Practical theories for service life prediction of critical aerospace structural components

A new second-order theory was developed for predicting the service lives of aerospace structural components. The predictions based on this new theory were compared with those based on the Ko first-order theory and the classical theory of service life predictions. The new theory gives very accurate service life predictions. An equivalent constant-amplitude stress cycle method was proposed for representing the random load spectrum for crack growth calculations. This method predicts the most conservative service life. The proposed use of minimum detectable crack size, instead of proof load established crack size as an initial crack size for crack growth calculations, could give a more realistic service life

Development and production of a flame retardant, general purpose, pressure sensitive adhesive tape

The specification results for the finished tape properties were as follows: (1) adhesive strength (180 deg peel) on aluminum from 107 to 143 grams per centimeter (0.6 to 0.8 pounds per inch); (2) adhesive strength (180 deg peel) on stainless steel from 71 to 107 grams per centimeter (0.4 to 0.6 pounds per inch); (3) unwind resistance of 536 to 714 grams per centimeter (3 to 4 pounds per inch); (4) tensile strength minimum of 7143 grams per centimeter (40 pounds per inch); (5) elongation from 5 to 10% at break; (6) tear strength, Elmendorf from 200 to 350 grams (0.44 to 0.77 pounds); and (7) tear strength, tongue from 363 to 408 grams (0.8 to 0.9) pounds)

Late Devonian-Carboniferous tectonic evolution within the Firth of Forth, Midland Valley : as revealed from 2D seisimic reflection data

Results of integrated seismic mapping, within the Firth of Forth in the offshore Midland Valley of Scotland, are presented and illustrate aspects of the subsurface structure and tectonic evolution of the Upper Devonian to Carboniferous succession. Evidence for three main phases of tectonic activity has been recognized: (1) Late Devonian to Dinantian fault-controlled subsidence; (2) basin-wide Silesian subsidence, localized inversion and growth folding; (3) Late Silesian dextral transtensional and transpressional strike-slip faulting. During the first phase of tectonic activity, the NNE-trending Mid Forth Fault is interpreted to represent a Late Devonian to Dinantian extensional fault, with a small, mainly Dinantian depocentre developed in the hangingwall block that has subsequently been inverted during Silesian times. A major Late Devonian to Dinantian depocentre also occurs in the hangingwall block of the NE-trending offshore continuation of the Crossgatehall Fault, although it remains unclear whether this mainly Dinantian depocentre was developed during pull-apart as a result of extension or transtensional strike-slip fault movement. The NNE-trending Leven Syncline and Mid Forth Anticline within the hangingwall block of the Mid Forth Fault are interpreted as Silesian synsedimentary growth folds that formed during the second phase of tectonic activity. The peak of this activity occurred during intra-Westphalian B to Westphalian C times. In the third phase, the ENE-trending Inchkeith Fault Zone is interpreted as a Late Silesian transtensional–transpressional strike-slip fault that dextrally offsets the axial trace of the Leven Syncline. Evidence from the Firth of Forth could provide support for regional tectonic models involving mainly dextral strike-slip fault activity during Devonian–Carboniferous times, or mainly sinistral strike-slip during Devonian to Early Carboniferous followed by dextral strike-slip during Late Carboniferous times, for the development of the Upper Devonian and Carboniferous succession. However, the latter model is preferred as it provides the more convincing explanation for our interpretation that the NNE-trending Mid Forth Fault represents a Late Devonian to Dinantian extensional or transtensional fault that was inverted during Silesian times. This inversion may therefore reflect a major change in the regional stress field

What’s the monetary value of your premerchantable timber?

