Energy spectrum of quasigeostrophic turbulence

We consider the energy spectrum of a quasigeostrophic model of forced, rotating turbulent flow. We provide a rigorous a priori bound E(k)相似文献   

Anisotropic scaling of magnetohydrodynamic turbulence

We present a quantitative estimate of the anisotropic power and scaling of magnetic field fluctuations in inertial range magnetohydrodynamic turbulence, using a novel wavelet technique applied to spacecraft measurements in the solar wind. We show for the first time that, when the local magnetic field direction is parallel to the flow, the spacecraft-frame spectrum has a spectral index near 2. This can be interpreted as the signature of a population of fluctuations in field-parallel wave numbers with a k(-2)_(||) spectrum but is also consistent with the presence of a "critical balance" style turbulent cascade. We also find, in common with previous studies, that most of the power is contained in wave vectors at large angles to the local magnetic field and that this component of the turbulence has a spectral index of 5/3.     

Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wave number ranges in a Beta > or approximately = 1 plasma. The k(-5/3) inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfvén speed. At smaller wavelengths krho(i) > or = 1 the electric spectrum is enhanced and is consistent with the expected dispersion relation of short-wavelength kinetic Alfvén waves. Kinetic Alfvén waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluidlike nature of the solar wind.     

Stagnation pressure of imploding shells and ignition energy scaling of inertial confinement fusion targets

The stagnation pressure p(s) of imploding cylindrical ( n = 2) and spherical ( n = 3) shells is found to scale as p(s)/p(0)~M(2(n+1)/(gamma+1))(0), where M0 is the Mach number of the imploding shell and p(0) its maximum pressure. The result holds approximately for Mach numbers in the range 2相似文献   

Wave-number spectra and intermittency in the terrestrial foreshock region

Wave-number spectra of magnetic field fluctuations are directly determined in the terrestrial foreshock region (upstream of a quasiparallel collisionless shock wave) using four-point Cluster spacecraft measurements. The spectral curve is characterized by three ranges reminiscent of turbulence: energy injection, inertial, and dissipation range. The spectral index for the inertial range spectrum is close to Kolmogorov's slope, -5/3. On the other hand, the fluctuations are highly anisotropic and intermittent perpendicular to the mean magnetic field direction. These results suggest that the foreshock is in a weakly turbulent and intermittent state in which parallel propagating Alfvén waves interact with one another, resulting in the phase coherence or the intermittency.     

Finite-mode spectral model of homogeneous and isotropic Navier-stokes turbulence: a rapidly depleted energy cascade

An eddy-viscous term is added to Navier-Stokes dynamics at wave numbers k greater than the inflection point kc of the energy flux F(log(k)). The eddy viscosity is fixed so that the energy spectrum satisfies E(k) = E(kc) (k/kc)(-3) for k>kc. This resulting forcing induces a rapid depletion of the energy cascade at k>kc. It is observed numerically that the model reproduces turbulence energetics at k< or =kc and statistics of two-point velocity correlations at scales r>lambda (Taylor microscale). Compared to a direct numerical simulation of R(lambda) = 130 an equivalent run with the present model results in a gain of a factor 20 in CPU time.     

Bose-Einstein condensation in solid 4He

We present neutron scattering measurements of the atomic momentum distribution n(k) in solid helium under a pressure p=41 bar (molar volume Vm=20.01+/-0.02 cm3/mol) and at temperatures between 80 and 500 mK. The aim is to determine whether there is Bose-Einstein condensation (BEC) below the critical temperature, Tc=200 mK, where a superfluid density has been observed. Assuming BEC appears as a macroscopic occupation of the k=0 state below Tc, we find a condensate fraction of n0=(-0.10+/-1.20)% at T=80 mK and n0=(0.08+/-0.78)% at T=120 mK, consistent with zero. The shape of n(k) also does not change on crossing Tc within measurement precision.     

