New General Principle of Mechanics and Its Application to General Nonideal Nonholonomic Systems

In this paper we develop a general minimum principle of analytical dynamics that is applicable to nonideal constraints. The new principle encompasses Gauss’s Principle of Least Constraint. We use this principle to obtain the general, explicit, equations of motion for holonomically and/or nonholonomically constrained systems with non-ideal constraints. Examples of a nonholonomically constrained system where the constraints are nonideal, and of a system with sliding friction, are presented.     

Lagrangian Approach to Structural Collapse Simulation

Computer analysis of structures has traditionally been carried out using the displacement method combined with an incremental iterative scheme for nonlinear problems. In this paper, a Lagrangian approach is developed, which is a mixed method, where besides displacements, the stress resultants and other variables of state are primary unknowns. The method can potentially be used for the analysis of collapse of structures subjected to severe vibrations resulting from shocks or dynamic loads. The evolution of the structural state in time is provided a weak formulation using Hamilton’s principle. It is shown that a certain class of structures, known as reciprocal structures, has a mixed Lagrangian formulation in terms of displacements and internal forces. The form of the Lagrangian is invariant under finite displacements and can be used in geometric nonlinear analysis. For numerical solution, a discrete variational integrator is derived starting from the weak formulation. This integrator inherits the energy and momentum conservation characteristics for conservative systems and the contractivity of dissipative systems. The integration of each step is a constrained minimization problem and it is solved using an augmented Lagrangian algorithm. In contrast to the traditional displacement-based method, the Lagrangian method provides a generalized formulation which clearly separates the modeling of components from the numerical solution. Phenomenological models of components, essential to simulate collapse, can be incorporated without having to implement model-specific incremental state determination algorithms. The state variables are determined at the global level by the optimization method.     

Linear equality restrictions in regression and loglinear models.

Describes a simple method for implementing general linear equality restrictions on the parameters of linear models. These techniques, unlike those involving Lagrangian multipliers, can be easily implemented on common computer programs such as SPSS, BMDP, and SAS. For multiple regression, both homogenous and nonhomogenous constraints can be made, whereas for loglinear models only homogenous constraints can be made. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonlinear Dynamical Model for Hysteresis Based on Nonconvex Potential Energy

A model for hysteretic dynamics is proposed in the current paper. Hysteresis is treated as an input–output relation for a dynamic system. The Lagrangian of the dynamic system is constructed on the basis of a nonconvex potential energy and governing equations of the system dynamics are obtained using the Lagrangian equation. Bifurcations will be induced in the nonlinear dynamics due to the nonconvexity of the potential energy. It is shown that when the coefficients are chosen appropriately, the bifurcation diagram will lead to hysteretic behavior. Both the third- and fifth-order nonlinear terms are investigated and it is shown that the fifth-order nonlinearity is able to give a perfect prediction of experimental hysteretic behaviors. Hysteretic damping force of a magneto-rheological fluid damper and polarization hysteresis in piezoelectric materials are modeled successfully using the current model. The parameter identification for the model is also presented.     

Characterization of rice endo-beta-glucanase genes (Gns2-Gns14) defines a new subgroup within the gene family

