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91.
Mononitration of indane produces a mixture of 4- and 5- nitroindanes. Crystallization from mixtures occurs after distillation improves composition of a major component to above 80%. 4-Nitroindane: triclinic, space group
(#2),a=7.332(4) Å,b=8.304(4) Å,c=8.358(4) Å, =61.43(4)°, =67.60(4)°, =70.15(4)°,V=405.4(4) Å3,Z=2. Non-H-atoms are nearly planar, aliphatic H's are eclipsed. 5-Nitroindane: monoclinic, space groupP21/c (#14),a=10.946(8) Å,b=15.643(10) Å,c=9.415(6) Å, =92.34(5)°,V=1611(2) Å3,Z=8. Non-H-atoms in the two molecules differ in torsion of the nitro group with respect to indane and fold of the nonbenzylic methylene group. Semiempirical calculations (PM3) suggest that distorsion from planarity may be associated with the two lowest energy vibrational modes. Uv, ir, ms, proton, and13C-nmr spectra are correlated with the solid state structures. 相似文献
92.
93.
Werner-Michael Kulicke Ulf Reinhardt Gerald G. Fuller Oliver Arendt 《Rheologica Acta》1999,38(1):26-33
Sodium carboxymethylcellulose (NaCMC) in solution represents a complex rheological system, since it forms aggregates and
associations and hence higher-level structures and, depending on the synthesis, is only found in a molecularly dispersed form
in exceptional cases. Rheo-mechanical investigations of the viscoelasticity showed that the Cox-Merz rule is not fulfilled.
The aim was therefore to examine whether rheo-optics could be employed to provide more detailed conclusions about the parameters that influence the flow behavior of NaCMC than
has hitherto been available with mechanical methods. The flow birefringence, Δn
′, rises as the degree of polymerization increases, and exhibits the same dependence on molar mass as does the viscosity: Δn
′∝M
w
3.4. As the degree of polymerization increases while the shear rate remains constant, the polymer segments become more distinctly
aligned in the direction of shear. Hence increasing the degree of polymerization also affects the solution structure, i.e.
the interaction of the molecules with one another. The stress-optical rule only applies to a limited extent for this system.
The stress-optical coefficient, C, is almost independent of the shear rate, but is strongly influenced by the concentration and attains a limiting value of
3 × 10−8 Pa−1. C was determined for a polymer in dilute solution and the curve obtained also enabled transitions in the solution structure to be recognized.
Received: 1 May 1998 Accepted: 5 October 1998 相似文献
94.
95.
Cold preservation of endothelial cells was studied, comparing primary endothelial cells (human umbilical vein endothelial cells - HUVECs) and a continuously growing cell line (ECV304 cells). Viability at the end of 24h cold preservation was measured by dye exclusion, whilst metabolism was assessed by Alamar blue conversion. Two preservation solutions were studied (UW solution) and sucrose-based (SbS) in both cell types. The response was similar in both cell types to preservation under normoxic conditions (with percentage dye exclusion maintained at about 80 percent in both preservation solutions) whereas under hypoxic conditions ECV304 were more sensitive to preservation in UW solution (dye exclusion reduced to 43.5+/-1.4 percent versus 73.6+/-14 percent (P<0.01). Metabolism assessed by Alamar blue conversion after cold preservation and rewarming was similar in both ECV304 and HUVECs after storage under normoxic conditions in UW solution, but in both cell types, metabolism was higher in SbS (P<0.05 and p<0.01) than in UW solution. Under hypoxic conditions, both cell types showed similar recovery of metabolism after storage in either UW or SbS. If the cells (in this case ECV304 under aerobic conditions) were stored for 24h and then allowed to rewarm in either of the respective preservation solutions (UW or SbS for 1h) before the Alamar blue test, metabolism was higher (p less than 0.01) in those exposed to SbS. UW solution and SbS provide similar protection for endothelial cells under hypoxic conditions, but SbS has some advantages under normoxic storage or if the cells experience variable temperatures in the presence of residual preservation solution at the end of cold preservation period. 相似文献
96.
Necessary and sufficient conditions are presented to insure that the direct sum of two reflexive representations of a finite dimensional algebra is reflexive, and it is shown that for each such algebra, there is an integer such that the direct sum of copies of each of its representations is reflexive. Given a ring our results are actually presented in the more general setting of -representations of a ring
97.
We point out that the baryon loading problem in gamma-ray burst (GRB) models can be ameliorated if a significant fraction of the baryons which inertially confine the fireball is converted to neutrons. A high neutron fraction can result in a reduced transfer of energy from relativistic light particles in the fireball to baryons. The energy needed to produce the required relativistic flow in the GRB is consequently reduced, in some cases by orders of magnitude. A high neutron-to-proton ratio has been calculated in neutron star-merger fireball environments. Significant neutron excess also could occur near compact objects with high neutrino fluxes. 相似文献
98.
99.
The thermoelectric power and the electrical resistance of the two low-dimensional conductors, HfTe5 and ZrTe5 have been measured over the temperature range of 7K to 380K. The thermoelectric power for both materials is large and positive at high temperatures and then drops precipitously and crosses zero at the temperature of the anomalous resistivity peak, Tp. At lower temperatures, the thermoelectric power reaches a large negative peak and then decreases to zero in a metallic fashion. The abrupt change in thermopower, which occurs at Tp for both materials, is indicative of a phase transition where the carrier type changes from hole-like to electron-like. 相似文献
100.
William Fuller Brown 《Journal of magnetism and magnetic materials》1976,3(4):295-304
In standard coercivity theory, formulae derived for homogeneous material are applied to inhomogeneous situations. The model considered here contains inherent inhomogeneity in the form of competing volume and surface anisotropies. Its coercivity never exceeds half the Stoner-Wohlfarth value, decreases with particle size, and vanishes at a finite critical size. 相似文献