1,721,910 research outputs found
Mitogenic signal transduction by integrin- and growth factor receptor-mediated pathways
No full textEngagement of cells with the extracellular matrix (ECM) proteins is crucial for various biological processes, including cell adhesion, spreading, proliferation, differentiation, migration, apoptosis, and gene induction, contributing to maintenance of tissue integrity, embryogenesis, wound healing, and the metastasis of tumor cells (Hynes, 2002b; Juliano, 2002). The engagement involves cell adhesion mediated by integrins, a large family of cell adhesion receptors that are transmembrane glycoproteins which bind to ECM or to counter-receptors on neighbor cells. In this review, the molecular basis of signaling mediated by integrins and their collaboration with growth factor receptors will be discussed, based on recent observations. Although other cell adhesion receptors including cadherins, selectins, syndecans, and the immunoglobulin superfamily of cell adhesion molecules (IgCAMs) can play important roles or be involved in these processes, we suggest readers refer to recent outstanding reviews on them.N
Characteristics of kinetic energy transfer in collisions between a rigid and a fragile nano particles
No full textThe characteristics of kinetic energy transfer during a collision between a rigid target particle on a surface and a fragile bullet particle (BP) moving at a high velocity were analyzed by Molecular Dynamics (MD) simulation. Ar, N-2, and CO2 BPs were considered; their size, temperature and velocity were varied over a wide range. The fraction (F-K) of kinetic energy transferred from the BP to the target particle was almost independent of BP size or velocity, but was sensitively dependent on BP type and temperature. The rigidity or the average potential energy of the BP was a dominant factor determining the post-collision behavior of the target particle and F-K. F-K was almost linearly proportional to the average potential energy per molecule of the BP. (C) 2015 Elsevier Ltd. All rights reserved.1111sciescopu
Monte-Carlo simulation of turbulent deposition of charged particles in a plate-plate electrostatic precipitator
No full textThe characteristics of turbulent deposition of charged particles in a plate-plate electrostatic precipitator (ESP) are analyzed by the Lagrangian simulation method which uses the concept of time series analysis for the particle motion in a turbulent flow field. With the advantage of the Lagrangian method, several important parameters are taken into account such as the effect of nonuniform diffusivity on the particle motion and the effects of particle inertia including the crossing trajectory effect, boundary layer trapping and the lift force near the wall. Collection efficiencies are obtained without any simplified treatment for a wide range of Peclet number (Pe*) of interest, where it is found that the collection efficiency is mainly the function of Pe* and Deutsch number, and the dependency on particle relaxation time is negligible in the range about Pe* > 0.1. Moreover, the characteristics of deposition at the intermediate Pe* is analyzed clearly, where both the diffusion and migration by external force play an important role on the deposition.X1113sciescopu
Analysis of the compression characteristics of vapor jet injected into high vacuum
No full textThe working principle of diffusion pump, a kind of vacuum pumps, is to use the high momentum of vapor jet which is injected into high vacuum. Since flow regime inside the diffusion pump consists of continuum, transition and free molecular, a continuum approach is not valid to calculate the flow field. In this paper, the compression characteristics of a vapor jet into high vacuum were simulated using the direct simulation Monte Carlo (DSMC) method. The hard sphere model is used as a molecular model and the no time counter (NTC) scheme is employed as a collision sampling technique. Steady state flow characteristics such as velocity, temperature, density distributions of the pumped gas and oil vapor are calculated by simulating about hundreds of thousand molecules. The main result is that the pumping speed of a single stage pump can be described based on the transmission probabilities which have nearly constant values irrespective of pressures at the inlet and outlet. Using these features, compression characteristics of diffusion pump can also be described by transmission probability concept as in the case of other high vacuum pump.X11sciescopu
NUMERICAL-SIMULATION OF AIR-FLOW AND INERTIAL DEPOSITION OF PARTICLES IN A BIFURCATING CHANNEL OF SQUARE CROSS-SECTION
