Electric correlation function for the eight-vertex model for T→T−c to first order in the four-spin coupling

We study the arrow-arrow correlation function of the eight-vertex model in the scaling limit as T→T⁻_c to first order in the four- spin coupling. Our result shows that the Fredholm determinant structure of the correlation which is present in the decoupling limit is destroyed by the four-spin coupling.     

Ionic conductivity and crystal structure for the Li3−2xCr2−xTax(PO4)3 system

The monoclinic phase (P2₁/n) was formed for 0≤x≤0.6 and the NASICON-type rhombohedral phase (R3̄c) was obtained for the region 0.8≤x≤1.2 in the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The activation energy for Li⁺ migration was ca. 0.45 eV for the monoclinic structure and ca. 0.36 eV for the rhombohedral structure. The maximum conductivity of 8.4×10⁻⁶ S cm⁻¹ at 298 K was obtained for x=0.8 of the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The conductivity of LiCrTa(PO₄)₃ was enhanced about three to five times by the addition of the lithium salt due to the improvement of the sinterablity. The maximum conductivity was 2.4×10⁻⁵ S cm⁻¹ at 298 K for LiCrTa(PO₄)₃–0.2Li₃BO₃.     

High-resolution spectroscopy of the a4Σ−3/2 − X12Π3/2 system of gold monosulphide in the near infrared

ABSTRACT

We have recorded the a⁴Σ^? _3/2 ? X₁ ²Π_3/2 (0,0), (1,0), and (2,0) bands of gaseous gold monosulphide (AuS) at sub-Doppler resolution in the near-infrared region. The molecules were made in a hollow cathode discharge source by the reaction of sputtered gold with carbonyl sulphide. The high resolution of the laser excitation spectrum enabled the determination of molecular constants describing the rotational and ¹⁹⁷Au hyperfine structure in both states, as well as the spin–rotation interaction in the a⁴Σ^? _3/2 state. The natures of the two electronic states are discussed in the context of the observed hyperfine structure.     

Method for vessel attitude estimation by spatial correlation function for bottom reverberation

Under the assumption that the sea bottom is an almost-flat and randomly rough thin layer, a spatial correlation model for bottom reverberation is constructed. At high signal noise ratio, the phase of the spatial correlation function is the product of sound wave number and the vertical vector between two hydrophones. In a nominally horizontal plane, roll and pitch bring on the vertical vector between the hydrophones. Then an equation including roll, pitch and the phase of the spatial correlation function is found. If a parallelogram can be constructed by 3 hydrophones and the rat ios of its acreage to diagonals are not smaller than half of the wavelength, roll and pitch can be obtained analytically or by optimal method. However, the ranges of roll and pitch are restricted because of the phase ambiguity. Using Fisher information matrix, the Cramer-Rao lower bound is obtained. Results from computer simulation and sea test data prove the feasibility of the method.     

Parameterization of a potential function for the Ca2+ −Ne and Ca2+ −N2 interactions using high-level ab initio data

Ab initio calculations have been carried out at the CCSD(T)/aug-cc-pVTZ level on di-nitrogen and neon interacting with a calcium (II) cation. The interaction of nitrogen with the Ca²⁺ cation is examined for end-on and side-on approaches. The two adjustable parameters in the TrAZ potential (A ^Ca2+-Ne , b ^Ca2+-Ne ) are fitted to the Ca²⁺-Ne potential energy curve and combination rules are then applied in reverse to get A ^Ca2+-Ca2+ , b ^Ca2+-Ca2+ . Combining these with values of A^NN, 6^NN enables the Ca²⁺-N₂ potential energy curves to be predicted a priori. Agreement with the ab initio data is found to improve dramatically when the anisotropy of the nitrogen polarizability is included in the induced interaction energy. Other combination rules are tried but are not found to have an impact on the agreement between the a priori potential and the ab initio data     

The dynamical correlation function for isotropic ferromagnets forT≧T c

The dynamic correlation function for an isotropic ferromagnet forTT _c is calculated in first order in =6–d. Applying an exponentiation procedure then leads to results which are relevant for the analysis of neutron scattering experiments in the vicinity of the critical point.Supported by the Fonds zur Förderung der wissenschaftlichen Forschung     

