Dynamic instability of seasonally thawing silty soils

1994 ◽  
Vol 31 (3) ◽  
pp. 454-462
Author(s):  
Eugene A. Voznesensky ◽  
Vladimir Y. Kalachev ◽  
Victor T. Trofimov ◽  
Victoria V. Kostomarova
Keyword(s):  
Grain Size ◽  
Dynamic Loading ◽  
Laboratory Experiments ◽  
Dynamic Behaviour ◽  
Dynamic Instability ◽  
Dynamic Properties ◽  
Clayey Soils ◽  
Mining Equipment ◽  
Silty Soils ◽  
Key Words Dynamic

The peculiarities of the dynamic behaviour of silty soils in laboratory experiments that simulate their interaction with gas mining equipment are analyzed. These seasonally thawing soils appear to be very sensitive to dynamic loading and sometimes even liquefaction. Several peculiarities of their dynamic behaviour include: (i) their special sensitivity to very definite and narrow vibration frequency ranges, which vary with grain size and moisture content, and result from the resonant effects in the soil; (ii) the redistribution of pore water during the vibration and subsequent regain; (iii) the thixotropic recovery of the soil after vibration, resulting in the regain of its strength over initial levels, water content and density being constant. Both dilatant and thixotropic effects take place in such soils during dynamic loading, distinguishing them from both clean sands and clayey soils. On the basis of the peculiarities of dynamic behaviour discussed, the authors consider such soils as dilatantly thixotropic dispersed systems. Key words : dynamic properties, soils, thixotropy, liquefaction, resonance, silts.

scholarly journals Structural Transitions at Microtubule Ends Correlate with Their Dynamic Properties in Xenopus Egg Extracts

2000 ◽  
Vol 149 (4) ◽  
pp. 767-774 ◽  
Author(s):  
Isabelle Arnal ◽  
Eric Karsenti ◽  
Anthony A. Hyman
Keyword(s):  
Dynamic Instability ◽  
Dynamic Properties ◽  
Microtubule Assembly ◽  
Two Dimensional ◽  
Egg Extracts ◽  
Xenopus Egg ◽  
Xenopus Egg Extracts ◽  
First Time ◽  
The Relationship ◽  
Dynamic Populations

Microtubules are dynamically unstable polymers that interconvert stochastically between growing and shrinking states by the addition and loss of subunits from their ends. However, there is little experimental data on the relationship between microtubule end structure and the regulation of dynamic instability. To investigate this relationship, we have modulated dynamic instability in Xenopus egg extracts by adding a catastrophe-promoting factor, Op18/stathmin. Using electron cryomicroscopy, we find that microtubules in cytoplasmic extracts grow by the extension of a two- dimensional sheet of protofilaments, which later closes into a tube. Increasing the catastrophe frequency by the addition of Op18/stathmin decreases both the length and frequency of the occurrence of sheets and increases the number of frayed ends. Interestingly, we also find that more dynamic populations contain more blunt ends, suggesting that these are a metastable intermediate between shrinking and growing microtubules. Our results demonstrate for the first time that microtubule assembly in physiological conditions is a two-dimensional process, and they suggest that the two-dimensional sheets stabilize microtubules against catastrophes. We present a model in which the frequency of catastrophes is directly correlated with the structural state of microtubule ends.

scholarly journals The effect of grain size on deformation and failure of copper under dynamic loading

1994 ◽  
Vol 04 (C8) ◽  
pp. C8-195-C8-199
Author(s):  
D. H. Lassila ◽  
M. M. LeBlanc ◽  
F. H. Magness
Keyword(s):  
Grain Size ◽  
Dynamic Loading ◽  
Deformation And Failure

scholarly journals The Influence of Grain Size Distribution on the Hydraulic Gradient for Initiating Backward Erosion

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2644 ◽  
Author(s):  
Willem-Jan Dirkx ◽  
Rens Beek ◽  
Marc Bierkens
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Laboratory Experiments ◽  
Hydraulic Gradient ◽  
Concentrated Flow ◽  
Pipe Formation ◽  
Novel Method ◽  
Flow Through ◽  
The Stability

