磷酸盐玻璃中Yb3+和Nd3+之间的声子参助能量转移

本文中报道了磷酸盐玻璃中Nd³⁺,Yb³⁺的时间分辨谱和激发能量的转移。通过实验确定了在不同温度下的转移速率。证实了Nd³⁺→Yb³⁺的能量转移机构为从⁴F_3/2(Nd³⁺)到²F_5/2(Yb³⁺)并同时产生单声子发射的过程;而从Yb³⁺到Nd³⁺关键词：     

A simple chiral Lagrangian approach toK→πππ decays andε′+0−

We analyse theK→πππ decays in the framework of a chiral Lagrangian supplemented by the 1/N expansion (N being the number of colors). The measuredK _L →π⁺π⁰π⁺ Dalitz plot is very well reproduced. Contrary to a recent claim, the Li-Wolfenstein relation between the CP impurities associated with theK→πππ(ε′_+0?) and theK→ππ(ε′) decay amplitudes is rather stable against isospin-breaking effects and higher-order (in the chiral expansion) weak operator corrections. We also predict a branching ratio of 2.1 10^?7 for the CP-conservingK _S →π⁺π⁰π⁺ decay.     

Relativistic effects in the 3N continuum and the A y puzzle

The three-nucleon (3N) Faddeev equation is solved in a Poincaré-invariant model of the three-nucleon system. Two-body interactions are generated so that when they are added to the two-nucleon invariant mass operator (rest energy) the two-nucleon S-matrix is identical to the non-relativistic S-matrix with a CD Bonn interaction. Cluster properties of the three-nucleon S-matrix determine how these two-nucleon interactions are embedded in the three-nucleon mass operator. Differences in the predictions of the relativistic and corresponding non-relativistic models for elastic and breakup processes are investigated. Of special interest are the lowering of the A _y maximum in elastic nucleon-deuteron (Nd) scattering below ≈25?MeV caused by the Wigner spin rotations and the significant changes of the breakup cross sections in certain regions of the phase space.     

A global design of high power Nd-Yb co-doped fiber lasers

A global optimization method - niche hybrid genetic algorithm (NHGA) based on fitness sharing and elite replacement is applied to optimize Nd³⁺-Yb³⁺ co-doped fiber lasers (NYDFLs) for obtaining maximum signal output power. With a objective function and different pumping powers, five critical parameters (the fiber length, L; the proportion of pump power for pumping Nd³⁺, η; Nd³⁺ and Yb³⁺ concentrations, N_Nd and N_Yb and output mirror reflectivity, R_out) of the given NYDFLs are optimized by solving the rate and power propagation equations. Results show that dividing equally the input pump power among 808 nm (Nd³⁺) and 940 nm (Yb³⁺) is not an optimal choice and the pump power of Nd³⁺ ions should be kept around 10-13.78% of the total pump power. Three optimal schemes are obtained by NHGA and the highest slope efficiency of the laser is able to reach 80.1%.     

A study of meson-baryon couplings in the constituent quark model

Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (³P₀-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the³P₀ vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the³P₀-model, only.     

A second-quantized few-fermion Monte Carlo scheme

We propose a new Monte Carlo algorithm for the solution of the few-fermion Schrödinger equation. Antisymmetry is maintained by working in the space of N-fermion determinants for an N-fermion system. This does not solve the problem of cancelling positive and negative contributions to the wave function. The problem appears in a different form, however, due to negative signs introduced by dynamic correlations instead of statistics and appears also for boson systems in this approach. Since the determinants are constructed from plane-wave states use may be made of the long range of nuclear forces in momentum space to cancel negative and positive contributions more efficiently. Incorporation of non-radial interactions, i.e. interactions with spin dependence and tensor forces, reduces the problem to a quantitative problem.     

Statistical properties of Auger amplitudes and rates

The statistical properties of Auger transitions are investigated for the first time. The fairly accurate approximate formula for the number of Auger amplitudes is derived. The symmetry property for this number and its approximation for semicomplementary arrays is determined. The results of calculations of the statistical characteristics (distribution function, initial and central moments, skewness, excess) for the distributions of Auger amplitudes and rates are presented in the case of transitions p⁵d^N→p⁶d^N−2ε, sd^N→s²d^N−2ε, d⁹p^N→d¹⁰p^N−2ε and their dependence on the number of electrons N in the sequences of atoms is investigated. It is shown that statistical properties of Auger spectra mainly depend on the orbital quantum numbers of shells involved in the transitions. For some characteristics the clearly expressed dependence on the even and odd numbers of electrons in outer open shell having integer or half-integer values of spins takes place. The rather large values of skewness and especially excess indicate a significant deviation of distribution of Auger amplitudes from the normal distribution.     

