Trimorphodon tau

Number of Pages: 2Integrative BiologyGeological Science

Error detection and control for nonlinear shell analysis

A problem-adaptive solution procedure for improving the reliability of finite element solutions to geometrically nonlinear shell-type problem is presented. The strategy incorporates automatic error detection and control and includes an iterative procedure which utilizes the solution at the same load step on a more refined model. Representative nonlinear shell problem are solved

Study of a Proposed Infrared Horizon Scanner for Use in Space-Orientation Control Systems

An attitude-sensing device for space vehicles which detects the thermal radiation discontinuity at opposite horizons of a planetary body to produce an attitude error signal is described. The planetary body may be the Earth, its Moon, Mars, or Venus. The sensor is expected to have an accuracy of 0.25 degrees for the Earth, a long continuous operating lifetime, a wide altitude range, a wide capture capability, and an inherent ability to produce signals indicating vehicle altitude. An experimental model incorporating many of the features of the proposed sensor indicates that the proposed sensor will be low in weight, volume, and power consumption. The sensor's altitude range, accuracy, lifetime, and sensitivity to radiation from the Moon and planets are discussed

Global/local stress analysis of composite panels

A method for performing a global/local stress analysis is described, and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as boundary conditions for the local model. Then, the local model is analyzed independent of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. This approach also reduces the computational effort necessary to obtain the detailed stress state. Criteria for applying the method are developed. The effectiveness of the method is demonstrated using a classical stress concentration problem and a graphite-epoxy blade-stiffened panel with a discontinuous stiffener

The Buoyant Behavior of Viral and Bacterial DNA in Alkaline CsCl

In equilibrium density gradient centrifugation, the banding polymer species is electrically neutral. The banding species for a negative polyelectrolyte with a polyanion P_(n)^(-z)n (where n is the degree of polymerization, and z the titration charge per monomer unit) in a CsCl salt gradient is CS_(zn)P_n. If the ion P_(n)^(-z)n is itself a weak acid, it may be titrated to the state P_(n)^(-(Zn+y)) by CsOH; the banding species is then Cs_(zn+y)P_n. Because of the large mass and high effective "density" of a Cs^+ ion, it is to be expected that the buoyant density in a CsCl gradient of a polymer acid will be increased by such a partial alkaline titration with CsOH. This expectation has been confirmed for polyglutamic acid (where z = 0 at low pH). The guanine and thymine monomer units of DNA are weak acids. The present communication is concerned with the increase in buoyant density of DNA in alkaline CsCl solutions. It is well known that the guanine and thymine protons are more readily titrated in denatured DNA than in native DNA. We find that the buoyant density of denatured DNA and of single strand ϕX-174 DNA gradually increases as the pH of the solution is increased beyond pH 9.8. The density of native DNA is not affected until a critical pH > 11 is reached, where the DNA abruptly denatures and increases in density. Similar increases in buoyant density have been observed independently by Baldwin and Shooter in their studies of 5BU[overbar]-substituted DNA's in alkaline solutions

Josephson Junctions with a synthetic antiferromagnetic interlayer

We report measurements of the critical current vs. Co thickness in Nb/Cu/Co/Ru/Co/Cu/Nb Josephson junctions, where the inner Co/Ru/Co trilayer is a "synthetic antiferromagnet" with the magnetizations of the two Co layers coupled antiparallel to each other via the 0.6 nm-thick Ru layer. Due to the antiparallel magnetization alignment, the net intrinsic magnetic flux in the junction is nearly zero, and such junctions exhibit excellent Fraunhofer patterns in the critical current vs. applied magnetic field, even with total Co thicknesses as large as 23 nm. There are no apparent oscillations in the critical current vs. Co thickness, consistent with theoretical expectations for this situation. The critical current of the junctions decays over 4 orders of magnitude as the total Co thickness increases from 3 to 23 nm. These junctions may serve as useful templates for future explorations of spin-triplet superconducting correlations, which are predicted to occur in supercon- ducting/ferromagnetic hybrid systems in the presence of certain types of magnetic inhomogeneity.Comment: 4 pages, 5 figure