The rari-constant theory of linear elasticity is based on the assumption that elasticity in solids is caused by only pair potentials with coaxial forces acting between atoms. The strain energy of ...each pair potential depends on the square of the strain between the atoms in the pair. This strain can be determined by taking the inner product of the strain tensor with a structural tensor that is the tensor product of a unit vector with itself. It is shown that the 15 independent constants in the rari-constant theory can be generated by a complete set of 15 structural tensors. It is also shown that the 6 additional independent constants in the multi-constant theory can be generated by taking the inner product of 6 of these structural tensors with the square of the strain tensor. A generalization of these results for nonlinear elasticity is discussed with reference to recent work which compares the structural and generalized structural tensor approaches to modeling fibrous tissues.
This study investigated a number of invariant based orthotropic and transversely isotropic constitutive equations for their suitability to fit three-dimensional simple shear mechanics data of passive ...myocardial tissue.
A number of orthotropic laws based on Green strain components and one microstructurally based law have previously been investigated to fit experimental measurements of stress-strain behaviour. Here we extend this investigation to include several recently proposed functional forms, i.e. invariant based orthotropic and transversely isotropic constitutive relations.
These laws were compared on the basis of (i) 'goodness of fit': how well they fit a set of six shear deformation tests, (ii) 'variability': how well determined the material parameters are over the range of experiments. These criteria were utilised to discuss the advantages and disadvantages of the constitutive laws.
It was found that a specific form of the polyconvex type as well as the exponential Fung-type law from the previous study were most suitable for modelling the orthotropic behaviour of myocardium under simple shear.
Analogues of the κ-receptor agonist methyl (R)-4-(3,4-dichlorophenylacetyl)-3-(pyrrolidin-1-ylmethyl)piperazine-1-carboxylate (GR-89,696, 6) bearing an additional methyl substituent in the side chain ...are synthesized and evaluated for their κ-receptor affinity and selectivity. A key step in the synthesis is the stereoselective reductive amination of the ketones 9, 18, and 19 with pyrrolidine and NaBH3CN, which succeeds only in the presence of the Lewis acid Ti(OiPr)4. Whereas the BOC-substituted ketone 9 affords the unlike and like diastereomers of 10 in a ratio of 70:30, the diastereoselectivity during the reductive amination of the butyl and phenyl substituted ketones 18 and 19 is enhanced to 85:15 (butyl derivative) and >95:<5 (phenyl derivative) in favor of the unlike diastereomers. In receptor binding studies using the radioligand 3HU-69,593 the (S,S)-configured methyl carbamate (S,S)-14 reveals the highest κ-receptor affinity (K i = 0.31 nM) within this series, even exceeding the lead κ-agonist 6 (GR-89,696). A slightly reduced κ-receptor affinity is observed with the propionamide (S,S)-13 (K i = 0.67 nM). The κ-receptor affinity of piperazines with acyl or alkoxycarbonyl residues at both nitrogen atoms (11, 13, 14) decreases in the order (S,S) > (R,R) > (S,R) > (R,S). The methyl carbamate (S,S)-14 discloses a unique activity profile also binding at μ-receptors in the subnanomolar range (K i = 0.36 nM). In a functional assay, i.e., by measuring acetylcholine release in rabbit hippocampus slices, the agonistic effects of the methyl carbamate (S,S)-14 and the propionamide (S,S)-13 are demonstrated. Only weak κ- and μ-receptor affinities are found with the butyl- and phenyl-substituted piperazines 22 and 23. However, considerable σ1-receptor affinity is determined for the enantiomeric, unlike-configured butyl derivatives (R,S)-22 and (S,R)-22 with K i-values of 40.2 nM and 81.0 nM, respectively.
