Dynamical Reactions Research Articles

Effects of Chalcogen Atoms on Excited-State Double-Proton Transfer Behavior for 3,6-bis(4,5-Dihydroxyoxazo-2-yl)benzene-1,2-diol Derivatives: A Computational Investigation.

The impact of the chalcogen atomic electronegativity (O, S, and Se atoms) of new organic molecules on excited-state dynamical reactions is self-evident. Inspired by this kind of distinguished photochemical characteristic, in this work, we performed a computational investigation of chalcogen-substituted 3,6-bis(4,5-dihydroxyoxazo-2-yl)benzene-1,2-diol (BDYBD) derivatives (i.e., BDYBD-O, BDYBD-S, and BDYBD-Se). In this paper, we pay close attention to characteristic BDYBD derivatives that contain intramolecular double hydrogen bonds (O1-H2···N3 and O4-H5···N6). The main goal of this study was to explore how changes in atomic electronegativity affect the way hydrogen bonds interact and how excited molecules affect transfer protons. We go into further detail in the main text of the paper. By fixing our attention to geometrical variations and infrared (IR) vibrational spectra between the S0 and S1 states, exploring hydrogen bonding behaviors using the core-valence bifurcation (CVB) index, and simulating hydrogen bonding energy (EHB) via the atom in molecule (AIM) method, we clarified the photo-induced strengthened dual hydrogen bonding interactions that facilitate the excited-state dual-proton transfer (ESDPT) behavior of BDYBD derivatives. The reorganization of charge stemming from photoexcitation further verifies the tendencies of ESDPT reactions. We relied on constructing potential energy surfaces (PESs) by adopting a restrictive optimization approach, and herein, we finally clarify the gradual ESDPT mechanism of BDYBD derivatives. Particularly, we confirm that the variation in chalcogen atomic electronegativity has a regulatory effect on the ESDPT behavior of BDYBD derivatives; that is, the lower the atomic electronegativity, the more favorable it is for the gradual ESDPT reaction.

On parametric representation of brachistochrone problem with Coulomb friction

The motion of a material point along a trajectory located in a vertical plane and connecting two given fixed points is considered. It is assumed that the motion occurs in a homogeneous field of gravity and taking into account the Coulomb friction caused by statical and dynamical reactions of the support curve. The classical problem of finding a curve of fastest descent for a material point sliding with friction from one fixed point to another, that is, a trajectory for which the descent time is the shortest, i.e. the problem of brachistochrone, is discussed. A parametric method for solving the brachistochrone problem with Coulomb friction is proposed and the solution of the variational problem is given in the form of quadratures.

On the problem of the dynamical reactions of a rolling wheelset to real track irregularities

We investigate numerically the dynamical reactions of a moving wheelset model to real measured track irregularities. The background is to examine whether the dynamics are suitable as the input to the inverse problem: determine the true track geometry from measured wheelset dynamical reactions. It is known that the method works well for the vertical position of the rails but the computed lateral position is often flawed. We find that the lateral motion of the wheelset often may differ from the track geometry. The cases are investigated closely but the reasons remain unknown. While the wheelset dynamics reflect the larger (> 4–6 mm) aperiodic track disturbances and single large disturbances quite well, this does not seem to be the case for general smaller or periodic track irregularities or sections behind single large disturbances. The resulting dynamics of a wheelset to lateral track irregularities are in general not sufficiently accurate to be used as the basis for a description of the track irregularities.

