Antiferromagnetic metallic state of NiS2

The neutron diffraction experiment we have made on NiS_1.91 single crystal under increasing pressure (0<P<30 kbar) indicates a constant increase of the Néel temperature of the sample. For high pressures (P>20 kbar) and low temperatures the sample is in an antiferromagnetic metallic state as suggested by theoretical considerations for a Mott-Hubbard insulator. The pressure dependence of the second magnetic transition in NiS₂ (T = 31 K for P = 0) is also reported.     

New evaluation of muon (g − 2) hadronic anomaly

The hadronic part a_H of the muon g-factor anomaly $\text{a ≡}\text{(g ? 2)}\text{2}$ is evaluated from latest data on σ(e⁺e^? → hadrons). For a p-wave ππ scattering length of a₁ = 0.04±0.005 we calculate a_H = (66±10) × 10^?9, compared to a(experiment) ? a(QED) = (60±29) × 10^?9. Half of the uncertainty on a_H is associated with the energy interval $\text{0.92 <}\text{s}\text{< 2}\text{GeV}$.     

New determination of the neutron-proton scattering amplitude and precise measurements of the scattering amplitudes on carbon,chlorine, fluorine and bromine

After an improvement on the theory of the neutron-gravity-refractometer and after refinements of the experimental procedure we have performed new measurements of the absolute value of the neutron-proton scattering amplitude at low neutron energies. In order to obtain and to confirm a very high accuracy we carried out neutron-reflection experiments on 18 various liquids of 11 different organic substances containing the elements carbon, hydrogen and/or chlorine. Compounds with fluorine and bromine were used to measure the scattering amplitudes of these elements. We found the coherent scattering amplitudes of the bound atoms to be:a _H=?3.7409(1l)fm,a _c=6.6484(13)fm,a _c1=9.5792(8)fm,a _F=5.66(2)fm anda _Br=6.79(2)fm. The low energy (n, p)-parametersa _t anda _s were calculated with the presenta _H and a new value of the (n, p) scattering cross-sectionσ ₀. By comparing the measureda _C with values obtained from precise transmission experiments we could determine the gravitational accelerationg _f of the free neutron in terms of the local value g. We found the two values to be equal:g _f =0.9996(7)g.     

Tsallis’ statistics in the variability of El Niño/Southern Oscillation during the Holocene epoch

Analysis of the Tsallis q-triplet for the variability of El Niño Southern Oscillation (ENSO) index during the Holocene epoch (last 11,000 years) is presented. Three periods are analyzed, 0-7000, 7000-9700, 9700-11,000 years before the present. During the first and the third periods, the q-index values have the expected usual relations between them (q_sens<1<q_stat<q_rel), and in the second one there is an inversion between q_stat and q_rel (q_stat>q_rel).     

Gedanken experiments to destroy a black hole

It is widely believed that the complete gravitational collapse of a body always results in a black hole (i.e., “naked singularities” can never be produced) and that all black holes eventually “settled down” to Kerr-Newman solutions. An important feature of the Kerr-Newman black holes is that they satisfy relation m² ? a² + e² where m is the mass of the black hole, e is its charge, $\text{a =}\text{J}\text{m}$ is its angular momentum per unit mass and geometrized units G = c = 1 are used. (For m² <a² + e² the Kerr-Newman solutions describe naked singularities.) In this paper, we test the validity of the above conjectures on gravitational collapse by attempting to create a spacetime with m² <a² + e² starting with a Kerr-Newman black hole with m² = a² + e². Such a spacetime would either have to be a new black hole solution or a “naked singularity,” in violation of the above conjectures. In the first gedanken experiment we attempt to make the black hole capture a test particle having large charge and orbital angular momentum compared with energy. In the second gedanken experiment we attempt to drop into the black hole a spinning test body having large spin to mass ratio. In both cases we find that bodies which would cause violation of m² ? a² + e² will not be captured by the black hole, and, thus, we cannot obtain m² <a² + e², although we can come arbitrarily close in the sense that m² = a² + e² can be maintained in these processes.     

“Artificial vacuum” for T-violation experiment

We point out the possible use of matrix isolation spectroscopy in experimental tests of fundamental physics. As a concrete example we show how this technique might be applied to measuring the T-violation electron electric dipole moment d_e. We estimate that a dipole moment could be detected down to d_e ∼ 6 × 10⁻²⁸e cm, in comparison to the current limit of d_e < 10⁻²⁴e cm.     

Magnetic and crystal structure of copper(II) fluoride

A powder sample of the monoclinic, weak ferromagnet CuF₂ was investigated by neutron diffraction. Using the profile method, the crystal structure was refined and the spin configuration determined. The layer type structure with planar quadratic fluorine coordination of Cu²⁺ (3d⁹) and the magnetic structure are remarkably similar to those of AgF₂. The spin configuration is however different from the magnetic structures of other 3d-fluorides; the magnetic unit cell is doubled with respect to the chemical cell (a_m = 2a, P2₁/c). The ordered magnetic saturation moment corresponds to quenched orbital momentum.     

