An eddy-current-shielded room with a partially closed entrance

Summary We show that substantial improvements can be obtained in the shielding properties of an eddy-current-shielded room by covering the doorway with conductive plates. Results suggest that it is unnecessary to install a conductive door and show that it is worthwhile covering a small part of the doorway permanently. Paper presented at the ?IV International Workshop on Biomagnetism?, held in Rome, September 14–16, 1982.     

Über Tantalnitride mit der Zusammensetzung TaN1.0

Zusammenfassung Eine früher als TaN_0.8–0.9 beschriebene Tantalnitridphase mit einer Kristallstruktur vom WC-Typ konnte wieder aufgefunden werden. Sie entsteht vorzugsweise beim Nitridieren von Tantalmetallpulver mit NH₃-Gas bei 850 bis 1200° C, jedoch stets nur im Gemisch mit anderen Tantalnitriden (Ta₂N, -TaN, Ta₅N₆).Obgleich eine Reindarstellung dieser als -TaN bezeichneten Phase nicht gelang, konnte indirekt ihre chemische Zusammensetzung mit Sicherheit als der Formel TaN_1.0 entsprechend festgestellt werden. Ein Homogenitätsgebiet meßbarer Breite scheint die Verbindung -TaN nicht zu haben, wenn sie frei von Verunreinigungen fremder Elemente ist.

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Tantalum nitrides with the composition TaN_1.0

A tantalum nitride phase with the WC-type structure which formerly was believed to be TaN_0.8–0.9 has been re-detected. This phase is formed preferentially by nitriding tantalum metal powder with ammonia gas at 850° to 1200° C, the reaction products, however, always containing additionally other tantalum nitrides (Ta₂N, -TaN, Ta₅N₆). Though this phase, called -TaN, could not be prepared free from other tantalum nitrides, it could be proved to have a composition corresponding to TaN_1.0. The phase seems to have no homogeneity range if prepared free from contamination with other elements.

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Über endliche lineare Gruppen von Primzahlgrad

Ohne Zusammenfassung Carl Ludwig Siegel zum siebzigsten Geburtstag gewidmet     

Über das kubische Vanadiummonoxid

Reinvestigation of the homogeneity range of the cubic vanadium monoxide phase showed that this oxide exhibits two closely related phase sections (VO_0.86 to VO_0.91,and VO_1.05 to VO_1.25) divided by a miscibility gap. This largely confirms observations of VOL'F et al.     

Buchbesprechungen

Ohne Zusammenfassung     

Direct observation of ion emission from charged aqueous nanodrops: effects on gaseous macromolecular charging

Mechanistic information about how gaseous ions are formed from charged droplets has been difficult to establish because direct observation of nanodrops in a size range relevant to gaseous macromolecular ion formation by optical or traditional mass spectrometry methods is challenging owing to their small size and heterogeneity. Here, the mass and charge of individual aqueous nanodrops between 1–10 MDa (15–32 nm diameter) with ∼50–300 charges are dynamically monitored for 1 s using charge detection mass spectrometry. Discrete losses of minimally solvated singly charged ions occur, marking the first direct observation of ion emission from aqueous nanodrops in late stages of droplet evaporation relevant to macromolecular ion formation in native mass spectrometry. Nanodrop charge depends on the identity of constituent ions, with pure water nanodrops charged slightly above the Rayleigh limit and aqueous solutions containing alkali metal ions charged progressively below the Rayleigh limit with increasing cation size. MS2 capsid ions (∼3.5 MDa; ∼27 nm diameter) are more highly charged from aqueous ammonium acetate than from its biochemically preferred, 100 mM NaCl/10 mM Na phosphate solution, consistent with ion emission reducing the nanodrop and resulting capsid charge. The extent of charging indicates that the capsid partially collapses inside the nanodrops prior to the charging and formation of the dehydrated gaseous ions. These results demonstrate that ion emission can affect macromolecular charging and that conformational changes to macromolecular structure can occur in nanodrops prior to the formation of naked gaseous ions.

Ion evaporation from aqueous nanodrops is measured for the first time using charge detection mass spectrometry, and the origin of solute ion dependent charging of large (MDa) macromolecules is revealed.     

Influence of a polar near-neighbor on incipient proton transfer in a strongly hydrogen bonded complex

Rotational spectroscopy and ab initio calculations have been used to characterize the complexes H(3)N-HF and H(3)N-HF-HF in the gas phase. H(3)N-HF is a C(3v) symmetric, hydrogen bonded system with an NF distance of 2.640(21) A and an N...H hydrogen bond length of 1.693(42) A. The H(3)N-HF-HF complex, on the other hand, forms a six-membered HN-HF-HF ring, in which both the linear hydrogen bond in the H(3)N-HF moiety and the F-H-F angle of (HF)(2) are perturbed relative to those in the corresponding dimers. The N...F and F...F distances in the trimer are 2.4509(74) A and 2.651(11) A, respectively. The N...H hydrogen bond length in H(3)N-HF-HF is 1.488(12) A, a value which is 0.205(54) A shorter than that in H(3)N-HF. Similarly, the F...F distance, 2.651(11) A, is 0.13(2) A shorter than that in (HF)(2). Counterpoise-corrected geometry optimizations are presented, which are in good agreement with the experimental structures for both the dimer and trimer, and further characterize small, but significant, changes in the NH(3) and HF subunits upon complexation. Analysis of internal rotation in the spectrum of H(3)N-HF-HF gives the potential barrier for internal rotation of the NH(3) unit, V(3), to be 118(2) cm(-1). Ab initio calculations reproduce this number to within 10% if the monomer units and the molecular frame are allowed to fully relax as the internal rotation takes place. The binding energies of H(3)N-HF and H(3)N-HF-HF, calculated at the MP2/aug-cc-pVTZ level and corrected for basis set superposition error are 12.3 and 22.0 kcal/mol, respectively. Additional energy calculations have been performed to explore the lowest frequency vibration of H(3)N-HF-HF, a ring-opening motion that increases the NFF angle. The addition of one HF molecule to H(3)N-HF represents the first step of microsolvation of a hydrogen bonded complex and the results of this study demonstrate that a single, polar near-neighbor has a significant influence on the extent of proton transfer across the hydrogen bond. As measured using the proton-transfer parameter rho(PT), previously defined by Kurnig and Scheiner [Int. J. Quantum Chem., Quantum Biol. Symp. 1987, 14, 47], the degree of proton transfer in H(3)N-HF-HF is greater than that in either (CH(3))(3)N-HF or H(3)N-HCl but less than that in (CH(3))(3)N-HCl.     

Supercritical fluid extraction of organic and inorganic mercury from solid materials

Mercuric ions (Hg(2+)) can be extracted from solid samples (cellulose matrix) using methanol modified supercritical CO(2) containing the fluorinated chelating agent lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC). Methylmercuric chloride (CH(3)HgCl) and dimethylmercury [(CH(3))(2)Hg] can be extracted by supercritical CO(2) without chelating agent and modifier. The solubility of Hg(FDDC)(2) in supercritical CO(2) has been determined to be 5 x 10(-3)M at 5O degrees C and 150 atm, which is about 3 orders of magnitude greater than that of the non-fluorinated analogue Hg(DDC)(2). Use of methanol (5%)-modified CO(2) further enhances the solubility of Hg(FDDC)(2) by a factor of 2.4. A small amount of water added to the sample matrix tends to facilitate the extraction of Hg(FDDC)(2) and CH(3)HgCl. Potential applications of this in situ chelation-supercritical fluid extraction method for the preconcentration of mercury species and treatment of mercury contaminated wastes are discussed.