Density dependent effects due to residual susceptibilities in a four-wave mixing scheme with electromagnetically induced transparency

We have studied the generation of vacuum ultraviolet radiation (at 123.6 nm) produced in a resonant four-wave-mixing scheme in krypton, enhanced by electromagnetically induced transparency. The interplay between the non-linear susceptibility (governing the wave-mixing), the linear susceptibility (governing the absorption and dispersion), and the density-length product was examined both experimentally and numerically. We observe favourable scaling of the yield with density-length product (NL) up to a value of 5×10¹⁶ cm⁻². Above this NL value the yield decreases due to the background wave-vector mismatch (Δk_resid), which arises from the additional atomic energy levels outside the three considered in the EIT enhanced mixing scheme. Our results suggest that further enhancements in frequency up-conversion can be achieved by employing a buffer gas as a phase matching agent.     

Non affinity of Fe2+ for B sites in iron thiochromites and compared band structures of oxides and sulfides spinels

Departure from stoichiometry in vapor grown FeCr₂S₄ was studied using Mössbauer spectroscopy. The paramagnetic Mössbauer spectra give evidence of two singlets and two doublets which correspond respectively to A site Fe²⁺ ? Fe³⁺, Fe^II in T_d symmetry and in symmetry lower than T_d. The following ionic distribution has been deduced:

$\text{(Fe}{}^{\mathrm{2+}}{}_{\mathrm{1?y}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{y}}\text{)|Cr}{}^{\mathrm{3+}}{}_{\mathrm{2?x}}\text{□}{}_{\mathrm{x}}\text{|S}{}_{\mathrm{4?z}}\text{□}{}_{\mathrm{z}}$

Compounds in the system Fe_1+xCr_2?xS₄ have been studied for 0 ? x ? 0.1. The spectra are solved assuming Fe^II in A site with T_d symmetry, A site Fe^II with lower symmetry and B site Fe³⁺. No Fe²⁺ appears in B site. These features are discussed in terms of schematic band structures implying single electron narrow bands. The non-affinity of Fe²⁺ for B sites of iron thiochromites is discussed in relation with B site Cr²⁺ level.     

Liquid chromatography–atmospheric pressure photoionization tandem mass spectrometry for analysis of 36 halogenated flame retardants in fish

A comprehensive, sensitive and high-throughput liquid chromatography–atmospheric pressure photoionization tandem mass spectrometry (LC–APPI-MS/MS) method has been developed for analysis of 36 halogenated flame retardants (HFRs). Under the optimized LC conditions, all of the HFRs eluted from the LC column within 14 min, while maintaining good chromatographic separation for the isomers. Introduction of the pre-heated dopant to the APPI source decreased the background noise fivefold, which enhanced sensitivity. An empirical equation was proposed to describe the relation between the ion intensity and dopant flow. The excellent on-column instrument detection limits averaged 4.7 pg, which was similar to the sensitivity offered by gas chromatography–high-resolution mass spectrometry (GC–HRMS). This method was used to analyze a series of fish samples. Good agreement was found between the results for PBDEs from LC–APPI-MS/MS and GC–HRMS.     

Improved search for Muon-neutrino to electron-neutrino oscillations in MINOS

We report the results of a search for ν(e) appearance in a ν(μ) beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2 × 10(20) protons on the NuMI target at Fermilab, we find that 2 sin(2) (θ(23))sin(2)(2θ(13))<0.12(0.20) at 90% confidence level for δ = 0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin(2) (θ(23))sin(2)(2θ(13)) = 0.041(-0.031)(+0.047) (0.079(-0.053) (+0.071)). The θ(13) = 0 hypothesis is disfavored by the MINOS data at the 89% confidence level.     

