Dual-stage tertiary creep of a ceramic matrix composite

The creep behaviour of an alumina fibre/silicon carbide matrix composite has been studied. The creep curves are characterised by a short primary stage followed by one or two tertiary stages. The secondary regime of this composite is limited to a single point. The occurrence of one or two tertiary stages in the creep behaviour is discussed, and some theoretical considerations are invoked to explain this behaviour. Creep in this composite is controlled by two mechanisms, namely viscoplastic creep of the alumina fibres and damage accumulation within the composite. The two tertiary stages differ in the damage mechanisms occurring, the first one being related to fibre–matrix debonding only, whereas successive fibre failure dominates in the second part. The second tertiary regime occurs only at low creep stresses, for which a non-catastrophic rupture of the composite is observed.     

Primary epiploic appendagitis: US and CT findings

A retrospective review is presented of seven cases of epiploic appendagitis, with surgical confirmation in one case. The main clinico-analytical data and the US and CT findings are described, as well as the histopathologic features in the sole case that underwent surgical resection. We also calculated the frequency of this entity in patients undergoing emergency abdominal US on clinical suspicion of diverticulitis. In all seven cases the clinico-analytical evidence was nonspecific (localized acute abdominal pain and slight leukocytosis), mimicking in six cases the clinical presentation of sigmoid diverticulitis and in one case that of acute appendicitis. US imaging findings were characteristic: a hyperechoic mass localized under the point of maximum pain, adjacent to the anterior peritoneal wall and fixed during deep breathing. In none of the cases did color Doppler US show flow. CT findings were also typical and showed a mass with a peripheral hyperattenuated rim surrounding an area of fatty attenuation. Overall 7.1 % of patients investigated to exclude sigmoid diverticulitis finally showed findings of primary epiploic appendagitis. Primary epiploic appendagitis thus shows characteristic US and CT findings that allow its diagnosis and follow-up. This entity is much more frequent than previously reported, especially in patients referred for US to exclude sigmoid diverticulitis.     

Mapping of B epitopes in GRA4, a dense granule antigen of Toxoplasma gondii and protection studies using recombinant proteins administered by the oral route

GRA4, a dense granule protein of Toxoplasma gondii elicits both mucosal and systemic immune responses following oral infection of mice with cysts. We studied the antigenicity and immunogenicity of truncated and soluble forms of GRA4 expressed as glutathione S-transferase fusion proteins in Escherichia coli. Protein C (amino-acids 297-345) was particularly well recognized by serum IgG antibodies, milk IgA antibodies and intestinal IgA antibodies from T. gondii infected mice and by serum IgG antibodies from T. gondii infected humans and T. gondii infected sheep. One major B epitope was localized within the last 11 C-terminal residues of GRA4. A second epitope, recognized with lower frequency, was mapped within the region 318-334. In contrast, the N domain of GRA4 (amino acids 25-276) was poorly recognized. Oral immunization of C57BL/6 mice with N, C or NC (amino acids 25-276 fused to 297-345) in association with cholera toxin induced a significant production of serum anti-GRA4 IgG antibodies but a weak and inconsistent intestinal anti-GRA4 IgG antibody response and afforded partial resistance to oral infection with T. gondii. These results provide new molecular and immunological understanding of GRA4 and indicate that it is a potential candidate for oral vaccination against T. gondii.     

Antibody responses in humans against coli surface antigen 6 of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains expressing only coli surface antigen 6 (CS6) have previously been isolated from patients with diarrhea, but the immunogenicity of CS6 has not been established in humans. We have detected CS6-specific immunoglobulin A responses in the feces and blood of patients convalescing from natural ETEC disease and of volunteers given an oral ETEC vaccine.     

A Fast Method for Finding the Basis of Non-negative Solutions to a Linear Diophantine Equation

We present a complete characterization of the set of minimal solutions of a single linear Diophantine equation in three unknowns over the natural numbers. This characterization, for which we give a geometric interpretation, is based on well-known properties of congruences and we use it as the foundation of direct algorithms for solving this particular kind of equation. These direct algorithms and an enumeration procedure are then put together to build an algorithm for solving the general case of a Diophantine equation over the naturals. We also put forth a statistical method for comparing algorithms for solving Diophantine equations which is more sound than comparisons based on times observed for small sets of equations. From an extensive comparison with algorithms described by other authors it becomes clear that our algorithm is the fastest known to date for a class of equations. Typically the equations in this class have a small number of unknowns in one side, the maximum value for their coefficients being greater than 3.     

Structure and photoluminescence of the a-Gex Se1-x, system

Alloys of this system in the composition range 0 < x < $\text{1}\text{2}$ are composed of Se chains, Se₈ rings, Ge(Se_{$\text{1}\text{2}$})₄ tetrahedral, Ge₂$\text{(Se}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_6$ ethane-like and Ge(Se_{$\text{1}\text{2}$})₂ structural units in proportions varying to comply with the actual x values. The glass forming tendency has minima at the stoichiometric compositions GeSe₂ and GeSe and maxima at $\text{x =}\text{1}\text{6}$ and $\text{x =}\text{3}\text{7}$ where the fractions of two coexisting structural units are nearly equal, $\text{i.e.}$ the number product of different bounds (Se-Se, Ge-Se) is maximal. Within the $\text{1}\text{3}$ < x < $\text{1}\text{2}$ composition range, and in non-relaxed samples even at smaller x values, ethane-like 2 (Se₃Ge)-[Ge(Se_{$\text{1}\text{2}$})₃]_n -units probably also exist. Photoluminescence (PL) is most efficient in the stoichionetric compound GeSe₂ having a rigid three-dimensional structure. The PL band is strongly Stokes shifted and thus situated in the middle of the forbidden band except for x = 0.5 where the PL is due to band-toband transitions. Defects of the bonding configurations attributable either to distortions in the structure or to irregular under-and over-coordinated atoms formed during preparation or irradiation witn band gap photons serve as PL centres. The decrease of PL intensity (fatigue) during excitation is caused by the creation of non-radiative centres whose concentration can reach 10²⁰ cm^t3?. Different models accounting for most of the observations are coinpared and discrepancies between their predictions and the experimental data are pointed out.