Variations in software development practices

Research on over 18 years of software projects reveals that developing large systems involves substantially more activities and a greater variety of specialized personnel than developing smaller systems. Perhaps the most significant observation is that good quality control is the best overall indicator of a successful project. Schedule delays and cost overruns most often occur when you discover during testing that the application has so many bugs that it doesn't work. Projects using QA teams, formal design and code inspections, and pretest defect tracking always had shorter testing cycles and therefore were more likely to be deliverable on schedule.     

Demonstration of an endurance limit in cast 319 aluminum

An investigation of the fatigue properties of cast W319-T7, an Al-Si-Cu alloy used in automotive engine components, was conducted using ultrasonic testing equipment with operating frequencies of 20 kHz. The stress-life (S-N) behavior at room temperature was determined for three solidification conditions of this alloy, where stresses for fatigue lives ranging from 10⁵ to 10⁹ cycles were determined. The results are compared to fatigue data acquired using servohydraulic equipment operating at 40 Hz. No influence of loading frequency has been observed. A discrete endurance limit is indicated for each of the three solidification conditions of W319-T7. The scientific and practical implications of this result are discussed. A material model presented previously is modified by introducing a crack growth threshold condition in order to predict the observed endurance limits. The model is shown to effectively predict the influence of solidification time on the fatigue properties of W319-T7.     

Effects of volatile anesthetics on the kinetics of inhibitory postsynaptic currents in cultured rat hippocampal neurons

1. The effects of the volatile anesthetics enflurane, halothane, and isoflurane on gamma-aminobutyric acid (GABA) receptor-mediated inhibitory postsynaptic currents (IPSCs) were studied in cultured rat hippocampal neurons. The experimental concentrations of anesthetics were measured directly using gas chromatography. All three anesthetics increased the overall duration of IPSCs, measured as the time to half-decay (T1/2). Clinically effective concentrations of anesthetics [between 0.5 and 1.5 times MAC (minimum alveolar concentration)] produced between 100 and 400% increases in T1/2. These effects were fully reversible, and did not involve alterations in the reversal potential for the IPSC (EIPSC). 2. The decay of the IPSC was fitted as a sum of two exponential functions, yielding a fast component (tau fast = 20 ms), and a slow component (tau slow = 77 ms), such that the fast component accounted for 79% of the IPSC amplitude and 52% of the total charge transfer. All three anesthetics produced concentration-related increases in the amplitude and charge transfer of the slow component, while simultaneously decreasing the amplitude and charge transfer of the fast component. Thus T1/2 approximated tau fast under control conditions, but approximated tau slow in the presence of the anesthetics. 3. Varying the calcium chelating agents in the recording pipettes had no effect on the quality or magnitude of alterations in IPSC kinetics produced by halothane, suggesting that variations in intracellular calcium levels are not required for the effect of halothane on the time course of the IPSC. 4. The (+)-stereoisomer of isoflurane produced greater increases in the duration of the IPSC than the (-)-isomer when applied at approximately equal concentrations, suggesting that there is a structurally selective site of interaction for isoflurane that modulates the GABAA receptor. 5. These results suggest that the previously shown abilities of volatile anesthetics to potentiate responses to exogenously applied GABA and to prolong the duration of GABA-mediated synaptic inhibition may be due to an alteration in the gating kinetics of the GABAA receptor/channel complex. Prolongation of synaptic inhibition in the CNS is consistent with the physiological effects that accompany anesthesia and may contribute to the mechanism of anesthetic action.     

Intravitreal tolerance of a new perfluorocarbon vitreous replacement, Multifluor APF-144

OBJECTIVE: To evaluate the intravitreal tolerance of a new perfluorocarbon vitreous replacement, Multifluor APF-144 (perfluorotetramethylcyclohexane). DESIGN: Ten New Zealand albino rabbits (one eye from each) underwent vitrectomy. The vitreous was replaced in five eyes with Multifluor APF-144 and in five eyes with saline (control group). OUTCOME MEASURES: Appearance on indirect ophthalmoscopy, electroretinography recordings before and 2, 4 and 8 weeks after vitrectomy, findings on electron and light microscopy at 8 weeks. RESULTS: Endophthalmitis did not develop in any of the eyes. There was no significant change in electroretinography values for the experimental eyes after vitrectomy. No evidence of retinal toxicity was found on light or electron microscopic examination. CONCLUSIONS: Multifluor APF-144 shows promise as a short-term postoperative retinal tamponading agent.     

Human papillomavirus investigation of patients with cervical intraepithelial neoplasia 3, some of whom progressed to invasive cancer

Unstable expansion of the CTG repeats in the 3' untranslated region encoding a member of the protein kinase family in the q13.3 band on chromosome 19 is a mutation specific for myotonic dystrophy. To examine the correlation between clinical expression and CTG trinucleotide repeat length, we carried out Southern blot analysis in a family with myotonic dystrophy. In this pedigree, the expanded CTG repeats were transmitted maternally. The mother had three female children. The mother had about 200 CTG repeats, and the number of repeats for each child was about 800, 1500 and 1600 in birth order. The mother and the patient with 800 repeats were unaware of muscle weakness or myotonia. Symptoms were present from age 3 years in the patient with 1500 repeats and from birth in the one with 1600 repeats. Although the mother menstruated regularly, the patients with 800 and 1500 repeats both menstruated irregularly, and the one with 1600 repeats has never menstruated. The age of onset and severity of the disease were correlated with the size of the expanded repeats. Endocrinological studies revealed that the basal levels of the gonadotropins, PRL and E2 were within normal range, and a pituitary response to LHRH was observed. These data suggest that the amenorrhea and menstrual irregularities were caused by a suprahypophyseal dysfunction. When expanded CTG repeats are transmitted maternally, abnormal products resulting from the metabolic disturbance in the affected mother may harm the fetus in utero. A heterozygous fetus, who has more CTG repeats, may be unable to metabolize the pathologic products sufficiently and therefore may become more severely affected. This may explain the exclusive maternal transmission of congenital myotonic dystrophy.     

Ultrastructural and immunocytochemical features of a case of neuroendocrine carcinoma developing in a prior ileostomy site

A patient who developed a mixed neuroendocrine carcinoma and adenocarcinoma at the site of a previous long-standing ileostomy is reported. The neuroendocrine features are documented by both ultrastructural and immunocytochemical findings. Carcinoma arising in an ileostomy site is rare but has been recorded in patients with long-standing ileostomies after colectomy for chronic inflammatory bowel disease, as in this patient. Neuroendocrine carcinoma developing in this setting apparently has not been described before, however.