Collisional excitation among the seven lowest states of TiXII

Collision strengths have been calculated for electron impact excitation of sodium-like TiXII for all 21 transitions amongst its lowest seven states. Configuration interaction wave functions have been used to represent the target states. The standard and no-exchangeR-matrix codes have been used to calculate the contribution of partial waves withL⩽8 andL>8 respectively. Collision strengths are tabulated at selected energies in the range 26 to 50 Ryd. Effective collision strengths are tabulated for electron temperatures in the range logT _e=4.0 to logT _e=6.0, withT _e in K. This is the first detailed calculation on this ion in which the effects of exchange, channel couplings and short-range correlation are taken into account.     

Electron impact excitation of Ni XIX using theR-matrix method

Collision strengths for all the transitions between the 15 lowest states of neon-like Ni XIX have been calculated for electron impact in the 80–140 Ry energy range. Configuration-interaction wavefunctions have been used to represent the target states. The standardR-matrix code has been used to calculate the lower scattering partial waves (L≤9), while a no-exchange version of the same code has been used to compute efficiently the higher partial waves (L≥10). Effective collision strengths for 105 excitation transitions between the ground state 2s ²2p ^{6 1} S ^e and the 142s ²2p ⁵3l Rydberg states are tabulated for electron temperatures in the range logT=5.40 to logT=7.00, withT expressed in °K.     

The collective bands of positive parity states in odd-A (fp) shell nuclei

The low-lying collective bands of positive parity states in (fp) shell nuclei are described in the deformed Hartree-Fock method by projecting states of definite angular momenta from ‘the lowest energy intrinsic states in (sd)⁻¹ (fp) ⁿ⁺¹ configurations. The modified Kuo-Brown effective interaction for (fp) shell and modified surface delta interaction (MSDI) for a hole in (sd) shell with a particle in (fp) shell have been used. The collective bands of states are in general well reproduced by the effective interactions. The excitation energies of the band head states are however off by about one MeV. The calculated magnetic moments of the band headj=3/2⁺ states are in reasonable agreement with experiment. Using effective chargese _p=1.33e ande _n=0.64e we get fairly good agreement forE(2) transitions. The hinderedM(1) transition strengths are reproduced to the correct order however they are slightly higher compared to experiment.     

Gamow-Teller transitions from 58Ni to discrete states of 58Cu

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T _z = ±1 nuclei to the common excited states of the T _z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T _z = 1 with those from the β-decay of the T _z = - 1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from ⁵⁸Ni (T _z = 1) to ⁵⁸Cu (T _z = 0) by using the zero-degree (³ He, t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., near to the Q window limitation ( Q _EC = 9.37 MeV) of the β-decay from ⁵⁸Zn (T _z = - 1) to ⁵⁸Cu. The strength distribution is compared with that from shell-model calculations. Received: 24 November 2001 / Accepted: 30 January 2002     

Effect of upflowing field-aligned electron beams on the electron cyclotron waves in the auroral magnetosphere

The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at the frequencies ω _r < Ω_e, propagating downward in the direction of the Earth’s magnetic field, has been analysed in the auroral region at ω _e/Ω_e < 1 where ω _e is the plasma frequency and Ω_e is the gyrofrequency. The FEBs with low to high energy (E _b) but with low temperature (T _‖b) have no effect on these waves. The FEBs with E _b < 1 keV and T _‖b (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T _‖b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T _‖b. The FEBs with less E _b (giving drift velocity) reduce growth rate more than the beams with larger E _b. The inhibition of growth rate increases with the increase in the ratio ω _e/Ω_e indicating that the beams are more effective at higher altitudes.      

Laser photoacoustic spectroscopy of iodine molecule: Single and two-photon absorption

Photoacoustic spectroscopy of iodine molecule has been studied in gas phase using nitrogen laser-pumped tunable dye laser. The experiment yielded the vibrational spectrum corresponding toX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _g ⁺ ) transition up to the convergence limit. The photo-acoustic spectrum in the region 17580–18850 cm⁻¹ is presented along with the vibrational analysis. Five of the vibrational bands reported earlier by Venkateswarlu, Kumar and McGlynn have been partially resolved and the structure of one of them has been analyzed and shown to be due to an overlap of (14, 2) and (12, 1) bands. The analysis was based on a comparison with the highly resolved spectrum of Gerstenkorn and Luc. The structure observed in the region 20200–20750 cm⁻¹ which is beyond the convergence limit of the transitionX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _u ⁺ ) has been analyzed as due to two-photon absorption. Most of the bands could be assigned to two transitions both originating in the ground state and terminating in two different electronic states 1 _g andE(0 _g ⁺ ), atT _e=40821 cm⁻¹ (orT ₀=41355 cm⁻¹) andT _e=41411 cm⁻¹ (orT ₀=41355 cm⁻¹) respectively.     