Because of its importance to cell function, the free-energy metabolism of the living cell is subtly and homeostatically controlled. Metabolic control analysis enables a quantitative determination of what controls the relevant fluxes. However, the original metabolic control analysis was developed for idealized metabolic systems, which were assumed to lack enzyme-enzyme association and direct metabolite transfer between enzymes (channelling). We here review the recently developed molecular control analysis, which makes it possible to study non-ideal (channelled, organized) systems quantitatively in terms of what controls the fluxes, concentrations, and transit times. We show that in real, non-ideal pathways, the central control laws, such as the summation theorem for flux control, are richer than in ideal systems: the sum of the control of the enzymes participating in a non-ideal pathway may well exceed one (the number expected in the ideal pathways), but may also drop to values below one. Precise expressions indicate how total control is determined by non-ideal phenomena such as ternary complex formation (two enzymes, one metabolite), and enzyme sequestration. The bacterial phosphotransferase system (PTS), which catalyses the uptake and concomitant phosphorylation of glucose (and also regulates catabolite repression) is analyzed as an experimental example of a non-ideal pathway. Here, the phosphoryl group is channelled between enzymes, which could increase the sum of the enzyme control coefficients to two, whereas the formation of ternary complexes could decrease the sum of the enzyme control coefficients to below one. Experimental studies have recently confirmed this identification, as well as theoretically predicted values for the total control. Macromolecular crowding was shown to be a major candidate for the factor that modulates the non-ideal behaviour of the PTS pathway and the sum of the enzyme control coefficients.     

Influence of animation on dynamical judgments.

The motions of objects in the environment reflect underlying dynamical constraints and regularities. The conditions under which people are sensitive to natural dynamics are considered. In particular, the article considers what determines whether observers can distinguish canonical and anomalous dynamics when viewing ongoing events. The extent to which such perceptual appreciations are integrated with and influence commonsense reasoning about mechanical events is examined. It is concluded that animation evokes accurate dynamical intuitions when there is only 1 dimension of information that is of dynamical relevance. This advantage is lost when the observed motion reflects higher dimension dynamics or when the kinematic information is removed or degraded. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dyed Microspheres for Quantification of UV Dose Distributions: Photochemical Reactor Characterization by Lagrangian Actinometry

Lagrangian actinometry represents a new method of photochemical reactor characterization. The method is based on an application of dyed microspheres, which were developed by attachment of (E)-5-[2-(methoxycarbonyl)ethenyl]cytidine (hereafter referred to as S) to polystyrene microspheres. S is a nonfluorescent molecule that when subjected to ultraviolet (UV) irradiation yields a single product, 3-β-D-ribofuranosyl-2,7-dioxopyrido[2,3-d]pyrimidine (hereafter referred to as P), which displays a strong fluorescence signal. Dyed microspheres were subjected to UV irradiation under a collimated beam and using a single-lamp, monochromatic (low pressure Hg), continuous-flow reactor. In parallel with these experiments, a biodosimetry experiment was conducted using Bacillus subtilis spores as the challenge organism. Particle-specific fluorescence intensity measurements were conducted on samples from the collimated-beam experiments and the flow-through reactor experiments by flow cytometry. Estimates of the dose distribution delivered by the flow-through reactor for each operating condition were developed by deconvolution of data resulting from flow cytometry analysis of these samples. In conjunction with these experiments, a numerical model was developed to simulate the behavior of the reactor system. A commercially available computational fluid dynamics package was used to simulate the flow field, while line-source integration was used to simulate the irradiance field. A particle-tracking algorithm was employed to interrogate the flow and irradiance field simulations for purposes of developing particle-specific (Lagrangian) estimates of dose delivery. Dose distribution estimates from the microspheres assays and the numerical simulations were combined with the measured dose–response behavior of B. subtilis spores to yield estimates of spore inactivation in the flow-through experiments. For the range of operating conditions used in these experiments, predictions of spore inactivation based on dose distribution estimates from both methods were in good agreement with each other, and with the measured spore inactivation behavior. Lagrangian actinometry is capable of yielding accurate, detailed measurements of dose delivery by continuous-flow UV systems. This method represents a substantial improvement over existing experiment-based methods of UV reactor characterization (e.g., biodosimetry) in that it yields a measurement of the dose distribution for a given operating condition. This method also represents an improvement over existing methods for validation of numerical simulations. Specifically, because this method yields a measurement of the dose distribution, it is possible to compare these measurements with predicted dose distributions from the numerical simulation. The combined application of biodosimetry, numerical modeling, and Lagrangian actinometry represents an extremely robust approach to reactor characterization and validation.     

