THE AB INITIO CALCULATION FOR THE BONDING STATE OF THE Hn CTUSTERS

The equilibrium geometries of several Hn（n=4,5,6,7,9,13) clsters with certain symmetry have been optimized by the ab inito Murtaug-Sargent(MS) method.We find that the stability of a centered cluster depends on the structure,the spin symmetry and the coordinate number,and the latter plays a more important role.     

THE MACQM CALCULATION OF THE TOTAL ENERGY CURVE OF THE BODY-CENTERED CUBIC STRUCTURE OF THE H_9~- CLUSTER

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ON THE IRREDUCIBLE REPRESENTATIONS OF THE SIMPLE LIE GROUPS I——THE TENSOR BASIS FOR THE INFINITESIMAL GENERATORS OF THE CLASSICAL SIMPLE LIE GROUPS

In this paper, we analyse the commutation relations of the infinitesimal generatorsof all simple classical Lie groups and establish a new basis for these generators, calledthe tensor basis. In tensor basis, the infinitesimal, generators can be written as somescalar operators, some sets of angular momentum operators and some sets of irreducibletensor operators. The commutation relations, of these operators are very simple andhave many regularities. By means of the method that has been used in the earlier papers, "On the irre-ducible representations of the compact simple Lie groups of rank 2, I,II,III" and thetensor basis, all the irreducible representations of the classical simple Lie groups canbe calculated systematically.     

THE MACQM CALCULATION OF THE TOTAL ENERGY CURVE FOR THE ICOSAHEDRAL CENTRAL STRUCTURE OF THE CLUSTER H_13~-

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THE ACOUSTIC FUNCTIONS OF THE MELON OF THE CHINESE RIVER DOLPHIN(Lipotes vexillifer)

In this paper,the acoustic functions of the melon of the Chinese river dolphin(Lipotes vexillifer)are studied.Based on the comparison between the directivity patterns of the whole head and the skull,it is suggested that the melon plays an important role in beamforming.At the frequencuy of 40 kHz,the—3 dB beamwidth of the emitted vertical beam of the whole head is approximately 21.6°,withthe major axis elevated 10°above the ristrum plane;the—3 dB beamwidth of the horizontal beam ofthe whole head is approximately 20°,with the major axis deviated 12°rightward from the body axis.The vertical and horizontal—3dB beamwidths of the whole head are 9.4°and 13°,narrower than thoseof the skull respectively,and the directions of the major axes are different for both cases.It canbe seen that the melon narrows the width of the main beam and greatly reduces the side lobes of thebeam formed by the skull.The distribution of the sound velocity in the melon tissue is measured andthe distribution pattern is drawn.Fr     

ON THE CONTROL OF RINGING NOISE EXCITED BY IMPACT II:THE ENERGY OF RINGING NOISE AND THE BUFFERING OF THE IMPACT

In the first of these two papers,the expression for the total energy of vibration excited by impacthas been obtained.In this paper the energy equation of ringing noise was derived from the resultof the first paper.This energy equation indicates the approaches to control ringing noise.Thebuffering method was discussed here in detail.The experiment which has been conducted was describedalso.     

THE ι-E PUZZLE AND THE GENERALIZED MOMENT ANALYSIS

We have introduced the photon angular distribution for moments of the process e⁺e^－→J/ψ→γB,B→P₁P₂P₃ to discuss the ι-E puzzle and got an effective criterion to distinguish whether there exist E(1⁺⁺) component in the peak for the process e⁺e^－→J/ψ→γKKπ.     

THE TWO-BOSON SCATTERING PHASE SHIFTS IN THE GENERAL φ6 THEORY WITH THE GAUSSIAN WAVE-FUNCTIONAL APPROACH

The two-particle scattering phase shifts with a λφ⁴ +ξφ⁶ interaction are com-puted in (1 + 1) and (2 + 1) dimensions using the Gaussian wave-functional approach.Through numerical analysis, we give the phase-shift curves with respect to the scat-tering energy for most cases of this theory. In (1 + 1) and (2 + 1 ) dimensions, for the symmetry vacuum the phase shifts are positive or negative depending on the signs of the renormalized parameter, while for the asymmetric vacuum the phase shifts are negative.     