Analysis of two recent tests of T-invariance

Inequality of the rates for K ⁰ → π⁺ e ⁻ υ₋ and K ⁰ → π⁻ e ⁺ ν transitions, reported by CPLEAR, and an asymmetry in the distribution of the dihedral angle between the π⁺π⁻ and e ⁺ e ⁻ planes in K _L → π⁺π⁻ e ⁺ e ⁻ decays, found by KTeV, have been announced as demonstrations of T-noninvariance. These results are critically interpreted and compared as proofs of the failure of reciprocity.     

New transitions in the β-decay of 36Ca

The β-decay of the T _z = - 2 nucleus ³⁶Ca was studied at the LISE3 magnetic spectrometer at GANIL. Two new proton-emitting states have been detected and the other nine known βp and βγ transitions have been remeasured with improved resolution. A simulation with the GEANT code has been applied to this experimental setup. A comparison with shell model calculations is given. Received: 19 September 2000 / Accepted: 28 February 2001     

Electronic thermal capacity in one-dimensional mesoscopic rings

Summary We have investigated the Aharonov-Bohm (AB) effects of electronic thermal capacityC _v in a one-dimensional normal ring using the free-electron model. The results show that the thermal capacity is an oscillation function of external magnetic flux with periods ϕ₀=hc/e, ϕ₀/2, ϕ₀/3,... The amplitude of the capacity fluctuation decreases when temperature increases forT>3T ^* (T ^*=ħ V _F/(K _BπL)). We suggest an appropriate temperatureT∼3T ^* to observe in experiment the capacity-flux characteristic for metallic rings. The authors of this paper have agreed to not receive the proofs for correction.     

Effect of excited state absorption on the transmissivity of organic-dye-based media under two-photon excitation

duration ranging from femtoseconds to nanoseconds has been simulated. The effect of the absorption from excited singlet and triplet states on the transmissivity of the medium under two-photon excitation has been investigated. It has been shown that in a medium excited by monopulses, the S ₁→ S _n and T ₁→ T _m absorption makes a considerable contribution to the total nonlinear absorption of the medium only for nanosecond pulse durations. When a medium is excited by a sequence of femtosecond pulses with a repetition frequency of some tens of megahertz, significant additional nonlinear absorption can arise only due to T ₁→T _m transitions that occur due to accumulation of molecules in triplet states. This effect should be taken into account in determining the cross-section for two-photon absorption in dyes and also in developing radiation intensity limiters for femtosecond lasers.     

Spatiotemporal spectroscopic diagnostics of a pulse-periodic strontium vapor laser

Results of spectroscopic investigations into plasma of a pulse-periodic strontium vapor laser operating in the superradiance mode on the infrared transition at λ = 6.45 μm are presented. The method of determining the electron temperature and concentration as well as the gas temperature – T _e , n _e , and T _g – based on measuring the absolute intensities of some SrI and SrII and buffer gas (helium or neon) spectral lines is used. Time dependences of the line intensities during a current pulse (τ = 150 ns) and near afterglow (up to 3 μs) are obtained under conditions of non-equilibrium plasma ionization and recombination. The optical system collects radiation from the entire length of the plasma column by means of separating radial volume zones, includingthe central zone and the zone closer to the walls, with the monochromator slit. The results obtained allow us not only to calculate T _e , n _e , and T _g values, but also to trace the spatiotemporal plasma evolution.     