Phase Space Reduction in Stochastic Dynamics

In the field of structural engineering, various analytical procedures have been developed for the analysis of nonlinear structural systems subjected to random dynamic loading. To date, the Monte Carlo simulation (MCS) seems to be the most generally applicable approach for the reliability analysis of large nonlinear multi-degree-of-freedom systems. In this paper, a method that allows for reduction of the computational effort when using the MCS method is presented. First, the method requires the application of digital or analytical techniques (such as equivalent linearization) to obtain the response covariance matrix. Then, by means of the well-known Karhunen-Loéve expansion, the dimension of the system is reduced and MCS is applied. Moreover, in the transformed space the variables with smaller variance are approximated by Gaussian variables. It is shown that this technique allows for a considerable reduction of the computational effort without a significant loss of accuracy. As numerical examples, a 9-degree-of-freedom hysteretic structure and a conservative system (i.e., a 10-degree-of-freedom Duffing structure), respectively, are examined.     

Modeling and Simulation of Porous Elastoviscoplastic Material

Many materials exhibit elasto–visco–plastic behavior when subjected to loadings with certain strain rate. Examples include natural materials such as metals, clays, and soils and manmade materials such as some biomimic materials. Some voids may exist or be introduced in these materials. The effects of the voids on the material response are important in predicting the strength, reliability, and service life of structural systems containing these materials. This paper presents the results of applying a statistical micromechanical approach to describe the macroscopic behavior of elasto–visco–plastic materials containing many randomly dispersed spherical voids. Most existing micromechanics based models are only applicable to monotonic proportional loadings. The limitation is removed by integrating the material model into the framework of continuum plasticity. With the discrete integration algorithm and local return mapping algorithm, the proposed computation method is applicable to any loading and unloading histories and is ready for implementing into finite element analysis.     

Alternative Approaches to Modeling Fluence Distribution and Microbial Inactivation in Ultraviolet Reactors: Lagrangian versus Eulerian

A study was performed to evaluate alternative methods for predicting the ultraviolet (UV) reactor performance using computational fluid dynamics. The study consists of modeling the UV fluence distribution and microbial inactivation using either Lagrangian or Eulerian methods for both low- and medium-pressure UV reactors. In the Eulerian method, fluence distributions were calculated using a flow-weighted and a mass-weighted fraction technique. The results show that the Eulerian flow-weighted fraction fluence distribution agreed well with the Lagrangian particle tracking fluence distribution when applied to the UV reactor outlet plane. However, when applied to planes downstream from effluent hydraulic structures, the Eulerian fluence distribution method was influenced by the additional convective mixing from these hydraulic structures and predicts a tighter fluence distribution range than the Lagrangian method. The Eulerian approach to modeling microbial inactivation seems comparable to the Lagrangian particle tracking approach and can be viewed as a suitable alternative to the Lagrangian approach. The results also show that the Eulerian mass-weighted fraction distribution is comparable to the microbial kinetic weighted Lagrangian particle tracking approach, which can provide greater sensitivity to the low fluence regions in the UV reactor.     

A thermodynamic method for determining the activities from ternary miscibility gap data: The Cu-Pb-O system

A thermodynamic method is developed for determining the activities of all three component elements along a ternary miscibility gap from a knowledge of the line distributions and the pertinent binary thermodynamic properties. The thermodynamic treatment outlined is particularly applicable when the ternary miscibility gap lies close to one of the boundary binaries. Its usefulness is demonstrated by successfully deriving the activities in the ternary system Cu-Pb-O at 1473 K. The method presented is of general applicability to ternary systems consisting of two metals and a nonmetal such as oxygen, sulfur or selenium.     

