快重离子辐照聚酰亚胺潜径迹的电子能损效应

快重离子辐照聚合物材料时，由于密集电离激发在其路径上产生几纳米直径的潜径迹，径迹形貌受离子种类、离子能量等多种因素的影响.为了研究电子能损对径迹形成所起的作用，利用1.158GeV 的Fe⁵⁶离子和 1.755GeV Xe¹³⁶离子在室温真空环境下辐照叠层聚酰亚胺(PI)薄膜，结合傅里叶转换红外光谱(FTIR)分析技术对辐照引起的化学变化进行了测量.聚酰亚胺官能团的降解及炔基的生成是离子辐照聚合物的主要特征，在注量1×10¹¹到6×10¹²/cm²范围及较宽的电子能损(dE/dX)_e范围 (Fe⁵⁶ 离子：2.2 到 5.2 keV/nm， Xe¹³⁶ 离子：8.6 到 11.3 keV/nm)对官能团的断键率及炔基生成率进行了研究. 红外结果显示在实验涉及的能损范围都有炔基生成，应用径迹饱和模型对实验结果进行拟合，不同能损下的平均损伤径迹半径及炔基生成径迹半径被得到，通过热峰模型对实验结果拟合，给出了离子在聚酰亚胺中产生潜径迹的能损阈值，实验给出的径迹形貌的电子能损效应曲线与热峰模型预言走势基本一致. 关键词： 离子辐照 潜径迹 红外光谱 热峰模型     

Energy levels,luminescence and electronic structure of ZnS:Tm3+

Energy levels, densities of states, electronic densities, electrostatic interaction integral parameters F_k and spin-orbit coupling parameters ζ_4f for ZnS: Tm³⁺ are calculated self-consistently, using both one-electron local density discrete variational non-relativistic Hartree-Fock-Slater (HFS) and relativistic Dirac-Slater (DS) cluster models. In these calculations, both spin-restricted and spin-polarized models are considered. The finite clusters calculated include TmS₄ and TmS₄Zn₁₂ clusters for cubic ZnS, which are embedded in the crystal environment. The spin-orbit coupling parameter ζ_4f derived from DS cluster calculations is equal to 2689 cm^-1, rather near the result of the relativistic Hartree-Fock free ion model. The parameters F_k and ζ_4f are further calculated from the 4f radial wave function obtained by solving the HFS and the DS atomic equations. It is shown that by decreasing the effective exchange-correlation potential, these parameters can be reduced to approximately match empirical values. A comparison of the excited energy level scheme of ZnS:Tm derived from the calculated parameters and the experimental spectra is presented.     

A single parameter scaling theory in a disordered layered system

We show that in a disordered layered system all states are localized if k_Fl<4Πg_c, irrespective of the interlayer coupling t _⊥. The crossover of dimensionality depends on t_⊥. Near the critical value t_⊥^c at which the Anderson transition occurs, the correlation length ζ^m and the localization length ζ^loc are calculated.     

Solution of the Eliashberg equations for a very strong electron-phonon coupling with a low-energy cutoff

We solve the Eliashberg equations for the case of an explicit k dependence of the interactions, and of the resulting self-energies Σ₁(k,ω), Σ₂(k,ω). We consider a strong energy-dependence of the electron-electron scattering-rate τ, which is associated with a strong energy-dependence of the electron-phonon matrix element g(k,k′). We characterize this energy-dependence by a cutoff ζ₁, which is of the order of the phonon frequency ω_ph. We find that we can account for a large number of unexpected features of the superconductivity of the cuprates by the BCS electron-phonon theory, if we consider very large values of the McMillan coupling constant λ_ph, and small values of the cutoff ζ₁. Specifically, the Coulomb interaction is found not to depress T_c; the isotope effect is strongly reduced when ζ₁ < ω_ph. We find solutions in which the gap function Δ(k, ω) has extended s-wave symmetry but is very anisotropic. These large anisotropies are in good agreement with various experiments. We suggest that the underlying cause of the strong energy-dependence is a very small electronic screening parameter at the Fermi surface; the electron-phonon matrix element g is abnormally large, and this accounts for the high transition temperatures of the cuprates. An order of magnitude estimate suggests that the electron-phonon mechanism can account for transition temperatures up to about 200 K. We thus propose a very-strong-coupling theory, in which the renormalization functions, in particular the energy-renormalization X, depend very strongly on the superconducting gap Δ, and thus display a very strong temperature-dependence between T_c and T = 0. An experimental manifestation of the very strong coupling with a small cutoff is a zero bias anomaly sometimes observed in tunneling experiments.     

