Vol. 47, No. 11 (1998)
1998, 47 (11): 1761-1768. doi: 10.7498/aps.47.1761
In this paper we present an entirely random traffic flow model by introducing brake, creation and disappearance probabilities into 1D local interactive cellular automota. By means of epuilibrium spin theory, we find that when Pin=Pout≠0, the final density of the model is ρｔ＝0.5 and indepen-dent of initial density distribution. When the conditions Pin+Pb=1 and Pin=Pout are satisfied, we get a simple “linear” traffic flow model that displays long distance correlation under the condition |1-2Pin|=1 and leads to a serious traffic jam. The cemputer simulation results agree with the the-oretical prediction.
1998, 47 (11): 1769-1775. doi: 10.7498/aps.47.1769
We investigate a 1D multi-speed stochastic model for traffic flow with injection and exfraction, and get the analytical results of the dependence of the car probability and traffic flow on the stochas-tic factors when the traffic flow is stationary. Then a 1D cellular automation model is used to simulate the model, the theoretic analytical results agree with the simulation.
ATOMIC AND MOLECULAR PHYSICS
1998, 47 (11): 1776-1782. doi: 10.7498/aps.47.1776
A pulsed dc discharge in a pulsed supersonic beam has been developed as an efficient source of producing free radicals. Spectra of the SF2 radical were observed between 272 and 294 nm by (2+1) resonance-enhanced multiphoton ionizition (REMPI) spectroscopy. Vibrational progressions associat-ed with 3d and 5s Rydberg states were assigned. The spectroscopic values ω＇1 (a1, symmetric stretch-ing), band origin T0 and quantum defect δ of these Rydberg states were reported.
1998, 47 (11): 1783-1789. doi: 10.7498/aps.47.1783
Based on the BBK theory, triple differential cross sections (TDCS) have been calculated for ionization of Li+ (1s2) by electron impact. A coplanar, equal-energy, fixed-relative angle kinematics is chosen and the particular case where the scattered and ionized electrons emerge perpendicular to each other is emphasized The incoming electron state is considered by a Coulomb wave from the long-range attraction between the incident electron and the screened ionic nucleus or approximated by a plane wave. It is shown that the maximum probability for emission near threshold is a configuration in which the interelectronic vector is aligned along the beam direction and the minimum probability when this vector is perpendicular to the beam, and that the initial channel Coulomb field play a major role in determining the TDCS at near threshold energy.
CLASSICAL AREA OF PHENOMENOLOGY
1998, 47 (11): 1790-1797. doi: 10.7498/aps.47.1790
Numerical calculations were carried out on light scattering by randomly oriented cubic particles for several size parameters. The scattering properties were analyzed and compared with those of the equivalent spherical particles. Results show that the differences between the scattering properties of cubic and spherical particles are similar to those between other non-spherical and spherical particles. The results imply the intrinsic symmetry and discontinuity of the normal direction of the particle surface have little effects on the scattering properties.
