Analysis of Effect of Chromatic Dispersion for Wavelength Tunable Ultrashort Soliton Pulse Generation

The performance characteristics of generated soliton and anti-Stokes pulses for the wavelength tunable ultrashort soliton pulse generation system are discussed for different fiber dispersion parameters of β₂ and β₃ at the pump wavelength. Numerical analysis showed that the broadband wavelength tunability is improved as both the absolute value of negative β₂ and the value of β₃ are decreased. When β₃ is the usual value, the best performance of broadband continuous wavelength tunability which broadens symmetrically to the pump wavelength is obtained for β₃ of around 蜢2 psβ²/km. The reason for this is that the behaviors of both the generated soliton and anti-Stokes pulses are due to the β₂. Through simulations for different fiber dispersion parameters of β₂ or β₃ we obtained interesting results. When β₃ is negative and the zero dispersion wavelength is set at the longer wavelength side than the pump wavelength, such as around 2 μm, it is possible to convert the generated soliton into new components at the longer wavelength side over 2 μm.     

Measurement of the proton spin polarizabilities at MAMI

The spin polarizabilities of the nucleon are fundamental structure constants which describe the response of the nucleon spin to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is the Compton scattering with polarization degrees of freedom. Three Compton scattering asymmetries on the proton were measured in the Δ(1232) region using a polarized incident photon beam and a polarized (or unpolarized) proton target at the Mainz Microtron (MAMI). These asymmetries are sensitive to values of the spin polarizabilities. Fits to asymmetry data were performed using a dispersion model calculation, and a separation of all four proton spin-polarizabilities in the multipole basis was achieved. The values of the proton spin polarizabilities are presented.     

Casimir Force on a Dielectric Cylinder

The Casimir surface force density on a compact material cylinder of radius a is calculated, at zero temperature. A Green function approach is followed. The general theory is formulated so as to hold for arbitrary permittivities ε(ω) and permeabilities μ(ω), whereas when it comes to explicit calculations the condition ε(ω) μ(ω) = 1 is assumed to hold. A simple dispersion relation is chosen, implying a high frequency cutoff ω₀. The theory yet diverges, at high angular momenta. Divergences of this sort usually appear whenever there are curved boundaries present. On physical grounds an angular momentum cutoff m₀ can be introduced, being of order ω₀a. A semi-quantitative calculation of the force thereby becomes possible. The calculated force is attractive.     

Triple differential cross-section for the ionization of H<Superscript>-</Superscript> at low energies

The triple differential cross-sections (TDCS) for the ionization of H^- at excess energies of 8, 10 and 12 eV are calculated using distorted-wave Born approximation in the equal energy sharing and θ_ab=180^○ kinematics. The final state electron-electron correlation is included through effective charges and exchange distortion in semi-classical local approximation. The spin state of the exchanging electrons is taken care of. The angular distribution of the TDCS is very different from the case of helium and is found to show peaks at θ_a≈30^○ and 150^○. The capture process is found to contribute quite significantly around θ_a = 90^○ and is supported by the PCI.     

Spin polarizability of hyperons

We review the recent progress of the theoretical understanding of spin polarizabilities of the hyperon in the framework of SU(3) heavy baryon chiral perturbation theory (HBChPT). We present the results of a systematic leading-order calculation of hyperon Compton scattering and extract the forward spin polarizability (γ ₀) of hyperons. The results obtained for γ ₀ in the case of nucleons agree with the known results of SU(2) HBChPT when kaon loops are not considered.     

Reentrant transitions in the van Hemmen model of a spin glass

The van Hemmen model of a spin glass, which is an Ising model with random couplings J_ij between sites i and j equal to J₀ + J(ξ_iη_j + ξ_jη_i), where (ξ_i, η_i) are independent, identically distributed random variables, is studied in the pair approximation of the cluster variation method. For the family of probability distributions (1 − p)δ(ξ_i − a) + pδ(ξ_i) + (1 − p)δ(ξ_i + a), where p is varied, phase diagrams are constructed. They are qualitatively different from the mean-field phase diagrams and display a competition between tendencies towards spin-glass and towards ferromagnetic ordering, which results in reentrant transitions. It is argued that the observed effects are not accidental but are borne by the competition of bonds of the underlying lattice system.     

