Automated determination of fluoride ion in the parts per milliard range

Fluoride, down to 2 ppM, has been determined by automated direct potentiometry using a fluoride ion-selective electrode. The method reduces the dilution and contamination effects of TISAB and takes the electrode response-time into consideration. The relative standard deviation for water samples is 1.5-1.8% and the recovery varies from 96 to 107%.     

Collective excitations in solid hydrogen as observed by incoherent neutron scattering

Incoherent neutron scattering experiments are reported at a number of scattering angles for solid H₂ using the time-of-flight technique. The samples had an ortho concentration ofX0.91 and the temperatures were 4.2, 2.2 and 1.2 K. The recorded scattering functions exhibit the elastic line, the ortho-para conversion line, the phonon spectrum on the energy-gain side of the neutrons and finally the phonon spectrum on the energy-loss side. Analysis of the data shows multiple scattering to be very important especially at small scattering angles. Accordingly, the results of an extensive calculation are reported that include up to four-fold scattering. The phonon spectrum that brings calculation and experiment in agreement at all angles is presented. It is concluded from the comparison between the spectra at various temperatures that unexpectedly the samples have always remained in the hexagonal close-packed phase even below the usual transition temperature into the cubic phase. Comparison is made with the spectrum (also in thehcp phase) obtained from coherent neutron scattering. The high-energy phonon tail, to be expected for quantum crystals, is observed and is qualitatively consistent with that in a similar spectral density derived theoretically from ortho-para conversion data under pressure. No evidence of a libron spectrum atT=2.2 K for a sample withX=0.91 could be found, which is consistent with the absence of the cubic orientationally ordered phase in these experiments.Supported in this research by a grant from the National Science Foundation     

Low-lying (K π = 0+) states of gadolinium isotopes

The sd-interacting boson approximation (sd-IBA) and the df-interacting boson approximation (df-IBA) can be related to each other and the states of the interacting boson approximation model can be identified with the fully symmetric states in the sdf interacting boson approximation model. A systematic study of the sdf-IBA model showed that the constructed Hamiltonian can successfully describe the strong octupole correlations in the deformed nuclei. We showed that the interacting boson approximation may account for many of these K ^π ?=?0⁺ states. It was found that the calculated energy spectra of the gadolinium isotopes agree quite well with the experimental data. The observed B(E2) values were also calculated and compared with the experimental data.     

Raman spectroscopy of isolated carbyne chains confined in carbon nanotubes: Progress and prospects

Carbyne is an infinitely long linear chain of carbon atoms with sp¹ hybridization and the truly one-dimensional allotrope of carbon. While obtaining freestanding carbyne is still an open challenge, the study of confined carbyne, linear chains of carbon encapsulated in carbon nanotubes, provides a pathway to explore carbyne and its remarkable properties in a well-defined environment. In this review, we discuss the basics and recent advances in studying single confined carbyne chains by Raman spectroscopy, which is their primary spectroscopic characterization method. We highlight where single carbyne chain studies are needed to advance our understanding of confined carbyne as a material system and provide an overview of the open questions that need to be addressed and of those aspects currently under debate.     

New precision measurements of the strong interaction in kaonic hydrogen

The DEAR experiment performed at the DAΦNE electron-positron collider (Frascati, Italy) studied the strong interaction shift and width of the 1s state in kaonic hydrogen using X-ray spectroscopy. The repulsive character of the kaon-proton interaction at threshold was confirmed and the most precise values of the shift and width were obtained. However, high precision data at the percent level are highly requested to further develop the theories and thus our understanding of the low-energy antikaon-nucleon interaction. Therefore, a new series of precision experiments on kaonic hydrogen and kaonic deuterium are planned at LNF.     

New Organotin Compounds Including a Tin–Zinc Bond

Abstract

The reaction of dialkyltinhydrides with dialkylzinc results in a tin metal bond formation. Crystal structures of 1,1,1,2,3,3,3-hepta-phenyl-2-(ethylzincio)tristannane *TMEDA 1, 1,1,2,2,3,3,4,4-octaphenyl-1,4-(ethylzincio)tetrastannane*2TMEDA 2, and triphenyl(phenylzincio)stannane*TMEDA 3 could be obtained.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT     

Percolative phenomena in lecithin reverse micelles: the role of water

 The role played by the solvation water molecules on the macroscopically observed sol–gel transition in lecithin/cyclohexane/water reverse micelles is investigated by quasielastic neutron scattering, dielectric relaxation and conductivity measurements. The experimental results are juxtaposed to those from spherical Aerosol OT reverse micelles. It is shown how the results from lecithin-based system can be interpreted only assuming that, in contrast to Aerosol OT systems, the water molecules are entrapped at the interfaces without coalescing into an inner water pool. It is suggested that, in the case of lecithin, the solvation water can induce a change in the surface curvature, in such a way promoting the formation of branch points. Such a hypothesis is supported by the temperature dependence of the conductivity which agrees with the hypothesis of an intermicellar bond percolation. The investigation of the structures imposed by an external electric field is also studied. The observed electrorheological behaviour seems to confirm the existence of a percolated transient network in the gel phase. Received: 21 March 2001 Accepted: 24 August 2001     

Increased Flexibility in Multicolumn Chromatography (MC[sbnd]HPLC) via On-line Effluent Mixing Technique

Abstract

In continuation of our work dealing with multicolumn HPLC (MC[sbnd]HPLC) we describe in this paper an on-line on-column fraction trapping technique based on effluent mixing.

To a normal two-column switching set-up (in this case with two RP columns) an additional high-pressure pump gets inserted into the connection line between column A and column B via a low dead volume mixing tee. The in-line respectively off-line switching of pump B and the mobile phase B is time controlled by using a high pressure switching valve. With this set-up it is possible to mix on-line an effluent fraction from column A and transferred onto column B with a highly polar and pH-controlled (e.g. aqueous buffer) new effluent, to reduce or adjust significantly the overall elution strength of this mixed transferred solvent. Thus, several chromatographically effective possibilities can be created in a simple manner, which are for example: (a) pronounced peak compression respectively on-column concentration on column B; (b) due to low elution strength and/or pH adjustment during the trapping period on column B, increments to the overall selectivity of the column switching set-up can be added creating multidimensionality via mobile phase switching; (c) combining the heart cut with the effluent mixing technique enables analysis of trace peaks eluted on the back flank of an overloaded main peak.     

Nitraza-/Oxa-Propylene- and Hydrazonemethylene-Bridged 1,2,4-Nitraminotriazoles and Selected Salts

Two new bridged nitraminotriazoles with bridging oxapropylene and nitrazapropylene moieties were synthesized, and converted into several salts, as well as from the hydrazonemethylene bridged nitraminotriazole. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis as well as differential thermal analysis. The sensitivity towards friction and impact were determined according to BAM standard technics and the energetic properties were calculated by using the EXPLO5 computer code. The neutral compounds as well as the various salts were examined in terms of their physicochemical properties and detonation performance to each other and compared to the commonly used secondary explosive RDX.