Comparisons between finite-element analysis predictions and pipe fracture experiments

This paper presents the results of ten finite-element analyses of cracked pipe subjected to bending loads compared to the corresponding experimental results produced from full-scale tests. As part of the presentation, detailed results from two international round-robin problems are presented. In all, nine through-wall cracked pipe and one surface cracked pipe is considered. The cracked pipe includes stainless, carbon, and welded pipe.     

The determinants of pKas in proteins

Although validation studies show that theoretical models for predicting the pKas of ionizable groups in proteins are increasingly accurate, a number of important questions remain: (1) What factors limit the accuracy of current models? (2) How can conformational flexibility of proteins best be accounted for? (3) Will use of solution structures in the calculations, rather than crystal structures, improve the accuracy of the computed pKas? and (4) Why does accurate prediction of protein pKas seem to require that a high dielectric constant be assigned to the protein interior? This paper addresses these and related issues. Among the conclusions are the following: (1) computed pKas averaged over NMR structure sets are more accurate than those based upon single crystal structures; (2) use of atomic parameters optimized to reproduce hydration energies of small molecules improves agreement with experiment when a low protein dielectric constant is assumed; (3) despite use of NMR structures and optimized atomic parameters, pKas computed with a protein dielectric constant of 20 are more accurate than those computed with a low protein dielectric constant; (4) the pKa shifts in ribonuclease A that result from phosphate binding are reproduced reasonably well by calculations; (5) the substantial pKa shifts observed in turkey ovomucoid third domain result largely from interactions among ionized groups; and (6) both experimental data and calculations indicate that proteins tend to lower the pKas of Asp side chains but have little overall effect upon the pKas of other ionizable groups.     

Interpretation of electron microscope autoradiographs: correction for cross-fire when membrane components are highly labelled

The interpretation of electron microscope autoradiographs concerns the estimate of the relative concentration of a radiolabelled molecule in subcellular compartments. Because of the radiation spread, an autoradiographic grain underlying a subcellular compartment cannot be directly assigned to the latter. Observed data must therefore be corrected for cross-fire (CF). We studied the efficiency of several methods designed for the CF correction when membrane components possess a high concentration of labelling, resulting in a high proportion of CF. Grains generated from simulated sources were subjected to the CF method, to an original method based on the simulated annealing optimization algorithm, and to the expectation-maximization algorithm. The expectation-maximization algorithm appears to be clearly superior to the two other methods. Nevertheless, the variances of the estimates were higher than expected. Since no analytical expression of the estimates is available, an objective comparison of the labelling in different compartments is not possible with a standard test. Consequently, the interpretation of autoradiographs in electron microscopy is still an open problem.     

Implantable catheter systems. Experiences with 1000 patients with central venous ports

OBJECTIVE: To assess retrospectively duration of functioning and rate of complications of a totally implantable venous access system used for long-term chemotherapy. PATIENTS AND METHODS: Between 1985 and 1993, a central venous access system (Port-a-Cath) had been implanted subcutaneously for long-term chemotherapy in 1000 patients (479 males, 521 females; mean age 49 [15-86] years). Follow-up observations lasted until the end of the chemotherapy or the removal of the system. RESULTS: Mean time of functioning of the catheter system was 284 (2-1563) days. The complication rate was 12.8%: catheter infection in 4.9% and catheter thrombosis in 3.2%. A further 4.7% of patients had less common complications (malfunction, catheter dislocation, skin necrosis, catheter break or disconnection, pneumothorax). A total of 119 (11.9%) systems had to be removed because of complications. The rates of infection and of other complications were significantly lower in patients with solid tumours (2 and 4%, respectively) than in those with haematological disease (6 and 8%) (P < 0.05 for each). CONCLUSION: Totally implantable venous access systems are suitable for long-term chemotherapy and cause few complications.     

Experiences in surgical management of cavernous hemangioma of the liver

BACKGROUND/AIMS: Observation is usually recommended for managing patients with cavernous hemangioma of the liver. To assess the indications for surgical management, we make a retrospective analysis. PATIENTS AND METHODS: There were 14 patients with cavernous hemangioma of the liver who were surgically treated in National Taiwan University Hospital from 1984 to 1993. RESULTS: The surgical indications included uncertain diagnosis in 10 patients, progressive tumor enlargement in two, symptomatic tumor in one and subcapsular bleeding in one. The tumors were 2-15 cm in diameter and the median was 6 cm. The operation procedures included atypical hepatectomy in 6 patients, lateral segmentectomy in 4, right lobectomy in one, extended right lobectomy in one and open biopsy in two. There was no mortality. Wound infection occurred in one patient. The average blood transfusion was 0.79 unit (range: 0-3 units)(1 unit=500 ml). The postoperative hospital stay was 13.2 days (range: 10-18 days). CONCLUSION: Surgical management of cavernous hemangioma of the liver is safe.     

Volume of blood required to detect common neonatal pathogens

OBJECTIVE: To determine the minimum volume of blood and the absolute number of organisms required for detection of bacteremia and fungemia by an automated colorimetric blood culture system (BacT/Alert, Organon Teknika). DESIGN: Common neonatal pathogens, Escherichia coli, Streptococcus agalactiae (group B streptococcus (GBS): one American Type Culture Collection (ATCC) strain and one clinical isolate), Staphylococcus epidermidis, and Candida albicans, were seeded into blood to produce bacteremia or fungemia with low colony counts (1 to 3 colony-forming units (CFU) per milliliter) and ultra-low colony counts (<1 CFU/ml). For each organism, 96 culture bottles were inoculated with either 0.25, 0.5, 1.0, or 4.0 ml of the two seeded blood concentrations. Blood culture bottles were incubated in the BacT/Alert device for 5 days, and time to positivity was noted when applicable. All bottles were subcultured on plated media. DATA ANALYSIS: The Poisson statistic was used to calculate the probability of finding at least one viable CFU per inoculated culture bottle. The fraction of culture bottles with positive findings per group was divided by the probability of one or more organisms present to give the positivity index. RESULTS: Plated subculture identified no growth of organisms not detected by the colorimetric detection system. The false-positive rate for the automated device was less than 1%. The positivity index for the GBS clinical isolate was 1.13, for the GBS ATCC isolate 0.96, for S. epidermidis 0.94, for C. albicans 0.97, and for E. coli 0.95. There was a statistically significant difference with time to positivity and inocula volume (p <0.01), but the difference was not clinically important. CONCLUSIONS: If one or two viable colony-forming units are in the blood inoculated into culture media, the BacT/Alert system will detect growth rapidly. Because there appears to be a sizable subset of neonates who are at risk of sepsis with a colony count less than 4 CFU/ml, then a 0.5 ml inoculum of blood into the culture media is inadequate for sensitive and timely detection of bacteremia. One to two milliliters of blood should increase microorganism recovery in the face of low-colony-count sepsis.