2,725 research outputs found
Onset of thermal ripples at the interface of an evaporating liquid under a flow of inert gas
peer reviewe
Non-yrast nuclear spectra in a model of coherent quadrupole-octupole motion
A model assuming coherent quadrupole-octupole vibrations and rotations is
applied to describe non-yrast energy sequences with alternating parity in
several even-even nuclei from different regions, namely Sm,
Gd, U and Mo. Within the model scheme the yrast
alternating-parity band is composed by the members of the ground-state band and
the lowest negative-parity levels with odd angular momenta. The non-yrast
alternating-parity sequences unite levels of -bands with higher
negative-parity levels. The model description reproduces the structure of the
considered alternating-parity spectra together with the observed B(E1), B(E2)
and B(E3) transition probabilities within and between the different
level-sequences. B(E1) and B(E3) reduced probabilities for transitions
connecting states with opposite parity in the non-yrast alternating-parity
bands are predicted. The implemented study outlines the limits of the
considered band-coupling scheme and provides estimations about the collective
energy potential which governs the quadrupole-octupole properties of the
considered nuclei.Comment: 38 pages, 9 figure
Influence of the 6^1S_0-6^3P_1 Resonance on Continuous Lyman-alpha Generation in Mercury
Continuous coherent radiation in the vacuum-ultraviolet at 122 nm
(Lyman-alpha) can be generated using sum-frequency mixing of three fundamental
laser beams in mercury vapour. One of the fundamental beams is at 254 nm
wavelength, which is close to the 6^1S_0-6^3P_1 resonance in mercury.
Experiments have been performed to investigate the effect of this one-photon
resonance on phasematching, absorption and the nonlinear yield. The efficiency
of continuous Lyman-alpha generation has been improved by a factor of 4.5.Comment: 8 pages, 7 figure
Heat-conserving three-temperature model for ultrafast demagnetization of 3d ferromagnets
We study the ultrafast magnetization dynamics of bcc Fe and fcc Co using the
recently suggested heat-conserving three-temperature model (HC3TM), together
with atomistic spin- and lattice dynamics simulations. It is shown that this
type of Langevin-based simulation is able to reproduce observed trends of the
ultrafast magnetization dynamics of fcc Co and bcc Fe, in agreement with
previous findings for fcc Ni. The simulations are performed by using parameters
that to as large extent as possible are obtained from electronic structure
theory. The one parameter that was not calculated in this way, was the damping
term used for the lattice dynamics simulations, and here a range of parameters
were investigated. It is found that this term has a large influence on the
details of the magnetization dynamics. The dynamics of iron and cobalt is
compared with previous results for nickel and similarities and differences in
the materials' behavior are analysed following the absorption of a femtosecond
laser pulse. Importantly, for all elements investigated so far with this model,
we obtain a linear relationship between the value of the maximally demagnetized
state and the fluence of the laser pulse, which is in agreement with
experiments.Comment: 9 pages, 9 figures, Submitted to Physical Review
Flexible structure control laboratory development and technology demonstration
An experimental structure is described which was constructed to demonstrate and validate recent emerging technologies in the active control and identification of large flexible space structures. The configuration consists of a large, 20 foot diameter antenna-like flexible structure in the horizontal plane with a gimballed central hub, a flexible feed-boom assembly hanging from the hub, and 12 flexible ribs radiating outward. Fourteen electrodynamic force actuators mounted to the hub and to the individual ribs provide the means to excite the structure and exert control forces. Thirty permanently mounted sensors, including optical encoders and analog induction devices provide measurements of structural response at widely distributed points. An experimental remote optical sensor provides sixteen additional sensing channels. A computer samples the sensors, computes the control updates and sends commands to the actuators in real time, while simultaneously displaying selected outputs on a graphics terminal and saving them in memory. Several control experiments were conducted thus far and are documented. These include implementation of distributed parameter system control, model reference adaptive control, and static shape control. These experiments have demonstrated the successful implementation of state-of-the-art control approaches using actual hardware
Collective Modes of Tri-Nuclear Molecules
A geometrical model for tri-nuclear molecules is presented. An analytical
solution is obtained provided the nuclei, which are taken to be prolately
deformed, are connected in line to each other. Furthermore, the tri-nuclear
molecule is composed of two heavy and one light cluster, the later sandwiched
between the two heavy clusters. A basis is constructed in which Hamiltonians of
more general configurations can be diagonalized. In the calculation of the
interaction between the clusters higher multipole deformations are taken into
account, including the hexadecupole one. A repulsive nuclear core is introduced
in the potential in order to insure a quasi-stable configuration of the system.
The model is applied to three nuclear molecules, namely Sr + Be +
Ba, Mo + Be + Te and Ru + Be +
Sn.Comment: 24 pages, 9 figure
Nuclear collective motion with a coherent coupling interaction between quadrupole and octupole modes
A collective Hamiltonian for the rotation-vibration motion of nuclei is
considered, in which the axial quadrupole and octupole degrees of freedom are
coupled through the centrifugal interaction. The potential of the system
depends on the two deformation variables and . The system is
considered to oscillate between positive and negative -values, by
rounding an infinite potential core in the -plane with
. By assuming a coherent contribution of the quadrupole and octupole
oscillation modes in the collective motion, the energy spectrum is derived in
an explicit analytic form, providing specific parity shift effects. On this
basis several possible ways in the evolution of quadrupole-octupole
collectivity are outlined. A particular application of the model to the energy
levels and electric transition probabilities in alternating parity spectra of
the nuclei Nd, Sm, Gd and Dy is presented.Comment: 25 pages, 13 figures. Accepted in Phys. Rev.
Extracting current-induced spins: spin boundary conditions at narrow Hall contacts
We consider the possibility to extract spins that are generated by an
electric current in a two-dimensional electron gas with Rashba-Dresselhaus
spin-orbit interaction (R2DEG) in the Hall geometry. To this end, we discuss
boundary conditions for the spin accumulations between a spin-orbit coupled
region and contact without spin-orbit coupling, i.e. a normal two-dimensional
electron gas (2DEG). We demonstrate that in contrast to contacts that extend
along the whole sample, a spin accumulation can diffuse into the normal region
through finite contacts and detected by e.g. ferromagnets. For an
impedance-matched narrow contact the spin accumulation in the 2DEG is equal to
the current induced spin accumulation in the bulk of R2DEG up to a
geometry-dependent numerical factor.Comment: 18 pages, 7 figures, submitted to NJP focus issue on Spintronic
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