Motion Sickness Simulation Based on Sensorimotor Control

AbstractSensorimotor control is an essential mechanism for human motions, from involuntary reflex actions to intentional motor skill learning, such as walking, jumping, and swimming. Humans perform various motions according to different task goals and physiological sensory perception; however, most existing computational approaches for motion simulation and generation rarely consider the effects of human perception. The assumption of perfect perception (i.e., no sensory errors) of existing approaches restricts the generated motion types and makes dynamical reactions less realistic. We propose a general framework for sensorimotor control, integrating a balance controller and a vestibular model, to generate perception‐aware motions. By exploiting simulated perception, more natural responses that are closer to human reactions can be generated. For example, motion sickness caused by the impairments in the function of the vestibular system induces postural instability and body sway. Our approach generates physically correct motions and reasonable reactions to external stimuli since the spatial orientation estimation by the vestibular system is essential to preserve balance. We evaluate our framework by demonstrating standing balance on a rotational platform with different angular speeds and duration. The generated motions show that either faster angular speeds or longer rotational duration cause more severe motion sickness. Our results demonstrate that sensorimotor control, integrating human perception and physically‐based control, offers considerable potential for providing more human‐like behaviors, especially for perceptual illusions of human beings, including visual, proprioceptive, and tactile sensations.

Variational principle for the determination of unstable periodic orbits and instanton trajectories at saddle points

The complexity of arbitrary dynamical systems and chemical reactions, in particular, can often be resolved if only the appropriate periodic orbit---in the form of a limit cycle, dividing surface, instanton trajectories, or some other related structure---can be uncovered. Determining such a periodic orbit, no matter how beguilingly simple it appears, is often very challenging. We present a method for the direct construction of unstable periodic orbits and instanton trajectories at saddle points by means of Lagrangian descriptors. Such structures result from the minimization of a scalar-valued phase-space function without the need for any additional constraints or knowledge. We illustrate the approach for two-degree of freedom systems at a rank-1 saddle point of the underlying potential-energy surface by constructing both periodic orbits at energies above the saddle point as well as instanton trajectories below the saddle-point energy.

Lateral spread of dose distribution by therapeutic proton beams in liquid water

We have calculated the lateral spread of the dose distribution of protons in liquid water by means of the SEICS (Simulation of Energetic Ions and Clusters through Solids) code, which properly accounts for the electronic stopping force (including energy-loss straggling), multiple elastic scattering with the target nuclei, dynamical electron charge-exchange processes and nuclear fragmentation reactions between the projectile and the nuclei of the target. Due to the multiple elastic scattering processes part of the proton energy may be deposited at a given lateral distance from the initial beam direction, which is quantified by the root mean square radius (rrms). We find in our simulations that the rrms follows a parabolic dependence as a function of the depth in the target and the quotient between the rrms at the Bragg peak and the depth of the Bragg peak is around 3% independently of the proton energy. A rather good agreement is obtained when comparing our results of rrms with experimental data and with other models.

Reduction of dynamical biochemical reactions networks in computational biology.

Biochemical networks are used in computational biology, to model mechanistic details of systems involved in cell signaling, metabolism, and regulation of gene expression. Parametric and structural uncertainty, as well as combinatorial explosion are strong obstacles against analyzing the dynamics of large models of this type. Multiscaleness, an important property of these networks, can be used to get past some of these obstacles. Networks with many well separated time scales, can be reduced to simpler models, in a way that depends only on the orders of magnitude and not on the exact values of the kinetic parameters. The main idea used for such robust simplifications of networks is the concept of dominance among model elements, allowing hierarchical organization of these elements according to their effects on the network dynamics. This concept finds a natural formulation in tropical geometry. We revisit, in the light of these new ideas, the main approaches to model reduction of reaction networks, such as quasi-steady state (QSS) and quasi-equilibrium approximations (QE), and provide practical recipes for model reduction of linear and non-linear networks. We also discuss the application of model reduction to the problem of parameter identification, via backward pruning machine learning techniques.

Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick–slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt [32], a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions, are consistent as attested by the comparison of the two available versions of the string dynamical motion and of the friction force. Furthermore, the method seems adequate to investigate the interface force for the bowed string.

