42,913 research outputs found
Weakly Interacting Stable Pions
An unbroken discrete symmetry, analogous to G-parity in QCD, exists in
standard model extensions with vector-like coupling of electroweak SU(2) to
"hidden sector" fermions that are confined by a strong gauge force. For an
irreducible SU(2) representation of the hidden sector fermions, the lightest
hidden sector states form an isotriplet of "pions" with calculable mass
splittings and couplings to standard model fields. The parity can be extended
to fermions in real representations of color SU(3), and can provide dark matter
candidates with distinct collider signatures.Comment: 5 pages; final version in PR
Scanning tunneling microscopy investigation of 2H-MoS_2: A layered semiconducting transitionāmetal dichalcogenide
Scanning tunneling microscopy (STM) has been enormously
successful in solving several important problems in the geometric and electronic structure of homogeneous metallic and semiconducting surfaces. A central question which remains to be answered with respect to the study of
compound surfaces, however, is the extent to which the
chemical identity of constituent atoms may be established.
Recently, progress in this area was made by Feenstra et al.
who succeeded in selectively imaging either Ga or As atoms
on the GaAs (110) surface. So far this is the only case where such selectivity has been achieved. In an effort to add to our understanding of compound surface imaging we have undertaken a vacuum STM study of 2H-MoS_2, a material which has two structurally and electronically different atomic species at its surface
Discrimination between Nested Two- and Three-Parameter Distributions : An Application to Models of Air Pollution
Chemoviscosity modeling for thermosetting resin systems, part 3
A new analytical model for simulating chemoviscosity resin has been formulated. The model is developed by modifying the well established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature (T sub g (t)) and the degree of cure alpha(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature-dependent functions of the modified WLF theory parameters C sub 1 (T) and C sub 2 (T) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic heating cure cycles were shown to compare favorably with the experimental data. This work represents a progress toward establishing a chemoviscosity model which is capable of not only describing viscosity profiles accurately under various cure cycles, but also correlating viscosity data to the changes of physical properties associated with the structural transformations of the thermosetting resin systems during cure
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