The reaction of CH3 + O2: experimental determination of the rate coefficients for the product channels at high temperatures

The reaction of methyl radicals (CH₃) with molecular oxygen (O₂) has been investigated in high-temperature shock tube experiments. The overall rate coefficient, k₁ = k_1a + k_1b, and individual rate coefficients for the two high-temperature product channels, (1a) producing CH₃O + O and (1b) producing CH₂O + OH, were determined using ultra-lean mixtures of CH₃I and O₂ in Ar/He. Narrow-linewidth UV laser absorption at 306.7 nm was used to measure OH concentrations, for which the normalized rise time is sensitive to the overall rate coefficient k₁ but relatively insensitive to the branching ratio of the individual channels and to secondary reactions. Atomic resonance absorption spectroscopy measurements of O-atoms were used for a direct measurement of channel (1a). Through the combination of measurements using the two different diagnostics, rate coefficient expressions for both channels were determined. Over the temperature range 1590–2430 K, k_1a = 6.08 × 10⁷T^1.54 exp (−14005/T) cm³ mol⁻¹ s⁻¹ and k_1b = 68.6 T^2.86 exp (−4916/T) cm³ mol⁻¹ s⁻¹. The overall rate coefficient is in close agreement with a recent ab initio calculation and one other shock tube study, while comparison of k_1a and k_1b to these and other experimental studies yields mixed results. In contrast to one recent experimental study, reaction (1b) is found to be the dominant channel over the entire experimental temperature range.     

Solar neutrino oscillations in the quasi-vacuum regime

Motivated by recent experimental data, we study solar neutrino oscillations in the range δm²/E ε [10⁻¹⁰, 10⁻⁷] eV²/MeV. In this range vacuum oscillations become increasingly affected by (solar and terrestrial) matter effects for increasing δm², smoothly reaching the MSW regime. A numerical study of matter effects in such “quasi-vacuum” regime is performed. The results are applied to the analysis of the recent solar neutrino phenomenology.     

Eigenvalue problem for arbitrary linear combinations of a boson annihilation and creation operator

The eigenvalue problem for arbitrary linear combinations kα + μα^? of a boson annihilation operator α and a boson creation operator α^? is solved. It is shown that these operators possess nondegenerate eigenstates to arbitrary complex eigenvalues. The expansion of these eigenstates into the basic set of number states | n >, (n = 0, 1, 2, …), is found. The eigenstates are normalizable and are therefore states of a Hilbert space for | ζ | < 1 with ζ ? μ/k and represent in this case squeezed coherent states of minimal uncertainty product. They can be considered as states of a rigged Hilbert space for | ζ | ? 1. A completeness relation for these states is derived that generalizes the completeness relation for the coherent states | α 〉. Furthermore, it is shown that there exists a dual orthogonality in the entire set of these states and a connected dual completeness of the eigenstates on widely arbitrary paths over the complex plane of eigenvalues. This duality goes over into a selfduality of the eigenstates of the hermitian operators kα + k* α^? to real eigenvalues. The usually as nonexistent considered eigenstates of the boson creation operator α^? are obtained by a limiting procedure. They belong to the most singular case among the considered general class of eigenstates with ζ ? μ/k as a parameter.     

Γ(Z → b ): A signature of hard mass terms for a heavy top

We calculate analytically the weak radiative corrections to the weak neutral current gauge boson-bottom fermion vertex, keeping the mass m_t of the internal fermion line for the relevant diagrams. We find, to order α, a hard mass-term dependence m_t²/M_W² of the amplitude, for large m_t values. Its origin comes from the unphysical charged Higgs coupling to fermions in the renormalizable gauge or, equivalently, from the longitudinal charged gauge boson couplings. The diagonal Z⁰ decay width to b-quarks decreases, due to these weak radiative corrections, by 0.6%–2.5% when the top mass m_t varies from 45 to 200 GeV.     

Noncommutative theories, the axial anomaly, Fujikawa's method and the Atiyah–Singer index

Fujikawa's method is employed to compute at first order in the noncommutative parameter the U(1)_A anomaly for noncommutative SU(N). We consider the most general Seiberg–Witten map which commutes with hermiticity and complex conjugation and a noncommutative matrix parameter, θ^μν, which is of “magnetic” type. Our results for SU(N) can be readily generalized to cover the case of general nonsemisimple gauge groups when the symmetric Seiberg–Witten map is used. Connection with the Atiyah–Singer index theorem is also made.     

Principal Fibrations from Noncommutative Spheres

We construct noncommutative principal fibrations S_θ⁷→S_θ⁴ which are deformations of the classical SU(2) Hopf fibration over the four sphere. We realize the noncommutative vector bundles associated to the irreducible representations of SU(2) as modules of coequivariant maps and construct corresponding projections. The index of Dirac operators with coefficients in the associated bundles is computed with the Connes-Moscovici local index formula. “The algebra inclusion is an example of a not-trivial quantum principal bundle.”     

