457 research outputs found
Theoretical Study on Forming of Twisted T-section Longitudinals (1^<St> Report) : Investigation from the Aspect of Inherent Strain(Mechanics, Strength & Structure Design)
Effect of Primordial Magnetic Field on Seeds for Large Scale Structure
Magnetic field plays a very important role in many astronomical phenomena at
various scales of the universe. It is no exception in the early universe.
Since the energy density, pressure, and tension of the primordial magnetic
field affect gravitational collapses of plasma, the formation of seeds for
large scale structures should be influenced by them. Here we numerically
investigate the effects of stochastic primordial magnetic field on the seeds of
large scale structures in the universe in detail. We found that the amplitude
ratio between the density spectra with and without PMF ( at
Mpc) lies between 75% and 130% at present for the range of PMF
strengths 0.5 nG nG, depending on the spectral index of PMF
and the correlation between the matter density and the PMF distributions.Comment: 20 pages, 5 figures, submitted to PRD 23 Jan 2006, Revised 02 Oct
2006, accepted for publication in PR
Magnetic excitations and electronic interactions in SrCuTeO: a spin-1/2 square lattice Heisenberg antiferromagnet
SrCuTeO presents an opportunity for exploring low-dimensional
magnetism on a square lattice of Cu ions. We employ ab initio
multi-reference configuration interaction calculations to unravel the Cu
electronic structure and to evaluate exchange interactions in SrCuTeO.
The latter results are validated by inelastic neutron scattering using linear
spin-wave theory and series-expansion corrections for quantum effects to
extract true coupling parameters. Using this methodology, which is quite
general, we demonstrate that SrCuTeO is an almost realization of a
nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling
of 7.18(5) meV.Comment: 10 pages, 7 figure
Contrasting pressure evolution of f-electron hybridized states in CeRhIn5 and YbNi3 Ga9 : An optical conductivity study
Optical conductivity [σ (ω)] of CeRhIn5 and YbNi3Ga9 have been measured at external pressures to 10 GPa and at low temperatures to 6 K. Regarding CeRhIn5, at ambient pressure the main feature in σ (ω) is a Drude peak due to free carriers. With increasing pressure, however, a characteristic midinfrared (mIR) peak rapidly develops in σ (ω), and its peak energy and width increase with pressure. These features are consistent with an increased conduction (c)- f electron hybridization at high pressure and show that pressure has tuned the electronic state of CeRhIn5 from very weakly to strongly hybridized ones. As for YbNi3Ga9, in contrast, a marked mIR peak is observed already at ambient pressure, indicating a strong c- f hybridization. At high pressures, however, the mIR peak shifts to lower energy and becomes diminished and seems to merge with the Drude component at 10 GPa. Namely, CeRhIn5 and YbNi3Ga9 exhibit some opposite tendencies in the pressure evolution of σ (ω) and electronic structure. These results are discussed in terms of the pressure evolution of c- f hybridized electronic states in Ce and Yb compounds, in particular in terms of the electron-hole symmetry often considered between Ce and Yb
Enhanced Next Generation Millimeter-Wave Multicarrier System with Generalized Frequency Division Multiplexing
Orthogonal Frequency Division Multiplexing (OFDM) is a popular multicarrier technique used to attain high spectral efficiencies. It also has other advantages such as multipath tolerance and ease of implementation. However, OFDM based systems suffer from high Peak-to-Average Power Ratio (PAPR) problem. Because of the nonlinearity of the power amplifiers, the high PAPR causes significant distortion in the transmitted signal for millimeter-wave (mmWave) systems. To alleviate the high PAPR problem, this paper utilizes Generalized Frequency Division Multiplexing (GFDM) which can achieve high spectral efficiency as well as low PAPR. In this paper, we show the performance of GFDM using the IEEE 802.11ad multicarrier frame structures. IEEE 802.11ad is considered one of the most successful industry standards utilizing unlicensed mmWave frequency band. In addition, this paper indicates the feasibility of using GFDM for the future standards such as IEEE 802.11ay. This paper studies the performance improvements in terms of PAPR reduction for GFDM. Based on the performance results, the optimal numbers of subcarriers and subsymbols are calculated for PAPR reduction while minimizing the Bit Error Rate (BER) performance degradation. Moreover, transmitter side ICI (Intercarrier Interference) reduction is introduced to reduce the receiver load
Molecular cloning and functional expression of a novel brain-specific inward rectifier potassium channel
