33,608 research outputs found
Music enrichment for gifted children in the first grade
Thesis (Ed.M.)--Boston Universit
Kepler problem in Dirac theory for a particle with position-dependent mass
Exact solution of Dirac equation for a particle whose potential energy and
mass are inversely proportional to the distance from the force centre has been
found. The bound states exist provided the length scale which appears in
the expression for the mass is smaller than the classical electron radius
. Furthermore, bound states also exist for negative values of
even in the absence of the Coulomb interaction. Quasirelativistic expansion of
the energy has been carried out, and a modified expression for the fine
structure of energy levels has been obtained. The problem of kinetic energy
operator in the Schr\"odinger equation is discussed for the case of
position-dependent mass. In particular, we have found that for highly excited
states the mutual ordering of the inverse mass and momentum operator in the
non-relativistic theory is not important.Comment: 9 page
The Heritage of War and State Collapse in Somalia and Somaliland: Local Level Effects, External Interventions and Governance Reconstitution
On the Casimir effect for parallel plates in the spacetime with one extra compactified dimension
In this paper, the Casimir effect for parallel plates in the presence of one
compactified universal extra dimension is reexamined in detail. Having
regularized the expressions of Casimir force, we show that the nature of
Casimir force is repulsive if the distance between the plates is large enough,
which is disagree with the experimental phenomena.Comment: 7 pages, 3 figure
TFD Approach to Bosonic Strings and -branes
In this work we explain the construction of the thermal vacuum for the
bosonic string, as well that of the thermal boundary state interpreted as a
-brane at finite temperature. In both case we calculate the respective
entropy using the entropy operator of the Thermo Field Dynamics Theory. We show
that the contribution of the thermal string entropy is explicitly present in
the -brane entropy. Furthermore, we show that the Thermo Field approach
is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second
Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002,
Londrina-Pr, Brazil. To appear in a special issue of IJMP
Energy gap of the bimodal two-dimensional Ising spin glass
An exact algorithm is used to compute the degeneracies of the excited states
of the bimodal Ising spin glass in two dimensions. It is found that the
specific heat at arbitrary low temperature is not a self-averaging quantity and
has a distribution that is neither normal or lognormal. Nevertheless, it is
possible to estimate the most likely value and this is found to scale as L^3
T^(-2) exp(-4J/kT), for a L*L lattice. Our analysis also explains, for the
first time, why a correlation length \xi ~ exp(2J/kT) is consistent with an
energy gap of 2J. Our method allows us to obtain results for up to 10^5
disorder realizations with L <= 64. Distributions of second and third
excitations are also shown.Comment: 4 pages, 4 figure
D-instanton partition functions
Duality arguments are used to determine D-instanton contributions to certain
effective interaction terms of type II supergravity theories in various
dimensions. This leads to exact expressions for the partition functions of the
finite N D-instanton matrix model in d=4 and 6 dimensions that generalize our
previous expression for the case d=10. These results are consistent with the
fact that the Witten index of the T-dual D-particle process should only be
non-vanishing for d=10.Comment: 20 pages, harvmac, typos corrected, reference adde
Poincar\'e recurrences in Hamiltonian systems with a few degrees of freedom
Hundred twenty years after the fundamental work of Poincar\'e, the statistics
of Poincar\'e recurrences in Hamiltonian systems with a few degrees of freedom
is studied by numerical simulations. The obtained results show that in a
regime, where the measure of stability islands is significant, the decay of
recurrences is characterized by a power law at asymptotically large times. The
exponent of this decay is found to be . This value is
smaller compared to the average exponent found previously
for two-dimensional symplectic maps with divided phase space. On the basis of
previous and present results a conjecture is put forward that, in a generic
case with a finite measure of stability islands, the Poncar\'e exponent has a
universal average value being independent of number of
degrees of freedom and chaos parameter. The detailed mechanisms of this slow
algebraic decay are still to be determined.Comment: revtex 4 pages, 4 figs; Refs. and discussion adde
Remarks on the Classical Size of D-Branes
We discuss different criteria for `classical size' of extremal Dirichlet
p-branes in type-II supergravity. Using strong-weak coupling duality, we find
that the size of the strong-coupling region at the core of the (p<3)-branes, is
always given by the asymptotic string scale, if measured in the weakly coupled
dual string metric. We also point out how the eleven-dimensional Planck scale
arises in the classical 0-brane solution, as well as the ten-dimensional Planck
scale in the D-instanton solution.Comment: 8 pp, harvma
- …