Improved accuracy for finite element structural analysis via a new integrated force method

A comparative study was carried out to determine the accuracy of finite element analyses based on the stiffness method, a mixed method, and the new integrated force and dual integrated force methods. The numerical results were obtained with the following software: MSC/NASTRAN and ASKA for the stiffness method; an MHOST implementation method for the mixed method; and GIFT for the integrated force methods. The results indicate that on an overall basis, the stiffness and mixed methods present some limitations. The stiffness method generally requires a large number of elements in the model to achieve acceptable accuracy. The MHOST method tends to achieve a higher degree of accuracy for course models than does the stiffness method implemented by MSC/NASTRAN and ASKA. The two integrated force methods, which bestow simultaneous emphasis on stress equilibrium and strain compatibility, yield accurate solutions with fewer elements in a model. The full potential of these new integrated force methods remains largely unexploited, and they hold the promise of spawning new finite element structural analysis tools

REJECTION OF ASCITES TUMOR ALLOGRAFTS : I. ISOLATION, CHARACTERIZATION, AND IN VITRO REACTIVITY OF PERITONEAL LYMPHOID EFFECTOR CELLS FROM BALB/c MICE IMMUNE TO EL4 LEUKOSIS

Peritoneal exudate cells (PEC), obtained after the rejection of EL4 leukemia by BALB/c mice, are much more effective in the specific in vitro destruction of 51Cr-labeled EL4 cells than are spleen, thymus, lymph node, or peripheral blood lymphocytes. The presence of a large number of effector cells at the site of graft rejection is reflected in the potent cytolytic activity seen in vitro. Effector cells temporarily lose cytolytic reactivity when treated with trypsin but regain reactivity with time. This recovery occurs in normal as well as in immune serum. The destructive reactivity of PEC is increased when macrophages are removed. The remaining population of nonadherent PEC is composed primarily of small- to medium-sized lymphocytes. Complex tissue culture media are not needed, but there is a definite requirement for serum. The required serum component is heat stable, nondialyzable, and is not consumed during the reaction. The use of an ascites allograft system made these observations possible and permitted the isolation of those host cells intimately associated with rejection

REJECTION OF ASCITES TUMOR ALLOGRAFTS : II. A PATHWAY FOR CELL-MEDIATED TUMOR DESTRUCTION IN VITRO BY PERITONEAL EXUDATE LYMPHOID CELLS

A pathway for cell-mediated tumor destruction in vitro by immune peritoneal exudate lymphoid cells has been proposed. The union of lymphocytes and tumor cells precedes the formation of an intermediate phase leading to lysis. The initial interaction is only partially temperature dependent. The cytolytic process per se is highly temperature dependent, being negligible at 25°C but proceeding rapidly at 37°C. 51Cr release from tumor cells is demonstrable within 10 min at 37°C and can be reversibly arrested by cooling. Once initiated, lysis is largely independent of additional interactions and continues at almost full rate for 30 min. The effector cells are not lysed and appear to be free to enter into further effector cycles

ICDP workshop on the Lake Victoria Drilling Project (LVDP):Scientific Drilling of the World’s Largest Tropical Lake

