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PubMed1998

Vortex dynamics in three-dimensional continuous myocardium with fiber rotation: Filament instability and fibrillation.

Wave propagation in ventricular muscle is rendered highly anisotropic by the intramural rotation of the fiber. This rotational anisotropy is especially important because it can produce a twist of electrical vortices, which measures the rate of rotation (in degree/mm) of activation wavefronts in successive planes perpendicular to a line of phase singularity, or filament. This twist can then significantly alter the dynamics of the filament. This paper explores this dynamics via numerical simulation. After a review of the literature, we present modeling tools that include: (i) a simplified ionic model with three membrane currents that approximates well the restitution properties and spiral wave behavior of more complex ionic models of cardiac action potential (Beeler-Reuter and others), and (ii) a semi-implicit algorithm for the fast solution of monodomain cable equations with rotational anisotropy. We then discuss selected results of a simulation study of vortex dynamics in a parallelepipedal slab of ventricular muscle of varying wall thickness (S) and fiber rotation rate (theta(z)). The main finding is that rotational anisotropy generates a sufficiently large twist to destabilize a single transmural filament and cause a transition to a wave turbulent state characterized by a high density of chaotically moving filaments. This instability is manifested by the propagation of localized disturbances along the filament and has no previously known analog in isotropic excitable media. These disturbances correspond to highly twisted and distorted regions of filament, or "twistons," that create vortex rings when colliding with the natural boundaries of the ventricle. Moreover, when sufficiently twisted, these rings expand and create additional filaments by further colliding with boundaries. This instability mechanism is distinct from the commonly invoked patchy failure or wave breakup that is not observed here during the initial instability. For modified Beeler-Reuter-like kinetics with stable reentry in two dimensions, decay into turbulence occurs in the left ventricle in about one second above a critical wall thickness in the range of 4-6 mm that matches experiment. However this decay is suppressed by uniformly decreasing excitability. Specific experiments to test these results, and a method to characterize the filament density during fibrillation are discussed. Results are contrasted with other mechanisms of fibrillation and future prospects are summarized. (c)1998 American Institute of Physics.

Journal Article↗
PubMed2004

Rotational state-dependent mixings between resonance states of vibrationally highly excited DCO (X2A').

Rotational state-dependent mixings between highly excited resonance states of DCO (X (2)A(')) were investigated by stimulated emission pumping spectroscopy via a series of intermediate rotational levels in the B (2)A(') electronic state of the radical. Two examples for such interactions, between pairs of accidentally nearly degenerate vibrational states at energies of E(v) approximately 6450 and E(v) approximately 10 060 cm(-1), respectively, were analyzed in detail. Deperturbations of the measured spectra provided the zeroth-order vibration-rotation term energies, widths, and rotational constants of the states and the absolute values of the vibrational coupling matrix elements. The coupled states turned out to have very different A rotational constants so that their mixings switch on or off as they are tuned relative to each other as function of the K(a) rotational quantum number. The respective zeroth-order states could be assigned to different interlaced vibrational polyads. Thus, when two states belonging to different polyads are accidentally nearly isoenergetic, even very weak interpolyad interactions may start to play important roles. The derived interpolyad coupling elements are small compared to the typical intrapolyad coupling terms so that their influences on the vibrational term energies are small. However, large effects on the widths (i.e., decay rates) of the states can be observed even from weak coupling terms when a narrow, long-lived state is perturbed by a broad, highly dissociative state. This influence contributes to the previously observed strong state-to-state fluctuations of the unimolecular decay rates of the DCO radical as function of vibrational excitation. Similar mechanisms are likely to promote the transition to "statistical" rates in many larger molecules.

Journal Article↗
PubMed2004

Rotational excitations of N2O in small helium clusters and the role of Bose permutation symmetry.

