Distortions of the statistical distribution of Barkhausen noise measured by magneto-optical Kerr effect

In magneto-optical Kerr measurements of the Barkhausen noise, a magnetization jump ΔM due to a domain reversal produces a variation ΔI of the intensity of a laser beam reflected by the sample, which is the physical quantity actually measured. Due to the non-uniform beam intensity profile, the magnitude of ΔI depends both on ΔM and on its position on the laser spot. This could distort the statistical distribution p(ΔI) of the measured ΔI with respect to the true distribution p(ΔM) of the magnetization jumps ΔM. In this work the exact relationship between the two distributions is derived in a general form, which will be applied to some possible beam profiles. It will be shown that in most cases the usual Gaussian beam produces a negligible statistical distortion. Moreover, for small ΔI the noise of the experimental setup can also distort the statistical distribution p(ΔI), by erroneously rejecting small ΔI as noise. This effect has been calculated for white noise, and it will be shown that it is relatively small but not totally negligible as the measured ΔI approaches the detection limit.     

Analysis of the active region of overheating temperature in green LEDs based on Group III nitrides

For the first time, the overheating temperature ΔT _p-n of the active region in green light-emitting diodes based on Group III nitrides has been determined as a function of the forward current amplitude I. It has been shown that in contrast to light-emitting diodes, in which the current-voltage characteristics are adequately described by known theories of rectification in p-n junctions and ΔT _p-n ∝ I, in the structures under study, the dependence ΔT _p-n (I) in the current range of 2×10^?3?3×10^?2 A is quadratic in current. At higher currents, the variation of ΔT _p-n with I in the green light-emitting diodes based on Group III nitrides becomes linear, which is the same as in the light-emitting diodes based on known infrared and red III-V structures.     

Problems associated with stark effect in F-center emission

In this paper, we examine some of the basic data on the Stark effect in F-center emission at very low temperatures, namely the ΔI/Is. Usually, these quantities are only used to calculate the polarization. The ΔI/Is have additional information, however, as this analysis indicates. One way to understand these ratios is to consider the nonradiative transition probability and specifically, the effect of the field on this quantity.     

Influence of uniaxial stress on the Mössbauer spectrum of α-iron

The Mössbauer spectrum of a 20 μm rolled foil of α-iron has been studied as a function of an applied tensile stress. A constant velocity spectrometer was used in transmission geometry. A method involving three-point observations on single lines combined with chopping between two absorbers was used to minimize and evaluate effects of drift. Line displacements amount to approximately one percent of the line width and vary reversibly and linearly with stress. They can be interpreted in terms of changes in isomer shift ΔI, magnetic splitting ΔH and quadrupole shift ΔQ. Comparison with data from hydrostatic pressure experiments indicate that ΔI and ΔH are mainly influenced by volume changes. Observed variations in the area ratio of lines 6 and 5 amount to a few percent and reflect that changes in the magnetization direction are caused by stress. The complicated, irreversible behaviour is interpreted in terms of magnetization rotation and domain wall motion.     

Identification of hyperfine structure components of the iodine molecule at 640 nm wavelength

The frequencies and the relative intensities of rotation-vibration transitions of ¹²⁷I₂, ¹²⁹I₂ and ¹²⁷I¹²⁹I near the HeNe laser emission wavelength of 640 nm have been calculated. Interpolation formulas for the differences of the electric quadrupole constants ΔeQq and of the spin-rotation constants ΔC of ¹²⁷I₂ are given. Most of the weak saturated-aborption lines, elsewhere published, have been identified as cross-over and forbidden lines of the transitions P(10)8-5 and R(16)8-5.     

Moments of inertia of neutron stars in relativistic mean field theory: The role of the isovector scalar channel

With the inclusion of the isovector scalar channel in the meson-nucleon couplings, taking DD-MEδ as an effective interaction, the moments of inertia of neutron stars possessing various stellar masses are studied within the density dependent relativistic mean field(RMF) theory. The isovector scalar channel contributes to the softening of the neutron-star matter equation of state(EOS)and therefore the reduction of the maximum mass and radius of neutron stars. Smaller values of the total moment of inertia I and the crustal moment of inertia ?I are then obtained in DD-MEδ via numerical procedure in comparison with those in other selected RMF functionals. In addition, the involvement of the isovector scalar channel lowers the thickness of the neutron star crust and its mass fraction as well. The sensitivity to both the crustal mass and stellar radius causes the crustal moment of inertia to be more obviously reduced than the total one, eventually leading to a suppression on the fraction of crustal moment of inertia?I/I in DD-MEδ. The results indicate the crustal moment of inertia as a more sensitive probe of the neutron-star matter EOS than the total one, and demonstrate that the isovector scalar meson-nucleon couplings in the RMF theory could exert influence over the physics of pulsar glitches.     

