Monte Carlo simulations of homogeneous upconversion in erbium-dopedsilica glasses

Quenching of Er³⁺ ions by homogeneous energy-transfer upconversion in high-concentration erbium-doped silica glasses has been theoretically investigated, The results indicate that at Er³⁺ concentrations of 1.0-2.0·10²⁶ m^-3 or below, the kinetic limit of strong migration is not reached, and hence the widely accepted quadratic upconversion model is not generally valid. Nevertheless, the results offer an explanation of the experimental observations of quadratic upconversion. Furthermore, it has been shown that at a given population inversion, the quenching rate depends on the rate of exchange of the excited Er³⁺ ions by emission and absorption     

Effects of six different highlighting modes on visual search performance in menu options

Highlighting (HI), for example of menu options, is usually considered as improving information processing efficiency. Particularly relevant are the attention effects of valid (target) highlighting, when contrasted with the effects of highlighting distracting information (invalid HI). A visual search experiment was conducted to analyze the requirements of such an overall performance gain under valid HI. The efficiency of six different modes of highlighting (brightness increase, reverse video, color [red], reverse color, blue‐on‐yellow, and red‐on‐green) on a black screen background was determined. Sixty‐two subjects indicated the presence of a prespecified menu option in a list of CAD menu options, of which a subset was highlighted on every trial. Also varied was familiarity of highlighting. Dependent measures were the absolute performance scores (search time and accuracy) and highlighting benefits. Significant absolute performance differences between the modes were found. They were accompanied by a marked dissociation between the absolute and the benefit measures. The HI benefits were calculated as the individual performance differences between target‐highlighted trials (valid HI) and target‐standard (invalid HI) conditions. The bright white mode, which caused the shortest absolute search time, did not result in a benefit. In contrast, the red color condition produced a large benefit, accompanied by only mid‐range absolute performance. The widely used reverse video modes generally led to the poorest performance. Familiarity of highlighting had a differential effect, depending on the dependent measure preferred. Recommendations for the use of highlighting in display design are given.     

Detection of skin cancer by classification of Raman spectra

Skin lesion classification based on in vitro Raman spectroscopy is approached using a nonlinear neural network classifier. The classification framework is probabilistic and highly automated. The framework includes a feature extraction for Raman spectra and a fully adaptive and robust feedforward neural network classifier. Moreover, classification rules learned by the neural network may be extracted and evaluated for reproducibility, making it possible to explain the class assignment. The classification performance for the present data set, involving 222 cases and five lesion types, was 80.5%+/-5.3% correct classification of malignant melanoma, which is similar to that of trained dermatologists based on visual inspection. The skin cancer basal cell carcinoma has a classification rate of 95.8%+/-2.7%, which is excellent. The overall classification rate of skin lesions is 94.8%+/-3.0%. Spectral regions, which are important for network classification, are demonstrated to reproduce. Small distinctive bands in the spectrum, corresponding to specific lipids and proteins, are shown to hold the discriminating information which the network uses to diagnose skin lesions.     

Resonance and nonresonant laser ionization of sputtered uranium atoms from thin films and single microparticles: evaluation of a combined system for particle trace analysis

The resonance and nonresonant laser ionization of uranium atoms sputtered from thin metal films and individual micrometer-size uranium oxide particles, respectively, was studied to evaluate a new setup for the analysis of actinide-containing micrometer-size particles. Experiments using nonresonant (193-nm) ionization of atoms and molecules sputtered from micrometer-size uranium oxide particles have shown that the uranium detection efficiencies for sputtered neutral atoms are approximately 2 orders of magnitude higher than for secondary ions. In uranium particles of 0.5-microm diameter, 6 x 10(6) atoms of 235U were easily detected and the isotopic ratio of 235U/238U = 0.0048 +/- 4.6% is in excellent agreement with the certified value. The use of two-color, two-step resonance ionization of the sputtered neutral uranium atoms from thin films was investigated. Several excitation schemes were tested, and a significant population of several low-lying metastable states after ion sputtering was observed. Autoionizing states for double-resonant ionization were determined, and the high selectivity of ionization schemes involving these autoionizing states was illustrated by comparing the flight-time distributions of different sputtered species obtained both by resonance and nonresonant multiphoton (355-nm) laser postionization. Ideally, the options for resonance as well as nonresonant ionization would be combined in a single setup, to obtain a large gain in sensitivity and selectivity. Thus, information about the main components as well as specific isotopic information of a trace element could be obtained from the same single particle.     

