Nuclear structure relevant to neutrinoless double beta decay: 76Ge and 76Se

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of 76Ge (a candidate for such decay) and 76Se (the daughter nucleus) were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations, the changes are confined primarily to one orbit.     

Use of GC-QMS for stable isotope analysis of environmentally relevant main and trace gases in the air

Abstract

When tracing the fluxes of N compounds (especially N oxides) and carbon dioxide in the system soil-atmosphere and applying ¹⁵N and ¹³C, it is necessary to simultaneously determine both the concentration of the substances and their isotopic composition. GC separation (packed column) was coupled to a mass spectrometer by a special interface. Variable sample volumes can be delivered by changing the split by means of the interface in front of the MS. Thus, both the concentration of a gaseous compound and its ¹⁵N content can be measured. Supplying sample volumes in a range between 5 μl and 5 ml, it is possible to measure both components of high content (e.g., nitrogen) and at the lower ppm(v)-content (e.g., dinitrogen oxide) in the air. Measurements of N₂, N₂O, NO and CO₂ are demonstrated, too.     

Environmental perturbations on foreign atoms and molecules in solid argon,krypton and xenon

Perturbations which are responsible for the shifts of electronic and vibrational spectra of species trapped in a solid are considered in terms of the intermolecular potential which describes interactions between these species and neighbouring atoms. It is shown that in certain instances London's theory can give an adequate approximation to the dispersion energy between an electronically excited species and a rare gas atom. The experimental shifts in the electronic absorption spectra of Hg, NH and C₂ at lattice sites in rare gas crystals at 4·2°k are explained quantitatively on the basis of a Lennard-Jones (6-12) or (6-8-12) potential between the trapped species and the rare gas atoms. The theory does not adequately explain the shifts in those cases where strong angular dependent forces differing appreciably in the two electronic states are present, data on trapped NH₂ free radicals being presented as a case in point. The interaction of sodium atoms with argon at 4·2°k is very complex, the data being consistent with multiple trapping sites for the atoms, a large repulsive interaction between the excited state of sodium and the rare gas, and apparent removal of the three-fold orbital degeneracy in the excited state by the environmental perturbation. The three-fold orbital degeneracy in the ³P₁ state of mercury was found also to be removed. The blue shift of 1281 cm^-1 for the ³P₁ ← ¹S₀ transition of mercury in solid argon at 4·2°k corresponds almost exactly with the position of one of the two prominent features in the spectrum of mercury in argon gas at comparable densities and illustrates the similarity of structure in the two physical states. The interesting perturbations on the vibrational states of NH and C₂ suggest a close similarity to the effect which causes environmental variations of coupling constants for hyperfine interactions in trapped hydrogen atoms.     

Static and time-dependent perturbations on nuclear angular correlations

The case of static and statistical perturbations for τ?τ _N is considered in a general form. The resulting Bloch-Wangness-Redfield equation is solved by means of the Laplace transform. A derivation of the time-differential and time-integrated attenuation factor is presented.     

Fill-tube-induced mass perturbations on x-ray-driven, ignition-scale, inertial-confinement-fusion capsule shells and the implications for ignition experiments

On the first inertial-confinement-fusion ignition facility, the target capsule will be DT filled through a long, narrow tube inserted into the shell. microg-scale shell perturbations Delta m' arising from multiple, 10-50 microm-diameter, hollow SiO2 tubes on x-ray-driven, ignition-scale, 1-mg capsules have been measured on a subignition device. Simulations compare well with observation, whence it is corroborated that Delta m' arises from early x-ray shadowing by the tube rather than tube mass coupling to the shell, and inferred that 10-20 microm tubes will negligibly affect fusion yield on a full-ignition facility.     

Effect of noise and perturbations on limit cycle systems

This paper demonstrates that the influence of noise and of external perturbations on a nonlinear oscillator can vary strongly along the limit cycle and upon transition from limit cycle to stationary point behaviour. For this purpose we consider the role of noise on the Bonhoeffer-van der Pol model in a range of control parameters where the model exhibits a limit cycle, but the parameters are close to values corresponding to a stable stationary point. Our analysis is based on the van Kampen approximation for solutions of the Fokker-Planck equation in the limit of weak noise. We investigate first separately the effect of noise on motion tangential and normal to the limit cycle. The key result is that noise induces diffusion-like spread along the limit cycle, but quasistationary behaviour normal to the limit cycle. We then describe the coupled motion and show that noise acting in the normal direction can strongly enhance diffusion along the limit cycle. We finally argue that the variability of the system's response to noise can be exploited in populations of nonlinear oscillators in that weak coupling can induce synchronization as long as the single oscillators operate in a regime close to the transition between oscillatory and excitatory modes.     

