Measuring small compartments with relatively weak gradients by angular double-pulsed-field-gradient NMR

NMR diffusion–diffraction patterns observed in compartments in which restricted diffusion occurs are a useful tool for direct extraction of compartment sizes. Such diffusion–diffraction patterns may be observed when the signal intensity E_(q,?) is plotted against the wave-vector q (when q = (2π)^− 1γδG). However, the smaller the compartment sizes are, the higher are the q-values needed to observe such diffractions. Moreover, these q-values should be achieved using short gradient pulses requiring extremely strong gradient systems. The angular double-pulsed-field gradient (d-PFG) NMR methodology has been proposed as a tool to extract compartment sizes using relatively low q-values. In this study, we have used single-PFG (s-PFG) NMR and angular d-PFG NMR to characterize the size of microcapillaries of about 2 ± 1 μm in diameter. We found that these microcapillaries are characterized by relatively strong background gradients that completely masked the effects of the microscopic anisotropy (μA) of the sample, resulting in a completely unexpected E(φ) profile in the angular d-PFG NMR experiments. We also show that bipolar angular d-PFG NMR experiments can largely suppress the effect of these background gradients resulting in the expected E(φ) profile from which the compartment dimensions could be obtained with relatively weak gradient pulses. These results demonstrate that the above methodology provides a quick, reliable, non-invasive means for estimating small pore sizes with relatively weak gradients in the presence of large magnetic susceptibility.     

Observation of restricted diffusion in the presence of a free diffusion compartment: Single- and double-PFG experiments

Theoretical and experimental studies of restricted diffusion have been conducted for decades using single pulsed field gradient (s-PFG) diffusion experiments. In homogenous samples, the diffusion–diffraction phenomenon arising from a single population of diffusing species has been observed experimentally and predicted theoretically. In this study, we introduce a composite bi-compartmental model which superposes restricted diffusion in microcapillaries with free diffusion in an unconfined compartment, leading to fast and slow diffusing components in the NMR signal decay. Although simplified (no exchange), the superposed diffusion modes in this model may exhibit features seen in more complex porous materials and biological tissues. We find that at low q-values the freely diffusing component masks the restricted diffusion component, and that prolongation of the diffusion time shifts the transition from free to restricted profiles to lower q-values. The effect of increasing the volume fraction of freely diffusing water was also studied; we find that the transition in the signal decay from the free mode to the restricted mode occurs at higher q-values when the volume fraction of the freely diffusing water is increased. These findings were then applied to a phantom consisting of crossing fibers, which demonstrated the same qualitative trends in the signal decay. The angular d-PGSE experiment, which has been recently shown to be able to measure small compartmental dimensions even at low q-values, revealed that microscopic anisotropy is lost at low q-values where the fast diffusing component is prominent. Our findings may be of importance in studying realistic systems which exhibit compartmentation.     

Effect of the molecular structure on the gas-surface scattering studied by supersonic molecular beam

The experimental apparatus for investigating the gas-surface interaction has been newly developed. The coherent length of the helium, the energy resolution and the angular spread of the beam in the apparatus were established as ω= 16 nm, DE/E = 2.4%\Delta E/E = 2.4{\%} and Δθ= 0.5^○, respectively, through the measurements of the time-of-flight of He beam and of the angular intensity distributions of He scattered from LiF(001). The angular intensity distributions of Ar, N₂ and CO scattered from the LiF(001) surface along the [100] azimuthal direction were then measured as a function of incident translational energy. The effects of the molecular structural anisotropy and center-of-mass position on the gas-surface inelastic collision at the corrugated surface are discussed with predictions based on a recently developed simple classical theory of the ellipsoid-washboard model.     

