5,741 research outputs found
Effect of CF3H and CF3Br on laminar diffusion flames in normal and microgravity
Chemical inhibition of diffusion flames through addition of halogenated inhibitors is a problem of significant practical and scientific interest. Extensive studies on diffusion flames in microgravity have shown that these flames have significantly different characteristics than those under normal gravity. However, the mechanisms through which inhibitors reach the reaction zone to suppress combustion in diffusion flames and the effectiveness of these compounds under reduced gravity have yet to be investigated. This study reports preliminary results of investigations on the behavior of laminar jet diffusion flames upon the addition of bromotrifluoromethane (CF3Br) and trifluoromethane (CF3H) to the surroundings under normal and microgravity conditions. The results show that the flame structure in microgravity is significantly different from that under normal gravity conditions, and more importantly, that conditions for flame stability are less stringent under microgravity. Experiments show that flames that cannot be stabilized under normal gravity are quite stable under microgravity conditions. In addition, normal gravity experiments at reduced pressure (low buoyancy) did not reproduce the structure or stability limits of inhibited flames in microgravity
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
B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T
We have measured the magnetization and specific heat of multiferroic CoCr2O4
in magnetic fields up to 14 T. The high-field magnetization measurements
indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the
lock-in transition at 15 K is characterized by magnetic irreversibility. At
higher magnetic fields, the irreversibility increases. Specific-heat
measurements confirm the transition at T*, and also show irreversible behavior.
We construct a field-temperature phase diagram of CoCr2O4.Comment: 4 page
Nuclear magnetic resonance probe head design for precision strain control
We present the design and construction of an NMR probe to investigate single crystals under strain at cryogenic temperatures. The probe head incorporates a piezoelectric-based apparatus from Razorbill Instruments that enables both compressive and tensile strain tuning up to strain values on the order of 0.3% with a precision of 0.001%. As NMR in BaFe2As2 reveals large changes to the electric field gradient and indicates that the strain is homogeneous to within 16% over the volume of the NMR coil
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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