2,361 research outputs found
Vortex Fractionalization in a Josephson Ladder
We show numerically that, in a Josephson ladder with periodic boundary
conditions and subject to a suitable transverse magnetic field, a vortex
excitation can spontaneously break up into two or more fractional excitations.
If the ladder has N plaquettes, and N is divisible by an integer q, then in an
applied transverse field of 1/q flux quanta per plaquette the ground state is a
regular pattern of one fluxon every q plaquettes. When one additional fluxon is
added to the ladder, it breaks up into q fractional fluxons, each carrying 1/q
units of vorticity. The fractional fluxons are basically walls between
different domains of the ground state of the underlying 1/q lattice. The
fractional fluxons are all depinned at the same applied current and move as a
unit. For certain applied fields and ladder lengths, we show that there are
isolated fractional fluxons. It is shown that the fractional fluxons would
produce a time-averaged voltage related in a characteristic way to the ac
voltage frequency.Comment: 13 Figures. 10 page
Effect of the chemical state of pyrolysis gases on heat-shield mass
Effect of chemical properties of pyrolysis gases on heat shield mass required for lifting reentry vehicle in typical reentry trajector
Mass loss of TEOS-coated RCC subjected to the environment at the shuttle wing leading edge
Coated, reinforced carbon-carbon (RCC) is used for the leading edges of the Space Shuttle. The mass loss characteristics of RCC specimens coated with tetra-ethyl-ortho-silicate (TEOS) were determined for conditions which simulated the entry environment expected at the stagnation area of the wing leading edge. Maximum specimen temperature was 1632 K. Specimens were exposed for up to 100 missions. Stress levels up to 8.274 MPa caused an average increase in oxidation of 6 percent over unstressed specimens. Experimentally determined mass losses were compared with those predicted by an existing empirical analysis
Static and dynamic properties of Single-Chain Magnets with sharp and broad domain walls
We discuss time-quantified Monte-Carlo simulations on classical spin chains
with uniaxial anisotropy in relation to static calculations. Depending on the
thickness of domain walls, controlled by the relative strength of the exchange
and magnetic anisotropy energy, we found two distinct regimes in which both the
static and dynamic behavior are different. For broad domain walls, the
interplay between localized excitations and spin waves turns out to be crucial
at finite temperature. As a consequence, a different protocol should be
followed in the experimental characterization of slow-relaxing spin chains with
broad domain walls with respect to the usual Ising limit.Comment: 18 pages, 13 figures, to be published in Phys. Rev.
Recent development in the design, testing and impact-damage tolerance of stiffened composite panels
Structural technology of laminated filamentary-composite stiffened-panel structures under combined inplane and lateral loadings is discussed. Attention is focused on: (1) methods for analyzing the behavior of these structures under load and for determining appropriate structural proportions for weight-efficient configurations; and (2) effects of impact damage and geometric imperfections on structural performance. Recent improvements in buckling analysis involving combined inplane compression and shear loadings and transverse shear deformations are presented. A computer code is described for proportioning or sizing laminate layers and cross-sectional dimensions, and the code is used to develop structural efficiency data for a variety of configurations, loading conditions, and constraint conditions. Experimental data on buckling of panels under inplane compression is presented. Mechanisms of impact damage initiation and propagation are described
Excitation of the classical-limit state of an atom
We describe a technique designed to excite a classical-limit state of an atom. A picosecond electric field pulse converts a circular state into a Rydberg wave packet which is localized in all three dimensions and travels along a classical Kepler orbit with arbitrary ellipticity
Excitation of the classical-limit state of an atom
We describe a technique designed to excite a classical-limit state of an atom. A picosecond electric field pulse converts a circular state into a Rydberg wave packet which is localized in all three dimensions and travels along a classical Kepler orbit with arbitrary ellipticity
Kinetic Inductance of Josephson Junction Arrays: Dynamic and Equilibrium Calculations
We show analytically that the inverse kinetic inductance of an
overdamped junction array at low frequencies is proportional to the admittance
of an inhomogeneous equivalent impedance network. The bond in this
equivalent network has an inverse inductance
, where is the Josephson
coupling energy of the bond, is the ground-state phase
of the grain , and is the usual magnetic phase factor. We use this
theorem to calculate for square arrays as large as .
The calculated is in very good agreement with the low-temperature
limit of the helicity modulus calculated by conventional equilibrium
Monte Carlo techniques. However, the finite temperature structure of ,
as a function of magnetic field, is \underline{sharper} than the
zero-temperature , which shows surprisingly weak structure. In
triangular arrays, the equilibrium calculation of yields a series of
peaks at frustrations , where is an integer , consistent with experiment.Comment: 14 pages + 6 postscript figures, 3.0 REVTe
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