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At least 199 records · Page 11Linked to original sources
PubMedDate not supplied

A new force-plate technology measure of dynamic postural stability: the dynamic postural stability index.

CONTEXT: New measures of dynamic postural stability are needed to address weaknesses of previous measures. OBJECTIVE: To assess the feasibility, reliability, and precision of a new measure of dynamic postural stability. DESIGN: A single within-subjects design was used to determine optimal sampling interval as well as intersession reliability. SETTING: Biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: Eighteen subjects (7 men [age = 22 +/- 3 years, height = 175 +/- 5 cm, mass = 75 +/- 16 kg] and 11 women [age = 23 +/- 2 years, height = 163 +/- 6 cm, mass = 68 +/- 13 kg]) without lower extremity impairment. INTERVENTION(S): A jump protocol that required subjects to perform a 2-legged jump to a height equivalent to 50% of their maximum vertical leap and land on a single leg. MAIN OUTCOME MEASURE(S): The Dynamic Postural Stability Index (DPSI) and the directional components (medial-lateral, anterior-posterior, and vertical) after a jump landing. RESULTS: We observed a significant sampling-interval main effect (F(2,51) = 26.88, P < .01) for the DPSI; the 10-second trial duration produced significantly smaller means than the 5- and 3-second trial durations, whereas the 5-second trial result was also significantly smaller than that of the 3-second trial. The DPSI was highly reliable between test sessions (intraclass correlation coefficient = .96) and very precise (SEM = .03). CONCLUSIONS: These results suggest that the DPSI can be used in conjunction with a functional single-leg hop stabilization test and is a reliable and precise measure of dynamic postural stability. We believe the shortest sampling interval (3 seconds) is the best choice for studying and mimicking athletic performance as closely as possible.

Journal Article↗
PubMed1990

Mechanical analysis of the factors affecting dynamization of the Orthofix Dynamic Axial Fixator.

Loading trials were conducted to identify mechanical factors affecting dynamization of a commercially available external fixator (Orthofix) that is designed to undergo free telescopic motion when axially loaded. Angular variations between the proximal and distal screw clamps and the telescoping fixator body failed to produce fixator binding (failure to dynamize) in any of the loading trials. However, binding was produced by applying external torques in magnitudes that occasionally occur during routine ambulation. The specific torque necessary to induce binding (typically 3-4 Nm) was only a weak function of axial load magnitude, axial loading frequency, or simulated fracture stiffness. Among several geometrical variables of fixator application, only the pre-extension of the telescoping body and circumferential misalignment between proximal and distal pin clusters had an appreciable influence on the threshold binding torque. Axial fixator motions were also monitored in a small adjunct clinical series of 22 dynamized tibial fractures. The fixator dynamized appropriately in 15 cases (68%). Three patients (14%) showed evidence of fixator binding, and another four (18%) had less than predicted slider excursions. The role of several design factors implicated in torque-induced fixator binding is discussed in light of the benchtop and clinical observations.

Biomechanical Phenomena↗
PubMed1979

[Dynamic behavior of the adaptive control system, hypothalamus--anterior pituitary--adrenal cortex. Animal experimental study of the adequate system dynamics of the direct and indirect parameters of the adaptive control system].

The dynamic response of the adaptive closed-loop control system hypothalamus-anterior pituitary-adrenal cortex after application of short-time disturb pulses were examined experimentally in the pig. Blood sampling was performed biologically non-reactive by chronically implanted vascular catheters in the upper vena cava. A circadian biphase periodical dynamics characterizes the distrubance response of the adaptive control system, respectively, its direct and indirect parameters. After distrubance variables induced initial excess the plasma corticosteriods undershoot the basic level over a long period. Conversely, the dynamics of the eosinophils is determined through an initial eosinopenic phase and a subsequent typical overshoot. Periodical dynamic is absent in the steady state. The controller of the adaptive system does not show any spontaneous activity in the steady state without stress. The absence of an endogenic periodicity of the dependent parameters likewise gives evidence of an active oscillator. On the other hand, the controlling unit of the adaptive system constitutes a control response of circadian periodicty after activation by disturbance variables in pulse shape. The high damping of the control system terminates the transient state within 24 hours, and the corticosteriods and the eosinophils reach the steady state level. This control quality of the adaptive control system gains a high importance in the origination of the spontaneous circadian periodicity by corticosteriods and eosinophils and for the biological compensation of exogenous distrubance variables.

11-Hydroxycorticosteroids↗
PubMed1983

Statico-dynamic palatopharyngoplasty with transmitted dynamism--a new technique.