Premerchantable timber is not yet merchantable-in most cases this means the trees are too small to be sold for pulpwood or other commercial products. Sometimes referred to as \u27\u27precommercial or \u27\u27immature, timber stands with average tree diameters less than five inches occupy over 50 million acres in the South-an area roughly the size of North and South Carolina combined

Enhancement of thrust reverser cascade performance using aerodynamic and structural integration

This paper focuses on the design of a cascade within a cold stream thrust reverser during the early, conceptual stage of the product development process. A reliable procedure is developed for the exchange of geometric and load data between a two dimensional aerodynamic model and a three dimensional structural model. Aerodynamic and structural simulations are carried out using realistic operating conditions, for three different design configurations with a view to minimising weight for equivalent or improved aerodynamic and structural performance. For normal operational conditions the simulations show that total reverse thrust is unaffected when the performance of the deformed vanes is compared to the un-deformed case. This shows that for the conditions tested, the minimal deformation of the cascade vanes has no significant affect on aerodynamic efficiency and that there is scope for reducing the weight of the cascade. The pressure distribution through a two dimensional thrust reverser section is determined for two additional cascade vane configurations and it is shown that with a small decrease in total reverse thrust, it is possible to reduce weight and eliminate supersonic flow regimes through the nacelle section. By increasing vane sections in high pressure areas and decreasing sections in low pressure areas the structural performance of the cascade vanes in the weight reduced designs, is improved with significantly reduced levels of vane displacement and stress

Hydrodynamic simulations with the Godunov SPH

We present results based on an implementation of the Godunov Smoothed Particle Hydrodynamics (GSPH), originally developed by Inutsuka (2002), in the GADGET-3 hydrodynamic code. We first review the derivation of the GSPH discretization of the equations of moment and energy conservation, starting from the convolution of these equations with the interpolating kernel. The two most important aspects of the numerical implementation of these equations are (a) the appearance of fluid velocity and pressure obtained from the solution of the Riemann problem between each pair of particles, and (b the absence of an artificial viscosity term. We carry out three different controlled hydrodynamical three-dimensional tests, namely the Sod shock tube, the development of Kelvin-Helmholtz instabilities in a shear flow test, and the "blob" test describing the evolution of a cold cloud moving against a hot wind. The results of our tests confirm and extend in a number of aspects those recently obtained by Cha (2010): (i) GSPH provides a much improved description of contact discontinuities, with respect to SPH, thus avoiding the appearance of spurious pressure forces; (ii) GSPH is able to follow the development of gas-dynamical instabilities, such as the Kevin--Helmholtz and the Rayleigh-Taylor ones; (iii) as a result, GSPH describes the development of curl structures in the shear-flow test and the dissolution of the cold cloud in the "blob" test. We also discuss in detail the effect on the performances of GSPH of changing different aspects of its implementation. The results of our tests demonstrate that GSPH is in fact a highly promising hydrodynamic scheme, also to be coupled to an N-body solver, for astrophysical and cosmological applications. [abridged]Comment: 19 pages, 13 figures, MNRAS accepted, high resolution version can be obtained at http://adlibitum.oats.inaf.it/borgani/html/papers/gsph_hydrosim.pd

Magnetic field structure due to the global velocity field in spiral galaxies

We present a set of global, self-consistent N-body/SPH simulations of the dynamic evolution of galactic discs with gas and including magnetic fields. We have implemented a description to follow the evolution of magnetic fields with the ideal induction equation in the SPH part of the Vine code. Results from a direct implementation of the field equations are compared to a representation by Euler potentials, which pose a div(B)-free description, an constraint not fulfilled for the direct implementation. All simulations are compared to an implementation of magnetic fields in the Gadget code which includes also cleaning methods for div(B). Starting with a homogeneous seed field we find that by differential rotation and spiral structure formation of the disc the field is amplified by one order of magnitude within five rotation periods of the disc. The amplification is stronger for higher numerical resolution. Moreover, we find a tight connection of the magnetic field structure to the density pattern of the galaxy in our simulations, with the magnetic field lines being aligned with the developing spiral pattern of the gas. Our simulations clearly show the importance of non-axisymmetry for the evolution of the magnetic field.Comment: 17 pages, 18 figure

