3,059 research outputs found
Optical spectroscopy study on pressure-induced phase transitions in the three-dimensional Dirac semimetal CdAs
We report a room-temperature optical reflectivity study performed on
[112]-oriented CdAs single crystals over a broad energy range under
external pressure up to 10 GPa. The abrupt drop of the band dispersion
parameter (-parameter) and the interruption of the gradual redshift of the
bandgap at 4~GPa confirms the structural phase transition from a
tetragonal to a monoclinic phase in this material. The pressure-induced
increase of the overall optical conductivity at low energies and the continuous
redshift of the high-energy bands indicate that the system evolves towards a
topologically trivial metallic state, although a complete closing of the band
gap could not be observed in the studied pressure range. Furthermore, a
detailed investigation of the low-pressure regime suggests the possible
existence of an intermediate state between 2 and 4~GPa , that might be a
precursor of the structural phase transition or due to the lifted degeneracy of
the Dirac nodes. Several optical parameters show yet another anomaly at 8~GPa,
where low-temperature superconductivity was found in an earlier study.Comment: submitted to PR
Application of Navier-Stokes analysis to stall flutter
A solution procedure was developed to investigate the two-dimensional, one- or two-dimensional flutter characteristics of arbitrary airfoils. This procedure requires a simultaneous integration in time of the solid and fluid equations of motion. The fluid equations of motion are the unsteady compressible Navier-Stokes equations, solved in a body-fitted moving coordinate system using an approximate factorization scheme. The solid equations of motion are integrated in time using an Euler implicit scheme. Flutter is said to occur if small disturbances imposed on the airfoil attitude lead to divergent oscillatory motions at subsequent times. The flutter characteristics of airfoils in subsonic speed at high angles of attack and airfoils in high subsonic and transonic speeds at low angles of attack are investigated. The stall flutter characteristics are also predicted using the same procedure
Draft genome sequence of the naturally competent Bacillus simplex strain WY10
ABSTRACT
We sequenced a naturally competent bacterial isolate, WY10, cultured from a Wyoming soil sample. Sequence analysis revealed that WY10 is a novel strain of
Bacillus simplex
. To our knowledge, WY10 is the first
B. simplex
strain to be characterized as naturally competent for DNA uptake by transformation.
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Interaction of Phonons and Dirac Fermions on the Surface of Bi2Se3: A Strong Kohn Anomaly
We report the first measurements of phonon dispersion curves on the (001)
surface of the strong three-dimensional topological insulator Bi2Se3. The
surface phonon measurements were carried out with the aid of coherent helium
beam surface scattering techniques. The results reveal a prominent signature of
the exotic metallic Dirac fermion quasi-particles, including a strong Kohn
anomaly. The signature is manifest in a low energy isotropic convex dispersive
surface phonon branch with a frequency maximum of 1.8 THz, and having a
V-shaped minimum at approximately 2kF that defines the Kohn anomaly.
Theoretical analysis attributes this dispersive profile to the renormalization
of the surface phonon excitations by the surface Dirac fermions. The
contribution of the Dirac fermions to this renormalization is derived in terms
of a Coulomb-type perturbation model
Comparison of impact results for several polymeric composites over a wide range of low impact velocities
Static indentation, falling weight, and ballistic impact tests were conducted in clamped plates made of AS4/3501-6 and IM7/8551-7 prepreg tape. The transversely isotropic plates were nominally 7-mm thick. Pendulum and ballistic tests were also conducted on simply supported plates braided with Celion 12000 fibers and 3501-6 epoxy. The 20 degree braided plates were about 5-mm thick. The impactors had spherical or hemispherical shapes with a 12.7 mm diameter. Residual compression strength and damage size were measured. For a given kinetic energy, damage size was least for IM7/8551-7 and greatest for the braided material. Strengths varied inversely with damage size. For a given damage size, strength loss as a fraction of original strength was least for the braided material and greatest for AS4/3501-6 and IM7/8551-7. Strength loss for IM7/8551-7 and AS4/3501-6 was nearly equal. No significant differences were noticed between damage sizes and residual compression strengths for the static indentation, falling weight, and ballistic tests of AS4/3501-6 and IM7/8551-7. For the braided material, sizes of damage were significantly less and compression strengths were significantly more for the falling weight tests than for the ballistic tests
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