Local Maximum Value Research Articles

Cell Guidance on Nanogratings: A Computational Model of the Interplay between PC12 Growth Cones and Nanostructures

BackgroundRecently, the effects of nanogratings have been investigated on PC12 with respect to cell polarity, neuronal differentiation, migration, maturation of focal adhesions and alignment of neurites.Methodology/Principal FindingsA synergistic procedure was used to study the mechanism of alignment of PC12 neurites with respect to the main direction of nanogratings. Finite Element simulations were used to qualitatively assess the distribution of stresses at the interface between non-spread growth cones and filopodia, and to study their dependence on filopodial length and orientation. After modelling all adhesions under non-spread growth cone and filopodial protrusions, the values of local stress maxima resulted from the length of filopodia. Since the stress was assumed to be the main triggering cause leading to the increase and stabilization of filopodia, the position of the local maxima was directly related to the orientation of neurites. An analytic closed form equation was then written to quantitatively assess the average ridge width needed to achieve a given neuritic alignment (R2 = 0.96), and the alignment course, when the ridge depth varied (R2 = 0.97). A computational framework was implemented within an improved free Java environment (CX3D) and in silico simulations were carried out to reproduce and predict biological experiments. No significant differences were found between biological experiments and in silico simulations (alignment, p = 0.3571; tortuosity, p = 0.2236) with a standard level of confidence (95%).Conclusions/SignificanceA mechanism involved in filopodial sensing of nanogratings is proposed and modelled through a synergistic use of FE models, theoretical equations and in silico simulations. This approach shows the importance of the neuritic terminal geometry, and the key role of the distribution of the adhesion constraints for the cell/substrate coupling process. Finally, the effects of the geometry of nanogratings were explicitly considered in cell/surface interactions thanks to the analytic framework presented in this work.

Pulsatile MHD Arterial Blood Flow in the Presence of Double Stenoses

The hemodynamics provides a way to predict effect of atherosclerosis by means of mathematical models. The pulsatile flow of blood through an artery with two side-to-side axisymmetric stenoses has been considered. A static transverse magnetic field to the flow is taken into account. The velocity profile, Wall Shear Stress and Wall Shear Stress Gradient to the flow have been simulated under the influence of magnetic field for various values of length and thickness of the stenosis. The upstream flow velocity in the subsequent stenosis region is significantly lower down from the velocity in the preceding stenosis region. The flow velocity decreases with the increase of Hartmann number. In the stenosis region wall shear stress (WSS) increases from unstenosed region to maximum thickness of stenosis. The wall shear stress (WSS) increases with the increase of Hartmann number and Womersley number. The WSSG have local maximum value in the vicinity of the throat of the stenoses and oscillates in the stenosed portion of the artery. The magnitude of WSSG is directly proportional to the Hartmann number. WSSG increases in magnitude on the upstream and downstream section of both the stenoses with the increase of Womersley number. Generated data are analyzed and discussed through graphs.

The effect of geometric parameters on mixed convection in an inclined eccentric annulus

Laminar mixed convection in an inclined eccentric straight annulus is studied numerically in this article. The coupled Navier–Stokes and energy equations are solved using finite difference method. The projection algorithm is employed for solution and to cope with the problem geometry, the cylindrical bipolar coordinate is used. To model natural convection, Boussinesq approximation is used for the body force term in the equations of motion. Developing hydrodynamic and thermal conditions are assumed for simulation. The inner wall is subjected to a fixed heat flux and the outer one is insulated. The effect of different parameters such as eccentricity, radius ratio and inclination on flow field and thermal characteristics is studied. It has been found that the Nusselt number has a local maximum value about 55° from vertical by laying down the annuli.