广义非线性薛定谔方程描述的波坍缩及其演变

介绍了广义非线性薛定谔方程, 并且运用分步傅里叶方法进行了数值求解. 在外部势场一定的情况下, 给定系统一个小的初始扰动, 讨论了广义非线性薛定谔方程中复系数p, q 对波场演变过程的影响. 通过数值研究发现波场会相继出现调制不稳定性、波坍缩、逆级联以及整个空间的湍流现象. 而当改变非线性频移系数的量级时, 数值研究发现在波坍缩之后出现了逆级联, 最终系统的能量主要凝聚在3个不同波矢终端的附近区域.     

Quantum critical point of an itinerant antiferromagnet in a heavy fermion

A quantum critical point of the heavy fermion Ce(Ru(1-x)Rh(x))2Si2, (x = 0,0.03) has been studied by single-crystalline neutron scattering. By accurately measuring the dynamical susceptibility at the antiferromagnetic wave vector k3 = 0.35c*, we have shown that the inverse energy width gamma(k3), i.e., the inverse correlation time, depends on temperature as gamma(k3) = c1 + c2T((3/2)+/-0.1), where c1 and c2 are x dependent constants, in a low temperature range. This critical exponent 3/2 +/- 0.1 proves that the quantum critical point is controlled by that of the itinerant antiferromagnet.     

Quadrupole parameters of 11B in crystalline CaO.B2O3.

The quadrupole coupling constant (Qcc) and asymmetry parameter (eta) of 11B in crystalline CaO.B2O3 have been measured employing three different NQR and NMR methods: (1) 11B and 10B NQR; (2) 11B NQR and NMR; and (3) the 11B Zeeman NQR powder pattern. It is found that Qcc = 2594.3 +/- 0.5 kHz and eta = 0.515 +/- 0.001 at 77 K, and Qcc = 2573.5 +/- 0.5 kHz and eta = 0.511 +/- 0.002 at 300 K. These values are in agreement with, but far more accurate than, values obtained from a fourth procedure: measurement of the second-order quadrupolar effects evident in the m = + 1/2<-->m = - 1/2 transition of the 11B NMR spectrum.     

Turbulent transport of material particles: an experimental study of finite size effects

We present experimental Lagrangian statistics of finite sized, neutrally bouyant, particles transported in an isotropic turbulent flow. The particle's diameter is varied over turbulent inertial scales. Finite size effects are shown not to be trivially related to velocity intermittency. The global shape of the particle's acceleration probability density functions is not found to depend significantly on its size while the particle's acceleration variance decreases as it becomes larger in quantitative agreement with the classical k(-7/3) scaling for the spectrum of Eulerian pressure fluctuations in the carrier flow.     

Anomalous self-similarity in a turbulent rapidly rotating fluid

Our velocity measurements on quasi-two-dimensional turbulent flow in a rapidly rotating annulus yield self-similar (scale-independent) probability distribution functions for longitudinal velocity differences, deltav(l) = v(x+l)-v(x). These distribution functions are strongly non-Gaussian, suggesting that the coherent vortices play a significant role. The structure functions <[deltav(l)](p)> approximately l(zeta)p exhibit anomalous scaling: zeta(p) = p / 2 rather than the expected zeta(p) = p / 3. Correspondingly, the energy spectrum is described by E(k) approximately k(-2) rather than the expected E(k) approximately k(-5/3).     

少量氩气对大气介质阻挡放电光谱的增强

采用双水电极介质阻挡放电装置,测量了大气介质阻挡放电的光谱,并研究了加入少量氩气后光谱的变化。在300～800 nm波长范围内,发现了氮分子(C3Π_u(v′=0)→B3Π_g(v″=0～4))的光谱和氮原子(4d4D_7/2→3p4P0_1/2)的光谱。在大气中加入少量氩气后,击穿电压明显降低,在相同电压条件下,氮分子光谱线和氮原子光谱线强度都增强。同时,加入氩气后上述谱线的半宽度明显加大。由于谱线的Stark加宽与电子密度成正比, 说明加入氩气后等离子体的电子密度增大, 使得电子碰撞激发氮分子及氮原子的概率增大,激发到较高激发态的氮原子或氮分子增多,从而使光谱强度增强。     