Per cent ‘covalency’ and the nephelauxetic effect in lanthanide complexes

The use of the nephelauxetic ratio for the calculation of percent covalency is examined. Values of F_k and E^k obtained from four parameter fits (e.g. F ₂, F ₄, F ₆ and ζ_4f) neglecting configuration interaction for Pr³⁺ in various host lattices are compared to those of the free ion. By including the effects of 4f-ligand overlap one can account for the empirically obtained order of sensitivity to the environment for F_k : F ₂ > F ₄ > F ₆ and for E^k : E ² > E ³ > E ¹. The results further indicate that by using the nephelauxetic effect and the relationship b = (1 - β)/2 one is likely to overestimate the degree of covalency of a complex.     

引力场的能量动量赝张量与轴对称体系的引力辐射

本文计算了轴对称体系的引力辐射总功率。用胡宁的τ^(n)αβ表达式和Bondi的柱面波解直接计算导出-(dE)/(dt)=1/2∫^x₀c₀²sinθdθ。这个结果与Bondi不用任何τ^αβ表达式得到的公式完全相同,并证明辐射总功率是恒正的。但是,由郑玉昆的τ^αβ表达式得到的结果与Bondi的公式不一致,并表明辐射总功率不是恒正的。 关键词：     

Nitrogen-15 Fractionation in the Thermal Decomposition of Nitrous Oxide of Natural Isotopic Composition

Abstract

The ¹⁵N fractionation in the thermal decompostion of nitrous oxide (N₂O) of natural isotopic composition has been investigated in quartz reaction vessel in the temperature interval 888–1073K. The formulas relating the observed experimentally ¹⁵N fractionations with the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p for ¹⁴N¹⁵N¹⁶O, and secondary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_s for ¹⁵N¹⁴N¹⁶O, have been derived. The experimentally estimated ¹⁵N kinetic isotope effects have been compared with the primary and secondary ¹⁵N kinetic isotope effects calculated with the absolute rate theory formulations applied to linear three atom molecules. A good agreement was found for the primary ¹⁵N kinetic isotope effect, (k ¹⁴/k ¹⁵)_p, in the temperature interval 888–1007K. But at 1073K the decompositions of N₂O, accompanied by NO (nitric oxide) formation proceed with a twice times smaller primary kinetic isotope effect, (k ¹⁴/k ¹⁵)_p of 1.0251 ± 0.0009, only, suggesting the nonlinear transition state structures with participation of the fourth external atom at high temperature decompositions of nitrous oxide. The nitrogen isotope effects determined in this study correlate well with nitrogen isotope fractionations observed in the natural biological, earth and atmospheric processes.     

Local BRST cohomology in the antifield formalism: I. General theorems

We establish general theorems on the cohomologyH ^* (s/d) of the BRST differential modulo the spacetime exterior derivative, acting in the algebra of localp-forms depending on the fields and the antifields (=sources for the BRST variations). It is shown thatH ^–k (s/d) is isomorphic toH _k (/d) in negative ghost degree–k (k>0), where is the Koszul-Tate differential associated with the stationary surface. The cohomology groupH ₁ (/d) in form degreen is proved to be isomorphic to the space of constants of the motion, thereby providing a cohomological reformulation of Noether's theorem. More generally, the groupH _k (/d) in form degreen is isomorphic to the space ofn–k forms that are closed when the equations of motion hold. The groupsH _k (/d)(k>2) are shown to vanish for standard irreducible gauge theories. The groupH ₂ (/d) is then calculated explicitly for electromagnetism, Yang-Mills models and Einstein gravity. The invariance of the groupsH ^k (s/d) under the introduction of non-minimal variables and of auxiliary fields is also demonstrated. In a companion paper, the general formalism is applied to the calculation ofH ^k (s/d) in Yang-Mills theory, which is carried out in detail for an arbitrary compact gauge group.Supported by Deutsche Forschungsgemeinschaft     

Steric effects on the mechanism of reaction of nucleophilic substitution of β‐substituted alkoxyvinyl trifluoromethyl ketones with four secondary amines