Turbulence induced by a solitary wave propagating over a submerged object using particle image velocimetry

Wu, Y.-T. and Hsiao, S.-C., 2013. Turbulence induced by a solitary wave propagating over a submerged object using particle image velocimetry.We present an experimental study for solitary wave propagation over a submerged rectangular obstacle using the particle image velocimetry (PIV) technique. The PIV system, mainly consisting of a digital high-resolution camera and a dual-head pulse laser, is used to measure instantaneous free surface motion and corresponding velocity properties around the submerged object. Four fields of view (FOVs) are set in order to form a continuous flow fields around the structure. Quantitative mean properties are obtained by ensemble averaging 30 repeated measurements for each FOV. Therefore, the entire data of the time histories of the free surface elevation recorded by wave gauge is 120 sets, and the standard deviation (STD) for incident wave height is 0.61 mm or 1.3% of mean incident wave height. The experiments show high degree of repeatability. After gaining the mean velocity properties, the vorticity field can be calculated by taking curl of mean velocity field and the turbulent kinetic energy can be estimated from velocity fluctuations. It is found that the measured turbulence in the weather side is much larger than that in the lee side of object. A local maximum value of turbulent intensity in the weather side of object is about 63.4% of depth-averaged velocity as the crest of solitary wave approaches but not yet reaches the front edge of breakwater. On the other hand, a local maximum value of turbulent intensity in the trailing edge is around 37.1% of depth-averaged velocity.

高质量ZnO及BeZnO薄膜的发光性质

High-quality ZnO and BeZnO films were grown on c-plane sapphire substrate using plasma-assisted molecular beam epitaxy(P-MBE) by inserting metal oxide buffer layers.X-ray diffraction(XRD) results show that all films have hexagonal wurtzite structure and highly c-axis orientation.The full width at half maximum(FWHM) of ZnO film is as low as 108 arcsec,and the FWHM of BeZnO film is less than 600 arcsec.The resonance Raman spectra show that both A1(LO) and A1(2LO) phonon modes shift to larger wavenumber with more Be doping.For the first time,the local vibration mode related to Be doping is found.The photoluminescence(PL) spectrum of ZnO films has only one emission peak(378 nm) at room temperature.However,another peak due to the strong free exciton emission is observed at low temperature(80 K).With the temperature increasing,the free exciton emission dominated over the bound exciton emission,and its peak shows gradual red shift.As for BeZnO film,the strong free exciton emission peak is not found at low temperature (80K) due to the declined crystal quality caused by the incorporation of Be.It is also found that the peak position of BeZnO films in the PL and Raman spectra have local maximum values between 100～200 K,which is suggested to be caused by the stress effect due to the thermal expansion mismatch of the alloy lattices.

Rules for predicting regime change in the Lorenz chaotic system based on the Lorenz map

Corresponding to two strange Lorenz attractors, in the Lorenz model there exist two opposite regimes which can be called as positive and negative regimes. Despite the trajectory of the Lorenz system changing between the two regimes back and forth with an unfixed period, the regime change is predictable. In this paper, with the help of the Lorenz map, three rules for predicting regime change are obtained. In particular, besides two generic predictable rules for the condition of regime transition and duration in new regime, a new rule about length for reaching transition condition, which has not been reported in previous work, is also very important. It provides another approach to forecasting the evolution of the nonlinear dynamical system. The results show that the position for highest point in cusps is the critical value for regime change. When the value of variable z is greater than the corresponding critical value, the current regime is about to end, and the Lorenz model will move to other regime in the next cycle. The length for reaching transition condition in the current regime decreases monotonically with local maximum value zmax, and the smaller zmax in current status implies the bigger length for reaching transition condition. The duration in new regime increases monotonically with the maximum value zM in the previous regime, and the bigger the value of zM, the larger the range for the duration increase is. In addition, the forcing is also associated with the prediction rules for regime change. It not only makes transition conditions for positive and negative regimes different, but also determines the speed of decrease in length for reaching transition condition and the range of increase for duration in new regime.