Ω− non-leptonic decays

Non-leptonic decay rates for Ω^? are calculated in a model where strong interactions introduce new ΔI = 1/2 operators in the effective hamiltonian. Both Ω^?→Ξ^0,?π^?,0 and Ω^?→Λ⁰K^? are predicted to be nearly parity conserving. ΔI = 1/2 contributions are found to dominate the sum of the pionic rates, while ΔI = 3/2 contributions are non-negligible in each of them. Rough agreement in magnitude with experimental data is obtained.     

Positron annihilation studies on molybdenum irradiated with neutrons at temperatures from 350° C to 1000° C

We performed measurements of positron lifetimes and the lineshape parameter on molybdenum samples irradiated with neutrons at temperatures from 350° to 1000° C. The results show that the correlation between swelling and positron characteristics depends strongly on irradiation temperature. From 350° to 500° C, ΔS, and notI ₂, correlates with sweelling; from 500° to 800° C, both ΔS andI ₂ correlate with swelling; and at higher temperatures, none of them correlates with swelling.     

Bounds on theK-Π matrix elements

Using Machet's method, we derive bounds on theK-Π matrix elements. Our bounds on matrix elements with left-left operators show that quark model calculations always overestimate these matrix elements. In all cases the vacuum insertion method gives an upper bound. No conclusive indication of an enhancement of the penguin matrix element is observed. Its contribution to the ΔI=1/2 amplitude could possibly be destructive and would rule out the penguins as an explanation to the ΔI=1/2 rule.     

Analysis ofK→3Π decays in chiral perturbation theory

Using the recently proposed higher-order chiral Lagrangians determined from the integration of nontopological chiral anomalies, we calculate corrections to the current-algebra analysis ofK→3Π decay amplitudes expanded in powers of the Dalitz variables. Effects of quartic-derivative weak chiral Lagrangians are determined through the use of short-distance effective weak Hamiltonian and the factorization method. We find that (1) the constant and linear terms in the amplitude for ΔI=1/2K→3Π are in excellent agreement with experiment; the previous discrepancy of (20–35)% between current algebra and data is thus accounted for by the higher-order effective Lagrangians, (2) the penguin interaction does not play an essential role in the ΔI=1/2 rule, for otherwise it will lead to a large disagreement for the constant and linear terms, (3) one of the two quadratic terms in the ΔI=1/2 process, which arise from the quartic chiral Lagrangians, is in accord with data within experimental errors, while the other is off by four standard deviations, (4) the linear term in the ΔI=3/2 transitions is in good agreement with experiment and contributions from quadratic terms are sizable.     

Excess current in contacts based on magnesium diboride

The excess current I _exc in In/MgB₂ and Pb/MgB₂ contacts was investigated as a function of the energy gaps Δ_σ and Δ_π in magnesium diboride MgB₂. It was shown that, even in the “dirty” limit, electrons from the σ and π bands do not undergo mixing; i.e., they remain confined to their bands over a long period of time. On this basis, the measurements of the excess current I _exc for contacts prepared in different crystallographic directions of the MgB₂ crystals made it possible to determine the energy gaps Δ_π ≈ 3.0 meV and Δ_σ = 7.5 meV.     

Study of Three-Quasiparticle Band in 83 Kr

Excited states of ⁸³Kr, populated in the ⁷⁶Ge(¹¹B, 3npγ) reaction at a beam energy of 50 MeV, have been studied. The ΔI?=?1 band, built upon the 2,510.0 keV state, has been observed up to 5,639.4 keV with spin (27/2^???). Mean lifetimes have been measured up to spin 23/2^?? in ΔI?=?1 band using the Doppler shift attenuation method. The B(M1) rates derived from the measured lifetimes decrease smoothly with spin indicating that the angular momentum belonging to this band are generated by the shears mechanism.     