Noise estimation based on time–frequency correlation for speech enhancement

As a fundamental part of speech enhancement, noise estimation is particularly challenging in highly non-stationary noise environments. In this work, we propose an effective algorithm on the basis of the “Improved Minima Controlled Recursive Averaging (IMCRA)” with the objective to improve the performance of noise estimation. The main contributions of this work are: (i) in the algorithm, a rough decision about speech presence is proposed by calculating the autocorrelation and cross-channel correlation of the T–F (Time–Frequency) units; (ii) with this decision, we refine the smoothing parameters for the smoothing of noisy power spectrum and the recursive averaging in noise spectrum estimation as well as the weighting factor for the a priori SNR (Signal to Noise Ratio) estimation in the IMCRA; (iii) we improve the search of local minima during spectral bursts by adding a minimum search with a shorter window. Extensive experiments are carried out to evaluate the performance of our proposed algorithm. The experimental results illustrate that, compared with the IMCRA, the proposed approach significantly improves the accuracy of noise spectrum estimation and the quality of enhanced speech in the typical noise situations.     

Transient fields for Ag and Pd ions IN Fe and Co;g-Factor measurements of the lowest 3/2− and 5/2− states in107,109 Ag

Transient field precessions of the 2 ₊ ¹ state of¹⁰⁸Pd were measured simultaneously with those of the 3/2 _– ¹ and 5/2 _– ¹ states of¹⁰⁷Ag and¹⁰⁹Ag as their ions traversed thin Co and Fe foils. Precessions of the 2 ₊ ¹ states of^{104,106,108,110}Pd were also measured using a natural Pd target evaporated onto 0.9 m thick Co. The results of these studies are in accord with prior predictions that the AgFe transient field might be diminished relative to that for PdFe at ion velocities appropriate for molecular orbital vacancy sharing. Transient field strengths for PdCo and PdFe were found to be consistent with scaling according to bulk magnetization of the ferromagnetic host. Gyromagnetic ratios were inferred for the first 3/2^– and 5/2^– states of^107,109Ag relative to theg factor of the 2 ₊ ¹ state of¹⁰⁸Pd. Values obtained usingg(2 ₊ ¹ ;¹⁰⁸Pd)=0.36± 0.03 are:g(3/2;¹⁰⁷Ag) =0.63±0.09,g(5/2;¹⁰⁷Ag)=0.37±0.06,g(3/2;¹⁰⁹Ag)=0.77 ±0.10,g(5/2;¹⁰⁹Ag)=0.36±0.05.     

Measurement of the Electric Quadrupole Moment of the 9/2− and 21/2− Isomers in 173Ta

The electric quadrupole moments of the 9/2⁻ and 21/2⁻ isomeric states of ¹⁷³Ta at 165.8 keV and 1713.2 keV, respectively, were measured as Q(9/2⁻)=2.92(15) b and Q(21/2⁻)=6.23(18) b for the first time using the TDPAD technique. A 66 MeV pulsed ¹²C ion beam from the 15UD pelletron accelerator facility of the Nuclear Science Centre at New Delhi was used in the reaction ¹⁶⁵Ho(¹²C, 4nγ)¹⁷³Ta. The experimental values of equilibrium deformations β₂(9/2⁻)=0.251(7) and β₂(21/2⁻)=0.391(7) were extracted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exponential rational function method for space–time fractional differential equations

In this paper, exponential rational function method is applied to obtain analytical solutions of the space–time fractional Fokas equation, the space–time fractional Zakharov Kuznetsov Benjamin Bona Mahony, and the space–time fractional coupled Burgers’ equations. As a result, some exact solutions for them are successfully established. These solutions are constructed in fractional complex transform to convert fractional differential equations into ordinary differential equations. The fractional derivatives are described in Jumarie’s modified Riemann–Liouville sense. The exact solutions obtained by the proposed method indicate that the approach is easy to implement and effective.     

