Unusually flat hole dispersion relation in the two-dimensional Hubbard model and restoration of coherence by addition of pair-hopping processes

The dispersion relation of a doped hole in the half-filled 2D Hubbard model is shown to follow a law around the and points in the Brillouin zone. Upon addition of pair-hopping processes this dispersion relation is unstable towards a law. The above follows from T=0 Quantum Monte-Carlo calculations of the single particle spectral function on lattices. We discuss finite dopings and argue that the added term restores coherence to charge dynamics and drives the system towards a d _{x2 - y2} superconductor. Received 22 March 1999     

Stability of Waves in Relativistic Plasma

The dispersion relation of electromagnetic waves propagating perpendicular to an applied uniform magnetic field B₀ in relativistic plasma is derived. Waves propagating perpendicular to the uniform applied magnetic field can be separated into two modes - one is the linearly polarized transverse wave and the other is a hybrid mode. In the present analysis, dispersion relation of the first mode i. e., for a pure transverse wave is analysed under the assumption that the wavelength is much longer than the cyclotron radii of the electrons. A stability criterion which limits the thermal energy of the electrons along B₀ is obtained.     

The ppπ0 coupling constant and electromagnetic effects in p-p forward dispersion relations

We show that a “Coulomb-renormalized” ppπ⁰ coupling constant can be defined and deduced from experiment by applying a forward dispersion relation to Coulomb-modified p-p scattering amplitudes. The value determined in this model-independent way from the Livermore phase shifts is G²_ppπ⁰ = 15.3 ± 0.3.     

Comment on the real part of the K±p forward scattering amplitude

It is observed that the K_L⁰n→K_S⁰n regeneration measurements require positivity of the real part of the K^?p forward scattering amplitude above p ～ 1.3 GeV/c. This invalidates some of the earlier dispersion relation predictions and the preliminary experimental results from Batavia.     

K+介子的三体轻子衰变

本文利用色散关系方法,假设普适V-A弱相互作用和奇异矢量流不守恒,从而对形状因子f₀,f₁的色散关系进行一次减去,计算了K_μ3⁺、K_e3⁺衰变中的π⁰能谱,K_μ3⁺衰变中的μ⁺能谱和μ⁺的纵向极化。计算中只考虑了K₁^*(m_*=888MeV)中间态对色散积分的贡献。参数σ取为+2.1的结果和实验在误差范围内相符合。放弃奇异矢量流部分守恒假设与实验符合的程度比保持这一假设要好一些。     

Dispersion relation of over-damped soft E-polariton in tetragonal BaTiO3

In tetragonal BaTiO₃, the over-damped E-polariton frequency of ωχ''(ω, Q), obtained from the near-forward Raman spectra, has been found to follow the usual dispersion relation. From the dispersion relation in a very small q region, ?_a has been determined with precision.     

离子动力参数区托卡马克电阻性内扭曲模稳定性分析

利用离子动力参数区的内扭曲模色散关系分析了托卡马克等离子体电阻性内扭曲模的频率和增长率随磁剪切量s₀的变化。我们发现:存在一个临界磁剪切量s_0c,只有当s₀>s_0c时,即中心安全因子q₀小于某个临界值q_0c时,电阻性内扭曲模才能被激发。另一方面,随着磁剪切量s₀的加大,增长率增大的趋势比相应的磁流体电阻性内扭曲模快得多,因而与锯齿的快崩裂有内在的联系。所 关键词：     

Instability of electromagnetic waves in transversely magnetised semiconductor-plasmas

Using the hydrodynamic model of plasmas the general dispersion relation is derived in the collisiondominated regime when a d.c. magnetic field is applied (Y-axis) transversly to the propagation vector k (Z-axis), and the d.c. electric field is inclined to the Z-axis in the X-Z plane. The dispersion relation is solved for intrinsic and extrinsic semiconductors to explore the possibility of wave instability. The threshold conditions of wave oscillations are obtained. In n-InSb the frequency of the oscillation attains a maximum value when the electron cyclotron frequency is equal to the electron collision frequency. In intrinsic InSb instability is possible only in the long wavelength region for E₀ ? 10 kVm^?1 when B₀> 0.2 T, while for lower values of B₀, E₀ should be greater 20kVm^?1. The energy dependent collision frequency has a significant effect on the threshold frequency of oscillation.     