The kinetics of the reaction of β‐substituted β‐alkoxyvinyl trifluoromethyl ketones R¹O‐CR²?CH‐COCF₃ ( 1a – e ) [( 1a ), R¹?C₂H₅, R²?H; ( 1b ), R¹?R²?CH₃; ( 1c ), R¹?C₂H₅, R²?C₆H₅; ( 1d ), R¹?C₂H₅, R²?V^?pNO₂C₆H₄; ( 1e ), R¹?C₂H₅, R²?C(CH₃)₃] with four aliphatic amines ( 2a – d ) [( 2a ), (C₂H₅)₂NH; ( 2b ), (i‐C₃H₇)₂NH; ( 2c ), (CH₂)₅NH; ( 2d ), O(CH₂CH₂)₂NH] was studied in two aprotic solvents, hexane and acetonitrile. The least reactive stereoisomeric form of ( 1a – d ) was the most populated ( E‐s‐Z‐o‐Z ) form, whereas in ( 1e ), the more reactive form ( Z‐s‐Z‐o‐Z ) dominated. The reactions studied proceeded via common transition state formation whose decomposition occurred by ‘uncatalyzed’ and/or ‘catalyzed’ route. Shielding of the reaction centre by bulky β‐substituents lowered abruptly both k′ (‘uncatalyzed’ rate constant) and k″ (‘catalyzed’ rate constant) of this reaction. Bulky amines reduced k″ to a greater extent than k′ as a result of an additional steric retardation to the approach of the bulky amine to its ammonium ion in the transition state. An increase in the electron‐withdrawing ability of the β‐substituent increased ‘uncatalyzed’ k′ due to the acceleration of the initial nucleophile attack (k₁) and ‘uncatalyzed’ decomposition of transition state (k₂) via promoting electrophilic assistance (through transition state 8 ). The amine basicity determined the route of the reaction: the higher amine basicity, the higher k₃/k₂ ratio (a measure of the ‘catalyzed’ route contribution as compared to the ‘uncatalyzed’ process) was. ‘Uncatalyzed’ route predominated for all reactions; however in polar acetonitrile the contribution of the ‘catalyzed’ route was significant for amines with high pK_a and small bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

Entire Solutions of Hydrodynamical Equations with Exponential Dissipation

We consider a modification of the three-dimensional Navier–Stokes equations and other hydrodynamical evolution equations with space-periodic initial conditions in which the usual Laplacian of the dissipation operator is replaced by an operator whose Fourier symbol grows exponentially as e^|k|/k_d{{{\rm e}^{|k|/k_{\rm d}}}} at high wavenumbers |k|. Using estimates in suitable classes of analytic functions, we show that the solutions with initially finite energy become immediately entire in the space variables and that the Fourier coefficients decay faster than e^{-C(k/k_d) ln(|k|/k_d)}{{{\rm e}^{-C(k/k_{\rm d})\,{\rm ln}(|k|/k_{\rm d})}}} for any C < 1/(2 ln 2). The same result holds for the one-dimensional Burgers equation with exponential dissipation but can be improved: heuristic arguments and very precise simulations, analyzed by the method of asymptotic extrapolation of van der Hoeven, indicate that the leading-order asymptotics is precisely of the above form with C = C _* = 1/ ln 2. The same behavior with a universal constant C _* is conjectured for the Navier–Stokes equations with exponential dissipation in any space dimension. This universality prevents the strong growth of intermittency in the far dissipation range which is obtained for ordinary Navier–Stokes turbulence. Possible applications to improved spectral simulations are briefly discussed.     

The determination by an independent method ofP k electron capture probabilities in133Ba and139Ce decays gamma decay of133Ba

The electron capture decays of¹³³Ba (10.4 y) and¹³⁹Ce (140 d) were investigated with high resolution Ge(Li) detectors. By x-ray — γ-ray coincidences values of the quantityP _k ω _k ? _k for various transitions in the decay of¹³³Ba and¹³⁹Ce are obtained. The factor ω _k ? _k was measured independently by means ofK-conversion electron-K x-ray coincidences and was then used to determineP _k , theK-capture probability. The independent measurement of the product ω _k ? _k , together with recent accurate values of ω _k , provides a new method for the accurate calibration of semiconductor x-ray detectors. In the decay of¹³⁹Ce, a value ofP _k =0.78±0.03 is found (where the error represents twice the standard deviation) from whichQ _ec =326 _?30 ⁺⁷⁰ keV to the¹³⁹La ground-state is found by use of theory. In¹³³Ba decay, values are found ofP _k 1=0.72±0.04 for theEC transition to the 437 keV level in¹³³Cs,P _k 2=0.80±0.07 to the 384 keV level, and from an independent measurement, the ratioP _k 1/P _k 2=0.87±0.07. From these results the ground-state value ofQ _ec =522 _?10 ⁺²⁰ keV is derived from theory for¹³³Ba decay. The gamma spectrum of¹³³Ba also was remeasured. From the present gamma intensities and previous conversion electron intensities, new values forK-shell conversion coefficients are obtained. Previously reported γ-rays at 35 and 391 keV are not confirmed.     

The high energy double photon bremsstrahlung processe ± e −→e ± e −γγ at small angles for arbitrary polarizations of the particles

The amplitude of the processe ^± e ^?→e ^± e ^? γγ is found in the main region of the scattering anglesm/E?θ _i ?1. The result has a simple form convenient for the calculations of various cross sections. The energydσ/dω ₁ dω ₂ and the energy-angulardσ/d ³ k ₁ dω ₂,dσ/d ³ k ₁ d ³ k ₂ distributions of the photons are found for the case when the initial electrons are polarized and the photon polarizations are measured. It is shown that the measurement of the mean photon helicities allows to determine the polarizations of the initial electrons.     

