The resummation of one particle lines

We propose a partial resummation for a weak coupling cluster expansion. The resummation gives one particle lines with in/out field propagators. We give a Bethe-Salpeter equation in which one particle subtractions are defined using physical one particle states. By these methods, we show thatP()₂ quantum fields in the weak coupling region have only isolated bound state spectrum below the 2m threshold. HereP is not restricted to be even.Supported in part by the National Science Foundation under Grants PHY 78-08066 and PHY 77-18762. Both authors thank the I.H.E.S., Bures-sur-Yvette, and A. J. thanks C.E.N., Saclay, for their hospitality.     

Indication for a delocalized precursor μ+ state in CeAl3

The low temperature ( 0.6 K) ZF-SR signal in the heavy electron compound CeAl₃ displays a three component structure with one component revealing the precession of ⁺ in a static internal field of 220 G. Surprisingly the phase of this signal is shifted by the order of 90° which indicates the presence of a precursor state. The precursor state manifests itself by a quickly decaying nonoscillating component. A simple two state model with zero average field in the precursor state and 220 G in the final state can describe the results except for the magnitude of the phase shift.     

Electeostatic equilibrium of a modulated electron beam in a magnetoactive plasma

The two-dimensional (axisymmetric) equilibrium of a modulated electron beam (sequence of bunches) in a magnetoactive plasma under resonance conditions, when the frequency of modulation of the beam _M is close to (less than) the plasma frequency _p, is studied. The field of the collective electrostatic wave, focusing the bunches, is compensated by the thermal repulsion of the beam electrons. Based on the solutions obtained, it is established that the external magnetic field has a twofold effect on the equilibrium beam: first, to a weakening of the radial component of the focusing field because of the appearance of anisotropy in the dielectric permittivity tensor of the plasma and, second, an additional radial focusing of the bunches when they are rotated by the Lorentz force. The regions of the beam and plasma parameters in which one or another of the indicated effects predominates are determined and the conditions for the predominance of magnetic over electrostatic focusing are found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 3–8, March, 1985.The author thanks V. B. Krasovitskii for proposing the subject and for constant interest in this work.     

Resonance acceleration of ions in a variable magnetic field

The motion of a particle is considered in a variable magnetic field — the superposition of a driving field H(t) and a weak field oscillating at the frequency =eH(t)/mc. The law of motion is found by the averaging method, and it is shown that the particle energy increases exponentially.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 75–78, October, 1978.In conclusion, thanks are due to the participants in Prof. Sokolov's seminar for discussion of the work.     

Contribution to the expression of particle movement in magnetic mirror systems in cyclic variables

The aim of this paper is to express the Hamiltonian function of a particle in a static, axially symmetric magnetic field in convenient variables. Assuming adiabaticity (the relative change of the magnetic field during one cyclotron revolution can be neglected), the Hamiltonian function is determined with cyclicity in two degrees of freedom.For the determination of the Hamiltonian function either the Carthesian, or the orthogonal curvilinear system was used as a starting coordinate system. The latter consists of a natural system of lines of force and equipotentials of the field. In both cases a Hamiltonian function of the formH=H(P₁ P ₂,P ₃,Q ₃) is obtained, where P_i are generalized impulses and Q₃ longitudinal coordinates.The form of the Hamiltonian function is very simple; it facilitates appreciably the integration of the equations of motion and provides simple expressions for the integrals of motion.The author wishes to express his thanks to Ing. J. Váa, the Director of the Institute, for his interest in the work and to Dr. M. Scidl for encouragement.     

Mössbauer Spectroscopy Study of Iron Nickel Alloys

Three samples of Fe_100–x Ni _x (with x=30, 35 and 40) were prepared by arc melting technique. The Mössbauer spectra of the three samples were collected and analyzed. The spectrum of the sample with x=30 consists of a singlet and a sextet. The singlet component which has isomer shift (IS=–0.08 mm/s) is attributed to a superparamagnetic phase. The value of the magnetic hyperfine field associated with the sextet component, 34.0 T, is consistent with that of -Fe–Ni alloy. In the spectra of the other samples the central line disappears. The magnetic component, used in fitting the spectrum of the sample with x=40 has a hyperfine magnetic field B _hf=30.0 T. This component is assigned to the high-spin -FCC Fe–Ni phase. Two magnetic components of 16.3 T and 27.3 T are used to fit the spectrum of the sample with x=35. The 27.3 T component is associated with the typical high-spin -FCC Fe–Ni phase while the 16.3 T component is associated with a -FCC Fe–Ni phase with magnetic relaxation.     

Ein Beschleuniger für schwere Ionen

A heavy ion accelerator on the basis of the multiple-stage operation of a small tandem-generator is proposed. The ions will be accelerated in the first half of the tandem in a charge state equilibrated in a foil stripper and then slowed down in the second half of the tandem in a charge state equilibrated in a gas atmosphere where the average charge is much lower than in a solid. One passage through the tandem results in a gain of energy of (Z _solid-Z _gas)·eU MeV. The gain expected for the acceleration of iodine ions will be of the order of 4 MeV for potentials at the high voltage electrode of about 1 MV. The application of many of these systems in line or the application of a magnet system bending the ions many times through the same electric field and stripper will allow to accelerate very heavy ions up to energies of about 1000 MeV. The transmission of this accelerator as a function of scattering, solid angle and final particle energy is estimated.     