Enhancement of MR ratios using thin oxide layers in PtMn and α-Fe2O3-based spin valves

Spin valves having thin oxide layers in the pinned and/or free layers were prepared by sputtering. MR ratios of the spin valves were increased from 8.1 to 11.9% by inserting the oxide layer into the pinned layer in Ta/PtMn/CoFe/Cu/CoFe/Ta spin valves. MR ratio of 13.9% and considerably large sheet ΔR of 2.55 Ω were obtained in the PtMn-based spin valves having the oxide layer in the pinned and free layer. Larger MR ratio of 17.3% and the sheet ΔR of 1.3 Ω were obtained in the PtMn-based dual-type spin valves having the oxide layer in both pinned layers. α-Fe₂O₃ based spin valves having thin oxide layers were also prepared. MR ratios of the spin valves were increased from 11.9 to 14.3% by inserting the oxide layer into the free layer in α-Fe₂O₃/CoFe/Cu/CoFe/Ta spin valves. The enhancement of the MR ratios may be attributed to the specular scattering effect of the conduction electrons by the thin oxide layers.     

Properties of the πη,$ \eta{^\prime}$,σ, f0(980) and a0(980) mesons and their relevance for the polarizabilities of the nucleon

The signs and values of the two-photon couplings F _Mγγ of mesons (M) and their couplings g_MNN to the nucleon as entering into the t -channel parts of the difference of the electromagnetic polarizabilities (α - β) and the backward angle spin polarizabilities γ_π are determined. The excellent agreement achieved with the experimental polarizabilities of the proton makes it possible to make reliable predictions for the neutron. The results obtained are α_n = 13.4±1.0 , β_n = 1.8±1.0 (10^-4fm^3), and γ⁽ⁿ⁾ _π = 57.6±1.8 (10^-4fm^4). New empirical information on the flavor wave functions of the f ₀(980) - and the a ₀(980) -meson is obtained.     

Highlights and perspectives of the JLab spin physics program

Nucleon spin structure has been an active, exciting and intriguing subject of interest for the last three decades. Recent precision spin-structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure in the valence quark (high-x) region and improved our understanding of higher-twist effects, spin sum rules and quark-hadron duality. First, results of spin sum rules and polarizabilities in the low to intermediate Q ² region are presented. Comparison with theoretical calculations, in particular with Chiral Perturbation Theory (ChPT) calculations, are discussed. Surprising disagreements of ChPT calculations with experimental results on the generalized spin polarizability, δ _LT, were found. Then, precision measurements of the spin asymmetry, A ₁, in the high-x region are presented. They provide crucial input for global fits to world data to extract polarized parton distribution functions. The up and down quark spin distributions in the nucleon were extracted. The results for Δd/d disagree with the leading-order pQCD prediction assuming hadron helicity conservation. Results of precision measurements of the g ₂ structure function to study higher-twist effects are presented. The data indicate a significant higher-twist (twist-3 or higher) effect. The second moment of the spin structure functions and the twist-3 matrix element d ₂ results were extracted. The high Q ² result was compared with a Lattice QCD calculation. Results on the resonance spin-structure functions in the intermediate Q ² range are presented, which, in combination with DIS data, enable a detailed study of quark-hadron duality in spin-structure functions. Finally, an experiment to study neutron transversity and transverse spin asymmetries is discussed. A future plan with the 12 GeV energy upgrade at JLab is briefly outlined.     

Atomic C 6 dispersion coefficients: a four-component relativistic Kohn–Sham study

We present C ₆ homo- and heteroatomic dispersion coefficients for all closed-shell atoms of the periodic table based on dipole–dipole polarizabilities at imaginary frequencies calculated using our recent extension of the complex polarization propagator approach to the four-component relativistic Kohn–Sham approach. Lack of proper reference data bars definite conclusions as to which density functional shows the overall best performance, and we therefore call for state-of-the-art wave function-based correlated calculations of dispersion coefficients. Scalar relativistic effects are significant already for elements as light as zinc, whereas spin–orbit effects must be taken into account only for very heavy elements.     

