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PubMed2002

Adolescent alcohol and tobacco use: onset, persistence and trajectories of use across two samples.

AIMS: We examined the alcohol-tobacco relationship using two prospective, ethnically diverse samples. Trajectories of alcohol and tobacco use are portrayed overall and by sex and ethnicity. Using prospective analyses, we examine directional influences between alcohol and tobacco use, and we characterize initiation versus persistence of drinking and smoking as a function of use of the other substance. DESIGN, SETTING: Data were from the National Longitudinal Study of Adolescent Health (AddHealth) and the Adolescent Health Risk Study (AHRS). Follow-up intervals for AddHealth and AHRS were 1 and 5 years, respectively. PARTICIPANTS: AddHealth respondents (n = 4831) were on average 14.8 years old (48% male, 23% black, 61% white) and AHRS respondents (n = 1814) were on average 16.7 years old (47% male, 44% black, 49% white). MEASUREMENTS: Two alcohol consumption variables and two smoking variables were used: drinking frequency and heavy drinking frequency, and regular (current) smoking and daily number of cigarettes. FINDINGS: Alcohol and tobacco use exhibited monotonic increases over adolescence and young adulthood. Men and white respondents reported more use than women and black respondents. Alcohol and tobacco were moderately associated at both times. Analyses revealed that prior alcohol use predicted tobacco use more strongly than the converse. Initiation of smoking was a function of prior drinking; to a lesser extent, initiation of drinking was a function of prior smoking. Persistence of smoking was a function of prior drinking and persistence of drinking was a function of prior smoking. CONCLUSIONS: Provisional support exists for the claim that alcohol use predicts tobacco use more strongly than the converse. For both drinking and smoking, onset and persistence are predicted by prior use of the other substance, and these associations were robust across sex and ethnicity.

Adolescent↗

PubMed2001

Shaping the trajectory of patients with venous ulceration in primary care.

OBJECTIVE: To explore the patient's experience of venous ulceration and how it is shaped within primary care. DESIGN: Qualitative grounded theory study. PARTICIPANTS AND SETTING: Thirty-nine patients, 33 nurses and 14 general practitioners in a major health district in England. RESULTS: The findings indicate that patients with the chronic condition of venous hypertension are handled in an anomalous way within primary care when they present with ulcers on their lower limbs. The trajectory projections for the patients are not developed from the usual basis of a medically defined condition-specific diagnosis but from a symptom-specific diagnosis. This leads to an unusual context of care where there is a serious but unrecognized conflict of focus between the nurses and their patients. The nurses in this study tended to set priorities related to the ulcer and to the underlying pathology, whereas the patients wanted help in pain management and in normalizing their lives. The patients eventually came to a position of 'guarded alliance'2 that in this study took one of three forms: adapting and enduring, emphasizing the positive, or negotiating for comfort. CONCLUSION: The acute care approach applied to patients with this chronic condition led to a situation where the professionals usurped the self-care potential of the patients and navigated rather than piloted them through an acute phase of an underlying chronic illness. This in turn, led to poor quality of life for many of the patients and to frustration for the nurses who were failing to achieve the outcomes they desired. Both perspectives need to be encapsulated into the treatment approach for patients with this condition: healing the ulcer and normalizing the patients' lives can and should form the basis of care.

Aged↗

PubMed2003

Phenotypic variation in growth trajectories in the Arctic charr Salvelinus alpinus.

Animals with determinate growth have shown little variation in individual growth patterns, but similar analyses for animals with indeterminate growth have been lacking. We analysed the amount of phenotypic variation in growth patterns across ages among individuals of a hatchery-based population of Arctic charr, Salvelinus alpinus, Salmonidae, using the infinite-dimensional model and including the effects of group size structure. There was little phenotypic variation in growth trajectories: individuals that were small (in relation to the mean) early in life were among the smallest 2.5 years later. If the genetic variation reflects phenotypic variation, not much evolutionary change can be expected. Our results show that there are ecological conditions that determine the strong covariation of size across ages, most likely size-related dominance behaviour, which can mask the true variation of growth patterns. Thus, social interactions can have strong evolutionary effects on traits not directly involved in the behavioural interactions.

Adaptation, Physiological↗

PubMed2000

Main trajectories of nerves that traverse and surround the tympanic cavity in the rat.

