In-vivo study of the nuclear quadrupole interaction of99Mo (β- 99)Tc in nitrogenase of Klebsiella pneumoniaein nitrogenase of Klebsiella pneumoniae

We report on the first TDPAC-measurements of the nuclear quadrupole interaction (NQI) of (NQI) of⁹⁹Mo(β^-)⁹⁹Tc in the nitrogenase of the bacteria Klebsiella pneumoniae. Because nitrogenase is the only Mo-containing enzyme in Klebsiella pneumoniae under the chosen conditions, no further isolation of this enzyme was necessary. The majority of the incorporated⁹⁹Mo is subjected to a well defined NQI with ω=365(7) Mrad/s, η=1 and a reorientational correlation time of τ_coττ≈10nsec and is attributed to the active site of the FeMo cofactor. During sample preparation we noted a pronounced affinity of the bacteria to^99mTc.     

Matter-induced ω→ππ decay

We calculate the width for the ω→ππ decay in nuclear matter in a hadronic model including mesons, nucleons and Δ isobars. We find a substantial width of the longitudinally polarized ω modes, reaching ∼100 MeV for mesons moving suitably fast with respect to the nuclear medium. Received: 7 June 1999 / Revised version: 14 October 1999     

Constraints on the time scale of nuclear breakup from thermal hard-photon emission

Measured hard-photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal model to estimate the breakup times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies. The obtained nuclear breakup time for the ¹²⁹Xe + ^natSn reaction at 50 A MeV is Δτ ≈ 100-300 fm/c for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions studied by the TAPS experiment is consistent with Δτ ≈ 100 fm/c, such relatively long thermal photon emission times do not seemingly support the interpretation of nuclear breakup as due to a fast spinodal process for the heavy nuclear systems studied.     

A chiral anomaly channel in τ-decay. II

The decay rate for τ→νηππ is calculated from an amplitude that has the chiral anomaly term as low-energy constraint and has realistic vectormeson meson pole continuation to physical energies. Work supported in part by the US Department of Energy under grant DOE/ER/01545 Supported by Bundesministerium für Forschung und Technologie, 05 4HH 92P/3, Bonn, FRG     

Solid-echo in solids with molecular motions: Effects of nonzero pulse widths

The effects of nonzero pulse widths on the solid-echo signals in solids with molecular motions have been investigated. It has been shown that in the slow-motion region (M ₂τ_c² ≈ 1) the amplitude of the echo signal is reduced and the maximum of the echo signal is shifted to the end of the second pulse. Comparison of the developed theory with experimental results obtained on polycrystalline C₆H₆ and NH₄Cl demonstrates good agreement between them.     

Determination of the spectral parameters of nuclear quadrupole resonance from nutation spectra of powdered samples

An analytical expression I(ω) is obtained for a normalized function of the shape of an idealized nuclear quandrupole resonance nutation line of a powdered sample for spins I=3/2 (η≠0). Calculations are made of the initial moments <ωⁿ> of the nutation spectrum of the powder in the form of functions of ω₀=γB₁ and the asymmetry parameter η of the electric field gradient tensor. A method is proposed for determining the spectral parameters η and eQq_zz from the experimentally measured values of <ω>, <ω²>, <ω⁴>, and ω_1/2 of the nuclear quadrupole resonance nutation spectrum of the powder. State University, Kaliningrad. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–8, July, 1997.     

Di-pion emission in heavy quarkonia decays

The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|², with x = q ² − 4m _π² / (ΔM)² − 4m _π² < q ² ≡ M _ππ², and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays: 3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively. The text was submitted by the author in English.     

Multiple structure of two-pulse nuclear spin echo in cobalt films

The conditions for the formation of two-pulse echo signals from ⁵⁹Co nuclei in thin magnetic films at T=4.2 K are investigated. In the framework of the existing mechanisms, numerical simulation of the conditions for the formation of extra 3τ and 4τ echo signals (τ is the time delay between pulses) is carried out. It is shown that the multiple structure of the echo from ⁵⁹Co nuclei at T=4.2 K is due to a mechanism in which an additional hyperfine magnetic field proportional to nuclear magnetization is acting on the nuclear spin system.     

