共查询到20条相似文献,搜索用时 31 毫秒
1.
为研究超高速碰撞天然白云石板产生闪光温度衰减阶段的演化特征,利用二级轻气炮和瞬态光纤高温计,进行入射角度(与靶板平面的夹角)为45°、碰撞速度分别为1.9,4.2km/s两种条件下的超高速碰撞实验。根据冲击波理论,推导出超高速碰撞天然白云石板产生闪光温度衰减阶段的半理论半经验公式。分析结果表明,弹丸撞击靶板的速度越高,闪光辐射温度衰减的持续时间越长。闪光辐射温度衰减阶段的理论推导与实验数据一致性较好,闪光辐射温度衰减阶段的理论推导可对类似碰撞问题闪光辐射温度衰减阶段进行预估。 相似文献
2.
根据Fresnel-Kirchhoff衍射理论,结合临床实际,考虑振幅近似和相位缓变条件,由傅里叶变换和卷积定理,导出了微聚焦X射线相衬成像(X-ray Phase-contrast Imaging,X-PCI)在像平面上焦斑尺寸范围内的能量密度分布函数.结果显示,像密度函数是吸收效应滤波函数FA(x)和相位效应滤波函数FP(x)分别与吸收项A2(x)和相位项A2(x)φ(x)作卷积运算后的和.利用mathematica软件分析讨论了该函数的分布规律,并给出了理论解释.结果表明,吸收效应对像密度的影响在焦斑范围内保持不变|相位效应对像密度的影响在焦斑范围内逐渐加强|在焦斑一定范围内,相位效应的影响远大于吸收效应. 相似文献
3.
Theoretical approaches to studying protonic decays of nuclei and interpretation of experimental data
S. G. Kadmensky 《Physics of Atomic Nuclei》2000,63(4):551-561
A comparison of various theoretical approaches to describing deep-subbarrier protonic decays of nuclei leads to the conclusion that the multiparticle theory of protonic decays of nuclei that is based on the use of an integral formula for decay widths is quite correct and general. A theoretical scheme for computing the protonic widths of odd-odd deformed nuclei is developed. The dependence of the fine structure in the protonic spectrum of the 141Ho nucleus on the type of the odd-proton orbital is investigated. It is shown that the nuclear-deformation parameters as extracted from the analysis of protonic decays are consistent with analogous parameters predicted in some compilations. 相似文献
4.
We discuss the decays ψ';'→J/ψ+π0 and ψ';'→J/ψ+η. We obtain a reliable, model-independent theoretical prediction for the ratio of the decay rates based only on the QCD lagrangian and certain low-energy theorems. The theoretical formula, apart from kinematical factors, contains only the ratio of the current quark masses, md/mu. Under a standard choice of md/mu theory and experiment are in good agreement with each other. 相似文献
5.
微聚焦X射线成像的相位效应分析 总被引:1,自引:1,他引:0
根据Fresnel-Kirchhoff衍射理论,结合临床实际,考虑振幅近似和相位缓变条件,由傅里叶变换和卷积定理,导出了微聚焦X射线相衬成像(X-ray Phase-contrast Imaging,X-PCI)在像平面上焦斑尺寸范围内的能量密度分布函数.结果显示,像密度函数是吸收效应滤波函数FA(x)和相位效应滤波函数FP(x)分别与吸收项A2(x)和相位项A2(x)φ(x)作卷积运算后的和.利用mathematica软件分析讨论了该函数的分布规律,并给出了理论解释.结果表明,吸收效应对像密度的影响在焦斑范围内保持不变;相位效应对像密度的影响在焦斑范围内逐渐加强;在焦斑一定范围内,相位效应的影响远大于吸收效应. 相似文献
6.
M. Vinduška 《Czechoslovak Journal of Physics》1964,14(3):143-151
The influence of the dimensions of a nucleus on the form of the spectra of unique first forbidden transitions is investigated. The results of a theoretical analysis are compared with the experimental results. Experiments are proposed whereby the exactness of the different approximations used in the theory of beta decay could be verified. The questions have a direct relation to the proofs of the presence of weak magnetism during beta decay. 相似文献
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The nondecay probability of an unstable particle at a definite moment of time is investigated provided this particle existed at all earlier observation moments separated with the time interval Δ. Using the usual postulates for quantum measurements it is proved that this probability is described by the exponential function of Δ>0, and it tends to 1 as Δ → 0. An approximate formula is found for the effective decay width Γ(Δ) appearing in the case of multiple measurements. It is shown that Γ(Δ) → 0 as Δ → 0. For Δ → ∞, the width Γ(Δ) → Γ0, with Γ0 being the standard decay with in Weisskopf-Wigner theory. At finite δ's Γ(Δ) may be smaller or greater than Γ0 depending on the parameters of the theory. 相似文献
10.
