Search

We designed long-term in vivo experiments to study rabbit urethral regeneration and remodelling over a hyaluronan biodegradable prosthesis. Seven months after the resection of a 1.5-cm-long tract of the urethra and its substitution with the prosthesis, radiological analysis showed the disappearance of the implant and the re-establishment of urethral continuity along the transmural defect. The regenerated tissue remodelled around the implant and exhibited good distensibility under pressure. Histological evaluation showed that the neo-urethra was lined with transitional epithelium and the stroma contained abundant elastic fibres. An examination of the pattern of the major cytoskeletal and cytocontractile proteins of smooth muscle cells and fibroblasts was able to distinguish fibroblasts from smooth muscle cells and myofibroblasts in the neo-urethra. These experiments provide evidence for the potential, successful use of biocompatible/bioresorbable devices for reconstructive surgery of the urethra.

The optical and electronic properties of organic molecules suggest application in hybrid optical-electronic integrated circuits and thin film devices, but pure, high quality, organic solid films are difficult to make. A better approach is to trap organic molecules as guests at high concentration in a durable host-guest film. Polymer, plastic, and sol-gel films can serve as hosts,1–3but their properties are less than ideal, and the techniques for making them time consuming and involved. Here we describe our Jet Vapor Deposition (JVD) technology for trapping complex organic dyes in hard, adherent inorganic hosts. Jet vapor deposition is the only vapor deposition technique able to make organic-ceramic films, and it offers a number of advantages over other approaches. Individual organic guests can be trapped at high doping levels of several percent, and the possible combinations of guest and host are nearly unlimited. The properties of vapor deposited ceramic hosts are superior to those of polymer hosts. Deposition at high rate and room temperature enables reliable, high throughput, economic production, and renders JVD compatible with semiconductor vapor deposition technology. Here we review the principles of JVD, describe experimental applications to thin film waveguides, lasers, and chemical sensors, and discuss some of the properties of JVD host-guest materials.

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.

A large body of experimental data suggests that neurotrophic molecules and/or substances that facilitate their action could be pharmaceutical agents for neurodegenerative pathologies. In particular, it has been demonstrated that nerve growth factor (NGF) exerts a physiological role for forebrain cholinergic neurons, while brain-derived neurotrophic factor (BDNF) seems to play a relevant role in rescuing dopaminergic neurons following damage. In addition, gangliosides are reported to potentiate neurotrophic factor effects in vitro as well as in vivo. In this study we examined the effects of the monosialoganglioside GM1 in different experimental models. The responsiveness of forebrain cholinergic neurons following NGF +/- GM1 was evaluated by assessing choline acetyltransferase (ChAT) activity in hippocampus, septal area and striatum of behaviorally impaired 24-month-old rats. NGF was intracerebroventricularly (i.c.v.) infused for 2 weeks while GM1 was given systemically for 3 weeks, starting from the beginning of NGF infusion. Moreover, the possible protective effects of GM1 were assessed following exposure of cultured cerebellar granule cells and dopaminergic mesencephalic neurons to different doses of 6-OH-DOPA, a metabolite of the dopamine pathway which has excitotoxic properties and has been hypothesized to participate in the pathology of Parkinson's disease. GM1 treatment to aged rats was seen to potentiate the NGF-induced increase of ChAT activity in the striatum ipsilateral to the NGF infusion. Moreover, in the striatum contralateral to the NGF infusion, GM1 increased ChAT activity above the control values, whereas NGF treatment alone did not affect enzymatic activity. GM1 treatment of cerebellar granule cells and mesencephalic neurons counteracted the dose- and time-dependent neurotoxicity of 6-OH-DOPA. These data support the notion that GM1 might prove useful in treating those pathological conditions where trophic factor deficits and/or excitotoxin-related toxicity play an important role.

Numerical studies of nonlinear prism coupling into thin-film organic material waveguides have been carried out. Results are presented showing that, for an undiluted, low absorption material, the electronic response dominates at pulse widths of tens of nanoseconds. The result of an increase in the absorption is that shorter pulses are necessary for access to the Kerr law nonlinearity alone. Guidelines are provided for distinguishing between electronic and thermal responses.

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.

Single-polarization interferometric measurements of intensity-induced refractive index changes using an intensity-modulated mode-locked laser are reported. The technique is used to determine the electronic and thermal intensity-dependent index changes in a polydiacetylene waveguide. Monte Carlo analysis shows that a sensitivity of at least 0.02 rad is expected from the configuration. >

We derive exact dispersion relations for transverse magnetic polarized guided waves at an interface between either a linear dielectric or a metal and a nonlinear dielectric. The nonlinearity is taken to be a Kerr-type nonlinearity. Numerical results are presented for the dielectric–metal case.

