Pilocytic astrocytomas of the posterior fossa. A follow-up study in 33 patients

The extent of resection in pilocytic astrocytoma of the posterior fossa often remains undefined and the indications for further treatment in incompletely resected tumours are a matter of debate. It has been also realized that the problem of hydrocephalus in patients with pilocytic astrocytoma of the posterior fossa has not yet been solved and the diagnostic impact of postoperative CT findings remains questionable. We retrospectively reviewed the data from 33 patients harbouring a pilocytic astrocytoma of the posterior fossa to evaluate the impact of surgical technique in terms of radicality and of postoperative imaging results upon prognosis and adjunctive treatment. In addition, the issue of hydrocephalus was considered and related to different treatment modalities. Thirty patients underwent surgical treatment whereas 3 had open biopsy of the tumour. Macroscopically gross total resection of the tumour was performed in 20 patients, whereas resection was partial in 10. Follow-up was obtained in 29 patients for a period which ranged between 2 and 184 months (85 months +/- 56 months). Outcome was good in 24 patients who had only slight neurological deficit and poor in 3 patients, who were severely disabled. Two patients died during the follow-up period. Recurrent tumour growth occurred in 2 cases with incompletely resected tumours. From the series presented, it was concluded that long-term follow-up with CT seems mandatory in cases with contrast-enhancing residual tumour. Recurrent tumour growth should be assumed in postsurgical patients with an enlarging area of enhancement shown in follow-up CT studies. Permanent ventriculoperitoneal shunting is required in certain patients with pre- or postoperative hydrocephalus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impurity Distribution Behavior in Caprolactam Extraction with Environmentally Benign Mixed Solvents

In a previous study a solvent mixture of heptane containing 40 mass % heptanol was selected as an alternative in the industrial extraction of caprolactam to replace benzene, toluene, or chlorinated hydrocarbons. This work reports the equilibrium distribution ratio of caprolactam and four model impurities of organic nature, namely, cyclohexanone, aniline, n‐methylcaprolactam, and cyclohexane‐carboxamide, comparing the mixed solvents with toluene as a reference. The resulting phase equilibria were interpreted using the equilibrium stage model. Based on these calculations it was found that, compared to toluene, the co‐extracted fraction of cyclohexanone and aniline was higher, that of n‐methylcaprolactam was comparable, and that of cyclohexane‐carboxamide was lower using the mixed solvent. Overall, the mixed solvent reduced the fraction of co‐extracted impurities by almost 10 %.     

Occurrence of the mycotoxins ochratoxin A, zearalenone and deoxynivalenol in feed components.

The mycotoxin contamination of feed components used by the Dutch cooperative feed industry was surveyed to estimate the risk for animal production losses. Of 89 randomly and 6 selectively taken samples of raw materials harvested in 1988 and 1989 27% were contaminated with ochratoxin A (OCHRA), 31% with zearalenone (ZEA) and 20% with deoxynivalenol (DON). The mean content (microgram/kg) of all positive randomly taken samples was 18 (OCHRA), 62 (ZEA) and 630 (DON). The highest level (microgram/kg) for all samples was 120 (OCHRA) in barley, 3100 (ZEA) in corn cob mix and 1900 (DON) in maizegluten feed. The results of this survey show that feed components are often contaminated with mycotoxins. However, the contamination level could only sporadically cause production losses in animal husbandry.     

Hydrological simulations in the Rhine basin.

Simulations with regional climate models (RCMs), carried out for the Rhine basin, have been analyzed in the context of implications of the possible future discharge of the Rhine river. In a first analysis, the runoff generated by the RCMs is compared to observations, in order to detect the way the RCMs treat anomalies in precipitation in their land surface component. A second analysis is devoted to the frequency distribution of area averaged precipitation, and the impact of selection of various driving global climate models.     

Analysis of Restart Mechanisms in Software Systems

Restarts or retries are a common phenomenon in computing systems, for instance, in preventive maintenance, software rejuvenation, or when a failure is suspected. Typically, one sets a time-out to trigger the restart. We analyze and optimize time-out strategies for scenarios in which the expected required remaining time of a task is not always decreasing with the time invested in it. Examples of such tasks include the download of Web pages, randomized algorithms, distributed queries, and jobs subject to network or other failures. Assuming the independence of the completion time of successive tries, we derive computationally attractive expressions for the moments of the completion time, as well as for the probability that a task is able to meet a deadline. These expressions facilitate efficient algorithms to compute optimal restart strategies and are promising candidates for pragmatic online optimization of restart timers     

Accidents,often the result of an ‘uncontrolled business process’—a study in the (Dutch) chemical industry

Often companies in the (petro‐) chemical industry claim that all possible countermeasures against potential accidents have been taken and therefore accidents are unforeseeable. In this paper we question this statement by analysing the pre‐warning signals (precursors) preceding a number of industrial accidents. 17 accidents that occurred in the (petro‐) chemical industry have been investigated by exploring FACTS, an accident database containing information about industrial accidents worldwide. This paper will demonstrate that the existence of precursor information could have been used to foresee and even prevent these accidents if a proper control action had been initiated. The accidents are analysed further, according to a control model, which was adapted from that of C. Argyris. It demonstrates the ineffectiveness of several elements of business process control loops and that the so‐called ‘double‐loop learning’ cycle is more important than the ‘single‐loop learning’ cycle if one considers safety improvement. Copyright © 2003 John Wiley & Sons, Ltd.     

A method to estimate the initial length of equine tendons

A procedure is described by which the length of a tendon at the onset of loading is determined objectively. The procedure includes the fitting of third-order polynomial functions on the load-elongation data. The onset of loading is detected by an increasing fit of the polynomial by selective data reduction of the initial part of the load-elongation curve. The procedure results in an objective and reproducible definition of the zero strain level of a tendon.