THE PROPERTIES OF DISPLACED BINOMIAL STATES AND DISPLACED NEGATIVE BINOMIAL STATES AND THEIR INTERACTION WITH TWO-LEVEL ATOMS
1998, 47 (11): 1798-1803. doi: 10.7498/aps.47.1798
In this article, we propose two new quantum field states, displaced binomial state and displaced negative binomial state. Their photon number distributions and sub-Poissonian properties are discussed. The results show that the displaced binomial state is a kind of intermediate quantum state between the coherent state and displaced number state and it may be sub-Poissonian and super-Poissonian at different parameters. The displaced negative binomial state is always super-Poissonian and is an intermediate state between coherent state and displaced Sussking-Glogower phased state. Finally, we study the dynamical evolution of atomic population inversion in the intensity-dependent interaction between these two states and two-level atoms.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
The line shape of CⅥ 207.1nm has been measured with optical spectroscope multichannel analyzer on HT-6M Tokamak. The result of the analysis of line shape showed that CⅥ 207.1nm line emission arised mainly from the charge exchange-recombination processes. The temporal behavior of CⅥ line emission also proved this conclusion. The radial profile of C6+ ion has been deduced from the measurements of neutral hydrogen density and the volume emission coefficient of CⅥ 207.1nm line emission.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1998, 47 (11): 1811-1817. doi: 10.7498/aps.47.1811
When the functional forms of non-coulombic inter-ionic short-range potentials have been defined, the bulk properties of ionic crystals can be calculated. The parameters presented in potential functions are determined by fitting procedure, to reproduce as colsely as possible the measured crystal data. In the present study, the shell model is employed for the investigations of CaF2, SrF2 and BaF2 ionic crystals. Remarkable feature of the present fitting procedure is that shell charges are sure to be negative and recent experimental data are adopted. The anion (F-) charge, which is assumed to be common to the three fluorides, is adjusted to 0.97e. In so doing, the obtained model parameter set is able to produce a satisfactory agreement between the calculated results and the experimental data, such as lattice formation energies, elastic constants, dielectric constants, ionic polarizabilities, transverse optic and Raman frequencies, for the alkaline earth fluorides.
1998, 47 (11): 1818-1826. doi: 10.7498/aps.47.1818
Anomalous transmission of X-rays for plance-parallel perfect crystals under asymmetrical Bragg reflection condition near the atomic absorption edge is studied in detail. When diffraction is induced mainly by the imaginary part of atomic scattering factor, the nodes of the standing wave within the crystal lie on the atomic plane at the exact Bragg angle, which results in an anomalous transmission. The transmitted beam comes mainly from the wave-field with its Poynting vector Poynting toward the lower surface of the crystal (the entrance surface being the upper one). The effective absorption coefficient of this wave-field decreases with the asymmetrical factor a. Therefore, the transmitted coefficient of the whole crystal increases as a increases. For a given ratio between the contributions of the real and imaginary parts of atomic scattering factor to diffraction, the deviation of Poynting vector from the normal of the real part of the dispersion surface increases with the degree of asymmetrical reflection condition.
1998, 47 (11): 1827-1839. doi: 10.7498/aps.47.1827
In order to elucidate the action of the STM tip in the manipulation of atom on a sample surface, the interaction between W tip atom and sample Al(111) surface atom is studied with cluster model by employing the first principles method—discrete variational method. The calculated results show that if the distance S between the tip and sample surface is short enough (S≤10 a.u.), when the sample surface Al atom, which is just under the W trp, escapes from the surface, it fells a stable potential well. This indicates that even without an external field, the Al atom can be extracted from the sample surface to the tip ty the attraction of the W tip, if the tip is very close to the sample surface.
“A Full Potential Linearized Augmented Plane Wave” scheme is applied to the study of the electronic and magnetic features on a simple organic ferromagnet modified by an organic high-spin segment (CH2) to trans-polyacetylene. Some physical quantities, i.e., band structure, the total and partial spin densities of states, magnetic moment and splitting energy, are shown quantitatively in our report. An anti-ferromagnetic order is expected and a specific π orbital is announced to be important for the magnetic features in an organic ferromagnet.
1998, 47 (11): 1847-1852. doi: 10.7498/aps.47.1847
The electrical transport of polycrystalline samples SmxC60 has been investigated by resistivity and magnetoresistance (MR) measurements. The transport mechanism is different for the samples with different x in SmxC60 system. The temperature-dependent resistivity can be explained by the fluctuation-induced-tunneling model for the sample SmC60. The transport properties for the sample Sm2.75C60 appear to be dominated by weak localization and electron-electron interactions. The MR data of the sample Sm2.75C60 can be fitted by a weak-localized model with strong electron-electron interactions, but that of the sample SmC60 cannot.
