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At least 73 records · Page 4Linked to original sources
PubMed1999

Effect of elution modes on protein separation by cross-axis coil planet centrifuge with two different types of coiled columns.

Effect of elution modes on protein separation was investigated using cross-axis coil planet centrifuge (cross-axis CPC) with two different types of coiled columns, i.e., eccentric coil and toroidal coil assemblies. Myoglobin and lysozyme were separated with an aqueous two-phase solvent system composed of 12.5% (w/w) polyethylene glycol 1000 and 12.5% (w/w) dibasic potassium phosphate. The substantial effect of elution modes was observed by the toroidal coil, while the negative result was given at the eccentric coil. Using the toroidal coil, higher peak resolution of proteins was attained at the tail to head elution mode. In the outward lower phase mobile elution mode, the satisfactory separation was obtained by both eccentric coil and toroidal coil assemblies. However, in the inward upper phase mobile elution mode, the toroidal coil produced a broad and asymmetric myoglobin peak. The analysis using polyacrylamide gel electrophoresis revealed that the toroidal coil partially separated the components originally present in the myoglobin sample. As the result, a modified equation was devised to express the peak resolution (Rs) using the lysozyme peak. The overall results indicated that the toroidal coil produced better partition efficiency than the eccentric coil under the optimized experimental condition including the direction of the Coriolis force acting on the mobile phase in the toroidal coil.

Centrifugation↗
PubMed1999

Timing Spectroscopy of Quasi-Periodic Oscillations in the Low-Mass X-Ray Neutron Star Binaries.

Precise simultaneous measurements of the frequencies of the two kilohertz quasi-periodic oscillations (referred in the literature as upper and lower kHz QPOs) cast doubts on the validity of the simple beat-frequency interpretation and some of the modifications introduced to explain the results of the varying frequency difference. A new model explains the variation of the frequency difference, suggesting that the upper kHz QPO, namely nuh, is an upper hybrid frequency of the Keplerian oscillator under the influence of the Coriolis force and the lower kHz QPO is the Keplerian frequency nuK. Such an oscillator has two branches characterized by a high frequency nuh ( approximately 1 kHz) and by a low frequency nuL ( approximately 50 Hz). The frequency nuL depends strongly on the angle delta between the normal to the neutron star disk and Omega-the angular velocity of the magnetosphere surrounding the neutron star. In the lower part of the QPO spectrum ( approximately 10 Hz), this model identifies the frequency of radial viscous oscillations nuV (previously called "extra noise component") and the break frequency nub, which is associated with the diffusive process in the transition region (the innermost part of the disk). According to this model, all frequencies (namely nuh, nuL, nub, and nuV) have specific dependences on nuK. This Letter focuses on the verification of the predicted relations. For the source 4U 1728-34, the best theoretical fit is obtained for delta=8&fdg;3+/-1&fdg;0, which is slightly larger than the value of delta=5&fdg;5+/-0&fdg;5 previously found for Scorpius X-1. In addition, we show that the theoretically derived power-law relation nub~nu1.61V is consistent with the recent observations of other atoll and Z-sources.

Journal Article↗
PubMed1999

Haltere-mediated equilibrium reflexes of the fruit fly, Drosophila melanogaster.

Flies display a sophisticated suite of aerial behaviours that require rapid sensory-motor processing. Like all insects, flight control in flies is mediated in part by motion-sensitive visual interneurons that project to steering motor circuitry within the thorax. Flies, however, possess a unique flight control equilibrium sense that is encoded by mechanoreceptors at the base of the halteres, small dumb-bell-shaped organs derived through evolutionary transformation of the hind wings. To study the input of the haltere system onto the flight control system, I constructed a mechanically oscillating flight arena consisting of a cylindrical array of light-emitting diodes that generated the moving image of a 30 degrees vertical stripe. The arena provided closed-loop visual feedback to elicit fixation behaviour, an orientation response in which flies maintain the position of the stripe in the front portion of their visual field by actively adjusting their wing kinematics. While flies orientate towards the stripe, the entire arena was swung back and forth while an optoelectronic device recorded the compensatory changes in wing stroke amplitude and frequency. In order to reduce the background changes in stroke kinematics resulting from the animal's closed-loop visual fixation behaviour, the responses to eight identical mechanical rotations were averaged in each trial. The results indicate that flies possess a robust equilibrium reflex in which angular rotations of the body elicit compensatory changes in both the amplitude and stroke frequency of the wings. The results of uni- and bilateral ablation experiments demonstrate that the halteres are required for these stability reflexes. The results also confirm that halteres encode angular velocity of the body by detecting the Coriolis forces that result from the linear motion of the haltere within the rotating frame of reference of the fly's thorax. By rotating the flight arena at different orientations, it was possible to construct a complete directional tuning map of the haltere-mediated reflexes. The directional tuning of the reflex is quite linear such that the kinematic responses vary as simple trigonometric functions of stimulus orientation. The reflexes function primarily to stabilize pitch and yaw within the horizontal plane.

