Diffusion of ammonium ions in [(NH4)1−xRbx]3H(SO4)2 studied by 1H spin–lattice relaxation in the rotating frame

Translational diffusion of NH₄⁺ ions in [(NH₄)_1?xRb_x]₃H(SO₄)₂ has been evaluated quantitatively by means of ¹H spin–lattice relaxation times in the rotating frame, T_1ρ. In the high-temperature phase (phase I), the mean residence times of NH₄⁺ ions are three or four orders of magnitude larger than those of the acidic protons. In the room-temperature phase (phase II), they are two or three orders of magnitude larger than those of the acidic protons. The transition from phases II to I causes one order of magnitude enhancement in the diffusion of NH₄⁺ ions. The mean residence time of NH₄⁺ ions increases with increase in the Rb content. The similar trend is also observed in phase II.     

Proton diffusion in the superprotonic phase of [(NH4)1 − xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation

Proton diffusion in [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 < x < 1) has been studied by means of ¹H spin-lattice relaxation times, T₁. The relaxation times were measured at 200.13 MHz in the range of 296–490 K and at 19.65 MHz in the range of 300–470 K. In the high-temperature phase (phase I), translational diffusion of the acidic protons relaxes both the acidic protons and the ammonium protons. Spin diffusion averages the relaxation rate of the two kinds of protons, whereas proton exchange between them are slow. The spin-lattice relaxation times in phase I were analyzed theoretically, and parameters of proton diffusion were obtained. The mean residence time of the acidic protons increases with increase in x for [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 ≤ x ≤ 0.54). Rb₃H(SO₄)₂ does not obey this trend. The results of NMR well explain the macroscopic proton conductivity.     

Measurement of the S-Factor of the T(1H, γ)4He Reaction at Astrophysical Energies

JETP Letters - The T(1H, γ)4He reaction has been studied for the first time in the energy range Elab = 12–34 keV in the laboratory coordinate system (E = 7.8–20.1 keV in the...     

Proton conductivity in the layer compound H3OUO2AsO4·3H2O (HU As)

The proton conductivity in tetragonal H₃OUO₂AsO₄·(3-)H₂O has been measured above the transition temperature at 299 K. The conductivity, calorimetric and spectroscopic data depend on the water content and the transition is suggested to be a peritectic reaction setting free a small amount of solution, which stays strongly adsorbed between the layers of the structure and gives rise to the high conductivity.     

Low-temperature phase transitions and dynamics of ammonium in (NH4)3H(SO4)2 and [(NH4)1−x Rbx]3H(SO4)2 crystals

The (NH₄)₃H(SO₄)₂ and [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystals are investigated by dielectric spectroscopy, inelastic incoherent neutron scattering (IINS), and neutron powder diffraction. A comparative analysis of the data obtained is given. It is shown that the phase transitions II ? III, III ? IV, IV ? V, and V ? VII in the (NH₄)₃H(SO₄)₂ crystal are accompanied by changes in the orientation ordering of the NH ₄ ⁺ ions. In the [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystal, these phase transitions are completely suppressed and the long-range order inherent in the II phase is retained over the entire temperature range covered (6–300 K). It is revealed that this crystal at the temperature T _g≈70 K undergoes a transition to the dipole glass phase, which is attended by “freezing” the orientation disordering of the ammonium ions.     

Phase transitions in the (Cs1−x Rbx)2ZnI4 system

(Cs_1−x Rb_x)₂ZnI₄ crystals were grown by two different methods with Rb concentrations varying from x=0 to 2.5%. ¹²⁷I NQR and calorimetric measurements showed that crystals grown by the Bridgman technique contain residual impurities (∼0.5%) for all x. While x=0 crystals grown from solution do not contain detectable impurities, they allow incorporation only of a low Rb concentration, not above 0.5%. A transition-temperature-concentration (x) phase diagram has been constructed for Bridgman-grown crystals from NQR data. Rb doping shifts the normal-incommensurate and incommensurate-ferroelastic phase-transition points toward higher temperatures with different rates. The P2₁/m↔P1 first-order transition shifts toward lower temperatures. The region of low Rb concentrations lies closest to the critical point. Fiz. Tverd. Tela (St. Petersburg) 41, 143–147 (January 1999)     

Competitive solvation of K+ by C6H6 and H2O in the K+-(C6H6)n-(H2O)m (n = 1–4; m = 1–6) aggregates