1998, 47 (11): 1853-1857. doi: 10.7498/aps.47.1853
Here we report a carbon sample generated by sonicating high oriented pyrolytic graphite (HOPG) in ethanol, water or ethanol-water mixed solution. High resolution transmission electron microscopy (HRTEM) revealed many multilayer graphite sheets with a total curved angle that is multiples of θ0(=30°). Close examination of the micrographs showed that the curvature is accomplished by bending the lattice planes. A possible explanation for the curvature in multilayer graphite sheets is discussed based on the conformation of graphite symmetry axes and the formation of sp3-like line defects in the sp2 graphitic network.
1998, 47 (11): 1858-1861. doi: 10.7498/aps.47.1858
A structural defect of incipient edge dislocation in epitaxial wurtzite GaN film is confirmed in this paper. The defect is observed as an isolated (1120) boundary segment within one large perfect crystal area by high-resolution electron microscopy. It has the local atom configuration as a part of (1120) high-energy like-atom bonding boundary together with two 1/6［1120］ partial edge dislocations at its two ends. The origin of the defect is explored from the mechanism of epitaxial growth.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1998, 47 (11): 1862-1869. doi: 10.7498/aps.47.1862
Ab initio effective core potential calculations have been carried out on Hf8C12 metallo-carbohedrene cluster. First, the geometries of the ground states have been optimized for structures of T and Td-symmetry, respectively. It has been shown that the Td-symmetry structure is more stable than T's. Then Hf8C12 cluster with Td-symmetry is studied by unlimited Hartree-Fock method and Natural Bonding Orbital analyzing. It has been found that there are three stable states of different spins, which are related to the bonding mechanism, electronic configuration and structure of the electron energies. For S=0, the Hf。atoms of the outer tetrahedron link the six ethylene-like C2units through Hf—C polar covalent bonds within Hf8C12 cluster. For S=1, six acetylene-like C2 units are adsorpted on the Hf8 framework. For S=2, some ｐπ bonds on the C2 units are found broken and bonded with Hf atoms in d←ｐπ bond-type. Most of Hf—C bonds are of Hf。—C type. Furthermore, it is found that the structure model of Hf8C12 cluster with Td-symmetry is (Hf8)+4.5(C-0.752)6, which is ferromagnetic at the high spin states. Meanwhile, the distribution of electron energies also changes with spin states.
1998, 47 (11): 1870-1878. doi: 10.7498/aps.47.1870
The Gaussian wave functional method is applied to a boson system with an array of local potentials cos［β（ｎR）］to study the phase transition of its ground of its ground state. The stable ground state is determined by the parameter γ＝β2/4π and the renormalized mass μ．In different regions, μ can have different multiplicity, the phase diagram is thus depicted. The phase boundary γ＝γ1 depends on the concentration c; for c←0, it coincides with that of the single impurity model, while for γ=2 it coincides with the conclusion of the continuous model.
1998, 47 (11): 1879-1884. doi: 10.7498/aps.47.1879
The total-energy minimization method is applied to the determination of the surface structure of the ZnS(110) surface. The predicted surface atomic geometry agrees well with that obtained from elastic low-energy electron diffraction intensity analysis. The electronic structure of ZnS(110) surface has been studied by using the method of Green's function scattering theory. Our results are eonsis-tent with the first principle calculations, and the influence of lattice relaxation on surface electronic properties are discussed.
1998, 47 (11): 1885-1895. doi: 10.7498/aps.47.1885
In this paper, with the use of Larmor clock, the tunneling times of one-dimensional combined potential are calculated. According to the results, the characters of Larmor times which are defined by Larmor clock method are discussed. It was found that the equality τyT=τyR=τD does not hold in general. Whether the equality τyT=τyR holds is determined by the symmetry of the potential. The Larmor times τyT and τyR may offer definition for transmitted time τT and reflected time τR, but τxT,τxR,τyT and τyR cannot. In addition, τyT and τyR can satisfy the equality τD=TτyT+RτyR.