Guided modes in slab waveguides with a left handed material cover or substrate

We study guided modes propagating along a dielectric slab waveguide with a left handed material (LHM) cover or substrate. The dispersion relation is derived by using normalized waveguide parameters. An analytical method is then proposed to calculate the universal dispersion curves. Different from a slab waveguide with a LHM core, we find that guidance properties are strongly dependent on dielectric permittivity ε and magnetic permeability μ of the substrate and cover layers. For oscillating guided modes, fundamental zero order mode is not always absence, sometimes it exists in a restricted range of normalized propagation constant. First order mode behaves as other higher order modes and exists up to infinite high frequency. Higher order modes have no double degeneracy in the case of LHM cover layer. For surface guided modes, the existence and the type of the mode solutions with respect to different parameters are classified systematically and discussed in detail. Unlike a slab waveguide with a LHM core where the dispersion curve of TE₁ surface mode continues with that of oscillating TE₁ mode, the dispersion curve of TE₁ surface mode continues with that of oscillating TE₀ mode. It seems that the two different kinds of modes compensate each other to form one whole mode. Both TE and TM guided modes are discussed.     

应变Si价带色散关系模型

基于K.P理论框架,通过引入应变哈密顿微扰项,详细推导并建立了应变Si的价带色散关系模型.所得模型适用于任意晶向弛豫Si_1－xGe_x(0≤x≤0.6)衬底上生长的应变Si,并且,通过该模型可以获取任意K矢方向的应变Si价带结构及空穴有效质量,对器件研究设计可提供有价值的参考. 关键词： 应变Si K.P理论 色散关系     

The πN partial waves at low energies and in the unphysical region

The real parts of theπN partial wave amplitudesf _l± ^(?) have been calculated from fixed-t dispersion relations, using phase shifts up to 2 GeV and the reggeizedp-exchange model at higher energies. The comparison with Ref _l± ^(?) as calculated directly from phase shifts shows to what extent the input is consistent with the fixed-t relation. The result is also of interest for the test of simple models, in particular for the comparison with predictions from current algebra. — A new evaluation of the partial wave dispersion relation forf ₀₊ ^(?) is presented. Combined with the first method it shows that the determination of thep-coupling parameter is based on an assumption which is difficult to justify.     

非均匀等离子体湍流的重正化准线性理论(Ⅱ)——湍性等离子体中的共振扩散

本文在文献[1]的理论基础上,导出了用稳态湍流谱S_k⁰(0)表出的共振扩散张量的具体表式,与Birmingham等人的结果做了比较。我们在文献[1]中导出的色散关系也同时在这里与Birmingham等人的相应结果做了比较。 关键词：     

弛豫型铁电体铌镁酸铅陶瓷的玻璃化行为研究

钛酸铅与铌镁酸铅组成比为1:9的固溶体陶瓷是典型的弛豫型铁电体,其介电行为与偶极玻璃的介电行为极为相似,并已将玻璃学中的Vogel-Fulcher关系用于处理其介电常数峰值温度与频率的关系。本文测定了其介电行为随温度的变化,对其微观局域极化行为进行了分析,讨论了其局域极化的产生、增大及冻结过程,研究了弛豫型铁电体与Debye介质、玻璃体的关系和区别。在此基础上,提出了一个更合理的函数关系式,用以表征其介电常数峰值温度与频率的关系,并得出其介电弛豫激活能为0.037eV。实际应用表明,对于弛豫型铁电体,该函数关系较原有Vogel-Fulcher关系更有效。 关键词：     

BaTiO3和Ce:BaTiO3晶体极性声子和电磁激元的喇曼散射研究

从声子-电磁激元频率色散关系的普遍公式出发,推导出了单轴晶体的Merten方程和电磁激元的频率色散关系。测量了BaTiO₃和Ce:BaTiO₃晶体的简正模和斜声子的喇曼散射谱,并根据Merten方程,拟合出了斜声子的方向色散曲线;记录了A₁类电磁激元在不同波矢值下的喇曼谱,观察到其频率色散现象.根据以上结果,对A₁(TO)模喇曼谱中两个宽的非对称峰的归属和BaTiO₃晶体的结构相变机制进行了讨论;计算出了这两种晶体的受夹介电常数;分析了掺Ce对BaTiO₃晶体结构的影响。 关键词：     

Dispersion characteristic of hexagonal and square lattice chalcogenide As2Se3 glass photonic crystal fiber

In this paper, we report a chalcogenide As₂Se₃ glass photonic crystal fiber (PCF) for dispersion compensating application. We have used the improved fully vectorial effective index method (IFVEIM) for comparing the dispersion properties (negative and zero dispersion) and effective area in hexagonal and square lattice of As₂Se₃ glass PCF using different wavelength windows. It has been demonstrated that due to their negative dispersion parameter and negative dispersion slope in wavelength range 1.2-2.5 μm, both lattice structures of As₂Se₃ glass PCFs, with pitch (Λ = 2 μm), can be used as dispersion compensating fibers. Further, design parameters have been obtained to achieve zero dispersion in these fibers. It is also shown that As₂Se₃ glass PCF provides much higher negative dispersion compared to silica PCF of the same structure, in wavelength range 1.25-1.6 μm and hence such PCF have high potential to be used as a dispersion compensating fiber in optical communication systems.     

