48,671 research outputs found
Far-infrared reflectance of spacecraft coatings
Far infrared reflectance and transmittance as function of wavelength for spacecraft coating
Specification of inputs and instrumentation for flutter testing of multivariable systems
The application of system identification methods in flutter testing of aeroelastic structure is discussed. The accuracy with which flutter parameters are estimated depends upon the test plan and on the algorithms used to reduce the data. The techniques for selecting the kinds and optimal positions of inputs and instrumentation, under typical test constraints, are presented. Identification results for both the input/output transfer function and the value of physical parameters are given. Numerical results on the optimal input spectrum and the accelerometer location for estimating flutter parameters of a two dimensional wing are obtained using these algorithms. Current work on applying system identification methods to high order three dimensional aeroelastic structures is reported
Input design for identification of aircraft stability and control derivatives
An approach for designing inputs to identify stability and control derivatives from flight test data is presented. This approach is based on finding inputs which provide the maximum possible accuracy of derivative estimates. Two techniques of input specification are implemented for this objective - a time domain technique and a frequency domain technique. The time domain technique gives the control input time history and can be used for any allowable duration of test maneuver, including those where data lengths can only be of short duration. The frequency domain technique specifies the input frequency spectrum, and is best applied for tests where extended data lengths, much longer than the time constants of the modes of interest, are possible. These technqiues are used to design inputs to identify parameters in longitudinal and lateral linear models of conventional aircraft. The constraints of aircraft response limits, such as on structural loads, are realized indirectly through a total energy constraint on the input. Tests with simulated data and theoretical predictions show that the new approaches give input signals which can provide more accurate parameter estimates than can conventional inputs of the same total energy. Results obtained indicate that the approach has been brought to the point where it should be used on flight tests for further evaluation
Computer program to generate attitude error equations for a gimballed platform
Computer program for solving attitude error equations related to gimballed platform is described. Program generates matrix elements of attitude error equations when initial matrices and trigonometric identities have been defined. Program is written for IBM 360 computer
A two-compartment mechanochemical model of the roles of\ud transforming growth factor β and tissue tension in dermal wound healing
The repair of dermal tissue is a complex process of interconnected phenomena, where cellular, chemical and mechanical aspects all play a role, both in an autocrine and in a paracrine fashion. Recent experimental results have shown that transforming growth factor−β (TGFβ) and tissue mechanics play roles in regulating cell proliferation, differentiation and the production of extracellular materials. We have developed a 1D mathematical model that considers the interaction between the cellular, chemical and mechanical phenomena, allowing the combination of TGFβ and tissue stress to inform the activation of fibroblasts to myofibroblasts. Additionally, our model incorporates the observed feature of residual stress by considering the changing zero-stress state in the formulation for effective strain. Using this model, we predict that the continued presence of TGFβ in dermal wounds will produce contractures due to the persistence of myofibroblasts; in contrast, early elimination of TGFβ significantly reduces the myofibroblast numbers resulting in an increase in wound size. Similar results were obtained by varying the rate at which fibroblasts differentiate to myofibroblasts and by changing the myofibroblast apoptotic rate. Taken together, the implication is that elevated levels of myofibroblasts is the key factor behind wounds healing with excessive contraction, suggesting that clinical strategies which aim to reduce the myofibroblast density may reduce the appearance of contractures
A fibrocontractive mechanochemical model of dermal wound\ud closure incorporating realistic growth factor kinetics
Fibroblasts and their activated phenotype, myofibroblasts, are the primary cell types involved in the contraction associated with dermal wound healing. Recent experimental evidence indicates that the transformation from fibroblasts to myofibroblasts involves two distinct processes: the cells are stimulated to change phenotype by the combined actions of transforming growth factor β (TGFβ) and mechanical tension. This observation indicates a need for a detailed exploration of the effect of the strong interactions between the mechanical changes and growth factors in dermal wound healing. We review the experimental findings in detail and develop a model of dermal wound healing that incorporates these phenomena. Our model includes the interactions between TGFβ and collagenase, providing a more biologically realistic form for the growth factor kinetics than those included in previous mechanochemical descriptions. A comparison is made between the model predictions and experimental data on human dermal wound healing and all the essential features are well matched
Experimental realization of a Dirac monopole through the decay of an isolated monopole
We experimentally observe the decay dynamics of deterministically created
isolated monopoles in spin-1 Bose-Einstein condensates. As the condensate
undergoes a change between magnetic phases, the isolated monopole gradually
evolves into a spin configuration hosting a Dirac monopole in its synthetic
magnetic field. We characterize in detail the Dirac monopole by measuring the
particle densities of the spin states projected along different quantization
axes. Importantly, we observe the spontaneous emergence of nodal lines in the
condensate density that accompany the Dirac monopole. We also demonstrate that
the monopole decay accelerates in weaker magnetic field gradients.Comment: 10 pages, 7 figure
A comparison of ultraviolet sensitivities in universal, nonuniversal, and split extra dimensional models
We discuss the origin of ultraviolet sensitivity in extra dimensional
theories, and compare and contrast the cutoff dependences in universal,
nonuniversal and split five dimensional models. While the gauge bosons and
scalars are in the five dimensional bulk in all scenarios, the locations of the
fermions are different in different cases. In the universal model all fermions
can travel in the bulk, in the nonuniversal case they are all confined at the
brane, while in the split scenario some are in the bulk and some are in the
brane. A possible cure from such divergences is also discussed.Comment: 9 pages, Latex, no figure, v2: further clarifications and references
added, accepted for publication in Phys. Rev.
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