Animals↗
PubMed2002

Quasiperiodic waves at the onset of zero-Prandtl-number convection with rotation.

We show the possibility of temporally quasiperiodic waves at the onset of thermal convection in a thin horizontal layer of slowly rotating zero-Prandtl-number Boussinesq fluid confined between stress-free conducting boundaries. Two independent frequencies emerge due to an interaction between straight rolls and waves along these rolls in the presence of Coriolis force, if the Taylor number is raised above a critical value. Constructing a dynamical system for the hydrodynamical problem, the competition between the interacting instabilities is analyzed. The forward bifurcation from the conductive state is self-tuned.

Journal Article↗
PubMed2004

Ray and wave instabilities in twisted graded-index optical fibers.

We study ray and wave propagation in an elliptical graded-index optical fiber or lens with a twisted axis and show analytically the existence of an instability for both ray trajectories and beam moments in a finite range of axis twist rate embedded within the spatial frequencies of periodically focused rays for the untwisted fiber. By considering the paraxial ray equations and the paraxial wave dynamics in a rotating frame that follows the fiber axis twist, we reduce the dynamical problem of ray trajectories to the classical Blackburn's pendulum, which shows a dynamical instability, corresponding to classical diverging trajectories, due to the competing effects of confining potential, Coriolis force, and centrifugal force. A closed set of linear evolution equations for generalized beam moments are also derived from the paraxial wave equation in the rotating reference frame, revealing the existence of a dynamical moment instability in addition to the trajectory instability. A detailed analysis of beam propagation is presented in case of a Gaussian beam, and different dynamical regimes are discussed.

Journal Article↗
PubMed2001

Bose-Einstein condensates with large number of vortices.

We show that as the number of vortices in a three dimensional Bose-Einstein condensate increases, the system reaches a "quantum Hall" regime where the density profile is a Gaussian in the xy plane and an inverted parabolic profile along z. The angular momentum of the system increases as the vortex lattice shrinks. However, Coriolis force prevents the unit cell of the vortex lattice from shrinking beyond a minimum size. Although the recent MIT experiment is not exactly in the quantum Hall regime, it is close enough for the present results to be used as a guide. The quantum Hall regime can be easily reached by moderate changes of the current experimental parameters.

Journal Article↗
PubMed2003

Observation of long-lived vortex aggregates in rapidly rotating Bose-Einstein condensates.

We study the formation of large vortex aggregates in a rapidly rotating dilute-gas Bose-Einstein condensate. When we remove atoms from the rotating condensate with a tightly focused, resonant laser, the density can be locally suppressed, while fast circulation of a ring-shaped superflow around the area of suppressed density is maintained. Thus a giant vortex core comprising 7 to 60 phase singularities is formed. The giant core is only metastable, and it will refill with distinguishable single vortices after many rotation cycles. The surprisingly long lifetime of the core can be attributed to the influence of strong Coriolis forces in the condensate. In addition we have been able to follow the precession of off-center giant vortices for more than 20 cycles.

Journal Article↗
PubMed1999

Artificial gravity considerations for a mars exploration mission.

Artificial gravity (AG), as a means of preventing physiological deconditioning of astronauts during long-duration space flights, presents certain special challenges to the otolith organs and the adaptive capabilities of the CNS. The key issues regarding the choice of AG acceleration, radius, and rotation rate are reviewed from the viewpoints of physiological requirements and human factors disturbances. Head movements and resultant Coriolis forces on the rotating platform may limit the usefulness of economical short centrifuges for other than brief periods of intermittent stimulation.

