1,3-二烷基咪唑离子液体-水二元混合物的溶致显色参数和优先溶剂化行为

Binary mixtures of 1,3-dialkylimidazolium based ionic liquids (ILs) and water were selected as solvent systems to investigate the solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators at 25℃. Empirical solvatochromic parameters, dipolarity/polarizability (π^*), hydrogen-bond donor acidity (α), hydrogen-bond acceptor basicity (β), and Reichardt''s polarity parameters (E_T^N) were measured from the ultraviolet-visible spectral shifts of 4-nitroaniline, 4-nitroanisole, and Reichardt''s dye. The solvent properties of the IL-water mixtures were found to be influenced by IL type and IL mole fraction (x_IL). All these studied systems showed the non-ideal behavior. The maximum deviation to ideality for the solvatochromic parameters can be obtained in the xIL range from 0.1 to 0.3. For most of the binary mixtures, the π^* values showed the synergistic effects instead of the E_T^N, α and β values. The observed synergy extent was dependent on the studied systems, such as the dye indicator and IL type. A preferential solvation model was utilized to gather information on the molecular interactions in the mixtures. The dye indicator was preferentially solvated on the following trend: IL >IL-water complex >water.     

Muon transfer from protium to helium isotopes at low temperature

The transfer reaction of negative muons from muonic protium to ³ and ⁴ in binary and triple gas mixtures was studied. In the binary mixtures the transfer rates to the two helium isotopes were determined from the time distribution of the 7-keV X-rays of the intermediate muonic molecule (pμHe)*. The experimental transfer rate to ⁴ is in good agreement with theoretical predictions, whereas the rate to ³ is a factor 2 to 3 smaller than the predicted ones. Radiative branching ratios of the (pμHe)8 molecular decay were obtained. Muon transfer from excited states of muonic protium gives the main contribution to the total intensity of the μHe Lyman series in the binary mixtures. Values of q _1s ^He are determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

C<Subscript>60</Subscript> fullerene as an η<Superscript>6</Superscript> ligand in π complexes of transition metals

The possible existence of complexes formed by the C₆₀ fullerene or its derivatives with transition metals interacting with the carbon cage via η⁶−π type bonding is discussed. The derivatives C₆₀ R ₆ of the C₆₀ fullerene (R = −, H, F, Cl, Br, CN) are analyzed using the density functional method within the Perdew-Burke-Ernzerhof approximation. In these molecules, the R groups are attached to carbon atoms located in the α positions with respect to the common hexagon of the C₆₀ fullerene. The structure and electron configuration of complexes formed by these molecules with Cr(C₆H₆), Cr(CO)₃, MoC₆H₆, and Mo(CO)₃ particles are modeled. The “dimer” systems C₆₀R₆-M-R ₆C₆₀ (M = Cr, Mo, R =-, H, F) are investigated in which two fullerene molecules interact via a transition-metal atom. It is found that the introduction of six R groups in the α sites with respect to the common hexagon of C₆₀ favors the formation of complexes of these derivatives of the C₆₀ fullerene with the Cr(C₆H₆), Cr(CO), Mo(C₆H₆), and Mo(CO)₃ particles in which η⁶-π type bonds arise between the metal and the atoms of the hexagon fringed with the R groups. It is also demonstrated that analogous complexes with a “bare” C₆₀ fullerene are possible, but they are significantly less stable. The (C₆H₆) M-R ₆C₆₀ R ₆-M (C₆H₆) complexes of particles M(C₆H₆) (M= Cr, Mo) and derivatives R ₆C₆₀ R ₆ (R =-, H, F, Cl, Br) are studied. In the R ₆C₆₀ R ₆ molecule, six R groups are located in the α sites with respect to the common hexagon of the C₆₀ fullerene and six other groups fringe the opposite hexagon. The obtained results can be applied to planning synthesis of new complexes that C₆₀ fullerene derivatives can form with transition metals. Original Russian Text ￠ E.G. Gal’pern, A.R. Sabirov, I.V. Stankevich, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 12, pp. 2220–2223.     

Diffusing wave spectroscopy of dense colloids: Liquid,crystal and glassy states

Using intensity autocorrelation of multiply scattered light, we show that the increase in interparticle interaction in dense, binary colloidal fluid mixtures of particle diameters 0.115μm and 0.089μm results in freezing into a crystalline phase at volume fractionφ of 0.1 and into a glassy state atφ=0.2. The functional form of the field autocorrelation functiong ⁽¹⁾(t) for the binary fluid phase is fitted to exp[−γ(6k ₀ ² D _eff t)^1/2] wherek ₀ is the magnitude of the incident light wavevector andγ is a parameter inversely proportional to the photon transport mean free pathl*. TheD _eff is thel* weighted average of the individual diffusion coefficients of the pure species. Thel* used in calculatingD _eff was computed using the Mie theory. In the solid (crystal or glass) phase, theg ⁽¹⁾(t) is fitted (only with a moderate success) to exp[−γ(6k ₀ ² W(t))^1/2] where the mean-squared displacementW(t) is evaluated for a harmonically bound overdamped Brownian oscillator. It is found that the fitted parameterγ for both the binary and monodisperse suspensions decreases significantly with the increase of interparticle interactions. This has been justified by showing that the calculated values ofl* in a monodisperse suspension using Mie theory increase very significantly with the interactions incorporated inl* via the static structure factor.     