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.

We evaluated the effects of treatment with the inner ester derivative of the monosialoganglioside GM1 on cortical electroencephalographic activity and hippocampal CA1 morphology after transitory, near-complete cerebral ischemia in rats. Ischemia was induced by the four-vessel occlusion method, and we studied only the 58 rats that showed flattening of the cortical electroencephalogram for the entire 30 minutes of occlusion. The ganglioside (n = 30) or saline (n = 28) was administered intravenously immediately after release of the carotid clips and then intramuscularly for 21 days of observation. Cortical electroencephalographic activity was monitored throughout the experiment. After 21 days of recirculation we assessed hippocampal CA1 damage by light microscopy. The results indicate that treatment with the ganglioside reduces postischemic secondary damage to the cortical circuitry (as indicated by significantly higher cortical electroencephalographic activity late after reperfusion) and limits neuronal loss in the CA1 region. Our results lend support to the possible therapeutic use of ganglioside in human pathologic conditions associated with cerebrovascular insufficiencies.

The objective of this study is to propose a project management model which includes the unified process (UP) and UML language, for e-business software development in a physically distributed environment. The research is a qualitative study, aiming to develop methods and models. The main research method is the case study, according to Yin (1992). Initial results point towards a model, which includes the spiral life cycle type, the development process of object-oriented systems (using UML specification language and the unified process as proposed by RUP), and the incorporation of the procedural approach proposed by PMBOK (2000). The proposed model is divided into 6 phases, where each one of these phases contains a set of associated activities. In the future, the intention is to develop a support software for the model and apply this software into the environment in study. This extremely important study line demonstrates that the business world and business practices in the software development area are moving ahead of existent theories and conceptual models in this area. This study, yet in its initial phases, starts to bring significant results that contribute to meet market expectations nowadays.

Third‐harmonic generation has been used to measure the magnitude and phase of the nonlinear susceptibility χ(3)(3ω) of SiO2‐TiO2 sol‐gel thin films as a function of TiO2 concentration. Nonlinearities 20 times larger than those of fused silica were found, making such films useful for nonlinear optics in glass waveguides.

Nonlinear optical measurements in strip‐loaded channel waveguides of poly(4‐BCMU) at 1.319 μm are reported. Using a pulse‐modulated interferometry method, the intensity‐dependent refractive index is found to have an electronic contribution, n2=(4.8±2.7)×10−8 cm2/MW, and an estimated thermal contribution, n2=−(7.9±4.5)×10−11 cm2/MW, for 60 pS laser pulses at 76 MHz. The two‐photon absorption coefficient β is less than 0.25 cm/GW. Figures‐of‐merit suggest that poly(4‐BCMU) has properties desirable for all‐optical devices, but that fabrication losses and thermal effects due to absorption will limit device performance.

We present theoretical investigations of electrical and optical phenomena in the near breakdown regime of pseudomorphic HEMTs. The main effect of the drain current enhancement is found to be a parasitic bipolar effect due to holes, created by impact ionization, which accumulate in the substrate. Calculated electroluminescense spectra of holes, radiatively recombining with electrons in the source-sided channel, exhibit transitions which are allowed due to the bias-induced band bending of the channel. The calculated electroluminescence of the gate-source region agrees well with available experimental data. We predict that the hole accumulation in the source side of the channel region takes place on a time scale of ∼150 ps, thus allowing a direct time-resolved experimental observation.

Double-clad optical fibers are a robust, convenient medium for efficient optical amplification. Their compatibility with high-power semiconductor laser pump sources allows them to operate at saturated power levels of several watts, significantly higher than the level achievable with conventional diode-pumped fiber amplifiers. When coupled with a high-speed master oscillator, such an amplifier becomes an efficient high-speed, high-power optical transmitter. Such a source is of considerable interest for a high-speed space link. The transmitter consisted of a high-speed master laser diode, a high-gain fiber preamplifier, and a high-efficiency fiber power amplifier. The master oscillator was a Fabry-Perot laser diode centered at /spl lambda/=1072 nm, mounted in a high-speed, fiber-coupled package. The laser operated kink free to >50 mW and exhibited a 3-dB roll-off frequency of 11.1 GHz. Both the pre-amp and power amp were based on Yb-doped double-clad fibers pumped with /spl lambda/=915 nm fiber-coupled laser diodes. A polarization-independent optical isolator prevented feedback from the amplifier destabilizing the master oscillator. A free-space WDM module used to combine the signal and pump light into the core and cladding, respectively, of the pre-amp fiber, is shown.

