多量子位Heisenberg XX链中的杂质纠缠

通过分析系统的杂质位与其余部分间的纠缠N_1-A以及单个正常位与其余部分间的纠缠N_L-A研究了匀强磁场作用下含杂质Heisenberg XX链的纠缠特性.研究表明三量子位时纠缠存在的临界温度依赖于杂质参数J₁和匀强磁场B.研究发现,当量子位L为奇数时,纠缠N_1-A随量子位的增加而增大,而L为偶数时则相反,并且量子位L为偶数时的纠缠大于量子位L为奇数时的纠缠;对N_L-A, 量子位L为奇数时,纠缠随杂质参数J₁的变化与L=3类似,而L为偶数时纠缠随杂质参数|J₁|的增加而增加.     

小世界神经网络的二次超谐波随机共振

随机共振现象是非线性系统中普遍存在的自然现象.主要通过研究小世界生物神经网络中的输出信噪比与反映小世界效应的重连概率p、耦合强度c以及输入信号振幅A之间的关系，来揭示小世界生物神经网络的二次超谐波随机共振的一些规律.发现对于Hodgkin-Huxley小世界神经网络，并不是信号越强，信噪比越大，而是输入信号的振幅A存在一个最优值A_O，此时网络信噪比最大.     

铁基纳米晶合金的介观阻抗率及应用

提出了铁基纳米晶合金介观阻抗率的物理概念，用Maxwell方程组求得其计算公式ρ=-μ{A}/{t}/Δ×H，该式表明铁基纳米晶合金的介观阻抗率与材料内部的介观磁场强度H、介观磁矢势A和介观磁导率μ有关，磁矢势A是由介观结构引起的量子力学效应，是由合金的微观结构决定的.这个理论很好地解释了铁基纳米晶粉末、粉芯     

Stability of the positively charged manganese centre in GaAs heterostructures examined theoretically by the effective mass approximation calculation near the Γ critical point

This paper describes an n-i-p-i-n model heterostructure with a manganese (Mn)-doped p-type base region to check the stability of a positively charged manganese A_Mn⁺ centre with two holes weakly bound by a negatively charged 3d⁵(Mn) core of a local spin S=5/2 in the framework of the effective mass approximation near the Γ critical point (k～0). By including the carrier screening effect, the ground state energy and the binding energy of the second hole in the positively charged centre A_Mn⁺ are calculated within a hole concentration range from 1 × 10¹⁶ cm^-3 to 1 × 10¹⁷ cm^-3, which is achievable by biasing the structure under photo-excitation. For comparison, the ground-state energy of a single hole in the neutral A_Mn⁰ centre is calculated in the same concentration range. It turns out that the binding energy of the second hole in the A_Mn⁺ centre varies from 9.27 meV to 4.57 meV. We propose that the presence of the A_Mn⁺ centre can be examined by measuring the photoluminescence from recombination of electrons in the conduction band with the bound holes in the A_Mn⁺ centre since a high frequency dielectric constant of varepsilon _∞ =10.66 can be safely adopted in this case. The novel feature of the ability to tune the impurity level of the A_Mn⁺ centre makes it attractive for optically and electrically manipulating local magnetic spins in semiconductors.     

On the Absorption of antibaryons in nuclei

Antiproton (ˉp) and antilambda (ˉΛ) production has been measured for minimum bias in p+A collisions and central A₁+ A₂ collisions at the CERN-SPS by the collaborations NA35/49 and NA44. The measurements are extrapolated from rapidity distributions to absolute minimum bias cross sections. It is shown that the ˉp cross sections divided by A₁· A₂ follow an exponential trend as a function of a characteristic length obtained from a Glauber type absorption model, while the ˉΛ cross sections divided by A₁· A₂ are constant. The exponential trend also holds for ˉp production at the lower energies of the Brookhaven AGS. A discussion of the physics interpretation of the established trends in terms of an effective absorption cross section is presented. Received: 15 July 1999 / Revised version: 10 November 1999     

反应物NO的转动激发对反应N(4S)+NO(X2Π)→N2(X3Σg-)+O(3P)影响的立体动力学研究

采用准经典轨线方法,在碰撞能为0.6 eV时,研究了反应物NO分子的转动激发对发生在³A"和³A'势能面上的反应N(⁴S)+NO(X²Π)→N₂(X³Σ_g^-)+O(³P)的立体动力学性质的影响. 详细讨论了在反应物分子的不同转动态下发生在两个势能面上反应的矢量性质. 结果表明, 反应物分子NO的转动激发对发生在³A′势能面上的立体动力学性质产生重大影响, 这可能与该势能面上存在一个早期势垒有关.     