Characterization of edge radial electric field structures in the Large Helical Device and their viability for determining the location of the plasma boundary

This paper provides a systematic investigation on how plasma conditions (magnetic configuration, collisionality and beta) affect the edge radial electric field (Er) structure derived from charge exchange spectroscopic measurements in the Large Helical Device. We found that the location at which the spatial derivative in the Er structure (∇Er) had a local maximum value shifts outwards from the vacuum last closed flux surface location as the volume-averaged plasma beta (the ratio of the plasma pressure to the magnetic pressure, β ≡ 〈βdia〉 measured by a diamagnetic loop) becomes large. The loss of electrons on the open field lines, leaving the ions behind, might be the physics that determines the positive Er structure just outside the plasma boundary. The collisionality dependence of the experimentally observed Er values inside the plasma boundary is found to be consistent with a neoclassical ambipolar condition, while the Er formation outside the plasma boundary is different from the trend that is predicted by the neoclassical theory inside the plasma boundary. Furthermore, experimental data on saturation in the shift of the location even in a higher β regime (3% ⩽ β ⩽ 4.5%) are presented, inferring and predicting shrinkage of the plasma (i.e. a reduction in the averaged minor radius) in the higher β regime in which the Shafranov shift becomes larger.

A quantitative study on accumulation of age mass around stagnation points in nested flow systems

The stagnant zones in nested flow systems have been assumed to be critical to accumulation of transported matter, such as metallic ions and hydrocarbons in drainage basins. However, little quantitative research has been devoted to prove this assumption. In this paper, the transport of age mass is used as an example to demonstrate that transported matter could accumulate around stagnation points. The spatial distribution of model age is analyzed in a series of drainage basins of different depths. We found that groundwater age has a local or regional maximum value around each stagnation point, which proves the accumulation of age mass. In basins where local, intermediate and regional flow systems are all well developed, the regional maximum groundwater age occurs at the regional stagnation point below the basin valley. This can be attributed to the long travel distances of regional flow systems as well as stagnancy of the water. However, when local flow systems dominate, the maximum groundwater age in the basin can be located around the local stagnation points due to stagnancy, which are far away from the basin valley. A case study is presented to illustrate groundwater flow and age in the Ordos Plateau, northwestern China. The accumulation of age mass around stagnation points is confirmed by tracer age determined by 14C dating in two boreholes and simulated age near local stagnation points under different dispersivities. The results will help shed light on the relationship between groundwater flow and distributions of groundwater age, hydrochemistry, mineral resources, and hydrocarbons in drainage basins.

A comprehensive method of contour extraction for industrial computed tomography images

A novel contour extraction method is presented in this paper. In reverse engineering based on industrial computed tomography, quality of extracted contours greatly influences the reverse results. As a widely used method of edge extraction, the wavelet transform modulus maximum algorithm is also employed to extract contours. It often gets results through thresholding wavelet transform coefficients and then follows it up by edge tracking. Generally, threshold affects the accuracy of edge localization, and additional edge tracking increases complexity. To overcome these shortcomings, in this paper, we present a method of contour extraction synchronizing with edge tracking but omitting the thresholding process. Firstly, wavelet transform is performed on an original gray image to get modulus matrix. Secondly, by manually clicking inside and outside of the desired contour on the original image, a starting contour point can be obtained through determination of local modulus maximum value. Thirdly, on the mask centered on the starting contour point, a next contour point can be automatically detected by searching local modulus maximum value. Then, starting from that new contour point and recursively seeking the local modulus maximum value, an occlusive contour can be correctly found. Experiments show that this method can directly extract continuous and single-pixel wide contours from gray image.

Residual Stress and Deformation After Finishing of a Shell Structure Fabricated by Direct Metal Lamination Using Arc Discharge

Arc welding technology has been used to melt metal, and a fabrication system for three-dimensional metallic parts has been developed around it: direct metal lamination using arc discharge. Here, the relationship between residual stress in the shell structure and temperature distribution in the shell structure after lamination are explored. Deformation caused by residual stress release is also measured. The results clarify that the local maximum value of the residual stress is small when the temperature in the shell structure is high. It is also found that the temperature distribution can be controlled through heat-input conditions and a cooling method using water. The residual stress distribution is formed by a non-uniform compressive plastic strain distribution. Plastic deformation is caused by the temperature distribution. No significant deformation due to residual stress release is observed when the lateral surface is finished.

