Shear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations.

Nanolaminates such as the M(n + 1)AX(n) (MAX) phases are a material class with ab initio derived elasticity tensors published for over 250 compounds. We have for the first time experimentally determined the full elasticity tensor of the archetype MAX phase, Ti(3)SiC(2), using polycrystalline samples and in situ neutron diffraction. The experimental elastic constants show extreme shear stiffness, with c(44) more than five times greater than expected for an isotropic material. Such shear stiffness is quite rare in hexagonal materials and strongly contradicts the predictions of all published MAX phase elastic constants derived from ab initio calculations. It is concluded that second order properties such as elastic moduli derived from ab initio calculations require careful experimental verification. The diffraction technique used currently provides the only method of verification for the elasticity tensor for the majority of new materials where single crystals are not available.

Phenotypic and genotypic characterisation of Pasteurella multocida isolated from pigs at slaughter in New Zealand.

AIMS: To examine pigs at slaughter in New Zealand for the presence of Pasteurella multocida, and to determine for isolates, their biochemical profiles, somatic and capsular types, and the presence or absence of the HSB and toxA genes, associated with haemorrhagic septicaemia (HS) and progressive atrophic rhinitis (PAR), respectively. METHODS: Swabs from 173 lungs, 158 palatine tonsils and 82 nasal passages of pigs at two abattoirs in New Zealand were cultured for P. multocida using conventional techniques, and isolated colonies were subjected to biochemical tests for identification of biovars. Somatic serotyping was conducted using an agar gel immunodiffusion (AGID) test. Polymerase chain reaction (PCR) assays were used to confirm phenotypic identification of colonies using species-specific primers, capsule type using serogroup-specific primers and multiplex PCR, and to test for the presence of HSB and toxA genes. RESULTS: Pasteurella multocida was isolated from 11/173 (6.4%) lung, 32/158 (20.2%) palatine tonsil and 5/82 (6.1 %) nasal swab samples, a total of 48 isolates from 413 samples (11.6%). Isolation rates per farm ranged from 1-53% of tissue samples collected from pigs 5-6 months of age. On phenotypic characterisation, isolates were allocated to seven main biovars, viz 1, 2, 3, 5, 9, 12, and a dulcitol-negative variant of Biovar 8, the majority (30/48) being Biovar 3. Of the 42 isolates for which somatic serotyping was conducted, 10% were Serovar 1, 79% were Serovar 3, 2% were Serovar 6,1, 2% were Serovar 12, and 7% could not be typed. All 48 isolates were confirmed as P. multocida using a species-specific PCR. In the capsular multiplex PCR, 92% of isolates were Capsular (Cap) type A, 2% were Cap D, and 6% could not be typed. None of the samples were positive for the HSB or toxA genes. CONCLUSION: Serovars or capsular types of P. multocida associated with HS or PAR in pigs were not detected. Establishment of species-specific, capsular and toxin PCR assays allowed the rapid screening of isolates of P. multocida, while serotyping provided an additional tool for epidemiological and tracing purposes.

New cross sectional stature, weight, and head circumference references for Down's syndrome in the UK and Republic of Ireland.

AIM: To present a growth reference for children with uncomplicated Down's syndrome living in the UK and Republic of Ireland. Data are available for height and weight in the age range 0-18 years, including the first three months of life, and for head circumference in the first year. METHODS: The study sample was drawn from 16 discrete geographical areas and was representative of children age 19 years of age or less who are now living in the UK and Republic of Ireland. Multiple growth measurements for 1507 children were obtained retrospectively by case note search. Data from children with significant cardiac or other major pathology were excluded from analysis. Data from preterm babies were excluded up to age 2 years. Centile curves were constructed from 5913 selected measurements from 1089 children and were derived using Cole's LMS method. RESULTS: The resulting centiles differ substantially from those previously available in the UK, which were based on selective US data published in 1988. CONCLUSIONS: We propose that these charts should now be adopted as the standard UK/Republic of Ireland reference.

The fragmentation pathways of protonated glycine: a computational study.

Numerous studies have demonstrated that protonated aliphatic amino acids, [H2NCHRCO2H + H]+, fragment in the gas phase to form iminium ions, H2N=CHR+. Unfortunately none of these studies have probed the structure of the neutral(s) lost as well as the mechanism of fragmentation. Three main mechanisms have been previously proposed: (1) loss of the combined elements of H2O and CO; (2) loss of dihydroxycarbene (HO)2C: and (3) loss of formic acid, HC(=O)OH. Herein, ab initio and density functional theory calculations have been used to calculate the key reactants, transition states, and products of these and several other competing reaction channels in the fragmentation of protonated glycine. The loss of the combined elements of H2O and CO is thermodynamically and kinetically favored over the alternative formic acid or (HO)2C fragmentation processes.

An international perspective: APN credentialing.

This article identifies the global environment for the development and regulation of advanced practice nursing; provides a conceptual framework within which to examine regulatory concepts and methods and identify contemporary issues; introduces the worldwide diversity of nursing practice roles, standards, and regulatory systems, including some examples; and proposes a role for American nurse experts in the development of an international movement in advanced practice and in credentialing.