On the phase transition in KH2PO4

The dynamical theory of the phase transition in KDP recently developed by Kobayashi (J. Phys. Soc. Japan24 (1968), 497) is modified by taking into account the interaction of the a-polarized transverse acoustic phonon both with the proton tunnelling mode and the transverse optic phonon polarized along thec-axis. The coupled modes of this three-component system are found in the paraelectric phase within the framework of the RPA approximation. The expressions for the sound velocity in the short-circuited (E = 0) crystal and the static susceptibility at constant stress are derived and well known thermodynamic formulae are obtained if the re-normalized elastic constantc ₆₆ ^P and the piezoelectric constanta ₃₆ are introduced. It is shown that these so-called true constants should in principle exhibit anomalies near the proton ordering temperature. Also the role of the depolarizing energy in the phase transition of KDP is discussed. The shift of the phase transition temperature of a small insulated particle of KDP is shown to be only a few degrees. Finally, it is explained why the domain structure of a short-circuited or insulated crystal should be essentially the same.The author thanks Dr. J. Fousek and Dr. V.Janovec of the Institute of Physics in Prague for many valuable discussions of this problem.     

Further studies in aesthetic field theory. II: Equations fore αi

In a previous paper (Muraskin, 1973), we obtained a bounded particle in aesthetic field theory. The field equations there are implied by a set of equations for a system of basis vector variables,e _i . In this paper, we propose a simpler set of field equations fore _i . We find that a bounded particle solution to the equations still appears (as determined by axes runs). The particle appears basically similar to the particle found previously.     

Field-induced particle pairing in an Ising system

We study the thermodynamic behavior of an Ising system on a Bethe lattice in which rearranging particles are decorating with their presence the bonds of the system, causing the local exchange coupling to depend on the decoration status. Such magnetic models have been proposed in efforts to understand the mechanisms responsible for the pairing of electrons in high-T_c superconductivity. In order to study in some detail this aspect, we focus on the question of conditions under which particle pairing occurs, and more specifically, on the role of an external magnetic field. We find a low-temperature region of the phase diagram where significant particle clustering occurs when the field is introduced.     

Fermion pair generation in isotropic cosmology

The generation of particles with a spin of 1/2 in a nonstationary gravitational field corresponding to the quasi-Euclidian Friedman model is considered. Particle generation probability and particle density are evaluated for both the present epoch and near the cosmological singularity. It is shown that the effect is most significant at t m^–1, where m is the particle mass.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 58–63, March, 1976.The author thanks A. A. Grib, V. M. Mostepanenko, and E. L. Silakov for their valuable advice.     

The Phase of a Quantum Mechanical Particle in Curved Spacetime

We investigate the quantum mechanical wave equations for free particles of spin 0, 1/2, 1 in the background of an arbitrary static gravitational field in order to explicitly determine if the phase of the wavefunction is S/ = p dx /, as is often quoted in the literature. We work in isotropic coordinates where the wave equations have a simple manageable form and do not make a weak gravitational field approximation. We interpret these wave equations in terms of a quantum mechanical particle moving in medium with a spatially varying effective index of refraction. Due to the first order spatial derivative structure of the Dirac equation in curved spacetime, only the spin 1/2 particle has exactly the quantum mechanical phase as indicated above. The second order spatial derivative structure of the spin 0 and spin 1 wave equations yield the above phase only to lowest order in . We develop a WKB approximation for the solution of the spin 0 and spin 1 wave equations and explore amplitude and phase corrections beyond the lowest order in . For the spin 1/2 particle we calculate the phase appropriate for neutrino flavor oscillations.     

Type-IV superconductivity: Cooper pairs with broken inversion and time-reversal symmetries in conventional superconductors

The vortex phase in a singlet superconductor in the absence of impurities is shown to be absolutely unstable with respect to the appearance of a triplet component that breaks both the inversion and time-reversal symmetries of Cooper pairs. The symmetry breaking paramagnetic effects are demonstrated to be of the order of unity if the orbital upper critical field, H_c2(0), is of the order of the Clogston paramagnetic limiting field, H_p. We suggest a generic phase diagram of such a type-IV superconductor that is a singlet one at H = 0 and characterized by a mixed singlet-triplet order parameter with broken time-reversal symmetry in the vortex phase. The possibility to observe type-IV superconductivity in clean organic, high-T_c, MgB₂, and other superconductors is discussed.     