Local structure distortion and spin Hamiltonian parameters for Cr3＋-Vzn tetragonal defect centre in Cr3＋ doped KZnF3 crystal

The quantitative relationship between the spin Hamiltonian parameters (D, g_‖, Δg) and the crystal structure parameters for the Cr³⁺—V_Zn tetragonal defect centre in a Cr³⁺:KZnF₃ crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr³⁺—V_Zn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the V_Zn vacancy and the differences in mass, radius and charge between the Cr³⁺ and the Zn²⁺ ions induce the local lattice distortion of the Cr³⁺ centre ions in the KZnF₃ crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F^- ion along [001] and the other five F^- ions move towards the central Cr³⁺ by distances of Δ₁ = 0.0121 nm and Δ₂ = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr³⁺ ions in the Cr³⁺:KZnF₃ crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.     

Feshbach resonances in an ultracold mixture of 87Rb and 40K

We report the experimental preparations of the absolute ground states of ⁸⁷Rb and ⁴⁰K atoms (| F=1, m_F=1,〉+ |F=9/2, m_F=-9/2,〉) by means of the radio-frequency and microwave adiabatic rapid passages, and the observation of magnetic Feshbach resonances in an ultracold mixture of bosonic ⁸⁷Rb and fermionic ⁴⁰K atoms between 0 T and 6.0 × 10^-2 T, including 7 homonuclear and 4 heteronuclear Feshbach resonances. The resonances are identified by the abrupt trap loss of atoms induced by the strong inelastic three-body collisions. These Feshbach resonances should enable the experimental control of interspecies interactions.     

CuH分子A1∑+态的寿命和预解离研究

A combined cavity ringdown (CRD) and laser induced fluorescence (LIF) spectroscopic study on the A¹∑⁺-X¹∑⁺ transition of CuH has been presented.The CuH molecule,as well as its deuterated isotopologue CuD,are produced in a supersonic jet expansion by discharging H₂(or D₂) and Ar gas mixtures using two copper needles.Different profiles of relative line intensities are observed between the measured LIF and CRD spectra,providing an experimental evidence for the predissociation behavior in the A¹∑⁺ state of CuH.The lifetimes of individual upper rotational levels are measured by LIF,in which the J''-dependent predissociation rates are obtained.Based on the previous theoretical calculations,a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A¹∑⁺ state and the lowest-lying triplet ³∑⁺ state,and a tunneling effect may also be involved in the predissociation.Similar experiments are also performed for CuD,showing that the A¹∑⁺ state of CuD does not undergo a predissociation process.     

Ar原子偶宇称3p5(2P1/2)nl''[K'']J(l''=1,3)自电离态激发谱线形研究

The even-parity autoionizing resonance series 3p⁵np''[3/2]_1,2, 3p⁵np''[1/2]₁, and 3p⁵nf''[5/2]₃ of Ar have been investigated exciting from the two metastable states 3p⁵4s[3/2]₂ and 3p⁵4s''[1/2]₀ in the photon energy range of 32500-35600 cm^-1 with an experimental bandwidth of ~0.1 cm^-1. The excitation spectra of the even-parity autoionizing resonance series show typical asymmetric line shapes. New level energies, quantum defects, line profile index and resonance widths, resonance lifetime and reduced widths of the autoionizing resonances are derived by a Fano-type line-shape analysis. The line profile index q and the resonance widths Γ are shown to be approximately proportional to the effective principal quantum number n^*. The line separation of the 3p⁵np'' autoionizing resonances is discussed.     

Effective ionization coefficients and electron drift velocities in gasmixtures of CF3I with N2 and CO2 obtained from Boltzmannequation analysis

The electron swarm parameters including the density-normalized effective ionization coefficients (α-η)/N and the electron drift velocities V_e are calculated for the gas mixture of CF₃I with N₂ and CO₂ by solving the Boltzmann equation in the condition of steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td=10^-17 V·cm²), while the CF₃I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (α-η)/N with the CF₃I mixture ratio k, the limiting field strength (E/N)_lim for each CF₃I concentration is derived. It is found that for the mixtures with 70% CF₃I, the values of (E/N)_lim are essentially the same as that for pure SF₆. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of applying in the gas insulation of power equipment.     

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMn_xFe_1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ₀(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ ₀ ^m ∼220 μΩ cm at x _C∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 193–197. Original Russian Text Copyright ? 2002 by Kourov, Korotin, Volkova.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.