To guide surgery of nerves that traverse and surround the tympanic cavity in the rat, anatomical illustrations are required that are topographically correct. In this study, maps of this area are presented, extending from the superior cervical ganglion to the otic ganglion. They were derived from observations that were made during dissections using a ventral approach. Major blood vessels, bones, transected muscles of the tongue and neck and supra and infrahyoid muscles serve as landmarks in the illustrations. The course of the mandibular, facial, glossopharyngeal, vagus, accessory and hypoglossal nerves with their branches, and components of the sympathetic system, are shown and discussed with reference to data available in the literature. Discrepancies in this literature can be clarified and new data are presented on the trajectories of several nerves. The course of the tympanic nerve was established. This nerve originates from the glossopharyngeal nerve, enters the tympanic cavity, crosses the promontory, passes the tensor tympani muscle dorsally, and continues its route intracranially to the otic ganglion as the lesser petrosal nerve after intersecting with the greater petrosal nerve. Auricular branches of the glossopharyngeal and of the vagus nerve were noted. We also observed a pterygopalatine branch of the internal carotid nerve, that penetrates the tympanic cavity and courses across the promontory.

Accessory Nerve↗

PubMed2002

Control of long-period orbits and arbitrary trajectories in chaotic systems using dynamic limiting.

We demonstrate experimental control of long-period orbits and arbitrary chaotic trajectories using a new chaos control technique called dynamic limiting. Based on limiter control, dynamic limiting uses a predetermined sequence of limiter levels applied to the chaotic system to stabilize natural states of the system. The limiter sequence is clocked by the natural return time of the chaotic system such that the oscillator sees a new limiter level for each peak return. We demonstrate control of period-8 and period-34 unstable periodic orbits in a low-frequency circuit and provide evidence that the control perturbations are minimal. We also demonstrate control of an arbitrary waveform by replaying a sequence captured from the uncontrolled oscillator, achieving a form of delayed self-synchronization. Finally, we discuss the use of dynamic limiting for high-frequency chaos communications. (c) 2002 American Institute of Physics.

Journal Article↗

PubMed2002

Chaotic maps derived from trajectory data.

We assume that we have the following information from observed trajectory data about a discrete time dynamical process: (1) a rough graph of the phase plot, (2) the probability density function and (3) the metric entropy. We describe a method for constructing a nonlinear map whose graph is "within" the rough graph of the phase plot, and which has the observed probability density function and entropy.(c) 2002 American Institute of Physics.

Journal Article↗

PubMed2004

Quantum wave packet and quasiclassical trajectory studies of OH+CO: influence of the reactant channel well on thermal rate constants.

We study the OH+CO-->H+CO2 reaction with both six-dimensional quantum wave packets (QM) and quasiclassical trajectories (QCT), determining reaction probabilities and thermal rate constants (or coefficients), and studying the influence of the reactant channel hydrogen-bonded complex well on the reaction dynamics. The calculations use the recently developed Lakin-Troya-Schatz-Harding (LTSH) ground electronic state potential energy surface, along with a modified surface developed for this study (mod-LTSH), in which the reactant channel well is removed. Our results show that there can be significant differences between the QM and QCT descriptions of the reaction for ground-state reactants and for energies important to the thermal rate constants. Zero-point energy violation plays an important role in the QCT results, and as a result, the QCT reaction probability (for ground-state reactants and zero impact parameter) is much higher than its QM counterpart at moderate to low reagent translational energies. The influence of the reactant channel well in the QCT results is to enhance reactivity at moderate energies and to suppress reactivity at the very lowest collision energies. The QM results also show the enhancement at moderate energies but, while the very lowest translational energies cannot be adequately converged, they do not indicate any tendency toward suppression as energy is reduced. QCT calculations for excited rotational states of the reactants show that the suppression of reactivity associated with the reactant channel well is less important when the reactants are rotating, and as a result, the influence of the reactant channel well on the thermal rate coefficients is relatively small, being important below 200 K. Our results indicate that there still remain important discrepancies between experiment and theory in this low temperature regime and that further improvements of the potential are needed.

Journal Article↗

PubMed2004

Ab initio potential energy surface, variational transition state theory, and quasiclassical trajectory studies of the F+CH4-->HF+CH3 reaction.