Fuzzy random processes and their application to dynamic analysis of structures

In many engineering problems the dynamical reactions of structures depend on uncertain data. For considering this uncertainty, fuzzy random processes are applied. An enhanced dynamic analysis method called fuzzy stochastic finite element method (FSFEM) has been developed in order to consider the fuzzy random processes within the dynamic analysis of structures. A suitable discretization strategy enables the repeated processing of FE algorithms as deterministic fundamental solution. In this paper the FE multi-reference-plane model is extended to fuzzy randomness and dynamic loads. The numerical solution is based on the fuzzy stochastic sampling (FSS). FSS and FSFEM are applied for the numerical simulation of the load-bearing capacity of a strengthened RC plate under static and dynamic loads.

Extreme reduction of the capillary lumen in segments of the venular legs of human cutaneous capillaries

While structure and function of precapillary sphincter cells were assured in skin capillaries it is unclear whether segmental reduction of capillary lumina can occur in human capillaries. It has been shown that endothelial cells are able to exert dynamical reactions. Since the first description of the vascular endothelium a great variety of findings were described concerning the active role of capillary endothelial cells in regulation of the capillary lumen applying intravital microscopy. The intravital microscopy was performed in the framework of an observational study to document the long-term stability of capillaries in healthy subjects over many years. In the second year one of the participants showed remarkable changes in capillaries compared to recent recordings. Control recordings were performed 1, 3, 4, 5 and 20 h after the initial examination — until a complete normalization of the capillaries occurred. This case report is documenting for the first time clearly that extreme luminal narrowing of long segments of cutaneous capillaries can also appear in humans, in this case restricted exclusively to the venular leg of the capillaries. Different from the reductions of the capillary lumen induced by electrical irritation in frogs which lasted only for seconds, the capillary lumen narrowing in this case lasted considerably longer, almost over a whole day. It is important to note that the demonstrated findings did not occur in all capillaries and it remains unclear whether such findings are restricted to skin capillaries or might occur also in other regions of the body or even systemically. It could be demonstrated clearly, however, that segmental narrowing of capillary lumina can occur in humans possibly leading to a temporary stillstand of perfusion.

Synthesis of a Sequential Model of Muscles of a Man during Drop Landing on a Hard Platform

The objective of this paper is to identify the parameters of a new plane biodynamic model of a man jumping down on a hard base. In the modelling of this kind of dynamic phenomena, with dominant directions of human body motion and reactions, many simple and complex models have already been applied. Some of them were lumped parameter and unidirectional [Książek, 1999], [Fritz, 2001] or plane [Pandy, 1990], [Farley, 1998]. There are also spatial models, applied in the sport and medical investigations of the kinematics and dynamics of the human body [Morecki, 1990], [A. Nagano and col., 2005]. The presented approach has been founded on the results of experiments described in [Nosiadek, 2006] where body motions of 40 men volunteers were registered during drop jumping and landing from several assumed heights. By means of video cameras in 3D space and a dynamic platform linear and angular displacements of participants’ bodies and three mutually perpendicular components of the dynamical reactions between the feet and platform were measured. The numerical results of the displacements were numerically remodelled by the authors of the present paper and used for synthesis of models of muscles of a man during drop landing. Similar investigations can be found in [Pain and Challis, 2006].

Coexistence of Covalent Superdeformation and Molecular Resonances in an Unbound Region ofBe12

The generalized two-center cluster model, which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, 12Be=alpha+alpha+4N. We discuss the change of the neutrons' configuration around two alpha cores from the covalent structure to the ionic one. We show that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of alpha+8He, 6He+6He, and 5He+7He. A new type of superdeformation is possible, and we find here a covalent superdeformation with a hybrid configuration of both the covalent and ionic structures. The excitation of these exotic structures through the two-neutron transfer reaction is also discussed.

Exotic molecular structures in highly-excited states of 12Be

The generalized two-center cluster model (GTCM), which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons' configuration around two α-cores from the covalent structure to the ionic one. It is shown that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of α+8He, 6He+6He and 5He+7He. A new type of superdeformation is possible, and we find here the covalent superdeformation which has a hybrid configuration of the covalent and ionic ones. The excitation of these exotic structures through the two neutron transfer reaction is also discussed.