Cellular Automaton Modeling of the Interaction between Vehicles and Pedestrians at Signalized Crosswalk

Characteristics of mixed traffic on a road with a signalized crosswalk are investigated by cellular automaton modeling. The interaction mechanism between vehicles and pedestrians is taken into account. Also, the inordinate behavior of vehicles near the crosswalk, and various behaviors of three types of pedestrians (i.e., careful pedestrians, normal pedestrians, and riskers), are incorporated into the proposed model. By using numerical simulations, the case for pedestrian flow consisting of careful and normal pedestrians is investigated. Phase diagrams and spatiotemporal diagrams are presented to show different traffic states. The results show that there is a critical value that divides the vehicle flow into a free flow portion and a congested flow portion. Interestingly, there are two critical values for pedestrian flow for a large signal cycle value, whereas there is only one critical value when the signal cycle value is smaller than a critical value. Finally, the variation of violating frequency against time during a signal cycle is investigated. It is found that there are two local maximum values on the frequency curves when the pedestrians consist of all three types, and this phenomenon is coincident with the qualitatively real traffic.

Response characteristics and tomographic monitoring of the electric capacitance after irrigation in the soil–plant (ginkgo tree) continuum in a laboratory

The temporal and spatial variations of electrical capacitance of the soil–plant continuum in a laboratory were investigated. Based on a potted ginkgo tree with six irrigations, the electrical capacitance of the soil, trunk, and soil–trunk electrode pairs was measured, corresponding soil water content was computed, and spatial imaging was conducted. The soil electrical capacitance increases to a local maximum value immediately after irrigation, and then decreases gradually with time. During the late period of each drying procedure, there is a decussation area of high water content at the middle part of the circular region in the spatial imaging, which indicates root distribution in soil to some degree. Upon irrigation under a dry soil condition, the trunk electrical capacitance gradually increases for a period, and then begins to fluctuate with time; whereas, under a wet soil condition, it always fluctuates with time. Under a stable condition of overall change, the trunk electrical capacitance changes saltatorially and daily periodically. The temporal variation of the soil–trunk electrical capacitance exhibits both the character of soil and trunk.

Propagation of solitary waves over a bottom-mounted barrier

The interactions between a solitary wave and a submerged, vertical, bottom-mounted barrier are investigated experimentally and numerically. Numerical results are calculated using the well-validated two-dimensional volume of fluid (VOF)-type model, named COBRAS (COrnell BReaking And Structure), based on the Reynolds-Averaged Navier–Stokes (RANS) equations and the non-linear k–ε turbulence closure model. Experiments are conducted to measure the free surface motion and velocity fields using a particle image velocimetry (PIV) system to provide data for model validation. Fairly good agreements at both the pre- and post-breaking stages are obtained. Then, the verified numerical results are employed to illustrate the free surface motion and the vortex evolution in detail. Wave breaking occurs in the direction opposite to that of the wave after a solitary wave propagates over the barrier. A local maximum value of turbulence intensity is observed for both experimental and numerical results at the impinging point of the breaking wave. An almost linear relationship between the maximum net force and the wave non-linearity is obtained. The effectiveness of the bottom-mounted barrier is estimated by evaluating the wave reflection, transmission, and dissipation coefficients using the energy integral method. Finally, the trajectories of marked fluid particles that are initially located around the barrier help understand the possible sediment transport.

