16,796 research outputs found
Lessons learned for composite structures
Lessons learned for composite structures are presented in three technology areas: materials, manufacturing, and design. In addition, future challenges for composite structures are presented. Composite materials have long gestation periods from the developmental stage to fully matured production status. Many examples exist of unsuccessful attempts to accelerate this gestation period. Experience has shown that technology transition of a new material system to fully matured production status is time consuming, involves risk, is expensive and should not be undertaken lightly. The future challenges for composite materials require an intensification of the science based approach to material development, extension of the vendor/customer interaction process to include all engineering disciplines of the end user, reduced material costs because they are a significant factor in overall part cost, and improved batch-to-batch pre-preg physical property control. Historical manufacturing lessons learned are presented using current in-service production structure as examples. Most producibility problems for these structures can be traced to their sequential engineering design. This caused an excessive emphasis on design-to-weight and schedule at the expense of design-to-cost. This resulted in expensive performance originated designs, which required costly tooling and led to non-producible parts. Historically these problems have been allowed to persist throughout the production run. The current/future approach for the production of affordable composite structures mandates concurrent engineering design where equal emphasis is placed on product and process design. Design for simplified assembly is also emphasized, since assembly costs account for a major portion of total airframe costs. The future challenge for composite manufacturing is, therefore, to utilize concurrent engineering in conjunction with automated manufacturing techniques to build affordable composite structures. Composite design experience has shown that significant weight savings have been achieved, outstanding fatigue and corrosion resistance have been demonstrated, and in-service performance has been very successful. Currently no structural design show stoppers exist for composite structures. A major lesson learned is that the full scale static test is the key test for composites, since it is the primary structural 'hot spot' indicator. The major durability issue is supportability of thin skinned structure. Impact damage has been identified as the most significant issue for the damage tolerance control of composite structures. However, delaminations induced during assembly operations have demonstrated a significant nuisance value. The future challenges for composite structures are threefold. Firstly, composite airframe weight fraction should increase to 60 percent. At the same time, the cost of composite structures must be reduced by 50 percent to attain the goal of affordability. To support these challenges it is essential to develop lower cost materials and processes
Polarization perception device
A polarization perception device comprises a base and a polarizing filter having opposite broad sides and a centerline perpendicular thereto. The filter is mounted on the base for relative rotation and with a major portion of the area of the filter substantially unobstructed on either side. A motor on the base automatically moves the filter angularly about its centerline at a speed slow enough to permit changes in light transmission by virtue of such movement to be perceived as light-dark pulses by a human observer, but fast enough so that the light phase of each such pulse occurs prior to fading of the light phase image of the preceding pulse from the observer's retina. In addition to an observer viewing a scene in real time through the filter while it is so angularly moved, or instead of such observation, the scene can be photographed, filmed or taped by a camera whose lens is positioned behind the filter
CRIMES AND OFFENSES Amendments to Criminal Statutes: Allow Previous Prosecutions to Continue
The Act provides a universal saving clause for pending criminal prosecutions when the prosecution is pursuant to a statute which has been legislatively repealed, repealed and reenacted, or amended prior to conviction. March 16, 198
CRIMES AND OFFENSES Amendments to Criminal Statutes: Allow Previous Prosecutions to Continue
The Act provides a universal saving clause for pending criminal prosecutions when the prosecution is pursuant to a statute which has been legislatively repealed, repealed and reenacted, or amended prior to conviction. March 16, 198
A Recursion Formula for Moments of Derivatives of Random Matrix Polynomials
We give asymptotic formulae for random matrix averages of derivatives of
characteristic polynomials over the groups USp(2N), SO(2N) and O^-(2N). These
averages are used to predict the asymptotic formulae for moments of derivatives
of L-functions which arise in number theory. Each formula gives the leading
constant of the asymptotic in terms of determinants of hypergeometric
functions. We find a differential recurrence relation between these
determinants which allows the rapid computation of the (k+1)-st constant in
terms of the k-th and (k-1)-st. This recurrence is reminiscent of a Toda
lattice equation arising in the theory of \tau-functions associated with
Painlev\'e differential equations
CRIMINAL PROCEDURE Bills of Indictment: Limit Presentations to Grand Jury
The Act limits to two the number of times a prosecutor can offer a true bill of indictment to a grand jury for the same offense where the indictment was previously quashed by a court. July 1, 198
Behavior of shell-model configuration moments
An important input into reaction theory is the density of states or the level
density. Spectral distribution theory (also known as nuclear statistical
spectroscopy) characterizes the secular behavior of the density of states
through moments of the Hamiltonian. One particular approach is to partition the
model space into subspaces and find the moments in those subspaces; a
convenient choice of subspaces are spherical shell-model configurations. We
revisit these configuration moments and find, for complete
many-body spaces, the following behaviors: (a) the configuration width is
nearly constant for all configurations; (b) the configuration asymmetry or
third moment is strongly correlated with the configuration centroid; (c) the
configuration fourth moment, or excess is linearly related to the square to the
configuration asymmetry. Such universal behavior may allow for more efficient
modeling of the density of states in a shell-model framework.Comment: 12 pages, 8 figure
The Skylab concentrated atmospheric radiation project
The author has identified the following significant results. Comparison of several existing infrared radiative transfer models under somewhat controlled conditions and with atmospheric observations of Skylab's S191 and S192 radiometers illustrated that the models tend to over-compute atmospheric attenuation in the window region of the atmospheric infrared spectra
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