Scheduling∕Cost Optimization and Neural Dynamics Model for Construction

A general mathematical formulation is presented for the scheduling of construction projects and is applied to the problem of highway construction scheduling. Repetitive and nonrepetitive tasks, work continuity constraints, multiple-crew strategies, and the effects of varying job conditions on the performance of a crew can be modeled. An optimization formulation is presented for the construction project scheduling problem, with the goal of minimizing the direct construction cost. The nonlinear optimization is then solved by the neural dynamics model developed recently by Adeli and Park. For any given construction duration, the model yields the optimum construction schedule for minimum construction cost automatically. By varying the construction duration, one can solve the cost-duration trade-off problem and obtain the global optimum schedule and the corresponding minimum construction cost. The new construction scheduling model provides the capabilities of both the critical path method (CPM) and linear scheduling method (LSM) approaches. In addition, it provides features desirable for repetitive projects, such as highway construction, and allows schedulers greater flexibility. It is particularly suitable for studying the effects of change order on the construction cost. This research provides the mathematical foundation for development of a new generation of more general, flexible, and accurate construction scheduling systems.     

Bounds on System Reliability by Linear Programming

Bounds on system probability in terms of marginal or joint component probabilities are of interest when exact solutions cannot be obtained. Currently, bounding formulas employing unicomponent probabilities are available for series and parallel systems, and formulas employing bi- and higher-order component probabilities are available for series systems. No theoretical formulas exist for general systems. It is shown in this paper that linear programming (LP) can be used to compute bounds for any system for any level of information available on the component probabilities. Unlike the theoretical bicomponent and higher-order bounds, the LP bounds are independent of the ordering of the components and are guaranteed to produce the narrowest possible bounds for the given information. Furthermore, the LP bounds can incorporate any type of information, including an incomplete set of component probabilities or inequality constraints on component probabilities. Numerical examples involving series, parallel and general structural systems are used to demonstrate the methodology.     

Optimal Control: Basis for Performance Comparison of Passive and Semiactive Isolation Systems

Passive damping in shock and vibration isolation systems reduces the deformation of the isolation system but can increase the acceleration sustained by the isolated object. Semiactive (i.e., controllable) damping systems offer a solution to the problem of increased vibration transmissibility at high frequencies. Semiactive damping is especially relevant to protecting acceleration-sensitive components to the effects of large impulsive earthquakes. In this paper, we compare three semiactive control policies, i.e., pseudonegative-stiffness control, continuous pseudoskyhook-damping control, and bang-bang pseudoskyhook-damping control, in terms of their effectiveness in addressing the deficiencies of passive isolation damping. In order to establish a performance goal for these suboptimal semiactive control rules, we present a method for true optimization of the response of dynamically excited, semiactively controlled structures subjected to constraints imposed by the dynamics of a particular semiactive device. The optimization procedure involves solving Euler–Lagrange equations. The closed-loop dynamics of structures with semiactive control systems are nonlinear due to the parametric nature of the control actions. These nonlinearities preclude an analytical evaluation of Laplace transforms. In this paper, frequency response functions for semiactively controlled structural systems are compiled from the computed time history responses to sinusoidal and pulse-like base excitations. For control devices with no saturation forces, the closed-loop frequency response functions are independent of the excitation amplitude. We make use of this homogeneity of the solution of semiactive control systems and present results in dimensionless form.     

Toward a taxonomy of human performance.

Discusses general problems in the development of taxonomic systems for describing human tasks and performance. Alternative approaches and provisional classification schemes are presented. Specific techniques of measurement and scaling, applicable to certain task classification systems, are described and their reliability evaluated. Attempts to evaluate these systems are summarized, and attempts to apply them to several areas of human performance research (e.g., studies of drug effects, learning procedures, alcohol, and vigilance) are examined. A series of studies linking task characteristics with ability requirements is described. Some of this research is considered encouraging, in that the generalizability of data on performance increases when certain classification systems are used to describe the tasks utilized in such research. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Improvement of the Parameterized Identification Model Using Quasi-Steady and Nonuniform Inflow Aerodynamic Model