Lake Victoria, which is bordered by Uganda, Tanzania, Kenya and has a catchment that extends to Rwanda and Burundi, is home to the largest human population surrounding any lake in the world and provides critical resources across eastern Africa. Lake Victoria is also the world’s largest tropical lake by surface area, but it is relatively shallow and without a major inlet, making it very sensitive to changes in climate, and especially hydroclimate. Furthermore, its size creates abundant habitats for aquatic fauna, including the iconic hyper-diverse cichlids, and serves as a major geographic barrier to terrestrial fauna across equatorial Africa. Given Lake Victoria’s importance to the eastern African region, its sensitivity to climate, and its influences on terrestrial and aquatic faunal evolution and dispersal, it is vital to understand the connection between the lake, regional climate, and how the lake size, shape, and depth has changed through its depositional history. This information can only be ascertained by collecting a complete archive of Lake Victoria’s sedimentary record. To evaluate Lake Victoria basin as a potential drilling target, ~50 scientists from 10 countries met in Dar es Salaam, Tanzania in July 2022 for the International Continental Scientific Drilling Program (ICDP) sponsored Lake Victoria Drilling Project (LVDP) workshop. Discussions of the main scientific objectives for a future drilling project included: 1) recovering the Pleistocene and Holocene sedimentary records of Lake Victoria that document the dynamic nature of the lake, including multiple lacustrine and paleosol sequences; 2) establishing the chronology of recovered sediments, including using extensive tephra fingerprinting and other techniques from deposits in the region; 3) reconstructing past climate, environment, lacustrine conditions, and aquatic fauna, using an integrated multi-proxy approach, combined with climate and hydrologic modeling; and 4) connecting new records with existing sedimentary snapshots and fossils exposed in deposits around the lake, tying archeological, paleontological, sedimentological, tectonic, and volcanic findings to new drilling results. The LVDP provides an innovative way to address critical geological, paleontological, climatological, and evolutionary biological questions about Quaternary to modern landscapes and ecosystems in eastern Africa. Importantly, this project affords an excellent opportunity to help develop conservation and management strategies for regional responses to current and future changes in climate, land use, fisheries, and resiliency of at-risk communities in equatorial Africa

Chemistry of chromium bis-acetylide complexes

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)2Cr(dmpe)2] n+ (R=Ph, SiMe3, SiEt3, C≡C-SiMe3 n=0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. Graphical Abstrac

Structural Optimization Using the Newton Modified Barrier Method

The Newton Modified Barrier Method (NMBM) is applied to structural optimization problems with large a number of design variables and constraints. This nonlinear mathematical programming algorithm was based on the Modified Barrier Function (MBF) theory and the Newton method for unconstrained optimization. The distinctive feature of the NMBM method is the rate of convergence that is due to the fact that the design remains in the Newton area after each Lagrange multiplier update. This convergence characteristic is illustrated by application to structural problems with a varying number of design variables and constraints. The results are compared with those obtained by optimality criteria (OC) methods and by the ASTROS program

A General-Purpose Optimization Engine for Multi-Disciplinary Design Applications

A general purpose optimization tool for multidisciplinary applications, which in the literature is known as COMETBOARDS, is being developed at NASA Lewis Research Center. The modular organization of COMETBOARDS includes several analyzers and state-of-the-art optimization algorithms along with their cascading strategy. The code structure allows quick integration of new analyzers and optimizers. The COMETBOARDS code reads input information from a number of data files, formulates a design as a set of multidisciplinary nonlinear programming problems, and then solves the resulting problems. COMETBOARDS can be used to solve a large problem which can be defined through multiple disciplines, each of which can be further broken down into several subproblems. Alternatively, a small portion of a large problem can be optimized in an effort to improve an existing system. Some of the other unique features of COMETBOARDS include design variable formulation, constraint formulation, subproblem coupling strategy, global scaling technique, analysis approximation, use of either sequential or parallel computational modes, and so forth. The special features and unique strengths of COMETBOARDS assist convergence and reduce the amount of CPU time used to solve the difficult optimization problems of aerospace industries. COMETBOARDS has been successfully used to solve a number of problems, including structural design of space station components, design of nozzle components of an air-breathing engine, configuration design of subsonic and supersonic aircraft, mixed flow turbofan engines, wave rotor topped engines, and so forth. This paper introduces the COMETBOARDS design tool and its versatility, which is illustrated by citing examples from structures, aircraft design, and air-breathing propulsion engine design

Soft computing methods in design of superalloys

Soft computing techniques of neural networks and genetic algorithms are used in the design of superalloys. The cyclic oxidation attack parameter K(sub a), generated from tests at NASA Lewis Research Center, is modeled as a function of the superalloy chemistry and test temperature using a neural network. This model is then used in conjunction with a genetic algorithm to obtain an optimized superalloy composition resulting in low K(sub a) values