The cubic autocatalator: The influence of degenerate singularities in a closed system

The appearance of apparently chaotic behaviour in this two-dimensional system is examined from an analytical point of view. The original two-parameter model exhibiting numerical solutions resembling chaos is unfolded to a three-parameter model. This enlarged model is shown to have a codimension-two degenerate Hopf bifurcation the unfolding of which contains phase portraits showing three concentric limit cycles. In some regions these limit cycles are so close to each other that numerical integration causes transitions across the unstable limit cycle, giving the appearance of chaotic behaviour. The region in parameter space of the ‘chaotic’ behaviour agrees well with the degenerate behaviour of the enlarged model.     

Tetralogy of Fallot in adults--107 cases

Clinical and haemodynamic profile of 107 adult patients above the age of 15 years with TOF was analysed. Cardiac catherization and selective cine-angiography were performed in all cases. Infundibular pulmonary stenosis, mal-alignment type of ventricular septal defect, mitral-aortic fibrous continuity and equal systolic pressures in both the ventricles and aorta were considered mandatory for the diagnosis of Tetralogy of Fallot. Aortic regurgitation was seen in 26 cases (24%), tricuspid regurgitation in 22 cases (21%), absent pulmonary valve in 3 cases (3%), branch pulmonary artery stenosis in 9 case (8.4%), major aortopulmonary collaterals in 15 cases (14%), right atrial pressure was more than 10 mmHg in 10 cases (11%) and right ventricular end diastolic pressure more than 9 mmHg in 73 cases (68%). The left ventricular end diastolic pressure was above 13 mmHg in 58 cases (54%).     

Distribution of thyrotrophin-releasing hormone receptor messenger RNA in rat pituitary and brain

X-ray diffraction methods have been used to determine the structure of the 8.3 kDa hydrophobic protein from soybean and to refine the atomic co-ordinates to a crystallographic R-factor of 18.7% at 1.8 A resolution. The molecule is a four-helix bundle, which together with the connecting loops and a twisted beta-strand form a spiral. The surface contains 70% apolar atoms, and the crystal packing is dominated by hydrophobic interactions, producing a two-dimensional sheet of protein molecules. Most of the 59 water molecules located are involved in hydrophilic contacts and their structural organization does not seem to be affected by the high hydrophobicity of the molecule. From the protein fold it appears that three of the four disulphide bridges are important for keeping the amino and carboxyl-terminal segments in place in the native form, while the central part of the molecule is stabilized by many hydrophobic interactions. Although the protein function is not known, a number of possibilities can be excluded on experimental grounds and by comparison with other members of the family.     

Exercise hemodynamics in small (< or = 21 mm) aortic valve prostheses assessed by Doppler echocardiography

Exercise Doppler echocardiography was used to assess hemodynamics in 25 patients with a < or = 21 mm aortic valve prosthesis (14 with a Medtronic-Hall 21 mm valve, three with a Medtronic-Hall 20 mm valve, three with a Sorin 21 mm valve, one with a Duromedics 21 mm valve, and four with a Carpentier-Edwards 21 mm valve). A symptom-limited upright bicycle exercise test was performed, and Doppler gradients were recorded during exercise. Gradients increased with exercise from 30 +/- 8/16 +/- 4 mm Hg (peak/mean) at rest to 46 +/- 12/24 +/- 7 mm Hg during exercise; both p < 0.001. Mean exercise gradient exceeded 30 mm Hg in five patients, and the highest mean gradient recorded was 37 mm Hg. Within the group of mechanical valves, gradients at exercise were similar for different types of valves. A linear relationship was found between gradients at rest and during exercise (peak r = 0.75, mean r = 0.77; both p < 0.001). Additional findings were midventricular velocities exceeding 1.5 m/sec in late systole in 10 patients (40%) and intraventricular flow (> or = 0.2 m/sec) toward the apex during isovolumic relaxation in 11 patients (44%). The patients with these velocity patterns had significantly smaller left ventricular cavities (end-diastolic diameter 39.8 +/- 4.8 vs 46.5 +/- 4.2 mm, p < 0.01; end-systolic diameter 24.2 +/- 3.0 vs 28.5 +/- 4.5 mm, p = 0.013).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevention of bacterial endocarditis: recommendations by the American Heart Association