Can the optical excitations of surface plasmons be used to study (liquid) metal surfaces?

The surface plasmon dispersion relation is obtained for a metal with a free electron density given by N(z) = N_b + (N_s ? N_b) exp $\text{(}\text{?z}\text{a}\text{)}$ for z ? 0 and N = 0 for z < 0. We have used a local theory which includes the effects of retarded fields and found the dispersion relation to be sensitive to the parameters $\text{(N}{}_{\mathrm{s}}\text{? N}{}_{\mathrm{b}}\text{)}\text{N}{}_{\mathrm{b}}$ and a, which characterize our density profile.     

Temperature dependences of phonon and mobile-ion spectra in superionic conductor CuBr

The temperature dependence of far-infrared reflectivity spectra in sintered CuBr has been measured from 18 to 570 K. Phonon and mobile-ion parameters are evaluated by the fitting procedure with the factored form of the dispersion relation. A strong fourth order anharmonicity is assigned. Estimated values of optical dielectric constant and optical ionic mobility μ_op decrease with increasing temperature within a limited temperature region. For μ_op value, the effects of mobile ion scattering by optical phonons and of the expansion of interionic distance are discussed with respect to the phonon damping constant and the ionic character of the interionic force.     

Theoretical Analysis of the Einstein Relation in n-Channel Inversion Layers on A3IIB2V Semiconductors under Magnetic Quantization

We have investigated the Einstein relation in n-channel inversion layers on A₃^IIB₂^V semiconductors at low temperatures on the basis of a newly derived dispersion relation of the carriers under arbitrary magnetic quantization for the general case which occurs from the consideration of the anisotropies of the band parameters within the frame work of k · p formalism. It is found by incorporating both the effects of electron spin and broadening of Landau levels, using n-Cd₃As₂ as an example, that the theoretical formulation is in qualitative agreement with the suggested experimental method of determining the Einstein relation in degenerate semiconductors having arbitrary dispersion law. In addition, the corresponding well-known results for bulk specimens of two band Kane model both in the presence and absence of magnetic quantization, are also obtained from the generalized expressions as special cases.     

Coupled channel study on the S-wave ππ → KK interaction

We perform a dispersion relation type calculation of the I = 0 S-wave amplitude g₀⁺ (t) for the process $\text{ππ →}\text{K}\text{K}$, in the region from t = 4μ² to t = (1100 MeV)². Crossing is imposed by generalizing the newly developed hyperbolic partial-wave relations to our reaction and by imposing them on our amplitude using experimental Kπ phase-shift information as input. Analyticity and unitarity is imposed by generalizing the formalism of BFP [1] for parametrizing partial-wave amplitudes. This readily allows us to impose the experimental $\text{ππ →}\text{K}\text{K}$ cross section. Finally the low energy behaviour is constrained to lie within certain limits recently deduced from fixed-tKπ dispersion relation studies [2] and including the current algebra prediction as a special case. We are able to resolve a previous controversy regarding the sign of Im g₀⁽⁺⁾ (t).     

Rayleigh instability in liquid-crystal jets

Capillary instability of isothermal incompressible liquid-crystal (LC) jets is considered within the linear hydrodynamics of uniaxial nematic LCs. Free boundary conditions with strong tangential anchoring of director n at the surface are formulated in terms of the mean surface curvature ? and the Gaussian surface curvature G. The static version of the capillary instability is shown to depend on the elasticity modulus Κ, the surface tension σ₀, and the radius r₀ of the LC jet, expressed in terms of the characteristic parameter κ = Κ/σ₀r₀. The problem of the capillary instability in LC jets is solved exactly, and a dispersion relation that reflects the effect of elasticity is derived. It is shown that increase in the elasticity modulus results in decrease in both the cut-off wavenumber k and the disturbance growth rate s. This implies an enhanced stability of LC jets in comparison to ordinary liquids. In the specific case where the hydrodynamic and orientational LC modes can be decoupled, the dispersion equation is given in a closed form.