Vol. 35, No. 2 (1986)
We propose in this paper a seheme ealled Jet Charge Gross Section Method. In this method, the results of ealculations in pertubative QCD a.re not only less affected by the sea quark and gluon distribution functions in hadrons, just like in the calculations of cross section difference of hadrons: dσ(AB→h+X)-dσ(AB→h-X), but also independent of any fragmentation functions of partons. Furthermore, it is possible to measure the mean electric charges of various quark jets indirectly without distinguishing the quark flavors.
1986, 35 (2): 152-160. doi: 10.7498/aps.35.152
We analyse the jet-charge-cross section of the following three reactions: p+p→γ+Jet+X, γ+P→2Jets+X, γ+p→h+Jet+X, and present the methods respectively for test-ing gluon distribution function in proton, extracting the information of gluon jets and determining the fragmentation function of gluon.
Information theory provides a constructive criterion for setting up probability distributions on the basis of partial knowledge, and leads to a type of statistical inference which is called the maximumentropy estimate. It is the least biased estimate possible on the given information, i.e., it is maximally noncommittal with regard to missing information.The principle of maximum entropy, which has proven useful in other contexts, is adopted here to design a procedure for obtaining structural information from an incomplete set of diffraction data. A comparison is made between the proposed procedure and the conventional Fourier inversion method used in RDF analysis of non-crystalline materials. The maximum-entropy method is found to have a higher resolution and also the advantage of no adjustable parameters with a high degree of reliability.This method is iterative and uses more computer time than direct techniques; however, a number of comparative examples indicate that a significant improvement on the resultant structure in quality and resolution is possible with only a few iterations.
COUPLING PAIR MODEL FOR NEGATIVE MAGNETORESISTANCE OF MAGNETIC ALLOY WITH SLIGHTLY HIGH CONCENTRATION OF IMPURITY
1986, 35 (2): 177-187. doi: 10.7498/aps.35.177
This report discussed the dependence of the electrical resistance and magnetoresis-tance on temperature and magnetic field, which are resulted from the scattering of conducting electrons with coupled pairs in magnetic field for magnetic alloy with slightly high concentration of impurity. Rohrer's empirical formula of magnetoresistance variation with concentration for AuFe alloy is obtained here theoretically.
1986, 35 (2): 188-195. doi: 10.7498/aps.35.188
Birefringence images of screw dislocations in Gadolinium Gallium Garnet (GGG) and Yttrium Aluminum Garnet YAG) crystals are studied in detail. Birefringence images of screw dislocations viewed end-on were observed for the first tiane. The one-to-one correspondence between birefringence images of screw dislocations viewed end-on and that viewed from the side was demonstrated. The contour of equal intensity of birefringence image of screw dislocation viewed end-on in GGG and YAG crystals was derived by considering the photo-elastieal anisotropy of garnet, and the result yields good agreement Avith experimental observations.
1986, 35 (2): 196-202. doi: 10.7498/aps.35.196
Acoustical activity of isomorphous crystals Bi12GeO20 and Bi12SiO20 has been studied by measuring the splitting of degeneracy of transverse acoustical waves propagating along high symmetric direction with inelastic neutron scattering. One of the interesting results is that the left and right circularly polarized modes of acoustical phonons propagating along direction are subjected to different attenuation. This conclusion is verified by both kinds of crystals. The experimental result is observed for the first time in the study of acoustical activity. The life-time of the phonon with larger attenuation is found to be about 2×10-11 s. experimentally.
1986, 35 (2): 203-212. doi: 10.7498/aps.35.203
Based on two properties of the generalized oscillator strength densities: (1) continuity in an excitation channel and (2) quasiscaling relation along an isoelectronic sequence, the corresponding parameters in the Bethe's formula (namely the Bethe's physical parameter set) have similar behaviors. According to the Bethe's formula, excitation cross sections for spin allowed processes can be easily calculated in terms of the Bethe 's physical parameter set which characterizes the excitations of target atoms. In the present article, we introduce corrected functions defined as the ratios between the exact cross sections and the Bethe's cross sections. The corrected functions reveal a nice universal scaling feature within 50%. Thus, various cross sections as well as rates, which correspond to electron impact excitations from an initial state to infinite final states-forming a so called "excitation channel", can be obtained conveniently.
1986, 35 (2): 213-219. doi: 10.7498/aps.35.213
Thermal shifts of sub-levels R1 and R2 in YA1O3:Nd3+ has been measured. The behavious of the principal value of the integral in the single-phonon term have been investigated and the contribution of optical frequency branch to thermal shifts of sub-levels has been considered.By using the formulas involving Raman term, single-phonon term and term of optical frequency branch, thermal shifts of sub-levels R1 and R2 are calculated. Satisfactory agreement between the results of the theory and experimental values is obtained.
1986, 35 (2): 220-227. doi: 10.7498/aps.35.220
Computer-generated hologram for elliptical gaussian beam correction lias been investigated, detail mathematical equations of calculating hologram phase difference arc derived. The holograms which are drawn by a computer-driven plotter are given. The holographic optical elements are obtained from CGH. The experiment result to demonstrate the correct calculation is also shown in this paper.
1986, 35 (2): 228-234. doi: 10.7498/aps.35.228
The formation and quenching kinetics of ArF* and Ar2F* have been studied by ive-stigating their timeresolved spectra. Analysis shows that the decay process of ArF* depands on the time evolution of it's main precursor Ar*, but that of Ar2F* is determined by its own effective lifetime. Thereby the two-body quenching rate constant of Ar* by F2, three-body quenching rate constant of Ar* by Ar, as well as two-body quenching rate constant of Ar2F* by He, Ar and F2, and the radiative lifetime of Ar2F* are determined.