We present a detailed study of the energetics, structures, and Bose properties of small clusters of (4)He containing a single nitrous oxide (N(2)O) molecule, from N=1 (4)He up to sizes corresponding to completion of the first solvation shell around N(2)O (N=16 (4)He). Ground state properties are calculated using the importance-sampled rigid-body diffusion Monte Carlo method, rotational excited state calculations are made with the projection operator imaginary time spectral evolution method, and Bose permutation exchange and associated superfluid properties are calculated with the finite temperature path integral method. For N< or =5 the helium atoms are seen to form an equatorial ring around the molecular axis, at N=6 helium density starts to occupy the second (local) minimum of the N(2)O-He interaction at the oxygen side of the molecule, and N=9 is the critical size at which there is onset of helium solvation all along the molecular axis. For N> or =8 six (4)He atoms are distributed in a symmetric, quasirigid ring around N(2)O. Path integral calculations show essentially complete superfluid response to rotation about the molecular axis for N> or =5, and a rise of the perpendicular superfluid response from zero to appreciable values for N> or =8. Rotational excited states are computed for three values of the total angular momentum, J=1-3, and the energy levels fitted to obtain effective spectroscopic constants that show excellent agreement with the experimentally observed N dependence of the effective rotational constant B(eff). The non-monotonic behavior of the rotational constant is seen to be due to the onset of long (4)He permutation exchanges and associated perpendicular superfluid response of the clusters for N> or =8. We provide a detailed analysis of the role of the helium solvation structure and superfluid properties in determining the effective rotational constants.

Journal Article↗
PubMed2005

Rotational distributions following van der Waals molecule dissociation: comparison between experiment and theory for benzene-Ar.

The translational energy release distribution for dissociation of benzene-Ar has been measured and, in combination with the 6(1)(0) rotational contour of the benzene product observed in emission, used to determine the rotational J,K distribution of 0(0) benzene products formed during dissociation from 6(1). Significant angular momentum is transferred to benzene on dissociation. The 0(0) rotational distribution peaks at J=31 and is skewed to low K:Javerage=27, (K)average=10.3. The average angle between the total angular momentum vector and the unique rotational axis is determined to be 68 degrees. This indicates that benzene is formed tumbling about in-plane axes rather than in a frisbeelike motion, consistent with Ar "pushing off" benzene from an off-center position above or below the plane. The J distribution is very well reproduced by angular momentum model calculations based on an equivalent rotor approach [A. J. McCaffery, M. A. Osborne, R. J. Marsh, W. D. Lawrance, and E. R. Waclawik, J. Chem. Phys. 121, 1694 (2004)], indicating that angular momentum constraints control the partitioning of energy between translation and rotation. Calculations for p-difluorobenzene-Ar suggest that the equivalent rotor model can provide a reasonable prediction of both J and K distributions in prolate (or near prolate) tops when dissociation leads to excitation about the unique, in-plane axis. Calculations for s-tetrazine-Ar require a small maximum impact parameter to reproduce the comparatively low J values seen for the s-tetrazine product. The three sets of calculations show that the maximum impact parameter is not necessarily equal to the bond length of the equivalent rotor and must be treated as a variable parameter. The success of the equivalent rotor calculations argues that angular momentum constraints control the partitioning between rotation and translation of the products.

Journal Article↗
PubMed2005

A velocity map ion-imaging study on ketene photodissociation at 208 and 213 nm: Rotational dependence of product angular anisotropy.

Photodissociation dynamics of ketene following excitation at 208.59 and 213.24 nm have been investigated using the velocity map ion-imaging method. Both the angular distribution and translational energy distribution of the CO products at different rotational and vibrational states have been obtained. No significant difference in the translational energy distributions for different CO rotational state products has been observed at both excitation wavelengths. The anisotropy parameter beta is, however, noticeably different for different CO rotational state products at both excitation wavelengths. For lower rotational states of the CO product, beta is smaller than zero, while beta is larger than zero for CO at higher rotational states. The observed rotational dependence of angular anisotropy is interpreted as the dynamical influence of a peculiar conical intersection between the (1)B(1) excited state and (1)A(2) state along the C(S)-I coordinate.

Journal Article↗
PubMed2005

Rotational effects in the dissociative adsorption of H2 on the Pt211 stepped surface.

