Influence Of External Forces Research Articles

Influence of braking force in low-speed vehicle collisions

The aim of this research is to find out the influence of braking force on the impact dynamics in low-speed rear-end collisions. The method used to simulate the crash is a step-by-step impulsive model including tyre friction and the rolling resistance effect. The simulation allows a separate analysis of the compression and restitution phases. The first is based upon experimental data of the crash test between the vehicles, the latter leads to two different choices of reconstruction, considering the bumper rebound or neglecting it. The coefficient of restitution is calculated by the force reached at compression ending, thus including the influence of external forces (as friction). The results show a great accuracy and matching with experimental data. The main changes in the impact dynamics due to the rise in braking force are the enlargement of the crush with a delay of the restitution start and a lowering of the coefficient of restitution, the increase of the impact duration and the decrease of the velocities at the collision end. These effects depend on the closing velocity and are more marked at low speed. This study therefore demonstrates that the braking force is not negligible in a good reconstruction of impact dynamics at low speed.

Numerical modelling of an electric arc and its interaction with the anode: part II. The three-dimensional model—influence of external forces on the arc column

This paper reports the second part of the study of an electric arc and its interaction with the anode material. First, a three-dimensional model is presented and validated in a natural symmetric configuration for which many experimental results exist. In the three-dimensional model, two situations are considered for the anode surface: the classical zero heat flux condition and the use of the anode model. In the second case, the specific properties of the anode material are taken into account and play a role in the current conservation between the plasma and the anode, and therefore, affect the arc behaviour near the electrode. The results for the two approaches are similar in two dimensions, but differences exist in real three-dimensional cases when external forces such as cross flow or magnetic field tend to bend the arc. Second, we present a comparison between the two methods in the case where the arc is deviated by an external magnetic field. For this comparison, we adopt a configuration used at Odeillo during the 1970s and compare the results obtained by our code with the experimental ones. We find that it is essential to consider the complete anode model if the arc deflection is to be predicted correctly. Once our developments are validated, the computational code is applied in a free-burning arc configuration, where the plasma column is deflected by an external cross flow.

The critical phenomena in a hysteretic model due to the interaction between hysteretic damping and external force

A self-excited system involving a van der Pol-type damping and a hysteretic damper representing restoring force is investigated in this paper. The influence of external force on the dynamic behavior of the hysteretic system is analyzed in detail. Numerical simulations show that, under an external force, the original hysteretic system can exhibit the so-called critical phenomena, where the hysteretic resorting force of the system may no longer obey the traditional piecewise function form. This new finding reveals that the system's behavior changes dramatically when an external force is present. Modified bilinear force paths are proposed to accommodate the new phenomena. It is shown that a hysteretic system can exhibit more complex dynamical behavior when an external forcing is applied, and that the critical phenomena may exist even when the system reaches its steady state. A study is presented on the necessary condition for the existence of the critical phenomena. More interestingly, it has been found that the hysteretic forcing can suppress chaotic motions, suggesting an alternative approach to control chaos.

Export performance as an antecedent of export commitment and marketing strategy adaptation

This paper argues that performance should be investigated as an independent variable. Using survey data of over 400 managers responsible for the main export ventures of Portuguese SMEs (small and medium exporters), this paper shows that past performance plays a crucial role in building SMEs' commitment to exporting and to the determination of their current marketing strategy. Findings also show that marketing strategy adaptation to the foreign market is particularly noted in firms exporting to the most developed markets, rather than in firms exporting to the most competitive environments. Future international marketing research is encouraged to focus on understanding both the direct and indirect relationships among past performance, firm's commitment to exporting, and current marketing strategy under the influence of external forces. Such a focus has the potential to enrich the theory and generate relevant managerial and public policy implications.

Controlling complexity using forcing: simulations and experiments

We report the successful manipulation of non-linear dynamics using external forcing. In the case of temporal systems, a model system involving ordinary differential equations (ode’s) was used for simulations. Experiments were carried out in a single anode electrochemical cell. Numerical and experimental results indicate that under the influence of external forcing, control of complexity and a change in periodicity of the autonomous dynamics can be achieved. A natural extension of this work involves analyzing the effects of global and local forcing on complex spatio-temporal behavior. A numerical model involving partial differential equations (pde’s) was used for simulating the dynamics of this extended system. An electrochemical cell involving multiple anodes was used for the corresponding experiments. In simulations and in experiments, suppression of spatio-temporal complexity is observed for the two forcing (global and local) methods.