Compared with those of a fixed-wing aircraft, the dynamics of a rotorcraft are significantly more complex. One of the major challenges in the design of an autonomous helicopter is the development of a flight dynamic model, which can be useful for simulation studies and for the design of control law and navigational aspects. There is always a trade-off from the accuracy of the mathematical model to the more simplified model required for a control design as far as the helicopter rotor/fuselage dynamics is concerned. Small-scale helicopters posses a higher bandwidth of dynamics; hence, models developed from the first principle alone do not fulfill the needs, and more-sophisticated mathematical models are thus required. The main objective of the present work is to improve the parameterized identification model by replacing it with a most-general flight dynamic model for a minihelicopter. This model includes the rotor blade flap dynamics, stabilizer bar dynamics, and vehicle dynamics, which will be applicable for a general maneuvering flight. A systematic study is undertaken to analyze the influence of inflow models and flap response on the helicopter trim. Stability of the minihelicopter is also analyzed; except for phugoid, all other modes are stable in hover and high forward flight conditions.     

Estimating net joint torques from kinesiological data using optimal linear system theory

Net joint torques (NJT) are frequently computed to provide insights into the motor control of dynamic biomechanical systems. An inverse dynamics approach is almost always used, whereby the NJT are computed from 1) kinematic measurements (e.g., position of the segments), 2) kinetic measurements (e.g., ground reaction forces) that are, in effect, constraints defining unmeasured kinematic quantities based on a dynamic segmental model, and 3) numerical differentiation of the measured kinematics to estimate velocities and accelerations that are, in effect, additional constraints. Due to errors in the measurements, the segmental model, and the differentiation process, estimated NJT rarely produce the observed movement in a forward simulation when the dynamics of the segmental system are inherently unstable (e.g., human walking). Forward dynamic simulations are, however, essential to studies of muscle coordination. We have developed an alternative approach, using the linear quadratic follower (LQF) algorithm, which computes the NJT such that a stable simulation of the observed movement is produced and the measurements are replicated as well as possible. The LQF algorithm does not employ constraints depending on explicit differentiation of the kinematic data, but rather employs those depending on specification of a cost function, based on quantitative assumptions about data confidence. We illustrate the usefulness of the LQF approach by using it to estimate NJT exerted by standing humans perturbed by support-surface movements. We show that unless the number of kinematic and force variables recorded is sufficiently high, the confidence that can be placed in the estimates of the NJT, obtained by any method (e.g., LQF, or the inverse dynamics approach), may be unsatisfactorily low.     

Dynamics of the site visit: Laboratory for the small group study of scientific administration.

Site visits are conducted by National Institutes of Health (NIH) review groups when obstacles arise in peer appraisal of research projects. Because such visits provide a window into the state of a scientific community and present highly charged group dynamics that revolve about significant scientific issues, examples from the 1970s and 1980s were subjected to behavioral analysis. H. Selye's (1946) general adaptation syndrome was used to model the forms of coping behavior manifested by investigators targeted for a site visit. A Lewinian approach was taken to analyze the course and outcome of site visit team deliberations. The perspective was that of the NIH official responsible for the operation of the review process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A general model for site-specific recombination by the integrase family recombinases

We present here a general model for integrase family site-specific recombination using the geometric relationships of the cleavable phosphodiester bonds and the disposition of the recombinase monomers (defined by their binding planes) with respect to them. The 'oscillation model' is based largely on the conformations of the recombinase-bound DNA duplexes and their dynamics within Holliday junctions. The duplex substrate or the Holliday junction intermediate is capable of 'oscillating' between two cleavage-competent asymmetric states with respect to corres-ponding chemically inert 'equilibrium positions'. The model accommodates several features of the Flp system and predicts two modes of DNA cleavage during a normal recombination event. It is equally applicable to other systems that mediate recombination across 6, 7 or 8 bp long strand exchange regions (or spacers). The model is consistent with approximately 0-1, 1-2 and 2-3 bp of branch migration during recombination reactions involving 6, 7 and 8 bp spacers, respectively.