More on Zeta-Function Regularization of High-Temperature Expansions

A recent paper using the Riemann ζ-function to regularize the (divergent) coefficients occurring in the high-temperature expansions of one-loop thermodynamic potentials is extended. This method proves to be a powerful tool for converting Dirichlet-type series Σ_ma_m(x_i)/m^s into powerseries in the dimensionless parameters x_i. The coefficients occurring in the power series are (proportional to) ζ-functions evaluated away from their poles - this is where the regularization occurs. High-temperature expansions are just one example of this highly-nontrivial rearrangement of Dirichlet series into power series form. We discuss in considerable detail series in which a_m(x_i) is a product of trigonometrie, algebraic and Bessel function factors. The ζ-function method is carefully explained, and a large number of new formulae are provided. The means to generalize these formulae are also provided. Previous results on thermodynamic potentials are generalized to include a nonzero constant term in the gauge potential (time component) which can be used to probe the electric sector of temperature gauge theories.     

Joint theoretical and experimental study of the gas‐phase elimination kinetics of tert‐butyl ester of carbamic,N, N‐dimethylcarbamic,N‐hydroxycarbamic acids and 1‐(tert‐butoxycarbonyl)‐imidazole

The gas‐phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200–280 °C and 22–201.5 Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first‐order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate‐determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four‐membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert‐butyl carbamate logk₁ (s^?1) = (13.02 ± 0.46) – (161.6 ± 4.7) kJ/mol(2.303 RT)^?1, for tert‐butyl N‐hydroxycarbamate logk₁ (s^?1) = (12.52 ± 0.11) – (147.8 ± 1.1) kJ/mol(2.303 RT)^?1, and for 1‐(tert‐butoxycarbonyl)‐imidazole logk₁ (s^?1) = (11.63 ± 0.21)–(134.9 ± 2.0) kJ/mol(2.303 RT)^?1. Theoretical studies of these elimination were performed at Møller–Plesset MP2/6‐31G and DFT B3LYP/6‐31G(d), B3LYP/6‐31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six‐membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd.     

Microwave spectra of phosphoryl trifluoride in vibrationally excited states

The ground-state rotational spectra of ¹⁶OPF₃ and ¹⁸OPF₃ have been recorded and analysed to yield a structure and accurate centrifugal distortion constants.

The pure rotational spectrum of ¹⁶OPF₃ has been recorded and analysed for five of the molecule's vibrationally excited states. The analysis of the ν₅ = 1 and ν₆ = 1 states is discussed in detail and values of ζ₅₅ ^z and ζ₆₆ ^z have been obtained. In addition, information is obtained about the elusive A rotational constant for ν₆ = 1 due to an accidental near degeneracy which yields the value A _ν=4797·86 MHz.

Some of the information obtained is used to derive the harmonic force field for the OPF₃ molecule. The use of ground-state distortion constants instead of their equilibrium values is discussed.     

The reaction of CH3 + O2: experimental determination of the rate coefficients for the product channels at high temperatures

The reaction of methyl radicals (CH₃) with molecular oxygen (O₂) has been investigated in high-temperature shock tube experiments. The overall rate coefficient, k₁ = k_1a + k_1b, and individual rate coefficients for the two high-temperature product channels, (1a) producing CH₃O + O and (1b) producing CH₂O + OH, were determined using ultra-lean mixtures of CH₃I and O₂ in Ar/He. Narrow-linewidth UV laser absorption at 306.7 nm was used to measure OH concentrations, for which the normalized rise time is sensitive to the overall rate coefficient k₁ but relatively insensitive to the branching ratio of the individual channels and to secondary reactions. Atomic resonance absorption spectroscopy measurements of O-atoms were used for a direct measurement of channel (1a). Through the combination of measurements using the two different diagnostics, rate coefficient expressions for both channels were determined. Over the temperature range 1590–2430 K, k_1a = 6.08 × 10⁷T^1.54 exp (−14005/T) cm³ mol⁻¹ s⁻¹ and k_1b = 68.6 T^2.86 exp (−4916/T) cm³ mol⁻¹ s⁻¹. The overall rate coefficient is in close agreement with a recent ab initio calculation and one other shock tube study, while comparison of k_1a and k_1b to these and other experimental studies yields mixed results. In contrast to one recent experimental study, reaction (1b) is found to be the dominant channel over the entire experimental temperature range.     

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。