光弹调制器定标新方法

对于光弹调制器的定标,传统的是寻找探测信号中基频分量最大值的方法,本文对此进行了讨论.根据贝塞耳函数J₀(A)、J₁(A)及其一阶导数的变化规律,提出一种通过测量直流分量来精确定标的新方法,该方法对延迟幅值A在的较大范围(103°～108°)内都能实现精确标定,同时由于在系统中省去了波片,可以实现在多波长的定标.     

LiO2(C2V，X2A2)分子的结构与势能函数

使用二次组态相互作用方法，在aug-cc-pvtz基组水平上对LiO₂(C_2V，X²A₂)基态分子进行了几何优化，得到了它的平衡几何构型和力常数.根据原子分子反应静力学原理得到可能的电子状态和离解极限.应用多体展式理论方法推导出了LiO₂(C_2V，X²A₂)基态分子的解析势能函数.     

CuH分子A1∑+态的寿命和预解离研究

A combined cavity ringdown (CRD) and laser induced fluorescence (LIF) spectroscopic study on the A¹∑⁺-X¹∑⁺ transition of CuH has been presented.The CuH molecule,as well as its deuterated isotopologue CuD,are produced in a supersonic jet expansion by discharging H₂(or D₂) and Ar gas mixtures using two copper needles.Different profiles of relative line intensities are observed between the measured LIF and CRD spectra,providing an experimental evidence for the predissociation behavior in the A¹∑⁺ state of CuH.The lifetimes of individual upper rotational levels are measured by LIF,in which the J''-dependent predissociation rates are obtained.Based on the previous theoretical calculations,a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A¹∑⁺ state and the lowest-lying triplet ³∑⁺ state,and a tunneling effect may also be involved in the predissociation.Similar experiments are also performed for CuD,showing that the A¹∑⁺ state of CuD does not undergo a predissociation process.     

Probing the interactions of charmed mesons with nuclei in ¯p-induced reactions

We study the perspectives of resonant and nonresonant charmed-meson production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(3770),Ψ(4040) and Ψ(4160) on various nuclei, their propagation and decay to D,ˉD, D ^*,ˉD^*, D _s,ˉD_s in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV. Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can be related to (u, d )-, s- or c-quark exchange with nucleons. It is found that by studying the D/ˉD ratio for low momenta in the laboratory ( ? 2 - 2.2 GeV/c) as a function of the target mass A stringent constraints on the c-quark exchange cross-section can be obtained. On the other hand, the ratios D ^- _s/D ⁺ _s as well as D/D ^- _s and D/D ⁺ _s at low momenta as a function of A will permit to fix independently the strength of the s-quark exchange reaction in D ^- _s N scattering. Received: 1 March 2002 / Accepted: 21 March 2002     

15N Photo-CIDNP MAS NMR To Reveal Functional Heterogeneity in Electron Donor of Different Plant Organisms

In plants and cyanobacteria, two light-driven electron pumps, photosystems I and II (PSI, PSII), facilitate electron transfer from water to carbon dioxide with quantum efficiency close to unity. While similar in structure and function, the reaction centers of PSI and PSII operate at widely different potentials with PSI being the strongest reducing agent known in living nature. Photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) nuclear magnetic resonance (NMR) measurements provides direct excess to the heart of large photosynthetic complexes (A. Diller, Alia, E. Roy, P. Gast, H.J. van Gorkom, J. Zaanen, H.J.M. de Groot, C. Glaubitz, J. Matysik, Photosynth. Res. 84, 303–308, 2005; Alia, E. Roy, P. Gast, H.J. van Gorkom, H.J.M. de Groot, G. Jeschke, J. Matysik, J. Am. Chem. Soc. 126, 12819–12826, 2004). By combining the dramatic signal increase obtained from the solid-state photo-CIDNP effect with ¹⁵N isotope labeling of PSI, we were able to map the electron spin density in the active cofactors of PSI and study primary charge separation at atomic level. We compare data obtained from two different PSI proteins, one from spinach (Spinacia oleracea) and other from the aquatic plant duckweed (Spirodella oligorrhiza). Results demonstrate a large flexibility of the PSI in terms of its electronic architecture while their electronic ground states are strictly conserved.     

