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Open abdominal surgery is frequently complicated by the subsequent development of an incisional hernia. Consequently, more than 400,000 incisional hernia repairs are performed each year, adding over $15 billion per year to U.S. health-care expenditures. While the vast majority of studies have focused on improved surgical techniques or prosthetic materials, we examined the use of metallic silver microparticles to prevent incisional hernia formation through enhanced wound healing.A rodent incisional hernia model was used. Eighty-two rats were randomly placed into two control groups (saline alone and silver microparticles alone), and three experimental groups (0 mg/cm, 2.5 mg/cm, and 25 mg/cm of silver microparticles applied with a fibrin sealant). Incisional hernia incidence and size, tensile strength, and tissue histology were assessed after 28 days.A significant reduction of both incisional hernia incidence and hernia size was observed between the control groups and 2.5 mg/cm group, and between the control and 25 mg/cm group by nearly 60% and 90%, respectively (P 0.05). Histological samples showed a noticeable increase in new fibrosis in the treated animals as compared with the controls, whereas the tensile strength between the groups did not differ.The novel approach of using silver microparticles to enhance wound healing appears to be a safe and effective method to prevent incisional hernias from developing and could herald a new era of medicinal silver use.

We give a brief overview of the GGMRES method, the MGMRES method, and the LAN/MGMRES method, which are generalizations and modifications of the Generalized Minimum Residual (GMRES) method.

Background. Without angiogenesis, tumor growth is limited to a few millimeters, the limit of diffusion. Vascular endothelial growth factor (VEGF) is an endothelial-specific mitogen and a major regulator of angiogenesis. Methods. To investigate the relationship between VEGF and thyroid tumor angiogenesis, we xenografted human dermal matrix inoculated with FTC-133 cells into nude mice or directly injected FTC-133 cells subcutaneously. To block the function of VEGF, the neutralizing anti-VEGF monoclonal antibody A.4.6.1 (mAb A.4.6.1) was injected intraperitoneally twice weekly. As control, an antibody of the same isotype (Ab 5B6) or phosphate buffer saline solution (PBS) was used. To evaluate the dermal matrix as a model for angiogenesis studies, recombinant human VEGF was inoculated into the dermal matrix pocket and xenografted into mice. Results. In the dermal matrix angiogenesis model, the number of blood vessels paralleled the concentration of recombinant human VEGF and was highest at 100 ng/mL. Mice that were treated with the mAb A4.6.1 developed fewer blood vessels (mean, 6.6 per HPF) than control mice (18 per HPF in Ab 5B6 and 22 per HPF in PBS; P

This paper is concerned with parallel alternating-type iterative methods for solving large sparse linear systems of the form Au = b arising in the numerical solution of partial differential equations by finite difference methods. Examples of alternating-type methods include the alternating direction implicit (ADI) method and the unsymmetric SOR (USSOR) method. Each iteration of an alternating-type method involves the use of two parameters, say ϱ and ϱ ′. We consider parallel alternating-type methods where, given an initial vector u (0) , the positive integer m , and two sets of m parameters “ϱ i ” and “ϱ′ j ” , one carries out m 2 single iterations in parallel, each involving one pair ( ϱ i , ϱ ′ j ) of the parameters. It is shown that in some cases a linear combination v ∗ of the vectors thus obtained is the same as the vector v ∗∗ which would be obtained by a sequential process involving m iterations based on the successive use of the parameter pairs ( ϱ 1 , ϱ ′ 1 ), ( ϱ 2 , ϱ ′ 2 ),…, ( ϱ m , ϱ ′ m ). Thus, the parallel procedure offers the potential of reducing the wall-clock time by a factor of m as compared with the sequential procedure. Preliminary numerical results based on the use of a virtual parallel system of sequential computers confirm the expected reductions in the number of iterations.

The object of this paper is to present a historical overview of the development of iterative methods for the solution of large sparse systems of linear equations. The emphasis is on methods which are applicable to linear systems arising in the numerical solution of partial differential equations. Aspects to be covered including the methods of L.F. Richardson and of Liebmann as well as relaxation methods used by Southwell and others; the SOR method and extensions such as block SOR methods, and p-cyclic matrices; Chebyshev polynomial methods; alternating direction implicit methods; the SSOR method; approximate matrix factorization methods including the strongly implicit method (SIP) and the incomplete Cholesky method (ICC); fast direct methods; conjugate gradient methods; adaptive methods for the automatic determination of iteration parameters; multigrid methods; methods for nonsymmetric systems; and iterative software. Future developments will be discussed with emphasis on the use of vector and parallel processors.