Aerospace Medicine↗
PubMed1997

Transitions between blocked and zonal flows in a rotating annulus with topography

The mid-latitude atmosphere is dominated by westerly, nearly zonal flow. Occasionally, this flow is deflected poleward by blocking anticyclones that persist for 10 days or longer. Experiments in a rotating annulus used radial pumping to generate a zonal jet under the action of the Coriolis force. In the presence of two symmetric ridges at the bottom of the annulus, the resulting flows were nearly zonal at high forcing or blocked at low forcing. Intermittent switching between blocked and zonal patterns occurs because of the jet's interaction with the topography. These results shed further light on previous atmospheric observations and numerical simulations.

Journal Article↗
PubMed1998

Visual input to the efferent control system of a fly's "gyroscope".

Dipterous insects (the true flies) have a sophisticated pair of equilibrium organs called halteres that evolved from hind wings. The halteres are sensitive to Coriolis forces that result from angular rotations of the body and mediate corrective reflexes during flight. Like the aerodynamically functional fore wings, the halteres beat during flight and are equipped with their own set of control muscles. It is shown that motoneurons innervating muscles of the haltere receive strong excitatory input from directionally sensitive visual interneurons. Visually guided flight maneuvers of flies may be mediated in part by efferent modulation of hard-wired equilibrium reflexes.

Animals↗
PubMedDate not supplied

Low frequency oscillatory flow in a rotating curved pipe.

The low frequency oscillatory flow in a rotating curved pipe was studied by using the method of biparameter perturbation. Perturbation solutions up to the second order were obtained and the effects of rotation on the low frequency oscillatory flow were examined in detail. The results indicated that there exists evident difference between the low frequency oscillatory flow in a rotating curved pipe and in a curved pipe without rotation. During a period, four secondary vortexes may exist on the circular cross-section and the distribution of axial velocity and wall shear stress are related to the ratio of the Coriolis force to centrifugal force and the axial pressure gradient.

Computer Simulation↗
PubMed1996

Transvaginal sonographic orientation detection system using ceramic gyroscopes.

Use of three-dimensional ultrasonograms in daily clinical medicine requires the development of data accumulation techniques and image reconstruction techniques . We describe an image position and orientation detection technique using small piezoelectric vibratory gyroscopes. Such gyroscopes, of the same type that is used in an automobile navigation system, produce angular velocity by Coriolis force. After attaching three gyroscopes to an ordinary transvaginal probe, we attempted to detect image orientation to assist transvaginal scanning and to reconstruct three-dimensional projection images. Three-dimensional images were reconstructed by simple white and black inversion thresholding technique. Using free hand transvaginal scanning, the direction of the transvaginal ultrasound beam was displayed with B-mode ultrasonography. Using a personal computer, three-dimensional images of follicles and fetuses were successfully reconstructed within a few minutes. Our system provides easy understanding of transvaginal sonographic images and potentially might allow ordinary ultrasound machines to handle three-dimensional images in a day-to-day clinical practice.

Equipment Design↗
PubMed2002

Adapting to artificial gravity (AG) at high rotational speeds.

Short-radius centrifugation offers a promising countermeasure to the adverse effects of prolonged weightlessness. Head movements made in a rotating environment elicit Coriolis effects, which seriously compromise sensory and motor processes. We have previously found that, contrary to common belief, participants can adapt to the Coriolis effects associated with single-quadrant yaw head turns during 23-rpm short-radius centrifugation, while maintaining their adaptation to stationary environments. Here, we focus on motion sickness and illusory motion, the most problematic subjective side effects. We present encouraging data that such context-specific adaptation generalizes immediately to a different centrifuge environment. It also generalizes quickly to Coriolis forces in the opposite direction. Implications for AG implementation are discussed.

NASA Discipline Neuroscience↗
PubMed2005

A rodent model for artificial gravity: VOR adaptation and Fos expression.

