11,661 research outputs found
Forestland type identification and analysis in Western Massachussetts: A linkage of a LANDSAT forest inventory to an optimization study
Digital land cover files derived from computer processing of LANDSAT and soil productivity data were linked and used by linear programming model to determine production of forested areas under different management strategies. Results of model include maps and data graphics for four-county region in Western Massachusetts
Conductivity of a graphene strip: width and gate-voltage dependencies
We study the conductivity of a graphene strip taking into account
electrostatically-induced charge accumulation on its edges. Using a local
dependency of the conductivity on the carrier concentration we find that the
electrostatic size effect in doped graphene strip of the width of 0.5 - 3 m can result in a significant (about 40%) enhancement of the effective
conductivity in comparison to the infinitely wide samples. This effect should
be taken into account both in the device simulation as well as for verification
of scattering mechanisms in graphene.Comment: 3 pages, 4 figure
Monopole Vector Spherical Harmonics
Eigenfunctions of total angular momentum for a charged vector field
interacting with a magnetic monopole are constructed and their properties
studied. In general, these eigenfunctions can be obtained by applying vector
operators to the monopole spherical harmonics in a manner similar to that often
used for the construction of the ordinary vector spherical harmonics. This
construction fails for the harmonics with the minimum allowed angular momentum.
These latter form a set of vector fields with vanishing covariant curl and
covariant divergence, whose number can be determined by an index theorem.Comment: 21 pages, CU-TP-60
Effect of quasi-bound states on coherent electron transport in twisted nanowires
Quantum transmission spectra of a twisted electron waveguide expose the
coupling between traveling and quasi-bound states. Through a direct numerical
solution of the open-boundary Schr\"odinger equation we single out the effects
of the twist and show how the presence of a localized state leads to a
Breit-Wigner or a Fano resonance in the transmission. We also find that the
energy of quasi-bound states is increased by the twist, in spite of the
constant section area along the waveguide. While the mixing of different
transmission channels is expected to reduce the conductance, the shift of
localized levels into the traveling-states energy range can reduce their
detrimental effects on coherent transport.Comment: 8 pages, 9 color figures, submitte
Wave localization in binary isotopically disordered one-dimensional harmonic chains with impurities having arbitrary cross section and concentration
The localization length for isotopically disordered harmonic one-dimensional
chains is calculated for arbitrary impurity concentration and scattering cross
section. The localization length depends on the scattering cross section of a
single scatterer, which is calculated for a discrete chain having a wavelength
dependent pulse propagation speed. For binary isotopically disordered systems
composed of many scatterers, the localization length decreases with increasing
impurity concentration, reaching a mimimum before diverging toward infinity as
the impurity concentration approaches a value of one. The concentration
dependence of the localization length over the entire impurity concentration
range is approximated accurately by the sum of the behavior at each limiting
concentration. Simultaneous measurements of Lyapunov exponent statistics
indicate practical limits for the minimum system length and the number of
scatterers to achieve representative ensemble averages. Results are discussed
in the context of future investigations of the time-dependent behavior of
disordered anharmonic chains.Comment: 8 pages, 10 figures, submitted to PR
Uniqueness of a Negative Mode About a Bounce Solution
We consider the uniqueness problem of a negative eigenvalue in the spectrum
of small fluctuations about a bounce solution in a multidimensional case. Our
approach is based on the concept of conjugate points from Morse theory and is a
natural generalization of the nodal theorem approach usually used in one
dimensional case. We show that bounce solution has exactly one conjugate point
at with multiplicity one.Comment: 4 pages,LaTe
Collisionless Magnetic Reconnection via Alfven Eigenmodes
We propose an analytic approach to the problem of collisionless magnetic
reconnection formulated as a process of Alfven eigenmodes' generation and
dissipation. Alfven eigenmodes are confined by the current sheet in the same
way that quantum mechanical waves are confined by the tanh^2 potential. The
dynamical time scale of reconnection is the system scale divided by the
eigenvalue propagation velocity of the n=1 mode. The prediction of the n=1 mode
shows good agreement with the in situ measurement of the
reconnection-associated Hall fields
Resonance modes in a 1D medium with two purely resistive boundaries: calculation methods, orthogonality and completeness
Studying the problem of wave propagation in media with resistive boundaries
can be made by searching for "resonance modes" or free oscillations regimes. In
the present article, a simple case is investigated, which allows one to
enlighten the respective interest of different, classical methods, some of them
being rather delicate. This case is the 1D propagation in a homogeneous medium
having two purely resistive terminations, the calculation of the Green function
being done without any approximation using three methods. The first one is the
straightforward use of the closed-form solution in the frequency domain and the
residue calculus. Then the method of separation of variables (space and time)
leads to a solution depending on the initial conditions. The question of the
orthogonality and completeness of the complex-valued resonance modes is
investigated, leading to the expression of a particular scalar product. The
last method is the expansion in biorthogonal modes in the frequency domain, the
modes having eigenfrequencies depending on the frequency. Results of the three
methods generalize or/and correct some results already existing in the
literature, and exhibit the particular difficulty of the treatment of the
constant mode
Fermions on one or fewer Kinks
We find the full spectrum of fermion bound states on a Z_2 kink. In addition
to the zero mode, there are int[2 m_f/m_s] bound states, where m_f is the
fermion and m_s the scalar mass. We also study fermion modes on the background
of a well-separated kink-antikink pair. Using a variational argument, we prove
that there is at least one bound state in this background, and that the energy
of this bound state goes to zero with increasing kink-antikink separation, 2L,
and faster than e^{-a2L} where a = min(m_s, 2 m_f). By numerical evaluation, we
find some of the low lying bound states explicitly.Comment: 7 pages, 4 figure
Elastodynamics of radially inhomogeneous spherically anisotropic elastic materials in the Stroh formalism
A method is presented for solving elastodynamic problems in radially
inhomogeneous elastic materials with spherical anisotropy, i.e.\ materials such
that in a spherical coordinate system
. The time harmonic displacement field is expanded in a separation of variables form with dependence on
described by vector spherical harmonics with -dependent
amplitudes. It is proved that such separation of variables solution is
generally possible only if the spherical anisotropy is restricted to transverse
isotropy with the principal axis in the radial direction, in which case the
amplitudes are determined by a first-order ordinary differential system.
Restricted forms of the displacement field, such as ,
admit this type of separation of variables solutions for certain lower material
symmetries. These results extend the Stroh formalism of elastodynamics in
rectangular and cylindrical systems to spherical coordinates.Comment: 15 page
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