共查询到20条相似文献,搜索用时 31 毫秒
1.
Ding-Zong Zhang 《中国物理 B》2023,32(1):15201-015201
The linear behavior of the dominant unstable mode ($m=2$, $n=1$) and its high order harmonics ($m=2n$, $n\ge 2$) are numerically investigated in a reversed magnetic shear cylindrical plasma with two $q=2$ rational surfaces on the basis of the non-reduced magnetohydrodynamics (MHD) equations. The results show that with low beta (beta is defined as the ratio of plasma pressure to magnetic field pressure), the dominant mode is a classical double tearing mode (DTM). However, when the beta is sufficiently large, the mode is driven mainly by plasma pressure. In such a case, both the linear growth rate and mode structures are strongly affected by pressure, while almost independent of the resistivity. This means that the dominant mode undergoes a transition from DTM to pressure-driven mode with the increase of pressure, which is consistent with the experimental result in ASDEX Upgrade. The simulations also show that the distance between two rational surfaces has an important influence on the pressure needed in mode transition. The larger the distance between two rational surfaces, the larger the pressure for driving the mode transition is. Motivated by the phenomena that the high-$m$ modes may dominate over low-$m$ modes at small inter-resonance distance, the high-$m$ modes with different pressures and $q$ profiles are studied too. 相似文献
2.
In this paper, the properties of dark energy are
investigated according to the parameterized deceleration parameter
q(z), which is used to describe the extent of the accelerating
expansion of the universe. The potential of dark energy V(φ)
and the cosmological parameters, such as the dimensionless energy
density \varOmega_φ, \varOmega_m, and the state parameter
w_φ, are connected to it. Concretely, by giving two kinds of
parameterized deceleration parameters q(z)=a+bz/(1+z) and
q(z)=1/2+(az+b)/(1+z)^2, the evolution of these parameters
and the reconstructed potentials V(φ) are plotted and analysed.
It is found that the potentials run away with the evolution of
universe. 相似文献
3.
We have theoretically and experimentally studied the quantum coherence effects of a degenerate transition Fg =3←→Fe=2 system interacting with a weak linearly polarized (with σ+ components) probe light and a strong linearly polarized (with σ+ components) coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) are present at the different values of applied magnetic field in the case where the Zeeman splitting of excited state Δe is larger than the Zeeman splitting of ground state Δg (i.e.Δe 〉 Δg). 相似文献
4.
D. V. Bugg 《The European Physical Journal C - Particles and Fields》2004,33(4):505-509
The latest
elastic scattering data are re-analysed to determine the coupling constant gc of the charged pion, using the dispersion relation for the invariant amplitude B(+ ). Depending on the choice of data-base, values
to 13.65 are obtained with errors of
. The mass difference between charge states of
is
MeV, close to twice the mass difference between neutron and proton. The difference in widths on resonance is
MeV. One may account for a width difference of 4.5 MeV from phase space for decays and the extra channel
.Received: 21 January 2004, Published online: 3 March 2004 相似文献
5.
For any classical Lie algebra $\mathfrak{g}$,
we construct a family of
integrable generalizations of Toda mechanics labeled a pair of ordered
integers $(m,n)$. The universal form of the Lax pair, equations of motion,
Hamiltonian as well as Poisson brackets are provided, and explicit examples
for $\mathfrak{g}=B_{r},C_{r},D_{r}$ with $m,n\leq3$ are also given. For all
$m,n$, it is shown that the dynamics of the $(m,n-1)$- and the $(m-1,n)$-Toda
chains are natural reductions of that of the $(m,n)$-chain, and for $m=n$,
there is also a family of symmetrically reduced Toda systems, the
$(m,m)_{\mathrm{Sym}}$-Toda systems, which are also integrable. In the quantum
case, all $(m,n)$-Toda systems with $m>1$ or $n>1$ describe the dynamics of
standard Toda variables coupled to noncommutative variables. Except for the
symmetrically reduced cases, the integrability for all $(m,n)$-Toda systems
survive after quantization. 相似文献
6.
ZnO films have been prepared on p-type Si substrates by metal-organic chemical vapour deposition (MOCVD) at different total gas flow rates. The current versus voltage and temperature (I - V - T) characteristics, the deep-level transient spectroscopy (DLTS) and the photoluminescence (PL) spectra of the samples were measured. DLTS shows two deep-level centres of E1 (Ec-0.13±0.02eV) and E2 (Ec-0.43±0.05eV) in sample 1202a, which has a ZnO/p-Si heterostructure. A deep level at Ec-0.13±0.01 eV was also obtained from the I -T characteristics. It was considered to be the same as E1 obtained from DLTS measurement. The emission related to this deep level center was detected by PL spectra. In addition, the energy location and the relative trap density of E1 was varied when the total gas flow rate was changed. 相似文献
7.