The multiple scattering and N-body approaches to nuclear reactions

The relationship between conventional multiple scattering approaches and the recently developed N-body approaches to nuclear reactions is considered with a view towards elastic scattering applications. Connectivity expansions in the N-body approach and multiple scattering expansions in the Watson approach are developed by a common technique so that a comparison of the physical content of each can be made. In the N-body case this leads to a new derivation of the equations of Bencze, Redish, and Sloan in both particle-labelled and partition-labelled form and this yields new insight into the minimal dimensionality of these equations and into the role of channel coupling schemes within this formulation. The relative simplicity and generality with which these results are obtained is designed to be easily understood by those unfamiliar with N-body formalisms. The two approaches are contrasted first for the three-particle problem and subsequently for the many-body problem. We argue that a strict adherence to the connected-kernel property which is advantageous for the three-particle problem may not be so advantageous for the many-body elastic scattering problem. Undesirable physical characteristics of the connectivity expansion for elastic scattering are identified and their rectification is discussed. The off-shell transformation associated with the N-body approach is examined critically. The origin of the multiplicity of N-body coupling schemes is elucidated. It is shown that a modified concept of connectivity, called inclusive connectivity, can be introduced to guide expansions which can be truncated in a physically meaningful way. The inclusive connectivity expansion is seen to be identical to the spectator expansion for an elementary projectile but differs in the case of a composite projectile. Extant elastic scattering optical potential formulations based on the two concepts of connectivity are compared and contrasted. We show that connected kernel integral equations of the few-body type are required for computation of the individual low-order terms of the inclusive connectivity expansion of the optical potential.     

Spectral study of reactions involving organic vapours and the pink afterglow of nitrogen

Chemiluminescent reactions resulting from addition of C₂H₂ and BrCN to nitrogen showing a pink afterglow have been investigated. The spectra show CN(B→A), CN(B→X), CN(A→X), and N₂(IIP) bands. The CN(B→X) bands are intense and exhibit abnormal rotational distributions with two rotational temperatures (T₁ = 2400°K, T₂ = 400°K). New perturbations and high-J rotational lines are reported. Comparisons of intensities of bands of the CN(B→A) and (B→X) systems yield 1:80 as the ratio of electronic transition probabilities for the two systems.     

Infrared spectroscopy of the Nd3+ ion in Nd2BaCuO5 and Nd2BaZnO5

Absorption spectra of the Nd³⁺ ion in the Nd₂BaCuO₅ and Nd₂BaZnO₅ ternary oxides were measured within broad spectral (1500–17000 cm^?1) and temperature (4.2–200 K) intervals. The positions and widths of the Stark sublevels were determined. The exchange splittings of the Nd³⁺ Kramers doublets in several multiplets were found for the magnetically ordered state of Nd₂BaCuO₅ (T _N =7.5 K).     

Regge pole model for invariant functions. IV

TheNN→NN andγN→πN differential cross sections for polarized targets are discussed in terms of invariant functions. In former fits of high energy experimental data certain of these invariant functions came out to be small. Based on these fits thepn→np,p¯p→ n¯n, γp→ nπ ⁺ andγn→ pπ ^? differential cross sections are predicted to be independent of the target polarization.     

Synthesis and near-infrared luminescence properties of LaOCl:Nd3+/Yb3+

Near-infrared emitting phosphors LaOCl:Nd³⁺/Yb³⁺ were prepared by the solid-state method, and their structures and luminescent properties were investigated by using X-ray diffraction and photoluminescence analysis, respectively. The studies shows that tetragonal LaOCl:Nd³⁺/Yb³⁺ can be synthesized by the solid-state reaction at 600 °C for 3 h. Upon 353 nm UV excitation, LaOCl:Nd³⁺/Yb³⁺ sample shows strong near-infrared emission lines in the region of 1060–1150 nm (corresponding to ⁴F_3/2 → ⁴I_J′ transition of Nd³⁺, J′ = 9/2, 11/2, 13/2, 15/2) and 980–1050 nm (corresponding to ²F_5/2 → ²F_7/2 transition of Yb³⁺). The decreasing emission intensity of Nd³⁺ with increasing doping concentration of Yb³⁺ proved the energy transfer in LaOCl:Nd³⁺/Yb³⁺. The possible near-infrared emission and energy transfer mechanism between Nd³⁺ and Yb³⁺, as well as the energy transfer efficiency of LaOCl:Nd³⁺/Yb³⁺ were discussed.     

Synthesis of TiO2 nanoparticles and spectroscopic upconversion luminescence of Nd3+-doped TiO2–SiO2 composite glass

Nd³⁺-doped TiO₂–SiO₂ composites were prepared by sol–gel method. Optical properties such as radiative life-time (τ), stimulated emission cross-section (σ_p) and branching ratio (β) were calculated using Judd–Ofelt theory. Violet to blue upconversion emissions at 380 nm (⁴D_3/2→⁴I_11/2), 399 nm (²P_3/2→⁴I_11/2), 420 nm (²D_5/2→⁴I_9/2) and 452 nm (²P_3/2→⁴I_13/2) were obtained under 578 nm xenon-lamp excitation. The choice of 578 nm is justified by the absorption spectra of the same samples, which shows a strong absorption peak at 578 nm. This 578 nm excitation pump produces upconversion in Nd³⁺ by a sequential two-photon absorption process.     