Particle size effects on La0.7Ca0.3MnO3: size-induced changes of magnetic phase transition order and magnetocaloric study

The structure, magnetic properties, and magnetocaloric effect of La_0.7Ca_0.3MnO₃ ceramics with different particle sizes have been investigated. It is found that the Curie temperature increases first, and then decreases as particle size decreases and the type of magnetic phase transition changes from first-order to second-order, which may be attributed to surface pressure effects. The maximum magnetic entropy change and relative cooling power (RCP) show non-monotonic behaviors with decreasing the particle size. However, for the 3400 nm sample, the magnetic entropy change −ΔS_M reaches the maximum values of 6.41 and 8.63 J/kg K for the field changes of 2.0 and 4.5 T, respectively. Furthermore, the estimated large RCP values under lower magnetic fields in La_0.7Ca_0.3MnO₃ are comparable with those of typical magnetic refrigerant materials in the corresponding temperature range, suggesting those compounds might be promising candidates for magnetic refrigeration.     

Magnetic phase transitions of antiperovskite Mn3−xFexSnC (0.5≤x≤1.3)

The magnetization and electrical resistivity of Mn_3−xFe_xSnC (0.5≤x≤1.3) were measured to investigate the behavior of the complicated magnetic phase transitions and electronic transport properties from 5 to 300 K. The results obtained demonstrate that Fe doping at the Mn sites of Mn₃SnC induces a more complicated magnetic phase transition than that in its parent phase Mn₃SnC from a paramagnetic (PM) state to a ferrimagnetic (FI) state consisting of antiferromagnetic (AFM) and ferromagnetic (FM) components, while, with the change of Fe-doped content and magnetic field, there is a competition between the AFM component and FM component in the FI state. Both the Curie temperature (T_C) and the saturated magnetization M_s increase with increasing x. The FM component region becomes broader with further increasing Fe-doped content x. The external magnetic field easily creates a saturated FM state (and increased T_C) when . Fe doping quenches the negative thermal expansion (NTE) behavior from 200 to 250 K reported in Mn₃SnC.     

Alpha-decaying low-spin levels in155Lu and157Lu

Using an on-line mass separator, the -particle decays of¹⁵⁵Lu and¹⁵⁷Lu were investigated. A new -emitting level in¹⁵⁷Lu was identified [T_1/2=5.7(5) s,E =4924(20) keV]. In addition, a half-life of 140(20) ms was measured for the recently discovered second, low-lying, -decaying level [E =5579 (5)keV] in¹⁵⁵Lu.We wish to thank L.F. Archambault, R.B. Firestone, A.A. Shihab-Eldin, and A.A. Wydler for their contributions to this experimental program. We also express thanks to the staff of the SuperHILAC for providing smooth operation of the accelerator.     

Low-frequency instability of an inhomogeneous weakly ionized plasma in crossed electric and inhomogeneous magnetic fields

The paper discusses the drift dissipative instability that arises in a weakly ionized inhomogeneous plasma in crossed electric and magnetic fields. The potential perturbations are studied in the WKB (Wentzel-Krammers-Brillouin) approximation, i.e. for k = d lnn ₀/dx. The critical magnetic field, beyond the value of which the plasma is again stable against the studied perturbations, is computed. The effect of the inhomogeneity of the magnetic field modelled by a gravitational field is analyzed and the effect of a magnetic field, growing in the direction opposite to that of the plasma density, is pointed out. Under certain circumstances similar phenomena also arise in the current-convective instability.The author wishes to express his thanks to J. Václavík, K. Jungwirth and J. Preinhaelter for their stimulating discussions and comments.     

The effect of inelastic processes on theP 11 phase shift inπN scattering

Assuming that the nucleon is a bound state in the N system we derive the approximate formula for a phase shift in theP ₁₁ wave. The left-hand cut is approximated by two poles and the effect of inelastic processes on the scattering amplitude of the partial waveP ₁₁ is discussed in terms of Froissart's method. The values of the inelastic parameter are taken from the experimental data. In this way the agreement with the experimental values of the phase shift in theP ₁₁ wave for low energies can be obtained.The author thanks Dr. M. Petrá for a valuable discussion and Mr. M. Noga for a discussion of the calculations.     

Letter: Normal Forces in Stationary Spacetimes

For geodesic motion of a particle in a stationary spacetime the U ₀ component of particle 4-velocity is constant and is considered to be a conserved mechanical energy. We show that this concept of a conserved mechanical energy can be extended to particles that move under the influence of a normal force, a force that, in the stationary frame, is orthogonal to the motion of the particle. We illustrate the potential usefulness of the concept with a simple example.     

Surface-induced disordering at first-order transitions in body-centered cubic binary alloys: A Monte-Carlo simulation

Surface effects on the phase transition from theDO ₃ phase to the disordered phase are studied for a bcc Ising antiferromagnet with nearest and next-nearest neighbor exchange interactions in a magnetic field. This model can also be considered to represent binary alloys such as the FeAl-system; missing interactions near the surface translate then into surface magnetic fields. The change of the local magnetization near the surface then corresponds to surface enrichment of one component. For a plausible choice of parameters surface-induced disordering is found and the associated critical behavior is studied. Varying the bulk fieldH near the transition fieldH _c , we find that the thickness of the disordered layer increases proportional to ln(H-H _c ) while the local order parameter at the surface vanishes as (H-H _c )^1/2. These results are consistent with mean field predictions for the single order parameter case, although several ordering fields occur (sublattice magnetizations and magnetization).