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e
+
e
-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e
+
e
-and
spectral functions in the
channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and
, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are
where the errors have been separated according to their sources: experimental, missing radiative corrections in e
+
e
-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read
where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be
(1.9
) and
(0.7
) for the e
+
e
-- and
-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003 相似文献
8.
We have studied the interaction of
$F=2$ spinor Bose condensate with a combination of static and
sinusoidal magnetic field $b_l(t)=b_0+b\cos(\omega t)$. We find
that the tunneling current among spin 0 and spin $\pm1$, spin 0
and spin $\pm2$, spin $\pm1$ and spin $\pm2$ may exhibit the
incremental oscillation behavior, which depends on the field
parameters of the reduced amplitudes of the transverse and the
longitudinal magnetic fields respectively. This means that the
dynamics spin localization can be adjusted experimentally by
selecting the less values of the reduced amplitudes of the
transverse magnetic field $b_x/\omega$ and those of the
longitudinal magnetic field $b/\omega$. 相似文献
9.
H. Mohammadi S. J. Akhtarshenas F. Kheirandish 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(3):439-447
We study the entanglement dynamics of an anisotropic two-qubit Heisenberg XYZ system in
the presence of intrinsic decoherence. The usefulness of such a system for performance of
the quantum teleportation protocol T0\mathcal{T}_0
and entanglement teleportation protocol T1\mathcal{T}_1
is also investigated. The results depend on the initial conditions and the parameters of
the system. The roles of system parameters such as the inhomogeneity of the magnetic field
b and the spin-orbit interaction parameter D, in
entanglement dynamics and fidelity of teleportation, are studied for both product and
maximally entangled initial states of the resource. We show that for the product and
maximally entangled initial states, increasing D amplifies the effects of
dephasing and hence decreases the asymptotic entanglement and fidelity of the
teleportation. For a product initial state and specific interval of the magnetic field
B, the asymptotic entanglement and hence the fidelity of teleportation
can be improved by increasing B. The XY and XYZ Heisenberg systems
provide a minimal resource entanglement, required for realizing efficient teleportation.
Also, in the absence of the magnetic field, the degree of entanglement is preserved for
the maximally entangled initial states $\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.. The
same is true for the maximally entangled initial states
$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right., in the
absence of spin-orbit interaction D and the inhomogeneity parameter
b. Therefore, it is possible to perform quantum teleportation protocol
T0\mathcal{T}_0
and entanglement teleportation T1\mathcal{T}_1,
with perfect quality, by choosing a proper set of parameters and employing one of these
maximally entangled robust states as the initial state of the resource. 相似文献
10.
D. Demir Y. Şahin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):17-22
The effect of an external magnetic field on the L3
subshell fluorescence yields (ω3 ) and level widths ($\Gamma_{L_3}$) for paramagnetic Ta, W, Tl, Th and U have been investigated using the
59.54 keV incident photon energy in the external magnetic field of
intensities ±0.60 T. L3 X-ray fluorescence cross sections ($\sigma_{L_3}^{X}$)
have been measured for the same elements. The measured ω
3, $\Gamma_{L_3} $
and $ \sigma_{L_3}^X$ values for B = 0 are in good
agreement with the theoretical values. It was observed that the values of
$\sigma_{L_3}^X$
and ω3 with the applied magnitude of the
magnetic field in both directions show a decreasing trend for paramagnetic
Ta, W, Tl, Th and U. Furthermore, in the presence of an external magnetic
field, the values of
$\Gamma_{L_3}$
show an increasing trend for
the same elements. The results show that the atomic parameters such as
spectral linewidth, radiation rates, photoionization cross section and
fluorescence yield can change when the irradiation is conducted in a
magnetic field. 相似文献
11.
在室温条件下的激光晶体MgF2单晶中,实验发现含有130多条峰的电子自旋共振(ESR)波谱。两个样品分别取自MgF2单晶生长放肩的尖锥部位和MgF2:Co晶体.两个样品都没有经过任何辐照处理。两个样品具有相同的各向异性谱,说明掺入的Co2+离子引发了与MgF2单晶放肩部位相同的位错缺陷,产生了相同的多核固体自由基。这些顺磁固体自由基稳定且寿命长,产生的ESR信号是各向异性的。经初步计算拟合,谱线是由三种不同的多核自由基产生的。当磁场方向与晶体的[100]或[010]方向平行时,样品的ESR信号出现在磁场从0.2292特斯拉(T)到0.4654T的0.2362T范围内(相当于能带宽度为0.233eV)。最窄的线宽DH约为0.00128特斯拉,DH相当于相邻的能级差,是非常小的,仅有1.85×10-7eV 或1.46×10-3cm-1。这一事实表明其基态简并度是相当高的,在不太高的直流磁场下几乎是一个由准连续的能级组成的能带。这有可能成为可调谐的固体激光介质的新基点。 相似文献
12.
