铯原子里德堡态Stark能量及电偶极矩的测量和理论计算

里德堡原子由于具有体积大、寿命长、易极化及在外电场中能级易于操控等特点, 已经成为了目前物理学领域研究的热点之一. 本文在磁光阱中实验测量了铯原子15P_3/2和16P_3/2态的Stark光谱,根据光谱给出了15P_3/2和16P_3/2|m|=1/2 Stark态在0-1400 V/cm场强范围适用的Stark 能量和偶极矩的经验性解析表达式; 用数值方法求解薛定谔方程获得了这些态的Stark能量、偶极矩和电子几率密度分布. 电子几率密度分布定性说明了计算的偶极矩矢量的方向是正确的. 计算的Stark能量、偶极矩与实验结果相一致.     

The interaction energy of three molecules united in a nanocluster by long-range attraction forces with account for Coulomb repulsion

The interaction energy of three neutral molecules that form a nanocluster is studied. It is assumed that one molecule (M₀) has a dipole moment, while the other two (M₁ and M₂) are nonpolar. The molecule interaction energy in such a nanocluster is determined by the sum of dispersion interaction energies of each pair of molecules and the sum of inductive energies of the molecules. Analytical expressions for these energies as functions of the distance between the centers of mass of the molecules have been obtained. A method for the determination of damping functions which takes the contribution of repulsive forces into account has been developed. Analytical expressions for the molecule interaction energies for a two-molecule cluster in an external field of the third molecule have been obtained. A nanocluster consisting of a molecule of polar isomer pentene C₅H₁₀ and a nonpolar molecule of polycyclic aromatic hydrocarbon pyrene C₁₆H₁₀ in the external electrostatic field of another pyrene molecule is considered. The calculation showed that the interaction energy of the two-molecule nanocluster increases by a factor of 1.5 if this cluster is in the field of the induced dipole moment of an external pyrene molecule.     

Dipole oscillator strength properties and dispersion energies for CI2

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the chlorine molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength and molar refractivity data. It has been used to evaluate a variety of dipole oscillator strength sums, logarithmic dipole oscillator strength sums, and mean excitation energies for the molecule. A pseudo-DOSD for C1₂ is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C₆, for the interaction of Cl₂ with itself and forty-two other species, and the triple-dipole dispersion energy coefficient C₉ for (Cl₂)₃.     

Dipole oscillator strengths,dipole properties and dispersion energies for SiF4

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the silicon tetrafluoride (SiF₄) molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength data. The constraints are furnished by experimental molar refractivity data and the Thomas-Reiche-Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums and mean excitation energies for the molecule. A pseudo-DOSD for SiF₄ is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C₆, for the interaction of SiF₄ with itself and with 43 other species and the triple-dipole dispersion energy coefficient C₉ for (SiF₄)₃.     

Carbon nanotube diameter tuning using hydrogen amount and temperature on SiO2/Si substrates

Carbon nanotubes (CNTs) were grown on thin iron (Fe) films on SiO₂/Si substrates by chemical vapor deposition (CVD) at four different hydrogen (H₂)/methane (CH₄) ratios at temperatures ranging from 925 to 1000°C. The effects of temperature and the amount of hydrogen gas on the mean diameter at increasing temperature were examined. We demonstrated that the mean diameter and its distribution depend not only on temperature but also on the H₂ amount. We showed that increasing H₂ amount strongly affects the structure of CNTs, especially at high growth temperature; the mean diameter at 1000°C reduced from about 383 to 34 nm by increasing H₂ amount from 24 to 50 sccm. We observed that at high temperature growth the mean diameter was decreasing very fast initially with increasing H₂ amount suggesting the dominance of H₂ over the growth temperature. A decrease in the slope of diameter vs. H₂ amount with further increment in H₂ amount implied that the temperature was, then, deciding the CNT diameter through catalyst particle coarsening. The statistical analysis presented implies that the H₂ amount has to be adjusted according to the growth temperature for given CH₄ amount to keep CNT diameter under control, and the large diameter distributions at high temperature and high H₂ amount can be associated with the large variation in the catalyst particle sizes.     

