7,829 research outputs found
Neutron diffraction studies of magnetostrictive Fe–Ga alloy ribbons
Melt-spun Fe–Ga ribbons were prepared and some ribbons were annealed at 1000 °C for 1 h then
slowly cooled to room temperature. X-ray diffraction patterns revealed no evidence of texture and
only bcc phase in the as-quenched ribbons. However, high-resolution neutron diffraction patterns
gave more information on the structure of these ribbons. Only diffractions from the disordered bcc
A2 phase were found in as-quenched ribbons with 15, 17.5, and 19.5 at. % Ga content, without any
trace of satellite peaks or splitting peaks from the proposed Ga–Ga pairing superlattice structure.
The broadening of the base of the �110� peaks for all samples except the as-quenched 15 at. % Ga
ribbon might indicate the existence of some kind of short range ordering. Ribbons developed L12
phase after annealing especially in the Fe 19.5 at. % Ga ribbon where the formation of L12 phase
reduced the Ga content in the remaining A2 phase and decreased its lattice parameter dramatically.
D03 phase formed in the as-quenched 22.5 at. % Ga ribbon and the following annealing treatment
transformed more A2 phase into D03 phase
Suppressing the Rayleigh-Taylor instability with a rotating magnetic field
The Rayleigh-Taylor instability of a magnetic fluid superimposed on a
non-magnetic liquid of lower density may be suppressed with the help of a
spatially homogeneous magnetic field rotating in the plane of the undisturbed
interface. Starting from the complete set of Navier-Stokes equations for both
liquids a Floquet analysis is performed which consistently takes into account
the viscosities of the fluids. Using experimentally relevant values of the
parameters we suggest to use this stabilization mechanism to provide controlled
initial conditions for an experimental investigation of the Rayleigh-Taylor
instability
Crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates
Dynamical instabilities at the interface between two Bose--Einstein
condensates that are moving relative to each other are investigated using
mean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant
when the interface thickness is much smaller than the wavelength of the
unstable interface mode, whereas the counter-superflow instability becomes
dominant in the opposite case. These instabilities emerge not only in an
immiscible system but also in a miscible system where an interface is produced
by external potential. Dynamics caused by these instabilities are numerically
demonstrated in rotating trapped condensates.Comment: 10 pages, 9 figure
The Bouncing Jet: A Newtonian Liquid Rebounding off a Free Surface
We find that a liquid jet can bounce off a bath of the same liquid if the
bath is moving horizontally with respect to the jet. Previous observations of
jets rebounding off a bath (e.g. Kaye effect) have been reported only for
non-Newtonian fluids, while we observe bouncing jets in a variety of Newtonian
fluids, including mineral oil poured by hand. A thin layer of air separates the
bouncing jet from the bath, and the relative motion replenishes the film of
air. Jets with one or two bounces are stable for a range of viscosity, jet flow
rate and velocity, and bath velocity. The bouncing phenomenon exhibits
hysteresis and multiple steady states.Comment: 9 pages, 7 figures. submitted to Physical Review
Stretching Instability of Helical Spring
We show that when a gradually increasing tensile force is applied to the ends
of a helical spring with sufficiently large ratios of radius to pitch and twist
to bending rigidity, the end-to-end distance undergoes a sequence of
discontinuous stretching transitions. Subsequent decrease of the force leads to
step-like contraction and hysteresis is observed. For finite helices, the
number of these transitions increases with the number of helical turns but only
one stretching and one contraction instability survive in the limit of an
infinite helix. We calculate the critical line that separates the region of
parameters in which the deformation is continuous from that in which stretching
instabilities occur, and propose experimental tests of our predictions.Comment: 5 pages, 4 figure
Cavitation and bubble collapse in hot asymmetric nuclear matter
The dynamics of embryonic bubbles in overheated, viscous and non-Markovian
nuclear matter is studied. It is shown that the memory and the Fermi surface
distortions significantly affect the hinderance of bubble collapse and
determine a characteristic oscillations of the bubble radius. These
oscillations occur due to the additional elastic force induced by the memory
integral.Comment: Revtex file (10 pages) and 3 figure
Stochastic time-dependent current-density functional theory: a functional theory of open quantum systems
The dynamics of a many-body system coupled to an external environment
represents a fundamentally important problem. To this class of open quantum
systems pertains the study of energy transport and dissipation, dephasing,
quantum measurement and quantum information theory, phase transitions driven by
dissipative effects, etc. Here, we discuss in detail an extension of
time-dependent current-density-functional theory (TDCDFT), we named stochastic
TDCDFT [Phys. Rev. Lett. {\bf 98}, 226403 (2007)], that allows the description
of such problems from a microscopic point of view. We discuss the assumptions
of the theory, its relation to a density matrix formalism, and the limitations
of the latter in the present context. In addition, we describe a numerically
convenient way to solve the corresponding equations of motion, and apply this
theory to the dynamics of a 1D gas of excited bosons confined in a harmonic
potential and in contact with an external bath.Comment: 17 pages, 7 figures, RevTex4; few typos corrected, a figure modifie
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