13.
We report the constraints of $H_0$ obtained from Wilkinson Microwave Anisotropy Probe (WMAP) 9-year data combined with the latest baryonic acoustic oscillations (BAO) measurements. We use the BAO measurements from 6dF Galaxy Survey (6dFGS), the SDSS DR7 main galaxies sample (MGS), the BOSS DR12 galaxies, and the eBOSS DR14 quasars. Adding the recent BAO measurements to the cosmic microwave background (CMB) data from WMAP, we constrain cosmological parameters $\Omega_m=0.298\pm0.005$, $H_0=68.36^{+0.53}_{-0.52} {\rm km}\cdot {\rm s}^{-1}\cdot {\rm Mpc}^{-1}$, $\sigma_8=0.8170^{+0.0159}_{-0.0175}$ in a spatially flat $\Lambda$ cold dark matter ($\Lambda$CDM) model, and $\Omega_m=0.302\pm0.008$, $H_0=67.63\pm1.30 {\rm km}\cdot{\rm s}^{-1}\cdot {\rm Mpc}^{-1}$, $\sigma_8=0.7988^{+0.0345}_{-0.0338}$ in a spatially flat $w$CDM model, respectively. Our measured $H_0$ results prefer a value lower than 70 ${\rm km}\cdot {\rm s}^{-1}\cdot{\rm Mpc}^{-1}$, consistent with the recent data on CMB constraints from Planck (2018), but in $3.1$ and $3.5\sigma$ tension with local measurements of SH0ES (2018) in $\Lambda$CDM and $w$CDM framework, respectively. Our results indicate that there is a systematic tension on the Hubble constant between SH0ES and the combination of CMB and BAO datasets. 相似文献
14.
The magnetic and dielectric properties of multiferroic Sr- substituted Zn2-Y hexagonal ferrites 下载免费PDF全文
The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites (Ba2-x SrxZn2Fe12O22, 1.0 〈 x ≤ 1.5) are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due to the transformation from ferrimagnetic to antiferromagnetic phase. Moreover, permittivity rises with increasing Sr content. Under a certain external magnetic field, the phase transition of helical spin structure of Ba0.5Srl.5Zn2Fe12O22 at about 295 K seems to open a possibility for the room-temperature ferroelectricity induced by magnetic field. But its low resistivity prevents the observation of ferroelectric and magnetoelectric properties at room-temperature. 相似文献
15.
Magnetism and giant magnetocaloric effect in rare-earth-based compounds R_3BWO_9(R = Gd,Dy, Ho) 下载免费PDF全文
《中国物理 B》2021,30(7):77501-077501
The magnetism and magnetocaloric effect(MCE) of rare-earth-based tungstate compounds R_3 BWO_9(R=Gd,Dy,Ho) have been studied by magnetic susceptibility,isothermal magnetization,and specific heat measurements.No obvious long-range magnetic ordering can be found down to 2 K.The Curie-Weiss fitting and magnetic susceptibilities under different applied fields reveal the existence of weak short-range antiferromagnetic couplings at low temperature in these systems.The calculations of isothermal magnetization exhibit a giant MCE with the maximum changes of magnetic entropy being 54.80 J/kg-K at 2 K for Gd_3 BWO_9,28.5 J/kg-K at 6 K for Dy_3 BWO_9,and 29.76 J/kg-K at 4 K for Ho_3 BWO_9,respectively,under a field change of 0-7 T.Especially for Gd_3 BWO_9,the maximum value of magnetic entropy change(-ΔS_M~(max)) and adiabatic temperature change(-ΔT_(ad)~(max)) are 36.75 J/kg·K and 5.56 K for a low field change of 0-3 T,indicating a promising application for low temperature magnetic refrigeration. 相似文献
16.
The low-energy structures and the electronic and the
magnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure,
electronic and magnetic properties Project supported by the National
Natural Science Foundation of China (Grant No.~10874039), and the
Natural Science Foundation of Hebei Province of China (Grant
Nos.~A2009000246 and 2009000243). 3120A, 3640B, 2110K 7/3/2009 12:00:00 AM The low-energy structures and the electronic and the
magnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure,
electronic and magnetic properties Project supported by the National
Natural Science Foundation of China (Grant No.~10874039), and the
Natural Science Foundation of Hebei Province of China (Grant
Nos.~A2009000246 and 2009000243). 3120A, 3640B, 2110K 7/3/2009 12:00:00 AM The low-energy structures and the electronic and the
magnetic properties of small Ni$_{n}$Ti$_{n}$ ($n=1$--$6$) and
Ni$_{m}$Ti$_{n}$ ($1 \le n \le 4$, $1 \le m \le 4$, $n \ne m$)
clusters are investigated by performing all-electron calculations
based on density functional theory. Ground states and several
isomers near the ground states are determined for these clusters.