ωN final state interactions and ω-meson production from heavy-ion collisions

We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in ¹²C +¹²C, ⁴⁰Ca +⁴⁰Ca and ⁵⁸Ni +⁵⁸Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative to a general m _T-scaling (for π⁰ and η mesons) might be controlled experimentally by the TAPS Collaboration. Received: 28 April 1999 / Revised version: 7 June 1999     

Strong isospin violation andη−π mixing in |ΔS|=1 weak transition

We consider the effects ofη−π mixing on the violation of the |ΔI|=1/2 rule in |ΔS|=1 weak transitions. The processes considered are theK→2π,K→3π, Λ, Ξ and Λ hyperon decays.     

Nutation electron spin echo ofE-centers in quartz

Attenuation of the signals of the nutation echo of E’-centers in crystalline and glass quartz was experimentally investigated at room temperature. The nutation echo in EPR was excited in the single-photon regime and formed by two Zeeman-field pulses with duration t₁ and t₂ (t₁<t₂) and time interval between them τ. The echo signal was recorded during the second pulse at t≈2t₁+τ. It was established that this signal attenuation, measured as t₁ increased, follows an, exponential law, its rate Γ is much less than 1/T₂ (T₂ is the transverse relaxation time), and it linearly increases with an increase in the amplitude of the exciting SHF field B₁. The parameters of the dependence of Γ on B₁ correlate with the parameters of the analogous dependence revealed previously for attenuation of nutation of E’-centers in quartz in the two-photon regime at T=4.2 K. At the same time, the value of Γ measured with different values of τ is independent of B₁ and is equal to 1/T₁, where T₁ is the longitudinal relaxation time. A. N. Sevchenko Scientific Research Institute of Applied Physical Problems, 7, Kurchatov St., Minsk, 220064, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 405–411, May–June, 1998.     

Two-pion production in deuteron-deuteron collisions at low energies

The cross-section for the dd →^4Heππ reaction is estimated near threshold in a two-step model where a pion created in a first interaction produces a second pion in a subsequent interaction. This approach, which describes well the rates of 2π and η production in the pd →^3Heππ and dd →^4Heη reactions, leads to predictions that are much too low compared to experiment. Alternatives to this and the double-Δ model will have to be sought to explain these data.     

Analysis of angular distributions in γN → πeta;N

Angular distributions in the final state of π⁰η photoproduction on nucleons are considered. As a formal base the familiar isobar model is used in which the π⁰ηN state is a product of the resonance decay into ηΔ(1232) and πS ₁₁(1535) channels. One of the principal assumptions used is that in the actual energy region the reaction is dominated by a single resonance state. The developed formalism can serve as a tool for testing spin and parity of that resonance.     

An Isoperimetric Inequality for Fundamental Tones of Free Plates

We establish an isoperimetric inequality for the fundamental tone (first nonzero eigenvalue) of the free plate of a given area, proving the ball is maximal. Given τ > 0, the free plate eigenvalues ω and eigenfunctions u are determined by the equation ΔΔu − τΔu = ωu together with certain natural boundary conditions. The boundary conditions are complicated but arise naturally from the plate Rayleigh quotient, which contains a Hessian squared term |D ² u|².     

Hyperfine Interactions in the Sr0.88Ba0.12HfO3 Compound

The temperature dependence of the hyperfine parameters in a powder sample of the Sr_0.88Ba_0.12HfO₃ compound has been investigated for the first time using perturbed angular correlation spectroscopy. The time spectra were measured as a function of the temperature from 293 to 1273 K. Activated ¹⁸¹Ta nuclei were used as hyperfine probes at the Hf sites. The analysis of the time spectra indicates the presence of two different surroundings for the Ta probes. The most populated site (f ₁≈75% at laboratory temperature) was fitted with the usual static quadrupole hyperfine interactions found in most perovskite-type compounds. The resulting quadrupole frequency is ω _Q ≈24 Mrad/s at this temperature. This frequency continuously decreases to nearly 9 Mrad/s at 1273 K. Its line width temperature dependence displays three regions and the changes observed probably correspond to phase transitions. The other site has a large and temperature independent quadrupole frequency ω _Q ≈120 Mrad/s that reversibly transforms into the first at high temperatures and probably originates from some defect in the structure. This revised version was published online in September 2006 with corrections to the Cover Date.     

