8,097 research outputs found
Stability, vibration and passive damping of partially restrained imperfect columns
A theoretical and experimental study of slender tubular columns for possible use in space structures is conducted in the presence of partial rotational end restraints. Explicit formulas are derived for computing the buckling load and the lowest natural frequency of perfectly straight uniform elastic members with rotational end restraints possessing linear moment-rotation characteristics. An exact solution in the form of a transcendental equation, and a numerical solution using second-order finite-differences are also presented. The presence of an initial imperfection is also incorporated into the numerical procedure. Vibration tests are conducted on an imperfect tubular steel member in the absence of an axial load. A damping concept consisting of a string-mass assembly is explored. Three passive damping configurations involving combinations of three lead shots were investigated. The three lead shot configurations provided considerably greater damping than the single lead shot
Uniaxial strain control of spin-polarization in multicomponent nematic order of BaFeAs
The iron-based high temperature superconductors exhibit a rich phase diagram
reflecting a complex interplay between spin, lattice, and orbital degrees of
freedom [1-4]. The nematic state observed in many of these compounds epitomizes
this complexity, by entangling a real-space anisotropy in the spin fluctuation
spectrum with ferro-orbital order and an orthorhombic lattice distortion [5-7].
A more subtle and much less explored facet of the interplay between these
degrees of freedom arises from the sizable spin-orbit coupling present in these
systems, which translates anisotropies in real space into anisotropies in spin
space. Here, we present a new technique enabling nuclear magnetic resonance
under precise tunable strain control, which reveals that upon application of a
tetragonal symmetry-breaking strain field, the magnetic fluctuation spectrum in
the paramagnetic phase of BaFeAs also acquires an anisotropic
response in spin-space. Our results unveil a hitherto uncharted internal spin
structure of the nematic order parameter, indicating that similar to liquid
crystals, electronic nematic materials may offer a novel route to
magneto-mechanical control.Comment: 11 pages, 5 figure
Chaotic and pseudochaotic attractors of perturbed fractional oscillator
We consider a nonlinear oscillator with fractional derivative of the order
alpha. Perturbed by a periodic force, the system exhibits chaotic motion called
fractional chaotic attractor (FCA). The FCA is compared to the ``regular''
chaotic attractor. The properties of the FCA are discussed and the
``pseudochaotic'' case is demonstrated.Comment: 20 pages, 7 figure
Magnetic phase diagram of the frustrated S=1/2 chain magnet LiCu_2O_2
We present the results of the magnetization and dielectric constant
measurements on untwinned single crystal samples of the frustrated S=1/2 chain
cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop
transition of the spiral spin plane was observed for the field orientations
H||a,b. The second magnetic transition was observed at H~15 T for all three
principal field directions. This high field magnetic phase is discussed as a
collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor
ferromagnetic and next-nearest-neighbor antiferromagnetic chain system
Deployable-erectable trade study for space station truss structures
The results of a trade study on truss structures for constructing the space station are presented. Although this study was conducted for the reference gravity gradient space station, the results are generally applicable to other configurations. The four truss approaches for constructing the space station considered in this paper were the 9 foot single fold deployable, the 15 foot erectable, the 10 foot double fold tetrahedral, and the 15 foot PACTRUSS. The primary rational for considering a 9 foot single-fold deployable truss (9 foot is the largest uncollapsed cross-section that will fit in the Shuttle cargo bay) is that of ease of initial on-orbit construction and preintegration of utility lines and subsystems. The primary rational for considering the 15 foot erectable truss is that the truss bay size will accommodate Shuttle size payloads and growth of the initial station in any dimension is a simple extension of the initial construction process. The primary rational for considering the double-fold 10 foot tetrahedral truss is that a relatively large amount of truss structure can be deployed from a single Shuttle flight to provide a large number of nodal attachments which present a pegboard for attaching a wide variety of payloads. The 15 foot double-fold PACTRUSS was developed to incorporate the best features of the erectable truss and the tetrahedral truss
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