109,253 research outputs found
Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering
We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer
Simulation of valveless micropump and mode analysis
In this work, a 3-D simulation is performed to study for the solid-fluid
coupling effect driven by piezoelectric materials and utilizes asymmetric
obstacles to control the flow direction. The result of simulation is also
verified. For a micropump, it is crucial to find the optimal working frequency
which produce maximum net flow rate. The PZT plate vibrates under the first
mode, which is symmetric. Adjusting the working frequency, the maximum flow
rate can be obtained. For the micrpump we studied, the optimal working
frequency is 3.2K Hz. At higher working frequency, say 20K Hz, the fluid-solid
membrane may come out a intermediate mode, which is different from the first
mode and the second mode. It is observed that the center of the mode drifts.
Meanwhile, the result shows that a phase shift lagging when the excitation
force exists in the vibration response. Finally, at even higher working
frequency, say 30K Hz, a second vibration mode is observed.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
A Consistent Calculation of Heavy Meson Decay Constants and Transition Wave Functions in the Complete HQEFT
Within the complete heavy quark effective field theory (HQEFT), the QCD sum
rule approach is used to evaluate the decay constants including 1/m_Q
corrections and the Isgur-Wise function and other additional important wave
functions concerned at 1/m_Q for the heavy-light mesons. The 1/m_Q corrections
to the scaling law f_M \sim F/\sqrt{m_M} are found to be small in HQEFT, which
demonstrates again the validity of 1/m_Q expansion in HQEFT. It is also shown
that the residual momentum v.k of heavy quark within hadrons does be around the
binding energy \bar{\Lambda} of the heavy hadrons. The calculations presented
in this paper provide a consistent check on the HQEFT and shows that the HQEFT
is more reliable than the usual HQET for describing a slightly off-mass shell
heavy quark within hadron as the usual HQET seems to lead to the breakdown of
1/m_Q expansion in evaluating the meson decay constants. It is emphasized that
the introduction of the `dressed heavy quark' mass is useful for the
heavy-light mesons (Qq) with m_Q >> \bar{\Lambda} >> m_q, while for heavy-heavy
bound states (\psi_1\psi_2) with masses m_1, m_2 >> \bar{\Lambda}, like
bottom-charm hadrons or similarly for muonium in QED, one needs to treat both
particles as heavy effective particles via 1/m_1 and 1/m_2 expansions and
redefine the effective bound states and modified `dressed heavy quark' masses
within the HQEFT.Comment: 20 pages, revtex, 22 figures, axodraw.sty, two irrelevant figures are
moved awa
Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current
The Duke storage ring is a dedicated driver for the storage ring based
oscillator free-electron lasers (FELs), and the High Intensity Gamma-ray Source
(HIGS). It is operated with a beam current ranging from about 1 mA to 100 mA
per bunch for various operations and accelerator physics studies. High
performance operations of the FEL and gamma-ray source require a stable
electron beam orbit, which has been realized by the global orbit feedback
system. As a critical part of the orbit feedback system, the electron beam
position monitors (BPMs) are required to be able to precisely measure the
electron beam orbit in a wide range of the single-bunch current. However, the
high peak voltage of the BPM pickups associated with high single-bunch current
degrades the performance of the BPM electronics, and can potentially damage the
BPM electronics. A signal conditioning method using low pass filters is
developed to reduce the peak voltage to protect the BPM electronics, and to
make the BPMs capable of working with a wide range of single-bunch current.
Simulations and electron beam based tests are performed. The results show that
the Duke storage ring BPM system is capable of providing precise orbit
measurements to ensure highly stable FEL and HIGS operations
Dynamics of Neural Networks with Continuous Attractors
We investigate the dynamics of continuous attractor neural networks (CANNs).
Due to the translational invariance of their neuronal interactions, CANNs can
hold a continuous family of stationary states. We systematically explore how
their neutral stability facilitates the tracking performance of a CANN, which
is believed to have wide applications in brain functions. We develop a
perturbative approach that utilizes the dominant movement of the network
stationary states in the state space. We quantify the distortions of the bump
shape during tracking, and study their effects on the tracking performance.
Results are obtained on the maximum speed for a moving stimulus to be
trackable, and the reaction time to catch up an abrupt change in stimulus.Comment: 6 pages, 7 figures with 4 caption
SO(3) Gauge Symmetry and Nearly Tri-bimaximal Neutrino Mixing
In this note I mainly focus on the neutrino physics part in my talk and
report the most recent progress made in \cite{YLW0}. It is seen that the
Majorana features of neutrinos and SO(3) gauge flavor symmetry can
simultaneously explain the smallness of neutrino masses and nearly
tri-bimaximal neutrino mixing when combining together with the mechanism of
approximate global U(1) family symmetry. The mixing angle and
CP-violating phase are in general nonzero and testable experimentally at the
allowed sensitivity. The model also predicts the existence of vector-like
Majorana neutrinos and charged leptons as well as new Higgs bosons, some of
them can be light and explored at the LHC and ILC.Comment: 8 pages, invited talk, contribute to the Proceedings of the 4th
International Conference on Flavor Physics (ICFP2007
Discovery of gamma-ray emission from the supernova remnant Kes 17 with Fermi Large Area Telescope
We report the discovery of GeV emission at the position of supernova remnant
Kes 17 by using the data from the Large Area Telescope on board the Fermi
Gamma-ray Space Telescope. Kes 17 can be clearly detected with a significance
of ~12 sigma in the 1 - 20 GeV range. Moreover, a number of gamma-ray sources
were detected in its vicinity. The gamma-ray spectrum of Kes 17 can be well
described by a simple power-law with a photon index of ~ 2.4. Together with the
multi-wavelength evidence for its interactions with the nearby molecular cloud,
the gamma-ray detection suggests that Kes 17 is a candidate acceleration site
for cosmic-rays.Comment: 13 pages, 3 figures, 1 table, accepted for publication in ApJ Lette
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