A new operation, 'Statico-dynamic palatopharyngoplasty with transmitted dynamism', is described for correction of rhinolalia aperta and nasal regurgitation in palato-pharyngeal incompetence. This is a simple one-stage operation and, besides offering good speech correction, prevents nasal regurgitation. The principle involves imparting dynamism to the conventional static posterior pharyngeal flap, based superiorly, by a muscle sling created by transplanting the palatopharyngeus/salpingopharyngeus complex. This mechanism brings about dynamic competence in the palato-pharyngeal mechanism.

Humans↗
PubMed1994

[Dynamics of fluoroquinolone agents in tear fluid--a comparison of the dynamic in tears of human and rabbit eyes].

We compared the dynamics of fluoroquinolones administered either systemically or locally, in the tears of human and rabbit eyes. The concentrations of locally administered ofloxacin (OFLX) in the human and rabbit tear fluid were similar. However, there was a difference between the norfloxacin (NFLX) concentrations in human and rabbit tear fluid measured after instillation. The NFLX concentrations in the tear fluid were significantly higher than the OFLX concentrations and they were retained longer with oral administration. On the other hand, the drug dynamics depended on the concentrations of the drug in the serum, and were better in the rabbit eyes than in the human eyes. Knowing the correlation of drug dynamics in rabbit and human eyes may supply useful information about drug dynamics in human eyes, and may be a useful index for clinical treatment.

Administration, Oral↗
PubMedDate not supplied

[Molecular dynamics of oligopeptides. 2. Dynamic correlation functions of the conformational modes of the modified dipeptides].

The method of investigation of dynamic correlation functions in molecules with conformational mobility on an example of modified dypeptides by molecular dynamics is proposed. Comparison of results for different types torsion angles and internuclear distances are carried out. Connection between the chemical structure of peptides and the peculiarities of internal dynamic correlations is established. A question about dynamic isomorphism of amino acids is discussed.

Dipeptides↗
PubMed1998

Hybrid phantoms for testing the measurement of regional dynamics in dynamic renal scintigraphy.

A hybrid phantom is a synthetic dynamic scintigraphic study reconstructed from dynamic components of real clinical data. The aim of a hybrid simulation is to provide realistic reference studies with systematically varying quantitative diagnostic parameters for testing the quality of measurement of regional dynamics. The components of the phantom are extracted from a representative patient study using factor analysis. Prior to the construction of the phantom, selected components are modified in a known way or substituted with heterologous data. The phantom study is constituted from the altered components using a procedure inverse to factor analysis, and completed by the addition of residual noise. The hybrid phantom is a compromise between simulated and software phantoms. Unlike simulated phantoms, it preserves a significant part of data variability and the natural complex structure of scintigraphic images. Unlike software phantoms, it provides values for selected diagnostic parameters or magnitudes of their relative changes. A set of hybrid phantoms from a dynamic renal study and the results of a pilot clinical evaluation are presented.

Databases as Topic↗
PubMed2005

Emergence of complex patterns induced by dynamic systems implemented in dynamic structures (DS)2.

We present the evolution of the simple system of Meinhardt implemented in both static or dynamic two-dimensional structures of almost-squared cells. In a static structure of 8 x 4=32 to 128 x 128=16384 cells, the pattern observed is periodic. An algorithm allows us to divide the cells following the greater size, and to define a dynamic structure. The implementation of the same Meinhardt system in this dynamic structure varying from 32 to 16 384 cells and a context of the same genotypic complexity for the model provides aperiodic patterns, with a higher phenotypic complexity than those observed in static structures, while the number of computations is comparable. We define that emergence occurs each time the ratio of phenotypic/genotypic complexities increases.

Algorithms↗
PubMed2005

Constructing dynamical systems with specified symbolic dynamics.

In this paper we demonstrate how to construct signals (time series) of continuous-time dynamical systems that exhibit a given symbolic dynamics. This is achieved without construction of the ordinary differential equations that generate the flow. This construction is of theoretical interest and is useful as a source of dynamical data that can be used to test various data analysis algorithms.

Algorithms↗
PubMed2004

Measles metapopulation dynamics: a gravity model for epidemiological coupling and dynamics.

Infectious diseases provide a particularly clear illustration of the spatiotemporal underpinnings of consumer-resource dynamics. The paradigm is provided by extremely contagious, acute, immunizing childhood infections. Partially synchronized, unstable oscillations are punctuated by local extinctions. This, in turn, can result in spatial differentiation in the timing of epidemics and, depending on the nature of spatial contagion, may result in traveling waves. Measles epidemics are one of a few systems documented well enough to reveal all of these properties and how they are affected by spatiotemporal variations in population structure and demography. On the basis of a gravity coupling model and a time series susceptible-infected-recovered (TSIR) model for local dynamics, we propose a metapopulation model for regional measles dynamics. The model can capture all the major spatiotemporal properties in prevaccination epidemics of measles in England and Wales.