The competitive solvation of the potassium ion by benzene and water is investigated at molecular level by means of Molecular Dynamics simulations on the K⁺-(C₆H₆) _n -(H₂O) _m (n = 1–4; m = 1–6) ionic aggregates. The preference of K⁺ to bind C₆H₆ or H₂O is investigated in the range of temperatures in which isomerisation processes are likely by adding water and benzene to the K⁺-(C₆H₆) _n and K⁺-(H₂O) _m aggregates, respectively. Hydrogen bonds and the π-hydrogen bond, in spite of their weakness with respect to the K⁺-π and K⁺-H₂O interactions, play an important role in stabilising different isomers, thus favouring isomerisation processes. Accordingly with experimental information it has been found that K⁺ bind preferably C₆H₆ rather than H₂O and that the fragmentation of C₆H₆ is only observed for aggregates containing four molecules of benzene.     

GEANT4 in the AliRoot Framework

The development of the GEANT4 application for ALICE simulation within the aliRoot framework is described.The G3toG4 approach adopted by ALICE collaboration is explained.The overview of the design,present implementation and functionality is presented and the remaining problems are discussed.     

Spectrum of the H− Ion in the s-Wave Model

 The H⁻ ion in the s-wave model has one bound state and a Rydberg series of resonances, one associated with each inelastic threshold of the electron hydrogen system. We calculate the energy of the bound state and the energies of the resonances as well as their total widths up to N = 9 and partial widths up to N = 7. Received July 5, 1999; revised February 18, 2000; accepted for publication February 22, 2000     

Inelastic production of neutral pions in the4He(γ, πℴp)3H reaction

The yield of the⁴He(, p)³H reaction has been studied in a bremsstrahlung beam of photons with a maximum energy of 450 MeV. The measurements were made on an experimental setup consisting of a total absorption Cerenkov gamma spectrometer and a helium streamer chamber. A kinematic analysis is made of the angular distributions of the disintegration products of the⁴He nucleus to study the mechanism of inelastic photoproduction of neutral pions. The relatively high event density in the region of small proton-triton separation angles is attributable to the quasielastic mechanism of the reaction in which pion photoproduction is accompanied by excitation of the⁴He nucleus.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 51–56, September, 1989.     

Magnetization of type-ii superconductors in the range of fields H c 1 ≤ H ≤ H c 2Variational Method

A variational method is proposed to find the magnetic field dependence of the magnetization of type-II superconductors in the mixed state by a self-consistent technique. This model allows for suppression of the order parameter to zero at the centers of Abrikosov vortices and also for the magnetic field dependence of the order parameter. The results can be applied to the entire range of fields H _c 1 ≤ H ≤ H _c 2 for any values of the Ginzburg-Landau parameter $\kappa > 1/\sqrt 2$ . It is shown that in weak fields where κ ? 1 the behavior of the magnetization can be described exactly in the London approximation provided that the correct value of H _c 1 is used. Near the second critical field this dependence shows good agreement with the well-known Abrikosov result. It is also shown that using the concept of isolated vortices and applying the principle of superposition of the fields and currents generated by these vortices to calculate the magnetization gives inaccurate quantitative results even in fairly weak fields. By going beyond these concepts, it was possible to allow more accurately for the influence of the vortex cores on the magnetization behavior in the intermediate range of fields H _c 1 ?H ? H _c 2 and to identify the range of validity of various approximations used widely in the literature.     

Semileptonic decays of the hypernucleus4HΛ

Two-channel type semileptonic decays of the hypernucleus⁴H are considered:⁴H_A ³H+p+^–+ and⁴H³He+n+^–+ . The particle energy spectra are computed taking into account the presence of strong interaction in the final state and the Pauli principle both in the direct and in the charge-exchange decay channels.The importance of the role played by interactions in forming the spectra of particles created in decays, is noted. Characteristic features of energy spectra and angular correlations of particles in the charge-exchange decay channel are discussed. The importance of such effects is noted for the dynamics of multichannel mesonless hypernuclear decays with similar energy release values.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 42–45, July, 1990.     

Proton nuclear magnetic resonance in paramagnetic NiSO4 · 1 H2O

Parameters characterizing the magnetic interactions between the paramagnetic ions Ni²⁺ and the protons of crystalline water in powderedNiSO ₄ · 1H ₂O were derived from the field and temperature dependences of the second moment of NMR spectra. The Curie-Weiss constant, magnetic moment _i and the part of second momentM ₂O corresponding to the nuclear dipoledipole interaction were evaluated from the experimental data. The parameters characterizing the local magnetic field acting on the proton-pairs were calculated and compared with those obtained from the analysis of the shape of the NMR spectrum.The authors express their grateful acknowledgement to Prof. Dr. hab. Z. Pajak, Dr. S. GIo-winkowski, Dr. J. Kapturczak and Ing. W. Porzuckoviak from Institute of Physics, A. Mickiewicz University in Poland for their help in NMR measurements and fruitful discussions.     

