5,996 research outputs found
Domain wall switching: optimizing the energy landscape
It has recently been suggested that exchange spring media offer a way to
increase media density without causing thermal instability
(superparamagnetism), by using a hard and a soft layer coupled by exchange.
Victora has suggested a figure of merit xi = 2 E_b/mu_0 m_s H_sw, the ratio of
the energy barrier to that of a Stoner-Wohlfarth system with the same switching
field, which is 1 for a Stoner-Wohlfarth (coherently switching) particle and 2
for an optimal two-layer composite medium. A number of theoretical approaches
have been used for this problem (e.g., various numbers of coupled
Stoner-Wohlfarth layers and continuum micromagnetics). In this paper we show
that many of these approaches can be regarded as special cases or
approximations to a variational formulation of the problem, in which the energy
is minimized for fixed magnetization. The results can be easily visualized in
terms of a plot of the energy as a function of magnetic moment m_z, in which
both the switching field [the maximum slope of E(m_z)] and the stability
(determined by the energy barrier E_b) are geometrically visible. In this
formulation we can prove a rigorous limit on the figure of merit xi, which can
be no higher than 4. We also show that a quadratic anistropy suggested by Suess
et al comes very close to this limit.Comment: Acccepted for proceedings of Jan. 2007 MMM Meeting, paper BE-0
Two-Particle Schroedinger Equation Animations of Wavepacket-Wavepacket Scattering (revised)
A simple and explicit technique for the numerical solution of the
two-particle, time-dependent Schr\"{o}dinger equation is assembled and tested.
The technique can handle interparticle potentials that are arbitrary functions
of the coordinates of each particle, arbitrary initial and boundary conditions,
and multi-dimensional equations. Plots and animations are given here and on the
World Wide Web of the scattering of two wavepackets in one dimension.Comment: 13 pages, 8 figures, animations at
http://nacphy.physics.orst.edu/ComPhys/PACKETS
Teaching systematic reflection to novice educational designers
How to help students in the field of instructional design and educational technology to develop their professional expertise through systematic reflection? This question is answered by describing the intended, implemented and attained curriculum of a third year university bachelor course on systematic reflection for design students. In this course, students learn four modes of reflection that originate in the work of the philosopher Kant. This approach is perceived as a different, yet productive addition to existing reflection approaches
Comment on "Peierls Gap in Mesoscopic Ring Threated by a Magnetic Flux"
In a recent letter, Yi et al. PRL 78, 3523 (1997), have considered the
stability of a Charge Density Wave in a one-dimensional ring, in the presence
of an Aharonov-Bohm flux. This comment shows that, in one dimension, the
stability of the Charge Density Wave depends on the parity of the number of
electrons in the ring. This effect is similar to the parity effect known for
the persistent current in one-dimensional rings.Comment: Latex, 1 page, 2 figure
Relativistic general-order coupled-cluster method for high-precision calculations: Application to Al+ atomic clock
We report the implementation of a general-order relativistic coupled-cluster
method for performing high-precision calculations of atomic and molecular
properties. As a first application, the static dipole polarizabilities of the
ground and first excited states of Al+ have been determined to precisely
estimate the uncertainty associated with the BBR shift of its clock frequency
measurement. The obtained relative BBR shift is -3.66+-0.44 for the 3s^2
^1S_0^0 --> 3s3p ^3P_0^0 transition in Al+ in contrast to the value obtained in
the latest clock frequency measurement, -9+-3 [Phys. Rev. Lett. 104, 070802
(2010)]. The method developed in the present work can be employed to study a
variety of subtle effects such as fundamental symmetry violations in atoms.Comment: 4 pages, 3 tables, submitte
Investigations on a diffusion porometer with a fast humidity sensor.
A commercially available small humidity sensor with a very fast response was used in an unventilated diffusion porometer to measure leaf epidermal resistance. Measurements over calibrated dummy resistances showed that such a porometer had definite advantages in transpiration measurements in the field. In particular the waiting time before each measurement, necessary to obtain reproducible results with the commonly used LiCl sensor, could be shortened from 2 min to 15 s or even less. (Abstract retrieved from CAB Abstracts by CABI’s permission
Conductance Fluctuations in a Metallic Wire Interrupted by a Tunnel Junction
The conductance fluctuations of a metallic wire which is interrupted by a
small tunnel junction has been explored experimentally. In this system, the
bias voltage V, which drops almost completely inside the tunnel barrier, is
used to probe the energy dependence of conductance fluctuations due to disorder
in the wire. We find that the variance of the fluctuations is directly
proportional to V. The experimental data are consistently described by a
theoretical model with two phenomenological parameters: the phase breaking time
at low temperatures and the diffusion coefficient.Comment: 9 pages RevTeX and 4 PS figures (accepted for publication in Physical
Review Letters
Measurement of the rate of water flow in plants.
A non-destructive thermo-electric method is described for the measurement of water flow in the stems of plants such as wheat and potatoes. The 2 temp. sensors are 10 or 20 mm apart. The miniature sensing is made by evaporation techniques. The sensor is suitable for laboratory as well as for field work. Flow rate in the stem can be monitored for several wk at relatively low cost. (Abstract retrieved from CAB Abstracts by CABI’s permission
The electronic spectrum of CUONg(4) (Ng = Ne, Ar, Kr, Xe): New insights in the interaction of the CUO molecule with noble gas matrices
The electronic spectrum of the CUO molecule was investigated with the IHFSCC-SD (intermediate Hamiltonian Fock-space coupled cluster with singles and doubles) method and with TD-DFT (time-dependent density functional theory) employing the PBE and PBE0 exchange-correlation functionals. The importance of both spin-orbit coupling and correlation effects on the low-lying excited-states of this molecule are analyzed and discussed. Noble gas matrix effects on the energy ordering and vibrational frequencies of the lowest electronic states of the CUO molecule were investigated with density functional theory (DFT) and TD-DFT in a supermolecular as well as a frozen density embedding (FDE) subsystem approach. This data is used to test the suitability of the FDE approach to model the influence of different matrices on the vertical electronic transitions of this molecule. The most suitable potential was chosen to perform relativistic wave function theory in density functional theory calculations to study the vertical electronic spectra of the CUO and CUON
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