1986, 35 (2): 235-242. doi: 10.7498/aps.35.235
For "the general eases (paraxial approximation and non-paraxial ease), the ways of effective design of optical system to be composed of a single mask for the purpose of realizing any given linear transform are presented. Tinder various manners of choice of parameters, the solutions of equations to determine the amplitude-phase distribution of mask are investigated, and the stability of solution is also discussed. Under non-paraxial case, the solutions available in real situation are also found. Applying 4- and 8-dimen-sion Walsh transforms in the three different orders as examples, we investigate the effects of various parameters, such as the spacings between input plane, mask and output plane, and the number of sampling points in mask, on ‘approach distance', which describes the degree of approach of the transform to be performed by the system to any given linear transform. It would provide a realizable way to choose the relevant parameters and an usuful enlightment in the real design of an optical system for realizing a given linear transform.
1986, 35 (2): 243-246. doi: 10.7498/aps.35.243
M?ssbauer spectroseopy has been used to study the dispersity of Eu2O3 on the surface of different supports. Changes in M?ssbauer parameters as a function of the europium content reveal the difference of the interaction between Bu2O3 and the support. On the surface of γ-Al2O3, the M?ssbauer isome shift progressively increases toward to that of bulk Eu2O3 with increasing metal loading, suggesting that the crystal phase of Eu2O3 forms gradually. In contrast, on the surfaces of two types of SiO2 the isomer shifts do not change with changing the metal loading in the range of our study. This suggests that Eus03 tends to spread out on the surface as a second layer over monola-yer dispersion. The conclusion obtained by M?ssbauer spectroseopy is in agreement with that obtained by X-ray diffraction
1986, 35 (2): 247-253. doi: 10.7498/aps.35.247
By means of the Darboux transformation and an integral transformation, two classes of solvable double-well potential models are obtained for the Fokker-Planck equation. The exact results are compared with Kramers' approximation.
1986, 35 (2): 254-260. doi: 10.7498/aps.35.254
The electronic transport processes in metallic superlattices are studied by solving Boltzmann's equation with inclusion of a temperature gradient as well as an external magnetic field and by adopting the treatment of interface scattering processes in our revious interpretation of electric conduction characteristics. Variations with modulation wavelength of the thermoelectric power, the electronic thermal conductivity, the Thomson and Hall coefficients are derived for Nb/Ti superlattices. Further experimental investigations on the transport properties of metallic superlattices are expected to help the understanding of the electronic processes in such artificial materials.
1986, 35 (2): 261-265. doi: 10.7498/aps.35.261
The difficulty in indexing back-reflection Kossel diffraction patterns, especially for non-cubic systems arises from the fact that the diffraction cones do not have common vertex.Two methods which can be used for indexing diffraction patterns, both in cubic and non-cubic systems, are presented in this paper. By means of the stereographic pro-jction or computer programm described here, one can easily determine the diffraction indices of back-reflection Kossel lines.The advantage of the frst method is simple and direct. For the second method, the degree of automatization is higher, and measured data with some errors can be employed.
A NEW METHOD FOR DETERMINING THE ENERGY GAP OF A SUPERCONDUCTOR USING THE MAXIMUM IN DIFFERENTIAL CONDUCTANCE OF ELECTRON TUNNELING SPECTRUM
1986, 35 (2): 266-268. doi: 10.7498/aps.35.266
A new method for determining the energy gap of a superconductor using the maximum in the differential conductance curve of electron tunneling spectrum is given in this paper. The Vmax/kT versus △/kT curve was caculated from tunneling theory, Vmax, the voltage of the conductance maximum, can be measured from electron tunneling spectrum.△/kT can be found from this curve, then the energy gap △ can be caeulated. This method is simple, fast and accurate. The accuracy almost approaches that of the curve fitting method.
1986, 35 (2): 269-273. doi: 10.7498/aps.35.269
The high quality modulation doped GaAs/N-AlGaAs heterostructures have been grown by a vertical molecular beam epitaxy system (MBE). Electron mobility of two dimentional electron gas (2DBG) at 4.2 K has reached as high as 4.26×105cm2/V·s (in the dark) and 5.9×105cm2/V·s (under light illumination). The polaron mass of 2DEG was determined by analysis of oscillatory resistance change of magnetophonon resonance in pulsed magnetic field. The mobility enhancement of 2DEG in low field and quantum Hall effect in high field at 4.2 K were also studied.
1986, 35 (2): 274-278. doi: 10.7498/aps.35.274
Convergent-beam electron diffraction zone-axis patterns have been obtained from transverse basal stacking faults in graphite and molybdenite. These patterns show a reduced symmetry and split reflections. The splitting and unsplitting of the reflections correspond to the visibility and invisibility of the stacking faults in the theory of diffraction contrast of imperfect crystals. This analysis can be extended to zone-axis patterns obtained from other crystal defects.
1986, 35 (2): 279-282. doi: 10.7498/aps.35.279
Convergent-beam electron diffraction near a dislocation in silicon shows that some of the higher-order Laue zone lines and Kikuchi lines are split. The splitting of crystal-lographically equivalent reflections is different. These can be explained in terms of the theory of diffraction contrast of imperfect crystals. The splitting and unsplitting of the reflections correspond to the visibility and in visibility of the dislocation. Convergent-beam electron diffraction provides a powerful means for the study of crystal defects with high spatial resolution.