ALBERT

Description: Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well-understood. This study aims to quantify the effects of a grass species, Cynodon dactylon , and a tree species, Schefflera heptaphylla , on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of Asia and U.S. A series of in-situ double-ring infiltration tests was conducted during a wet summer, while the responses of soil suction were mointored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity, due to the clogging of soil pore by plant roots. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root-water uptake by the selected species on suction were insignificant due to the small evapotranspiration (〈 0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass-covered and the tree-covered soil. However, it is identified that the grass and tree species having deeper root depth and greater root area retained higher suction. This article is protected by copyright. All rights reserved.

Description: It has been hypothesized that some of the irreversible microrheologic abnormalities of sickle red blood cell (RBC) membranes could result from autoxidative perturbation. To model this possibility, we used micromechanical manipulation to examine the static extensional rigidity and inelastic or plastic behavior of normal RBCs exposed to phenazine methosulfate (PMS), an agent that generates superoxide from within the cell. In response to this stress, RBC membranes became stiff as evidenced by increasing extensional rigidity. At 50 mumol/L PMS they were as stiff as the membranes of most dense, dehydrated sickle RBCs; and at 25 mumols/L PMS the membranes were similar to somewhat less dense sickle RBCs. When examined for inelastic behavior, RBCs exposed to PMS even at 10 mumols/L showed hysteresis in loading and unloading phases of the curve relating aspiration length to suction pressure, and they developed membrane bumps that persisted after RBC release from the pipette. Examination of single cells in both isotonic and hypotonic buffers showed that the effect of PMS on RBC microheology is not mediated by cellular dehydration. Independent confirmation of the membrane stiffening effect of PMS was obtained by ektacytometric analysis of resealed RBC ghosts, with sickle-like increases in membrane rigidity observed between 50 and 100 mumol/L PMS. The rigidity of these ghosts was partially ameliorated by exposure to a thiol reductant. In terms of biochemical abnormalities, treated RBCs became significantly different from control RBCs at 25 mumol/L PMS, at which point they just began to enter the sickle range for amounts of membrane thiol oxidation and membrane-associated heme. The sickle average was achieved at 50 mumol/L PMS (for thiol oxidation) to 100 mumol/L PMS (for membrane heme). Thus, micromolar concentrations of PMS induce abnormalities of membrane microrheology that closely mimic those of unmanipulated sickle RBCs while reproducing similar degrees of oxidative biochemical change. We conclude that membrane protein oxidation could explain existence of an irreversible component to the abnormal rheology of the sickle membrane.

Description: Membrane skeletal and cytoskeletal remodeling occurs throughout erythroid maturation. Microtubules and microfilaments have been identified morphologically in the nucleated erythroblast but the functional capability of these cytoskeletal structures during reticulocyte maturation has not been studied. Reticulocytes are formed from orthochromatic normoblasts by the process of nuclear extrusion. Two recognizable stages of reticulocyte maturation follow. The least mature reticulocytes are motile and multilobular, while the more mature reticulocytes are cup-shaped and nonmotile. To study the respective roles of microtubules and microfilaments in nuclear extrusion and cell motility, experiments were performed with agents that perturb these structures. Following the injection into rats of colchicine, a microtubule-disrupting substance, the number of normoblasts arrested at the stage of nuclear extrusion increased linearly over four hours. Similar results were obtained when bone marrow cells were incubated in culture in the presence of colchicine. In contrast, cell motility was dramatically decreased by cytochalasin B, a microfilament-disrupting agent, but not by colchicine. These results imply that microtubules are essential for the nuclear extrusion process, while microfilaments are essential for cell motility. Simultaneous changes in membrane skeletal assembly were assessed by measuring membrane deformability and stability, two properties regulated by the skeletal proteins. In ektacytometric assays, membrane deformability and mechanical stability of immature reticulocytes were markedly decreased to approximately 10% of normal, while that of more mature reticulocytes were nearly normal. Since the skeletal protein organization regulates these membrane properties, our findings imply that substantial membrane skeletal remodeling occurs during reticulocyte maturation. Thus we have identified major remodeling of both skeletal and cytoskeletal components during reticulocyte maturation.

Description: Membrane skeletal and cytoskeletal remodeling occurs throughout erythroid maturation. Microtubules and microfilaments have been identified morphologically in the nucleated erythroblast but the functional capability of these cytoskeletal structures during reticulocyte maturation has not been studied. Reticulocytes are formed from orthochromatic normoblasts by the process of nuclear extrusion. Two recognizable stages of reticulocyte maturation follow. The least mature reticulocytes are motile and multilobular, while the more mature reticulocytes are cup-shaped and nonmotile. To study the respective roles of microtubules and microfilaments in nuclear extrusion and cell motility, experiments were performed with agents that perturb these structures. Following the injection into rats of colchicine, a microtubule-disrupting substance, the number of normoblasts arrested at the stage of nuclear extrusion increased linearly over four hours. Similar results were obtained when bone marrow cells were incubated in culture in the presence of colchicine. In contrast, cell motility was dramatically decreased by cytochalasin B, a microfilament-disrupting agent, but not by colchicine. These results imply that microtubules are essential for the nuclear extrusion process, while microfilaments are essential for cell motility. Simultaneous changes in membrane skeletal assembly were assessed by measuring membrane deformability and stability, two properties regulated by the skeletal proteins. In ektacytometric assays, membrane deformability and mechanical stability of immature reticulocytes were markedly decreased to approximately 10% of normal, while that of more mature reticulocytes were nearly normal. Since the skeletal protein organization regulates these membrane properties, our findings imply that substantial membrane skeletal remodeling occurs during reticulocyte maturation. Thus we have identified major remodeling of both skeletal and cytoskeletal components during reticulocyte maturation.