DOES PARISI'S SOLUTION OF THE SHERRINGTON-KIRKPATRICK MODEL LOCATE ON THE ABSOLUTEMAXIMUM OF THE FREE ENERGY?

In the spin glass phase near the critical temperature we find in aparticular replica symmetry breaking pattern an order parameter with free energy greater than that of the Parisi's.     

THE BOUND STATES OF THE ISOBAR △ (1236)

We have discussed the single particle energies and wave functions of a boundisobar in O¹⁶ by using the O¹⁶ equation.     

Spin reorientations in R2Fe14-xCoxB systems (R = Pr,Nd and Er)

The effect of cobalt substitution on spin reorientation phenomena in R₂Fe_14-xCo_xB systems (R = Pr, Nd, Er) was studied by means of bulk magnetometry in the temperature range 4.2–1100 K. It was established that in the Nd-based system the introduction of cobalt resulted not only in a shift of the low temperature spin reorientation (cone to axis) but also triggered, for x ⩾ 10, an appearance of a second spin reorientation (axis to plane) at high temperature. In the Pr-based system, for x ⩾ 9.5, a high temperature spin reorientation (axis to plane) was also observed. Its dependence on Co content was determined. For the Er-based system, an increase of the spin reorientation temperature (plane to axis) was observed as more cobalt was introduced into that system. It was also established that the tetragonal single-phase materials in this system exist only up to x = 5. Temperature-composition diagrams are presented, indicating types of spin arrangements observed in the investigated systems.     

Cerium influence on the spin reorientation in Er2−xCexFe14B evidenced by Mössbauer and DSC techniques

Polycrystalline Er_2−xCe_xFe₁₄B (x=0.25, 0.5, 1.0) compounds have been studied by ⁵⁷Fe Mössbauer spectroscopy and by differential scanning calorimetry (DSC) in the temperature range 80–470 K. The spin reorientation phenomenon has been studied extensively by narrow step temperature scanning in the vicinity of the spin reorientation temperature. It was found that in the region of transition, each Mössbauer subspectrum splits into two Zeeman sextets, which are characterised by different hyperfine magnetic fields and quadrupole splittings. A consistent way of describing the Mössbauer spectra in the reorientation region, below and above, was proposed. The composition and temperature dependencies of hyperfine interaction parameters and subspectra contributions were derived from experimental spectra.The endothermic DSC peaks were observed for all studied compounds, which correspond to the transition from basal plane to axial easy magnetisation direction on increasing the temperature. The spin reorientation temperatures and the enthalpies of transitions were established from DSC data. The spin arrangement diagram was constructed and the spin reorientation temperatures obtained by the two methods were compared.     

Temperature variation of the spin reorientation in Er2−xDyxFe14B alloys

The competition between the uniaxial magnetic anisotropy of the iron sublattice and the basal anisotropy of the rare earth sublattice in the R₂Fe₁₄B alloys, occuring for the rare earths with a positive Steven's factor (a_j> 0), leads to spin reorientation at 316 K for the Er₂Fe₁₄B compound. We have succeeded, by making a series of pseudoternaries of the type Er_2−xDy_xFe₁₄b, to establish a correlation between the spin reorientation temperature and the quantity x. Mossbauer spectra of aligned powders show a smooth decrease of the spin reorientation temperature for values of x up to 1, while for larger values spin reorientation is absent.     

Spin configurations and spin reorientations in pure and impurity doped Fe3BO6

The spin configurations of Fe₃BO₆ above and below the spin reorientation temperature are analysed by magnetic measurements and a symmetry consideration. The effects of dopants on the magnetic properties are investigated. The dopants induces a different spin configuration and spin reorientation from the pure Fe₃BO₆.     