OBJECTIVE: To update recommendations issued by the American Heart Association last published in 1990 for the prevention of bacterial endocarditis in individuals at risk for this disease. PARTICIPANTS: An ad hoc writing group appointed by the American Heart Association for their expertise in endocarditis and treatment with liaison members representing the American Dental Association, the infectious Diseases Society of America, the American Academy of Pediatrics and the American Society for Gastrointestinal Endoscopy. EVIDENCE: The recommendations in this article reflect analyses of relevant literature regarding procedure-related endocarditis, in vitro susceptibility data of pathogens causing endocarditis, results of prophylactic studies in animal models of endocarditis and retrospective analyses of human endocarditis cases in terms of antibiotic prophylaxis usage patterns and apparent prophylaxis failures. MEDLINE database searches from 1936 through 1996 were done using root words endocarditis, bacteremia and antibiotic prophylaxis. Recommendations in this document fall into evidence level III of the U.S. Preventive Services Task Force categories of evidence. CONSENSUS PROCESS: The recommendations were formulated by the writing group after specific therapeutic regimens were discussed. The consensus statement was subsequently reviewed by outside experts not affiliated with the writing group and by the Science Advisory and Coordinating Committee of the American Heart Association. These guidelines are meant to aid practitioners but are not intended as the standard of care or as a substitute for clinical judgment. CONCLUSIONS: Major changes in the updated recommendations include the following: (1) emphasis that most cases of endocarditis are not attributable to an invasive procedure; (2) cardiac conditions are stratified into high-, moderate- and negligible-risk categories based on potential outcome if endocarditis develops; (3) procedures that may cause bacteremia and for which prophylaxis is recommended are more clearly specified; (4) an algorithm was developed to more clearly define when prophylaxis is recommended for patients with mitral valve prolapse; (5) for oral or dental procedures the initial amoxicillin dose is reduced to 2 g, a follow-up antibiotic dose is no longer recommended, erythromycin is no longer recommended for penicillin-allergic individuals, but clindamycin and other alternatives are offered.     

Novel mutants define genes required for the expression of human histocompatibility leukocyte antigen DM: evidence for loci on human chromosome 6p

We and others have shown that the products of the HLA-DM locus are required for the intracellular assembly of major histocompatibility complex class II molecules with cognate peptides for antigen presentation. HLA-DM heterodimers mediate the dissociation of invariant chain (Ii)-derived class II-associated Ii peptides (CLIP) from class II molecules and facilitate the loading of class II molecules with antigenic peptides. Here we describe novel APC mutants with defects in the formation of class II-peptide complexes. These mutants express class II molecules which are conformationally altered, and an aberrantly high percentage of these class II molecules are associated with Ii-derived CLIP. This phenotype resembles that of DM null mutants. However, we show that the defects in two of these new mutants do not map to the DM locus. Nevertheless, our evidence suggests that the antigen processing defective phenotype in these mutants results from deficient DM expression. These mutants thus appear to define genes in which mutations have differential effects on the expression of conventional class II molecules and DM molecules. Our data are most consistent with these factors mapping to human chromosome 6p. Previous data have suggested that the expression of DM and class II genes are coordinately regulated. The results reported here suggest that DM and class II can also be differentially regulated, and that this differential regulation has significant effects on class II-restricted antigen processing.     

Hematologic disorders in children from southeast Asia

The overall laboratory features of the common RBC disorders occurring in Southeast Asians is summarized in Table 4. These erythrocyte disorders will continue to be important public health issues, and it has been predicted that most new cases of thalassemia in the United States will occur in this population group. The fertility rate in Southeast Asian families is very high, with an average of more than five children delivered by each married woman. This number of children is consistent with perceptions of ideal family size, and, to date, no evidence suggests any change in the size of Southeast Asian families who now reside in the United States. Moreover, attitudes about health care, reasons why one seeks medical attention, and a variety of other cultural issues may impair the effectiveness of genetic counseling and other preventive measures designed to reduce the incidence of serious blood diseases. Genetic screening and prenatal diagnosis clearly have led to a markedly decreased incidence of homozygous thalassemia disorders in high-risk Mediterranean populations throughout the world. With further assimilation into Western culture, a similar disease may occur in the Southeast Asian population also.     

Detection of a novel mutation at amino acid position 614 in the ryanodine receptor in malignant hyperthermia

Postural alignment is not an inherent trait. Proper alignment is acquired through training postural muscle groups. This training is based on scientific principles associated with improving the physiological parameters of muscle mechanics. The purpose of this report is to describe and demonstrate the application of exercise physiology training principles to the improvement of postural alignment, which may enhance vocal performance. Specific exercise principles are explained and key concepts highlighted. Selected exercises for training postural muscles are presented to assist in establishing techniques that result in the expected adaptations. The application of training principles to postural muscles has been shown to improve postural alignment by strengthening synergistic muscles and establishing a balance between the agonistic and antagonistic activity of these muscles. Since posture has been well established as an important component of vocal performance, the application of these principles to vocal training seems to warrant the attention of vocal trainers and performers.