No full textAir flow pattern and inertial deposition of particles in a bifurcating channel of square cross section have been studied numerically. The Navier-Stokes equation for the air flow are solved in an Eulerian grid system first, and then the particle trajectories are tracked in a Lagrangian coordinate system. The three dimensional flow pattern in a bifurcating airway is analysed, and the role played by the secondary flow is studied. Geometry of the channel, radius of curvature at the bend comer, bifurcation angle, particle size, average flow velocity and the velocity profile at the inlet are the important parameters considered in the present study. The roundness at the bend comer and the intensity of secondary flow were found to play an important role in both the air flow pattern and the particle deposition. The characteristics of particle deposition could be well explained by the flow characteristics. Under certain conditions, the present results are in good agreement with the experimental data in the literature, and the discrepancy existing under other conditions could also be explained by considering the characteristics of the secondary flow .X1117sciescopu
A singular fixed-point homotopy method to locate the closest unstable equilibrium point for transient stability region estimate
No full textThe closest unstable equilibrium point (UEP) method is a well-known direct method of the Lyapunov type for optimally estimating stability regions of nonlinear dynamical systems. One key step involved in the closest UEP methodology is the computation of the closest unstable equilibrium point that has the lowest Lyapunov function value on the stability boundary. In this papers a new computational algorithm to compute the closest UEP is presented. The proposed algorithm is based on a homotopy-continuation method combined with the singular fixed-point strategy. Numerical simulation results show that the algorithm outperforms previously reported existing techniques.X1121sciescopu
AN OBSERVER DESIGN FOR TIME-DELAY CONTROL AND ITS APPLICATION TO DC SERVO MOTOR
No full textThis paper addresses the estimation problem of states and their derivatives for the Time Delay Control (TDC), a robust control technique for nonlinear systems. To this end, an observer design method is presented. Then, in simulations, the controller/observer has been applied to a nonlinear plant, with satisfactory results. Finally, experiments were undertaken on a DC servo motor subject to substantial inertia variations and external disturbances. The results showed that the controller/observer performs quite robustly under those variations and disturbances, and is much less sensitive to sensor noise than the controller using numerical differentiations
THERMAL-ANALYSIS OF CRYOPUMP 1ST STAGE ARRAY
No full textDetailed numerical analysis of the heat transfer in the first stage array of a model cryopump 20 cm dia was performed for both the steady state and the unsteady cooldown period, to find the effect on the temperature distribution and the cooldown time of several design parameters such as thickness and surface emissivity of the radiation shield, the use of thermal struts, shape of the thermal anchor, and the choice of shield material between aluminum and OFHC copper. The variation of thermal conductivity and heat capacity with temperature was taken into account. Some important results with typical parameters are: the aluminum shield cools down faster than the copper, especially for heavy thermal load; for copper shields thinner than 1 mm, a thicker shield gives shorter cooldown time; the use of thermal struts can shorten the cooldown time if only the mass of the struts is less than about 25% of that of the shield; there exists an optimum thickness for a thermal anchor which minimizes the temperature difference in the first stage array.X110sciescopu
Condensation and evaporation of a nano-sized particle moving in a fluid environment
No full textCondensation and evaporation of a low temperature nano-sized argon particle moving in a gas/vapor environment were analyzed using the molecular dynamics simulation. First evaporation temperature for various heating rates was found and successfully compared with the analytic result. Condensation and evaporation rates observed through simulation depended on particle velocity and thermodynamic properties of the gas, and the radial distribution of particle temperature was found to be a good indicator to characterize the process. Characteristics of condensation and evaporation for four different particle velocities and various environmental conditions were discussed in detail. In low gas density environments all the gas atoms got condensed on the particle, and in high gas density environment condensation/evaporation characteristics became much different depending on particle velocity. (c) 2007 Elsevier Ltd. All rights reserved.X117sciescopu
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