The physics of the weak decay of hypernuclei is briefly reviewed from a theoretical point of view. Special regard is devoted to the recent progress concerning the determination of the non-mesonic decay widths and the asymmetry parameters. Convincing evidence has been achieved for a solution of the long-standing puzzle on the ratio Γn/Γp. Very recently, it has been shown that the exchange of a ππ pair in the weak mechanism plays a crucial role in explaining the discrepancies between theory and experiment on the decay asymmetries. 相似文献
11.
We show existence and give an implicit formula for the escape rate of the n-centre problem of celestial mechanics for high energies. Furthermore we give precise computable estimates of this rate. This
exponential decay rate plays an important role especially in semiclassical scattering theory of n-atomic molecules. Our result shows that the diameter of a molecule is measurable in a (classical) high-energy scattering
experiment. 相似文献
12.
An algorithm for obtaining the number of Kekulé and Dewar structures for the radical cations of aromatic hydrocarbons is described. The procedure is fully automatic and requires only the Hückel adjacency matrix as input information. For several important annelation series, closed analytical expressions are derived; where this proved impossible an approximate formula is given. The procedure is used to calculate the first IP's of a large body of aromatic hydrocarbons according to a resonance theoretical model proposed by Herndon. Comparison with the IP1 values measured by photoelectron spectroscopy shows that there is nothing in these results to encourage the use of resonance theory, unless the theory is substantially improved. In particular inclusion of the Dewar structures into the wavefunction of the ground state seems mandatory. Hückel theory with four adjustable parameters gives superior results for much less computer time (standard deviation 0.07 eV, compared with 0.17 eV for resonance theory for the same set of compounds). 相似文献
13.
Studies on some superheavy nuclei are performed. The α decay energies are calculated by an improved local binding energy formula, and the α decay half-lives are calculated by the Viola-Seaborg formula. Good agreements between theoretical and experimental results are reached. 相似文献
14.
Yu. Ts. Oganessian 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):17-23
Experiments are described and main results presented on the synthesis and decay properties of superheavy nuclides, produced
in fusion reactions induced by a 48Ca-beam on heavy actinide targets. In such reactions neutron-rich nuclei are formed. For them, according to theory, an abrupt
enhancement of stability due to nuclear shell effects is expected. The decay properties of the new nuclides are compared with
calculations of theoretical models, which predict the existence of “islands of stability” in the region of hypothetical superheavy
elements. 相似文献
15.
Dunn KJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):171-180
We present a detailed comparison between the theoretically computed spin echo decay of a fluid-saturated periodic porous medium with strong internal field gradients and that obtained from various approximations using the free diffusion formula which is strictly valid only for infinite uniform fluids. The theoretical computation of the spin echo amplitude was carried out by using the diffusion eigenstates in Fourier representation, and the internal field gradients induced by magnetic susceptibility contrast were calculated by using a two-component composite theory. The comparison allows us to have an assessment of the regime of validity of various approximations for a periodic porous medium where a rigorous theoretical computation of the enhanced transverse relaxation due to magnetic susceptibility contrast induced field heterogeneity is possible. 相似文献
16.
A. E. Dorokhov 《Physics of Particles and Nuclei Letters》2010,7(4):229-234
Experimental and theoretical progress concerning the rare decay π0 → e
+
e
− is briefly reviewed. It includes the latest data from KTeV and a new model-independent estimate of the decay branching which
show the deviation between experiment and theory at the level of 3.3σ. The predictions for η and η′ decays into lepton pair
are presented. We also comment on the impact on the pion rare decay estimate of the data of BABAR collaboration on the pion
transition form factor at large momentum transfer. 相似文献
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An experimental Dalitz plot distribution for the decay η → π
+
π
−
π
0 is fitted by the theoretical one obtained in chiral perturbation theory with unitarity corrections taken into account. The
fit shows that the difference of light-quark masses is larger than is expected from electromagnetic mass differences of neutral
and charged kaons.
From Yadernaya Fizika, Vol. 67, No. 2, 2004, pp. 443–445.
Original English Text Copyright ? 2004 by Martemyanov, Sopov.
This article was submitted by the authors in English. 相似文献
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Systematic study of α decay half-lives for even–even nuclei within a deformed two-potential approach
In this work, we systematically study the α decay half-lives of 196 even–even nuclei using a two-potential approach improved by considering nuclear deformation. The results show that the accuracy of this model has been improved after considering nuclear deformation. In addition, we extend this model to predict the α decay half-lives of Z = 118 and 120 isotopes by inputting the α decay energies extracted from the Weizsacker–Skyrme-type (WS-type) mass model, a simple nuclear mass formula, relativistic continuum Hartree–Bogoliubov theory and Duflo-Zuker-19 (DZ19) mass model. It is useful for identifying the new superheavy elements or isotopes for future experiments. Finally, the predicted α decay energies and half-lives of Z = 118 and 120 isotopes are analyzed, and the shell structure of superheavy nuclei is discussed. It shows that the shell effect is obvious at N = 184, while the shell effect at N = 178 depends on the nuclear mass model. 相似文献