Dipole properties of PH3, PF3, PF5, PCl3, SiCl4, GeCl4, and SnCl4

Experimental and theoretical photoabsorption cross sections combined with constraints provided by the Kuhn–Reiche–Thomas sum rule, the high-energy behaviour of the dipole oscillator strength density, static dipole polarisabilities, and molar refractivity data when available are used to construct dipole oscillator strength distributions for PH₃, PF₃, PF₅, PCl₃, SiCl₄, GeCl₄, and SnCl₄. The distributions are used to predict dipole sum rules S(k), mean excitation energies I(k), and van der Waals C₆ coefficients.     

Mean Particle Diameters. Part IV: Empirical Selection of the Proper Type of Mean Particle Diameter Describing a Product or Material Property

Mean particle diameters may be used to describe and to model physical, chemical or physiological properties of products or materials containing dispersed phases. An empirical method was developed to select the proper type of mean diameter from experimental data, if this mean diameter is not known a priori from theoretical reasoning. The present method uses mean diameters, D?_{p, q}, defined according to the Moment‐Ratio (M‐R) definition system. They are expressed as the 1/(p‐q)‐th power of the ratio of the p‐th and the q‐th raw moment of the number density distribution of the particle sizes. After calculation of the mean diameters, D?_{p, q}, the relationships between the product property and these mean diameters are investigated statistically. The selection method has been illustrated by four examples, three of which stem from a high shear granulation experiment in the field of detergent processing. The fourth example is concerned with a visual ranking of bubble size distributions of chocolate mousse samples. The data set of each example consists of a set of particle size distributions and the corresponding physical product properties that are influenced by the particle sizes. Hypotheses are formulated to explain the types of selected mean diameters. Application of the selection method gives mean diameters, D?_{p, q}, a clear physical look and identity, replacing their anonymity. Sharing worldwide results of applications of the newly developed selection method, will lead to a build‐up of knowledge of physical meanings and application areas for the types of the mean particle diameters. This will support decision‐making in product development. The examples used to develop the selection method clearly demonstrate the physical relevance of the previously developed nomenclature system for mean particle diameters, D?_{p, q}.     

Absorption and scattering of light in quasi-zero-dimensional structures. I. Transition dipole moments of the charge carriers

A theory is developed for of the interaction of an electromagnetic field with local charge-carrier states of arising near a small dielectric particle. It is shown that the transition dipole moments between local states are large, higher than the typical values of the transition dipole moments for semiconductors. Fiz. Tverd. Tela (St. Petersburg) 39, 720–722 (April 1997)     

N.M.R. studies of cis-1,2-difluoroethylene and vinyl fluoride in a nematic solvent

Constrained anisotropic dipole oscillator strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of NO, including most anisotropic components of the dipole-dipole dispersion energy coefficients for the interaction of NO with NO, O₂, H₂, N₂, CO, He, Ne, Ar, Kr and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multi-reference configuration interaction wavefunctions for NO. The individual dipole properties of NO considered include the dipole oscillator strength sums S_k , k = 2,1,0(? 1/2)? 2,? 3,? 4,..., the logarithmic dipole sums L_k and mean excitation energies I_k , k = 2(? 1)? 2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarizaiton ratio, and the Rayleigh scattering cross-section. Our constrained dipole oscillator strength results are often the only reliable, and often the only available, values for many of the properties and dispersion energies considered.     

Error Estimates in the Sampling From Particle Size Distributions

It is often necessary to estimate the properties of particle size distributions from limited samples taken from large populations. When the distributions are broad, and higher order moments required, as in the case of volume based particle size distributions, the inferred parameters d_3,50 (volume median diameter) and GSD (geometric standard deviation) can have high intrinsic errors not immediately obvious to the measuring scientist. We show that there is a critical number of particles, N_crit, which must be counted or else the error may blow up catastrophically. N_crit is very sensitive to the width of the distribution, and is approximately proportional to GSD¹¹ We develop formulae to estimate the random sampling error inherent in measured values of the d_3,50 and GSD for the log-normal distribution; compare the predictions to a typical experimental particle size measurement; and then generalize to the median of any arbitrary moment, d_{r, 50}.     

