Influence of mass moment of inertia on normal modes of preloaded solar array mast

Earth-orbiting spacecraft often contain solar arrays or antennas supported by a preloaded mast. Because of weight and cost considerations, the structures supporting the spacecraft appendages are extremely light and flexible; therefore, it is vital to investigate the influence of all physical and structural parameters that may influence the dynamic behavior of the overall structure. The study primarily focuses on the mast for the space station solar arrays, but the formulations and the techniques developed in this study apply to any large and flexible mast in zero gravity. Furthermore, to determine the influence on the circular frequencies, the mass moment of inertia of the mast was incorporated into the governing equation of motion for bending. A finite element technique (MSC/NASTRAN) was used to verify the formulation. Results indicate that when the mast is relatively flexible and long, the mass moment inertia influences the circular frequencies

Null-controllability for weakly dissipative heat-like equations

We study the null-controllability properties of heat-like equations posed on the whole Euclidean space $\mathbb R^n$. These evolution equations are associated with Fourier multipliers of the form $\rho(\vert D_x\vert)$, where $\rho\colon[0,+\infty)\rightarrow\mathbb C$ is a measurable function such that $\Re\rho$ is bounded from below. We consider the ``weakly dissipative'' case, a typical example of which is given by the fractional heat equations associated with the multipliers $\rho(\xi) = \xi^s$ in the regime $s\in(0,1)$, for which very few results exist. We identify sufficient conditions and necessary conditions on the control supports for the null-controllability to hold. More precisely, we prove that these equations are null-controllable in any positive time from control supports which are sufficiently thick at all scales. Under assumptions on the multiplier $\rho$, in particular assuming that $\rho(\xi) = o(\xi)$, we also prove that the null-controllability implies that the control support is thick at all scales, with an explicit lower bound of the thickness ratio in terms of the multiplier $\rho$. Finally, using Smith-Volterra-Cantor sets, we provide examples of non-trivial control supports that satisfy these necessary or sufficient conditions.Comment: 14 pages. Previously this version appeared as arXiv:2309.07533 which was submitted as a new work by acciden

On the bounded cohomology of semi-simple groups, S-arithmetic groups and products

We prove vanishing results for Lie groups and algebraic groups (over any local field) in bounded cohomology. The main result is a vanishing below twice the rank for semi-simple groups. Related rigidity results are established for S-arithmetic groups and groups over global fields. We also establish vanishing and cohomological rigidity results for products of general locally compact groups and their lattices

ending civil conflict through rebel demobilization

We examine the role of FM radio in mitigating violent conflict. We collect original data on radio broadcasts encouraging defections during the Lord's Resistance Army (LRA) insurgency. This constitutes the first quantitative evaluation of an active counterinsurgency policy that encourages defections through radio messages. Exploiting random topography-driven variation in radio coverage along with panel variation at the grid-cell level, we identify the causal effect of messaging on violence. Broadcasting defection messages increases defections and reduces fatalities, violence against civilians, and clashes with security forces. Income shocks have opposing effects on both the conflict and the effectiveness of messaging.publishersversionpublishe

Deflecting Stereotype Threat Through Downward Comparison: When Comparison with Immigrants Boosts the Performance of Stigmatized Native Students

Two experiments examined the effect of comparison with immigrants on the intellectual performance of stigmatized native students (i.e., women and students from low socioeconomic backgrounds). It was predicted that such a comparison may boost the test performance of both groups of students rather than comparison with their counterparts who are not stigmatized. In line with this hypothesis, we found that female European students (Study 1) performed better on a math test when they were led to compare with a female immigrant rather than with another female European student. Study 2 replicated this finding in regard to the performance of native students with low socioeconomic status on a general intelligence test. Results are discussed in terms of stereotype susceptibility predicaments and their implications for native-immigrant performance gap

A Variety Metric Accounting for Unbalanced Idea Space Distributions

AbstractProving the effectiveness of an idea generation method is key to its acceptance in an industrial and academic environment. This necessitates the development of a set of widely accepted metrics covering the different aspects on which idea generation methods can be characterized. This paper gives an overview of the existing metrics, and demonstrates a number of shortcomings in the variety metric, such as not accounting for the fairness of the distribution of ideas over nodes on an abstraction level. A level-based, correctly normalized variety metric, based on the Shannon entropy, is proposed which is shown to resolve the identified issues

A Piecewise Line-Search Technique for Maintaining the Positive Definiteness of the Matrices in the SQP Method

Projet PROMATHA technique for maintaining the positive definiteness of the matrices in the quasi-Newton version of the SQP algorithm is proposed. In our algorithm, approximations of the Hessian of the augmented Lagrangian are updated. The positive definiteness of these matrices in the space tangent to the constraint manifold is ensured by a piecewise line-search technique, while their positive definiteness in a decoupled complementary subspace is obtained by setting the augmentation parameter. The combination of these two ideas makes the new approach more robust in our experiment with respect to existing approache

Second-order cone programming for rolling friction contact mechanics

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