71 research outputs found
Recommended from our members
Design, Analysis, and Fabrication of Two Lightweight, High L’ Railguns
Design, analysis, and fabrication of two railguns with 90 and 30 mm bores utilizing a laminated containment structure are discussed. Laminations are insulated from each other by layers of sheet adhesive, and a composite overwrap is applied to the laminations for longitudinal stiffness. The 90 mm-bore gun is being fabricated for testing as the 9 MJ range gun. Performance specifications for the 90 mm-bore gun are 3.2 MA peak current, 4.0 km/s maximum velocity, and 12 MJ muzzle energy. The 30 mm-bore gun is a one-third scale version of the 90 mm-bore gun, built to develop construction techniques and verify performance. It is designed to be operated at 1 MA with a maximum muzzle energy of 400 kJCenter for Electromechanic
Recommended from our members
Pulsed Power Accelerators at CEM-UT
An overview of four accelerator programs utilizing pulsed power is presented. The goals of each project, a description of the power supplies and launchers utilized and test results from each program are provided. The four projects presented illustrate a variety of uses for electromagnetic (EM) launchers and the potential advantages and disadvantages of four different launcher systems. Included in the paper are micrometeorite impact studies of 50 to 500 μm diameter glass beads accelerated up to 11 km/s with plasma armatures and 2.5- kg solid armature packages launched at 2.6 km/s (a record 8.1 MJ of muzzle energy). A compact rep-rateable augmented rail launcher and compulsator system weighing less than 1,100 kg is also described. Finally a skid mounted rep-rateable launcher system capable of providing 9 MJ of muzzle energy is discussed.Center for Electromechanic
Various spin-polarization states beyond the maximum-density droplet: a quantum Monte Carlo study
Using variational quantum Monte Carlo method, the effect of Landau-level
mixing on the lowest-energy--state diagram of small quantum dots is studied in
the magnetic field range where the density of magnetic flux quanta just exceeds
the density of electrons. An accurate analytical many-body wave function is
constructed for various angular momentum and spin states in the lowest Landau
level, and Landau-level mixing is then introduced using a Jastrow factor. The
effect of higher Landau levels is shown to be significant; the transition lines
are shifted considerably towards higher values of magnetic field and certain
lowest-energy states vanish altogether.Comment: 4 pages, 2 figures. Submitted to Phys. Rev.
Thermal Conductivity Tensor in YBaCuO: Effects of a Planar Magnetic Field
We have measured the thermal conductivity tensor of a twinned
YBaCuO single crystal as a function of angle between
the magnetic field applied parallel to the CuO planes and the heat current
direction, at different magnetic fields and at T=13.8 K. Clear fourfold and
twofold variations in the field-angle dependence of and
were respectively recorded in accordance with the d-wave pairing
symmetry of the order parameter. The oscillation amplitude of the transverse
thermal conductivity was found to be larger than the
longitudinal one in the range of magnetic field studied here
(). From our data we obtain quantities that are free
from non-electronic contributions and they allow us a comparison of the
experimental results with current models for the quasiparticle transport in the
mixed state.Comment: 9 Figures, Phys. Rev. B(in press
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Local and macroscopic tunneling spectroscopy of Y(1-x)CaxBa2Cu3O(7-d) films: evidence for a doping dependent is or idxy component in the order parameter
Tunneling spectroscopy of epitaxial (110) Y1-xCaxBa2Cu3O7-d films reveals a
doping dependent transition from pure d(x2-y2) to d(x2-y2)+is or d(x2-y2)+idxy
order parameter. The subdominant (is or idxy) component manifests itself in a
splitting of the zero bias conductance peak and the appearance of subgap
structures. The splitting is seen in the overdoped samples, increases
systematically with doping, and is found to be an inherent property of the
overdoped films. It was observed in both local tunnel junctions, using scanning
tunneling microscopy (STM), and in macroscopic planar junctions, for films
prepared by either RF sputtering or laser ablation. The STM measurements
exhibit fairly uniform splitting size in [110] oriented areas on the order of
10 nm2 but vary from area to area, indicating some doping inhomogeneity. U and
V-shaped gaps were also observed, with good correspondence to the local
faceting, a manifestation of the dominant d-wave order parameter
Quantum dots in high magnetic fields: Rotating-Wigner-molecule versus composite-fermion approach
Exact diagonalization results are reported for the lowest rotational band of
N=6 electrons in strong magnetic fields in the range of high angular momenta 70
<= L <= 140 (covering the corresponding range of fractional filling factors 1/5
>= nu >= 1/9). A detailed comparison of energetic, spectral, and transport
properties (specifically, magic angular momenta, radial electron densities,
occupation number distributions, overlaps and total energies, and exponents of
current-voltage power law) shows that the recently discovered
rotating-electron-molecule wave functions [Phys. Rev. B 66, 115315 (2002)]
provide a superior description compared to the
composite-fermion/Jastrow-Laughlin ones.Comment: Extensive clarifications were added (see new footnotes) regarding the
difference between the rotating Wigner molecule and the bulk Wigner crystal;
also regarding the influence of an external confining potential. 12 pages.