AbstractWe have cloned a novel brain-specific inward rectifier K+ channel from a mouse brain cDNA library and designated it MB-IRK3. The mouse brain cDNA library was screened using a fragment of the mouse macrophage inward rectifier K+ channel (IRK1) cDNA as a probe. The amino acid sequence of MB-IRK3 shares 61% and 64% identity to MB-IRK1 and RB-IRK2, respectively.Xenopus oocytes injected with cRNA derived from this clone expressed a potassium current which showed inward-rectifying channel characteristics similar to MB-IRK1 and RB-IRK2 currents, but distinct from ROMK1 or GIRK1 current. However, the single channel conductance of MB-IRK3 was ∼ 10 pS with 140 mM extracellular K+, which was distinct from that of MB-IRK1 (20 pS). MB-IRK3 mRNA expressed specifically in the forebrain, which clearly differed from MB-IRK1 and RB-IRK2 mRNAs. These results indicate that members of the IRK family with distinct electrophysiological properties express differentially and may play heterogenous functional roles in brain functions
Robust hybridization gap in the Kondo insulator YbB12 probed by femtosecond optical spectroscopy
In heavy fermions the relaxation dynamics of photoexcited carriers has been found to be governed by the low energy indirect gap Eg resulting from hybridization between localized moments and conduction band electrons. Here, carrier relaxation dynamics in a prototype Kondo insulator YbB12 is studied over a large range of temperatures and over three orders of magnitude. We utilize the intrinsic nonlinearity of dynamics to quantitatively determine microscopic parameters, such as electron-hole recombination rate. The extracted value reveals that hybridization is accompanied by a strong charge transfer from localized 4 f levels. The results imply the presence of a hybridization gap up to temperatures of the order of Eg/kB ≈ 200 K, which is extremely robust against electronic excitation. Finally, below 20 K the data reveal changes in the low energy electronic structure, attributed to short-range antiferromagnetic correlations between the localized levels
Random Bond Effect in the Quantum Spin System (TlK)CuCl
The effect of exchange bond randomness on the ground state and the
field-induced magnetic ordering was investigated through magnetization
measurements in the spin-1/2 mixed quantum spin system
(TlK)CuCl for . Both parent compounds TlCuCl and
KCuCl are coupled spin dimer systems, which have the singlet ground state
with excitation gaps K and 31 K, respectively. Due to
bond randomness, the singlet ground state turns into the magnetic state with
finite susceptibility, nevertheless, the excitation gap remains. Field-induced
magnetic ordering, which can be described by the Bose condensation of excited
triplets, magnons, was observed as in the parent systems. The phase transition
temperature is suppressed by the bond randomness. This behavior may be
attributed to the localization effect.Comment: 19 pages, 7 figures, 12 eps files, revtex, will appear in PR
Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar field in the Bianchi type I model
In this paper we study the isotropisation of a Generalized Scalar-Tensor
theory with a massive scalar field. We find it depends on a condition on the
Brans-Dicke coupling function and the potential and show that asymptotically
the metric functions always tend toward a power or exponential law of the
proper time. These results generalise and unify these of De Sitter in the case
of a cosmological constant and of Cooley and Kitada in the case of an
exponential potential.Comment: 10 page
Laser-induced topological spin switching in a 2D van der Waals magnet
Two-dimensional (2D) van der Waals (vdW) magnets represent one of the most
promising horizons for energy-efficient spintronic applications because their
broad range of electronic, magnetic and topological properties. Of particular
interest is the control of the magnetic properties of 2D materials by
femtosecond laser pulses which can provide a real path for low-power
consumption device platforms in data storage industries. However, little is
known about the interplay between light and spin properties in vdW layers.
Here, combining large-scale spin dynamics simulations including biquadratic
exchange interactions and wide-field Kerr microscopy (WFKM), we show that
ultrafast laser excitation can not only generate different type of spin
textures in CrGeTe vdW magnets but also induce a reversible transformation
between them in a toggle-switch mechanism. Our calculations show that
skyrmions, anti-skyrmions, skyrmioniums and stripe domains can be generated via
high-intense laser pulses within the picosecond regime. The effect is tunable
with the laser energy where different spin behaviours can be selected, such as
fast demagnetisation process (250 fs) important for information
technologies. The phase transformation between the different topological spin
textures is obtained as additional laser pulses are applied to the system where
the polarisation and final state of the spins can be controlled by external
magnetic fields. We experimentally confirmed the creation, manipulation and
toggle switching phenomena in CrGeTe due to the unique aspect of
laser-induced heating of electrons. Our results indicate laser-driven spin
textures on 2D magnets as a pathway towards ultrafast reconfigurable
architecture at the atomistic level
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