On the character of the unusual morin type transition in a cobalt-substituted dysprosium orthoferrite

Magnetic measurements and Mössbauer spectroscopy revealed two types of spin reorientation in DyFe_0.9975Co_0.0025O₃ in the temperature range 77–300 K. The higher temperature transition was a continuous rotation of Fe³⁺ spins from the a to the c axes of the single crystal in the region 260-145 K. The lower temperature transition was from a weakly ferromagnetic to the purely antiferromagnetic state. A peculiarity was observed with both methods. When the Fe³⁺ spins, turning from the a towards the c axis, form an angle of about 20° with the latter, they do not proceed to reach c, but jump to the b axis and the crystal becomes a pure antiferromagnet. An external magnetic field of 10 kOe, H_ext  c, does not change this reorientation pattern, but a smaller field along a completes the reorientation along the c axis. Mössbauer spectra indicate two hyperfine fields during the continuous spin reorientation.     

A STUDY ON THE ULTRASONIC VELOCITY AND ATTENU-ATION IN NdFeB MAGNET WITHIN THE TEMPERATURE RANGE OF 80 - 300K (Ⅱ)

Based on the ultrasonic measurements of an isotropic NdFeB magnet in the temperature range of 77 - 300 K, it was found that the elastic parameters, such as Young's modulus E, and Poisson ratio v, change abruptly near the spin reorientation temperature Tsr. This indicates that soft mode emerges in the process of spin reorientation. Thermal hysteresis was observed during heating-up and cooling-down processes. Both Debye temperature and heat capacity were calculated, which suggests that the magnetic entropy of the Nd-sublattice is larger in easy-cone state than in easy-axis state.     

Magnetic properties of (NdxY1-x)Co2(1⩾ x ⩾ 0)

The concentration dependence of T_c and T_R (T_c magnetic ordering temperature, T_R spin reorientation temperature) of the pseudobinary system (Nd, Y)Co₂ is reported. Furthermore the influence of an external magnetic field on the spin reorientation and the magnetization is studied. The observed variation of the magnetization in the vicinity of the spin reorientation is compared with theoretical results. For the calculation a Hamiltonian with terms describing a molecular field, a cubic crystal field, and an external field is used.     

Study of the spin reorientation phenomenon in Nd2(Fe, Si)14BHy

We have studied the influence of the Si for Fe substitution and of the H insertion on the spin reorientation phenomenon in the Nd₂Fe₁₄B phases. To determine the temperature of spin reorientation and the tilt angle between the c-axis and the easy magnetisation direction, we have measured the angular dependence of the components of the magnetisation vector. Our measurements are based on powder samples that have been previously aligned under an external magnetic field. The Si for Fe substitution induces a decrease of the spin reorientation temperature and of the tilt angle. Meanwhile, we have found that the tilt angles are almost the same for Nd₂Fe₁₃SiB and Nd₂Fe₁₂Si₂B. These features are analysed in terms of changes in the crystal electric field and the unit cell volume induced by the Si for Fe substitution. The insertion of hydrogen in the Si-containing samples leads to an additive decrease of the spin reorientation temperature. This decrease is not linked to a change in the tilt angle at 4 K but to a different thermal behaviour in the H-containing samples. The magnitude of the effects of H insertion on the crystal electric field in comparison with the Si for Fe substitution is discussed together with the role of the lattice expansion.     

Mössbauer spectroscopy studies of Dy(Fe,M)12 (M=Si,V,Ti) alloys

The⁵⁷Fe Mössbauer spectra have shown that the hyperfine field of DyFe₁₀Si₂ alloy and its quadrupole splitting at the 8i sites change steeply at 210 K, which are attributed to the spin reorientation transition. The stabilizing elements for the formation of the ThMn₁₂-structure can affect on the spin reorientation transition temperature. The differences of spin reorientation transition temperature of DyFe₁₀Si₂, DyFe₁₀V₂ and DyFe₁₁Ti alloys had been discussed. The quadrupole splitting at 8i sites of DyFe₁₀Si₂ alloy changes its sign at 210 K.