Demography↗
PubMed1995

Human-like dynamic programming neural networks for dynamic time warping speech recognition.

This paper presents a human-like dynamic programming neural network method for speech recognition using dynamic time warping. The networks are configured, much like human's, such that the minimum states of the network's energy function represent the near-best correlation between test and reference patterns. The dynamics and properties of the neural networks are analytically explained. Simulations for classifying speaker-dependent isolated words, consisting of 0 to 9 and A to Z, show that the method is better than conventional methods. The hardware implementation of this method is also presented.

Humans↗
PubMedDate not supplied

[The relationship of the population dynamics of gamasid mites with the population dynamics of their murine rodent hosts in the Sikhote-Alin].

22,500 mites were collected from 4515 rodents over a period of 5 years in the Sikhote-Alin reserve. The abundance dynamics of 4, out of 5, most numerous species of mites (Laelaps pavlovskyi, L. clethrionomydis, Eulaelaps stabularis, Haemogamasus serdjukovae) depends on the cyclic fluctuations in the number of rodents. A direct connection between the annual and, to some extent, seasonal dynamics of the abundance of parasites and that of their hosts is most distinct in L. pavlovskyi, an epizoon parasite of the large Japanese field mouse. At the same time the abundance of Hg. ambulans, a multihost parasite of small mammals, does not depend on the number of animals. Certain regularities in the abundance dynamics of gamasid mites in connection with that of their hosts, rodents, is discussed on the basis of obtained material and literary data.

Altitude↗
PubMed1990

Internal dynamics of tRNA(Phe) studied by depolarized dynamic light scattering.

The collective internal dynamics of transfer RNA(Phe) from brewer's yeast in solution was studied by depolarized dynamic light scattering (DDLS). Within the melting region of tRNA the depolarized spectra consist of two Lorentzian, where the narrow (slow) component describes the overall rotation of the macromolecule. The broad component is attributed to the collective reorientation of the bases within the biopolymer. At high temperature only this relaxation process is observed in the spectrum. The viscosity dependence of the collective internal relaxation process is described by the Stokes-Einstein-Debye equation for rotational diffusion. Estimates of the internal orientational pair correlation factor from the integral depolarized intensities of tRNA(Phe) solutions indicates that the observed dynamics correspond to the collective reorientation of approximately 5 bases. A comparison of the results presented with DDLS studies on the aggregation of the mononucleotide guanosine-5'-monophosphate confirms this result. For a further characterization of the relaxation process we studied the effect of hydrostatic pressure (1-1000 bar) on the depolarized spectra of tRNA. While other spectroscopic methods like nmr, fluorescence polarization anisotropy decay, or ESR give information about the very local motion of a single base within the DNA or RNA, this study shows that by DDLS one can characterize collective internal motions of macromolecules.

Light↗
PubMed1993

Persistence analysis of the static and dynamical helix deformations of DNA oligonucleotides: application to the crystal structure and molecular dynamics simulation of d(CGCGAATTCGCG)2.

A theory and graphical presentation for the analysis of helix structure and deformations in oligonucleotides is presented. The parameters "persistence" and "flexibility" as defined in the configurational statistics of polymers of infinite length are reformulated at the oligonucleotide level in an extension of J. A. Schellman's method [(1974) Biopolymers, Vol. 17, pp. 217-226], and used as a basis for a systematic "Persistence Analysis" of the helix deformation properties for all possible subsequences in the structure. The basis for the analysis is a set of link vectors referenced to individual base pairs, and is limited to sequences exhibiting only perturbed rod-like behavior, i.e., below the threshold for supercoiling. The present application of the method is concerned with a physical model for the angular component of bending, so the link vectors are defined as the unit components of a global helix axis obtained by the procedure "Curves" of R. Lavery and H. Sklenar [(1988) J. Biomol. Struct. Dynam., Vol. 6, pp. 63-91; (1989) ibid., Vol. 6, pp. 655-667]. A discussion of the relationship between global bending and relative orientation of base pairs is provided. Our approach is illustrated by analysis of some model oligonucleotide structures with intrinsic kinks, the crystal structure of the dodecamer d(CGCGAATTCGCG)2, and the results of two molecular dynamics simulations on this dodecamer using two variations of the GROMOS force field. The results indicate that essentially all aspects of curvature in short oligonucleotides can be determined, such as the position and orientation of each bend, the sharpness or smoothness, and the location and linearity of subsequences. In the case of molecular dynamics simulations, where a Boltzmann ensemble of structures is analyzed, the spatial extent of the deformations (flexibility) is also considered.

