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The introduction of endoscopy of the upper digestive tract as a routine diagnostic procedure has increased the number of duodenal biopsy specimens. Consequently, the pathologist is often asked to evaluate them. In this review, a practical approach to the evaluation of a duodenal biopsy specimen is discussed. An overview of the handling of specimens is given and the normal histology and commonly encountered diseases are discussed. Finally, a description of commonly seen infections is provided, together with an algorithmic approach for diagnosis. [ABSTRACT FROM AUTHOR]

Large 2-level Toeplitz systems arise in a variety of applications (see, e.g., [R. H. Chan and M. Ng, SIAM Rev., 38 (1996), pp. 427-482]) for which efficient numerical methods for their solution are required. Some successful numerical techniques need the explicit knowledge of the generating function f of the considered system Tn(f)x = b, an assumption that usually is not fulfilled in real applications. In this paper we analyze and complete the procedure proposed in [D. Noutsas, S. Serra Capizzano, and P. Vassalos, Numer. Linear Algebra Appl., 12 (2005), pp. 231-239] for the 2-level case. In such a way, from the knowledge of the coefficients of Tn(f), we determine optimal preconditioning strategies for the solution of our systems. Finally, some numerical experiments are performed and discussed in connection with our theoretical analysis. [ABSTRACT FROM AUTHOR]

Abstract: A series of pyrrolidine-based β-amino alcohols derived from malic acid, citramalic acid and pantolactone with primary amines was prepared and their activity as chiral ligands in the enantioselective alkylation of benzaldehyde using diethylzinc was studied. [Copyright &y& Elsevier]

Large 2-level Toeplitz systems arise in many applications and thus an efficient strategy for their solution is often needed. The already known methods require the explicit knowledge of the generating function ƒ of the considered system Tnm(ƒ)x=b, an assumption that usually is not fulfilled in real applications. In this paper, we extend to the 2-level case a technique proposed in the literature in such a way that, from the knowledge of the coefficients of Tnm(ƒ), we determine optimal preconditioning strategies for the solution of our systems. More precisely, we propose and analyse an algorithm for the economical computation of minimal features of ƒ that allow us to select optimal preconditioners. Finally, we perform various numerical experiments which fully confirm the effectiveness of the proposed idea. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Starting from the finite difference discretization of an elliptic second order PDE as−∑i,j=1d∂/∂xiai,j(x)∂/∂xjai,j(x)∂/∂xju(x)=b(x)over a bounded domain, we introduce the notion of generalized locally Toeplitz sequence of matrices. The singular value distribution (the eigenvalue distribution in the Hermitian case) is studied and characterized for generalized locally Toeplitz sequences in terms of weighted multidimensional Szego˝ formulas. This extends preceding results attributed to Tilli which concern the unilevel case. The application of this theoretic analysis to the numerical solution of PDEs is finally discussed. [Copyright &y& Elsevier]

Superlinear preconditioners (those that provide a proper cluster at 1) are very important for the cg-like methods since they make these methods converge superlinearly. As is well known, for Toeplitz matrices generated by a continuous symbol, many circulant and circulant-like (related to different matrix algebras) preconditioners were proved to be superlinear. In contrast, for multilevel Toeplitz matrices there has been no proof of the superlinearity of any multilevel circulants. In this paper we show that such a proof is not possible since any multilevel circulant preconditioner is not superlinear, in the general case of multilevel Toeplitz matrices. Moreover, for matrices not necessarily Toeplitz, we present some general results proving that many popular structured preconditioners cannot be superlinear. [ABSTRACT FROM AUTHOR]

A multi-scale dataset consisting of multi-beam echo-sounder, 2D multi-channel seismic and sidescan sonar (TOBI) data allows us to identify a large variety of morphologies originating from sedimentary and tectonic processes along the São Vicente Canyon (SVC), which is the largest submarine canyon developed in the external part of the Gulf of Cadiz. The SVC is located in one of the most seismogenic areas of Western Europe. The convergence between the Eurasian and African plates has controlled the formation and evolution of the canyon. The SVC is tectonically controlled by three main thrust faults: the Marquês de Pombal Fault, the São Vicente Fault and the Horseshoe Fault. No major rivers feed sediment to the canyon head, but the main sediment source is related to the dismantling of canyon flanks and the MOW (Mediterranean Overflow Water). This current contributes sediments by two different processes: a) conturites deposition at the head and flanks of the SVC that periodically fail into the canyon; and b) the coarser-grained and denser sediment of the MOW might be trapped at the head of the canyon and could develops into hyperpycnal flows. The SVC is characterized by retrogressive erosion being submarine landslide deposits and scars the main seafloor morphologies. The tectonic and stratigraphic interpretation of seismic profiles indicate that the SVC is a clear example of a diachronous and segmented canyon developed since the Late Miocene in an area of present-day active plate tectonics. This study investigates the interaction between active tectonics, the dynamics of submarine canyons and the resulting geomorphologies. • Largest submarine canyons may not be associated to river systems. • Canyons can be generated by folding during a compressive stage. • Young canyons are conditioned by active fault systems. • Flank erosion and bottom currents are the sediment sources of canyons without a river connection. • Submarine landslides are the main source of retrogressive erosion. [ABSTRACT FROM AUTHOR]

‐ Several novel organocatalysts derived from β‐ and γ‐lactam‐fused thiazolidines and L‐phenylalanine‐based thiazolidines were efficiently synthetized. These organocatalysts, as well as other previously developed thiazolidine‐derived thioureas, were tested in the asymmetric one‐pot Neber reaction of β‐ketoxime‐1H‐tetrazoles towards chiral 2‐(tetrazol‐5‐yl)‐2H‐azirines. The results obtained when using thioureas only differing in the lactam ring size demonstrate that the presence of the 6β‐lactam ring in the catalysts is a requirement to achieve high enantioselectivity in the studied transformation. The new 6β‐aminopenicillanic acid‐derived thiourea afforded the R enantiomer of 3‐phenyl‐2‐(tetrazol‐5‐yl)‐2H‐azirine with >99 % ee. [ABSTRACT FROM AUTHOR]