Polarised neutron diffraction study of Mn1.09Sb

In order to study the influence of interstitial site occupancy on the electronic structure of MnSb, a polarised neutron diffraction experiment was performed on Mn_1.09Sb. The composition of the sample was obtained from the refinement of single crystal neutron diffraction data. The polarised neutron diffraction experiment yielded unpaired electron populations of the levels a^t_1g, e_g^t and e_g as follows: μ_x0 = 0.57 μ_B, μ_x± = 1.60 μ_B, μ_u± = 1.28μ_B. The comparison of these numbers with results of Yamaguchi et al shows that the spin density for this composition is reduced for the low energy level a^t_1g. This finding is interpreted by an occupation of minority spin states by electrons of the interstitial Mn atoms. In agreement with this, increasing Mn excess leads to a decreasing magnetic moment magnitude/Mn-atom and to a contraction of the lattice parameter c, indicating the strengthening of the Mn-Mn bond in [001].     

Zur Chronologie des alten Ägypten

The velocityv of the propagation of discharge along the anode of a self-quenchingG—M-counter is a function of total pressureP, pressure of the quenching gasP _D, radius of the cathoder _a and of the anoder _i andV _ü the difference between working- and starting-potential. For the mixtures argon-methylal, argon-alcohol and helium-alcohol isv=v ₀·exp[k·(V _ü/V _e)^1/2] withv ₀ the velocity at the starting potentialV _e v ₀=(a+b·P _D/P)·V _n ^1/2 ·exp [(c?d·P_D/P·V _n ^?1/2 ] andV _n=V _e·(lnr _a/r _i)^?1.k, a, b, c andd are characteristical constants of the filling gas.     

Pressure-induced structural transformations,orbital order and antiferromagnetism in La<Subscript>0.75</Subscript>Ca<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript>

High pressure evolution of structural, vibrational and magnetic properties of La_0.75Ca_0.25MnO₃ was studied by means of X-ray diffraction and Raman spectroscopy up to 39 GPa, and neutron diffraction up to 7.5 GPa. The stability of different magnetic ground states, orbital configurations and structural modifications were investigated by LDA + U electronic structure calculations. A change of octahedral tilts corresponding to the transformation of orthorhombic crystal structure from the Pnma symmetry to the Immaone occurs above P ~ 6 GPa. At the same time, the evolution of the orthorhombic lattice distortion evidences an appearance of the e _g d _{x² ? z²} orbital polarization at high pressures. The magnetic order in La_0.75Ca_0.25MnO₃ undergoes a continuous transition from the ferromagnetic 3D metallic (FM) ground state to the A-type antiferromagnetic (AFM) state of assumedly 2D pseudo-metallic character under pressure, that starts at about 1 GPa and extends possibly to 20–30 GPa.     

Simple model for spin-crisis

Starting from the additive quarkSU(6) model and taking into account the pion and kaon (η) emission during the initial stage of evolution (fromq ²～m _quark ² toq ²～1 GeV²) we convert the main fraction of the proton spin into the orbital momentum of the pseudoscalar mesons. The results are in a good agreement with the experimental data. We get ∫g ₁(x)dx=0.152 for proton and +0.007 for the Λ hyperon (i.e. the quarks carry out only about 39% of the Λ spin). In the same model we explain the violation of the Gottfried sum rule ?∫(F ₂ ^p(x)?F ₂ ⁿ(x))dx=0.23 due to the charged meson exchanges at the beginning of the evolution. The Gribov-Lipatov relation between the polarized structure functions in DIS ande ⁺ e ^?-annihilation is discussed. It gives the possibility to study the spin structure of Λ hyperon produced through the decay of the jet originated by a polarized quark ine ⁺ e ^?-annihilation or in DIS.     

Franck-condon factors for diatomic molecules and the factorization method

By means of the factorization method, recurrence relations for the matrix elementS$\text{<ψ}{}_{\mathrm{<mtext>v\text{'}</mtext>}}\text{¦r}{}^{\mathrm{N}}\text{¦ψ}{}_{\mathrm{<mtext>v</mtext>}}\text{<}$ for an arbitrary positive integer N are obtained in the framework of α-averaging for the Morse potential. The method of calculating the matrix element$\text{<ψ}{}_{\mathrm{<mtext>v\text{'}</mtext>}}\text{¦R}{}_{\mathrm{<mtext>e</mtext>}}\text{¦ψ}{}_{\mathrm{<mtext>v</mtext>}}\text{<}$ is outlined, provided a dependence of the electronic transition moment R_e on the internuclear distance r can be approximated by the polynomial R_e(r)=a₀+a₁r+a₂r²+…+ainNr^N. Recurrence relations are also obtained for the case of the exponential dependence R_e(r).     

