Gain without inversion in a medium of 1/2→1/2 atoms

Amplification of a probe field without inversion in a medium of non-degenerate two-level atoms pumped by a circularly polarized optical field in resonance with a 1/2→1/2 atomic transition in the presence of a dc magnetic field orthogonal to the wave vector of the pump field is demonstrated. It is shown that gain without inversion is possible in strong optical and magnetic fields in the case of a pump with a finite spectral width which can be much greater than the natural width of the excited level. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 364–369 (10 September 1998)     

Proximity Effect in a Superconducting Triplet Spin Valve S1/F1/S2/F2

Physics of the Solid State - Сritical temperatures of multilayer structures of the superconductor/ferromagnet/ferromagnet (S/F/F) type are obtained using the matrix method for solving the...     

Magnetic properties of a random diluted spin-1/2, 1, 3/2 superlattice

Using the effective-field theory we studied the magnetic properties of a random diluted spin-1/2, 1, 3/2 superlattice which consists of three different ferromagnetic materials. The critical temperature of the system is studied as a function of the concentration of magnetic atoms and exchange interactions in each layer. The temperature dependence of magnetization shows that the properties of the diluted system are different from those of the corresponding pure system.     

Pseudopotential calculations of relaxation and formation energy of a (1/2, 1/2, 1/2) interstitial defect in aluminum

The pseudopotential form factors used previously by the authors to study the vacancy formation in aluminum are employed to calculate the atom displacements around and formation energy of an interstitial aluminum atom placed at the center (1/2, 1/2, 1/2) of the face-centered cubic unit cell with encouraging results.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1/2-1/2-1-1 and 3/2-3/2 -1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1／2-1／2-1-1 and 3／2-3／2-1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of 1/2-1/2-1-1 and 3/2-3/2-1-1 are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it hastwo phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain,the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameter α=J2/J1.     

Tetramerization of a frustrated spin-1/2 chain

We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to adiabatic phonons with a general form of magnetoelastic coupling. For large enough frustration and lattice coupling, a new tetramerized phase with three different bond lengths is found. We argue that the zigzag spin-1/2 chain LiV2O5 might be a good candidate to observe such a phase.     

Polarization switching in a ring cavity with resonantly drivenJ=1/2 toJ=1/2 atoms

We have solved within the mean field limit for the steady state behaviour of a gas ofJ=1/2 toJ=1/2 model atoms in a ring cavity excited by an incident laser field of arbitrary polarization. Results are presented for the case of zero applied magnetic field and exact resonance between the laser frequency, the atomic transition and a cavity resonance (pure absorptive case). We find that the behaviour of the polarization switching between ⁺ and ^– outputs depends on the values of the upper and lower state collisional relaxation rates, expressed via a single parameter . The case of linearly polarized input is of particular interest since optical bistability is found to occur for 2, being pre-empted by polarization switching for >2. The results are discussed in terms of an atomic feedback mechanism coupling the ⁺ and ^– modes.     

On the 2S1/2–1S1/2 photon-plasmon transition in hydrogenous atoms

The probabilities of the two-quantum induced (according to the number of plasmons) photon-plasmon transitions 2S_1/2–1S_1/2 are calculated for hydrogenous atoms. In a turbulent plasma medium this process may be more effective than conventional two-photon radiation and collisions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 305–307, February, 1972.The authors thank L. A. Vainshtein and Yu. P. Nikitin for discussing the work and for their valuable comments.     

Kinetics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model

We present a study, within a mean-field approach, of the kinetics of a mixed ferrimagnetic model on a square lattice in which two interpenetrating square sublattices have spins that can take two values, , alternated with spins that can take the four values, . We use the Glauber-type stochastic dynamics to describe the time evolution of the system with a crystal-field interaction in the presence of a time-dependent oscillating external magnetic field. The nature (continuous and discontinuous) of transition is characterized by studying the thermal behaviors of average order parameters in a period. The dynamic phase transition points are obtained and the phase diagrams are presented in the reduced magnetic field amplitude (h) and reduced temperature (T) plane, and in the reduced temperature and interaction parameter planes, namely in the (h, T) and (d, T) planes, d is the reduced crystal-field interaction. The phase diagrams always exhibit a tricritical point in (h, T) plane, but do not exhibit in the (d, T) plane for low values of h. The dynamic multicritical point or dynamic critical end point exist in the (d, T) plane for low values of h. Moreover, phase diagrams contain paramagnetic (p), ferromagnetic (f), ferrimagnetic (i) phases, two coexistence or mixed phase regions, (f+p) and (i+p), that strongly depend on interaction parameters.     