Passively mode-locked fiber lasers have been a subject of great attention because of their potential as sources of ultrashort transform-limited pulses. The figure-8 laser has produced pulses as short as 98 fs (close to being transform limited).1 However, mode-locking instability has been a subject of great concern.2,3 We now understand the origin of the mode-locking instability of the figure-8 laser, and with proper design we have stabilized its performance.

We report on the optical characterization of poly-4BCMU slab waveguides, and on the fabrication of efficient grating guided-wave couplers using this material. Thin film samples were obtained, by spin coating, from a cyclopentanone solution. Grating couplers were used to measure the film refractive indices and thicknesses. Waveguide attenuation was obtained from measurements of the variation in scattering with propagation distance in the visible and near infrared. These parameters allowed us to design, fabricate and test a grating coupler with a coupling efficiency of 45% at 1 .064 pm.

Strip-loading is a convenient and effective method to design and fabricate channel waveguides in multilayer active polymer structures. Several micron wide strip-loaded poly(4-BCMU) waveguides are observed to be single mode at 1.06 im and 1.32 rim. Based on the optical nonlinearity for poly(4-BCMU) measured by THG at 1.32 pm, an intensity of 650 MW/cm2 is required to satisfy the optical phase shift material figure of merit, 4ir, for a directional coupler with 1 cm interaction length. To estimate the optical power for directional coupler operation, we initially assume no index saturation effects, negligible one or two photon absorption, waveguide propagation losses less than 1 dB/cm, and unity coupling efficiency. 40 W is the lowest estimated peak pulse power of operation for a device with 6 .tm2 area waveguides. Actual coupling efficiencies of light incident on our 6 pj2 ea waveguides are between 30 % and 40 %. The propagation losses for our sixip-Ioaded waveguides are between 4 dB/cm (i'M) and 9dB/cm (TE). The guided wave intensities are at least ten fold lower than the input intensities. Incident peak pulse powers of at least several hundred watts will be required for 1 cm long (lirectional coupler device operation. Initial interferometry results suggest that average power dependent thermal phase shifts dominate peak power dependent electronic phase shifts at duty cycles approaching unity. Polymer superlattices are considered as advanced nonlinear optical materials.

Poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxycarbonyl-methyl-urethane)], or poly-4BCMU, thin films permanently bleach when irradiated with light in the absorption band. The resulting decrease in refractive index has been measured and is sufficient to allow formation of waveguide channels and gratings. The optical properties of the bleached material are discussed. A waveguide grating coupler is fabricated by periodic bleaching and demonstrated.

The effects of dispersion on the pulsewidth of a mode‐locked fiber ring laser are examined. We have identified two different modes of operation, one where the pulsewidth is determined by the path‐integrated (global) dispersion of the cavity and another novel mode where pulsewidth is not limited by the global dispersion. Experimental results show that for some configurations, the local dispersion of the cavity plays an important role in determining the pulsewidth of the laser.

We investigated the outcome of reconstructive surgery of the urethra through guides composed of a novel biodegradable and highly biocompatible polymer, Hyaff-11. A tract of about 1.5 cm of the rabbit pendulous urethra was totally resected and replaced by a Hyaff-11 tubular graft. Eleven animals were analysed at each of the time points ranging from 7 days to 4 weeks following surgery. Histological and radiological evaluation showed a satisfactory remodelling of the neo-urethra around the implant. The regenerated connective tissue connected both urethral stumps within the first 7 days. On postoperative week 3, the Hyaff-11 guide had disappeared. At the 4-week time point the retrograde urethrogram showed a good distensibility of the neourethra. The regenerated stroma consisted of fibroblastic cells, and collagenous and elastic fibres. The neo-epithelium was pluristratified and exhibited cells of the cuboidal type.

The effects of taper in a nonlinear slab waveguide with a distributed feedback grating are studied. The role of taper in the operation of the bistable gate is analysed with regard to switching intensity and transmission for various detunings from the Bragg condition. A comparison is made between three different functional forms of taper, namely linear, quadratic and triangular, which could occur in the preparation of a working device.

We report measurements of the refractive indices of poly-4BCMU films and the fabrication of an efficient integrated optical distributed coupler. The refractive index measurements were performed in the visible and near IR using blazed-grating couplers. The analysis led to the optimization of an input coupler with a coupling efficiency larger than 45% at 1.064 microm.

