7,809 research outputs found
The Two Modes of Visual Processing: Implications for Spatial Orientation
The roles of the focal and ambient visual systems in spatial orientation are discussed. The two modes are defined and compared. The contribution of each system is illustrated through examples such as spatial disorientation/motion sickness, vehicle guidance/night driving, visual narrowing under stress/cortical brain damage, and aircraft instrumentation. Emphasis is placed on the need for testing procedures for the ambient system
Free edge strain concentrations in real composite laminates: Experimental-theoretical correlation
The magnitude of the maximum shear strain at the free edge of axially loaded theta (2)/-theta(2)(s) and (+ or - theta(2) (s) composite laminates was investigated experimentally and numerically to ascertain the actual value of strain concentration in resin matrix laminates and to determine the accuracy of finite element results. Experimental results using moire interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates. Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isoparametric finite element provided the best and most trouble free numerical results. The results indicate that the ratio of maxium shear strain at the free edge to applied axial strain varies with fiber orientation and does not exceed nine for the most critical angle which is 15 deg
Thermal expansion of composites using Moire interferometry
An experimental technique for precise measurement of the thermal response of fiber-reinforced composite materials uses moire interferometry with fringe multiplication which yield a sensitivity of 833 nm (32.8 mu in.) per fringe. Results from the technique are compared with those obtained from electrical resistance strain gages, and also those predicted from classical lamination theory. Temperature dependent coefficients of thermal expansion for composite materials subjected to thermal cycling in the temperature range of 297 K (75 F) to 422 K (300 F) were determined for four laminate configurations (0, 90, 0/ + or - 45/90 sub s and 0/90/ + or - 45 sub s) of T300/5208 graphite epoxy, and ranged from -0.107 mu epsilon K/1 (-0.059 mu epsilon deg F/-) for the 0 laminate to 32.18 mu epsilon K/1 (17.88 mu epsilon F/1) for the 90 laminate. Moisture was found to greatly influence the thermal response of a quasi-isotropic laminate, resulting in hysteresis and residual compressive strain as the moisture content was reduced. Comparisons between moire and strain gage measurements were inconclusive with both techniques giving consistent but systematically different results. Differences of as much as 29% were observed
A New Pathway for the Preparation of Highly Qualified Teachers: The Master of Arts in Teaching (MAT)
This article reports on the development and initial implementation of a Master of Arts in Teaching (MAT) degree, an accelerated graduate program that encourages and scaffolds individuals with existing disciplinary expertise in entering the teaching profession. First, the context for developing the program is outlined. Next, the unique structure of the 15-month program, which consists of three blocks, is described. Expectations about students are then shared, quality control features of the program are highlighted, and the lessons we learned about program development and implementation are detailed. Finally, thoughts about the future of this program and others of its type are shared based upon our experience
Maxwell's theory on a post-Riemannian spacetime and the equivalence principle
The form of Maxwell's theory is well known in the framework of general
relativity, a fact that is related to the applicability of the principle of
equivalence to electromagnetic phenomena. We pose the question whether this
form changes if torsion and/or nonmetricity fields are allowed for in
spacetime. Starting from the conservation laws of electric charge and magnetic
flux, we recognize that the Maxwell equations themselves remain the same, but
the constitutive law must depend on the metric and, additionally, may depend on
quantities related to torsion and/or nonmetricity. We illustrate our results by
putting an electric charge on top of a spherically symmetric exact solution of
the metric-affine gauge theory of gravity (comprising torsion and
nonmetricity). All this is compared to the recent results of Vandyck.Comment: 9 pages, REVTeX, no figures; minor changes, version to be published
in Class. Quantum Gra
Regulation of Acetylated Low Density Lipoprotein Uptake in Macrophages by Pertussis Toxin-Sensitive G Proteins
Class A scavenger receptors (SR-A) mediate the uptake of modified low density lipoprotein (LDL) by macrophages. Although not typically associated with the activation of intracellular signaling cascades, results with peritoneal macrophages indicate that the SR-A ligand acetylated LDL (AcLDL) promotes activation of cytosolic kinases and phospholipases. These signaling responses were blocked by the treatment of cells with pertussis toxin (PTX) indicating that SR-A activates Gi/o-linked signaling pathways. The functional significance of SR-A-mediated Gi/o activation is not clear. In this study, we investigated the potential role of Gi/o activation in regulating SR-A-mediated lipoprotein uptake. Treatment of mouse peritoneal macrophages with PTX decreased association of fluorescently labeled AcLDL with cells. This inhibition was dependent on the catalytic activity of the toxin confirming that the decrease in AcLDL uptake involved inhibiting Gi/o activation. In contrast to the inhibitory effect on AcLDL uptake, PTX treatment did not alter β-VLDL-induced cholesterol esterification or deposition of cholesterol. The ability of polyinosine to completely inhibit AcLDL uptake, and the lack of PTX effect on β-VLDL uptake, demonstrated that the inhibitory effect is specific for SR-A and not the result of non-specific effects on lipoprotein metabolism. Despite having an effect on an SR-A-mediated lipoprotein uptake, there was no change in the relative abundance of SR-A protein after PTX treatment. These results demonstrate that activation of a PTX-sensitive G protein is involved in a feedback process that positively regulates SR-A function
Merging fragments of classical logic
We investigate the possibility of extending the non-functionally complete
logic of a collection of Boolean connectives by the addition of further Boolean
connectives that make the resulting set of connectives functionally complete.
More precisely, we will be interested in checking whether an axiomatization for
Classical Propositional Logic may be produced by merging Hilbert-style calculi
for two disjoint incomplete fragments of it. We will prove that the answer to
that problem is a negative one, unless one of the components includes only
top-like connectives.Comment: submitted to FroCoS 201
Relativistic contraction and related effects in noninertial frames
Although there is no relative motion among different points on a rotating
disc, each point belongs to a different noninertial frame. This fact, not
recognized in previous approaches to the Ehrenfest paradox and related
problems, is exploited to give a correct treatment of a rotating ring and a
rotating disc. Tensile stresses are recovered, but, contrary to the prediction
of the standard approach, it is found that an observer on the rim of the disc
will see equal lengths of other differently moving objects as an inertial
observer whose instantaneous position and velocity are equal to that of the
observer on the rim. The rate of clocks at various positions, as seen by
various observers, is also discussed. Some results are generalized for
observers arbitrarily moving in a flat or a curved spacetime. The generally
accepted formula for the space line element in a non-time-orthogonal frame is
found inappropriate in some cases. Use of Fermi coordinates leads to the result
that for any observer the velocity of light is isotropic and is equal to ,
providing that it is measured by propagating a light beam in a small
neighborhood of the observer.Comment: 15 pages, significantly revised version, title changed, to appear in
Phys. Rev.
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