NMR relaxation study of disorder in the mixed system BP x GPI(1–x) and the low temperature transition from classical to quantum rotation

¹H NMR spin-lattice relaxation time (T ₁) studies have been carried out in the temperature range 100 K to 4 K, at two Larmor frequencies 11.4 and 23.3 MHz, in the mixed system of betaine phosphate and glycine phosphite (BP_xGPI_(1–x)), to study the effects of disorder on the proton group dynamics. Analysis of T ₁ data indicates the presence of a number of inequivalent methyl groups and a gradual transition from classical reorientations to quantum tunneling rotations. At lower temperatures, microstructural disorder in the local environments of the methyl groups, result in a distribution in the activation energy (E_a ) and the torsional energy gap (E ₀₁). For certain values of x, the magnetisation recovery shows biexponential behaviour at lower temperatures.     

ΛΛ,ΛΛγ and ΛΛπ0 Productions in J/ψ Decay

The channels of J/ψ decay into,ΛΛ,ΛΛγ and ΛΛπ⁰ are analyzed with 7.8×10⁶ J/ψ events collected by BES detector at BEPC Collider.The branching ratios for three channels and the angular distribution for the first channel are measured.The branching ratios are Br(J/ψ→ΛΛ)=(l.08±0.06±0.24)×10^－3,Br(J/ψ→ΛΛγ)－4(90% CL)and Br(J/ψ→ΛΛπ⁰)=(2.3±0.7±0.8)×l0^－4 respectively. The angular distribution for J/ψ→ΛΛ is dN dcosθ=N₀(1+αcos²0),α=0.52±0.33±0.13.     

Computable upper bounds for the adiabatic approximation errors

For a given Hermitian Hamiltonian H(s)(s∈[0,1])with eigenvalues Ek(s)and the corresponding eigenstates|Ek(s)(1 k N),adiabatic evolution described by the dilated Hamiltonian HT(t):=H(t/T)(t∈[0,T])starting from any fixed eigenstate|En(0)is discussed in this paper.Under the gap-condition that|Ek(s)-En(s)|λ0 for all s∈[0,1]and all k n,computable upper bounds for the adiabatic approximation errors between the exact solution|ψT(t)and the adiabatic approximation solution|ψadi T(t)to the Schr¨odinger equation i|˙ψT(t)=HT(t)|ψT(t)with the initial condition|ψT(0)=|En(0)are given in terms of fidelity and distance,respectively.As an application,it is proved that when the total evolving time T goes to infinity,|ψT(t)-|ψadi T(t)converges uniformly to zero,which implies that|ψT(t)≈|ψadi T(t)for all t∈[0,T]provided that T is large enough.     

态|ψ3(3)〉q广义电场分量的等幂次N次方H压缩

构造了由多模复共轭相干态|{iZ_j^*}〉_q、多模复共轭虚相干态|{iZ_j^*}〉_q(j=1,2,…q)和多模真空态|{0_j}〉_q线性叠加所组成的第Ⅲ类三态叠加多模叠加态光场|ψ₃⁽³⁾〉_q.利用多模压缩态理论,研究了态|ψ₃⁽³⁾〉_q中广义电场分量(即第二正交相位分量)的广义非线性等幂次N次方H压缩特性.发现:态|ψ₃⁽³⁾〉_q是一种典型的三态叠加多模非经典光场;当腔模总数q与压缩次数N之积q·N为偶数时,在一定条件下,态|ψ₃⁽³⁾〉_q的广义电场分量可分别呈现出周期性变化的广义非线性等幂次奇数模-偶数次、偶数模-奇数次、偶数模-偶数次N次方H压缩效应.     

Emission of electrons from mim systems: Discussion of processes in the cathode

Experimentally derived emission characteristics — the transfer ratio, angular distribution, energy distributionsN(E) andN(E _x ) and energy-angular distribution of emitted electrons — are discussed on the basis of our theoretical model of the sandwich cathode. It was found that electrons during their transfer through the cathode are scattered in the dielectric layer mostly by interactions with optical phonons and traps and in the top metal electrode by collisions with conduction electrons. Comparison of our model with experimental results gave us approximate values of mean free paths and further cathode parameters.     

