Toward understanding the morphology-related crack initiation and propagation behavior in polypropylene systems as assessed by the essential work of fracture approach

Fracture mechanical terms related to the crack initiation and propagation, respectively, were assessed by the essential work of fracture (EWF) method for compression-molded polypropylene (PP) blends and elastomeric polypropylenes (ELPPs). The resistance to crack initiation (RCI) was characterized by the essential work of fracture w_e The w_e of the PP blends with 20 vol% ethyiene-co-butylene (EB) copolymers of various butylene (B) contents (58 and 90 wt%) and morphology (EB58 is amorphous, whereas EB90 is semicrystalline) increased with increasing butylene content and thus crystallinity. At the same time, in the slope of the EWF resistance curves, which inform about the resistance to crack propagation (RCP) of the PP/EB blends, an adverse change was observed. For the ELPPs of various crystallinity and morphology, the opposite tendency was found, that is, the RCI decreased, but the RCP increased with increasing crystallinity. The above findings were interpreted by considering the morphology and its rearrangement due to loading. It was suggested that the RCI is improved by the order of the crystalline structure and by the density of tie molecules that transfer the stress from the amorphous toward the crystalline phase. On the other hand, the RCP is controlled by a stress redistribution process that is influenced by possible changes in the local morphology.     

Instability of the molecular structure of monobenzoporphin to the alternation of the macrocycle bond lengths and its manifestation in the electronic spectra

Quantum-chemical calculations of the geometric structure of the molecules of monobenzoporphin (H₂ MBP) and monobenzoporphin with methyl and ethyl substituents in the five-member rings (H₂MBPm) have been carried out by the restricted and unrestricted Hartree-Fock methods with the AM1 Hamiltonian (AM1 RHF and AM1 UHF methods). The calculation of the above-indicated molecules by the AM1 RHF method without restrictions on their symmetry has given, for them, a planar structure with an alternation of the lengths of the bonds along the 18-member azacyclopolyene and the symmetry C _1h for their aromatic part. The calculation of the transitions to the excited electron Q states in such a structure by the CNDO/S method has shown that these states are characterized by large hypsochromic shifts (~3000–4000 cm^–1 ) relative to the Q levels of porphin (H₂P), which is in contradiction with the experimental data, according to which these shifts are bathochromic and comprise = –330 cm ^–1 and = –750 cm^–1. Optimization of the geometry of the H₂ MBP and H₂MBPm molecules by the AM1 UHF method gives, for them, a structure with equal lengths of the bonds along the 18-member azacyclopolyene with a symmetry differing insignificantly from the D _2h symmetry; elements of the structure with a lower symmetry and an alternation of the lengths of the bonds are retained in the condensed pyrrolenine and benzene rings. The calculation of the shifts of the Q levels in the H₂MBPm molecule of this geometry relative to the analogous levels in H₂P has shown that they are bathochromic and equal to = –520 cm^–1, and the RHF calculation with optimization of the geometry of the molecule and restrictions on the effective symmetry D _2h of the 18-member azacyclopolyene has given = –350 cm^–1 and = –430 cm^–1. The restrictions imposed on the C ₂ symmetry of the H₂MBP molecules by the RHF method are inadequate to equalize the lengths of the bonds along the 18-member azacyclopolyene. The calculations of the energy of the B levels of the monobenzoporphyrins considered also lend credence to their geometric structure with equal lengths of the bonds along the 18-member azacyclopolyene.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 712–721, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Detection of diminished response to cold pressor test in smokers: Assessment using phase-contrast cine magnetic resonance imaging of the coronary sinus

Purpose

The purposes of this study were to evaluate the reproducibility for measuring the cold pressor test (CPT)-induced myocardial blood flow (MBF) alteration using phase-contrast (PC) cine MRI, and to determine if this approach could detect altered MBF response to CPT in smokers.

Materials and methods

After obtaining informed consent, ten healthy male non-smokers (mean age: 28 ± 5 years) and ten age-matched male smokers (smoking duration ≥ 5 years, mean age: 28 ± 3 years) were examined in this institutional review board approved study. Breath-hold PC cine MR images of the coronary sinus were obtained with a 3 T MR imager with 32 channel coils at rest and during a CPT performed after immersing one foot in ice water. MBF was calculated as coronary sinus flow divided by the left ventricular (LV) mass which was given as a total LV myocardial volume measured on cine MRI multiplied by the specific gravity (1.05 g/mL).

Results

In non-smokers, MBF was 0.86 ± 0.25 mL/min/g at rest, with a significant increase to 1.20 ± 0.36 mL/min/g seen during CPT (percentage change of MBF (?MBF (%)); 39.2% ± 14.4%, p < 0.001). Inter-study reproducibility for ?MBF (%) measurements by different MR technologist was good, as indicated by the intraclass correlation coefficient of 0.93 and reproducibility coefficient of 10.5%. There was no significant difference between smokers and non-smokers for resting MBF (0.85 ± 0.32 mL/min/g, p = 0.91). However, ?MBF (%) in smokers was significantly reduced (-4.0 ± 32.2% vs. 39.2 ± 14.4%, p = 0.011).

Conclusion

PC cine MRI can be used to reproducibly quantify MBF response to CPT and to detect impaired flow response in smokers. This MR approach may be useful for monitoring the sequential change of coronary blood flow in various potentially pathologic conditions and for investigating its relationship with cardiovascular risk.