Mean sojourn times in two-queue fork-join systems: bounds and approximations

This paper considers a fork-join system (or: parallel queue), which is a two-queue network in which any arrival generates jobs at both queues and the jobs synchronize before they leave the system. The focus is on methods to quantify the mean value of the ‘system’s sojourn time’ S: with S _i denoting a job’s sojourn time in queue i, S is defined as max{S ₁, S ₂}. Earlier work has revealed that this class of models is notoriously hard to analyze. In this paper, we focus on the homogeneous case, in which the jobs generated at both queues stem from the same distribution. We first evaluate various bounds developed in the literature, and observe that under fairly broad circumstances these can be rather inaccurate. We then present a number of approximations, that are extensively tested by simulation and turn out to perform remarkably well.     

Predicted mechanical properties of a coiled carbon nanotube

Nanostructured carbon materials continue to attract much interest for use in devices and as fillers in composites. Here, classical molecular dynamics simulations are carried out using many-body empirical potentials to contrast the mechanical properties of straight and coiled carbon nanotubes. The specific properties of a coiled carbon nanotube (CCNT) are investigated under compression, tension, re-compression, re-tension and pullout from a polyethylene (PE) matrix. The stress–strain curves, spring constants, and yielding strains under compression and tension are given for each system, and the corresponding reasons for the differences in their behavior are discussed. They indicate that the interaction between a CCNT and a PE matrix is stronger than the corresponding interactions between CNTs and PE. Thus, the results indicate that CCNTs are good potential candidates for lightweight, tough composites.     

Kinetic and kinematic responses of post mortem human surrogates and the Hybrid III ATD in high-speed frontal sled tests

Despite improvements in vehicle design and safety technologies, frontal automotive collisions continue to result in a substantial number of injuries and fatalities each year. Although a considerable amount of research has been performed on PMHSs and ATDs, matched dynamic whole-body frontal testing with PMHSs and the current ATD aimed at quantifying both kinetic and kinematic data in a single controlled study is lacking in the literature. Therefore, a total of 4 dynamic matched frontal sled tests were performed with three male PMHSs and a Hybrid III 50th percentile male ATD (28.6 g, Δv = 40 kph). Each subject was restrained using a 4 kN load limiting, driver-side, 3-point seatbelt. Belt force was measured for the lap belt and shoulder belt. Reaction forces were measured at the seat pan, seat back, independent foot plates, and steering column. Linear head acceleration, angular head acceleration, and pelvic acceleration were measured for all subjects. Acceleration of C7, T7, T12, both femurs, and both tibias were also measured for the PMHSs. A Vicon motion analysis system, consisting of 12 MX-T20 2 megapixel cameras, was used to quantify subject 3D motion (±1 mm) at a rate of 1 kHz. Excursions of select anatomical regions were normalized to their respective initial positions and compared by test condition and between subject types. Notable discrepancies were observed in the responses of the PMHSs and the ATD. The reaction forces and belt loading for the ATD, particularly foot plate, seat back, steering column, and lap belt forces, were not in agreement with those of the PMHSs. The forward excursions of the ATD were consistently within those of the PMHSs with the exception of the left upper extremity. This could potentially be due to the known limitations of the Hybrid III ATD shoulder and chest. The results presented herein demonstrate that there are some limitations to the current Hybrid III ATD under the loading conditions evaluated in the current study. Overall, this study presents a comprehensive data set of belt forces, reaction forces, accelerations, and bilateral displacement data that can be used to evaluate the performance of ATDs and validate computational models.     

Disseminated islands of gastric mucosa in jejunum and ileum detected by technetium-99m-pertechnetate scintigraphy

Disseminated islands of gastric mucosa are very rare in the small intestine. The secretion of hydrochloric acid can lead to ulceration which results in gastrointestinal bleeding. It is often difficult to localize the focus in case of gastrointestinal blood loss especially in the small bowel. Technetium-99m-pertechnetate scintigraphy may be a helpful tool in detecting ectopic gastric mucosa. We report a case of a 21-mo-old boy with recurrent gastrointestinal bleeding. By using pertechnetate scintigraphy, extensive tracer accumulation in the jejunum and proximal ileum was detected. Histologically, multiple islands of ectopic gastric mucosa were found in about 50 excited mucosal and transmural biopsies. The unusual finding of disseminated accumulation of 99mTc-pertechnetate in the small intestine was the diagnostic clue for such a rare disease.     

Ability to obtain medical care for the uninsured: how much does it vary across communities?

The genes for p53, neu (c-erbB-2) and nm23 are all located on chromosome 17. Abnormal expression of their protein products is an important prognostic parameter. The aim of this study was to investigate if numerical aberrations of chromosome 17 are reflected in the expression of these markers. The immunohistochemical expression was analysed on histological specimens from 33 breast carcinomas. In situ hybridization (ISH) was performed on interphase cell nuclei in air-dried fine-needle aspirates from the same cases using a digoxigenin-labelled alpha-satellite probe for chromosome 17. ISH for chromosome 6, 7 and 12 was used additionally to give an estimate of ploidy. Of the carcinomas 76% were aneuploid, and numerical abnormalities of chromosome 17 were found in 34%. Abnormal p53 protein was expressed in 15% (five cases). All of these were aneuploid, but only one of them revealed aneusomy of chromosome 17. Neu overexpression was found in 18% of the tumours (six cases). Five of these were aneuploid, whereas two were aneusome for chromosome 17. Four cancers showed full (normal) expression of nm23 protein, whereas 29 had reduced expression. Reduced expression was found in 23 of 25 aneuploid tumours. Numerical aberrations of chromosome 17 were found equally in carcinomas with reduced and full nm23 protein expression. Abnormal numbers of chromosome 17 seem only to have a minor impact on these markers and are not reflected significantly in their expression.