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PubMed1999

Electron spin transition solution applicable to an ensemble of isolated electrons.

An electron spin aligned with a static magnetic field changes its orientation when subjected to a time-varying magnetic field which is directed perpendicular to the static magnetic field. This well-known phenomenon is readily calculated when the time-varying magnetic field is circularly polarized; however, the evolution of the spin-state wavefunctions becomes much more difficult to calculate when the time-varying magnetic field is linearly polarized. For linear polarization and isolated spins, an analytic solution has been derived for the dynamical spin-state wavefunctions. Part of the solution procedure relies on an expansion using a small parameter, which is the ratio of the amplitude of the time-varying magnetic field to the static magnetic field. To verify the validity of the expansion technique, a numerical solution of the basic equations is compared to the analytic solution. Results are found to agree to better than 10% for exact resonance and better than 5% in general.

Electron Spin Resonance Spectroscopy↗
PubMed1993

A complex ensemble of cis-regulatory elements controls the expression of a Vicia faba non-storage seed protein gene.

We have identified cis-regulatory elements within the 5'-upstream region of a Vicia faba non-storage seed protein gene, called usp, by studying the expression of usp-promoter deletion fragments fused to reporter genes in transgenic tobacco seeds. 0.4 kb of usp upstream sequence contain at least six, but probably more, distinct cis-regulatory elements which are responsible for seemingly all quantitative, spatial and temporal aspects of expression. Expression-increasing and -decreasing elements are interspersed and include an AT-rich sequence, a G-box element and a CATGCATG motif. The latter acts as a negative element in contrast to what has been found for the same motif in legumin- and vicilin-type seed storage protein gene promoters. Seed specificity of expression is mainly determined by the -68/+51 region which confers, however, only very low levels of expression. The data support the combinatorial model of promoter function.

Base Sequence↗
PubMed1992

Effect of ensemble averaging on amplitude and feature variabilities of Doppler spectrograms recorded in the lower limb arteries.

The objective of the present study was to analyse the effect of averaging Doppler blood flow signals in lower limb arteries on amplitude and feature variabilities. Doppler signals recorded in 41 iliac and 35 superficial femoral arteries having different categories of stenosis were averaged over 1-15 cardiac cycles. Based on the relative decreasing rate of an index of variability, results indicated that amplitude variability of the spectrograms was exponentially reduced to 30, 6 and 1 per cent when averaging five, ten and 15 cardiac cycles, respectively. Nine diagnostic features were extracted from Doppler spectrograms and their variations from one cardiac cycle to the next quantified. Based on the relative decreasing rate of these variations, results indicated that feature variability was exponentially reduced to 30, 4 and 1 per cent when averaging five, ten and 15 cardiac cycles, respectively. The effect of averaging on the discriminant power of the features to separate the different categories of stenosis was also investigated by performing t-test analyses. Results showed that averaging between five and ten cardiac cycles provided the better discriminant power for most cases, whereas averaging over more than ten cardiac cycles was of little benefit. Based on the spectral analysis technique used in the present study, we conclude that averaging over ten cardiac cycles is sufficient for the analysis of Doppler spectrograms recorded in the lower limbs.

Blood Flow Velocity↗
PubMed2001

In a complex sequential movement, what component of the motor program is improved with intensive practice, sequence timing or ensemble motor learning?

We investigated whether the higher maximum speed of complex athletic movements attained by experts compared with novices might solely be ascribed to the acquisition of a more efficient timing of the initiation of the simple movements that comprise complex sporting gestures. Six novices in fencing and five experts in fencing performed three experimental series: 7 trials of touche, 7 trials of lunge (control series) and 50 trials of lunge + touche (test series), where the touche and lunge were initiated with different chronological sequences imposed by the experimenter. The lunge and the touche can be assimilated to a fast forward step and to a pointing task, respectively. We compared the maximum speed of touche between the two groups, recorded by an accelerometer fixed to the hand guard of the foil, and the speed of the centre of mass obtained from a force plate. The speed of the centre of mass was not statistically different between the two groups in the control and in the test series. The maximum speed of touche was not statistically different between the two groups in the control series. In contrast, in the test series, the maximum speed of touche was higher in the fencers' than in novices' groups, while the timing of initiation of the lunge and the touche was similar. The results of the test series show that the higher maximum speed of touche of fencers compared with novices cannot solely be ascribed to the acquisition of a more efficient initiation timing in motor programming. In a complex fencing gesture, the higher maximum speed of touche following intensive practice is discussed with regard to the inhibition of negative effects linked to the "refractory period" associated with the initiation of two closely spaced motor programs.

