7,246 research outputs found
Dynamical Monte Carlo investigation of spin reversals and nonequilibrium magnetization of single-molecule magnets
In this paper, we combine thermal effects with Landau-Zener (LZ) quantum
tunneling effects in a dynamical Monte Carlo (DMC) framework to produce
satisfactory magnetization curves of single-molecule magnet (SMM) systems. We
use the giant spin approximation for SMM spins and consider regular lattices of
SMMs with magnetic dipolar interactions (MDI). We calculate spin reversal
probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and
thermal-assisted LZ tunnelings in the presence of sweeping magnetic fields. We
do systematical DMC simulations for Mn systems with various temperatures
and sweeping rates. Our simulations produce clear step structures in
low-temperature magnetization curves, and our results show that the thermally
activated barrier hurdling becomes dominating at high temperature near 3K and
the thermal-assisted tunnelings play important roles at intermediate
temperature. These are consistent with corresponding experimental results on
good Mn samples (with less disorders) in the presence of little
misalignments between the easy axis and applied magnetic fields, and therefore
our magnetization curves are satisfactory. Furthermore, our DMC results show
that the MDI, with the thermal effects, have important effects on the LZ
tunneling processes, but both the MDI and the LZ tunneling give place to the
thermal-activated barrier hurdling effect in determining the magnetization
curves when the temperature is near 3K. This DMC approach can be applicable to
other SMM systems, and could be used to study other properties of SMM systems.Comment: Phys Rev B, accepted; 10 pages, 6 figure
Phase-field-crystal modeling of the (2x1)-(1x1) phase-transitions of Si(001) and Ge(001) surfaces
We propose a two-dimensional phase-field-crystal model for the
(21)-(11) phase transitions of Si(001) and Ge(001) surfaces.
The dimerization in the 21 phase is described with a
phase-field-crystal variable which is determined by solving an evolution
equation derived from the free energy. Simulated periodic arrays of
dimerization variable is consistent with scanning-tunnelling-microscopy images
of the two dimerized surfaces. Calculated temperature dependence of the
dimerization parameter indicates that normal dimers and broken ones coexist
between the temperatures describing the charactristic temperature width of the
phase-transition, and , and a first-order phase transition takes
place at a temperature between them. The dimerization over the whole
temperature is determined. These results are in agreement with experiment. This
phase-field-crystal approach is applicable to phase-transitions of other
reconstructed surface phases, especially semiconductor 1 reconstructed
surface phases.Comment: 10 pages with 4 figures include
Quark energy loss and shadowing in nuclear Drell-Yan process
The energy loss effect in nuclear matter is another nuclear effect apart from
the nuclear effects on the parton distribution as in deep inelastic scattering
process. The quark energy loss can be measured best by the nuclear dependence
of the high energy nuclear Drell-Yan process. By means of three kinds of quark
energy loss parameterizations given in literature and the nuclear parton
distribution extracted only with lepton-nucleus deep inelastic scattering
experimental data, measured Drell-Yan production cross sections are analyzed
for 800GeV proton incident on a variety of nuclear targets from FNAL E866. It
is shown that our results with considering the energy loss effect are much
different from these of the FNAL E866 who analysis the experimental data with
the nuclear parton distribution functions obtained by using the deep inelastic
lA collisions and pA nuclear Drell-Yan data . Considering the existence of
energy loss effect in Drell-Yan lepton pairs production,we suggest that the
extraction of nuclear parton distribution functions should not include
Drell-Yan experimental data.Comment: 12 page
Signals of Unparticles in Low Energy Parity Violation and NuTeV Experiment
We have studied the possible signals of unparticle in atomic parity
violation(APV) along an isotope chain and in the NuTeV experiment. The effects
of unparticle physics could be observed in APV, if the uncertainty in relative
neutron/proton radius shift is less than a few
times by measuring the parity violating electron scattering. The
constraints imposed by NuTeV experiment on unparticle physics are discussed in
detail. If the NuTeV results are confirmed by future experiments, we suggest
that unparticle could account for a part of NuTeV anomaly. There exist certain
regions for the unparticle parameters (, ,
and ), where the NuTeV discrepancy could be
completely explained by unparticle effects and the strange quark asymmetry,
even with or without the contributions from the isoscalarity violation etc. It
is remarkable that these parameter regions are consistent with the constraints
from Comment: 19 pages, 7 figure
Doing academic assignments: Whether to use a wiki or an alternative platform
Using a wiki in a group project can be a valuable experience, particularly when students are able to learn about collaboration between group members. Because they are not given a defined structure, students can flexibly design content with multimodality through the use of a wiki. However, students commonly experience some form of technical difficulty when using a wiki. A pilot study of two courses explored what preferred applications students used when preparing group wiki-based projects in one course, and it examined why some students preferred to use platforms other than a wiki in the other course. Results from the end-of-course survey suggest that while students were aware of features available in wikis, they preferred to use web tools that they were already familiar with to develop web-based products. Many students remarked that there was a lack of technical preparation for this learning platform, or they did not see the value in continuing to use wikis after completing the course. Also, some indicated that they favoured email applications such as Hotmail for collaboration and feedback purposes. Suggestions are offered to educators on how to improve student reception of wikis and other Web 2.0 e-learning tools. © 2010 IADIS.postprintThe 2010 IADIS International Conference on e-Learning, Freiburg, Germany, 26-30 July 2010. In Proceedings of the IADIS International Conference on e-Learning, 2010, v. 2, p. 209-21
Modified Bennett-Brassard 1984 Quantum Key Distribution With Two-way Classical Communications
The quantum key distribution protocol without public announcement of bases is
equipped with a two-way classical communication symmetric entanglement
purification protocol. This modified key distribution protocol is
unconditionally secure and has a higher tolerable error rate of 20%, which is
higher than previous scheme without public announcement of bases.Comment: 5 pages. To appear in Physical Review
Comment on "Atomic Scale Structure and Chemical Composition across Order-Disorder Interfaces"
Interfaces have long been known to be the key to many mechanical and electric
properties. To nickel base superalloys which have perfect creep and fatigue
properties and have been widely used as materials of turbine blades, interfaces
determine the strengthening capacities in high temperature. By means of high
resolution scanning transmission electron microscopy (HRSTEM) and 3D atom probe
(3DAP) tomography, Srinivasan et al. proposed a new point that in nickel base
superalloys there exist two different interfacial widths across the
{\gamma}/{\gamma}' interface, one corresponding to an order-disorder
transition, and the other to the composition transition. We argue about this
conclusion in this comment
Warped flavor symmetry predictions for neutrino physics
A realistic five-dimensional warped scenario with all standard model fields
propagating in the bulk is proposed. Mass hierarchies would in principle be
accounted for by judicious choices of the bulk mass parameters, while fermion
mixing angles are restricted by a flavor symmetry broken on the
branes by flavon fields. The latter gives stringent predictions for the
neutrino mixing parameters, and the Dirac CP violation phase, all described in
terms of only two independent parameters at leading order. The scheme also
gives an adequate CKM fit and should be testable within upcoming oscillation
experiments.Comment: 19 pages, 2 figue
Analysis and discussion on electronic resource construction and information service of libraries in Mainland China
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