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1.
It is demonstrated on the basis of the Dirac equation that quarks cannot be confined by a vector gluon potential of the form(r/r 0)a or[ln(r/r 0]a, a>0, if the quark-gluon interaction conserves parity. In order to confine quarks with the parity-conserving interaction, the effective gluon potential must be a pseudovector or a scalar. These are shown in a simple Yang-Mills field with theSU(2) group.  相似文献   

2.
We demonstrate that in the Breit equation with a central potentialV(r) having the propertyV(r 0)=E there appears a Klein paradox atr=r 0. This phenomenon, besides the previously found Klein paradox arr→∞ appearing ifV(r)→∞ atr→∞, seems to indicate that in the Breit equation valid in the singleparticle theory the sea of particle-antiparticle pairs is not well separated from the considered two-body configuration. We conjecture that both phenomena should be absent from the Salpeter equation which is consistent with the hole theory. We prove this conjecture in the limit ofm (1)→∞ andm (2)→∞, where we neglect the terms ~1/m (1) and 1/m (2). In Appendix I we show that in the Breit equation the oscillations accumulating atr=r 0 in the case ofm (1)m (2) are normalizable to the Dirac δ-function. In Appendix II the analogical statement is justified for the nonoscillating singular behaviour appearing atr=r 0 in the case ofm (1)=m (2).  相似文献   

3.
The stability and convergence of the inverse spectroscopic problem is investigated for diatomic molecules in the1 electron state for a potential representation by series in the Dunham variable zd=(r-re)/re, the Ogilvie-Tipping zot=(r-re)/(r + re), the Simmond-Parr-Finlan zS= (r-re)/r and the Tucker zt=sign (p)[1 -(re/r)P]. None among the representations under investigation was that which would give a significant systematic improvement in stability as compared with others. The convergence is related to the selection of the initial approximation in the method of least squares, and is practically independent of the functional form of the potential. For the Dunham representation the solutions of the inverse problem yield quantities close to the true values of the expansion coefficients.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 98–101, May, 1984.  相似文献   

4.
We have characterized the wavelength dispersion of the high- and low-frequency values of the linear electro-optic coefficient r c = r 33–(n o/n e)3 r 13 of poled 0.88 Pb(Zn1/3Nb2/3)O3–0.12 PbTiO3 single crystal. The measurements have been investigated as a function of the laser wavelength from 0.465 to 1.32 m. Clamped r S and unclamped r T values of the electro-optic coefficient as well as the acoustic contribution r a have been established. We obtained a ratio of r S/r T = 30%, which is independent of the wavelength of the light beam. The value of r S c at the wavelength of 633 nm was found to be equal to 50±5 pm/V, which is a rather high value.This revised version was published online in March 2005. In the previous version, the published online date was missing  相似文献   

5.
The time dependence of remanence coercivity and thermal stability were investigated for hard/soft-stacked media consisting of a magnetically hard granular layer underneath a very thin soft layer with a large saturation magnetization, Ms. The values of remanence coercivity at measurement times t′=103 and 10−5 s (pulse field) were measured, and defined as Hr and HrP. The remanence coercivity on the recording time scale, Hr (1 ns), and the energy barrier, ΔE/kT, were evaluated by fitting Hr and HrP to Sharrock's equation taking into account the power law variation of the energy barrier, n. The value of Hr (1 ns) for a (Co–Pt)–SiO2 (9 nm)/Co–SiO2 (2 nm) stacked medium with an interfacial coupling control layer was about 9 kOe, which was less than half of that of a (Co–Pt)–SiO2 (9 nm) conventional medium (=21.3 kOe). The value of ΔE/kT for the stacked medium was about 111 (n=0.7), and was not significantly different from the conventional medium. Moreover, no significant difference in the rate of decrease of Hr with increasing temperature was observed between media with and without interlayers. These results indicate that the use of a thin soft layer with high Ms was effective at significantly reducing Hr with no notable change in thermal stability.  相似文献   

6.
Systematic measurements of the relative ion number stored in a Paul trap within the stability diagram given by the solution of the equation of motion reveal many lines, where only few or no ions can be confined. The observations can be explained by the presence of perturbations from higher-order components in the trapping potential, which is a quadrupole potential in the ideal case. The resonances follow the equation (n r /2) r + (n r /2) z = 1,n r +n z =N, where 2N is the order of the perturbation,n r ,n z are integer and r , z are stability parameters of the trap. The experiments were performed on H+ and H 2 + ions, which are detected after a storage time of 0.3 s by ejection from the trap.  相似文献   

7.
Perturbation theory is used to consider expansions for the radial distribution function, g 2(r), of a fluid with a soft core. We consider the Lennard-Jones (12, 6) potential and divide it into repulsive and attractive regions. In the repulsive region we expand the function exp (β u(r))g 2(r) about a hard sphere value. For the first-order contribution of the attractive region we consider a simple approximation to the exact analytical expression. The resulting g 2(r) is accurate at densities below about ρσ 3=0·5.  相似文献   

8.
We report on dynamics of excitons in CdxZn1−xTe/ZnTe quantum dots (QDs) and present information of excitonic transport and recombination. Due to different growth methods, samples with different QD's densities were obtained. Time-resolved measurements reveal three decay mechanisms: (i) radiative recombination of excitons in the individual QDs; (ii) thermally activated escape of excitons and (iii) escape due to tunneling (hopping). In the high QD-density samples the hopping (rHB=2700 ns−1) is two orders of magnitude more efficient than in the low QD-density samples (rHB=33 ns−1). Radiative recombination rates are similar in both types of samples, rR=1-1.3 ns−1. Due to the good radiative to nonradiative recombination ratio, the low-density QDs can be a potential source of entangled photon pairs.  相似文献   

9.
We consider a class of random matching problems where the distance between two points has a probability law which, for a small distance l, goes like lr. In the framework of the cavity method, in the limit of an infinite number of points, we derive equations for pk, the probability for some given point to be matched to its kth nearest neighbor in the optimal configuration. These equations are solved in two limiting cases: r = 0 -- where we recover p k = 1/2k, as numerically conjectured by Houdayer et al. and recently rigorously proved by Aldous -- and r→ + ∞. For 0 < r < + ∞, we are not able to solve the equations analytically, but we compute the leading behavior of pk for large k. Received 14 February 2001  相似文献   

10.
Monte Carlo calculations are reported for the radial distribution function g 2(r; λ) of a fluid in which the intermolecular pair potential is [u ref(r) + λu p(r)], u ref(r) being the Weeks-Chandler-Andersen (WCA) reference fluid, and [u ref(r) + u p(r)] being the Lennard-Jones (6, 12) fluid. The calculations are performed for λ values in the range 0 to 1, at the state condition ρσ3 = 0·80, kT/ε = 0·719. It is shown that at high densities the perturbation expansion of g 2(r; λ = 1) about g 2(r; λ = 0) is rapidly convergent, but that the corresponding expansion for y 2(r; λ) = exp [βu(r; λ)] × g 2(r; λ) is not. In addition Monte Carlo estimates of the individual terms that contribute to the first-order perturbation term, (?g 2/?λ)λ=0, are presented. It is shown that these terms are individually large, but that (?g 2/?λ)λ=0 is small because there is strong cancellation between the various terms. Consequently, the calculation of (?g 2/?λ)λ=0 is highly sensitive to the approximation used to evaluate the individual terms.  相似文献   

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