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  • 1
    Electronic Resource
    Electronic Resource
    Lorazepam impairs perceptual integration of visual forms: a central effect (1996)
    Springer
    Psychopharmacology 126 (1996), S. 260-270 
    Details
    ISSN: 1432-2072
    Keywords: Benzodiazepine ; Lorazepam ; Human ; Visual perception ; Oculomotor balance ; Integration processes ; Symmetry perception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have shown a lorazepam effect on visual perception. We tested whether this impairment resulted from a peripheral effect induced by benzodiazepines. A first experiment showed that a single dose of lorazepam induces an oculomotor imbalance without impairing visual acuity or accommodation. In a second experiment, we tested whether the impairment induced by lorazepam on visual perception still occurred in monocular vision. Subjects matched incomplete forms controlled on the spacing and alignment of their local contour elements. A reference object was first displayed and followed by two laterally displayed objects, a target and a distractor. The distractor was the mirror-reversed version of the target. Performance was impaired in the lorazepam group when the reference was an incomplete form with a spacing of 10.8' or 22.2' of arc. These results were not correlated with sedation. They confirm that lorazepam has a central deleterious effect on visual perception. A posthoc analysis also suggested that lorazepam-treated subjects used asymmetry in the stimuli as a compensatory strategy. This result is discussed in relation to previous hypotheses about the physiological mechanisms that determine the effects of lorazepam on visual perception.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02246456
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of haloperidol and amisulpride on motor and cognitive skill learning in healthy volunteers (1997)
    Springer
    Psychopharmacology 131 (1997), S. 329-338 
    Details
    ISSN: 1432-2072
    Keywords: Key words Haloperidol ; Amisulpride ; Human ; Cognitive ; Motor ; Skill learning ; Memory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of a typical neuroleptic, haloperidol (1 and 2 mg orally), of an atypical neuroleptic, amisulpride (50 and 100 mg) and of a placebo on motor and cognitive skill learning were assessed in 60 healthy volunteers using repeated testing on the Tower of Toronto puzzle. Subjects were asked to solve three blocks of eight trials and, at distance from drug administration, a fourth block. The puzzle was connected to a computer in order to obtain a precise timing of individual moves. Two components of cognitive skill learning were assessed, the ability to learn to solve the puzzle and the acquisition of a problem-solving routine. Subjective feelings of effort and automatisation of the task were assessed using a questionnaire. Like placebo-treated subjects, neuroleptic-treated subjects were able to acquire a motor skill, to learn to solve the puzzle and to acquire a routine. However, haloperidol 2 mg-treated subjects needed significantly more moves to solve the puzzle in blocks 3 and 4, some of them having routinised a non-optimal solution. A significant cognitive slowing was observed in the haloperidol 1mg group in block 4. The performance pattern and verbal reports suggested that haloperidol impaired the higher cognitive functions such as the ability to shift from one strategy to another and/or to assess one’s performance accurately, possibly leading to the development of compensatory strategies. The only deleterious amisulpride effect was a cognitive slowing in block 4, which was observed in the lower dose group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050300
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  • 3
    Electronic Resource
    Electronic Resource
    Drop deformation during elongational flow in blends of viscoelastic fluids. Small deformation theory and comparison with experimental results (1995)
    Springer
    Rheologica acta 34 (1995), S. 525-533 
    Details
    ISSN: 1435-1528
    Keywords: Emulsion model ; polymer blends ; drop deformation ; elongational flow ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The deformation of dispersed droplets in immiscible polymer blends was studied in elongational flow, with an original method based on quenching specimens elongated in the melt. Results for high capillary numbers and different viscosity ratios were compared to the linear theory of viscoelastic emulsions of Palierne. Simple expressions for the drop deformation could be obtained for Maxwell fluids, and the influence of viscoelasticity of matrix and inclusions on the drop deformation process was discussed. With respect to the Newtonian approximation, the description of some experimental data could be improved. However, the predictions of the viscoelastic model appeared to be very sensitive to the choice of relaxation times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712313
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  • 4
    Electronic Resource
    Electronic Resource
    Rheology/morphology/flow conditions relationships for polymethylmethacrylate/rubber blend (1996)
    Springer
    Rheologica acta 35 (1996), S. 369-381 
    Details
    ISSN: 1435-1528
    Keywords: Melt rheology ; linear and non-linear viscoelasticity ; polymer blends ; reinforced polymers ; morphology ; Cox-Merz rule ; aggregation ; percolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Viscoelastic behavior, phase morphology and flow conditions relationships in polymer/rubber blends have been investigated. The importance of such correlations is illustrated on polymethylmethacrylate (PMMA)/rubber blends subjected to different flow conditions both under small and large deformations. In small-amplitude oscillatory shear (the morphology does not change during the flow) the elastic modulus G′ of the concentrated blends shows a secondary plateau, G′ p , in the low frequency region. This solid-like behavior appears for rubber particle contents beyond the percolation threshold concentration (15%). Morphological observations revealed that for concentrations higher than 15%, the particles are dispersed in a three-dimensional network-type structure. In capillary flow it was found that the network-type structure was destroyed and replaced by an alignment of particles in the flow direction. This morphological modification resulted in a decrease in both viscosity and post-extrusion swell of the blends. Morphological observations revealed that the ordered structure in the flow direction was concentrated only in the skin region of the extrudate, where the shear stress is higher than the secondary plateau, G′ p . A simple kinetic mechanism is proposed to explain the observed morphology. Similarly, steady shear measurements performed in the cone-and-plate geometry revealed alignment of particles in the flow direction for shear stress values higher than G′p.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403538
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  • 5
    Electronic Resource
    Electronic Resource
    Relationship between structure and rheological properties in the melt of polymers containing spherical inclusions (1995)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 301-308 
    Details
    ISSN: 1042-7147
    Keywords: polymer blends ; melt rheology ; crosslinked rubber ; structured latex ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1995.220060508
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