Electron Green's function in the planar t − J model

The electron Green's functions G(k, ω) within the t ? J model and in the regime of intermediate doping is studied analytically using equations of motion for projected fermionic operators and the decoupling of the self energy into the single-particle and spin fluctuations. It is shown that the assumption of marginal spin dynamics at T = 0 leads to an anomalous quasiparticle damping. Numerical results show also a pronounced asymmetry between the hole (ω < 0) and the electron (ω > 0) part of the spectral function, whereby hole-like quasiparticles are generally overdamped.     

Search for the decay τ− → vτηπ−

We have searched for the decay τ⁻ → v_τηπ⁻ using data accumulated by the ARGUS detector at the e⁺e⁻ storage ring DORIS II at DESY. No η signal was found in the π⁺π⁻π⁰ subsystems of the decay τ⁻ →v_τπ⁻π⁻π⁺ π⁰. We obtain an upper limit for the branching ratio of the decay τ⁻ → v_τηπ⁻ of 1.3% at the 95% confidence level.     

Mapping the current–current correlation function near a quantum critical point

The current–current correlation function is a useful concept in the theory of electron transport in homogeneous solids. The finite-temperature conductivity tensor as well as Anderson’s localization length can be computed entirely from this correlation function. Based on the critical behavior of these two physical quantities near the plateau–insulator or plateau–plateau transitions in the integer quantum Hall effect, we derive an asymptotic formula for the current–current correlation function, which enables us to make several theoretical predictions about its generic behavior. For the disordered Hofstadter model, we employ numerical simulations to map the current–current correlation function, obtain its asymptotic form near a critical point and confirm the theoretical predictions.     

Evidence for electronic localization in YBa2−yLayCu3Ox

Electrical resistivity, thermoelectric power, magnetic susceptibility and neutron scattering experiments on YBa_2−yLa_yCu₃O_x, with y = 1, show that this compound is neither superconductive nor magnetically ordered but are consistent with it being an electronically localized system.     

A computational study of the electron detachment energies of Al2As2 − and Al3As3 −

Ab initio and density functional theory calculations are reported for the low-lying electronic states of Al₂As₂ ^?, Al₂As₂, Al₃As₃ ^?, and Al₃As₃. The ²B_2g ground electronic state of Al₂As₂ ^? has a rhombic structure with the Al atoms occupying the shorter diagonal. In contrast, the As atoms occupy the shorter diagonal of the ground state rhombic structure of Al₂As₂. Electron detachment energies computed for Al₂As₂ ^? are presented and discussed. The adiabatic electron affinity of Al₂As₂ ^? is calculated to be 2.1 eV at the CCSD(T) level, using B3LYP and MP2 optimized geometries. The ground states of both Al₃As₃ ^? (²A₁′) and Al₃As₃ (¹A₁′) have planar hexagonal D_3h geometry. Electron detachment energies computed for the anion are reported. At the CCSD(T)//B3LYP level, the electron affinity of Al₃As₃ is calculated to be 2.47 eV.     

Sonochemical nitrogen fixation for the generation of NO2− and NO3− ions under high-powered ultrasound in aqueous medium

Sonochemical species such as nitrite (NO₂⁻) and nitrate (NO₃⁻) were detected in ultrapure aqueous medium with 28 kHz low frequency ultrasound (US) in the range of 200–1200 W output power. The concentration of their anionic ions monitored with a high-performance liquid chromatography increased with increasing US power especially under air atmosphere. When the generation of NO₂⁻ and NO₃⁻ ions under US exposure was investigated for N₂, O₂ and Ar-bubbled solutions, no trace of NO₂⁻ was observed while NO₃⁻ was slightly generated. Under air atmosphere, the concentration of dissolved oxygen in the aqueous medium increased especially when 1200 W power was used. In addition, the bulk pH shifted towards the acidic side with an increase in exposure time, which indicated that NO₂⁻ was formed. The formation of oxidizing species under 28 kHz low frequency ultrasonic treatment was confirmed with an absorption spectrum which was dominated by two maxima peaks at 288 nm and 352 nm representing triiodide I₃⁻ anion.