Rotational effects in the dissociative adsorption of H2 on the Pt211 stepped surface have been studied using classical trajectory calculations on a six-dimensional, density-functional theory potential-energy surface. Reaction of rotating molecules via an indirect trapping mechanism exhibits an unexpected nonmonotonic dependence on the initial rotational quantum number J. Indirect reaction is first quenched with increasing J but is enhanced again for high J initial states. The quenching is attributed to rotational-to-translational energy transfer, which facilitates escape from the chemisorption wells responsible for molecular trapping. For high J, rotational and translational motions decouple, and the energy transfer is no longer possible, which leads again to trapping. Degeneracy-resolved calculations show that for high initial J, molecules rotating in a "cartwheel" fashion (mJ=0) are more likely to become trapped and react indirectly than "helicoptering" molecules (mJ=J). Experimental confirmation of this finding would lend strong support to the existence of the chemisorption wells that trap molecules prior to reaction.

Journal Article↗
PubMed2006

The role of molecular rotation in activated dissociative adsorption on metal surfaces.

The role of molecular rotation in dissociative adsorption of H2 on the activated NiAl(110) metal surface is systematically investigated by means of classical dynamics calculations performed on ab initio six-dimensional potential energy surfaces. The calculations show that molecules rotate abruptly when they are close to the surface and that this rotation allows the molecules to adopt the orientation that is more convenient for dissociation (i.e., nearly parallel to the surface). Also, in reactive sectors of the NiAl(110) unit cell, there is an "angular threshold" below which molecules cannot dissociate. This angular threshold goes down as the incidence energy increases, which explains the rise of the dissociation probability and the fact that it reaches a value close to 1 at incidence energies of the order of 2 eV. The fact that switching on molecular rotation favors dissociation establishes a competition between dissociation and rotational excitation of reflected molecules above the dissociation threshold. Measurements on rotational excitation might thus bring indirect evidence on the dissociation dynamics. Sample calculations for nonactivated Pd(111) and activated Cu(110) metal surfaces suggest that some of these conclusions may be of general validity.

Journal Article↗
PubMed2006

Femtosecond degenerate four-wave mixing of carbon disulfide: high-accuracy rotational constants.

Femtosecond degenerate four-wave mixing (fs-DFWM) rotational coherence spectroscopy (RCS) has been used to determine the rotational and centrifugal distortion constants of the 00 (0)0 ground and 01 (1)0 vibrationally excited states of gas-phase CS(2). RCS transients were recorded over the 0-3300 ps optical delay range, allowing the observation of 87 recurrences. The fits yield rotational constants B(00 (0)0)=3.271 549 2(18) GHz for (12)C(32)S(2) and B(00 (0)0)=3.175 06(21) GHz for the (12)C(32)S(34)S isotopomer. The rotational constants of the degenerate 01 (1)0 bending level of (12)C(32)S(2) are B(01 (1)0)=3.276 72(40) and 3.279 03(40) GHz for the e and f substrates, respectively. These fs-DFWM rotational constants are ten times more accurate than those obtained by CO(2) laser/microwave heterodyne measurements and are comparable to those obtained by high-resolution Fourier transform infrared spectroscopy. Ab initio calculations were performed at two levels, second-order Moller-Plesset theory and coupled-cluster singles, doubles, and iterative triples [CCSD(T)]. The equilibrium and vibrationally averaged C=S distances were calculated using large Dunning basis sets. An extrapolation procedure combining the ab initio rotational constants with the experiment yields an equilibrium C=S bond length of 155.448 pm to an accuracy of +/-20 fm. The theoretical C=S bond length obtained by a complete basis set extrapolation at the CCSD(T) level is r(e)(C=S)=155.579 pm, or 0.13 pm longer than that in the experiment.

Journal Article↗
PubMed2006

Are people with high and low mental rotation abilities differently susceptible to the alignment effect?

We investigated whether the alignment effect (Levine et al, 1982 Journal of Experimental Psychology: General 111 157-175) is influenced by mental rotation abilities. In two experiments, groups of undergraduate students with high and low performance in mental rotation tasks were required to study either schematic (experiment 1) or more complex (experiment 2) maps, and to perform a number of pointing tasks adopting a perspective which could be aligned, misaligned (45 degrees, 135 degrees), or counteraligned (180 degrees) with the perspective assumed during learning. Cognitive styles in spatial representation have also been considered. Results of experiment 1 show that people with low performance in mental rotation tasks prefer to adopt a representation of space focused more on landmarks. Their performance in the pointing tasks depends on the alignment conditions, with more errors in the counteraligned condition followed by the two misaligned and aligned ones. In contrast to this, high-ability mental rotators prefer survey and route spatial representations and are affected only by the aligned and non-aligned conditions. In the second experiment, practice was studied as a function of mental rotation and alignment. The group high in mental rotation ability was found to be free from the alignment effect in the pointing tasks performed after the final of four learning phases.

