20,986 research outputs found
CsCl-type compounds in binary alloys of rare-earth metals with gold and silver
In binary alloys of silver with Sm, Tb, Ho, and Tm, and of gold with Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm, intermediate phases containing stoichiometric proportions of the two metals were found to crystallize into the CsCl (B2)-type structure. The lattice parameters of these phases are reported and a correlation has been found between these lattice parameters and the trivalent ionic radii of the rare-earth metals
On the Classical Algebra
We consider the classical \w42 algebra from the integrable system viewpoint.
The integrable evolution equations associated with the \w42 algebra are
constructed and the Miura maps , consequently modifications, are presented.
Modifying the Miura maps, we give a free field realization the classical \w42
algebra. We also construct the Toda type integrable systems for it.Comment: 14 pages, latex, no figure
Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
The south-north travel-time differences are measured by applying
time-distance helioseismology to the MDI and HMI medium-degree Dopplergrams
covering May 1996-April 2017. Our data analysis corrects for several sources of
systematic effects: P-angle error, surface magnetic field effects, and
center-to-limb variations. An interpretation of the travel-time measurements is
obtained using a forward-modeling approach in the ray approximation. The
travel-time differences are similar in the southern hemisphere for cycles 23
and 24. However, they differ in the northern hemisphere between cycles 23 and
24. Except for cycle 24's northern hemisphere, the measurements favor a
single-cell meridional circulation model where the poleward flows persist down
to 0.8 , accompanied by local inflows toward the activity belts
in the near-surface layers. Cycle 24's northern hemisphere is anomalous:
travel-time differences are significantly smaller when travel distances are
greater than 20. This asymmetry between northern and southern
hemispheres during cycle 24 was not present in previous measurements (e.g.,
Rajaguru & Antia 2015), which assumed a different P-angle error correction
where south-north travel-time differences are shifted to zero at the equator
for all travel distances. In our measurements, the travel-time differences at
the equator are zero for travel distances less than 30, but they
do not vanish for larger travel distances. This equatorial offset for large
travel distances need not be interpreted as a deep cross-equator flow; it could
be due to the presence of asymmetrical local flows at the surface near the end
points of the acoustic ray paths.Comment: accepted for publication in A&
Improved Approximation Algorithms for Computing k Disjoint Paths Subject to Two Constraints
For a given graph with positive integral cost and delay on edges,
distinct vertices and , cost bound and delay bound , the bi-constraint path (BCP) problem is to compute disjoint
-paths subject to and . This problem is known NP-hard, even when
\cite{garey1979computers}. This paper first gives a simple approximation
algorithm with factor-, i.e. the algorithm computes a solution with
delay and cost bounded by and respectively. Later, a novel improved
approximation algorithm with ratio
is developed by constructing
interesting auxiliary graphs and employing the cycle cancellation method. As a
consequence, we can obtain a factor- approximation algorithm by
setting and a factor- algorithm by
setting . Besides, by setting , an
approximation algorithm with ratio , i.e. an algorithm with
only a single factor ratio on cost, can be immediately obtained. To
the best of our knowledge, this is the first non-trivial approximation
algorithm for the BCP problem that strictly obeys the delay constraint.Comment: 12 page
The Color-Octet intrinsic charm in and decays
Color-octet mechanism for the decay B\to \eta^\prime X is proposed to explain
the large branching ratio of Br(B\to \eta^\prime X)\sim 1\times 10^{-3}
recently announced by CLEO. We argue that the inclusive \eta^\prime production
in B decays may dominantly come from the Cabbibo favored b\to (\bar c c)_8s
process where \bar c c pair is in a color-octet configuration, and followed by
the nonperturbative transition (\bar c c)_8\to \eta^\prime X. The color-octet
intrinsic charm component in the higher Fock states of \eta^\prime is crucial
and is induced by the strong coupling of \eta^\prime to gluons via QCD axial
anomaly.Comment: 9 pages, RevTex, 1 PS figur
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