Visions: The coming revolutions in particle physics

We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ⁺τ⁻ in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ⁺τ⁻ are promising.     

Thermal property of binary tetrahedral semiconductors

In this paper we present an expression relating the lattice thermal expansion coefficient α_L (10⁻⁶ K⁻¹) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂), melting temperature (T_m) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (T_m), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for A^IIIB^V and A^IIB^VI semiconductors.     

Fractals,coherent states and self-similarity induced noncommutative geometry

The self-similarity properties of fractals are studied in the framework of the theory of entire analytical functions and the q-deformed algebra of coherent states. Self-similar structures are related to dissipation and to noncommutative geometry in the plane. The examples of the Koch curve and logarithmic spiral are considered in detail. It is suggested that the dynamical formation of fractals originates from the coherent boson condensation induced by the generators of the squeezed coherent states, whose (fractal) geometrical properties thus become manifest. The macroscopic nature of fractals appears to emerge from microscopic coherent local deformation processes.     

Macroscopic and microscopic parameters of laser dye solvents: m-xylene and dioxane

For the laser designer and other users the optical, electrical and refractive parameters have been obtained for pure nonpolar laser dye solvents m-xylene and dioxane. The refractive index (n) and its thermo-optic constant (dn/dT) at argon laser wavelength 514.5 nm and He–Ne laser wavelength 632.8 nm, are measured. The values of n and dn/dT are used to calculate the optical permittivity ε=n² and its variation with temperature dε/dT. Applying Cauchy's equation the optical and dielectric dispersion (dn/dλ and dε/dλ) are determined. The variation of −dn/dT, −dε/dT, molar refractivity and thermal volume expansion coefficient as a function of wavelength are calculated and represented. Furthermore Cauchy's constants A and B as a function of temperature are plotted. The specific and molar refractivities, specific and molar dispersivity total polarizability, distortion polarizability, ratio of atomic to electronic polarizability, molecular radius, relaxation time, electric susceptibility characteristic impedance, and other physical parameters were calculated. Additionally, density, thermal linear expansion coefficient and molar polarization as a function of temperature were calculated at the laser wavelengths 514.5 nm.     

Search for the standard model Higgs boson at the LEP2 collider near

During 1997 the ALEPH experiment at LEP gathered 57 pb⁻¹ of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e⁺e⁻→HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m_H>87.9 GeV/c² at 95% confidence level.     

Internal dynamics of hydroxymethyl rotation from CH2 cross-correlated dipolar relaxation in methyl-β- -glucopyranoside

Conventional relaxation parameters (T₁⁻¹, T₂⁻¹, and NOE), obtained at different temperatures and magnetic fields, are reported for the hydroxymethyl (C6) carbon in methyl-β- -glucopyranoside in a D₂O/DMSO cryosolvent. These data are interpreted with the Lipari–Szabo model. In addition, two-field measurements of longitudinal and spin-locked relaxation rates related to the cross-correlated carbon–proton dipole–dipole interactions for the same carbon are reported. The complete data set consisting the conventional and cross-correlated relaxation parameters is interpreted using a new “hybrid” approach, in which the Lipari–Szabo model for the auto-correlated spectral densities is combined with the two-site jump model for the cross-correlated spectral densities, with the global correlation time as a common parameter. The two-site jump rates thus obtained are in reasonable agreement with the ultrasonic relaxation measurements, and have reasonable temperature dependence.     

Modelling the quark propagator

We are interested in developing covariant, confining, and asymptotically free models of hadrons. With this goal in mind we have carried out a study of dynamical chiral symmetry breaking without imposing the frequently used approximation α_s(−(p−k)²) α₅(−p_>²), where p_>² ≡ max(p², k²) for the running coupling constant in the quark Schwinger-Dyson equation. We present numerical results in Landau gauge and compare these with earlier results obtained when using this approximation. We see in this context that a gluon propagator which has the form 1/q⁴ in the infrared is too singular and must be regulated. We derive a suitably generalized expression for the pion decay constant f_π. With essentially one free parameter we are able to reproduce reasonable results for various physical quantities of interest including , and Λ_QCD.     

