2,132 research outputs found
Damping characterization in large structures
This research project has as its main goal the development of methods for selecting the damping characteristics of components of a large structure or multibody system, in such a way as to produce some desired system damping characteristics. The main need for such an analytical device is in the simulation of the dynamics of multibody systems consisting, at least partially, of flexible components. The reason for this need is that all existing simulation codes for multibody systems require component-by-component characterization of complex systems, whereas requirements (including damping) often appear at the overall system level. The main goal was met in large part by the development of a method that will in fact synthesize component damping matrices from a given system damping matrix. The restrictions to the method are that the desired system damping matrix must be diagonal (which is almost always the case) and that interbody connections must be by simple hinges. In addition to the technical outcome, this project contributed positively to the educational and research infrastructure of Tuskegee University - a Historically Black Institution
Auxin regulates SCFTIR1-dependent degradation of AUX/IAA proteins
The plant hormone auxin is central in many aspects of plant development. Previous studies have implicated the ubiquitin-ligase SCFTIR1 and the AUX/IAA proteins in auxin response. Dominant mutations in several AUX/IAA genes confer pleiotropic auxin-related phenotypes, whereas recessive mutations affecting the function of SCFTIR1 decrease auxin response. Here we show that SCFTIR1 is required for AUX/IAA degradation. We demonstrate that SCFTIR1 interacts with AXR2/IAA7 and AXR3/IAA17, and that domain II of these proteins is necessary and sufficient for this interaction. Further, auxin stimulates binding of SCFTIR1 to the AUX/IAA proteins, and their degradation. Because domain II is conserved in nearly all AUX/IAA proteins in Arabidopsis, we propose that auxin promotes the degradation of this large family of transcriptional regulators, leading to diverse downstream effects
Assessment of Axial Wave Number and Mean Flow Uncertainty on Acoustic Liner Impedance Education
A key parameter in designing and assessing advanced broadband acoustic liners to achieve the current and future noise reduction goals is the acoustic impedance presented by the liner. This parameter, intrinsic to a specific liner configuration, is dependent on sound pressure level and grazing flow velocity. Current impedance eduction approaches have, in general, provided excellent results and continue to be employed throughout the acoustic liner community. However, some recent applications have indicated a possible dependence of the educed impedance on the direction of incident waves relative to the mean flow. The purpose of the current study is to investigate this unexpected behavior for various impedance eduction methods based on the Pridmore-Brown and convected Helmholtz equations. Specifically, the effects of flow profile and axial wavenumber uncertainties on educed impedances for upstream and downstream sources are investigated. The uniform flow results demonstrate the importance of setting a correct Mach number value in obtaining consistent educed impedances for upstream and downstream sources. In fact, the consistency of results over the two source locations was greatly improved by a slight modification of the uniform flow Mach number. In addition, uncertainty in educed axial wavenumber was also illustrated to correlate well with differences in the educed impedances, even with modified uniform flow Mach number. Finally, while less straightforward than in the uniform flow case, it appears that modification of the mean flow profile may also improve consistency of results for upstream and downstream results when shear flow is included
Hubble-Lema\^itre fragmentation and the path to equilibrium of merger-driven cluster formation
This paper discusses a new method to generate self-coherent initial
conditions for young substructured stellar cluster. The expansion of a uniform
system allows stellar sub-structures (clumps) to grow from fragmentation modes
by adiabatic cooling. We treat the system mass elements as stars, chosen
according to a Salpeter mass function, and the time-evolution is performed with
a collisional N-body integrator. This procedure allows to create a
fully-coherent relation between the clumps' spatial distribution and the
underlying velocity field. The cooling is driven by the gravitational field, as
in a cosmological Hubble-Lema\^itre flow. The fragmented configuration has a
`fractal'-like geometry but with a self-grown velocity field and mass profile.
We compare the characteristics of the stellar population in clumps with that
obtained from hydrodynamical simulations and find a remarkable correspondence
between the two in terms of the stellar content and the degree of spatial
mass-segregation. In the fragmented configuration, the IMF power index is ~0.3
lower in clumps in comparison to the field stellar population, in agreement
with observations in the Milky Way. We follow in time the dynamical evolution
of fully fragmented and sub-virial configurations, and find a soft collapse,
leading rapidly to equilibrium (timescale of 1 Myr for a ~ 10^4 Msun system).
The low-concentration equilibrium implies that the dynamical evolution
including massive stars is less likely to induce direct collisions and the
formation of exotic objects. Low-mass stars already ejected from merging clumps
are depleted in the end-result stellar clusters, which harbour a top-heavy
stellar mass function.Comment: 22 pages, accepted for publication in MNRA
An adjustment inventory for primary grades
Thesis (M.A.)--Boston Universit
Transport on a Lattice with Dynamical Defects
Many transport processes in nature take place on substrates, often considered
as unidimensional lanes. These unidimensional substrates are typically
non-static: affected by a fluctuating environment, they can undergo
conformational changes. This is particularly true in biological cells, where
the state of the substrate is often coupled to the active motion of
macromolecular complexes, such as motor proteins on microtubules or ribosomes
on mRNAs, causing new interesting phenomena. Inspired by biological processes
such as protein synthesis by ribosomes and motor protein transport, we
introduce the concept of localized dynamical sites coupled to a driven lattice
gas dynamics. We investigate the phenomenology of transport in the presence of
dynamical defects and find a novel regime characterized by an intermittent
current and subject to severe finite-size effects. Our results demonstrate the
impact of the regulatory role of the dynamical defects in transport, not only
in biology but also in more general contexts
Reflection Positivity and Monotonicity
We prove general reflection positivity results for both scalar fields and
Dirac fields on a Riemannian manifold, and comment on applications to quantum
field theory. As another application, we prove the inequality
between Dirichlet and Neumann covariance operators on a manifold with a
reflection.Comment: 11 page
Recognition of Biometric Unlock Pattern by GMM-UBM
International audienceUnlock patterns are used for authentication in mobile smart devices, yet they are vulnerable to attacks, since only the pattern draw is required. Extra biometric data of the user while drawing the unlock pattern passwords may strengthen the authentication, such as the speed of drawing, the pressure of the finger on the touch screen. Such biometric modality is referred to as behavioral biometrics. Besides, voice is also a behavioral biometric modality, as well as a physiological one. Hence, statistical models such as Gaussian mixture models (GMM) with universal background modeling (UBM) are widely used in speaker verification systems. In this work, we propose to apply and adapt a framework usually dedicated to speaker verification to recognize the unlock patterns based on users' behavior. We evaluate the performance using equal error rate for different combinations of features and varying number of mixtures. As a result of the combination of features, an equal error rate as low as 9.25% on average is obtained, which is promising for a preliminary study on GMM-UBM applied to unlock pattern based biometric recognition
Metaphors for a Change:
Two premises guide this paper: first, music education, like all educational enterprises, is shaped by its grounding metaphors which affect its aims, pedagogies, curriculum, and administration. Second, music education, like all educational endeavors, is increasingly encouraged to address issues of social justice and contribute in real ways to the benefit of the community through positive social change. In this conversation, the authors, each of whom have written about metaphors and social change, build on these two premises to explore ways of bringing together the two lines of inquiry in search of metaphors that would guide an education for social change. In their dialogue they propose four metaphors but acknowledge that these alone do not address the full array of meanings a metaphor for social change would need to capture
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