Shift automorphisms in the Hénon mapping

We investigate the global behavior of the quadratic diffeomorphism of the plane given byH(x,y)=(1+y–Ax ²,Bx). Numerical work by Hénon, Curry, and Feit indicate that, for certain values of the parameters, this mapping admits a strange attractor. Here we show that, forA small enough, all points in the plane eventually move to infinity under iteration ofH. On the other hand, whenA is large enough, the nonwandering set ofH is topologically conjugate to the shift automorphism on two symbols.Partially supported by NSF Grant MCS 77-00430     

Chaotic behavior in the Hénon mapping

In a previous work Hénon investigated a two-dimensional difference equation which was motivated by a hydrodynamical system of Lorenz. Numerically solving this equation indicated for certain parameter values the existence of a strange attractor, i.e., a region in the plane which attracts bounded solutions and in which solutions wander erratically. In the present work it is shown that this behavior is related to the mathematical concept of chaos. Using general methods previously developed, it is proven analytically that for some parameter values the mapping has a transversal homoclinic orbit, which implies the existence of the chaotic behavior observed by Hénon.     

Two new low-temperature phase transitions in the Li(NH4)1 − x Na x SO4 system

Dielectric measurements, X-ray diffraction and Raman scattering techniques have been used to investigate Li(NH₄)_0.99Na_0.01SO₄ (LASS1%) and Li(NH₄)_0.80Na_0.20SO₄ (LASS20%) crystals in the temperature range from 200 to 10?K. These are interesting systems because of the presence of hydrogen bonds and structural defects and because the mother crystal, LiNH₄SO₄, is ferroelectric at room temperature. From the analysis of the results we can conclude that the substitution of Na⁺ ions in the structure of LiNH₄SO₄, even at quantities as low as 1%, is sufficient to induce additional phase transitions to the LiNH₄SO₄ system. The new phase transitions are observed at 181 and 115?K for LASS1% and at 208 and 133?K for LASS20% and both are reversible.     

Novel behavior in the M–H and field cooled (FC) curves of the MnFe2O4 nanoparticles synthesized by the coprecipitation method

MnFe₂O₄ nanoparticles were prepared by a coprecipitation chemical method. The average size of the obtained nanoparticles was about 30 nm. The hysteresis measured at T=300 K clearly shows ferromagnetic order at room temperature while that measured at T=450 K shows superparamagnetic behavior. The difference in the magnetization curves in the field increasing cycle and field decreasing cycle at higher temperatures (450 K or higher) is very unusual. In this case, a hysteresis in magnetization in higher magnetic fields with an opening up of the magnetization curve was observed. In this work, the effect of temperature and time of application of the applied field on the magnetization behavior was studied.     

Investigation of the EPR parameters of the rhombic Cu2+ center in (NH4)2Mg(SO4)2·6H2O single crystal

The electron paramagnetic resonance (EPR) parameters (g factors g_x, g_y, g_z and hyperfine structure constants A_x, A_y, A_z) for Cu²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O (DHMS) crystal are theoretically investigated using the high-order perturbation formulas of these parameters. In the calculations, the ligand orbital and spin–orbit coupling for the impurity Cu²⁺ are taken into account; the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the impurity center. The ligand orbital and the spin–orbit coupling contributions are included on the basis of the cluster approach. Based on the calculation, the theoretical EPR parameters show good agreement with the observed values. The results are discussed.     

Lyapunov exponents in the Hénon-Heiles problem

The maximal Lyapunov characteristic exponent of chaotic motion was calculated as a function of the system energy by numerical integration of the Hénon-Heiles problem. Contrary to the conclusions of Benettin et al.     

Polarization transfer in 4He(e-->,e'p-->)3H: is the ratio G E p/G M p ) modified in the nuclear medium?

Polarization observables in the (4)He(e-->,e'p-->)(3)H reaction are calculated using accurate three- and four-nucleon bound-state wave functions, a realistic model for the nuclear electromagnetic current operator, and a treatment of final-state interactions with an optical potential. In contrast to earlier studies, no significant discrepancies are found between theory and experiment both for the ratio of transverse to longitudinal polarization transfers and for the induced polarization, when free-nucleon electromagnetic form factors are used in the current operator. The present results challenge the current interpretation of the experimental data in terms of medium-modified form factors.