In this work we present a study of the F+CH(4)-->HF+CH(3) reaction (DeltaHdegrees(298 K)=-32.0 kcal mol(-1)) using different methods of the chemical reaction theory. The ground potential energy surface (PES) is characterized using several ab initio methods. Full-dimensional rate constants have been calculated employing the variational transition state theory and using directly ab initio data. A triatomic analytical representation of the ground PES was derived from ab initio points calculated at the second- and fourth-order Møller-Plesset levels with the 6-311+G(2df,2pd) basis set, assuming the CH(3) fragment to be a 15 a.m.u. pseudoatom in the fitting process. This is suggested from experiments that indicate that the methyl group is uncoupled to the reaction coordinate. A dynamics study by means of the quasiclassical trajectory (QCT) method and employing this analytical surface was also carried out. The experimental data available on the HF internal states distributions are reproduced by the QCT results. Very recent experimental information about the reaction stereodynamics is also borne out by our QCT calculations. Comparisons with the benchmark F+H(2) and analogous Cl+CH(4) reactions are established throughout.

Journal Article↗

PubMed2004

Ab initio analytical potential energy surface and quasiclassical trajectory study of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+))-->OH(+)(X (3)Sigma(-))+H((2)S) reaction and isotopic variants.

An analytical potential energy surface (PES) representation of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+)) system was developed by fitting around 600 CCSD(T)/cc-pVQZ ab initio points. Rate constant calculations for this reaction and its isotopic variants (D(2) and HD) were performed using the quasiclassical trajectory (QCT) method, obtaining a good agreement with experimental data. Calculations conducted to determine the cross section of the title reaction, considering collision energies (E(T)) below 0.3 eV, also led to good accord with experiments. This PES appears to be suitable for kinetics and dynamics studies. Moreover, the QCT results show that, although the hypotheses of a widely used capture model are not satisfied, the resulting expression for the cross section can be applied within a suitable E(T) interval, due to errors cancellation. This could be a general situation regarding the application of this simple model to ion-molecule processes.

Journal Article↗

PubMed2004

Computing minimal entropy production trajectories: an approach to model reduction in chemical kinetics.

Advanced experimental techniques in chemistry and physics provide increasing access to detailed deterministic mass action models for chemical reaction kinetics. Especially in complex technical or biochemical systems the huge amount of species and reaction pathways involved in a detailed modeling approach call for efficient methods of model reduction. These should be automatic and based on a firm mathematical analysis of the ordinary differential equations underlying the chemical kinetics in deterministic models. A main purpose of model reduction is to enable accurate numerical simulations of even high dimensional and spatially extended reaction systems. The latter include physical transport mechanisms and are modeled by partial differential equations. Their numerical solution for hundreds or thousands of species within a reasonable time will exceed computer capacities available now and in a foreseeable future. The central idea of model reduction is to replace the high dimensional dynamics by a low dimensional approximation with an appropriate degree of accuracy. Here I present a global approach to model reduction based on the concept of minimal entropy production and its numerical implementation. For given values of a single species concentration in a chemical system all other species concentrations are computed under the assumption that the system is as close as possible to its attractor, the thermodynamic equilibrium, in the sense that all modes of thermodynamic forces are maximally relaxed except the one, which drives the remaining system dynamics. This relaxation is expressed in terms of minimal entropy production for single reaction steps along phase space trajectories.

Journal Article↗

PubMed1995

Variational principle for periodic trajectories of hyperbolic billiards.

We prove for some classes of hyperbolic billiards that the action functional has only one local minimum or only one local maximum for any finite admissible sequence of regular components of the boundary. This result suggests an effective algorithm for the search of all periodic trajectories of these billiards. (c) 1995 American Institute of Physics.

Journal Article↗

PubMed1997

Synchronization of chaotic systems: Transverse stability of trajectories in invariant manifolds.

We examine synchronization of identical chaotic systems coupled in a drive/response manner. A rigorous criterion is presented which, if satisfied, guarantees that synchronization to the driving trajectory is linearly stable to perturbations. An easy to use approximate criterion for estimating linear stability is also presented. One major advantage of these criteria is that, for simple systems, many of the calculations needed to implement them can be performed analytically. Geometrical interpretations of the criterion are discussed, as well as how they may be used to investigate synchronization between mutual coupled systems and the stability of invariant manifolds within a dynamical system. Finally, the relationship between our criterion and results from control theory are discussed. Analytical and numerical results from tests of these criteria on four different dynamical systems are presented. (c) 1997 American Institute of Physics.

Journal Article↗

PubMed2004

Quantum trajectories in atom-surface scattering with single adsorbates: the role of quantum vortices.

In this work, a full quantum study of the scattering of He atoms off single CO molecules, adsorbed onto the Pt(111) surface, is presented within the formalism of quantum trajectories provided by Bohmian mechanics. By means of this theory, it is shown that the underlying dynamics is strongly dominated by the existence of a transient vortitial trapping with measurable effects on the whole diffraction pattern. This kind of trapping emphasizes the key role played by quantum vortices in this scattering. Moreover, an analysis of the surface rainbow effect caused by the local corrugation that the CO molecule induces on the surface, and its manifestation in the corresponding intensity pattern, is also presented and discussed.

