46,399 research outputs found
Step Bunching with Alternation of Structural Parameters
By taking account of the alternation of structural parameters, we study
bunching of impermeable steps induced by drift of adatoms on a vicinal face of
Si(001). With the alternation of diffusion coefficient, the step bunching
occurs irrespective of the direction of the drift if the step distance is
large. Like the bunching of permeable steps, the type of large terraces is
determined by the drift direction. With step-down drift, step bunches grows
faster than those with step-up drift. The ratio of the growth rates is larger
than the ratio of the diffusion coefficients. Evaporation of adatoms, which
does not cause the step bunching, decreases the difference. If only the
alternation of kinetic coefficient is taken into account, the step bunching
occurs with step-down drift. In an early stage, the initial fluctuation of the
step distance determines the type of large terraces, but in a late stage, the
type of large terraces is opposite to the case of alternating diffusion
coefficient.Comment: 8pages, 16 figure
A quick-retrieval high-speed digital framing camera
A new high-speed digital framing camera is described. The design is built around a rotating polygon mirror that provides a framing rate of 24 000 frames/s. The camera electronics digitizes an image into a 32×104 grid of pixels, where the second dimension of the grid can be varied and is determined by the 8 bit computer-aided measurement and control digitizer sampling rate. Available digitizer memory provides for 314 frames at this horizontal resolution. The advantages over other available high-speed framing cameras are (1) low cost of the system provided the digitizers are available, (2) rapid retrieval of a recorded event, and (3) the ease with which the system can be used. Sample results from an application in high-power arc photography are given to illustrate the system's spatial and temporal resolution
Phase control of La2CuO4 in thin-film synthesis
The lanthanum copper oxide, La2CuO4, which is an end member of the prototype
high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the
"K2NiF4" structure in high-temperature bulk synthesis. The crystal chemistry,
however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and
that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures.
In this article we demonstrate that low-temperature thin-film synthesis
actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the
phase control of "K2NiF4"-type La2CuO4 versus "Nd2CuO4"-type La2CuO4 can be
achieved by varying the synthesis temperature and using different substrates.Comment: 4 pages, 5 figures, submitted to PRB, revte
Laughlin states on the Poincare half-plane and its quantum group symmetry
We find the Laughlin states of the electrons on the Poincare half-plane in
different representations. In each case we show that there exist a quantum
group symmetry such that the Laughlin states are a representation of
it. We calculate the corresponding filling factor by using the plasma analogy
of the FQHE.Comment: 9 pages,Late
Investigation of the components of the NAL high Reynolds number two-dimensional wind tunnel. Part 4: Design, construction and performance of the exhaust silencer
Presented is a description of the design construction and performance of the exhaust silencer for the NAL high Reynolds number two-dimensional transonic blow down wind tunnel, which was completed in October 1979. The silencer is a two-storied construction made of reinforced concrete, 40 m. long, 10 m. wide and 19 m. high and entirely enclosed by thick concrete walls. The upstream part of the first story, particularly, is covered with double walls, the thickness of the two walls being 0.3 m. (inner wall) and 0.2 m. (outer wall), respectively. A noise reduction system using three kinds of parallel baffles and two kinds of lined bends is adopted for the wind tunnel exhaust noise
On the Existence of Local Observables in Theories With a Factorizing S-Matrix
A recently proposed criterion for the existence of local quantum fields with
a prescribed factorizing scattering matrix is verified in a non-trivial model,
thereby establishing a new constructive approach to quantum field theory in a
particular example. The existence proof is accomplished by analyzing nuclearity
properties of certain specific subsets of Fermionic Fock spaces.Comment: 13 pages, no figures, comment in sect. 3 adde
Four-spin-exchange- and magnetic-field-induced chiral order in two-leg spin ladders
We propose a mechanism of a vector chiral long-range order in two-leg
spin-1/2 and spin-1 antiferromagnetic ladders with four-spin exchanges and a
Zeeman term. It is known that for one-dimensional quantum systems, spontaneous
breakdown of continuous symmetries is generally forbidden. Any vector chiral
order hence does not appear in spin-rotationally [SU(2)]-symmetric spin
ladders. However, if a magnetic field is added along the S^z axis of ladders
and the SU(2) symmetry is reduced to the U(1) one, the z component of a vector
chiral order can emerge with the remaining U(1) symmetry unbroken. Making use
of Abelian bosonization techniques, we actually show that a certain type of
four-spin exchange can yield a vector chiral long-range order in spin-1/2 and
spin-1 ladders under a magnetic field. In the chiral-ordered phase, the Z_2
interchain-parity (i.e., chain-exchange) symmetry is spontaneously broken. We
also consider effects of perturbations breaking the parity symmetry.Comment: 8 pages, 1 figure, RevTex, published versio
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