Electron spin polarization in consecutive spin-correlated radical Pairs: Application to short-lived and long-lived precursors in type 1 photosynthetic reaction centres

An analytical treatment of the spin dynamics in sequential photoinduced correlated coupled radical pairs is presented and applied to the spectra of the states P⁺A ₁ ^? and P⁺F _x ^? in type 1 photo-synthetic reaction centres. Expressions for the spin polarized spectra are derived for the specific limiting cases of a very short-lived and very long-lived primary radical pair which correspond to the situation found in heliobacteria and photosystem I (PSI), respectively. The inhomogeneous line-broadening due to the unresolved hyperfine couplings is taken explicitly into account. It is shown that the density matrix of the secondary pair ρ₂ can be written as the sum of two terms corresponding to (i) the part which is independent of the spin dynamics in the precursor, (ii) the additional spin polarization which is generated during the lifetime of the precursor and transferred to the secondary pair. The latter term contains two contributions which arise from the difference of the Zeeman interactions of the radicals in the primary pair and from the inhomogeneous line broadening. The predicted polarization patterns are compared to those established for chemically induced dynamic electron polarization (CIDEP) when uncoupled radicals are generated from a radical pair precursor. The expressions are then used to simulate the experimental spectra of the consecutive pairs P⁺A ₁ ^? and P⁺F _x ^? in PSI using parameters derived entirely from independent experimental data. Excellent agreement with the experimental results is obtained. The spectra of P⁺F _x ^? in heliobacteria at X- and K-band are also simulated and it is shown that the observed polarization patterns can be reproduced assuming direct electron transfer from A₀ to F_x with a time constant ofτ = 600 ps.     

Development and applications of high-frequency ESR up to 55 T

A multiextreme (high-field, low-temperature, high-pressure and nanoscale) electron spin resonance (ESR) measurement system is under development in Kobe. In this connection, our recent development is introduced and two applications of our high-frequency high-field ESR are described. High-frequency high-field ESR measurements of dioptase (Cu₆Si₆O₁₈·6H₂O), which has an interesting antiferromagnetic Cu²⁺ network, have been performed using a pulsed magnetic field of up to 55 T. Antiferromagnetic resonances (AFMR) are clearly observed at 4.2 K with the light sources of up to 1017 GHz. However, a deviation from the conventional two-sublattice AFMR theory is observed in the high field. Temperature dependence of the X-band and high-frequency ESR has been also observed in the triangular lattice antiferromagnet EtMe₃P[Pd(dmit)₂]₂ which shows the spin-Peierls-like transition below T _c = 25 K. The preliminary field dependence of the spin gap estimated from the analyses of our ESR results has been shown in connection with the previous magnetic susceptibility results.     

Electron Spin Resonance and Ground State Wave Functions of Vanadyl Ion in LiNaSO<Subscript>4</Subscript>

Electron spin resonance (ESR) of VO²⁺ doped into LiNaSO₄ has been studied at 300 K on an X-band spectrometer. The ESR powder spectra have been analyzed and spin Hamiltonian parameters have been evaluated. Using the crystal-field approach, a theoretical estimate of the ground state wave functions of VO²⁺ in LiMSO₄ (M = Na, K) has been made from the ESR data. The dipolar hyperfine coupling constant P and Fermi contact parameter K have also been estimated.     

Quantum registers based on single NV + <Emphasis Type="Italic">n</Emphasis><Superscript>13</Superscript>C centers in diamond: I. The spin Hamiltonian method

Details of the application of the spin Hamiltonian method for studying spin characteristics of a quantum register that includes an electron spin S = 1 of a single NV center in the ground electronic state and nuclear spins I = 1/2 of several isotopic atoms ¹³C located at different lattice sites near the vacancy of the NV center. Two methods of finding the hyperfine interaction tensors for these NV + n ¹³C spin systems are considered, one of which is based on the conventional electron spin resonance (ESR) method, while the other involves methods of quantum chemistry. The results of the latter method are compared with ESR data and with spectra of optically detected magnetic resonance (ODMR) and with the character of the modulation of the ODMR echo decay observed in single NV + n ¹³C systems. This comparison shows that the ab initio modeling of the spin characteristics of diamond nanoclusters containing NV centers makes it possible to obtain quantitative spin characteristics of the quantum registers under study.     