Adult↗
PubMed2005

Information coding by ensembles of resonant neurons.

In the present paper, we propose a novel neural procedure for signal processing and coding based on the subthreshold oscillations and resonance of the neural membrane potential that could be used by real neurons to perform frequency spectra analysis and information coding of incoming signals. Taking into account the biophysical properties of the neural membranes, we note that the subthreshold resonant behaviour they exhibit can be used to analyse incoming signals and represent them in the frequency domain. We study the reliability of the representation of signals depending on the biophysical parameters of the neurons, the fault-tolerance of this coding scheme and its robustness against noise and in the presence of spikes. The principal characteristics of our system are the use of the physical phenomenon of neural resonance (rarely considered in the literature for signal coding); it fits well with the biophysical parameters of most neurons that exhibit subthreshold oscillations; it is compatible with experimental data; and it can be easily integrated in a more general model of information processing and coding that includes communication between neurons based on spikes.

Action Potentials↗
PubMed2006

A self-organized ensemble of fluorescent 3-hydroxyflavone-Al (III) complex as sensor for fluoride and acetate ions.

Aluminum chloride addition results in a self-organized TURN-ON fluorescence of 3-hydroxyflavone (3HF) by a complexation reaction in MeOH and subsequent ligand exchange reaction with fluoride or acetate ions causes a fluorescence TURN-OFF of this complex, delivering a quantitative estimation route for fluoride and acetate ions. The ternary complex of 3HF with Al (III), a hard acid provides for a sensitive signalling system for fluoride ion, a hard base in the concentration range from 6 muM to 50 mM by a concerted co-ordination of fluoride ion involving an intermediate mechanistic pathway, while the complex is sensitive to acetate addition between 0-68 muM. The ligand exchange reaction of Al (3HF)(2) complex by fluoride or acetate ion, without interference from other common anions, has been investigated by UV-visible and fluorescence spetroscopies. The structure of the in-situ intermediate isolated at higher Al (3HF)(2) complex and acetate concentrations was inferred from the FT-IR spectrum and ESI-MS of the sample.

Acetates↗
PubMed1987

Protein kinase assay by paper-trichloroacetic acid method: high performance using phosphocellulose paper and washing an ensemble of samples on flat sheets.

Phosphocellulose paper has been found to be the paper of choice in assaying protein kinase activities using [gamma-32P]ATP by the trichloroacetic acid method of precipitation and washing. A study of binding of ATP of increasing concentrations at constant specific activity with Whatman 3MM or ATP-coated Whatman 3 MM papers (in vogue) versus phosphocellulose paper (proposed here) has shown that the latter has the least affinity for ATP when washing is done with either trichloracetic acid or trichloroacetic acid containing pyrophosphate. In an experiment where the placental cytosolic protein kinase was serially diluted, the phosphocellulose paper was found to give higher signal/noise ratios at all dilutions studied compared to the other two papers. With regard to the technological side of washing the papers, we have found that the traditional method of cutting papers into small squares before loading the samples is perhaps not the best. Instead, we propose the use of a flat sheet matrix for loading the samples because this method ensures uniformity of washing among the samples while shaking is performed on a simple shaker. In addition, the whole paper matrix can provide an almost instantaneous autoradiogram of hundreds of samples facilitating biochemical experimentation with protein kinases.

Adenosine Triphosphate↗
PubMed1987

Collicular ensemble coding of saccades based on vector summation.

The superior colliculus in the monkey contains a topographically organized representation of the target in its upper layers and saccade-related activity in its deeper layers. Since collicular movement fields are quite large, a considerable region of the colliculus is active whenever a saccade is made. We have modelled the collicular role in saccade generation based on the idea, proposed earlier in the literature, that each movement cell causes a movement tendency in the direction of the external world point which it represents in the collicular map. The model is organized as follows: An anisotropic logarithmic mapping transforms retinal coordinates into collicular coordinates. A two-dimensional Gaussian function describes the spatial extent of the movement-related activity in the deeper layers. An efferent mapping function specifies how the direction and the size of the movement contribution of each colliculus neuron depends on its location and its firing rate. The total saccade is the vector sum of the individual cell contributions. This very simple model (seven fixed parameters) has been used to simulate metrical properties of saccades: in response to visual targets; in response to electrical stimulation in one colliculus, and after a colliculus lesion. Model performance appears to be remarkably realistic but cannot account for some border effects and responses to double stimulation. Suggestions on how the model can be improved and extended will be presented.

Brain Mapping↗