Backward erosion by piping is one of the processes that threaten the stability of river embankments in the Netherlands. During high river stages, groundwater flow velocities underneath the embankment increase as a result of the steepened hydraulic gradient. If a single outflow point exists or forms, the concentrated flow can entrain soil particles, leading to the formation of a subsurface pipe. The processes controlling this phenomenon are still relatively unknown due to their limited occurrence and because piping is a subsurface phenomenon. To study the initiation of piping, we performed laboratory experiments in which we induced water flow through a porous medium with a vertically orientated outflow point. In these experiments, we explicitly considered grain size variations, thus adding to the existing database of experiments. Our experiments showed that the vertical velocity needed for the initiation of particle transport can be described well by Stokes’ law using the median grain size. We combine this with a novel method to relate bulk hydraulic conductivity to the grain size distribution. This shows that knowledge of the grain size distribution and the location of the outflow point are sufficient to estimate the hydraulic gradient needed to initiate pipe formation in the experiment box.

scholarly journals Detailed Study on the Mechanical Properties and Activation Energy of Natural Rubber/Chloroprene Rubber Blends during Aging Processes

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Quang Nguyen Trong ◽  
Hung Dang Viet ◽  
Linh Nguyen Pham Duy ◽  
Chuong Bui ◽  
Duong Duc La
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Dynamic Loading ◽  
Dynamic Properties ◽  
Activation Energies ◽  
Rubber Matrix ◽  
Static Properties ◽  
Rubber Blends ◽  
Aging Conditions ◽  
Mechanical Aging

Selection of a suitable thermal aging process could render desirable mechanical properties of the rubbers or blended rubbers. In this work, the effect of the aging processes on the mechanical properties and activation energies of natural rubbers (NR) and NR/chloroprene rubbers (CR) blends with low CR contents (5–10%) was investigated. Three aging processes including heat aging (at 110°C for 22 hours), mechanical aging (under dynamic loading to 140% strain for 16000 cycles), and complex aging (heat and mechanical aging) were studied. The results revealed that the compatibility of CR in natural rubber matrix had a significant effect on the dynamic properties of the blended rubber and negligible effect on the static properties. The changes in activation energies of the blended rubber during aging processes were calculated using Arrhenius relation. The calculated changes (ΔUc, ΔUd, and ΔUT) in activation energies were consistent with the results of mechanical properties of the blended rubber. Interestingly, the change in activation energies using complex aging conditions (ΔUc) was mostly equal to the total changes in activation energies calculated separately from heat aging (ΔUT) and mechanical aging (ΔUd) conditions. This indicates that, in complex aging conditions, the heat and dynamic loading factors act independently on the properties of the blended rubber.

Dissipation Pattern of Excess Pore Pressure After Liquefaction in Saturated Sand Deposits

2003 ◽  
Vol 1821 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Ik Soo Ha ◽  
Young Ho Park ◽  
Myoung Mo Kim
Keyword(s):  
Grain Size ◽  
Pore Pressure ◽  
Dynamic Loading ◽  
Time History ◽  
Excess Pore Pressure ◽  
Pore Pressures ◽  
Dissipation Pattern ◽  
Effective Grain Size ◽  
Coefficient Of Uniformity ◽  
Excess Pore

In liquefied areas, the amount of damage to a structure is mainly affected by the postliquefaction behavior of the liquefied ground. Understanding postliquefaction behavior requires understanding the dissipation pattern of excess pore pressure after liquefaction. It is difficult to measure pore pressures generated and dissipated during an earthquake because of the more-or-less randomness of earthquake events. Researchers have artificially generated liquefaction with sand samples in the laboratory and have simulated curves for the time history dissipation of excess pore pressure. To estimate variation in permeability during dynamic loading, which should be known for settlement predictions of the ground undergoing liquefaction, 1-g shaking table tests were carried out on five kinds of sands, all with high liquefaction potentials. During tests, excess pore pressures at various depths and surface settlements were measured. The measured curve of the excess pore pressure dissipation was simulated using the solidification theory. From analysis of the velocity of dissipation, the dissipation pattern of excess pore pressure after liquefaction was examined. Permeability during dissipation was calculated using the measured settlement and dissipation velocity, also used for estimating permeability during dynamic loading. The dissipation velocity of excess pore pressure after liquefaction had a linear correlation with the effective grain size divided by the coefficient of uniformity. The increase in the ground’s initial relative density played a role in shifting this correlation curve toward increased dissipation velocity. Permeability during liquefaction increased 1.4 to 5 times compared with the permeability of the original ground, the increase becoming greater as the effective grain size of the test sand increased and the coefficient of uniformity decreased.

