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PubMed2006

Comparison of perturbative and variational treatments of molecular vibrations: application to the vibrational spectrum of HFCO up to 8000 cm(-1).

We calculated highly excited states of the HFCO molecule, comparing results from two methods. In the first method, Van Vleck perturbation theory is used to transform away all off-diagonal couplings except those between nearly degenerate states. This perturbative transformation leads to a matrix representation where eigenvalues are obtained with relatively small matrices. In the second method, variational eigenvalues are obtained by combining the Jacobi-Wilson approach with the block-Davidson scheme. The key ingredient here is a prediagonalized-perturbative scheme applied to a subspace of a curvilinear normal-mode basis set. Comparisons of the two methods provide a critical test of the less time-consuming perturbation theory. Two different coordinate sets are used to test the sensitivity of the results to coordinate choice. Perturbation theory also requires a polynomial fit to the potential. The implications of this restriction are investigated.

Journal Article↗
PubMed1982

Resonance Raman and electron paramagnetic resonance studies on oxidized and ferricyanide-treated Clostridium pasteurianum ferredoxin. Vibrational assignments from 34S shifts and evidence for conversion of 4 to 3 iron-sulfur clusters via oxidative damage. Vibrational assignments from 34S shifts and evidence for conversion of 4 to 3 iron-sulfur clusters via oxidative damage.

Resonance Raman spectra are reported for oxidized ferredoxin from Clostridium pasteurianum and for protein reconstituted with 34S2-, using 4579 A laser excitation. The spectra are of much higher quality than that previously reported, and the 34S shifts provide assignments of the Fe-S modes. After treatment with ferricyanide, the resonance Raman spectrum closely resembles that of the [3Fe-3S] protein, ferredoxin II from D. gigas; the 34S shifts aid in assignments of the [3Fe-3S] modes. The epr signal associated with the [3Fe-3S] cluster (g = 2.01) corresponds maximally to 0.80 spin/molecule. Anaerobic addition of excess sulfide to the reduced, ferricyanide-treated protein regenerates a [4Fe-4S]1+ epr spectrum, equivalent in intensity to the [3Fe-3S] signal. The ubiquitous occurrence of a g = 2.01 signal in preparations of [4Fe-4S] proteins can be attributed to variable amounts of [3Fe-3S] cluster generated by adventitious oxidation. The ready conversion of [4Fe-4S] to [3Fe-3S] clusters in C. pasterianum raises the possibility that some [3Fe-3S] proteins may actually arise by oxidative damage of [4Fe-4S] proteins during aerobic isolation.

Clostridium↗
PubMed1995

Proprioceptive consequences of tendon vibration during movement.

1. Previous studies have used tendon vibration to investigate kinesthetic illusions in the isometric limb and end point control in the moving limb. These previous studies have shown that vibration distorts the perceptions of static joint angle and movement and causes systematic errors in the end point of movement. In this paper we describe the effects of tendon vibration during movement while human subjects performed a proprioceptively coordinated motor task. In an earlier study we showed that the CNS coordinates this motor task-a movement sequence-with proprioceptive information related to the dynamic position and velocity of the limb. 2. When performing this movement sequence, each subject sat at a table and opened the right hand as the right elbow was passively rotated in the extension direction through a prescribed target angle. Vision of the arm was prevented, and the movement velocity was changed randomly from trial to trial, leaving proprioception as the only useful source of kinematic information with which to perform the task. 3. In randomly occurring trials, vibration was applied to the tendon of the biceps brachii, a muscle that lengthens during elbow extension. In some experiments the timing of tendon vibration was varied with respect to the onset of elbow rotation, and in other experiments the frequency of vibration was varied. In each experiment we compared the accuracy of the subject's response (i.e., the elbow angle at which the subject opened the hand) in trials with tendon vibration with the accuracy in trials without tendon vibration. 4. The effect of tendon vibration depended on the frequency of vibration. When the biceps tendon was vibrated at 20 Hz, subjects opened the hand after the elbow passed through the target angle ("overshooting"). Overshooting is consistent with an underestimate of the actual displacement or velocity of the elbow. Vibration at 30 Hz had little or no effect on the elbow angle at hand opening. Vibration at 40 Hz caused subjects to open the hand before the elbow reached the target angle ("undershooting"). Undershooting is consistent with an overestimate of the actual displacement or velocity of the elbow. The size of the error depended on the velocity of the passively imposed elbow rotation. 5. The effect of tendon vibration also depended on the timing of vibration. If 40-Hz vibration began at the onset of movement, the subject undershot the target. If 40-Hz vibration started 5 s before movement onset and continued throughout the movement, the undershoot error increased in magnitude. However, if 40-Hz vibration started 5 s before movement onset and then stopped at movement onset, the subject overshot the target. When vibration was shut off during movement, a transition occurred from an over-shooting error to an undershooting error at a time that depended on the velocity of elbow rotation. 6. In a separate experiment, subjects were instructed to match either the perceived dynamic position or the perceived velocity of rotation imposed on the right elbow by actively rotating the left elbow. In both matching tasks, tendon vibration produced oppositely directed errors depending on the frequency of vibration. Vibration at 20 Hz produced a perception of decreased elbow velocity and a bias in dynamic position in the flexion direction, and vibration at 40 Hz produced the opposite perceptions. 7. We conclude that muscle spindle afferents, which are activated by tendon vibration, are an important source of the dynamic position and velocity information that the CNS uses to coordinate this movement sequence task. The observed effects of vibration timing and frequency suggest that perceptual changes evoked by vibration cannot be explained by the simple summation of sensory input evoked by movement and by vibration. Rather, the bias in perception produced by vibration appears to be related to the difference between vibration- and movement-evoked activity in muscle spindle afferents.