A modified SCF treatment of aza-naphthalenes

A Monte Carlo method is described for evaluating quantities such as E = <ψ|H|ψ>/<ψ|ψ> and other expectation values. The method is in principle applicable to a wave function of any number of electrons. As an example, a two-parameter wave function for helium is studied.     

核物质状态方程中动量相关作用可能的探针

研究了动量相关作用对于中子-质子比动能谱rb(Ek)的效应,发现rb(Ek)灵敏的依赖于动量相关作用而弱的依赖于介质中核子-核子碰撞截面和对称势.因此rb(Ek)是提取重离子碰撞中动量相关作用信息的可能探针.同时,对于丰中子弹核和相同质量稳定弹核在相同入射道条件下,丰中子碰撞系统明显加强了动量相关作用对rb(Ek)的效应.故两个碰撞系统rb(Ek)结果的比较为在重离子碰撞中提取动量相关作用的知识提供了另一个重要的判据。     

Dynamical Correlation Functions for an Impenetrable Bose Gas with Neumann or Dirichlet Boundary Conditions

Abstract

We study the time and temperature dependent correlation functions for an impenetrable Bose gas with Neumann or Dirichlet boundary conditions ψ(x ₁, 0)ψ ^?(x ₂ , t) _±,T . We derive the Fredholm determinant formulae for the correlation functions, by means of the Bethe Ansatz. For the special case x ₁ = 0, we express correlation functions with Neumann boundary conditions ψ(0, 0)ψ ^?(x ₂ , t) _+,T , in terms of solutions of nonlinear partial differential equations which were introduced in [1] as a generalization of the nonlinear Schrödinger equations. We generalize the Fredholm minor determinant formulae of ground state correlation functions ψ(x ₁)ψ ^?(x ₂) _±,0 in [2], to the Fredholm determinant formulae for the time and temperature dependent correlation functions ψ(x ₁, 0)ψ ^?(x ₂ , t) _±,T , t ∈ R, T ≥ 0.     

Beta-gamma-gamma directional correlation in103Rh

β-γ-γ directional correlation studies for the cascades (i)β-rays ofE _max=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofE _max=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P ₂(cosθ)+(0.004±0.035)P ₄(cosθ) forβ-rays ofE _max 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P ₂(cosθ)+(−0.035±0.058)P ₄(cosθ) forβ rays ofE _max=0.21 MeV→444 keV→53 keV cascade. Spins and parities of the 650, 537 and 93 keV levels of¹⁰³Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions are also determined.     

TD-DFT investigation of electronic structures,photophysical properties and the theoretical design of OLEDs based on phosphorescent Ir(III) complexes bearing the non-π electron-conjugated carbene ligand

In the search for efficient phosphorescent materials, a rational design is presented for the iridium complex material (dfbmb)Ir(fptz)₂ (2) (dfbmb?=?1-(2,4-difluorobenzyl)-3-methylbenzimidazolium), which involves the use of two 2-pyridyl triazolate (fptz) chromophores and a non-π electron-conjugated high-field ligand dfbmb assembled by a saturated σ-bond methylene group, and a comparison with the benchmark (dfbmb)₂Ir(fptz) (1). In this work the electronic structures, absorption and phosphorescence spectra were investigated using the TD-DFT method. In order to obtain the mechanism of high phosphorescence yield in (1) and estimate the radiative rate constant k _r for (2), the radiative rate constant k _r, the spin-orbital coupling (SOC) matrix element, ΔE(S???T), and the square of the SOC matrix element (?ψ_S1|H_SO|ψ_T1?²) for (1) and (2) were measured. It is concluded that the switch of the cyclometalated ligand from the main chelate to the ancillary chelate seems to enhance the splitting of ΔE(S???T) in the current system. Finally, using the information gained, a PhOLED utilizing (1) and (2) was designed.     

