5,233 research outputs found
Early Air Force Flight Test Center (AFFTC) experience with Peripheral Vision Horizon Displays (PVHD)
Three separate Air Force Flight Test Center (AFFTC) tests were conducted in 1980 and 1981 on two models of the peripheral vision horizon displays (PVHD) (Malcolm Horizon). A fixed base simulator test was conducted with twenty test pilot subjects using the Flight Simulator Demonstration Model which incorporated a Helium Neon laser as the light bar medium. Two separate flight tests were conducted by the Test Pilot School classes 80A and 80B in a Twin Otter commuter aircraft using the Stage A Model PVHD. The Xenon lighted A Model was tested in its original configuration by class 80A. Class 80B used a modified configuration which incorporated an AFFTC designed and manufactured hood. With the hood, the PVHD projected a thinner, distinct light bar. Only a few general remarks concerning the tests and unrestricted, overall conclusions reached by the author are presented. The conclusions of all three AFFTC evaluations of the PVHD concept were that it has not yet been adequately evaluated. There seems to be a significant learning curve associated with the PVHD and the project pilots for Test Pilot School Class 80B only got a good start on the learning curve. A lengthy learning curve for the PVHD should be anticipated in view of the training period required for the attitude display indicator (ADI). This does seem to point out that the PVHD, in its present form, is simply not as compelling as the natural horizon. It can also be concluded that any attempt at a valid evaluation of the PVHD concept can be done only under instrument meteorological conditions (IMC) or validly simulated IMC conditions. The knee in the learning curve, however, may be reached without full IMC, although it may take much longer to reach
Interaction Correction of Conductivity Near a Ferromagnetic Quantum Critical Point
We calculate the temperature dependence of conductivity due to interaction
correction for a disordered itinerant electron system close to a ferromagnetic
quantum critical point which occurs due to a spin density wave instability. In
the quantum critical regime, the crossover between diffusive and ballistic
transport occurs at a temperature ,
where is the parameter associated with the Landau damping of the spin
fluctuations, is the impurity scattering time, and is the Fermi
energy. For a generic choice of parameters, is few orders of
magnitude smaller than the usual crossover scale . In the ballistic
quantum critical regime, the conductivity has a temperature
dependence, where is the dimensionality of the system. In the diffusive
quantum critical regime we get dependence in three dimensions, and
dependence in two dimensions. Away from the quantum critical regime
we recover the standard results for a good metal.Comment: 15 pages, 8 figure
The Use of Cognitive Ability Measures As Explanatory Variables In Regression Analysis
Cognitive ability measures are often taken as explanatory variables in regression analysis, e.g., as a factor affecting a market outcome such as an individual’s wage, or a decision such as an individual’s education acquisition. Cognitive ability is a latent construct; its true value is unobserved. Nonetheless, researchers often assume that a test score, constructed via standard psychometric practice from individuals’ responses to test items, can be safely used in regression analysis. We examine problems that can arise, and suggest that an alternative approach, a “mixed effects structural equations” (MESE) model, may be more appropriate in many circumstances
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Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins.
Human gut Bacteroides use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B12 transport in B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut
Energetic Instability Unjams Sand and Suspension
Jamming is a phenomenon occurring in systems as diverse as traffic, colloidal
suspensions and granular materials. A theory on the reversible elastic
deformation of jammed states is presented. First, an explicit granular
stress-strain relation is derived that captures many relevant features of sand,
including especially the Coulomb yield surface and a third-order jamming
transition. Then this approach is generalized, and employed to consider jammed
magneto- and electro-rheological fluids, again producing results that compare
well to experiments and simulations.Comment: 9 pages 2 fi
Predictive Inference Using Latent Variables With Covariates
Plausible values (PVs) are a standard multiple imputation tool for analysis of large education survey data, which measures latent proficiency variables. When latent proficiency is the dependent variable, we reconsider the standard institutionally generated PV methodology and find it applies with greater generality than shown previously. When latent proficiency is an independent variable, we show that the standard institutional PV methodology produces biased inference because the institutional conditioning model places restrictions on the form of the secondary analysts’ model. We offer an alternative approach that avoids these biases based on the mixed effects structural equations model of Schofield (Modeling measurement error when using cognitive test scores in social science research. Doctoral dissertation. Department of Statistics and Heinz College of Public Policy. Pittsburgh, PA: Carnegie Mellon University, 2008)
The effect of curvature and topology on membrane hydrodynamics
We study the mobility of extended objects (rods) on a spherical liquid-liquid
interface to show how this quantity is modified in a striking manner by both
the curvature and the topology of the interface. We present theoretical
calculations and experimental measurements of the interfacial fluid velocity
field around a moving rod bound to the crowded interface of a water-in-oil
droplet. By using different droplet sizes, membrane viscosities, and rod
lengths, we show that the viscosity mismatch between the interior and exterior
fluids leads to a suppression of the fluid flow on small droplets that cannot
be captured by the flat interface predictions.Comment: 4 pages, 3 figure
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