Cognition↗
PubMed1977

Bacterial flagella rotating in bundles: a study in helical geometry.

Bacterial flagella are semi-rigid helices that undergo true rotation. In peritrichously flagellated bacteria (e.g., Escherichia and Salmonella) there are many flagella on each cell; during translational cell movement these operate as a coordinated bundle that actively disperses upon reversal of the rotation sense. The dynamic behavior of a set of helices originating on separate rotational axes is explored by a working model, geometrical analysis, and hydrodynamic calculations. A critical relationship exists between the interaxial separation and phase difference of parallel helices with overlapping domains; in the subcritical case the filaments are not intertwisted, whereas in the supercritical case they are intertwisted in the same sense (left-handed) as the helices, with one twist per helical turn. During counter-clockwise rotation (the sense operative in forward swimming) any preexisting twists of this kind are automatically cancelled and the helices brought progressively into phase. Hydrodynamic calculations suggest that some wrapping then occurs in a right-handed sense, opposite to that of the helices; this necessitates a distortion from true helical geometry which is minimized by maintaining a coaxial in-phase relationship. A highly coordinated helical bundle results that is capable of operating smoothly for an indefinite period, in agreement with the observed behavior of swimming bacteria. During reverse rotation, the supercritical case develops to cause jamming of the bundle, as has been observed with bacteria in high-viscosity medium. The explosive dispersal of the bundle during reversal in low-viscosity medium is a consequence of a complicating phenomenon, namely, a drastic change in flagellar quaternary structure. The overall conclusion is that bundle formation and function are perfectly compatible with a rotational mechanism for the individual flagella.

Bacterial Physiological Phenomena↗
PubMed1979

A general ellipsoid cannot always serve as a model for the rotational diffusion properties of arbitrarily shaped rigid molecules.

An ellipsoidally shaped body, or more commonly, an ellipsoid of revolution, is generally assumed to serve as a convenient model for evaluating the rotational diffusion properties of macromolecules. If Perrin's equations for the rotational diffusion coefficients of general ellipsoids can be shown to generate all possible rotational diffusion coefficients, then there would exist at least one equivalent ellipsoidal shape for every arbitrarily shaped rigid body. We investigated the problem by first generating a space, r-space, representing all possible ellipsoidal shapes. We then generated another space, D-space, representing all possible combinations of rotational diffusion coefficients. We then mapped r-space into D-space by using Perrin's equations. Ellipsoidal shapes map into diffusion space in a well-defined manner. The mapping is either 1:1, 2:1, or 3:1; several distinctly different regions of r-space map onto the same regions of D-space. Thus, for some combinations of rotational diffusion coefficients, more than one ellipsoid can be used as a model. Not all of D-space is covered by the mapping of r-space. Therefore, there are combinations of rotational diffusion coefficients that cannot be generated from ellipsoidally shaped bodies. Several examples of rigid body shapes with nonellipsoidal diffusion properties are described.

Journal Article↗
PubMed1986

Restoration of flagellar clockwise rotation in bacterial envelopes by insertion of the chemotaxis protein CheY.

When cells of the bacterium Salmonella typhimurium are incubated with penicillin and lysed in a dilute buffer, flagellated cytoplasm-free envelopes are formed. When the envelopes are tethered to glass by their flagella and then energized, some of them spin. The direction of rotation of wild-type envelopes is exclusively counterclockwise (CCW). We perturbed this system by including in the lysis medium (and hence in the envelopes) the chemotaxis protein CheY. As a result, some of the envelopes rotated exclusively clockwise (CW). The fraction of envelopes that did so increased with the concentration of CheY; at a concentration of 48 microM (pH 8), all functional envelopes spun CW. The fraction also increased with the pH of the lysis medium in the range of 6.6-8.4. The results were the same in the presence or absence of intracellular Ca2+. Reconstituted envelopes failed to respond to chemotactic stimuli. None of them changed the direction of their rotation. However, when the intracellular pH was lowered to 6.6 or below, envelopes that spun CW stopped rotating, while envelopes that spun CCW continued to rotate. This phenomenon was reversible. We conclude that CheY per se, without any additional free cytoplasmic mediators, interacts with a switch at the base of the flagellum to cause CW rotation.

