Detecting and localizing the foci in human epileptic seizures

We consider the electrical signals recorded from a subdural array of electrodes placed on the pial surface of the brain for chronic evaluation of epileptic patients before surgical resection. A simple and computationally fast method to analyze the interictal phase synchrony between such electrodes is introduced and developed with the aim of detecting and localizing the foci of the epileptic seizures. We evaluate the method by comparing the results of surgery to the localization predicted here. We find an indication of good correspondence between the success or failure in the surgery and the agreement between our identification and the regions actually operated on.     

Validation of a gas chromatographic method for determination of fatty alcohols in 10 mg film-coated tablets of policosanol

A gas chromatographic method using a packed column and 1-eicosanol as an internal standard was validated for the determination of the fatty alcohols that compose policosanol in 10 mg film-coated tablets. The alcohols were determined as trimethylsilyl derivatives, prepared with N-methyl-N-trimethylsilyltrifluoroacetamide. The method can detect degradation products with high retention times, without interfering with the peaks of the active principle. Good linearity (correlation coefficient = 0.9992) and accuracy (mean recovery -100.27 +/- 1.66%) were proven over a range of 25-200% of the nominal concentration. Within- and between-day precision at the nominal 100% value met the acceptance criteria (<2%). Ruggedness was examined through an intralaboratory experimental study in which 6 operational changes were made; the changes were found to have no effect on quantitation, repeatability, resolution, and relative retention time. The method is suitable for the quality control process and stability studies of these tablets.     

Stochastic simulation of the partition mechanism with a heterogeneous surface phase

A three-dimensional stochastic model of chromatography has been used to determine the effect of multiple sites on the partition mechanism. The effect of additional sites on mass transfer rates, zone profiles, and their statistical moments are investigated as a function of the partition coefficient, diffusion coefficient, and interfacial barrier to mass transfer. These studies have demonstrated that changes in the partition coefficient alone are not sufficient to alter the system response from that of a single site. Changes in the diffusion coefficient and the barrier to mass transfer do cause changes in the response compared to that of a single site. The zone profiles produced by the systems become more asymmetric as the difference between the diffusion coefficients or the barriers to mass transfer increases. The site with the slower mass transfer rate plays the dominant role in the total system response.     

Interarticulator programming in VCV sequences: lip and tongue movements

This study examined the temporal phasing of tongue and lip movements in vowel-consonant-vowel sequences where the consonant is a bilabial stop consonant /p, b/ and the vowels one of /i, a, u/; only asymmetrical vowel contexts were included in the analysis. Four subjects participated. Articulatory movements were recorded using a magnetometer system. The onset of the tongue movement from the first to the second vowel almost always occurred before the oral closure. Most of the tongue movement trajectory from the first to the second vowel took place during the oral closure for the stop. For all subjects, the onset of the tongue movement occurred earlier with respect to the onset of the lip closing movement as the tongue movement trajectory increased. The influence of consonant voicing and vowel context on interarticulator timing and tongue movement kinematics varied across subjects. Overall, the results are compatible with the hypothesis that there is a temporal window before the oral closure for the stop during which the tongue movement can start. A very early onset of the tongue movement relative to the stop closure together with an extensive movement before the closure would most likely produce an extra vowel sound before the closure.     

Desynchronization of chaos in coupled logistic maps

When identical chaotic oscillators interact, a state of complete or partial synchronization may be attained in which the motion is restricted to an invariant manifold of lower dimension than the full phase space. Riddling of the basin of attraction arises when particular orbits embedded in the synchronized chaotic state become transversely unstable while the state remains attracting on the average. Considering a system of two coupled logistic maps, we show that the transition to riddling will be soft or hard, depending on whether the first orbit to lose its transverse stability undergoes a supercritical or subcritical bifurcation. A subcritical bifurcation can lead directly to global riddling of the basin of attraction for the synchronized chaotic state. A supercritical bifurcation, on the other hand, is associated with the formation of a so-called mixed absorbing area that stretches along the synchronized chaotic state, and from which trajectories cannot escape. This gives rise to locally riddled basins of attraction. We present three different scenarios for the onset of riddling and for the subsequent transformations of the basins of attraction. Each scenario is described by following the type and location of the relevant asynchronous cycles, and determining their stable and unstable invariant manifolds. One scenario involves a contact bifurcation between the boundary of the basin of attraction and the absorbing area. Another scenario involves a long and interesting series of bifurcations starting with the stabilization of the asynchronous cycle produced in the riddling bifurcation and ending in a boundary crisis where the stability of an asynchronous chaotic state is destroyed. Finally, a phase diagram is presented to illustrate the parameter values at which the various transitions occur.     

A new bis-andrographolide ether from Andrographis paniculata nees and evaluation of anti-HIV activity

Novel bis-andrographolide ether (1) and six known compounds andrographolide, 14-deoxy-11,12-didehydroandrographolide, andrograpanin, 14-deoxyandrographolide, (+/-)-5-hydroxy-7,8-dimethoxyflavanone, and 5-hydroxy-7,8-dimethoxyflavone have been isolated from the aerial parts of Andrographis paniculata and their structures were established by spectral data. All the isolates were tested for the anti-HIV and cytotoxic activity.