Hadronic decays of η and η′ in the large-N limit

Working in the large-N approximation (N being the number of colors), we relate thestrong η′→ηππ processes to theweak K _L→πππ decays. Chiral corrections are crucial to reproduce the experimental data. The isospin-violating η(η′)→πππ and the weakη→K ⁺π^- decays are also treated in this framework. We comment on the predictions of a “QCD-inspired” approach which determines in principle the chiral symmetry-breaking scales considered, and consequently the Skyrme coupling.     

A study of the reactions γp→ωp and γp→ωp and γp→ωΔ+

The differential and total corss sections and the decay density matrix elements have been measured for the reactions, γp→ωp and γp→ωΔ⁺ (1232) in the photon energy range 2.8 to 4.8 GeV. The total cross sections for ωΔ⁺ (1232) photo-production are found to be slightly larger than those for elastic ω photo-production in this energy range. The data are compared to the predictions of a theoretical model and the contributing exchange mechanics are discussed.     

Singlet-to-triplet ratio in the deuteron breakup reaction pd→pnp at 585 MeV

Available experimental data on the exclusive pd→pnp reaction at 585 MeV show a narrow peak in the proton–neutron final-state interaction region. It was supposed previously, on the basis of a phenomenological analysis of the shape of this peak, that the final spin-singlet pn state provided about one third of the observed cross section. By comparing the absolute value of the measured cross section with that of pd elastic scattering using the Fäldt–Wilkin extrapolation theorem, it is shown here that the pd→pnp data can be explained mainly by the spin-triplet final state with a singlet admixture of a few percent. The smallness of the singlet contribution is compatible with existing pN→pNπ data and the one-pion exchange mechanism of the pd→pnp reaction.     

Measurements of the Cross Sections and A y for D(p, n) Inclusive Breakup Reaction at 170 MeV

The effects of three-nucleon force (3NF) has been actively studied by using the nucleon–deuteron (Nd) scattering states. The differential cross sections of the elastic Nd scattering at the energy below 150 MeV can be well reproduced by incorporating 3NF in the Faddeev calculation based on modern nucleon–nucleon (NN) interactions. On the other hand, the differential cross sections of Nd elastic and inelastic scatterings at 250 MeV show large discrepancies between the data and the Faddeev calculations with 3NF. It indicates the presence of the missing features of the three nucleon system at this energy region. For the systematic study about the energy dependence of this large discrepancies, we measured the differential cross sections and the vector analyzing power A _y for the ²H(p, n) inclusive breakup reaction at 170 MeV. The experiment was carried out at RCNP by detecting scattered neutrons by using the neutron detector NPOL3. The data was compared with the results of the Faddeev calculations with and without the 3NF.     

Resonances of any spin in pion photoproduction and nucleon Compton scattering

Describing the vertices by form factors and the propagators by their spectral representations, we calculate the contribution of the exchange diagramsγπ→M ^j→ ¯N N andγN→N ^j+1/2→γN to the invariant and helicity amplitudes, for meson (M _j) and baryon (N ^j+1/2) resonances of any spin (j integer ≧ 1) and both parities ((?)^j and (?)^j+1).     

The π N → e +e−N reaction close to the vector-meson production threshold

The π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections are calculated below and in the vicinity of the vector-meson (?⁰,ω) production threshold. These processes are largely responsible for the emission of e ⁺e^? pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector-meson-nucleon channels. The vector mesons materialize subsequently into e ⁺ e^? pairs. Using πN→?⁰ N and πN→ωN, amplitudes calculated in the center of mass energy interval 1.4 < √s<1.8 GeV, we compute the π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections in these kinematics. Below the vector-meson production threshold, the π⁰?ω interference in the e ⁺ e^? channel appears largely destructive for the π^? p→e ⁺ e ^? n cross section and constructive for the π⁺ n→e ⁺ e ^? p cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector-meson-nucleon channels to low-lying baryon resonances.     

Analysis of the processes¯NN→3π,¯pp→ηπ+π− and¯pp→ωπ+π− as a test of a dual four-point-function without parity doublets

The five annihilation processes at rest:¯pn→π⁺π^?π^?,¯pp→π⁰π⁺π^?,¯pp→3π⁰,¯pp→ηπ⁺π^? and¯pp→ωπ⁺π^? are simultaneously analyzed by means of a dual quark-symmetric four-point-function without parity doublets. The qualitative features of the mass-spectra are reproduced without free parameters. Predictions for¯pp→3π⁰ are made and compared with the results of Lovelace's model. In connection with the calculation of the ratios of rates we discuss the problem of the mass extrapolation for the external particles. The ?—? puzzle turns out to be a key problem for the processes under consideration.