Magnetocrystalline symmetry, spin statics and dynamics in high-temperature superconductors

The symmetry analysis of the magnetic structures of La₂CuO₄ and YBa₂Cu₃O_6+δ (δ 0.4) antiferromagnetic oxide has been carried out. The spin configurations and spin-reorientation transition fields have been found. The frequencies of uniform spin oscillations and the external field dependence of their polarization properties have been calculated. It has been shown that the spin excitation branches may include exchange modes among which some dipole-active modes can be present. The spectrum of the inelastic light scattering accompanied with the excitation of spin and libration (tilting) freedom degrees has been discussed.     

Magnetische untersuchungen an mischkristallen der quasibinären legierungssysteme (Cd Te)1-x (Mn Te)x und (Sn Te)1-x (Mn Te)x

The magnetic susceptibility and magnetization are presented for polycrystalline samples of the alloy systems Cd_1-xMn_xTe 0 < x 0.1 and Sn_1-xMn_xTe 0 < 4 0.4. The magnetic measurements were performed between 2.3 K and 300 K in external magnetic fields up to 11 kOe. At sufficiently high temperatures the susceptibility can be described by a Curie-Weiss law. In the system Sn_1-xMn_xTe θ_p is positive. A linear dependence θ_p ∞ x was found with θ_p(0.4) = 49 K. In the series Cd_1-xMn_xTe θ_p changes sign. For θ < x < 0.04 θ_p is positive with a maximum θ_p ≈ 10 K at x = 0.02. In the region x #62; 0.04 θ_p becomes negative with θ_p = -35 K at x = 0.1. The effective spin value of manganese is S_eff #62; 5/2 for all the samples. The investigation was done to check the assumption that ferromagnetic coupling may exist in tellurides of manganese if the shortest distance d_MnMn is greater than 3.4 Å. This hypothesis has been stated. In the case θ_p #62; 0 the results are partly explained by the RKKY exchange coupling.     

Spin-dependent magnetotransport through one or more rings in the presence of the Rashba and Dresselhaus terms of the spin–orbit interaction

Magnetotransport through one or several quasi-one-dimensional rings, in the presence of the Rashba (RSOI) and Dresselhaus (DSOI) terms of the spin–orbit interaction (SOI) and of a magnetic field B, is investigated. The RSOI field and an effective DSOI field are taken as E_R=E_R(sinγ₁e_r+cosγ₁e_z) and E_D=E_D(sinγ₂e_r+cosγ₂e_z), their strengths are denoted by α and β, respectively. The exact one-electron eigenvalues and eigenfunctions are obtained and used to evaluate the transmission as a function of α, β, and of the angles γ₁,γ₂. Because the RSOI term couples the electronic orbit (along the θ direction) with the Pauli matrices σ_z and σ_r while the DSOI term couples it with σ_θ, they affect the electronic spin transport through a ring in distinctly different ways. The resulting transmission shows a considerable structure as a function of the angles γ₁ or γ₂. The same holds for the transmission, versus α or β, with the SOI present only in one arm of the ring and for that through two rings with the same or different radii. Various results of the literature, valid for β=0, are readily recovered. For weak magnetic fields the influence of the Zeeman term on the transmission, assessed by perturbation theory, is negligible.     

Spin fluctuations in the skutterudite compound LaFe<Subscript>4</Subscript>Sb<Subscript>12</Subscript>

We report transport, magnetic and thermodynamic properties of the skutterudite compound LaFe₄Sb₁₂. The basic features are a large magnetic susceptibility χ(T), and large electronic coefficient γ of the heat capacity. In particular, a T^1.35, T^1.7, and T^-2/3 temperature dependence of the magnetic susceptibility χ(T), resistivity ρ(T), and Grüneisen parameter Γ(T), respectively, is found at low temperature. An overall understanding of these physical properties is achieved, assuming that LaFe₄Sb₁₂ is a non-Fermi liquid system close to a ferromagnetic quantum critical point, with a spin fluctuation temperature T_sf=50±15 K.     

Microscopic foundation of the phenomenological few-level approach to coherent semiconductor optics

We present the results of inelastic neutron scattering experiments for Cr₂O₃ carried out using the single-crystal time-of-flight spectrometer PRISMA at ISIS (U.K.) as well as the three-axis spectrometer TAS-1 at JAERI(J). The collected data are analysed on the basis of phenomenological shell models showing convincing agreement between calculation and experiment both for the frequencies and intensities. All together the dispersion relations of 12 out of 20 phonon branches along the three-fold axis are determined. By a comparison with the Cr₂O₃ iso-type sapphire (Al₂O₃) it is found that the dynamical response of the oxygen ion is only little affected by the ionic substitution. The chromiumd electrons find their expression mainly in a strengthening of the metal-oxygen bonding. The problem of ionic polarizabilities is addressed in detail both for the oxygen and chromium ions.     