Interventional neuropediatrics: treatment of dystonic and spastic muscular hyperactivity with botulinum toxin A

Therapeutic effect of botulinum toxin A was studied in a group of pediatric patients (n = 28) aged between 6 months and 18 years. The patients were diagnosed with cervical dystonia (n = 6), adductor spasm of the hip (n = 8), spastic drop foot (n = 7) and various other focal motor problems associated with spastic muscular hyperactivity (n = 7). The mean dose of botulinum toxin A (Dysport) used to inject into the affected muscle was 22 U/kg body weight. Reduced muscular hyperactivity with a significant increase in joint mobility was achieved for dystonic (p < 0.0001) as well as for spastic conditions in patients with adductor spasm (p < 0.0002). For these patients the improved joint mobility represented a significant benefit for both daily activities and nursing care. Local paresis and local hematoma were observed in 1/28 and 1/28 patients, respectively; 1/28 patients developed a secondary non-response. However, apart from these side effects, no other adverse reactions to botulinum toxin A treatment were recorded during the treatment and observation period (12-64 months). Our results suggest that botulinum toxin A represents an effective and safe therapeutic substance for the treatment of pediatric patients suffering of focal motor problems due to dystonic or spastic muscular hyperactivity.     

Melanocortin analogue Org2766 binds to rat Schwann cells, upregulates NGF low-affinity receptor p75, and releases neurotrophic activity

Binding of the stable melanocortin(4-9) analogue, Org2766 [Met(O2)-Glu-His-Phe-D-Lys-Phe] to cultured rat sciatic nerve Schwann cells was demonstrated using a biotinylated derivative in semiquantitative histochemical and CELISA assays. Org2766 bound to Schwann cells, but not to fibroblasts, and was displaced maximally by unlabeled Org2766, alpha-MSH and ACTH(1-24). Displacement of Org2766 from the binding sites was considerably reduced by N- and C-truncation of the peptide. Specific binding of Org2766 was also demonstrated in the immortal rat Schwann cell line SCL4.1/F7 and was more pronounced in cells displaying a differentiated morphology. Org2766 and alpha-MSH increased cyclic AMP content of Schwann cells but neither stimulated DNA synthesis when applied alone. However, in the presence of a priming (subthreshold) concentration of the mitogen, cholera toxin, Org2766 and alpha-MSH caused a delayed increase in DNA synthesis. Org2766 did not modulate the expression of several differentiation-related Schwann cell markers. However, Org2766 increased immunoreactivity for p75 low-affinity NGF receptor on Schwann cells and evoked the release of neurotrophic factor(s) that synergized with NGF in stimulating neurite outgrowth in rat DRG neurons. The results indicate that Schwann cells are a primary target for the action of Org2766 and provide evidence for an indirect mechanism by which melanocortins might stimulate neurite sprouting in regenerating peripheral nerve axons.     

Microstructural characterization of aromatic copolyesters made by step reactions,by gradient polymer elution chromatography

The potentials of Gradient Polymer Elution Chromatography (GPEC) in both the Reversed‐Phase (RP) and Normal‐Phase (NP) mode, for the characterization of aromatic copolyesters made by step reactions, according to their chemical microstructure, were studied. Hereto, a number of copolyesters, varying in molar mass and chemical composition (CC) were synthesized, which allowed a systematic study on the effects of those parameters in GPEC. By RP‐GPEC, highly detailed separations were obtained. Information on chemical composition differences could, however, only be obtained for the lower molar masses. From these results, qualitative evidence for differences in the chemical microstructure of two strongly resembling copolyesters was found that could not be obtained by other methods such as SEC and NMR. Nevertheless, it was found difficult to unambiguously assign observed differences in the high molar mass parts of RP‐GPEC chromatograms. Therefore, RP‐GPEC must mainly be considered as a versatile, qualitative fingerprinting tool. In contrast, NP‐GPEC provides more and quantitative information on microstructural differences. By a combination of SEC and NP‐GPEC the Molar‐Mass‐Functionality‐Type‐Distribution (MMFTD) of the (co)polyesters, and the Molar‐Mass‐Chemical‐Composition‐Distribution (MMCCD) of the fraction containing two alcoholic end groups of the copolyesters could be studied. Significant differences between strongly resembling copolyesters were found which, for the MMCCDs, can only be the cause of the relative importance of reaction kinetics in step reaction copolymers. This makes the assumption that a predictable, theoretical statistically determined CCD is formed in all cases, questionable. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 183–201, 1999