Inversion of rational polynomial matrices

The letter is concerned with automatic computational procedures for the inversion of a matrix where every element is a rational function. Two possible methods are considered: one based on the Gaussian elimination algorithm and the other based on the Faddeev algorithm.     

Radiation patterns of paraboloid with log-periodic dipole feed

The effect of axial displacement of phase centre on the secondary performance of a parabolic reflector is described, with particular reference to a log-periodic dipole-array feed. Computed and experimental results are presented.     

Analysis of a structural polymorphism in the 5-HT2A receptor and clinical response to clozapine

Clozapine is an atypical antipsychotic with affinity for a broad range of receptors, including serotonin (5-HT) and dopamine receptors. It is successful in treating about 60% of patients refractory to other antipsychotic drugs. Since genetic variation in clozapine's neurotransmitter receptor targets may affect clinical response through altering drug binding or receptor expression, we have studied a His452Tyr polymorphism in the 5-HT2A receptor (HTR2A) in a sample of 153 schizophrenic patients undergoing clozapine treatment and 178 normal controls. An association was found between the allele Tyr452 and poor clinical response.     

Reflections on replacement

In the United States, the total fertility rate is about 1.9 births per woman, down from a peak of 3.2 a generation ago and below the replacement level of 2.1 children. The proportion of women who will never have children has risen from 8% a generation ago to approximately 18% in 1993. The increase in the proportion of women in the labor force, a proximate explanation of the recent decline in intended fertility, is expected to continue. The demographic consequence is declining population with an older age structure. A pronatalist policy to alleviate this outcome, through monetary transfers from taxpayers to potential parents, is not only unlikely to succeed, it is politically unfeasible. An alternative solution, immediately effective but politically unpalatable, would be a generous immigration policy. Even with replacement level fertility, the population is destined to become much older. This inevitable aging of the population should be countered by appropriate institutional transformations: 1) with lower fertility, a larger proportion of women will be available to participate in the labor force to generate taxes needed to support a larger number of pensioners; 2) the institutional practice of ascribing a dependent status to anyone above a particular age can be changed; 3) concerns that an older labor force will have an obsolete education (and fewer years of it) can be countered by changing access to education. Yet, the most serious question is not merely the net reproduction rate, but producing adequate numbers of new adult citizens with responsibility and technical training in the modern world. The fundamental process of socializing children may be jeopardized by replacing the full-time parent with the hired care-giver, the peer group, and the television set. The attenuation of the bonds between parent and child may devalue the worth of childbearing itself. These portentous consequences deserve consideration.     

Space-use strategy is an important determinant of PCB concentrations in female polar bears in the Barents Sea

Space-use was examined in 54 female polar bears (Ursus maritimus) from Svalbard and the Barents Sea that were collared with satellite transmitters to provide information on their spatial positions and annual home range sizes. Plasma samples from the same animals were analyzed for concentrations of six relevant PCB congeners (PCB-99, -153, -156, -180, -194, and -118). Factors related to space-use strategy (such as home range size; annual, spring, and winter longitudinal position; and spring and summer latitudinal position) were important determinants of PCB concentrations in plasma. In addition, reproductive status of the polar bears and plasma lipid content affected PCB concentrations. Among the tested variables, annual home range size was the variable that affected sigmaPCB5 (sum of PCB-99, -153, -156, -180, and -194) to the largest degree (r2 = 0.22). We propose that the positive effect of home range size on sigmaPCB5 in female polar bears is related to the higher energetic costs required to occupy large home range sizes as compared to small home range sizes. Polar bears with large home range sizes would need to consume more prey than bears with small home range sizes, and increased feeding without a change in elimination of persistent compounds can explain their higher sigmaPCB5 concentrations. Polar bears with large home range sizes were also more pelagic, inhabiting areas further east, closer to the ice-edge zone than animals with small home range sizes. Thus, prey choice associated with a pelagic space-use strategy may also explain the higher sigmaPCB5 in polar bears with large home range sizes.     

Strain hardening and anisotropy in tensile fracture properties of sheared model Mozzarella cheeses

We studied the tensile fracture properties of model Mozzarella cheeses with varying amounts of shear work input (3.3–73.7 kJ/kg). After manufacture, cheeses were elongated by manual rolling at 65°C followed by tensile testing at 21°C on dumbbell-shaped samples cut both parallel and perpendicular to the rolling direction. Strain hardening parameters were estimated from stress–strain curves using 3 different methods. Fracture stress and strain for longitudinal samples did not vary significantly with shear work input up to 26.3 kJ/kg and then decreased dramatically at 58.2 kJ/kg. Longitudinal samples with shear work input <30 kJ/kg demonstrated significant strain hardening by all 3 estimation methods. At shear work inputs <30 kJ/kg, strong anisotropy was observed in both fracture stress and strain. After a shear work input of 58.2 kJ/kg, anisotropy and strain hardening were absent. Perpendicular samples did not show strain hardening at any level of shear work input. Although the distortion of the fat drops in the cheese structure associated with the elongation could account for some of the anisotropy observed, the presence of anisotropy in the elongated nonfat samples reflected that shear work and rolling also aligned the protein structure.