Bacterial Proteins↗
PubMed1998

Direct observation of the rotation of epsilon subunit in F1-ATPase.

Rotation of the epsilon subunit in F1-ATPase from thermophilic Bacillus strain PS3 (TF1) was observed under a fluorescence microscope by the method used for observation of the gamma subunit rotation (Noji, H., Yasuda, R., Yoshida, M., and Kinosita, K., Jr. (1997) Nature 386, 299-302). The alpha3 beta3 gamma epsilon complex of TF1 was fixed to a solid surface, and fluorescently labeled actin filament was attached to the epsilon subunit through biotin-streptavidin. In the presence of ATP, the filament attached to epsilon subunit rotated in a unidirection. The direction of the rotation was the same as that observed for the gamma subunit. The rotational velocity was slightly slower than the filament attached to the gamma subunit, probably due to the experimental setup used. Thus, as suggested from biochemical studies (Aggeler, R., Ogilvie, I. , and Capaldi, R. A. (1997) J. Biol. Chem. 272, 19621-19624), the epsilon subunit rotates with the gamma subunit in F1-ATPase during catalysis.

Actin Cytoskeleton↗
PubMed2002

Genetic fusions of globular proteins to the epsilon subunit of the Escherichia coli ATP synthase: Implications for in vivo rotational catalysis and epsilon subunit function.

The rotational mechanism of ATP synthase was investigated by fusing three proteins from Escherichia coli, the 12-kDa soluble cytochrome b(562), the 20-kDa flavodoxin, and the 28-kDa flavodoxin reductase, to the C terminus of the epsilon subunit of the enzyme. According to the concept of rotational catalysis, because epsilon is part of the rotor a large domain added at this site should sterically clash with the second stalk, blocking rotation and fully inhibiting the enzyme. E. coli cells expressing the cytochrome b(562) fusion in place of wild-type epsilon grew using acetate as the energy source, indicating their capacity for oxidative phosphorylation. Cells expressing the larger flavodoxin or flavodoxin reductase fusions failed to grow on acetate. Immunoblot analysis showed that the fusion proteins were stable in the cells and that they had no effect on enzyme assembly. These results provide initial evidence supporting rotational catalysis in vivo. In membrane vesicles, the cytochrome b(562) fusion caused an increase in the apparent ATPase activity but a minor decrease in proton pumping. Vesicles bearing ATP synthase containing the larger fusion proteins showed reduced but significant levels of ATPase activity that was sensitive to inhibition by dicyclohexylcarbodiimide (DCCD) but no proton pumping. Thus, all fusions to epsilon generated an uncoupled component of ATPase activity. These results imply that a function of the C terminus of epsilon in F(1)F(0) is to increase the efficiency of the enzyme by specifically preventing the uncoupled hydrolysis of ATP. Given the sensitivity to DCCD, this uncoupled ATP hydrolysis may arise from rotational steps of gammaepsilon in the inappropriate direction after ATP is bound at the catalytic site. It is proposed that the C-terminal domain of epsilon functions to ensure that rotation occurs only in the direction of ATP synthesis when ADP is bound and only in the direction of hydrolysis when ATP is bound.

ATP Synthetase Complexes↗
PubMed2005

Accommodation and repair of a UV photoproduct in DNA at different rotational settings on the nucleosome surface.

Cyclobutane-thymine dimers (CTDs), the most common DNA lesion induced by UV radiation, cause 30 degrees bending and 9 degrees unwinding of the DNA helix. We prepared site-specific CTDs within a short sequence bracketed by strong nucleosome-positioning sequences. The rotational setting of CTDs over one turn of the helix near the dyad center on the histone surface was analyzed by hydroxyl radical footprinting. Surprisingly, the position of CTDs over one turn of the helix does not affect the rotational setting of DNA on the nucleosome surface. Gel-shift analysis indicates that one CTD destabilizes histone-DNA interactions by 0.6 or 1.1 kJ/mol when facing away or toward the histone surface, respectively. Thus, 0.5 kJ/mol energy penalty for a buried CTD is not enough to change the rotational setting of sequences with strong rotational preference. The effect of rotational setting on CTD removal by nucleotide excision repair (NER) was examined using Xenopus oocyte nuclear extracts. The NER rates are only 2-3 times lower in nucleosomes and change by only 1.5-fold when CTDs face away or toward the histone surface. Therefore, in Xenopus nuclear extracts, the rotational orientation of CTDs on nucleosomes has surprisingly little effect on rates of repair. These results indicate that nucleosome dynamics and/or chromatin remodeling may facilitate NER in gaining access to DNA damage in nucleosomes.