Influence of Bottom Bubbling Rate on Formation of Metal Emulsion in Al^|^ndash;Cu Alloy and Molten Salt System

In steel refining process, an increase of interfacial area between the metal and slag through the metal droplets emulsified into the slag, so-called “metal emulsion”, is one prevailing view for improving the reaction rate. The formation of metal emulsion was experimentally evaluated using Al–Cu alloy as metal phase and chloride salt as slag phase under the bottom bubbling condition. Samples were collected from the center of the salt phase in the container. Large number of metal droplets were separated from the salt by dissolving it into water. The number, surface area, and weight of the droplets increased with the gas flow rate and have local maximum values. The formation and sedimentation rates of metal droplets were estimated using a mathematical model. The formation rate increased with the gas flow rate and has a local maximum value as a function of gas flow rate, while the sedimentation rate is independent of the gas flow rate under the bottom bubbling condition. Three types of formation mode of metal emulsion, which occurred by the rupture of metal film around the bubble, were observed using high speed camera. During the process, an elongated column covered with metal film was observed with the increasing gas flow rate. This elongated column sometimes reached to the top surface of the salt phase. In this case, it is considered that fine droplets were not formed and in consequence, the weight of metal emulsion decreased at higher gas flow rate.

Behavior of silk protein at the air–water interface

The inability to link silk biomacromolecules' activity to their self-assembly and further fiber formation has limited a true implementation of a silk biotechnology. In this paper, we describe the application of video-enhanced drop shape analysis and interfacial shear rheological measurement to characterize the dynamic surface activity and interfacial interactions, as well as molecular structure within the interfacial layer of silk proteins. Quantitative analysis of the dynamic surface tension highlights two major mechanisms: (i) a mixed model at low concentration, and, (ii) a diffusion limited model at higher concentration. Once regenerated silk fibroin (RSF) is adsorbed at the air–water interface, interfacial gel-like structures are formed. The interfacial elastic modulus (G′) of the adsorbed membranes exhibited a non-monotonic concentration dependence with a local maximum value at 1.0 × 10−5 g mL−1, indicating a different surface structure formed in RSF solution. The viscoelastic behavior varies with RSF concentration corresponding to three states of a soft glassy system, i.e. below, above and near the glass transition. A structural model for RSF adsorbed layers at the air–water interface at different bulk concentrations is suggested.

Impact of a monotonic advection scheme with low numerical diffusion on transport modeling of emissions from biomass burning

An advection scheme, which maintains the initial monotonic characteristics of a tracer field being transported and at the same time produces low numerical diffusion, is implemented in the Coupled Chemistry‐Aerosol‐Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT‐BRAMS). Several comparisons of transport modeling using the new and original (non‐monotonic) CCATT‐BRAMS formulations are performed. Idealized 2‐D non‐divergent or divergent and stationary or time‐dependent wind fields are used to transport sharply localized tracer distributions, as well as to verify if an existent correlation of the mass mixing ratios of two interrelated tracers is kept during the transport simulation. Further comparisons are performed using realistic 3‐D wind fields. We then perform full simulations of real cases using data assimilation and complete atmospheric physics. In these simulations, we address the impacts of both advection schemes on the transport of biomass burning emissions and the formation of secondary species from non‐linear chemical reactions of precursors. The results show that the new scheme produces much more realistic transport patterns, without generating spurious oscillations and under‐ and overshoots or spreading mass away from the local peaks. Increasing the numerical diffusion in the original scheme in order to remove the spurious oscillations and maintain the monotonicity of the transported field causes excessive smoothing in the tracer distribution, reducing the local gradients and maximum values and unrealistically spreading mass away from the local peaks. As a result, huge differences (hundreds of %) for relatively inert tracers (like carbon monoxide) are found in the smoke plume cores. In terms of the secondary chemical species formed by non‐linear reactions (like ozone), we found differences of up to 50% in our simulations.

Research on Measurement of Void Fraction for Vertically Rising Pipes by Optical Fiber Probe

A way of measuring the average cross-sectional void fraction for vertically rising oil pipes by using closing valves quickly and optical fiber probe has been researched. Experiments were performed in oil-gas two-phase flow and the range of the average void fraction is 0.1～0.5. The relationship between average cross-sectional void fraction of a oil-gas two-phase flow and pipe’s center void fraction in vertically rising oil pipes, for different pipe diameters and varying oil flow, is obtained. An exponential model of average void fraction is also obtained with reference to Bankoff’s[1] variable density model. It is found that local void fraction reduces from center in radial direction and the local void fraction maximum value appears in the pipe’s center.