Oxygen nonstoichiometry of Sr(Co,Fe)O3−δ-based perovskites: I. Coulometric titration of SrCo0.85Fe0.10Cr0.05O3−δ by the two-electrode technique

The p(O₂)–T–δ diagram of perovskite-type SrCo_0.85Fe_0.10Cr_0.05O_3−δ was determined by the coulometric titration technique in the temperature range 770–1250 K at oxygen partial pressures from 8 10⁻¹⁰ to 0.5 atm. Stability of the cubic perovskite phase of SrCo_0.85Fe_0.10Cr_0.05O_3−δ, existing down to the oxygen pressures of 10⁻³–10⁻⁵ atm, was found to be slightly higher than that of SrCo_0.80Fe_0.20O_3−δ, probably due to stabilization of oxygen octahedra neighboring Cr⁴⁺ cations. When the oxygen nonstoichiometry of the Cr-containing perovskite decreases from 0.47 to 0.38, the partial molar enthalpy and entropy for overall oxygen incorporation reaction vary in the ranges −165 to −60 kJ mol⁻¹ and 90 to 150 J mol⁻¹ K⁻¹, respectively. Within the stability limits of the single perovskite phase, the p(O₂)–T–δ diagram can be adequately described by equilibrium processes of oxygen incorporation, cobalt disproportionation and interaction of cobalt and iron cations, with the thermodynamic functions independent of defect concentrations. Increasing grain size in SrCo_0.85Fe_0.10Cr_0.05O_3−δ ceramics from submicron size to 100–200 μm has no effect on the oxygen thermodynamics. The two-electrode coulometric titration technique, based on the alternate use of electrodes for oxygen pumping and e.m.f. measurements, is described and verified by studying oxygen nonstoichiometry of La_0.3Sr_0.7CoO_3−δ and PrO_x.     

Elementary reactions of formyl (HCO) radical studied by laser photolysis—transient absorption spectroscopy

Several elementary reactions of formyl radical of combustion importance were studied using pulsed laser photolysis coupled to transient UV–Vis absorption spectroscopy: HCO → H + CO (1), HCO + HCO → products (2), and HCO + CH₃ → products (3). One-pass UV absorption, multi-pass UV absorption as well as cavity ring-down spectroscopy in the red spectral region were used to monitor temporal profiles of HCO radical. Reaction (1) was studied over the buffer gas (He) pressure range 0.8–100 bar and the temperature range 498–769 K. Reactions (2a), (2b), (2c), (3a) and (3b) as well as the UV absorption spectrum of HCO, were studied at 298 and 588 K, and the buffer gas (He) pressure of 1 bar. Pulsed laser photolysis (308, 320, and 193 nm) of acetaldehyde, propionaldehyde, and acetone was used to prepare mixtures of free radicals. The second-order rate constant of reaction (1) obtained from the data at 1 bar is: k₁(He) = (0.8 ± 0.4) × 10⁻¹⁰exp(−(66.0 ± 3.4) kJ mol⁻¹/RT) cm³ molecule⁻¹ s⁻¹. The HCO dissociation rate constants measured in this work are lower than those reported in the previous direct work. The difference is a factor of 2.2 at the highest temperature of the experiments and a factor of 3.5 at the low end. The experimental data indicate pressure dependence of the rate constant of dissociation of formyl radical 1, which was attributed to the early pressure fall-off expected based on the theory of isolated resonances. The UV absorption spectrum of HCO was revised. The maximum absorption cross-section of HCO is (7.3 ± 1.2) × 10⁻¹⁸ cm² molecule⁻¹ at 230 nm (temperature independent within the experimental error). The measured rate constants for reactions (2a), (2b), (2c), (3a) and (3b) are: k₂ = (3.6 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ (298 K); k₃ = (9.3 ± 2.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹(298 and 588 K).     

Fermion tunnels of higher-dimensional anti-de Sitter Schwarzschild black hole and its corrected entropy

Applying the method beyond semiclassical approximation, fermion tunneling from higher-dimensional anti-de Sitter Schwarzschild black hole is researched. In our work, the “tortoise” coordinate transformation is introduced to simplify Dirac equation, so that the equation proves that only the (r−t) sector is important to our research. Because we only need to study the (r−t) sector, the Dirac equation is decomposed into several pairs of equations spontaneously, and we then prove the components of wave functions are proportional to each other in every pair of equations. Therefore, the suitable action forms of the wave functions are obtained, and finally the correctional Hawking temperature and entropy can be determined via the method beyond semiclassical approximation.     

Gauge Theory on a Discrete Noncommutative Space

In this paper, we apply Connes' noncommutative geometry and the Seiberg—Witten map to a discrete noncommutative space consisting of n copies of a given noncommutative space R ^m . The explicit action functional of gauge fields on this discrete noncommutative space is obtained.     

Effects of superstrings in collisions

Superstring theory in d = 10 dimensions after Calabi—Yau compactification yields a minimum low-energy gauge group SU(3)_C × SU(2)_L × U(1)_Y × U(1)_E. The low-energy theory includes particles with the quantum numbers of 27 representations of E₆, each of which contains an extra neutrino ν^c conventionally called a “right-handed neutrino”. The contributions of ν and ν^c to through Z⁰ and Z_E mixing is calculated. Small contributions are found of the new right-handed neutrino and of the superstring boson Z_E to σ(e⁺e⁻ → γ + nothing).     

Electron heating in a submicron-size n GaAs wire

We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τ_E⁻¹ = α + βT_eⁿ where α, β are constants and T_e is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3.