Flip Probability Research Articles

Aging in 1D discrete spin models and equivalent systems.

We derive exact expressions for a number of aging functions that are scaling limits of nonequilibrium correlations, R(t(w),t(w)+t) as t(w)-->infinity, t/t(w)-->theta, in the 1D homogenous q-state Potts model for all q with T = 0 dynamics following a quench from T = infinity. One such quantity is <sigma-->(0)(t(w));sigma-->(n)(t(w)+t)> when n/square root of ([t(w))-->z. Exact, closed-form expressions are also obtained when an interlude of T = infinity dynamics occurs. Our derivations express the scaling limit via coalescing Brownian paths and a "Brownian space-time spanning tree," which also yields other aging functions, such as the persistence probability of no spin flip at 0 between t(w) and t(w)+t.

Magnetoresistance in single Fe(001) ultrathin films

Magnetoresistance in Au(001)-sandwiched Fe(001) ultrathin films was investigated at T=1.6 K. Effects of both the Fe layer and the Au cap layer were investigated using wedge-shaped Fe and Au cap layers. The total thicknesses of the films were kept much thinner than the mean free path of the conduction electrons in order to enhance the magnetoresistance by electron channeling between the surface and the substrate. The Fe wedge-shaped films in the range dFe=0–4 Å showed a granular-type giant magnetoresistance (GMR) because of a discontinuity in the Fe layer. The films with dFe=4–25 Å also showed that the GMR component through the Fe layer is continuous. In the Au cap wedge-shaped films, the GMR component nearly vanished at dAu cap=0. The MR ratio increased linearly with dAu cap in the range dAu cap=0–50 Å and saturated at dAu cap∼130 Å. Moreover, the CuO overlayer on the Au cap wedge-shaped film resulted in a 25% decrease in the MR ratio in the whole dAu cap range. These phenomena can be interpreted as differences in spin flip probability for electron reflections on the surface and at the interfaces.

Markov Chain Analysis of Single Spin Flip Ising Simulations

The Markov processes defined by random and loop-based schemes for single spin flip attempts in Monte Carlo simulations of the 2D Ising model are investigated, by explicitly constructing their transition matrices. Their analysis reveals that loops over all lattice sites using a Metropolis-type single spin flip probability often do not define ergodic Markov chains, and have distorted dynamical properties even if they are ergodic. The transition matrices also enable a comparison of the dynamics of random versus loop spin selection and Glauber versus Metropolis probabilities.

Peculiarities of the construction and application of a broadband adiabatic flipper of cold neutrons

An available mathematical model for calculation of a broadband adiabatic flipper for cold polarized neutrons is suggested. This model of the sine-cosine modulation of an effective field enables one to optimize and to simplify the calculation for constructing the flipper. A functional relation between spin flip probability and the main parameters of the device such as the length of the flipper, the neutron wavelength and both form and size of the magnetic fields have been found. Tests of flippers constructed on the base of this model has been successfully carried out.

Configurational kinetics for disorder-L12 transition studied by the path probability method

The path probability method of the non-equilibrium statistical mechanism is employed to study the configurational kinetics of the disorder-L12 transition. Spinodal ordering is examined from the standpoint of kinetics. The kinetic path traced in the thermodynamic configurational space deviates from the sleepest descent direction. Assuming a temperature dependent spin flip probability, the calculated aging kinetics exhibit qualitatively the behavior observed in resistivity measurements.

Optical addressing and switching of water molecules in hole-burning systems: a TLS model system

Light-induced spectral diffusion in photochemical hole-burning systems is investigated with respect to its dependence on the frequency of the irradiated infrared light in the wavelength range between 2 μm and 11 μm. The investigated system is polymethylmethacrylate (PMMA) doped with free-base phthalocyanine (H 2Pc). Different resonant contributions to the infrared-induced spectral diffusion show that reorientation of H 2O molecules is the microscopic origin of the observed diffusion process. Within a simple kinetic model based on the idea of two possible sites for each H 2O molecule, the dependence of the hole broadening on infrared intensity and illumination time can be very welldescribed in a quantitative fashion. The most surprising result is a flip probability of 52% for one individual H 2O molecule per excitation process.

