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  • 1995-1999  (5)
  • 1975-1979
  • 1970-1974
  • 1925-1929
  • 1905-1909
  • Boger fluid  (3)
  • Memory  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Shear rheology of polymer solutions near the critical condition for elastic instability (1997)
    Springer
    Rheologica acta 36 (1997), S. 97-109 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer migration ; anomalous rheology ; Boger fluid ; normal stress ; elastic instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The use of constant viscosity, highly elastic polymer solutions, so called Boger fluids, has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. However, the behavior of these fluids is still complicated by many different physical processes occurring within a narrow window of observation time and applied shear rate. In this study, we investigate the long-time shear behavior of an ideal Boger fluid: a well characterized, athermal, dilute, binary solution of high molecular weight polystyrene in oligomeric polystyrene. Rheological measurements show that under an applied steady shear flow, this family of polymer solutions undergoes a transient decay of normal stresses on a timescale much longer than the polymer molecule‘s relaxation time. Rheological and flow visualization results demonstrate that the observed phenomenon is not caused by polymer degradation, phase separation, viscous heating, or secondary flows from elastic instabilities. Although the timescale is much shorter than that associated with polymer migration in the same solutions (MacDonald and Muller, 1996), the appearance of this phenomenon only at the rates where migration has been observed suggests that it may be a prerequisite for observing migration. In addition, we note that through sufficient pre-shearing of the sample, the normal stress decrease suppresses the elastic instability. These results show that there is considerable uncertainty in choosing the appropriate measure of the fluid relaxation time for consistently modeling the critical condition for the elastic instability, the decay of normal stresses, and the migration of polymer species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366816
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Confidence level and feeling of knowing for episodic and semantic memory: an investigation of lorazepam effects on metamemory (1998)
    Springer
    Psychopharmacology 138 (1998), S. 318-325 
    Details
    ISSN: 1432-2072
    Keywords: Key words Benzodiazepines ; Lorazepam ; Memory ; Metamemory ; Confidence level ; Feeling of knowing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The effects of lorazepam (0.026 or 0.038 mg/kg), a benzodiazepine, and of a placebo on metamemory, i.e. knowledge about one’s own memory capabilities, were investigated in 36 healthy volunteers. Accuracy of confidence levels (CL) in the correctness of recalled answers and accuracy of feeling of knowing (FOK) the answers when recall fails were measured using a sentence memory task assessing episodic memory and a task consisting of general information questions and assessing semantic memory. Lorazepam impaired episodic memory. Unexpectedly, it also impaired performance in both the recall and recognition phases of the task assessing semantic memory, suggesting that it decreased the ability to distinguish between correct and incorrect information. In episodic memory, lorazepam 0.038 mg/kg-treated subjects exhibited an impaired CL accuracy, compared to placebo-treated subjects, and their FOK accuracy was at chance. In semantic memory, their overall CL and FOK accuracy was apparently spared. However, these subjects selectively overestimated their CL judgements for incorrect answers; moreover, secondary analyses showed that FOK accuracy for a subset of low-accuracy items was virtually nil. These results suggest that lorazepam impairs metamemory for both episodic and semantic memory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050677
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    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
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Shear rheology of polymer solutions near the critical condition for elastic instability (1997)
    Springer
    Rheologica acta 36 (1997), S. 97-109 
    Details
    ISSN: 1435-1528
    Keywords: Polymer migration ; anomalous theology ; Boger fluid ; normal stress ; elastic instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The use of constant viscosity, highly elastic polymer solutions, so called Boger fluids, has been remarkably successful in elucidating the behavior of polymeric materials under flowing conditions. However, the behavior of these fluids is still complicated by many different physical processes occurring within a narrow window of observation time and applied shear rate. In this study, we investigate the long-time shear behavior of an ideal Boger fluid: a well characterized, athermal, dilute, binary solution of high molecular weight polystyrene in oligomeric polystyrene. Rheological measurements show that under an applied steady shear flow, this family of polymer solutions undergoes a transient decay of normal stresses on a timescale much longer than the polymer molecule's relaxation time. Rheological and flow visualization results demonstrate that the observed phenomenon is not caused by polymer degradation, phase separation, viscous heating, or secondary flows from elastic instabilities. Although the timescale is much shorter than that associated with polymer migration in the same solutions (MacDonald and Muller, 1996), the appearance of this phenomenon only at the rates where migration has been observed suggests that it may be a prerequisite for observing migration. In addition, we note that through sufficient preshearing of the sample, the normal stress decrease suppresses the elastic instability. These results show that there is considerable uncertainty in choosing the appropriate measure of the fluid relaxation time for consistently modeling the critical condition for the elastic instability, the decay of normal stresses, and the migration of polymer species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366816
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Study of mixed solvent quality in a polystyrene-dioctyl phthalate-polystyrene system (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 181-192 
    Details
    ISSN: 0887-6266
    Keywords: ternary solutions ; solvent quality ; polystyrene-dioctyl phthalate ; light scattering ; Boger fluid ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymer solvent interactions in the ternary system high molecular weight polystyrene (HMPS), low molecular weight polystyrene (LMPS), and dioctyl phthalate (DOP) have been characterized by means of intrinsic viscometry (IV), dynamic light scattering (DLS), and static light scattering (SLS). Excluded volume exponents have been extracted from the scaling of intrinsic viscosity and translational diffusivity with polymer molecular weight for a mixed solvent of 13 wt % LMPS/87 wt % DOP. The value of the excluded volume exponent, v = 0.45, indicates that HMPS in the mixed solvent DOP/LMPS has apparently assumed a reduced conformation relative to the theta condition. However, SLS measures of the second virial coefficient (A2) confirm that DOP is a theta solvent at our experimental temperature of 22°C and indicate that the addition of LMPS increases A2. SLS also suggests that neither solvent component is strongly preferentially adsorped into the HMPS coil. Our system then is a mixture of a theta solvent and a good solvent that exhibits poor solvent scaling behavior. We believe this to be the first demonstration of such behavior in a system that does not exhibit appreciable preferential adsorption. We conclude by examining our observations in the context of current descriptions of mixed solvent thermodynamics. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
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