Recent papers by Faber and Manteuffel characterize the cases where ORTHODIR, a generalized conjugate-gradient algorithm for solving complex non-Hermitian linear systems, can be defined by a short recurrence formula and thus simplified. In the present paper similar results are obtained for two other generalized conjugate-gradient algorithms, namely, ORTHOMIN and ORTHORES. Necessary and sufficient conditions on the coefficient matrix A are given so that simplification is possible. Illustrative examples are given.

The conjugate-gradient (CC) method, developed by Hestenes and Stiefel in 1952, can be effectively used to solve the linear system Au = b when A is symmetrixable in the sense that ZA and Z are symmetric and positive definite (SPD) for some Z. A number of generalizations of the CG method have been proposed by the authors and by others for handling the nonsymmetrizable case. For many problems the amount of computer memory and computational effort required may be so large as to make the procedures not feasible. Truncated schemes are often used, but in some cases the truncated methods may not converge even though the nontruncated schemes converge. However, it is well known that if A is symmetric, the generalized CG schemes can be greatly simplified, even though A is not SPD, so that the truncated schemes are equivalent to the nontruncated schemes. In the present paper it is shown that such a simplification can occur if a nonsingular matrix H is available such that HA = ATH. (Of course, if A = AT, then H can be taken to be the identity matrix.) It is also shown that such an H always exists; however, it may not be practical to compute H. These results are used to derive three variations of the Lanczos method for solving nonsymmetrizable systems. Two of the forms are well known, but the third appears to be new. An argument is given for choosing the third form over the other two.

A preliminary report is given on the ITPACK project for developing adaptive iterative algorithms and software for solving large sparse PDE-related linear systems of equations. These iterative procedures are implemented in a collection of Fortran subroutines.

Conjugate-gradient acceleration provides a powerful tool for speeding up the convergence of a symmetrizable basic iterative method for solving a large system of linear algebraic equations with a sparse matrix. The object of this paper is to describe three generalizations of conjugate-gradient acceleration which are designed to speed up the convergence of basic iterative methods which are not necessarily symmetrizable. The application of the procedures to some commonly used basic iterative methods is described.

The incidence of infection with Campylobacter jejuni was determined in individuals with and without diarrheal disease seen at a hospital in Changsha, China. Stool specimens were cultured by two methods: one developed by the Chinese and a second control method used commonly in the United States. Among people with diarrhea, 18.7% of the 48 children and 8.7% of 104 adults were infected with Campylobacter jejuni . In the group without diarrhea, 8.6% of 105 children but none of 76 adults tested had the organism in their stool. Of the 27 total positive cultures, the Chinese method was positive in 26, compared with 21 for the control method. The Chinese culture method was at least as sensitive and specific as the American method. The biochemical characteristics and antibiotic sensitivities of Chinese isolates were similar to organisms isolated in other parts of the world. This study shows that Campylobacter jejuni is a common enteric pathogen in China and that the asymptomatic carrier state of this organism is significant in children.

Mice were chronically exposed to between 1 × 10 −8 and 5 × 10 −9 M plasma methotrexate (MTX) for 2 months. No signs of toxicity were manifested except minor facial hair loss. At the end of this time they were sacrificed, and the activity of dihydrofolate reductase in crude Tris extracts of small intestine, femur, liver and kidney was determined at pH 7.0 and 8.6. At pH 7.0 the enzyme activity was maintained at control levels in small intestine and femur but was decreased to half of controls in liver and kidney. The enzyme activity at pH 8.6 was increased significantly above controls in small intestine and femur but remained at control levels in liver and kidney. These results suggest that some organs adapt to the chronic presence of MTX by increasing their enzyme synthesis rate while other organs are able to function normally for prolonged periods of time with less than normal amounts of active enzyme.

Over the past several years a number of research-oriented software packages for solving large sparse systems of linear algebraic equations have been developed within the Center for Numerical Analysis as part of the ITPACK Project. This report includes a brief discussion of each of the packages. References are given to other reports and papers which describe the individual packages in more detail.