QCD studies with e+e− annihilation data at 161 GeV

We have studied hadronic events produced at LEP at a centre-of-mass energy of 161 GeV. We present distributions of event shape variables, jet rates, charged particle momentum spectra and multiplicities. We determine the strong coupling strength to be α_s(161 GeV) = 0.101±0.005(stat.)±0.007(syst.), the mean charged particle multiplicity to be 〈n _ch〉(161 GeV) = 24.46 ± 0.45(stat.) ± 0.44(syst.) and the position of the peak in the ξ_p = ln(1/x _p) distribution to be ξ₀(161 GeV) = 4.00 ±0.03(stat.)±0.04(syst.). These results are compared to data taken at lower centre-of-mass energies and to analytic QCD or Monte Carlo predictions. Our measured value of α_s(161 GeV) is consistent with other measurements of α_s. Within the current statistical and systematic uncertainties, the PYTHIA, HERWIG and ARIADNE QCD Monte Carlo models and analytic calculations are in overall agreement with our measurements. The COJETS QCD Monte Carlo is in general agreement with the data for momentum weighted distributions like Thrust, but predicts a significantly larger charged particle multiplicity than is observed experimentally.     

Experimental investigation of dipolar interaction in suspensions of magnetic nanoparticles

The structure and the magnetisation behaviour of two different systems of magnetic nanoparticles (MNP), namely Resovist^® with a wide core size distribution (diameter, σ=0.3) and SHP-20 with a rather narrow distribution (σ=0.1), were investigated by magnetorelaxometry (MRX) and magnetisation measurements in a wide concentration range. MRX on fluid and solid suspensions yielded the distribution of hydrodynamic diameters and effective magnetic anisotropy energies (E_A), where towards higher iron concentrations the spatial particle correlation, i.e. aggregation, and also the width of the E_A distribution were increased significantly. It was further found that these effects quantitatively depend on the suspension medium, where an increased salt concentration enhanced the aggregate size distribution and E_A dispersion. At mentioned higher MNP concentrations, the quasistatic magnetisation, normalised with respect to the iron content, decreased by up to 40%. In the case of SHP-20, where single core MNPs dominate, the maximum of this drop down of the magnetisation occurred at a field strength that corresponds to the strength of mean squared dipolar interaction.     

Relativistic mean-field description of collective motion in nuclei: the pion field

The influence of the pion field on isovector dipole and spin-dipole collective oscillations is investigated in a time-dependent model based on relativistic mean field theory. We find that the inclusion of the long range pion-nucleon interaction provides an additional strong damping mechanism for the isovector dipole vibrations. The inclusion of the pion field has also a strong effect on the dynamics of spin-dipole vibrations, and in particular on the splitting of excitation energies of theJ ^π (0^?,1^?,2^?) components of the isovector spin-dipole resonance.     

A study of charged particle multiplicities in hadronic decays of theZ0

We present an analysis of multiplicity distributions of charged particles produced inZ ⁰ hadronic decays. The results are based on the analysis of 82941 events collected within 100 MeV of theZ ⁰ peak energy with the OPAL detector at LEP. The charged particle multiplicity distribution, corrected for initial-state radiation and for detector acceptance and resolution, was found to have a mean n _ch=21.40±0.02(stat.)±0.43(syst.) and a dispersionD=6.49±0.02(stat.)±0.20(syst.). The shape is well described by the Lognormal and Gamma distributions. A negative binomial parameterisation was found to describe the shape of the multiplicity distribution less well. A comparison with results obtained at lower energies confirms the validity of KNO(-G) scaling up to LEP energies. A separate analysis of events with low sphericity, typically associated with two-jet final states, shows the presence of features expected for models based on a stochastic production mechanism for particles. In all cases, the features observed in the data are well described by the Lund parton shower model JETSET.deceased 25th March 1991     

On Measuring and Modeling Local Average Particle Velocities for particle ensembles in classifying systems

In most multi-phase flow problems, the particulate phase is exposed to an external field which causes dispersion. Therefore, local velocity measurements of the disperse phase are no longer equivalent with respect to averaging in time and averaging in volume. While the local time-averaged velocity still characterizes the transport of the ensemble in the Eulerian sense, one has to be be careful in modeling this velocity average by considering the ensemble's composition. It is shown for different particle ensembles that the conventional particle velocity average M_1,0 calculated with respect to the dispersion relationship and a particle size number density distribution is far below the measured ensemble average; the deviation depends on the width of the particle size distribution. It is deduced that Eulerian particle velocity values referring to a certain time interval can be modeled by a ratio of velocity moments M_2,0/M_1,0 calculated with particle size number distributions referring to a certain probe volume. This relationship was confirmed by measurements.     