Nonlinear global and local document degradation models

AbstractTwo sources of document degradation are modeled: (1) perspective distortion that occurs while photocopying or scanning thick, bound documents; and (2) degradation due to perturbation in the optical scanning and digitization process: speckle, blurr, jitter, and threshold. Perspective distortion is modeled by studying the underlying perspective geometry of the optical system of photocopiers and scanners. An illumination model is described to account for the nonlinear intensity change occurring across a page in a perspective‐distorted document. The optical distortion process is modeled morphologically. First, a distance transform on the foreground is performed; this is followed by a random inversion of binary pixels in which the probability of flip is a function of the distance of the pixel to the boundary of the foreground. Correlating the flipped pixels is modeled by a morphological closing operation.©1994 John Wiley &amp; Sons Inc

Spin flip probabilities in the 3-D diluted Ising model

According to Ray and Jan the cluster development in a spin glass can be described by calculating spin flip probabilities and by association of rarely flipping spins. We show that for the pure ferromagnetic Ising model the predicted Ray-Jan percolation transition temperature does not agree with the phase transition of the Ising system. Both diluted and undiluted Ising model show critical percolation spin flipping rates bigger that the Ray-Jan values

Method of constrained global optimization.

We present a new method for optimization: constrained global optimization (CGO). CGO iteratively uses a Glauber spin flip probability and the Metropolis algorithm. The spin flip probability allows changing only the values of variables contributing excessively to the function to be minimized. We illustrate CGO with two problems---Thomson's problem of finding the minimum-energy configuration of unit charges on a spherical surface, and a problem of assigning offices---for which CGO finds better minima than other methods. We think CGO will apply to a wide class of optimization problems.

Superconducting Proximity Effect in Cu Clad Nb Wires Doped with Mn, Fe, Co and Ni

The proximity effect in Cu clad Nb wires of which Cu is doped with dilute magnetic impurities, has first been investigated in relation to the Kondo effect. As for Cu doped with dilute Fe, Co and Ni impurities, the probability of the spin flip scattering of conduction electrons, α, by Fe, Co and Ni impurities decreases linearly with decreasing temperature. As for Cu doped with dilute Mn impurities, the probability, α, by Mn impurities is concluded to be suppressed by the RKKY interaction between Mn impurities which depends on the electronic mean free path. The temperature dependence of the resistivity of the Mn alloy may be understood as a result of the coexistence of the dilute Kondo effect and the RKKY interaction between Mn impurities.

The Implication of Kamiokande-II Sun Neutrino Data

The cross section of solar neutrino scattering involving the contribution of neutrino magnetic moment (NMM) is investigated. The constraints on the probability of flip of neutrino helicity and the possible value of NMM are extracted from the Kamiokande-II solar neutrino data and calculated cross section of , scattering. It is found that the probability of neutrino helicity flip allowed by the Kamiokande-II data may be small, which would be difficult to understand the data.

Superconducting Proximity Effect in Cu-Clad Nb Wires Doped with Fe, Co and Ni

The proximity effect in Cu clad Nb wires of which Cu is doped with dilute magnetic impurities, has first been investigated in relation to the Kondo effect. As for Cu doped with dilute Fe, Co and Ni impurities, the probability of the spin flip scattering of conduction electrons, α, by Fe, Co and Ni impurities decreases linearly with decreasing temperature. As for Cu doped with dilute Mn impurities, the probability, α, by Mn impurities is concluded to be suppressed by the RKKY interaction between Mn impurities which depends on the electronic mean free path. The temperature dependence of the resistivity of the Mn alloy may be understood as a result of the coexistence of the dilute Kondo effect and the RKKY interaction between Mn impurities.

On the use of a gradient resonance neutron spin flipper

A realization of a gradient resonance spin flipper for cold neutrons on an uninterrupted neutron guide is described. Measurements of the spin flip probability are reported. The device is part of an in-beamβ-NMR spectrometer, working in the external neutron guide laboratory at the research reactor FRJ-2, KFA-Jülich.

