36,822 research outputs found
On the Magnetic Excitation Spectra of High Tc Cu Oxides up to the Energies far above the Resonance Energy
Magnetic excitation spectra c"(q,w) of YBa2Cu3Oy and La214 systems have been
studied. For La1.88Sr0.12CuO4, c"(q,w) have been measured up to ~30 meV and
existing data have been analyzed up to the energy w~150 meV by using the
phenomenological expression of the generalized magnetic susceptibility
c(q,w)=c0(q,w)/{1+J(q)c0(q,w)}, where c0(q,w) is the susceptibility of the
electrons without the exchange coupling J(q) among them. In the relatively low
energy region up to slightly above the resonance energy Er, it has been
reported by the authors' group that the expression can explain characteristics
of the q- and w-dependence of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here,
it is also pointed out that the expression can reproduce the rotation of four
incommensurate peaks of c"(q,w) within the a*-b* plane about (p/a, p/a) {or
so-called (p, p)} point by 45 degree, which occurs as w goes to the energy
region far above Er from E below Er. For La2-xSrxCuO4 and La2-xBaxCuO4,
agreements between the observed results and the calculations are less
satisfactory than for YBCO, indicating that we have to take account of the
existence of the "stripes" to consistently explain the observed c"(q,w) of
La214 system especially near x=1/8.Comment: 14 pages, 5 figure
Reconfiguration on sparse graphs
A vertex-subset graph problem Q defines which subsets of the vertices of an
input graph are feasible solutions. A reconfiguration variant of a
vertex-subset problem asks, given two feasible solutions S and T of size k,
whether it is possible to transform S into T by a sequence of vertex additions
and deletions such that each intermediate set is also a feasible solution of
size bounded by k. We study reconfiguration variants of two classical
vertex-subset problems, namely Independent Set and Dominating Set. We denote
the former by ISR and the latter by DSR. Both ISR and DSR are PSPACE-complete
on graphs of bounded bandwidth and W[1]-hard parameterized by k on general
graphs. We show that ISR is fixed-parameter tractable parameterized by k when
the input graph is of bounded degeneracy or nowhere-dense. As a corollary, we
answer positively an open question concerning the parameterized complexity of
the problem on graphs of bounded treewidth. Moreover, our techniques generalize
recent results showing that ISR is fixed-parameter tractable on planar graphs
and graphs of bounded degree. For DSR, we show the problem fixed-parameter
tractable parameterized by k when the input graph does not contain large
bicliques, a class of graphs which includes graphs of bounded degeneracy and
nowhere-dense graphs
Reconfiguring Independent Sets in Claw-Free Graphs
We present a polynomial-time algorithm that, given two independent sets in a
claw-free graph , decides whether one can be transformed into the other by a
sequence of elementary steps. Each elementary step is to remove a vertex
from the current independent set and to add a new vertex (not in )
such that the result is again an independent set. We also consider the more
restricted model where and have to be adjacent
Developing Cloud Chambers with High School Students
The result and outcome of the \textit{cloud chamber project}, which aims to
develop a cloud chamber useful for science education is reported in detail. A
project includes both three high school students and a teacher as a part of
Super Science High School (SSH) program in our school. We develop a
dry-ice-free cloud chamber using salt and ice (or snow). Technical details of
the chamber are described. We also argue how the project have affected
student's cognition, motivation, academic skills and behavior. The research
project has taken steps of professional researchers, i.e., in planning
research, applying fund, writing a paper and giving a talk in conferences. From
interviews with students, we have learnt that such style of scientific activity
is very effective in promoting student's motivation for learning science.Comment: 9 pages, accepted to the proceedings of APPC12 - the 12th Asia
Pacific Physics Conferenc
Integrability of a Generalized Ito System: the Painleve Test
It is shown that a generalized Ito system of four coupled nonlinear evolution
equations passes the Painleve test for integrability in five distinct cases, of
which two were introduced recently by Tam, Hu and Wang. A conjecture is
formulated on integrability of a vector generalization of the Ito system.Comment: LaTeX, 5 page
Radion effective theory in the detuned Randall-Sundrum model
We compute the two-derivative low-energy effective action for the radion in
the (supersymmetric) Randall-Sundrum scenario with detuned brane tensions. At
the classical level, a potential automatically stabilizes the distance between
the branes. In the supersymmetric case, supersymmetry can be broken
spontaneously by a vacuum expectation value for the fifth component of the
graviphoton.Comment: 17 pages. JHEP class. New Appendix. Published versio
Continuous vacua in bilinear soliton equations
We discuss the freedom in the background field (vacuum) on top of which the
solitons are built. If the Hirota bilinear form of a soliton equation is given
by A(D_{\vec x})\bd GF=0,\, B(D_{\vec x})(\bd FF - \bd GG)=0 where both
and are even polynomials in their variables, then there can be a continuum
of vacua, parametrized by a vacuum angle . The ramifications of this
freedom on the construction of one- and two-soliton solutions are discussed. We
find, e.g., that once the angle is fixed and we choose
as the physical quantity, then there are four different solitons (or kinks)
connecting the vacuum angles , (defined modulo
). The most interesting result is the existence of a ``ghost'' soliton; it
goes over to the vacuum in isolation, but interacts with ``normal'' solitons by
giving them a finite phase shift.Comment: 9 pages in Latex + 3 figures (not included
A Note on the Picard-Fuchs Equations for N=2 Seiberg-Witten Theories
A concise presentation of the PF equations for N=2 Seiberg-Witten theories
for the classical groups of rank r with N_f massless hypermultiplets in the
fundamental representation is provided. For N_f=0, all r PF equations can be
given in a generic form. For certain cases with N_f\neq zero, not all equations
are generic. However, in all cases there are at least r-2 generic PF equations.
For these cases the classical part of the equations is generic, while the
quantum part can be formulated using a method described in a previous paper by
the authors, which is well suited to symbolic computer calculations.Comment: 25 pages, Latex; some new references adde
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