Full relativistic calculations of the quadrupole and electric field gradients for C2, N2, and O2

In the present work we calculate the energies,quadrupole moments,and electric field gradients(EFGs) of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force constant k2 is the product of charge and EFG at its equilibrium nuclear distance.The dipole charge distributions for these symmetrical molecules are all in equilibrium,however,the quadrupole charge distributions are far from equilibrium;among these,there is the most remarkable deviation from equilibrium for N2,for its many charges concentrate on two sides of the molecule,which is in agreement with the well-known characteristic of the nitrogen molecule.The relativistic effect is remarkable even for the same period.     

Green’s function approach to the low temperature properties of Cs<Subscript>2</Subscript>CuCl<Subscript>4</Subscript>: anisotropy effects

We have studied the effect of both axial and transverse anisotropy on the critical field and thermodynamic properties of the field induced three dimensional antiferromagnetic Heisenberg model on the frustrated hexagonal lattice for Cs₂CuCl₄ compound. The spin model is mapped to a bosonic one with the hard core repulsion constraint and the Green’s function approach has been implemented to get the low energy spectrum and the corresponding thermodynamic properties. To find the critical field (B _c ) we have looked for the Bose-Einstein condensation of quasi-particles (magnons) which takes place when the magnon spectrum vanishes at the ordering spiral wave vector. We have also obtained the dispersion of magnon spectrum in the critical magnetic field for each anisotropy parameter to find the spiral wave vector where the spectrum gets its minimum. The magnon energies show a linear dispersion relation close to the quantum critical point. The effect of hard core boson interaction on the single particle excitation energies leads to a temperature dependence of the magnon spectrum versus magnetic field. We have also studied the behavior of specific heat and static structure factor versus temperature and magnetic field.     

Stability of the director profile of a nematic liquid crystal around a spherical particle under an external field

We study numerically the effect of an external magnetic or electric field on the director profiles of a nematic liquid crystal around a spherical particle. We pay particular attention to the stability of a hyperbolic hedgehog defect accompanying the particle, which transforms into a Saturn-ring defect encircling the particle under a sufficiently strong external field. We focus on the particle size dependence of the two important threshold field strengths: the “thermodynamic-transition” field strength H₁ at which the hedgehog and the Saturn-ring configurations have the equal free energy, and the critical field strength H₂ at which the hedgehog loses its (meta)stability. Our numerical results demonstrate that while H₁ is non-monotonically dependent on the particle radius R₀, H₂ monotonically increases with R₀ and the dependence of H₂ is weak for large R₀. The non-monotonic dependence of H₁ on R₀ can be explained by comparing the energies of the two configurations and assuming the dependence of those energies on a rescaled field. A crude argument of the energetics of a hyperbolic hedgehog defect under an external field shows that for an asymptotically large R₀ the critical field strength is independent of R₀, which agrees with our numerical finding.     

Plasmon resonance coupling in strongly coupled gold nanotube arrays with structural defects

We theoretically investigate the transmission spectra and the field distributions with different defects in the gold nanotube arrays by using the finite-difference time-domain method.It is found that the optical properties of the nanotube arrays are strongly influenced by different defects.When there are no defects in the central nanotube,the values of peaks located at both sides of the photonic band gap have their maxima.Based on the distributions of electric field component E x and the total energy distribution of the electric and the magnetic field,we show that mainly a dipole field distribution is exhibited for the plasmon mode at the long-wavelength edge of the band gap but higher order modes of the composite are excited at the short-wavelength edge of the band gap.The plasmon resonant modes can also be controlled by introducing defects.     

Momentum spectra of identified hadrons at e+e? annihilations: comparison with QCD calculations

Charged particle momentum distributions are studied in the reaction e⁺e⁻ → hadrons, using data collected with the AMY detector at center of mass energy of 58 GeV. The measured distributions and derived quantities in combination with the corresponding results obtained at both lower and higher center of mass energies are compared to QCD predictions in theoretical approach to study the energy dependence of the strong interaction, and to test QCD as the theory describing it. To achieve this, the mean charged particle multiplicity, the charged particle momentum spectrum and its peak position are compared with predictions of the modified-leading logarithmic approximation. In general, good agreement is observed between the data and the above approximation in the regions where the model is expected to be valid. In addition the strong coupling constant α _s is determined from a fit of the QCD prediction to x _p distribution of the Feynman scaling. When we leave α _s as a free parameter in the fit we obtain α _s = 0.115 ± 0.008.