Adult↗
PubMed2001

Response of finger circulation to energy equivalent combinations of magnitude and duration of vibration.

OBJECTIVES: To investigate the acute response of finger circulation to vibration with different combinations of magnitude and duration but with the same "energy equivalent" acceleration magnitude according to current standards for hand transmitted vibration. METHODS: Finger skin temperature (FST) and finger blood flow (FBF) were measured in the middle fingers of both hands of 10 healthy men who had not used hand held vibrating tools regularly. With a static load of 10 N, the right hand was exposed to 125 Hz vibration with the following unweighted root mean square (rms) acceleration magnitudes and durations of exposure: 44 m/s(2) for 30 minutes; 62 m/s(2) for 15 minutes; 88 m/s(2) for 7.5 minutes; 125 m/s(2) for 3.75 minutes; and 176 m/s(2) for 1.88 minutes. These vibration exposures produce the same 8 hour energy equivalent frequency weighted acceleration magnitude (approximately 1.4 m/s(2) rms) according to international standard ISO 5349 (1986). Finger circulation was measured in both the right (vibrated) and the left (non-vibrated) middle fingers before application of the vibration, and at fixed intervals during exposure to vibration and during a 45 minute recovery period. RESULTS: The FST did not change during exposure to vibration, whereas vibration with any combination of acceleration magnitude and duration produced significant percentage reductions in the FBF of the vibrated finger compared with the FBF before exposure (from -40.1% (95% confidence interval (95% CI) -24.3% to -57.2%) to -61.4% (95% CI -45.0% to -77.8%). The reduction in FBF during vibration was stronger in the vibrated finger than in the non-vibrated finger. Across the five experimental conditions, the various vibration stimuli caused a similar degree of vasoconstriction in the vibrated finger during exposure to vibration. There was a progressive decrease in the FBF of both fingers after the end of exposure to vibration with acceleration magnitudes of 44 m/s(2) for 30 minutes and 62 m/s(2) for 15 minutes. Significant vasoconstrictor after effects were not found in either finger after exposure to any of the other vibration stimuli with greater acceleration magnitudes for shorter durations. CONCLUSIONS: For the range of vibration magnitudes investigated (44 to 176 m/s(2) rms unweighted; 5.5 to 22 m/s(2) rms when frequency weighted according to ISO 5349), the vasoconstriction during exposure to 125 Hz vibration was independent of vibration magnitude. The after effect of vibration was different for stimuli with the same energy equivalent acceleration, with greater effects after longer durations of exposure. The energy equivalent acceleration therefore failed to predict the acute effects of vibration both during and after exposure to vibration. Both central and local vasoregulatory mechanisms are likely to be involved in the response of finger circulation to acute exposures to 125 Hz vibration.

Adult↗