Revtex4 with 6 EPS figures and 5 tables . For related papers, see
http://www.prism.gatech.edu/~ph274c
Broken-Symmetry States in Quantum Hall Superlattices
We argue that broken-symmetry states with either spatially diagonal or
spatially off-diagonal order are likely in the quantum Hall regime, for clean
multiple quantum well (MQW) systems with small layer separations. We find that
for MQW systems, unlike bilayers, charge order tends to be favored over
spontaneous interlayer coherence. We estimate the size of the interlayer
tunneling amplitude needed to stabilize superlattice Bloch minibands by
comparing the variational energies of interlayer-coherent superlattice miniband
states with those of states with charge order and states with no broken
symmetries. We predict that when coherent miniband ground states are stable,
strong interlayer electronic correlations will strongly enhance the
growth-direction tunneling conductance and promote the possibility of Bloch
oscillations.Comment: 9 pages LaTeX, 4 figures EPS, to be published in PR
Chiral properties of domain-wall fermions from eigenvalues of 4 dimensional Wilson-Dirac operator
We investigate chiral properties of the domain-wall fermion (DWF) system by
using the four-dimensional hermitian Wilson-Dirac operator. We first derive a
formula which connects a chiral symmetry breaking term in the five dimensional
DWF Ward-Takahashi identity with the four dimensional Wilson-Dirac operator,
and simplify the formula in terms of only the eigenvalues of the operator,
using an ansatz for the form of the eigenvectors. For a given distribution of
the eigenvalues, we then discuss the behavior of the chiral symmetry breaking
term as a function of the fifth dimensional length. We finally argue the chiral
property of the DWF formulation in the limit of the infinite fifth dimensional
length, in connection with spectra of the hermitian Wilson-Dirac operator in
the infinite volume limit as well as in the finite volume.Comment: Added a reference and modified the acknowledgmen
Group theoretical analysis of symmetry breaking in two-dimensional quantum dots
We present a group theoretical study of the symmetry-broken unrestricted
Hartree-Fock orbitals and electron densities in the case of a two-dimensional
N-electron single quantum dot (with and without an external magnetic field).
The breaking of rotational symmetry results in canonical orbitals that (1) are
associated with the eigenvectors of a Hueckel hamiltonian having sites at the
positions determined by the equilibrium molecular configuration of the
classical N-electron problem, and (2) transform according to the irreducible
representations of the point group specified by the discrete symmetries of this
classical molecular configuration. Through restoration of the total-spin and
rotational symmetries via projection techniques, we show that the point-group
discrete symmetry of the unrestricted Hartree-Fock wave function underlies the
appearance of magic angular momenta (familiar from exact-diagonalization
studies) in the excitation spectra of the quantum dot. Furthermore, this
two-step symmetry-breaking/symmetry-restoration method accurately describes the
energy spectra associated with the magic angular momenta.Comment: A section VI.B entitled "Quantitative description of the lowest
rotational band" has been added. 16 pages. Revtex with 10 EPS figures. A
version of the manuscript with high quality figures is available at
http://calcite.physics.gatech.edu/~costas/uhf_group.html For related papers,
see http://www.prism.gatech.edu/~ph274c
- …