Search

The efficacy of monosialoganglioside GM1 treatment was evaluated in a model of experimental stroke. Cerebral ischemia was induced by permanent occlusion of left middle cerebral artery. GM1 was administered intravenously soon after the occlusion of the artery and then intramuscularly daily for 7 days. Results indicate that GM1 can reduce the extent of infarct volume and neurochemical deficits associated with the ischemic event. The protection was more evident in the cortex than in the caudate-putamen. These observations confirm and extend the evidence of the GM1 efficacy in experimental models of stroke and further support the usefulness of gangliosides in the treatment of these pathologies.

Nonlinear optical properties of conjugated polymers can be measured using various techniques, including third-harmonic generation, two-photon absorption, nonlinear grating coupling and interferometry. These methods will be compared with regard to their suitability for obtaining specific parameters. We illustrate the application of these techniques to the study of π-conjugated polymeric systems, such as poly(4-BCMU), poly(3-decylthiophene) and 4-dialkylamino-4′-nitrostilbene (DANS) side-chain polymer, all of them regarded as candidates for the realization of all-optical switching devices, and outline relevance and limits of each technique.

Third Harmonic Generation (THG) in trans-β-carotene/polystyrene films is reported for fundamental wavelengths ranging from 0.95 μm to 1.9 μm. The results are analyzed with a four electronic level model which includes vibrational sub-structure. Our analysis indicates that the complex third order susceptibility deduced from the THG Maker fringe is strongly dominated by the presence of a two-photon state (an A g state) located above the first one-photon allowed B u state. Our results show little evidence for the presence of the 2A g state located at lower energy than the 1B u state. Two-photon absorption at 1.13 μm and 0.77 μm confirms our THG results.

The near infrared dispersion of the third order nonlinear optical susceptibility, χ (3) , of poly [5, 7-dodecadiyn-1, 12-diol-bis (n- butoxycarbonyl-methyl-urethane)], poly (4-BCMU), is investigated by third-harmonic-generation and two-photon-absorption. A four level model gives a good fit to the measured dispersions in the range of 0.770 μm to 1.904μm. The coupling between the first 1 B u state and the two 1 A g states, located above and below it, control the dispersion of χ (3) in the linear transparency region of poly (4-BCMU).

Optical third harmonic generation at 1.904, 1.579 and 1.064 μm experiments have been performed on thin films fabricated from side chain polymers containing effectively 4-dialkylamino-nitro-benzene, 4-dialkylamino-4′-nitro-stilbene, 4-dialkylamino-4′-nitro-diphenylbutadiene, 4-dialkylamino-4′-nitro-diphenylhexatriene as the side groups. We have measured values of χ (3) (−3ω; ω, ω, ω) in the range of 0.54 × 10 −12 to 7.42 × 10 −12 esu, at 1.904 μm incident radiation, which are comparable to the nonresonant values found in fully conjugated back-bone polymers [1]. The values of χ (3) at both 1.904 and 1.579 μm change by a factor of 15 as the conjugation length is increased.

Studies of rock drilling with water-based mud have indicated the existence of a current of electrons from the rock to the drill. If this so-called “normal current” is reduced to zero or is reversed by an applied potential, there is a significant reduction in drill wear. The wear rate is enhanced if oxygen is bubbled through the drilling mud and reduced if nitrogen is used, but in any case the electrical effects can still be observed. Observation of the normal drilling current with an oscilloscope has suggested that, when the drill is “sharp”, the normal current is a time-varying d.c. signal with most of the signal levels at frequencies below 25 Hz. As the drill becomes dull, the number of higher frequency signals and the overall signal amplitude increase. We suggest that this change in signal frequency with wear can be used to monitor the condition of an operational drill.

The elastic properties of molybdenum films, Cu/Nb and Mo/Ta superlattices and cadmium arachidate Langmuir-Blodgett films have been measured using Brillouin scattering. Specifically the in-plane shear constant of Cu/Nb superllatices was obtained through the first observation of the Love modes by Brillouin scattering. The Rayleigh and Stoneley waves, confined to the air-molybdenum and substrate-molybdenum interfaces respectively, were measured to determine the mechanical homogeneity of a molybdenum film. The elastic constants of Langmuir-Blodgett organic films of cadmium arachidate were also evaluated and an anomalously small shear constant was observed.

Rat soleus muscle was partially denervated by resecting the L5 mixed nerve. Muscle reinnervation was monitored 10, 30 and 50 days after surgery. The extent of recovery was found to be dependent on the number of axons remaining in the muscle and appeared not to be influenced by the time allowed. If animals were treated daily with 5 mg/kg of gangliosides the enlargement of the motor units was further enforced. The index of sprouting (expressed as the ratio between the percentage of muscle reinnervation due to a certain number of motor neurons in reinnervation and in normal conditions) was increased in a significant way by gangliosides treatment, i.e. one motor unit can expand up to about 4.5-fold, but if the animal was treated with gangliosides the motor unit can expand up to about 6.3-fold. These results showed that motoneuron sprouting capacity is increased by treatment animals with gangliosides.

Using Brillouin scattering we have been able to measure the Brillouin Spectra of thin cadmium arachidate (CdA) films which were deposited by the Langmuir-Blodgett (L-B) technique onto aluminum film substrates. A 9-pass tandem Fabry-Perot interferometer [1] was used to frequency analyze light scattered by multiple, high frequency, thermally-excited surface acoustic waves guided by the CdA film.

Organic films with specifically engineered optical properties hold considerable promise for applications in integrated optics. Light can be propagated for up to centimeter distances in waveguides to interact with organic films of thicknesses 1–5000 nm which are either deposited onto the waveguide or form the guiding medium, depending on the application. The potential advantage of using organic materials is that the molecules can be optimized for their optical response, e.g. second- and/or third-order optical non-linearities for efficient modulation, harmonic generation, all-optical signal processing etc. The basic concepts of integrated optics, non-linear guided wave interactions, material requirements for various applications and progress to date are reviewed.

Brillouin scattering has been performed on Cu/Nb metal superlattices with a multipass tandem interferometer. Behavior similar to that reported by Kueny et al. [Phys. Rev. Lett., 48, 166 (1982)] has been observed for the Rayleigh wave dispersion with bilayer periodicity. Multiple guided acoustic waves have been observed and their dispersion measured in order to obtain the variation in the c44 and c33 elastic constants with bilayer thickness.