Reoperations after operation on the thoracic aorta: etiology, surgical techniques, and prevention

Recurrent aortic aneurysms, persistent or new dissection, new onset of valvular and coronary artery disease, graft infection, and prosthetic endocarditis are not rare after thoracic aortic operations; they can be difficult to diagnose and represent a formidable surgical challenge. Between 1977 and 1991, 876 operations were performed on the thoracic aorta in our institution: 340 in dissections, 299 in true aneurysms, 150 for aortic remodeling and external wall support during aortic valve replacement, and 87 for miscellaneous causes. During the same period, there were 193 additional reoperations. Vascular reoperations on abdominal aorta and peripheral arteries accounted for 73 cases and are not further discussed in this study. The reasons for reoperation (n = 130) in 120 patients were: failure of biologic valves (n = 23); aneurysm recurrence in a proximal or distal aortic segment (n = 21); pseudoaneurysm formation at suture lines (n = 13); new dissection or dilatation involving ascending aorta (n = 11), aortic arch (n = 13), and descending aorta (n = 10); aneurysm after aortic remodeling (n = 13); new onset of valvular disease (n = 5); and new onset of coronary disease (n = 5). Infected aortic graft and prosthetic endocarditis accounted for 10 reoperations, and a planned two-staged procedure was performed in 6 patients. Omitting the failed biologic valves, reoperations were performed on the aortic segment previously operated on in 69.3% of the cases and on other thoracic segments in 30.7%. Overall hospital mortality rate after reoperation was 5.8%. A significant decrease in operative mortality was observed in the most recent period (3.0% between 1989 and 1991). Reoperations are technically demanding, and some of them are preventable; therefore (1) graft inclusion technique should be abandoned in ascending aortic operation due to formation of false aneurysms; (2) in patients with Marfan syndrome, complete repair of the diseased aorta should be attempted during the initial operation; (3) aortic arch dissection should be repaired definitively during the first operation in low-risk patients; (4) biological valves should be avoided in aneurysm operations; and (5) homograft replacement is the treatment of choice in prosthetic endocarditis or in infected composite graft after an aortic valve or ascending aortic operation.     

Effect of processing conditions on the yield and failure response of an aliphatic polyketone terpolymer

The effect of processing conditions on the yield and failure behavior of an aliphatic polyketone terpolymer was studied. Testing and characterization were performed on samples that were extruded in the form of hollow cylinders. We performed the extrusion process at different shear rates and at different cooling rates to assess the effect that process conditions had on the polymer properties. We performed biaxial testing on the samples to characterize the failure envelopes, including the ductile–brittle transition condition for each process condition. The effect of shear rate was negligible, whereas the cooling rate significantly affected the failure behavior. To explain these differences in behavior, we performed characterization via differential scanning calorimetry, wide‐angle X‐ray diffraction, attenuated total reflection IR spectroscopy, dynamic mechanical thermal analysis, scanning electron microscopy, and residual stress measurements. A broad glass transition was found for all samples at temperatures higher than previously reported for this material. Alteration of the processing conditions did not influence the crystalline phase (percentage crystallinity, crystalline orientation, crystallite size, etc.). A change in spherulitic structure was also observed with altered cooling rate and is suggested to have contributed to the change in failure behavior. Residual stresses also affected the behavior of all samples. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 318–334, 2002; DOI 10.1002/app.10334     

A new method for evaluating the subjective image quality of photographs: dynamic reference

The Dynamic Reference (DR) method has been developed for subjective image quality experiments in which original or undistorted images are unavailable. The DR method creates reference image series from test images. Reference images are presented to observers as a slide show prior to evaluating their quality. As the observers view the set of reference images, they determine the overall variation in quality within the set of test images. This study compared the performance of the DR method to that of the standardized absolute category rating (ACR) and paired comparison (PC) methods. We measured the performance of each method in terms of time effort and discriminability. The results showed that the DR method is faster than the PC method and more accurate than the ACR method. The DR method is especially suitable for experiments that require highly accurate results in a short time.     

