material. The balance is a synergic action of multi-body solids. A solid (of whatever density) may stay in equilibrium at an arbitrary depth inside the GM. It is shown that there exists only a minimum set-in depth and there is no maximum or optimal depth. The set-in depth of a moving robot is a combination of its weight, footprint, thrusting/stroking frequency, surface property of the legs against GM with which it has direct contact, and internal mechanical properties of the GM. If the vehicle’s working environment is known, the wheel-granular interaction and the granular mechanical properties can be grouped together. The unitless combination of the other three can form invariants to scale the performance of various designs of wheels/legs. Wider wheel/leg widths increase the maximum achievable speed if all other parameters are unchanged.

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