Analytical solution of the time-dependent Bloch NMR flow equations: a translational mechanical analysis

Various biological and physiological properties of living tissue can be studied by means of nuclear magnetic resonance techniques. Unfortunately, the basic physics of extracting the relevant information from the solution of Bloch nuclear magnetic resource (NMR) equations to accurately monitor the clinical state of biological systems is still not yet fully understood. Presently, there are no simple closed solutions known to the Bloch equations for a general RF excitation. Therefore the translational mechanical analysis of the Bloch NMR equations presented in this study, which can be taken as definitions of new functions to be studied in detail may reveal very important information from which various NMR flow parameters can be derived. Fortunately, many of the most important but hidden applications of blood flow parameters can be revealed without too much difficulty if appropriate mathematical techniques are used to solve the equations. In this study we are concerned with a mathematical study of the laws of NMR physics from the point of view of translational mechanical theory. The important contribution of this study is that solutions to the Bloch NMR flow equations do always exist and can be found as accurately as desired. We shall restrict our attention to cases where the radio frequency field can be treated by simple analytical methods. First we shall derive a time dependant second-order non-homogeneous linear differential equation from the Bloch NMR equation in term of the equilibrium magnetization M 0, RF B 1( t) field, T 1 and T 2 relaxation times. Then, we would develop a general method of solving the differential equation for the cases when RF B 1( t)=0, and when RF B 1( t)≠0. This allows us to obtain the intrinsic or natural behavior of the NMR system as well as the response of the system under investigation to a specific influence of external force to the system. Specifically, we consider the case where the RF B 1 varies harmonically with time. Here the complete motion of the system consists of two parts. The first part describes the motion of the transverse magnetization M y in the absence of RF B( t) field. The second part of the motion described by the particular integral of the derived differential equation does not decay with time but continues its periodic behavior indefinitely. The complete motion of the NMR flow system is then quantitatively and qualitatively described.

A three-dimensional vertex dynamics cell model of space-filling polyhedra simulating cell behavior in a cell aggregate

We developed a three-dimensional (3D) cell model of a multicellular aggregate consisting of several polyhedral cells to investigate the deformation and rearrangement of cells under the influence of external forces. The polyhedral cells fill the space in the aggregate without gaps or overlaps, consist of contracting interfaces and maintain their volumes. The interfaces and volumes were expressed by 3D vertex coordinates. Vertex movements obey equations of motion that rearrange the cells to minimize total free energy, and undergo an elementary process that exchanges vertex pair connections when vertices approach each other. The total free energy includes the interface energy of cells and the compression or expansion energy of cells. Computer simulations provided the following results: An aggregate of cells becomes spherical to minimize individual cell surface areas; Polygonal interfaces of cells remain flat; Cells within the 3D cell aggregate can move and rearrange despite the absence of free space. We examined cell rearrangement to elucidate the viscoelastic properties of the aggregate, e.g. when an external force flattens a cell aggregate (e.g. under centrifugation) its component cells quickly flatten. Under a continuous external force, the cells slowly rearrange to recover their original shape although the cell aggregate remains flat. The deformation and rearrangement of individual cells is a two-step process with a time lag. Our results showed that morphological and viscoelastic properties of the cell aggregate with long relaxation time are based on component cells where minimization of interfacial energy of cells provides a motive force for cell movement.

Power-Spectrum Behavior of Yearly Mean Grain Yields

Advanced statistical approaches have been applied to determine the temporal scaling-invariance laws in annual mean yields registered in Mexico during the period 1897–1999. When the maize, bean, wheat and rice series are treated as self-affine profiles through power spectrum analysis, the temporal fluctuation f-β is detected in each case for time scales of 2 to 103 years. β values (p < 0.0001) of -1.84 ± 0.15, -1.71 ± 0.218, -1.62 ± 0.194 and -1.7 ± 0.139 for maize, bean, wheat and rice profiles, respectively, suggest that short-term variation is important and are influencing the dynamic evolution of the yearly mean yields. Thus, in addition to the linear trends driven by endogenous factors of agricultural systems, grain yield variation may be due to external forcings such as climatic oscillations and/or solar signals. Through the spectral analysis using the maximum entropy method, the influence of external forcings on the behavior of the annual mean yields in all four crops was evidenced. The detected main external forcings are: a 6- to 8-year political oscillation, the magnetic and sunspot cycles of the Sun, and El Niño Southern Oscillation (ENSO). Taking into account the number of significant periodicities, the order of annual mean yield series' sensitivity to external forcings influencing their short-term variation is as follows: maize < wheat < rice < bean.

