18,264 research outputs found
Characterization of soft stripe-domain deformations in Sm-C and Sm-C* liquid-crystal elastomers
The neoclassical model of Sm-C (and Sm-C*) elastomers developed by Warner and Adams predicts a class of “soft” (zero energy) deformations. We find and describe the full set of stripe domains—laminate structures in which the laminates alternate between two different deformations—that can form between pairs of these soft deformations. All the stripe domains fall into two classes, one in which the smectic layers are not bent at the interfaces, but for which—in the Sm-C* case—the interfaces are charged, and one in which the smectic layers are bent but the interfaces are never charged. Striped deformations significantly enhance the softness of the macroscopic elastic response
Selective extinction of marine plankton at the end of the Mesozoic era: The fossil and stable isotope record
Floral, faunal and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow water marine deposits in the Mangyshlak Peninsula, USSR suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno, micro and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen isotopic analyses of the bulk sediments, composed of nanno and microplankton skeletal remains, show a sharp positive spike at the K/T boundary. This shift is primarily attributed to severe cooling possibly accompanied by increased salinities of the surface mixed layer. Floral and faunal extinctions were selective, affecting approximately 90 percent of the warm water calcareous phyto and zooplankton genera in the Tethyan-Paratethyan regions. These highly diverse taxa with many endemic representatives were at the peak of their evolutionary development. Geologic evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanic activity which reached a peak at the close of the Mesozoic Era. Increased acidity temporarily prohibited calcite nucleation of the surface dwelling warm-water plankton. Superimposed upon decreased alkalinity, severe and rapid climatic changes caused the extinction of calcareous phyto and zooplankton
Sharp change over from compound nuclear fission to shape dependent quasi fission
Fission fragment mass distribution has been measured from the decay of
Bk nucleus populating via two entrance channels with slight difference
in mass asymmetries but belonging on either side of the Businaro Gallone mass
asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb
barrier, at similar excitation energies the width of the fission fragment mass
distribution was found to be drastically different for the N +
Th reaction compared to the B + U reaction. The entrance
channel mass asymmetry was found to affect the fusion process sharply.Comment: 4 pages,6 figure
Evaporation of alpha particles from P nucleus
The energy spectra of alpha particles have been measured in coincidence with
the evaporation residues for the decay of the compound nucleus P produced
in the reaction F (96 MeV) + C. The data have been compared with the
predictions of the statistical model code CASCADE. It has been observed that
significant deformation effect in the compound nucleus need to be considered in
order to explain the shape of the evaporated alpha particle energy spectra.Comment: 4 pages, 3 figures, revtex, epsf styl
Elasticity of Polydomain Liquid Crystal Elastomers
We model polydomain liquid-crystal elastomers by extending the neo-classical
soft and semi-soft free energies used successfully to describe monodomain
samples. We show that there is a significant difference between polydomains
cross-linked in homogeneous high symmetry states then cooled to low symmetry
polydomain states and those cross-linked directly in the low symmetry
polydomain state. For example, elastomers cross-linked in the isotropic state
then cooled to a nematic polydomain will, in the ideal limit, be perfectly
soft, and with the introduction of non-ideality, will deform at very low stress
until they are macroscopically aligned. The director patterns observed in them
will be disordered, characteristic of combinations of random deformations, and
not disclination patterns. We expect these samples to exhibit elasticity
significantly softer than monodomain samples. Polydomains cross-linked in the
nematic polydomain state will be mechanically harder and contain characteristic
schlieren director patterns. The models we use for polydomain elastomers are
spatially heterogeneous, so rather than solving them exactly we elucidate this
behavior by bounding the energies using Taylor-like (compatible test strain
fields) and Sachs (constant stress) limits extended to non-linear elasticity.
Good agreement is found with experiments that reveal the supersoft response of
some polydomains. We also analyze smectic polydomain elastomers and propose
that polydomain SmC* elastomers cross-linked in the SmA monodomain state are
promising candidates for low field electrical actuation.Comment: 13 pages, 11 figure
Supersoft elasticity in polydomain nematic elastomers
We consider the equilibrium stress-strain behavior of polydomain liquid crystal elastomers (PLCEs). We show that there is a fundamental difference between PLCEs cross-linked in the high temperature isotropic and low temperature aligned states. PLCEs cross-linked in the isotropic state then cooled to an aligned state will exhibit extremely soft elasticity (confirmed by recent experiments) and ordered director patterns characteristic of textured deformations. PLCEs cross-linked in the aligned state will be mechanically much harder and characterized by disclination textures
Study of Dissipative Collisions of Ne (7-11 MeV/nucleon) + Al
The inclusive energy distributions of complex fragments (3 Z 9)
emitted in the reactions Ne (145, 158, 200, 218 MeV) + Al have
been measured in the angular range 10 - 50. The fusion-fission and
the deep-inelastic components of the fragment yield have been extracted using
multiple Gaussian functions from the experimental fragment energy spectra. The
elemental yields of the fusion-fission component have been found to be fairly
well exlained in the framework of standard statistical model. It is found that
there is strong competition between the fusion-fission and the deep-inelastic
processes at these energies. The time scale of the deep-inelastic process was
estimated to be typically in the range of 10 - 10 sec.,
and it was found to decrease with increasing fragment mass. The angular
momentum dissipations in fully energy damped deep-inelastic process have been
estimated from the average energies of the deep-inelastic components of the
fragment energy spectra. It has been found that, the estimated angular momentum
dissipations, for lighter fragments in particular, are more than those
predicted by the empirical sticking limit.Comment: 16 pages, 9 figure
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