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At least 1,009 records · Page 56Linked to original sources
PubMed1986

Optic fibers follow aberrant pathways from rotated eyes in Xenopus laevis.

The rotated eye paradigm has been a major experimental test of the neuronal specificity model for the development of ordered retinotectal connections in amphibians. In most studies, however, no optic fiber pathways were traced from rotated eyes and correlated with visuotectal projections. As an initial approach to this question, optic fibers from eyes rotated at different embryonic stages were traced with 3H-proline autoradiography. Three experimental series were prepared: in situ eye rotations, isochronic transplants of eyes rotated between embryos at the same stage, and heterochronic transplants of eyes rotated between embryos at different stages. Single or multiple optic fiber pathways developing from rotated eyes are identified by their sites of entry and trajectory in the brain. These include a normal chiasmatic (CH) pathway, and three aberrant pathways, identified as trigeminal (TR), diencephalic (DI), and oculomotor (OC). The latter three enter the brain ipsilaterally, some crossing contralaterally via commissural pathways. Depending on stage and type of operation, TR pathways develop in 50-100% of the animals, while CH pathways are more common after rotation at stage 21/22. The surgical procedure affects the initial trajectory of fibers from the retina, perturbs guidance cues in the surrounding orbit, and determines the patterns of optic pathways that develop. In most cases, optic fibers follow motor (oculomotor) or sensory (trigeminal) nerves, usually the first fibers encountered near the orbit by axonal pioneers exiting the retina. Evidently, optic fibers exhibit no pathway selectivity; any axon serves as a guidance cue. Tecta are innervated in about 50% of the cases, usually by fibers following abnormal trajectories from CH and OC pathways. The results suggest that the development of ordered visuotectal projections from rotated eyes is a complex process that may be independent of the trajectory of fiber arrival. Unless pathways and visuotectal maps are directly compared in each animal, however, the question remains open because we still do not know which anomalous pathways, if any, correlate with ordered projections.

Animals↗
PubMed2005

Faraday rotation in a two-dimensional photonic crystal with a magneto-optic defect.

We study the magneto-optic (MO) Faraday rotation in a two-dimensional square-lattice photonic crystal with a central MO defect layer in the optical wavelength range. We show that when a TM plane wave is incident upon a photonic crystal, an enhancement of Faraday rotation takes place in a region where a resonance peak appears in the photonic bandgap. In this region the mode conversion is high.

Journal Article↗
PubMed1999

The perception and discrimination of speed in complex motion.

Random dot kinematograms were used to simulate radial, rotational and spiral optic flow. The stimuli were designed so that, while dot speed increased linearly with distance from the centre of the display, the density of dots remained uniform throughout their presentation. In two experiments, subjects were required to perform a temporal 2AFC speed discrimination task. Experiment 1 measured the perceived speed of a range of optic flow patterns against a rotational comparison stimulus. Radial motions were found to appear faster than rotations by approximately 10%, with a smaller but significant effect for spirals. Experiment 2 measured discrimination thresholds for pairs of similar optic flow stimuli identical in all respects except mean speed. No consistent differences were observed between the speed discrimination thresholds of radial, rotational and spiral motions and a control stimulus with the same speed profile in which motion followed fixed random trajectories. The perceived speed results are interpreted in terms of a model satisfying constraints on motion-in-depth and object rigidity, while speed discrimination appears to be based upon the pooled responses of elementary motion detectors.

Differential Threshold↗
PubMed2004

One rotary mechanism for F1-ATPase over ATP concentrations from millimolar down to nanomolar.

F(1)-ATPase is a rotary molecular motor in which the central gamma-subunit rotates inside a cylinder made of alpha(3)beta(3)-subunits. The rotation is driven by ATP hydrolysis in three catalytic sites on the beta-subunits. How many of the three catalytic sites are filled with a nucleotide during the course of rotation is an important yet unsettled question. Here we inquire whether F(1) rotates at extremely low ATP concentrations where the site occupancy is expected to be low. We observed under an optical microscope rotation of individual F(1) molecules that carried a bead duplex on the gamma-subunit. Time-averaged rotation rate was proportional to the ATP concentration down to 200 pM, giving an apparent rate constant for ATP binding of 2 x 10(7) M(-1)s(-1). A similar rate constant characterized bulk ATP hydrolysis in solution, which obeyed a simple Michaelis-Menten scheme between 6 mM and 60 nM ATP. F(1) produced the same torque of approximately 40 pN.nm at 2 mM, 60 nM, and 2 nM ATP. These results point to one rotary mechanism governing the entire range of nanomolar to millimolar ATP, although a switchover between two mechanisms cannot be dismissed. Below 1 nM ATP, we observed less regular rotations, indicative of the appearance of another reaction scheme.