Temperature dependence of spin injection efficiency in an epitaxially grown Fe/GaAs hybrid structure

The electrical spin injection from Fe into an n-doped GaAs channel through Schottky-tunnel-barrier is observed from 1.8 K to room temperature. The magnitude of local spin valve signal (ΔR/R₀) decreases as the temperature increases. In each temperature, we calculated the injected polarization (η) considering the spin drift effect induced by the electric field. The interfacial polarizations of 19.3% and 12.6% are acquired for Fe/GaAs junction at T=1.8 and 300 K, respectively. The temperature dependence of spin injection efficiency is matched with interface resistance variation. As the temperature increases, Schottky-tunnel-barrier property is diminished so that the spin injection efficiency would be reduced.     

Electric-dipole polarizabilities of molecules of CFxCl4−x (x=1–4) Freons. Coefficients of dispersion interaction between different freons and between freons and noble gases

Average values of dynamic electric-dipole polarizabilities of molecules of CFCl₃, CF₂Cl₂, CF₃Cl, and CF₄ Freons in a wide frequency range (from near-infrared to far-ultraviolet regions of the spectrum) were calculated on the basis of the latest data on the distributions of oscillator strengths in the absorption spectra of these Freons. An accurate analytical approximation of the polarizability dispersion is suggested for these Freons. Values of polarizabilities at imaginary frequencies were calculated. Coefficients of dispersion interaction of different Freon molecules with each other and with noble-gas atoms were determined for the first time. The high accuracy of the geometric mean combination rule used to estimate interaction constants for pairs of unlike particles is demonstrated.     

Determination of Backbone Angle ψ in Proteins Using a TROSY-Based α/β-HN(CO)CA-J Experiment

Transverse relaxation-optimized NMR experiment (TROSY) for the measurement of three-bond scalar coupling constant between ¹H^α_i−1 and ¹⁵N_i defining the dihedral angle ψ is described. The triple-spin-state-selective experiment allows measurement of ³J_H^αN from ¹³C^α, ¹⁵N, and ¹H^N correlation spectra H₂O with minimum resonance overlap. Transverse relaxation of ¹³C^α spin is minimized by using spin-state-selective filtering and by acquiring a signal longer in ¹⁵N-dimension in a manner of semi-constant-time TROSY evolution. The ³J_H^αN values obtained with the proposed α/β-HN(CO)CA-J TROSY scheme are in good agreement with the values measured earlier from ubiquitin in D₂O using the HCACO[N] experiment.     

Preequilibrium α-emission in the Au(p,αx)-reaction at Ep = 72 MeV

Proton-induced α-spectra from ¹⁹⁷Au have been measured at E_p = 72.3 MeV and the angle-integrated cross section is compared to an exciton model Monte-Carlo calculation and to the spectral distribution of α-particles emitted after the absorption of negative pions at rest.     

Contrasting routes to the Kostka coefficients of λ [boxvr] n (ln)-permutational module expansions for 6n8: Applications to NMR spin clusters under SU(mn)×Ln spin symmetries

Aspects of the higher-n λ( _n) permutational modules associated with Young subgroups of various highly-branched high-n fold algebras, which are pertinent to identical spin NMR clusters, are presented for λ [boxvr] _n (or λ [boxvR] n), aRota p-tuple or number partition; the method of optimal choice for deriving the Λ_[λ′] Kostka coefficients, found in {[λ′]} sets derived from λ permutational module expansions, rests on the ordering of the λ-(shape) to the self-associated diagram(s) in the dominance hierarchy. Hence, physical insight into these cage-cluster NMR systems is developed both from these properties and from the inter-related induced symmetries of GL(n, ) and _n groups. From these associated combinatorial, mapping or scalar invariant aspects of SU(mn)× _n symmetry, one may define the [A]_n( _n) systems of [AX]_n NMR problems in a general semi-topological limit. This corresponds to a high-n _n limit in which the individual spin cluster exhibits a lack of any (intracluster) ‘magnetic equivalence’ properties.