Description: It has been hypothesized that some of the irreversible microrheologic abnormalities of sickle red blood cell (RBC) membranes could result from autoxidative perturbation. To model this possibility, we used micromechanical manipulation to examine the static extensional rigidity and inelastic or plastic behavior of normal RBCs exposed to phenazine methosulfate (PMS), an agent that generates superoxide from within the cell. In response to this stress, RBC membranes became stiff as evidenced by increasing extensional rigidity. At 50 mumol/L PMS they were as stiff as the membranes of most dense, dehydrated sickle RBCs; and at 25 mumols/L PMS the membranes were similar to somewhat less dense sickle RBCs. When examined for inelastic behavior, RBCs exposed to PMS even at 10 mumols/L showed hysteresis in loading and unloading phases of the curve relating aspiration length to suction pressure, and they developed membrane bumps that persisted after RBC release from the pipette. Examination of single cells in both isotonic and hypotonic buffers showed that the effect of PMS on RBC microheology is not mediated by cellular dehydration. Independent confirmation of the membrane stiffening effect of PMS was obtained by ektacytometric analysis of resealed RBC ghosts, with sickle-like increases in membrane rigidity observed between 50 and 100 mumol/L PMS. The rigidity of these ghosts was partially ameliorated by exposure to a thiol reductant. In terms of biochemical abnormalities, treated RBCs became significantly different from control RBCs at 25 mumol/L PMS, at which point they just began to enter the sickle range for amounts of membrane thiol oxidation and membrane-associated heme. The sickle average was achieved at 50 mumol/L PMS (for thiol oxidation) to 100 mumol/L PMS (for membrane heme). Thus, micromolar concentrations of PMS induce abnormalities of membrane microrheology that closely mimic those of unmanipulated sickle RBCs while reproducing similar degrees of oxidative biochemical change. We conclude that membrane protein oxidation could explain existence of an irreversible component to the abnormal rheology of the sickle membrane.

Description: [No abstract available]

Description: Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well-understood. This study aims to quantify the effects of a grass species, Cynodon dactylon, and a tree species, Schefflera heptaphylla, on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of the world and South China, respectively. A series of in-situ double-ring infiltration tests was conducted during a wet summer, while the responses of soil suction were monitored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root-water uptake by the selected species on suction were insignificant because of the small evapotranspiration (〈0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass-covered and the tree-covered soil. However, the grass and tree species having deeper root depth and greater Root Area Index (RAI) retained higher suction. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Description: A simple structure under earthquake excitation is modeled as a single-degree-of-freedom system with nonlinear stiffness subject to modulated Kanai-Tajimi excitation. The nonstationary responses including the nonstationary probability densities of the system responses and the statistical moments are obtained in semi-analytical form. By applying the stochastic averaging method based on the generalized harmonic functions, the averaged Fokker-Planck-Kolmogorov(FPK) equation governing the nonstationary probability density of the amplitude is derived. Then, the solution of the FPK equation is approximately expressed by a series expansion in terms of a set of properly selected basis functions with time-dependent coefficients. According to the Galerkin method, the time-dependent coefficients are solved from a set of linear first-order differential equations. Thus, the nonstationary probability densities of the amplitude and the state responses as well as the statistic moments of the amplitude are obtained. Finally, two types of the modulating functions, i.e. constant function and exponential function, are considered to give some semi-analytical formulae. The proposed procedures are checked against the Monte Carlo simulation. The effects of the structure natural frequency and the intensity of the excitation as well as the ground stiffness on the system responses are discussed. It should be pointed out that the proposed method is good for broadband excitation and light damping. © 2011 John Wiley & Sons, Ltd.

Description: There are many traditional methods to find the optimum parameters of a tuned mass damper (TMD) subject to stationary base excitations. It is very difficult to obtain the optimum parameters of a TMD subject to non-stationary base excitations using these traditional optimization techniques. In this paper, by applying particle swarm optimization (PSO) algorithm as a novel evolutionary algorithm, the optimum parameters including the optimum mass ratio, damper damping and tuning frequency of the TMD system attached to a viscously damped single-degree-of-freedom main system subject to non-stationary excitation can be obtained when taking either the displacement or the acceleration mean square response, as well as their combination, as the cost function. For simplicity of presentation, the non-stationary excitation is modeled by an evolutionary stationary process in the paper. By means of three numerical examples for different types of non-stationary ground acceleration models, the results indicate that PSO can be used to find the optimum mass ratio, damper damping and tuning frequency of the non-stationary TMD system, and it is quite easy to be programmed for practical engineering applications. Copyright © 2008 John Wiley & Sons, Ltd.

Description: A damper device based on shape memory alloy (SMA) wires is developed for structural control implementation. The design procedures of the SMA damper are presented. As a case study, eight such SMA dampers are installed in a frame structure to verify the effectiveness of the damper devices. Experimental results show that vibration decay of the SMA damper controlled frame is much faster than that of the uncontrolled frame. The finite-element method is adopted to conduct the free and forced vibration analysis of the controlled and uncontrolled frame. The experimental and numerical results illustrate that the developed SMA dampers are very effective in reducing structural response and have great potential for use as efficient energy dissipation devices with the advantages of good control of force and no lifetime limits, etc. © 2003 John Wiley and Sons, Ltd.