Theoretical studies of absorption spectra and microstructure of Ni2+ at the octahedral site of the NiFe2O4 nanoparticle

The optical absorption spectra, microstructure and electronic spin resonance parameters (electronic spin resonance (ESR) g factor) for Ni²⁺ ions at octahedral centers of nickel ferrite nanoparticles are calculated from the two-spin–orbit-parameter model. The effect of spin–orbital coupling of the central metal 3d⁸ ions and ligand oxygen ions has been taken into account in the full energy matrix and ESR g formula. The calculated results are in good agreement with the observed values. In addition, the microstructures of Ni²⁺ ions at octahedral centers in NiFe₂O₄ are reasonably determined from the calculations.     

ESR and TL studies of irradiated Anatolian laurel leaf (Laurus nobilis L.)

Laurel leaf (Laurus nobilis L.) samples that originated from Turkey were analyzed by electron spin resonance (ESR) and thermoluminescence (TL) techniques before and after γ-irradiation. Unirradiated (control) laurel leaf samples exhibit a weak ESR singlet centered at g=2.0020. Besides this central signal were two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. The dose–response curve of the radiation-induced ESR signal at g=2.0187 (the left satellite signal) was found to be described well by a power function. Variation of the left satellite ESR signal intensity of irradiated samples at room temperature with time in a long term showed that cellulosic free radicals responsible for the ESR spectrum of laurel leaves were not stable but detectable even after 100 days. Annealing studies at four different temperatures were used to determine the kinetic behavior and activation energy of the radiation-induced cellulosic free radicals responsible from the left satellite signal (g=2.0187) in laurel leaves. TL measurements of the polymineral dust isolated from the laurel leaf samples allowed distinguishing between irradiated and unirradiated samples.     

CrHn(n=0,+1,+2)分子及离子的势能函数

用原子分子反应静力学原理推导出CrHⁿ(n=0，+1，+2)的电子状态及其离解极限. 对H原子采用6-311++G^**基组，对Cr原子采用SVP(split valence polarization)全电子基组，用B3PW91方法计算了它们的平衡几何、电子状态，在此基础上分别计算CrH，CrH⁺的Murrell-Sorbie解析势能函数和CrH²⁺的解析势能函数及其对应的力常数、光谱参数，理论计算值与实验值和文献计算值符合较好. 从离解极限和通道解释了不同的势能函数形状. 计算表明：CrH⁺的势能曲线均具有对应于稳定平衡结构的极小点，说明CrH⁺可稳定存在. 而CrH²⁺离子的势能曲线对应于不稳定的排斥态，说明CrH²⁺是不稳定的. 关键词： n(n=0')" href="#">CrHⁿ(n=0 +2) 势能函数 光谱参数 稳定性     

Characterization of X-Ray-Irradiated β-Ca3(PO4)2:Dy by means of ESR Spectroscopy

Electron spin resonance (ESR) spectra caused by a stable trapped H atom, a Dy³⁺ ion, and a PO₄ unit were observed in X-ray-irradiated dysprosium-doped β-tricalcium phosphate (β-Ca₃(PO₄)₂:Dy, β-TCP:Dy) phosphor. The ESR spectrum of the H atom in the X-ray-irradiated β-TCP:Dy phosphor was slightly different from that of nondoped X-ray-irradiated β-TCP, suggesting that the Dy³⁺ spin state has a significant effect on the relaxation time of electron spins. The electron spin echo of the H atom was observed in the X-ray-irradiated β-TCP but not in the corresponding X-ray-irradiated β-TCP:Dy phosphor. Authors' address: Kouichi Nakashima, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba-ku, Sendai 980-8577, Japan     

Effect of protonation on individual hydrogen bonds in the 8-oxoguanine-cytosine base pair: NMR,NBO and AIM analyses

Protonation increases the total binding energy of the 8-oxoguanine-cytosine (8OG:C) base pair by 60–70% at the B3LYP/6-311++G(d,?p) level of theory. It changes the individual H-bond energies, estimated from electron charge densities at bond critical points, by 1.16 to ?16.41?kcal?mol^?1. The individual H-bond energies and the two bond X–Y spin–spin coupling constants (^2hJ_X–Y) increase with protonation where 8OG behaves as an H-bond donor; the reverse is true for the H-bonds in which the 8OG unit acts as an H-bond acceptor. Similar to ^2hJ_X–Y, the value of ^1hJ_O–H (a one-bond H?···?Y spin–spin coupling constant) is distance dependent and in linear correlation with the O?···?H distance, but the ^1hJ_N–H values are independent of the N–H distance and the PSO term is the predominant portion in it. The ¹J_X–H spin–spin coupling constant is dominated by the negative FC term for all hydrogen bonds, although the PSO term is the best to investigate the behaviour of ¹J_X–H across the X–H?·?Y H-bond.