Exact relation for correlation functions in compressible isothermal turbulence

Compressible isothermal turbulence is analyzed under the assumption of homogeneity and in the asymptotic limit of a high Reynolds number. An exact relation is derived for some two-point correlation functions which reveals a fundamental difference with the incompressible case. The main difference resides in the presence of a new type of term which acts on the inertial range similarly as a source or a sink for the mean energy transfer rate. When isotropy is assumed, compressible turbulence may be described by the relation -2/3ε(eff)r = F(r)(r), where F(r) is the radial component of the two-point correlation functions and ε(eff) is an effective mean total energy injection rate. By dimensional arguments, we predict that a spectrum in k(-5/3) may still be preserved at small scales if the density-weighted fluid velocity ρ(1/3)u is used.     

Quantized turbulence physics

We elaborate the physics of systems of unconstrained, reconnecting vortex filaments with dynamic finite cores of uniform ("quantized") circulation interacting via Biot-Savart and viscous forces. The phenomenology of this purely structured turbulent system includes an inertial range with Kolmogorov's k(-5/3) scaling for the energy spectrum, as well as Kolmogorov's linear in r scaling for the third order longitudinal structure function.     

Observation of an exotic baryon with S=+1 in photoproduction from the proton

The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.     

NO2分子在440～495 nm范围内的激光诱导荧光激发谱

以 NdYAG脉冲激光器泵浦的光学参量发生器/放大器作激发光源, 获得了室温、低气压条件下, NO2分子在440～495 nm波长范围内的激光诱导荧光激发谱, 将所得谱线峰归属为NO2由基电子态X2A1态向第二电子激发态B2B1态的跃迁, 利用实验所得峰值波长计算了NO2分子B2B1态的角振动频率ωe. 通过对NO2分子B2B1→X2A1跃迁的荧光时间分辨光谱进行实验研究, 得到15 Pa气压下B2B1(0, 9, 0)振动态的能级寿命τ=49 μs. 测量了荧光寿命随气压的变化关系, 利用曲线拟合得到NO2 B2B1(0, 9, 0)振动态的自发辐射寿命τ0≈55 μs和无辐射跃迁弛豫速率常数. kq=1.2×10-9 cm3 molecule-1s-1.     

Experimental study of the Doppler shift generated by a vibrating scatterer

We report an experimental study of the backscattering of a sound wave of frequency f by a surface vibrating harmonically at frequency F (F < f) and amplitude A in the regime where the Doppler effect overcomes bulk nonlinear effects. When the duration to of the analyzed time series of the scattered wave is small compared to the vibration period, the power spectrum of the backscattered wave is proportional to the probability density function of the scatterer velocity, which presents two peaks shifted from f by roughly 2fAomega/c (omega = 2piF). On the contrary, when t0 > F(-1), sidebands at frequencies f +/- nF (n integer) appear in the power spectrum, which are due to the phase modulation of the backscattered wave induced by its reflection on a moving boundary. We use the backscattered power spectrum to validate the phase modulation theory of the Doppler effect in the latter case for 2kA < 1 and 2kA approximately > 1 (k = 2pif/c, where c is the wave velocity) and we test the validity of an acoustic nonintrusive estimator of A as a function of power spectrum bandwidth and of A itself.     

Observation of a near-threshold enhancement in the omega(phi) mass spectrum from the doubly OZI-suppressed decay J/psi-->gamma(omega)phi

An enhancement near threshold is observed in the omega(phi) invariant mass spectrum from the doubly Okubo-Zweig-Iizuka-suppressed decays of J/psi-->gamma(omega)phi, based on a sample of 5.8 x 10(7) J/psi events collected with the BESII detector. A partial wave analysis shows that this enhancement favors JP=0+, and its mass and width are M=1812(+19)(-26)(stat)+/-18(syst) MeV/c2 and Gamma=105+/-20(stat)+/-28(syst) MeV/c2. The product branching fraction is determined to be B(J/psi-->gammaX)B(X-->omega(phi))=[2.61+/-0.27(stat)+/-0.65(syst)]x10(-4).