The Need for a Self-Consistent Model of the ISM

The interstellar medium of the Milky Way possesses a remarkable rangeof components, which have individual lifetimes considerably less than aHubble time. Consequently, there has been a major effort inunderstanding the properties of these components, their heating andcooling mechanisms, and the process by which one component istransformed into another. We review several of the issues in an effort tohighlight controversies that are under study presently. One of the centraldebates involves star formation, where there are two general andconflicting theoretical models. Another issue deals with the efforts tounderstand the fractional amounts of gas in the various phases, whichbrings together star formation with global gas dynamical reactions. Thisinteraction is responsible for heating of the gas by supernovae, causingsuperbubbles, and subsequently, either galactic winds or galacticfountains. The relative amounts of material in the hot and cold phasesnot only depends upon the supernova rate, it also depends upon details ofinterstellar models, such as whether thermal conduction is an importantprocess. We review the progress that people have made onself-consistent modeling of the ISM. The constraints on such models comefrom a wide variety of observations of molecular, neutral atomic, warmionized, and X-ray gas. Both observations and theory are represented atthis meeting and we highlight areas in which contributions are likely toresolve the existing controversies.

A Fortran package for the planar analysis of limb intersegmental dynamics from spatial coordinate-time data

Limbs in humans and animals are systems of linked bodies, in which motion of any one part of the linkage exerts forces on the remaining parts. Thus, during natural movements, forces can act on a limb segment even if a segment is not exposed to active muscle forces. Passive reactions arise from forces in tendons, ligaments, and peri-articular tissues, as well as from dynamical limb reactions related to inertial, Coriolis, and centripetal forces. Consequently, limb trajectories are influenced not only by active muscle forces but also by passive, intersegmental forces. For a more complete understanding of movement control, it is important to explain the mechanisms by which active and passive forces are coordinated. To achieve this, an analysis of limb intersegmental dynamics is essential, and here we provide a detailed description of the equations used for the planar analysis of limb intersegmental dynamics from spatial coordinate-time data, as well as the FORTRAN software to perform those calculations.

Theoretical approaches to the microphonics

The cochlea microphonics have two components; the first component is very sensitive to lack of oxygen and disappears immediately upon the death of the animal; the second component is the smaller fraction (5–25 %) but persists after the death of the animal, and is anaerobic. This paper gives a simple model which can be applied to the understandings of the later part of the microphonic potential. Both perilymph and endolymph in the inner ear may be electrolyte solutions which will behave like homogeneous liquids. If, however, the dynamical reactions are taken in account, these reactions will be different for ions of different masses. As a result, the motion, say of the positive ions, may differ from that of the negative ions. This means that periodically changing electric charge densities will accompany the sound waves. Theoretical approaches to the microphonics in the cochlea are presented.

THEORETICAL SOLUTION OF THE UNSTEADY UNSATURATED FLOW PROBLEMS IN SOILS

Synopsis The mathematical description of the state of a moving fluid is effected by means of functions which give the distribution of the fluid velocity v = v(x, y, z, t) and of any two thermodynamic quantities pertaining of the fluid. These two quantities can be taken to be the pressure p(x, y, z, t) and the density q(x, y, z, t). The above quantities v, p and q are functions of the coordinates x, y, z and of the time t. Dealing with flow of water through soils the following three general laws of mechanics but in hydrodynamic terms are applied to all kinds of water movement: 1) The dynamical equation of motion which specifies the dynamical reactions of the fluid to pressure gradients or external forces (Darcy's equation replacing the Navier-Stokes relations which are the hydrodynamical restatement of Newton's first law of motion), 2) The equation of continuity which is the analytical statement of the law of the conservation of matter taken from mechanics; and 3) The equation of state which defines thermo...