2,853,753 research outputs found
Tight-binding study of high-pressure phase transitions in titanium: alpha to omega and beyond
We use a tight-binding total energy method, with parameters determined from a
fit to first-principles calculations, to examine the newly discovered gamma
phase of titanium. Our parameters were adjusted to accurately describe the
alpha Ti-omega Ti phase transition, which is misplaced by density functional
calculations. We find a transition from omega Ti to gamma Ti at 102 GPa, in
good agreement with the experimental value of 116 GPa. Our results suggest that
current density functional calculations will not reproduce the omega Ti-gamma
Ti phase transition, but will instead predict a transition from omega Ti to the
bcc beta Ti phase.Comment: 3 encapsulated Postscript figures, submitted to Phyical Review
Letter
Measurement of the Mass Splittings between the States
We present new measurements of photon energies and branching fractions for
the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the
chi_b states are determined from the measured radiative photon energies. The
ratio of mass splittings between the chi_b substates,
r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information
on the nature of the bbbar confining potential. We find
r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world
average, but more consistent with the theoretical expectation that r(1P)<r(2P);
i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than
for the chi_b(2P) triplet.Comment: 11 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Kodaira Dimension and the Yamabe Problem
The Yamabe invariant Y(M) of a smooth compact manifold is roughly the
supremum of the scalar curvatures of unit-volume constant-scalar curvature
Riemannian metrics g on M. (To be absolutely precise, one only considers
constant-scalar-curvature metrics which are Yamabe minimizers, but this does
not affect the sign of the answer.) If M is the underlying smooth 4-manifold of
a complex algebraic surface (M,J), it is shown that the sign of Y(M) is
completely determined by the Kodaira dimension Kod (M,J). More precisely, Y(M)
0 iff Kod (M,J)=
-infinity.Comment: LaTeX file. With minor typographical errors correcte
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