1,289,029 research outputs found
Properties of nano-graphite ribbons with zigzag edges -- Difference between odd and even legs --
Persistent currents and transport properties are investigated for the
nano-graphite ribbons with zigzag shaped edges with paying attention to system
length dependence. It is found that both the persistent current in the
isolated ring and the conductance of the system connected to the perfect leads
show the remarkable dependences. In addition, the dependences for the
systems with odd legs and those with even legs are different from each other.
On the persistent current, the amplitude for the cases with odd legs shows
power-low behavior as with being the number of legs, whereas the
maximum of it decreases exponentially for the cases with even legs. The
conductance per one spin normalized by behaves as follows. In the even
legs cases, it decays as , whereas it reaches to unity for in the odd legs cases. Thus, the material is shown to have a remarkable
property that there is the qualitative difference between the systems with odd
legs and those with even legs even in the absence of the electron-electron
interaction.Comment: 4 pagaes, 8 figures, LT25 conference proceeding, accepted for
publication in Journal of Physics: Conference Serie
Componentwise and Cartesian decompositions of linear relations
Let be a, not necessarily closed, linear relation in a Hilbert space
\sH with a multivalued part \mul A. An operator in \sH with \ran
B\perp\mul A^{**} is said to be an operator part of when A=B \hplus
(\{0\}\times \mul A), where the sum is componentwise (i.e. span of the
graphs). This decomposition provides a counterpart and an extension for the
notion of closability of (unbounded) operators to the setting of linear
relations. Existence and uniqueness criteria for the existence of an operator
part are established via the so-called canonical decomposition of . In
addition, conditions are developed for the decomposition to be orthogonal
(components defined in orthogonal subspaces of the underlying space). Such
orthogonal decompositions are shown to be valid for several classes of
relations. The relation is said to have a Cartesian decomposition if
A=U+\I V, where and are symmetric relations and the sum is
operatorwise. The connection between a Cartesian decomposition of and the
real and imaginary parts of is investigated
Controlling the Short-Range Order and Packing Densities of Many-Particle Systems
Questions surrounding the spatial disposition of particles in various
condensed-matter systems continue to pose many theoretical challenges. This
paper explores the geometric availability of amorphous many-particle
configurations that conform to a given pair correlation function g(r). Such a
study is required to observe the basic constraints of non-negativity for g(r)
as well as for its structure factor S(k). The hard sphere case receives special
attention, to help identify what qualitative features play significant roles in
determining upper limits to maximum amorphous packing densities. For that
purpose, a five-parameter test family of g's has been considered, which
incorporates the known features of core exclusion, contact pairs, and damped
oscillatory short-range order beyond contact. Numerical optimization over this
five-parameter set produces a maximum-packing value for the fraction of covered
volume, and about 5.8 for the mean contact number, both of which are within the
range of previous experimental and simulational packing results. However, the
corresponding maximum-density g(r) and S(k) display some unexpected
characteristics. A byproduct of our investigation is a lower bound on the
maximum density for random sphere packings in dimensions, which is sharper
than a well-known lower bound for regular lattice packings for d >= 3.Comment: Appeared in Journal of Physical Chemistry B, vol. 106, 8354 (2002).
Note Errata for the journal article concerning typographical errors in Eq.
(11) can be found at http://cherrypit.princeton.edu/papers.html However, the
current draft on Cond-Mat (posted on August 8, 2002) is correct
Inverse Avalanches On Abelian Sandpiles
A simple and computationally efficient way of finding inverse avalanches for
Abelian sandpiles, called the inverse particle addition operator, is presented.
In addition, the method is shown to be optimal in the sense that it requires
the minimum amount of computation among methods of the same kind. The method is
also conceptually nice because avalanche and inverse avalanche are placed in
the same footing.Comment: 5 pages with no figure IASSNS-HEP-94/7
Thermodynamics of the one-dimensional half-filled Hubbard model in the spin-disordered regime
We analyze the Thermodynamic Bethe Ansatz equations of the one-dimensional
half-filled Hubbard model in the "spin-disordered regime", which is
characterized by the temperature being much larger than the magnetic energy
scale but small compared to the Mott-Hubbard gap. In this regime the
thermodynamics of the Hubbard model can be thought of in terms of gapped
charged excitations with an effective dispersion and spin degrees of freedom
that only contribute entropically. In particular, the internal energy and the
effective dispersion become essentially independent of temperature. An
interpretation of this regime in terms of a putative interacting-electron
system at zero temperature leads to a metal-insulator transition at a finite
interaction strength above which the gap opens linearly. We relate these
observations to studies of the Mott-Hubbard transition in the limit of infinite
dimensions.Comment: 15 pages, 3 figure
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