Journal Article↗

PubMed2004

Classical trajectory calculations of intramolecular vibrational energy redistribution. II. Phenol-water complex.

Ab initio classical trajectory calculations have been applied to the intramolecular vibrational energy redistribution process of an O-H stretching vibration for phenol cation, [phenol]+, and its hydrogen-bonded water complex, [phenol-water]+. In phenol cation, a single narrow peak in the power spectrum, obtained by Fourier transformation of the autocorrelation function of its total momentum, indicates that the initial energy given to the O-H stretching oscillator of the phenol moiety is conserved and no energy flow occurs. On the other hand, for phenol-water cation, the calculated broadened power spectrum implies that the initial energy is not conserved and the energy flow causes an energy redistribution among various vibrational modes.

Journal Article↗

PubMed2004

Quasiclassical trajectory study of the collision-induced dissociation of CH3SH+ + Ar.

Quasiclassical trajectory calculations were carried out to study the dynamics of energy transfer and collision-induced dissociation (CID) of CH(3)SH(+) + Ar at collision energies ranging from 4.34 to 34.7 eV. The relative abundances calculated for the most relevant product ions are found to be in good agreement with experiment, except for the lowest energies investigated. In general, the dissociation to form CH(3)(+) + SH is the dominant channel, even though it is not among the energetically favored reaction pathways. The results corroborate that this selective dissociation observed upon collisional activation arises from a more efficient translational to vibrational energy transfer for the low-frequency C-S stretching mode than for the high-frequency C-H stretching modes, together with weak couplings between the low- and high-frequency modes of vibration. The calculations suggest that CID takes place preferentially by a direct CH(3)(+) + SH detachment, and more efficiently when the Ar atom collides with the methyl group-side of CH(3)SH(+).

Journal Article↗

PubMed2004

Statistics of defect trajectories in spatio-temporal chaos in inclined layer convection and the complex Ginzburg-Landau equation.

For spatio-temporal chaos observed in numerical simulations of the complex Ginzburg-Landau equation (CGL) and in experiments on inclined-layer convection (ILC) we report numerical and experimental data on the statistics of defects and of defect loops. These loops consist of defect trajectories in space-time that are connected to each other through the pairwise annihilation or creation of the associated defects. While most such loops are small and contain only a few defects, the loop distribution functions decay only slowly with the quantities associated with the loop size, consistent with power-law behavior. For the CGL, two of the three power-law exponents are found to agree, within our computational precision, with those from previous investigations of a simple lattice model. In certain parameter regimes of the CGL and ILC, our results for the single-defect statistics show significant deviations from the previously reported findings that the defect dynamics are consistent with those of random walkers that are created with fixed probability and annihilated through random collisions.

Models, Theoretical↗

PubMed2004

Complex autocorrelation function and energy spectrum by classical trajectory calculations.

A quasiclassical method which enables evaluation of complex autocorrelation function from classical trajectory calculations is proposed. The method is applied for two highly excited nonlinearly coupled harmonic oscillators in regimes prevailed either by regular or chaotic classical motions. A good agreement of classical and quantum autocorrelation functions is found within short (Ehrnfest) time limit. Fourier transforms of the autocorrelation functions provide moderate resolved energy spectra, where classical and quantum results nearly coincide. The actual energy levels are obtained from approximate short-time autocorrelation functions with the help of filter diagonalization. This study is a follow up to our previous work [P. Zdanska and N. Moiseyev, J. Chem. Phys. 115, 10608 (2001)], where the complex autocorrelation has been obtained up to overall phase factors of recurrences.

Algorithms↗

PubMed2004

Ultrafast excited state dynamics of the Na3F cluster: quantum wave packet and classical trajectory calculations compared to experimental results.

Short-time, excited-state dynamics of the lowest isomer of the Na(3)F cluster is studied theoretically in order to interpret the features of recent time-resolved pump-probe ionization experiments [J. M. L'Hermite, V. Blanchet, A. Le Padellec, B. Lamory, and P. Labastie, Eur. Phys. J. D 28, 361 (2004)]. In the present paper, we propose an identification of the vibrational motion responsible for the oscillations in the ion signal, on the basis of quantum mechanical wave packet propagations and classical trajectory calculations. The good agreement between experiment and theory allows for a clear interpretation of the detected dynamics.

Journal Article↗