Adenosine Triphosphate↗
PubMed2006

Effect of orbital rotation and mixing on the optical properties of orthorhombic RMnO3 (R=La, Pr, Nd, Gd, and Tb).

We investigated the ab-plane absorption spectra of RMnO3 (R=La, Pr, Nd, Gd, and Tb) thin films. As the ionic radius of the R ion decreases, we observed a drastic suppression of the 2 eV peak, i.e., the intersite optical transition between spin- and orbital-aligned states across the Mott gap. We found that, in addition to orbital rotation, orbital mixing in the orbital-ordered state should play an important role in the suppression of 2 eV peak. We also found that the spectral weight of 2 eV peak is proportional to the A-type antiferromagnetic ordering temperature, which suggests that the magnetic interaction should be sensitively coupled to the orbital degree of freedom.

Journal Article↗
PubMedDate not supplied

[New determinations of the eye rotation center and criteria for the formation of its membrane in terms of the floating eye model and experimental support of the latter].

It is well known that the eye is a phylogenetically stabilized body with rotation properties. The eye has an elastic cover and is filled with uniform fluid. According to the theory of covers and other concepts on the configuration of turning fluid mass we concluded that the eyeball has an elliptic configuration. Classification of the eyeball is here presented with simultaneous studies of the principles of the eye situation. The parallelism between the state and different types of heterophory and orthophory was studied. To determine normal configuration it is necessary to have in mind some principles of achieving advisable correct situation of the eye in orbit. We determined the centre of the eye rotation and showed that it is impossible to situate it out of the geometrical centre of the eyeball. It was pointed out that for adequate perception the rotation centre must be situated on the visual axis. Using the well known theory of floating we experimentally determined that the centre of the eye rotation lies on the level of the floating eye, just on the point of cross of the visual line with the optical axis. It was shown experimentally on the basis of recording the eye movements in the process of eyelid closing that weakening of the eye movements is of gravitational pattern and proceeds under the action of stability forces, which directly indicates the floating state of the eye. For the first time using the model of the floating eye it was possible to show the formation of extraeye vacuum by straining the back wall. This effect can be obtained without any difficulty, if the face is turned down. The role of negative pressure in the formation of the eye ametropy, as well as new conclusions and prognostications about this new model are discussed.

Eye↗
PubMed2002

Empirical model for the molar rotations of syn-2,2-dimethyl-1,3-dioxanes.

[structure: see text] A useful method for the prediction of molar rotation ([Phi]) of syn-2,2-dimethyl-1,3-dioxanes (acetonides) is described. A series of acetonides were prepared by standard methods. A simple additive relationship between the substituents (R, R') and molar rotation was realized.

Biological Factors↗
PubMed1982

Fluorescent triplet probes for measuring the rotational diffusion of membrane proteins.

We have previously described a method for measuring the rotational diffusion of membrane proteins by using fluorescent triplet probes [Johnson & Garland (1981) FEBS Lett. 135, 252-256]. We now describe the criteria by which the suitability of such probes may be judged. In general, the greatest sensitivity is achievable with probes where the ratio of the quantum yields for prompt fluorescene (phi f) and triplet formation (phi t) are high, as with Rhodamine (phi f/phi t congruent to 10(3)). However, considerations of heat generation at the sample membrane, of time resolution of fast rotations and of irreversible bleaching of the fluorescent probe also apply. The immediate environment of a probe molecule at a membrane protein must also be important in determining the performance of a given probe. Nevertheless, we describe guidelines for evaluating the likely usefulness of fluorescent triplet probes in measurements of membrane protein rotation.

Diffusion↗
PubMed1994

Spatial reference systems in the comprehension of rotational motion.

In certain simple rotations of objects, the orientation of the axis and planes of rotation can determine whether people are able to visualize the motion or perceive it as simple and coherent. This finding affords the opportunity to investigate the spatial reference systems used to define the orientation of the axis and planes of rotation. The results of two experiments suggest that the permanent environment is the primary reference system, apart from the rotating object, used for this purpose. Subjects also were able to use a local spatial environment to determine the orientation of the motion; some subjects were particularly adept at this. The viewer perspective, in contrast, was irrelevant as a reference system in these experiments. These results argue strongly for the primacy of environmental reference systems in the perception and imagination of orientation and extend the set of findings common between the comprehension of rotational motion and orientation-sensitive form perception.

Environment↗