Animals↗
PubMed2003

Energy cost and physiological responses of males snowshoeing with rotating and fixed toe-cord designs in powdered snow conditions.

The purpose of this study was to measure the energy cost and physiological responses of males while snowshoeing with two separate toe-cord designs (rotating toe-cord system vs. fixed toe-cord design) in powdered snow conditions. Eight males snowshoed at self-selected intensity for two, 1600 m trials in two snowshoes, with a rotating toe-cord system and a fixed-toe cord design. It was found that heart rate (HR) (140 vs. 134 beats min(-1)), oxygen consumption (VO(2)) (63.4 vs. 34.0 ml kg(-1)min(-1)), energy cost (56.0 vs. 52.4 kJ min(-1)), and ratings of perceived exertion (RPE) (13 vs. 12) were significantly (p < 0.05) higher while snowshoeing with the fixed toe-cord design than with the rotating toe-cord system. Snowshoeing with the rotating toe-cord system at an average speed of 3.96 km h(-1) produced mean VO(2) values that were 56% of VO(2) max, while snowshoeing with the fixed toe-cord design at 3.86 km h(-1) evoked mean VO(2) values that were 60% of VO(2) max. Mean HR while snowshoeing with the rotating toe-cord system was 70% of HR max, while the mean HR when snowshoeing with the fixed toe-cord design was 74% of HR max. These findings suggest that snowshoeing with a rotating toe-cord system results in lower cardiorespiratory strain in powdered snow conditions compared to snowshoeing with a fixed toe-cord design.

Energy Metabolism↗
PubMedDate not supplied

The repeatability of scapular rotations across three planes of humeral elevation.

Measurement of scapular kinematics is an important component in the assessment of shoulder function; however, repeatability of these measurements has not been established. The purpose of this study, therefore, was to determine the repeatability of scapular rotation measures for different humeral elevation planes between trials, sessions, and days. Three-dimensional scapular rotations were collected using an electromagnetic tracking system in three planes of humeral elevation. Coefficient of multiple correlation (CMC) values were calculated between trials, sessions, and days for curves of scapular rotations. CMC values were compared with repeated measures analysis of variance (ANOVAs) and Tukey's post-hoc procedures. Tests of simple main effects were performed for significant interaction effects. Our results suggest that scapular rotation measures are repeatable between trials within the same testing session, but less repeatable between testing sessions and days. Sagittal plane elevation consistently yielded the highest CMC values for all scapular rotations. These results suggest sagittal plane elevation should be considered to evaluate differences in scapular rotations.

Adult↗
PubMed2004

Therapist rotation--a new element in the outpatient treatment of alcoholism.

For nine years, the so-called "therapist rotation" has been a central part of OLITA, the Outpatient Longterm Intensive Therapy for Alcoholics. Thus far, the participation of several equally responsible therapists in the treatment of a patient has rarely been seen as a specific therapeutic approach. The present article analyzes the therapist rotation from a theoretical and clinical perspective. Articles concerned with the therapeutic alliance in the treatment of substance use disorders are reviewed. Furthermore, the literature on multiple psychotherapy, which may be seen as the precedent of the therapist rotation is surveyed. Based on the efficacy of multiple psychotherapy and the importance of the therapeutic alliance in the treatment of substance use disorders, the present work discusses the therapist rotation as an essential factor for the success of OLITA. It considers both potential advantages and disadvantages for patients and therapists and tries to identify conditions under which this approach appears to promote therapeutic interactions. Finally, the implementation of therapist rotation into OLITA is described, including the theoretical background of the program itself and the treatment procedure. New areas of application for the therapist rotation are discussed.

Alcoholism↗