Monies,economies and democracy: cultivating ambivalence in the co-design of digital currencies

ABSTRACT

Systematised collaborative design of complementary currencies is still a largely unexplored area that offers underutilised opportunities for supporting a fair and sustainable sharing economy. Future currency design necessitates attention to the systemic factors and the social particularities in which new monetary alternatives, i.e. ‘monies’, and the technological solutions that serve these alternatives, are created. This paper argues for a socially and contextually sensitive design of complementary currency innovation. It considers the technological conditions and the tendencies to exploitation from contemporary capitalism. Based on the literature review, we propose collaborative design of complementary currencies with particularist and inclusive approaches. New directions for open-ended economic innovation are explored in finding opportunities in the future-oriented Transition Design, supported by an empathic and ambivalent design mindset.     

Yield behavior and failure response of an aliphatic polyketone terpolymer subjected to multi-axial stress states

The yield behavior of an engineering thermoplastic under biaxial stress states has been investigated. The material considered is an aliphatic polyketone terpolymer. Multiaxial testing was performed on thin-walled hollow cylinders at four different temperatures and three strain rates. Various stress states were applied in order to develop failure envelopes. Within each envelope, the nominal strain rate along the octahedral shear plane, ^oct, was held constant. These tests were performed at 0, 20, 50 and 80°C at ^oct = 0.05 min^–1. At 20°C, samples were also tested at ^oct = 0.005 and 0.5 min^–1. Below the T^g of 12°C, failures in all stress states investigated, except axial compression, were brittle. At temperatures of 50 and 80°C, all failures were ductile. At 20°C, both ductile and brittle failures were observed. Although the rate affected the yield strength of the material, it had little effect on the mode of failure. In contrast, the temperature had a significant effect on the yield strength and mode of failure. While the effect of strain rate on yield strength was greater in the hoop direction than axial, the opposite was true for the effect of temperature. It was also observed that the state of stress played a significant role in the material failure.     

Fermentative hydrogen production by Clostridium butyricum and Escherichia coli in pure and cocultures

The effect of coculture of Clostridium butyricum and Escherichia coli on hydrogen production was investigated. C. butyricum and E. coli were grown separately and together as batch cultures. Gas production, growth, volatile fatty acid production and glucose degradation were monitored. Whilst C. butyricum alone produced 2.09 mol-H₂/mol-glucose the coculture produced 1.65 mol-H₂/mol-glucose. However, the coculture utilized glucose more efficiently in the batch culture, i.e., it was able to produce more H₂ (5.85 mmol H₂) in the same cultivation setting than C. butyricum (4.62 mmol H₂), before the growth limiting pH was reached.     

Prospecting hydrogen production of Escherichia coli by metabolic network modeling

Genome-scale model was applied to analyze the anaerobic metabolism of Escherichia coli. Three different methods were used to find deletions affecting fermentative hydrogen production: flux balance analysis (FBA), algorithm for blocking competing pathways (ABCP), and manual selection. Based on these methods, 81 E. coli mutants possessing one gene deletion were selected and cultivated in batch experiments. Experimental results of H₂ and biomass production were compared against the results of FBA. Several gene deletions enhancing H₂ production were found. Correctness of gene essentiality predictions of FBA for the selected genes was 78% and 77% in glucose and galactose media, respectively. 33% of the mutations that were predicted by FBA to increase H₂ production had a positive effect in experiments. Batch cultivation is a simple and straightforward experimental way to screen improvements in H₂ production. However, the ability of FBA to predict the H₂ production rate cannot be evaluated by batch experiments. Metabolic network models provide a method for gaining broader understanding of the complicated metabolic system of a cell and can aid in prospecting suitable gene deletions for enhancing H₂ production.     

Schooling space: where South Africans learnt to position themselves within the hierarchy of apartheid society

In setting out to understand how South African school space was harnessed to the political project of apartheid, the author explores memory accounts from several adults who attended school during the apartheid era. Her analysis of their reminiscences found that non-pedagogic areas of the school and public domain beyond school premises were places where learners encountered their Other. Those sites provided the conditions for poignant awakenings to racialised identifications within discriminatory hierarchies. The article ends with the author reflecting on the effectiveness of spatially segregated schooling, when she works towards understanding her informants' uncritical tributes to the educational and moral value of their apartheid-era schooling.