Permeability of Marine Sediments and Tropical Volcanic Soils

2012 ◽  
Author(s):  
Horst G. Brandes
Keyword(s):  
Grain Size ◽  
Marine Sediments ◽  
Deep Sea ◽  
Carbonate Content ◽  
Clayey Soils ◽  
Index Properties ◽  
Volcanic Soils ◽  
Fine Grained ◽  
Deep Sea Sediments ◽  
Tropical Volcanic Soils

Permeability values for a range of fine-grained deep-sea sediments are presented and evaluated in terms of index properties such as plasticity, grain size and carbonate content. It is found that whereas clay-rich sediments have similar permeabilities to those of equivalent land-based fine-grained soils, the presence of volcanic, carbonate and other non-clay fractions tends to increase permeability somewhat. Volcanic silty-clayey soils from Hawaii have comparable permeability values, although they can be slightly more permeable.

scholarly journals Granulometric characterization of sediments transported by surface runoff generated by moving storms

2008 ◽  
Vol 15 (6) ◽  
pp. 999-1011 ◽  
Author(s):  
J. L. M. P. de Lima ◽  
C. S. Souza ◽  
V. P. Singh
Keyword(s):  
Grain Size ◽  
Surface Runoff ◽  
Laboratory Experiments ◽  
Overland Flow ◽  
Temporal Distribution ◽  
Surface Flow ◽  
Constant Speed ◽  
Stream Power ◽  
Sediment Grain Size ◽  
Rain Simulator

Abstract. Due to the combined effect of wind and rain, the importance of storm movement to surface flow has long been recognized, at scales ranging from headwater scales to large basins. This study presents the results of laboratory experiments designed to investigate the influence of moving rainfall storms on the dynamics of sediment transport by surface runoff. Experiments were carried out, using a rain simulator and a soil flume. The movement of rainfall was generated by moving the rain simulator at a constant speed in the upstream and downstream directions along the flume. The main objective of the study was to characterize, in laboratory conditions, the distribution of sediment grain-size transported by rainfall-induced overland flow and its temporal evolution. Grain-size distribution of the eroded material is governed by the capacity of flow that transports sediments. Granulometric curves were constructed using conventional hand sieving and a laser diffraction particle size analyser (material below 0.250 mm) for overland flow and sediment deliveries collected at the flume outlet. Surface slope was set at 2%, 7% and 14%. Rainstorms were moved with a constant speed, upslope and downslope, along the flume or were kept static. The results of laboratory experiments show that storm movement, affecting the spatial and temporal distribution of rainfall, has a marked influence on the grain-size characteristics of sediments transported by overland flow. The downstream-moving rainfall storms have higher stream power than do other storm types.

Mathematical modeling of microtubule dynamic instability: new insight into the link between gtp-hydrolysis and microtubule aging

2018 ◽  
Vol 52 (6) ◽  
pp. 2433-2456 ◽  
Author(s):  
Ayuna Barlukova ◽  
Diana White ◽  
Gérard Henry ◽  
Stéphane Honoré ◽  
Florence Hubert
Keyword(s):  
Dynamic Instability ◽  
Dynamic Properties ◽  
Model Parameters ◽  
Microtubule Dynamic ◽  
Gtp Hydrolysis ◽  
Unique Type ◽  
Microtubule Targeting Agents ◽  
Age Dependent ◽  
Type Of Behavior ◽  
Insight Into

Microtubules (MTs) are protein polymers that exhibit a unique type of behavior referred to as dynamic instability. That is, they undergo periods of growth (through the addition of GTP-tubulin) and shortening (through the subtraction of GDP-tubulin). Shortening events are very fast, where this transition is referred to as a catastrophe. There are many processes that regulate MT dynamic instability, however, recent experiments show that MT dynamics may be highly regulated by a MTs age, where young MTs are less likely to undergo shortening events than older ones. In this paper, we develop a novel modeling approach to describe how the age of a MT affects its dynamic properties. In particular, we extend on a previously developed model that describes MT dynamics, by proposing a new concept for GTP-tubulin hydrolysis (the process by which newly incorporated GTP-tubulin is hydrolyzed to lower energy GDP-tubulin). In particular, we assume that hydrolysis is mainly vectorial, age-dependent and delayed according to the GTP-tubulin incorporation into the MT. Through numerical simulation, we are able to show how MT age affects certain properties that define MT dynamics. For example, simulations illustrate how the aging process leads to an increase in the rate of GTP-tubulin hydrolysis for older MTs, as well as increases in catastrophe frequency. Also, since it has been found that MT dynamic instability is affected by chemotherapy microtubule-targeting agents (MTAs), we highlight the fact that our model can be used to investigate the action of MTAs on MT dynamics by varying certain model parameters.

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