The role of electrical and potassium (K
+)-induced depolarisation on choline-acetyltransferase (ChAT) activity in human and mouse neocortical slices was studied. When
3
H
-ACh release was evoked by ...two K
+ stimulations in
human neocortex, the mean
S
2/
S
1 ratio was significantly below unity. ChAT inhibitors, like bromo-acetylcholine and ocadaic acid, raised this ratio by 79 and 63%, respectively, suggesting that the diminished
S
2/
S
1 value in the absence of ChAT inhibitors reflected an increased ChAT activity at
S
2 following K
+ depolarisation at
S
1. When stimulated electrically, however, the
S
2/
S
1 ratio in human neocortex was near unity and ocadaic acid remained without effect. In parallel experiments on
mouse neocortical slices, the
S
2/
S
1 ratio was near unity in both electrically or K
+-evoked
3
H
-ACh release and was not altered by ChAT inhibition. ChAT activity following K
+ depolarisation was also determined directly. ChAT activation in human neocortical slices was highest at 10 and 20
mM K
+. ChAT activity in mouse neocortical tissue was not altered by K
+ depolarisation. These results suggest that in human, but not in mouse, neocortex ChAT activity may be increased due to ongoing K
+ depolarisation. This increase of ChAT activity supports a cholinergic degeneration hypothesis which has been entitled “autocannibalism” by Wurtman TINS 15 (1992) 177.
Male Long–Evans rats sustained injections of 5,7-dihydroxytryptamine (5,7-DHT) into the fimbria-fornix and the cingular bundle or/and intraseptal injections of 192 IgG-saporin to induce serotonergic ...or/and cholinergic hippocampal denervations; Sham-operated rats served as controls. Four to ten weeks after lesioning, we measured (i) the electrically evoked release of acetylcholine (
3
H
ACh), noradrenaline (
3
H
NA) and serotonin (
3
H
5-HT) in hippocampal slices in the presence of drugs acting on auto- or heteroreceptors, (ii) the nicotine-evoked release of NA and (iii) the choline acetyltransferase (ChAT) activity and the concentration of monoamines in homogenates. Saporin lesions reduced the accumulation of
3
H
choline, the release of
3
H
ACh and the ChAT activity, but increased the concentration of NA and facilitated the release of
3
H
NA evoked by nicotine. 5,7-DHT lesions reduced the accumulation and the release of
3
H
5-HT, the concentration of 5-HT, and also facilitated the release of
3
H
NA evoked by nicotine. Accumulation and electrically evoked release of
3
H
NA were not altered by either lesion. The combination of both toxins resulted in an addition of their particular effects. The 5-HT
1B receptor agonist, CP 93,129, and the muscarinic agonist, oxotremorine, reduced the release of
3
H
ACh in control and 5,7-DHT-lesioned rats; in rats injected with saporin, their effects could not be measured reliably. CP 93,129 and the
α
2-adrenoceptor agonist, UK 14,304, reduced the release of
3
H
5-HT in all groups by about 65%. In conclusion: (i) selective neurotoxins can be combined to enable controlled and selective damage of hippocampal transmitter systems; (ii) 5-HT exerts an inhibitory influence on the nicotine-evoked release of NA, but partial serotonergic lesions do not influence the release of ACh at a presynaptic level and (iii) presynaptic modulatory mechanisms involving auto- and heteroreceptors may be conserved on fibres spared by the lesions.
The energetic requirements for electron transfer to the conduction band of silver bromide from a series of cyanine dyes have been studied using both picosecond time-resolved and steady state ...fluorescence techniques. The selected dyes exhibit monomeric absorption spectra in the adsorbed state and have excited state donor energies that are calculated to span a range about the conduction band edge of AgBr. Rate constants and yields for these electron transfers were extracted from the picosecond fluorescence lifetime measurements. Yields were also obtained through independent measurements of the steady state fluorescence of these dyes and were correlated with estimates of the free energy of the reaction to depict a threshold for electron transfer with respect to the conduction band of AgBr. The threshold compares well with model curves from electron transfer theory and with literature reports of photographic relative quantum yield measurements on similar monomeric systems at silver halide surfaces. This correlation supports the electron transfer model for spectral sensitization of the silver halides. Contrasts are drawn with the sharp energetic thresholds expected for aggregated dyes.
One peculiarity of relationship marketing is that the pioneers drew to some extent on theory; the motivation behind relationship marketing being rooted in empirical observations and managerial ...problems, which highlighted the value added of relationship-based managing. The perception of these issues led the pioneers to challenge established, mostly transaction based theories on the market and marketing. Early contributors, such as Arndt, perceived relationships as attempts to domesticate the market. Currently research is moving its focus to the economic value of relationship based managing. A major objective of this e-book is to provide a forum for the discussion and further development of relationship theory.