The results indicate that the growth of small Ni$_{m}$Ti$_{n}$
clusters prefers to form rich Ti--Ni and Ti--Ti bonds. When the
percentage of titanium atoms is significantly greater than that of
nickel atoms, the nickel atoms are most frequently found above
the surface; in contrast, the titanium atoms prefer the bridging
sites. A M\"{u}lliken spin population analysis indicates that the
total spin of titanium-nickel clusters is not always zero. http://cpb.iphy.ac.cn/CN/10.1088/1674-1056/19/4/043102 https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=111644 NimTin;clusters;lowest-energy;structure;electronic;and;magnetic;properties The low-energy structures and the electronic and the magnetic properties of small Nin Tin(n = 1-6) and Ni m Ti n(1 ≤ n ≤ 4,1 ≤ m ≤ 4,n ≠ m) clusters are investigated by performing all-electron calculations based on density functional theory.Ground states and several isomers near the ground states are determined for these clusters.The results indicate that the growth of small Ni m Ti n clusters prefers to form rich Ti-Ni and Ti-Ti bonds.When the percentage of titanium atoms is significantly greater than that of nickel atoms,the nickel atoms are most frequently found above the surface;in contrast,the titanium atoms prefer the bridging sites.A Mu¨lliken spin population analysis indicates that the total spin of titanium-nickel clusters is not always zero. 相似文献
17.
In this paper we calculate the production of a charged top pion in
association with a $W$ boson at the CERN Large Hadron Collider
(LHC) in the context of the topcolor assisted technicolor
model. We find that the cross section of $pp \rightarrow b\bar{b}
\rightarrow W^{\pm}\pi_t^{\mp}$ is roughly corresponding to the
result of the process $pp \rightarrow b\bar{b} \rightarrow
W^{\pm}H^{\mp}$ in the minimal supersymmetric standard model, and
for reasonable ranges of the parameters, the cross section can
reach a few hundred fb. The $W^{\pm}\pi_t^{\mp}$ signal
should be clearly visible at LHC unless $\pi_t^{\pm}$ is very heavy. 相似文献
18.
We study the periodic cosmic transit behavior of the accelerated universe in the framework of symmetric teleparallelism. The exact solution of field equations is obtained by employing a well-known deceleration parameter (DP) called periodic varying DP, $q=m\cos {kt}-1$. The viability and physical reliability of the DP are studied by using observational constraints. The dynamics of periodicity and singularity are addressed in detail with respect to time and redshift parameter. Several energy conditions are discussed in this setting. 相似文献
19.
Tailored martensitic transformation and enhanced magnetocaloric effect in all-d-metal Ni35Co15Mn33Fe2Ti15 alloy ribbons 下载免费PDF全文
The crystal structure, martensitic transformation and magnetocaloric effect have been studied in all-$d$-metal Ni$_{35}$Co$_{15}$Mn$_{33}$Fe$_{2}$Ti$_{15}$ alloy ribbons with different wheel speeds (15 m/s (S15), 30 m/s (S30), and 45 m/s (S45)). All three ribbons crystalize in B2-ordered structure at room temperature with crystal constants of 5.893(2) Å, 5.898(4) Å, and 5.898(6) Å, respectively. With the increase of wheel speed, the martensitic transformation temperature decreases from 230 K to 210 K, the Curie temperature increases slightly from 371 K to 378 K. At the same time, magnetic entropy change ($\Delta S_{\rm m}$) is also enhanced, as well as refrigeration capacity ($RC$). The maximum $\Delta S_{\rm m}$ of 15.6(39.7) J/kg$\cdot$K and $RC$ of 85.5 (212.7) J/kg under $\Delta H = 20$ (50) kOe (1 ${\rm Oe}=79.5775$ A$\cdot$m$^{-1}$) appear in S45. The results indicate that the ribbons could be the candidate for solid-state magnetic refrigeration materials. 相似文献
20.
Anomalous magnetic properties of an iron film system deposited on fracture surfaces of α-Al2O3 ceramics 下载免费PDF全文
An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of α-Al2O3 ceramics. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field He of the iron film exhibits a minimum peak around the temperature T=5 K, which is independent of the magnitude of the cooling field Hcf. However, for T 〉 10K, (1) He is always negative when Hcf=2kOe and (2) for Hcf= 20 kOe (1Oe≈80 A/m), He changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase. 相似文献