The two particle-phonon multiplet πh 11/2 νf 7/2 × 3− and higher-lying four-nucleon yrast states in the doubly-odd nucleus 146 63 Eu83

The isotopes¹⁵B,¹⁸C,^19,20N,^34,35Al and³⁹P have been produced as projectile-like fragments from the interaction of a⁸⁶Kr beam of 45 MeV/u from GANIL with a¹⁸¹Ta target. Separated by the 0° magnetic analyser LISE, the nuclei are identified by means of aΔE- E semiconductor telescope. It is surrounded, in a geometry close to 4π, by a thin plastic scintillator (NE 102) and a large volume liquid scintillator (NE 213) for the detection of betas and neutrons, respectively, from the decay of the implanted nuclei. By observation of theβ-delayed neutrons, the half-livesT _1/2 and neutron emission probabilitiesP _n have been measured. TheT _1/2 of¹⁸C,²⁰N,³⁵Al,³⁹P and P_n of¹⁸C,^19,20N,^34,35Al and³⁹P are determined for the first time. For the isotopes¹⁷C,^36,37Si and³⁸P upper limits of P_n are deduced.     

Attempt to calculation of delayed neutron emission probabilities using simple statistical model considerations

Delayed neutron emission probabilities,P _n , have been calculated using usual nuclear statistical model considerations. The influence of the incident parameters on the calculatedP _n -values is discussed. The observed systematic deviation from the experimental neutron emission probabilities may be explained by the persistence of nuclear structure effects not contained in a simple statistical model.     

Electromagnetic transition strengths and nuclear moments in123Xe

The level structure of¹²³Xe has been studied with the¹¹⁴Cd (¹²C, 3n) and^?Cd (¹³C, 4n) reactions using in-beamγ-ray spectroscopy. The yrast cascade on the low lying odd parity states originating from theh _11/2 neutron orbital has been investigated yielding lifetimesτ of 18(3) ps, 2.2 (4) ns and 17(2) ns for the 15/2^?, 11/2^? and 9/2^? states, respectively. Theg-factor of thet _1/2=5.2 μs isomer has been measured to beg=?0.256(2). From the time differential observation of the electric quadrupole interaction in a¹¹⁴Cd single crystal the spin of this isomer has been determined to be 7/2 and from the coupling constante ² Qq/h=116(2) MHz the quadrupole moment was deduced. The results are discussed in the framework of the triaxial rotor plus particle model.     

Solution of Faddeev-type equations in the problem of two coulomb centers

The hyperfine structure of the 7p ² P _1/2,3/2 levels of¹¹⁵In and the 5p ² P _1/2 level of²⁷Al has been measured using high-resolution laser spectroscopy on atomic beams. For the magnetic-dipole and electric-quadrupole interaction constants,a andb, the following values were obtained;a(7p ² P _1/2)=90.7(10) MHz,a(7p ² P _3/2)=32.3(2) MHz andb(7p ² P _3/2)=24.5(1.5) MHz for¹¹⁵In anda(5p ² P _1/2)=20(2) MHz for²⁷Al. Many-body calculations on² P states in aluminum, gallium and indium have also been performed.     

Nuclear dissipation,fission probability and neutron multiplicity prior to fission

We discuss the effects of nuclear dissipation on fission probabilities that are characteristic of a diffusion model of the fission process. Reproducing the experimental fission probabilities at low excitation energies fixes the ratioa _f/a_n of the level density parameters for a given strength of the reduced dissipation coefficientβ. These low energy constraints ona _f/a_n andβ balance the effects of transients on neutron multiplicities prior to fission at higher excitation energies. For the competitive decay of¹⁵⁸Er formed in the reaction¹⁶O+¹⁴²Nd at 207 MeV we show that dueto transients only the multiplicity of pre-fission neutrons is enhanced with respect to the prediction of the statistical model in a manner consistent with our earlier general analysis.     

Penning ionization electron spectroscopy and photo-electron spectroscopy of molecular solids. II. Ammonia and water

The Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) of ammonia and water molecules condensed on a cold metal substrate have been measured using thermal He*(2³S, 2¹S) metastable atoms and He(I) (58.4 nm) photons. The shifts of the observed positions of the PIES peaks relative to those of the UPS peaks in the condensed phase are roughly equal to the corresponding shifts in the gas phase. The relative intensities of the 3a₁ and 1e orbital peaks are reversed in the PIES and UPS for both gaseous and condensed ammonia; the origin of this reversal is interpreted as the difference between the interactions with metastable atoms and photons. On the other hand, the relative intensities of the 3a₁ orbital peak in the PIES and UPS for condensed water decrease as compared to the gas-phase spectra. This implies participation of the 3a₁ orbital of water in the hydrogen bonding.