T-violation and neutron optics experiments

It is shown that a two-step model of the reaction pd→³HeX (X=η, η′ eω, φ), involving the subprocesses pp) →dπ⁺ and π⁺ n→Xp, can account for the form of the energy dependence of experimental cross sections above the thresholds under the assumption that the singlet part of the pp→dπ⁺ amplitude dominates. The spin-spin asymmetry for the reaction dp→³HeX has been found to be ∼;−1 in the forward-backward approximation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 3–7 (10 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

np → ηd near threshold and the s -wave ηN amplitude

We calculate the process np → ηd near threshold using a separable potential model of the coupled ηN - πN - ππN subystems, and a relativistic three-body calculation for the ηd scattering amplitude. The ππN channels are represented by an effective σN channel, and we compare the case where the σ and π masses are related by m _σ = 2m _π and no width is considered, to another where the mass and width of the σ -meson are taken from ππ scattering data. The np → ηd cross-section can be well described up to about 60MeV by models where the real part of the ηN scattering length lies between 0.4≤Re(a _ηN)≤0.6 fm which allows us to determine the s -wave ηN scattering amplitude for -60≤E≤60 MeV.     

ρ(ω) → π0π0γ, ρ(ω) → ηπ0γ decays in the local quark Nambu-Jona-Lasinio model

The branching ratios and photon spectra of the rare processes ρ(ω) → π ⁰ π ⁰ γ, ρ(ω) → ηπ ⁰ γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered: the quark box and the pole diagrams with scalar (σ, α ₀(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π ⁰ π ⁰ γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ ⁰ γ. The text was submitted by the authors in English.     

Nonadiabatic effects in the phonon spectra of superconductors

The nonadiabatic corrections to the self-energy part Σ_s(q, ω) of the phonon Green’s function are studied for various values of the phonon vectors q resulting from electron-phonon interactions. It is shown that the long-range electron-electron Coulomb interaction has no direct influence on these effects, aside from a possible renormalization of the corresponding constants. The electronic response functions and Σ_s(q, ω) are calculated for arbitrary vectors qand energy ω in the BCS approximation. The results obtained for q=0 agree with previously obtained results. It is shown that for large wave numbers q, vertex corrections are negligible and Σ_s(q, ω) possesses a logarithmic singularity at ω=2Δ, where Δ is the superconducting gap. It is also shown that in systems with nesting, Σ_s(Q, ω) (where Q is the nesting vector) possesses a square-root singularity at ω=2Δ, i.e., exactly of the same type as at q=0. The results are used to explain the recently published experimental data on phonon anomalies, observed in nickel borocarbides in the superconducting state, at large q. It is shown, specifically, that in these systems nesting must be taken into account in order to account for the emergence of a narrow additional line in the phonon spectral function S(q, ω)≈−π ⁻¹ Im D _s (q, ω), where D _s (q, ω) is the phonon Green’s function, at temperatures T<T _c . Zh. éksp. Teor. Fiz. 115, 1799–1817 (May 1999)     

Mixing and decays of ρ- and ω-mesons

Isospin-violating mixing of ρ- and ω-mesons is reconsidered in terms of propagators. Its influence on various pairs of (ρ,ω)-decays to the same final states is demonstrated. Some of them, (ρ,ω)↦π⁺π^- and (ρ,ω)↦πγ, have been earlier discussed in the literature, others (e.g., (ρ,ω)↦ηγ and (ρ,ω)↦e ⁺ e ^-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present experimental data, though yet inconclusive, provides some limits for the direct (ρω)-coupling and indirectly supports enhancement of ρ↦πγ in comparison with ρ^±↦π^±γ, though not so large as in some previous estimates. Received: 16 September 2002 / Accepted: 23 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: azimov@pa1400.spb.edu Communicated by V.V. Anisovich