Correlations between two ising chains subjected to a common thermal noise

We study analytically two copies s and s′ of a one-dimensional Ising chain subjected to a common thermal noise for a special choice of the spin flip probabilities. The combined system ( s, s′) goes to an equilibrium with an unknown Hamiltonian H 2(s, s′) . We show by explicit calculation that in the equilibrium state the interchain correlations < s i s′ i s j s′ k > eq decay in space according to a sum of two or three exponentials plus an integral on a continuum of decay lengths. We conclude from this that H 2(s, s′) cannot be of strictly finite range. The approach to equilibrium is also discussed.

Gamow–Teller strength functions from scattering experiments

We present here recent [Formula: see text] results from TRIUMF that are relevant to the determination of spin-flip isovector strength functions in nuclei. Distortion factors needed for the extraction of nuclear-structure information have been deduced from cross sections and analyzing powers in elastic scattering for several energies and targets. Nonrelativistic optical potentials obtained by folding effective nucleon (N)–nucleus interactions with nuclear densities are found to overpredict both elastic and reaction cross sections, whereas Dirac calculations that include Pauli blocking are in good agreement with the data. Spin observables (Snn and Ay) for the quasi-elastic region in 54Fe[Formula: see text] at 290 MeV provide some evidence for the reduction of the effective proton mass predicted in relativistic mean-field theories as a consequence of the attractive scalar field in the nuclear medium. The energy dependence of the effective N–nucleus interaction at small momentum transfers has been investigated using isoscalar and isovector 1+ states in 28Si as probe states. We find that the cross sections for the isovector transitions are in good agreement with predictions for the dominant Vστ part of the Franey–Love interaction. Gamow–Teller (GT) strength functions have been obtained in 24Mg and 54Fe from measurements of both cross sections and spin–flip probabilities Snn. The spin-flip cross sections σSnn are particularly useful in heavier nuclei to discriminate against a continuous background of ΔS = 0 excitations. In the (s, d) shell where full shell-model wave functions are available, the GT quenching factors [Formula: see text] are in good agreement with those from recent (p, n) and (n, p) experiments. We show that a state-by-state comparison of (p, p′) and (e, e′) results has the potential of identifying pionic current contributions in (e, e′). The GT quenching factors in 54Fe are smaller than in the (s, d) shell probably because of severely truncated shell-model wave functions, particularly those of the nuclear ground state.

An examination of the contributions to electron-spin scattering processes in aluminium

In an endeavour to understand the various contributions to the spin scattering of conduction electrons in aluminium, the conduction-electron spin resonance linewidths of polycrystalline, pure and dilute alloy foils of aluminium have been measured in reflection at 42.5 MHz, 9.27 GHz and 20.9 GHz, over the temperature range 4.2-100K. From these linewidths the phonon spin scattering contribution at 42.5 MHz and 9.27 GHz is obtained and is found to be proportional to the phonon contribution to the resistivity scattering. At 42.5 MHz and below 25K a temperature dependence proportional to T2 is recorded, indicative of an electron-electron scattering process. The probability of a spin flip when an electron collides with the surface is also calculated from measurements of the linewidth at 42.5 MHz, and is found to agree with earlier measurements. At higher frequencies there are other contributions to the linewidth which may be attributed either to the complex Fermi surface of aluminium or to the breakdown of motional narrowing by the conduction electrons of the g anisotropy over the Fermi surface. In pure samples, one contribution is found at low temperatures and is linearly dependent on both the observational frequency and the resistivity scattering time. A second contribution, which is also linearly dependent on the frequency but independent of temperature, is reported as well. Finally, at the highest frequencies used or at high impurity levels an extra contribution to the temperature dependence is found, which is evident even at temperatures as high as 100K where motional narrowing is expected to be complete.