Bound s-state energies for the exponential cosine screened Coulomb potential in Ecker-Weizel approximations

Bound s-state energies of an electron in the exponential cosine screened Coulomb potential, V(r) = ?e²e^?δrcos(δr)/r, are obtained analytically using the Ecker-Weizel approximation. For reasonable values of the screening parameter δ, the predicted results are in excellent agreement with the variational calculation of Lam and Varshni. The effect of screening on the shift of the quantum numbers from their normal values is also studied for various s-states.     

On the energy levels for the screened Coulomb potentialV(r)=−Z/r+Gλ/(1+λr)

The energy eigenvalues of various eigenstates for the potentialV(r)=?Z/r+Gλ/(1+λr) are accurately evaluated within the framework of the hypervirial-Padé scheme. An approximate formula for energy levels is also obtained with the use of the Ecker-Weizel approximation. The results of the present calculations are compared with those of a dispersion calculation.     

Multilayer relaxation of the Mg(0001) surface

We have Investigated the interplanar relaxation of the clean (0001)-(1 × 1) surface of magnesium at 100 K using a dynamical LEED I-V analysis. In contrast to almost all other metal surfaces, an expansion has been observed for the first interlayer spacing of this clean surface. Using an extended database, the results indicate that the first three interlayer spacings are relaxed from the bulk value by Δd₁₂ = +1.9 ± 0.3%, Δd₂₃ = +0.8 ± 0.4%, and Δd₃₄ = −0.4 ± 0.5%. A comparison of this observed multi relaxation with experimental and theoretical results for similar free-electron closepacked metal surfaces, e.g. Al(111), suggests that a surface expansion is a normal property of high electron density simple metals.     

Temperature dependence of azimuthal X-ray Photoelectron Diffraction (XPD) from Cu2p32 core level of Cu(001): Experiment and single scattering cluster calculations

The temperature dependence of X-ray photoelectron diffraction (XPD) affects in azimuthal distributions of $\text{Cu}\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core level intensities from a clean copper (001) single crystal has been measured in the range from ambient to 1010 K and for polar angles of emission relative to the surface of θ = 7° (corresponding to very high surface sensitivity) and θ = 45°. The XPD anisotropy ΔI/I_max at θ = 7° shows a decrease of 42.5% between ambient temperature and 1010 K while that for θ = 45° shows a 22.7% decrease over the same temperature range. Single scattering cluster calculations including Debye-Waller factors very well predict the variation of anisotropy with temperature at θ = 7°, while at θ = 45° theory significantly underestimates the decrease in ΔI/I_max, probably due to multiple scattering effects. The effective surface Debye temperature of 202 K deduced from theory and experiment for θ = 7° agrees well with prior determinations. The 7° XPD data give no evidence for surface melting effects on Cu(001) at temperatures up to T/T_melting = 0.74.     

The chiral-bag model andK→2π decays

Nonleptonic kaon decays (K→2π) have been analyzed using the chrial-bag model. This continues the research of nonleptonic decays by the authors (Ref. [7] below). The results obtained are in qualitative agreement with those based on QCD-duality. the decay amplitudeA(K ⁺→π⁺π⁰) (ΔI=3/2) can be explained while the ΔI=1/2 decay amplitudes are 4 to 5 times smaller then the observed values. The ratio ofK ⁰ decay amplitudes ξ=|A(K ⁰→π⁺π^?)/A(K ⁰→π⁰π⁰| is larger than one, as it is experimentally. This is an improvement in comparison with MIT-bag model, where ζ was always smaller than one, even if ΔI=1/2 pieces in the theoretical expressions were enhanced.     

On the influence of reactive gases on sputtering and secondary ion emission

As a continuation of earlier sputtering yield measurements in an ion microprobe, the influence of oxygen and nitrogen on sputtering yield, ionisation efficiency and depth resolutions has been studied. For inert gas bombardment the yield of Ti and V falls sharply at a certain oxygen exposure. While this decrease in yield can be correlated with an increase in surface binding energy in the case of titanium, cone formation causes the yield to drop for oxygen exposed vanadium. In contrast, during nitrogen bombardment the only effect of oxygen exposure is a drastic increase of the ionisation efficiency; the sputtering yield or the depth resolution Δz/z is hardly influenced by oxygen coverage. As was observed earlier in the case of Cu?Ni layers, Δz is essentially constant for erosion depthsz?800 Å, thus yielding better resolution at large depths than is to beexpected from a sequential layer removal model. The extent of the transition zone Δz, is determined by surface topography and thus depends on the target composition as well as its structure.