Composition Mixing during Blue Straggler Formation and Evolution

We use smoothed-particle hydrodynamics to examine differences between direct collisions of single stars and binary star mergers in their roles as possible blue straggler star formation mechanisms. We find in all cases that core helium in the progenitor stars is largely retained in the core of the remnant, almost independent of the type of interaction or the central concentration of the progenitor stars. We have also modelled the subsequent evolution of the hydrostatic remnants, including mass loss and energy input from the hydrodynamical interaction. The combination of the hydrodynamical and hydrostatic models enables us to predict that little mixing will occur during the merger of two globular cluster stars of equal mass. In contrast to the results of Proctor Sills, Bailyn, & Demarque (1995), we find that neither completely mixed nor unmixed models can match the absolute colors of observed blue stragglers in NGC 6397 at all luminosity levels. We also find that the color distribution is probably the crucial test for explanations of BSS formation - if stellar collisions or mergers are the correct mechanisms, a large fraction of the lifetime of the straggler must be spent away from the main sequence. This constraint appears to rule out the possibility of completely mixed models. For NGC 6397, unmixed models predict blue straggler lifetimes ranging from about 0.1 to 4 Gyr, while completely mixed models predict a range from about 0.6 to 4 Gyr.Comment: AASTeX, 28 pg., accepted for ApJ, also available at http://ucowww.ucsc.edu/~erics/bspaper.htm

Kelvin-Helmholtz instabilities in Smoothed Particle Hydrodynamics

In this paper we investigate whether Smoothed Particle Hydrodynamics (SPH), equipped with artificial conductivity, is able to capture the physics of density/energy discontinuities in the case of the so-called shearing layers test, a test for examining Kelvin-Helmholtz (KH) instabilities. We can trace back each failure of SPH to show KH rolls to two causes: i) shock waves travelling in the simulation box and ii) particle clumping, or more generally, particle noise. The probable cause of shock waves is the Local Mixing Instability (LMI), previously identified in the literature. Particle noise on the other hand is a problem because it introduces a large error in the SPH momentum equation. We also investigate the role of artificial conductivity (AC). Including AC is necessary for the long-term behavior of the simulation (e.g. to get $\lambda=1/2, 1$ KH rolls). In sensitive hydrodynamical simulations great care is however needed in selecting the AC signal velocity, with the default formulation leading to too much energy diffusion. We present new signal velocities that lead to less diffusion. The effects of the shock waves and of particle disorder become less important as the time-scale of the physical problem (for the shearing layers problem: lower density contrast and higher Mach numbers) decreases. At the resolution of current galaxy formation simulations mixing is probably not important. However, mixing could become crucial for next-generation simulations.Comment: 16 pages, 23 figures, accepted for publication in MNRA

A protein microarray assay for serological determination of antigen-specific antibody responses following Clostridium difficile infection

We provide a detailed overview of a novel high-throughput protein microarray assay for the determination of anti-C. difficile antibody levels in human sera and in separate preparations of polyclonal IVIg. The protocol describes the methodological steps involved in sample preparation, printing of arrays, assay procedure and data analysis. In addition, this protocol could be further developed to incorporate diverse clinical samples including plasma and cell culture supernatants. Herein, a combination of isotype (IgG, IgA IgM), subclass (IgG1, IgG2, IgG3, IgG4, IgA1, IgA2), and strain-specific antibodies to highly purified whole C. difficile toxins A and B (toxinotype 0, strain VPI 10463, ribotype 087), toxin B from a C. difficile toxin-B-only expressing strain (CCUG 20309), precursor form of B fragment of binary toxin, pCDTb, ribotype-specific whole surface layer proteins (SLPs; 001, 002, 027) and control proteins (Tetanus toxoid and Candida albicans) were determined by protein microarray. Microarrays were probed with sera from individuals with C. difficile infection (CDI), cystic fibrosis (CF) without diarrhea, healthy controls and individuals pre- and post-IVIg therapy for treatment of CDI, combined immunodeficiency disorder and chronic inflammatory demyelinating polyradiculopathy. Significant differences in toxin neutralization efficacies and multi-isotype specific antibody levels were seen between patient groups, commercial preparations of IVIg and sera before and following IVIg administration. A significant correlation was observed between microarray and enzyme-linked immunosorbent assay (ELISA) for antitoxin IgG levels in serum samples. These results suggest that microarray could become a promising tool for profiling antibody responses to C. difficile antigens in vaccinated or infected humans. With further refinement of antigen panels and a reduction in production costs, it is anticipated that microarray technology may help optimize and select the most clinically useful immunotherapies for C. difficile infection in a patient-specific manner