Computer simulation of solid particle erosion

A micro-scale dynamic model (MSDM) was applied to simulate solid particle erosion. In this model, the target material and solid particles are discretized and mapped onto a square grid or lattice. Each lattice site represents a small volume of the materials. During an erosion process, a lattice site may move under the influence of external force and the interaction between the site and its adjacent sites. The site–site interaction is a function of mechanical properties of the materials. A bond connecting two adjacent sites fails when its strain exceeds a critical value. A site or a cluster of sites will be worn away if all bonds connecting the site or the cluster are broken. Influences of the shape, size, velocity and impact angle of solid particles on erosion were studied. The mechanisms responsible for the erosion behavior of both brittle and ductile materials are discussed.

On the influence of external forces on the Bloch wall thickness in a nickel single crystal

We studied the influence of external forces (pressure and torque) on the Bloch wall thickness in a nickel single crystal. Although the theory predicts an enhancement of the Bloch wall thickness of about 6% for torque force, this effect is—until now—too small to be proved experimentally owing to the difficulties in determining the domain size which were elucidated during the study of the influence of pressure force on the Bloch wall thickness.

Debates on religion among Montreal physicians

This article discusses the debate which took place at the beginning of the 20th century on the relationship between Church and State, and reveals the resulting ideological schisms among members of the Montreal medical leadership. These divisions explain, at least in part, the delayed application of health policies and professionalization evolution of physicians and the configuration of the medical institutional framework. Its broader implications relate to the influence of external forces upon medical practice.

Artifact-resistant power-efficient design of finger-ring plethysmographic sensors.

A miniaturized, telemetric, photoplethysmograph (PPG) sensor for long-term, continuous monitoring is presented in this paper. The sensor, called a "ring sensor," is attached to a finger base for monitoring beat-to-beat pulsation, and the data is sent to a host computer via a radio-frequency transmitter. Two major design issues are addressed: one is to minimize motion artifact and the other is to minimize the consumption of battery power. An efficient double ring design is developed to lower the influence of external force, acceleration, and ambient light, and to hold the sensor gently and securely on the skin, so that the circulation at the finger may not be obstructed. Total power consumption is analyzed in relation to characteristics of individual components, sampling rate, and CPU clock speed. Optimal operating conditions are obtained for minimizing the power budget. A prototype ring sensor is designed and built based on the power budget analysis and the artifact-resistive attachment method. It is verified through experiments that the ring sensor is resistant to interfering forces and acceleration acting on the ring body. Benchmarking tests with FDA-approved PPG and electrocardiogram reveal that the ring sensor is comparable to those devices in detecting beat-to-beat pulsation despite disturbances.

Dielectric study of the phase transition in NaNH 4SeO 4·2H 2O crystals

The influence of external forces, bias electric field and mechanical shear stress σ 6 on electric permittivity ε c of NaNH 4SeO 4·2H 2O crystals is reported. The shear stress σ 6 influences strongly on electric permittivity ε c of the crystal in the ferroelectric phase. The dielectric constant is also measured in the paraelectric phase as a function of electric field at constant temperature. The value of coefficient B (non-linear coefficient) on the basis of the classical state equation was calculated. The B sign and ε c( E) dependence point out of the second-order phase transition in this crystal.

The macroscopic scanning force `microscope'

A homemade, macroscopic version of the scanning force microscope is described.It consists of a cantilever under the influence of external forces, whichmimic the tip-sample interactions. The use of this piece of equipment istwofold. First, it serves as a direct way to understand the parts andfunctions of the scanning force microscope, and thus it is effectively used asan instructional tool. Second, due to its large size, it allows for simplemeasurements of applied forces and parameters that define the state of motionof the system. This information, in turn, serves to compare the interactionforces with the reconstructed ones. This comparison is in itself extremelyrelevant, as it cannot be done directly with the standard microscopic set-up.