1+3/2与1+1/2对转涡轮对比分析

为理清1 1/2对转涡轮及1 3/2对转涡轮使用范围和效能,从而帮助设计决策,本文采用Stewart方法,从速度三角形基本分析入手,以速功比为主要变量,考察、对比1 3/2和1 1/2对转涡轮性能特点.研究表明:各转速比下,1 3/2对转涡轮高效率范围都比1 1/2对转涡轮窄,但其高效区发生在更小的总速功比区域;随转速比绝对值增加,两种涡轮高效率区都增加,高效率区位置都偏向大的总速功比区域;相比于1 1/2对转涡轮,1 3/2对转涡轮具有较低出功比,且偏向于低速功比区域;随转速比绝对值增加,两种对转涡轮出功比范围均拓展.这些结果为未来先进航空发动机涡轮选型提供了重要借鉴.     

The mixed-spins 1/2 and 3/2 Blume—Capel model with a random crystal field

The random crystal field(RCF) effects are investigated on the phase diagrams of the mixed-spins 1/2 and 3/2 Blume-Capel(BC) model on the Bethe lattice.The bimodal random crystal field is assumed and the recursion relations are employed for the solution of the model.The system gives only the second-order phase transitions for all values of the crystal fields in the non-random bimodal distribution for given probability.The randomness does not change the order of the phase transitions for higher crystal field values,i.e.,it is always second-order,but it may introduce first-order phase transitions at lower negative crystal field values for the probability in the range about 0.20 and 0.45,which is only the second-order for the non-random case in this range.Thus our work claims that randomness may be used to induce first-order phase transitions at lower negative crystal field values at lower probabilities.     

(1/2+1/2+1)腔型热阴极微波电子枪

 介绍了一种新型的轴耦合热阴极微波电子枪的设计，该枪采用了缩短首腔以及在首腔与主加速腔间插入耦合半腔的设计思想，在不破坏粒子束性能的基础上尽量减小反轰功率，给出了用Superfish 及Pamela软件进行物理设计以及粒子动力学计算的结果，在脉冲宽度为6μs, 重复频率为25Hz时，阴极上平均反轰功率为3.6W,达到设计要求。     

New phase in a spin-1/2 Falicov-Kimball model

In this investigation we present exact results on the spin-1/2 Falicov-Kimball model. We obtain ground-state results for arbitrary dimensions using the method of in-equalities as well as results on the thermodynamics for large dimensions. As a new feature (not possible in a spinless model) we obtain a transition (which may be discontinuous) into a new state with a high density of pairs of thef-electrons.Supported in part by the Deutsche Forschungsgemeinschaft     

Bose quantization of a new spin-1/2 equation

We second quantize a relativistic Schrödinger equation involving a HamiltonianH that describes free spin-1/2 particles and that depends on a parameterG. We require a positive definite metric and a positive definite energy in the Fock space in which the field ψ(x,t) and its adjoint operate. IfG=±i, one obtains the usual second-quantized Dirac theory, but for real values ofG one has Bose statistics. Whereas the anticommutator [ψ(x,t), ψ * (x′,t′)]₊ vanishes for a Dirac field when the interval between (x,t) and (x′,t′) lies outside the light cone, whenG is real the commutator [ψ (x,t), ψ * (x′,t′)_? vanishes for such points.     

Observation of rubidium 5S1/2 --> 7S1/2 two-photon transitions with a diode laser

The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidium, which is 100 times weaker than the 5S-5D transition, is observed with an extended-cavity diode laser and a vapor cell. Signals with a signal-to-noise ratio of 280 are obtained with a laser power of 10 mW, and the observed linewidth is 3 MHz. The laser wavelength is 760 nm and is locked on the transitions to a stability of 2 x 10(-11). For the first time to our knowledge, the isotope shift of this transition is measured to be 130(4) MHz in atomic frequency.     

Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

Magnetoelectricity in the PbFe1/2Nb1/2O3 Ceramics

The magnetodielectric effect (the influence of a magnetic field H on the dielectric constant ?) and the magnetoelectric effect (the influence of an electric field E on the magnetoelectric constant ??) of the PbFe_1/2Nb_1/2O₃ ceramics have been investigated at temperatures T in the range from 50 to 200°C, including the Curie point T _C ? 98°C. It has been demonstrated that there is a correlation of these effects with the shift of the ferroelectric-paraelectric phase transition temperature in a magnetic field.