(EC+β +) decay of 130Nd and 140Tb

The available astrophysical S(E) factor data for the reaction ⁷Li (p,α)α at 10 < E < 1000keV exhibit an exponential increase at low energies due to the effects of electron screening. A parametrisation of the data using a non-resonant, direct process and two subthreshold resonances reproduces the data at energies E≥ 100keV, while at lower energies this calculated S _b(E) factor curve for bare nuclides drops below the data, which in turn represent the case of electron-shielded nuclides, i.e. the electron-shielded S _s(E) factor. The comparison between S _b(E) and S _s(E) leads to an electron-screening potential energy U _e = 350eV, which is much higher than the adiabatic limit of 175eV and not understood at present. The deduced value of S _b(0) is considerably smaller than the previously adopted value of 59keV b, significantly increasing the calculated abundance of ⁷Li in big-bang nucleosynthesis. The Trojan-horse method was applied to the reaction ⁷Li (p,α)α to determine the energy dependence of the S _b(E) factor for 10 < E < 370keV, free from the effects of the Coulomb barrier and electron screening. The THM results are close to the calculated S _b(E) curve and suggest that the THM may become a powerful way to obtain improved information on low-energy cross-sections and associated electron-screening effects in a model-independent way. Received: 9 September 2000 / Accepted: 5 December 2000     

Surface boundary conditions and angular dependence of the spin-wave resonance spectra

General surface boundary conditions with regard to the surface anisotropy energy E_s(iitv, ø) and changes of the static magnetization tM₀ in the presurface region layer have been formulated. On the example of uniaxial surface anosotropy the influence of these factors on the angular dependence of the SWR spectrum is briefly discussed.     

第Ⅲ及第Ⅳ类两态叠加多模叠加态光场的等阶N次方Y压缩与等阶N次方H压缩——兼论“相似压缩”与“压缩简并”现象

本文根据量子力学中的线性叠加原理,分别构造了由多模(即q模)相干态|{Z_j}>_q与多模真空态|{0_j}>_q以及由多模相干态的相反态|{-Z_j}>_q与多模真空态|{0_j}>_q等的线性叠加所组成的第及第类两态叠加多模叠加态光场|ψ_+,3⁽²⁾>_q和|ψ_-,4⁽²⁾>_q.利用新近建立的多模压缩态理论,首次对态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q的广义非线性等阶N次方Y压缩和等阶N次方H压缩特性进行了详细研究.结果发现:1)态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q是两种典型的多模非经典光场,当各模的初始相位φ_j(j=1,2,3,…,q)或者各模的初始相位和 =φ_j以及态间的初始相位差(θ_±^(R)-θ^(0)_±)等分别满足一些特定的量子化条件时,态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q均可呈现出周期性变化的、任意阶的等阶N次方Y压缩效应和等阶N次方H压缩效应;2)当组成态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q的各对应复几率幅不相等亦即C₊^(R)≠C_-^(R)和C₊⁽⁰⁾≠C_-⁽⁰⁾时,态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q这两者的压缩条件和压缩特征虽然相同,但其压缩幅度(即压缩程度和压缩深度)却不相等,这种现象称为“相似压缩”;3)当组成态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q的各对应复几率幅相等亦即C₊^(R)=C_-^(R)和C₊⁽⁰⁾=C_-⁽⁰⁾时,态|ψ_+,3⁽²⁾>_q及态|ψ_-,4⁽²⁾>_q这两种截然不同的多模叠加态光场不仅具有完全相同的压缩条件和压缩特征,而且还具有完全相等的压缩幅度,这种现象就称为“压缩简并”.     

Formation mechanism of nanostructures in austenitic stainless steel during equal channel angular pressing

An ultra-low carbon austenitic stainless steel was successfully pressed from one to eight passes by equal channel angular pressing (ECAP) at room temperature. By using X-ray diffraction, optical microscopy and transmission electron microscopy, the microstructural evolution during ECAP was investigated to reveal the formation mechanism of strain-induced nanostructures. The refinement mechanism involved the formation of shear bands and deformation twins, followed by the fragmentation of twin lamellae, as well as successive martensite transformation from parent austenitic grains with sizes ranging from microns to nanometres through the processes γ(fcc)?→?ε(hcp)?→?α′(bcc). After pressing for eight passes, two types of nanocrystalline grains were achieved: (a) nanocrystalline austenite with a mean grain size of ～31?nm and (b) strain-induced nanocrystalline α′-martensite with a size of ～74?nm. The formation mechanisms are discussed in terms of microstructural subdivision via deformation twinning and martensite transformation.     