The conversion of 2,x-disubstituted cyclohexanones to their less stable isomers—the stereochemical implications of enamine hydrolysis

When 2-methyl-x-alkylcyclohexanones (x≠2) are converted to their enamines and the latter are hydrolysed under kinetic conditions the process leads to a substantial increase in the proportion of the less stable ketone, over that present at equilibrium. Pyrrolidine appears to be the most effective amine in this process. Hydrolysis of the enamine isomer having a tetrasubstituted double bond proceeds with little or no stereoelectronic control during the protonation step. Low temperature thermal isomerization of simple enamines is shown not to exist; when equilibration does occur, it is due to traces of acid impurity.     

Classical trajectory calculations with time-dependent forces in heavy-ion collisions

The applicability of a phenomenological time-dependent nucleus-nucleus potential to deep inelastic collisions is studied. We present its general shape and make a particular choice of the diabatic and adiabatic parts. From trajectory calculations we find that the angle-energy correlation is well described when a time-dependent friction force is used. We also compare our results to some TDHF calculations.     

超声速化学反应流动中燃料预喷研究述评

研制基于超声速燃烧的高效吸气式推进装置(运行Mach数在3.5以上)需要寻求改善混合效率的有效机制, 这对于采用常规碳氢燃料(特别是可以增加密度的液体燃料)的装置尤为重要. 延长混合时间的一种途径是在飞行器燃料室的上游喷入部分燃料. 壁面喷射一直是超声速气动力学最具挑战性的课题, 这里包括使比冲损失最小、改善燃料-空气的混合、减少入口段/燃烧室的相互作用以及增进火焰稳定性等. 综述了超声速入口段或燃烧室的隔离器中液体燃料(个别情况下为气体燃料)喷射的研究进展. 在这些研究中, 燃料都是从后掠型细支架尾迹中的壁面处喷射出来的, 动压比很低($q_{\rm {jet}}/q_{\rm {air}}$=0.6$\sim$1.5). 它们涉及入口段和燃烧室的隔离器中单个支架/喷射器的几何结构及其组合方式、各种各样的喷射条件、不同的引射剂, 并且评估了这些因素对于燃料羽流喷散、比冲损失以及混合效率的影响. 述评引用了46篇参考文献.     

Solar-neutrino variations: A manifestation of nonzero neutrino mass and magnetic moment, and mixing

Time variations of solar neutrino flux are investigated on the basis of available Homestake experimental data for more than two solar cycles (1970–1994). At first, we determine (with the weight-time function by taking into account ³⁷Ar decay), for each solar neutrino run n, the effective Earth’s heliolatitude L _eff(n), the effective Zurich sunspots number Z _eff(n), the effective latitude of sunspots distribution Λ_eff(n), and the effective surfaces of sunspots in different heliolatitude belts. Then, we consider the correlation of solar-electron-neutrino fluxes with these parameters for different periods of solar activity. It is found that correlation coefficients change sign in different periods of solar activity, so that for total period 1970–1994 the correlation coefficient is very small. The obtained information indicates that a neutrino should have nonzero mass and nonzero magnetic moment.     

Development of liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry for analysis of halogenated flame retardants in wastewater

Until recently, atmospheric pressure photoionization (APPI) has typically been used for the determination of non-polar halogenated flame retardants (HFRs) by liquid chromatography (LC) tandem mass spectrometry. In this study, we demonstrated the feasibility of utilizing liquid chromatography atmospheric pressure chemical ionization (APCI) tandem mass spectrometry (LC-APCI-MS/MS) for analysis of 38 HFRs. This developed method offered three advantages: simplicity, rapidity, and high sensitivity. Compared with APPI, APCI does not require a UV lamp and a dopant reagent to assist atmospheric pressure ionization. All the isomers and the isobaric compounds were well resolved within 14-min LC separation time. Excellent instrument detection limits (6.1 pg on average with 2.0 μL injection) were observed. The APCI mechanism was also investigated. The method developed has been applied to the screening of wastewater samples for screening purpose, with concentrations determined by LC-APCI-MS/MS agreeing with data obtained via gas chromatography high resolution mass spectrometry.