10,958 research outputs found
Metamagnetic Transition in NaCoO Single Crystals
We report the magnetization, specific heat and transport measurements of high
quality NaCoO single crystals in applied magnetic fields up to
14T. In high temperatures, the system is in a paramagnetic phase. It undergoes
a magnetic phase transition below about 20K. When the field is applied along
the c-axis, the measurement data of magnetization, specific heat and
magnetoresistance reveal a metamagnetic transition from an antiferromagnetic
state to a quasi-ferromagnetic state at about 8T in low temperatures. However,
no transition is observed in the magnetization measurements up to 14T when the
field is applied perpendicular to the c-axis. The low temperature magnetic
phase diagram of NaCoO is determined.Comment: 4 pages, 5 figure
Fate of non-Fermi liquid behavior in QED at finite chemical potential
The damping rate of two-dimensional massless Dirac fermions exhibit non-Fermi
liquid behavior, , due to gauge field at zero
temperature and zero chemical potential. We study the fate of this behavior at
finite chemical potential. We fist calculate explicitly the temporal and
spatial components of vacuum polarization functions. The analytical expressions
imply that the temporal component of gauge field develops a static screening
length at finite chemical potential while the transverse component remains
long-ranged owing to gauge invariance. We then calculate the fermion damping
rate and show that the temporal gauge field leads to normal Fermi liquid
behavior but the transverse gauge field leads to non-Fermi liquid behavior
at zero temperature. This energy-dependence is more
regular than and does not change as chemical potential
varies.Comment: 12 pages, 1 figur
Multiresolution spatiotemporal mechanical model of the heart as a prior to constrain the solution for 4D models of the heart.
In several nuclear cardiac imaging applications (SPECT and PET), images are formed by reconstructing tomographic data using an iterative reconstruction algorithm with corrections for physical factors involved in the imaging detection process and with corrections for cardiac and respiratory motion. The physical factors are modeled as coefficients in the matrix of a system of linear equations and include attenuation, scatter, and spatially varying geometric response. The solution to the tomographic problem involves solving the inverse of this system matrix. This requires the design of an iterative reconstruction algorithm with a statistical model that best fits the data acquisition. The most appropriate model is based on a Poisson distribution. Using Bayes Theorem, an iterative reconstruction algorithm is designed to determine the maximum a posteriori estimate of the reconstructed image with constraints that maximizes the Bayesian likelihood function for the Poisson statistical model. The a priori distribution is formulated as the joint entropy (JE) to measure the similarity between the gated cardiac PET image and the cardiac MRI cine image modeled as a FE mechanical model. The developed algorithm shows the potential of using a FE mechanical model of the heart derived from a cardiac MRI cine scan to constrain solutions of gated cardiac PET images
Spatially and Spectrally Resolved Observations of a Zebra Pattern in Solar Decimetric Radio Burst
We present the first interferometric observation of a zebra-pattern radio
burst with simultaneous high spectral (~ 1 MHz) and high time (20 ms)
resolution. The Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed
(FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe
the X1.5 flare on 14 December 2006. By using OVSA to calibrate the FST the
source position of the zebra pattern can be located on the solar disk. With the
help of multi-wavelength observations and a nonlinear force-free field (NLFFF)
extrapolation, the zebra source is explored in relation to the magnetic field
configuration. New constraints are placed on the source size and position as a
function of frequency and time. We conclude that the zebra burst is consistent
with a double-plasma resonance (DPR) model in which the radio emission occurs
in resonance layers where the upper hybrid frequency is harmonically related to
the electron cyclotron frequency in a coronal magnetic loop.Comment: Accepted for publication in Ap
Full one-loop electroweak corrections to associated productions at linear colliders
We study the complete one-loop electroweak(EW) corrections to the processes
of single charged Higgs boson production associated with a neutral Higgs
boson and a gauge boson in the framework of the minimal
supersymmetric standard model(MSSM). Numerical results at the
benchmark point as proposed in the SPA project, are presented for
demonstration. We find that for the process the EW
relative correction can be either positive or negative and in the range of
in our chosen parameter space. While for the processes
the corrections generally reduce the Born cross
sections and the EW relative corrections are typically of order .Comment: 22 pages, 20 figures, LaTex, to be appeared in PR
Current-driven skyrmionium in a frustrated magnetic system
Magnetic skyrmionium can be used as a nanometer-scale non-volatile
information carrier, which shows no skyrmion Hall effect due to its special
structure carrying zero topological charge. Here, we report the static and
dynamic properties of an isolated nanoscale skyrmionium in a frustrated
magnetic monolayer, where the skyrmionium is stabilized by competing
interactions. The frustrated skyrmionium has a size of about nm, which can
be further reduced by tuning perpendicular magnetic anisotropy or magnetic
field. It is found that the nanoscale skyrmionium driven by the damping-like
spin-orbit torque shows directional motion with a favored Bloch-type helicity.
A small driving current or magnetic field can lead to the transformation of an
unstable N\'eel-type skyrmionium to a metastable Bloch-type skyrmionium. A
large driving current may result in the distortion and collapse of the
Bloch-type skyrmionium. Our results are useful for the understanding of
frustrated skyrmionium physics, which also provide guidelines for the design of
spintronic devices based on topological spin textures.Comment: 5 pages, 5 figure
Gap solitons of a super-Tonks-Girardeau gas in a one-dimensional periodic potential
We study the stability of gap solitons of the super-Tonks-Girardeau bosonic
gas in one-dimensional periodic potential. The linear stability analysis
indicates that increasing the amplitude of periodic potential or decreasing the
nonlinear interactions, the unstable gap solitons can become stable. In
particular, the theoretical analysis and numerical calculations show that,
comparing to the lower-family of gap solitons, the higher-family of gap
solitons are easy to form near the bottoms of the linear Bloch band gaps. The
numerical results also verify that the composition relations between various
gap solitons and nonlinear Bloch waves are general and can exist in the
super-Tonks-Girardeau phase.Comment: 7 pages,6 figure
Quantum secure communication scheme with W state
Recently, Cao et al. proposed a new quantum secure direct communication
scheme using W state. In their scheme, the error rate introduced by an
eavesdropper who takes intercept-resend attack, is only 8.3%. Actually, their
scheme is just a quantum key distribution scheme because the communication
parties first create a shared key and then encrypt the secret message using
one-time pad. We then present a quantum secure communication scheme using
three-qubit W state. In our scheme, the error rate is raised to 25% and it is
not necessary for the present scheme to use alternative measurement or Bell
basis measurement. We also show our scheme is unconditionally secure.Comment: Comments are welcom
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