The authors review progress in the application of nonlinear optical phenomena to integrated optics. Essentially all integrated optics devices such as directional couplers, Mach-Zehnder interferometers, prism couplers, etc., can be used for all-optical signal processing when at least one of the waveguiding media exhibits an intensity-dependent refractive index. Experimental and theoretical results on the operating characteristics and figures of merit of such devices, as well as a new class of phenomena based on large nonlinear changes in waveguide properties will be summarized. Also discussed are measurement techniques for evaluating waveguide nonlinearities. Progress in the implementation of other nonlinear third order interactions, such as degenerate four-wave mixing and nonlinear spectroscopy, will also be reviewed. >

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.

We demonstrate that when a nonlinear coupler is operated in the switching regime, small amounts of either nonlocality in the optically induced refractive index change or of longitudinal feedback can lead to optical bistability. Outside the switching regime, there is a threshold for the amount of nonlocality or feedback required for bistability. The diverse predictions of previous theoretical formulations are therefore reconciled.

Proprietes elastiques de couches minces d'arachidate de cadmium composees de 11 a 401 monocouches

Degenerate four‐wave mixing in a thin‐film waveguide is demonstrated for the first time. A reflectivity of 10−9 at a power density of 5 MW/cm2 was obtained for liquid CS2 placed on top of a glass waveguide.

The dispersion of Rayleigh, Stonely, and Sezawa acoustic waves guided by deposited thin molybdenum films has been used to evaluate selected elastic constants and film homogeneity. This work includes the first experimental observation of Stonely waves by Brillouin scattering.

Love waves have been observed for the first time by Brillouin scattering. The c12 constant of the metallic superlattice Cu/Nb has been measured.

Spin‐coated and solution‐cast films of poly[5,7‐dodecadiyn‐1,12‐diol‐bis(n‐butoxycarbonyl‐methyl‐urethane)], or briefly, poly‐4BCMU, irreversibly bleach when irradiated by light tuned within the absorption band of the polymer sample. Characteristic bleaching times have been measured at several wavelengths. The refractive index of poly‐4BCMU has been measured at 1.064 μm for various photobleaching energies. Refractive index changes as large as −0.08 have been measured, and the decrease in refractive index has been used to define waveguide channels and gratings.

Substance P and Met-enkephalin were detected by radioimmunoassay and immunocytochemistry in the rat lumbar spinal cord. The sciatic nerve was lesioned by resecting a piece and the proximal stump was either ligated, for limiting neurite outgrowth, or intraperitoneally sutured, allowing the formation of a large neuroma. Ten days post lesioning both peptide levels dropped approximately 50% and the punctate immunoreactivity decreased in the dorsal horn. Lesioning both sciatic nerves did not accelerate nor increase the extent of peptide loss compared to monolateral lesions. Immunocytochemistry showed that after bilateral lesioning also the punctate immunoreactivity in the dorsal horn decreased less drastically. However, FRAP staining of the dorsal horn decreased according to the lesion paradigms, mono- and bilaterally with the same intensity. Therefore nerve lesions trigger the process, but the peptidergic loss seems intraspinally regulated. In addition, both kinds of abnormal neurite outgrowth similarly altered peptide levels and distribution in the spinal cord. Our data suggest that pain states related to peripheral nerve lesions may be due to opiate peptide loss rather than to neuroma.

Spontaneous diabetes can develop a neuropathy that affects function and morphology of the peripheral nerves both in men and in animals (7, 14, 16, 22). Diabetes can also be induced by a single injection of Alloxan or Streptozotocin (15), drugs that exert a toxic effect on the beta-cells of the Langerhans islets. In rats treated with either. Alloxan or Streptozotocin a decrease in nerve conduction velocity is evident within a few weeks after intoxication (3, 20).

The elastic properties of Mo/Ta superlattices and the dependences on bilayer wavelength over the range 7--200 A are investigated. These are the first such measurements for a bcc-bcc system, and significant differences from previously studied metal superlattices are found. Surface velocities of as many as 12 acoustic modes guided by the thin-film samples have been measured using Brillouin spectroscopy. The elastic constants c/sub 11/,c/sub 13/,c/sub 33/ and c/sub 44/ for the superlattices are determined by fitting the data to an acoustic model of supported hexagonal films. We compare these stiffnesses with those predicted from the bulk constituent properties. The relative Brillouin cross section is found to be accurately represented by a pure ripple scattering theory with no photoelastic contribution.