Study of mechanisms of formation of X-ray emission bands in crystals by the density functional method: The Mg <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> bands in metal and in MgO

Using the density functional method in the pseudopotential approximation, we calculate the probabilities of X-ray emission transitions and shapes of the L _2,3 X-ray emission bands of Mg in crystals of metallic magnesium and monoxide MgO. We have paid special attention to the study of mechanisms by which these bands were formed; therefore, along with the total intensities, we determine the partial s- and d-contributions. In addition, the intensities of the L _2,3 bands of Mg have been separated into contributions from direct (intra-atomic) transitions and charge-transfer crossover transitions. We show that an unexpectedly large contribution of partial d-transitions in magnesium oxide is caused by crossover transitions of electrons of valence states of ligands to the core 2p-level of Mg, i.e., charge-transfer transitions. In metallic magnesium, the contribution of these transitions proved to be insignificant. An appreciable contribution of crossover transitions has also been revealed in s-contributions of X-ray emission bands. To estimate the calculation accuracy, we have compared the shapes of theoretical spectra with the shapes of experimental L _2,3 X-ray emission bands of Mg.     

Intervalley electron scattering by phonons in (AlAs)1(GaAs)3(001) superlattices

Intervalley electron scattering by phonons in (AlAs)₁(GaAs)₃(001) superlattices is studied using the pseudopotential method and a phenomenological model of the bonding forces. The deformation potentials between the conduction band extrema of the superlattice involving short-and long-wavelength phonons are calculated. It is shown that the mixing of states from the zinc-blende L valleys plays a greater role in intervalley scattering in a superlattice than the Γ-X mixing. In particular, due to L-L mixing, the Γ-X ₃ transitions, analogous to Γ-L transitions in zinc blende, have higher intensities than the analogues of Γ-X transitions (Γ₁-M ₅ and (Γ₁-Γ₃ transitions). The deformation potentials averaged over the scattering channels in the superlattice agree with the corresponding potentials in a solid solution, but all transitions in the superlattice have higher intensities for the lower states.     

Calorimetric study of phase transitions in the perovskite BaCeO3

Differential scanning calorimetry was used to study phase transitions (PT) in the perovskite BaCeO₃. It is shown that its phase state is determined by a second-order λ transition at T _tr=520–540 K and a first-order δ transition at T _tr=600–670 K. Differences in PT parameters between ceramic and fused BaCeO₃ have been established. Fiz. Tverd. Tela (St. Petersburg) 40, 2109–2112 (November 1998)     

On the Mixing Time of the 2D Stochastic Ising Model with “Plus” Boundary Conditions at Low Temperature

We consider the Glauber dynamics for the 2D Ising model in a box of side L, at inverse temperature β and random boundary conditions τ whose distribution P either stochastically dominates the extremal plus phase (hence the quotation marks in the title) or is stochastically dominated by the extremal minus phase. A particular case is when P is concentrated on the homogeneous configuration identically equal to +  (equal to ?). For β large enough we show that for any ${\varepsilon >0 }We consider the Glauber dynamics for the 2D Ising model in a box of side L, at inverse temperature β and random boundary conditions τ whose distribution P either stochastically dominates the extremal plus phase (hence the quotation marks in the title) or is stochastically dominated by the extremal minus phase. A particular case is when P is concentrated on the homogeneous configuration identically equal to +  (equal to −). For β large enough we show that for any ${\varepsilon >0 }${\varepsilon >0 } there exists c=c(b,e){c=c(\beta,\varepsilon)} such that the corresponding mixing time T _mix satisfies lim_L?￥ P(T_mix 3 exp(cL^e)) = 0{{\rm lim}_{L\to\infty}\,{\bf P}\left(T_{\rm mix}\ge {\rm exp}({cL^\varepsilon})\right) =0}. In the non-random case τ ≡ +  (or τ ≡ −), this implies that T_mix ￡ exp(cL^e){T_{\rm mix}\le {\rm exp}({cL^\varepsilon})}. The same bound holds when the boundary conditions are all +  on three sides and all − on the remaining one. The result, although still very far from the expected Lifshitz behavior T _mix = O(L ²), considerably improves upon the previous known estimates of the form T_mix ￡ exp(c L^{\frac 12 + e}){T_{\rm mix}\le {\rm exp}({c L^{\frac 12 + \varepsilon}})}. The techniques are based on induction over length scales, combined with a judicious use of the so-called “censoring inequality” of Y. Peres and P. Winkler, which in a sense allows us to guide the dynamics to its equilibrium measure.     