Base Sequence↗
PubMed2004

Loop flexibility and solvent dynamics as determinants for the selective inhibition of cyclin-dependent kinase 4: comparative molecular dynamics simulation studies of CDK2 and CDK4.

The design and discovery of selective cyclin-dependent kinase 4 (CDK4) inhibitors have been actively pursued in order to develop therapeutic cancer treatments. By means of a consecutive computational protocol involving homology modeling, docking experiments, and molecular dynamics simulations, we examine the characteristic structural and dynamic properties that distinguish CDK4 from CDK2 in its complexation with selective inhibitors. The results for all three CDK4-selective inhibitors under investigation show that the large-amplitude motion of a disordered loop of CDK4 is damped out in the presence of the inhibitors whereas their binding in the CDK2 active site has little effect on the loop flexibility. It is also found that the binding preference of CDK4- selective inhibitors for CDK4 over CDK2 stems from the reduced solvent accessibility in the active site of the former due to the formation of a stable hydrogen-bond triad by the Asp99, Arg101, and Thr102 side chains at the top of the active-site gorge. Besides the differences in loop flexibility and solvent accessibility, the dynamic stabilities of the hydrogen bonds between the inhibitors and the side chain of the lysine residue at the bottom of the active site also correlate well with the relative binding affinities of the inhibitors for the two CDKs. These results highlight the usefulness of this computational approach in evaluating the selectivity of a CDK inhibitor, and demonstrate the necessity of considering protein flexibility and solvent effects in designing new selective CDK4-selective inhibitors.

Amino Acid Sequence↗
PubMed2006

Tunable fluorene-based dynamers through constitutional dynamic chemistry.

Dynamic covalent iminofluorene-based oligomers and polymers have been generated. They undergo constitutional recomposition under the effect of two parameters, acidity and ZnII metal ions. As a result, marked changes in physical properties take place. The results illustrate the response of such a dynamic system to chemical effectors (H+ nd ZnII), thus demonstrating the adaptive behavior of the system under the pressure of external factors. They also point to the possibility of modulating optical properties (UV-visible absorption and fluorescence) by constitutional recomposition in response to a specific trigger. Such features allow the development of dynamic materials, the functional properties of which may respond to external stimuli.

Journal Article↗
PubMed2002

Structure and dynamics of liquid water with different long-range interaction truncation and temperature control methods in molecular dynamics simulations.

We have used molecular dynamics simulations to study the physical properties of modified TIP3P water model included in the CHARMM program, using four different methods-the Ewald summation technique, and three different spherical truncation methods-for the treatment of the long-range interactions. Both the structure and dynamics of the liquid water model were affected by the methods used to truncate the long-range interactions. For some of the methods artificial structuring of the model liquid was observed around the cutoff radius. The model liquid properties were also affected by the commonly applied temperature control methods. Four different methods for controlling the temperature of the system were studied, and the effects of these methods on the bulk properties for liquid water were analyzed. The system size was also found to change the dynamics of the model liquid water. Two control simulations with the SPC/E water model were carried out. The self-diffusion coefficient (D), the radial distribution function (g(OO)), the distance dependent Kirkwood G-factor [G(k)(r)] and the intermolecular potential energy (E(pot)) were determined from the different trajectories and compared with the experimental data.

Journal Article↗
PubMed2006

Structural dynamics of the mitochondrial ADP/ATP carrier revealed by molecular dynamics simulation studies.

The mitochondrial adenosine diphosphate/adenosine triphosphate (ADP/ATP) carrier has been recently crystallized in complex with its specific inhibitor carboxyatractyloside (CATR). In the crystal structure, the six-transmembrane helix bundle that defines the nucleotide translocation pathway is closed on the matrix side due to sharp kinks in the odd-numbered helices. The closed conformation is further sealed by the loops protruding into the matrix that interact through an intricate network of charge-pairs. To gain insight into its structural dynamics we performed molecular dynamics (MD) simulation studies of the ADP/ATP carrier with and without its cocrystallized inhibitor. The two trajectories sampled a conformational space around two different configurations characterized by distinct salt-bridge networks with a significant shift from inter- to intrarepeat bonding on the matrix side in the absence of CATR. Analysis of the geometrical parameters defining the transmembrane helices showed that even-numbered helices can undergo a face rotation, whereas odd-numbered helices can undergo a change in the wobble angle with a conserved proline acting as molecular hinge. Our results provide new information on the dynamical properties of the ADP/ATP carrier and for the first time yield a detailed picture of a stable carrier conformation in absence of the inhibitor.

Animals↗