Marginal singularities,almost invariant sets,and small perturbations of chaotic dynamical systems

For a class of piecewise monotone locally noncontracting maps f:X-->X with small "traps" Y( varepsilon ) subset, dbl equals X (diam(Y( varepsilon )) infinity conditional probabilities that f(n+1)x in X\Y( varepsilon ) if x,fx,.,f(nx) in X\Y( varepsilon ) and the point x is chosen at random. Also proven is the convergence of &mgr;( varepsilon ) to smooth f-invariant measures as varepsilon -->0. By means of this construction, the numerical phenomenon of the convergence of histograms of trajectories of maps with marginal singularities to densities of nonfinite smooth invariant measures in the computer modeling was investigated.     

Effects of correlated perturbations on dark soliton propagation and interaction

Correlated perturbations are considered in a dark soliton system, and their effects on soliton propagation and interaction are investigated numerically. These perturbations result in large sidebands, lead to submergence of dark soliton, and enhance the interaction. The correlation amplifies these effects and shortens the distance until submergence. The comparison of the distinction is made between the degradations of these effects on dark soliton and the corresponding bright soliton. It is found that these effects on dark soliton are less than those on bright soliton. Finally the nonlinear gain is introduced to suppress efficiently these effects.     

Traveling perturbations in the F-region of the ionosphere,and the sporadic E-layer

Radiophysics and Quantum Electronics -     

Structural isomers,double wells,resonances, and Dirichlet decoupling

How some Schrodinger operators associated with structural isomers, double wells, resonances, and Dirichlet decouping can be investigated by imposing a Dirichlet boundary condition along a surface chosen by geometrical considerations is explained. Bounds on the tunneling rate and similar quantities can then be obtained by functional integration.     

Spinful fermionic ladders at incommensurate filling: Phase diagram,local perturbations,and ionic potentials

We study the effect of external potential on transport properties of the fermionic two-leg ladder model. The response of the system to a local perturbation is strongly dependent on the ground state properties of the system and especially on the dominant correlations. We categorize all phases and transitions in the model (for incommensurate filling) and introduce “hopping-driven transitions” that the system undergoes as the inter-chain hopping is increased from zero. We also describe the response of the system to an ionic potential. The physics of this effect is similar to that of the single impurity, except that the ionic potential can affect the bulk properties of the system and in particular induce true long range order.     

Chaotic scattering on a double well: Periodic orbits,symbolic dynamics,and scaling

We investigate classical scattering of particles by a double-well potential. Irregularity in the scattering functions, such as scattering angle and escape time, appears when the collision energy is lowered below a threshold value. This threshold is closely related to the appearance of periodic orbits with energies above the potential maxima. We study the scattering as a function of the energy and impact parameter. In this initial parameter space the scattering functions consist of regular regions interlaced with chaotic rivers. A symbolic dynamics has been developed to organize these structures and used to reveal their scaling properties.     

Chemical bonding in representative astrophysically relevant neutral,cation, and anion HCnH chains

Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from ab initio computations for representative members of the astrophysically relevant neutral and charged HC_2k/2k+1H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes, e.g., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC_2k/2k+1H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study.     

啁啾光脉冲的振幅调制和相位扰动对压缩光脉冲的影响

 通过采用分步傅里叶变换法求解非线性薛定谔方程,模拟了啁啾光脉冲有振幅调制和相位扰动下的自相位调制（SPM）对压缩光脉冲对比度和预脉冲宽度的影响。结果表明：啁啾光脉冲的振幅调制深度和相位扰动深度越大,则压缩后的光脉冲对比度越小;啁啾光脉冲的振幅调制周期和相位扰动周期越小,则压缩光脉冲的预脉冲宽度越大。     

Experimental and theoretical investigation of boundary layer perturbations on a low-aspect-ratio wing

Laminar-turbulent transition in a boundary layer of low-aspect-ratio wing was investigated. Experiments clarifying the flow structure, its mean and oscillatory characteristics were carried out accompanied by linear stability analysis of the wind tunnel data on the laminar flow velocity profiles. Theoretical results obtained in a parallel flow approximation are in a good agreement with the experimental data on disturbances evolution at the initial stage of transition to turbulence. The study was supported by the Ministry of Education and Science of the Russian Federation (Grant No. RNP 2.1.1.471) and Russian Foundation for Basic Research (Grant No. 03-01-06145)