Analyzing Power-Polarization Inequality in the Inelastic Scattering of Protons on 12C for Incident Energies from 22.0 to 29.0 MeV

The difference between the analyzing power (A) and polarization (P) in the inelastic scattering of protons on 12 C (4.44 MeV 2 + state) are determined by measuring the spin flip probability of polarized protons at intervals of incident energy of about 0.5 MeV at lab. scattering angles of 45°, 60°, 75°, 105°, 120°, 135° and 150°. The spin flip asymmetry (SFA), spin flip probability (SF) and A are also measured. The angular distributions of SF, SFA, A, (A-P) and partial differential cross sections are investigated at 24.1, 26.2 and 28.7 MeV at intervals of lab. angle of 7.5° or 15°. The (A-P) and SFA show pronounced interferencelike energy dependence and the (A-P) has large values of more than 50% at 135° and 150° for 26.2 MeV. The measurement was done by using the (p, p'γ) coindidence technique developed by Schmidt.

Simulation of Cosmic Ray-Induced Soft Errors in CMOS/SOS Memories

A follow-up series of simulation experiments have been conducted to study cosmic ray-induced soft errors in CMOS/SOS memories. Devices were tested in beams of krypton and argon ions from the Lawrence Berkeley Laboratory (LBL) 88-inch Cyclotron at energies near 2 MeV/nucleon. The SOS test samples consisted of three versions of the TCS 146, 4K, static memory, constructed with buried contact technology. Small differences in processing have a significant effect on the electrical parameters, and these were observed to correlate with the sensitivity to cosmic ray-induced errors of the three versions. Differences in the probability of flips from 0 → 1 and 1 → 0 were observed. These differences are explained in terms of the geometrical details of the memory storage element and the nodal capacitances of the element. The predicted error rate in space was calculated to be 2.6×10-9 errors/ day-bit based on the observed critical charge for soft error failure.

ReactionCd114(p,p′) by use of polarized protons and proton-γangular correlations

The reactions $^{114}\mathrm{Cd}$($p$,${p}^{\ensuremath{'}}$) and $^{114}\mathrm{Cd}$($p$,${p}^{\ensuremath{'}}\ensuremath{\gamma}$) have been studied for polarized and unpolarized protons at a bombarding energy of 11 MeV. Differential and double differential cross sections as well as analyzing powers, correlation asymmetries, and the spin flip probability have been measured by use of a multidetector arrangement consisting of 11 silicon surface barrier detectors and two Ge(Li) detectors. The experimental data have been analyzed in terms of coupled channels on the basis of a harmonic vibrator and a rigid symmetric rotator model. The correlation data are found to be more sensitive to the models used and the sign of the quadrupole deformation than differential cross sections and analyzing powers. Considering the correlation data, the rotator model with oblate deformation must be ruled out for $^{114}\mathrm{Cd}$. The best description of the experiment is obtained by the harmonic vibrator model. Compound nucleus contributions can be neglected.

Surface relaxation effects in conduction-electron spin-resonance transmission

Theoretical line shapes are calculated for conduction-electron spin-resonance transmission, including the effects of surface relaxation, in the regime of completely damped spin waves. Surface relaxation is introduced via the boundary condition $\stackrel{^}{n}\ifmmode\cdot\else\textperiodcentered\fi{}\ensuremath{\nabla}\stackrel{\ensuremath{\rightarrow}}{\mathrm{M}}=(\frac{3\ensuremath{\epsilon}}{4\ensuremath{\Lambda}})\stackrel{\ensuremath{\rightarrow}}{\mathrm{M}}$, where $\ensuremath{\epsilon}$ is the probability of a spin flip in a surface collision and $\ensuremath{\Lambda}$ is the mean free path. For specimens of thickness $d$ large compared with the spin diffusion length ${\ensuremath{\delta}}_{s}^{*}\ensuremath{\equiv}{(2{D}^{*}{T}_{2}^{*})}^{\frac{1}{2}}$, the on-resonance intensity as a function of specimen thickness if found to vary as ${e}^{\ensuremath{-}\frac{\ensuremath{\surd}2d}{{\ensuremath{\delta}}_{s}^{*}}}$, independent of surface relaxation. Line-shape expressions are given for several limiting cases of experimental interest.