Study of carotid arterial plaque stress for symptomatic and asymptomatic patients

Stroke is one of the leading causes of death in the world, resulting mostly from the sudden ruptures of atherosclerosis carotid plaques. Until now, the exact plaque rupture mechanism has not been fully understood, and also the plaque rupture risk stratification. The advanced multi-spectral magnetic resonance imaging (MRI) has allowed the plaque components to be visualized in-vivo and reconstructed by computational modeling. In the study, plaque stress analysis using fully coupled fluid structure interaction was applied to 20 patients (12 symptomatic and 8 asymptomatic) reconstructed from in-vivo MRI, followed by a detailed biomechanics analysis, and morphological feature study. The locally extreme stress conditions can be found in the fibrous cap region, 85% at the plaque shoulder based on the present study cases. Local maximum stress values predicted in the plaque region were found to be significantly higher in symptomatic patients than that in asymptomatic patients (200±43 kPa vs. 127±37 kPa, p=0.001). Plaque stress level, defined by excluding 5% highest stress nodes in the fibrous cap region based on the accumulative histogram of stress experienced on the computational nodes in the fibrous cap, was also significantly higher in symptomatic patients than that in asymptomatic patients (154±32 kPa vs. 111±23 kPa, p<0.05). Although there was no significant difference in lipid core size between the two patient groups, symptomatic group normally had a larger lipid core and a significantly thinner fibrous cap based on the reconstructed plaques using 3D interpolation from stacks of 2D contours. Plaques with a higher stenosis were more likely to have extreme stress conditions upstream of plaque throat. The combined analyses of plaque MR image and plaque stress will advance our understanding of plaque rupture, and provide a useful tool on assessing plaque rupture risk.

A Fusion CMAC Neural Network Based on Global Dynamic Information

CMAC neural network has two advantages: the local generalization and no local maximum value. Currently, ICA-CMAC and FCMAC models are used extensively. However, the two models cannot reasonably characterize the direction and magnitude of network weight in the weight correction algorithm. To solve the problem, an improved CMAC learning algorithm is proposed. It takes iterative errors, iteration number and a window function as the performance. Based on information fusion strategy, it introduces global information into the calculation to optimize the network weight. Through a simulation test, it can be found that the model has significant improvement in terms of convergence speed and prediction control.

효율적인 전처리와 개선된 하프변환을 이용한 무선 이동로봇 영상에서 직선검출

본 논문은 무선 이동로봇의 영상에서 빠르고 정확하게 직선을 검출하는 방법에 대한 연구이다. 직선검출 처리시간 향상을 위하여 무선 이동로봇으로부터 전송 받은 영상의 특성을 분석하고 기존의 전처리 방법들 중 효율적인 전처리 방법을 선택하였다. 그리고 직선검출 정확도 향상을 위하여 하프변환의 결과를 저장하는 하프배열에서 지역 최대값을 선택하는 방법을 마스크를 설계하고 하프배열에 적용하여 개선하였다. 무선 이동로봇으로부터 획득한 실험영상을 가지고 실험을 실시하였고 제안방법은 처리시간과 직선검출에 있어 기존 방법들에 비해 좋은 성능을 보였다. This paper presents a research on the fast and accurate method of line detection in the image of a wireless mobile robot (WMR). For the improvement of the processing time to detect lines, the characteristics of the transmitted image from the WMR was analyzed, and the efficient preprocessing method among the existing preprocessing methods was selected. And for the improvement of the accuracy to detect lines, the selection method of local maximum value at the Hough array (HA) which has the result of Hough transform was improved by designing a mask and applying it to HA. The experiment was performed with acquired images from the WMR, and the proposed method outperformed the existing methods in terms of processing time and line detection.