Vestibulo-ocular reflex (VOR) adaptation and brainstem Fos expression as a result of short radius cross-coupling stimuli were investigated to find neural correlates of the inherent Coriolis force asymmetry from an artificial gravity (AG) environment. Head-fixed gerbils (Meriones unguiculatus, N=79) were exposed, in the dark, to 60--90 minutes of cross-coupled rotations, combinations of pitch (or roll) and yaw rotation, while binocular horizontal, vertical, and torsional eye position were determined using infrared video-oculography. Centripetal acceleration in combination with angular cross-coupling was also studied. Simultaneous sinusoidal rotations in two planes (yaw with roll or pitch) provided a net symmetrical stimulus for the right and left labyrinths. In contrast, a constant velocity yaw rotation during sinusoidal roll or pitch provided the asymmetric stimulus model for AG. We found orthogonally oriented half-cycle VOR gain changes. The results depended on the direction of horizontal rotation during asymmetrical cross-coupling, and other aspects of the stimulus, including the phase relationship between the two rotational inputs, the symmetry of the stimulus, and training. Fos expression also revealed laterality differences in the prepositus and inferior olivary C subnucleus. In contrast the inferior olivary beta and ventrolateral outgrowth were labeled bilaterally. Additional cross-coupling dependent labeling was found in the flocculus, hippocampus, and several cortical regions, including the perirhinal and temporal association cortices. Analyses showed significant differences across the brain regions for several factors (symmetry, rotation velocity and direction, the presence of centripetal acceleration or a visual surround, and training). Finally, animals compensating from a unilateral surgical labyrinthectomy who received multiple cross-coupling training sessions had improved half-cycle VOR gain in the ipsilateral eye with head rotation toward the intact side. We hypothesize that cross-coupling vestibular training can benefit aspects of motor recovery or performance.

Adaptation, Physiological↗
PubMed2005

[Zooplankton in north branch waters of Changiiang Estuary].

Based on the investigation data during the high-water (July, 2003) and low-water (January, 2004) periods, a causal analysis was made on the variation of zooplankton distribution in the north branch waters of the Changjiang Estuary. The results showed that in high-water period, the average of zooplankton biomass was 234.38 mg x m(-3), being 141.35 mg x m(-3) in flood tide and 327.40 mg x m(-3) in ebb tide, while in low-water period, it was 188.81 mg x m(-3), being 184.69 mg x m(-3) in flood tide and 192.93 mg x m(-3) in ebb tide. The biomass increased from the east to the west in flood tide, but a contrary trend was observed in ebb tide. The species number did not change obviously both in flood tide and in ebb tide. The value of diversity index (H') was higher in flood tide than in ebb tide. In high-water period, the biomass near the north shore was higher than that near the south shore, but it was contrary in the ebb tide. The difference between the waters of two shores was not obvious in low-water period as in high-water period, though the trend of biomass variation was similar. The variation of zooplankton distribution in the north branch waters of the Changjiang Estuary had a close relation with the seasonal changes of zooplankton biomass outside the Changjiang Estuary and the tide, but not significantly related with the Changjiang runoff water. Coriolis force accounted for the difference of zooplankton biomass in the waters of two shores via tide movement.

Animals↗
PubMed1994

[Experimental studies of motion sickness on board of a research ship].

To date the incidence and treatment of motion sickness have not been satisfactorily elucidated. Discrepancies among individuals in tolerating strong velocities and accelerations are well-known. To prevent motion sickness evaluations of individual predispositions are important. There are several current theories on the nature of motion sickness. These include the mismatching of sensory inputs, a Coriolis force, non-physiological stimuli and modulation of vestibuloocular reflexes (VOR). The main influence of the vestibular organ in generating kinetosis is obvious. Analysis of the chief movements of a ship demonstrates that linear acceleration is the principle factor in stimulating the vestibular organ. The moving gravity vector causes an intense otolith stimulation. By this means VOR is temporarily shut down. This effect can also be used for documenting motion sickness. A battery of vestibular tests was performed on the military research ship "Planet" during a 2-week autumny voyage on the Atlantic Ocean. Spontaneous nystagmus, bithermal bilateral responses and rotatory testing (slow harmonic acceleration) results were recorded by electronystagmography. Findings before starting and during the voyage were compared. A group of 3 unexperienced volunteers and 9 professional seamen were investigated. All unexperienced volunteers suffered from sea sickness, while none of the professionals showed any symptoms. At the beginning of the voyage the gain in nystagmus in harmonic acceleration testing was significantly lower in the professionals than in the unexperienced volunteers. During the voyage all professionals showed nearly constant gain values. All unexperienced individuals showed a decrease in gain only during the time of acute symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