1998, 47 (11): 1896-1899. doi: 10.7498/aps.47.1896
Thin film of Sb(111) was grown on GaAs(001) substrate by molecular beam epitaxy. The growth process of the film was characterized in-situ by reflective high energy electron diffraction and the film structure was investigated by transmission electron microscrope. The resistivity as a function of growth temperature was measured by van de Pauw method. We have observed the quantum size effect in Sb film grown on GaAs substrate.
1998, 47 (11): 1900-1905. doi: 10.7498/aps.47.1900
The diffusion and aggregation characteristics of silver atoms deposited on liquid substrates are studied. Experimental results indicate that the silver atoms first form compact clusters. Then the clusters diffuse and aggregate on the liquid surfaces. Finally they shape into ramified aggregate. We find that both the average radius of the compact clusters and the aggregation rate depend on the deposition rate. An aggregation rate possibility model is established and the theoretical result is in good agreement with the experimental data.
1998, 47 (11): 1906-1911. doi: 10.7498/aps.47.1906
The effects of heat treatments on the resistivity of BPSCCO-2223 superconductor were studied. The anomalous behavior in high-temperature resistivity was observed. It was shown that upon annealing in N2 at high temperatures, the oxygen escaped not only from Bi-O layer but also from Cu-O layer accompanied with the movement of metal ions. The change in oxygen content and the redistri-bution of oxygen and metal atoms diversified the microstructure of BPSCCO-2223 phase.
1998, 47 (11): 1912-1916. doi: 10.7498/aps.47.1912
In this paper, the effect of Ti doping on the phase stability of α″-Fe16N2 was investigated. Experimental results show that appropriate Ti addition may benefit the α″-Fe16N2 phase formation. Theoretical calculation shows that the formation enthalpy of α″-(Fe,Ti)16N2 phase in (Fe,Ti)-N films is smaller than that of α″-Fe16N2 phase in Fe-N system. This suggests that the stability of α″-Fe16N2 can be enhanced by Ti addition. Therefore, the α″ alloy phase and exhibit high saturation magnetization μ0Ms=2.3—2.6T．
1998, 47 (11): 1917-1922. doi: 10.7498/aps.47.1917
The ultrathin molecular organized films of hemicyanine dyes were prepared by langmuir-Blod-gett technique. The films show ferroelectric hysteresis loop and pyroelectric effect. The pyroelectric coefficient measured by the method of integrated charges is 12μC·m-2·K-1 at 300 K, and the relationship between the orientaton of DAEP in the films and temperature was studied by polarized FTIR spectroscopy. The microscopic mechanism of pyroelectricity in the films was discussed.
The C60 films have been implanted with 120—360 keV H,N, Ar and Mo ions by using a 200 keV heavy ion accelerator. The samples were investigated by Raman spectra. The results showed an exponential decrease of intensity for 1469 cm-1 line depending on the kind of ions and dose. There appeared a structural transformation of C60 to amorphous carbon at certain doses, which is correlated to the nuclear energy transfer. H ions implantation resulted in an asymmetrical broadening of 1469 cm-1 line, which is due to the electronic energy transfer.
1998, 47 (11): 1928-1936. doi: 10.7498/aps.47.1928
The chemisorption of acetylene molecules on a reconstructed diamond (001)-(2×1) surface and the dynamic behavior of this reaction are studied by molecular dynamics simulation using many-body interatomic Brenner (#2) potential. Six chemisorption configurations are observed. About 95% of the chemisorption events invole the formation of two C—Cs bonds between the acetylene molecule and the diamond surface. The dependence of the adsorption configuration upon the binding energy, the incident energy and the position of the molecule, as well as the local spatial structure of the diamond surface are analyzed. In order to provide an intensive understanding of the chemisorption, snapshots of atomic position are provided. The energy exchange characteristics between the incident molecules and the surface are discussed.