A statistical analysis of the growth of small abdominal aortic aneurysms

Screening for abdominal aortic aneurysm has been offered to 13,000 patients. An overall compliance of 76% (range 51-99%) has been achieved. For those with an initial aortic diameter between 29 mm and 45 mm serial ultrasound scans are offered to monitor aortic change. Of the 302 cases followed up by repeated scans, 93 have had more than 5 scans (mean of 7 scans) over a mean time period of 32.1 months (range 15-63 months). The rate of change of all these aneurysms has been calculated using all data points and robust linear regression. It has been possible to postulate an algorithm for aortic growth. The influence of measurement precision and ultrasound quality assurance on the rescan interval is demonstrated and it is suggested that 2 years is a suitable rescan interval for aortas with diameter less than 40 mm.     

When two souls meet

As a nurse specialist working in a regional gender identity unit, Rosemary Grimshaw is frequently called on for advice. Here she describes her role and some common misconceptions about transsexualism.     

A source of response regulator autophosphatase activity: the critical role of a residue adjacent to the Spo0F autophosphorylation active site

Two-component signaling systems are used by bacteria, plants, and lower eukaryotes to adapt to environmental changes. The first component, a protein kinase, responds to a signal by phosphorylating the second component; a response regulator protein that often acts by inducing the expression of specific genes. Response regulators also have an autophosphatase activity that ensures that the proteins are not permanently activated by phosphorylation. The magnitude of this activity varies by at least 1000-fold between various response regulators, and the molecular features responsible for this varied autophosphatase activity have not been clearly defined. Using wild-type and mutant derivatives of the sporulation response regulator Spo0F, it has been demonstrated that a key residue in determining the magnitude of this activity is that at position 56 of Spo0F approximately P; this residue is adjacent to the site of phosphorylation, Asp 54. For example, Spo0F approximately P K56N has a 23-fold greater autophosphatase activity (t1/2 = 8 min) than wild-type Spo0F approximately P (t1/2 = 180 min). It is suggested that, by analogy to the GTPase activity of p21(ras) and by examining the crystallographic structure of Spo0F, that the carboxyamide of the mutant Asn 56 may favorably position a catalytic water near the protein acyl phosphate to promote Spo0F approximately P K56N hydrolysis. It is also deduced that Lys 56 in the wild-type protein is critical for the efficient interaction and phosphoryl transfer between Spo0F and it's cognate protein kinase, KinA. Comparison of the known response regulators shows that inefficient autophosphatases (t1/2 on the order of hours) typically contain an amino acid residue with a long side chain at the position equivalent to 56 in Spo0F, whereas efficient autophosphatases (t1/2 on the order of minutes) frequently contain a residue with a carboxyamide or carboxylate side chain at this position. It appears that, by altering residues adjacent to the active site, the autophosphatase activity of response regulator proteins has been attenuated to match the diverse biological roles played by these proteins.     

First-language acquisition in adolescence: evidence for a critical period for verbal language development

It has been hypothesized that there is a critical period for first-language acquisition that extends into late childhood and possibly until puberty. The hypothesis is difficult to test directly because cases of linguistic deprivation during childhood are fortunately rare. We present here the case of E.M., a young man who has been profoundly deaf since birth and grew up in a rural area where he received no formal education and had no contact with the deaf community. At the age of 15, E.M. was fitted with hearing aids that corrected his hearing loss to 35 dB, and he began to learn verbal Spanish. We describe his language development over the 4-year period since his acquisition of hearing aids and conclude that the demonstrates severe deficits in verbal comprehension and production that support the critical period hypothesis.     

A new model of security for metasystems

With the rapid growth of high-speed networking and microprocessing power, metasystems have become increasingly popular. The need for protection and security in such environments has never been greater. However, the conventional approach to security, that of enforcing a single system-wide policy, will not work for the large-scale distributed systems we envision. Our new model shifts the emphasis from ‘system as enforcer’ to user-definable policies, making users responsible for the security of their objects. This security model has been implemented as part of the Legion project. Legion is an object-oriented metacomputing system, with strong support for autonomy. This includes support for per-object, user-defined policies in many areas, including resource management and security. This paper briefly describes the Legion system, presents our security model, and discusses the realization of that model in Legion.     

Reliability of variables in the kinematic analysis of spring hurdles

The purpose of this study was to investigate the reliability of kinematic variables in spring hurdles and to find out how many trials are needed to achieve reliable data. Seven British National level athletes in sprint hurdles were videotaped and all eight trials of each athlete were digitized from two camera views to produce three dimensional coordinates. The reliability of 28 kinematic variables across eight trials ranged from 0.54 to 1.00 for females and from 0.00 to 0.99 for males. The number of trials needed to reach a certain reliability level was evaluated using Spearman-Brown prophecy formula, and in the worst case (horizontal velocity lost for males) 78 trials would be needed to reach 0.90 reliability. The results showed reasonably high reliability, and the values for the female trials were generally higher than the male trials. The relative height of the hurdles enforces a more demanding clearance for males that can lead to increased variation within the subjects and thus lowered reliability. Subsequently, the results indicate that often more than one trial is needed to provide accurate quantitative results of the technique.