Late Quaternary evolution of fluvial sediment composition: a modeling case study of the River Meuse

This paper addresses the influence of external forcing (changes in tectonics, sea level and climate) on the downstream and long-term (10 3–10 5 years) evolution of sediment composition along a fluvial longitudinal profile. The River Meuse served as a case study for a semi 2-D forward-modelling approach to simulate the downstream sediment transport in the 200- to 0-ka period. This has been related to bulk geochemical properties of the tributary catchments to quantify the bulk composition of the sediment load in the main river. The model was used to test the hypothesis that long-term fluvial dynamics influences sediment composition. The simulation exercise showed that long-term fluvial dynamics can yield systematic temporal changes in fluvial sediment composition, especially in high-relief areas. We tested a scenario of minimal discharges and maximum hillslope erosion during cold glacial periods (weathering-limited sediment supply), alternating with maximal discharges and minimal hillslope erosion during prolonged interstadials or interglacials (transport-limited sediment supply). This scenario largely reproduced the timing and direction of measured changes in the bulk and clay geochemistry of fine-grained sediments, which were deposited in the River Meuse lower reach from 13 to 0 ka. However, it failed to reproduce the measured amplitude of change, which was five to six times larger than the modelled amplitude. This suggests that climate-dependent changes in weathering intensity of rocks and saprolite in the source areas were more important and that aeolian inputs from outside the drainage basin have co-determined the sediment composition.

Small-world Rouse networks as models of cross-linked polymers

We use the recently introduced small-world networks (SWNs) to model cross-linked polymers, as an extension of the linear Rouse chain. We study the SWN dynamics under the influence of external forces. We focus on the (structurally and thermally averaged) stretching of the SWN, which we determine numerically through diagonalization and analytically using an approximate expression for the SWN density of states. We show that stretching is related to the probability of a random walker over the network to return to its origin. We compare our SWN results to the corresponding ones for Cayley trees.

Young Women's Work Values and Role Salience in Grade 11: Are There Changes Three Years Later?

Eleventh graders participated in a longitudinal study of career decision making in which they completed a series of career‐related inventories and follow‐up interviews. There was little change in work‐related values between the 2 administrations of the Values Scale (G.W. Fitzsimmons, D. Macnab, & C. Casserly, 1985); however, greater variation occurred on the Salience Inventory (G. W. Fitzsimmons et al., 1985), particularly Role Value Implementation. Role salience seems less stable than values, perhaps reflecting the transition from high school to postsecondary education or the world of work. Implications for D. E. Super's (1981, 1990, 1994, 1995) theory of career development and applications to career counseling are outlined.

Identification of homeostatic dynamics for a circadian signal source using BP neural networks

System identification of biological signal sources is useful for analyses of biological functions and medical diagnoses. Homeostatic dynamics of circadian rhythms are identified here by using an MA model composed of BP neural networks. Wake-sleep rhythms measured for normal subjects are supplied for the identification. The rhythms are regulated to keep their activity constant by homeostasis, while fluctuating by incessant influences of external forces. The neural networks can acquire the regularity included in the data. The order of the MA neural network model depends on subjects, but the first three orders are dominant, usually in the case of no strong external force. The adaptive change of the homeostatic dynamics can be evaluated by the change of weight vectors, a kind of internal representation of the trained network. The dynamics are kept in a steady state for ten to 20 days at most. Identified properties reflect each subject, and hence may be useful for medical diagnoses of disorders related to circadian rhythms.

Influence of external forces on the behaviour of redundant manipulators

The paper considers the influence of external forces on the behaviour of a redundant manipulator. It is assumed that the forces can act anywhere on the body of the manipulator. First, the equivalent generalized forces in the task space and the null space are defined and several special manipulator configurations regarding the equivalent forces and torques are identified. Next, two measures for the quantification of the influence of external forces on the task space are proposed. These measures are then used in the control algorithm to minimize the influence of external forces on the task space position accuracy. The control is based on the redundancy resolution at the acceleration level and the gradient projection technique. Improvement of the position accuracy is illustrated using the simulation of a four link planar manipulator.

Dynamical simulation of an abrasive wear process

A dynamic computer model was developed to simulate wear behavior of materials on micro-scales. In this model, a material system is discretized and mapped onto a lattice or grid. Each lattice site represents a small volume of the material. During a wear process, a lattice site may move under the influence of external force and the interaction between the site and its adjacent sites. The site–site interaction is a function of mechanical properties of the material such as the elastic modulus, yield strength, work hardening and the fracture strain. Newton's law of motion is used to determine the movement of lattice sites during a wear process. The strain between a pair of sites is recoverable if it is within the elastic deformation range; otherwise plastic deformation takes place. A bond between two adjacent sites is broken when its strain exceeds a critical value. A site or a cluster of sites is worn away if all bonds connecting the site or the cluster to its nearest neighbors are broken. The model well describes the strain distribution in a contact region, in consistence with a finite element analysis. This model was applied to several metallic materials abraded under the ASTM G65 abrasion condition, and the results were compared to experimental observations. Good agreement between the modeling and the experiment was found.