We survey the known results characterising those monoids S such that the classes of free, projective or (weakly, strongly) flat S-acts are first order axiomatisable. The conditions on the monoid S that arise are finitary, and intricately related. We examine their inter-connections and illustrate the independence of certain pairs.

We have studied some geometric properties of conharmonically flat Sasakian manifold and an Einstein-Sasakian manifold satisfying R(X, Y ).N = 0. We have also obtained some results on special weakly Ricci symmetric Sasakian manifold and have shown that it is an Einstein manifold. AMS Mathematics Subject Classification (2000): 53C21, 53C25

Let M4 be an open 4-manifold with boundary. Conditions are given under which M4 is homeomorphic to <9Afx[0, 1). Applications include a 4-dimensional weak /¡-cobordism theorem and a classification of weakly flat embeddings of 2-spheres in 5"*. Specific examples of (n-2)-spheres embedded in S" (including n = 4) are also discussed.

Longevity is a life-history trait that is shaped by natural selection. Evolution will shape mortality trajectories and lifespans, but until now the evolutionary analysis of longevity is based principally on a density-independent (Euler-Lotka) framework. The effects of density dependence on the evolution of lifespan and mortality remain largely unexplored. We investigate the influence of differe...

Flat panel catheter angiotomography, a recently developed angiographic technique, offers a spinal equivalent to the venous phase obtained during cerebral angiography. This report of 8 clinical cases discusses the flat panel catheter angiotomography appearance of a type of spinal venous structure until now principally known through the analysis of postmortem material, transmedullary venous anast...

We evaluated the role of aberrant crypt foci (ACF) as biomarkers of colon cancer by studying the sequential development (6-28 weeks) from early lesion to tumor in the colon of azoxymethane-exposed F344 rats (15 mg/kg bw x 2). Surface examination of unsectioned methylene blue-stained colon preparations, transilluminated in the inverse light microscope, revealed two types of early lesions: classi...

We study a class of timelike weakly extremal surfaces in flat Minkowski space R, characterized by the fact that they admit a C parametrization (in general not an immersion) of a specific form. We prove that if the distinguished parametrization is of class C, then the surface is regularly immersed away from a closed singular set of euclidean Hausdorff dimension at most 1 + 1/k, and that this bou...