Dual fluorescence (S1, S2) in chrysene and 3,4-benzophenanthrene

S₂ and S₁ fluorescence of chrysene and 3,4 benzophenanthrene has been observed in the vapour phase under collision free conditions. It is shown that the intermediate strong couplinng model can be applied to these molecules. The efficiency of the transfer of the excess energy to collision partners is given for different gases.     

Gaussian overlap approximation in the projected Hartree–Fock method

A method for the approximate calculation of matrix elements with respect to projected Hartree–Fock wave functions is proposed. The method is tested on some calculations in the many-parameter AMO method. It is found that the approximation reduces the amount of work, involved in the evaluation of the energy, by a factor of five and that it reproduces the exact values to within a few per cent.     

拟薄水铝石/陶瓷胶态加工浆料的流变性能

用拟薄水铝石纳米胶粒分散微米二硼化钛形成固含量为60Wt%的稳定陶瓷浆料,实验考察了拟薄水铝石固含量、二硼化钛固含量、温度对浆料流变性、稳定性的影响,对纳米γ-AlOOH胶粒分散微米TiB2的机制进行了讨论.大小约20nm的γ-AlOOH颗粒相互网联,成为外加微米陶瓷颗粒的骨架.浆料粘度随二硼化钛固含量的增加而增大,温度升高有利于胶体中薄水铝胶团与二硼化钛颗粒的相互作用并促进分散.     

Three-dimensional simulation of time-coded emission tomography

In this paper we discuss the potentialities of a time-coded single photon emissive imaging system for thyroid tomography. We have performed three-dimensional simulation studies in order to answer two questions: 1) does this coded aperture device produce good quality reconstructions, and 2) can the reconstruction be carried out sufficiently fast on a microcomputer. Our study leads to the conclusion that both questions can be answered affirmatively. Hence, time-coded emission tomography is a potentially useful imaging technique for diagnostic clinical practice.     

Restoration of signal polarity in a set of inversion recovery NMR images

A method is described which enables unambiguous retrieval of sign information in a set of magnetic resonance magnitude images of the inversion recovery type. The proposed method starts from the observation that the inversion recovery curve S is a monotonically increasing function of the inversion time TI, and comes down to finding the zero-crossing time TI0 of this curve for each pixel within the image. Absolute Value(S)and S are then related by S(TI) = -Absolute Value(S(TI)) for TI =/< TI(0) and S(TI) = + Absolute Value(S(TI)) for TI =/> TI0. The method, which does not require additional knowledge with respect to any of the NMR parameters involved, is shown to be effective when at least four inversion recovery images with different inversion times of a particular object slice are available. The efficacy of sign retrieval is demonstrated by imaging experiments on phantoms and human subjects. The validity of the polarity restoration method is established by viewing its results against the results of conventional methods, i.e., NMR spectroscopy.     

A potentiometric study of the water-soluble silver(I) complexes of n,n'-bis(2-hydroxyethyl)dithiooxamide : Part III. Determination of the different species

Silver(I) and N,N'-bis(2-hydroxyethyl)dithiooxamide (H₂X) in acidic solutions, form a series of water-soluble polynuclear complexes. These complexes can be represented by two general formulae: H_2qAg_pX_q and H_2q-1Ag_pX_q with q=1,2,3 and p=q, q-1.     

Spectroscopic evidence for the intermediacy of a 6-R-2,4-diazabicyclo-[3.1.0]hex-2-(3)ene in the photoisomerization of 4-R-1,4-(3,4)-dihydropyrimidines

¹H- and ¹³C-nmr spectroscopy is presented showing that photolysis of 4-(p-trifluoromethylphenyl)-1,4-(3,4)-dihydropyrimidine yields 6-(p-trifluoromethylphenyl)-2,4-diazabicyclo[3.1.0]hex-2-(3)ene.     

The determination of all the platinum group elements and gold in rocks and ore by neutron activation analysis after preconcentration by a nickel sulphide fire-assay technique on large samples

The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques.     

Investigations on the conditional kinetic and thermodynamic stability of aquatic humic substance-metal complexes by means of EDTA exchange, ultrafiltration and atomic spectrometry

The conditional metal availability and the kinetic stability of humic substance-metal species in humic-rich waters (e.g. bog water) was characterized by means of EDTA exchange. For this purpose a combined procedure consisting of time-controlled ligand exchange by EDTA, species differentiation by a fast single-stage tangential-flow ultrafiltration (TF-UF) technique (cut-off 1 kDa) and sensitive atomic spectrometry methods (e.g. AAS, ICP-OES, TXRF) was developed. The kinetics and the yield of the EDTA exchange served as operational parameters for assessing the kinetic stability and EDTA availability of HS-metal species, respectively. Considerable fractions of natural HS-metal species studied were shown to be EDTA-inert (e.g. 31% of the total Fe, 44% of the total Al) even after long reaction times (48 h), in contrast to artificial ones formed in solutions of isolated HS. Moreover, the conditional thermodynamic stability of HS-metal complexes formed by successive loading of an aquatic reference HS (HO14) with a number of heavy metal ions (e.g. Cr(III), Cu(II), Fe(III), Mn(II), Zn(II)) was also evaluated discriminating the free metal concentrations by means of TF-UF. In addition, from the loading isotherms obtained conditional complexation capacities could be derived for the studied HS exhibiting the order Fe(III)>Cu(II)>Cr(III)>Co(II)>Mn(II).