Collision broadening of spectral lines corresponding to transitions between excited levels of the cesium atom

The constants of pressure self-broadening of cesium have been measured for the transitions 6P _1/2−8D _3/2, 6P _3/2−10S _1/2, and 5D _5/2−nF(n=14−19). The constants of the resonance broadening of the 6P _1/2 and 6P _3/2 cesium levels, the constants of electron collisional broadening of thenF levels at a temperature ofT≈1500 K, and the oscillator strengths of the 5D _5/2−nF(n=14−18) transitions have been determined. Translated from Trudy Fizicheskogo Instituta im. P. N. Lebedeva, Lebedev Physics Institute, Russian Academy of Sciences, Moscow, Vol. 195, pp. 217–233, 1989.     

Atom in an elliptically polarized resonance field: Exact stationary solution

An analytical method is developed for finding the exact stationary solution for the density matrix of atoms in a monochromatic resonance field of arbitrary ellipticity and intensity. A solution for the transitions F _g=F → F _e=F+1 (F _g and F _e are the angular momenta of the ground and excited states) is obtained in an analytical invariant form. The properties of this solution are investigated. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 8–12 (10 July 1996)     

A comprehensive,time-resolved SANS investigation of temperature-change-induced sponge-to-lamellar and lamellar-to-sponge phase transformations in comparison with <Superscript>2</Superscript>H -NMR results

Time-resolved small-angle neutron scattering (TR-SANS) was employed to observe temperature-induced phase transitions from the sponge (L ₃ to the lamellar ( L _α phase, and vice versa, in the water-oil (n -decane)-non-ionic surfactant ( C₁₂E₅ system using both bulk and film contrast. Samples of different bilayer volume fractions φ and solvent viscosities η were investigated applying various amplitudes of temperature jump ΔT . The findings of a previous ²H -NMR study could be confirmed, where the lamellar phase formation was determined to occur through a nucleation and growth process, while it was concluded that the L ₃ -phase develops in a mechanistically different and more rapid manner involving uncorrelated passage formation. Likewise, the kinetic trends of the nucleation and growth transition (decreased transition time with increase of φ and ΔT were witnessed once again. Additionally, NMR and SANS data that demonstrate a strong dependency of that process on solvent viscosity η are presented. Contrariwise, it is made evident via both SANS and NMR results that the L _α -to-L ₃ transition time is independent (within experimental sensitivity) of the varied parameters (φ , ΔT , η . Unusual scattering evolution in one experiment, originating from a highly ordered lamellar phase, intriguingly hints that a major rate determining factor is the disruption of long-range order. Furthermore, the bulk contrast investigations give insight into structure peak shifts/development during the transitions, while the film contrast experiments prove the bilayer thickness to be constant throughout the phase transitions and show that there is no evidence for a change in the short-range order of the bilayer structure. The latter was considered possible, due to the different topology of the L ₃ and L _α phases. Lastly, an unexpected yet consistent appearance of anisotropic scattering is detected in the L ₃ -to- L _α transitions.     

Hyperfine interaction of111Cd in antiferromagnetic cobalt oxide

The temperature dependence of the hyperfine field of substitutional¹¹¹Cd in antiferromagnetic CoO has been measured by means of the perturbed angular correlation technique. The Larmor frequency ω_L is found to obey a power law ω_L(t=ω₀ t ^β) up tot _max=0.4 wheret=1−T/T _N is the reduced temperature withT _N=291.2(3) K and β=0.393 (5) the critical exponent. The results are discussed and compared with PAC experiments on¹¹¹Cd in NiO and Ni and with results obtained by other methods.     

Flavor symmetry L μ-L τ and quasidegenerate neutrinos

Current data implies three simple forms of the neutrino mass matrix, each corresponding to the conservation of a nonstandard lepton charge. While models based on L _e and L _e-L _μ-L _τ are well known, little attention has been paid to L _μ-L _τ. A low-energy mass matrix conserving L _μ-L _τ implies quasidegenerate light neutrinos. Moreover, it is μ-τ symmetric and therefore (in contrast to L _e and L _e-L _μ-L _τ) automatically predicts maximal atmospheric neutrino mixing and zero U _e3. A seesaw model based on L _μ-L _τ is investigated and testable predictions for the neutrino mixing observables are given. Renormalization group running below and in between the seesaw scales is taken into account in our analysis, both numerically and analytically. The text was submitted by the authors in English.