Structure of <Emphasis Type="Italic">A</Emphasis>∼130 nuclei in La-Ce region

The variety of shapes and structures, observed in light rare earth A ∼ 130 nuclei, have been discussed in view of different angular momentum coupling schemes and their interplay that comes into effect at high spin. The N = 79 and 80 isotopes in La-Ce region, produced via fusion evaporation reaction, have been studied using the Indian National Gamma Array (INGA) consisting of 18 clover HPGe detectors. Two nearly degenerate ΔI = 1 bands have been observed at high spin of ¹³⁷Ce and a triaxial deformation of γ = ±30° has been assigned to the bands, from the total Routhian surface (TRS) calculations. The high-spin candidates of the yrast band of ¹³⁸Ce show signature splitting both in energy and B(M1)/B(E2) values. The bandcrossing due to the alignment of a pair of h _11/2 proton particles has been conjectured at ℏω ∼ 0.3 MeV, from the single-particle Routhians obtained from TRS calculations. Lifetime measurements by Doppler shift attenuation method (DSAM) has been carried out and from the estimated reduced transition probability B(M1), the ΔI = 1 band in ¹³⁸Ce has been characterized as a magnetic rotation (MR) band. The rise in the values of B(M1), for the higher spin candidates of the band, has been conjectured as the reopening of a different shear at the top of the Band B1. The characteristic of the MR bands in A ∼ 130 region has been discussed in the light of a phenomenological calculation and compared to the MR bands in other mass regions.     

多模叠加态光场|ψ5(3)〉q中广义磁场4m次方Y压缩

构造了由多模复共轭相干态|{Z_j^*}〉_q、多模复共轭相干态的相反态|{-Z_j^*}〉_q以及多模虚相干态|{iZ_j^*}〉_q的线性叠加所组成的第Ⅴ类三态叠加多模叠加态光场|ψ₅⁽³⁾〉_q.利用多模压缩态理论研究了态|ψ₅⁽³⁾〉_q中广义磁场分量的等幂次N次方Y压缩特性.结果发现:当压缩次数N=2p且p=2m(m=1,2,3,…,…)时,只要各模的初始相位φ_j(j=1,2,…,…,q)、态间的初始相位差(θ₁-θ₂)、(θ₁-θ₃)和(θ₂-θ₃)以及受各模的初始相位φ_j调制的各单模相干态光场的平均光子数之和 等分别满足一定的取值条件,则态|ψ₅⁽³⁾〉_q的广义磁场分量就可呈现出周期性变化的广义非线性等幂次4m次方Y压缩效应.     

The influence of cone-covered surface structures on sputtering and secondary electron emission: Model

Abstract

The yield and the polar angular distributions of secondary particles emitted from cone-covered surfaces were studied. A model taking into account both the influence of the local incidence angle I and the blocking of the emitted particles by the surface relief was elaborated. For an emission angle a, the transport effect of the particles generated inside the solid was simulated by the standard relation F(a) = (cos a) ⁿ and the emission dependence on the local incidence angle was assumed to behave as E(I) = (cos I) ^-m . Calculations showed that for m= 1 the surface topography only slightly alters the polar angular distribution shape but the yield of the collected particles is always higher than that from a flat surface when m is more than unity. For n= 2, the shape of the distribution curve is significantly different from that of the corresponding flat surface whatever the m values. For n=0, when E(I) very rapidly increases with the incidence angle both the angular distributions shape and the yield are strongly modified by the surface topography.